Antiferro- to ferromagnetic crossover in diphenoxido bridged (Ni2MnII)-Mn-II complexes derived from N2O2 donor Schiff base ligands

Abstract

Three new trinuclear Ni-II-Mn-II complexes have been synthesized using three different 'metalloligands' [NiL1], [NiL2] and [NiL3] derived from the Schiff bases H2L1 = N,N'-bis(salicylidene)-1,3-pentanediamine, H2L2 = N,N'-bis(salicylidene)-1,3-propanediamine and H2L3 = N,N'-bis(salicylidene)-1,3,-diaminopropan-2-ol), respectively. In all three complexes, [(NiL1)(2)Mn(OOCPh)(2)(H2O)(2)]center dot CH3OH (1), [(NiL2)(2)Mn(OOCPh)(2)(CH3OH)(2)]center dot CH3OH (2) and [(NiL3)(2)Mn(OOCPh)(2)(H2O)(2)]center dot CH3OH (3), in addition to the double phenoxido bridge, the two terminal Ni-II atoms are linked to the central Mn-II by means of a syn-syn bridging benzoate, giving rise to a linear structure. Complex 1 with Ni-O-Mn angle of 97.35 degrees exhibits antiferromagnetic interactions (J(Ni-Mn) = -0.60 cm(-1)) whereas ferromagnetic exchange is observed in 2 and 3 (J(Ni-Mn) = +2.00 and +1.10 cm(-1) respectively) having Ni-O-Mn angle 97.34 degrees (in 2), 97.27 degrees (in 3). Theoretical calculations have been performed in order to understand the effect of structural parameters that can tune the magnetic properties of this type of complexes such as small differences in the Ni-O-Mn angle and/or slight variations in intermolecular contacts within the crystal. (C) 2016 Elsevier Ltd. All rights reserved.