Variety of polymorphic forms contrasted with uniform crystal packing in sparteine ML_2 complexes: Crystal structure, spectroscopic and magnetic properties of (–)-a-isosparteine and (–)-sparteine complexes with CuBr_2

摘要

This paper reports the synthesis, thermogravimetric and magnetic measurements for (-)-a-isosparteine CuBr_2 complex (1) and the existence of the fourth polymorph (2) of( -)-sparteine CuBr_2 complex. The two CuBr_2 complexes have been structurally characterized by X-ray crystallography. A diverse supramolecu lar aggregation of (-)-sparteine CuBr_2 complex has been contrasted with strong tendency for isostruct uralism observed in a series of ML_2 complexes (M = metal, L= halogen or pseudohalogen) with both sparteine (3) and a-isosparteine (4). The incidence of polymorphism in a group of compounds which readily form the isomorphic series is quite unusual. Moreover, the reported crystal structure of 2 consti tutes the first example showing that the organization of metal complexes of sparteine isomers into sim ilar packing architecture is possible, although in general configurational changes within the sparteine ligand differentiate packing of otherwise similar (-)-sparteine-ML_2 or (-)-a-isosparteine-ML_2 molecules.