4584 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Inorg. Chem. 1989, zyxwvut 28, zyxwv 4584-4588 Contribution from the Departments of Chemistry, University of Missouri-Rolla, Rolla, Missouri 65401, and University of California, Irvine, California 927 17, Department of Inorganic, Analytical, and Applied Chemistry, University of Geneva, CH-1211 Geneva 4, Switzerland, and Institut de Physique, Universite de Liege, B-4000 Sart Tilman, Belgium zyxwvutsrqpo Europium- 151 Mossbauer Effect Study of Several Organoeuropium( 11) Complexes Alan F. Williams, Fernande Grandjean, Gary J. Long,* Tamara A. Ulibarri, and William J. Evans Received zyxwvutsrqponmlk March zyxwvutsrqp IS, zyxwvutsrqponm 1989 The europium-151 Mossbauer spectra of several organoeuropium(I1) compounds have been measured at 77 and 4.2 K. All the compounds give isomer shifts of ca. -12 to -13 mm/s, typical of ionic europium(I1). For (C5Me5)2Eu, (C5Me5),Eu(THF),and (C5Me5)2Eu(THF)(Et20), broad absorptions were observed, arising from spherical paramagnetic relaxation at a rate comparable to the Mossbauer time scale of 9.7 X lO-’s. The relaxation rates are 490, 450, and 420 MHz, respectively, at 4.2 K, and the values for (C5Me5),Eu(THF) and (C5Me5)2E~(THF)(Et20) increase to 635 and 650 MHz at 77 K as a result of greater coupling of the spin with the lattice vibrations. For [(C5Me5)Eu(THF),(p-I)1, the spectrum corresponds to a relaxation rate of 1710 MHz at 4.2 K. [(C5Me5)2Eu(THF)], shows a symmetric spectrum that is close to the fast relaxation limit with an estimated relaxation rate of 5580 MHz. Eu12(THF), shows a narrow line width spectrum with a quadrupole interaction of -12.9 mm/s and an asymmetric parameter of 0.58 at 4.2 K. The rate of paramagnetic relaxation correlates well with the inverse of the distance between Eu(l1) ions, suggesting that the relaxation occurs via a spinspin interaction. The magnetic susceptibility of (C5Me5),Eu, measured between 2 and 320 K, shows it to be paramagnetic in this temperature range with a moment of 6.99 zyxw wB and a Curie-Weiss temperature of 3.28 K. Introduction Europium- 15 1 Mossbauer spectroscopy is well suited for the study of the oxidation state and the local environment of europium in solid compounds.’ The isomer shift, relative to EuF3, of europium( 111) in organic compounds or coordination complexes is in the range 0-1 mm/s, whereas that of europium(I1) ions is in the range -12 to -15 mm/s. Because the typical experimental line width for a europium-151 Mossbauer spectrum is 2.4 mm/s, the two oxidation states of europium are easily distinguished. The quadrupole interaction, which is determined by the symmetry of the environment of the europium, removes the degeneracy of both the ground and the excited states of the Mossbauer nucleus and gives rise to Mossbauer spectra composed of eight overlapping lines. In europium(II1) coordination complexes, as in most eu- ropium(II1) compounds,’ the quadrupole interaction is small, typically less than 10 mm/s, and the observed spectrum is a broad line, from which it is difficult to obtain an accurate value of the quadrupole interaction. In order to observe a resolved quadrupolar hyperfine structure, quadrupole interactions of 20 mm/s or more are required. EuRh3B2, with a quadrupole interaction of 45 is one of the few examples of a compound that shows a well-resolved quadrupole interaction for europium. Organoeuropium(I1) compounds are rare,4 but recently, a number of bis(pentamethylcyclopentadieny1) complexes of euro- pium( 11) have been synthesi~ed.~,~ The crystal structure of (CSMeJ2Eu consists of discrete monomeric units possessing a bent metallocene geometry., The compound is monoclinic with four molecules per unit cell and a minimum europium-europium distance of 6.2 A. By comparison with the X-ray crystal structure of (CSMes)2Yb(THF).0.5toluene6 and (C5Mes)zSm(OC5H,o),7 (C,Me&Eu(THF) is also expected to have a bent metallocene geometry. The very distorted environment of the europium(I1) ions in these compounds suggested the possible presence of a large quadrupole interaction and stimulated a preliminary study of (C,Me,),Eu and (C5Me5)2Eu(THF) at 77 K using the europium-I51 Miissbauer effect.s The results of this study confirmed the divalent nature of europium in these complexes, but showed very broad absorption lines that were attributed to the presence of slow paramagnetic relaxation of the electronic ground state of the Eu(1I) ion, and were explainedby a model using spherical relaxation of the hyperfine field. To confirm these results, and to obtain further information on the relaxation mechanism, we have studied the Mossbauer spectra of these two compounds and a number of related Eu(I1) compounds at 77 and 4.2 K, and the *To whom correspondence should be addressed at the University of Missouri-Rolla. results of this study are given in this paper. Experimental Section The synthesis and subsequent manipulations of the complexes under study were conducted with the rigorous exclusion of air and water by using Schlenk-line and glovebox (Vacuum/Atmospheres HE-553 Dri- Lab) techniques. Solvents were dried as previously de~cribed.~ KC5Me5,9 NaC5H5,I0 (C5Me5),Eu,’ (C5Me5)2Eu(THF),6 and (C5Me,)2Eu(THF)(Et20)6 were obtained by following published litera- ture procedures. Europium was obtained from Research Chemicals of Phoenix, AZ. EuI,(THF),~I [(C5H5)2Eu(THF)],,12J3 and [(C5Me5)- EU(THF)~(~-I)]~ were obtained by modifications of literature procedures as described below. Complexometric metal analysis was performed as previously described.14 EUI~(THF)~. In an inert-atmosphere glovebox, diiodoethane (2.67 g, 9.5 mmol) was added to europium metal (10.48 g, 60 mmol) in a 500-mL round-bottom flask containing a Teflon-coated stir bar. T H F (50 mL) was added, and the reaction was stirred for approximately 48 h. The solution was centrifuged to remove the excess metal, and the resulting yellow-purple solution was dried by rotary evaporation to yield Eu12(T- HF)2 (4.97 g, 95%) as a greenish yellow powder. Anal. Calcd for EuC~H~~I~~~: Eu, 27.63. Found: Eu, 27.5. [(C5H5)2Eu(THF)],. In the glovebox, NaC5H5 (0.131 g, 1.48 mol) was added to a stirred solution of Eu12(THF), (0.406 g, 0.74 mmol) in 8 mL of THF. The solution immediately became light yellow and was stirred for 3 h. The solution was centrifuged, and the slightly cloudy yellow solution was discarded. The solid consisted of two layers: a light yellow layer on the bottom and a white layer on the top. The solids were resuspended in THF (IO mL) and centrifuged eight times, after which the cloudiness of the solution had disappeared and only the light yellow Grandjean, F.; Long, G. J. In Mossbauer Spectroscopy Applied to Inorganic Chemistry; Long, G. J., Grandjean, F., Eds.; Plenum Press: New York, Vol. 3; 1989. DD 513-597. Shaheen, S. A.; Abd-Elmegiid, M.; Micklitz, H.; Pontkees, F.; Schilling, J. S.; Klavins, P.; Shelton, R. N. J. Magn. Magn. Mater. 1986, 54-57, 487-48 8. Malik,-S. K.; Shenoy, G. K.; Heald, S. M.; Tranquada, J. M. Phys. Reu. Lett. 1985, 55, 316-319. Marks, T. L.; Ernst, R. D. In Comprehensive Organometallic Chem- istry; Wilkinson, G., Stone, F. G. A,, Abel, E. W., Eds.; Pergamon: London, 1982; Vol. 3, pp 173-270. Evans, W. J.; Hughes, L. A.; Hanusa, T. P. Organometallics 1986,5, Tilley, T. D.; Andersen, R. A.; Spencer, B.; Ruben, H.; Zalkin, A,; Templeton, D. H. Inorg. Chem. 1980, 19, 2999-3003. Evans, W. J.; Ulibarri, T. A. Polyhedron 1989, 8, 1007-1014. Grandjean, F.; Long, G. J.; Buhl, M. L.; Evans, W. J.; Ulibarri, T. A. Hyperfine Interact. 1988, 40, 307-309. Evans, W. J.; Grate, J. W.; Choi, H. W.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem. Sot. 1985, 107, 941-946. Evans, W. J.; Meadows, J. H.; Wayda, A. L.; Hunter, W. E.; Atwood, J. L. J. Am. Chem. SOC. 1982, 104, 2008-2014. Okaue, Y.; Isobe, T. Inorg. Chim. Acta 1988, 144, 143-146. Fischer, E. 0.; Fischer, H. J. Organomet. Chem. 1965, 3, 181-187. Namy, J. L.; Girard, P.; Kagan, H. B. NOUL’. J. Chim. 1981,5,479-484. Evans, W. J.; Coleson, K. M.; Engerer, S. C. Inorg. Chem. 1981, 20, 1285-1291, 43 20-43 25. 0020-1 669/89/ 1328-4584$01.50/0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0 1989 American Chemical Society