Synthesis and luminescence studies of lanthanide complexes (Gd, Tb, Dy) with phenyl- and 2-pyridylthiolates supported by a bulky β-diketiminate ligand. Impact of the ligand environment on terbium(iii) emission

The range of lanthanide complexes with bulky N,N '-bis(Dipp)-substituted beta-diketiminate ligand Nacnac(-) = CH(CMe(NDipp))(2)(-) (Dipp = 2,6-diisopropylphenyl) has been expanded to the complexes [Ln(Nacnac)I-2(thf)(n)] (1(Ln), Ln = Gd, Tb, n = 2; Dy, n = 1; thf = tetrahydrofuran). They were further used in salt metathesis reactions with KSPh and KS(2-Py) (2-Py = 2-pyridyl), resulting in thiolato complexes [Ln(Nacnac)(SPh)(2)(thf)] (2(Ln)) and [Ln(Nacnac)(SPy)(2)] (3(Ln)). As an analogue of 2(Tb) without coordinated thf molecules, binuclear complex [{Tb(Nacnac)(SPh)}(2)(mu-SPh)(2)] (4(Tb)) was obtained by reaction of dry TbI3 with K(Nacnac) and KSPh in Et2O followed by recrystallization from toluene. The diiodo complexes possess different numbers of coordinated thf molecules and different coordination polyhedra owing to the lanthanide contraction. On the contrary, all 2(Ln) and 3(Ln) have the same molecular and crystal structures for a given thiolate, owing to the coordination rigidity provided by edge coordination of a Ph cycle or by chelating binding of a S(2-Py)(-) ligand. UV-vis and photoluminescence spectra were registered for all compounds. A triplet level of the Nacnac(-) ligand of 2.22 x 10(4) cm(-1) was determined from the solid-state emission of Gd complex 1(Gd) at 77 K; the triplet level in 2(Gd) and 3(Gd) was found at 2.16 x 10(4) cm(-1). Emission lifetimes and quantum yields were measured for all Tb compounds with the highest values for thiolato complexes 2(Tb) and 3(Tb), while 1(Tb) showed only weak emission. The relationship of the emission properties with the molecular and crystal structures is discussed, and better antenna properties are proposed for thiolato rather than for Nacnac(-) ligands.