Modular assembly of Co₄-thiacalix[4]arene units and Keggin-type SiW₁₂O₄₀ for visible-light photothermal conversion

The construction of metal–organic coordination clusters (MCCs) using modular secondary building units is an important method for preparing functional materials. In this study, two new MCCs modularly assembled from Keggin-type {SiW₁₂O₄₀} H₄TC₄A = p-tert-Butylthiacalix[4]arene (SiW₁₂) units and thiacalixarene-supported Co₄‑thiacalix[4]arene （Co₄-TC4A polynuclear second-building units (PSBUs, H₄TC4A = p-tert-Butylthiacalix[4]arene) are presented. The two MCCs, abbreviated as Co₄-SiW₁₂ and Co₈-SiW₁₂, were structurally characterized by single-crystal X-ray diffraction. The Co₄-SiW₁₂ is a supramolecular structure involving cation–anion interactions between Co₄-TC4A PSBUs and SiW₁₂. Co₈-SiW₁₂ features “barbell-like” shapes with two Co₄-TC4A coordinatively linked to a Keggin-type SiW₁₂ unit on opposite via W−O_t−Co bonds. The coordination of Co₄-TC4A to SiW₁₂ in Co₈-SiW₁₂ resulted in significantly improved photothermal conversion performances compared with Co₄-SiW₁₂ and pure SiW₁₂ or H₄TC4A. Band-gap determination and photophysical analysis combined with density functional theory calculations indicated the binding mode between Co₄-TC4A PSBUs and SiW₁₂, which considerably influences the way of electron transport and the conversion ability of visible light to heat.