Bridge vs Terminal Cyano-coordination in Binuclear Cobalt Porphyrin Dimers: Interplay of Electrons between Metal and Ligand and Spin-Coupling via Bridge

Three cyano-coordinated cobalt porphyrin dimers were synthesized and thoroughly characterized. The X-ray structure of the complexes reveals that cyanide binds in a terminal fashion in both the anti and trans isomers of ethane- and ethylene-bridged cobalt porphyrin dimers, while in the cis ethylene-bridged dimer, cyanides bind in both terminal and bridging modes. The nonconjugated ethane-bridged complex stabilizes exclusively a diamagnetic metal-centered oxidation of type CoIII(por)(CN)2 both in the solid and in solution. In contrast, the complexes with the conjugated ethylene-bridge contain signatures of both paramagnetic ligand-centered oxidation of the type CoII(por•+)(CN)2 and diamagnetic metal-centered oxidation of type CoIII(por)(CN)2 with the metal-centered oxidized species being the major component in the solid state as observed in XPS, while the ligand-centered oxidized species are present in a significant amount in solution. 1H NMR spectrum in solution displays two set of signals corresponding to the simultaneous presence of both the diamagnetic and paramagnetic species. EPR and magnetic investigation reveal that there is a moderate ferromagnetic coupling between the unpaired electrons of the low-spin CoII center and the porphyrin π-cation radical in CoII(por•+)(CN)2 species as well as an antiferromagnetic coupling between the two CoII(por•+) units through the ethylene and CN bridges.

Water-Mediated Charge Transfer and Electron Localization in a Co3Fe2 Cyanide-Bridged Trigonal Bipyramidal Complex

The effects of temperature and chemical environment on a pentanuclear cyanide-bridged, trigonal bipyramidal molecular paramagnet have been investigated. Using element- and oxidation state-specific near-ambient pressure X-ray photoemission spectroscopy (NAP-XPS) to probe charge transfer and second order, nonlinear vibrational spectroscopy, which is sensitive to symmetry changes based on charge (de)localization coupled with DFT, a detailed picture of environmental effects on charge-transfer-induced spin transitions is presented. The molecular cluster, Co3Fe2(tmphen)6(μ-CN)6(t-CN)6, abbrev. Co3Fe2, shows changes in electronic behavior depending on the chemical environment. NAP-XPS shows that temperature changes induce a metal-to-metal charge transfer (MMCT) in Co3Fe2 between a Co and Fe center, while cycling between ultrahigh vacuum and 2 mbar of water at constant temperature causes oxidation state changes not fully captured by the MMCT picture. Sum frequency generation vibrational spectroscopy (SFG-VS) probes the role of the cyanide ligand, which controls the electron (de)localization via the superexchange coupling. Spectral shifts and intensity changes indicate a change from a charge delocalized, Robin-Day class II/III high spin state to a charge-localized, class I low spin state consistent with DFT. In the presence of a H-bonding solvent, the complex adopts a localized electronic structure, while removal of the solvent delocalizes the charges and drives an MMCT. This change in Robin-Day classification of the complex as a function of chemical environment results in reversible switching of the dipole moment, analogous to molecular multiferroics. These results illustrate the important role of the chemical environment and solvation on underlying charge and spin transitions in this and related complexes.

Heterobimetallic cyanide-bridged FeIII(μ-CN)MII complexes (M = Mn and Cu): synthesis, structure and magnetism

Systematic magneto-structural studies reveal ‘[FeIII(Tp)(CN)2(μ-CN)MnIICl(L1/L2)]′ (both antiferromagnetic) and [FeIII(Tp)(CN)2(μ-CN)CuII(L1/L2)]+′(L1 ferro- and L2 antiferromagnetic).

Electrodeposited cobalt hexacyanoferrate electrode as a non-enzymatic glucose sensor under neutral conditions

A CoFe Prussian blue analogue (CoFe PB) modified FTO electrode, prepared via a facile electrodeposition method, is investigated as a non-enzymatic glucose sensor under neutral conditions. The electrode exhibits a linear detection of glucose in the 0.1-8.2 mmol/L range with a detection limit of 67 μM, a sensitivity of 18.69 μA/mM.cm², and a fast response time of less than 7 s under neutral conditions. Its stability is confirmed with both electrochemical experiments and characterization studies performed on the pristine and post-mortem electrode. We also conducted a comprehensive electrochemical analysis to elucidate the identity of the active site and the glucose oxidation mechanism on the Prussian blue surface.

X-ray Structure and Magnetic Properties of Heterobimetallic Chains Based on the Use of an Octacyanidodicobalt(III) Complex as Metalloligand

The assembly of [Co2III(μ-2,5-dpp)(CN)8]2− anions and [MII(CH3OH)2(DMSO)2]2+ cations resulted into the formation of two heterobimetallic 1D coordination polymers of formula [MII(CH3OH)2(DMSO)2(μ-NC)2Co2III(μ-2,5-dpp)(CN)6]n·4nCH3OH [M = CoII (1)/FeII (2) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine. The [Co2III(μ-2,5-dpp)(CN)8]2− metalloligand coordinates the paramagnetic [MII(CH3OH)2(DMSO)2]2+ complex cations, in a bis-monodentate fashion, to give rise to neutral heterobimetallic chains. Cryomagnetic dc (1.9–300 K) and ac (2.0–13 K) magnetic measurements for 1 and 2 show the presence of Co(II)HS (1) and Fe(II)HS (2) ions (HS – high-spin), respectively, with D values of +53.7(5) (1) and −5.1(3) cm−1 (2) and slow magnetic relaxation for 1, this compound being a new example of SIM with transversal magnetic anisotropy. Low-temperature Q-band EPR study of 1 confirms that D value is positive, which reveals the occurrence of a strong asymmetry in the g-tensors and allows a rough estimation of the E/D ratio, whereas 2 is EPR silent. Theoretical calculations by CASSCF/NEVPT2 on 1 and 2 support the results from magnetometry and EPR. The analysis of the ac magnetic measurements of 1 shows that the relaxation of M takes place in the ground state under external magnetic dc fields through dominant Raman and direct spin-phonon processes.

Rational Design of Polyamine-Based Cryogels for Metal Ion Sorption

Here we report the method of fabrication of supermacroporous monolith sorbents (cryogels) via covalent cross-linking of polyallylamine (PAA) with diglycidyl ether of 1,4-butandiol. Using comparative analysis of the permeability and sorption performance of the obtained PAA cryogels and earlier developed polyethyleneimine (PEI) cryogels, we have demonstrated the advantages and disadvantages of these polymers as sorbents of heavy metal ions (Cu(II), Zn(II), Cd(II), and Ni(II)) in fixed-bed applications and as supermacroporous matrices for the fabrication of composite cryogels containing copper ferrocyanide (CuFCN) for cesium ion sorption. Applying the rate constant distribution (RCD) model to the kinetic curves of Cu(II) ion sorption on PAA and PEI cryogels, we have elucidated the difference in sorption/desorption rates and affinity constants of these materials and showed that physical sorption contributed to the Cu(II) uptake by PAA, but not to that by PEI cryogels. It was shown that PAA cryogels had significantly higher selectivity for Cu(II) sorption in the presence of Zn(II) and Cd(II) ions in comparison with that of PEI cryogels, while irreversible sorption of Co(II) ions by PEI can be used for the separation of Ni(II) and Co(II) ions. Using IR and Mössbauer spectroscopy, we have demonstrated that strong complexation of Cu(II) ions with PEI significantly affects the in situ formation of Cu(II) ferrocyanide nanosorbents leading to their inefficiency for Cs⁺ ions selective uptake, whereas PAA cryogel was applicable for the fabrication of efficient monolith composites via the in situ formation of CuFCN or loading of ex situ formed CuFCN colloids.

Homo- and Hetero-Oligonuclear Complexes of Platinum Group Metals (PGM) Coordinated by Imine Schiff Base Ligands

Chemistry of Schiff base (SB) ligands began in 1864 due to the discovery made by Hugo Schiff (Schiff, H., Justus Liebigs Ann. der Chemie 1864, 131 (1), 118-119). However, there is still a vivid interest in coordination compounds based on imine ligands. The aim of this paper is to review the most recent concepts on construction of homo- and hetero-oligonuclear Schiff base coordination compounds narrowed down to the less frequently considered complexes of platinum group metals (PGM). The combination of SB and PGM in oligonuclear entities has several advantages over mononuclear or polynuclear species. Such complexes usually exhibit better electroluminescent, magnetic and/or catalytic properties than mononuclear ones due to intermetallic interactions and frequently have better solubility than polymers. Various construction strategies of oligodentate imine ligands for coordination of PGM are surveyed including simple imine ligands, non-innocent 1,2-diimines, chelating imine systems with additional N/O/S atoms, classic N2O2-compartmental Schiff bases and their modifications resulting in acyclic fused ligands, macrocycles such as calixsalens, metallohelical structures, nano-sized molecular wheels and hybrid materials incorporating mesoionic species. Co-crystallization and formation of metallophilic interactions to extend the mononuclear entities up to oligonuclear coordination species are also discussed.

A cyanide-bridged FeIII-MnII heterobimetallic one-dimensional coordination polymer: synthesis, crystal structure, experimental and theoretical magnetism investigation

A new cyanide-bridged Fe^III-Mn^II heterobimetallic coordination polymer (CP), namely catena-poly[[[N,N'-(1,2-phenylene)bis(pyridine-2-carboxamidato)-κ⁴N,N',N'',N''']iron(III)]-μ-cyanido-κ²C:N-[bis(4,4'-bipyridine-κN)bis(methanol-κO)manganese(II)]-μ-cyanido-κ²N:C], {[FeMn(C₁₈H₁₂N₄O₂)(CN)₂(C₁₀H₈N₂)₂(CH₃OH)₂]ClO₄}_n, (1), was prepared by the self-assembly of the trans-dicyanidoiron(III)-containing building block [Fe(bpb)(CN)₂]^- [bpb^2- = N,N'-(1,2-phenylene)bis(pyridine-2-carboxamidate)], [Mn(ClO₄)₂]·6H₂O and 4,4'-bipyridine, and was structurally characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography and powder X-ray diffraction (PXRD). Single-crystal X-ray diffraction analysis shows that CP 1 possesses a cationic linear chain structure consisting of alternating cyanide-bridged Fe-Mn units, with free perchlorate as the charge-balancing anion, which can be further extended into a two-dimensional supramolecular sheet structure via inter-chain π-π interactions between the 4,4'-bipyridine ligands. Within the chain, each Mn^II ion is six-coordinated by an N₆ unit and is involved in a slightly distorted octahedral coordination geometry. Investigation of the magnetic properties of 1 reveals an antiferromagnetic coupling between the cyanide-bridged Fe^III and Mn^II ions. A best fit of the magnetic susceptibility based on the one-dimensional alternating chain model leads to the magnetic coupling constants J₁ = -1.35 and J₂ = -1.05 cm^-1, and the antiferromagnetic coupling was further confirmed by spin Hamiltonian-based density functional theoretical (DFT) calculations.

Dicyanometalates as Building Blocks for Multinuclear Iron(II) Spin-Crossover Complexes

A synthetic strategy featuring dicyanometalates [M(CN)₂]^- (M = Ag, Au) as N-coordinating ditopic linkers connecting partially blocked Fe^II centers has been employed to produce heterometallic hexanuclear complexes, which exhibit spin-crossover (SCO) behavior at the Fe^II sites. The reaction between tris(2-pyridylmethyl)amine (tpma)-capped Fe^II ions and [Ag(CN)₂]^- proceeded with partial decomposition of the dicyanoargentate and led to the formation of {[Fe(tpma)]₄(μ-CN)₂[μ-Ag(CN)₂]₂}(ClO₄)₄·3H₂O (1), in which both [Ag(CN)₂]^- and CN^- act as bridging ligands, and the opposite [Ag(CN)₂]^- bridges are engaged in a pronounced argentophilic d¹⁰-d¹⁰ interaction. In an analogous synthesis, the more stable [Au(CN)₂]^- species remained intact and furnished the complex {[Fe(tpma)]₂[μ-Au₂(CN)₄]₂} (2), which features two Fe^II centers bridged by two [Au₂(CN)₄]^2- dimers. The use of S,S'-bis(2-pyridylmethyl)-1,2-thioethane (bpte) as a mixed-donor, N₂S₂-coordinating capping ligand yielded {[Fe(bpte)]₂[μ-Au₂(CN)₄]₂} (3), with a structure analogous to that of 2. Variable-temperature magnetic susceptibility measurements revealed that complexes 1-3 exhibit an onset of SCO above 350 K. Measurements above 400 K further confirmed the occurrence of a gradual spin-state conversion for complex 2.

The electronic structure of f-element Prussian blue analogs determined by soft X-ray absorption spectroscopy

In molecular solids derived from Prussian blue, intermetallic charge transfer is fostered through a cyano bridge two metal ions. In this study, isostructural trivalent lanthanide and tetravalent actinide Prussian blue analogs' valence orbitals are probed by soft X-ray absorption measurements.

Two-electron redox-active tricyano iron(ii) complex with 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine as a building block for coordination polymers

A new tricyano iron(ii) building unit, [{K(H2O)4}{FeII(CN)3(L)}]·3H2O (1), was synthesized by the reaction of Moor's salts with 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (L) as a capping ligand. X-ray structural analysis reveals that the mononuclear iron(ii) tricyano complex consists of one ligand and three cyanide groups, with K+ ions coordinated between neighboring units to form a one-dimensional chain network structure. 1 shows two reversible redox waves at +0.713 and -0.849 V vs. SCE, which are assigned as Fe(ii)/Fe(iii) and L/L˙- processes, respectively. One-dimensional 4,2-ribbon chain type coordination polymers, [MII(H2O)2{FeII(CN)3(L)}2]·6H2O (M = Fe (2) and Mn (3)), were synthesized by using 1 as a building unit. Cryomagnetic studies reveals that 2 and 3 show paramagnetic behaviour of S = 2 and 5/2, respectively. On the other hand, reaction of 1 and Gd(NO3)3·6H2O forms another one-dimensional chain, [GdIII(NO3)2(H2O)3{FeII(CN)3(L)}]·0.5H2O·2CH3OH (4), showing S = 7/2 paramagnetic behaviour.

Syntheses, structures, and magnetic properties of three new MnII-[MoIII(CN)7]4- molecular magnets

By reaction of K4[MoIII(CN)7]·2H2O, Mn(ClO4)2·6H2O and bidentate chelating ligands, three new cyano-bridged compounds, namely Mn2(3-pypz)(H2O)(CH3CN)[Mo(CN)7] (1), Mn2(1-pypz)(H2O)(CH3CN)[Mo(CN)7] (2) and Mn2(pyim)(H2O)(CH3CN)[Mo(CN)7] (3) (3-pypz = 2-(1H-pyrazol-3-yl)pyridine, 1-pypz = 2-(1H-pyrazol-1-yl)pyridine, pyim = 2-(1H-imidazol-2-yl)pyridine), have been synthesized and characterized structurally and magnetically. Single crystal X-ray analyses revealed that although the chelating ligands are different, compounds 1 to 3 are isomorphous and crystallize in the same monoclinic space group C2/m. Connected by the bridging cyano groups, one crystallographically unique [Mo(CN)7]4- unit and three crystallographically unique MnII ions of different coordination environments form similar three-dimensional frameworks, which have a four-nodal 3,4,4,7-connecting topological net with a vertex symbol of {43}{44·62}2{410·611}. Magnetic measurements revealed that compounds 1-3 display long-range magnetic ordering with critical temperatures of 64, 66 and 62 K, respectively. These compounds are rare examples of a small number of chelating co-ligand coordinated [Mo(CN)7]4--based magnetic materials. Specifically, the bidentate chelating ligands were successfully introduced into the heptacyanomolybdate system for the first time.

MnIII-FeIII Heterometallic Compounds within Hydrogen-Bonded Supramolecular Networks Promoted by an [Fe(CN)5(CNH)]2- Building Block: Structural and Magnetic Properties

The reaction of [Fe(CN)₆]^3- and [Mn(acacen)]⁺ (H₂acacen = N, N'-bis(acetylacetone)ethylenediamine) building units in the presence of supramolecular cations, [(F-Anil)(18-crown-6)]⁺ (F-Anil⁺ = 3-fluoroanilinium) or [(Me-F-Anil)(18-crown-6)]⁺ (Me-F-Anil⁺ = 3-fluoro-4-methylanilinium), affords two new bimetallic compounds, [(F-Anil)(18-crown-6)][Mn(acacen)Fe(CN)₅(CNH)]·MeOH (1) and [(Me-F-Anil)(18-crown-6)][Mn(acacen)(MeOH)Fe(CN)₅(CNH)]·MeOH (2), respectively. Compound 1 exhibits a one-dimensional topology, while compound 2 is a dinuclear discrete system due to the coordination of a MeOH molecule at the axial position of the [Mn(acacen)]^- unit. For both systems, the acidity of the corresponding supramolecular cation triggers the protonation of the Fe^III moiety as [Fe(CN)₅(CNH)]^2-. Moreover, the resulting -CNH ligand induces hydrogen bonding interactions connecting the chains for 1 or the molecules for 2 into higher dimensional supramolecular networks. Magnetic properties of compounds incorporating these [Fe(CN)₅(CNH)]^2- building blocks were, for the first time, thoroughly investigated, indicating a three-dimensional antiferromagnetic order of single-chain magnets for 1 and an antiferromagnetically interacting S = 3/2 spin ground state for 2.

Bis(μ-chloro) bridged 1D CuI and CuII coordination polymer complex and mononuclear CuII complex: Synthesis, crystal structure and biological properties

A novel one-dimensional coordination polymer containing Cu(I)Cu(II) core with chloro bridge on Cu(I) and ligand bridge on Cu(II) ions (1) and a mononuclear Cu(II) complex (2) have been synthesized from the reactions of 3- and 4-methoxy-3-quinolin-3-ylimino-methyl-2-phenol with [CuCl₂(PPh₃)₂]. The ligands and the complexes have been characterized by spectral and analytical methods. In addition, the structures of both the ligands and the copper complexes were confirmed by single crystal X-ray diffraction studies. In both complexes, the phenolic oxygen and azomethine nitrogen atom of the ligand coordinate to the copper ions in a monobasic bidentate manner resulting in an approximately square planar geometry around the copper ion. In the polymeric complex, the N atom of the quinoline ring is coordinated to Cu(I) in addition to the phenolic oxygen and azomethine nitrogen atom coordinating to Cu(II) ion, thus bridging Cu(I) and Cu(II) ions in the complex. The interactions of the compounds with calf thymus DNA (CT-DNA) have been followed by absorption and emission titration methods, which revealed that the compounds interact with CT-DNA through intercalation. Further, the interactions of the compounds with bovine serum albumin (BSA) were also investigated using UV-visible, fluorescence spectroscopic methods. The results indicated that complex 1 exhibited a stronger binding to CT-DNA and BSA than the free ligands and complex 2. In addition, the in vitro cytotoxicity experiment showed that complexes 1 and 2 exhibit potent cytotoxic properties against PANC-1and Hela cells. Moreover, while complex 1 showed prominent cytotoxic activity against both PANC-1 and Hela cells with IC₅₀ of 17.91 and 11.67 μM, complex 2 showed moderate cytotoxic activities with IC₅₀ of 25.13 and 16.41 μM in PANC-1 and Hela cells. Further, apoptosis was confirmed by fluorescence image using EB/AO reagent.

Syntheses, crystal structures, and magnetic properties of cyanide-bridged complexestrans-RuII(dppe)2(CN)2(FeIIIX3)2(X = Cl and Br)

Cyanide-bridged complexestrans-Ru^II(dppe)₂(CN)₂(Fe^IIIX₃)₂(X = Cl,2; X = Br,3) and their parenttrans-ClRu^II(dppe)₂(CN) (1) were synthesized and fully characterized. The magnetic properties of2and3have been investigated.

Mixed-metal clusters with a {Re3Mo3Se8} core: from a polymeric solid to soluble species with multiple redox transitions

Soluble compounds based on new heterometallic {Re₃Mo₃Se₈}ⁿcluster cores were synthesized and investigated.

2D and 3D mixed MII/CuIImetal–organic frameworks (M = Ca and Sr) withN,N′-2,6-pyridinebis(oxamate) and oxalate: preparation and magneto-structural study

Heterobimetallic coordination polymers with either antiferro- of ferromagnetic interactions are described herein.

Synthesis and characterization of cyano and isocyano complexes of bis(dithiolato) molybdenum using Me3SiCN: a route to a cyanide-bridged multimer to a monomer

The Mo(iv) bis (dithiolate) complex showed diverse reactions with Me₃SiCN in the presence and absence of a coligand and under protic and aprotic media.

Crystal structure of tris(cyano-(hydrogen tris(3,5-dimethylpyrazolyl)borate))-iron(III) 4-methoxypyridinium monohydrate, C24H32BN10O2Fe

C24H32BN10O2Fe, orthorhombic, Pca21 (no. 29), a = 19.053(4) Å, b = 9.0666(18) Å, c = 16.439(3) Å, V = 2839.8(10) Å3, Z = 4, Rgt(F) = 0.0482, wRref(F2) = 0.1194, T = 123(2) K.

Cyanide Ligand Assembly by Carbon Atom Transfer to an Iron Nitride

The new iron(IV) nitride complex PhB(ⁱPr₂Im)₃Fe≡N reacts with 2 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) to provide PhB(ⁱPr₂Im)₃Fe(CN)(N₂)(BAC). This unusual example of a four-electron reaction involves carbon atom transfer from BAC to create a cyanide ligand along with the alkyne ⁱPr₂N-C≡C-NⁱPr₂. The iron complex is in equilibrium with an N₂-free species. Further reaction with CO leads to formation of a CO analogue, which can be independently prepared using NaCN as the cyanide source, while reaction with B(C₆F₅)₃ provides the cyanoborane derivative.

Redox effects of low-spin Ru(ii/iii) on slow magnetic relaxation of Ru-Mn(iii) 1D cyanide-bridged complexes

A new one-dimensional cyanide-bridged complex [Mn^III(salphen)Ru^II(DMAP)₄(CN)₂](PF₆) (1) and its oxidized derivative [Mn^III(salphen)Ru^III(DMAP)₄(CN)₂](PF₆)₂ (2) have been synthesized and fully characterized. Magnetic measurements showed that 1 shows simple paramagnetism but 2 shows intrachain ferromagnetic interaction with slow magnetic relaxation.

Effects of Ru(ii/iii) redox on the Co(ii) coordination number and magnetic properties of 1D cyanide-bridged Co-Ru compounds

A new 1D cyanide-bridged Co-Ru compound, {[trans-Ru^III(dmap)₄(CN)₂Co(dipic)(MeOH)](PF₆)}_n (1a) (dmap = 4-dimethylaminopyridine, dipic = pyridine-2,6-dicarboxylate), and its reduced state, [trans-Ru^II(dmap)₄(CN)₂Co(dipic)]_n (1b) have been synthesized. Upon the Ru center reduction from iii to ii, the MeOH solvent molecule bound to Co(ii) in 1a is expelled. 1a displays ferrimagnetic properties but 1b is only a paramagnetic compound.