Thermotropic Structure Phase Transitions and Two Types of Thermochromic Behaviors in a Bromoargentate Cluster [Pr-dabco]₂Ag₄Br₆

Abstract

Organic−inorganic silver halide hybrids show abundant phase transitions and thermochromism. However, it is very rare that silver halides exhibit thermochromism related to thermotropic structure phase transition. Herein, a bromoargentate hybrid, [Pr-dabco] 2 Ag 4 Br 6 (1) (Pr-dabco + = 1-propyl-1,4diazabicyclo-[2.2.2]octan-1-ium), with tetranuclear [Ag 4 Br 6 ] 2− clusters was prepared and characterized by microanalysis, ultraviolet−visible (UV−vis) diffuse reflectance spectroscopy, and thermogravimetric (TG) and differential scanning calorimetry (DSC) techniques. Interestingly, 1 undergoes an irreversible structure phase transition at ∼436 K in the first heating process, which is accompanied by an abrupt color change from colorless to yellow; however, a reversible color change between pale yellow and yellow is observed in the next heating−cooling cycles. Notably, DSC measurement revealed that a reversible phase transition is associated with the change in color between pale yellow and yellow, while the powder X-ray diffraction (PXRD) patterns corresponding to pale yellow and yellow phases are quite similar to each other. These observations demonstrate that thermochromism in the next heating−cooling runs is associated with a reversible structure phase transition, which perhaps concerns the disorder−order transformation of alkyl chains in the cationic ligand [Pr-dabco] + , and relevant to the anharmonic fluctuations of the Ag−Br and Ag−N bonds, a strong electron−phonon coupling effect is seen within the bromoargentate cluster.

Bromoargentate/g-C3N4 heterojunction by in situ growth: 2-D bromoargentate framework with a transition metal complex linker and cocatalyst for enhanced photocatalytic activity via g-C3N4 hybrid

“…9 A large number of iodoargentate hybrids with different compositions and structures have been prepared using organic cations, transition metal (TM), and lanthanide (Ln) metal complex cations as counter cations or structural directing agents. 10–12 However, the photocatalytic activity and stability of the iodoargentate hybrid materials need to be enhanced for the purpose of application.…”