FTIR study of the synthesis of anionic platinum carbonyl complexes in faujasites

Abstract

[{Pt₃(CO)₃(µ-CO)₃ }_n]^2- complexes (Chini complexes) have been synthesized by the ‘ship-in-bottle’ technique in X and Y zeolites with different charge-compensating alkali-metal cations. The reaction kinetics of the reductive carbonylation of the [Pt(NH₃)₄]²⁺ complex was examined by FTIR spectroscopy in order to understand the mechanism of the formation of the Chini complexes. It was found that three geometrical arrangements of the [Pt(NH₃)₄]²⁺ complexes are formed in the cavities and that their occurrence depends on the zeolite composition (Si/Al ratio, alkali-metal cation) and amount of water. A decreased content of Al and increasing electropositivity and radius of the alkali-metal cations accelerate the decomposition of the [Pt(NH₃)₄]²⁺ complex during the carbonylation and consequently also the formation of Chini complexes. A higher content of water reduces the rate of the carbonylation process but causes the formation of a higher fraction of smaller Chini complexes.

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