Atoms Of Ligand Research Articles

Synthesis, characterization and exploration of supramolecular interactions of a Cu(II) based 1D zig-zag coordination polymer: X-ray structure determination and DFT study

A novel Cu(II) based one-dimensional (1D) zig-zag coordination polymer (CP) formulated as [Cu(muco)(4,4′-Me2bpy)(H2O)]·2H2O (1; H2muco = trans, trans-1,3-butadiene-1,4-dicarboxylic acid or trans, trans-muconic acid and 4,4′-Me2bpy = 4,4′-dimethyl-2,2′-bipyridine) was synthesized in a self-assembly reaction using slow evaporation technique. Single crystal X-ray analysis reveals that the compound 1 crystallizes in the triclinic system, space group Pī witha = 9.7436(12) Å,b = 11.1836(14) Å,c = 11.5063(14) Å; α = 61.520(1)°, β = 85.019(1)°, γ = 66.864(1)° and V = 1005.6(2) Å3. Its structure is composed of Cu(II) centres with a distorted square pyramidal configuration interconnected by muco ligand in an array to generate zig-zag chain. A three- dimensional (3D) supramolecular network is formed among 1D chains of 1 via hydrogen bonding and π··π interactions. Interestingly, the connectivity of lattice water molecules shows a water dimer cluster, which further undergoes hydrogen bonding along with coordinated water molecules and oxygen atoms of muco ligands to generate an octameric cluster with chair-like hexameric unit. The excellent coordinating characteristics of muco and bipyridine ligands owing to non-covalent interactions to stabilize compound1have been investigated by means of Hirshfeld analysis. The density functional theory (DFT) study is performed to calculate the HOMO-LUMO gap which enlightens the possible future application of 1 as a semiconducting device. The theoretical findings are also validated experimentally by band gap calculation utilising Tauc’s plot exploring the UV data.

SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL STUDIES OF SOME METAL (II) COMPLEXES OF TRIDENTATE LIGAND DERIVED FROM ETHYLENEDIAMINE, NITROBENZALDEHYDE AND AMINOBENZOPHENONE

The Schiff base ligand and its metal complexes derived from ethylenediamine, nitrobenzaldehyde and aminbenzophenone were prepared using hydrated metal salts of Ni(II), Co(II) and Mn(II) and characterized by molar conductivity, magnetic susceptibility measurement elemental analysis, FTIR, GC-MS, UV-Vis spectroscopy and (1H, 13C) NMR spectra. Some physical parameters were obtained using molar conductance measurement and melting point determination. From the analytical and spectroscopic data, N donor atoms of the Schiff base ligand and N of NH2 group participated in coordination with metal (II) ions proposed to be a tridentate ligand and octahedral geometry was proposed for the complexes of Co, Ni while tetrahedral geometry proposed for Mn respectively. The antimicrobial activity of the ligand and its metal complexes were compared with the standard drugs Amoxicillin and Nystatin by screening them against isolates of two Gram-positive, three Gram-negative and two fungal strain, using agar well diffusion method for bacteria while the fungal cultures were maintained on Sabouraud liquid medium. The results obtained showed that the metal complexes were more potent against Gram-positive bacterial and fungi than the free ligand, while the ligand showed greater activity against Gram-negative bacterial than the metal complexes.

Theoretical Probing of Size-Selective Crown Ether Macrocycle Ligands for Transplutonium Element Separation.

Effective separation and recovery of chemically similar transplutonium elements from adjacent actinides is extremely challenging in spent fuel reprocessing. Deep comprehension of the complexation of transplutonium elements and ligands is significant for the design and development of ligands for the in-group separation of transplutonium elements. Because of experimental difficulties of transplutonium elements, theoretical calculation has become an effective means of exploring transplutonium complexes. In this work, we systematically investigated the coordination mechanism between transplutonium elements (An = Am, Cm, Bk, Cf) and two crown ether macrocyclic ligands [N,N'- bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-18-crown-6 (H2bp18c6) and N,N'-bis[(6-methylphosphinic-2-pyridyl)methyl]-1,10-diaza-18-crown-6 (H2bpp18c6)] through quasi-relativistic density functional theory. The extraction complexes of [Anbp18c6]+ and [Anbpp18c6]+ possess similar geometrical structures with actinide atoms located in the cavity of the ligands. Bonding nature analysis indicates that the coordination ability of the coordinating atoms in pendent arms is stronger than that in the crown ether macrocycle because of the limitation of the macrocycle. Most of the coordination atoms of the H2bp18c6 ligand have a stronger ability to coordinate with metal ions than those of the H2bpp18c6 ligand. In addition, the bonding strength between the metal ions and ligands gradually weakens from Am to Cf, which is mainly attributed to the size selectivity of the ligands. Thermodynamic analysis shows that the H2bp18c6 ligand has a stronger extraction capacity than the H2bpp18c6 ligand, while the H2bpp18c6 ligand is superior in terms of the in-group separation ability. The extraction capacity of the two ligands for metal ions gradually decreases across the actinide series, indicating that these crown ether macrocycle ligands have size selectivity for these actinide cations as a result of steric constraint of the crown ether ring. We hope that these results offer theoretical clues for the development of macrocycle ligands for in-group transplutonium separation.

Symmetry-Adapted Restraints for Binding Free Energy Calculations.

Binding free energy calculations rely critically on a precise definition of the bound state and well-designed ligand restraints to ensure that binding free energy calculations converge rapidly and yield estimates of well-defined thermodynamic quantities. The distance-to-bound-configuration (DBC) is a single variable that can precisely delineate the bound state of a ligand including translational, rotational and conformational degrees of freedom and has been successfully used to capture binding modes with complex geometries. DBC is defined as the root-mean-square deviation (RMSD) of ligand coordinates in the frame of reference of the binding site. In the special case where the ligand features symmetry-equivalent atoms, a standard RMSD arbitrarily distinguishes equivalent poses, mixing equivalent and nonequivalent degrees of freedom, and preventing the precise delineation of the bound state ensemble, which negates the benefits of defining a flat-bottom binding restraint. To remedy this, we introduce a symmetry-adapted DBC coordinate where the RMSD is minimized over permutations of equivalent ligand atoms. This coordinate is implemented in a portable software library, the Collective Variables Module. We tested the approach by computing the absolute binding free energy of benzene to the engineered site of a mutant lysozyme (L99A/M102H) using alchemical free energy perturbation. We found that the symmetry-adapted restraint leads to well-behaved convergence of both the decoupling free energy in the binding site and the restrained free energy in the gas phase, recovering the affinity computed using a classic center-of-mass restraint. Thus, symmetry-adapted DBC seamlessly generalizes the benefits of DBC restraints to the case of symmetric ligands. The underlying symmetric RMSD coordinate can also be used for analyzing or biasing simulations in other contexts than affinity predictions.

Probing electron diffusion length in an accumulation layer in a ligand-free lead sulfide colloidal quantum dot monolayer

Developing an understanding of the minority carrier diffusion in the effective channel close to the gate dielectric in a field effect transistor (FET) configuration has proven to be challenging because the minority carriers are affected by the gate electric field. We, for the first time, have investigated the minority carrier (electron) diffusion length in ultrathin lead sulfide (PbS) colloidal quantum dots (CQDs) treated with ammonium sulfide ((NH4)2S) using photocurrent microscopy (PCM). With increasing gate voltage, an electron diffusion length is found to be gate-dependent, which can be explained by the increased hole occupancy in the midgap states.Using the FET mobility in the (NH4)2S-treated PbS CQDs, we calculated the electron lifetime. We present the first demonstration of the electric field -modulated electron diffusion length in a PbS CQD film treated with an atomic ligand using PCM.

Microwave assisted synthesis of rhodium(Ⅰ) N-heterocyclic carbene complexes and their cytotoxicity against tumor cell lines

Organometallic rhodium(Ⅰ) complexes of the general type [(COD)(NHC)RhCl] (where COD = 1,5-cyclooctadiene, NHC = N-heterocyclic carbene) were prepared according to a two-step transmetalation method via a silver carbene intermediate. The procedure was supported by microwave irradiation allowing reduced reaction periods. The complexes were evaluated for cytotoxic effects in selected cancer cell lines, namely HT-29 colon adenocarcinoma, MDA-MB-231 breast carcinoma and MCF-7 breast adenocarcinoma, and generally triggered strong cytotoxic effects with IC50 values in the low micromolar range. Evaluation of structure-activity relationships clearly indicated a preference for branched isopropyl side chains at the nitrogen atoms of the NHC ligands versus non-branched ethyl side chains. Further studies on selected examples in HT-29 cells indicated that this could be the result of a higher cellular uptake.

Cobalt(II)-disulfide compounds with the unusual PF2O2– anion. ligand-dependent redox conversion to a cobalt(III)-thiolate complex

Herein we describe the synthesis of the cobalt(II) disulfide compounds [CoII2(LxSSLx)(μ–PO2F2)2](PF6)2 and [CoII2(LxSSLx)(NO3)4] (x = 1: di-2-(bis(2-pyridylmethyl)amino)-ethyl disulfide; x = 2: di-2-((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amino)-ethyl disulfide). The crystal structures show the cobalt(II) centers in [CoII2(LxSSLx)(μ-PO2F2)2](PF6)2 to be in distorted octahedral geometries, whereas in [CoII2(L1SSL1)(NO3)4] the geometries are distorted trigonal bipyramidal. The cobalt(II) centers in [CoII2(LxSSLx)(PO2F2)2](PF6)2 are coordinated by three nitrogen and one sulfur donor atom of the disulfide ligand, and two oxygen atoms of two bridging difluoridophosphate anions. The cobalt(II) centers in [CoII2(L1SSL1)(NO3)4] are coordinated by three nitrogen donors of the ligand and three oxygen atoms of one monodentate and one bidentate nitrate anion, the latter two oxygen atoms together occupying one of the equatorial sites of the trigonal bipyramid. It was found that the dinuclear compound [CoII2(L1SSL1)(PO2F2)2](PF6)2 is stable as such in methanol and dichloromethane solution, but in acetonitrile redox conversion occurs forming the cobalt(III) thiolate compound [CoIII(L1S)(MeCN)2]2+. The compound [CoII2(L1SSL1)(NO3)4] and the disulfide compounds of the ligand L2SSL2 do not show this redox conversion and remain in the disulfide form in all investigated solvents.

Preparation, Characterization of Some Metal Complexes of New Mixed Ligands Derived from 5-Methyl Imidazole and Study the Biological Activity of Palladium (II) Complex as Anticance

A new series of mixed ligand complexes synthesized and characterized using of azo ligand derived from (5-methyl— imidazole) with (8-hydroxy quinolone). New mix-ligand structures and their transitional metal complexes were fully characterized using several techniques, including molar conductance, elemental analysis (C.H.N), electronic spectral, magnetic measurements, 1HNMR, spectral studies, and mass spectra. The data shows that these complexes have a composition of [ML(8-HQ) Cl2] H2O where M = Co(II), Zn(II), Cu(II), X=0, and Ni(II), X=1, [ML(8-HQ)] Cl. where M=Pd. The electronic spectral data and magnetic susceptibility calculations of the complexes indicate that the octahedral geometry of all complexes, except for the Pd(II) complex, indicates a planar-square geometry. The results demonstrate that the nitrogen of the imidazole ring and azo nitrogen atom of the primary ligand are coordination sites with a nitrogen atom and oxygen atom of a secondary ligand of the (8-HQ) in the basic medium. Biological effects of the palladium (II) complex are screening against human breast cancer (MCF-7 and AMJ-13) and normal cells (HBL) were examined, which indicated colon cancer cell line LS-174. The results show the highest activity effect for the complex.

Synthesis and crystal structure of poly[[di-μ3-tetra-thio-anti-monato-tris-[(cyclam)cobalt(II)]] aceto-nitrile disolvate dihydrate] (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-deca-ne).

Reaction of Co(ClO4)2·6H2O with cyclam (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-deca-ne) and Na3SbS4·9H2O (Schlippesches salt) in a mixture of aceto-nitrile and water leads to the formation of crystals of the title compound with the composition {[Co3(SbS4)2(C10H24N4)3]·2CH3CN·2H2O} n or {[(Co-cyclam)3(SbS4)2]·2(aceto-nitrile)·2H2O} n . The crystal structure of the title compound consists of three crystallographically independent [Co-cyclam]2+ cations, which are located on centers of inversion, one [SbS4]3- anion, one water and one aceto-nitrile mol-ecule that occupy general positions. The aceto-nitrile mol-ecule is disordered over two orientations and was refined using a split model. The CoII cations are coordinated by four N atoms of the cyclam ligand and two trans-S atoms of the tetra-thio-anti-monate anion within slightly distorted octa-hedra. The unique [SbS4]3- anion is coordinated to all three crystallographically independent CoII cations and this unit, with its symmetry-related counterparts, forms rings composed of six Co-cyclam cations and six tetra-thio-anti-monate anions that are further condensed into layers. These layers are perfectly stacked onto each other so that channels are formed in which acetontrile solvate mol-ecules that are hydrogen bonded to the anions are embedded. The water solvate mol-ecules are located between the layers and are connected to the cyclam ligands and the [SbS4]3- anions via inter-molecular N-H⋯O and O-H⋯S hydrogen bonding.

Crystal structures, electrochemical properties and theoretical studies of three New Zn(II), Mn(III) and Co(III) Schiff base complexes derived from 2-hydroxy-1-allyliminomethyl-naphthalen

Three novel complexes of the Schiff base, 2-hydroxy-1-allyliminomethyl-naphthalen (HL), namely ZnII(HL)2 (1), polymeric [(MnIII(HL)2)(N3)2]n (2), and CoIII(HL)3 (3) were synthesized from the reaction of ZnBr2•2H2O, MnCl2•2H2O and Co(OAc)2•4H2O with the Schiff base ligand. The complexes were characterized by elemental analysis, FT-IR, UV-vis, as well as by the single-crystal X-ray diffraction technique. In all these complexes, central metal ions were coordinated by O and N atoms of the Schiff base ligand. It was found that the Zn complex (1) was C2-symmetrical, with the Zn ion in quite a regular tetrahedral environment. In turn, the Mn complex (2) made 1D-coordination polymer with N3 linkers between also symmetrical (Ci) Mn(HL)2 monomers, with six-coordinated Mn ion in an octahedral environment. Finally, the Co ion in Co(HL)3 complex (3) was also octahedrally 6-coordinated. Additional solvent (DMSO) molecules are built in the crystal architecture. The electrochemistry of complexes in DMSO displayed a metal-centered reduction peak corresponding to the ZnII/I- ZnI/0, MnIII/II- MnII/I, and CoIII/II - CoII/I at (-1.15,-1.53), (-0.11,-1.79) and (-0.76, -1.69) V, respectively. The molecular geometry of the complexes was optimized using the density functional theory with the basic set (B3LYP / 6-311G). After optimal DFT, the electron transfer spectrum was calculated theoretically and compared with the experimental results. Hirshfeld surfaces and fingerprint plots are used to visualize and analyze intermolecular interactions. The Hirshfeld surface analysis showed that the crystal cohesion of the structures of the three complexes is established via H•••H, C•••H/H•••C, and O•••H/H•••O the dominant contacts. As well as, molecular docking studies were carried out for all complexes to find their binding affinity with protein (PDB ID: 1LRI). Molecular binding studies have shown good interaction with the intended drug targets.

Synthesis and structural characterization of three new mixed ligand alkaline-earth metal picrates

Abstract The dissolution of alkaline-earth metal carbonate in aqueous picric acid followed by reaction with nicotinamide results in the formation of [M(H2O) n (nic)2(pic)2] (nic = nicotinamide; pic = picrate; n = 1 and M = Ba 1; n = 2 and M = Ca (or Sr) 2 (or 3)). In [Ba(H2O)(nic)2(pic)2] 1, the barium and the oxygen atoms of a terminal aqua ligand are located on a two-fold axis. Compound 1 exhibits a {BaO7N2} coordination sphere, where the barium atom is bonded to a unique bidentate picrate and the crystallographically independent nicotinamide bridges to two symmetry related barium atoms with a Ba···Ba separation of 9.799 Å via the pyridine nitrogen and the amide oxygen atoms leading to the formation of a two-dimensional coordination polymer. The compounds 2 and 3 are isostructural with discrete molecules. The central Ca atom in 2 (or Sr in 3) located on a two-fold axis is bonded to a crystallographically unique terminal aqua ligand, an independent monodentate nicotinamide and a unique bidentate picrate anion resulting in a distorted {MO8} polyhedron. The mixed ligand alkaline-earth metal picrates 1–3 exhibit three varieties of hydrogen bonding and π–π stacking interactions. Several alkaline-earth metal picrates are compared in this study.

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C 2 H 2 /CO 2 Separation

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C ₂ H ₂ /CO ₂ Separation

Ligand Optimization of Exchange Interaction in Co(II) Dimer Single Molecule Magnet by Machine Learning.

Designing single-molecule magnets (SMMs) for potential applications in quantum computing and high-density data storage requires tuning their magnetic properties, especially the strength of the magnetic interaction. These properties can be characterized by first-principles calculations based on density functional theory (DFT). In this work, we study the experimentally synthesized Co(II) dimer (Co2(C5NH5)4(μ-PO2(CH2C6H5)2)3) SMM with the goal to control the exchange energy, ΔEJ, between the Co atoms through tuning of the capping ligands. The experimentally synthesized Co(II) dimer molecule has a very small ΔEJ < 1 meV. We assemble a DFT data set of 1081 ligand substitutions for the Co(II) dimer. The ligand exchange provides a broad range of exchange energies, ΔEJ, from +50 to -200 meV, with 80% of the ligands yielding a small ΔEJ < 10 meV. We identify descriptors for the classification and regression of ΔEJ using gradient boosting machine learning models. We compare one-hot encoded, structure-based, and chemical descriptors consisting of the HOMO/LUMO energies of the individual ligands and the maximum electronegativity difference and bond order for the ligand atom connecting to Co. We observe a similar overall performance with the chemical descriptors outperforming the other descriptors. We show that the exchange coupling, ΔEJ, is correlated to the difference in the average bridging angle between the ferromagnetic and antiferromagnetic states, similar to the Goodenough-Kanamori rules.

Observation of Spin‐Induced Ferroelectricity in a Layered van der Waals Antiferromagnet CuCrP2S6

AbstractCuCrP2S6, a van der Waals magnet having stacked layers of 2D honeycomb lattice made of CuS3 triangles and CrS6 octahedra, exhibits an A‐type antiferromagnetic order with the Néel temperature (TN) = 32 K. Upon in‐plane magnetic field (H) being applied below TN, H‐induced modulation of the c*‐axis electric polarization (ΔPc*) is found at fields lower than the saturation field µ0HS = 6.1 T, at which a forced ferromagnetic alignment sets in. Based on the symmetry analyses and dependence of ΔPc* on H and the azimuthal angle of applied H direction, a microscopic origin of the magnetoelectric (ME) coupling is attributed to the spin‐direction‐dependent p–d hybridization that is allowed due to the presence of off‐centered Cr3+ octahedra. A comparative study on CuCrP2Se6, however, finds no H‐induced P modulation due to cancellation of P between neighboring layers with the doubling of a crystallographic unit cell at TN. As the p–d hybridization mechanism allows generation of P in a single Cr atom–ligand pair, the results imply that large ME coupling should exist even in a single layer limit of CuCrP2S6.

Prediction of heptagonal bipyramidal nonacoordination in highly viable [OB-M\xa9B7O7-BO]\u2212 (M\u2009=\u2009Fe, Ru, Os) complexes

Non-spherical distributions of ligand atoms in coordination complexes are generally unfavorable due to higher repulsion than for spherical distributions. To the best of our knowledge, non-spherical heptagonal bipyramidal nonacoordination is hitherto unreported, because of extremely high repulsion among seven equatorial ligand atoms. Herein, we report the computational prediction of such nonacoordination, which is constructed by the synergetic coordination of an equatorial hepta-dentate centripetal ligand (B7O7) and two axial mono-dentate ligands (-BO) in the gear-like mono-anionic complexes [OB-M©B7O7-BO]– (M = Fe, Ru, Os). The high repulsion among seven equatorial ligand B atoms has been compensated by the strong B–O bonding. These complexes are the dynamically stable (up to 1500 K) global energy minima with the HOMO-LUMO gaps of 7.15 to 7.42 eV and first vertical detachment energies of 6.14 to 6.66 eV (being very high for anions), suggesting their high probability for experimental realization in both gas-phase and condensed phases. The high stability stems geometrically from the surrounded outer-shell oxygen atoms and electronically from meeting the 18e rule as well as possessing the σ + π + δ triple aromaticity. Remarkably, the ligand-metal interactions are governed not by the familiar donation and backdonation interactions, but by the electrostatic interactions and electron-sharing bonding.

Synthesis and structural characterization of a new heterometallicmolybdate coordination polymer based on a µ3-bridging amino alcohol

Abstract The reaction of Na2MoO4·2H2O with 2-amino-2-(hydroxymethyl)propane-1,3-diol (LH) in water at room temperature results in the formation of the heterometallic coordination polymer [Mo2O6L2(Na2(H2O)4)]·2H2O 1 (L = 2-amino-3-hydroxy-2-(hydroxymethyl)propan-1-olato). The structure of 1 consists of a neutral (Mo2O6) unit located on an inversion center. The Mo atoms exhibit hexa-coordination and are bonded to two terminal and two bridging oxido ligands, an alkoxide oxygen and the amine N atoms of an anionic ligand L– resulting in the formation of an edge-sharing {Mo2O8N2} bioctahedron. The Na+ cations of a centrosymmetric bis(μ2-aqua)-bridged (Na2(H2O)4)2+ unit are penta-coordinated and bonded to two symmetry related L– ligands via the oxygen atoms of their OH groups. The µ3-bridging tetradentate binding mode of L– results in the formation of a two-dimensional heterometallic coordination polymer. The constituents of 1 viz. (Mo2O6), (L)–, (Na2(H2O)4)2+ and lattice water molecules are interlinked with the aid of three varieties of hydrogen bonding interactions. The corresponding tungstate reported recently has been obtained through a similar synthetic protocol and is isostructural.

Identification of a Stable Ozonide Ion Bound to a Single Cadmium Site within the Zeolite Cavity

Molecular metal oxides are invoked as the key intermediate in a variety of oxidative reactions. Although an atomic oxygen ligand and molecular O2 ligands are well known, the triatomic oxygen ligand (ozonide) is very limited due to its instability. Here, we report a successful preparation and characterization of stable cadmium ozonide species. Our approach used the negatively charged local environments within the zeolite pore, which allowed us to isolate the single cadmium ozonide species as the counter cation even at room temperature. Its state was characterized by vibronic progressions closely similar to those observed in the cryogenic inert-element matrix system. Density functional theory calculations determined the lowest-energy geometry as the side-on [CdII(O3–•)]+ having C2v symmetry. This model was stable within the ab initio molecular dynamics simulation at 300 K, rationalizing the abnormal stability of [CdII(O3–•)]+observed experimentally. The O3-a1 → Cd-5s-donation orbital interaction was the driving force for the formation of the stable CdII–(O3–•) bond. The zeolite lattice plays a pivotal role in the enhancement of the acidity of the cadmium ion and stabilizes the donation interaction but constrains the O3 adduct as a pseudo-free ozonide ion. The findings in the present work will be applicable for designing new metal ozonide compounds.

Syntheses, characterization, and crystal structures of cobalt(III) complexes derived from 2-(((2-(pyrrolidin-1-yl)ethyl)imino)methyl)phenol with the antibacterial activity

A mononuclear cobalt(III) complex [CoL(NCS)2(OH2)] (1) and a trinuclear cobalt(III—II—III) complex [Co{CoLN3(m1,1-N3)2(CH3OH)}2] (2), derived from the Schiff base ligand 2-(((2-(pyrrolidin-1-yl)ethyl)imino)methyl)phenol (HL), are synthesized and characterized by IR and electronic spectra. The structures of both complexes are studied in detail by single crystal X-ray diffraction. In complex 1, the Co(III) atom is coordinated by three donor atoms of the Schiff base ligand, two thiocyanate N atoms, and one water O atom, forming an octahedral geometry. In complex 2, the terminal Co(III) atom is coordinated by three donor atoms of the Schiff base ligand, two end-on azide N atoms, and one terminal azide N atom, forming an octahedral geometry. The central Co(II) atom is coordinated by four end-on azide N atoms and two methanol O atoms, forming an octahedral geometry. The complexes exhibit interesting antibacterial activities against B. subtilis and E. coli.

Окисление трис(2-метокси-5-бромфенил)сурьмы трет-бутилгидропероксидом в присутствии соединений, содержащих подвижный атом водорода

Oxidation of tris(2-methoxy-5-bromophenyl)antimony with tertiary butylhydroperoxide in the presence of water, benzoic acid, 2,6-dihydroxybenzoic acid and 2-chloro-4-fluorophenol in diethyl ether leads to formation of tris(2-methoxy-5-bromophenyl)antimony oxide (1), tris(2-methoxy-5-bromophenyl)antimony dibenzoate (2), -oxo[hexakis(2-methoxy-5-bromophenyl)-bis(2,6-dihydroxybenzoato)diantimony] (3), -oxo[hexakis(2-methoxy-5-bromophenyl)-bis(2-chloro-4-fluorophenoxo)diantimony] (4), respectively. The compounds have been identified by X-ray diffraction analysis. According to the X-ray diffraction data, the crystal of solvate 1 with chloroform consists of centrosymmetric binuclear molecules containing the Sb2O2 cycle with tetragonal coordination of the antimony atoms (the Sb–O bond lengths are 1.961(4) and 2.041(5) Å, the Sb–C distances are 2.114(6)–2.153(6) Å). In solvate 2 with benzene the antimony atoms have a distorted trigonal-bipyramidal coordination with the oxygen atoms of carboxylate ligands in axial positions (Sb–O 2.075(4), 2.105(4) Å), the carbonyl oxygen atoms are coordinated with the central metal atom (Sb∙∙∙O=C 3.023(6), 3.077(8) Å), the Sb–C bond lengths (2.104(5)–2.112(5) Å) are significantly less than in 1. The ranges of variation in the Sb–C bond lengths in the practically linear binuclear molecule of solvate 3 with acetonitrile are 2.101(5)–2.106(5) and 2.100(5)–2.104(5) Å (the SbOSb angle equals 178.05(18)). The bond lengths of antimony atoms with the bridging oxygen atom (1.925(4), 1.936(4) Å) are less than the sum of the covalent radii of antimony and oxygen, as well as the distances between the antimony atom and the terminal carboxyl ligand (Sb–O 2.263(4), 2.214(4) Å). The carbonyl oxygen atoms are coordinated with the central metal atom (Sb∙∙∙O=C 3.484(8), 3.512(9) Å) to a lesser extent than in 2. The crystal of solvate 4 with benzene contains two types of crystallographically independent corner molecules (the SbOSb angles are 163.75(18), 164.27(19)), the difference in lengths of the Sb–Obridge (1.939(11)–1.981(13) Å) and Sb–Oterm (2.096(11)–2.208(11) Å) is not as sharp as in the case of complex 3. Complete tables of atom coordinates, bond lengths and valence angles are deposited at the Cambridge Crystallographic Data Center (No. 2070383 (1); No. 2074511 (2); No. 1970910 (3); No. 2064392 (4); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk/data_request/cif).

Probing the redox-conversion of Co(II)-disulfide to Co(III)-thiolate complexes: the effect of ligand-field strength.

The redox-conversion reaction of cobalt(II)-disulfide to cobalt(III)-thiolate complexes triggered by addition of the bidentate ligand 2,2'-bipyridine has been investigated. Reaction of the cobalt(II)-disulfide complex [Co2(L1SSL1)(X)4] (L1SSL1 = di-2-(bis(2-pyridylmethyl)amino)-ethyldisulfide; X = Cl or Br) [1X] with 2,2'-bipyridine (bpy) resulted in the formation of two different products, namely the cobalt(III)-thiolate complex [Co(L1S)(bpy)]X2 and the unexpected side product [Co2(L1SSL1)(bpy)2(X)2]X2. Crystals of [Co2(L1SSL1)(bpy)2(Cl)2](BPh4)2 [2Cl](BPh4)2 obtained after anion exchange showed the cobalt(II) ions to be in octahedral geometries with the nitrogen donors of the disulfide ligand arranged in a facial conformation and the chloride ion trans to the tertiary amine nitrogen. Remarkably, this side product cannot be converted to the cobalt(III)-thiolate compound [Co(L1S)(bpy)](SbF6)2 [3](SbF6)2 by removal of the chloride ion with use of a silver salt, as this causes scrambling of the ligands, resulting in the formation of [Co(bpy)3]n+. [Co(L1S)(bpy)](SbF6)2 was obtained in a pure form by addition of bpy to a solution in acetonitrile of the compound [Co(L1S)(MeCN)2]2+ [4]2+. Addition of NEt4Cl to [3](SbF6)2 regenerates the cobalt(II)-disulfide complex [1Cl] as confirmed spectroscopically. DFT studies revealed that the conversion from [1Cl] to [3]2+ most likely occurs via the hypothetical intermediate species [2Cl]2+mer, in which the nitrogen atoms of the disulfide ligand are arranged in a meridional conformation. Interestingly, the estimated d-orbital splitting energy of [3]2+ is lower than that of [4]2+, indicating that the ligand-field strength of bpy is lower than anticipated, which hampers clean conversion in the redox-conversion reaction. This study shows that the redox-conversion reaction between cobalt(II)-disulfide and cobalt(III)-thiolate complexes is intricate rather than straightforward.