A rhenium carbonyl bonded to highly dealuminated zeolite Y: structure determination by infrared and X-ray absorption spectroscopies

Abstract

Rhenium carbonyls bonded to dealuminated Y zeolite (DAY) were synthesized from HRe(CO)₅ and characterized by infrared and extended X-ray absorption fine structure spectroscopies. In the zeolite calcined at 573 K, a mixture of rhenium carbonyls was formed, but in the zeolite calcined at 773 K, a nearly unique rhenium carbonyl characterized by narrow infrared bands in the ν_CO region was formed, represented as Re(CO)₃{O_R4²⁻}₂{O_R6²⁻}, with rhenium bonded to three surface oxygen atoms at a T5 site located at an aluminum center in the zeolite (the braces signify sites on the zeolite surface and the subscript R4 refers to a surface oxygen atom bridging two four-ring sites and R6 refers to a surface oxygen atom bridging a four-ring and a six-ring site). The three surface oxygen atoms in the complex are not all equivalent, giving rise to a slightly distorted C_3v symmetry, consistent with the observed infrared spectra. Two Re-support oxygen distances were found by EXAFS spectroscopy, 2.09 and 2.47 Å. The Re–C and Re–carbonyl–oxygen distances were found to be 1.96 and 3.14 Å, respectively. The data show that rhenium carbonyls are good probes of three-fold surface sites of zeolites and oxides.