Syntheses, structures, and properties of Co(III) complexes derived from polypyridine ligands containing one carboxamido nitrogen donor

Four cobalt(III) complexes containing the polypyridine pentadentate ligands N,N-bis(2-pyridylmethyl)amine-N′-ethyl-2-pyridine-2-carboxamide (PaPy₃H), N,N-bis(2-pyridylmethyl)amine-N′-[1-(2-pyridylethyl)acetamide (MePcPy₃H), and N,N-bis(2-pyridylmethyl)amine-N′-(2-pyridylmethyl)acetamide (PcPy₃H), have been synthesized. All three ligands bind the Co(III) center in the same fashion with the exception of loss of conjugation between the carboxamide moiety and the pyridine ring in the latter two. The structures of [(PaPy₃)Co(OH)][(PaPy₃)Co(H₂O)](ClO₄)₃ · 3H₂O (1), [(PaPy₃)Co(NO₂)](ClO₄) · 2MeCN (2), [(MePcPy₃)Co(MeCN)](ClO₄)₂ · 0.5MeCN (3), and [(PcPy₃)Co(Cl)](ClO₄) · 2MeCN (4) have been determined. These ligands with strong-field carboxamido N donor stabilize the +3 oxidation state of the Co center as demonstrated by the facile oxidation of the corresponding Co(II) complexes (prepared in situ) by H₂O₂, [Fe(Cp)₂](BF₄), or nitric oxide (NO). The Co-N_amido bond distances of 1-4 lie in the narrow range of 1.853-1.898 Å. ¹H NMR spectra of these complexes confirm the low-spin d⁶ ground states of the metal centers.     

Synthesis, characterization, electrochemical and spectroscopic investigation of cobalt(III) Schiff base complexes with axial amine ligands: The layered crystal structure of [Co(salophen)(4-picoline)2]ClO4 · CH2Cl2

Cobalt(III) complexes with potentially tetradentate salophen (H₂salophen = N,N′-bis(salicylidene)-1,2-phenylenediamine) as equatorial ligand and with different axial amine ligands (NH₃, cyclohexylamine, aniline, 4-picoline and pyridine) were synthesized and characterized by IR, ¹H NMR, elemental analysis. Electronic spectra and electrochemical properties of the complexes were studied in DMF solutions. The lowest energy transitions, which occur between 464.8 and 477 nm, are attributed mainly to the intraligand charge transfer, confirmed by Zindo/S electronic structure calculations. The reduction potentials of Co(III)/Co(II) are more affected than those of Co(II)/Co(I) by the axial amine ligands. The crystal structure of the [Co^III(salophen)(4- picoline)₂]ClO₄ · CH₂Cl₂ was determined, indicating that the cobalt(III) center is six coordinated surrounded by the tetradentate salophen ligand and two 4-picoline ligands. The crystal packing of the complex shows a layered structure, in which the perchlorate counter ions and also the lattice solvent molecules are intercalated between the bc planes of the complex cations.     

Mercaptoethanesulfonic acid (CoM imitator) interaction studies with nickel(II) complexes of pyridyl groups containing tetradentate ligands: Synthesis, structure, spectra and redox properties

Nickel(II) complexes of N,N′-dimethyl-N,N′-bis(pyridyl-2yl-methyl)ethylene-diamine (L¹), N,N′-dimethyl-N,N′-bis(pyridyl-2-ylmethyl)-1,2-diaminopropane (L²) and N,N′-dimethyl-N,N′-bis(pyridyl-2-ylmethyl)-1,3-diaminopropane (L³) were prepared and their spectroscopic and redox properties studied. The distorted octahedral structure was determined for [NiL³ClCH₃OH](ClO₄) by using X-ray crystallography. The electronic spectral behavior of the complexes at different pHs was analyzed; it is shown that a new band grew at the expense of the other band intensity in acid media. The redox properties of ligands and their complexes show the peaks of Ni(II) → Ni(III) and Ni(II) → Ni(0) as these were detected at low concentration while Ni(II) → Ni(I) process was detectable clearly at high concentration. Furthermore, the interaction studies of 2-mercaptoethanesulfonic acid as a simulator of coenzyme M reductase (CoM) with NiN₄ chromophores are discussed.     

Copper(II) complexes with unsymmetrical pentadentate ed3a-type diamino-tricarboxylate ligands. Crystal structures, configurational analysis and DFT study of complexes

The O-O-N-N-O-type pentadentate ligands H₃ed3a, H₃pd3a and H₃pd3p (H₃ed3a stands ethylenediamine-N,N,N′-triacetic acid; H₃pd3a stands 1,3-propanediamine-N,N,N′-triacetic acid and H₃pd3p stands 1,3-propanediamine-N,N,N′-tri-3-propionic acid) and the corresponding novel octahedral or square-planar/trigonal-bipyramidal copper(II) complexes have been prepared and characterized. H₃ed3a, H₃pd3a and H₃pd3p ligands coordinate to copper(II) ion via five donor atoms (three deprotonated carboxylate atoms and two amine nitrogens) affording octahedral in case of ed3a³⁻ and intermediate square-pyramidal/trigonal-bipyramidal structure in case of pd3a³⁻ and pd3p³⁻. A six coordinate, octahedral geometry has been established crystallographically for the [Mg(H₂O)₆][Cu(ed3a)(H₂O)]₂ · 2H₂O complex and five coordinate square-pyramidal for the [Mg(H₂O)₅Cu(pd3a)][Cu(pd3a)] · 2H₂O. Structural data correlating similar chelate Cu(II) complexes have been used for the better understanding the pathway: octahedral → square-pyramidal ↔ trigonal- bipyramid geometry. An extensive configuration analysis is discussed in relation to information obtained for similar complexes. The infra-red and electronic absorption spectra of the complexes are discussed in comparison with related complexes of known geometries. Molecular mechanics and density functional theory (DFT) programs have been used to model the most stable geometric isomer yielding, at the same time, significant structural data. The results from density functional studies have been compared with X-ray data.     

Iron(III) complexes of tridentate N3 ligands as models for catechol dioxygenases: Stereoelectronic effects of pyrazole coordination

The iron(III) complexes of the tridentate N₃ ligands pyrazol-1-ylmethyl(pyrid-2-ylmethyl)amine (L1), 3,5-dimethylpyrazol-1-ylmethyl(pyrid-2-ylmethyl)amine (L2), 3-iso-propylpyrazol-1-ylmethyl(pyrid-2-ylmethyl)amine (L3) and (1-methyl-1H-imidazol-2-ylmethyl)pyrid-2-ylmethylamine (L4) have been isolated and studied as functional models for catechol dioxygenases. They have been characterized by elemental analysis and spectral and electrochemical methods. The X-ray crystal structure of the complex [Fe(L1)Cl₃] 1 has been successfully determined. The complex possesses a distorted octahedral coordination geometry in which the tridentate ligand facially engages iron(III) and the Cl⁻ ions occupy the remaining coordination sites. The Fe-N_pz bond distance (2.126(5) Å) is shorter than the Fe-N_py bond (2.199(5) Å). The systematic variation in the ligand donor substituent significantly influences the Lewis acidity of the iron(III) center and hence the interaction of the present complexes with a series of catechols. The catecholate adducts [Fe(L)(DBC)Cl], where H₂DBC = 3,5-di-tert-butylcatechol, have been generated in situ and their spectral and redox properties and dioxygenase activities have been studied in N,N-dimethylformamide solution. The adducts [Fe(L)(DBC)Cl] undergo cleavage of DBC²⁻ in the presence of dioxygen to afford major amounts of intradiol and smaller amounts extradiol cleavage products. In dichloromethane solution the [Fe(L)(DBC)Cl] adducts afford higher amounts of extradiol products (64.1-22.2%; extradiol-to-intradiol product selectivity E/I, 2.6:1-4.5:1) than in DMF (2.5-6.6%; E/I, 0.1:1-0.4:1). The results are in line with the recent understanding of the function of intra- and extradiol-cleaving catechol dioxygenases.     

First example of well-characterized Re and Tc tricarbonyl complexes of ciprofloxacin and norfloxacin in the development of infection-specific imaging agents

Aiming at the development of ^99mTc-based infection-specific imaging agents, the synthesis and characterization of rhenium and technetium-99m tricarbonyl complexes with derivatized ciprofloxacin and norfloxacin is hereby reported. The ligands were prepared by coupling the tridentate chelator picolylamino-N,N-diacetic acid (PADA) with the piperazinyl (NH) nitrogen of ciprofloxacin or norfloxacin, through the employment of the PADA anhydride. The corresponding rhenium complexes were synthesized using the fac-[NEt₄]₂[ReBr₃(CO)₃] precursor and were fully characterized by elemental analysis and NMR spectroscopy. X-ray crystallography of the ciprofloxacin complex showed that the geometry about rhenium is distorted octahedral defined by the NNO donor atom set of the tridentate chelator and the three carbonyl groups. The analogous technetium-99m complexes were prepared quantitatively through the use of the fac-[^99mTc(H₂O)₃(CO)₃]⁺ precursor and their structure was established by comparative HPLC studies using the well-characterized rhenium complexes as reference. Preliminary studies with the technetium-99m complexes showed high bacterial uptake in vitro.     

Synthesis, structure and properties of di- and mononuclear ruthenium(III) complexes with N-(benzoyl)-N′-(salicylidene)hydrazine and its derivatives

The reactions of [Ru(PPh₃)₃Cl₂], N-(benzoyl)-N′-(5-R-salicylidene)hydrazines (H₂bhsR, R = H, OCH₃, Cl, Br and NO₂) and triethylamine (1:1:2 mole ratio) in methanol afford mononuclear ruthenium(III) complexes having the general formula trans-[Ru(bhsR)(PPh₃)₂Cl]. In the case of R = H, a dinuclear ruthenium(III) complex of formula [Ru₂(μ-OCH₃)₂(bhsH)₂(PPh₃)₂] has been isolated as a minor product. The complexes are characterized by elemental analysis, magnetic, spectroscopic and electrochemical measurements. The crystal structures of the dinuclear complex and two mononuclear complexes have been determined. In the dinuclear complex, each metal centre is in distorted octahedral NO₄P coordination sphere constituted by the two bridging methoxide groups, one PPh₃ molecule and the meridionally spanning phenolate-O, imine-N and amide-O donor bhsH²⁻. The terminal PPh₃ ligands are trans to each other. In the mononuclear complexes, bhsR²⁻ and the chlorine atom form an NO₂Cl square-plane around the metal centre and the P-atoms of the two PPh₃ molecules occupy the remaining two axial sites to complete a distorted octahedral NO₂ClP₂ coordination sphere. All the complexes display ligand-to-metal charge transfer bands in the visible region of the electronic spectra. The cryomagnetic measurements reveal the antiferromagnetic character of the diruthenium(III) complex. The low-spin mononuclear ruthenium(III) complexes as well as the diruthenium(III) complex display rhombic EPR spectra in frozen solutions. All the complexes are redox active in CH₂Cl₂ solutions. Two successive metal centred oxidations at 0.69 and 1.20 V (versus Ag/AgCl) are observed for the dinuclear complex. The mononuclear complexes display a metal centred reduction in the potential range −0.53 to −0.27 V. The trend in these potential values reflects the polar effect of the substituents on the salicylidene moiety of the tridentate ligand.     

Azo-containing pyridine amide ligand. A six-coordinate nickel(II) complex and its one-electron oxidized species: Structure and properties

A new potentially tridentate ligand HL¹¹ consisting of 2-pyridinecarboxamide unit and azo functionality has been used, in its deprotonated form, to prepare a nickel(II) complex which has been structurally characterized. The ligand L¹¹(−) affords a bis-complex [Ni^II(L¹¹)₂] (1). In 1, the two L¹¹(−) ligands bind to the Ni^II center in a mer configuration. The relative orientations within the pairs of pyridyl-N, deprotonated amido-N, and azo-N atoms are cis, trans, and cis, respectively. The Ni^IIN₂(pyridyl)N′₂(amide)N″₂(azo) coordination environment is severely distorted from ideal octahedral geometry. The Ni-N_am (am = amide) bond lengths are the shortest and the Ni-N_azo bond lengths are the longest. Complex 1 exhibits a quasireversible Ni^III/Ni^II redox process. Moreover, the complex displays two ligand-centered (azo group) quasireversible redox processes. Spectroscopic (absorption and EPR) properties have been studied on coulometrically-generated nickel(III) species. To understand the nature of metal-ligand bonding interactions Density Functional Theory (DFT) calculations have been performed on 1 at the B3LYP level of theory. Calculations have also been done for closely related nickel(II) complexes of deprotonated pyridine amide ligands and comparative discussion has been made using observed results.     

New bis(azolylcarbonyl)pyridine chromium(III) complexes as initiators for ethylene polymerization

Reaction of 2,6-pyridinedicarbonyl dichloride with 3,5-dimethylpyrazole and 1H-indazole, respectively, yield the tridentate ligands 2,6-bis(3,5-dimethylpyrazol-1-ylcarbonyl)pyridine (1) and 2,6-bis(indazol-1-ylcarbonyl)pyridine (2). The molecular structure of the new compound (2) was determined by single-crystal X-ray diffraction. These ligands react with CrCl₃(THF)₃ in THF to form neutral complexes of general formula [CrCl₃{2,6-bis(azolylcarbonyl)pyridine-N,N,N}] (3, 4) which were isolated in high yield as air stable green solids and characterized by elemental analysis, magnetic moment, IR, and mass spectroscopies. Theoretical calculations predict that the thermodynamically preferred structure of the complexes is the fac configuration. After reaction with methylaluminoxane (MAO) the chromium(III) complexes are active for the polymerization of ethylene.     

Synthesis and characterization of gold(III) complexes with alkyldiamine ligands

A series of gold(III) metalacycle of five-, six- and seven-membered ring was prepared by reacting Auric acid (HAuCl₄ · 3H₂O) with 1 equiv. unsubstituted ethylenediamine (en), propylene diamine (pn) and butylenediamine (bn) ligands and with some N-mono-substituted as well as N,N′-disubstituted ethylenediamine ligands. The general formula of these complexes is [Au(alkyldiamine)Cl₂]Cl. These complexes are characterized by melting point and elemental analysis, while structural analysis was done by spectroscopic techniques such as UV-Vis, Far-IR, IR spectroscopy, ¹H and ¹³C solution as well as ¹³C and ¹⁵ N solid-state NMR. The solid-state ¹⁵ N NMR shows that the chemical shift difference between free and bound ligand decreases as bn > pn > en, indicating stronger Au-N bond for bn complex compared to pn and en. UV-Vis shows relative stability of the Au(III) complexes of unsubstituted ethylenediamine with respect to N,N′-di-substituted ethylenediamine. Far-IR data show the six-membered metalacycle gold(III) alkanediamine complexes to be more stable. Spectroscopic data are evaluated by comparisons with calculated data of the built and optimized structure by gaussian03 at the RB3LYP level with LanL2DZ bases set.     

Structural studies of iron and cobalt phthalocyanine-substituted cytochromes c: Carboxymethylation and peptide fragments investigations

In order to obtain information on a way of prosthetic group binding by apocytochrome c in phthalocyanine-substituted cytochrome c, modification of these complexes by carboxymethylation at methionines, as well as cleavage with cyanogen bromide, has been performed. Properties of the reaction products have been investigated by spectroscopic methods, gel electrophoresis, column chromatogrdphy, peptide mapping, and amino acid analysis. Spectrophotometric data indicate that carboxymethylation results in a complete loss of the S-Fe sensitive 695 nm absorption band that appears in absorption spectra of the phthalocyanine-substituted cytochromes c. Unlike unmodified complexes, carboxymethylated derivatives are capable of ligating with typical iron ligands, in both oxidation states. Studies of iron and cobalt tetrasulfonated phthalocyanine interactions with fragments of cytochrome c demonstrate complex formation solely with the heme fragment apopeptides. These complexes do not exhibit a 695 nm absorption band. The results of the chemical examination suggest that the metal phthalocyanine of the model complexes is coordinated axially with histidine-18 and methionine-80 of apocytochrome c, in spite of the weakening of its heme crevice. Identification of these ligands by nuclear magnetic resonance method is difficult due to low solubility of the model complexes.     

Coordination of (aminoalkyloxymethyl)dimethylphosphine oxides with palladium(II). Crystal structure of trans-bis[2-(dimethylphosphinoylmethoxy-1,1-dimethylethylamine)]palladium(II) dichloride

The synthesis, structure and spectroscopic properties of novel palladium(II) chloro complexes with a series of (aminoalkyloxymethyl)dimethylphosphine oxides (AOPO) are reported. The complexes with general formula PdCl₂(N,N′-AOPO₂) were obtained by the reaction of PdCl₂(CH₃CN)₂ with the ligands in dry ethanol. The crystal structure of the trans-bis[2-(dimethylphosphinoylmethoxy-1,1-dimethylethylamine)]palladium(II) dichloride has been determined from single-crystal X-ray diffraction data. The compound crystallizes in monoclinic crystal system with P2₁/n space group. The square-planar coordination sphere of palladium consists of two N atoms from two aminoalkyldimethylphosphine ligands and two Cl atoms in trans-arrangement. The AOPO ligand has monodentate coordination through the NH₂ group. The Pd-N and Pd-Cl distances are 2.0610(14) and 2.3225(4) Å, respectively. The preparation of complexes with a composition PdCl₂(AOPO)₂ in chloroform solution are also reported.     

Iron(III) Schiff base complexes of arginine and lysine as netropsin mimics showing AT-selective DNA binding and photonuclease activity

Iron(III) complexes [Fe(L)₂]Cl (1-3), where L is monoanionic N-salicylidene-arginine (sal-argH for 1), hydroxynaphthylidene-arginine (nap-argH for 2) and N-salicylidene-lysine (sal-lysH for 3), were prepared and their DNA binding and photo-induced DNA cleavage activity studied. Complex 3 as its hexafluorophosphate salt [Fe(sal-lysH)₂](PF₆)·6H₂O (3a) was structurally characterized by single crystal X-ray crystallography. The crystals belonged to the triclinic space group P-1. The complex has two tridentate ligands in FeN₂O₄ coordination geometry with two pendant cationic amine moieties. Complexes 1 and 2 with two pendant cationic guanidinium moieties are the structural models for the antitumor antibiotics netropsin. The complexes are stable and soluble in water. They showed quasi-reversible Fe(III)/Fe(II) redox couple near 0.6 V in H₂O-0.1 M KCl. The high-spin 3d⁵-iron(III) complexes with μ_eff value of ∼5.9 μ_B displayed ligand-to-metal charge transfer electronic band near 500 nm in Tris-HCl buffer. The complexes show binding to Calf Thymus (CT) DNA. Complex 2 showed better binding propensity to the synthetic oligomer poly(dA)·poly(dT) than to CT-DNA or poly(dG)·poly(dC). All the complexes displayed chemical nuclease activity in the presence of 3-mercaptopropionic acid as a reducing agent and cleaved supercoiled pUC19 DNA to its nicked circular form. They exhibited photo-induced DNA cleavage activity in UV-A light and visible light via a mechanistic pathway that involves the formation of reactive hydroxyl radical species.     

Nickel(II) complexes of terdentate or symmetrical tetradentate Schiff bases: Evidence of the influence of the counter anions in the hydrolysis of the imine bond in Schiff base complexes

Two sets of ligands, set-1 and set-2, have been prepared by mixing 1,3-diaminopentane and carbonyl compounds (2-acetylpyridine or pyridine-2-carboxaldehyde) in 1:1 and 1:2 ratios, respectively, and employed for the synthesis of complexes with Ni(II) perchlorate, Ni(II) thiocyanate and Ni(II) chloride. Ni(II) perchlorate yields the complexes having general formula [NiL₂](ClO₄)₂(L = L¹ [N³-(1-pyridin-2-yl-ethylidene)-pentane-1,3-diamine] for complex 1 or L²[N³-pyridin-2-ylmethylene-pentane-1,3-diamine] for complex 2) in which the Schiff bases are monocondensed terdentate, whereas Ni(II) thiocyanate results in the formation of tetradentate Schiff base complexes, [NiL(SCN)₂] (L = L³[N,N′-bis-(1-pyridin-2-yl-ethylidine)-pentane-1,3-diamine] for complex 3 or L⁴ [N,N′-bis(pyridin-2-ylmethyline)-pentane-1,3-diamine] for complex 4) irrespective of the sets of ligands used. Complexes 5 {[NiL³(N₃)₂]} and 6 {[NiL⁴(N₃)₂]} are prepared by adding sodium azide to the methanol solution of complexes 1 and 2. Addition of Ni(II) chloride to the set-1 or set-2 ligands produces [Ni(pn)₂]Cl₂, 7, as the major product, where pn = 1,3-diaminopentane. Formation of the complexes has been explained by the activation of the imine bond by the counter anion and thereby favouring the hydrolysis of the Schiff base. All the complexes have been characterized by elemental analyses and spectral data. Single crystal X-ray diffraction studies confirm the structures of three representative members, 1, 4 and 7; all of them have distorted octahedral geometry around Ni(II). The bis-complex of terdentate ligands, 1, is the mer isomer, and complexes 4 and 7 possess trans geometry.     

Preliminary chemico-biological studies on Ru(III) compounds with S-methyl pyrrolidine/dimethyl dithiocarbamate

[RuCl₃ · nH₂O] and Na(trans-[RuCl₄(DMSO)₂]) were reacted with 1-pyrrolidinedithiocarbamate (PDT), its S-methyl ester (PDTM), and N,N-dimethylcarbamodithioic acid methyl ester (DMDTM) in water or methanol in order to obtain the corresponding Ru(III) derivatives. Once isolated and purified, the complexes were characterized by means of elemental analysis, conductivity measurements, FT-IR and ¹H NMR spectroscopy, ion electrospray mass spectrometry (ESI-MS), and thermal analyses. The crystal structure of mer-[Ru(DMDTM)(DMSO)Cl₃] has been also determined by X-ray crystallography. In vitro cytotoxic activity of all the synthesized complexes was eventually evaluated on some selected human tumor cell lines.     

Preparation and characterization of manganese(III) halide derivatives of N,N′-bis(aminobenzylidene)-1,2-ethanediamine

The preparation and characterization of manganese(III) complexes containing the quadridenate ligand, N,N′-bis(aminobenzylidene)-1,2-ethanediamine (H₂amben), and its previously unreported analogue, N,N′-bis(2-amino-5-nitro-benzylidene)-1,2-ethanediamine (H₂nitroamben), are described. The new manganese(III) halide/pseudohalide complexes, Mn(amben)X · nH₂O and Mn(nitroamben)X · nH₂O (X = Cl, Br, I, NCS; n =  0.5 or 1), were isolated as red-brown, microcrystalline solids, which were characterized fully.     

Square-planar copper(II) complexes with tetradentate amido-carboxylate ligands. Crystal structure of Na2[Cu(obap)]2 · 2H2O. Strain analysis and spectral assignments of complexes

Novel N-N-N-O-type of tetradentate ligands H₃obap (H₃obap = oxamido-N-aminopropyl-N′-benzoic acid) and H₃maeb (H₃maeb = malamido-N-aminoethyl-N′-benzoic acid) and the corresponding square-planar copper(II) complexes have been prepared and characterized. The obap³⁻ and maeb³⁻ ligands coordinate to the copper(II) ion via four ligating atoms (three deprotonated atoms: one carboxylate oxygen and two deprotonated amide nitrogens; one amine nitrogen) with in-plane square chelation. A four coordinate, square-planar geometry has been established crystallographically for the binuclear Na₂[Cu(obap)]₂ · 2H₂O complex. Structural data correlating the square-planar geometry of the [Cu(obap)]⁻ unit and an extensive strain analysis are discussed in relation to the information obtained for similar complexes. The infrared and electronic absorption spectra of the complexes are discussed in comparison to the related complexes of known geometries. Antibacterial activity of ligands and copper(II) complexes towards common Gram-negative and Gram-positive bacteria are reported as well.     

X-ray crystallographic investigation and biological activities of Ru(III) complexes containing Schiff base and triphenyl phosphine/arsine

The crystal structures of the complexes [RuCl(Nap-o-phd)(AsPh₃)] and [RuBr(Nap-o-phd)(PPh₃)] (where H₂-Nap-o-phd = N,N′-bis(2-hydroxy-1-naphthaldehyde) o-phenylenediamine) have been determined by single crystal X-ray diffraction techniques. The antibacterial properties of the complexes have also been examined.     

Structural comparison of (pentamethylcyclopentadienyl)iridium(III) azido complexes containing potentially N,S-bidentate N-heterocyclic thiolates: 2- or 8-quinolinethiolate and benzimidazole-2-thiolate

The crystal structures of mononuclear (azido)(pentamethylcyclopentadienyl)iridium(III) complexes bearing 2- or 8-quinolinethiolate (n-Sqn⁻), [Cp^∗Ir(N₃)(n-Sqn)] {n = 2 (1) or 8 (2); Cp^∗ = η⁵-C₅Me₅} have been determined by X-ray analysis. The 2-Sqn complex, 1, acquires severe steric strains in the four-membered κ²N,S chelate ring, while the 8-Sqn isomer, 2, forms a strain-free five-membered planar κ²N,S chelate ring. It has also been revealed that the corresponding benzimidazole-2-thiolate (Hbimt⁻) complex, which was obtained similarly to the above n-Sqn complexes from [Cp^∗Ir(N₃)₂]₂ and Na(Hbimt), takes an unsymmetrical dinuclear structure bridged by two Hbimt⁻ ligands with different bonding modes, [Cp^∗Ir(N₃){μ(S:N¹)-Hbimt}{μ(S:S)-Hbimt}Ir(N₃)Cp^∗] · MeOH (3).     

Solid state and solution NMR, X-ray and antimicrobial studies of 1:1 and 2:1 complexes of silver(I) cyanide with alkanediamine ligands

Several complexes of AgCN with alkanediamine ligands (where the ligands are ethylenediamine, propane-1,3-diamine, butane-1,4-diamine, N,N′-dimethyl-ethylenediamine, N,N′-di-iso-propyl-ethylenediamine, etc.) have been synthesized and structurally characterized. In these species, alkanediamine ligands act as chelating ligands. The X-ray structure of the complex cyano-(N,N′-di-iso-propyl-ethylenediamine)-silver(I) was determined. These complexes have been also characterized by IR, solution as well as solid-state NMR studies. There are two types of IR absorptions observed for mono and dinuclear complexes. For the mono nuclear complexes, a sharp CN band is observed between 2111 and 2131 cm⁻¹ range, whereas for binuclear complexes the bands are in the range 2136-2140 cm⁻¹. The effect of the size of the ligands as well as their substituents is discussed. The antimicrobial activity studies of AgCN and its complexes show that the former exhibits substantial antibacterial activities compared to its complexes.