Gas-Phase Model Studies Relevant to the Decomposition of Transition-Metal Nitrates M(NO3)2 (M =Co, Ni) into Metal-Oxo Species

Electrospray ionization (ESI) of aqueous cobalt(II) and nickel(II) nitrate solutions inter alia affords the solvated, mono- and oligonuclear nitrato complexes [M-m(NO3)(2m-1)(H2O)(n)](+) (M = Co, Ni; m = 1-5; n = 1-4). The collision-induced dissociation spectra of the mass-selected ions imply that these ions correspond to genuine hydrated metal(II) nitrato complexes in that either cluster degradation through expulsion of neutral M(NO3)(2) or sequential loss of water ligands take place. In the case of the lowest member of the series (in, n = 1), however, loss of water competes with homolytic cleavage of the N-O bond, which leads to the formation of [M,O-2,H-2](+) cations containing formal M-III. For m > 1, similar activation of the nitrato ligand was observed under harsher ionization conditions in ESI and provides access to cationic transition-metal oxide clusters in the gas phase. In addition to the collision experiments, thermal reactions of the solvated nitrato complexes with nitrogen monoxide reveal bond-activation pathways, which shed some light on the NO-assisted pyrolysis of solid metal nitrates for the preparation of metal oxide catalysts. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)