(N, N, N′, N′-tetramethylethylenediammonium)Cu₂X₆ (X=Cl, Br): crystal structure and magnetic interactions

Summary

The crystal structures of (Me₄enH₂)Cu₂Cl₆ and (Me₄enH₂)Cu₂Br₆ have been determined. The triclinic crystals contain chains of symmetrically bibridged [Cu₂X₆]²⁻ dimers. Within the dimers the Cu−X distances average 2.299 Å (Cl) and 2.408 Å (Br) and the Cu−X−Cu angles are 96.4(1)^o (Cl) and 95.7(1)^o (Br). Longer Cu−X bonds, 2.679(1)Å (Cl) and 2.761(3)Å (Br), link dimers together into infinite chains via asymmetrical bridges. The bridging angles for the asymmetric bridge are 92.2(1)^o (Cl) and 89.4(1)^o (Br). Magnetic susceptibility data for both compounds are indicative of antiferromagnetic coupling. Analyses of the data yields J/k=−23(1)K (Cl) and −82(2)K (Br) for the interdimer coupling and J′/k=−5(1)K (Cl) and −4(1)K (Br). The intradimer coupling for the chloride is in accord with magneto-structure relations deduced for similar salts. Similarly, the increased antiferromagnetic contribution upon substitution of Cl by Br follows trends previously observed.