Hydrates of the Alkali Trioxidomonosulfidomolybdates and -tungstates: K2[(Mo/W)O3S] · 1.5H2O and (Rb/Cs)2[(Mo/W)O3S] · H2O

Abstract

Abstract The trioxidomonosulfidomolybdate and -tungstate anions [(Mo/W)O3S]2– are the first products formed when passing H2S gas through a solution of the oxidometalates. Their potassium, rubidium and cesium salt hydrates form as crystalline precipitates from these solutions depending on pH, the polarity of the solvent, educt concentrations and temperature. The structures of the sesqui- (K) and mono- (Rb, Cs) hydrates have been determined by means of X-ray single crystal diffraction data. The potassium sesquihydrates K2[(Mo/W)O3S] · 1.5H2O are isotypic and crystallize with a new structure type (monoäclinic, space group C2/c, M = Mo/W: a = 987.0(2)/993.13(11), b = 831.75(14)/831.10(11), c = 1868.9(4)/1865.2(2) pm, β = 99.34(2)/99.153(8)°, R1 = 0.0352/0.0390). In the crystal structure the [(Mo/W)O3S]2– anions are connected via hydrogen bonds to form columns along the c direction. Channels containing only water molecules run along the [101] direction. The dehydration process proceeds in a topotactic reaction between 60 to 95 °C and yields crystals of the anhydrous salts K2[(Mo/W)O3S]. The two different K+ cations exhibit a 5 + 3 and 5 + 2 O/S coordination. The heavier alkali metal cations form the four monohydrates (Rb/Cs)2[(Mo/W)O3S] · H2O (trigonal rhombohedral, space group R-3m) with lattice parameters for the Rb/Cs molybdates of a = 621.17(6)/624.62(10), c = 3377.9(4)/3388.6(8) pm (R1 = 0.0505/0.0734) and the tungstates of a = 642.80(3)/643.3(4), c = 3532.8(3)/3566(4) pm (R1 = 0.0348/0.0660). In the structures the 3m symmetrical tetrahedra are arranged to form double layers in such a way, that the O3 bases of the tetrahedra are pointing towards each other in a staggered conformation. These double layers are stacked in the c direction in a rhombohedral sequence. In these hydrates, there are no distinct hyrdogen bonds. Instead, partially disordered pairs of H2O molecules are situated in large cavities between the double layers. With a number of 10, the cation coordination sphere is increased compared to the K salts. The crystallographic results are confirmed by vibrational spectroscopy (Raman/IR) and thermal analytical studies of the new compounds.