New 1H-1,2,4-triazolyl derivatives as antimicrobial agents. Synthesis, biological evaluation and molecular docking

Thirteen new 1H-1,2,4-triazolyl derivatives were synthesized, and six of them were selected based on docking prediction for the investigation of their antimicrobial activity against five bacterial and eight fungal strains. All compounds demonstrated antibacterial activity with MIC lower than that of the ampicillin and chloramphenicol. In general, the most sensitive bacteria appeared to be P.fluorescens, while the plant pathogen X.campestris was the most resistant. The antifungal activity of the compounds was much better than the antibacterial activity. All compounds were more potent (6 to 45 times) than reference drugs ketoconazole and bifonazole with the best activity achieved by compound 4a   A.versicolor, A.ochraceus, A.niger, and T.viride showed the highest sensitivity to compound 4b, while, T.viride,P. funiculosum, and P.ochrochloron showed good sensitivity to compound 4a. Molecular docking studies suggest that the probable mechanism of antibacterial activity involves the inhibition of the MurB enzyme of E.coli, while CYP51 of C. albicans appears to be involved in the mechanism of antifungal activity. It is worth mentioning that none of the tested compounds violated Lipinski's rule of five.

Nature of cyanoargentate bridges defining spin crossover in new 2D Hofmann clathrate analogues

Chemical composition is leading among the numerous factors that determine the spin transition properties of coordination compounds. Classic dicyanometallic bridges {M(CN)2}- are commonly used to build Hofmann-like spin-crossover frameworks, but some extended bridges are also synthetically available. In this paper, we describe a successful synthesis of two very similar spin-crossover frameworks that differ in the cyanometallic bridges involved, namely [Fe(etpz)2{Ag(CN)2}2] (1) and {Fe(etpz)2[Ag2(CN)3][Ag(CN)2]} (2) (where etpz = 2-ethylpyrazine). Magnetic and Mössbauer studies demonstrated the occurrence of abrupt one-step high-spin (HS) ↔ low-spin (LS) transitions for both complexes. The spin transition temperatures are T1/2 ↓ = 233 K and T1/2 ↑ = 243 K for 1 and T1/2 ↓ = 188 K and T1/2 ↑ = 191 K for 2 with thermal hysteresis loops of 10 K for 1 and 3 K for 2. The bridging mononuclear [Ag(CN)2]- units and FeII cations assemble to form infinite 2D layers in the structure of 1. Interestingly, compound 2 forms 2D layers of FeII cations bridged by both binuclear [Ag2(CN)3]- and mononuclear [Ag(CN)2]- units. The structures of 1 and 2 comprise different types of intermolecular interactions including Ag⋯Ag and Ag⋯Netpz, which induce the creation of supramolecular 3D frameworks. The synergy between metallophilic interactions and the spin transition is also confirmed by the variation of Ag⋯Ag distances during spin crossover. The characterization of such analogues allowed us to analyze in detail the effect of the cyanometallic bridge on the structure of new frameworks and on the bistability in Hofmann-like complexes.

New Library of Iodo-Quinoline Derivatives Obtained by an Alternative Synthetic Pathway and Their Antimicrobial Activity

6-Iodo-substituted carboxy-quinolines were obtained using a one-pot, three-component method with trifluoroacetic acid as a catalyst under acidic conditions. Iodo-aniline, pyruvic acid and 22 phenyl-substituted aldehydes (we varied the type and number of radicals) or O-heterocycles, resulting in different electronic effects, were the starting components. This approach offers advantages such as rapid response times, cost-effective catalysts, high product yields and efficient purification procedures. A comprehensive investigation was conducted to examine the impact of aldehyde structure on the synthesis pathway. A library of compounds was obtained and characterized by FT-IR, MS, 1H NMR and 13C NMR spectroscopy and single-ray crystal diffractometry. Their antimicrobial activity against S. epidermidis, K. pneumonie and C. parapsilosis was tested in vitro. The effect of iodo-quinoline derivatives on microbial adhesion, the initial stage of microbial biofilm development, was also investigated. This study suggests that carboxy-quinoline derivatives bearing an iodine atom are interesting scaffolds for the development of novel antimicrobial agents.

Crystal structure of a water oxidation catalyst solvate with composition (NH4)2[FeIV(L-6H)]·3CH3COOH (L = clathrochelate ligand)

The synthetic availability of mol-ecular water oxidation catalysts containing high-valent ions of 3d metals in the active site is a prerequisite to enabling photo- and electrochemical water splitting on a large scale. Herein, the synthesis and crystal structure of di-ammonium {μ-1,3,4,7,8,10,12,13,16,17,19,22-dodeca-aza-tetra-cyclo-[8.8.4.13,17.18,12]tetra-cosane-5,6,14,15,20,21-hexa-onato}ferrate(IV) acetic acid tris-olvate, (NH4)2[FeIV(C12H12N12O6)]·3CH3COOH or (NH4)2[FeIV(L-6H)]·3CH3COOH is reported. The FeIV ion is encapsulated by the macropolycyclic ligand, which can be described as a dodeca-aza-quadricyclic cage with two capping tri-aza-cyclo-hexane fragments making three five- and six six-membered alternating chelate rings with the central FeIV ion. The local coord-ination environment of FeIV is formed by six deprotonated hydrazide nitro-gen atoms, which stabilize the unusual oxidation state. The FeIV ion lies on a twofold rotation axis (multiplicity 4, Wyckoff letter e) of the space group C2/c. Its coordination geometry is inter-mediate between a trigonal prism (distortion angle φ = 0°) and an anti-prism (φ = 60°) with φ = 31.1°. The Fe-N bond lengths lie in the range 1.9376 (13)-1.9617 (13) Å, as expected for tetra-valent iron. Structure analysis revealed that three acetic acid mol-ecules additionally co-crystallize per one iron(IV) complex, and one of them is positionally disordered over four positions. In the crystal structure, the ammonium cations, complex dianions and acetic acid mol-ecules are inter-connected by an intricate system of hydrogen bonds, mainly via the oxamide oxygen atoms acting as acceptors.

Crystal structure and Hirshfeld-surface analysis of di-aqua-bis-(5-methyl-1H-1,2,4-triazole-3-carboxyl-ato)copper(II)

The title compound, [Cu(HL)2(H2O)2] or [Cu(C4H4N3O2)2(H2O)2], is a mononuclear octa-hedral CuII complex based on 5-methyl-1H-1,2,4-triazole-3-carb-oxy-lic acid (H2 L). [Cu(HL)2(H2O)2] was synthesized by reaction of H2 L with copper(II) nitrate hexa-hydrate (2:1 stoichiometric ratio) in water under ambient conditions to produce clear light-blue crystals. The central Cu atom exhibits an N2O4 coordination environment in an elongated octa-hedral geometry provided by two bidentate HL - anions in the equatorial plane and two water mol-ecules in the axial positions. Hirshfeld surface analysis revealed that the most important contributions to the surface contacts are from H⋯O/O⋯H (33.1%), H⋯H (29.5%) and H⋯N/N⋯H (19.3%) inter-actions.

Crystal structure of polymeric bis-(3-amino-1H-pyrazole)-cadmium dibromide

The reaction of cadmium bromide tetra-hydrate with 3-amino-pyrazole (3-apz) in ethano-lic solution leads to tautomerization of the ligand and the formation of crystals of the title compound, catena-poly[[di-bromido-cadmium(II)]-bis-(μ-3-amino-1H-pyrazole)-κ2 N 3:N 2;κ2 N 2:N 3], [CdBr2(C3H5N3)2]n or [CdBr2(3-apz)2]n. Its asymmetric unit consists of a half of a Cd2+ cation, a bromide anion and a 3-apz mol-ecule. The Cd2+ cations are coordinated by two bromide anions and two 3-apz ligands, generating trans-CdN4Br2 octa-hedra, which are linked into chains by pairs of the bridging ligands. In the crystal, the ligand mol-ecules and bromide anions of neighboring chains are linked through inter-chain hydrogen bonds into a two-dimensional network. The inter-molecular contacts were qu-anti-fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative qu-anti-tative contributions of the weak inter-molecular contacts.

Phase Transitions, Dielectric Response, and Nonlinear Optical Properties of Aziridinium Lead Halide Perovskites

Hybrid organic-inorganic lead halide perovskites are promising candidates for next-generation solar cells, light-emitting diodes, photodetectors, and lasers. The structural, dynamic, and phase-transition properties play a key role in the performance of these materials. In this work, we use a multitechnique experimental (thermal, X-ray diffraction, Raman scattering, dielectric, nonlinear optical) and theoretical (machine-learning force field) approach to map the phase diagrams and obtain information on molecular dynamics and mechanism of the structural phase transitions in novel 3D AZRPbX3 perovskites (AZR = aziridinium; X = Cl, Br, I). Our work reveals that all perovskites undergo order-disorder phase transitions at low temperatures, which significantly affect the structural, dielectric, phonon, and nonlinear optical properties of these compounds. The desirable cubic phases of AZRPbX3 remain stable at lower temperatures (132, 145, and 162 K for I, Br, and Cl) compared to the methylammonium and formamidinium analogues. Similar to other 3D-connected hybrid perovskites, the dielectric response reveals a rather high dielectric permittivity, an important feature for defect tolerance. We further show that AZRPbBr3 and AZRPbI3 exhibit strong nonlinear optical absorption. The high two-photon brightness of AZRPbI3 emission stands out among lead perovskites emitting in the near-infrared region.

Crystal structure and Hirshfeld surface analysis of poly[[tetra-aqua-(μ-1,3,4,7,8,10,12,13,16,17,19,22-dodeca-aza-tetra-cyclo-[8.8.4.13,17.18,12]tetra-cosane-5,6,14,15,20,21-hexaonato)iron(IV)dilithium] tetra-hydrate]

The title compound, [FeLi2(C12H12N12O6)(H2O)4]·4H2O, consists of iron complex anions, lithium cations and water mol-ecules. The complex anion shows a clathrochelate topology. The coordination geometry of the FeIV centre is inter-mediate between a trigonal prism and a trigonal anti-prism. In the crystal, the complex anions are connected through two Li cations into dimers, which are connected by Li-O bonds, forming infinite chains along the b-axis direction.

Crystal structure of bis-(3-carb-oxy-1-methyl-pyrid-inium) octa-bromide

The crystal structure of the title salt, bis-(3-carb-oxy-1-methyl-pyridinium) octa-bromide, 2C7H8NO2 +·Br8 2-, consists of 3-carb-oxy-1-methyl-pyridinium (N-methyl-nicotinic acid) cations, which are stacked between relatively rare [Br8]2- anions. The polybromide [Br8]2- anion has point group symmetry and can be described as being composed of two [Br3]- anions connected with a Br2 mol-ecule in a Z-shaped manner. Contacts between neighboring octa-bromide anions ensure the creation of pseudo-polymeric chains propagating along [111]. The organic cations are located between anionic chains and are connected to each other through O-H⋯O hydrogen bonds and to the [Br8]2- anions through π⋯Br inter-actions that induce the creation of a supra-molecular tri-periodic network. In addition, the presence of weak C-H⋯Br contacts leads to the creation of layers, which align parallel to (11).

Carbon dioxide capture from air leading to bis-[N-(5-methyl-1H-pyrazol-3-yl-κN2)carbamato-κO]copper(II) tetra-hydrate

A mononuclear square-planar CuII complex of (5-methyl-1H-pyrazol-3-yl)carbamate, [Cu(C5H6N3O2)2]·4H2O, was synthesized using a one-pot reaction from 5-methyl-3-pyrazolamine and copper(II) acetate in water under ambient conditions. The adsorption of carbon dioxide from air was facilitated by the addition of di-ethano-lamine to the reaction mixture. While di-ethano-lamine is not a component of the final product, it plays a pivotal role in the reaction by creating an alkaline environment, thereby enabling the adsorption of atmos-pheric carbon dioxide. The central copper(II) atom is in an (N2O2) square-planar coordination environment formed by two N atoms and two O atoms of two equivalent (5-methyl-1H-pyrazol-3-yl)carbamate ligands. Additionally, there are co-crystallized water mol-ecules within the crystal structure of this compound. These co-crystallized water mol-ecules are linked to the CuII mononuclear complex by O-H⋯O hydrogen bonds. According to Hirshfeld surface analysis, the most frequently observed weak inter-molecular inter-actions are H⋯O/O⋯H (33.6%), H⋯C/C⋯H (11.3%) and H⋯N/N⋯H (9.0%) contacts.

Novel Strigolactone Mimics That Modulate Photosynthesis and Biomass Accumulation in Chlorella sorokiniana

In terrestrial plants, strigolactones act as multifunctional endo- and exo-signals. On microalgae, the strigolactones determine akin effects: induce symbiosis formation with fungi and bacteria and enhance photosynthesis efficiency and accumulation of biomass. This work aims to synthesize and identify strigolactone mimics that promote photosynthesis and biomass accumulation in microalgae with biotechnological potential. Novel strigolactone mimics easily accessible in significant amounts were prepared and fully characterized. The first two novel compounds contain 3,5-disubstituted aryloxy moieties connected to the bioactive furan-2-one ring. In the second group of compounds, a benzothiazole ring is connected directly through the cyclic nitrogen atom to the bioactive furan-2-one ring. The novel strigolactone mimics were tested on Chlorella sorokiniana NIVA-CHL 176. All tested strigolactones increased the accumulation of chlorophyll b in microalgae biomass. The SL-F3 mimic, 3-(4-methyl-5-oxo-2,5-dihydrofuran-2-yl)-3H-benzothiazol-2-one (7), proved the most efficient. This compound, applied at a concentration of 10-7 M, determined a significant biomass accumulation, higher by more than 15% compared to untreated control, and improved the quantum yield efficiency of photosystem II. SL-F2 mimic, 5-(3,5-dibromophenoxy)-3-methyl-5H-furan-2-one (4), applied at a concentration of 10-9 M, improved protein production and slightly stimulated biomass accumulation. Potential utilization of the new strigolactone mimics as microalgae biostimulants is discussed.

Crystal structure of bis-{3-(3,4-di-meth-oxy-phen-yl)-5-[6-(pyrazol-1-yl)pyridin-2-yl]-1,2,4-triazol-3-ato}iron(II)-methanol-chloro-form (1/2/2)

The unit cell of the title compound, [Fe(C18H15N6O2)2]·2CH3OH·2CHCl3, consists of a charge-neutral complex mol-ecule, two methanol and two chloro-form mol-ecules. In the complex, the two tridentate 2-(5-(3,4-di-meth-oxy-phen-yl)-1,2,4-triazol-3-yl)-6-(pyrazol-1-yl)pyridine ligands coordinate to the central FeII ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octa-hedral coordination sphere. Neighbouring tapered mol-ecules are linked through weak C-H(pz)⋯π(ph) inter-actions into one-dimensional chains, which are joined into two-dimensional layers through weak C-H⋯N/C/O inter-actions. Furthermore, the layers stack in a three-dimensional network linked by weak inter-layer C-H⋯π inter-actions of the meth-oxy and phenyl groups. The inter-molecular contacts were qu-anti-fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative contributions of the contacts to the crystal packing to be H⋯H 32.0%, H⋯C/C⋯H 26.3%, H⋯N/N⋯H 13.8%, and H⋯O/O⋯H 7.5%. The average Fe-N bond distance is 2.185 Å, indicating the high-spin state of the FeII ion. Energy framework analysis at the HF/3-21 G theory level was performed to qu-antify the inter-action energies in the crystal structure.

Crystal structures of the complexes containing macrocyclic cations [M(cyclam)]2+ (M = Ni, Zn) and tetra-iodido-cadmate(2-) anion

The asymmetric units of the isostructural compounds (1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N)nickel(II) tetra-iodido-cadmate(II), [Ni(C10H24N4)][CdI4] (I), and tri-iodido-1κ3 I-μ-iodido-(1,4,8,11-tetra-aza-cyclo-tetra-decane-2κ4 N)cad-mium(II)zinc(II), [CdZnI4(C10H24N4)] (II) (C10H24N4 = 1,4,8,11-tetra-aza-cyclo-tetra-decane, cyclam, L), consist of the centrosymmetric macrocyclic cation [M(L)]2+ [M = NiII or ZnII] with the metal ion lying on a twofold screw axis, and the tetra-iodo-cadmate anion [CdI4]2- located on the mirror plane. In I, the anion acts as an uncoordinated counter-ion while in II it is bound to the ZnII atom via one of the iodide atoms, thus forming an electroneutral heterobimetallic complex [Zn(L)(CdI4)]. The NiII and ZnII ions are coordinated in a square-planar manner by the four secondary N atoms of the macrocyclic ligand L, which adopts the most energetically stable trans-III conformation. The [CdI4]2- anions in I and II are structurally very similar and represent slightly deformed tetra-hedrons with average Cd-I bond lengths and I-Cd-I angles of ca 2.79 Å and 109.6°, respectively. The supra-molecular organization of the complexes under consideration in the crystals is very similar and is determined by the hydrogen-bonding inter-actions between the secondary amino groups of the ligand L in the [M(L)]2+ cations and iodide atoms of the [CdI4]2- anion. In particular, the alternating cations and anions form chains running along the b-axis direction that are arranged into di-periodic sheets oriented parallel to the (101) and (01) planes. Because both kinds of sheets are built from the same cations and anions, this feature provides the three-dimensional coherence of the crystals of I and II.

Structural diversity in proline-based lead bromide chiral perovskites

Lead halide hybrid perovskites incorporating chiral organic cations attract considerable attention due to their promising application in multifarious optoelectronic devices. However, the examples of chiral hybrid perovskites are still limited, which greatly impedes their further studies in various optoelectronic fields. Herein, we report on new low-dimensional lead-halide hybrid perovskites incorporating the enantiopure chiral α-amino acid L-proline. Two hybrid perovskites (L-proH)PbBr₃·H₂O (Pro-PbBr₃) and (L-proH)₄Pb₃Br₁₀·4H₂O (Pro-Pb₃Br₁₀) have been synthesized by employing different ratios of organic and inorganic precursors. According to structural analysis, the inorganic sublattice of compound Pro-PbBr₃ is built of one-dimensional (1D) [PbX₃]_∞^n- lead halide chains, whereas the inorganic sublattice of compound Pro-Pb₃Br₁₀ is built upon a rare two-dimensional (2D) [Pb₃Br₁₀]_∞^4n- honeycomb-type inorganic framework. Hirshfeld surface analysis revealed an important role of various hydrogen bonding interactions in providing the binding between organic and inorganic parts of these hybrid perovskites. The optical band gap values of new hybrid perovskites as estimated using the Tauc plot approach are 4.19 eV (Pro-PbBr₃) and 4.13 eV (Pro-Pb₃Br₁₀). Also, new compounds display low-temperature broadband photoluminescence which can be attributed to the self-trapped excitons. These results show the potential of α-proline for constructing novel and highly demanded chiral hybrid perovskites, which will hold great promise for further optoelectronic applications.

Novel antimicrobial iodo-dihydro-pyrrole-2-one compounds

Aim: A series of new hybrid molecules with two iodine atoms on the sides were synthesized. Methods: A one-pot, two-component method with trifluoroacetic acid as an effective catalyst to obtain dihydro-pyrrol-2-one compounds was developed. Short reaction times, a cheap catalyst, high yields and clean work-up are benefits of this method. Results: The chemical structures of the newly synthesized compounds were verified through spectroscopic techniques. Their antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans was tested in vitro. Conclusion: NC- and OH- radicals confer broad-spectrum antimicrobial activity, including against Gram-positive and Gram-negative bacteria and yeasts. Compounds 3g >7 and >9 were most active on the two bacterial species, while 3l >9 and >3i were most active against the fungal strain.

Synthesis, Characterization and Cytotoxic Evaluation of New Pyrrolo[1,2-b]pyridazines Obtained via Mesoionic Oxazolo-Pyridazinones

New pyrrolo[1,2-b]pyridazines were synthesized by 3 + 2 cycloaddition reaction between mesoionic oxazolo-pyridazinones and methyl/ethyl propiolate. The mesoionic compounds were generated in situ by action of acetic anhydride on 3(2H)pyridazinone acids obtained from corresponding esters by alkaline hydrolysis followed by acidification. The structures of the compounds were confirmed by elemental analyses and IR, ¹H-NMR, ¹³C-NMR, and X-ray diffraction data. The regioselectivity of cycloaddition was evidenced by NMR spectroscopy and confirmed by X-ray analysis. The compounds were evaluated for their cytotoxicity on plant cells (Triticum aestivum L.) and crustacean animal cells (Artemia franciscana Kellogg and Daphnia magna Straus). The results indicated that the tested compounds exhibited low toxicity on the plant cell (IC₅₀ values higher than 200 µM), while on Artemia nauplii no lethality was observed. Daphnia magna assay showed that pyrrolo[1,2-b]pyridazines 5a and 5c could exhibit toxic effects, whereas, for the other compounds, toxicity was low to moderate. Also, the cytotoxic effects of the compounds were tested on three human adenocarcinoma-derived adherent cell lines (colon LoVo, ovary SK-OV-3, breast MCF-7). The in vitro compound-mediated cytotoxicity assays, performed by the MTS technique, demonstrated dose- and time-dependent cytotoxic activity for several compounds, the highest anti-tumor activity being observed for 5a, 2c, and 5f, especially against colon cancer cells.

Synthesis and crystal structure of a new copper(II) complex based on 5-ethyl-3-(pyridin-2-yl)-1,2,4-triazole

The title compound, bis-[μ-3-ethyl-5-(pyridin-2-yl)-1H-1,2,4-triazol-1-ido]bis[acetato-(di-methyl-formamide)-copper(II)], [Cu₂(C₉H₉N₄)₂(C₂H₃O₂)₂(C₃H₇NO)₂] or [Cu₂(L ^Et)₂(OAc)₂(dmf)₂], is a triazolate complex, which contains two 3-(2-pyrid-yl)-5-ethyl-triazolates (L ^Et)^- in bidentate-bridged coordination modes. Both copper atoms are involved in the formation of a planar six-membered metallocycle Cu-[N-N]₂-Cu. The inversion center of the complex is located at the mid-point of the Cu⋯Cu vector. Each Cu^II atom has a distorted trigonal-bipyramidal environment formed by the three nitro-gen atoms of the deprotonated bridging 3-(2-pyrid-yl)-5-ethyl-triazolate unit, oxygen atoms of the OAc^- group and dmf mol-ecule. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into chains running along the c-axis direction.

How Metal Nuclearity Impacts Electrocatalytic H2 Production in Thiocarbohydrazone-Based Complexes

Thiocarbohydrazone-based catalysts feature ligands that are potentially electrochemically active. From the synthesis point of view, these ligands can be easily tailored, opening multiple strategies for optimization, such as using different substituent groups or metal substitution. In this work, we show the possibility of a new strategy, involving the nuclearity of the system, meaning the number of metal centers. We report the synthesis and characterization of a trinuclear nickel-thiocarbohydrazone complex displaying an improved turnover rate compared with its mononuclear counterpart. We use DFT calculations to show that the mechanism involved is metal-centered, unlike the metal-assisted ligand-centered mechanism found in the mononuclear complex. Finally, we show that two possible mechanisms can be assigned to this catalyst, both involving an initial double reduction of the system.

Quantum dots assembled from an aziridinium based hybrid perovskite displaying tunable luminescence

3D hybrid perovskites based upon small organic cations gave start to a new intensively growing class of semiconducting materials. Here we report on the elaboration of quantum dots of a recently emerged new perovskite (AzrH)PbBr₃ (AzrH = aziridinium cation). By employing the antisolvent precipitation technique and stabilization with a cationic surfactant we succeeded in obtaining quantum dots that display tunable luminescence. This piece of work shows the perspective of aziridinium-based materials for the elaboration of advanced photonic nanostructures.

Synthesis and Antimicrobial Activity Evaluation of Homodrimane Sesquiterpenoids with a Benzimidazole Unit

Herein we report a feasible study concerning the synthesis and the in vitro antimicrobial activity of some new homodrimane sesquiterpenoids with a benzimidazole unit. Based on some homodrimane carboxylic acids, on their acyl chlorides and intermediate monoamides, a series of seven N-homodrimenoyl-2-amino-1,3-benzimidazoles and 2-homodrimenyl-1,3-benzimidazoles was synthesized. The syntheses involved the decarboxylative cyclization and condensation of the said acids or acyl chlorides with o-phenylendiamine and 2-aminobenzimidazole, as well as the p-TsOH-mediated cyclodehydration of the said monoacylamides. The structures of the synthesized compounds have been fully confirmed, including by the X-ray diffraction. Their biological activities were evaluated on five species of fungi (Aspergillus niger, Fusarium solani, Penicillium chrysogenum, P. frequentans, and Alternaria alternata) and two strains of bacteria (Bacillus sp. and Pseudomonas aeruginosa). Compounds 7 and 20 showed higher antifungal (MIC = 0.064 and 0.05 μg/mL) and antibacterial (MIC = 0.05 and 0.032 μg/mL) activities compared to those of the standards: caspofungin (MIC = 0.32 μg/mL) and kanamycin (MIC = 2.0 μg/mL), and compounds 4, 10, 14, and 19 had moderate activities.

1,3-Dipolar cycloaddition of cycloimmonium salts and 4-(trimethylsilyl)-3-butyn-2-one to access new functionalized indolizines with potential cytostatic activity

This study revealed that 4-(trimethylsilyl)-3-butyn-2-one was an effective dipolarophile in the [3+2] cycloaddition reaction with cycloimmonium salts to obtain non-silicon adducts, namely 1-acetylindolizines. In some cases, two possible isomeric trimethylsilyl-containing...

Some Theoretical and Experimental Evidence for Particularities of the Siloxane Bond

The specific features of the siloxane bond unify the compounds based on it into a class with its own chemistry and unique combinations of chemical and physical properties. An illustration of their chemical peculiarity is the behavior of 1,3-bis(2-aminoethylaminomethyl)tetramethyldisiloxane (AEAMDS) in the reaction with carbonyl compounds and metal salts, by which we obtain the metal complexes of the corresponding Schiff bases formed in situ. Depending on the reaction conditions, the fragmentation of this compound takes place at the siloxane bond, but, in most cases, it is in the organic moieties in the β position with respect to the silicon atom. The main compounds that were formed based on the moieties resulting from the splitting of this diamine were isolated and characterized from a structural point of view. Depending on the presence or not of the metal salt in the reaction mixture, these are metal complexes with organic ligands (either dangling or not dangling silanol tails), or organic compounds. Through theoretical calculations, electrons that appear in the structure of the siloxane bond in different contexts and that lead to such fragmentations have been assessed.

Novel Zn(II) Binuclear and Ni(II) 1D Polymeric Coordination Compounds Based on Dianilineglyoxime and Dicarboxylic Acids: Synthesis and Structure

Two coordinating compounds of zinc(II) (1) [Zn2(DAnH2)2(1,3-bdc)2(DMSO)4] and nickel(II) (2) [Ni(DAnH2)(1,4-bdc)(DMF)2]n were obtained based on dianilineglyoxime (DAnH2), 1,3-benzenedicarboxylic acid (1,3-bdcH2) and 1,4-benzenedicarboxylic acid (1,4-bdcH2), where DMSO is dimethylsulfoxide and DMF is dimethylformamide. The molecular and crystalline structure of reported compounds were established by infrared spectroscopy and single crystal X-ray diffraction, and for 1, additionally, the 1H and 13C NMR spectroscopy was used. According to data, the Zn(II) molecular complex is a binuclear and the Ni(II) is a 1D polymer compound.

Crystal structure and Hirshfeld surface analysis of dichloridotetrakis(4-methyl-1H-pyrazole-κN 2)nickel(II) acetonitrile disolvate

The title compound, [NiCl2(C4H6N2)4]·2CH3CN, is a mononuclear octahedral NiII pyrazole-based complex. Two acetonitrile molecules are linked to the NiII complex by N—H...N hydrogen bonds. The NiII atom is octahedrally coordinated by four N atoms of four 4-methyl-1H-pyrazole ligands, forming the equatorial plane. The axial positions are occupied by two Cl atoms. [NiCl2(C4H6N2)4]·2CH3CN was synthesized by the reaction of 4-methyl-1H-pyrazole with nickel(II) chloride hexahydrate in acetonitrile solution under ambient conditions and characterized by single-crystal X-ray diffraction analysis. A Hirshfeld surface analysis was performed, which suggests that the most important contributions to the surface contacts are from H...H (62.1%), H...N/N...H (13.7%), H...C/C...H (13.4%) and H...Cl/Cl...H (10.1%) interactions.

Crystal structure of poly[(μ6-benzene-1,3,5-tricarboxylato)tris(1-methylpyrrolidin-2-one)nitratodizinc(II)]

The asymmetric unit of the title compound, [Zn2(C9H3O6)(NO3)(C5H9NO)3] n , I, consists of two different zinc(II) ions bridged by the carboxylate group of benzene-1,3,5-tricarboxylate (BTC3−). The Zn1 center is tetra-coordinated by the carboxylate O atoms of three symmetrically equivalent BTC3− anions and one nitrate O atom in a distorted tetrahedral geometry with Zn—Ocarboxylate bond lengths (average value 1.958 Å) slightly shorter than the Zn—Onitrate distance [2.013 (6) Å]. The Zn2 center is hexa-coordinated by three O atoms from the carboxylic groups of different BTC3− linkers and three O atoms of 1-methylpyrrolidin-2-one (NMP) in a slightly distorted octahedral geometry with nearly equivalent Zn—O bond lengths (average values of 2.091 and 2.088 Å, respectively). Linking of the paddle-wheel dizinc building units by the three carboxylate groups of the BTC3− molecule results in the formation of the three-dimensional coordination framework.

Crystal structure of bis{3-(3,5-dichlorophenyl)-5-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-4H-1,2,4-triazol-4-ido}iron(II) methanol disolvate

The asymmetric unit of the title compound, [FeII(C16H9Cl2N6)2]·2CH3OH, consists of half of a charge-neutral complex molecule and a discrete methanol molecule. The planar anionic tridentate ligand 2-[5-(3,5-dichlorophenyl)-4H-1,2,4-triazol-3-ato]-6-(1H-pyrazol-1-yl)pyridine coordinates to the FeII ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a coordination sphere of the central ion that deviates moderately from an octahedral geometry. The average Fe—N bond distance is 1.953 Å, indicating the low-spin state of the FeII ion. The cone-like-shaped molecules, nested into each other, are linked through double weak C—H(pz)...π(ph) interactions into mono-periodic columns, which are further linked through weak C—H...N′/C′ interactions into di-periodic layers. The layers interact through double weak C–H(ph)...Cl bonds with neighbouring molecules. Energy framework analysis at the B3LYP/6–31 G(d,p) theory level reproduces the strong interaction within the layers and the weaker interlayer interactions. Intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, the relative contributions of the contacts to the crystal packing being H...H 26.1%, H...C/C...H 24.4%, H...Cl/Cl...H 18.9% and H...N/N...H 12.1%.

Crystal structure of bis{3-(3-bromo-4-methoxyphenyl)-5-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-1,2,4-triazol-3-ato}iron(II) methanol disolvate

The title charge-neutral complex is a low-spin complex with a moderately distorted pseudo-octa­hedral coordination environment of the metal ion. As a result of their asymmetric shape, the mol­ecules stack into chains, which eventually pack into layers and, finally, into a three-dimensional network connected by weak C—H⋯N, C—H⋯C hydrogen bonds and C—H⋯π inter­actions.

The unit cell of the title compound, [Fe^II(C₁₇H₁₂BrN₆O)₂]·2MeOH, consists of a charge-neutral complex mol­ecule and two independent mol­ecules of methanol. In the complex mol­ecule, the two tridentate ligand mol­ecules 2-[5-(3-bromo-4-meth­oxy­phen­yl)-4H-1,2,4-triazol-3-yl]-6-(1H-pyrazol-1-yl)pyridine coordinate to the Fe^II ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octa­hedral coordination sphere around the central ion. In the crystal, neighbouring asymmetric mol­ecules are linked through weak C—H(pz)⋯π(ph) inter­actions into chains, which are then linked into layers by weak C–H⋯N/C inter­actions. Finally, the layers stack into a three-dimensional network linked by weak inter­layer C—H⋯π inter­actions between the meth­oxy groups and the phenyl rings. The inter­molecular contacts were qu­anti­fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative contributions of the contacts to the crystal packing to be H⋯H 34.2%, H⋯C/C⋯H 25.2%, H⋯Br/Br⋯H 13.2%, H⋯N/N⋯H 12.2% and H⋯O/O⋯H 4.0%. The average Fe—N bond distance is 1.949 Å, indicating the low-spin state of the Fe^II ion. Energy framework analysis at the HF/3–21 G theory level was performed to qu­antify the inter­action energies in the crystal structure.

Crystal structure of bis{3-(3,4-dimethylphenyl)-5-[6-(1H-pyrazol-1-yl)pyridin-2-yl]-4H-1,2,4-triazol-4-ido}iron(II) methanol disolvate

The title compound, a charge-neutral bis­{2-(3,4-di­methyl­phen­yl)-4H-1,2,4-triazol-3-ato)-6-(1H-πyrazol-1-yl)pyridine} iron(II) complex di­methanol solvate, is a low-spin complex with a moderately distorted pseudo­octa­hedral coordination environment of the metal ion. As a result of the cone shape, the mol­ecules are stacked in mono-periodic columns that are bound by weak hydrogen bonds into di-periodic layers, which, in turn, are arranged in a three-dimensional lattice bound by weak inter­layer inter­actions.

As a result of the high symmetry of the Aea2 structure, the asymmetric unit of the title compound, [Fe^II(C₁₈H₁₅N₆)₂]·2MeOH, consists of half of a charge-neutral complex mol­ecule and a discrete methanol mol­ecule. The planar anionic tridentate ligand 2-[5-(3,4-di­methyl­phen­yl)-4H-1,2,4-triazol-3-ato]-6-(1H-pyrazol-1-yl)pyridine coordinates the Fe^II ion meridionally through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octa­hedral coordination sphere of the central ion. The average Fe—N bond distance is 1.955 Å, indicating a low-spin state of the Fe^II ion. Neighbouring cone-shaped mol­ecules, nested into each other, are linked through double weak C—H(pz)⋯π(ph’) inter­actions into mono-periodic columns, which are further linked through weak C—H⋯N′/C′ inter­actions into di-periodic layers. No inter­actions shorter than the sum of the van der Waals radii of the neighbouring layers are observed. Energy framework analysis at the B3LYP/6–31 G(d,p) theory level, performed to qu­antify the inter­molecular inter­action energies, reproduces the weak inter­layer inter­actions in contrast to the strong inter­action within the layers. Inter­molecular contacts were qu­anti­fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, showing the relative contributions of the contacts to the crystal packing to be H⋯H 48.5%, H⋯C/C⋯H 28.9%, H⋯N/N⋯H 16.2% and C⋯C 2.4%.

Syntheses and structural characterizations of the first coordination polymers assembled from the Ni(cyclam)2+ cation and the benzene-1,3,5-tricarboxylate linker

The coordination polyhedra of the complex cations in the one-dimensional coordination polymers I and II represent tetra­gonally distorted NiN₄O₂ octa­hedra with the four N atoms of the aza­macrocyclic cyclam ligand in the equatorial planes and two O atoms of the benzene­tri­carboxyl­ate anions in the axial positions. The crystals of both compounds are composed of parallel coordination polymeric chains running along the [010] direction in I and the [110] and [10] directions in II. As a result of hydrogen-bonding inter­actions, the chains are joined together in layers oriented parallel to the (10) and (001) planes in I and II, respectively.

The asymmetric unit of catena-poly[[[(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ⁴N¹,N⁴,N⁸,N¹¹)nickel(II)]-μ₂-5-carb­oxy­benzene-1,3-di­carboxyl­ato-κ²O¹:O³] octa­hydrate], {[Ni(C₉H₄O₆)(C₁₀H₂₄N₄)]·8H₂O}_n (I), consists of a macrocyclic Ni²⁺ cation, a carboxyl­ate dianion and eight highly disordered water mol­ecules of crystallization. The components of the compound catena-poly[[[(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ⁴N¹,N⁴,N⁸,N¹¹)nickel(II)]-μ₂-5-carb­oxy­benzene-1,3-di­carboxyl­ato-κ²O¹:O³] monohydrate], {[Ni(C₉H₄O₆)(C₁₀H₂₄N₄)]·H₂O}_n (II), are two crystallographically unique centrosymmetric macrocyclic dications, a carboxyl­ate dianion and one water mol­ecule of crystallization. In each compound, the metal ion is coordinated in the equatorial plane by the four secondary N atoms of the macrocyclic ligand, which adopts the most energetically stable trans-III conformation, and two mutually trans O atoms of the carboxyl­ate anions in a slightly tetra­gonally distorted trans-NiN₄O₂ octa­hedral geometry. The crystals of both compounds are composed of parallel coordination polymeric chains running along the [010] direction in I and the [110] and [10] directions in II. The bridging carboxyl­ate anions display different modes of coordination connected with the relative orientation of coordinated O atoms, i.e., remote in I and inter­mediate in II, thus resulting in essentially different distances between the Ni atoms in the chains [11.0657 (4) and 8.9089 (2) Å in I and II, respectively]. As a result of hydrogen-bonding inter­actions, the chains are joined together in sheets oriented parallel to the (10) and (001) planes in I and II, respectively.

Investigation by Chemical Substitution within 2p-3d-4f Clusters of the Cobalt(II) Role in the Magnetic Behavior of [vdCoLn]2 (vd = Verdazyl Radical)

1,5-Dimethyl-3-(3'-(hydroxymethyl)-2'-pyridine)-6-oxotetrazane (H₃vdpyCH₂OH) or its oxidized verdazyl form (vdpyCH₂OH) reacted with transition metal and/or lanthanide acetates to yield [(vdpyCH₂O)₂Co₂Ln₂(acO)₈] (Ln = Y(III): I_Co,Y; Gd(III): I_Co,Gd), [(vdpyCH₂O)₂M₃(acO)₄] (M = Zn(II): II_Zn; Co(II): II_Co) and [(vdpyCH₂OH)Zn(acO)₂] (III_Zn) through self-assembly implying a complex-as-ligand intermediate. Single-crystal diffraction reveals that I_MT,Ln are composed of 2p-3d-4f centrosymmetric clusters with verdazyl radicals at the two ends coordinated to the transition-metal ion in a tridentate mode and to the {Ln₂(acO)₄} lanthanide central core in a monodentate mode through its alkoxo moiety. In I_Co,Gd, the transition-metal ions adopt an irregular octahedral environment, and the {Ln₂(acO)₄} core adopts a paddlewheel motif, whereas in I_Co,Y, the transition metal is pentacoordinated, and the central core contains only two acetate bridges. Going from I_Co,Y to II_Co, the central {Y₂(acO)₄} core is replaced by an axially compressed octahedral cobalt(II) center, whereas the outer parts of the molecule remain still. The dc magnetic studies revealed that the alternate π-stacking of the verdazyl radicals in II_Zn led to the formation of alternate antiferromagnetically coupled 1D chains with J_vd-vd = -8.2(1) cm^-1 and J_vd-vd' = -7.6(1) cm^-1 (-2J convention). In I_Co,Y, a complex fitting procedure allowed us to retrieve a complete set of magnetic parameters to take into account both the magnetic anisotropy of the cobalt(II) centers and intra- and inter-molecular exchange effects. For I_Co,Y, it led to g_Co = 2.13(4), D_Co = 100(2) cm^-1, E_Co = 19.9(5) cm^-1, J_Co-vd = +26.5(4) cm^-1, and J_vd-vd = -7.95(4) cm^-1. ac magnetic susceptibility of I_Co,Y, I_Co,Gd and II_Co did not reveal any slow relaxation of the magnetization even when a dc external magnetic field up to 2000 Oe was applied.

Cooperative Spin Crossover above Room Temperature in the Iron(II) Cyanoborohydride-Pyrazine Complex

Hysteretic spin crossover in coordination complexes of 3d-metal ions represents one of the most spectacular phenomena of molecular bistability. In this paper we describe a self-assembly of pyrazine (pz) and Fe(BH₃CN)₂ that afforded the new 2D coordination polymer [Fe(pz)₂(BH₃CN)₂]_∞. It undergoes an abrupt, hysteretic spin crossover (SCO) with a T_1/2 of 338 K (heating) and 326 K (cooling) according to magnetic susceptibility measurements. Mössbauer spectroscopy revealed a complete transition between the low-spin (LS) and the high-spin (HS) states of the iron centers. This LS-to-HS transition induced an increase of the unit cell volume by 10.6%. Meanwhile, a modulation of multiple [C-H^δ+···H^δ--B] dihydrogen bonds stimulates a contraction in direction c (2.2%). The simplicity of the synthesis, mild temperatures of transition, a pronounced thermochromism, stability upon thermal cycling, a striking volume expansion upon SCO, and an easy processability to composite films make this new complex an attractive material for switchable components of diverse applications.

New Pyrrole Derivatives as Promising Biological Agents: Design, Synthesis, Characterization, In Silico, and Cytotoxicity Evaluation

The current study describes the synthesis, physicochemical characterization and cytotoxicity evaluation of a new series of pyrrole derivatives in order to identify new bioactive molecules. The new pyrroles were obtained by reaction of benzimidazolium bromide derivatives with asymmetrical acetylenes in 1,2-epoxybutane under reflux through the Huisgen [3 + 2] cycloaddition of several ylide intermediates to the corresponding dipolarophiles. The intermediates salts were obtained from corresponding benzimidazole with bromoacetonitrile. The structures of the newly synthesized compounds were confirmed by elemental analysis, spectral techniques (i.e., IR, 1H-NMR and 13C-NMR) and single-crystal X-ray analysis. The cytotoxicity of the synthesized compounds was evaluated on plant cells (i.e., Triticum aestivum L.) and animal cells using aquatic crustaceans (i.e., Artemia franciscana Kellogg and Daphnia magna Straus). The potential antitumor activity of several of the pyrrole derivatives was studied by performing in vitro cytotoxicity assays on human adenocarcinoma-derived cell lines (i.e., LoVo (colon), MCF-7 (breast), and SK-OV-3 (ovary)) and normal human umbilical vein endothelial cells (HUVECs). The obtained results of the cytotoxicity assessment indicated that the tested compounds had nontoxic activity on Triticum aestivum L., while on Artemia franciscana Kellogg nauplii, only compounds 2c and 4c had moderate toxicity. On Daphnia magna, 4b and 4c showed high toxicity; 2a, 2b, and 2c moderate to high toxicity; only 4a and 4d were nontoxic. The compound-mediated cytotoxicity assays showed that several pyrrole compounds demonstrated dose- and time-dependent cytotoxic activity against all tested tumor cell lines, the highest antitumor properties being achieved by 4a and its homologue 4d, especially against LoVo colon cells.

Synthesis and crystal structure of hydrated μ-oxalato-bis{bis[3-methyl-5-(pyridin-2-yl)-1H-1,2,4-triazole]iron(II)} bis(toluenesulfonate) 2.75-hydrate

In the title compound [Fe2(C2O4)(C8H8N4)4](CH3C6H4SO3)2·2.75H2O, the two FeII ions have a highly distorted octahedral FeN4O2 environment formed by two bidentate triazole-based chelating ligands and a bis-bidentate oxalate bridging anion that connects the metal ions. Stabilization within the crystal structure is provided via a system of O—H...O and N—H...O hydrogen bonding, which determines the formation of a two-dimensional architecture along the a-axis direction.

Synthesis and crystal structure of bis[trans-diaqua(1,4,8,11-tetraazacyclotetradecane-κ4 N 1,N 4,N 8,N 11)nickel(II)] trans-(1,4,8,11-tetraazacyclotetradecane-κ4 N 1,N 4,N 8,N 11)bis[4,4′,4′′-(1,3,5-trimethylbenzene-2,4,6-triyl)tris(hydrogen phenylphosphonato-κO)]nickel(II) decahydrate

The components of the title compound, [Ni(C10H24N4)(H2O)2]2[Ni(C10H24N4)(C27H24O9P3)2]·10H2O are two centrosymmetric [Ni(C10H24N4)(H2O)2]2+ dications, a centrosymmetric [Ni(C10H24N4)(C27H24O9P3)2]4− tetra-anion and five crystallographically unique water molecules of crystallization. All of the nickel ions are coordinated by the four secondary N atoms of the macrocyclic cyclam ligands, which adopt the most energetically stable trans-III conformation, and the mutually trans O atoms of either water molecules in the cations or the phosphonate groups in the anion in a tetragonally distorted NiN4O2 octahedral coordination geometry. Strong O—H...O hydrogen bonds between the protonated and the non-protonated phosphonate O atoms of neighboring anions result in the formation of layers oriented parallel to the bc plane, which are linked into a three-dimensional network by virtue of numerous N—H...O and O—H...O hydrogen bonds arising from the sec-NH groups of the macrocycles, phosphonate O atoms and coordinated and non-coordinated water molecules.

Synthesis and crystal structure of diaqua(1,4,8,11-tetraazacyclotetradecane)zinc(II) bis(hydrogen 4-phosphonatobiphenyl-4′-carboxylato)(1,4,8,11-tetraazacyclotetradecane)zinc(II)

The coordination polyhedra of the zinc(II) ions in the complex cation and the anion of the title compound, viz. trans-ZnN₄O₂, are distorted octa­hedra. In the crystal, the hydrogen-bonding inter­actions between the N—H groups of the tetra­amine, the acidic groups of the anion and coordinated water mol­ecules result in formation of one-dimensional tapes running along the [10] direction, which are further arranged in sheets lying parallel to the (001) plane.

In the asymmetric unit of the title compound, trans-di­aqua­(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ⁴N¹,N⁴,N⁸,N¹¹)zinc(II) trans-bis­(hydrogen 4-phospho­natobiphenyl-4′-carboxyl­ato-κO)(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ⁴N¹,N⁴,N⁸,N¹¹)zinc(II), [Zn(C₁₀H₂₄N₄)(H₂O)₂][Zn(C₁₃H₉O₅P)₂(C₁₀H₂₄N₄)], both Zn atoms lie on crystallographic inversion centres and the atoms of the macrocycle in the cation are disordered over two sets of sites. In both macrocyclic units, the metal ions possess a tetra­gonally elongated ZnN₄O₂ octa­hedral environment formed by the four secondary N atoms of the macrocyclic ligand in the equatorial plane and the two trans O atoms of the water mol­ecules or anions in the axial positions, with the macrocyclic ligands adopting the most energetically favourable trans-III conformation. The average Zn—N bond lengths in both macrocyclic units do not differ significantly [2.112 (12) Å for the anion and 2.101 (3) Å for the cation] and are shorter than the average axial Zn—O bond lengths [2.189 (4) Å for phospho­nate and 2.295 (4) Å for aqua ligands]. In the crystal, the complex cations and anions are connected via hydrogen-bonding inter­actions between the N—H groups of the macrocycles, the O—H groups of coordinated water mol­ecules and the P—O—H groups of the acids as proton donors, and the O atoms of the phospho­nate and carboxyl­ate groups as acceptors, resulting in the formation of layers lying parallel to the (110) plane.

Aziridinium cation templating 3D lead halide hybrid perovskites

This study describes the synthesis of the first aziridinium-based compounds, namely hybrid perovskites (AzrH)PbHal₃ (where AzrH = aziridinium, Hal = Cl, Br or I). This highly reactive species was stabilized in 3D lead halide frameworks and was found to be a small enough organic cation to promote the formation of semiconducting organo-inorganic materials.

Diastereomeric dinickel(II) complexes with non-innocent bis(octaazamacrocyclic) ligands: isomerization, spectroelectrochemistry, DFT calculations and use in catalytic oxidation of cyclohexane

Diastereomeric dinickel(II) complexes with bis-octaazamacrocyclic 15-membered ligands [Ni(L1-3-L1-3)Ni] (4-6) have been prepared by oxidative dehydrogenation of nickel(II) complexes NiL1-3 (1-3) derived from 1,2- and 1,3-diketones and S-methylisothiocarbohydrazide. The compounds were characterized by elemental analysis, ESI mass spectrometry, and IR, UV-vis, 1H NMR, and 13C NMR spectroscopy. Single crystal X-ray diffraction (SC-XRD) confirmed the isolation of the anti and syn isomers of bis-octaazamacrocyclic dinickel(II) complexes 4a and 4s, the syn-configuration of 5s and the anti-configuration of the dinickel(II) complex 6a. Dimerization of prochiral nickel(II) complexes 1-3 generates two chiral centers at the bridging carbon atoms. The anti-complexes were isolated as meso-isomers (4a and 6a) and the syn-compounds as racemic mixtures of R,R/S,S-enantiomers (4s and 5s). The syn-anti isomerization (epimerization) of the isolated complexes in chloroform was disclosed. The isomerization kinetics of 5a was monitored at five different temperatures ranging from 20 °C to 50 °C by 1H NMR spectroscopy indicating the clean conversion of 5a into 5s. The activation barrier determined from the temperature dependence of the rate constants via the Eyring equation was found to be ΔH‡ = 114 ± 1 kJ mol-1 with activation entropy ΔS‡ = 13 ± 3 J K-1 mol-1. The complexes contain two low-spin nickel(II) ions in a square-planar coordination environment. The electrochemical behavior of 4a, 4s, 5s and 6a and the electronic structure of the oxidized species were studied by UV-vis-NIR-spectroelectrochemistry (SEC) and DFT calculations indicating the redox non-innocent behavior of the complexes. The dinickel(II) complexes 4a, 4s, 5s and 6a/6s were investigated as catalysts for microwave-assisted solvent-free oxidation of cyclohexane by tert-butyl hydroperoxide to produce a mixture of cyclohexanone and cyclohexanol (KA oil). The best value for KA oil yield (16%) was obtained with a mixture of 6a/6s after 2 h of microwave irradiation at 100 °C.

catena-Poly[[tetrakis(3,5-dimethyl-1H-pyrazole-κN 2)copper(II)]-μ2-sulfato-κ2 O:O′]: crystal structure and Hirshfeld surface analysis of a CuII coordination polymer

The title coordination pyrazole-containing coordination polymer, was synthesized using a one-pot reaction of copper powder, anhydrous copper(II) sulfate and 3,5-dimethyl-1H-pyrazole (Hdmpz) in aceto­nitrile under ambient conditions. The crystal structure is built up from packed parallel polymeric chains, which are stabilized by an extensive hydrogen-bond network, which forms with the participation of bridging sulfate ligands.

The title coordination polymer, [Cu(SO₄)(C₅H₈N₂)₄]_n, was synthesized using a one-pot reaction of copper powder, anhydrous copper(II) sulfate and 3,5-dimethyl-1H-pyrazole (Hdmpz) in aceto­nitrile under ambient conditions. The asymmetric unit can be described as a chain consisting of four [Cu(SO₄)(Hdmpz)₄] formula units that are connected to each other by a μ₂-sulfato-bridged ligand. The octa­hedral coordination geometry (O₂N₄) of all copper atoms is realized by coordination of four pyrazole ligands and two sulfate ligands. Four pyridine-like N atoms of the pyrazole ligands occupy the equatorial positions, while two oxygen atoms of two sulfate ligands are in axial positions. As a result of the sulfate ligand rotation, there is a pairwise alternation of terminal O atoms (which are not involved in coordination to the copper atom) of the SO₄ tetra­hedra. The Cu⋯Cu distances within one asymmetric unit are in the range 7.0842 (12)–7.1554 (12) Å. The crystal structure is built up from polymeric chains packed in a parallel manner along the b-axis direction. Hirshfeld surface analysis suggests that the most important contributions to the surface contacts are from H⋯H (74.7%), H⋯O/O⋯H (14.8%) and H⋯C/C⋯H (8.2%) inter­actions.

1D iron(II)-1,2,4-triazolic chains with spin crossover assembled from discrete trinuclear complexes

We report on a molecular cationic iron(II) complex with a 4-amino-1,2,4-triazole ligand and a tetraiodomercurate anion exhibiting an incomplete spin crossover (SCO). The complex exhibits an unusual disordered structure with a linear arrangement of ligand and water molecules that can potentially accommodate up to four iron atoms, but both terminal metal positions have half chemical occupancies, while occupancies of all ligands are full. This corresponds to the crystallisation of disordered trinuclear complexes arranged into 1D supramolecular chains. Iron cations have different N₆ or N₃O₃ coordination environments, leading to the thermally induced SCO in two thirds of the metal centres. This SCO behaviour was characterised by magnetic susceptibility measurements and Mössbauer spectroscopy.

Crystal structure of poly[[diaquatetra-μ2-cyanido-platinum(II)iron(II)] methanol 4/3-solvate]: a three-dimensional Hofmann clathrate analogue

The crystal structure of the title polymeric coordination compound, {[FePt(CN)₄(H₂O)₂]·1.33CH₃OH}_n, features a framework structure with pores in which disordered methanol solvent mol­ecules are situated.

In the title polymeric coordination compound, {[FePt(CN)₄(H₂O)₂]·1.33CH₃OH}_n, the Fe^II cation (site symmetry 4/mm.m) is coordinated by the N atoms of four cyanide anions (CN⁻) and the O atoms of two water mol­ecules, forming a nearly regular [FeN₄O₂] octa­hedron. According the Fe—N and Fe—O bond lengths, the Fe^II atom is in the high-spin state. The cyanide anions act in a bridging manner to connect the Fe^II and Pt^II atoms. The [Pt(CN)₄]^2– moieties (Pt with site symmetry 4/mm.m) have a perfect square-planar shape. The latter anion is located perpendicular to the FeN₄ plane, thus ensuring the creation of a three-dimensional framework. The crystal structure features methanol solvent mol­ecules of which 4/3 were located per Fe^II cation. These solvent mol­ecules are located in hexa­gonal pores; they inter­act with coordinating water mol­ecules through weak hydrogen bonds. Other guest mol­ecules could not be modelled in a satisfactory way and their contribution to the scattering was removed by a mask procedure.

Two-Step Spin Crossover in Hofmann-Type Coordination Polymers [Fe(2-phenylpyrazine)2{M(CN)2}2] (M = Ag, Au)

Two 2D Hofmann-type complexes of the composition [Fe(Phpz)₂{M(CN)₂}₂] (where Phpz = 2-phenylpyrazine; M = Ag, Au) have been synthesized, and their spin-crossover (SCO) behavior has been thoroughly characterized. Single-crystal X-ray analysis reveals that these complexes contain a crystallographically unique Fe(II) center surrounded by two axial Phpz ligands and four equatorial cyanide [M(CN)₂]^- bridges. It is shown that, using of a ligand with two aromatic rings, an advanced system of weak supramolecular interactions (metal-metal, C-H···M, and π···π stacking contacts) is realized. This ensures additional stabilization of the structures and the absence of solvent-accessible voids due to dense packing. Both complexes are characterized by a highly reproducible two-step SCO behavior, as revealed by different techniques (superconducting quantum interference device magnetometry, optical microscopy, etc.). Research shows the exceptional role of the presence of various supramolecular interactions in the structure and the influence of the bulky substituent in the ligand on SCO behavior. Moreover, the perspective of substituted pyrazines for the design of new switchable materials is supported by this work.

Crystal structures of 5-bromo-1-arylpyrazoles and their halogen bonding features

Single crystal X-ray diffraction analysis was employed to investigate the supramolecular properties of five 5-brominated pyrazoles in order to evaluate the role of the Br atom in the formation of...

Solvatomorphism, polymorphism and spin crossover in bis[hydrotris(1,2,3-triazol-1-yl)borate]iron(ii)

We describe a detailed characterization of the spin crossover bis[hydrotris(1,2,3-triazol-1-yl)borate]iron(ii) complex ([Fe(HB(1,2,3-tz)3)2]) and solvatomorphs obtained by recrystallisation or single crystal to single crystal transformation.