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) Å, c = 15.5718(8) Å, space group I4₁/amd, V = 867.20 ų, Z = 4. With increasing temperature to 400 K, the unit cell parameters change in different directions: a increases by 0.032 Å, c decreases by 0.036 Å. The total increase in the unit cell volume is 5 ų. In a range of 150 K to 400 K, the observed W-O distances decrease by 0.019 Å from 1.778(18) Å to 1.759(3) Å. For the [Pd(NH₃)₄]₃W₇O₂₄·4.4H₂O structure at 298 K the crystallographic data are as follows: a = 8.3409(2) Å, b = 22.2654(6) Å, c = 10.5450(3) Å, β = 104.449(1)°, space group P2₁/m, V = 1896.41 ų, Z = 2. In the heptatungstate anion the shortest are the W—O distances with the terminal O atoms (1.731–1.745 Å). The distances to the bridging O atoms connecting two W atoms are 1.930–2.406 Å; those connecting three W atoms are 1.882–2.234 Å, and those connecting four W atoms are 2.192–2.220 Å. 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.