First row transition metal complexes of 1-methylcyclobutenedione, a monosubstituted squarate ligand

Reaction of 1-methylcyclobutenedione with M(NO3)(2). xH(2)O [M = Co (1) and Ni (2)] produces isomorphous polymeric complexes of formula M(CH3C4O3)(NO3 )(H2O)(4). 2H(2)O that crystallize in the monoclinic space group P2(1)/m (N o. 11) with, for 1, a = 6.409(5) Angstrom, b = 14.717(10) Angstrom, c = 7.2 59(6) Angstrom, beta = 114.73(4)degrees, and Z = 2 (the metal atom being po sitioned on a center of symmetry). In both cases, adjacent metal centers ar e bridged mu-1,3 by the 1-methylcyclobutenedione ligand, which exhibits dis tinct multiple bond localization. The positive charges on the polymer chain s are in each case balanced by nitrate ions. The metal atoms are six-coordi nate with trans-oriented 1-methylcyclobutenedione ligands, and with four aq ua ligands completing the coordination sphere. Reduction of the crystalliza tion temperature, however, resulted, with Co, in the formation of the monom eric complex CO(CH3C4O3)(2). 4H(2)O (4) Isomorphous Mn (3), Cu (5), and Zn (6) analogues have also been synthesized. These crystallize in the monoclin ic space group P2(1)/n (No. 14) with, for 3, a 8.8258(8) Angstrom, b = 16.1 527(14) Angstrom, c = 9.9084(8) Angstrom, beta = 93.230(7)degrees, and Z = 4. The central metal atom in each of these compounds is six-coordinate, bei ng bound to two trans-oriented 1-methylcyclobutenedione ligands and four aq ua ligands, the former coordinating in a monodentate fashion via the oxygen atom trans to the methyl substituent. In both the polymeric and monomeric complexes extensive three-dimensional hydrogen-bonded networks are formed i n the solid state.