Synthesis, crystal structure and green luminescence of a novel manganese(II)-based hybrid: bis[(tert-butoxycarbonyl)methyltriphenylphosphonium] tetrachloridomanganate(II).

The title novel phosphonium-based manganese(II) hybrid crystal, {(C24H26O2P)2[MnCl4]}n or (TBTP)2[MnCl4], was synthesized via slow evaporation. Single-crystal X-ray diffraction reveals that it crystallizes in the monoclinic space group P21/n, featuring discrete slightly distorted tetrahedral [MnCl4]2- anions and bulky (TBTP)+ cations [(TBTP)+ is (tert-butoxycarbonyl)methyltriphenylphosphonium] with weak C-H...Cl interactions. The material exhibits green luminescence centred at 515 nm with a millisecond-scale lifetime (2.83 ms), which is unequivocally assigned to the long-lived spin-forbidden Mn2+ 4T1→6A1 d-d transition. Electronic structure calculations reveal a direct band gap (with the noted underestimation typical of the PBE functional) and, more importantly, a clear spatial separation of the frontier orbitals between the inorganic and organic components. This orbital separation, likely aiding in the isolation of the luminescent [MnCl4]2- centres, is consistent with the observed long emission lifetime. This work enriches the family of phosphonium-based hybrid metal halides and provides insights into the structure-property relationships governing Mn2+ emission in such systems.