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 (HmbtCl2) 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.