Crystal structure of potassium molybdate, K2MoO4

Abstract

K₂MoO₄ crystallises in the monoclinic system, space group C2/m, with unit-cell dimensions a= 12·348, b= 6·081, c= 7·538 Å, and β= 115·74°. Its structure, determined by three-dimensional Patterson and Fourier syntheses and refined by least-squares techniques contains isolated, almost regular MoO₄ tetrahedra with average Mo–O distance 1·76 ± 0·01 Å and potassium ions occupying eight-co-ordinate positions. The potassium–oxygen co-ordination may be described basically as somewhat distorted trigonal prismatic, where the K–O distances are all <3 Å, with the co-ordination polyhedron completed by two longer contacts of 3·21 Å. The similarity to the β-K₂SO₄ structure is discussed; K₂WO₄ and [NH₄]₂MoO₄ have been shown to be isomorphous with K₂MoO₄.