Group 10 and group 12 one-dimensional selenodiphosphates:: A2MP2Se6 (A = K, Rb, Cs; M = Pd, Zn, Cd, Hg)

The reaction of M (M=Pd, Zn, Cd, Hg) with a molten mixture of A(2)Se/P2Se5/Se produced the quaternary compounds A(2)MP(2)Se(6) (A = K, Rb, Cs; M = Pd, Zn, Cd, Hg). The crystals of A(2)MP(2)Se(6) are air- and water-stable. For Cs2PdP2Se6 (1): monoclinic C2/c (No, 15) with a = 12.9750(4) Angstrom, b = 8.3282(2) Angstrom, c = 13.0568(1) Angstrom, beta = 102.940(2)degrees, Z = 4, and R/R-w = 6.7/7.5%, K2ZnP2Se6 (2), K2CdP2Se6 (3), Rb2CdP2Se6 (4), and Cs2CdP2Se6 (5) are isostructural, Rb2CdP2Se6 (4): monoclinic P2(1)/n (No. 14) with a = 6.640(1) Angstrom, b = 12.729(2) Angstrom, c = 7.778(1) Angstrom, beta = 98.24(1)degrees, Z = 2, and R/R-w = 3.7/4.9%. K2HgP2Se6 (6) and Rb2HgP2Se6 (7), are isostructural, K2HgP2Se6 (6): monoclinic P2(1)/c (No. 14) with a = 13.031(2) Angstrom, b = 7.308(2) Angstrom, c = 14.167(2) Angstrom, beta = 110.63(1)degrees, Z = 4, and R/R-w = 5.6/7.1%, Compounds 1-7 contain the ethane-like [P2Se6](4-) group. Compound 1 has a one-dimensional structure with Pd2+ in square-planar coordination. Compounds 2-5 also have one-dimensional structures related to the TiI3 structure type. The M2+ ions and the P-P pairs reside in Se octahedra that share opposite faces in the chain direction, Compounds 6 and 7 have a related one-dimensional structure but with Hg2+ in tetrahedral coordination. The solid state single-crystal optical absorption and far-IR spectra of the compounds are reported. Compounds 2-7 melt congruently in the 540-773 degrees C region, whereas 1 melts incongruently. (C) 1998 Academic Press.