Solvent effects on binuclear complex formation between aquopentacyanoferrate(II) and tetraamminepyrazinecarboxylatocobalt(III) in binary aqueous mixtures

The substitution reaction between aquopentacyanoferrate(II) and tetraamminepirazynecarboxylatocobalt(III) to form a binuclear species is studied in various binary aqueous mixtures at different temperatures. Values of activation parameters seem to indicate no change in the mechanism of the reaction in the different mixtures. Medium effects have been rationalized by using a multiparameter regression of solvent parameters. Results show that the reaction follows a dissociative mechanism. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterisation of binuclear oxo molybdenum(V) hypophosphite

Summary A binuclear oxo Mo^V hypophosphite of composition [Mo₂O₄(H₂PO₂)₂(H₂O)₂], is prepared by direct reduction of Mo^VI oxide hydrate (MoO₃·H₂O) with hypophosphorus acid in an argon atmosphere, and characterised by i.r., and electronic spectra, magnetic susceptibility and cyclic voltammetry measurements.¹H and³¹Pn.m.r., x-ray diffraction and thermal analysis data contribute to its molecular structure elucidation, and a dioxobridged dioxo Mo^V with bidentate hypophosphite ion and water molecule completing the octahedral coordination around each Mo atom is proposed.     

Synthesis, spectra and biomimetic properties of copper(II)-copper(II) and copper(II)-zinc(II) binuclear complexes with CuN5 chromophores

X-band electron spin resonance (ESR) and UV-vis spectra of a homobinuclear [(Bipy)2Cu-E-Im-Cu(Bipy)2](BF4)3 and a heterobinuclear [(Bipy)2Cu-E-Im-Zn(Bipy)2](BF4)3 complexes, E-Im=2-ethylimidazolate ion have been described as possible models for superoxide dismutase (SOD). Magnetic moment and ESR spectral measurements of the homobinuclear complex have shown an antiferromagnetic exchange interaction. From pH-dependent ESR and UV-vis spectral measurements studies, these complexes have been found to be stable over 8.5-10.5 pH range. These complexes catalyze the dismutation of superoxide (O2-) at biological pH. All the observations indicate that these complexes act as good possible models for superoxide dismutase.     

Redox properties of thiolate-bridged binuclear nickel(II) complexes and correlation of their electronic spectra

Summary The redox properties of a series of thiolate-bridged binuclear nickel(II) complexes with NNS-tridentate and SNNS-tetradentate thiolic ligands have been studied by cyclic voltammetry. The first redox potential (E_1/2=–0.63 to –0.95 Vversus Ag/AgCl) has a linear correlation with the absorption maxima of the transition.     

Diazadiene-isonitrile complexes of molybdenum(II) and molybdenum(III)

Summary [MoCl₃(THF)₃] reacts with CNMe and diazadienes or a diamines, NN (RN=CHCH=NR, RN=CMeCMe=NR where R = 4-C6₆H₄OMe, and Me₂NCH₂CH₂NMe₂) to give molybdenum(III) complexes [MoCl₃(CNMe) NN] and molybdenum(II) complexes [MoCl₂(CNMe)₂NN]. The i.r. and magnetic data of these complexes are interpreted on the basis of the electronic properties of the ligands.     

Reaction between palladium(II) and gallium(III) halogenides in arenes: influence of halogen nature on the formation of binuclear palladium(I) clusters

Palladium(II) bromide reacts with gallium(III) bromide in the presence of arenes yielding binuclear palladium(I) complexes [Pd₂(GaBr₄)₂(arene)₂], where arene=benzene (1), toluene (2) and p-xylene (3). Reaction of palladium(II) chloride with gallium(III) chloride in p-xylene leads to the analogous palladium(I) compound [Pd₂(GaCl₄)₂(p-xylene)₂] (4); the X-ray structures of 1-4 were determined.     

The electronic spectra and structure of palladium(II) molecular complexes and clusters

The electronic absorption spectra of palladium(II) diacetate (PDA) complexes with phosphines and sulfides (D) with the composition Pd(OAc)₂ · 2D (1: 2) contain an intense charge transfer band at λ_max ∼ 300 nm (ɛ ∼ 15 000) and do not absorb in the region of 400 nm. Polynuclear compounds such as PDA trimer [Pd(OAc)₂]₃, trimer complexes with D, and four- and six-membered palladium metallocyclic compounds formed in the interaction of PDA with mercaptans absorb at longer wavelengths. The electronic absorption spectra of all the palladium polynuclear compounds (clusters) contain bands at λ_max ∼ 400 nm (ɛ ∼ 1000). The appearance of these bands in the spectra of palladium clusters is evidence of the formation of chemical bonds between neighboring Pd atoms, although Pd…Pd distances substantially exceed the sum of the covalent radii of palladium atoms.     

The chemistry of binuclear palladium(II) and platinum(II) complexes

The chemistry of binuclear palladium(II) and platinum(II) complexes has been reviewed. This review deals with complexes derived from various classes of ligands and covers various aspects, viz. synthesis, spectroscopic and structural features and chemical reactivity, of these complexes. Applications of these complexes are briefly described in the respected sections.     

Vibrational spectra of germanium-carbon clusters. II. GeC(7) and GeC(9)

Experimental and theoretical studies of a novel family of germanium-carbon clusters (Ge(n)C(m)) that were initiated with our earlier identification of the GeC(3)Ge cluster have now been extended to the GeC(7) and GeC(9) chains. The new clusters, which were formed by laser ablation and trapped in solid Ar at approximately 10 K, have been identified using Fourier-transform infrared (FTIR) measurements coupled with density-functional theory (DFT) calculations. The nu(1)(sigma) vibrational fundamental of linear GeC(7) has been identified at 2063.6 cm(-1), and an absorption at 1928.3 cm(-1) has been assigned to the nu(4)(sigma) fundamental of linear GeC(9). FTIR measurements of the isotopic shifts for the assignments are in good agreement with the DFT predictions.     

Structure and EPR spectra of binuclear copper(II) complexes with acyldihydrazones of benzenedicarboxylic acids and trifluoroacetylacetone

Binuclear copper(II) complexes with acyldihydrazones of benzenedicarboxylic acid and trifluoroacetylacetone have been synthesized and studied. The structure of the copper(II) complex with diacylhydrazone of 1,3-benzenedicarboxylic acid (H₄L) of composition [Cu₂L · 2LPy] has been studied by X-ray diffraction. The crystals are triclinic: a = 9.2298(4) Å, b = 11.8510(6) Å, c = 13.8314(7) Å, α = 90.780(3)°, β = 96.124(3)°, γ = 99.264(3)°, space group \(P\bar 1\), Z = 2. The number of symmetry-unrelated reflections with I > 2σ(I) 5941; R = 0.0357, R _w = 0.0589. The complex contains two equivalent copper atoms at a distance of 9.56 Å from each other in the square-planar coordination environment. The high-temperature EPR spectra of the complexes show a signal of seven HFS lines indicating the coupling of unpaired electrons to two equivalent copper nuclei (g = 2.113?2.116, a _Cu = 37.0?37.2 × 10^?4 cm^?1).     

A potassium-encapsulated Preyssler-based structure modified by binuclear cyclic copper(II) clusters: photocatalytic and electrochemical properties

Transition Metal Chemistry - Through the use of a flexible ligand 1,1′-bis(3,5-dimethyl-1H-pyrazolate)methane (H2bdpm), a K-encapsulated Preyssler-based complex,...     

Stereoselectivity and exciton cotton effects in mixed complexes of zinc(II)

Mixed complexes of Zn(II) with chiral aminoacids and 1,10-phenanthroline have been prepared and their C.D. and O.R.D. spectra measured. All the C.D. spectra exhibited an exciton splitting at 268 nm and their intensities depended on the chiral ligand. These results were interpreted in terms of steric effects through the exciton theory.     

Correlation between i.r. spectra and thermal decomposition of cobalt(II), nickel(II), copper(II) and mercury(II) complexes with piperidinedithiocarbamate and pyrrolidinedithiocarbamate

The thermal decomposition of pyrrolidinedithiocarbamate and piperidinedithiocarbamate complexes of Co^II, Ni^II, Cu^II and Hg^II have been studied by thermogravimetry and differential scanning calorimetry. The decomposition intermediates and final products were identified by their X-ray diffraction patterns. The i.r. spectra are discussed in terms of the thermal decomposition pathways.     

Telluride clusters of molybdenum: Synthesis, structures, and NMR spectra

High-temperature reactions of Mo, chalcogen (S or Se), Te, and Br₂ in molar ratio Mo: S/Se: Te: Br = 3: 1: 6: 4 were carried out. The reaction products were subjected to mechanochemical activation with K(Dtp) (Dtp = (EtO)₂PS₂) in a vibrational mill, resulting in the formation of new compounds [Mo₃(μ₃-Q)_0.5(μ₃-O)_0.5(μ₂-Te₂)₃(Dtp)₃](Dtp) (Q = Se (I) and S (II)). The structure of compound I has been established by X-ray diffraction analysis. Solutions of compounds I and II contain mixtures of [Mo₃(μ₃-Q)(μ₂-Te₂)₃(Dtp)₃]⁺ and [Mo₃(μ₃-O)(μ₂-Te₂)₃(Dtp)₃]⁺, which is confirmed by mass spectrometry and ³¹P, ⁷⁷Se, and ¹²⁵Te NMR spectroscopy. Quantum-chemical calculations of the ¹²⁵Te NMR chemical shifts were performed. The compounds are also characterized by IR spectroscopy, Raman spectroscopy, and elemental analysis. Structure I contains short nonvalent contacts between the sulfur atom of the out-of-sphere Dtp anion and the axial tellurium atoms of the cluster.     

Reversible formation of binuclear complexes between pyridine-2-carboxylato(tetraethylenepentamine)cobalt(III) and nickel(II)/cobalt(II) in aqueous solution. Anomalous behaviour in the dissociation of binuclear complexes

The kinetics of the reversible formation of binuclear species between M(OH₂) ₆ ²⁺ (M = Ni^II and Co^II) and oxygen-bonded (tetren)Co(pycH)³⁺ (tetren = tetraethylenepentamine, pycH = N-protonated pyridine-2-carboxylate) have been investigated by stopped-flow spectrophotometry at 25°C, I = 0.3 mol dm^-3. Both the protonated (pyridine-N) and deprotonated forms of the Co^III complex were involved in the formation of the binuclear complex (tetren)Co(pyc)Co⁴⁺, whereas only the deprotonated form of the complex was involved in the formation of (tetren)Co(pyc)Ni⁴⁺. The rate date forthe formation of the binuclear complex are consistent with an Id mechanism. Interestingly, the dissociation of the binuclear Co^II complex (tetren)Co(pyc)Co⁴⁺ was acid-catalysed while that with Ni^II was acid-independent. A suitable explanation for this anomalous behaviour has been discussed.     

Synthesis and catalytic activity of binuclear cobalt(II) and nickel(II) complexes

Summary Binuclear Ni^II and Co^II complexes derived from 2,6-diformyl-4-methylphenol and various aromatic monoamines have been prepared and investigated. The Ni^II complexes have Ni₂LCl₃ composition while the Co^II complexes have Co₂L₂Cl₂ composition, where L represents the organic ligand. The complexes are active catalysts in the oxidation of 3,5-di-t-butylcatechol (3,5-DTBC) by dioxygen, but less so than their Cu analogues. This result is attributed to the absence of antiferromagnetic coupling between the metal centres.     

A new class of binuclear and trinuclear iron-sulfur clusters derived from bis[bis(trimethylsilyl)amido]iron(II)

The compound Fe[N(SiMe 3) 2] 2 is shown to be a useful precursor to dinuclear and trinuclear iron-sulfur-silylamido complexes by reaction with thiols or thiols and sulfur in tetrahydrofuran (THF) or toluene. Reaction with 1 equiv of p-tolylthiol affords [Fe 2(mu 2-S- p-tol) 2(N(SiMe 3) 2) 2(THF) 2] ( 1); with 0.5 equiv of adamantane-1-thiol, [Fe 2(mu 2-S-1-Ad)(mu 2-N(SiMe 3) 2)(N(SiMe 3) 2) 2] ( 2) is formed. The clusters [Fe 3(mu 3-Q)(mu 2-SR) 3(N(SiMe 3) 2) 3] are available by three methods: (i) self-assembly in the systems Fe[N(SiMe 3) 2] 2/RSH/S or Se [Q = S, R = p-tol ( 3) and 1-Ad ( 5)]; (ii) reaction of 1 with Q = S or Se to yield 3 or [Fe 3Se(S- p-tol) 3(N(SiMe 3) 2) 3] ( 4); (iii) reaction of 2 with 1-AdSH and S to give 5. Structures of 1- 5 are presented. Complexes 1 and 2 contain planar Fe 2S 2 and Fe 2SN rhombs. Clusters 3- 5 contain a mixed-valence Fe 3Q(SR) 3 core with trigonal (cuboidal) geometry. Of known iron-sulfur clusters, these most closely resemble previously reported [Fe 3S(S-R-S) 3] (2-) stabilized by bidentate thiolate ligands. Complexes 1- 5, together with a small set of recently described clusters of nuclearities 2, 4, and 8, constitute a new class of iron-sulfur-silylamido clusters. Complexes 3- 5 constitute a new structure type of mixed-valence iron-sulfur clusters.     

Kinetics and mechanism of ligand substitution in binuclear nickel(II) and cobalt(II) complexes

The kinetics and mechanism of the removal of M²⁺ from bis-(heptane-2,4,6-trionato)M(II) [M = Ni, Co] by ethylenediminetetraacetic acid (EDTA), nitrilotriacetic acid (NAT), 1,2-cyclohexanediamine-N, N, N′, N′-tetraacetic acid (C_yDTA), and ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA) have been investigated using stopped-flow spectrophotometry in methanol-water at 25°C and ionic strength 0.1 mol dm^?3 KNO₃. The reactions were investigated at a number of different pHs. An associative mechanism is proposed to account for the kinetic data. Although all the ligands have similar functional groups, their reactivity towards the parent complex is quite different. The pH dependence of the rate constants has been used to determine the relative reactivities of the various ligand species present. In the case of nitrilotriacetic acid, a nonlinear dependence on ligand concentration is observed, thus confirming the mechanism proposed. © 1995 John Wiley & Sons, Inc.