Structural Insights into AgBi(SC sub(12)H sub(25))sub(4) Mixed-Metal n-Alkanethiolate: Heterometallic Thiolate Bridging and Metallophilic Interaction-Directed Self-Assembly

Abstract

Long-chain metal n-alkanethiolates (MTs) are inorganic-organic hybrid materials, characterized by a metal-sulfur inorganic central plane sandwiched between hydrocarbon bilayers. Though MTs are known for over a century now, their crystal structures are conclusively established only recently. Mixed-metal thiolates (MMTs) are structurally similar to MTs and contain heterometals in the inorganic plane. With a very limited number of MMTs explored to date, their structures remain completely unknown. Here we report the synthesis and structural elucidation of a mixed-metal thiolate, AgBi(SC sub(12)H sub(25))sub(4), providing direct insight into heterometal arrangement by combining X-ray absorption fine structure spectroscopy and density functional theory calculations. The results establish that the AgBi MMT contains discrete molecular units like [RS-Ag-SR-Bi(SR) sub(2)] containing both Ag and Bi metals with an intramolecular heterometallic Mu sub(2)-thiolate bridging. The units further share strong intermolecular Ag...Bi metallophilic interactions at a very short distance of 2.72 angstrom, playing a crucial role in the self-assembly. Intermolecular metal-to-metal charge transfer occurring both directly and via the thiolate bridge gives rise to the absorption maxima observed in the UV-Vis spectrum. The intermolecular interactions predominantly arise from the thiolate group (RS-) of one unit interacting with the Ag sup(+) and Bi sup(3+) centers of the adjacent units, in addition to the Ag...Bi metallophilic interaction.