Transition-metal complexes of the 1,2-dipyridylethylene isomers. Part I. Copper(II), nickel(II), and cobalt(II) derivatives of the symmetrically substituted isomers

Copper(II), nickel(II), and cobalt(II) halides form complexes of the type MX2L, where L is 1,2-di-(2-pyridyl)-ethylene and 1,2-di-(4-pyridyl)-ethylene and -ethane. The complexes appear to be polymeric, differing mainly in the stereochemistry at the metal ion, which may be planar, tetrahedral, or octahedral. The 2-pyridyl isomer also forms the complex Ni2Cl4L, and the 4-pyridyl isomer forms the complex NiBr2L4. The copper(II) acetate complexes of the ethylene ligands are of the form Cu2acetate4L, and are believed to be polymeric with copper–copper bonding, in contrast to the nickel acetate complexes.