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

Abstract

The range of lanthanide complexes with bulky N,N′-bis(Dipp)-substituted β-diketiminate ligand Nacnac⁻ = CH(CMe(NDipp))₂⁻ (Dipp = 2,6-diisopropylphenyl) has been expanded to the complexes [Ln(Nacnac)I₂(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(μ-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 × 10⁴ 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 × 10⁴ 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.