JOURNAL OF SOLID STATE CHEMISTRY 58,98-102 (1985) Synthesis and Crystal Chemistry of NH&MOO& JORGE L. GARIN* AND JOHNNY M. BLANC Departamento de Ingenieria Metaltirgica, Universidad de Santiago de Chile, Casilla 10233, Santiago, Chile Received August 16, 1984; in revised form November 6, 1984 NHp(MoO& crystallizes with hexagonal symmetry, space group F4&/m, lattice constants (I = 10.568A, c = 3.726 A, and Z = 2. The crystal structure has been determined by Patterson synthesis and refined assuming isotropic temperature factors to a final conventional R value of 0.085. The structure shows a three-dimensional arrangement built up of double chains of distorted Moo6 octahedra, parallel to the [OOl] direction. The octahedral double chains are linked among each other through common oxygen atoms. In addition to the shared oxygen atoms, each molybdenum is coordinated to one terminal oxygen. MO-O distances range from 1.645 to 2.378 A and O-MO-O angles from 74.3 to 114.3”. These results are consistent with the fact that molybdenum in high-valence states shows octahedral coordina- tion with terminal oxygens. 0 1985 Academic PKSS, Inc. Introduction Molybdenum compounds have been given considerable attention because of the interest in the chemistry of the transition metals and their industrial applications. Ammonium molybdates constitute impor- tant kinds of compounds for applications demanding high-purity molybdenum triox- ide. Production of ammonium molybdates is usually used as a purification step in ob- taining pure raw material for metal powder and steelmaking purposes. It is well known that many compounds are formed in the ternary system NHr Mo03-Hz0 but few crystal chemistry data have been reported (Z-8). This paper re- ports the crystallography and structure de- termination of NHj(MoO&. * To whom correspondence should be addressed. 0022-4596/85 $3.00 98 Copyright 0 1985 by Academic Press, Inc. All rights of reproduction in any form reserved. Experimental Powder and single crystals of NH3 (MOO& were prepared by direct reac- ion of MoOj, NHx, and Hz0 in sealed glass vessels. Reagent-grade Moo3 and NH3 (E. Merck) were mixed with distilled water in a molar weight ratio of 1lMo0, : 8NH3 : 8 lH20, and then heated at 80°C for a period of 20 days. Chemical equi- librium was monitored by measuring the par- tial pressure of NH3. Quantitative reaction is achieved when the pressure reaches a constant value. Colorless and transparent prismatic single crystals of about 0.05mm length, free from inclusions and twins, were obtained on the bottom of the vessel. The specimens were chemically identified by usual analysis techniques. The content of NHs(3.70 wt%) was determined by the Kjedahl method and molybdenum trioxide (%.3 wt%) by the Jones reduction tech- nique .