The complexing properties of the phenylsquarate ligand with Ru(II), Pt(II), Gd(III) and Tb(III) ions

Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with Ru(dmso)4Cl2 in acetonitrile afforded crystals of the monomeric species Ru(dmso)3Cl(H2O)(C6H5C4O3)·H2O (1) in which the ruthenium is in a slightly distorted octahedral geometry with three fac S-bonded dmso ligands. No complexation occurs when Pt(NH3)4Cl2 is reacted with the same ligand in aqueous solution; instead, the hydrogen-bonded salt [Pt(NH3)4][C6H5C4O3]2·H2O (2) is produced. The isomorphous complexes {[M(μ-C6H5C4O3)(C6H5C4O3)2(H2O)4]·H2O}n [M=Tb (3), Gd (4)] formed by the reaction of the phenylsquarate ligand with the respective metal nitrate contain eight-coordinate metal centres surrounded by two μ-1,3-bridged and two pendant phenylsquarate ligands and four aqua ligands. In the solid state, 3 and 4 form interleaved π-stacked and hydrogen-bonded sheets with pronounced hydrophobic and hydrophilic surfaces. In compounds 1–4, the phenylsquarate ligands participate in π–π interactions and exhibit multiple bond localisation, the pattern of bonding being the same in each structure.