Redetermination of the structure of Gd2CuO4: a site population analysis

Abstract

MoO2DPO4.D20 Table 2. Bond distances (A)and angles (o) with e.s.d.'s i in parentheses -~-'L-~ :i ol oa Mo Mo--Ol Mo-O2 Mo--O4 Mo-O5 Mo-O6 DI-O4 D2--O3 O4--Mo-O6 O6--Mo--O2 O4--Mo-O5 O2-Mo-O5 O 1--Mo-O2 O l--Mo-O4 O l--Mo-O5 OI--Mo-O6 Fig. 2. Portion of the structure MoO2DPO4.D20 viewed obliquely to the y = 0.25 plane. The hydrogen bonds are represented by broken lines. positions determined were significantly displaced from those obtained by Kierkegaard. The Mo environment consists of two short bonds to 0 4 and 06 typical of a bent molybdenyl group, three normal M o - O bonds linking to phosphate groups and a more weakly bound D20 molecule with an M o - O distance of 2.27 A. The phosphate group is protonated as is found in other transition-metal phosphates, for example Zr(HPO4)2.- H20. The P - O - H group hydrogen bonds reasonably strongly to 04, which is the sole interaction between the double chains. The water-molecule geometry is typical for this species in hydrated inorganic compounds; it is held in the y = 0.25 plane by a weak hydrogen bond between D2 and 03. The presence of this structural feature fits with the strong absorption at 1620cm -t in the IR spectrum which is due to the H20 symmetric bend. The coordination geometry of Mo is similar to that observed in molecular Mo[(CH3)2NCHO]202CI 2 (Flo- P--Ol P--O2 P--O3 O3--DI O5-D2 O5--D3 D2-D3 D2-O5-D3 P--O3--D I O3--D I--O4 O5-D2-O3 O I--P--O2 O 1-P--O3 O2-P--O3 I 12.9 rian & Corey, 1968) where a bent M o O 2 group' coordinated to oxygen and chlorine in an approxi- mately octahedral environment. In MoO2DPO4.D20, however, the phosphate groups link the molybdenyl moieties into infinite chains. The authors wish to thank the ILL, Grenoble, for the use of neutron beam facilities. We also thank the SERC for a grant for work in this field and a studentship for RGB. References FLORIAN, L. R. & COREY, E. R. (1968). Inorg. Chem. 7, 722-725. HAMILTON, W. C. (1965). Acta Cryst. 18, 502-510. HEWAT, A. W. (1973). Report AERE-R7350. UK Atomic Energy Authority, Harwell, Oxon, England. KmRKEGAARD, P. (1958). Acta Chem. Scand. 12, 1701-1714. KmRrmGAARD, P. (1962). Ark. Kemi, 19, 51-62. RETVELD, H. M. (1969). J. Appl. Cryst. 2, 65-71. SCnULYZ, I. (1955). Z. Anorg. Allg. Chem. 281, 99-112. Acta Cryst. (1988). C44, 1518-1520 R e d e t e r m i n a t i o n o f the Structure o f Gd 2CUO4: A Site P o p u l a t i o n A n a l y s i s BY KIMBERLY A. KUBAT-MARTIN,* ZACHARY FISKt AND ROBERT R. RYAN* Los Alamos National Laboratory, University of California, Los Alamos, New Mexico 87545, USA (Received 10 February 1988; accepted 25 April 1988) Abstract. In view of recent interest in compounds of the type Ln2CuO 4 (where Ln = lanthanide), a single-crystal X-ray study has been performed for the redeter- mination of the structure of Gd2CuO 4 including a site population analysis. M r = 442.04, tetragonal, I4/mmm, * Group INC-4, MS C346. I Group P10, MS K764. a = 3.892 (1), c = 11.878 (3) A, V = 179.91 A 3, Z = 2, D x = 8 . 1 5 g c m -a, MoKa~, 2 = 0 . 7 0 9 2 6 A , # = 423.5 cm -~, F(000) = 378, T = 295 K, R = 2.8%, 102 unique reflections used for refinement. The structure consists of a two-dimensional edge-linked square-planar network of [CuO2] 2- groups which are linked by planes of Gd, O and Gd atoms. The oxygen coordination environment around the Gd 3+ cations is cubic. The © 1988 International Union of Crystallography