The unusual thermochromic NIR luminescence of Cu(i) clusters: Tuned by Cu-Cu interactions and packing modes

摘要

Two hexanuclear Cu(i) clusters [Cu ~I _3(4-ptt) _3] _2·3DMF·3H _2O (1) and [Cu ~I(4-ptt)] _6·8DMF·7H _2O (2) (4-Hptt = 5-(pyridin-4-yl)-1H-1,2,4-triazole-3-thiol, DMF = N,N-dimethylformamide), were synthesized and characterized. Compounds 1 and 2 with similar coordination environments are isomers, but their detailed structures are different due to the reaction temperature tuning effect. Both 1 and 2 extend from monomers to 3D supramolecules with the help of hydrogen bonding between the triazole and pyridine from the 4-ptt ligands. The Cu _6S _6 units of 1 pack in a polydirectional array, while the Cu _6S _6 units in 2 extend in one direction and link the planes of adjacent ligands to enhance the delocalization of π electrons. Their varied Cu-Cu interactions and individual packing modes cause differences in luminescent and thermostable behaviors. Compound 1 exhibits an unusually long wavelength at about 900 nm and a higher thermal stability; while the emission of 2 splits into two bands (high-energy and low-energy emission bands) as the temperature decreases. Therefore, the emissions of 1 originate from a ~3CC transition, and those of 2 are from a mixture of ~3CC and MLCT.