SYNTHESIS, STRUCTURE, AND MAGNETIC PROPERTY OF LINEAR CHLORO-BRIDGED NICKEL(II) TETRAMER WITH DINUCLEATING BIS-DIMETHYLCYCLAM LIGAND

A new nickel(II) complex with the composition of Ni2Cl2(L)(ClO4)2.1.5H2O (L = alpha,alpha'-bis(5R(S), 7S(R)-5,7-dimethyl-1,4,8,11-tetraazacyclotetradecan-6-yl)-o-xylene) has been prepared via a four coordinate complex [Ni2(L)] (ClO4)4.3H2O from [Ni2(mu-Br)Br2(L)]Br.H2O. The compound crystallizes in orthorhombic space group Ccm2(1) with cell parameters at -80-degrees-C, a=21.90(1), b=20.28(1), c=19.63(1) angstrom, V =8718(1) angstrom3, Z=8. The crystal consists of the cationic dinuclear unit [Ni2(mu-Cl)Cl2(L)]+, the counter anion ClO4-, and water of crystallization. In [Ni2(mu-Cl)Cl2(L)]+, three chloride ions and two nickel ions are alternately arranged in an almost linear manner, and two cyclam rings with the most stable trans-III type conformation are arranged in a face-to-face manner. This cationic dinuclear unit is further connected to each other by sharing the terminal Cl ligand to form pseudo one-dimensional chain structure of the ...Cl-Ni-Cl-Ni-Cl... type. However, one of the Cl atoms which bridges the dinuclear units is statistically disordered at two positions along the chain and thereby the repeating unit in the chain is a chloro bridged dimer of the dinucleating ligand complex. The neighboring Ni-Cl distances range from 2.568(4) to 2.855(4) angstrom. The temperature dependent magnetic behavior in the range of 25-300 K has been interpreted by the usual Heisenberg-Dirac-Van Vleck model, assuming that only three Ni(II) ions in {Ni2Cl2(L)}2 are paramagnetic. The best fit parameters were J = -48.2(3) and J' = - 11.2(3) cm-1 for H=- 2J(S1.S1') -2J' (S1.S2).