Intrazeolite chemistry of nickel(0) complexes and Ni(0,II) clusters studied by EXAFS, solid-state NMR and FT-IR spectroscopy

Abstract

Adsorption, thermal decomposition, and reactivity of NI(CO)/sub 4/ in the cage system of dehydrated zeolite Y has been studied with EXAFS and near-edge spectroscopies, in particular monitoring changes in oxidation states and Ni ligation. Ni(CO)/sub 4/ is adsorbed as an intact molecule in cation-free zeolite Y, LiY, and NaY. Symmetry changes of the molecule in LiY and NaY are assigned to the formation of cation--OC-Ni bridges. Thermal treatment of the Ni(CO)/sub 4/NaY adduct leads to loss of CO concomitant with the formation of a bimodal Ni phase. A major part of the Ni forms small clusters (approximately 0.5 to 1.5 nm), in addition to larger crystallites (5-30 nm), sticking at the outer surface of the zeolite crystals. Oxidation of Ni(CO)/sub 4/NaY to NiONaY with molecular oxygen occurs almost to completion below 295 K. The small NiO particles are stable to sintering up to 670 K. Nickel-phosphineNaY adducts have been prepared by direct adsorption from solution (Ni(CO)/sub 3/PMe/sub 3/, Ni(CO)/sub 2/(PMe/sub 3/)/sub 2/), and by synthesis inside the NaY supercage (Ni(CO)/sub 3/PMe/sub 3/, Ni(CO)/sub 3/(PPh/sub 2/CHMe/sub 2/), Ni(CO)/sub 3/P(tau-Bu)/sub 3/, Ni(PMe/sub 3/)/sub x/). The NaYNi(CO)/sub 3/(PPh/sub 2/CHMe/sub 2/) adduct is a ship-in-a bottle complex, i.e., the Ni complex is too largemore » to exit the zeolite supercage. The substitution of carbonyl ligands by phosphines was monitored in the near-edge and EXAFS modulations as well as with /sup 31/P MAS NMR. EXAFS is an excellent method to monitor ligand coordination and provides information that is complimentary to IR spectroscopy.« less