Synthetic methodology, structures and properties of mixed valence copper(I/II) complexes with various Schiff bases and their reduced analogues

Synthesis and Study of Photothermal Properties of a Mixed-Valence Nanocluster CuI/CuII 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 DMF₂⊂[(CO₃)^2-@Cu^II₆Cu^I₃(Calix4)₃Cl₂(DMF)₅(H₃O)]•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^I₄Cu^II clusters and Cu^II compounds.

Construction of eight mixed-valence pentanuclear CuI4CuII clusters using ligands with inhomogeneous electron density distribution: synthesis, characterization and photothermal properties

To enhance light absorption in the visible region for the utilization of sunlight, eight mixed-valence polynuclear Cu^I/Cu^II clusters have been synthesized for evaluating their photothermal conversion performance. They are fabricated considering the ligand's electron density distribution inhomogeneity using 1,2,3-triazole (3N) or tetrazole (4N) and different mono-phosphine ligands. We report here the synthesis, crystal structure, characterization, optical properties, and photothermal conversion performance of these clusters. X-ray crystal structures reveal that those pentanuclear clusters are neutral clusters with octahedrally-coordinated copper(II) ion being surrounded by four tetrahedrally coordinated copper(I) ions. Interestingly, with the introduction of the mixed-valence centers, these compounds show additional light absorption centers in 350-600 nm via the IVCT transition mechanism, compared with our previously reported Cu(II) compounds. These clusters show excellent photothermal conversion performance, with an average equilibrium temperature (∼60 °C) and a temperature increment (∼40 °C), which are also superior to Cu(II) complexes (the average equilibrium temperature ∼55 °C). This work proves that it is possible to design and prepare new polynuclear mixed-valence Cu^I/Cu^II clusters for achieving high-performance photothermal conversion materials.