Structural variations in Ni(II) complexes of salen type di-Schiff base ligands

Three di-Schiff-base ligands, N,N 0-bis(salicylidene)-1,3-propanediamine (H2Salpn), N,N 0-bis(salicylidene)-1,3-pentanediamine (H2Salpen) and N,N 0-bis(salicylidine)-ethylenediamine (H2Salen) react with Ni(SCN)2 Æ 4H2O in 2:3 molar ratios to form the complexes; mononuclear [Ni(HSalpn)(NCS)(H2O)] Æ H2O (1a), trinuclear [{Ni(Salpen)}2Ni(NCS)2] (2b) and trinuclear [{Ni(Salen)}2Ni(NCS)2] (3) respectively. All the complexes have been characterized by elemental analyses, IR and UV–VIS spectra, and room temperature magnetic susceptibility measurements. The structures of 1a and 2b have been confirmed by X-ray single crystal analysis. In complex 1a, the Ni(II) atom is coordinated equatorially by the tetradentate, mononegative Schiff-base, HSalpn. Axial coordination of isothiocyanate group and a water molecule completes its octahedral geometry. The hydrogen atom attached to one of the oxygen atoms of the Schiff base is involved in a very strong hydrogen bond with a neighboring unit to form a centrosymmetric dimer. In 2b, two square planar [Ni(Salpen)] units act as bidentate oxygen donor ligands to a central Ni(II) which is also coordinated by two mutually cis N-bonded thiocyanate ligands to complete its distorted octahedral geometry. Complex 3 possesses a similar structure to that of 2b. A dehydrated form of 1a and a hydrated form of 2b have been obtained and characterized. The importance of electronic and steric factors in the variation of the structures is discussed. 2007 Elsevier Ltd. All rights reserved.