Isostructural crystals of aluminum hexamolybdenocobaltate(III) and hexamolybdenocromate(III) Al[MMo6O18(OH)6] · 16H2O (M = Co(III) and Cr(III)) were studied using X-ray diffraction analysis. These compounds crystallize in the triclinic system: space group P\documentclass[12pt]{minimal}
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\end{document}, Z = 1, ρ(calcd) = 2.665 and 2.611 g/cm3, respectively. The unit cell parameters were determined: for aluminum hexamolybdenocobaltate(III), a = 6.796(1) Å, b= 11.248(2) Å, c = 11.568(2) Å; α = 101.36(2)°, β = 96.95(2)°, γ = 102.23(2)°; for aluminum hexamolybdenocromate(III), a = 6.838(1) Å, b = 11.312(2) Å, c = 11.605(2) Å; α = 101.29(3)°, β = 97.13(3)°, γ = 102.15(3)°.