C–H⋯Au interactions and optical properties of [(P,P)4Au6]2+ molecular gold nanoclusters

Abstract

Two hexagold diphosphine-stabilized [(P,P)₄Au₆]²⁺ molecular nanoclusters with the same [core + exo] arrangement differing in the linker (phenylene or trimethylene) connecting the two P-donor sites have been subjected to theoretical studies with the aim of shedding light on two main questions. On one hand, from a previous study [J. Vícha, C. Foroutan-Nejadand M. Straka,Nat. Commun., 2019, 10, 1643], it is still unclear whether short C–H2⋯Au contacts revealed in the corresponding crystal structures are just forced by bulky P(Ph)₂ groups and, on the other hand, to what extent the linker affects the visible band position [M. A. Bakar, M. Sugiuchi, M. Iwasaki, Y. Shichibuand K. Konishi, Nat. Commun., 2017, 8, 576]. Here, it is demonstrated that even in simpler model systems in which bulky groups were replaced by PH₂ groups, C–H2⋯Au hydrogen bonding interactions are retained and show comparable values, as measured by NBO and QTAIM analyses, to those of 1 and 2. These analyses further confirmed a stronger HB in 1 than in 2. Also, the comparison of model systems without and with a linker connecting the phosphine groups showed a bathochromic shift of 47 and 60 nm, revealing the key role of the linker. The Δρ(r)^EE–GS plots of 1 and 2 revealed electron density depletion in the inter-nuclear C–H2 region upon electronic transition unveiling its contribution to their optical properties.