Structural and Luminescent Features of Lanthanide Ate Complexes with Polychlorinated 2-Mercaptobenzothiazolate Ligands

Partially and fully chlorinated 2-mercaptobenzothiazoles, namely 5,6-dichloro-1,3-benzothiazol-2(3H)-thione (Hmbt^Cl2) and 4,5,6,7-tetrachloro-1,3-benzothiazol-2(3H)-thione (Hmbt^Cl4), were utilized as sensitizers for lanthanide luminescence. Lanthanide ate complexes 1–6, having the general formula [Na(DME)₃]⁺[Ln(mbt^Cln)₄]⁻ (1: Ln = Nd, n = 2; 2: Ln = Gd, n = 2; 3: Ln = Tb, n = 2; 4: Ln = Nd, n = 4; 5: Ln = Gd, n = 4; and 6: Ln = Tb, n = 4), were synthesized using a convenient one-pot route, which included the interaction of the respective thiones with lanthanide and sodium silylamides. X-ray studies of complexes 1, 3, 4, and 6 revealed the difference in the coordinating fashion of the ionic lanthanide complexes with the mbt^Cl2 and mbt^Cl4 ligands. Furthermore, the electron density topologies for complexes 1, 3, 4, and 6 were investigated. The triplet levels of the mbt^Cl2 and mbt^Cl4 ligands, which were obtained from the phosphorescence spectra of the Gd complexes 2 and 5, lie at 21 800 and 19 400 cm^–1 respectively. In complexes 1, 3, and 4, mbt^Cl2 and mbt^Cl4 act as antenna ligands, sensitizing the visible f–f photoluminescence of Tb³⁺ and the near-infrared photoluminescence of Nd³⁺. In the case of the Nd complex 4, the intensity of the metal-centered luminescence is enhanced because of the optimal triplet level energy of mbt^Cl4, the efficient shielding from C–H quenchers, and the low symmetry of the ion environment.