Structure, photophysical properties and paramagnetic broadening in (2-Methylbenzimidazolium)MnCl₃.2H₂O

A new organic-inorganic hybrid compound (C₈H₉N₂)MnCl₃.2H₂O crystallized in monoclinic P2₁/c structure where Mn²⁺ ion is coordinated octahedrally by five Cl^- ions and one H₂O molecule and forms 1D chain by edge-sharing with the neighbouring Manganese octahedra. Upon UV light excitation, it displays intense red emission with an asymmetric broadening around 685 nm can be due to Mn-Mn magnetic coupling. Hitherto, it is believed that the asymmetric broadening at the longer red region can result from Mn-Mn ferromagnetic coupling. But our magnetic measurement confirms the paramagnetic nature of the compound and rules out the possibility of ferromagnetic interaction. The decay curves at different temperatures show biexponential decay nature where one decay component initially increases and later decreases with increasing temperature but the other decay component monotonously increases. So, it can be confirmed that the later component results from Mn-Mn coupled state since at low temperature, enhanced magnetic interaction causes quenching of emission, hence least τ₂ at 15 K. Therefore, our study reveals, not only ferromagnetic but also paramagnetic materials can exhibit longer red emission due to short-range interaction between Mn²⁺ ions and broadens the emission spectra.