Subnanometer platinum clusters in zeolite NaEMT via stoichiometric carbonyl clusters

The direct carbonylation of [Pt(NH3)(4)](2+)-exchanged zeolite NaEMT genera tes [Pt-3(CO)(3)(mu-CO)(3)](3)(2-) complexes nearly exclusively. The prefer ential formation of triplane complexes is attributed to the perfect matchin g of the complex with a nearly threefold symmetry axis to the hosting hyper cage exhibiting a threefold symmetry as well. The complexes are formed by a reductive carbonylation, where (i) the reducing hydrogen is produced via t he low-temperature water-gas shift reaction and (ii) the formed protons are stored in charge compensating ammonium ions. Small subnanometer platinum c lusters of zero (Pt-x(0)) and partial positive (Pt-x(delta+)) charge are fo und during the decarbonylation of the anionic platinum carbonyl clusters, g enerated by reoxidation with the aid of the stored protons. The smallest cl usters are assumed to exhibit a size-quantization (metal-insulator transiti on) effect. All transient states of the processes are monitored by UV-vis a nd IR spectroscopy in situ. (C) 2000 Elsevier Science B.V. All rights reser ved.