HELICAL 1(INFINITY(P(1)-) CHAINS IN THE STRUCTURES OF HG2P3BR AND HG2P3CL

The crystal structures of Hg2P3Br (I) and Hg2P3Cl (II) have been refin ed by least-squares full-matrix procedures to R = 0.037 (I) and R = 0. 035 (II). I is orthorhombic, space group Pbcn, a = 8.014(1) angstrom, b = 8.902(1) angstrom, c = 7.823(1) angstrom, Z = 4. II is monoclinic, space group C2/c, a = 7.834(2) angstrom, b = 8.844(1) angstrom, c = 7 .591(1) angstrom, beta = 98.68(1), Z = 4. Both structures consist of 1 infinity(P1-) helical chains running along the c-direction. The confor mation of the chains is the same in I and II but the arrangement of th e chains within the unit cells is different. The structures are also c ompared with those of Cd2Z3X (X = Cl, Br, I; Z = P, As).