Double complex salts based on [Rh(NH3)6]3+ as precursors for Rh–Nb and Rh–V alloy systems: synthesis, structure, and thermal properties

Abstract

The complex [Rh(NH₃)₆](NO₃)₃ (I) has been synthesized, and its crystal structure has been determined for the first time. The syntheses of double complex salts (DCS) [Rh(NH₃)₆][NbO(C₂O₄)₃]·4H₂O (II) and [Rh(NH₃)₆]₂[(μ₂-C₂O₄)(VO(C₂O₄)₂)₂]·6H₂O (III) were carried out. The complexes were characterized by single-crystal and powder X-ray diffraction, IR, UV-Vis (III), diffuse reflectance spectroscopy (III), and EPR (III). Thermal decomposition of DCS II and III in inert and reducing atmospheres was studied. Thermal decomposition of [Rh(NH₃)₆][NbO(C₂O₄)₃]·4H₂O (II) in a hydrogen atmosphere resulted in the formation of the bimetallic solid solution Rh_0.83Nb_0.17 and NbO₂, while in the case of [Rh(NH₃)₆]₂[(μ₂-C₂O₄)(VO(C₂O₄)₂)₂]·6H₂O (III), a phase with the structure of intermetallic Rh₃V and V₂O₃ was formed. The photocatalytic activity of thermolysis products in Rh–Nb and Rh–V systems was tested in the process of hydrogen production. The Rh–Nb/g-C₃N₄ catalyst showed a H₂ evolution rate of about 0.69 mmol h⁻¹ g_cat⁻¹ and Rh–Nb/TiO₂ catalysts showed about 0.29 mmol h⁻¹ g_cat⁻¹ under 410 nm irradiation.