Crystal structure of a gadolinium(III) complex of tripodal tris(((5-chlorosalicylidene)amino)ethyl)amine.

part from their potential applications as magnetic and/or optical probes. There is now a substantial number of lanthanide complexes known to have a coordination number of seven. Nearly all of them have the basic formulation [Ln(bidentate)3(unidentate)]. On the contrary, structurally characterized examples of a heptadentate ligand coordinating one metal ion are rare. Tris(2-aminoethyl)amine (tren) condenses with salicylaldehyde or its substituted analogs in a 1:3 molar ratio to form Schiff-bases which are potentially tribasic heptadentate ligands.1 Heptadentate ligands, tris(((5-chlorosalicylidene)amino)ethyl)amine (H3L) and tris(((salicylidene)amino)ethyl)amine (H3L′), are condensation products of tren with 3 equivalents of salicylaldehyde or its 5-substituted derivative. We have reported lanthanide complexes of the tripodal heptadentate ligands, H3L and H3L′. An X-ray crystallographic analysis revealed that these are examples of heptadentate complexes in which all of the N4O3 donor atoms coordinate to the central metal ions. Here, we report on the crystal structure of the title compound (Fig. 1) based on an Xray structural analysis. Preparation: The gadolinium complex was prepared by the following two different methods. To a hot solution of tris(((5chlorosalicylidene)amino)ethyl)amine (0.56 g, 1 mmol) in methanol (350 cm3) was added Gd(CF3SO3)3 (0.60 g, 1 mmol) and tren (0.15 g, 1 mmol) in hot methanol (50 cm3) and refluxed for 10 min. A pale-yellow crystalline solid was precipitated upon cooling for 6 h. The product was filtered off, washed with methanol, and dried under vacuum to yield 0.41 g (57.3%). IR (KBr) 2919, 2854, 1627, 1528, 1464, 1389, 1323, 1173, 1129, 1088, 1036, 831, 799, 706, 648 cm–1. Anal. Calcd for C27H24Cl3GdN4O3: C, 45.28; H, 3.38; N, 7.82; Cl, 14.85%. Found: C, 44.99; H, 3.28; N, 7.57; Cl, 14.78%. Tren (8 mmol) was added to a solution of Gd(CF3SO3)3 (4 mmol) in hot methanol (70 cm3) and refluxed for 10 min. Then, 5-chlorosalicylaldehyde (12 mmol) in methanol (30 cm3) was added to this solution and refluxed for 2 min. A pale-yellow crystalline solid was precipitated upon cooling for 6 h. The product was clarified by filtration. After the mother liquors were cooled for 7 d, single crystals suitable for single-crystal Xray diffraction were obtained. Yield: 1.85 g (64.6%). The complex gave an IR band at 1627 cm–1 due to C=N stretching vibration, but no bands corresponding to a primary amine nor to a trifluoromethanesulfonate anion were observed. Since the complex does not contain a counter anion, the ligand 1359 ANALYTICAL SCIENCES NOVEMBER 2001, VOL. 17 2001 © The Japan Society for Analytical Chemistry