Luminescent Manganese(II) Iminophosphorane Derivatives

The reaction between the iminophosphorane ligand N-phenyl-1,1,1-triphenylphosphanimine (NPh=PPh3) and anhydrous manganese(II) halides allowed the isolation of complexes with the general formula [MnX2(NPh=PPh3)2] (X = Cl, Br, I). The compounds showed luminescence in the green region attributed to the 4T1(4G)→6A1(6S) transition of the metal centre in the tetrahedral field, which was superimposed in the cases of X = Cl and X = Br on weak ligand-centred fluorescence. The emission and excitation spectra were compared with those of the free ligand and of the related zinc(II) bromo-complex. DFT calculations on the free ligand and on the manganese(II) bromo-complex helped to rationalise the experimental data. The protonation of NPh=PPh3 led to the formation of the iminium cation [NHPh=PPh3]+, which was used as a building block for the synthesis of organic–inorganic hybrids with the general formula [NHPh=PPh3]2[MnX4] (X = Cl, Br, I). The crystal structure of [NHPh=PPh3]2[MnBr4] was determined by means of X-ray diffraction. Green photoluminescence associated with the metal-centred transition was also observed for the organic–inorganic hybrids, with higher quantum yields with respect to the neutral [MnX2(NPh=PPh3)2] complexes. In the case of X = I, luminescence from the cation was superimposed on that from the tetraiodomanganate anion upon excitation of the compound with near–UV light.