COORDINATION POLYMERS OF CUII WITH THE LIGAND PYRAZINE-2,3,5,6-TETRACARBOXYLIC ACID

The ligand pyrazine-2,3,5,6-tetracarboxylic acid in the presence of Cu Cl2 and the buffers CH3CO2X/CH3CO2H, X = K+, Rb+, Cs+ and (CH3CO2)2Mg/ CH3CO2H, forms two quite different types of coordination polymers. Wit h the monovalent K+, Rb+, or Cs+ buffer an almost right-angled dimeric unit is formed which polymerizes to form a zig-zag polymer {CS4[Cu2(p ztc)22H2O].9H2O}infinity (1). This 'dimerizes' about a center of symme try to form a two-dimensional polymer sheet. With the divalent Mg2+ bu ffer a mononuclear unit polymerizes to form a quasi-linear polymer {Mg (H2O)6[Cu-(pztc)2H2O].2H2O}infinity (2). The X-ray crystal structures of 1 and 2 indicate that the Cu-atom exists in two quite different coo rdination environments (NO3 square pyramidal for 1 and N2O2, square pl anar for 2) and that the Cu-N(pyrazine) bond distances are much longer than normal.