(NH4)[LA(NH3)(9)]S5S - A LANTHANUM AMMINE SALT OF A PECULIARLY DISORDERED S-5(2-) CHAIN

The synthesis and low temperature structural characterization of (NH4) [La(NH3)(9)]S5S is reported. Yellow polyhedra of the title phase are p repared from a reaction of La and S-8 in supercritical ammonia at 170 degrees C for 3 days. It crystallizes in the orthorhombic space group Pnma with lattice parameters of a=16.622(4), b=15.739(3), c=7.626(2)An gstrom, V=1994.9(8)Angstrom(3), Z=4, R=0.0315 and wR = 0.0339. Althoug h polypentasulfides are common anionic species, and have been well cha racterized, the structure of (NH4)[La(NH3)(9)]S5S exhibits a number of interesting crystallographic features. It contains disordered, unbran ched S-5(2-) chains in all trans conformations, discrete S2- anions, a nd ammonium and trivalent lanthanum nonaammine cations, the latter of which has only been reported in one other phase. The title compound ha s a relatively low stability, with a propensity to lose ammonia, there by causing the lattice to collapse.