Complex hydroxides of chromium: Na-9[Cr(ON)(6)](2)(OH)(3)center dot 6H(2)Oand Na-4[Cr(OH)(6)]X center dot H2O (X = Cl, (S-2)(1/2)) - Synthesis, crystal structure, and thermal behaviour

Green plate-like crystals of Na-9[Cr(OH)(6)](2) (OH)(3) . 6H(2)O 6H(2)O (tr iclinic, P (1) over bar, a = 872.9(1) pm, b = 1142.0(1)pm, c = 1166.0(1) pm , alpha = 74.27(1)degrees, beta = 87.54(1)degrees, gamma = 70.69(1)degrees) are obtained upon slow cooling of a hot saturated solution of Cr-III in co ne. NaOH (50 wt%) at room temperature. In the presence of chloride or disul fide the reaction yields green prismatic crystals of Na-4[Cr(OH)(6)]Cl . H2 O (monoclinic, C2/c, a =1138.8(2) pm, b =1360.4(1) pm, c = 583.20(7) pm, be ta =105.9(1)degrees) or green elongated plates of Na-4[Cr(OH)(6)](S-2)(1/2) H2O (monoclinic, P2(1)/c, a=580.8(1) pm, b = 1366.5(3) pm, c =1115.0(2) pm , beta =103.71(2)degrees), respectively. The latter compounds crystallize i n related structures. All compounds can be described as distorted cubic clo sest packings of the anions and the crystal water molecules with the cation s occupying octahedral sites in an ordered way. The thermal decomposition o f 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.