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.

The main categories of transition metal–mercury heterometallic compounds are briefly summarized. The attention is focused on complexes and clusters where the {Hg-Y} fragment, where Y represents a halide atom, interacts with transition metals. Most of the structurally characterized derivatives are organometallic compounds where the transition metals belong to the Groups 6, 8, 9 and 10. More than one {Hg-Y} group can be present in the same compound, interacting with the same or with different transition metals. The main synthetic strategies are discussed, and structural data of representative compounds are reported. According to the isolobality with hydrogen, {Hg-Y} can form from one to three M-{Hg-Y} bonds, but further interactions can be present, such as mercurophilic and Hg···halide contacts. The formal oxidation state of mercury is sometimes ambiguous and thus {Hg-Y} can be considered as a Lewis acid or base on varying the transition metal fragment. Density functional theory calculations on selected Group 6 and Group 9 model compounds are provided in order to shed light on this aspect.