Control of nuclearity in heterometallic CuII-MnII complexes derived from asymmetric Schiff bases: structures and magnetic properties.

Abstract

Two new N2O3 donor ligands N-(3-methoxysalicylidene)-N'-(salicylidene)-1,3-propanediamine (H2L2) and N-(3-methoxysalicylidene)-N'-(α-methylsalicylidene)-1,3-propanediamine (H2L3) and their Cu(ii) complexes have been synthesized. Using these complexes and another Cu-complex with one asymmetric N2O2 donor ligand N-(α-methylsalicylidene)-N'-(salicylidene)-1,3-propanediamine (H2L1) as metalloligands, four new heterometallic Cu(ii)-Mn(ii) complexes [(CuL1)2Mn2Cl4]·3CH3OH (1), [(CuL1)2MnCl2]·2CH3CN (2), [CuL2MnCl2]·H2O (3) and [CuL3MnCl2] (4) have been synthesized with MnCl2·4H2O. The tetranuclear (1) and trinuclear (2) complexes were prepared by varying the ratio of the metalloligand [CuL1] and MnCl2 whereas dinuclear complexes 3 and 4 are the sole products irrespective of the metalloligand : MnCl2 ratio. All the complexes 1-4 were structurally characterized by single crystal X-ray diffraction. The tetranuclear (CuMn) structure of 1 is formed by the dimerization of phenoxido bridged CuIIMnII units whereas the bent CuMnII trinuclear species 2 is formed by the coordination of two metalloligands (CuL1) to Mn(ii) via a diphenoxido bridge. Complexes 3 and 4 possess a similar dinuclear CuIIMnII structure in which two phenoxido groups form a bridge between the two metal centres. The variable temperature dc magnetic susceptibility measurements reveal that the Cu(ii) and Mn(ii) ions are antiferromagnetically coupled in all the complexes, 1-4. The values of exchange coupling constants (JMn-Cu) are -45.54, -39.66, -71.54 and -48.40 cm-1 for complexes 1-4, respectively. A DFT study of all the complexes has also been performed to rationalize the experimental results of magnetic measurements.