Complex Hydroxides of Chromium: Na9[Cr(OH)6]2(OH)3 ? 6 H2O and Na4[Cr(OH)6]X ? H2O (X = Cl, (S2)1/2) - Synthesis, Crystal Structure, and Thermal Behaviour

Article abstract of DOI:10.1002/(sici)1521-3749(200004)626:4<1004::aid-zaac1004>3.0.co;2-c

Green plate-like crystals of Na₉[Cr(OH)₆]₂(OH)₃ · 6H₂O (triclinic, P1?, a = 872.9(1) pm, b = 1142.0(1) pm, c = 1166.0(1) pm, α = 74.27(1)°, β = 87.54(1)°, γ = 70.69(1)°) are obtained upon slow cooling of a hot saturated solution of Cr^III in cone. NaOH (50 wt%) at room temperature. In the presence of chloride or disulfide the reaction yields green prismatic crystals of Na₄[Cr(OH)₆]Cl · H₂O (monoclinic, C2/c, a = 1138.8(2) pm, b = 1360.4(1) pm, c = 583.20(7) pm, β = 105.9(1)°) or green elongated plates of Na₄[Cr(OH)₆](S₂)_1/2 · H₂O (monoclinic, P2₁/c, a = 580.8(1) pm, b = 1366.5(3) pm, c = 1115.0(2) pm, β = 103.71(2)°), respeclively. The latter compounds crystallize in related structures. All compounds can be described as distorted cubic closest packings of the anions and the crystal water molecules with the cations occupying octahedral sites in an ordered way. The thermal decomposition of the compounds was investigated by DSC/TG or DTA/TG and high temperature X-ray powder diffraction measurements. In all cases the final decomposition product is NaCrO₂.