Synthesis, Structure, and Magnetic Property of Linear Chloro-Bridged Nickel(II) Tetramer with Dinucleating Bis-dimethylcyclam Ligand

Abstract

Abstract A new nickel(II) complex with the composition of Ni2Cl2(L)(ClO4)2·1.5H2O (L = α,α′-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(μ-Br)Br2(L)]Br·H2O. The compound crystallizes in orthorhombic space group Ccm21 with cell parameters at −80 °C, a = 21.90(1), b = 20.28(1), c = 19.63(1) Å, V = 8718(1) Å3, Z = 8. The crystal consists of the cationic dinuclear unit [Ni2(μ-Cl)Cl2(L)]+, the counter anion ClO4−, and water of crystallization. In [Ni2(μ-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) Å. 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 = −2J(S1·S1′) − 2J′(S1·S2).