Mercury phosphates with the triangular Hg34+ cluster:: (Hg3)3(PO4)4 and (Hg3)2(HgO2)(PO4)2

Hydrothermal treatment of microcrystalline (Hg-2)(2)P2O7 in diluted phosphoric acid or demineralized water at 400 degreesC yields colorless crystals of (Hg-3)(3)(PO4)(4) and yellow crystals of(I-fg,), (HgO2)(PO4)(2), respectively. The crystal structures have been solved and refined from single crystal diffractometer data to residuals R[F-2 > 2 sigma (F-2)] = 0.021 and wR2[F-2] = 0.047 for (Hg-3)(3)(PO4)(4) and R[F-2 > 2 sigma (F-2)] = 0.028 and wR2 [F-2] = 0.072 for (Hg-3)(2)(HgO2)(PO4)(2). The crystal structure of (Hg-3)(3)(PO4)(4) (R3c (No. 161), Z = 6, a = 16.3957(10) Angstrom, c = 10.6606(9) Angstrom, V = 2481.9(3) Angstrom (3)) is isotypic with the corresponding arsenate (Hg-3)(3)(ASO(4))(4).(Hg-3)(2)(HgO2)(PO4)(2) crystallizes with two formula units in the monoclinic space group P2(1)/c (No. 14), with lattice parameters a = 6.2506(7) Angstrom, b = 9.9366(10) Angstrom, c = 9,6663(12) Angstrom, beta = 95,783(10)degrees, and V = 597.3(1) Angstrom (3), and shows a topological relationship to the mineral terlingeraite (Hg4O2Cl2). Both phosphates contain tetrahedral PO43- groups and the triangular mercury cluster Hg-3(4+) with (d) over bar (Hg-Hg) = 2.666 Angstrom for (Hg-3)(3)(PO4)(4) and 2.682 Angstrom for (Hg-3)(2)(HgO2)(PO4)(2), respectively. In the latter compound a linear mercurate group, HgO22- with (d) over bar (Hg-O) 2.031(7) Angstrom, 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 degreesC) to Hg-3(PO4), and elemental mercury. (C) 2001 Academic Press.