Gas-phase VUV photoionisation and photofragmentation of the silver deuteride nanocluster [Ag10D8L6]2+ (L = bis(diphenylphosphino)methane). A joint experimental and theoretical study

Abstract

The bis(diphenylphosphino)methane (L = Ph₂PCH₂PPh₂) ligated silver deuteride nanocluster dication, [Ag₁₀D₈L₆]²⁺, has been synthesised in the condensed phase via the reaction of bis(diphenylphosphino)methane, silver nitrate and sodium borodeuteride in the methanol : chloroform (1 : 1) mixed solvent system. The photoionisation and photofragmentation of this mass-selected cluster were studied using a linear ion trap coupled to the DESIRS VUV beamline of the SOLEIL Synchrotron. At 15.5 eV the main ionic products observed are [Ag₁₀D₈L₅]²⁺, [Ag₁₀D₈L₄]²⁺, [Ag₁₀D₈L₆]³⁺˙, [Ag₉D₈L₄]²⁺˙, and [AgL₂]⁺. The later two products arise from fragmentation of [Ag₁₀D₈L₆]³⁺˙. An analysis of the yields of these product ions as a function of the photon energy reveals the onset for the formation of [AgL₂]⁺ and [Ag₉D₈L₄]²⁺˙ is around 2 eV higher than that for ionisation to produce [Ag₁₀D₈L₅]³⁺˙. The onset of ionisation energy of [Ag₁₀D₈L₆]²⁺ was determined to be 9.3 ± 0.3 eV from a fit of the yield of the product ion, [Ag₁₀D₈L₆]³⁺˙, as a function of the VUV photon energy. DFT calculations at the RI-PBE/RECP-def2-SVP level of theory were carried out to search for a possible structure of the cluster and to estimate its vertical and adiabatic ionisation energies. The calculated lowest energy structure of the [Ag₁₀D₈L₆]²⁺ nanocluster contains a symmetrical bicapped square antiprism as a silver core in which hydrides are located as a mix of triangular faces and edges. Four of the bisphosphines bind to the edges of the cluster core as bidentate ligands, the remaining two bisphosphines bind via a single phosphorus donor atom to each of the apical silver atoms. The DFT calculated adiabatic ionisation energy for this structure is 8.54 eV, in satisfactory agreement with experiment.