Thermal Studies of Metal-quinone Complexes Role of Aqua Coligations with Copper(II) in Coordination of 2-hydroxy-1,4-naphthoquinone

Copper(II) complexes of lawsone (2-hydroxy-1,4-naphthaquinone, Lw) with variety of aqua ligation viz. Cu-1, [Cu(Lw)₂(H₂O)]₂; Cu-2, [Cu(Lw)₂(H₂O)₂] and Cu-3, [Cu(Lw)₂(H₂O)₂]₂ have been synthesized. The role of water as counter ligand on coordination propensity of redox active lawsone in naphthoquinone/naphthosemiquinone (NQ/NSQ) forms is quantified by studies of pyrolytic reactions, using non-isothermal TG and DTA techniques, coupled with IR studies. Mixed (NQ) (NSQ) ligation in Cu-1 and Cu-3 required energy of activation, E_a ∼67 kJ mol⁻¹ of (NQ) and ∼41 kJ mol⁻¹ of (NSQ). Comparable energies of aqua ligand (∼43 kJ mol⁻¹) with NSQ ligand in Cu-1 and Cu-3, dictate charge distributions in lawsone coordinations. A large difference between E_a of aqua and p-NQ ligand indicates coordination of lawsone in its fully oxidised quinone form in Cu-2. From thermoanalytical studies schematic oxidative decomposition mechanisms are proposed for Cu-1 and Cu-3. From pyrolytic reactions enthalpies are estimated by DTA technique. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ni(II) and Cu(II) complexes of new unsymmetrical N2O2 Schiff bases derived from 3-(2-aminobenzylimino)-1-phenylbutan-1-ol: synthesis,structure, antibacterial properties,and electrochemistry

Two new N₂O₂ unsymmetrical Schiff bases, H₂L¹ = 3-[({o-[(E)-(o-hydroxyphenyl)methylideneamino]phenyl}methyl)imino]-1-phenyl-1-buten-1-ol and H₂L² = 3-[({o-[(E)-(2-hydroxy-1-naphthyl)methylideneamino]phenyl}methyl)imino]-1-phenyl-1-buten-1-ol, and their copper(II) and nickel(II) complexes, [CuL¹] (1), [CuL²] (2), [NiL¹] (3), and [NiL²] (4), have been synthesized and characterized by elemental analyses and spectroscopic methods. The crystal structures of these complexes have been determined by X-ray diffraction. The coordination geometry around Cu(II) and Ni(II) centers is described as distorted square planar in all complexes with the CuN₂O₂ coordination more distorted than the Ni ones. The electrochemical studies of these complexes indicate a good correlation between the structural distortion and the redox potentials of the metal centers. The ligand and metal complexes were also screened for their in vitro antibacterial activity.     

Synthesis and magnetism of 6-nitrobenzimidazolate and imidazolate-bridged copper(II) complexes

Summary Four new trinuclear copper(II) complexes, [Cu(phen)-(NBzIm)] (ClO₄) (1), [Cu(bpy)(NBzIm)](ClO₄) (2), [Cu-(Me₂-bpy)(NBzIm)](Ac)·1/2H₂O (3) and [Cu(Me₂-bpy)-(Im)](ClO₄)·1/2H₂O (4) (phen = 1, 10-phenanthroline, bpy = 2,2-bipyridine, NBzIm = 6-nitrobenzimidazolate ion, Im=imidazolate ion) have been prepared and characterized by variable temperature magnetic susceptibility measurements. A weak antiferromagnetic spin exchange interaction operates between copper(II) ions, exchange integrals evaluated as J =-23.82 cm^-1 for (1); and J=-21.91 cm^-1 for (2).     

配位聚合物[Cu(pa)(vim)2]n的合成、晶体结构和电化学性质研究

本文合成了一种新型配位聚合物[Cu(pa)(vim)2]n(pa为邻苯二甲酸阴离子,vim为1-乙烯基-1H-咪唑),并用x射线单晶衍射仪和元素分析表征了其单晶结构。晶体属单斜晶系,C2/c空间群,晶胞参数分别为：a＝1.6527(3) nm, b＝0.81800(16) nm, c＝1.4463(3) nm, β＝113.19(3)°, V＝1.7973(7) nm3, Z＝4, Dc＝1.537 g?cm－3。 [I＞2σ(I)]时：R1＝0.0476, wR2＝0.1235,对所有数据：R1＝0.0693, wR2＝0.1355。配合物的结构中存在沿着c轴的zigzag聚合链。每个铜原子位于晶体中心,与两个N原子和两个O原子进行配位,形成了扭曲的平面结构。电化学研究表明在配合物中Cu2+/Cu+的氧化还原是一个单电子的准可逆过程。     

Formation of polymeric chain assemblies of transition metal complexes with a multidentate Schiff-base

The new multidentate Schiff-base (E)-6,6′-((1E,1′E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-ylidene))bis(4-methyl-2-((E)(pyridine-2-ylmethylimino)methyl)phenol) H₂L and its polymeric binuclear metal complexes with Cr(III), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) are reported. The reaction of 2,6-diformyl-4-methyl-phenol with ethylenediamine in mole ratios of 2:1 gave the precursor 3,3′-(1E,1′E)-(ethane-1,2-diylbis(azan-1-yl-1ylidene))bis(methan-1-yl-1-ylidene)bis(2-hydroxy-5-methylbenzaldehyde) W. Condensation of the precursor with 2-(amino-methyl)pyridine in mole ratios of 1:2 gave the new N₆O₂ multidentate Schiff-base ligand H₂L. Upon complex formation, the ligand behaves as a dibasic octadentate species with the involvement of the nitrogen atoms of the pyridine groups in coordination for all complexes. The mode of bonding and overall geometry of the complexes were determined through physico-chemical and spectroscopic methods. These studies revealed octahedral geometries for Cr(III), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Cd(II) and Hg(II) complexes of general formulae [Cr₂^III(L)Cl₂]Cl₂, [Ni₂^II(L)(H₂O)₂]Cl₂ and [M₂(L)Cl₂] and five co-ordinate Zn(II) complex of general formula [Zn₂^II(L)]Cl₂.     

Crystal structures,electrochemical properties,antioxidant screening and in vitro cytotoxic studies on four novel Cu(II) complexes of bidentate Schiff base ligands derived from 2-methoxyethylamine

Four novel Schiff base ligands and their copper(II) complexes, [Cu(L¹)₂] (1), [Cu(L²)₂] (2), [Cu(L³)₂] (3), and [Cu(L⁴)₂] (4), were synthesized and characterized by elemental analyses, FT-IR, and UV–Vis spectroscopy. The ligands were synthesized from the condensation of 2-methoxyethylamine with various salicylaldehyde derivatives (x-salicylaldehyde for HLⁿ, x = H (n = 1), 5-Br (n = 2), 3-OMe (n = 3), and 4-OMe (n = 4)). The molecular structures of 1, 2, and 3 were determined by the single crystal X-ray diffraction technique. The redox behavior studies of the complexes in acetonitrile display the electronic effects of the groups on the redox potential. The antioxidant activity of the Schiff base ligands and their Cu(II) complexes was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method and FRAP assay. Furthermore, the in vitro anticancer activity of compounds was screened, including MTT and migration assays against gastric cancer cell line (MKN-45). The results show that all ligands and complexes have antioxidant and anticancer activity in a concentration-dependent way.     

Supramolecular Interactions Direct the Formation of Two Structural Polymorphs from One Building Unit in a One‐Pot Synthesis

Two polymorphs of supramolecular isomers, a discrete dimer and a zig‐zag chain, having the same chemical composition, [Mn(Hbit)Cl₂] (Hbit=1‐methyl‐2‐(1H‐1,2,3‐triazol‐4‐yl)‐1H‐benzo[d]imidazole), were obtained solvothermally in a one‐pot synthesis. The isomers differ in a number of ways: orange blocks versus pale‐yellow needles, triclinic P versus orthorhombic Pbcn, double μ₂‐Cl versus alternate single and triple μ₂‐Cl, coordination number 5 versus 6, and antiparallel versus parallel near‐neighbor orientation of Hbit. The packing in each case is driven by the supramolecular interactions, H‐bonds (N?H???Cl, C?H???Cl) and π???π overlaps, calculated to be in the range 20–36 kcal mol^?1. Calculations gave a difference of only 2 kcal mol^?1 in favor of the dimer, which confirms with the observation of principally the dimer at short reaction time. ESI‐MS spectra of the dissolved crystals reveal the same fragments with similar distributions. The presence of two fragments at m/z 286.96 [Mn^IV(Hbit)Cl‐2H]⁺ and 323.94 [Mn^III(Hbit)Cl₂]⁺ indicates that [Mn(Hbit)Cl₂] is the building unit in both cases; thus, the different orientations of the ligands lead to the two polymorphs stabilized by the respective supramolecular interactions. Importantly, the chain form represents the first example with alternate single and triple μ₂‐Cl bridges. The magnetic interactions are weakly antiferromagnetic in both cases, with J in the range 0.07–0.34 cm^?1; however, high‐field EPR analysis reveals moderate magneto‐anisotropy with D=0.26(1) cm^?1, E=0.06(1) cm^?1 and D=0.17(1) cm^?1, E=0.03(1) cm^?1, respectively.     

Li17Sb13S28: A New Lithium Ion Conductor and addition to the Phase Diagram Li2S–Sb2S3

Li₁₇Sb₁₃S₂₈ was synthesized by solid‐state reaction of stoichiometric amounts of anhydrous Li₂S and Sb₂S₃. The crystal structure of Li₁₇Sb₁₃S₂₈ was determined from dark‐red single crystals at room temperature. The title compound crystallizes in the monoclinic space group C2/m (no. 12) with a=12.765(2) Å, b=11.6195(8) Å, c=9.2564(9) Å, β=119.665(6)°, V=1193.0(2) ų, and Z=4 (data at 20 °C, lattice constants from powder diffraction). The crystal structure contains one cation site with a mixed occupation by Li and Sb, and one with an antimony split position. Antimony and sulfur form slightly distorted tetragonal bipyramidal [SbS₅E] units (E=free electron pair). Six of these units are arranged around a vacancy in the anion substructure. The lone electron pairs E of the antimony(III) cations are arranged around these vacancies. Thus, a variant of the rock salt structure type with ordered vacancies in the anionic substructure results. Impedance spectroscopic measurements of Li₁₇Sb₁₃S₂₈ show a specific conductivity of 2.9×10^?9 Ω^?1 cm^?1 at 323 K and of 7.9×10^?6 Ω^?1 cm^?1 at 563 K, the corresponding activation energy is E_A=0.4 eV below 403 K and E_A=0.6 eV above. Raman spectra are dominated by the Sb?S stretching modes of the [SbS₅] units at 315 and 341 cm^?1 at room temperature. Differential thermal analysis (DTA) measurements of Li₁₇Sb₁₃S₂₈ indicate peritectic melting at 854 K.     

Ligand influence on the electrochemical behavior of some copper(II) thiosemicarbazone complexes

The redox properties of the title mono- and binuclear copper(II) chelates have been investigated by cyclic voltammetry in DMF at a working platinum electrode. The cathodic reduction and anodic oxidation of the investigated chelates produced the corresponding electrochemical Cu^I and Cu^IIIspecies stable only in the voltammetric time scale, The effects of substituents on E_1/2, redox properties and stability towards oxidation of the complexes were related to the electron-withdrawing or releasing ability of the substituents on the C=N¹[H, CH₃ or C₆H₅] and/or N⁴H [H, C₂H₅, C₆H₅ or pClC₆H₄] groups, The electron attracting substituents stabilize the Cu(II) complexes while electron-donating groups favor oxidation to Cu(III). Changes in the E_1/2 for the complexes due to remote substituent effects could be related to changes in basicity of N⁴H.Thus, variation in N⁴1-J has more influence on E_1/2 than changes in C=N¹. The correlation between E_1/2 of the complexes and pK_a of the ligands has been attributed to the spherical potential generated by the electron density of the donor atoms at the antibonding d orbitals.     

Complexes of 8-Aminoouinoline. II. The Infrared Spectra of the Bisand Mono(Aminoquinoline) Complexes of Metal(II) Halides

Abstract

The infrared spectra of the complexes M(aq)₂(H₂O)₂X₂ (M = Fe, Co, Ni, Cu; aq = 8-aminoquinoline; X =Cl, Br) have been determined over the range 4000-50 cm^?1. Absence of vM-X bands indicates that the halide is not coordinated to the metal ion and the complexes are correctly formulated [M(aq)₂-(H₂O)₂]X₂. Deuteration of the amino group and the effects of metal ion substitution enable assignment of the vM-NH₂, vM-N and vM-OH₂ modes as well as the amino group vibrations. ¹⁸ O-Labelling assists in identifying the vO-H, vO-H……X and δO-H bands. The spectra are consistent with trans-octahedral coordination and axial bonding of the water molecules. The far infrared spectra of the mono(aminoquinoline) complexes [M(aq)X₂]_n (M = Cu, Zn; X = Cl, Br) are consistent with the proposed structure of polymeric octahedral coordination involving both bridging and terminal M-X bonds. The vM-NH₂, vM-N, vM-X(terminal) and vM-X(bridging) bands are assigned by studying the effects of amino group deuteration, metal ion substitution and halide substitution.     

Binuclear Iron(I) Complex Containing Bridging Phenanthrene‐4,5‐dithiolate Ligand: Preparation,Spectroscopy, Crystal Structure,and Electrochemistry

A diiron hexacarbonyl complex containing bridging phenanthrene‐4,5‐dithiolate ligand is prepared by oxidative addition of Phenanthro[4,5‐cde][1,2]dithiin to Fe₂(CO)₉. The complex is investigated as a model for the active site of the [Fe–Fe] hydrogenase enzyme. The compound, [(μ‐PNT)Fe₂(CO)₆]; (PNT = phenanthrene‐4,5‐dithiolate), was characterized by spectroscopic methods (IR, UV/Vis and NMR) and X‐ray crystallography. The IR and proton NMR spectra of [(μ‐PNT)Fe₂(CO)₆] ( 4 ) are in agreement with a PNT ligand attached to a Fe₂(CO)₆ core. The infrared spectrum of 4 recorded in dichloromethane contains three peaks at 2001, 2040, and 2075 cm^–1 corresponding to the stretching frequency of terminal metal carbonyls. X‐ray crystallographic study unequivocally confirms the structure of the complex having a butterfly shape with an Fe–Fe bond length of 2.5365 Å close to that of the enzyme (2.6 Å). Electrochemical properties of [(μ‐PNT)Fe₂(CO)₆] have been investigated by cyclic voltammetry. The cyclic voltammogram of [(μ‐PNT)Fe₂(CO)₆] recorded in acetonitrile contains one quasi‐irreversible reduction (E_1/2 = –0.84 V vs. Ag/AgCl, I_pc/I_pa = 0.6, ΔE_p = 131 V at 0.1 V · s^–1) and one irreversible oxidation (E_pa = 0.86 V vs. Ag/AgCl). The redox of [(μ‐PNT)Fe₂(CO)₆] at E_1/2 = –0.84 V can be assigned to the one‐electron transfer processes; [Fe^I–Fe^I] → [Fe^I–Fe⁰] and [Fe^I–Fe⁰] → [Fe^I–Fe^I].     

Enhancement of electron transfer kinetics on a polyaniline-modified electrode in the presence of anionic dopants

The electrocatalytic redox behavior of 1,4-naphthoquinone (NQ) has been studied on a polyaniline-modified platinum electrode (PANI) using cyclic voltammetry and rotating disc electrode (RDE) as diagnostic techniques. The modified electrode was prepared by electropolymerization of aniline in different acidic solutions. The PANI showed electrocatalytic activity toward the redox behavior of NQ. This process includes the participation of PANI to the redox reaction of NQ via the surface catalysis phenomena. The cyclic voltammograms of NQ in HCl on the PANI-Cl-modified electrode showed an overlapped oxidation peak, the peak potential of which did not change with increasing scan rate. The influence of other anions including and as dopant was also studied and compared with Cl⁻. The use of HClO₄ as a supporting electrolyte resulted in well-separated redox peaks. The RDE voltammogram was used to obtain a quantitative assessment of reaction rate at the PANI-modified electrode. It was found that PANI acts as an electrocatalyst for NQ reduction with decreasing ΔE _p and increasing k°.     

White Light Emissive DyIII Single‐Molecule Magnets Sensitized by Diamagnetic [CoIII(CN)6]3− Linkers

The self‐assembly of Dy^III–3‐hydroxypyridine (3‐OHpy) complexes with hexacyanidocobaltate(III) anions in water produces cyanido‐bridged {[Dy^III(3‐OHpy)₂(H₂O)₄] [Co^III(CN)₆]}?H₂O ( 1 ) chains. They reveal a single‐molecule magnet (SMM) behavior with a large zero direct current (dc) field energy barrier, ΔE=266(12) cm^?1 (≈385 K), originating from the single‐ion property of eight‐coordinated Dy^III of an elongated dodecahedral geometry, which are embedded with diamagnetic [Co^III(CN)₆]^3? ions into zig‐zag coordination chains. The SMM character is enhanced by the external dc magnetic field, which results in the ΔE of 320(23) cm^?1 (≈460 K) at H_dc=1 kOe, and the opening of a butterfly hysteresis loop below 6 K. Complex 1 exhibits white Dy^III‐based emission realized by energy transfer from Co^III and 3‐OHpy to Dy^III. Low temperature emission spectra were correlated with SMM property giving the estimation of the zero field ΔE. 1 is a unique example of bifunctional magneto‐luminescent material combining white emission and slow magnetic relaxation with a large energy barrier, both controlled by rich structural and electronic interplay between Dy^III, 3‐OHpy, and [Co^III(CN)₆]^3?.     

Synthesis,structural characterization and substituent effects of two copper(II) complexes with benzaldehyde ortho-oxime ligands

Two new Cu(II) complexes, [Cu(L¹)₂] (1) and [Cu(L²)₂] (2) (HL¹ = (E)-3-bromo-5-chloro-2-hydroxy benzaldehyde O-methyl oxime; HL² = (E)-3-bromo-5-chloro-2-hydroxy benzaldehyde O-ethyl oxime), have been synthesized and characterized by physicochemical and spectroscopic methods. X-ray crystallographic analyses show that complexes 1 and 2 have similar structures, consisting of one Cu(II) atom and two L⁻ units. In both complexes, the Cu(II) atom, lying on an inversion center, is four-coordinated in a trans-CuN₂O₂ square-planar geometry by two phenolate O and two oxime N atoms from two symmetry-related N,O-bidentate oxime ligands. Moreover, both complexes form an infinite three-dimensional supramolecular structure involving intermolecular C–H···Br hydrogen bonds and π···π stacking interactions between the metal chelate rings and aromatic rings. Substituent effects in the two complexes are discussed.     

Cyano-bridged Heterotrinuclear Molybdenum(IV)-Nickel(II) Complexes: Synthesis,Crystal Structure and Magnetic Properties

Two novel cyano-bridged heterotrinuclear molybdenum(IV)-nickel(II) complexes ([Ni(en)₂(H₂O)]_2-[Mo(CN)₈]·2H₂O, 1, and [NiL(H₂O)]₂[Mo(CN)₈]·4H₂O, 2), where en=1,2-diaminoethane and L= 1,3,6,9, 11,14-hexaazacyclo[12,2,1,1^6,9]octodecanne were synthesized and characterized. The crystal structure of 1 was determined. The structure consists of trinuclear units, space group C2/c, with unit cell dimensions a=17.178(9), b=11.032(5), c=17.629(8) Å, α=108.484(8)°. The temperature dependence of the magnetic susceptibilities for 1 and 2 was analyzed by means of a Hamiltonian expression leading to J=-0.87cm^-1, ZJ'=0.65cm^-1, D=0.02cm^-1, g _Ni=2.45 for complex 1, and J=-0.87cm^-1, ZJ'=0.56cm^-1, D=0.02cm^-1, g, _Ni=2.45 for complex 2.     

A 1-D alternating copper(II) chain based on three acetate-bridging modes: synthesis,crystal structure,DNA binding and magnetic properties

A new 1-D alternating copper(II) polymer, [Cu₂(L)(OAc)₄]_n (1) (L = 5-chloro-2-(pyridine-2-yl)benzo[d]thiazole), has been isolated and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, and magnetic susceptibility. The complex crystallized in the triclinic space group P-1, a = 8.2277(16) Å, b = 9.4233(19) Å, c = 15.831(3) Å, α = 103.38(3)°, β = 99.95(3)°, γ = 92.70(3)°, V = 1171.3(4) Å³, and comprises a 1-D polymer linked by three kinds of acetate-bridging modes in an alternating manner. UV–visible and fluorescence spectra revealed that 1 is bound to CT-DNA in a partial intercalation mode. Through gel electrophoresis assays, 1 displayed an efficient oxidative cleavage activity on supercoiled plasmid DNA (pUC19) in the presence of H₂O₂. Magnetic measurements were performed from 2 to 300 K, and the experimental results were satisfactorily reproduced with J₁ = –160 ± 20 cm^?1, J₂ = 5.8 ± 0.2 cm^?1, zJ′ = 0.381 ± 0.005 cm^?1 and g = 2.1, showing antiferromagnetic coupling between Cu1 and Cu1i, ferromagnetic exchange between Cu2 and Cu2ii, and a weak ferromagnetic molecular field correction accounting for all interspecies interactions.     

希夫碱配合物的研究——Ⅵ.K[Fe(acaccn)(CN)2]·2H2O的合成及晶体结构

制备了K[Fe(acaccn)(CN)₂]·2H₂O.并测定了晶体结构.     

Redox potential of iron–sulfur clusters as a model of the Desulfovibrio vulgaris center

A theoretical study of Heisenberg exchange and double exchange effects in clusters with four and six iron ions has been performed for [Fe₄ S₃ O] ^m+, [Fe₄ S₄]^m+ (where m = 3, 2), and [Fe₆ S₆] ⁿ⁺ (where n = 5, 4) ions as models of the Desulfovibrio vulgaris iron–sulfur centers. Assuming that the redox potential mostly depends on the Heisenberg spin coupling and the resonance delocalization, we performed an analysis of the reduction process for the [Fe₄ S₃ O] ^3+/2+, [Fe₄ S₄] ^3+/2+, and [Fe₆ S₆] ^5+/4+ ions and showed that the redox potential can be calculated as a difference between average spin energies of the tetravalent and pentavalent double cubane superclusters. For the Heisenberg parameter of J₁ = 20 cm^-1, the redox potential amounts to about 0.03 V.It complies with close to zero experimental values of the redox potential.Electronic Supplementary Material: Supplementary material is available in the online version of this article at     

Could Redox‐Switched Binding of a Redox‐Active Ligand to a Copper(II) Centre Drive a Conformational Proton Pump Gate? A Synthetic Model Study

A proposal for a redox‐linked conformational gate to proton translocation—a proton pump gate—based upon a transition‐metal redox‐switchable hemilabile ligand (RHL) system is made. Consideration of the requirements for such a system reveals copper(II ) to be the ideal metal centre. To test the proposal and, thereby, to provide an artificial proton pump gate, the copper coordination chemistry of three tris(pyridylmethyl)amine (tpa) ligands with one “leg” (PY*) substituted at the 6‐position of the pyridine ring by a dimethoxyphenyl (L¹), a hydroquinone (H₂L²) or a quinone (L³) substituent has been investigated. Crystal structures of sp‐[Cu(κ⁴N‐L¹)Cl]Cl?3 H₂O (sp=square pyramidal), sp‐[Cu(κ³N‐H₂L²)Cl₂] and tbp‐[Cu(κ⁴N,κO‐HL²)][PF₆] (tbp=trigonal bipyramidal) have been determined. The Cu^I complexes [Cu(L)(MeCN)_n]⁺ (L=L¹, H₂L²) display physicochemical properties consistent with a “dangling” PY* leg; from the NMR spectra, the barriers to inversion of the ligand amine donor for the Cu^I complexes are estimated to be within the range of about 30–45 kJ mol^?1. In the Cu^II complexes, coordination of the PY* leg is finely balanced and critically depends on the nature of the PY* substituent and the availability of potential co‐ligand(s). For example, tbp‐[Cu(κ⁴N‐L¹)Cl]⁺ reacts cleanly with Cl^? ions to afford sp‐[Cu(κ³N‐L¹)Cl₂]; Vis/NIR spectrophotometric titrations suggest the affinity of tbp‐[Cu(κ⁴N‐L¹)Cl]⁺ for Cl^? ion in dichloromethane is 9.7×10² and is at least 10⁴‐fold greater than that of tbp‐[Cu(κ⁴N‐L³)Cl]⁺. The complex sp‐[Cu(κ³N‐H₂L²)Cl₂] has a “dangling” PY* leg, in which an intramolecular OH(hydroquinone)???N(pyridine) hydrogen bond “ties‐up” the pyridyl nitrogen atom, and reacts with Brønsted bases to give tbp‐[Cu(κ⁴N,κO‐HL²)]⁺. Two‐electron oxidation of sp‐[Cu(κ³N‐H₂L²)Cl₂] is linked to loss of two protons and a conformational change, and affords tbp‐[Cu(κ⁴N‐L³)Cl]⁺. The [Cu(κ³N‐H₂L²)Cl₂]–[Cu(κ⁴N‐L³)Cl]⁺ system provides a first demonstration of the critical step in the proposed proton pumping cycle, namely a redox‐driven and proton‐linked conformational change. The possible biological relevance of this work to proton pumping in cytochrome c oxidase is mentioned.     

Crystal structure, magnetic properties and conductivity of CuSbTeO3Cl2

CuSbTeO₃Cl₂ has been isolated during an investigation of the system Cu₂O:TeCl₄:Sb₂O₃:TeO₂. The new compound is light yellow and crystallises in the monoclinic system, space group C2/m, a=20.333(5) Å, b=4.0667(9) Å, c=10.778(2) Å, Z=6. The structure is layered and is built up from corner and edge sharing [(Sb,Te)O₄E] trigonal bipyramids that have the lone pair (E) directed towards one of the equatorial positions, those groups build up [(Sb,Te)₂O₃E₂⁺]_n layers. The copper and the chlorine atoms are located in between those layers. There are two different Cu positions. The [Cu1Cl₄] group is a slightly distorted tetrahedron and these tetrahedra make up chains by corner sharing. The electron density for the half occupied Cu2 atom is spread out in the structure like a worm that run along the b-axis in the space in between two chains of [Cu1Cl₄] tetrahedrons. Analysis of the diamagnetic response in magnetic susceptibility measurements is in perfect agreement with a Cu⁺ valence. Conductivity measurements in the temperature range 355–590 K gives an activation energy of 0.55 eV. The delocalised Cu2 position in the structure suggests that the compound is a Cu⁺ ionic conductor along the b-axis.