Complete and ‘incomplete’ [2 × 2] grids by self-assembly with a sterically hindered ditopic imidazole hydrazone ligand—structural and magnetic studies

Abstract

A ditopic hydrazone ligand (ioap) synthesized from the condensation of 4-methyl-5-imidazole carboxylic acid hydrazide with the iminoester of 2-pyridinecarbonitrile formed targeted [2 × 2] M₄L₄ (M = Cu(II), Ni(II); L = ioap) grids, and a mixed oxidation state dinuclear cobalt complex. An ‘incomplete’ trinuclear M₃L₄ (M = Mn(II)) grid, based on a [2 × 2] grid architecture, resulting from steric congestion of the imidazole methyl-substituent, was also produced. These results lead to the suggestion of one possible route to the self-assembly pathway of the [2 × 2] grids. The Mn(II), Ni(II) and Cu(II) complexes have hydrazone oxygen bridges between metal centres, which lead to antiferromagnetic exchange in the Mn(II)₃ and Ni(II)₄ cases, but, due to the presence of orthogonal bridging connections, to ferromagnetic exchange for the Cu(II)₄ example. Structural and magnetic properties are discussed based on the bridging connections.