Anionic Pt carbonyl complexes in faujasites: Matrix effect

UV-vis and FTIR spectroscopies and temperature-programmed decomposition were used for the identification and characterization of anionic Pt Chini complexes [Pt-3(CO)(3)(mu-CO)(3)](2-)(n) inside faujasite matrices of different Si/Al ratios (X, Y zeolites) and various character of the lattice charge-compensating cations (alkali metal(+), Mg2+, Ca2+). The ship-in bottle synthesis of these species from [Pt(NH3)(4)](2+) was carried out by carbonylation at 90 degrees C. It was found that Chini complexes of the nuclearities Pt-6, Pt-9, and Pt-15 are mostly formed in alkali metal faujasites, while the presence of Mg2+ and Ca2+ stimulates the formation of neutral Pt-0 particles. Larger Chini complexes are formed in Y zeolites rather than in X zeolites. Within the same zeolite type, the contribution of clusters with higher nuclearity increases in the sequence Cs+ < K+ < Na+ < Li+. Generally, the smallest Chini clusters are preferred in zeolite matrices with the highest basicity and largest size of alkali metal cations. The finest cluster size distribution is achieved in K faujasites where Pt-6 and Pt-9 dominate. Water in zeolites is essential for the formation of Chini complexes; increasing the number of H2O molecules lowers the cluster nuclearity. Compared to solutions, the faujasite matrix affects the vibrational frequencies of CO ligands while electronic transitions are not changed significantly. The transformation of Chini complexes to other Pt species followed by a release of CO occurs above 90 and below 130 degrees C for all the zeolite matrices studied.