Lanthanide Podates with Predetermined Structural and Photophysical Properties: Strongly Luminescent Self-Assembled Heterodinuclear d-f Complexes with a Segmental Ligand Containing Heterocyclic Imines and Carboxamide Binding Units Claude Piguet,* ,† Jean-Claude G. Bu 1 nzli,* ,‡ Ge ´ rald Bernardinelli, § Ge ´ rard Hopfgartner, ⊥ Ste ´ phane Petoud, ‡ and Olivier Schaad | Contribution from the Department of Inorganic, Analytical and Applied Chemistry, the Laboratory of X-ray Crystallography, and the Department of Biochemistry, UniVersity of GeneVa, CH-1211 GeneVa 4, Switzerland, the Institute of Analytical and Inorganic Chemistry, UniVersity of Lausanne, CH-1015 Lausanne, Switzerland, and Pharma DiVision, F. Hoffmann-La Roche Ltd., CH-4002 Basel, Switzerland ReceiVed December 11, 1995 X Abstract: The segmental ligand 2-{6-[N,N-diethylcarbamoyl]pyridin-2-yl}-1,1′-dimethyl-5,5′-methylene-2′-(5- methylpyridin-2-yl)bis[1H-benzimidazole] (L 2 ) reacts with stoichiometric amounts of Ln(III) (Ln ) La-Nd, Sm- Tb, Tm-Lu, Y) and Zn(II) in acetonitrile to yield quantitatively and selectively the heterodinuclear triple-helical complexes [LnZn(L 2 ) 3 ] 5+ under thermodynamic control. The crystal structure of [EuZn(L 2 ) 3 ](ClO 4 )(CF 3 SO 3 ) 4 (CH 3 - CN) 4 (13; EuZnC 111 H 111 N 25 O 19 F 12 S 4 Cl, monoclinic, C2/c, Z ) 8) shows the wrapping of the three ligands L 2 about a pseudo-C 3 axis passing through the metal ions. Zn(II) occupies the distorted pseudooctahedral capping coordination site defined by the three bidentate binding units while Eu(III) lies in the resulting “facial” pseudotricapped trigonal prismatic site produced by the three remaining tridentate units as exemplified by luminescence measurements using the Eu(III) structural probe. The separation of contact and pseudocontact contributions to the 1 H-NMR paramagnetic shifts of the axial complexes [LnZn(L 2 ) 3 ] 5+ (Ln ) Ce, Pr, Nd, Sm, Eu, Tm, Yb) establishes that the triple helical structure is maintained in solution. Photophysical measurements and quantum yields in acetonitrile indicate that the terminal N,N-diethylcarbamoyl group in L 2 favors efficient intramolecular L 2 f Eu(III) energy transfers leading to strong Eu-centered red luminescence. Improved resistance toward hydrolysis also results from the use of carboxamide groups, and no change in luminescence is observed for [EuZn(L 2 ) 3 ] 5+ in moist acetonitrile. The preparation of the segmental ligand L 2 from the new asymmetric synthon 6-(N,N-diethylcarbamoyl)pyridine-2-carboxylic acid is described together with its crystal and molecular structure (C 33 H 33 N 7 O, monoclinic, P2 1 /c, Z ) 4). The use of 3d metal ions as a noncovalent tripodal spacer for lanthanide podates is discussed together with the crucial role played by carboxamide groups for the control of structural, electronic, and photophysical properties. Introduction The design of organized molecular architectures containing lanthanide metal ions Ln(III) and working as nanometric light- converting devices 1,2 and luminescent probes 1 is a theme of considerable current interest in supramolecular 1,2 and analytical chemistry, 1,3 and biochemistry. 4 However, the selective intro- duction of Ln(III) into supramolecular complexes with tailored coordination sites and predetermined photophysical properties represents a synthetic challenge 5 since Ln(III) displays large and variable coordination numbers 6 with few stereochemical preferences. 6,7 The control of the coordination spheres around Ln(III) thus mainly depends on the preorganization 8 of the coordinating units which limits the structural flexibility and increases the thermodynamic stability. 9 Macrocyclic 10 and compartmental 11 Schiff bases have been systematically inves- tigated for the preparation of homo- and heteropolynuclear lanthanide complexes, but improved structural control and protection of Ln(III) are obtained with preorganized tri- to † Department of Inorganic, Analytical and Applied Chemistry, University of Geneva. ‡ University of Lausanne. § Laboratory of X-ray Crystallography, University of Geneva. ⊥ F. Hoffmann-La Roche Ltd. | Department of Biochemistry, University of Geneva. X Abstract published in AdVance ACS Abstracts, July 1, 1996. (1) Bu ¨nzli, J.-C. G. in Lanthanide Probes in Life, Chemical and Earth Sciences; Bu ¨nzli, J.-C. G., Choppin, G. R., Eds.; Elsevier Publishing Co.: Amsterdam, 1989; Chapter 7. Bu ¨nzli, J.-C. G.; Froidevaux, P.; Piguet, C. New J. Chem. 1995, 19, 661-668 and references therein. (2) Sabbatini, N.; Guardigli, M.; Lehn, J.-M. Coord. Chem. ReV. 1993, 123, 201-228. (3) Lehn, J.-M.; Regnouf de Vains, J.-B. HelV. Chim. Acta 1992, 75, 1221-1236. Richardson, F. S. Chem. ReV. 1982, 82, 541-552. (4) Selvin, P. R.; Rana, T. M.; Hearst, J. E. J. Am. Chem. Soc. 1994, 116, 6029-6030. Coates, J.; Sammes, P. G.; West, R. M. J. Chem. Soc., Chem. Commun. 1995, 1107-1108. Saha, A. K.; Kross, K.; Kloszewski, E. D.; Upson, D. A.; Toner, J. L.; Snow, R. A.; Black, C. D. V.; Desai, V. C. J. Am. Chem. Soc. 1993, 115, 11032-11033. (5) Piguet, C.; Bu ¨nzli, J.-C. 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Soc. 1996, 118, 6681-6697 S0002-7863(95)04163-1 CCC: $12 00 © 1996 American Chemical Society + +