Polymeric layer framework and chain structure of two three-component cadmium and copper phosphonates embedded with pyrazine

Abstract

Two metal phosphonate coordination polymers, [Cd2(H4tpmm)2(pz)2]n (1) and {[Cu2(H4tpmm)2(pz)2(H2O)4]·5H2O}n (2), have been synthesized from the self-assembly reactions of 2,4,6-tris(phosphorylmethyl)mesitylene (H6tpmm) with Cd(ClO4)2·6H2O or Cu(NO3)2·3H2O by introducing pyrazine (pz) as ancillary ligand. Cadmium phosphonate 1 possesses a layer framework, in which the two crystallographic distinct Cd(II) centers show two different coordination environments, one of which has a {CdO4N2} octahedral geometry in an approximately regular manner and the other suits a {CdO3N2} square pyramidal geometry. Copper phosphonate 2 displays a chain structure, in which the two crystallographic distinct Cu(II) centers both have the same {CuO4N2} octahedrons but distort in different ways; one is in a Jahn–Teller distortion while the other is in a rhombic distortion. For both Cd(II) and Cu(II) complexes, the pz ligand can be regarded to be embedded into the extended metal phosphonate architectures and form remarkable C–H … π interactions with the phenyl rings of the H4tpmm2− ligands, which cooperate with O–H⋯O hydrogen-bonding interactions in providing supports for stabilization. Thermogravimetric analysis reveals that 1 and 2 both are highly thermally stable with a decomposition process occurred at a temperature approaching 375 and 405 ​°C, respectively. The luminescence properties of 1 have also been studied.