Chem. Mater. zyxwvu 1994,6, zyxwvut 31-38 31 Synthesis, X-ray Diffraction, Differential Scanning Calorimetry, and Magnetic Susceptibility Studies of a Series of Binuclear Ruthenium(I1) Carboxylates Giving Liquid- Crystalline Phases Laurence Bonnet, Fabio D. Cukiernik, Pascale Maldivi,* Anne-Marie Giroud-Godquin, and Jean-Claude Marchon CEAIDbpartement de Recherche Fondamentale zyxwvuts sur la Matiere Condenske, CNRSILaboratoire de Chimie de Coordination (URA zyxwvuts 1194), SESAMICC, Centre d’Etudes Nuclkaires de Grenoble, BP 85 X, 38041 Grenoble, France Mohammed Ibn-Elhaj, Daniel Guillon, and Antoine Skoulios Groupe des Matbriaux Organiques, Institut de Physique et Chimie des Matbriaux de Strasbourg, UMR 46 CNRS- ULP-EHICS, 6, Rue Boussingault, 67083 Strasbourg Cedex, France Received June 29, 1993. Revised Manuscript Received October 14, 199P A wide series of diruthenium(I1,II) tetracarboxylates of general formula Ruz(RC00)4 was prepared; the carboxylate substituents include linear alkyl chains (R zyxw = C4Hg t o C19H39), unsaturated chains (R = CHz=CH(CH2)8-, (CH~)ZC=CHCH~CHZCH(CH~)CHZ-) as well as a fluorinated chain (R = C7F15-). An adduct obtained by pyrazine intercalation was also characterized (R = CllH23-). The mesomorphic behavior of these compounds was investigated by differential scanning calorimetry and X-ray diffraction. A thermotropic columnar mesophase was observed above ca. 100 “C for all complexes except the perfluoro compound and the pyrazine adduct. Unsaturation in the peripheral alkyl chains strongly depresses the transition temperature to the liquid-crystalline phase. The magnetic susceptibility of three members of the series was measured in the range 6-400 K. A rigorous analytical expression of the magnetic susceptibility vs temperature was derived from the ( ~ * ) ~ ( 6 * ) ~ electronic configuration for the ground state of a diruthenium(I1,II) core, by applying a spin-orbit Hamiltonian, and the data were successfully analyzed on this basis. Introduction Binuclear complexes of carboxylic acids with transition metals such as Cu(II),Rh(II),Ru(II), and Mo(I1)are known to exhibit the so-called “lantern” or ”paddle-wheel” core exemplified by the structure of copper acetate dihydrate CUZ(CH~COO)~.~HZO. In earlier work from our labora- tories, we have fully characterized the liquid-crystalline properties of long-chain carboxylate complexes of Cu(II),l Rh(II),z and Ru(II),~ using hot-stage polarizing optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction studies. Furthermore, we have taken advantage of the presence of metal atoms to gain additional information on the structural changes attending the crystal-to-mesophase transition using copper and rhodium K-edge EXAFS spectroscopy,4 infrared (IR) and Raman spectroscopies,5 and magnetic susceptibility measure- ment~.~~~ * Abstract published in Aduance ACS Abstracts, November 15,1993. (1) (a)Abied, H.; Guillon,D.;Skoulios, A.; Weber,P.; Giroud-Godquin, A.M.;Marchon, J. C. Liq. Cryst. 1987,2,269. (b) Ibn-Elhaj, M.; Guillon, D.;Skoulios, A.; Giroud-Godquin, A. M.; Maldivi, P. Liq. Cryst. 1992,Il, 731. (2) Giroud-Godquin, A. M.; Marchon, J. C.; Guillon, D.; Skoulios, A. J. Phys. Chem. 1986,90, 5502. (3) Maldivi, P.; Giroud-Godquin, A. M.; Marchon, J. C.; Guillon, D.; Skoulios, A. Chem. Phys. Lett. 1989, 157, 552. (4) (a) Abied, H.; Guillon, D.; Skoulios, A,; Dexpert, H.; Giroud- Godquin,A. M.;Marchon, J. C. J. Phys.,Paris. 1988,49,345. (b) Maldivi, P.; Guillon,D.;Giroud-Godquin, A. M.;Marchon, J. C.;Abied, H.;Dexpert, H.; Skoulios, A. zyxwvutsrqpo J. Chim. Phys. Paris. 1989,86, 1651. (c) Ibn-Elhaj, M.; Guillon, D.; Skoulios, A.; Maldivi, P.; Giroud-Godquin, A. M.: Marchon, J. C. J. Phys. 2 France. 1992,2,2237. The following structural features emerge from our studies of the Cu(I1) and Rh(I1) carboxylate mesogens. In both the crystalline and mesomorphic phases, the axial positions of the molecules are occupied by a carboxylate oxygen atom belonging to a neighboring complex+ leading to pseudopolymeric chains. In this respect, the solid-state structures of long-chain Cu(I1) or Rh(I1) carboxylates are similar to those of the short-chain analogues, copper and rhodium butyrates.’ In the liquid-crystalline phase, the axes of these chains are located at the nodes of a two- dimensional hexagonal array.l The backbone of each column is made up of regularly stacked binuclear cores, and it is surrounded by “melted” aliphatic chains. In- termolecular cohesion is brought about by axial metal- oxygen coordination. We were interested in extending these studies to the ruthenium(I1) analogues for several reasons. First, these compounds offer us an opportunity to investigate further the influence of the metal center and of multiple metal- metal bonding8 on mesomorphic behavior. This point has (5) (a)Strommen,D. P.;Giroud-Godquin,A. M.;Maldivi,P.;Marchon, J. C.; Marchon, B. Liq. Cryst. 1987,2,689. (b) Poizat, 0.; Strommen, D. P.; Maldivi, P.; Giroud-Godquin, A. M.; Marchon, J. C. Inorg. Chem. 1990,29,4851. (6) Giroud-Godquin, A. M.;Latour, J. M.;Marchon, J. C. Inorg. Chem. 1985,24, 4452. Cotton, F. A.; Shiu, K. B. Reu. Chim. Miner. 1986,23, 14. 101,5256. (7) (a) Campbell, G. C.; Haw, J. F. Inorg. Chem. 1988,27, 3706. (b) (8) Norman, J. G.;Renzoni, G. E.; Case, D. A. J. Am. Chem. SOC. 1979, 0897-4756/94/2806-0031$04.50/0 0 1994 American Chemical Society