Acta Chim. Slov. 2002, 49, 203-208. 203 MAGNETIC PROPERTIES OF SOME LANTHANOID FLUOROARSENATES AND FLUOROBORATES† Zoran Mazej* Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia Alain Tressaud, Jacques Darriet Institut de Chimie de la Matiere Condensée de Bordeaux, 87 Avenue Dr. A. Schweitzer, 33608 Pessac Cedex, France f This paper is dedicated to the memory of Dr. Karel Lutar Received 02-07-2001 Abstract GdF(AsF6)2, GdF3?2BF3, H3OGdF3BF4 and TbF(AsF6)2 obey Curie-Weiss law in the temperature range 4.2 K < T < 300 K with µeff = 7.35, 7.08, 7.51 and 8.72 B.M. Compounds can be considered as magnetically dilute. Deviations of observed values from predicted are not major, suggesting that 4f shell is not substantially affected by the environment of the cation. EuF3?2BF3 doesn't obey Curie-Weiss law. Data obtained in the 150 K < T < 300 K temperature range can be fitted to linear curve giving µeff = 3.10 B.M. Introduction Rare earth trifluorides (LnF3) reacts with Lewis acids (e.g. AsF5, BF3) in anhydrous hydrogen fluoride (aHF) at room temperature. In the system LnF3/AsF5/aHF stable solutions of solvated rare earth cations Ln(FH)x3+ and AsF6- anions were obtained. After removal of volatile components at room temperature La(AsF6)3, LnF(AsF6)2 (Ln = Ce-Nd, Sm-Er and Y) and Ln2F3(AsF6)3 with Ln = Tm, Yb and Lu were isolated.1 All attempts to grow single crystals of compounds LnFx(AsF6)3-x (x = 0, 1 or 1.5) failed. The stabilization of these compounds was finally achieved by using additional ligands (e.g. HF2, XeF23, AsF33) and the corresponding crystal structures could be determined. Products between LnF3 and BF3 are only slightly soluble in aHF. Characterization of the isolated products showed that they form two types of compounds: LnF3?2BF3 (Ln = La-Nd, Sm-Er) and LnF3?nBF3 (Ln = Ho-Lu). The composition of the last phase is still unclear (n = 1 or 1.5).4 Z. Mazej, A. Tressaud, J. Darriet: Magnetic properties of some lanthanoid fluororarsenates and 204 Acta Chim. Slov. 2002, 49, 203-208. When Ln2O3 oxides were used as starting materials in Lewis acid/aHF superacid medium new oxonium compounds of lanthanoids were isolated (e.g. (H3O)3La2F(AsF6)83,5, (H3O)8La2F(AsF6)133,5, H3OGdF3BF46). There are no structural reports of the measured compounds. The vibrational spectra of LnFx(AsF6)3-x compounds are consistent with distorted AsF6- octahedra, indicating the presence of covalent contribution to the fluorine bridges between LnF3 and AsF5.1 The vibrational spectra of fluoroborates also show significant distortions of BF4- and evidence an appreciable covalent character of the compounds. The bonding should be thus formulated as F3B???LnF???BF3 with bridging fluorine atoms.7 This work is devoted to the investigation of the magnetic behavior of some selected lanthanoid hexafluoroarsenates and fluoroborates. In the LnF3/AsF5 systems GdF(AsF6)2 (1) and TbF(AsF6)2 (2) were investigated. Two other examples were also taken from the LnF3/BF3 system (e.g. GdF3?2BF3 (3) and EuF3?2BF3 (4)). Additionally, results of magnetic measurements of H3OGdF3BF4 (5) are given. Results and discussion The temperature dependence of the inverse magnetic susceptibility of 1, 3, 5 under an applied field of 1.7 T and 2 under an applied field of 0.6 T are presented in Fig. 1-4. Comparison between experimental values of the effective moment µeff and the calculated ones from Ln3+ ions configurations is given in Table 1. In the temperature range 4.2 K < T < 300 K the reciprocal magnetic susceptibilities are linear with Table 1: Calculated and experimental values of µeff Compound g[J(J+1)]1/2 / B.M. µeff (experimental) / B.M. GdF(AsF6)2 7.94 7.35 GdF3-2BF3 7.94 7.08 H3OGdF3BF4 7.94 7.51 TbF3-2BF3 9.72 8.72 Z. Mazej, A. Tressaud, J. Darriet: Magnetic properties of some lanthanoid fluororarsenates and Acta Chim. Slov. 2002, 49, 203-208. 205 40 ?-1 (emu/mol)-1 30 20 10 40- ?-1 (emu/mol)-1' 30- 20 10 0 50 100 150 200 250 300 T / K 0 50 100 150 200 250 300 T / K Fig. 1: Temperature dependence of the reciprocal susceptibility of GdF(AsF6)2 Fig. 2: Temperature dependence of the reciprocal susceptibility of 40- ? -1 (emu/mol)-1 30- 20 10 0 50 100 150 200 250 300 T / K 30- ? -1 (emu/mmol)-1 20 10 0 50 100 150 200 250 300 T / K GdF3?2BF3 Fig. 3: Temperature dependence of the Fig. 4: Temperature dependence of the 0 0 0 0 Z. Mazej, A. Tressaud, J. Darriet: Magnetic properties of some lanthanoid fluororarsenates and 206 Acta Chim. Slov. 2002, 49, 203-208. reciprocal susceptibility of H3OGdF3BF4 reciprocal susceptibility of TbF(AsF6)2 temperature. In this temperature range measured compounds are paramagnetic and their magnetic susceptibility follow a Curie-Weiss law. Values of µeff derived from experimental results (Table 1) are close to the values calculated from the equation µeff = g[(J(J+1)]1/2, where g = 3/2 + [S(S+1)-L(L+1)]/[2J(J+1)], valid for Ln3+ ions. In these equations S is the spin contribution and L the orbital contribution to magnetic moment. They couple together to give a new quantum number J. (emu/mol)-1 200 150 100 50 0 0 50 100 150 200 250 300 T / K Fig. 5: Temperature dependence of the reciprocal susceptibility of EuF3-2BF3 For the Eu3+ compound the Curie-Weiss law is not followed. This is due to the small energy difference between the ground state and next energy state of the Eu3+ (^400 cm-1).8 Some electrons can be promoted by the energy of the thermal motion and partly populate the higher state. The consequence is that magnetic behavior is not solely determined by the ground state configuration as in the case of other Ln3+ ions with exception of Sm3+. Data obtained in the 150 K < T < 300 K temperature range can be fitted to linear curve giving \xeff = 3.10 B.M. The obtained value of \xeff is close to Z. Mazej, A. Tressaud, J. Darriet: Magnetic properties of some lanthanoid fluororarsenates and Acta Chim. Slov. 2002, 49, 203-208. 207 experimental data reported in the literature for other Eu3+ compounds (neff = 3.4-3.6 B.M.).9 Conclusions Magnetic data of 1, 2, 3, 5 show that these compounds can be treated as magnetically dilute. Deviations of neff observed values from the predicted ones are not important, suggesting that 4f shell is not substantially affected by the environment of the cation. Magnetic susceptibility of 4 does not follow a Curie-Weiss law. High temperature data of 4 can be fitted to a linear curve giving \ieff = 3.10 B.M. Experimental 1, 2 and 3, 4 compounds were prepared as white powders by reaction between LnF3 and AsF5 or BF3, respectively, in anhydrous hydrogen fluoride as a solvent.156 Oxonium compound was prepared from Ln2O3 and excess of BF3 as described in the literature.6 The compounds were prepared pure and characterized by chemical analysis, vibrational spectroscopy167 and in the case of the two LnF3-2BF3 (Ln = Gd, Eu) complexes also with X-ray analysis.67 Lanthanoid fluoroarsenates were nearly amorphous and X-ray photographs of poor quality were always obtained. All investigated compounds being extremely moisture-sensitive, the transfer into suitable sample containers was made in a dry-box. The residual amount of water present in the atmosphere of the dry-box never exceeded 1 ppm. Cylindrical screw-capped sample containers (V« 0.5 ml, m « 0.25 mg) were made of Kel-F (polytrifluorochloroethylene) and were additionally tightened with Teflon gaskets. Prior to their use, both the container and Kel-F packing tool were passivated with elemental fluorine. A known Z. Mazej, A. Tressaud, J. Darriet: Magnetic properties of some lanthanoid fluororarsenates and 208 Acta Chim. Slov. 2002, 49, 203-208. quantity of compound 4 (18.73 mg) was measured on a SQUID magnetometer (SHE Corp.) and compounds 1, 2, 3, 5 (20-24 mg) on MANICS DSM8 susceptometer. Acknowledgements The authors gratefully acknowledge the financial support of French-Slovenian scientific cooperation program PROTEUS (95032; 940YM) The part of the work carried out at JSI was supported by Ministry of Education, Science and Sport of the Republic of Slovenia. References and Notes 1. Fele-Beuermann, M.; Lutar, K.; Mazej, Z.; Milićev, S.; Žemva, B. J. Fluorine Chem. 1998, 89, 83-89. 2. Mazej, Z.; Borrmann, H.; Lutar, K.; Žemva, B. Inorg. Chem. 1998, 37, 5912-5914. 3. Lutar, K.; Borrmann, H.; Mazej, Z.; Tramšek, M.; Benkič, P.; Žemva, B. J. Fluorine Chem. 2000, 101, 155-160. 4. Mazej, Z.; Lutar, K.; Žemva B. 11th Eur. Symp. Fluorine Chem., Bled, Slovenia, 1995, Abstracts, p. 129. 5. Mazej, Z.; Borrmann, H.; Lutar, K.; Žemva, B. 15th Inter. Symp. Fluorine Chem., Vancouver, Canada, 1997, Abstracts, p. Ba(1) C-5. 6. Mazej, Z. Ph. D. Thesis, University of Ljubljana, Slovenia, 2000. 7. Fele-Beuermann, M. Ph. D. Thesis, University of Ljubljana, Slovenia, 1994. 8. Carlin, L.C. Magnetochemistry; Springer-Verlag, Berlin, Heidelberg., 1986, p. 238. 9. Lee, J.D. Concise Inorganic Chemistry; Chapman & Hill, London, 1991, p. 874. Povzetek Magnetne lastnosti spojin GdF(AsF6)2, GdF3?2BF3, H3OGdF3BF4 in TbF(AsF6)2 se podrejajo Curie-Weissovemu zakonu v temperaturnem območju 4.2 K < T < 300 K z µeff = 7.35, 7.08, 7.51 oziroma 8.72 B.M. Spojine lahko obravnavamo kot magnetno razredčene. Odstopanja izmerjenih vrednosti od teoretičnih niso velika. To kaže da okolica kationa zelo malo vpliva na 4f-orbitale. Magnetne lastnosti spojine EuF3?2BF3 se ne podrejajo Curie-Weissovemu zakonu. Rezultati meritev izmerjeni v temperaturnem območju 150 K < T < 300 K se prilegajo premici z µeff = 3.10 B.M. Z. Mazej, A. Tressaud, J. Darriet: Magnetic properties of some lanthanoid fluororarsenates and