Cs2[M(H2O)6]3(HPO3)4, M = Co, Ni: Crystal structures, IR and thermal studies

Cs2[M(H2O)6]3(HPO3)4, M = Co (1) Ni (2) are two isostructural phosphites. They crystallize in monoclinic (S.G.: C2/m, Z = 2) and the following cell parameters (Ǻ, °): [a = 12.6132(5), b = 7.2488(3), c = 16.7990(6), β = 92.591(4), V = 1534.37(10) Ǻ3 for (1) and a = 12.5509(3), b = 7.2452(2), c = 16.6690(4), β = 92.490(2), V = 1514.34(7) Ǻ3 for (2)]. The structure consists of isolated layers parallel to (001) crystallographic plane made from corner sharing [M(H2O)6] (M = Co, Ni) and [Cs(H2O)8] polyhedra. The HPO3 phosphite ions are linked to the Cs(H2O)8 and M(H2O)6 polyhedra via hydrogen bonds. The 3D framework is build upon these layers, which are interconnected by an intricate network of hydrogen bonds. IR spectra of the title compounds present the HPO3 characterizing bands. TG curves document the process of the full dehydration.