NaX-encaged Pt carbonyls: reversible substitution of CO ligands by oxygen and ammonia. Evidence for a conservation of the polynuclear Pt skeleton

Abstract

The carbonylation of platinum tetrammine ions in NaX zeolite to platinum anionic (Chini) carbonyl complexes ([Pt₃(CO)₆]_n²⁻, n=2), oxidation of these complexes and their recarbonylation were studied using in situ FTIR and UV/Vis spectroscopy. The near-surface layers as well as the Pt state were examined by XPS, and normalized absorbance of white line of the Pt L₃-edge, evaluated from EXAFS experiments, was monitored in the course of the formation and decomposition of anionic Pt carbonyl complexes. It follows that the positive charge of platinum of the starting complex [Pt(NH₃)₄]²⁺ in NaX is largely maintained during carbonylation as well as oxidation and recarbonylation. From the kinetics of recarbonylation of the oxidized complex, which is faster than the primary carbonylation by more than one order of magnitude, a preservation of the Pt skeleton of the primary carbonyl is deduced. Mass spectrometric analysis of the gases evolved during decomposition of the complexes formed by carbonylation, oxidation and recarbonylation, enabled two suggestions to be made: (i) the composition of the oxidized complex; and (ii) stoichiometries for the conversions in agreement with all experimental data.