Powder Diffraction

Technical Articles

X-ray powder diffraction analysis of a new magnesium chromate hydrate, MgCrO4·11H2O

A. Dominic Fortesa1a2 c1 and Ian G. Wooda1a2

a1 Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom

a2 Centre for Planetary Sciences at UCL/Birkbeck, Gower Street, London WC1E 6BT, United Kingdom

Abstract

A new hydrate of magnesium chromate is synthesized by quenching aqueous solutions of MgCrO4 in liquid nitrogen. MgCrO4·11H2O is isostructural with the rare mineral meridianiite (MgSO4·11H2O) being triclinic, $P{\bar 1}$, Z = 2, with unit-cell parameters a = 6.811 33(8) Å, b = 6.958 39(9) Å, c = 17.3850(2) Å, α = 87.920(1)°, β = 89.480(1)°, γ = 62.772(1)°, and V = 732.17(1) Å3 at −15 °C. The difference in unit-cell parameters between SO4- and CrO4-bearing species is only partially accounted for by the difference in S–O and Cr–O bond lengths; the remainder of the difference (over 90% in the cell volume) is attributed to weakening of the interpolyhedral hydrogen-bond network.

(Received December 13 2011)

(Accepted December 20 2011)

Key words

  • magnesium chromate;
  • undecahydrate;
  • meridianiite

Correspondence:

c1 Author to whom correspondence should be addressed. Electronic mail andrew.fortes@ucl.ac.uk