GROUP-10 AND GROUP-12 ONE-DIMENSIONAL SELENODIPHOSPHATES - A(2)MP(2)SE(6) (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/P 2Se5/Se produced the quaternary compounds A(2)MP(2)Se(6) (A = K, Rb, C s; M = Pd, Zn, Cd, Hg). The crystals of A(2)MP(2)Se(6) are air- and wa ter-stable. For Cs2PdP2Se6 (1): monoclinic C2/c (No, 15) with a = 12.9 750(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), K2Cd P2Se6 (3), Rb2CdP2Se6 (4), and Cs2CdP2Se6 (5) are isostructural, Rb2Cd P2Se6 (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 isost ructural, 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 e thane-like [P2Se6](4-) group. Compound 1 has a one-dimensional structu re with Pd2+ in square-planar coordination. Compounds 2-5 also have on e-dimensional structures related to the TiI3 structure type. The M2+ i ons 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-dimensio nal structure but with Hg2+ in tetrahedral coordination. The solid sta te single-crystal optical absorption and far-IR spectra of the compoun ds are reported. Compounds 2-7 melt congruently in the 540-773 degrees C region, whereas 1 melts incongruently. (C) 1998 Academic Press.