The utility of N-methylimidazole and acetonitrile as solvents for the direct reaction of europium with alcohols including the first example of acetonitrile as a μ-η1 : η1-bridging ligand

Article abstract of DOI:10.1039/a805750h

N-Methylimidazole and acetonitrile are suitable solvents for the direct reactions of europium metal with 2,6-Me₂C₆H₃OH and 2,6-Prⁱ₂C₆H₃OH, which lead to crystallographically characterizable (N-methylimidazole)₃Eu(μ-OC₆H₃Me ₂2,6)₃Eu(N-methylimidazole)₂(OC ₆H₃Me₂-2,6) 1 and [(MeCN)₂(2,6-Prⁱ₂C₆H ₃O)Eu]₂(μ-OC₆H₃Me ₂-2,6)₂(μ-NCMe) 2, a complex which contains a μ-η¹-acetonitrile ligand.

Full text of DOI:10.1039/a805750h

The utility of N-methylimidazole and acetonitrile as solvents for the direct
reaction of europium with alcohols including the first example of acetonitrile
1
1
as a m-h :h -bridging ligand
William J. Evans,* Michael A. Greci and Joseph W. Ziller
Department of Chemistry, University of California, Irvine, California 92697-2025, USA. E-mail: wevans@uci.edu
Received (in Corvallis, OR, USA) 13th July 1998, Accepted 23rd September 1998
N-Methylimidazole and acetonitrile are suitable solvents for
the direct reactions of europium metal with 2,6-Me2C6H3OH
and 2,6-Pri2C6H3OH, which lead to crystallographically
O(bridging) bond lengths in 1 are in the range of analogous
bond lengths in the literature.4,12
Complex 2, like 1, is also bimetallic and has a face sharing
bioctahedral arrangement of ligand donor atoms. However, its
structure differs in that each metal atom has the same set of
ligands. Although reactions in liquid ammonia and coordinating
solvent yielded structurally similar complexes 1 and 3, complex
2 is substantially different from the product obtained from
europium and HOC6H3Pri2-2,6 in liquid ammonia, Eu4(m-
OC6H3Pri2-2,6)4(OC6H3Pri2-2,6)2(m3-OH)2(NCMe3)6 4.5 The
2.286(6) and 2.289(5) Eu–O(terminal), 2.438(6), 2.463(5),
characterizable
(N-methylimidazole)3Eu(m-OC6H3Me2-
2,6)3Eu(N-methylimidazole)2(OC6H3Me2-2,6)
1
and
[(MeCN)2(2,6-Pri2C6H3O)Eu]2(m-OC6H3Me2-2,6)2(m-NCMe)
1
2, a complex which contains a m-h -acetonitrile ligand.
Owing to the special fluorescent properties of europium,1 it is
desirable to be able to synthetically manipulate this element in
a variety of ways in order to optimize its incorporation into
devices of practical utility.2 Syntheses starting from the metal
are best since they avoid the preparation of starting materials,
such as chlorides or nitrates, require no drying of these
materials, and eliminate the possibility of incorporating some of
the starting material ligands into the final product. Europium
alkoxide and aryloxide complexes, potentially useful in sol-gel
processing,3 can be made by direct reaction of europium with
alcohols and phenols in liquid ammonia,4–6 by reaction of
europium with Hg(C6F5)2 in phenols,7 by reaction of europium
with Tl(OAr) in THF,7 and by reaction of europium with PriOH
in the presence of HgII catalysts,8 but more convenient are the
direct reactions of europium solely with liquid alcohols.9,10
However, the latter route is not as suitable for solid 2,6-dialkyl-
phenols, which provide good ligands for stabilizing and
solubilizing europium ions and for making polyeuropium
complexes.4–6,9 We report here that by using N-methylimida-
zole and acetonitrile as solvents, direct reactions of europium
with 2,6-dialkylphenols can be achieved to form fully character-
izable europium aryloxide complexes. In addition, we report a
new type of bonding mode for acetonitrile.
2.487(5)
and
2.494(6)
Eu–O(bridging),
and
the
2.625(9)–2.667(9) Å Eu–N(terminal) bond lengths in 2 are not
unusual for europium(ii) aryloxide complexes.5,12
1
1
The most remarkable feature in 2 is that it contains a m-h :h -
acetonitrile ligand, which, to our knowledge, is the first
observation of this binding mode for acetonitrile. The 2.847(8)
and 2.913(9) Å Eu–N bond lengths of the bridging acetonitrile
are longer than the Eu–N(terminal) distances in 2, as expected.
Europium reacts slowly with 2,6-Me2C6H3OH and 2,6-Pri2-
C6H3OH at room temperature in N-methylimidazole or acetoni-
trile to form yellow solutions of paramagnetic divalent
europium complexes.† Each 2,6-R2C6H3OH reacts in each
solvent, but the R = Me/N-methylimidazole and R = Pri/
MeCN combinations readily provide crystallographically char-
Fig. 1 Plot of Eu2(OC6H3Me2-2,6)4(N-methylimidizole)5 1 with thermal
ellipsoids drawn at the 50% probability level and hydrogen atoms omitted
for clarity.
acterizable
complexes.‡
(N-methylimidazole)3Eu(m-
OC6H3Me2-2,6)3Eu(N-methylimidazole)2(OC6H3Me2-2,6)
1
(Fig. 1) and [(MeCN)2(2,6-Pri2C6H3O)Eu]2(m-OC6H3Me2-
2,6)2(m-NCMe) 2 (Fig. 2).
The bimetallic nature of 1 and the arrangement of the anionic
ligands are identical to those reported for (DME)2Eu(m-
OC6H3Me2-2,6)3Eu(OC6H3Me2-2,6)(DME) 3 (DME = 1,2-
dimethoxyethane), isolated from a Eu/HOC6H3Me2-2,6 liquid
ammonia reaction.4 This unsymmetrical arrangement has also
been observed in some calcium and barium alkoxide and
siloxide complexes.11 The structures of 1 and 3 differ in that
three N-methylimidazole ligands in 1 take the place of two
bidentate DME ligands in 3 and hence both europium atoms in
1 are six coordinate, whereas 3 contains one six- and one seven-
coordinate europium atom.
Each europium atom in 1 is surrounded by a distorted face
sharing bioctahedral arrangement of oxygen and nitrogen donor
atoms with the shared face consisting of anionic oxygen atoms.
The 2.365(3) Å Eu–O(terminal) and 2.479(3)–2.632(3) Å Eu–
Fig. 2 Thermal ellipsoid plot of Eu2(OC6H3Pri2-2,6)4(NCCH3)5 2 with
thermal ellipsoids drawn at the 50% probability level and hydrogen atoms
omitted for clarity.
Chem. Commun., 1998, 2367–2368
2367

comparison, for refinement on F, R1 = 0.0282 for those 7984 data with F >
4.0s(F)]. For 2: C58H83Eu2N5O4, M = 1218, monoclinic, space group Pn,
a = 11.8317(12), b = 21.6202(16), c = 12.9773(13) Å, b = 112.917(7)°,
V = 3057.6(5) Å, Z = 2, T = 158 K, m = 2.077 mm21, Mo-Ka radiation,
graphite monochromator. All 7348 data were collected using a Siemens P4
diffractometer, and handled as described for 1. All calculations were carried
out as described for 1 above and hydrogen atoms were included using a
riding model. At convergence, wR2 = 0.1141 and GOF = 0.766 for 627
variables refined against all 7348 unique data [in comparison, for
refinement on F, R1 = 0.0382 for those 6939 data with F > 4.0s(F)].
CCDC 182/1031.
The bridging is unsymmetrical with 164.5(8) and 105.0(7)° Eu–
N(5)–C(57) angles. This places C(57) closer to Eu(1) than
Eu(2), but the 3.391 Å Eu(1)–C(57) distance is too long to
2
constitute a Eu–C bond. Structurally characterized by m-h -
acetonitrile ligands have M–C(nitrile) interactions in the range
of 1.876(9) to 2.114(7) Å.13 The Eu(1)–N(5)–Eu(2) angle is
79.9(2)° and the Eu(1)–C(57)–Eu(2) angle is 59.9°. A space
1
1
filling model of 2 suggests that the m-h :h -nature of this ligand
and the inequivalence of the Eu–N(5)–C(57) angles arise
because there is only a limited space available for the
acetonitrile to fit between the bulky 2,6-diisopropylphenoxide
ligands.
1 R. C. Ropp, Luminescence and the Solid State, Elsevier, New York,
1991.
The results to date on divalent europium aryloxide chemistry
suggest that isolable, crystalline complexes more readily form
with either a combination of larger 2,6-dialkyl substituents,
such as isopropyl groups, and relatively small ligands, such as
acetonitrile, or with a combination of smaller 2,6-dialkyl
substituents, such as methyl groups, and larger ligands, such as
N-methylimidazole or 1,2-dimethoxyethane. Variable binding
modes are undoubtedly helpful in accommodating crowded
ligand environments and the structure of 2 demonstrates another
variation in the binding capacity of acetonitrile.
2 J. R. McColl and F. C. Palilla, in Industrial Applications of Rare Earth
Elements, ed. K. A. Gschneidner Jr., ACS Symp. Ser., American
Chemical Society, Washington, D.C., 1981, vol. 164, ch. 10;
W. A. Thorton, in Industrial Applications of Rare Earth Elements, ed.
K. A. Gschneidner Jr., ACS Symp. Ser., American Chemical Society,
Washington, D.C., 1981, vol. 164, ch. 11; R. C. Ropp, Studies in
Inorganic Chemistry 17, The Chemistry of Artificial Lighting Devices,
Lamps, Phosphors and Cathode Ray Tubes, Elsevier, New York,
1993.
3 D. C. Bradley, R. C. Mehrotra and D. P. Gaur, Metal Alkoxides,
Academic Press, London, 1978; D. C. Bradley, Chem. Rev., 1989, 89,
1317; L. G. Hubert-Pfalzgraf, New J. Chem., 1987, 11, 663.
4 W. J. Evans, W. G. McClelland, M. A. Greci and J. W. Ziller, Eur.
J. Solid State Inorg. Chem., 1996, 33, 145.
For support of this research, we thank the Division of
Chemical Sciences of the Office of Basic Energy Sciences of
the Department of Energy.
5 W. J. Evans, M. A. Greci and J. W. Ziller, J. Chem. Soc., Dalton Trans.,
1997, 3035.
6 Yb aryloxides can also be made in this way: B. Cetinkaya, P. B.
Hitchcock, M. F. Lappert and R. G. Smith, J. Chem. Soc., Chem.
Commun., 1992, 932.
7 G. B. Deacon, T. Feng, P. MacKinnon, R. H. Newham, S. Nickel,
B. W. Skelton and A. H. White, Aust. J. Chem., 1993, 46, 387.
8 L. M. Brown and K. S. Mazdiyasni, Inorg. Chem., 1970, 12, 2783.
9 W. J. Evans, M. A. Greci and J. W. Ziller, Inorg. Chem., in the press.
10 J. M. Carretas, J. Branco, J. Marçalo, J. C. Waerenborgh, N. Marques
and A. Pires de Matos, J. Alloys Compds., 1998, 275–277, 841.
11 K. G. Caulton, M. H. Chisholm, S. R. Drake and W. E. Streib, Angew.
Chem., Int. Ed. Engl., 1990, 29, 1483; S. R. Drake, W. E. Streib,
K. Folting, M. H. Chisholm and K. G. Caulton, Inorg. Chem., 1992, 31,
3205; J. A. Darr, S. R. Drake, M. B. Hursthouse and K. M. A. Malik,
Inorg. Chem., 1993, 32, 5704.
12 G. B. Deacon, C. M. Forsyth, B. M. Gatehouse and P. B. White, Aust.
J. Chem., 1990, 43, 795; J. R. van den Hende, P. B. Hitchcock,
S. A. Holmes, M. F. Lappert, W.-P. Leung, T. C. W. Mak and S. Prashar,
J. Chem. Soc., Dalton Trans., 1995, 1427.
13 F. A. Cotton and F. E. Ku¨hn, J. Am. Chem. Soc., 1996, 118, 5826;
J. L. Eglin, E. M. Hines, E. Valente and J. D. Zubkowski, Inorg. Chim.
Acta, 1995, 229, 113; D. Walther, H. Scho¨nberg, E. Dinjus and J. Sieler,
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Notes and references
† Compounds 1 and 2 are obtained by reaction of europium ingots (typically
5–10 mm in diameter) with HOC6H3Me2-2,6 in N-methylimidazole or
HOC6H3Pri2-2,6 in acetonitrile, respectively, over 2 days at room
temperature followed by centrifugation and recrystallization from the
supernatant. Single crystals of complex 2 were isolated in 40% yield from
the concentrated acetonitrile solution after several days. Single crystals of
complex 1 was isolated from the N-methylimidazole solution. However,
since the yield was low and the high boiling point of N-methylimidazole
made solvent removal tedious, an alternate procedure was developed. The
direct reaction of europium metal with HOC6H3Me2-2,6 in a dilute solution
of N-methylimidazole (0.5 ml) in toluene (7.0 ml), followed by centrifuga-
tion and removal of the toluene under vacuum, forms crystalline 1 in 20%
yield, based on reacted Eu. Both 1 and 2 give satisfactory elemental analyses
and the effective magnetic moments of 7.5 and 8.0 mB for 1 and 2,
respectively, are consistent with EuII.
¯
‡ Crystal data for 1: C52H66Eu2N10O4, M = 1199, triclinic, space group P1,
12.142(2), b 12.763(9), c 18.906(5) Å, a 71.60(4),
a
=
=
=
=
b = 73.718(10), g = 76.48(3)°, V = 2634.3(20) Å, Z = 2, T = 158 K,
m = 2.412 mm21, Mo-Ka radiation, graphite monochromator. The raw data
were processed with a local version of CARESS. All 9678 data points were
corrected for Lorentz and polarization effects and were placed on an
approximately absolute scale. All calculations were carried out using the
SHELXL program. The structure was solved by direct methods and refined
on F2 by full-matrix least-squares techniques. Hydrogen atoms were
included using a riding model. At convergence, wR2 = 0.0787 and
GOF = 1.036 for 613 variables refined against all 9199 unique data [in
Communication 8/05750H
2368
Chem Commun., 1998