Fluorinated thiolates of divalent and trivalent lanthanides. Ln-F bonds and the synthesis of LnF3

Article abstract of DOI:10.1021/ic0006908

Fluorinated thiolates from particularly stable chalcogenolate complexes with the lanthanides. Both Sm-(SC₆F₅)₃ and Eu(SC₆F₅)₂ were prepared by transmetalation. The Sm compopund is a dimer in the solid state, with a pair of bridging thiolate ligands connecting the two Sm(III) ions, while the Eu(II) compound is polymeric. In both compounds there are clearly define Ln - F interactions. Thermolysis of the Sm compound gives SmF₃ and (C₆F₄S)_n (n = 2, 3, 4).

Full text of DOI:10.1021/ic0006908

1078
Inorg. Chem. 2001, 40, 1078-1081
The successful synthesis of Ln compounds with SC6F5 ligands
would have three important chemical consequences. First,
fluorinated Ln thiolates are potentially volatile single-source
precursors to either LnSx or LnF3. Second, because the steric
characteristics of the SC6F5 group so closely resemble those of
SC6H5, the properties of molecules or clusters with SC6F5
ligands can be compared with their Ph derivatives and differ-
ences can be interpreted in terms of the electronic influence of
the F substitutions. Finally, C-H bonds often quench photo-
emission in Ln systems, and so the elimination of C-H bonds
is important in the synthesis of Ln coordination complexes with
efficient photoemission properties.18-23 This manuscript de-
scribes the synthesis, structure, and thermal decomposition of
the first Ln(SC6F5)x (x ) 2, 3) compounds.
Fluorinated Thiolates of Divalent and Trivalent
Lanthanides. Ln-F Bonds and the Synthesis of
LnF3
Jonathan H. Melman, Thomas J. Emge, and
John G. Brennan*
Department of Chemistry, Rutgers, The State University of
New Jersey, 610 Taylor Road,
Piscataway, New Jersey 08854-8087
ReceiVed June 23, 2000
Introduction
While the thiolate chemistry of the lanthanide (Ln) elements
has expanded dramatically in the past decade,1 relatively little
is known about how variations in the steric and electronic
properties of the organic substituent bound to S influence the
physical or chemical properties of lanthanide derivatives.
Compounds with SR (R ) Ph,2-5 trialkyl-substituted Ph,5-8
alkyl),9,10 are well documented, but unfortunately such vastly
different substituents preclude an understanding of how steric
and electronic forces influence the Ln-S bond. Because Ln
thiolate compounds are sensitive to water and oxygen, isolation
via fractional crystallization is the only routine method of
purification. As a result, Hammett-like analyses of compounds
with Ln-S bonds are essentially impossible.
Substitution of F for H in organic systems perturbs electronic
structure with minimal changes in steric properties.11 While
numerous 2,4,6-trialkyl-substituted arylthiolate derivatives of
Ln compounds have been investigated, the corresponding
fluorinated analogues are unknown even though HSC6F5 is
commercially available. Complexes of SC6F5 with the covalent
main group metals have been known for decades,12,13 while more
recently complexes with electropositive metals (i.e., Ca,14 Al,15
Ga,16 Ti17) have been synthesized and structurally characterized.
Experimental Section
General Methods. All syntheses were carried out under ultrapure
nitrogen (JWS), using conventional drybox or Schlenk techniques.
Solvents (Fisher) were refluxed continuously over molten alkali metals
or K/benzophenone and collected immediately prior to use. Anhydrous
pyridine (Aldrich) was purchased and refluxed over KOH. Hg(SC6F5)2
was prepared in a variation of literature procedures.24 HSC6F5 was
purchased from Aldrich. Sm and Eu were purchased from Strem.
Melting points were taken in sealed capillaries and are uncorrected. IR
spectra were taken on a Mattus Cygnus 100 FTIR spectrometer and
recorded from 4000 to 600 cm-1 as a Nujol mull on NaCl plates.
Electronic spectra were recorded on a Varian DMS 100S spectrometer
with the samples in a 0.10 mm quartz cell attached to a Teflon stopcock.
Elemental analyses were performed by Quantitative Technologies, Inc.
(Whitehouse NJ). 19F NMR spectra were obtained on a 400 MHz NMR
spectrometer with an external HSC6F5 reference, and chemical shifts
are reported in δ (ppm). Direct probe-EI mass spectra were obtained
at the Rutgers University Department of Food Science.
Synthesis of Hg(SC6F5)2. In a modification of the original literature
procedure, Hg(CH3COO)2 (1.169 g, 3.676 mmol) and HSC6F5 (1.468
g, 7.335 mmol) were combined in deionized water (∼100 mL). The
solution was stirred overnight, and the white precipitate was collected
by vacuum filtration and recrystallized by slowly cooling a saturated
hot toluene solution to give white crystals (3.194 g, 87%) that were
identified by IR and melting point.12
(1) Nief, F. Coord. Chem. ReV. 1998, 178-180, 13.
(2) Brewer, M.; Khasnis, D.; Buretea, M.; Berardini, M.; Emge, T. J.;
Brennan, J. G. Inorg. Chem. 1994, 33, 2743.
(3) Lee, J.; Brewer, M.; Berardini, M.; Brennan, J. Inorg. Chem. 1995,
34, 3215.
(4) Lee, J.; Freedman, D.; Melman, J.; Brewer, M.; Sun, L.; Emge, T. J.;
Long, F. H.; Brennan, J. G. Inorg. Chem. 1998, 37, 2512.
(5) Mashima, K.; Nakayama, Y.; Shibahara, T.; Fukumoto, H.; Nakamura,
A. Inorg. Chem. 1996, 35, 93.
(6) Mashima, K.; Nakayama, Y.; Fukumoto, H.; Kanehisa, N.; Kai, Y.;
Nakamura, A. J. Chem. Soc., Chem. Commun. 1994, 2523.
(7) Strzelecki, A. R.; Lihar, C. L.; Helsel, B. A.; Bianconi, P. A. Inorg.
Chem. 1994, 33, 5188.
(8) Cetinkaya, B.; Hitchcock, P. B.; Lappert, M. F.; Smith, R. G. J. Chem.
Soc., Chem. Commun. 1992, 932.
(9) Tatsumi, K.; Amemiya, T.; Kawaguchi, H.; Tank, K. J. Chem. Soc.,
Chem. Commun. 1993, 773.
(10) Aspinall, H.; Cunningham, S. A.; Maestro, P.; Macaudiere, P. Inorg.
Chem. 1998, 37, 5396.
Synthesis of [(THF)2Sm(µ2-SC6F5)(SC6F5)2]2 (1). Sm (0.150 g,
0.997 mmol) and Hg(SC6F5)2 (0.895 g, 1.50 mmol) were combined in
THF (25 mL), and the mixture was stirred until all the Sm was
consumed (1 h). The solution was filtered to separate the elemental
Hg (0.25 g, 78%), the volume was reduced (ca. 15 mL), and the solution
was layered with hexane (12 mL) and then cooled slowly (-20 °C) to
give yellow-orange (0.293 g, 33%) crystals that turn darker orange at
74 °C, start becoming lighter yellow at 150-185 °C, and melt at 252-
254 °C. Anal. Calcd for C26H16O2F15S3Sm: C, 35.0; H, 1.81. Found:
C, 34.6; H, 1.84. IR: 2931 (s), 2854 (s), 1506 (m), 1458 (s), 1378 (s),
1343 (m), 1264 (m), 1179 (w), 1170 (w), 1156 (w), 1139 (w), 1122
(w), 1097 (w), 1084 (m), 1065 (m), 1042 (w), 1006 (m), 974 (m), 957
(m), 866 (m), 686 (w) cm-1. The compound does not exhibit a well-
defined visible absorption maximum in either pyridine or THF. When
heated at 220 °C under vacuum, the compound eliminates white
crystalline material that was identified as a mixture of (C6F4S)n (M+
)
(11) Carey, F. A.; Sundberg, R. J. In AdVanced Organic Chemistry, 3rd
ed.; Plenum Press: New York, 1990; pp 397-402.
(12) Peach, M. E. J. Inorg. Nucl. Chem. 1973, 35, 1046.
(13) Peach, M. E. Can. J. Chem. 1968, 46, 2769.
(14) Chadwick, S.; Englich, U.; Noll, B.; Ruhlandt-Seng, K. Inorg. Chem.
1998, 37, 4718.
(18) Lee, J.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 1997, 36, 5064.
(19) Piguet, C.; Bu¨nzli, J. G.; Bernardinelli, G.; Hopfgartner, G.; Petoud,
S.; Schaad, O. J. Am. Chem. Soc. 1996, 118, 6681.
(15) De Mel, V. S. J.; Kumar, R.; Oliver, J. P. Organometallics 1990, 9,
1303.
(16) Hendershot, D. G.; Kumar, R.; Barber, M.; Oliver, J. P. Organome-
tallics 1991, 10, 1917.
(17) Delgado, E.; Hernandez, E.; Hedayat, A.; Tornero, J.; Torre, R. J.
Organomet. Chem. 1994, 466, 119.
(20) Bunzli, J.-C. G.; Petoud, S.; Renaud, F. J. Alloys Compd. 1997, 249,
14.
(21) Knoeppel, D. W.; Liu, J.; Shore, S. G. Inorg. Chem. 1998, 37, 4828.
(22) Decurtins, S.; Gross, M.; Ferlay, S. Inorg. Chem. 1998, 37, 2443.
(23) Cui, Y.; Zheng, F.; Huang, J. Chem. Lett 1999, 4, 281.
(24) Peach, M. E. Can. J. Chem. 1968, 46, 2699.
10.1021/ic0006908 CCC: $20.00 © 2001 American Chemical Society
Published on Web 02/02/2001

Notes
Inorganic Chemistry, Vol. 40, No. 5, 2001 1079
Table 1. Summary of Crystallographic Details for 1 and 2
1
2
empirical formula
fw
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C26H16F15O2S3Sm
891.92
C20H16EuF10O2S2
694.41
P21/c (No. 14)
11.923(10)
12.404(7)
19.869(14)
90.00(6)
92.27(7)
90.00(6)
2936(4)
4
C2/c (No. 15)
30.049(19)
4.936(2)
19.077(9)
90.00(4)
128.61(5)
90.00(3)
2211(2)
4
Z
D
calcd (g/cm-3
)
2.018
2.086
Figure 2. Molecular structure of [(THF)2Eu(µ-SC6F5)2]n. Thermal
ellipsoids are drawn at the 50% probability level. Significant dis-
tances (Å) for 2 are the following: Eu(1)-O(1), 2.554(5); Eu(1)-
F(6), 3.006(6); Eu(1)-S(1), 3.014(3); Eu(1)-S(1)′, 3.035(3); S(1)-
C(1), 1.750(7).
temp (°C)
λ (Å)
-120
-120
0.710 73
2.335
0.710 73
3.127
abs coeff (mm-1
)
R(F)a [I > 2σ(I)]
0.062
0.129
0.038
0.106
Rw(F2)a [I > 2σ(I)]
absorption, the last by a numerical (SHELX76)25 method. The structures
were solved by direct methods (SHELXS86).26 All non-hydrogen atoms
were refined (SHELXL97)27 on the basis of Fobs2. All hydrogen atom
coordinates were calculated with idealized geometries (SHELXL97).
Scattering factors (fo, f ′, f ′ ′) are as described in SHELXL97.
Crystallographic data and final R indices for 1 and 2 are given in Table
1. Complete crystallographic details are given in the Supporting
Information. ORTEP diagrams28 for 1 and 2 are shown in Figures 1
and 2, respectively. A packing diagram for 2 is shown in Figure 3.
2
a R(F) ) ∑||Fo| - |Fc||/∑|Fo|; Rw(F2) ) {∑[w(Fo - Fc2)2]/
∑[w(Fo )2]}1/2. Additional crystallographic details are given in the
2
Supporting Information.
Results
Transmetallation reactions of Hg(SC6F5)2 with Sm,
2Sm + 3Hg(SC6F5)2 f 2Sm(SC6F5)3 + 3Hg
(1)
(2)
and Eu,
Eu + Hg(SC6F5)2 f Eu(SC6F5)2 + Hg
Figure 1. Molecular structure of [(THF)2Sm(SC6F5)2(µ-SC6F5)]2.
Thermal ellipsoids are drawn at the 50% probability level. Significant
distances (Å) for 1 are the following: Sm(1)-O(1), 2.396(8); Sm(1)-
O(2), 2.427(7); Sm(1)-F(6), 2.582(7); Sm(1)-F(11), 2.641(6); Sm-
(1)-S(2), 2.740(4); Sm(1)-S(3), 2.771(4); Sm(1)-S(1)′, 2.852(4);
Sm(1)-S(1), 2.929(4); S(1)-C(1), 1.764(13).
in THF give [(THF)2Sm(SC6F5)2(µ-SC6F5)]2 (1) and [(THF)2Eu-
(µ-SC6F5)2]n (2), respectively. Both compounds are extremely
soluble in 1:1 THF/hexane mixtures, from which they can be
crystallized in high yield. The structure of the Sm compound 1
was determined by low-temperature single-crystal X-ray dif-
fraction and shown to be dimeric, with a pair of thiolates
bridging the eight-coordinate Sm(III) ions. Both terminal
thiolates chelate to each metal via both Ln-S and Ln-F bonds,
while the bridging thiolates do not interact through the fluoride.
Two THF ligands complete the inner coordination sphere. Figure
1 gives an ORTEP diagram of 1. The compound is light-yellow
in solution and in the solid state and is considerably more stable
than the SPh analogue both thermally and with respect to
reactions with water and oxygen. Dimeric 1 decomposes above
220 °C in vacuo by abstracting F to give SmF3 and a mixture
of three F products based on the oligiomerization of (C6F4S)n
(n ) 2, 3, 4).
360, 539, 719 for n ) 2, 3, 4, respectively) by DP-EI-MS. 19F NMR
(24 °C): -136 (w1/2 ) 180 Hz), -164.8 (w1/2 ) 60 Hz), -165.2 (w1/2
) 75 Hz).
Synthesis of [(THF)2Eu(µ2-SC6F5)2]n (2). Eu (0.115 g, 0.757 mmol)
and Hg(SC6F5)2 (0.678 g, 1.13 mmol) were combined in THF (25 mL),
and the solution was stirred until the Eu was consumed. Elemental Hg
was not found to precipitate from the yellow solution, suggesting that
the product was divalent. Additional Eu was added (0.108 g, 0.711
mmol), and the mixture was stirred for 3 days. The yellow solution
was filtered, reduced in volume (ca. 10 mL), and layered with hexane
(30 mL) to give pale-yellow needles of 2 (0.425 g, 54%). Anal. Calcd
for C20H16O2EuF10S2: C, 34.6; H, 2.32. Found: C, 33.7; H, 2.36. IR:
2933 (s), 2849 (s), 1506 (m), 1458 (s), 1377 (s), 1351 (m), 1301 (w),
1254 (m), 1083 (m), 1029 (m), 1014 (w), 993 (w), 962 (m), 921 (w),
867 (m), 740 (m), 621 (w) cm-1. The compound becomes increasingly
red up to 288 °C, with no further change up to 350 °C. UV-vis
(pyridine): λmax 340 nm (ꢀ ) 90 M-1 cm-1). 19F NMR (24 °C): -131.3
(d, J ) 22 Hz), -148.3 (t, J ) 20 Hz), -159.9 (t, J ) 20 Hz).
The Eu compound 2 was also characterized by low-temper-
ature single-crystal X-ray diffraction and shown to be a 1D
polymer in the solid state with each Eu ion connected to adjacent
(25) Sheldrick, G. M. SHELX76, Program for Crystal Structure Determi-
nation; University of Cambridge: Cambridge, England, 1976.
(26) Sheldrick, G. M. SHELXS86, Program for the Solution of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(27) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(28) (a) Johnson, C. K. ORTEP II; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976. (b) Zsolnai, L. XPMA and ZORTEP,
Programs for InteractiVe ORTEP Drawings; University of Heidel-
berg: Heidelberg, Germany, 1997.
X-ray Structure Determinations of 1 and 2. Data for 1 and 2 were
collected on an Enraf-Nonius CAD4 diffractometer with graphite
monochromatized Mo KR radiation (λ ) 0.710 73 Å) at -120 °C. The
check reflections measured every hour showed less than 2% intensity
variation. The data were corrected for Lorentz effects, polarization, and

1080 Inorganic Chemistry, Vol. 40, No. 5, 2001
Notes
Figure 3. Packing diagram for polymeric 2 along the short axis, which illustrates the stacking of the fluorinated arene rings along the 1D chain.
metals by a pair of thiolates. Figure 2 gives an ORTEP diagram
of three repeating polymeric units. In contrast to 1, the bridging
thiolates in 2 interact with the metal through Eu-F bonds
(Figure 2) to give an eight-coordinate (4S, 2F, 2O) Eu(II) ion.
While essentially colorless in crystalline form and in THF
solutions, 2 forms an orange solution with a well-defined
absorption maximum (λmax ) 340 nm) in pyridine that is
tentatively assigned as a metal to pyridine charge-transfer
absorption. Polymer 2 does not melt but becomes increasingly
red up to 280 °C.
ions, and the F substituents, by polarizing electron density away
from the S, reduce the tendency of SC6F5 to form oligiomeric
products.
This presumed polarization has a negligible effect on Sm-S
bond lengths. Compound 1 has terminal Ln-S bond lengths of
2.746(4) and 2.772(4) Å that are not significantly different from
the terminal Sm-S bond lengths (2.785(3) and 2.752(3) Å) in
the pyridine coordination complex4 (py)8Sm4(SPh)12. Both
terminal and bridging Sm-S bonds are within the normal values
defined by the diverse array of compounds with Sm-S bonds,
i.e., terminal Sm-S bonds in Sm(S-Mes)3 (2.643(9) Å)8 and
Sm(StBu)6 (2.829(3) Å)9 and bridging Sm-µ-S bonds in
3-
Discussion
[(THF)Sm(SPh)3]n (2.863(8) Å),4 [(THF)3Sm(SAr)3]2, (3.017(6)
Å),5 or [(COT)Sm(THF)(SAr)]2 (2.883(6) Å).31 Similarly, in
the divalent polymer 2 there is a complete insensitivity of Eu-S
bond length to the fluoro substituents. Distances of 3.014(3)
and 3.035(3) Å for the bridging Eu-S bond lengths in 2 are
essentially equivalent to the bridging thiolate-Eu(II) distances
in the literature, i.e., 2.987(2)-3.014(3) Å in [EuM(SPh)4]2 (M
) Zn, Cd, Hg)32 or 3.015(6) Å in [(THF)3Eu(SAr)2]2.6 Distances
from Ln to the O(THF) atoms are also in the normal range for
Ln-O bonds for both 1 and 2.
Coordination of fluoride as a neutral donor has relatively little
precedent in lanthanide chemistry. Early investigations of the
reactions between fluorinated compounds and organolanthanide-
(II) compounds resulted in reductive C-F bond cleavage and
the isolation of Ln(III) products with F- ligands.33-37 More
recently, a structural investigation of fluorinated arylamido
Ln(III) compounds38 revealed dative Ln-F bonds that are
similar to the dative interactions found in 1 and 2. In the report
of these amido complexes, both a homoleptic compound
Fluorinated thiolates of the lanthanides differ substantially
from their hydrocarbon analogues in both chemical and physical
properties. Most striking is the relative stability of the fluorinated
compounds, which decompose only slowly in air and are thus
similar to Ln complexes with the chelating, resonance-stabilized
pyridinethiolate (2-S-NC5H4, or SPy) ligands.29,30 The stability
of the fluorinated compounds can be attributed to the ability of
F to inductively stabilize the thiolate anionic charge, and to the
coordination of F to the Ln in a chelating interaction. While
the SC6F5 compounds are more thermally stable than their Ph
counterparts, these ligands are no better than Ph for stabilizing
higher oxidation states, in distinct contrast to the SPy ligand.
For example, SPy forms stable complexes with Eu(III), while
the SC6F5 ligand will only oxidize Eu to the divalent state, as
determined in earlier Eu-SR (R ) Ph, 2,4,6-iPrC6H2) synthetic
investigations.
Unlike the SPy and SPh compounds, these fluorinated
thiolates are extremely soluble, dissolving in 1:1 THF/hexane
mixtures. For comparison, the SPy compounds of the middle
lanthanides are soluble in pyridine only upon addition of
(31) Mashima, K.; Nakayama, Y.; Kanehisa, N.; Kai, Y.; Nakamura, A. J.
Chem. Soc., Chem. Commun. 1994, 1847.
-
additional SPy anion, which forms Ln(SPy)4 salts, while the
middle Ln(SPh)3 compounds are sparingly soluble in refluxing
THF from which they crystallize as 1D coordination polymers
with sets of three thiolates connecting adjacent metal ions.4 In
contrast 1 dissolves in THF and recrystallizes readily upon
addition of an equal volume of hexane. Solubility is presumably
related to the facility with which thiolate ligands bridge Ln(III)
(32) Brewer, M.; Lee, J.; Brennan, J. G. Inorg. Chem. 1995, 34, 5919.
(33) Watson, P. L.; Tulip, T. H.; Williams, I. Organometallics 1990, 9,
1999.
(34) Burns, C. J.; Andersen, R. A. J. Chem. Soc., Chem. Commun. 1987,
272.
(35) Burns, C. J.; Andersen, R. A. J. Chem. Soc., Chem. Commun. 1989,
136.
(36) Schumann, H.; Keitsch, M. R.; Winterfeld, J.; Demtschuk, J. J.
Organomet. Chem. 1996, 525, 279.
(29) Berardini, M.; Brennan, J. G. Inorg. Chem. 1995, 34, 6179.
(30) Berardini, M.; Lee, J.; Freedman, D.; Lee, J.; Emge, T. J.; Brennan,
J. G. Inorg. Chem. 1997, 36, 5772.
(37) Finke, R. G.; Keenan, S. R.; Schiraldi, D. A.; Watson, P. L.
Organometallics 1987, 6, 1356.
(38) Click, D. R.; Scott, B. L.; Watkin, J. G. Chem. Commun. 1999, 633.

Notes
Inorganic Chemistry, Vol. 40, No. 5, 2001 1081
Sm[N(SiMe3)(C6F5)]3 and two heteroleptic derivatives
(THF)3Sm(NHC6F5)3 and (toluene)Nd(N(C6F5)2)3 were de-
scribed, with the shortest Ln-F interactions found in the
homoleptic compound (2.556(6)-2.587(6) Å) and in the arene
derivative (2.572(5), 2.616(5), and 2.940(5) Å). With the more
strongly donating THF present in the primary coordination
sphere, the Sm-F bonds were all lengthened significantly, with
Sm-F distances of 2.847(4)-2.876(3) Å.
Both the amido and thiolate ligand systems have similar
[Ln-X-C-C-F-Ln (X ) N, S)] connectivity, but the
tendency of the thiolate to form right angle bonds at the
heteroatom center certainly enhances the relative ability of the
SC6F5 ligand to to coordinate through a Ln-F bond. This is
reflected in the relative Ln-F bond lengths of (THF)3Sm-
(NHC6F5)3 and eight-coordinate 1 (2.580(8) and 2.645(7) Å).
Presumably, basicity at the F is also enhanced in compounds
with the charge centered on the more electropositive heteroatom.
It is interesting to note that in the related octahedral Ca(II)
derivative14 (py)4Ca(SC6F5)2 there are no Ca-F interactions,
presumably because F is displaced by the stronger pyridine
donor.
produced by replacing the chalcogen (i.e., Eu(SePh)2 (λmax
392 nm)42 vs Eu(TePh)2, (λmax ) 382 nm)43).
)
A feature common to the structures of both 1 and 2 is a
distinctive arrangement of aromatic rings. This is particularly
noticeable in polymeric 2, which, from the unit cell packing
diagram in Figure 3, clearly shows that the thiolate rings in 2
are orientated for maximum π-π interactions, and dimeric 1
(Figure 1) also clearly has a stacked arrangement of the three
arene ligands (two terminal and one bridging) on the top and
bottom of the molecule in the figure. While there are no clearly
oriented C6F5 groups in the previously mentioned amido
compounds, in (py)4Ca(SC6F5)2 the two arenethiolates are
aligned with two of the pyridine ligands.
Early investigations into the thermolysis of fluorobenzenethi-
olates revealed that these compounds were potential single-
source precursors to metals, metal fluorides, or metal sulfides,
depending on the identity of the metal.12 Only the noble metals
Au and Pt reductively eliminated disulfide. Of the remaining
compounds studied, SC6F5 compounds of more covalent metals
Ag, Tl, Cu, Ni, Pb, and Hg gave MSx thermolysis products.
Both MS and MF2 were noted in the thermolysis of Zn(SC6F5)2
and Cd(SC6F5)2, while in Li chemistry, thermal decomposition
of LiSC6F5 gave LiF. Given that even the thermal decomposition
of the relatively chalcophilic metals Zn and Cd formed
predominantly metal fluorides, it was reasonable to expect that
the analogous chemistry with considerably more electropositive
Ln metals would also yield fluoride solids. An analysis of the
thermal decomposition of 1 confirms this supposition; XRPD
of the nonvolatile products revealed SmF3 was the only
crystalline phase present, while a GC-MS analysis of the
volatile products indicated a mixture of products, all oligiomers
of the F-abstracted SC6F4 ligand. The presence of higher order
products in addition to the predictable dimer octafluorodian-
threne (SC6F4)2 suggests these thermolyses may be an interesting
synthetic approach to novel fluorinated thiocrown compounds.
Ionic radii39 are not reliable predictors of Ln-F bond lengths
most likely because these bonds should be particularly suscep-
tible to external forces such as ligand-ligand repulsive interac-
tions or the impositions of the crystal lattice. While both the
Sm-O and Eu-O bond lengths fall within the expected range
of values, with Eu-O being larger by ca. 0.13 Å because of
the greater size of the Eu(II) ion relative to Sm(III), the Ln-F
bonds are ca. 0.30 Å greater in the Eu compound. Coordination
of F to Ln does not have a significant effect on the C-F bond
length in either 1 or 2.
Fluorination of the arene ligand has a moderate effect on the
electronic structure of these compounds. The yellow color of
trivalent 1 is tentatively attributed to a near-visible S to Sm(III)
charge-transfer absorption.3,4,40 The conflicting σ-withdrawing
and π-donor influences of perfluoro substitution do not produce
a dramatic change in electronic structure, with the color of 1
appearing to be indistinguishable, by eye, from the SPh
analogue, but an unambiguous assessment is precluded by the
inability to identify an absorption maximum for this transition.
Fortunately, the electronic properties of polymer 2 are measur-
ably perturbed by the F substituents. When dissolved in pyridine,
2 has a tentatively assigned metal-to-pyridine charge-transfer
absorption at 340 nm that, when compared with Eu(SPh)2 in
pyridine (λmax ) 380 nm),41 suggests that the net effect of the
10 fluoro substituents is a reduction of the electron density at
the Eu(II) center. Because SC6F5 and SPh coordinate differently
(and because Eu(SPh)2 has been isolated only as part of a
heterovalent polymer), it is impossible to confidently attribute
the differences solely to differences in electronic structure. Still,
the change in absorption energy is greater than the change
Conclusion
Lanthanide compounds with the fluorinated benzenethiolate
ligand have a number of attractive physical properties. These
compounds are considerably more stable than their hydrocarbon
analogues presumably because of inductive stabilization of the
sulfur based anion, as well as the ability of F to coordinate to
the Ln. They are more soluble than their SPh analogues, and
they decompose to give LnF3. Further synthetic investigations
of thermally stable derivatives are currently underway.
Acknowledgment. This work was supported by the National
Science Foundation under Grant CHE-9982625.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of 1 and 2. This material
is available free of charge via the Internet at http://pubs.acs.org.
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