Synthesis, characterization, magnetic and electrochemical studies of homo- and hetero-dinuclear complexes of a macrocyclic ligand with dissimilar compartments

Abstract

Abstract A series of mononuclear complexes [M (H2L) ] (ClO4) 2 (1–6) [M = MgII, CuII, NiII, CoII, FeII, MnII] , homo-\hetero-dinuclear complexes [MALMB] (ClO4) 2 (7–11) [MA = MB = CuII, NiII ; MA = NiII, MB = CuII, CoII ; MA = MnII, MB = CuII] , and a tetranuclear complex [ {NiIILFeIII (H2O) } 2 (μ-O) ] (ClO4) 4 (12) derived from an asymmetric tetraiminodiphenol macrocyclic ligand H2L have been synthesized and characterized. The dinucleating ligand is formally the condensation product 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) ] (ClO4) 2 (3) , [NiLCu] (ClO4) 2 (9) and [NiLCo (H2O) 2] (ClO4) 2 (10) , the 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 either of square planar or pseudo octahedral geometry. The nickel (II) centre continguous to the propylene chain in [NiLNi (H2O) 2] (ClO4) 2 (8) , however, has octahedral configuration. Variable-temperature magnetic susceptibility data for [MnLCu (H2O) ] (Cl) (ClO4) (11) reveal antiferromagnetic spin-exchange interaction (H = −2J S1 · S2) with J = −31 cm−1. The cyclic voltammograms of [CuLCu] (ClO4) 2 · 2H2O (7) and [NiLNi (H2O) 2] (ClO4) 2 (8) show the occurrence of two stepwise reduction couples MIIMII\MIIMI and MIIMI\MIMI and the corresponding comproportionation constants are 2.4×1012 and 1.7×104, respectively. The heterodinuclear complexes also undergo stepwise reduction, e.g. [NiLCu] 2 with E11\2 = −0.25 V and E21\2 = −1.45 V, and [NiLCo (H2O) 2] 2 with E11\2 = −1.10 V and E21\2 = −1.30 V. In the hetero-tetranuclear complex [ {NiIILFeIII (H2O) } 2 (μ–O) ] (ClO4) 4 (12) the electron transfer reactions take place in three steps at −0.04, −0.40 and −1.20 V.