POlymeric Complexes of 3-Hydroxy-4-Methoxy- And 3-Methoxy-4-Hydroxybenzoic Acids. Crystal Structure of the Linear-Chain Complex of COII With 3-Hydroxy-4-Methoxybenzoic Acid

Reaction of Cu II , Co II , and Ni II with 3-hydroxy-4-methoxy- and 3-methoxy-4-hydroxybenzoic acids (hmba and mhba, respectively) yields hydrated complexes exhibiting stoicheiometries with 1:2 and 1:1 metal to ligand mol ratios. The 1:2 complexes, formed by Co II with hmba and Cu II with mhba, involve carboxylate groups and water molecules as donors. The structure of [Co(hmba) 2 (H 2 O) 3 ] was determined by single-crystal X-ray analysis. It crystallizes in the monoclinic space group 12/a with a = 8.164(2), b = 11.171(3), c = 20.980(5) Å, β = 91.42(3)°, and Z = 4. The complex is a one-dimensional polymer with bridging water molecules (Co-H 2 O-Co = 128.04° and Co ... Co = 4.082 Å). The hexacoordination at each cobalt is completed by oxygens from two monodentate carboxylates and two water molecules. Stacking interactions between the parallel aromatic rings (3.5 Å) hold neighbouring chains together. Complexes with a 1:1 metal to ligand ratio (M = Cu II , Co II and Ni II , L = hmba; M = Co II and Ni II , L = mhba) also clearly involve phenolate groups in coordination to the metal. A structure for these compounds has been proposed on the basis of spectroscopic and thermogravimetric data.