Praparation and characterization of two novel mixed-ligand zinc(II) complex compounds [Zn(cinn)(2)(MPCM)](n) (1) and [Zn(p-HO-cinn)(2)(nia)(H2O)(2)]center dot H2O (2) (cinn = cinnamato, mpcm = methyl-3-pyridylearbamate, nia = nicotinamide)