Mercury Phosphates with the Triangular Hg_3~4+ Cluster:(Hg_3)_3 (PO_4)_4 and Hg_3)_2(HgO_2)(PO_4)_2

摘要

Hydrothermal treatment of microcrystalline (Hg_2)_2P_20_7 in diluted phosphoric acid or demineralized water at 400 deg C yields colorless crystals of (Hg_3)_3(P0_4)_4 and yellow crystals of (Hg_3)_2 (HgO_2)(P0_4)_2, respectively. The crystal structures have been solved and refined from single crystal diffractometer data to residuals R [F2> 2o (F2)] = 0.021 and wR2 [F2] = 0.047 for (Hg_3)_3(P0_4)_4 and R [F2> 2c(F2)] = 0.028 and wR2 [F2] = 0.072 for (Hg3)2(HgO2)(Po4)2. The crystal structure of (Hg_3)_3(P0_4)4 (R3c (No. 161), Z= 6, a = 16.3957(10) A, c = 10.6606(9) A, V 2481.9(3) A3) is isotypic with the corresponding arsenate (Hg~)3 (AsO4)4. (Hg_3)_2(HgO_2)(P0_4)_2 crystallizes with two formula units in the monoclinic space group P2,/c (No. 14), with lattice para-meters a = 6.2506(7) A, b =9.9366(10) A, c = 9.6663(12) A, p = 95.783(10)~, and V= 597.3(1) A~, and shows a topological rela-tionship to the mineral terlingualte (Hg_4O_2C_12). Both phosphates contain tetrahedral PO~ groups and the triangular mercury cluster Hg~~ with d(Hg—Hg) = 2.666 A for (Hg_3)_3(P0_4)_4 and 2.682 A for (Hg_3)_2(HgO_2)(P0_4)2, respectively. In the latter com-pound a linear mercurate group, HgO~ with d(Hg—O) = 2.031(7) A, is also present. For both structures the three-dimensional connection between the building units is achieved via common oxygen atoms. Both compounds disproportionate upon heating (T> 300 deg C) to Hg_3(P0_4)_2 and elemental mercury.