Hydrothermal single-crystal growth in the systems Ag/Hg/X/O (X = V-V,As-V): 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 str

摘要

Single crystals of (Ag3Hg)VO4 (I), (Ag2Hg2)(3)(VO4)(4) (II), AgHgVO4 (III), and (Ag2Hg2)(2)(HgO2)(ASO(4))(2) (IV) were grown under hydrothermal conditions (250 degreesC, 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) (l) over bar4, Z = 2, a = 7.7095(2) Angstrom, c = 4.6714(2) Angstrom, 730 structure factors, 24 parameters, R[F-2 > 2sigma(F-2)] = 0.0365; (II) l42d, Z = 4, a = 12.6295(13) Angstrom, c = 12.566(3) Angstrom, 1524 structure factors, 55 parameters, R[F-2 > 2sigma(F-2)] = 0.0508; (III) C2, Z = 4, a = 9.9407(18) Angstrom, b = 5.5730(8) Angstrom, c = 7.1210(19) Angstrom, = 94.561(10)degrees, 1129 structure factors, 48 parameters, R[F-2 > 2sigma(F-2)] = 0.0358; (IV) P31c, Z = 2, a = 6.0261(9) Angstrom, c = 21.577(4) Angstrom, 1362 structure factors, 52 parameters, R[F-2 > 2sigma(F-2)] = 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 Angstrom. 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 Angstrom. All crystal structures are completed tetrahedral oxo anions XO43- (X = V-v, As-v) and for IV additionally by a mercurate group, HgO22-.