Synthesis and photophysical properties of rare earth (La, Nd, Gd, Y, Ho) complexes with silanediamido ligands bearing a chelating phenylbenzothiazole chromophore

Abstract

A new silanediamide ligand bearing 2-phenylbenzothiazole (Pbt) chromophore groups SiMe2(HNPbt)₂ (1^H) was synthesized and introduced in lanthanide complexes. It was found that independent of the stoichiometry of the salt metathesis reaction, salts SiMe₂(ANPbt)₂ (A = Li, K) reacts with LnX₃ (X = Cl, I) to give bis–ligand anionic complexes [Ln(SiMe2(NPbt)₂)₂]⁻ (Ln = La, Nd, Gd, Y) with alkali metal counter-cations for larger lanthanides. For smaller Ho, the complex [Ho(SiMe₂(NPbt)₂)Cl₂Li(thf)₂]^∞ was obtained. The molecular structures were determined by X-ray diffraction and show enveloping of the chelating N–Pbt fragments around the central atom in bis–ligand complexes with notable π-interactions between the flat cycles. For silanediamine, alkali metal salts, and lanthanide complexes the photophysical properties were studied. The ligand triplet state energy was estimated by the measurement of the Gd complex [K(thf)_n][Gd(SiMe₂(NPbt)₂)₂] (2^Gd) emission at 77 K. Although the energy appeared sufficient for NIR emitter (Nd³⁺, Ho³⁺) sensitization, only intraligand emission was observed for them.