Synthesis and Study of Photothermal Properties of a Mixed-Valence Nanocluster Cu I /Cu II with Strong near-Infrared Optical Absorption Supported by 4- tert -Butylcalix[4]arene Ligand.

The first mixed-valence nanocluster Cu I /Cu II with the highest percentage of Cu II ions was synthesized by using 4- tert -butylcalix[4]arene (Calix4), with the formula DMF 2 ⊂[(CO 3 ) 2- @Cu II 6 Cu I 3 (Calix4) 3 Cl 2 (DMF) 5 (H 3 O)]•DMF ( 1 ), as a photothermal nanocluster. Its structure was characterized using single-crystal X-ray diffraction, Fourier-transform infrared spectroscopy, and powder X-ray diffraction. In addition, the charge state and chemical composition of the nanocluster were determined using electrospray ionization spectrometry and X-ray photoelectron spectroscopy (XPS) spectrum. The results of the XPS and X-ray crystallography revealed that there are two independent Cu II and Cu I centers in nanocluster 1 with the relative abundances of 66.6 and 33.3% for Cu II and Cu I , respectively. The nanocluster contains three four-coordinated Cu I ions with a square-planar geometry and six five-coordinated Cu II ions with a square pyramid geometry. The nanocluster shows strong near-infrared optical absorption in the solid state and excellent photothermal conversion ability (the equilibrium temperature ∼78.2 °C) with the light absorption centers in 286-917 nm over previous reported pentanucleus Cu I 4 Cu II clusters and Cu II compounds.