Beiträge zum thermischen Verhalten von Sulfaten XIV. Zum thermischen Verhalten von PdSO 4 · 2H 2O und PdSO 4 · 0,75H 2O sowie zur Struktur von M-PdSO 4

Abstract

Crystals of two modifications of PdSO 4 (both red—brown, edge length up to 0.2 mm) could be prepared by treatment of Pd powder with an excess of nitrating acid at T ≈ 200–240 °C. The low temperature modification (N-PdSO 4) which crystallizes with monoclinic symmetry is stable up to T ≈ 520 °C (from X-ray powder data and an electron microscopy investigation: a = 9.881(1) A ̊ , b = 9.888(1) A ̊ , c = 12.382(2) A ̊ , β = 92.81(1)°, Z = 16 , space group Pc or P2/c). According to single crystal data, the probably metastable modification (M-PdSO 4) crystallizes with monoclinic symmetry (space group C2/c) and lattice constants a = 7.8447(8) A ̊ ; b = 5.1793(3) A ̊ , c = 7.9092(6) A ̊ , β = 95.606(7)° and Z = 4 (R 1 = 0.019 for 31 free parameters and 827 F o with F o > 4σ(F o )). The structure consists of tetrahedral SO 4 groups. Four O atoms belonging to four different SO 4 tetrahedra coordinate the Pd atoms in a plane. Applying the high temperature Guinier technique and using differential thermal analysis (DTA)—thermogravimetry (TG) equipment, the thermal behaviour of PdSO 4·2H 2O and its decomposition products (PdSO 4 · 0.75H 2O, PdSO 4) was investigated. The thermodynamic data of PdSO 4 ( Δ F H 298 o = - 160.7 kcal mol −1 and S 298 o = 23.3 cal mol −1 K −1) could be determined by measurement of the pressure with respect to the temperature.