Heteroleptic Phenanthroline Complexes of Trinuclear Molybdenum Clusters with Luminescent Properties

Neutral Mo3(μ3-S)(μ-S2)3X3(diimine) (X = Cl–, Br–) heteroleptic cluster complexes containing the 1,10-phenanthroline ligands 1H-imidazo[4,5-f][1,10]phenanthroline-2-[3,4-bis(dodecyloxy)phenyl] (IPDOP), 4,7-diphenyl-1,10-phenanthroline (BPhen), and 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) were prepared in high yields by straightforward ligand-substitution reactions starting from the [Mo3(μ3-S)(μ-S2)3X6]2– cluster anion. The complexes Mo3S7X4(BPhen) [X = Br– (for 3) and Cl– (for 4)] and Mo3S7X4(tmpphen) [X = Br– (for 5) and Cl– (for 6)] crystallized as tetra-n-butylammonium salts of anionic aggregates (3–6·X)–, in which neutral Mo3S7X3(diiimine)3 cluster molecules participate in non-valence interactions between the axial sulfur atoms, Sax, and a halide anion. The complexes Mo3S7Br4(IPDOP) (1) and Mo3S7Cl4(IPDOP) (2) are luminescent when excited at 330 nm and have maximum emission intensities around 450 nm in DMF and around 435 nm in dichloromethane. The maximum fluorescence quantum yield and the maximum emission lifetime were achieved for complex 2 in DMF(φF = 0.15 and τ = 7.5 ns, respectively). The most important property of complexes 1 and 2 is the shift of their emission spectra in the presence of proton-abstractor anions, such as F–, OH–, and AcO–. When these anions are added to solutions of complexes 1 or 2 in DMF or dichloromethane, the maximum emission wavelength shifts by approximately 90 nm to higher wavelengths