Palladium(II)-Stabilized Pyridine-2-Diazotates: Synthesis, Structural Characterization, and Cytotoxicity Studies

Robust Supramolecular Dimers Derived from Benzylic-Substituted 1,2,4-Selenodiazolium Salts Featuring Selenium⋯π Chalcogen Bonding

The series of benzylic-substituted 1,2,4-selenodiazolium salts were prepared via cyclization reaction between 2-pyridylselenyl chlorides and nitriles and fully characterized. Substitution of the Cl anion by weakly binding anions promoted the formation supramolecular dimers featuring four center Se₂N₂ chalcogen bonding and two antiparallel selenium⋯π interactions. Chalcogen bonding interactions were studied using density functional theory calculations, molecular electrostatic potential (MEP) surfaces, the quantum theory of atoms-in-molecules (QTAIM), and the noncovalent interaction (NCI) plot. The investigations revealed fundamental role of the selenium⋯π contacts that are stronger than the Se⋯N interactions in supramolecular dimers. Importantly, described herein, the benzylic substitution approach can be utilized for reliable supramolecular dimerization of selenodiazolium cations in the solid state, which can be employed in supramolecular engineering.

Structural Organization of Dibromodiazadienes in the Crystal and Identification of Br···O Halogen Bonding Involving the Nitro Group

Nitro functionalized dibromodiazadiene dyes were prepared and fully characterized including X-ray single crystal analysis. Electron deficient dibromodiazadienes were found to be able to act as donors of halogen bonding (XB), while the nitro group acted as an acceptor of the XB. Depending on the substituents, the Br···O XB competed with other weak interactions, and for some of the dyes, they even outcompeted the XB involving the nitro group. However, the nitro functionalized dibromoalkenes 6a and 10a, which had only the nitro moiety as the most plausible acceptor of the XB, reliably formed 1D chains via Br⋯O XB. Experimental work was supported by the DFT calculations and topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method).

Towards Anion Recognition and Precipitation with Water-Soluble 1,2,4-Selenodiazolium Salts: Combined Structural and Theoretical Study

The synthesis and structural characterization of a series of supramolecular complexes of bicyclic cationic pyridine-fused 1,2,4-selenodiazoles with various anions is reported. The binding of trifluoroacetate, tetrachloroaurate, tetraphenylborate, perrhenate, and pertechnetate anions in the solid state is regarded. All the anions interact with selenodiazolium cations exclusively via a pair of “chelating” Se⋯O and H⋯O non-covalent interactions, which make them an attractive, novel, non-classical supramolecular recognition unit or a synthon. Trifluoroacetate salts were conveniently generated via novel oxidation reaction of 2,2′-dipyridyl diselenide with bis(trifluoroacetoxy)iodo)benzene in the presence of corresponding nitriles. Isolation and structural characterization of transient 2-pyridylselenyl trifluoroacetate was achieved. X-ray analysis has demonstrated that the latter forms dimers in the solid state featuring very short and strong Se⋯O and Se⋯N ChB contacts. 1,2,4-Selenodiazolium trifluoroacetates or halides show good solubility in water. In contrast, (AuCl₄)⁻, (ReO₄)⁻, or (TcO₄)⁻ derivatives immediately precipitate from aqueous solutions. Structural features of these supramolecular complexes in the solid state are discussed. The nature and energies of the non-covalent interactions in novel assembles were studied by the theoretical methods. To the best of our knowledge, this is the first study that regards perrhenate and pertechnetate as acceptors in ChB interactions. The results presented here will be useful for further developments in anion recognition and precipitation involving cationic 1,2,4-selenodiazoles.

Triarylazoimidazole-ZnII, CdII, and HgII Complexes: Structures, Photophysics, and Antibacterial Properties

Novel triarylazoimidazoles containing strong electron donors (p-NEt2) or acceptors (p-NO2) by the azoaryl group, and their group 12 metal complexes were synthesized and fully characterized, including X-ray analysis for several complexes. Novel complexes exhibit red photo-luminescence emission (Φ up to  0.21) in a solution. Moreover, the antibacterial activity of complexes was tested against Gram-positive microorganism S. aureus and Gram-negative microorganism E. coli.

Aurophilic Interactions in Cationic Three-Coordinate Gold(I) Bipyridyl/Isocyanide Complex

Gold(I) isocyanide complexes featuring Au···Au interactions attract considerable attention because of their tunable photophysical properties. Although the synthetic exploration of isocyanide gold(I) complexes seems reasonable, their structural diversity is mainly limited to linear gold(I) derivatives. The synthesis and structural characterization of cationic three-coordinate gold(I) mixed 2,2′-bipyridyl/isocyanide complex are presented here for the first time. Cationic gold species form supramolecular dimers in the solid state via attractive Au···Au interactions. The nature and energies of aurophilic contacts, which are responsible for dimerization in the solid state, were studied by DFT calculations together with QTAIM, ELF, RDG, and NCI techniques and Hirshfeld surface analysis. The estimated energy of the aurophilic interactions was 6.3 kcal/mol.

Exploring Supramolecular Assembly Space of Cationic 1,2,4-Selenodiazoles: Effect of the Substituent at the Carbon Atom and Anions

Chalcogenodiazoles have been intensively studied in recent years in the context of their supramolecular chemistry. In contrast, the newly discovered cationic 1,2,4-selenodiazole supramolecular building blocks, which can be obtained via coupling between 2-pyridylselenyl halides and nitriles, are virtually unexplored. A significant advantage of the latter is their facile structural tunability via the variation of nitriles, which could allow a fine tuning of their self-assembly in the solid state. Here, we explore the influence of the substituent (which derives from the nitrile) and counterions on the supramolecular assembly of cationic 1,2,4-selenodiazoles via chalcogen bonding.

2-Pyridylselenenyl versus 2-Pyridyltellurenyl Halides: Symmetrical Chalcogen Bonding in the Solid State and Reactivity towards Nitriles

The synthesis of 2-pyridyltellurenyl bromide via Br2 oxidative cleavage of the Te–Te bond of dipyridylditelluride is reported. Single-crystal X-ray diffraction analysis of 2-pyridyltellurenyl bromide demonstrated that the Te atom of 2-pyridyltellurenyl bromide was involved in four different noncovalent contacts: Te⋯Te interactions, two Te⋯Br ChB, and one Te⋯N ChB contact forming 3D supramolecular symmetrical framework. In contrast to 2-pyridylselenenyl halides, the Te congener does not react with nitriles furnishing cyclization products. 2-Pyridylselenenyl chloride was demonstrated to easily form the corresponding adduct with benzonitrile. The cyclization product was studied by the single-crystal X-ray diffraction analysis, which revealed that in contrast to earlier studied cationic 1,2,4-selenadiazoles, here we observed that the adduct with benzonitrile formed supramolecular dimers via Se⋯Se interactions in the solid state, which were never observed before for 1,2,4-selenadiazoles.

Unsymmetrical Trifluoromethyl Methoxyphenyl β-Diketones: Effect of the Position of Methoxy Group and Coordination at Cu(II) on Biological Activity

Copper(II) complexes with 1,1,1-trifluoro-4-(4-methoxyphenyl)butan-2,4-dione (HL1) were synthesized and characterized by elemental analysis, FT-IR spectroscopy, and single crystal X-ray diffraction. The biological properties of HL1 and cis-[Cu(L1)₂(DMSO)] (3) were examined against Gram-positive and Gram-negative bacteria and opportunistic unicellular fungi. The cytotoxicity was estimated towards the HeLa and Vero cell lines. Complex 3 demonstrated antibacterial activity towards S. aureus comparable to that of streptomycin, lower antifungal activity than the ligand HL1 and moderate cytotoxicity. The bioactivity was compared with the activity of compounds of similar structures. The effect of changing the position of the methoxy group at the aromatic ring in the ligand moiety of the complexes on their antimicrobial and cytotoxic activity was explored. We propose that complex 3 has lower bioavailability and reduced bioactivity than expected due to strong intermolecular contacts. In addition, molecular docking studies provided theoretical information on the interactions of tested compounds with ribonucleotide reductase subunit R2, as well as the chaperones Hsp70 and Hsp90, which are important biomolecular targets for antitumor and antimicrobial drug search and design. The obtained results revealed that the complexes displayed enhanced affinity over organic ligands. Taken together, the copper(II) complexes with the trifluoromethyl methoxyphenyl-substituted β-diketones could be considered as promising anticancer agents with antibacterial properties.

2,3,5-Metallotriazoles: Amphoteric Mesoionic Chelates from Nitrosoguanidines

Soluble nitrosoguanidine- and N-methylnitrosoguanidine-based metallotriazole complexes of ruthenium(II) monocarbonyls have been prepared and characterized. Both nitrosoguanidines prove to be strong chelates with the formally π-accepting nitroso nitrogen binding cis to carbon monoxide and a π-donating amide trans to the CO. The resulting ensemble consists of ruthenium examples of 1-metallo-2,3,5-triazoles. The ruthenium coordination sphere is completed by anions, either H^-, Cl^-, or Ph^-, trans to the nitroso group as well as two mutually trans PPh₃ groups. The π-donating amide group is formally sp² hybridized with a planar nitrogen to give a strongly bound five-membered chelating anion. Together, these results illustrate the remarkable potential for the nitrosoguanidinates as a family of new metal chelates.

Attractive fluorine···fluorine interactions between perfluorinated alkyl chains: a case of perfluorinated Cu(II) diiminate Cu[C2F5–C(NH)–CF=C(NH)–CF3]2

A synthesis of the perfluorinated copper diiminate complex Cu[C2F5–C(NH)–CF=C(NH)–CF3]2 (3) and its self-assembly into infinite 1D chains in the crystal via Type II C(sp3)–F···F–C(sp3) contacts between perfluoroethyl substituents is reported. Rare Type II F···F interactions were studied by DFT calculations and topological analysis of the electron density distribution within the formalism of Bader’s theory (QTAIM method). This is the first report which discusses Type II contacts between perfuoroalkyl chains.

Unprecedented Coordination-Induced Bright Red Emission from Group 12 Metal-Bound Triarylazoimidazoles

Arylazoimidazoles are important dyes which were intensively studied in the past. In contrast, triarylazoimidazoles (derivatives which carry aryl substituents at the imidazole core) received almost no attention in the scientific literature. Here, we report a new family of simple and easily accessible triarylazoimidazole-group 12 metal complexes, which feature highly efficient photo-luminescence emission (Φ up to  0.44). Novel compounds exhibit bright red emission in solution, which could be excited with a visible light.

Crystal structure of 2-[(E)-2-(4-bromo-phen-yl)diazen-1-yl]-4,5-bis-(4-meth-oxy-phen-yl)-1H-imidazole: the first example of a structurally characterized tri-aryl-azo-imid-azole

The title compound, C23H19BrN4O2, is a product of an azo coupling reaction between 3,4-bis-(4-meth-oxy-phen-yl)imidazole and 4-bromo-phenyl-diazo-nium tetra-fluoro-borate. Its crystal structure was determined using data collected at 120 K. The mol-ecule adopts a trans configuration with respect to the N=N double bond. The imidazole and aryl rings attached to the azo linkage are coplanar within 12.73 (14)°, which indicates significant electron delocalization within the mol-ecule. In the crystal, the mol-ecules form centrosymmetric dimers via pairs of N-H⋯O hydrogen bonds.

Modulation of Band Gaps toward Varying Conductivities in Heterometallic One-Dimensional Chains by Ligand Alteration and Third Metal Insertion

A heterometallic one-dimensional (1-D) chain consisting of multiple kinds of metals, Rh, Pt, and Pd, with direct metal-metal bonds was successfully obtained by mixing a Rh dinuclear complex and Pt-Pd-Pt trinuclear complex. The Pt-Pd-Pt trinuclear complex can be reversibly one-electron-oxidized or -reduced, where the electron paramagnetic resonance spectrum of the one-electron-oxidized one shows an axially symmetric signal with hyperfine splitting by two Pt and Pd, indicating that an unpaired electron is delocalized to the d _{z ²} orbital of Pt-Pd-Pt. Utilized with the highest occupied molecular orbital and lowest unoccupied molecular orbital interaction at the d _{z ²} orbital, simple mixing of the Pt-Pd-Pt trinuclear complex and Rh dinuclear complex in adequate solvents afforded heterometallic 1-D chains, which are aligned as -Rh-Rh-Pt-Pd-Pt-. Several physical measurements revealed that the metal oxidation state is +2. Diffuse reflectance spectra and theoretical calculations show that heterometallic 1-D chains have σ-type conduction and valence bands where π*(Rh₂) are lying between them, whose gaps become narrower than the prototype chains aligned as -Rh-Rh-Pt-Pt-Pt-Pt-. The narrower band gaps are induced by destabilization of the σ-type valence bands and accompanied by insertion of Pd ions because the d-orbital energy level of Pd is closer in value to Rh compared with Pt. Flash-photolysis time-resolved microwave conductivity measurements exhibited an increase in the product of charge carrier mobility and its generation efficiency (8.1 × 10^-5 to 4.6 × 10^-4 cm² V^-1 s^-1) with narrowing the band gaps, suggesting that the better conductivity is attributed to shorter metal-metal distances in 1-D chains. These results imply the possibilities of controlling band gap with ligand modification and third metal insertion in heterometallic 1-D chains to show various conductivities.

Unexpected synthesis and crystal structure of N-{2-[2-(2-acetyl-ethen-yl)phen-oxy]eth-yl}-N-ethenyl-4-methyl-benzene-sulfonamide

The title compound, C21H23NO4S, obtained by alkaline treatment of 1,5-bis-(1-phen-oxy)-3-aza-pentane at moderate heating, is a N-tosyl-ated secondary vinyl-amine. An intra-molecular S=O⋯H-C hydrogen bond generates a 13-membered ring. The benzalacetone moiety adopts a trans conformation with respect to the C=C double bond, which is slightly longer than usual due to the conjugation with a neighbouring acetyl group. Theoretical predictions of potential biological activities were performed, suggesting that the title compound can inhibit gluconate 2-de-hydrogenase (85% probability), as well as to act as a mucomembranous protector (73%).

Halogenated Diazabutadiene Dyes: Synthesis, Structures, Supramolecular Features, and Theoretical Studies

Novel halogenated aromatic dichlorodiazadienes were prepared via copper-mediated oxidative coupling between the corresponding hydrazones and CCl₄. These rare azo-dyes were characterized using ¹H and ¹³C NMR techniques and X-ray diffraction analysis for five halogenated dichlorodiazadienes. Multiple non-covalent halogen···halogen interactions were detected in the solid state and studied by DFT calculations and topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method). Theoretical studies demonstrated that non-covalent halogen···halogen interactions play crucial role in self-assembly of highly polarizable dichlorodiazadienes. Thus, halogen bonding can dictate a packing preference in the solid state for this class of dichloro-substituted heterodienes, which could be a convenient tool for a fine tuning of the properties of this novel class of dyes.

Attractive halogen···halogen interactions in crystal structure of trans-dibromogold(III) complex

A synthesis of the trans-dibromogold(III) t-Bu-Xantphos complex and its self-assembly into infinite 1-dimensional chain in the solid state is reported. The new complex characterized using elemental analyses (C, H, N), ESI-MS, 1H and 13C NMR techniques and X-ray diffraction analysis. Results of DFT calculations followed by the topological analysis of the electron density distribution within the framework of QTAIM method at the ωB97XD/DZP-DKH level of theory reveal that strength of attractive intermolecular non-covalent interactions Br···Br in the crystal is 1.2–1.6 kcal/mol.