SYNTHESIS AND CRYSTAL-STRUCTURE OF LN3(OH)(CRO4)4-CENTER-DOT-3.5H2O (LN=PR, ND) AND LN2(OH)2(CRO4)2 (LN=TB, GD) - THERMAL-BEHAVIOR AND INFRARED-SPECTRA OF PR3(OH)(CRO4)4-CENTER-DOT-3.5H2O AND GD2(OH)2(CRO4)2

Crystal structures of Ln2 (OH)2(CrO4)2 (Ln = Gd, Tb) and Ln3(OH)(CrO4)4 · 3.5H2O (Ln = Pr, Nd) were determined by a conventional single-crystal X-ray diffraction technique. Crystals of Ln2 (OH)2 (CrO4)2 (Ln = Gd, Tb) are monoclinic, space group P21/c (no. 14) with lattice parameters a = 8.2454(4) Å, b = 11.3834(5) Å, C = 12.1420(8) Å, and β = 136,590(5)°, Z = 4, Dx = 4.92 mg · m-3 for Gd2(OH)2(CrO4)2 and a = 8.214(1) Å, b = 11.348(1) Å, c = 12.094(2) Å, and β = 136.59(1)°, Z = 4, Dx = 5.01 Mg · m-3 for Tb2(OH)2(CrO4)2. Crystals of Ln3 (OH)(CrO4))4 · 3.5H2O (Ln = Pr, Nd) are monoclinic, space group C 2/c (No. 15) with lattice parameters a = 32.779 (3) Å, b = 7.137(1) Å, c = 14.183(4) Å, and β = 97.41(1)°, Z = 8, Dx = 3.90 mg · m-3 for Pr3(OH)(CrO4)4 · 3.5H2O and with lattice parameters a = 32.643(3) Å, b = 7.1093(7) Å c = 14.122(1) Å, and β = 97.421(8)°, Z = 8, Dx = 3.99 Mg · m-3 for Nd3(OH)(CrO4)4 · 3.5H2O. In Ln3(OH)(CrO4)4 · 3.5H2O (Ln = Pr, Nd) the coordination polyhedron of the nine oxygen atoms around Ln atoms is a tricapped trigonal prism. In Ln2 (OH)2(CrO4)2 (Ln = Gd, Tb) the coordination polyhedron of the eight oxygen atoms around Ln atoms is a square antiprism. Structures form a three-dimensional network. Thermal behavior was investigated and IR spectra were recorded for Pr3 (OH)(CrO4)4 · 3.5H2O and Gd2 (OH)2(CrO4)2. Thermal decomposition of Pr3(OH)(CrO4)4 · 3.5H2O begins by the loss of water molecules and follows by the mechanism described for Yb2(OH)2(CrO4)2 and Ln2 (CrO4)3 · 7H2O (Ln = La, Pr, Nd, Sm, Eu, Gd). © 1993 Academic Press. All rights reserved.