The formation, reactions and structures of binary cobalt phosphide clusters [CoxPy](-) in the gas phase

Laser ablation of CoP generated 152 binary anionic cobalt phosphide cluster s [CoxPy](-), ranging up to [Co25P16](-). This is a more extensive set of [ CoxPy](-) clusters than obtained in previous laser ablation of a mixture of Co metal and red phosphorus: the composition maps for the two experiments overlap, but with generally lesser y:x ratios for laser ablation of CoP. Th e reactivities, reactions, and collisional dissociation of selected ions ha ve been investigated by Fourier transform ion cyclotron resonance mass spec trometry. The majority of the [CoxPy](-) ions react with H2S by addition of (up to three) S atoms, substitution of P-2 by S, and with elimination of H P2-. Reaction with NO2 or N2O causes addition of one O atom. Collisional ac tivation causes dissociation of P-2, P-4, CoP2 or CoP4. The ions [CoP8](-), [Co4P8](-), [Co5P9](-) and [Co6P10](-) are unreactive, and for these and t he reactive [Co4P4](-) ion, density functional investigations of 30 postula ted structures have been performed. The probable structures, calculated ele ctron affinities, and electronic structures are reported. The structural pr inciples evident so far are that P atoms, P-2 groups, and P-3 groups bridge the faces, and to a lesser extent the edges, of Co-x polyhedra. The lack o f reactivity for relatively P-rich clusters correlates with the absence of co-ordinatively unsaturated metal sites on the clusters: it is postulated t hat the more reactive species undergo addition at under-co-ordinated Co ato ms. The calculated electronic structures generally have close-lying electro nic states with unpaired electrons, which explains the overall high reactiv ity of the [CoxPy](-) clusters. The structural differences between these [C oxPy](-) clusters and characterised molecules CoxPyLz with ancillary ligand s are discussed, as are possible applications of the new [CoxPy](-) cluster s in synthesis of novel materials.