U(IV) chalcogenolates synthesized via oxidation of uranium metal by dichalcogenides

Article abstract of DOI:10.1021/ic060560k

Treatment of uranium metal with dichalcogenides in the presence of a catalytic amount of iodine in pyridine affords molecular U(IV) chalcogenolates that do not require stabilizing ancillary ligands. Oxidation of U⁰ by PhEEPh yields monomeric se

Full text of DOI:10.1021/ic060560k

Inorg. Chem. 2006, 45, 7401−7407
U(IV) Chalcogenolates Synthesized via Oxidation of Uranium Metal
by Dichalcogenides
Andrew J. Gaunt, Brian L. Scott, and Mary P. Neu*
Actinide, Catalysis and Separations Chemistry (C-SIC), Chemistry DiVision, Los Alamos National
Laboratory, Mail Stop J-514, Los Alamos, New Mexico 87545
Received April 3, 2006
Treatment of uranium metal with dichalcogenides in the presence of a catalytic amount of iodine in pyridine affords
molecular U(IV) chalcogenolates that do not require stabilizing ancillary ligands. Oxidation of U0 by PhEEPh yields
monomeric seven-coordinate U(EPh)4(py)3 (E
2-EPh)2(CH3CN)2]2 (E S(3), Se(4)) are obtained by crystallization from solutions of 1 and 2 dissolved in acetonitrile.
Oxidation of U0 by pySSpy and crystallization from thf yields nine-coordinate U(Spy)4(thf) (5). Incorporation of
elemental selenium into the oxidation of U0 by PhSeSePh results in the isolation of [U(py)2(SePh)(
3-Se)-
2-SePh)]4 4py (6), a tetrameric cluster in which each U(IV) ion is eight-coordinate and the U4Se4 core forms a
distorted cube. The compounds were analyzed spectroscopically and the single-crystal X-ray structures of 1 and
6 were determined. The isolation of 1 6 represents six new examples of actinide chalcogenolates and allows
insight into the nature of “hard” actinide ion ”soft” chalcogen donor interactions.
) S(1), Se(2)). The dimeric eight-coordinate complexes [U(EPh)2-
(µ
)
µ
(
µ
‚
3
−
−
−
Introduction
prepare homoleptic complexes without the steric influences
of bulky stabilizing substituents. Relatively recently, it has
been shown that oxidation of elemental lanthanides is a viable
synthetic route to unsupported complexes containing only
chalcogenolate anions and solvent molecules bound to the
lanthanide ion.2 There are examples of molecular actinide
chalcogenolates; however, many include sterically bulky,
inert Cp* or other stabilizing ligands.3 There is a clear scope
for advancing actinide chalcogenolate chemistry, particularly
by isolating complexes in which the chalcogenolate is the
only coordinated anion. In this paper, we report the oxidation
of uranium metal by dichalcogenides as a method for pre-
paring tetravalent molecular uranium chalcogenolates without
ancillary stabilizing ligands.
Interest in 5f element chemistry with nontraditional donor
atom ligands is necessary for fully comprehending the
chemical-bonding possibilities and electronic interactions of
these elements. Bonding in actinide complexes is dominated
by ionic interactions with ligands containing “hard” donors
such as oxygen. The degree to which covalency is a fac-
tor in bonding with “softer” donors such as sulfur and
selenium is uncertain, largely because of a paucity of well-
characterized molecular compounds. Actinide coordination
complexes with thiolates and, in particular, selenolates have
received scant attention compared to transition metal and
lanthanide complexes. Historically, lanthanide-chalcogen
bonds were generally supported by sterically demanding
ancillary ligands.1 Although such compounds are of interest,
in order to move toward a more complete understanding of
the nature of f metal ion-chalcogen bonds, it is desirable to
Experimental Section
All reactions were performed in an MBraun Labmaster 130
helium atmosphere drybox. Diethyl ether and thf were dried using
activated alumina columns (A2, 12 32, Purify). Other solvents were
* To whom correspondence should be addressed. E-mail: mneu@lanl.gov.
Fax: 505-667-9905. Phone: 505-667-7717.
(1) (a) Hillier, A. C.; Liu, S.-Y.; Sella, A.; Elsegood, M. R. J. Inorg. Chem.
2000, 39, 2635. (b) Cary, D. R.; Ball, G. E.; Arnold, J. J. Am. Chem.
Soc. 1995, 117, 3492. (c) Evans, W. J.; Rabe, G. W.; Ziller, J. W.;
Doedens, R. J. Inorg. Chem. 1994, 33, 2719. (d) Berg, D. J.; Burns,
C. J.; Andersen, R. A.; Zalkin, A. Organometallics 1989, 8, 1865. (e)
Berg, D. J.; Andersen, R. A.; Zalkin, A. Organometallics 1988, 7,
1858. (f) Zalkin, A.; Berg, D. J. Acta Crystallogr., Sect. C 1988, 44,
1488. (g) Schumann, H.; Albrecht, I.; Hahn, E. Angew. Chem., Int.
Ed. 1985, 24, 985. (h) Nief, F. Coord. Chem. ReV. 1998, 178, 13.
(2) (a) Melman, J. H.; Rohde, C.; Emge, T. J.; Brennan, J. G. 2002, 41,
28. (b) Lee, J.; Freedman, D.; Melman, J. H.; Brewer, M.; Sun, L.;
Emge, T. J.; Long, F. H.; Brennan, J. G. Inorg. Chem. 1998, 37, 2512.
(c) Berardini, M.; Lee, J.; Freedman, D.; Lee, J.; Emge, T. J.; Brennan,
J. G. Inorg. Chem. 1997, 36, 5772. (d) Mashima, K.; Nakayama, Y.;
Shibahara, T.; Fukumoto, H.; Nakamura, A. Inorg. Chem. 1996, 35,
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10.1021/ic060560k CCC: $33.50
Published on Web 08/01/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 18, 2006 7401

Gaunt et al.
purchased in anhydrous grade from Aldrich and all solvents were
stored over a 1:1 mixture of 3 and 4 Å molecular sieves before
use. Oxide-free uranium metal foil was prepared in a manner
previously described.4 Infrared spectra were obtained as Nujol mulls
between KBr plates on a Nicolet Magna-IR 560 spectrometer
equipped with a DTGS detector. All 1H NMR spectra were
referenced to residual protio resonances and obtained on samples
in 4 mm Teflon NMR tube liners inserted into 5 mm NMR tubes
in order to multiply contain the radioactive samples. NMR spectra
were recorded at ambient temperature on a Bruker Avance 300
MHz spectrometer. Electronic absorption spectra were recorded on
a Varian Cary 6000i UV-vis-nIR spectrophotometer. Elemental
analyses were performed by the Micro-Mass facility at the Uni-
versity of California, Berkeley, CA. Some of the elemental analyses
are slightly lower than expected. Similar findings for trivalent
lanthanide complexes have been attributed to thermal dissociation
of neutral donor atom ligands at ambient temperature.2b
(0.3005 g, 0.963 mmol) and a catalytic amount of iodine (0.0103 g,
0.041 mmol). The mixture was heated at 60 °C for 36 h and then
stirred at ambient temperature for 6 days. The red-brown solution
was filtered through a glass fiber circle to remove unreacted uranium
metal. The solvent was removed in vacuo to give a viscous residue
that was washed with hexanes (10 cm3) and dried in vacuo to give
a red-brown powder that was washed with hexanes (5 cm3) on a
medium porosity frit and dried in vacuo again (0.4781 g, 90% yield
based on PhSeSePh).
IR (KBr, Nujol; cm-1): 1576(m), 1465(s), 1378(s), 1308(m),
1218(m), 1171(w), 1155(m), 1065(m), 1038(m), 1020(m), 1003-
(m), 977(w), 939(w), 921(w), 897(w), 846(w), 775(w), 765(w), 752-
(m), 733(s), 725(s), 691(s), 663(m), 622(m), 460(m). UV-vis-nIR
(solution of 2 in pyridine; λmax, nm): 687, 842, 894, 1170, 1266,
1368, 1492. 1H NMR (CD2Cl2): Three broad resonances for pyri-
dine at 8.62, 7.69, and 7.30 ppm. Anal. Calcd for C39H35N3Se4U:
C, 42.60; H, 3.21; N, 3.82. Found: C, 41.71; H, 3.01; N, 3.90.
[U(SPh)2(µ2-SPh)2(CH3CN)2]2 (3). Compound 1 (0.1033 g,
0.1133 mmol) was dissolved in actonitrile (3 cm3) and filtered to
remove a significant amount of undissolved material; the volume
of the filtrate was reduced in vacuo to 1.5 cm3, and diethyl ether
was allowed to vapor diffuse into the filtrate to give dark brown
blocks suitable for X-ray diffraction (0.0206 g, 24% yield based
on U).
U(SPh)4(py)3 (1). Uranium metal (0.1640 g, 0.689 mmol)
suspended in pyridine (7 cm3) was treated with diphenyl disulfide
(0.1918, 0.878 mmol) and a catalytic amount of iodine (0.0093 g,
0.037 mmol). The mixture was heated at 60 °C for 36 h and then
stirred at ambient temperature for 6 days. The brown solution was
filtered through a glass fiber circle to remove unreacted uranium
metal. The solvent was removed in vacuo to give a viscous residue
that was washed with hexanes (7 cm3) and dried in vacuo to give
a brown powder that was washed with hexanes (5 cm3) on a medium
porosity frit and dried in vacuo again (0.3579 g, 89% yield based
on PhSSPh). A single crystal suitable for X-ray diffraction was
grown by crystallization from a pyridine solution layered with
hexanes.
IR (KBr, Nujol; cm-1): 1559(w), 1540(w), 1466(s), 1377(s),
1304(m), 1170(m), 1156(m), 1079(m), 1065(w), 1038(w), 1023(m),
975(m), 938(w), 920(w), 893(w), 849(w), 734(s, sh), 723(s), 688-
(w). UV-vis-nIR (prepared in situ by dissolving 1 in CH3CN;
λmax, nm): 687, 1125, 1449. Anal. Calcd for C56H52N4S8U2: C,
44.44; H, 3.46; N, 3.70. Found: C, 43.43; H, 3.32; N, 3.58.
[U(SePh)2(µ2-SePh)2(CH3CN)2]2 (4). An X-ray diffraction qual-
ity single crystal of 4 was grown by vapor diffusion of hexanes
into an acetonitrile solution of 2.
IR (KBr, Nujol; cm-1): 1578(m), 1467(s), 1378(s), 1308(m),
1218(w), 1171(w), 1154(m), 1080(m), 1065(m), 1038(m), 1024(m),
1003(m), 975(w), 941(w), 920(w), 898(w), 849(w), 770(m), 737(s),
722(s), 688(s), 626(m), 475(m). UV-vis-nIR (solution of 1 in
U(Spy)4(thf) (5). Uranium metal (0.1615 g, 0.679 mmol) sus-
pended in pyridine (5 cm3) was treated with dipyridyl disulfide
(0.2243 g, 1.018 mmol) and a catalytic amount of iodine (0.0078
g, 0.031 mmol). The mixture was heated at 70 °C for 30 min and
then stirred at ambient temperature for 10 days. The solvent was
removed in vacuo to give a viscous dark brown residue that was
washed with hexanes (2 × 10 cm3) and dried in vacuo to give a
yellow powder (0.3574 g). The powder was dissolved in thf
(15 cm3) and filtered; the volume of the filtrate was reduced to
2.5 cm3 in vacuo, and diethyl ether was allowed to vapor diffuse
into the filtrate to give yellow-brown crystals over a few days. The
crystals were dried in vacuo to give a yellow-brown powder (0.2404
g, 65% yield based on pySSpy and a product formula of U(Spy)4).
The crystals that formed from vapor diffusion of diethyl ether into
the thf solution were of suitable quality for analysis by single-crystal
X-ray diffraction.
1
pyridine; λmax, nm): 609, 643, 686, 1165, 1245, 1353, 1483. H
NMR (CD2Cl2): Three broad resonances for pyridine at 8.61, 7.68,
and 7.26 ppm. Anal. Calcd for C39H35N3S4U: C, 51.63; H, 3.87;
N, 4.61. Found: C, 47.35; H, 3.32; N, 2.36.
U(SePh)4(py)3 (2). Uranium metal (0.1797 g, 0.755 mmol) sus-
pended in pyridine (7 cm3) was treated with diphenyl diselenide
(3) (a) Arliguie, T.; Lescop, C.; Ventelon, L.; Leverd, P. C.; Thue´ry, P.;
Nierlich, M.; Ephritikhine, M. Organometallics 2001, 20, 3698. (b)
Ventelon, L.; Lescop, C.; Arliguie, T.; Leverd, P. C.; Lance, M.;
Nierlich, M.; Ephritikhine, M. Chem. Commun. 1999, 659. (c) Lescop,
C.; Arliguie, T.; Lance, M.; Nierlich, M.; Ephritikhine, M. J.
Organomet. Chem. 1999, 580, 137. (d) Rose, D. J.; Chen, Q.; Zubieta,
J. Inorg. Chim. Acta 1998, 268, 163. (e) Leverd, P. C.; Ephritikhine,
M.; Lance, M.; Vigner, J.; Nierlich, M. J. Organomet. Chem. 1996,
507, 229. (f) Leverd, P. C.; Lance, M.; Vigner, J.; Nierlich, M.;
Ephritikhine, M. J. Chem. Soc., Dalton Trans. 1995, 237. (g) Rose,
D.; Chang, Y.-D.; Chen, Q.; Zubieta, J. Inorg. Chem. 1994, 33, 5167.
(h) Leverd, P. C.; Arliguie, T.; Lance, M.; Nierlich, M.; Vigner, J.;
Ephritikhine, M. J. Chem. Soc., Dalton Trans. 1994, 501. (i) Leverd,
P. C.; Lance, M.; Nierlich, M.; Vigner, J.; Ephritikhine, M. J. Chem.
Soc., Dalton Trans. 1994, 3563. (j) Leverd, P. C.; Lance, M.; Nierlich,
M.; Vigner, J.; Ephritikhine, M. J. Chem. Soc., Dalton Trans. 1993,
2251. (k) Leverd, P. C.; Arliguie, T.; Ephritikhine, M.; Nierlich, M.;
Lance, M.; Vigner, J. New. J. Chem. 1993, 17, 769. (l) Clark, D. L.;
Miller, M. M.; Watkin, J. G. Inorg. Chem. 1993, 32, 772. (m)
Domingos, A.; Pires de Matos, A.; Santos, I. Polyhedron 1992, 11,
1601. (n) Tatsumi, K.; Matsubara, I.; Inoue, Y.; Nakamura, A.; Cramer,
R. E.; Tagoshi, G. J.; Golen, J. A.; Gilje, J. W. Inorg. Chem. 1990,
29, 4928. (o) Lin, Z.; Brock, C. P.; Marks, T. J. Inorg. Chim. Acta
1988, 141, 145. (p) Jones, R. G.; Karmas G.; Martin Jr., G. A.; Gilman,
H. J. Am. Chem. Soc. 1956, 78, 4285.
IR (KBr, Nujol; cm-1): 1586(m), 1547(m), 1465(s), 1412(m),
1378(s), 1311(w), 1262(m), 1257(m), 1241(w), 1221(w), 1182(w),
1139(m), 1133(m), 1085(m), 1075(w), 1067(w), 1037(m), 1016-
(w), 1002(m), 967(w), 923(w), 860(m), 754(s), 738(m), 727(s),
697(m), 639(m), 624(w), 484(m), 451(m). UV-vis-nIR (solution
1
of 5 in benzene; λmax, nm): 606, 699, 893, 1130, 1215, 1568. H
NMR (CD2Cl2): Four broad resonances at 12.14, 8.34, 7.78, and
4.35 ppm and two less-intense broad resonances at 5.62 and
3.51 ppm. Two signals for thf at 3.12 and 1.58 ppm. Anal. Calcd
for C24H20N4S4U (excluding the thf molecule): C, 39.45; H, 2.76;
N, 7.67. Found: C, 37.84; H, 2.86; N, 7.87.
[U(py)2(SePh)(µ3-Se)(µ2-SePh)]4‚4py (6) Uranium metal (0.1756
g, 0.738 mmol) suspended in pyridine (7 cm3) was treated with
PhSeSePh (0.3453 g, 1.106 mmol) and a catalytic amount of iodine
(4) (a) Enriquez, A. E.; Scott, B. L.; Neu, M. P. Inorg. Chem. 2005, 44,
7403. (b) Avens, L. R.; Bott, S. G.; Clark, D. L.; Sattelberger, A. P.;
Watkin, J. G.; Zwick, B. D. Inorg. Chem. 1994, 33, 2248.
7402 Inorganic Chemistry, Vol. 45, No. 18, 2006

U(IV) Chalcogenolates
Scheme 1. Outline of the Syntheses of 1-6 through Oxidation of
Uranium Metal by Dichalcogenides. A Catalytic Amount of Iodine was
Included in All of the Oxidations.
analyses, and the analyses are consistently found to be lower
than the calculated values. Similar results were found by
other researchers for lanthanide complexes;2a,10e that is, lower
than expected EA values because of the thermal dissocia-
tion of solvent molecules. Unfortunately, we do not have
the capability to measure powder X-ray diffraction patterns
on air-sensitive samples to be able to establish with certainty
that the bulk powdered samples are identical to the single
crystals.
U(EPh)4(py)3, (E ) S(1), Se(2)). Oxidation of U0 with
diphenyl disulfide and diphenyl diselenide results in isolation,
after workup, of 1 as a brown powder and 2 as a red-brown
powder, in 89 and 90% yields, respectively. Compound 1 is
crystallized by layering a pyridine solution with hexanes,
and its X-ray structure has been determined. Complex 1 is
a U(IV) monomer bonded to four PhS- anions and three
coordinated pyridine molecules (Figure 1). The geometry
about the seven-coordinate uranium center is best described
as distorted pentagonal bipyramidal with the S atoms of two
thiolate ligands in the apical positions and the two remaining
thiolate S atoms and three N atoms of the pyridine molecules
in the equatorial plane. The average U-S distance is 2.734-
(3) Å, and the average U-N distance is 2.597(9) Å (Table
2), which is normal for a pyridine molecule coordinated to
U(IV). The thiolate anions coordinate in a bent fashion with
an average U-S-C angle of 115.9(4)°. Single crystals suit-
able for X-ray diffraction could not be grown for the seleno-
late complex 2, but spectroscopic analysis suggests that a
formulation analogous to 1 is correct.
[U(EPh)2(µ2-EPh)2(CH3CN)2]2, (E ) S(3), Se(4)). Com-
pounds 1 and 2 are moderately soluble in acetonitrile, and
crystallization by vapor diffusion with diethyl ether and
hexanes gives 3 and 4, respectively, in which uranium dimers
have formed and the pyridine molecules have been displaced.
The X-ray crystal structures of 3 and 4 are isostructural (Fig-
ures 2 and 3). Both U(IV) centers are eight-coordinate, best
described as having triangular dodecahedral geometry,6 and
are bound to the N atoms of two terminal acetonitrile mol-
ecules, the E atoms of two terminal chalcogenolate anions,
and the E atoms of four bridging chalcogenolate anions. In
3, the U-Sterminal distance is 2.813(2) Å, the average
U-Sbridging distances are longer at 2.9378(19) and 2.8667-
(19) Å, and the U-N distance is 2.478(6) Å (Table 3). The
acetonitrile molecule is bent slightly away from uranium,
with a U-N-C angle of 171.5(8)°. In 4, the U-Seterminal
distance is 2.8491(12) Å, the U-Sebridging distances are longer
at 3.0564(10) and 2.9935(11) Å, and the U-N distance is
2.479(8) Å (Table 4). The angle between the bridging anions
and the two uranium atoms, U-E-U, is 82.88(5)° for 3 and
81.55(3)° for 4. The terminal chalcogenolate anions are bent
away from the uranium atoms, with a U-S-C angle of
116.8(4)° in 3 and 113.9(3)° in 4.
(0.0101 g, 0.040 mmol). The mixture was heated at 50 °C for 36 h
and then stirred at ambient temperature for 7 days. Elemental selen-
ium (0.0437 g, 0.553 mmol) was added to the reaction mixture,
and stirring continued at ambient temperature for 5 days. The red-
brown solution was filtered and the filtrate volume was reduced in
vacuo to 4 cm3; the filtrate was layered with hexanes (10 cm3) and
stored at -35 °C. After 3 weeks, the deep red powder that had
precipitated was collected and dried in vacuo (0.3497 g, 36% yield
based on PhSeSePh). X-ray diffraction quality crystals were
obtained by layering a concentrated pyridine solution with hexanes
and storing at -35 °C, resulting in some dark red-brown needles
after 1 day.
IR (KBr, Nujol; cm-1): 1599(m), 1576(w), 1570(w), 1559(w)
1464(s), 1378(s), 1308(m), 1218(m), 1172(w), 1155(m), 1065(m),
1038(m), 1020(m), 1003(m), 976(w), 936(w), 922(w), 896(w),
845(w), 772(w), 765(w), 751(w), 740(s, sh), 732(s), 723(s, sh),
691(s), 663(w), 622(w), 461(w). UV-vis-nIR (solution of 6 in
1
pyridine; λmax, nm): 685, 1170, 1364, 1491. H NMR (CD2Cl2):
Multiple unresolved resonances between 6.5 and 9.0 ppm. Anal.
Calcd for C108H100N12Se12U4: C, 37.43; H, 2.91; N, 4.85. Found:
C, 37.35; H, 2.77; N, 3.72.
Results
Oxidation of uranium metal by ca. 1.5 equiv of dichalco-
genide in the presence of a catalytic amount of iodine and
the coordinating solvent pyridine proceeds, with initial heat-
ing, over the course of several days to yield U(IV) thiolates
and selenolates (Scheme 1). There were no observable
reactions when thf or acetonitrile was used as a solvent
instead of pyridine. In our work, we used a small quantity
of iodine to aid oxidation, whereas in the majority of related
lanthanide research, mercury is used to amalgamate the Ln0
metal. Radiological waste disposition options preclude us
from using mercury with uranium. Although there are exam-
ples of lanthanide tellurolates reported in the literature,1a,b,e,5
our attempts to oxidize uranium metal with diphenyl ditellu-
ride failed or resulted in intractable products. The single-
crystal structures of 1 and 3-6 were determined (Table 1).
Unfortunately, EA values are frequently determined to be
lower than the calculated values for these types of com-
pounds. We have sent some of the samples for duplicate
U(Spy)4(thf) (5). In addition to diphenyl disulfide and
diphenyl diselenide, U0 can also be oxidized with dipyridyl
disulfide in pyridine. Crystallization from thf affords 5, which
is a nine-coordinate uranium monomer bonded to four bi-
(5) (a) Freedman, D.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 2002, 41,
492. (b) Kornienko, A.; Freedman, D.; Emge, T. J.; Brennan, J. G.
Inorg. Chem. 2001, 40, 140. (c) Khasnis, D. V.; Brewer, M.; Lee, J.;
Emge, T. J.; Brennan, J. G. J. Am. Chem. Soc. 1994, 116, 7129.
(6) Haigh, C. W. Polyhedron 1995, 14, 2871.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7403

Gaunt et al.
Table 1. Selected Crystallographic Data for 1 and 3-6
1
3
4
5
6
empirical formula
fw
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
C39H35N3S4U
911.97
P21/c
11.6836(10)
16.1000(14)
19.6157(17)
93.162(2)
3684.2(6)
4
C56H52N4S8U2
1513.56
I41/a
20.0352(19)
20.0352(19)
13.988(3)
90.00
C56H52N4Se8U2
1888.76
I41/a
20.203(3)
20.203(3)
13.990(4)
90.00
C24H24N4OS4U
750.74
C108H100N12Se12U4
3465.64
C2/c
29.362(2)
12.5300(9)
31.388(2)
111.5500(10)
10740.8(13)
4
P212121
9.4765(7)
15.3112(12)
18.3780(14)
90.00
5615.0(13)
4
5709.8(18)
4
2666.6(4)
4
T (K)
141(2)
203(1)
141(2)
141(2)
141(2)
λ (Å)
0.71073
4.664
1.644
0.71073
6.099
1.790
0.71073
10.805
2.197
0.71073
6.425
1.870
0.71073
10.132
2.143
µ (mm-1
)
D
calcd (g/cm3)
R1
0.0453
0.0394
0.0415
0.0136
0.0325
wR2
0.0755
0.0548
0.0958
0.0141
0.0557
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
U(SPh)4(py)3 (1)
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
[U(SPh)2(µ2-SPh)2(CH3CN)2]2 (3)
U(1)-S(1)
U(1)-S(2)
U(1)-S(3)
U(1)-S(4)
2.7298(17)
2.7169(17)
2.7298(16)
2.7639(17)
U(1)-N(1)
U(1)-N(2)
U(1)-N(3)
2.563(5)
2.598(5)
2.629(5)
U(1)-S(1)
2.8667(19)
2.9378(19)
U(1)-S(2)
U(1)-N(1)
2.813(2)
2.478(6)
U(1)-S(1A)
U(1)-S(1)-U(1A)
U(1)-S(2)-C(7)
82.88(5)
116.8(4)
U(1)-N(1)-C(13)
171.5(8)
U(1)-S(1)-C(1)
U(1)-S(2)-C(7)
114.4(2)
115.7(2)
U(1)-S(3)-C(13)
U(1)-S(4)-C(19)
114.5(2)
119.0(2)
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
[U(SePh)2(µ2-SePh)2(CH3CN)2]2 (4)
dentate (through the S and N atoms) pyridyl sulfide anions
and the O atom of a thf molecule (Figure 4), in 65% yield.
The geometry about the U(IV) center is best described as
U(1)-Se(1)
2.9935(11)
3.0564(10)
U(1)-Se(2)
U(1)-N(1)
2.8491(12)
2.479(8)
U(1)-Se(1A)
U(1)-Se(1)-U(1A)
U(1)-Se(2)-C(7)
81.55(3)
113.9(3)
U(1)-N(1)-C(13)
171.3(8)
distorted tricapped trigonal prismatic, with two S atoms of
two pyridyl sulfide anions and one N atom of another pyridyl
sulfide anion occupying the capping positions of the trigonal
prism. One trigonal face of the prism is defined by one S
atom of a pyridyl sulfide anion, one N atom of another
pyridyl sulfide anion, and the O atom of the coordinated thf
molecule. The other trigonal face of the prism is defined by
the S and N atoms of one pyridyl sulfide anion and the N
atom of another pyridyl sulfide anion. The average U-S
distance is 2.8299(16) Å, the average U-N distance is 2.540-
(4) Å, and the U-O distance is 2.548(2) Å (Table 5). The
average S-U-N bite angle is 58.09(12)°.
[U(py)2(SePh)(µ3-Se)(µ2-SePh)]4‚4py (6). The addition of
0.75 equiv of Se0 with 1.5 equiv of diphenyl diselenide to
Figure 1. Thermal ellipsoid plot (50% probability level) of the structure
of 1; H atoms have been omitted for clarity.
Figure 2. Thermal ellipsoid plot (50% probability level) plot of the
structure of 3; H atoms have been omitted for clarity.
Figure 3. Thermal ellipsoid plot (50% probability level) plot of the
structure of 4; H atoms have been omitted for clarity.
7404 Inorganic Chemistry, Vol. 45, No. 18, 2006

U(IV) Chalcogenolates
uranium. There is only one mention in the literature of an
attempt to use uranium metal as a precursor in the syntheses
of U(IV) thiolates.3f U(SPh)4 was isolated as an insoluble
red powder in low yield (10%) by ultrasonication of U0 turn-
ings and excess PhSSPh in toluene. Sonication of U0 in pure
disulfide gave small amounts of U(SEt)4 and U(SiPr)4.
Many U(IV) thiolate compounds reported in the literature
contain supporting ligands such as Cp and Tp type groups.3b,c,l,m
There are a few examples in the Cambridge Structural Data-
base of homoleptic uranium(IV) thiolates that were prepared
from U(IV) precursors. The complex [NEt2H2][U(SPh)6]3i
has U-S bond lengths ranging from 2.705(3) to 2.759(3)
Å, consistent with those in 1. The U-S bond lengths in
[(thf)3Na(µ-SPh)3U(µ-SPh)3Na(thf)3] are 2.717(3) Å.3j The
homoleptic dithiolate complex [Li(dme)]4[U(SCH2CH2S)4]
has U-S bond lengths ranging from 2.789(4) to 2.900(4)
Å.3n To the best of our knowledge, the only reported U(IV)
selenolate complex is [U(C5H4SiMe3)3(SeMe)],3e which was
not structurally characterized. Indeed, more generally, there
are only three examples of structurally characterized molec-
ular U-Se bonds, which are those in UO2[Et2NCSe2]2Ph3-
AsO,7 [U(Se2)],4- 8 and U[N(SePPh2)2]3‚C6D6.9
Figure 4. Thermal ellipsoid plot (50% probability level) plot of the
structure of 5; H atoms have been omitted for clarity.
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
U(Spy)4(thf) (5)
U(1)-S(1)
U(1)-S(2)
U(1)-S(3)
U(1)-S(4)
U(1)-O(1)
2.8222(8)
2.8322(8)
2.8380(8)
2.8273(8)
2.548(2)
U(1)-N(1)
U(1)-N(2)
U(1)-N(3)
U(1)-N(4)
2.504(2)
2.575(2)
2.550(2)
2.531(2)
S(1)-U(1)-N(1)
S(2)-U(1)-N(2)
58.81(6)
57.60(6)
S(3)-U(1)-N(3)
S(4)-U(1)-N(4)
57.78(6)
58.15(6)
Complexes 1 and 2 are similar to the trivalent lanthanide
complexes Yb(SPh)3(py)3, M(SePh)3(py)3 (M ) Ho or Tm),
i
Yb(SC6H2 Pr3)3(py)3, Sm(SAr)3(py)3, and Yb(SAr)3(py)3 (Ar
uranium metal in pyridine oxidizes the metal, and crystal-
lization from pyridine results in the formation of a U(IV)
tetramer (Figure 5). Each U(IV) center is eight-coordinate,
with a distorted bicapped trigonal prismatic geometry,6 and
bonded to three µ3-Se2- anions, the Se atom of one terminal
PhSe- anion, the Se atoms of two µ2-PhSe- anions, and the
N atoms of two terminal pyridine molecules. The crystal
lattice also contains four pyridine solvent molecules of crys-
tallization per uranium tetramer. Complex 6 can be viewed
as being a distorted cubane type cluster (Figure 5), with the
four U(IV) atoms and four Se2- anions occupying alternate
vertices of the cube. The average U-SePhterminal distance is
2.9267(10) Å, the average U-SePhbridging distance is 3.0614-
(14) Å, the average U-Se2- distance is 2.8681(15) Å, and
the average U-N distance is 2.619(10) Å (Table 6). The
U4Se4 cube is heavily distorted, with the 12 internal angles
at the vertices ranging from 71.63(2)° for Se(2)-U(1)-Se-
(2A) to 106.48(2)° for U(1)-Se(2)-U(1A). The terminal
phenyl selenolate anions are bent away from the uranium
atoms by an average U-Se-U angle of 114.06(25)°. The
average U-Se-U angle between the uranium atoms and
bridging phenyl selenolate anions is 82.965(23)°.
) 2, 4, 6-triisopropylphenyl).2d,e 1 and 2 are monomeric,
soluble in pyridine, and moderately soluble in acetonitrile
and dichloromethane. Dissolution of 1 and 2 in acetonitrile
followed by crystallization results in the formation of 3 and
4, respectively, in which the coordination number of uranium
has increased from seven to eight upon formation of the
dimers, with the uranium atoms bridged by four PhE- anions.
The U-Se bond lengths in 4 are all slightly longer than the
corresponding U-S bond lengths in isostructural 3, reflecting
the difference in ionic radii of S and Se. The solubility of 3
is less than that of 1 and 2, which hindered the acquisition
of NMR and electronic absorption spectra. The formation
of dimers has also been observed in Ln(III) complexes such
as [Ln(SPh)3(py)3]2 (Ln ) Ho or Tm),2b which contain only
two bridging anions, as compared with four bridging anions
in 3 and 4, because of the lower charge of Ln(III) compared
to U(IV). There is an example of U(IV) bridged by four
thiolate anions in [U(cot)2(SiPr)2]2,3h in which the U-Sbridging
distances range from 2.806(3) to 2.895(3) Å, slightly shorter
than the U-Sbridging distances of 2.8667(19) and 2.9378(19)
Å in 3.
Oxidation with dipyridyl disulfide resulted in isolation of
the first example of a U(IV) complex with pyridyl sulfide
anions. Examples of U(VI) uranyl complexes with pyridyl
and pyrimidyl thiolate ligands are [Me4N][UO2(NO3)2(C5H4-
NS)], [C16H25N2S2Si2][UO2(NO3)2(C8H12NSSi)], [HNEt3]2-
[(UO2)2(O2)(SC4N2H3)4], [HNEt3][H(UO2)2(O2)(SC4N2H2-
Me)4], and [HNEt3]2[(UO2)4(O)2(SC5NH4)6].3d,g Ln(III) pyridyl
thiolates have been prepared by the oxidation of elemental
Discussion
The use of 1.5 equiv of dichalcogenide in the reaction
mixtures was intended to result in oxidation of uranium metal
to U(III) chalcogenolate complexes, similar to the way in
which uranium metal can be oxidized by 1.5 equiv of iodine
in pyridine to form UI3(py)4.4b However, we found in all
cases that uranium metal was oxidized to U(IV) by dichal-
cogenides. We have isolated six U(IV) thiolate or selenolate
complexes that contain only chalcogen atoms (and nitrogen
in 5) and solvent molecules in the coordination sphere of
(7) Zarli, B.; Graziani, R.; Forsellini, E.; Croatto, U.; Bombieri, G. J.
Chem. Soc., Dalton Trans. 1971, 1501.
(8) Sutorik, A. C.; Kanatzidis, M. G. J. Am. Chem. Soc. 1991, 113, 7754.
(9) Gaunt, A. J.; Scott, B. L.; Neu, M. P. Chem. Commun. 2005, 3215.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7405

Gaunt et al.
Figure 5. Thermal ellipsoid plots of 6. The molecular structure is shown on the left, omitting, for clarity, H atoms and C atoms except for those directly
bonded to the Se atoms of PhSe- anions. The U4Se4 distorted cubane core is shown on the right.
Table 6. Selected Bond Lengths (Å) and Angles (deg) for
[U(py)2(SePh)(µ3-Se)2(µ-SePh)]4‚4py (6)
difference from 6 is that it does not contain any bridging
PhSe- anions because of the +3 charge on ytterbium com-
pared to +4 for uranium. It was noted that the Yb-Se2-
bonds trans to the terminal PhSe- anion were longer than
either of the two Yb-Se2- bonds trans to the pyridine ligand;
this was attributed to a possible trans influence, indicative
of covalency in the bonding. In 6, the U-Se2- bond lengths
are different (ranging from 2.7928(6) to 2.9482(6) Å); how-
ever, the geometry of the cube is heavily distorted, and the
differences in bond lengths may well arise from steric influ-
ences of the bridging PhSe- anions.
The proton NMR spectra of 1, 2, 5, and 6 are difficult to
interpret, and not all the expected signals are observed,
largely because of the paramagnetism of U(IV). The proton
NMR of 3 was not recorded because of its low solubility in
CD3CN and noncoordinating deuterated solvents. Similarly
uninformative proton NMR spectra, offering very little struc-
tural information about the integrity of the complexes in
solution, have been reported for paramagnetic Ln(III)
chalcogenolates.2b
The electronic absorption spectra of 1, 2, 5, and 6 display
bands arising from f-f and f-d transitions.11 There are
distinctive bands in the spectra of 1, 2, and 6 in pyridine
between 685 and 687 nm and 1165 and 1170 nm, which
have previously been observed to be characteristic of U(IV)
in the solution UV-vis-nIR spectra of complexes such as
UI4(PhCN)4.4a The UV-vis-nIR spectrum of 5 in benzene
has distinctive absorptions at 699, 1130, and 1215 nm.
Compound 3 has poor solubility, but a UV-vis-nIR
spectrum of 3, presumed to form in situ, was recorded by
dissolving 1 in acetonitrile and has characteristic absorbance
bands at 687 and 1125 nm. There are also intense charge-
transfer transitions below 500 nm in the electronic spectra
of 1-3, 5, and 6. We have not reported the extinction
coefficients for the absorbances in the electronic spectra
because the NMR spectra do not conclusively demonstrate
that the structural integrity of the complexes are maintained
in solution.
U(1)-Se(1)
U(1)-Se(2)
U(1)-Se(2A)
U(1)-Se(3)
U(1)-Se(4)
U(1)-Se(5)
U(1)-N(1)
U(1)-N(2)
2.7928(6)
2.9252(6)
2.8704(7)
3.1225(7)
3.0355(7)
2.9185(7)
2.640(5)
U(2)-Se(1)
U(2)-Se(2)
U(2)-Se(1A)
U(2)-Se(3)
U(2)-Se(4A)
U(2)-Se(6)
U(2)-N(3)
U(2)-N(4)
2.8601(6)
2.8124(6)
2.9482(6)
3.0184(7)
3.0691(6)
2.9349(7)
2.590(5)
2.611(5)
2.636(5)
U(1)-Se(1)-U(2)
U(1)-Se(2)-U(2)
U(1)-Se(1)-U(2A)
U(1)-Se(2)-U(1A)
U(1A)-Se(2)-U(2)
Se(1)-U(1)-Se(2A) 87.544(18) Se(1)-U(2)-Se(1A) 71.92(2)
Se(1A)-U(2)-Se(2) 85.678(17) Se(2)-U(1)-Se(2A) 71.63(2)
U(1)-Se(5)-C(13)
91.491(18) U(2)-Se(1)-U(2A)
89.754(17) U(1)-Se(3)-U(2)
90.050(18) U(1)-Se(4)-U(2A)
106.48(2)
91.268(18) Se(1)-U(2)-Se(2)
106.38(2)
82.486(16)
83.443(16)
86.191(18)
87.083(18)
Se(1)-U(1)-Se(2)
114.55(18) U(2)-Se(6)-C(29)
113.57(17)
lanthanide with dipyridyl disulfide to form both anionic,
[PEt4][Ln(Spy)4], and neutral, Ln(Spy)3(py)2, complexes.2c
Finally, incorporation of 0.75 equiv of elemental Se into
the uranium metal oxidation by diphenyl diselenide yields
the novel tetrameric cubane-like U(IV) cluster, comprising
both PhSe- and Se2- anions. The occurrence of a cluster
such as 6 is likely through oxidation of U0 to form U(SePh)4-
(py)3 (as for 2), followed by reduction of Se0 to Se2- with
concomitant oxidative elimination of PhSeSePh. The most
comparable uranium cluster containing E2- is the trinuclear
complex U3(µ3-S)(µ3-StBu)(µ2-StBu)3(StBu)6, prepared by
protonation of [Na(thf)3]2[U(StBu)6] with NEt3HBPh4 in
diethyl ether.3k A range of molecular lanthanide clusters have
been reported,10 and the closest comparison to 6 is the cubane
type complex Yb4Se4(SePh)4(py)8,10g in which the major
(10) (a) Fitzgerald, M.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 2002,
41, 3528. (b) Kornienko, A.; Melman, J. H.; Hall, G.; Emge, T. J.;
Brennan, J. G. Inorg. Chem. 2002, 41, 121. (c) Melman, J. H.;
Fitzgerald, M.; Freedman, D.; Emge, T. J.; Brennan J. G. J. Am. Chem.
Soc. 1999, 121, 10247. (d) Kornienko, A. Y.; Emge, T. J.; Brennan,
J. G. J. Am. Chem. Soc. 2001, 123, 11933. (e) Freedman, D.; Emge,
T. J.; Brennan, J. G. Inorg. Chem. 1999, 38, 4400. (f) Melman, J. H.;
Emge, T. J.; Brennan, J. G. Inorg. Chem. 1999, 38, 2117. (g)
Freedman, D.; Melman, J. H.; Emge, T. J.; Brennan, J. G. Inorg. Chem.
1998, 37, 4162. (h) Freedman, D.; Emge, T. J.; Brennan, J. G. J. Am.
Chem. Soc. 1997, 119, 11112. (i) Melman, J. H.; Emge, T. J.; Brennan,
J. G. Chem. Commun. 1997, 2269.
(11) Cohen, D.; Carnall, W. T. J. Phys. Chem. 1960, 64, 1933.
7406 Inorganic Chemistry, Vol. 45, No. 18, 2006

U(IV) Chalcogenolates
In summary, we have shown that oxidation of uranium
metal by dichalcogenides is a useful synthetic approach for
isolating molecular uranium(IV) thiolates and selenolates
without the need for stabilizing ancillary ligands. Although
U(III) complexes were targeted, the oxidations proceed to
the tetravalent state in all cases, resulting in the characteriza-
tion of six new U(IV) chalcogenolate compounds. We are
currently investigating the oxidation of plutonium metal by
dichalcogenides in an effort to prepare trivalent actinide
chalcogenolates by this route.
Acknowledgment. We thank the Heavy Element Chem-
istry Research Program, Chemical Sciences Division of the
Office of Basic Energy Sciences, U.S. Department of Energy,
and the G. T. Seaborg Institute at the Los Alamos National
Laboratory for funding.
Supporting Information Available: CIF files, IR, UV-vis-
nIR, and 1H NMR spectra. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC060560K
Inorganic Chemistry, Vol. 45, No. 18, 2006 7407