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Synthesis and characterization of samarium, europium and ytterbium aryloxides
Journal of Alloys and Compounds 374 (2004) 289–292
Synthesis and characterization of samarium, europium and ytterbium aryloxides Crystal structure of [Yb6(OH)4 (OC6H4 OMe)14 ]·4THF José Carretas∗ , Joaquim Branco, Joaquim Marçalo, Nuno Valente, João Carlos Waerenborgh, ˆ Adelaide Carvalho, Noémia Marques, Angela Domingos, António Pires de Matos Departamento de Qu´ımica, Instituto Tecnológico e Nuclear, Estrada Nacional 10, P-2686-953 Sacavém, Portugal
Abstract The reactions of samarium, europium and ytterbium metals with the potential bidentate ligand 2-methoxyphenol were investigated. The europium and ytterbium aryloxides were synthesized by dissolution of the metals in liquid ammonia, whereas the samarium aryloxide was synthesized by metal vapour synthesis (MVS). The compounds obtained were formulated as Ln(OC6 H4 OMe)3 , Ln = Sm, Yb and Eu(OC6 H4 OMe)2 . Recrystallization of Yb(OC6 H4 OMe)3 in the presence of THF/pentane resulted in the crystallographically characterized complex [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 --OMe)2 (OC6 H4 OMe)2 ]·4THF. © 2003 Elsevier B.V. All rights reserved. Keywords: Samarium; Europium; Ytterbium; Aryloxides
1. Introduction
2. Experimental
Over the last years we have studied the reactions of lanthanide metals with several phenols using the metal vapour synthesis (MVS) technique [1,2], and the metal dissolution in liquid ammonia [2,3]. The type of ligands used was diverse ranging from the less to the more bulky phenols, including simple and polycyclic phenols. In the literature the lanthanide aryloxide chemistry consists mainly of derivatives of classical phenols, whereas examples of aryloxide ligands containing additional donor groups are scarce. Having in mind the preparation of very pure aryloxides as precursors of catalysts supported on amorphous and mesoporous silica [4,5] we have been investigating the reactions of lanthanide metals with potential polydentate phenols. In this work we studied the reactions of samarium, europium and ytterbium metals with 2-methoxyphenol by the MVS technique and by dissolution in liquid ammonia. We report here the crystal structure of the complex [Yb6 (OH)4 (OC6 H4 OMe)14 ]·4THF.
All manipulations were routinely performed under N2 using glove-box and Schlenk techniques. MVS experiments were made in a Planer products plant VPS 500. Solvents and 2-methoxyphenol were purified by standard methods [6]. Samarium, europium and ytterbium ingots were obtained commercially from the Baotou Research Institute of Rare Earth. C, H and N analyses were performed in a CE instruments EA1110 automatic analyser. Sm, Eu and Yb analyses were performed according to a standard gravimetric method [7]. IR spectra were registered in a 577 Perkin-Elmer spectrometer with samples prepared as Nujol mulls. 1 H NMR spectra were recorded using a Varian Unity Inova 300 MHz spectrometer. Europium Mössbauer spectra were measured with the absorber at 80 K. The spectrometer was operated in constant acceleration. The source was samarium-151 in a SmF3 matrix. All absorbers were encapsulated in a special air tight sample holder. 2.1. Sm(OC6 H4 OMe)3
∗ Corresponding author. Tel.: +351-1219946218; fax: +351-1219941455. E-mail address: [email protected] (J. Carretas).
0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.11.120
Samarium atoms (1.69 g, 11.24 mmol) were vaporised with a resistance heating furnace (480 W) and were co-condensed with 40 ml of 2-methoxyphenol (36.38 mmol)
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J. Carretas et al. / Journal of Alloys and Compounds 374 (2004) 289–292
onto a liquid nitrogen-cooled surface over a period of 3 h. The resultant mixture was allowed to warm slowly to room temperature under a nitrogen atmosphere. The product was washed out with THF and filtered through a Celite bed. Volatile components were removed under vacuum and the resultant grey solid was washed with pentane. The reaction product obtained was formulated as Sm(OC6 H4 OMe)3 (yield = 67%). Analysis found (%): Sm, 27.22; C, 50.19; H, 4.24. Calculated for SmO6 C21 H21 : Sm, 28.93; C, 48.52; H, 4.08. IR (cm−1 ): 3480w, 2700w, 2550w, 2400w, 2300w, 2240w, 2110w, 1640w, 1570s, 1440s, 1370m, 1310w, 1270w, 1250m, 1200w, 1160w, 1100m, 1030w, 1000s, 940w, 900w, 840s, 750s, 715s, 595m, 560w, 530w, 500w, 460w, 390m. 2.2. Eu(OC6 H4 OMe)2 Europium (3.52 g, 23.16 mmol) was added to a solution of 5 ml of 2-methoxyphenol (45.46 mmol) in THF (100 ml), in a 250 ml Schlenk flask. The flask was connected to a vacuum line and liquid ammonia was condensed into the reaction vessel at 195 K. After 3 h the reaction mixture was allowed to slowly warm to room temperature and was purged with N2 . This mixture was then filtered through a Celite bed and the solution evaporated. The product was washed several times with pentane and a greenish yellow solid formulated as Eu(OC6 H4 OMe)2 was obtained after drying under vacuum (yield = 74%). Analysis found (%): Eu, 37.05; C, 42.32; H, 3.60. Calculated for EuO4 C14 H14 : Eu, 38.16; C, 42.22; H, 3.55. IR (cm−1 ): 2540w, 1570s, 1470s, 1440s, 1370m, 1315m, 1280s, 1245s, 1200s, 1160m, 1100m, 1030m, 1010s, 880w, 840m, 780w, 750m, 715s, 595m, 560w, 525w, 460w, 385w. Mössbauer (80 K) {δ (mm s−1 ), e2 qQ (mm s−1 ), η, Γ (mm s−1 ), I (%)}: Eu2+ , −13.2(1), 16.7(3), 1, 3.3(1), 96(1); Eu3+ , 0.1(4), −, −, 3.7, 4(1). 2.3. Yb(OC6 H4 OMe)3 The procedure for the reaction of ytterbium (2.50 g, 14.45 mmol) with 2-methoxyphenol (4.7 ml, 42.73 mmol) was identical to that for the europium reaction. A greenish yellow solid formulated as Yb(OC6 H4 OMe)3 was obtained (yield = 77%). Analysis found (%): Yb, 30.80; C, 48.21; H, 3.75. Calculated for YbO6 C21 H21 : Yb, 31.90; C, 46.49; H, 3.91. IR (cm−1 ): 2580w, 2300w, 1580m, 1480s, 1450s, 1370m, 1320w, 1280w, 1250m, 1210w, 1160w, 1110s, 1035m, 1010s, 900w, 845s, 755s, 730s, 595w, 580w, 530w, 460w, 400w. X-ray quality crystals were grown from a solution of the product in THF/pentane at room temperature. 2.4. X-ray crystallographic analysis Yellow crystals were mounted in thin-walled glass capillaries in a nitrogen-filled glove-box. Data were collected at room temperature on an Enraf-Nonius CAD4-diffractometer with graphite-monochromatized Mo K␣ radiation, using a
Table 1 Crystallographic data for [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 -OMe)2 (OC6 H4 OMe)2 ]·4THF Formula Molecular weight Crystal system Space group a (Å) b (Å) c (Å) β (degree) V (Å3 ) Z Dcalc (g cm−3 ) µ(Mo K␣) (mm−1 ) R1 a , wR2 b (I > 2(I)) a R = ||Fo | − |Fc ||/ |Fo |. 1 1/2 b wR = (w(Fo2 − Fc2 )2 /(w(Fo2 )2 ) . 2
C114 H134 O36 Yb6 3118.45 Monoclinic C2/c 22.221(2) 16.803(2) 30.938(2) 90.711(6) 11551(2) 4 1.793 4.889 0.0881, 0.1923
-2 scan mode. A summary of the crystallographic data is given in Table 1. Data were corrected [8] for Lorentz and polarisation effects, for linear decay and for absorption by empirical corrections based on scans. The positions of ytterbium atoms were found by direct methods using SHELXS-86 [9], and all the other non-hydrogen atoms were located in subsequent Fourier difference maps. The structure was refined by full matrix least-squares procedures on F2 using SHELXL-93 [10]. The ytterbium, oxygen and carbon atoms of the methoxy groups were refined anisotropically. Phenyl rings were constrained to idealised hexagons and refined isotropically. In the asymmetric unit there are two molecules of THF solvent severely disordered to which all atoms were assigned as carbons and refined isotropically. The contributions of the hydrogen atoms were included in calculated positions (except the hydroxo and the solvent hydrogen atoms). In the final difference Fourier map the highest peaks were 2.3 and 2.0 e Å3 , near the Yb atom. Atomic scattering factors and anomalous dispersion terms were taken as in [10]. The drawing was made with SCHAKAL [11].
3. Results and discussion Metallic europium and ytterbium react with 2-methoxyphenol in liquid ammonia to produce greenish yellow solids, soluble in tetrahydrofuran, toluene, dichloromethane and acetonitrile. These compounds were formulated by elemental analysis as Eu(OC6 H4 OMe)2 and Yb(OC6 H4 OMe)3 . The reaction of samarium metal with 2-methoxyphenol by metal vapour synthesis gave a grey solid, soluble in THF and dichlorometane and formulated as Sm(OC6 H4 OMe)3 . These results were in agreement with analogue reactions involving phenols containing supplementary donor functions, namely 2-aminophenol, 2,6-dimethoxyphenol and 2-amino-p-cresol, for which similar formulations were obtained [12]. The IR spectra were consistent with the presence of aryloxide groups. The 1 H NMR spectra of the
J. Carretas et al. / Journal of Alloys and Compounds 374 (2004) 289–292
samarium and ytterbium compounds contained broad peaks in the aromatic region but did not reveal useful information. The Mössbauer spectrum of the europium compound was typical for a divalent compound [13]. Since these data were not structurally definitive we tried to characterise these products by X-ray crystallography. Crystallisation of the Yb/2-methoxyphenol reaction product in the presence of THF/pentane forms the hydroxo complex [Yb6 (OH)4 (OC6 H4 OMe)14 ]·4THF after 2 weeks. This presumed decomposition product was also obtained when the reaction and the process of recrystallization were repeated. The same result was obtained after recrystallization of a sample obtained by reaction of YbCl3 with the sodium phenoxide in THF. 3.1. Crystal structure of [Yb6 (µ3 -OH)4 (µ-OC6 H4 -η-OMe)10 (OC6 H4 -η-OMe)2 (OC6 H4 OMe)2 ]·4THF The X-ray structural analysis (Fig. 1) revealed a hexanuclear 3 -hydroxo complex of overall formula [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 --OMe)2 (OC6 H4 OMe)2 ]. The six ytterbium atoms form a nearly planar arrangement, being all eight-coordinate with a distorted square antiprismatic geometry. Although the hydrogen atoms of the hydroxo ligands could not be crystallographically located, unambiguous assignment as 3 -hydroxo was made on the basis of the overall charge of the Yb(III) complex and also on the basis of
291
the sum of the Yb–O–Yb angles of 314.7(6)◦ and 311.9(6)◦ around O(1) and O(2) atoms, respectively (close to the value of 328.4◦ expected for pure sp3 hybridized atoms). The molecule has crystallographically imposed C2 symmetry. The Yb(1) and Yb(2) atoms are located on a crystallographic two-fold axis and are joined to one another and to the other Yb atoms by four triply bridging hydroxo ligands and by 10 bridging–chelating aryloxides (atoms O(3)–O(7) and their symmetrical equivalents). Two terminal aryloxides with chelating methoxy groups (O(9), O(9 )) and two terminal aryloxides with no chelating groups (O(8), O(8 )) complete the cluster molecule. The four crystallographically independent ytterbium atoms are located in different coordinate environments. The Yb(1) atom is eight-coordinate to four -OH triple bridges, and to four aryloxide groups (O(3), O(3 ), O(4), O(4 )). Yb(2) is eight-coordinate to two 3 -OH brigdes, to four aryloxide groups (O(5), O(5 ), O(6), O(6 )), and two methoxy groups (O(15), O(15 )). Yb(3) is 8-coordinate to a terminal aryloxide group O(8), to two 3 -OH bridges, to three bridging aryloxides (O(5), O(6), O(7)), and to two methoxy groups (O(10), O(13)). Yb(4) is eight-coordinate to one 3 -OH bridge, to four aryloxide groups (O(3), O(4), O(7), O(9)) and to three methoxy groups (O(11), O(14), O(16)). The metal–oxygen bond lengths range from 2.09(2) to 2.49(2) Å and follow the order Yb-(OR-OMe) < Yb-(OR--OMe) < Yb-(-OR--OMe) < Yb--OH < Yb-OMe. The terminal aryloxides with no chelating methoxy groups have the shortest Yb–O bond length, Yb(3)–O(8) = 2.085(15) Å and the largest Yb–O–C bond angle of 162.2(17)◦ . The Yb–O bond distance of the terTable 2 Selected bond lengths (Å) and angles (degree) for [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 --OMe)2 (OC6 H4 OMe)2 ]·4THF Terminal Yb–O Yb(3)–O(8)
Fig. 1. Molecular structure of [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 --OMe)2 (OC6 H4 OMe)2 ]·4THF.
Yb(4)– O(9)
2.15(2)
Bridging Yb-(-OC6 H4 --OMe) Yb(1)–O(3) 2.31(2) Yb(4)–O(3) 2.271(15) Yb(1)–O(4) 2.353(15) Yb(4)–O(4) 2.284(14) Yb(2)–O(5) 2.27(2)
Yb(3)–O(5) Yb(2)–O(6) Yb(3)–O(6) Yb(3)–O(7) Yb(4)–O(7)
2.25(2) 2.227(14) 2.41(2) 2.28(2) 2.27(2)
Yb–OMe Yb(3)–O(10) Yb(4)–O(11) Yb(3)–O(13)
2.48(2) 2.45(2) 2.49(2)
Yb(4)–O(14) Yb(2)–O(15) Yb(4)–O(16)
2.37(2) 2.45(3) 2.49(2)
Yb-(3 -OH) Yb(1)–O(1) Yb(3)–O(1) Yb(4)–O(1)
2.288(13) 2.39(2) 2.34(2)
Yb(1)–O(2) Yb(2)–O(2) Yb(3)–O(2)
2.398(14) 2.311(13) 2.36(2)
Yb(3) –O(8)–C(86) Yb(1)–O(3)–C(36) Yb(4)–O(3)–C(36) Yb(1)–O(4)–C(46) Yb(4)–O(4)–C(46) Yb(2)–O(5)–C(56)
2.085(15)
162.2(17) 136.2(12) 123.9(11) 137.8(12) 119.2(13) 136.7(14)
Yb(4)–O(9)–C(96) Yb(3)–O(5)–C(56) Yb(2)–O(6)–C(66) Yb(3)–O(6)–C(66) Yb(3)–O(7)–C(76) Yb(4)–O(7)–C(76)
125.4(18) 124.5(16) 122.2(15) 141.9(16) 111.1(12) 128.0(12)
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minal aryloxide with the chelating methoxy is 2.15(2) Å (Yb(4)–O(9)). The average bridging Yb--OR, 2.29 Å, is shorter than the average Yb--OH bond length of 2.34 Å and than the value of 2.45 Å for the Yb–OMe distance (see Table 2). Hexanuclear alkoxide lanthanide clusters have been reported, such as [Gd6 (4 -O)(OC2 H4 OMe)16 [14] and [Nd6 (6 -Cl)(OPri )17 ] [15]. Bridging hydroxo bonds have been observed in the divalent europium complex [Eu4 (OC6 H3 Pri2 -2,6)6 (3 -OH)2 (NCMe)6 ] [16], in the mixed valent EuII /EuIII complex [Eu5 (4 -OH)(3 OH)4 (OC6 H3 Pri2 -2,6)6 (NCMe)8 ] [17] and in the trivalent complexes [Nd4 (3 -OH)2 (acac)10 ] [18], [Yb(OC6 H2 But3 2,4,6)2 (-OH)(THF)]2 [19], and [Lu4 (4 -O)(3 -OH) (OCMe2 CH2 OMe)9 ] [20].
4. Final remarks The 2-methoxyphenoxides of samarium, europium and ytterbium were synthesized by MVS and by dissolution in liquid ammonia. The recrystallization of the ytterbium aryloxide originated reproducibly the formation of the hydroxo complex [Yb6 (OH)4 (OC6 H4 OMe)14 ]·4THF.
Acknowledgements We are grateful to the Fundação Calouste Gulbenkian for supporting the participation of the corresponding author in the ICFE’5 and to Dr. I.C. Santos for helping draw the figure.
References [1] J.M. Carretas, A. Pires de Matos, Mater. Chem. Phys. 31 (1992) 123. [2] J. Carretas, J. Branco, J. Marçalo, A. Domingos, A. Pires de Matos, Polyhedron 22 (2003) 1425. [3] J. Carretas, J. Branco, J. Marçalo, P. Isolani, A. Domingos, A. Pires de Matos, J. Alloys Compd. 322–324 (2001) 169. [4] A. Dias, J. Branco, T. Gasche, J. Carretas, A. Valente, J. Rocha, A. Pires de Matos, VI Encontro da Divisão de Catálise e Materias Porosos, Évora, Portugal, 2003. [5] A. Dias, J. Branco, T. Gasche, J. Carretas, A. Valente, A. Pires de Matos, in: 7th FIGIPS, Lisbon, Portugal, 2003. [6] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemicals, 3rd ed., Pergamon Press, Oxford, 1988. [7] J.G. Dick, Analytical Chemistry, McGraw-Hill, New York, 1973. [8] C.K. Fair, MOLEN, Enraf-Nonius, Delft, The Netherlands, 1990. [9] G.M. Sheldrick, SHELXS-86: Program for the Solution of Crystal Structure, University of Gottingen, Germany, 1986. [10] G.M. Sheldrick, SHELXL-93: Program for the Refinement of Crystal Structure, University of Gottingen, Germany, 1993. [11] E. Keller, SCHAKAL, J. Appl. Cryst. 22 (1989) 12. [12] J. Carretas, Ph.D. thesis, Faculdade de Ciˆencias da Universidade de Lisboa, 2002. [13] F. Grandjean, G.J. Long, Mössbauer Spectroscopy of Eu-containing compounds in Mössbauer Spectroscopy Applied to Inorganic Chemistry, vol. 3, Plenum Press, New York, 1989. [14] S. Daniele, L.G. Hubert-Pfalzgraf, J.C. Daran, Polyhedron 15 (1996) 1063. [15] R.A. Andersen, D.H. Templeton, A. Zalkin, Inorg. Chem. 17 (1978) 1962. [16] W.J. Evans, M.A. Greci, J.W. Ziller, J. Chem. Soc., Dalton Trans., (1997) 3035. [17] W.J. Evans, M.A. Greci, J.W. Ziller, Inorg. Chem. 39 (2000) 3213. [18] O. Poncelet, L.G. Hubert-Pfalzgraf, Polyhedron 8 (1989) 2183. [19] G.B. Deacon, T. Feng, S. Nickel, M.I. Ogden, A.H. White, Aust. J. Chem. 45 (1992) 671. [20] R. Anwander, F.C. Munck, T. Priermeier, W. Scherer, O. Runte, W.A. Herrman, Inorg. Chem. 36 (1997) 3545.
Synthesis and characterization of samarium, europium and ytterbium aryloxides Crystal structure of [Yb6(OH)4 (OC6H4 OMe)14 ]·4THF José Carretas∗ , Joaquim Branco, Joaquim Marçalo, Nuno Valente, João Carlos Waerenborgh, ˆ Adelaide Carvalho, Noémia Marques, Angela Domingos, António Pires de Matos Departamento de Qu´ımica, Instituto Tecnológico e Nuclear, Estrada Nacional 10, P-2686-953 Sacavém, Portugal
Abstract The reactions of samarium, europium and ytterbium metals with the potential bidentate ligand 2-methoxyphenol were investigated. The europium and ytterbium aryloxides were synthesized by dissolution of the metals in liquid ammonia, whereas the samarium aryloxide was synthesized by metal vapour synthesis (MVS). The compounds obtained were formulated as Ln(OC6 H4 OMe)3 , Ln = Sm, Yb and Eu(OC6 H4 OMe)2 . Recrystallization of Yb(OC6 H4 OMe)3 in the presence of THF/pentane resulted in the crystallographically characterized complex [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 --OMe)2 (OC6 H4 OMe)2 ]·4THF. © 2003 Elsevier B.V. All rights reserved. Keywords: Samarium; Europium; Ytterbium; Aryloxides
1. Introduction
2. Experimental
Over the last years we have studied the reactions of lanthanide metals with several phenols using the metal vapour synthesis (MVS) technique [1,2], and the metal dissolution in liquid ammonia [2,3]. The type of ligands used was diverse ranging from the less to the more bulky phenols, including simple and polycyclic phenols. In the literature the lanthanide aryloxide chemistry consists mainly of derivatives of classical phenols, whereas examples of aryloxide ligands containing additional donor groups are scarce. Having in mind the preparation of very pure aryloxides as precursors of catalysts supported on amorphous and mesoporous silica [4,5] we have been investigating the reactions of lanthanide metals with potential polydentate phenols. In this work we studied the reactions of samarium, europium and ytterbium metals with 2-methoxyphenol by the MVS technique and by dissolution in liquid ammonia. We report here the crystal structure of the complex [Yb6 (OH)4 (OC6 H4 OMe)14 ]·4THF.
All manipulations were routinely performed under N2 using glove-box and Schlenk techniques. MVS experiments were made in a Planer products plant VPS 500. Solvents and 2-methoxyphenol were purified by standard methods [6]. Samarium, europium and ytterbium ingots were obtained commercially from the Baotou Research Institute of Rare Earth. C, H and N analyses were performed in a CE instruments EA1110 automatic analyser. Sm, Eu and Yb analyses were performed according to a standard gravimetric method [7]. IR spectra were registered in a 577 Perkin-Elmer spectrometer with samples prepared as Nujol mulls. 1 H NMR spectra were recorded using a Varian Unity Inova 300 MHz spectrometer. Europium Mössbauer spectra were measured with the absorber at 80 K. The spectrometer was operated in constant acceleration. The source was samarium-151 in a SmF3 matrix. All absorbers were encapsulated in a special air tight sample holder. 2.1. Sm(OC6 H4 OMe)3
∗ Corresponding author. Tel.: +351-1219946218; fax: +351-1219941455. E-mail address: [email protected] (J. Carretas).
0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.11.120
Samarium atoms (1.69 g, 11.24 mmol) were vaporised with a resistance heating furnace (480 W) and were co-condensed with 40 ml of 2-methoxyphenol (36.38 mmol)
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J. Carretas et al. / Journal of Alloys and Compounds 374 (2004) 289–292
onto a liquid nitrogen-cooled surface over a period of 3 h. The resultant mixture was allowed to warm slowly to room temperature under a nitrogen atmosphere. The product was washed out with THF and filtered through a Celite bed. Volatile components were removed under vacuum and the resultant grey solid was washed with pentane. The reaction product obtained was formulated as Sm(OC6 H4 OMe)3 (yield = 67%). Analysis found (%): Sm, 27.22; C, 50.19; H, 4.24. Calculated for SmO6 C21 H21 : Sm, 28.93; C, 48.52; H, 4.08. IR (cm−1 ): 3480w, 2700w, 2550w, 2400w, 2300w, 2240w, 2110w, 1640w, 1570s, 1440s, 1370m, 1310w, 1270w, 1250m, 1200w, 1160w, 1100m, 1030w, 1000s, 940w, 900w, 840s, 750s, 715s, 595m, 560w, 530w, 500w, 460w, 390m. 2.2. Eu(OC6 H4 OMe)2 Europium (3.52 g, 23.16 mmol) was added to a solution of 5 ml of 2-methoxyphenol (45.46 mmol) in THF (100 ml), in a 250 ml Schlenk flask. The flask was connected to a vacuum line and liquid ammonia was condensed into the reaction vessel at 195 K. After 3 h the reaction mixture was allowed to slowly warm to room temperature and was purged with N2 . This mixture was then filtered through a Celite bed and the solution evaporated. The product was washed several times with pentane and a greenish yellow solid formulated as Eu(OC6 H4 OMe)2 was obtained after drying under vacuum (yield = 74%). Analysis found (%): Eu, 37.05; C, 42.32; H, 3.60. Calculated for EuO4 C14 H14 : Eu, 38.16; C, 42.22; H, 3.55. IR (cm−1 ): 2540w, 1570s, 1470s, 1440s, 1370m, 1315m, 1280s, 1245s, 1200s, 1160m, 1100m, 1030m, 1010s, 880w, 840m, 780w, 750m, 715s, 595m, 560w, 525w, 460w, 385w. Mössbauer (80 K) {δ (mm s−1 ), e2 qQ (mm s−1 ), η, Γ (mm s−1 ), I (%)}: Eu2+ , −13.2(1), 16.7(3), 1, 3.3(1), 96(1); Eu3+ , 0.1(4), −, −, 3.7, 4(1). 2.3. Yb(OC6 H4 OMe)3 The procedure for the reaction of ytterbium (2.50 g, 14.45 mmol) with 2-methoxyphenol (4.7 ml, 42.73 mmol) was identical to that for the europium reaction. A greenish yellow solid formulated as Yb(OC6 H4 OMe)3 was obtained (yield = 77%). Analysis found (%): Yb, 30.80; C, 48.21; H, 3.75. Calculated for YbO6 C21 H21 : Yb, 31.90; C, 46.49; H, 3.91. IR (cm−1 ): 2580w, 2300w, 1580m, 1480s, 1450s, 1370m, 1320w, 1280w, 1250m, 1210w, 1160w, 1110s, 1035m, 1010s, 900w, 845s, 755s, 730s, 595w, 580w, 530w, 460w, 400w. X-ray quality crystals were grown from a solution of the product in THF/pentane at room temperature. 2.4. X-ray crystallographic analysis Yellow crystals were mounted in thin-walled glass capillaries in a nitrogen-filled glove-box. Data were collected at room temperature on an Enraf-Nonius CAD4-diffractometer with graphite-monochromatized Mo K␣ radiation, using a
Table 1 Crystallographic data for [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 -OMe)2 (OC6 H4 OMe)2 ]·4THF Formula Molecular weight Crystal system Space group a (Å) b (Å) c (Å) β (degree) V (Å3 ) Z Dcalc (g cm−3 ) µ(Mo K␣) (mm−1 ) R1 a , wR2 b (I > 2(I)) a R = ||Fo | − |Fc ||/ |Fo |. 1 1/2 b wR = (w(Fo2 − Fc2 )2 /(w(Fo2 )2 ) . 2
C114 H134 O36 Yb6 3118.45 Monoclinic C2/c 22.221(2) 16.803(2) 30.938(2) 90.711(6) 11551(2) 4 1.793 4.889 0.0881, 0.1923
-2 scan mode. A summary of the crystallographic data is given in Table 1. Data were corrected [8] for Lorentz and polarisation effects, for linear decay and for absorption by empirical corrections based on scans. The positions of ytterbium atoms were found by direct methods using SHELXS-86 [9], and all the other non-hydrogen atoms were located in subsequent Fourier difference maps. The structure was refined by full matrix least-squares procedures on F2 using SHELXL-93 [10]. The ytterbium, oxygen and carbon atoms of the methoxy groups were refined anisotropically. Phenyl rings were constrained to idealised hexagons and refined isotropically. In the asymmetric unit there are two molecules of THF solvent severely disordered to which all atoms were assigned as carbons and refined isotropically. The contributions of the hydrogen atoms were included in calculated positions (except the hydroxo and the solvent hydrogen atoms). In the final difference Fourier map the highest peaks were 2.3 and 2.0 e Å3 , near the Yb atom. Atomic scattering factors and anomalous dispersion terms were taken as in [10]. The drawing was made with SCHAKAL [11].
3. Results and discussion Metallic europium and ytterbium react with 2-methoxyphenol in liquid ammonia to produce greenish yellow solids, soluble in tetrahydrofuran, toluene, dichloromethane and acetonitrile. These compounds were formulated by elemental analysis as Eu(OC6 H4 OMe)2 and Yb(OC6 H4 OMe)3 . The reaction of samarium metal with 2-methoxyphenol by metal vapour synthesis gave a grey solid, soluble in THF and dichlorometane and formulated as Sm(OC6 H4 OMe)3 . These results were in agreement with analogue reactions involving phenols containing supplementary donor functions, namely 2-aminophenol, 2,6-dimethoxyphenol and 2-amino-p-cresol, for which similar formulations were obtained [12]. The IR spectra were consistent with the presence of aryloxide groups. The 1 H NMR spectra of the
J. Carretas et al. / Journal of Alloys and Compounds 374 (2004) 289–292
samarium and ytterbium compounds contained broad peaks in the aromatic region but did not reveal useful information. The Mössbauer spectrum of the europium compound was typical for a divalent compound [13]. Since these data were not structurally definitive we tried to characterise these products by X-ray crystallography. Crystallisation of the Yb/2-methoxyphenol reaction product in the presence of THF/pentane forms the hydroxo complex [Yb6 (OH)4 (OC6 H4 OMe)14 ]·4THF after 2 weeks. This presumed decomposition product was also obtained when the reaction and the process of recrystallization were repeated. The same result was obtained after recrystallization of a sample obtained by reaction of YbCl3 with the sodium phenoxide in THF. 3.1. Crystal structure of [Yb6 (µ3 -OH)4 (µ-OC6 H4 -η-OMe)10 (OC6 H4 -η-OMe)2 (OC6 H4 OMe)2 ]·4THF The X-ray structural analysis (Fig. 1) revealed a hexanuclear 3 -hydroxo complex of overall formula [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 --OMe)2 (OC6 H4 OMe)2 ]. The six ytterbium atoms form a nearly planar arrangement, being all eight-coordinate with a distorted square antiprismatic geometry. Although the hydrogen atoms of the hydroxo ligands could not be crystallographically located, unambiguous assignment as 3 -hydroxo was made on the basis of the overall charge of the Yb(III) complex and also on the basis of
291
the sum of the Yb–O–Yb angles of 314.7(6)◦ and 311.9(6)◦ around O(1) and O(2) atoms, respectively (close to the value of 328.4◦ expected for pure sp3 hybridized atoms). The molecule has crystallographically imposed C2 symmetry. The Yb(1) and Yb(2) atoms are located on a crystallographic two-fold axis and are joined to one another and to the other Yb atoms by four triply bridging hydroxo ligands and by 10 bridging–chelating aryloxides (atoms O(3)–O(7) and their symmetrical equivalents). Two terminal aryloxides with chelating methoxy groups (O(9), O(9 )) and two terminal aryloxides with no chelating groups (O(8), O(8 )) complete the cluster molecule. The four crystallographically independent ytterbium atoms are located in different coordinate environments. The Yb(1) atom is eight-coordinate to four -OH triple bridges, and to four aryloxide groups (O(3), O(3 ), O(4), O(4 )). Yb(2) is eight-coordinate to two 3 -OH brigdes, to four aryloxide groups (O(5), O(5 ), O(6), O(6 )), and two methoxy groups (O(15), O(15 )). Yb(3) is 8-coordinate to a terminal aryloxide group O(8), to two 3 -OH bridges, to three bridging aryloxides (O(5), O(6), O(7)), and to two methoxy groups (O(10), O(13)). Yb(4) is eight-coordinate to one 3 -OH bridge, to four aryloxide groups (O(3), O(4), O(7), O(9)) and to three methoxy groups (O(11), O(14), O(16)). The metal–oxygen bond lengths range from 2.09(2) to 2.49(2) Å and follow the order Yb-(OR-OMe) < Yb-(OR--OMe) < Yb-(-OR--OMe) < Yb--OH < Yb-OMe. The terminal aryloxides with no chelating methoxy groups have the shortest Yb–O bond length, Yb(3)–O(8) = 2.085(15) Å and the largest Yb–O–C bond angle of 162.2(17)◦ . The Yb–O bond distance of the terTable 2 Selected bond lengths (Å) and angles (degree) for [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 --OMe)2 (OC6 H4 OMe)2 ]·4THF Terminal Yb–O Yb(3)–O(8)
Fig. 1. Molecular structure of [Yb6 (3 -OH)4 (-OC6 H4 --OMe)10 (OC6 H4 --OMe)2 (OC6 H4 OMe)2 ]·4THF.
Yb(4)– O(9)
2.15(2)
Bridging Yb-(-OC6 H4 --OMe) Yb(1)–O(3) 2.31(2) Yb(4)–O(3) 2.271(15) Yb(1)–O(4) 2.353(15) Yb(4)–O(4) 2.284(14) Yb(2)–O(5) 2.27(2)
Yb(3)–O(5) Yb(2)–O(6) Yb(3)–O(6) Yb(3)–O(7) Yb(4)–O(7)
2.25(2) 2.227(14) 2.41(2) 2.28(2) 2.27(2)
Yb–OMe Yb(3)–O(10) Yb(4)–O(11) Yb(3)–O(13)
2.48(2) 2.45(2) 2.49(2)
Yb(4)–O(14) Yb(2)–O(15) Yb(4)–O(16)
2.37(2) 2.45(3) 2.49(2)
Yb-(3 -OH) Yb(1)–O(1) Yb(3)–O(1) Yb(4)–O(1)
2.288(13) 2.39(2) 2.34(2)
Yb(1)–O(2) Yb(2)–O(2) Yb(3)–O(2)
2.398(14) 2.311(13) 2.36(2)
Yb(3) –O(8)–C(86) Yb(1)–O(3)–C(36) Yb(4)–O(3)–C(36) Yb(1)–O(4)–C(46) Yb(4)–O(4)–C(46) Yb(2)–O(5)–C(56)
2.085(15)
162.2(17) 136.2(12) 123.9(11) 137.8(12) 119.2(13) 136.7(14)
Yb(4)–O(9)–C(96) Yb(3)–O(5)–C(56) Yb(2)–O(6)–C(66) Yb(3)–O(6)–C(66) Yb(3)–O(7)–C(76) Yb(4)–O(7)–C(76)
125.4(18) 124.5(16) 122.2(15) 141.9(16) 111.1(12) 128.0(12)
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minal aryloxide with the chelating methoxy is 2.15(2) Å (Yb(4)–O(9)). The average bridging Yb--OR, 2.29 Å, is shorter than the average Yb--OH bond length of 2.34 Å and than the value of 2.45 Å for the Yb–OMe distance (see Table 2). Hexanuclear alkoxide lanthanide clusters have been reported, such as [Gd6 (4 -O)(OC2 H4 OMe)16 [14] and [Nd6 (6 -Cl)(OPri )17 ] [15]. Bridging hydroxo bonds have been observed in the divalent europium complex [Eu4 (OC6 H3 Pri2 -2,6)6 (3 -OH)2 (NCMe)6 ] [16], in the mixed valent EuII /EuIII complex [Eu5 (4 -OH)(3 OH)4 (OC6 H3 Pri2 -2,6)6 (NCMe)8 ] [17] and in the trivalent complexes [Nd4 (3 -OH)2 (acac)10 ] [18], [Yb(OC6 H2 But3 2,4,6)2 (-OH)(THF)]2 [19], and [Lu4 (4 -O)(3 -OH) (OCMe2 CH2 OMe)9 ] [20].
4. Final remarks The 2-methoxyphenoxides of samarium, europium and ytterbium were synthesized by MVS and by dissolution in liquid ammonia. The recrystallization of the ytterbium aryloxide originated reproducibly the formation of the hydroxo complex [Yb6 (OH)4 (OC6 H4 OMe)14 ]·4THF.
Acknowledgements We are grateful to the Fundação Calouste Gulbenkian for supporting the participation of the corresponding author in the ICFE’5 and to Dr. I.C. Santos for helping draw the figure.
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