ANHYDROUS LANTHANUM ACETATE, LA(CH3COO)3, AND ITS PRECURSOR, (NH4)3[LA(CH3COO)6].1/2H2O - SYNTHESIS, STRUCTURES, THERMAL-BEHAVIOR

Single crystals of (NH4)3[La(CH3COO)6] . 1/2 H2O are obtained by refluxing La2O3 or La(CH3COO)3 . 1.5 H2O with an excess of NH4CH3COO in methanol. The crystal structure (trigonal, R3BAR, Z = 6, a = 1 365.0(3) pm, c = 2 360(1) pm, R = 0.088, R(w) = 0.061) exhibits the coordination number of nine for La3+ which is surrounded by three chelating-type bidentate and three unidentate acetate groups. Characteristic are monomeric units of [La(CH3COO)6]3- which are connected to a three-dimensional network by hydrogen bonds with the NH4+ ions. Thermal decomposition consists of four steps with La(CH3COO)3, La2(CO3)3 and La2O2CO3 as intermediates and La2O3 as the final product. Single crystals of La(CH3COO)3 are obtained from La2O3 in a melt of NH4CH3COO (molar ratio 1: 12) in a sealed glass ampoule. The crystal structure (trigonal, R3BAR, Z = 18, a = 2 203.0(5) pm; c = 987.1(3) pm, R = 0.027, R(w) = 0.023) shows the coordination number of ten for La3+. These are three-dimensionally connected by oxygen atoms of the acetate groups with two tetradentate double-bridging and one Z, Z-type-bridging bidentate acetate group.