SYNTHESIS, CHARACTERIZATION, MAGNETIC AND ELECTROCHEMICAL STUDIES OF HOMO-DINUCLEAR AND HETERO-DINUCLEAR COMPLEXES OF A MACROCYCLIC LIGAND WITH DISSIMILAR COMPARTMENTS

A series of mononuclear complexes [M(H2L)](ClO4)(2) (1-6) [M = Mg-II, Cu-II, Ni-II, Co-II, Fe-II, Mn-II], homo-/hetero-dinuclear complexes [ MALMB](ClO4)(2) (7-11) [M-A = M-B = Cu-II, Ni-II; M-A = Ni-II, M-B = C u-II, Co-II; M-A = Mn-II, M-B = Cu-II], and a tetranuclear complex [{( NiLFeIII)-L-II(H2O)}(2)(mu-O)](ClO4)(4) (12) derived from an asymmetri c tetraiminodiphenol macrocyclic ligand H2L have been synthesized and characterized. The dinucleating ligand is formally the condensation pr oduct of 2 equiv. of 2,6-diformyl-4-methylphenol and 1 equiv, each of 1,2-diaminoethane and 1,3-diaminopropane. In the complexes [Ni(H2L)](C lO4)(2) (3), [NiLCu](ClO4)(2) (9) and [NiLCo(H2O)(2)](ClO4)(2) (10), t he Ni2+ ion is located at the site having the ethylene chain and has a square planar geometry, while the second metal centre in 9 or 10 is e ither of square planar or pseudo octahedral geometry. The nickel(II) c entre continguous to the propylene chain in [NiLNi(H2O)(2)](ClO4)(2) ( 8), however, has octahedral configuration. Variable-temperature magnet ic susceptibility data for [MnLCu(H2O)](Cl)(ClO4) (11) reveal antiferr omagnetic spin-exchange interaction (H = -2J S-1. S-2) with J = -31 cm (-1). The cyclic voltammograms of [CuLCu](ClO4)(2). 2H(2)O (7) and [Ni LNi(H2O)(2)](ClO4)(2) (8) show the occurrence of two stepwise reductio n couples (MMII)-M-II/(MMI)-M-II and (MMI)-M-II/(MMI)-M-I and the corr esponding comproportionation constants are 2.4 x 10(12) and 1.7 x 10(4 ), respectively. The heterodinuclear complexes also undergo stepwise r eduction, e.g. [NiLCu](2+) with E-1/2(1) = -0.25 V and E-1/2(2) = -1.4 5 V, and [NiLCo(H2O)(2)](2+) with E-1/2(1) = -1.10 V and E-1/2(2) = -1 .30 V. In the hetero-tetranuclear complex [{(NiLFeIII)-L-II(H2O)}(2)(m u-O)](ClO4)(4) (12) the electron transfer reactions take place in thre e steps at - 0.04, - 0.40 and - 1.20 V. (C) 1998 Elsevier Science Ltd. All rights reserved.