A family of brightly emissive homo- and mixed-halomanganates(II): The effect of halide on optical and magnetic properties

A series of homo- and mixed-halide Mn(II) complexes of (MMTP)2[MnX4] [X = I, Br, Cl; MMTP is 1-methyl-2-(methylthio)pyridin-1-ium] and (MMTP)2[MnI2X2] types [X = Br, Cl] has been synthesized and studied in terms of photoluminescent and EPR spectroscopies. At ambient temperature, the complexes obtained in the solid state exhibit an bright green phosphorescence stemmed from the Mn(II)-centered d-d transitions (4T1 → 6A1). The homohalide complexes, (MMTP)2[MnX4], have a quantum yield of luminescence (and lifetime) of 83% (38 μs), 100% (270 μs), and 44% (2850 μs) at 300 K for X = I, Br, and Cl, respectively. Owing to iodide-enhanced spin-orbital coupling in [MnI2X2]2- anion, the phosphorescence quantum efficiency increases and is close to unity; whereas lifetime significantly decreases and is unusually short (54–64 μs). Except for (MMTP)2[MnCl4], the EPR spectra of the obtained complexes are characterized by the significant deviation of the g-factor from the ge free-electron value and by the high value of the zero-field splitting parameters on account of the spin-orbit coupling. The correlations between the luminescence and magnetic properties of the title complexes are discussed.