INTERMOLECULAR EFFECTS ON THE GEOMETRY OF [PTCL4]2- - X-RAY-DIFFRACTION STUDIES OF AQUEOUS H2PTCL4 AND CRYSTALLINE (NH4)2PTCL4

The structure of [PtCl4]2- has been determined in an aqueous solution of 1.20 M H2PtCl4 and 0.7 M HCl using the LAXS technique. Pt(II) is coordinated to four Cl in a square-planar configuration with a Pt-Cl distance of 2.32(1) angstrom. The crystal structure of (NH4)2PtCl4 has been determined from X-ray single-crystal intensity data collected at room temperature with a CAD4 diffractometer. Crystal data at room temperature (MoK-alpha; lambda = 0.7107 angstrom) are: M(r) = 372.98, tetragonal, P4/mmm, Z = 1, a = 7.1525(9), c = 4.2979(5) angstrom, V = 219.88(5) angstrom3, D(x) = 2.817 g cm-3 and mu = 17.26 mm-1. The refinement converged to R = 0.0275 for 750 reflexions with I > 2-sigma (I). The structure is composed of pseudotetrahedral NH4+ and square-planar PtCl4(2-) ions linked by hydrogen bonds N-H...Cl with an N...Cl distance of 3.326(1) angstrom. However, the hydrogen atoms are disordered, corresponding to two equally probable orientations of the ammonium ion with two identical sets of hydrogen bonds. The Pt-Cl bond length, 2.305(1) angstrom, is not significantly different from the corresponding distance in solution, 2.32(1) angstrom. A literature survey of accurate crystal structure determinations of ptCl4(2-) gives an average Pt-Cl distance of 2.304(7) angstrom; it is thus concluded that the geometry is very rigid, but variations due to intermolecular forces are slightly above the noise level of experimental errors for very accurate crystal structure determinations.