First-Row Transition-Metal Complexes of the 1-Methoxycyclobutenedionate(1-) Ion.

The synthesis and characterization by single-crystal X-ray crystallography of a series of monomeric first-row transition-metal complexes with the 1-methoxycyclobutenedionate(1-) ligand are described. The isomorphous compounds [M(CH(3)OC(4)O(3))(2)(H(2)O)(4)] (M = Mn, Co, Ni, Zn) are C(2) symmetric and crystallize in the monoclinic space group C2/c. The metal atom in each of these complexes is six-coordinate with two cis 1-methoxycyclobutenedionate(1-) ligands, the methoxy substituent being oriented cis with respect to the ligating oxygen atom. The remaining coordination sites are filled by four aqua ligands. Monomers are linked by O-H.O hydrogen bonds to form arrays of stepped tapes. Hydrolysis of the methoxy group on the ligand occurs during the formation of the copper complex and {[Cu(C(4)O(4))(H(2)O)(2)].0.25H(2)O}(n)() is produced. This complex crystallizes in the tetragonal space group P4/n and has a structure similar to, but differing significantly from, those of a series of 3-dimensional cage squarates which have been reported previously.