Thermal Property Engineering in Mn‐Based Hybrid Halides via Structural Tailoring of Phosphonium Cations

Organic–inorganic hybrid metal halide (OIMH) glasses have emerged as promising scintillator materials, distinguished by their exceptional optical transparency, straightforward synthesis, and tunable thermodynamic properties. The manufacturability and functional characteristics of these glasses are synergistically governed by the melting temperature ( T m ), glass transition temperature ( T g ), and decomposition temperature ( T d ), which can be effectively regulated through rational structural modulation. In this study, monophosphonium salts functionalized with secondary ammonium groups (─NH 2 + R) are prepared. By utilizing strategies such as carbon chain extension, branching increase, and structural isomerization, a series of Mn‐based OIMHs with tunable T m (110.0–256.6 °C) and T g (78.7–101.7 °C) are successfully constructed. To probe into the structure‐performance relationship, differential scanning calorimetry analysis and density functional theory calculations are conducted. Notably, the (4‐BATBP)MnBr 4 ·2H 2 O crystal (4‐BATBP 2+ = 4‐( n ‐butylamino)butyltriphenylphosphonium) exhibits the highest glass‐forming ability (GFA, T g /T m = 0.92). The corresponding (4‐BATBP)MnBr 4 glass scintillator demonstrates an impressive spatial resolution of 20–25 lp mm −1 under X‐ray irradiation and retains excellent stability after prolonged heat treatment at 65 °C for 130 days, underscoring its significant potential for high‐temperature X‐ray imaging applications.