Crystal Structure of the Transition-Metal Molybdates and Tungstates. III. Diamagnetic α-ZnMoO4

Abstract

Diamagnetic α-ZnMoO4, the stable phase at STP, is triclinic with lattice constants a=9.625±0.015 Å, b=6.965±0.010 Å, c=8.373±0.015 Å, α=103.28°±0.15°, β=96.30°±0.15°, and γ=106.72±0.15° at 298°K, with six formula weights in the unit cell. The integrated intensities of 6489 reflections in a reciprocal hemisphere with (sinθ)/λ≤1.02 Å−1 were measured with PEXRAD; 3269 independent Fmeas were significantly above background. The structure was solved in Space Group P1; the subsequent atomic arrangement, obtained using a minimum interatomic contact requirement together with three-dimensional Fourier series and least-squares model fitting, closely approximated a centrosymmetric distribution. Refinement by the method of least squares in Space Group P1̄ gave a final agreement factor between measured and calculated structure factors of 0.0726. Each of the three crystallographically independent Mo atoms is surrounded by distorted tetrahedra of oxygen atoms; the Mo–O distances vary between 1.707±0.009 and 1.842±0.009 Å, the average being 1.764 Å. Two of the independent zinc atoms occupy distorted octahedra of oxygen atoms; the octahedral Zn–O distances range from 1.977±0.011 to 2.243±0.010 Å, with an average of 2.078 Å. The remaining zinc atom is in a distorted ``square'' pyramidal arrangement of oxygen atoms with Zn–O distances that vary from 1.954±0.012 to 2.106±0.007 Å, the average being 2.025 Å. The thermal vibration of the metal atoms is significantly anisotropic.