Modular assembly of Co4-thiacalix[4]arene units and Keggin-type SiW12O40for 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-SiW12and Co8-SiW12, were structurally characterized by single-crystal X-ray diffraction. The Co4-SiW12is a supramolecular structure involving cation–anion interactions between Co4-TC4A PSBUs and SiW12. Co8-SiW12features “barbell-like” shapes with two Co4-TC4A coordinatively linked to a Keggin-type SiW12unit on opposite via W−Ot−Co bonds. The coordination of Co4-TC4A to SiW12in Co8-SiW12resulted in significantly improved photothermal conversion performances compared with Co4-SiW12and pure SiW12or 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.