Metal carbonyl cluster synthesis in nanocages:: Spectroscopic evidence of intermediates in the formation of Ir4(CO)12 in zeolite NaY

The assembly of Ir(4)(CO)(12) from Ir(CO)(2)(acac) precursors in the supercages of zeolite NaY was investigated by extended X-ray absorption fine structure (EXAFS) and in-situ infrared (IR) spectroscopies. The data show that the conditions of pretreatment of the zeolite significantly affect the formation process of Ir(4)(CO)(12). When the zeolite was initially largely dehydrated, so that the precursor molecules were well dispersed in the zeolite cages, dimeric intermediates in the formation of Ir(4)(CO)(12) (approximated as Ir(2)(CO)(8)) were observed by both IR and EXAFS spectroscopies. In contrast, when the zeolite initially contained a substantial amount of water, the resultant Ir(4) clusters were formed faster than those in dehydrated zeolite, and evidence of intermediates was not observed. The results show how synthesis in the confined spaces of the zeolite nanopores-in the absence of solvents-affords opportunities to control and elucidate the chemistry, different from that in solution.