Studies of monothiomalonamide and its palladium(II) and platinum(II) complexes

A project related to the crystal engineering of hydrogen bonded coordination complexes has been initiated and our first results are presented here. The cis and trans forms of monothiomalonamide (LH2) have been fully characterized by vibrational spectroscopy, thermal techniques and single-crystal X-ray diffraction. The cis form crystallizes in the monoclinic space group P2(1)/c and the trans form in the monoclinic space group C2/c. The respective lattice constants are a = 5.602(3), b = 9.055(2), c = 10.945(5) Angstrom, beta = 101.29(2)degrees (cis-LH2) and a = 20.336(7), b = 4.317(1), c = 12.432(5) Angstrom, beta = 92.16(1)degrees (trans-LH2). The new complexes [Pd(LH2)(4)]X-2 (X = Cl, Br), [Pt(LH2)(4)]X-2 (X = Br, 1), [PdX2(LH2)(2)] (X = Cl, Br, 1) and [PtX2(LH2)(2)] (X = Cl, I) were prepared and characterized by elemental analyses and spectroscopic (IR, far-IR, Raman) studies. All data are discussed in terms of the nature of bonding in conjunction with assigned structures. The LH2 molecule behaves as a monodentate ligand binding through the sulfur atom. Monomeric square planar structures are assigned for the metal complexes in the solid state; the 1:2 complexes have the trans geometry. A detailed comparison of the new complexes with the corresponding monothiooxamide complexes is also presented.