Zharchikhite, AlF(OH)2: a novel structure type related to α-PbO2.

The crystal structure of zharchikhite, AlF(OH)2, from the Zharchikhinskoe deposit (Buryatia, Russia) is solved here using single-crystal X-ray diffraction. The mineral is monoclinic, space group P21/c, a = 5.1788 (4), b = 7.8386 (4), c = 5.1624 (4) Å, ß = 116.276 (10)°, V = 187.91 (3) Å3 and Z = 4. Zharchikhite demonstrates a novel structure type roughly related to the α-PbO2 structure type and different from other compounds of the Al-F-OH system. The crystal structure of zharchikhite is based on the octahedral pseudoframework built from zigzag chains of edge-sharing AlF2(OH)4 octahedra; adjacent chains are linked via F vertices and the pseudoframework contains wide channels.

New data on the crystal chemistry of the natural two-layer aluminosilicates latiumite and tuscanite.

The crystal chemistry of the natural microporous two-layer aluminosilicates (2D zeolites) latiumite and tuscanite is re-investigated based on new data on the chemical composition, crystal structures, and infrared and Raman spectra. The CO32--depleted and P- and H-enriched samples from Sacrofano paleovolcano, Lazio, Italy, are studied. Both minerals are monoclinic; latiumite P21, a = 12.0206 (3), b = 5.09502 (10), c = 10.8527 (3) Å, ß = 107.010 (3)°, V = 635.60 (3) Å3 and tuscanite P21/a, a = 23.9846 (9), b = 5.09694 (15), c = 10.8504 (4) Å, ß = 107.032 (4)°, V = 1268.26 (8) Å3. The obtained crystal chemical formulae (Z = 2 for both minerals) are [(H3O)0.48(H2O)0.24K0.28](Ca2.48K0.21Na0.21Sr0.06Mg0.04)(Si2.86Al2.14O11)[(SO4)0.70(PO4)0.20](CO3)0.10 for latiumite and [(H3O)0.96(H2O)0.58K0.46](Ca4.94K0.44Na0.45Sr0.09Mg0.08)(Si5.80Al4.20O22)[(SO4)1.53(PO4)0.33](CO3)0.14 for tuscanite. These minerals are dimorphous. Both latiumite and tuscanite show distinct affinity for the PO43- anion. Hydrolytic alteration of these minerals results in partial leaching of potassium accompanied by protonation and hydration which is an important precondition for the existence of ion/proton conductivity of related materials.

Hydrothermal single-crystal growth in the systems Ag/Hg/X/O (X = VV, AsV): crystal structures of (Ag3Hg)VO4, (Ag2Hg2)3(VO4)4, and (Ag2Hg2)2(HgO2)(AsO4)2 with the unusual tetrahedral cluster cations (Ag3Hg)3+ and (Ag2Hg2)4+ and crystal structure of AgHgVO4.

Single crystals of (Ag3Hg)VO4 (I), (Ag2Hg2)3(VO4)4 (II), AgHgVO4 (III), and (Ag2Hg2)2(HgO2)(AsO4)2 (IV) were grown under hydrothermal conditions (250 degrees C, 5 d) from starting mixtures of elementary mercury, silver nitrate, ammonium vanadate, and disodium hydrogenarsenate, respectively. All crystal structures were determined from X-ray diffraction data, and their chemical compositions were confirmed by electron microprobe analysis. I crystallizes in the tillmannsite structure, whereas II-IV adopt new structure types: (I) I4, Z = 2, a = 7.7095(2) A, c = 4.6714(2) A, 730 structure factors, 24 parameters, R[F2 > 2sigma(F2)] = 0.0365; (II) I42d, Z = 4, a = 12.6295(13) A, c = 12.566(3) A, 1524 structure factors, 55 parameters, R[F2 > 2sigma(F2)] = 0.0508; (III) C2, Z = 4, a = 9.9407(18) A, b = 5.5730(8) A, c = 7.1210(19) A, beta = 94.561(10) degrees , 1129 structure factors, 48 parameters, R[F2 > 2sigma(F2)] = 0.0358; (IV) P31c, Z = 2, a = 6.0261(9) A, c = 21.577(4) A, 1362 structure factors, 52 parameters, R[F2 > 2sigma(F2)] = 0.0477. The most striking structural features of I, II, and IV are the formation of tetrahedral cluster cations (Ag3Hg)3+ and (Ag2Hg2)4+, respectively, built of statistically distributed Ag and Hg atoms with a metal-metal distance of about 2.72 A. The electronic structure of these clusters can formally be considered as two-electron-four-center bonding. The crystal structure of III differs from the protrusive structure types insofar as silver and mercury are located on distinct crystallographic sites without a notable metal-metal interaction >3.55 A. All crystal structures are completed by tetrahedral oxo anions XO4(3-) (X = VV, AsV) and for IV additionally by a mercurate group, HgO2(2-).