Synthesis, structure and gas-phase reactivity of the mixed silver hydride borohydride nanocluster [Ag3(μ3-H)(μ3-BH4)LPh3]BF4 (LPh = bis(diphenylphosphino)methane)

Borohydrides react with silver salts to give products that span multiple scales ranging from discrete mononuclear compounds through to silver nanoparticles and colloids. The cluster cations [Ag₃(H)(BH₄)L₃]⁺ are observed upon electrospray ionization mass spectrometry of solutions containing sodium borohydride, silver(I) tetrafluoroborate and bis(dimethylphosphino)methane (L^Me) or bis(diphenylphosphino)methane (L^Ph). By adding NaBH₄ to an acetonitrile solution of AgBF₄ and L^Ph, cooled to ca. −10 °C, we have been able to isolate the first mixed silver hydride borohydride nanocluster, [Ag₃(μ₃-H)(μ₃-BH₄)L^Ph₃]BF₄, and structurally characterise it via X-ray crystallography. Combined gas-phase experiments (L^Me and L^Ph) and DFT calculations (L^Me) reveal how loss of a ligand from the cationic complexes [Ag₃(H)(BH₄)L₃]⁺ provides a change in geometry that facilitates subsequent loss of BH₃ to produce the dihydride clusters, [Ag₃(H)₂L_n]⁺ (n = 1 and 2). Together with the results of previous studies (Girod et al., Chem. – Eur. J., 2014, 20, 16626), this provides a direct link between mixed silver hydride/borohydride nanoclusters, silver hydride nanoclusters, and silver nanoclusters.