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-me thoxycyclobutenedionate(1-) ligand are described. The isomorphous compounds [M(CH3OC4O3)(2)(H2O)(4)] (M = Mn, Co, Ni, Zn) are C-2 symmetric and crysta llize in the monoclinic space group C2/c. The metal atom in each of these c omplexes is six-coordinate with two cis 1-methoxycyclobutenedionate(1-) lig ands, the methoxy substituent being oriented cis with respect to the ligati ng oxygen atom. The remaining coordination sites are filled by four aqua li gands. Monomers an linked by O-H ... O hydrogen bonds to form arrays of ste pped tapes. Hydrolysis of the methoxy group on the ligand occurs during the formation of the copper complex and {[Cu(C4O4)(H2O)(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 se ries of 3-dimensional cage squarates which have been reported previously.