Variety of polymorphic forms contrasted with uniform crystal packing in sparteine ML sub(2 complexes: Crystal structure, spectroscopic and magnetic properties of (-)- alpha -isosparteine and (-)-sparteine complexes with CuBr) sub(2)

This paper reports the synthesis, thermogravimetric and magnetic measurements for (-)- alpha -isosparteine CuBr sub(2 complex ( 1) and the existence of the fourth polymorph ( 2) of (-)-sparteine CuBr) sub(2) complex. The two CuBr sub(2 complexes have been structurally characterized by X-ray crystallography. A diverse supramolecular aggregation of (-)-sparteine CuBr) sub(2) complex has been contrasted with strong tendency for isostructuralism observed in a series of ML sub(2 complexes (M = metal, L = halogen or pseudohalogen) with both sparteine ( 3) and alpha -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 constitutes the first example showing that the organization of metal complexes of sparteine isomers into similar packing architecture is possible, although in general configurational changes within the sparteine ligand differentiate packing of otherwise similar (-)-sparteine-ML) sub(2) or (-)- alpha -isosparteine-ML sub(2 molecules.)