Synthesis, Structure, and Magnetochemical Analysis of Selected First-Row Transition-Metal Anilino- and Anisolesquarate Compounds

The isomorphous polymeric complexes {M(μ-C6H5NHC4O3)2(CH3OH)2}n [M = Mn (1), Co (2), Cu (4), Zn (5)] are
produced by reacting the anilinosquarate anion with the appropriate metal nitrates in a methanolic solution. Each
of these complexes contains the central metal atom in a slightly distorted octahedral environment, with the coordination
polyhedron consisting of four μ-1,2-bridging anilinosquarate ligands and two trans-oriented methanols. The polymer
chains propagate to form a two-dimensional net of metal centers, with the conformation of the component sheets
in the net being controlled by intramolecular N−H···O and O−H···O hydrogen bonds. Under reaction conditions
similar to those used in the synthesis of the polymers 1, 2, 4, and 5, the nickel(II) monomer [Ni(C6H5NHC4O3)2(H2O)4]·2H2O (3) is produced in which each nickel center is attached to two cis-coordinated anilinosquarate and
four aqua ligands in a distorted octahedral arrangement. The ligand conformation in 3 is stabilized by both intra-
and intermolecular hydrogen bonding, which results in the formation of a sheet polymer having distinct hydrophobic
and hydrophilic surfaces. Magnetochemical analysis of 1 and 4 reveals normal paramagnetic behavior for 1 and a
very weak ferromagnetic interaction in 4; the absence of significant magnetic interactions is attributed to the distortion
of the C4 cycle of the anilinosquarate ligand (lower than C2v symmetry) in these complexes. Reaction of
anisolesquarate with M(NO3)2·xH2O in acetonitrile produced the set of isomorphous salts [M(H2O)6][CH3OC6H5C4O3]2
[M = Mn (6), Co (7), Ni (8), Zn (9)]. The anisolesquarate anions in 6−9 are hydrogen bonded to the [M(H2O)6]2+
ions to form polymer chains, which are further linked by hydrogen bonds to form complex sheets. Complexation
of the anisolesquarate ligand was not observed even when other solvents and reaction conditions were employed.