Inorg. Chem. 1987, 26, 938-943
938
Contribution from the Laboratories d e Chimie (UA CNRS 1194) and the Service d e Physique DCpartement d e Recherche Fondamentale, Centre d'Etudes NuclCaires d e Grenoble, 8 5 X F. 38041 Grenoble, France, and Department of Chemistry, University of Florence, Florence, Italy
Crystal and Molecular Structure and Magnetic Properties of the Adducts of Copper(I1) Hexafluoroacetylacetonate with the Nitroxide Ligand 2-Phenyl-4,4,5,5-tetramethylimidazoline-l-oxyl 3-Oxide D. Gatteschi,*la J. Laugier,lb P. Rey,*lb and C. Zanchinila Received July 17, 1986 Stable 1:l and 1:2 adducts were isolated from the reaction of copper(I1) hexafluoroacetylacetonate and the free radical 2phenyl-4,4,5,5-tetramethylimidazoline1-oxy1 3-oxide (NITPh), namely Cu(hfac),(NITPh) and c~(hfac),?(NITPh)~ The striking feature of the structure of the diamagnetic Cu(hfac),(NITPh) is the presence of two molecules in different conformations in the asymmetric unit with the copper ion in a distorted square-pyramidal environment and a trigonal-bipyramidal environment, respectively. The nitroxyl grou is equatorially bound in both molecules. Crystal data for Cu(hfac),(NITPh): triclinic, PI,a = 11.346 (5) A,b = 14.115 (6) c = 20.129 (9) A, a = 70.12 (3)O, j3 = 76.68 (4)O, y = 75.20 (3)O, 2 = 4. In Cu(hfac),(NITPh), the copper ion is in a tetragonally distorted octahedral environment with the axial coordination sites occupied by the oxygen atoms of the two nitroxyl ligands at bonding distances of 2.362 (5) and 2.393 (5) A. Crystal data for Cu(hfac),(NITPh),: monoclinic, P2,/c, a = 12.358 (6) A, b = 15.428 (7) A, c = 22.61 ( I ) A, p = 102.33 (3)O, Z = 4. Magnetic measurements show a weak ferromagnetic interaction. EPR spectra of Cu(hfac),(NITPh), show a g shift on varying the energy of the microwave quantum and nonparallelism of the two g tensors at X-and Q-band frequencies.
i,
Introduction
Table I. Crvsta~~oaraphic Data and Experimental Parameters
The mechanism of the magnetic coupling between paramagnetic transition-metal ions and stable nitroxides is under invwtigation,2-' d u e to the possibility of synthesizing novel magnetic materials and studying t h e n a t u r e of t h e bonding between metal ions and paramagnetic ligands. Several different coordination geometries have been observed, and the coupling between t h e metal ions a n d t h e nitroxides has been found to range from antiferromagneti~,8*~ implying a complete pairing of the spins and no thermally accessible excited state, to passing through systems in which spin weak pairing occurs only at low t e m p e r a t ~ r e . ' ~ - ' ~ Special interest has been devoted to t h e adducts formed by C ~ ( h f a c since ) ~ the metal center is a strong Lewis acid making it relatively easy to obtain complexes with the nitroxides. Adducts of C ~ ( h f a c )have ~ been obtained with 2,2,6,6-tetramethylpiperidine-1-oxy1 (TEMPO) and the 4-hydroxylated derivative (TEMPOL). Distinctly different structures and magnetic properties have been observed for these two adducts. The Cu( h f a ~ ) ~ T E M padduct 0 is a diamagnetic,I6 equatorially shortbonded complex17while in Cu(hfac),TEMPOL the nitroxyl group is axially coordinated through a long bond and a ferromagnetic behavior has been observed.' 1v18
(a) University of Florence. (b) Centre #Etudes NuclEaires de Grenoble. Dong, T. Y.;Hendrickson, D. N.; Felthouse, T. R.; Shieh, H. S.J. Am. Chem. SOC.1984, 106, 5313. Cotton. F. A,: Felthouse. T. R. Inorp. Chem. 1982. 21. 2667. Richman, R. M.;Kuechler, T. C.; Tanner, S. P.; Drago, R. S. J . Am. Chem. SOC.1977, 99, 1055. Brown, D. G.; Maier, T.; Drago, R. S . Inorg. Chem. 1971, 10, 2804. Eaton, S. S.; Eaton, G . R. Coord. Chem. Rev. 1978, 26, 207. Damoder, R.; Kundalika, M. M.; Eaton, G. R.; Eaton, S . S. J . Am. Chem. SOC.1983, 105, 2141. Porter, L. C.; Dickman, M. H.; Doedens, R. J. Inorg. Chem. 1986, 25, 618. Laugier, J.; Rey, P.; Benelli, C.; Gatteschi, D.; Zanchini, C. J . Am. Chem. SOC.1986, 108,6931. Grand, A.; Rey, P.; Subra, R. Inorg. Chem. 1983, 22, 391. Bencini, A.; Benelli, C.; Gatteschi, D.; Zanchini, C. J. Am. Chem. SOC. 1984, 106, 5813. Benelli, C.; Gatteschi, D.; Zanchini, C.; Latour, J. M.; Rey, P. Inorg. Chem. 1986, 25, 4242. Dickman, M. H.; Porter, L. C.; Doedens, R. J. Inorg. Chem. 1986, 25, 2595. Benelli, C.; Gatteschi, D.; Zanchini, C. Inorg. Chem. 1984, 23, 798. Beck, W.; Schmidter, K.; Keller, H. S . Chem. Ber. 1967, 100, 503. Lim, Y. Y.; Drago, R. S. Inorg. Chem. 1972, 1 1 , 1334. Dickman, H. M.; Doedens, R. J. Inorg. Chem. 1981, 20, 2677. 0020-1669/87/ 1326-0938$01.50/0
formula Mr cryst syst space group
v,A'
a, A
b, A c,
A
a,deg
P, deg Y, deg
Z
d(calcd), g/cm3
triclinic
monoclinic P2dC 4211.7 12.358 (6) 15.428 (7) 22.61 (1) 90 102.33 (3) 90 4 1.69
Pi 2894.1 11.346 (5) 14.1 15 (6) 20.129 (9) 70.12 (3) 76.68 (4) 75.20 (3) 4 1.72
Experimental Parameters for Both Compounds radiation Mo K a (A = 0.7107 A), graphite monochromator cryst detector dist, mm 368 detector window width, mm 2.25 3.5 tan 9 detector window height, mm 4 takeoff angle, deg 6 scan mode W max Bragg angle, deg 2
