Tuning of exchange coupling by the Mn–O distance and phenoxido bridging angle: an experimental and theoretical study of the family of Mn(<scp>iii</scp>) dimers with salen type ligands

Abstract

Three new Mn(III) complexes [Mn2L2(ClO4)2] (1), [Mn2L2(NCS)2] (2) and [Mn2L2N(CN)2]ClO4·CH3CN (3) have been synthesized from the Schiff base ligand H2L (where H2L = N,N′-bis(2-hydroxypropiophenone)-1,2- ethanediamine) and various anionic coligands e.g. perchlorate, thiocyanate and dicyanamide. X-ray crystal structure analysis reveals that 1 and 2 are dinuclear complexes, joined together by Mn⋯O (phenoxido) interactions. Whereas 3 consists of an alternating phenoxido and μ1,5 dicyanamido bridge, resulting in a 1D chain. In 1 and 2 ferromagnetic coupling exists between the Mn(III) centres within the dimer but 3 possesses antiferromagnetic interaction. This difference in magnetic exchange interactions has been rationalized on the basis of structural parameters like longer bridging Mn-O distance and Mn-O-Mn angle in these complexes with the help of DFT calculations.