Synthesis and structure of Ta4S9Br8. An emergent family of early transition metal chalcogenide clusters

Article abstract of DOI:10.1021/ic051014e

Single crystals of Ta₄S₉Br₈ are obtained by heating Ta, S, and Br₂ at 400°C in a 4.0:9.0:4.0 molar ratio in a 44% yield. The structure was determined by X-ray analysis and consists of molecular clusters [Ta₄(μ₄-S)(μ-S₂) ₄Br₈]. The tantalum atoms form a square with long Ta...Ta distances (3.30 A), with four S₂ ligands bridging the Ta-Ta edges and one capping the square. Each Ta atom has two terminal bromine atoms. The compound is diamagnetic and has only two electrons for metal-metal bonding. IR and Raman spectral studies with the use of ³⁴S allow to identify characteristic vibrations S-S (537 cm ^-1) and Ta₄-μ₄-S (407 cm^-1). The compound is soluble in CH₃CN, giving a dark-red solution with a characteristic electronic spectrum, which was assigned on the base of DFT calculations. ESI-MS spectra of the solutions show formation of {[Ta ₄S₉Br₈]Br}_- associates.

Full text of DOI:10.1021/ic051014e

Inorg. Chem. 2005, 44, 8756−8761
Synthesis and Structure of Ta4S9Br8. An Emergent Family of Early
Transition Metal Chalcogenide Clusters
Maxim N. Sokolov,*,† Artem L. Gushchin,† Pavel A. Abramov,† Alexandr V. Virovets,†
Eugenia V. Peresypkina,† Svetlana G. Kozlova,†,‡ Boris A. Kolesov,† Cristian Vicent,# and
Vladimir P. Fedin†
NikolaeV Institute of Inorganic Chemistry, Russian Academy of Sciences, pr. LaVrentyeVa 3,
NoVosibirsk 630090, BoreskoV Institute of Catalysis, Russian Academy of Sciences, pr.
LaVrentyeVa 5, 630090 NoVosibirsk, Russia, and Departament de Ciencies Experimentals,
UniVersitat Jaume I, Castellon, Spain
Received June 22, 2005
Single crystals of Ta4S9Br8 are obtained by heating Ta, S, and Br2 at 400
yield. The structure was determined by X-ray analysis and consists of molecular clusters [Ta4(
tantalum atoms form a square with long Ta‚‚‚Ta distances (3.30 Å), with four S2 ligands bridging the Ta
and one capping the square. Each Ta atom has two terminal bromine atoms. The compound is diamagnetic and
has only two electrons for metal
metal bonding. IR and Raman spectral studies with the use of 34S allow to
identify characteristic vibrations S
S (537 cm-1) and Ta4- 4-S (407 cm-1). The compound is soluble in CH3CN,
°
C in a 4.0:9.0:4.0 molar ratio in a 44%
4-S)( -S2)4Br8]. The
Ta edges
µ
µ
−
−
−
µ
giving a dark-red solution with a characteristic electronic spectrum, which was assigned on the base of DFT
-
calculations. ESI-MS spectra of the solutions show formation of
{
[Ta4S9Br8]Br
}
associates.
Introduction
where the [Ta2(S2)2]n+ (n ) 5, 6) or [Ta2(S2)(S)]6+ units are
linked together by anionic ligands.5 Ta-Ta bonding is
observed in TaS3 and Ta6Sn (n ) 1, 3, 4).6 Reactions between
Ta, S, and Br2 or I2 lead to chalcogen-poor trinuclear clusters
Despite strong interest in the chemistry of sulfide clusters
in general, sulfido-bridged cluster complexes of Ta remain
little studied.1 Self-assembly reactions in solution based on
metathesis of mononuclear Ta(V) precursors with a sulfide
source (generally, (Me3Si)2S) were used to prepare bi-, tri-,
tetra-, and pentanuclear complexes without direct Ta-Ta
7+
Ta3(µ3-S)(µ-X)3 in the structures of Ta3SBr7 and Ta3SI7‚
TaI4, respectively.7,8 We decided to explore high-temperature
reactions between tantalum, chalcogen, and halogen in a
chalcogen-richer area, with the hope to obtain ternary
chalcohalides, where TaxQyn+ cluster units would be coor-
dinated by exchangeable halide ligands, thus permitting their
further involvement into synthetic chemistry. Here we report
the synthesis, structure determination, and detailed spectro-
scopic studies of a new tetranuclear Ta cluster, [Ta4(µ4-S)(µ-
S2)4Br8].
bondingsmostly Cp derivatives and
[Ta6S17].4-2,3 The only clusters with metal-metal bonding
a thiotantalate,
4+
in this category are [Ta2S2Cl4(PR3)4] (a Ta2(µ2-S)2 core)
and a zigzag Ta4 chain in [Ta4S4Cl8(PMe3)6].4 High-temper-
ature reactions lead to ternary sulfides and thiophosphates,
* To whom correspondence should be addressed. E-mail:
caesar@che.nsk.su.
† Nikolaev Institute of Inorganic Chemistry.
Experimental Section
‡ Boreskov Institute of Catalysis.
# Universitat Jaume I.
Materials and Spectroscopy. High-purity Ta and S powders
were used. Br2 was dried over P4O10 and distilled. IR spectra
(4000-40 cm-1) were recorded on an IFS-85 Fourier spectrometer
(1) Sokolov, M. N.; Fedin, V. P. Coord. Chem. ReV. 2004, 248, 925.
(2) (a) Kawaguchi, H.; Tatsumi, K. Organometallics 1997, 16, 307. (b)
Tatsumi, K.; Inoue, Y.; Kawaguchi, H.; Kohsaka, M.; Nakamura, A.;
Cramer, R. E.; Van Coone, W.; Taogoshi, G. J.; Richmann, P. N.
Organometallics 1993, 12, 352. (c) Fenske, D.; Maue, P. G. Z.
Naturforsch. 1989, B44, 531.
(5) (a) Gutzmann, A.; Na¨ther, C.; Bensch, W. Inorg. Chem. 2004, 43,
2998. (b) Evain, M.; Queignec, M.; Brec, R.; Rouxel, J. J. Solid State
Chem. 1985, 56, 148. (c) Evain, M.; Queignec, M.; Brec, R.;
Sourisseau, C. J. Solid State Chem. 1988, 75, 413.
(3) Sola, J.; Do, Y.; Berg, J. M.; Holm, R. H. Inorg. Chem. 1985, 24,
1706.
(4) (a) Babaian-Kibala, E.; Cotton, F. A. Inorg. Chim. Acta 1991, 182,
77. (b) Babaian-Kibala, E.; Cotton, F. A.; Kibala, P. A. Inorg. Chem.
1990, 29, 4002.
(6) Rouxel, J. Acc. Chem. Res. 1992, 25, 328.
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8756 Inorganic Chemistry, Vol. 44, No. 24, 2005
10.1021/ic051014e CCC: $30.25
© 2005 American Chemical Society
Published on Web 10/19/2005

Synthesis and Structure of Ta4S9Br8
a
Table 1. Crystal Data and Structure Refinement for Ta4S9Br8
(Bruker) in KBr pellets. Raman spectra were obtained on a
Triplimate SPEX spectrometer using a 632.8 nm line of He-Ne
laser for excitation. UV/vis-spectroscopic measurements were
conducted at room temperature using an Ultrospec 3300pro
spectrometer. X-ray powder diffraction data were obtained on a
DRON-2 powder diffractometer (Cu KR radiation).
A Quattro LC (quadrupole-hexapole-quadrupole) mass spec-
trometer with an orthogonal Z-spray electrospray interface (Mi-
cromass, Manchester, UK) was used. The compound Ta4S9Br8 was
dissolved partially in acetonitrile by stirring thoroughly for 3 h.
Sample solutions (approximately 10-4 M) were infused to the mass
spectrometer via syringe pump directly to the interface at a flow
rate of 10 µL/min. The temperature of the source block was set to
100 °C and the interface to 150 °C. A capillary voltage of 3.3 kV
was used in the negative scan mode, and the cone voltage was kept
at 20 V to avoid fragmentation of the pseudo-molecular ions. The
drying gas, as well as nebulizing gas, was nitrogen at a flow of
400 and 80 L/h, respectively.
chemical formula
Mr
Br8S9Ta4
1651.62
cell setting, space group, Z
tetragonal, I4mm, 2
12.765 (5)
6.966 (4)
1135.0 (9)
4.833
a (Å)
c (Å)
V (Å3)
Dx (mg m-3
)
µ (mm-1
)
34.11
crystal form, color
crystal size (mm)
tetragonal prism, metallic black
0.50 × 0.02 × 0.02
no. of measured, independent,
and observed [I > 2σ(I)] reflns
Rint
2459, 656, 546
0.068
θ
max (°)
27.4
R1 [F > 4σ (F)], wR2 (F2),
0.034, 0.070, 1.02
GOF (F2)
no. of relns/params
weighting scheme
656/34
calcd w ) 1/[σ2(Fo ) + (0.0183P)2]
2
where P ) (Fo2 + 2Fc )/3
1.59, -1.11
2
∆Fmax, ∆Fmin (e Å-3
)
a Computer programs: APEX2 v.1.0-8 (Bruker, 2003); SHELXTL v.6.22
Cyclic voltammetry experiments were performed with a Echoche-
mie Pgstat 20 electrochemical analyzer. All measurements were
carried out with a conventional three-electrode configuration
consisting of Pt working and auxiliary electrodes and a Ag/AgCl
reference electrode filled with aqueous 3 M KCl. The solvent was
CH3CN (Merck isocratic grade). The supporting electrolyte was
0.1 M Bu4NPF6, prepared by reaction of tetrabutylammonium
bromide and HPF6, recrystallized from ethanol, and dried under
vacuum. Ec values were determined at a scan rate of 100 mV/s.
(Bruker, 1990-2003); local programs.
crystallochemical analysis TOPOS 4.0 Professional.11 The KPACK
program12 was used to calculate packing coefficients and the
following atomic radii: Ta, 1.43; S, 1.85; Se, 2.0; Br, 1.95; I, 2.15
Å.
Theoretical Calculations. The electronic structure and vibra-
tional spectra of the ground state of the isolated [Ta4S9Br8] molecule
(C4V symmetry) was analyzed with the ADF 2002 program
package.13 The geometry optimization was achieved with the spin-
restricted DFT, including zero-order scalar relativistic effects
(ZORA14), in which model electron density functional Hamiltonians
are represented as the sum of local density functionals LDA
(VWN15) and gradient exchange functional GGA (Becke16 and
Perdew17). Slater orbitals (ADF/TZ2P) with core potentials Ta-
(1s...5p), S(1s...2p), and Br(1s...3p) were used as basis wave
functions. The formation energy corresponds to the process: 4Ta
+ 9S + 8Br f [Ta4S9Br8]. Atomic charges were obtained by the
Hirshfeld method.18 Dipole-allowed electron transitions were
calculated using the TDDFT (time-dependent density functional
theory) method with the gradient exchange functional GGA LB94.19
Synthesis and Characterization. Ta powder (3.62 g, 0.020 mol),
S (1.44 g, 0.045 mol), and Br2 (3.20 g, 0.020 mol) were loaded in
a quartz ampule, which was evacuated after three cycles of freezing/
thawing by liquid N2, flame sealed, and heated at 200 (1 day) and
400 °C (5 days) in a furnace with a small natural temperature
gradient. Large single crystals of Ta4S9Br8 deposit in the colder
zone, together with some red-orange TaBr5. Most of Ta4S9Br8
remains in the hotter zone as pure single phase (powder diffraction).
Yield of the product (collected from the hotter zone) 3.60 g (44%).
Element ratio: Ta4.0:S9.1:Br7.8 (EDAX). Raman (cm-1): 537 m
(S-S vibrations), 407 w (Ta4-µ4-S), 373 w, 365 w, 339 w, 292 s,
252 m, 229 s, 218 w, 197 w, 178 w, 163 w, 145 w, 125 sh, 119 s,
87 s, 75 w, 57 m. IR/FTIR (KBr disc/polyethylene): 538 m, 467
w, 408 w, 395 s, 337 m, 290 s, 269 m, 251 s, 232 vs, 226 vs, 218
vs, 168 w, 146 w, 125 w, 118 w, 106 s. Absorption spectrum (CH3-
CN): λmax (ꢀM): 526 (1020), 750 (460) nm.
Results and Discussion
Synthesis. The title compound is obtained by heating the
elements in the required stoichiometric ratio at 400 °C. Some
TaBr5 also forms, together with an unidentified solid, which
may be TaOBr2, because its powder diffractogram resembles
that of structurally characterized TaOI2.20 Ta4S9Br8 is the
second ternary compound obtained in the system Ta-S-
Br2. Trinuclear Ta(III) thiobromide, Ta3SBr7, is formed from
the elements by heating the mixture at 550 °C in the
Cyclic voltammetry in the -1 to 1.2 V range displays two
irreversible oxidations at 0.74 and 1.07 V and two irreversible
reductions at -0.25 and -0.8 V, which most probably indicate a
cluster degradation/fragmentation.
Structure Determination. The diffraction data were collected
at room temperature on Bruker X8APEX CCD diffractometer with
Mo KR radiation (λ ) 0.71073 Å) using æ scans of narrow (0.5°)
frames. The structure was solved by direct methods and refined by
(11) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. J. Appl.
Crystallogr. 2000, 33, 1193; http://topos.ssu.samara.ru.
(12) Virovets, A. V.; Podberezskaya, N. V. Kristallografiya 1992, 37, 1017.
(13) Amsterdam Density Functional (ADF) program, release 2002.02; Vrije
Universteit: Amsterdam, The Netherlands, 2002.
(14) Van Lenthe, E.; Ehlers, A. E.; Baerends, E. J. J. Chem. Phys. 1999,
110, 8943.
2
the full-matrix least-squares method against |F| in anisotropic
approximation using the SHELXTL program set.9 Absorption
corrections were applied empirically using the SADABS program
(Tmin/Tmax ) 0.510).10 The detailed data are collected in Table 1.
Intermolecular interactions in crystals and topologies of molecular
packing were analyzed with the program set for multi-purpose
(15) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200.
(16) Becke, A. D. Phys. ReV. A. 1988, 38, 3098.
(17) Perdew, J. P. Phys. ReV. B. 1986, 33, 8822.
(9) SHELXTL, version 6.22; Bruker AXS, Inc.: Madison, WI, 2003.
(10) Sheldrick, G. M. SADABS, Program for absorption correction with
the SMART system; University of Go¨ttingen: Go¨ttingen, Germany,
1996.
(18) Hirshfeld, F. L. Theor. Chim. Acta 1977, 44, 129.
(19) van Gisbergen, S. J. A.; Snijders, J. G.; Bearends, E. J. J. Comput.
Phys. Commun. 1999, 118, 119.
(20) Ruck, M. Acta Cryst. C 1995, 51, 1960.
Inorganic Chemistry, Vol. 44, No. 24, 2005 8757

Sokolov et al.
a
Table 2. Bond Lengths [Å] and Angles [deg] for Ta4S9Br8
Ta(1)-S(1)
Ta(1)-S(2)
Ta(1)-S(3)
Ta(1)-Ta(1)b
2.461(3)
2.521(3)
2.500(4)
3.3018(15)
S(2)-S(3)
Ta(1)-Br(1)
Ta(1)-Br(2)
2.061(8)
2.483(3)
2.471(2)
Ta(1)b-Ta(1)-Ta(1)c
90.0
Ta(1)c-S(1)-Ta(1)
Br(2)-Ta(1)-Br(1)
S(1)-Ta(1)-S(3)
S(2)-Ta(1)-S(3)
S(1)-Ta(1)-S(2)
S(3)-Ta(1)-S(3)b
S(2)b-Ta(1)-S(2)
84.2(1)
99.1(1)
89.0(2)
48.5(2)
93.7(8)
87.0(2)
171.8(1)
S(1)-Ta(1)-Br(1)
86.1(2)
S(1)-Ta(1)-Br(2) 174.7(2)
Br(2)-Ta(1)-S(2)
Br(1)-Ta(1)-S(2)
86.5(9)
88.5(2)
Br(1)-Ta(1)-S(3) 136.2(1)
Br(2)-Ta(1)-S(3)
87.1(1)
a Symmetry transformations used to generate equivalent atoms: b, -y,
x, z; c, y, -x, z; d, -x, -y, z.
Figure 1. Structure of Ta4S9Br8 (ellipsoids of 50% probability level).
Table 3. Average Molecular Geometry of Ta4Q9X8
stoichiometric ratio given by the formula.7 The structural
analogue of Ta4S9Br8, the selenoiodide Ta4Se9I8, was recently
obtained from the elements.21 However, the system Ta-Se-
Br2 under the same conditions forms Ta3Se8Br6, which is
built from positively charged patronite-like chains, ‚‚‚Ta(µ-
Se2)2‚‚‚, separated by anions, [TaBr6]-.22 The behavior of
niobium, the closest analogue of tantalum, is very different.
Instead of tetranuclear Nb4Q9X8, which remains unknown,
it generally forms dinuclear chalcohalides [Nb2(µ-Q2)2X4]
or [Nb2(µ-Q2)(µ-X)2X4].23,24 As the mean oxidation state of
the metal is +4.5 in the Ta4Q9Br8 and +4 in Nb2Q4X4 and
Nb2Q2X6, this different behavior may result from the higher
electropositivity of Ta.
Crystal Structure. The molecule of Ta4S9Br8 (I) is shown
in Figure 1. The molecular structure is identical to that of
Ta4Se9I8 (II),21 save that in I strict square planar geometry
of the Ta4 core is symmetrically imposed. Four S2 ligands
are asymmetrically coordinated to the Ta-Ta edges in a µ2-
η2:η2manner. Four of the sulfur atoms lie almost in the Ta4
plane (within (0.02 Å, equatorial, Seq), and the other four
(axial, Sax) deviate from the plane by about 1.71 Å in the
direction opposite to the µ4-S atom. The terminal bromine
atoms are also coordinated asymmetrically. Four of them lie
closer to the Ta4 plane (Breq, at 0.99 Å trans to the µ4-S)
and the rest deviate from this plane by 2.40 Å (cis to the
µ4-S). The interatomic distances and some angles are
summarized in Table 2, and comparison of molecular
geometry of I and II is given in Table 3. The coordination
polyhedron around Ta can be described as pentagonal
bipyramide with µ4-S and one of the Br atoms trans to it in
the axial position (Brtrans) and the two groups, S2 and another
Br atom (Brcis), in the equatorial position. Rather long Ta-
Ta distances (3.30 Å) are in agreement with the average Ta
oxidation state of +4.5 in this highly electron-deficient
cluster. In [Ta(Se2)2]2(TaBr6) and [Ta(Se2)2]2I, the distances
between Ta atoms in the same average oxidation state are
deviation of the atoms from Ta4 plane, Å
compound
Ta‚‚‚Ta, Å
Ta
Qeq
Qax µ3-Q Xeq
Xax
Ta4S9Br8 (I),
Q ) S, X ) Br
Ta4Se9I8 (II),
Q ) Se, X ) I
3.301
0
-0.02 1.71 -0.78 0.99 -2.40
3.392
(0.006 -0.13 1.86 -1.02 0.93 -2.65
3.18-3.23 and 3.20 Å, respectively.22,25 This is expectedly
longer than in the clusters with Ta-Ta bond of order 1, such
as TaIII3SBr7 (2.86 Å) or in [Ta2(µ-S)2Cl4(PMe2Ph)4] (2.875
Å).4 The situation with no Ta-Ta bonding is found in TaV -
2
(µ-S2)26+, present in TaPS6 and Ta4P4S29.5b In this case Ta‚
‚‚Ta distances are 3.36-3.38 Å, i.e., somewhat longer than
in I, which has two electrons to provide a weak bonding
between Ta atoms, as supported by DFT calculations (vide
infra). The S-S distances correspond to a single bond, as
expected for the S22- formalism.26 The Ta-Br bond lengths
are practically the same as those found in the [TaBr6]- salts.22
There are other square planar clusters with capping
µ4-S, [Nb4(µ4-S)2(µ-SPh)8(SPh)4]4- and [Nb4(µ4-S)2(µ-SPh)8-
(PMe2R)4],27 but no Ta analogues are known. A µ4-STa4 unit
is found in [Cp4Ta4(S2)5(µ4-S)(µ-S)2]. In that case, the µ4-S
ligand is found in the center of a Ta4 tetrahedron, with very
long Ta-S distances (2.62-2.67 Å).2c On the other hand,
in the triangular cluster [Ta3(µ3-S)(µ-Br)3Br4], the Ta-capping
µ3-S distances (2.36-2.44 Å) are even shorter than in I,
which reflects the increasing electron deficiency of the
capping µ4-SM4 bonding vs µ3-SM3: in both cases, the
capping sulfur donates only four electrons.7
Despite similar molecular geometries, the intermolecular
interactions in the crystals of I and are different. In II, four
shortened nonvalent contacts Seax‚‚‚I (3.484(1)-3.581(1) Å)
are all directed to the same iodine atom so that the molecules
are joined into zigzag chains (Figure 2a). In I (Figure 2b),
relatively short Sax‚‚‚Br contacts are arranged in a quite
different way, forming a crownlike system of eight sym-
metrically equivalent contacts of 3.558(5) Å. Each Sax atom
forms two contacts with a pair of bromine atoms (3.550(5)
(21) Sokolov, M. N.; Gushchin, A. L.; Virovets, A. V.; Peresypkina, E.
V.; Kozlova, S. G.; Fedin, V. P. Inorg. Chem. 2004, 43, 7966.
(22) Sokolov, M.; Imoto, H.; Saito, T.; Fedorov V. Polyhedron 1998, 17,
3735.
(25) Gressier, P.; Guemas, L.; Meerchaut, A. Acta Crystallogr. B 1982,
38, 2877.
(23) (a) Rijnsdorp, J.; DeLonge G. L.; Wiegers, G. A. J. Solid State Chem.
1979, 30, 365. (b) von Schnering, H. G.; Beckmann, W. Z. Anorg.
Allg. Chem. 1966, 347, 231.
(24) Franzen, H. F.; Ho¨nle, W.; v. Schnering, H. G. Z. Anorg. Allg. Chem.
1983, 497, 13.
(26) Mu¨ller, A.; Jaegermann, W.; Enemark, J. H. Coord. Chem. ReV. 1982,
46, 245.
(27) (a) Seela, J. L.; Huffmann, J. C.; Christou, G. J. Chem. Soc. Chem.
Commun. 1987, 1258. (b) Babaian-Kibala, E.; Cotton, F. A.; Kibala,
P. A. Polyhedron 1990, 9, 1689.
8758 Inorganic Chemistry, Vol. 44, No. 24, 2005

Synthesis and Structure of Ta4S9Br8
Table 4. Calculated and Experimental Geometry of Ta4S9Br8
d(Ta-Ta), Å d(Ta-S), Å d(Ta-µ4-S), Å d(Ta-Br), Å d(S-S), Å
calcd exptl calcd exptl calcd exptl calcd exptl calcd exptl
3.346 3.301 2.533 2.500 2.497 2.461 2.509 2.471 2.198 2.061
2.551 2.521
2.521 2.483
Table 5. Calculated Atomic Charges in Ta4S9Br8
Ta
S
µ4-S
Br
0.245
0.009 (ax)
0.024 (eq)
-0.104
-0.121 (cis)
-0.131 (trans)
Figure 2. Comparison of crystal structures of Ta4Se9I8 (a) and Ta4S9Br8
(b). The short interatomic Q‚‚‚Xax and Xeq‚‚‚Xeq contacts are shown as
dashed lines. (a) The antiparallel chains of Ta4Se9I8 molecules in the crystal
packing of II. The chains are joined to the 3D framework by I‚‚‚I 3.948(1)
and 4.040(1) Å contacts. (b) The parallel chains of Ta4S9Br8 molecules in
the crystal packing of I. The chains are joined to the 3D framework by
short Breq‚‚‚Breq contacts.
their centers of gravity in I is of 6.966 Å, in II, the distance
is 7.744 Å.
Both I and II show a very strong structural similarity to
the recently prepared Ln(III)-Se clusters [Ln4(µ4-Se)(µ-Se2)4-
(THF)6I2] (Ln ) Tm, Ho, Er, Yb).28 The molecular Ti
thiochloride [Ti4(µ4-O)(µ-S2)2(µ-Cl)2Cl4] has a similar struc-
ture, with the difference that the coordination requirements
of Ti atoms are satisfied with a lower Cl/Ti ratio by making
two Cl ligands to bridge two opposite Ti atoms; the Ti4
arrangement is in fact a flattened tetrahedron.29 In a broader
sense, both I and the Ln clusters can be regarded as higher
homologues of M3(µ3-Q)(µ,η2-Q2)3 (M ) Ti, V, Mo, W, Re;
Q ) O, S, Se, Te) clusters with three metal atoms and three
bridging dichalcogen ligands instead of four in our case.30
In both cluster types, the µ2-Q2 ligands are tilted to the Mn
(n ) 3, 4) plane, permitting the distinction to be made
between axial and equatorial chalcogen atoms. The M-Qeq
bond distances are sufficiently longer than M-Qax (some-
times by up to 0.1 Å), though this difference is less
pronounced in the square clusters, probably due to the
elongation of metal-chalcogen bonds. In I, the difference
is only 0.02 Å. Each M atom both in M4Q9 and in M3Q7
cores coordinates two terminal atoms. The Q-Q bonds
remain almost unchanged. Moreover, just like I and II, the
crystal structures of M3Q7 clusters contain a negatively
charged atom or ion nearly equidistant from three Qax atoms,
with short nonbonding contacts between them.31 The contacts
are much shorter then the sum of van der Waals radii. Thus,
Figure 3. Crystal paking (a) in I (view along [001]) and (b) in II (view
along [100]).
Figure 4. ESI mass spectrum of Ta4S9Br8 in CH3CN in the presence of
1 equiv of PPh4Cl in the negative scan mode.
Å), thus involving all axial bromine atoms of the adjacent
molecule into intermolecular bonding. As in II, the Qax‚‚‚X
contacts join molecules into chains, but the chains in I are
strictly linear and run in the same direction, resulting in a
polar structure. Shortened intercontacts Breq‚‚‚Breq (3.572-
(3) Å) join the chains into a 3D framework. The different
way of intermolecular bonding in these two structures leads
to different arrangements in the first coordination sphere of
the molecules. Each molecule in crystal of I is surrounded
by 14 neighbors, while in II, they are only surrounded by 8
(Figure 3). In both structures, two of the closest molecules
are the adjacent molecules of the chain. The distance between
Figure 5. Experimental and calculated (vertical lines) electronic spectrum
of Ta4S9Br8 in CH3CN.
Inorganic Chemistry, Vol. 44, No. 24, 2005 8759

Sokolov et al.
Figure 6. The energy level diagram and schematic figures of MO calculated at the DFT level with GGA LB94 and allowed electron transitions (arrows)
in the Ta4S9Br8 molecule.
2-
the bridging Q2 group in [Ta4(µ4-Q)(µ,η2-Q2)4X8] has
similar electrophilic character as Q22- in the M3Q7 clusters.
Mass Spectrometry. In the ESI-MS of I (CH3CN solution,
negative scan mode), only one peak is observed, which is
attributed to the formation of ionic associate {[Ta4S9Br8]Br}-,
most probably via the four Sax‚‚‚X- interactions. Despite the
neutral nature of complex Ta4S9Br8, it readily ionizes in the
negative scan mode by capturing a bromide. The intensity
of the signal increases when some Bu4NBr is added. With
Ph4PCl (1 equiv), the formation of {[Ta4S9Br8]Cl}-(or, less
probably, {[Ta4S9Br7Cl]Br}-) is observed (Figure 4). This
ionization mode is unusual as compared with other neutral
halide metal complexes reported by Henderson et al.32 In
these complexes, the loss of one halide ligand appears to be
the dominant ionization process, though aggregation with
cationic species also was detected in some cases. Positive
ESI mass spectra of Ta4S9Br8 show no signals of any cluster
species present in the gas phase. The lack of the ionization
through a halide loss process might be attributed to the high
stability of the Ta-Br bonds in the compound. There are
close parallels with trinuclear clusters [Mo3S7X6]2-, which
tend form anionic associates {[Mo3S7X6]X}3-, also via
Sax‚‚‚X- contacts (X ) Cl, Br).33
structure parameters are given in Table 4. There is a
qualitative agreement between the calculated and experi-
mental data. The difference is to be explained by the
inevitable discrepancies between the values obtained for an
isolated molecule in a vacuum and the real fragment of the
crystal lattice. Table 5 shows the calculated atomic charges.
The Ta and S atoms are slightly positively charged, whereas
the µ4-S and Br atoms bear small negatively charges.
However, the small absolute values confirm the essentially
covalent bonding in the molecule. The HOMO is a nonde-
generate orbital 16b2, has ∼50% contribution of 5d Ta AO,
∼20% from 3p S AO (from Seq), and another ∼20% from
4p Br AO with bonding character for Ta-Seq and antibonding
character for Ta-Brtrans (Figure 6). The calculated ground
state of the Ta4S9Br8 molecule is spin-paired (diamagnetic)
and correlates well with the experimental data. Only two
electrons are thus available for metal-metal bonding, which
gives the bond order between each pair of Ta atoms as 0.25,
in accordance with the observed elongated Ta-Ta distance.
The LUMO is a double degenerate orbital 38e1, has a mixture
of bonding and antibonding character with ∼60% contribu-
tion of 5d Ta AO, ∼5% of 3p S AO (3.5% from µ4-S ligand),
and ∼20% of 4p Br AO (Figure 6).
Electronic Structure and UV-Vis Spectra. According
to the calculations, the formation of Ta4S9Br8 molecule is a
highly exothermic process (-101.0 eV). The optimized
To assign the bands in the electronic spectrum, it was
assumed that they correspond to the electron-dipole transi-
tions from HOMO to the LUMO and higher orbitals. For
the C4V symmetry, the selection rules allow b2 T e transitions.
In the window available for study, these are 16b2 T 38e1,
16b2 T 39e1, 16b2 T 40e1, and 16b2 T 41e1 transitions
(Figures 5 and 6). The TDDFT predicts almost equal
intensities for all four transitions. However, the experimental
data demonstrate that the intensity is higher at lower
(28) (a) Kornienko, A.; Melman, J. H.; Hall, G.; Emge, T. J.; Brennan, J.
C. Inorg. Chem. 2002, 41, 121. (b) Fitzgerald, M.; Emge, T. J.;
Brennan, J. G. Inorg. Chem. 2002, 41, 3528. (c) Melman, J. H.;
Fitzgerald, M.; Freedman, D.; Emge, T. J.; Brennan, J. G. J. Am. Chem.
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II 2003, 4, 761. (b) Saito, T. J. Chem. Soc., Dalton Trans. 1999, 97.
(c) Beck, J.; Mu¨ller-Buschbaum, K. Z. Anorg. Allg. Chem. 1999, 625,
1212.
(31) Mayor-Lopez, M. J.; Weber, J.; Hegetschweiler, K.; Meyenberger,
M. D.; Jobo, F.; Leoni, S.; Nesper, R.; Reiss, G.; Frank, W.; Kolesov,
B.; Fedin, V.; Fedorov, V. Inorg. Chem. 1998, 37, 2633.
(32) Henderson, W.; Evans, C. Inorg. Chim. Acta, 1999, 294, 183.
(33) (a) Lu, S.; Shang, M.; Huang, J. Chin. J. Struct. Chem. (Jiegou Huaxue)
1984, 3, 9. (b) Huang, J.; Shang, M.; Huang, J.; Zhuang, H.; Lu, S.;
Lu, J. Chin. J. Struct. Chem. (Jiegou Huaxue) 1982, 1, 1. (c)
Klingelho¨fer, P.; Mu¨ller, U.; Friebel, C.; Pebler, J. Z. Anorg. Allg.
Chem. 1986, 543, 22. (d) Fedorov, V. E.; Gerasko, O. A.; Mironov,
Yu. V.; Hegetschweiler, K.; Stoop, R.; Gallus, J.; Gramlich, F. Russ.
J. Struct. Chem., Engl. Transl. 1995, 36, 956.
8760 Inorganic Chemistry, Vol. 44, No. 24, 2005

Synthesis and Structure of Ta4S9Br8
together with the normal coordinates can be found in the
Supporting Information. The characteristic band at 537-
(Raman)/538(IR) cm-1 is due to the ν(S-S) vibration in the
bridging S2, and a weak doubly degenerate mode 407-
(Raman)/408(IR) cm-1 comes from Ta-µ4-S vibrations. The
band at 292(Raman)/292(IR) cm-1 corresponds to Ta-µ2-
S2. For the other vibrations, the calculated eigenvectors are
complex and include the participation of all the atoms in
each of them.
The position of ν(S-S) at 537(Raman)/538(IR) cm-1 in I
correlates well with the positions of this vibration in other
studied S2 complexes with the same disulfide bridging
modesin [W2(µ-S2)2Br8]2- (590(IR)/592(Raman) cm-1);
[Mo2(µ-S2)2Br8]2- (598(IR)/601(Raman) cm-1); [Mo3(µ3-
S)(µ-S2)3Cl6]2- (560(IR)/568(Raman) cm-1); [W3(µ3-S)(µ-
S2)3Br6]2- (550(IR)/560(Raman) cm-1);35 and [Nb2(µ-S2)2-
Br8]2- (576 cm-1, IR).36 The characteristic M-µ3-S vibrations
are observed at 461 cm-1 in [Mo3(µ3-S)(µ-S2)3Cl6]2- and at
449 cm-1 in [W3(µ3-S)(µ-S2)3Br6]2- (Raman, IR), that is,
higher than the Ta-µ4-S vibration in I.
Figure 7. Raman spectra of the isotopomeric Ta432S9Br8 and Ta434S9Br8.
Table 6. Isotopic Shifts in the Raman Spectra of Ta4S9Br8
ω (32S)
ω (34S)
∆ω
ω (32S)
ω (34S)
∆ω
57
87
57
86
0
1
2
2
2
2
5
2
216
229
243
251
292
407
537
215
228
240
249
286
398
522
1
1
3
2
6
119
125
145
163
176
196
117
123
143
161
171
194
Acknowledgment. Grants to M.N.S. of Russian Science
Support is gratefully acknowledged. The work was supported
by INTAS (Grant No. 2356), Russian Science Support
Foundation for Basic Research (grant 05-03-32126) and
Haldor Topsøe foundation (a grant for A.L.G.). The authors
thank Prof. V. A. Blatov for providing TOPOS 4.0 Profes-
sional software.
8
15
wavelengths and that HOMO-LUMO bands cannot be
observed. We suppose that this is due to the vibronic effects
when the electrons are excited into degenerate e1 levels.34
Vibration Spectra. For C4V Ta4S9Br8, the internal vibra-
tions are represented as Γ ) 10A1 (Raman, IR) + 4A2 +
6A1 (Raman) + 7A2 (Raman) + 14E (Raman, IR). The
experimental Raman spectra for Ta432S9Br8 and Ta434S9Br8
isotopomeric molecules are shown in Figure 7. The Raman
isotopic shifts upon 32S f 34S substitution are given in Table
6. It can be seen that most of the vibration modes undergo
some isotopic shift, but the most sensitive are the bands at
292, 407, 537 cm-1 and a very weak band at 176 cm-1. The
numerical values for the isotopic shifts in the IR spectra
Supporting Information Available: Crystallographic informa-
tion file (CIF) for I. This material is available free of charge via
the Internet at http://pubs.acs.org. The details of the theoretical IR
and Raman spectra calculations are available from the authors upon
request.
IC051014E
(35) (a) Fedin, V. P.; Kolesov, B. A.; Mironov, Yu. V.; Gerasko, O. A.;
Fedorov, V. Ye. Polyhedron 1991, 10, 997. (b) Fedin, V. P.; Sokolov,
M. N.; Gerasko, O. A.; Kolesov, B. A.; Fedorov, V. Ye.; Mironov,
A. V.; Yufit, D. S.; Slovohotov, Yu. L.; Struchkov, Yu. T. Inorg.
Chim. Acta 1990, 175, 217. (c) Fedin, V. P.; Sokolov, M. N.; Mironov,
Yu. V.; Kolesov, B. A.; Tkachev, S. V.; Fedorov, V. Ye. Inorg. Chim.
Acta 1990, 167, 39.
(34) Bersuker, I. B. Electronic Sructure and Poperties of Transition Metal
Compounds; Jonh Wiley and Sons: New York, 1996. Bersuker, I. B.
The Jahn-Teller Effect and Vibronic Interactions in Modern Chem-
istry; Plenum Press: New York, 1984.
(36) Sokolov, M.; Imoto, H.; Saito, T.; Fedorov, V. Z. Anorg. Allg. Chem.
1999, 625, 989.
Inorganic Chemistry, Vol. 44, No. 24, 2005 8761