Polymorphism and weak antiferromagnetic interactions in dibromo[(-)-sparteine-N,N ']copper(II)

摘要

Two polymorphic crystal structures of the title compound, dibromo[(-)-sparteine-N, N']copper(II), 1, were determined. The structures of two isomorphs of 1, 1a [orthorhombic, P2(1)2(1)2(1), a = 11.0463(9) Angstrom, b = 11.9839(15) Angstrom and c = 12.7835(19) Angstrom] and 1b [orthorhombic, P2(1)2(1)2(1), a = 7.6779(9) Angstrom, b = 12.0927(14) Angstrom and c = 18.090(2) Angstrom], are composed of the same basic structural unit, Cu(C15H26N2)Br-2. The bond distances in the molecular structures of 1a and 1b are identical to each other within the esds. However, there are slight differences in the bond angles around the Cu(11) center and considerable differences in their packing structure. Crystal la exhibits weak anti-ferromagnetism (J = -1.89 cm(-1)) as opposed to the magnetically isolated paramagnetism observed for the analogous dichloro[(-)-sparteine]copper(II), 2. The results of a magneto-structural investigation of 1a and 2, and other supporting evidence, suggest that the pathway for the weak antiferromagnetic super-exchange in la might be through a Cu-Br...Br-Cu contact. (C) 2004 Elsevier B.V. All rights reserved.