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

Abstract

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 P2 by S, and with elimination of HP2−. Reaction with NO2 or N2O causes addition of one O atom. Collisional activation causes dissociation of P2, P4, 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, P2 groups, and P3 groups bridge the faces, and to a lesser extent the edges, of Cox 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.