Lowering the melting point of ZIF via an anion competing effect in MOF hybrid glasses

Abstract

Metal–organic framework (MOF) glasses, as the fourth kind of melt-quenched glass, have attracted considerable attention in gas separation and optical materials. However, the development of MOF glasses is hindered by the limited choices of meltable MOF systems, as most crystalline MOFs decompose before melting at elevated temperatures. Herein, we employ an anion competition strategy to reduce the melting point and successfully prepare bulk MOF glasses with excellent optical properties. When ZIF-62 (Zn) is hybridized with ZnBr₂, competitive coordination between Br⁻ and ligands towards Zn metal nodes can replace the Zn–N bond and facilitate the depolymerization of the Zn–imidazolate network at elevated temperatures. The melting point of ZIF-62 could be significantly lowered from 430 to 145 °C while maintaining a relatively stable state under ambient conditions. The as-obtained ZIF/ZnBr₂ hybrid glass exhibits an ultrahigh glass-forming ability (∼0.94) and high infrared transmittance approaching 60% within the range of 290 nm to 6 µm. The halide-induced eutectic strategy enables the low-temperature processing of molecular hybrid MOF glasses with promising optical performance, expanding the MOF glass family and advancing low-density infrared optics for lightweight sensing and imaging systems.