Synthesis, magnetism and electrochemistry of tetranuclear nickel(II) and copper(II) complexes of an unsymmetrical bis-pentadentate Schiff-base ligand

A new unsymmetrical tetranucleating ligand, H6L, containing salicylideneimine and acetylacetoneimine end groups attached to a propan-2-ol backbone, has been synthesized. The ligand results from the Schiff-base condensation of 1-(1-methyl-3-oxobut-1-enylamino)-3-(amino)propan-2-ol and the dialdehyde, 5,5'-methylene-bis-salicyladehyde (2:1). Tetranuclear nickel(II) and copper(II) complexes of this ligand, of the type [M4L(X)(2)], containing either mu-pyrazolate (X = pz) or mu-3,5-dimethylpyrazolate (X = Me(2)pz) exogenous bridges in conjunction with mu-alkoxo endogenous bridges, have been synthesized. Magnetic susceptibility studies on powdered samples of [Cu4L(pz)(2)] (3) show medium-strength antiferromagnetic coupling (J(12) = -108 cm(-1)) within each half of the tetranuclear complex together with a weaker antiferromagnetic coupling (J(intermol.) = -55 cm(-1)) between the molecules. Cyclic (CV), Osteryoung square wave (OSWV) and Normal pulse (NPV) voltammetric studies on dimethylformamide solutions of [Ni4L(Me(2)pz)(2)] (2) revealed waves attributable to two sequential one-electron metal centred reduction processes (x2) to yield [Ni4L(Me(2)pz)(2)](2-) and [Ni4L(Me(2)pz)(2)](4-). (C) 1997 Elsevier Science Ltd.