Low-alkali metal content in beta-vanadium mixed bronzes: the crystal structures of β-Kx(V,Mo)6O15 (x = 0.23 and 0.32) by single-crystal X-ray diffraction

The vanadium–molybdenum mixed oxide bronzes of composition K0.23(V5.35Mo0.65)O15 and K0.32(V5.48Mo0.52)O15 have a monoclinic
structure with s.g. C2/m, Z ¼ 2, and unit-cell dimensions a ¼ 15.436(2), b ¼ 3.6527(5), c ¼ 10.150(1)A ˚ , b ¼ 108.604(3)1 and
a ¼ 15.452(2), b ¼ 3.6502(5), c ¼ 10.142(1)A ˚ , b ¼ 109.168(3)1, respectively, as determined by single-crystal X-ray diffraction. These
compounds show the b-NaxV6O15 tunnel structure, which is isostructural with bannermanite, natural sodium–potassium vanadate.
Structure refinements from diffracted intensities collected in the 2–381y range converged to final R ¼ 5.58% and 7.48% for the two
crystals, respectively. The V atoms are distributed on three different crystallographic sites. Partial substitution of V with Mo occurs in
only one of these positions. Oxygen atoms involved in vanadyl groups point toward the tunnels. The K ions in the tunnels are
coordinated by seven oxygen atoms. The alkali metal content in these crystals is much lower than the solubility limit found for the
analogous Na containing compound.