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 clusters [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. The reactivities, reactions, and collisional dissociation of selected ions have been investigated by Fourier transform ion cyclotron resonance mass spectrometry. 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 HP2-. Reaction with NO2 or N2O causes addition of one O atom. Collisional activation causes dissociation of P-2, P-4, CoP2 or CoP4. The ions [CoP8](-), [Co4P8](-), [Co5P9](-) and [Co6P10](-) are unreactive, and for these and the reactive [Co4P4](-) ion, density functional investigations of 30 postulated structures have been performed. The probable structures, calculated electron affinities, and electronic structures are reported. The structural principles 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 of reactivity for relatively P-rich clusters correlates with the absence of co-ordinatively unsaturated metal sites on the clusters: it is postulated that the more reactive species undergo addition at under-co-ordinated Co atoms. The calculated electronic structures generally have close-lying electronic states with unpaired electrons, which explains the overall high reactivity of the [CoxPy](-) clusters. The structural differences between these [CoxPy](-) clusters and characterised molecules CoxPyLz with ancillary ligands are discussed, as are possible applications of the new [CoxPy](-) clusters in synthesis of novel materials.