Magnetic Exchange Interactions in Transition Metal Dimers. 8. Di-µ-chloro-Bridged Nickel(II) Complexes

Variable-temperature (4.2-267 K) magnetic susceptibility data are presented for the three structurally characterized Ni(II) dimeric compounds: [Ni(qnqn)Cl2]2, [Ni(dmp)Cl2]2, and [HN(C2H4)3NCH3]2[Ni 2Cl8], where qnqn is trans-2-(2\u27-quinolyl)methylene-3-quinuclidinone and dmp is 2,9-dimethyl-1,10-phenanthroline. In each compound, there is a weak antiferromagnetic exchange interaction present with J = -4.4, -5.1, and -(2.0 ± 1.0) cm-1, respectively (-2JS1·S2 Hamiltonian). In the case of the last compound, the interaction is very weak and this, apparently in combination with a small amount of some monomeric paramagnetic impurity, leads to a greater uncertainty in the determination of J. The structures of all three nickel dimers are those of two square pyramids sharing a common basal edge with di-µ-chloro bridging. The relationship between structure and exchange parameter is discussed for the three nickel dimers and for related copper di-µ-chloro-bridged dimers. In addition, the susceptibility data for structurally uncharacterized [Ni2(dien)2(H2O)2Cl 2]Cl2 (dien is diethylenetriamine) point to a ferromagnetic interaction with J ≃ +5 cm-1 in support of the proposed structure of two octahedral nickel moieties bridged by two chloride ions