Synthesis of mononuclear nickel(II) and copper(II) complexes using compartmental ligands: X-ray and electrochemical studies

A series of mononuclear complexes ML1 (M = Ni, Cu) where L-1 = N,N'-bis[2-h ydroxy-3-(piperidin-1-ylmethyl)-5-methylbenzyl]alkyldiimine (alkyl = ethyle ne L-1a, propylene L-1b, butylene L-1c) and ML2 (M = Ni, Cu) where L-2 = N, N'-biS[2-hydroxy-3(piperidin-1-ylmethyl)-5-bromobenzyl]alkyldiimine (alkyl = ethylene L-2a, propylene L-2b, butylene L-2c) have been synthesized and c haracterized by C, H, N analysis, IR, electronic and ESR spectra. The cryst al structures of the complexes NiH2L1a (1) and CuH2L1a (6) were determined and the geometry around the metal ion is square planar. Electrochemical stu dies of the complexes show a quasi-reversible single redox wave at negative potential in the range 0 to -1.3 V. For nickel complexes (1-5) E-pc = -1.0 to -0.80 V and for copper complexes (6-9) E-pc = -0.40 to -0.72 V. The ESR spectra of nickel complexes are inactive due to square planar nature of th e complexes whereas copper complexes show an ESR spectrum characteristic of square planar complex with nuclear hyperfine spin 3/2. Copper complexes sh ow a normal magnetic moment value of mu (eff) = 1.70-1.75 B.M. which is clo se to the spin-only value of 1.73 B.M. (C) 2000 Elsevier Science Ltd. All r ights reserved.