Synthesis, crystal structure and magnetic properties of a dinuclear and a trinuclear Ni(II) complexes derived from tetradentate ONNO donor Mannich base ligands

Abstract

Two complexes, [Ni2(HL1)2(NCS)2]·CH2Cl2 (1) and [Ni3(L2)2(NCS)2(H2O)2]·CH3CN (2) have been synthesized using two different tetradentate ONNO donor Mannich base ligands N,N′-bis(3,5-dimethyl-2-hydroxybenzyl)-N,N′-dimethylethylenediamine(H2L1) and N,N′-bis(3-methoxy-5-methyl-2-hydroxybenzyl)-N,N′-dimethylethylenediamine(H2L2), respectively. Compound 1 is μ1,1 isothiocyanato bridged dinuclear compound whereas compound 2 is phenoxido bridged trinuclear compound with SCN− as a terminal ligand. In compound 1 one of the two phenoxido oxygen atoms from each ligand remains protonated and hence makes the compound electrically neutral. X-ray-crystallography reveals that the two Ni(II) centres in compound 1 are in a distorted octahedral geometry and N atom of each of the two SCN− groups bridge the two metal centres. On the other hand, compound 2 possesses a centrosymmetric trinuclear structure where two distorted square pyramidal terminal Ni(II) centres are connected to a central octahedral Ni(II) via phenoxido bridge. Here SCN− ligand occupies the axial positions of the terminal Ni(II) centres by coordinating through N atom. Variable temperature magnetic susceptibility measurements of solid samples reveal that the Ni(II) paramagnetic centres in both 1 and 2 are antiferromagnetically coupled with J values of −30.66cm−1 and −5.92cm−1 for 1 and 2, respectively. These values are in accordance with the magneto structural correlations of previously reported isothiocyanato bridged dinuclear and phenoxido bridged trinuclear Ni(II) compounds.