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Polymorphs and hydrates of lead squarate, Pb(C4O4).nH2O (n= 0, 1, 4): a powder diffraction study

Amira Bouhali 1,  Chahrazed Trifa 1,  Chaouki Boudaren 1,  Nathalie Audebrand 2,  Thierry Bataille 2

1. Laboratoire de Chimie Moléculaire, Contrôle de l'Environnement et de Mesures Physico-Chimiques, route de Ain El-Bey, Constantine 25000, Algeria
2. University of Rennes, Sciences Chimiques de Rennes, Rennes 35042, France

Abstract
Lead-based oxalate compounds have been widely investigated as precursors of PZT (lead zirconium titanate) derivatives that can be obtained at moderate temperatures [1]. In order to understand the role of the carboxylic ligand in the structural arrangement of metals, we have paid our attention on the squarate group, which resembles the oxalate anion in terms of design and possible connectivity. Among the syntheses of mixed metal squarates, lead squarate and its hydrates have been obtained. The thermal decomposition of Pb(C4O4).4H2O [2], studied by temperature-dependent X-ray powder diffraction (TDXD) and thermogravimetry (TGA), lead to Pb(C4O4).H2O and three polymorphs of anhydrous lead squarate. Their formation is strongly dependent on the experimental conditions used for the dehydration.
The powder patterns of three out of the four compounds have been indexed using DICVOL06 [3]. Pb(C4O4).H2O: a = 7.366(1) Å, b = 11.305(2) Å, c = 6.685(1) Å, β= 102.49(1)°, P21/c, Z = 4 [M20 = 46, F20 = 82(0.0071, 34)]; Pb(C4O4) (Polymorph I): a = 24.268(4) Å, b = 15.270(3) Å, c = 7.854(1) Å, Cmma [M20 = 26, F20 = 64(0.0051, 60)]; Pb(C4O4) (Polymorph II): a = 15.853(6) Å, b = 14.798(5) Å, c = 5.380(2) Å, α = 63.90(3)°, β = 103.33(4)°, γ = 115.95(3)°, P-1 [M20 = 27, F20 = 52(0.0065, 60)]. Pb(C4O4) (Polymorph III) could be obtained as single crystals and its structure has been consequently solved from single crystal diffraction data. The crystal structure of Pb(C4O4).H2O was solved ab initio with direct-space methods using FOX [4]. The structural filiation between tetrahydrate, monohydrate and anhydrous phases are discussed.

PbC4O4_Bataille.jpgReferences

[1] L. A. Hall, D. J. Williams, S. Menzer, A. J. P. White, Inorg. Chem. 36 (1997) 3096.
[2] C. Boudaren, J. P. Auffredic, M. Louër, D. Louër, Chem. Mater. 12 (2000) 2324.
[3] A. Boultif, D. Louër, J. Appl. Crystallogr. 37 (2004) 724.
[3] V. Favre-Nicolin, R. Cerny, J. Appl. Crystallogr. 35 (2002) 734.

 

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Presentation: Poster at 11th European Powder Diffraction Conference, Poster session, by Thierry Bataille
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-04-30 11:30
Revised:   2009-06-07 00:48