Dinuclear metal complexes. Part 1. Synthesis, characterisation, and electrochemical studies of macrocyclic dicopper(II) complexes

The synthesis, characterisation, and electrochemical studies of dicopper(II) complexes [Cu2L1][ClO4]2.nH2O of the macrocycle 7,11;19,23-dimetheno-9,21-dimethyl[1,5,13,17]-tetra-azacycloicosa-5,7,9,12,17,19,21,24-octaene-25,26-diol (H2L1), and of some 6,12,18,24-substituted (Me4; Prn4; Ph4; Ph, Me, Ph, Me) derivatives have been carried out. These compounds undergo sequential one-electron transfers at two different potentials. For all of these compounds, except for [Cu2L1][ClO4]2.2H2O, two reversible or almost reversible reduction steps have been observed in acetonitrile medium using a hanging mercury drop electrode. In the case of [Cu2L1][ClO4]2.2H2O, the second couple became obscured due to the presence of an adsorption phenomenon or secondary electrode reaction. However, in NN-dimethylformamide (dmf) medium, satisfactory voltammograms have been obtained only with [Cu2L1][ClO4]2.2H2O. The mixed-valent complexes are considerably more stable in acetonitrile than is [CuIICuIL1]+ in dmf. The potentials of the first reduction step (E1) remain practically invariant throughout the series and are independent of the extent of magnetic interactions in the dicopper(II) complexes. The potentials of the second reduction step (E2) vary with the alkyl and aryl groups present, and a linear plot has been obtained for E2vs. the Hammett function sm. On the basis of previously reported observations and the present study it is inferred that in acetonitrile medium the unpaired electron in the mixed-valent complexes remains localised on one of the copper atoms

Dinuclear metal complexes: Part 3 - Preparation and properties of hydroxo-bridged dicopper(II) complexes

Hydroxo-bridged dicopper(II) complexes of five-co-ordinate acyclic diazadiamine NNNNO-bonded ligands have been synthesised. These compounds are obtained in high yield by reacting the sodium salt of 2-hydroxy-5-methylbenzene-1,3-dicarbaldehyde, copper perchlorate, and the diamines 1,3-diaminopropane, 1,2-diaminoethane, and 1,2-diaminopropane, respectively in aqueous medium under high dilution. Similar reactions with 1,3-diacetyl- or 1,3-dibenzoyl-2-hydroxy-5-methylbenzene in water-methanol afford similar acyclic complexes in lower yield along with their corresponding NNNNOO-bonded macrocyclic complexes. The hydroxy bridging group in the acyclic complexes can be replaced by other bridges like methoxide, p-nitrophenolate, pyrazolyl, and by reaction with 2-hydroxy-5-methylacetophenone. Variously 6,12-substituted dicopper(II) complexes of the macrocycle 7,11; 19,23-dimetheno-9,21-dimethyl[1,5,13,17]tetra-azacyclotetracosa-5,7,9,12,17,19,21,24-octaene-25,26-diol (H2L5) can be obtained by reacting the above unsubstituted acyclic complex with 1,3-diacetyl- or 1,3-dibenzoyl-2-hydroxy-5-methylbenzene. The acyclic tetra-amine hydroxo-bridged dicopper(II) complex shows similar reactivity to the diazadiamine derivative and the corresponding macrocyclic complexes containing both aza and amine linkages have been synthesised. All these compounds have been characterised from their magnetic moments, i.r., and electronic spectra. The electrochemical studies of the acyclic diazadiamine and tetra-amine hydroxo-bridged dicopper(II) complexes have revealed irreversible reductions followed by decomposition of the reduced species. One of the diazadiamino macrocyclic complexes was found to undergo quasi-reversible one-electron reductions at two different potentials. The mechanism of formation of the unsubstituted macrocyclic complex [Cu2L5][ClO4]2·2H2O by reacting the corresponding hydroxo-bridged acyclic complex with 2-hydroxy-5-methylbenzene-1,3-dicarbaldehyde has been investigated

Synthesis of phenoxo-bridged dicopper(II) complexes of N-(2-aminoalkyl)salicylaldimines and their use in the formation of monohalogeno-complexes and non-symmetrical quadridentate Schiff-base complexes

Phenoxo-bridged dicopper(II) complexes, [Cu2L12][ClO4]2·2H2O, of N-(2-aminoethyl)salicylaldimine (HL1) and its analogues have been synthesised by a high dilution method. These compounds react with p-substituted o-acylphenols and 1,3-diketones to form non-symmetrical quadridentate Schiff-base complexes. The phenoxo-bridge in [Cu2L12][ClO4]2·2H2O can be split by strong nucleophiles, yielding the monomeric compounds [CuL1(X)](X = Cl, Br, I, N3, or NCS). Similar reactions occur with [Cu2L72][ClO4]2·2H2O, where HL7is the reduced version of HL1

E.p.r. spectra and bonding parameters of copper(ii) complexes of 2-methyl-4,6-diacylphenols, of the dibenzoyl analogues and of some of their derivatives

The e.p.r. spectra of mononuclear copper(II) complexes of 2-methyl-4,6-diacylphenols and dibenzoylphenols, and their condensation products with 1,3-diaminopropane have been examined. The MO coefficients evaluated from e.p.r. spectral parameters indicate that the in-plane-σ , in-plane- π and out-of-plane-π bondings are significantly covalent. The e.p.r. spectra of the macrocyclic dicopper(II) complexes derived from 2-methyl-4,6-diacyl(benzoyl)phenols and 1,3-diaminopropane measured at 77 K reveal the presence of mononuclear species of axial symmetry

<span style="font-size:12.0pt;font-family:"Times New Roman","serif"; mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-ansi-language: EN-IN;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">Synthesis and charaterisation of cobalt complexes of salicylaldehyde 4-methoxybenzoyl hydrazone (H₂ smbhon)</span>

1139-1144A number of mononuclear and dinuclear cobalt(II) and cobalt(III) complexes have been isolated by reacting salicylaldehyde 4- methoxybenzoyl hydrazone (H2smbhon) with CoCI2.6H2O, CO(NO3)26H2O, Co(CH3COO)2.4H2O and Co(acac)3 under varied reaction conditions. [CoII(smbhon)(H2O)3], isolated in this study, further reacts with pyridine (Py) dipyridine (dip) and triphenylphosphine (Ph3P) in presence of NaCIO4 to form new cobalt(III) complexes. Equimolar mixtures of [CoII(smbhon)(H2O)3] and the ligands like acetylacetone (Hacac), glycine (Hgly), N,N-bisethyleneacteophenoneimine (bape),N-phenylsalicylaldimine (Haslan), N-phenylorthohydroxyacetophenoneimine (Hohapan), N-hydroxymethylsalicylaldimine (H2salgly), N-2-hydroxyphenylsalicylaldimine (H2saloap) or N-2-carboxyphenylsalicylaldimine (H2salana) on refluxing in methanol-acetonitrile in the presence of oxygen at pH ~ 9 afford coloured heterochelates of cobalt (III) in high yields. Structures of the complexes have been assigned on the basis of elemental analyses, molecular weights, molar conductances, magnetic moments and spectral (UV -vis and IR) studies. The physico-chemical data suggest that H2smbhon can behave as a dibasic tridentate (ONO) donor, monobasic tridentate (ONO) (keto form) donor and monobasic bidentate (NO) donor depending on the reaction conditions