Complex Salts Containing [Pd(NH3)4]2+ Cations and $$\text{WO}_4^{2-}$$ and $$\text{W}_7\text{O}_{24}^{6-}$$ Anions: The Precursors of Pd–W Metal Alloys

Abstract

Two crystal structures containing [Pd(NH3)4]2+ cations and $$\text{WO}_4^{2-}$$ and $$\text{W}_7\text{O}_{24}^{6-}$$ anions are studied. For the [Pd(NH3)4]WO4 structure at 150 K the following crystallographic data are obtained: a = 7.4626(3) A, c = 15.5718(8) A, space group I41/amd, V = 867.20 A3, Z = 4. With increasing temperature to 400 K, the unit cell parameters change in different directions: a increases by 0.032 A, c decreases by 0.036 A. The total increase in the unit cell volume is 5 A3. In a range of 150 K to 400 K, the observed W-O distances decrease by 0.019 A from 1.778(18) A to 1.759(3) A. For the [Pd(NH3)4]3W7O24·4.4H2O structure at 298 K the crystallographic data are as follows: a = 8.3409(2) A, b = 22.2654(6) A, c = 10.5450(3) A, β = 104.449(1)°, space group P21/m, V = 1896.41 A3, Z = 2. In the heptatungstate anion the shortest are the W—O distances with the terminal O atoms (1.731–1.745 A). The distances to the bridging O atoms connecting two W atoms are 1.930–2.406 A; those connecting three W atoms are 1.882–2.234 A, and those connecting four W atoms are 2.192–2.220 A. It is shown that the [Pd(NH3)4]3W7O24·4.4H2O structure has a pseudohexagonal motif in the a direction. The thermal decomposition of the salts is performed in the presence of LiH in the He atmosphere at 1273 K. The ex situ powder X-ray diffraction study reveals the formation of Pd–W alloys.