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Synthesis and Crystal Structure of Ln3(OH)(CrO4)4 · 3.5H2O (Ln = Pr, Nd) and Ln2(OH)2(CrO4)2 (Ln = Tb, Gd): Thermal Behavior and Infrared Spectra of Pr3(OH) (CrO4)4 · 3.5H2O and Gd2(OH)2(CrO4)2

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Abstract Crystal structures of Ln 2 (OH) 2 (CrO 4 ) 2 ( Ln = Gd, Tb) and Ln 3 (OH)(CrO 4 ) 4 · 3.5H 2 O ( Ln = Pr, Nd) were determined by a conventional single-crystal X-ray diffraction technique. Crystals of Ln 2 (OH) 2 (CrO 4 ) 2 ( Ln = Gd, Tb) are monoclinic, space group P 2 1 / c (no. 14) with lattice parameters a = 8.2454(4) A, b = 11.3834(5) A, C = 12.1420(8) A, and β = 136,590(5)°, Z = 4, D x = 4.92 mg · m -3 for Gd 2 (OH) 2 (CrO 4 ) 2 and a = 8.214(1) A, b = 11.348(1) A, c = 12.094(2) A, and β = 136.59(1)°, Z = 4, D x = 5.01 Mg · m -3 for Tb 2 (OH) 2 (CrO 4 ) 2 . Crystals of Ln 3 (OH)(CrO 4 )) 4 · 3.5H 2 O ( Ln = Pr, Nd) are monoclinic, space group C 2/ c (No. 15) with lattice parameters a = 32.779 (3) A, b = 7.137(1) A, c = 14.183(4) A, and β = 97.41(1)°, Z = 8, D x = 3.90 mg · m -3 for Pr 3 (OH)(CrO 4 ) 4 · 3.5H 2 O and with lattice parameters a = 32.643(3) A, b = 7.1093(7) A c = 14.122(1) A, and β = 97.421(8)°, Z = 8, D x = 3.99 Mg · m -3 for Nd 3 (OH)(CrO 4 ) 4 · 3.5H 2 O. In Ln 3 (OH)(CrO 4 ) 4 · 3.5H 2 O ( Ln = Pr, Nd) the coordination polyhedron of the nine oxygen atoms around Ln atoms is a tricapped trigonal prism. In Ln 2 (OH) 2 (CrO 4 ) 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 Pr 3 (OH)(CrO 4 ) 4 · 3.5H 2 O and Gd 2 (OH) 2 (CrO 4 ) 2 . Thermal decomposition of Pr 3 (OH)(CrO 4 ) 4 · 3.5H 2 O begins by the loss of water molecules and follows by the mechanism described for Yb 2 (OH) 2 (CrO 4 ) 2 and Ln 2 (CrO 4 ) 3 · 7H 2 O ( Ln = La, Pr, Nd, Sm, Eu, Gd).