Synthesis, molecular structure and emission properties of benzoato-bridged lanthanide complexes with hydrotris(pyrazolyl)borate

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Abstract
Reaction of GdCl3 and TbCl3 with one equivalent of the potassium salt of the tridentate ligand hydrotris(pyrazol-1-yl)borate [K(tp)] and two equivalents of sodium p-X-benzoate (X = H, Cl, Br and NO2) yielded the complexes 1–6 of composition [{(tp)Ln(μ-p-X-OBz)2}2] (Ln = Gd, Tb) whereas the reaction of TbCl3 with 2 equivalents of [K(tp)] and one equivalent of sodium azide, gave the tetranuclear complex [{(tp)2Tb(μ-N3)}4] (7). The crystal structures of the benzoate complexes (X = H) of Gd (1) and Tb (2) and their analogous p-Cl-benzoate derivatives with Gd (3) and Tb (4) have been determined. The compounds consist of a seven-coordinate tetrakis carboxylato bridged dimetal unit with two capping hydrotris(pyrazolyl)borate ligands. Unit cell determinations suggested that [{(tp)Tb(μ-p-Cl-OBz)2}2] (5), and [{(tp)Tb(μ-p-NO2-OBz)2}2] (6), are isostructural with (3) and (4). Single crystal X-Ray analysis of (7) revealed its tetranuclear structure comprising a cyclic 16-membered Tb4(μ-N3)4-unit with two hydrotris(pyrazol-1-yl)borate ligands bound to each of the terbium ions resulting in a tetragonal antiprismatic N8-coordination sphere. The luminescence properties of the unsubstituted and para-substituted Gd and Tb benzoate complexes have been studied in solution at room temperature.