First-row transition metal complexes of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate)

Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with M(NO3)2·xH2O (M=Mn, Co, Ni, Zn) in acetonitrile solutions produced a linear polymer [Mn(μ-C6H5C4O3)(C6H5C4O3)(H2O)3]n (1) and a series of isomorphous monomeric complexes [M(C6H5C4O3)2(H2O)4] [M=Co (2), Ni (3), Zn (4)]. The complex 1 contains octahedral manganese with each metal centre being bridged μ-1,3 by a phenylsquarate ligand to two neighbouring metal atoms and further coordinated to a pendant phenylsquarate ligand group and three aqua ligands. The isomorphous monomeric complexes 2–4 all contain two phenylsquarate ligand groups oriented trans to each other, but with the substituent phenyl group on the ligand oriented cis to the ligating oxygen atom. The coordination polyhedron in each of these monomers is completed by four aqua ligands. The polymeric manganese complex shows no significant antiferromagnetic coupling and no semiconductivity.