Synthesis and crystal structures of two metal phosphonates, M(HO3PC6H5)2(M = Ba, Pb)

Divalent metal phosphonates, Ba(HO3PC6H5)2 and Pb(HO3PC6H5)2, have been synthesized and structurally characterized [crystal data: a= 32.18(l), b= 5.546(4), c= 8.495(4)Å, β= 103.21(3)°, space group C2/c and Z= 4 for Ba(HO3PC6H5)2; a= 31.8302(10), b= 5.5997(2), c= 8.2935(3)Å, β= 101.875(2)°, space group C2/c and Z= 4 for Pb(HO3PC6H5)2]. Their structures are isomorphous. The structure of the barium compound was solved from single-crystal data which was then used to refine the-structure of the lead compound by Rietveld methods. In these compounds the metal: phosphonate ratio is 1 : 2 and the phosphonates use all their oxygens to bridge the metal atoms, which are arranged in two-dimensional layers, One of the phosphonate oxygens is protonated. The phosphonate oxygens are involved in both chelation and bridging interactions. The metal atoms are eight-coordinate; four of the binding sites are due to symmetry-related positions of a single oxygen atom and two each from the remaining two oxygen atoms.