Stable subnanometre Pt clusters in zeolite NaX ia stoichiometric carbonyl complexes: Probing of negative charge by DRIFT spectroscopy of adsorbed CO and H2

Abstract

Negatively charged platinum carbonyl Chini complexes [Pt₃(CO)₆]_n²⁻ with n = 2–4 were synthesized by reductive carbonylation of Pt²⁺ in NaX zeolite and subsequently decomposed in vacuum at temperatures up to 773 K. The Pt clusters obtained preserved a low nuclearity, evidenced by rapid recarbonylation resulting in regeneration of the initial carbonyl Chini complexes. The electronic state of the metal clusters was probed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of chemisorbed CO and H₂. A strong electron donor capacity of Pt was indicated by the bands of (i) the linearly bonded CO at 1958–1976 cm⁻¹ and (ii) the stretching frequency of terminal platinum hydrides at 2040 cm⁻¹. It was concluded that the strong donor properties have to be attributed to negative charging of the Pt clusters, originating from the precursor carbonyl complex.