Thirteen new binuclear copper(II) complexes [LCu(µ-X)CuL]2+ with L = 1,4,7-trimethyl-1,4,7-triazacyclononane and X = 2Cl–, 2Br–, 2SCN–, C2O42–, (HN)2C2O22–, Cl2C6O42–, H2C6O42–, and 2CH3CO2– have been synthesized and characterized based on i.r., electronic, and e.s.r. spectroscopy and variable-temperature (100–300 K) magnetic susceptibility measurements. A varying range of magnetic interactions, no coupling, antiferromagnetic (2J=–460 cm–1), and ferromagnetic (J=+22 cm–1) coupling, has been observed between the copper(II) ions in these binuclear systems with variable metal–metal separation estimated to be in the range of 3.6–7.6 A. The interaction is more effective through a µ-oxamato bridge (2J=–460 cm–1) than through a µ-oxalato bridge (2J=–300 cm–1). A moderately strong antiferromagnetic interaction (2J=–60 cm–1) has been found for the Cl2C6O42-bridged compound, where the Cu ⋯ Cu separation is expected to be ≈ 7.6 A. The X-band e.s.r. spectra of the polycrystalline substances at 120 K indicate square-pyramidal geometry for the copper with a (dx2– y2)1 ground state. A mixed bridged compound (µ-1,1 -N3)(µ-OH), with a ferromagnetic interaction between the copper centres is also described. The difference in magnetic exchange interaction between the different copper(II) systems is discussed.

Binuclear copper(II) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane : synthesis, spectroscopy, and spin coupling across multiple-atom bridges of variable length (3.6―7.6 Å)

Metal-ion catalysed aquation of transition metal complexes

Zinc and cadmium

Synthesis, structure and magnetic properties of oxalate-bridged complex [Cu2(bpy)2(C2O4)(H2O2)][Cu(bpy)(C2O4)](NO3)2

In the base hydrolysis of the title complexes in aqueous-organic solvent media (water-ethanol and water-acetone) to the corresponding hydroxo-complexes the observed rate law is in accord with the expression: The observed K values (3.5 to 26 M−1 at 25°) and the nature of their solvent dependence suggest the formation of an ion-pair in a pre-equilibrium involving the substrate complex and OH− ion, and not of a conjugate base. Rate constants (k) for the transformation of the ion-pair to the product increase with increased proportions of the organic component in the solvent. The nature of the dependence of k on different solvent parameters indicates significant associative character with OH− ion acting as the attacking nucleophile. Activation enthalpy, ΔH≠, decreases with ethanol concentration; this along with the observed large positive slopes of the log k vs 1/D plots rule out the possibility of H2O acting as the attacking nucleophile. ΔH≠ and ΔS≠ corresponding to k in different solvent composition...

Base hydrolysis of iso-thiocyanatopentaammine complexes of cobalt(iii), chromium(iii) and rhodium(iii) in aqueous-organic mixed solvents

Metal ion catalyzed aquation of tris(malonato)chromate(III) ion has been followed spectrophotometrically in perchloric acid solution ([H+]=0.05 M) over a temperature range at an ionic strength of 2.0 M. Under these conditions kobsd=kH[H+]+kM[M2+] where kobsd is the observed first order rate constants for the protons and the metal ion catalyzed pathways. Metal ions exert appreciable catalytic effect on the aquation of the complex with kM following the sequence Cu(II)>Ni(II)>Co(II)>Zn(II)>Mn(II), which runs parallel to the metal monomalonato complex formation constants. A plausible mechanism for the metal promoted reactions is proposed.

Metal Catalyzed Aquation of Tris(malonato)chromate(III)ion. Kinetics and Mechanistic Study

The displacement of chloride ligands from α-cis-chloro-aquoethylenediamine-N,N′-diacetatocobalt(III) in nonacidic aqueous solutions was followed conductimetrically at 30–45° and the products of aquation were characterised by conductance, spectral and ion-exchange techniques. The rate constants for aquation in aqueous media and in 1 : 4 v : v mixed solvents at 25° are: 4.0 × 10−5 s−1 in H2O, 2.71 × 10−5 s−1 in MeOH : H2O, 2.74 × 10−5 s−1 in EtOH: H2,O and 2.58 × 10−5 s−1 n in Me2CO : H2O. The corresponding ΔH* and ΔS* values have also been evaluated. Solvent polarity has a marked influence on the rate of chloride ion release. The aquation rate constants and the activation parameters have been correlated with solvent parameters,e.g. D, Y-values, Dimroth's ET and Kosower's Z-values and, based on these correlations, a dissociative interchange (Id) mechanism is proposed rather than dissociative as observed for some other cobalt(III) complexes.

Aquation of α-cis-chloroaquoethylenediamine-N, N'-diacetatocobalt(III) in aqueous and in mixed solvents: A mechanistic study

The Cu(II), Ni(II), Co(II) and Zn(II) catalysed dissociation of the cis-diaquobis(malonato)chromate(III) ion has been studied kinetically in perchloric acid solution over a temperature range. Under these conditions k obs = kH[H+] + k cat[M2+] where k obs is the observed first order rate constants and k H and k cat are the appropriate rate constants for the proton and metal ion catalysed pathways respectively. The metal ion exert marked catalytic effects with k cat following the sequence Cu(II) > Ni(II) > Co(II) > Zn(II). A possible mechanism for the metal promoted reaction is proposed and the relevance of these results to the mechanism of the trans → cis isomerisation of [Cr(mal)2(H2O)2]− considered.

Chinmoy Chatterjee

Papers

Metal Catalyzed Aquation of Tris(malonato)chromate(III)ion. Kinetics and Mechanistic Study

Aquation of α-cis-chloroaquoethylenediamine-N, N'-diacetatocobalt(III) in aqueous and in mixed solvents: A mechanistic study

KINETICS AND MECHANISM OF THE METAL ION CATALYSED AQUATION OF cis-DIAQUOBIS(MALONATO) CHROMATE(III) ION IN AQUEOUS-ACID MEDIA