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(mu-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)(2)Tb(mu-N- 3)}(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(mu-p-Cl-OBZ)(2)}(2)] (5), and [{(tp)Tb(mu-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 Tb-4(mu- N-3)(4)-unit with two hydrotris(pyrazol-1-yl)borate ligands bound to each of the terbium ions resulting in a tetragonal antiprismatic N-8-coordination sphere. The luminescence properties of the unsubstituted and para-substituted Gd and Tb benzoate complexes have been studied in solution at room temperature

The solution studies of some binary (1:1) and ternary (1:1:1) complexes of Eu(III), Gd(III), and Tb(III) with benzoic acid/its derivatives and uracil/its halo derivatives in dioxane−water (30:70 v/v) medium (ionic strength I = 0.1 mol·dm-3 NaNO3) have been performed. The experimental pH titration data were analyzed with the help of the BEST computer program in order to evaluate the formation constants of various intermediate species formed. The stability constants of the binary (1:1) systems decrease in order of Tb(III) > Eu(III) > Gd(III). The formation constant of 1:1:1 mixed ligand complexes for Eu(III), Gd(III), and Tb(III) with benzoic acid/its derivatives as the primary ligand and uracil/its halo derivatives as the secondary ligand has also been studied. The available data suggested that the ternary complexes of Eu(III), Gd(III), and Tb(III) are more stable than the crossponding binary complexes.