An ultra-stable Cu I12 cluster built from a Cu I6 precursor sandwiched by two Cu I3-thiacalixarene units for efficient photothermal conversion

Abstract

We report the synthesis, crystal structure, optical properties, and photothermal conversion properties of an ultra-stable cuprous Cu₁₂ cluster, namely {[Cu^I₃(HTC4A)]₂[Cu^I₆(2-PyS)₆]}·H₂O (Cu₁₂, H₄TC4A = p-tert-butylthiacalix[4]arene, 2-PySH = 2-pyridinethiol), which was built from a pre-synthesized Cu^I₆(2-PyS)₆ (Cu₆) precursor and two Cu^I₃-HTC4A polynuclear secondary building units (PSBUs). The Cu₁₂ cluster features a sandwich-like framework in which the Cu₆ core is double surface capped by forming six Cu–S bonds with two Cu^I₃-HTC4A PSBUs. The “cluster–cluster” assembly strategy enables all the metal centers in the Cu₁₂ cluster to be monovalent and efficient organic ligand protection makes the cuprous cluster stable in common solvents (alcohol, acetonitrile, acetone, CHCl₃, N N-dimethylacetamide, etc.) as well as in strong acids (pH = 1) or bases (pH = 14). Band gap determination and photophysical analysis combined with density functional theory (DFT) calculations indicated that Cu^I₃-HTC4A PSBUs can tune the electron and hole distribution of the Cu₆ core, which makes Cu₁₂ a stable and efficient photothermal conversion material both in the solid state and in water/N,N-dimethylformamide solvents.