Hydrogen Bond-Driven Displacive Phase Transition and the Abrupt Optical/Magnetic Behavior in One-Dimensional Mn(II) Chloride Hybrid

摘要

Much efforts have been devoted to the research of hydrogen bonds (H-bonds) in metal halide hybrids for intriguing applications in optoelectronic devices, which plays a vital role in regulating structures and properties. Yet its temperature-dependent variation and the resulting magnetic/optical behavior have been barely investigated, especially for Mn-(II) halide hybrids with spin-related magnetism and photoluminescence (PL). This study focuses on C5H6NMnCl3 center dot H2O with plenty of H-bonds. The enhanced H-bond interaction between pyridine rings and one-dimensional (1D) chain of Mn-(Cl/O)(6) octahedra along the c-axis (negative thermal expansion of lattice) results in a displacive phase transition when elevating temperature. The resulting more rigid lattice can efficiently suppress the vibration or rotation of pyridine rings and the nonradiative transition rate. It is also found that the ferromagnetic (FM) interaction between Mn2+ and Mn2+ does not cause significantly shortened decay lifetime of Mn2+ emission as strong antiferromagnetic (AFM) interaction usually does. When angle Mn-Cl-Mn in edged-shared octahedra deviates from 90 degrees at elevated temperature, AFM becomes dominant over the FM interaction. Slightly varied temperature-dependent distance between Mn2+ and Mn2+ with AFM coupling likely leads to negligible thermal quenching. Thus, significant antithermal quenching of PL is achieved. This study sheds light on the relation of structure-properties concerning H-bond variation and helps design high-performance luminescent materials for optoelectronic devices.

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