Tetraalkylammonium Salts of Platinum Nitrato Complexes: Isolation, Structure, and Relevance to the Preparation of PtO_x/CeO₂ Catalysts for Low-Temperature CO Oxidation

A series of tetraalkylammonium salts with anionic platinum nitrato complexes (Me₄N)₂­[Pt₂­(μ-OH)₂­(NO₃)₈] (1), (Et₄N)₂­[Pt₂­(μ-OH)₂­(NO₃)₈] (2), (n-Pr₄N)₂­[Pt₂­(μ-OH)₂­(NO₃)₈] (3b), (n-Pr₄N)₂­[Pt­(NO₃)₆] (3a), and (n-Bu₄N)₂­[Pt­(NO₃)₆] (4) were isolated from nitric acid solutions of [Pt­(H₂O)₂­(OH)₄] in high yield. The structures of salts 2, 3a, 3b, and 4, prepared for the first time, were characterized by X-ray diffraction. The sorption of [Pt­(NO₃)₆]^2– and [Pt₂­(μ-OH)₂­(NO₃)₈]^2– complexes onto the ceria surface from acetone solutions of salts 4 and 1 was examined. The dimeric anion was shown to quickly and irreversibly chemisorb onto the CeO₂ carrier, selectively transforming into Pt­(II) centers after thermal treatment, becoming active in the low-temperature CO oxidation reaction (T_50% = 110 °C at a space velocity of 240 000 h^–1). By contrast, the homoleptic complex [Pt­(NO₃)₆]^2– did not interact with the ceria, which may be attributed to the substitutional inertness of the [Pt­(NO₃)₆]^2– anion. We believe that the strategy based on the sorption of polynuclear platinum nitrato complexes is an effective route to prepare ionic platinum species uniformly distributed on an oxide carrier for various catalytic applications.