Acta Crystallographica Section B

Structural Science

Volume 56, Part 3 (June 2000)

research papers

Acta Cryst. (2000). B56, 419-425 [ doi:10.1107/S0108768100000252 ]

Structures of [Pd(NH₃)₂X₂] and its chemical transformation in the solid state

S. D. Kirik, L. A. Solovyov, A. I. Blokhin and I. S. Yakimov

Abstract: Crystal structures of [Pd(NH₃)₂X₂] complexes, where X = Br or I, diamminediiodo-/-dibromopalladium(II), have been studied by X-ray powder diffraction. The series consists of five complexes: cis-[Pd(NH₃)₂Br₂] (I) [a = 13.3202 (7), b = 12.7223 (6), c = 7.05854 (3) Å, Z = 8, space group Pbca], trans-[Pd(NH₃)₂Br₂] (II) [a = 6.7854 (3), b = 7.1057 (3), c = 6.6241 (2) Å, [alpha] = 103.221 (3), [beta] = 102.514 (2), [gamma] = 100.386 (3)°, Z = 2, space group $P\overline 1$ ], [beta] -trans-[Pd(NH₃)₂Br₂] (III) [a = 8.4315 (3), b = 8.4206 (3), c = 8.0916 (2) Å, Z = 4, space group Pbca], cis-[Pd(NH₃)₂I₂] (IV) [a = 13.9060 (8), b = 13.5035 (8), c = 7.5050 (4) Å, Z = 8, space group Pbca], and [beta] -trans-[Pd(NH₃)₂I₂] (V) [a = 8.8347 (5), b = 8.8410 (5), c = 8.6081 (2) Å, Z = 4, space group Pbca]. Patterson synthesis and Rietveld refinement have been used for structural determination. Molecular structures with column- or parquet-type packing of flat complexes are characteristic of these substances. Corresponding cis- and [beta] -trans compounds are isostructural. The thermal transformations cis [rightwards arrow] trans [beta] -trans (cis [beta] -trans in the case of iodine) are considered. Cl derivatives are also discussed. The transformations proceed irreversibly and are accompanied by decreasing specific volume. Owing to these features, they can be classified as chemical reactions. High-temperature X-ray powder diffraction was used to study the transformations in air. The set of data is consistent with a solid state transformation from cis to trans. According to this model, the columns of molecules remain intact during the process, and the transformation proceeds via the breaking of PdX and PdN intermolecular bonds. The powder diffraction data have been deposited in ICDD-JCPDS (45-0596, 46-0876, 46-0879, 47-1690, 48-1185).