Cluster core controlled reactions of substitution of terminal bromide ligands by triphenylphosphine in octahedral rhenium chalcobromide complexes

Article abstract of DOI:10.1021/ja0668062

Reactions of rhenium chalcobromides Cs₄[{Re₆(μ ₃-S)₈}Br₆]·2H₂O, Cs ₃[{Re₆(μ₃-Se)₈}Br ₆]·2H₂O, Cs₃[{Re₆(μ ₃-Q)₇(μ₃-Br)}Br₆]·H ₂O (Q = S, Se), and K₂[{Re₆(μ₃-S) ₆(μ₃-Br)₂)Br₆] with molten triphenylphosphine (PPh₃) have resulted in a family of novel molecular hybrid inorganic-organic cluster compounds. Six octahedral rhenium cluster complexes containing PPh₃ ligands with general formula [{Re₆(μ₃-Q)_8-n(μ₃-Br) _n}(PPh₃)_4-nBr_n+2] (Q = S, n = 0, 1, 2; Q = Se, n = 0, 1) have been synthesized and characterized by X-ray single-crystal diffraction and elemental analyses, ³¹P{¹H} NMR, luminescent measurements, and quantum-chemical calculations. It was found that the number of terminal PPh₃ ligands in the complexes is controlled by the composition and consequently by the charge of the cluster core {Re₆Q_8-nBr_n}ⁿ⁺². In crystal structures of the complexes with mixed chalcogen/bromine ligands in the cluster core all positions of a cube [Q_8-nBr_n] are ordered and occupied exclusively by Q or Br atoms. Luminescence characteristics of the compounds trans-[{Re₆Q₈}(PPh₃) ₄Br₂] and fac-[{Re₆Se₇Br}(PPh ₃)₃Br₃] (Q = S, Se) have been investigated in CH₂Cl₂ solution and the broad emission spectra in the range of 600-850 nm were observed.

Full text of DOI:10.1021/ja0668062

Published on Web 03/03/2007
Cluster Core Controlled Reactions of Substitution of Terminal
Bromide Ligands by Triphenylphosphine in Octahedral
Rhenium Chalcobromide Complexes
Michael A. Shestopalov,† Yuri V. Mironov,† Konstantin A. Brylev,†
Svetlana G. Kozlova,† Vladimir E. Fedorov,*,† Hartmut Spies,‡
Hans-Ju¨rgen Pietzsch,‡ Holger Stephan,‡ Gerhard Geipel,§ and Gerd Bernhard§
Contribution from NikolaeV Institute of Inorganic Chemistry, Siberian Branch of the Russian
Academy of Sciences, 3 Acad. LaVrentieV Prosp., 630090 NoVosibirsk, Russia, and Institut fu¨r
Radiopharmazie and Institut fu¨r Radiochemie, Forschungszentrum Dresden-Rossendorf, PF
510119, 01314 Dresden, Germany
Received September 21, 2006; E-mail: fed@che.nsk.su
Abstract: Reactions of rhenium chalcobromides Cs4[{Re6(µ3-S)8}Br6]‚2H2O, Cs3[{Re6(µ3-Se)8}Br6]‚2H2O,
Cs3[{Re6(µ3-Q)7(µ3-Br)}Br6]‚H2O (Q ) S, Se), and K2[{Re6(µ3-S)6(µ3-Br)2}Br6] with molten triphenylphosphine
(PPh3) have resulted in a family of novel molecular hybrid inorganic-organic cluster compounds. Six
octahedral rhenium cluster complexes containing PPh3 ligands with general formula [{Re6(µ3-Q)8-n(µ3-
Br)n}(PPh3)4-nBrn+2] (Q ) S, n ) 0, 1, 2; Q ) Se, n ) 0, 1) have been synthesized and characterized by
X-ray single-crystal diffraction and elemental analyses, 31P{1H} NMR, luminescent measurements, and
quantum-chemical calculations. It was found that the number of terminal PPh3 ligands in the complexes is
controlled by the composition and consequently by the charge of the cluster core {Re6Q8-nBrn}n+2. In crystal
structures of the complexes with mixed chalcogen/bromine ligands in the cluster core all positions of a
cube [Q8-nBrn] are ordered and occupied exclusively by Q or Br atoms. Luminescence characteristics of
the compounds trans-[{Re6Q8}(PPh3)4Br2] and fac-[{Re6Se7Br}(PPh3)3Br3] (Q ) S, Se) have been
investigated in CH2Cl2 solution and the broad emission spectra in the range of 600-850 nm were observed.
compounds.5,6 Another effective way for preparation of com-
plexes with terminal organic ligands is the use of the proper
Introduction
Hexanuclear rhenium(III) cluster complexes of general for-
mula [{Re6Q8}L6], where Q is µ3-chalcogenide ligands (S, Se,
or Te) and L- inorganic acido ligands or organic species are
the subject of extensive current studies. Heightened attention
to these complexes is due to their structural, redox, and
photoluminescent properties as well as a rich chemistry which
descends from a versatility of the coordination environment of
the octahedral cluster core {Re6(µ3-Q)8}. Present interest is
focused on clusters coordinated by organic N- and P-donor
ligands.1-4 Such inorganic-organic hybrids show interesting
structural, electronic, and optical properties. The main strategy
in their preparation is the substitution of terminal ligands L that
can be controlled with respect to the number of the ligands
substituted and their geometrical arrangement around the cluster
core. The first representatives of the Re6 cluster complexes with
PEt3 and CH3CN terminal ligands have been obtained in solution
starting from the corresponding oxidized Re6 chalcohalide
molten organic compounds as a reaction media. Recently this
approach was used for preparation of cuboidal clusters of
molybdenum and tungsten with diphosphine terminal ligands7
and of octahedral rhenium cluster complexes with 3,5-dimeth-
ylpyrazole as terminal ligands (3,5-Me2pzH).8,9 By the examples
of octahedral rhenium cluster complexes with 3,5-Me2pzH
ligands we have shown that, in contrast to ligand substitution
reactions in solutions, both oxidized and nonoxidized Re6
chalcohalide cluster anions can be involved in direct ligand
substitution with organic ligands in their melt. Here we have
exploited this methodology with the use of molten triph-
enylphosphine as reaction media for the synthesis of rhenium
cluster complexes with terminal PPh3 ligands. Included in the
present investigation is the study of the influence of precursor
cluster core composition on the stoichiometry and structure of
(5) Zheng, Z. P.; Long, J. R.; Holm, R. H. J. Am. Chem. Soc. 1997, 119, 2163-
2171.
(6) Willer, M. W.; Long, J. R.; McLauchlan, C. C.; Holm, R. H. Inorg. Chem.
1998, 37, 328-333.
† Nikolaev Institute of Inorganic Chemistry.
‡ Institut fu¨r Radiopharmazie, Forschungszentrum Dresden-Rossendorf.
§ Institut fu¨r Radiochemie, Forschungszentrum Dresden-Rossendorf.
(1) Gabriel, J. C. P.; Boubekeur, K.; Uriel, S.; Batail, P. Chem. ReV. 2001,
101, 2037-2066.
(7) Feliz, M.; Llusar, R.; Uriel, S.; Vicent, C.; Humphrey, M. G.; Lucas, N.
T.; Samoc, M.; Luther-Davies, B. Inorg. Chim. Acta 2003, 349, 69-77.
(8) Mironov, Y. V.; Shestopalov, M. A.; Brylev, K. A.; Yarovoi, S. S.;
Romanenko, G. V.; Fedorov, V. E.; Spies, H.; Pietzsch, H. J.; Stephan,
H.; Geipel, G.; Bernhard, G.; Kraus, W. Eur. J. Inorg. Chem. 2005, 657-
661.
(2) Selby, H. D.; Roland, B. K.; Zheng, Z. Acc. Chem. Res. 2003, 36, 933-
944.
(3) Selby, H. D.; Roland, B. K.; Cole, J. R.; Zheng, Z. P. Macromol. Symp.
2004, 209, 23-39.
(4) Selby, H. D.; Zheng, Z. P. Comments Inorg. Chem. 2005, 26, 75-102.
(9) Mironov, Y. V.; Brylev, K. A.; Shestopalov, M. A.; Yarovoi, S. S.; Fedorov,
V. E.; Spies, H.; Pietzsch, H. J.; Stephan, H.; Geipel, G.; Bernhard, G.;
Kraus, W. Inorg. Chim. Acta 2006, 359, 1129-1134.
9
3714
J. AM. CHEM. SOC. 2007, 129, 3714-3721
10.1021/ja0668062 CCC: $37.00 © 2007 American Chemical Society

Octahedral Rhenium Chalcobromide Complexes
A R T I C L E S
the reaction mixture by three portions (10 mL) of CH2Cl2 to give a
dark red solution. The solution was chromatographed on a silica gel
column. Fraction 1 (CH2Cl2, Rf ) 0.97), orange band: 5. Red crystals
were obtained by slow evaporation of solution at room temperature in
air. Yield: 56 mg (24.6%). Anal. Calcd for C36H30Br6P2Re6S6 (5): C,
18.69; H, 1.31; S, 8.32. Found: C, 18.37; H, 1.78; S, 8.31. EDS: Re:
S:Br:P ratio is 6:5.8:5.9:2. Fraction 2 (CH2Cl2, Rf ) 0.82), orange
band: 3. Yield: 24 mg (9.9%). Fraction 3 (CH2Cl2, Rf ) 0.51) orange
band: 6. Red crystals were obtained by slow evaporation of solution
at room temperature in air. Yield: 120 mg (51.8%). Anal. Calcd for
C36H38Br6O4P2Re6S6 (6): C, 18.12; H, 1.60; S, 8.07. Found: C, 18.41;
H, 1.56; S, 8.16. EDS: Re:S:Br:P ratio is 6:5.8:6.1:2.1. Fraction 4 (Me2-
CO), brown band: unknown admixture.
the compounds formed. Most of previous research has been
focused on the use of cluster complexes with chalcogenide
cluster cores, {Re6S8} and {Re6Se8}, as starting compounds.
In the present work we report the syntheses, crystal and
electronic structures, and luminescent properties of the series
of complexes: trans-[{Re6(µ3-Q)8}(PPh3)4Br2] (Q ) S (1), Se
(2)), fac-[{Re6(µ3-Q)7(µ3-Br)}(PPh3)3Br3] (Q ) S (3), Se (4)),
cis-[{Re6(µ3-S)6(µ3-Br)2}(PPh3)2Br4] (5), and trans-[{Re6(µ3-
S)6(µ3-Br2)}(PPh3)2Br4]‚4H2O (6) with both chalcogenide {Re6Q8}
and mixed-ligand chalcobromide {Re6Q8-nBrn} (n ) 1, 2)
cluster cores.
Experimental Section
Crystallography. Single-crystal X-ray diffraction data were collected
with the use of graphite monochromatized Mo KR radiation (λ )
0.71073 Å) at 293 K on a Bruker Nonius X8Apex diffractometer
equipped with a 4K CCD area detector. The æ-scan technique was
employed to measure intensities. Absorption corrections were applied
using the SADABS program.14,15 The crystal structures were solved
independently by direct methods and were refined by full-matrix least-
squares techniques with the use of the SHELX package.16 All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms of the
water molecules in compound 4 were not located. The positions of
hydrogen atoms of PPh3 ligands were calculated corresponding to their
geometrical conditions and refined using the riding model. Crystal-
lographic data as well as details of data collection and refinement for
complexes 1-6 are given in Table 1 and in the Supporting Information.
Table 2 tabulates some metrical details for the present compounds.
CCDC 620891-620896 contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Materials and Synthesis. Cs4[Re6S8Br6]‚2H2O, Cs3[Re6Se8Br6]‚
2H2O, Cs3[Re6Q7Br7]‚H2O (Q ) S, Se), and K2[Re6S6Br8] were
synthesized as described previously.10-13 All other reagents were used
as purchased.
Elemental analyses for C, H, and S (Carlo Erba 1106) were
performed in the Laboratory of Microanalysis of the Institute of Organic
Chemistry, Novosibirsk. Energy dispersive spectroscopy (EDS) was
performed on an EDAX equipped (JEOL EX-23000BU) JEOL JSM-
6700F field emission scanning electron microscope. Infrared spectra
were measured on KBr pellets with a Bruker IFS-85 Fourier spectrom-
eter. The 31P{1H} NMR spectra of CD2Cl2 solutions were recorded at
20 °C on the Bruker CXP-300 spectrometer (57.2 MHz) using HP
detectors. X-ray powder diffraction data were collected on a Philips
APD 1700 instrument. The thermal properties were studied on
Derivatograph Q-1500 MOM (Hungary) in the temperature range 25-
500 °C.
General Procedure for Syntheses of Compounds 1-4. A 100 mg
amount of proper Re6 cluster compound and an excess of PPh3 (100
mg) were heated in sealed glass tube at 200 °C for 2 days. The reaction
mixture was cooled to room temperature with the rate of 10 °C/h. The
product of reaction was washed by ether for removing PPh3 excess
and by water to dissolve CsBr formed in the reaction. Yields: 103 mg
(98%) (1); 108 mg (95%) (2); 102 mg (93%) (3); 104 mg (97%) (4).
Single crystals for X-ray structural analyses were separated manually
from the reaction mixtures. Anal. Calcd. for C72H60Br2P4Re6S8 (1): C,
33.48; H, 2.34; S, 9.93. Found: C, 33.25; H, 2.26; S, 9.87. Anal. Calcd
for C72H60Br2P4Re6Se8 (2): C, 29.24; H, 2.04. Found: C, 28.99; H,
2.08. Anal. Calcd for C54H45Br4P3Re6S7 (3): C, 26.49; H, 1.85; S, 9.17.
Found: C, 26.21; H, 2.08; S, 9.12. Anal. Calcd for C54H45Br4P3Re6Se7
(4): C, 23.36; H, 1.63. Found: C, 23.07; H, 1.52. EDS shows the fol-
lowing: Re:S:Br:P ratio of 6:7.7:1.9:4.2 for C72H60Br2P4Re6S8 (1); Re:
Se:Br:P ratio of 6:8.1:1.8:4.3 for C72H60Br2P4Re6Se8 (2), Re:S:Br:P ratio
of 6:6.8:4.1:3.3 for C54H45Br4P3Re6S7 (3); Re:Se:Br:P ratio of 6:7.1:
4.2:2.9 for C54H45Br4P3Re6Se7 (4). In 31P{1H} NMR spectra of 1-6
only one signal is observed: δ -25.4 for 1; δ -22.5 for 2; δ -10.4 for
3; δ -18.2 for 4; δ -11.0 for 5; δ -6.4 for 6. IR spectra (400-4000
cm-1) of compounds 1-6 show all peaks expected for PPh3. In spectra
of compounds 1, 3, 5, and 6 the bands at 416, 420, 418, and 417 cm-1
correspondingly may be assigned to Re-(µ3-S) vibration. X-ray powder
patterns of the compounds 1-6 are in good agreement with the data
calculated on the basis of the results of the single-crystal study.
Synthesis of Compounds 5 and 6. K2Re6S6Br8 (200 mg, 0.099
mmol) and PPh3 (200 mg, 0.76 mmol) were heated in the sealed glass
tube at 200 °C for 2 days. The reaction mixture was cooled to room
temperature with the rate of 10 °C/h. The product was extracted from
Luminescent Measurements. The compounds trans-[{Re6S8}(PPh3)4-
Br2] (1), trans-[{Re6Se8}(PPh3)4Br2] (2), fac-[{Re6S7Br}(PPh3)3Br3] (3),
and fac-[{Re6Se7Br}(PPh3)3Br3] (4) were dissolved in CH2Cl2. The final
concentration of the compounds in the solvent was about 10-4 M. The
solutions were measured in a 1 cm fluorescence cuvette (Helma,
Germany).
These solutions were studied by time-resolved laser-induced fluo-
rescence spectroscopy. To excite the luminescence, a Nd:YAG laser
system (Inlite, Continnum Corp. USA) was used. The fundamental
output of the laser was two times frequency doubled to achieve a laser
wavelength of 266 nm. The repetition rate of the laser was set to be 20
Hz, and the pulse energy, applied to the samples, was attenuated to be
about 5 mJ/pulse. The luminescence emission was focused into an
optical fiber, and the spectrum was resolved in a 275 mm spectrograph
(Acton Research). The measurement of the spectrum was performed
by an intensified CCD camera system (Roper Scientific) with 1024 ×
1024 pixels. The settings of the intensifier are as follows: gain, 128;
gate width, 20 µs; and 100 accumulations on CCD. Each spectrum
was recorded 3 times. The time resolution was 500 ns, and the delay
range was from 0 to 20 µs.
Computational Details. Spin-restricted density functional calcula-
tions (DFT) were carried out on models with general formula [{Re6-
(µ3-Q)8-n(µ3-Br)n}Brn+2] and [{Re6(µ3-Q)8-n(µ3-Br)n}(PH3)4-nBrn+2] (Q
) S, n ) 0, 1, 2; Q ) Se, n ) 0, 1) using the ADF2003 code.17 The
PPh3 groups were substituted by the PH3 groups for ease of calculations.
The procedure of full optimization was used. The local-exchange VWN
correlation potential was used for the local density (LDA) approxima-
(10) Yarovoi, S. S.; Solodovnikov, S. F.; Mironov, Y. V.; Fedorov, V. E. J.
Struct. Chem. (Engl. Transl.) 2003, 44, 318-321.
(14) APEX2, Version 1.08; SAINT, Version 7.03; Bruker Advanced X-ray
Solutions, Bruker AXS Inc.: Madison, WI, 2004.
(11) Yarovoi, S. S.; Mironov, Y. V.; Naumov, D. Y.; Gatilov, Y. V.; Kozlova,
S. G.; Kim, S. J.; Fedorov, V. E. Eur. J. Inorg. Chem. 2005, 3945-3949.
(12) Yarovoi, S. S.; Mironov, Y. V.; Solodovnikov, S. F.; Virovets, A. V.;
Fedorov, V. E. Mater. Res. Bull. 1999, 34, 1345-1351.
(15) SADABS, Version 2.11; Bruker Advanced X-ray Solutions, Bruker AXS
Inc.: Madison, WI, 2004.
(16) SHELXTL, Version 6.12; Bruker Advanced X-ray Solutions, Bruker AXS
Inc.: Madison, WI, 2004.
(17) Amsterdam Density Functional (ADF) Program, Release 2003; Vrije
Universteit: Amsterdam, The Netherlands, 2003.
(13) Slougui, A.; Ferron, S.; Perrin, A.; Sergent, M. J. Cluster Sci. 1997, 8,
349-359.
9
J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3715

A R T I C L E S
Shestopalov et al.
Table 1. Crystal Data and Structure Refinements for 1-6
1
2
3
4
5
6
empirical formula
fw
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C72H60Br2P4Re6S8
2582.58
P21/c
12.4001(3)
16.1927(4)
19.1937(5)
C72H60Br2P4Re6Se8 C54H45Br4P3Re6S7
C54H45Br4P3Re6Se7 C36H30Br6P2Re6S6
C36H38Br6O4P2Re6S6
2385.62
P1h
2957.78
P21/c
2448.07
P1h
2776.37
P1h
2313.56
P21/m
10.302(2)
20.292(4)
12.108(2)
12.3444(2)
16.2377(4)
19.5427(4)
11.6455(3)
14.8271(4)
20.1655(5)
76.738(1)
74.951(1)
67.853(1)
3080.60(14)
2
11.6642(16)
14.880(2)
20.446(4)
77.159(5)
75.012(4)
67.931(5)
3145.7(8)
2
10.2225(6)
11.5987(7)
12.5588(6)
83.651(2)
74.953(2)
75.664(2)
1391.53(13)
1
101.780(1)
102.103(1)
105.38(3)
3772.75(16)
2
2.273
3830.16(14)
2
2440.5(9)
2
Z
F
calc (g/cm3)
2.565
2.639
2.931
181.99
3.148
200.81
2.847
176.19
µ (cm-1
cryst size (mm)
min; Tmax
)
109.93
144.11
146.86
0.20 × 0.20 × 0.10 0.30 × 0.07 × 0.02 0.18 × 0.10 × 0.08 0.19 × 0.13 × 0.13 0.20 × 0.08 × 0.05 0.08 × 0.06 × 0.02
T
0.1278; 0.3338
2.20-26.37
27 083
7705
0.0297
0.3101; 0.7515
2.73-29.43
28 140
0.1774; 0.3862
3.17-25.68
21 113
0.130; 0.201
3.10-25.68
21 371
0.118; 0.403
2.31-25.88
12 764
0.2910; 0.7010
2.53-27.18
9796
4843
0.0357
θ range, deg
reflecns collected
unique reflecns
Rint
6797
11 182
11 404
4626
0.0408
0.0215
0.0241
0.1789
param refined
415
415
0.0321
0.0798
559
0.0313
0.0947
559
0.0341
0.1025
229
0.0700
0.1934
265
0.0537
0.1764
2
R1(F) [Fo2 > 2σ(Fo )] 0.0303
Rw(F2) (all data)
0.0790
Table 2. Selected Bond Lengths (Å) for 1-6
compound
Re
−Re, Å
Re−µ3-Q, Å
Re−µ3-Br, Å
Re
−Brterminal, Å
Re−P, Å
1
2
3
4
5
6
2.5884(3)-2.5972(3)
2.6284(4)-2.6542(4)
2.5823(4)-2.6268(4)
2.6122(6)-2.6577(6)
2.595(2)-2.658(3)
2.381(2)-2.413(2)
2.5013(7)-2.5267(7)
2.383(2)-2.469(2)
2.4888(9)-2.5282(9)
2.410(7)-2.487(6)
2.430(4)-2.459(4)
2.5471(7)
2.5672(7)
2.5191(9)-2.5445(9)
2.538(1)-2.564(1)
2.507(3)-2.535(4)
2.511(2)-2.516(2)
2.517(2)-2.522(2)
2.515(2)-2.522(2)
2.497(2)-2.515(2)
2.504(2)-2.525(2)
2.509(7)
2.5867(9)-2.595(1)
2.6105(9)-2.619(1)
2.615(5)-2.637(4)
2.578(2)-2.594(2)
2.5844(9)-2.6302(9)
2.511(4)
Table 3. Calculated Atomic Charges in the Model Complexes [{Re6(µ3-Q)8-n(µ3-Br)n}Brn+2] and [{Re6(µ3-Q)8-n(µ3-Br)n}(PH3)4-nBrn+2] (Q )
S, n ) 0, 1, 2; Q ) Se, n ) 0, 1)
cluster core atomsa
ligandsa
model complexes
Re
Q
Br
Br
P
trans-[{Re6S8}Br2]
trans-[{Re6S8}(PH3)4Br2]
trans-[{Re6Se8}Br2]
trans-[{Re6Se8}(PH3)4Br2]
fac-[{Re6S7Br}Br3]
fac-[{Re6S7Br}(PH3)3Br3]
fac-[{Re6Se7Br}Br3]
fac-[{Re6Se7Br}(PH3)3Br3]
cis-[{Re6S6Br2}Br4]
cis-[{Re6S6Br2}(PH3)2Br4]
trans-[{Re6S6Br2}Br4]
trans-[{Re6S6Br2}(PH3)2Br4]
0.12 (2), 0.16 (4)
0.09 (2), 0.03 (4)
0.09 (2), 0.11 (4)
0.06 (2), 0.01 (4)
0.11 (3), 0.16 (3)
0.03 (3), 0.10 (3)
0.08 (3), 0.11 (3)
0.01 (3), 0.07 (3)
0.16 (2), 0.11 (4)
0.04 (2), 0.10 (4)
0.15 (2), 0.11 (4)
0.04 (2), 0.10 (4)
-0.07 (8)
-0.17 (2)
-0.10 (8)
-0.17 (2)
-0.20 (2)
-0.29(2)
-0.18 (3)
-0.23 (3)
-0.21 (3)
-0.26 (3)
0.19 (4)
0.17 (4)
0.19 (3)
0.17 (3)
0.20 (2)
0.20 (2)
-0.03 (8)
-0.04 (8)
-0.04 (3), -0.05 (3), -0.10 (1)
-0.07 (3), -0.08 (3), -0.12 (1)
0.00 (6), -0.06 (1)
-0.01 (3), -0.03 (3), -0.06 (1)
-0.03 (4), -0.05 (2)
-0.05 (4), -0.06 (2)
-0.03 (4), -0.04 (2)
-0.05 (4), -0.06 (2)
0.11 (1)
0.10 (1)
0.11 (1)
0.10 (1)
0.10 (2)
0.09 (2)
0.10 (2)
0.08 (2)
-0.18 (2), -0.19 (2)
-0.21 (2), -0.22 (2)
-0.18 (4)
-0.22 (4)
a Number of corresponding atoms is shown in parentheses.
tion,18 Becke’s nonlocal corrections to the exchange energy19 and
Perdew’s nonlocal corrections to the correlation energy were added.20
The ZORA (zero-order relativistic approximation) method was used
to account for the scalar relativistic effects.21 The STO basic set without
core potentials was used for all atoms (ZORA/TZ2P). The atomic net
(µ3-Q)8-n(µ3-Br)n}Brn+2] and [{Re6(µ3-Q)8-n(µ3-Br)n}(PH3)4-nBrn+2]
models with a precision of two decimal places (Table 3).
Also the bonding energies for all three possible isomeric forms of
[Re6Q6Br8]2- (Q ) S, Se) and atomic net charges on Re atoms for
starting complexes [{Re6Q7Br}Br6]3- and [{Re6S6Br2}Br6]2- were
calculated (see Discussion and the Supporting Information).
charges for several [{Re6(µ3-Q)8-n(µ3-Br)n}Brn+2] and [{Re6(µ3-Q)8-n
-
(µ3-Br)n}(PH3)4-nBrn+2] (Q ) S, n ) 0, 1, 2; Q ) Se, n ) 0, 1) models
presented in Table 3 are obtained using the Hirshfeld analysis.22
A special feature of charge calculations is that the group PH3 (it
may be that the PPh3 too) influences on the symmetry negligibly
because the symmetry of charge distribution is conserved for [{Re6-
Results
Syntheses. Six new octahedral rhenium cluster compounds,
namely, trans-[{Re6(µ3-Q)8}(PPh3)4Br2] (Q ) S (1), Se (2)),
fac-[{Re6(µ3-Q)7(µ3-Br)}(PPh3)3Br3] (Q ) S (3), Se (4)), cis-
[{Re6(µ3-S)6(µ3-Br)2}(PPh3)2Br4] (5), and trans-[{Re6(µ3-S)6-
(µ3-Br)2}(PPh3)2Br4]‚4H2O (6) have been prepared by the
reactions of the corresponding ionic chalcobromide complexes
Cs4[{Re6(µ3-S)8}Br6]‚2H2O, Cs3[{Re6(µ3-Se)8}Br6]‚2H2O, Cs3-
(18) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200-1211.
(19) Becke, A. D. Phys. ReV. A 1988, 38, 3098-100.
(20) Perdew, J. P. Phys. ReV. B 1986, 33, 8822-8824.
(21) van Lenthe, E.; Ehlers, A.; Baerends, E. J. J. Chem. Phys. 1999, 110, 8943-
8953.
(22) Hirshfeld, F. L. Theor. Chim. Acta 1977, 44, 129-38.
9
3716 J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007

Octahedral Rhenium Chalcobromide Complexes
A R T I C L E S
Figure 1. Structure of the cluster core {Re6Q7Br} (a) and three possible
isomers of cluster core {Re6Q6Br2} (b-d).
[{Re6(µ3-Q)7(µ3-Br)}Br6]‚H2O (Q ) S, Se), and K2[{Re6(µ3-
S)6(µ3-Br)2}Br6] with molten PPh3. All compounds obtained in
these reactions are molecular complexes. They are stable in air
and do not decompose in inert atmosphere (He) up to 200 (for
3-6) and 350 °C (for 1 and 2). For the separation of different
isomers, column chromatography was employed. In the case
of the {Re6S6Br2} cluster core, two isomers of the three possible
ones were isolated (Figure 1b-d).
All obtained compounds are 24e clusters with the Re atoms
in the +3 oxidation state, even in the case of use of the oxidized
complex [{Re6Se8}Br6]3- as precursor. This is not surprising,
because it was shown earlier that the reactions involving
substitution of terminal halogen ligands in 23e cluster complexes
[{Re6Q8}L6]3- (L ) Cl, Br, I) by organic ligands as a rule are
accompanied by the spontaneous one-electron reduction of the
cluster.5,6,9,23-27
It is interesting to note that the composition of the compounds
synthesized strongly depends on the charge of the cluster core
{Re6Q8-nBrn}n+2 in the starting cluster complexes. These results
differ from the previously described reactions of chalcobromide
octahedral rhenium cluster complexes with 3,5-dimethylpyrazol,
where all six terminal Br ligands were substituted by organic
molecules.8,9
The formation of octahedral cluster complexes with PPh3 as
terminal ligands is known for some transition metals. Recently,
several examples of neutral complexes with cluster cores
{M6Q8} coordinated by six PPh3 ligands were described, for
example, [Ru6Se8(PPh3)6],28 [W6S8(PPh3)6],29 and [Co6Q8-
(PPh3)6] (Q ) S, Se).30,31 The majority of studies on Re6
complexes with phosphine ligands were carried out with
PEt3.1,2,5,23,32 There are three examples of structurally character-
ized Re6 complexes containing PPh3 ligand, namely, cis-[Re6-
Se8(PPh3)4(4,4′-dipyridyl)2](SbF6)2 and its derivatives: [{Re6-
Se8 (PPh3 )4 (4,4′-dipyridyl)2 }2 {Cd(NO3 )2 }](SbF6 )4 ‚
21C4H10O‚21CH2Cl2 and [{Re6Se8(PPh3)4(4,4′-dipyridyl)2}-
{Cd(NO3)3}](NO3)‚2C4H10O‚CH2Cl2.33 In addition, the com-
pounds fac-[Re6Se8(PPh3)3(isonicotinamide)3](SbF6)2, fac-[Re6-
Se8(PPh3)3(MeCN)3](SbF6)2, and cis-[Re6Se8(PPh3)4(MeCN)2]-
Figure 2. Structure of trans-[{Re6S8}(PPh3)4Br2] in 1. Displacement
ellipsoids of the non-hydrogen atoms are drawn at the 30% probability level.
H atoms of the PPh3 ligands have been omitted for clarity.
(SbF6)2 were reviewed by Zheng et al.3,4 Also some related
complexes with phosphine derivatives are known: [Re6Se8-
(MePPh2)6](SbF6)2‚2H2O, [Re6Se8((Me2TTF)PPh2)6](SbF6)2, and
[Re6Se8(FcPPh2)6](SbF6)2‚5CH2Cl2.34
Structures. All compounds obtained were characterized by
single-crystal X-ray diffraction analysis. The most interesting
feature of these solids with mixed-ligand cluster cores is the
formation of crystal structures without disorder in the cluster
core. In the known Re6 cluster complexes with a mixed
chalcohalide cluster core {Re6Q8-nXn} as a rule each corner of
the cube [Q8-nXn] is occupied statistically by Q and X atoms.
There is only one example of a compound with an ordered
mixed-ligand cluster corescis-[{Re6Te6Cl2}(TeCl2)2Cl4],35 where
the structure of the cluster core is similar to that found in cis-
[{Re6S6Br2}(PPh3)2Br4] (5).
trans-[{Re6S8}(PPh3)4Br2] (1) and trans-[{Re6Se8}(PPh3)-
4Br2] (2). Compounds 1 and 2 are isostructural and were
obtained only in one isomeric form, as trans-isomers. The cluster
cores in 1 and 2 contain a Re6 octahedron residing inside a Q8
cube (Q ) S, Se). Re-Re and Re-Q distances are typical for
24e Re6 complexes, and their geometrical details do not differ
significantly from the starting material and related compounds.
Four Re atoms in the equatorial plane are coordinated by PPh3
molecules and the two remaining Re atoms in trans-positions
are coordinated by Br ligands. The structure of molecule 1 is
shown in Figure 2. Compound 2 has a similar structure. All
atoms in the structures 1 and 2 are located in general positions.
The unit cell contains three rhenium and four chalcogen atoms
that are crystallographically independent, all of which belong
to the same cluster core. The centers of the clusters coincide
with the centrosymmetrical special crystallographic position (0,
1/2, 0; 1/2, 1/2, 1/2). There are not any notable interactions between
molecules in the crystal structures. The Re-Re, Re-Q, Re-P,
and the Re-Br distances are tabulated in Table 2.
(23) Zheng, Z. P.; Gray, T. G.; Holm, R. H. Inorg. Chem. 1999, 38, 4888-
4895.
(24) Yoshimura, T.; Umakoshi, K.; Sasaki, Y.; Sykes, A. G. Inorg. Chem. 1999,
38, 5557-5564.
(25) Yoshimura, T.; Umakoshi, K.; Sasaki, Y.; Ishizaka, S.; Kim, H. B.;
Kitamura, N. Inorg. Chem. 2000, 39, 1765-1772.
(26) Chen, Z. N.; Yoshimura, T.; Abe, M.; Sasaki, Y.; Ishizaka, S.; Kim, H.
B.; Kitamura, N. Angew. Chem., Int. Ed. 2001, 40, 239-242.
(27) Chen, Z. N.; Yoshimura, T.; Abe, M.; Tsuge, K.; Sasaki, Y.; Ishizaka, S.;
Kim, H. B.; Kitamura, N. Chem. Eur. J. 2001, 7, 4447-4455.
(28) Eckermann, A. L.; Wunder, M.; Fenske, D.; Rauchfuss, T. B.; Wilson, S.
R. Inorg. Chem. 2002, 41, 2004-2006.
(29) Jin, S.; Zhou, R.; Scheuer, E. M.; Adamchuk, J.; Rayburn, L. L.; DiSalvo,
F. J. Inorg. Chem. 2001, 40, 2666-2674.
(30) Hong, M.; Huang, Z.; Lei, X.; Wei, G.; Kang, B.; Liu, H. Inorg. Chim.
Acta 1989, 159, 1-2.
(31) Hong, M.; Huang, Z.; Lei, X.; Wei, G.; Kang, B.; Liu, H. Polyhedron 1991,
10, 927-34.
(34) Perruchas, S.; Avarvari, N.; Rondeau, D.; Levillain, E.; Batail, P. Inorg.
(32) Zheng, Z. P.; Holm, R. H. Inorg. Chem. 1997, 36, 5173-5178.
(33) Selby, H. D.; Orto, P.; Carducci, M. D.; Zheng, Z. P. Inorg. Chem. 2002,
41, 6175-6177.
Chem. 2005, 44, 3459-3465.
(35) Mironov, Y. V.; Pell, M. A.; Ibers, J. A. Inorg. Chem. 1996, 35, 2709-
2710.
9
J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3717

A R T I C L E S
Shestopalov et al.
Figure 4. Structure of cis-[{Re6S6Br2}(PPh3)2Br4] in 5. Displacement
ellipsoids of the non-hydrogen atoms are drawn at the 30% probability level.
H atoms of the PPh3 ligands are not shown.
Figure 3. Structure of fac-[{Re6S7Br}(PPh3)3Br3] in 3. Displacement
ellipsoids of the non-hydrogen atoms are drawn at the 30% probability level.
H atoms of the PPh3 ligands have been omitted for clarity.
fac-[{Re6S7Br}(PPh3)3Br3] (3) and fac-[{Re6Se7Br}(PPh3)3-
Br3] (4). The compounds 3 and 4 are isostructural. All atoms
and centers of the cluster cores are located in general positions.
Each cluster core is built from six rhenium, one bromine, and
seven chalcogen atoms that are crystallographically independent.
The cluster cores {Re6Q7Br} contain a pseudocube [Q7Br]
(Figure 1a). There is no atom disorder in the cluster core: seven
positions are occupied only by S in 3 or Se in 4 and one position
is occupied by a bromine atom. Three Re atoms of the same
face are coordinated by PPh3 ligands, and three remaining Re
are coordinated by Br atoms forming a fac-isomer. The µ3-Br
atom occupies only one position in the cluster core and is
connected to three Re atoms bonded with terminal Br ligands.
The structure of molecule 3 is shown in Figure 3; 4 has a similar
structure. There are no remarkable interactions between the
molecular complexes fac-[{Re6Q7Br}(PPh3)3Br3] in crystal
structures 3 and 4. The Re-Re, Re-Q, Re-µ3-Br, Re-P, and
the Re-Brterminal distances are presented in Table 2. The Re-
µ3-Br distances for octahedral rhenium cluster complexes with
mixed-ligand cluster cores were not presented previously
because of disorder in such compounds.
Figure 5. Structure of trans-[{Re6S6Br2}(PPh3)2Br4] in 6. Displacement
ellipsoids of the non-hydrogen atoms are drawn at the 30% probability level.
H atoms of the PPh3 ligands have been omitted for clarity.
cis-[{Re6S6Br2}(PPh3)2Br4] (5). In this compound six corners
of the [S6Br2] cube are occupied exclusively by S atoms. The
two other corners of the cube, which lie on the edge of cube
(Figure 1b), are occupied exclusively by Br atoms. The four
Re atoms that are bonded to µ3-Br ligands have terminal Br
ligands (Figure 4). The unit cell contains one crystallographically
independent cluster unit. The Re3, Re4, S1, S4, Br5 and Br6
(µ3-ligands), and Br3 and Br4 (terminal ligands) atoms lay on
cluster core is built from three rhenium, three sulfur, and one
bromine atom, all of which are crystallographically independent.
All atoms are located in general positions, while the center of
the cluster coincides with the special crystallographic position
(1/2, 0, 1/2). The Re-Re, Re-S, Re-µ3-Br, Re-P, and the Re-
Brterminal distances are listed in Table 2. The cluster units do
not interact with each other. The water molecules are connected
in pairs by weak hydrogen bonds (the O‚‚‚O distance is 2.87
Å) and the pairs are linked via hydrogen bonding to the µ3-Br
atoms (the O‚‚‚Br distance is 3.45 Å) (Figure 6).
Luminescent Properties. The luminescent properties of CH2-
Cl2 solutions of compounds 1-4 were studied. Compound 1
shows a broad luminescence emission in the wavelength range
from 600 to 850 nm, with a maximum at about 725 nm. The
luminescence decay is found to be monoexponential with a
decay time of 5.6 ( 0.1 µs. The compound 3 shows almost no
1
the mirror plane (x, /4, z) that bisects the molecule. All other
atoms are located in general positions. The Re-Re, Re-S, Re-
µ3-Br, Re-P, and the Re-Brterminal distances are shown in Table
2. There are no noticeable interactions between the molecules
in the crystal structure.
trans-[{Re6S6Br2}(PPh3)2Br4]‚4H2O (6). In this compound
two Br atoms occupy the body diagonal of the cube [S6Br2]
(Figure 1c). Four Re atoms in a equatorial plane are coordinated
by Br atoms, and the two remaining Re atoms are coordinated
by PPh3 molecules to form the trans-isomer (Figure 5). The
9
3718 J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007

Octahedral Rhenium Chalcobromide Complexes
A R T I C L E S
Figure 6. Hydrogen bonding interactions (indicated by dashed lines)
between crystallization water molecules and µ3-Br ligands of cluster complex
in 6 (view down [001]). H atoms of the PPh3 ligands and water molecules
have been omitted.
Figure 8. Luminescence spectra of trans-[{Re6Se8}(PPh3)4Br2] (2) and fac-
[{Re6Se7Br}(PPh3)3Br3] (4).
Figure 9. Luminescence decay behavior of the compounds 1, 2, and 4.
Figure 7. Luminescence spectra of trans-[{Re6S8}(PPh3)4Br2] (1) and fac-
[{Re6S7Br}(PPh3)3Br3] (3).
luminescence. The maximum of the residual luminescence is
located at about 740 nm, and the decay time could not be
determined. At the moment there is no explanation for this
behavior. The luminescence spectra are shown in Figure 7.
The selenium-containing compounds show a completely
different behavior. Both compounds 2 and 4 show luminescence
spectra with nearly the same intensity at comparable delay time.
The spectra are shown in Figure 8. The emission maxima are
located at about 745 nm for 2 and 738 nm for 4. The
luminescence decay times are determined to be 3.2 ( 0.1 and
0.95 ( 0.05 µs for 2 and 4, respectively. The dependences of
the integrated luminescence intensities as a function of the delay
time for compounds 1, 2, and 4 are shown in Figure 9.
Figure 10. DFT energy level diagram for complexes trans-[{Re6S8}(PPh3)4-
Br2] (1) and fac-[{Re6S7Br}(PPh3)3Br3] (3) in the symmetries with the
approximation described in the text.
The negative intensities at high delay times for 2 and 4 are
a result of temperature problems in cooling of the CCD camera
chip, giving too high of a background correction. Compared to
the sulfur-containing compound 1, the selenium-containing
compounds show somewhat lower luminescence intensities.
The long-lived emission is accounted for by symmetry- and
spin-forbidden transitions between the HOMO and LUMO in
the [{Re6Q8}X6]4- (Q ) S, Se and X ) Cl, Br, and I)
complexes.36,37 The complexes are different in symmetry, which
demonstrates the role of cluster symmetry on luminescent
properties (Figures 10-12). For example, complexes 3 and 4
have the C3V symmetry (ignoring PPh3 influence) and the
In contrast to the recently published data for [{Re6Q7O}(3,5-
Me2pzH)6]Br2‚3,5-Me2pzH and [{Re6Q8}(3,5-Me2pzH)6]Br2‚2(3,5-
Me2pzH) (Q ) S, Se),8,9 the compounds described here have
only monoexponential luminescence decay. The decay times
are of the same order of magnitude (microseconds). The maxima
of the luminescence for the new compounds are shifted to longer
wavelength.
(36) Gray, T. G.; Rudzinski, C. M.; Meyer, E. E.; Holm, R. H.; Nocera, D. G.
J. Am. Chem. Soc. 2003, 125, 4755-4770.
(37) Gray, T. G.; Rudzinski, C. M.; Meyer, E. E.; Nocera, D. G. J. Phys. Chem.
A 2004, 108, 3238-3243.
9
J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3719

A R T I C L E S
Shestopalov et al.
considered.39-43 However, we believe that the approach pre-
sented here for analysis of cluster core symmetry would allow
the purposeful control of the luminescence lifetime.
31P{1H} NMR Spectra. In every 31P{1H} NMR spectrum
of compounds 1-6 one signal is observed. This result is in good
agreement with the structural data: the signals can be assigned
to only one isomeric form, namely, trans-[{Re6Q8}(PPh3)4Br2]
(for 1 and 2), fac-[{Re6Q7Br}(PPh3)3Br3] (for 3 and 4), cis-
[{Re6Q6Br2}(PPh3)2Br4] (for 5), or trans-[{Re6Q6Br2}(PPh3)2-
Br4] (for 6). The most negative chemical shift values correspond
to the compounds with the shortest average Re-P distances.
This dependence can be explained by an increase of electron
density on the P atoms due to the back-donation from the 5d
orbitals of the Re atoms. The chemical shift values decrease in
the following series: 3 (δ -10.4) < 5 (δ -11.0) < 4 (δ -18.2)
< 2 (δ -22.5) < 1 (δ -25.4), while the average Re-P distances
increase in the same sequence (2.507 Å (3) < 2.509 Å (5) <
2.513 Å (4) < 2.518 Å (2) < 2.520 Å (1)). Only the trans-
[{Re6Q6Br2}(PPh3)2Br4] complex (6) does not follow this trend
(δ -6.4; 2.511 Å).
Figure 11. DFT energy level diagram for complexes trans-[{Re6-
Se8}(PPh3)4Br2] (2) and fac-[{Re6Se7Br}(PPh3)3Br3] (4) in the symmetries
with the approximation described in the text.
Discussion
The series of octahedral rhenium cluster complexes with
cluster cores {Re6Q8-nBrn}n+2 (Q ) S, Se; n ) 0, 1, 2) and
terminal PPh3 ligands were prepared using molten triph-
enylphosphine as reaction medium. Additionally, solution
chemistry permitted isolation of different isomers.
Reactions of the anionic cluster complexes [{Re6S8}Br6]4-
,
[{Re6Se8}Br6]3-,[{Re6Q7Br}Br6]3- (Q)S,Se),and[{Re6S6Br2}-
Br6]2- with molten PPh3 lead to the formation of the complexes
with mixed Br/PPh3 terminal ligands. The original composi-
tions of the cluster cores in these reactions remain inalter-
able. In such complexes an octahedral Re6 cluster is inscribed
into a pseudocube [Q8-nBrn] of eight µ3-ligands. According to
the previous 77Se NMR study of (PPh4)2[Re6Se6Br8],44 for the
cluster core {Re6Se6Br2} all three possible isomeric units were
found with the ratio (%) of isomers b:c:d ) 27:61:12 (Figure
1). An interesting feature of c in comparison with the other
two isomers is the fact that all Re atoms in the cluster core in
c are equivalent: they have the same ligand environment
and, consequently, equal atomic charges (see Supporting
Information).
The calculated bonding energy values of [{Re6Se6Br2}Br6]2-
isomers (-116.18 for b (C2V symmetry), -116.26 for c (D3d),
and -116.03 eV for d (C2V)) are in good agreement with the
distribution of isomers determined by 77Se NMR data. The
bonding energy values of [{Re6S6Br2}Br6]2- isomers have the
same regularity (-120.57 for b, -120.65 for c, and -120.40
eV for d). Thus, the 77Se NMR and the bonding energy values
for isomers of [{Re6Q6Br2}Br6]2- (Q ) S, Se) suggest that the
ratio of isomers in system [Re6S6Br8]2- is similar to the selenium
Figure 12. DFT energy level diagram for for complexes cis-[{Re6S6-
Br2}(PPh3)2Br4] (5) and trans-[{Re6S6Br2}(PPh3)2Br4] (6) in the symmetries
with the approximation described in the text.
electron-dipole transitions between the HOMO and LUMO
(32a2 T 116e1 and 38a2 T137e1) are allowed. Experimentally
the decreasing of luminescence decay time for complex 4 and
practically the absence of luminescence effects for complex 3
are observed. Complexes 1 and 2 have D4h symmetry (ignoring
PPh3 influence also). The electron-dipole transitions are for-
bidden between the HOMO and LUMO (44a1g T 23b1g) in com-
plex 1 and for this complex the greatest decay time is observed.
The lowest unoccupied orbitals 56e1u and 26b1g have an energy
separation of 0.05 eV in complex 2. It is difficult to predict
which one of these two orbitals is the LUMO. The electron-
dipole transitions are allowed between 50a1g T 56e1u and
forbidden between 50a1g T 26b1g. In this case an intermediate
value of the luminescence decay time is observed (Figure 9).
Apparently, the existence of symmetry-forbidden transitions
increases the lifetime of emission. Hence one would expect a
decrease of lifetime for cis-[{Re6S6Br2}(PPh3)2Br4] (5) com-
plexes. The nature of luminescence kinetic processes is certainly
much more complicated36-38 than the qualitative explanation
proposed in our discussion. Moreover, we do not take into
account spin-orbital interactions, which principally should be
(39) Arratia-Perez, R.; Hernandez-Acevedo, L. J. Chem. Phys. 1999, 110, 2529-
2532.
(40) Arratia-Perez, R.; Hernandez-Acevedo, L. J. Chem. Phys. 1999, 111, 168-
172.
(41) Alvarez-Thon, L.; Hernandez-Acevedo, L.; Arratia-Perez, R. J. Chem. Phys.
2001, 115, 726-730.
(42) Arratia-Perez, R.; Hernandez-Acevedo, L. J. Chem. Phys. 2003, 118, 7425-
7430.
(43) Hernandez-Acevedo, L.; Arratia-Perez, R. J. Chil. Chem. Soc. 2003, 48,
125-128.
(38) Kitamura, N.; Ueda, Y.; Ishizaka, S.; Yamada, K.; Aniya, M.; Sasaki, Y.
(44) Yarovoi, S. S.; Solodovnikov, S. F.; Tkachev, S. V.; Mironov, Y. V.;
Fedorov, V. E. Russ. Chem. Bull. 2003, 52, 68-72.
Inorg. Chem. 2005, 44, 6308-6313.
9
3720 J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007

Octahedral Rhenium Chalcobromide Complexes
A R T I C L E S
Scheme 1. Charge Distribution on Rhenium Atoms According to
the rhenium atoms coordinated by a µ3-Br atom have less
positive charge than the atoms coordinated only by a µ3-S
(Scheme 1). Apparently, PPh3 as a nucleophilic agent prefers
to coordinate to Re atoms with a more positive charge.
Using an excess of triphenylphosphine in reactions with
cluster chalcobromides, we expected the substitution of all
terminal ligands in the starting compounds and the formation
of complexes with six terminal PPh3 ligands (as it was found
in the similar reactions with the melt of excess of 3,5-
dimethylpyrazole8,9). However, the compounds obtained here
have only four (1 and 2), three (3 and 4), or even two (5 and 6)
terminal PPh3 ligands. Such results may be explained by the
preferred formation of neutral molecular compounds with the
general formula [{Re6(µ3-Q)8-n(µ3-Br)n}(PPh3)4-nBrn+2] (Q )
S, n ) 0, 1, 2; Q ) Se, n ) 0, 1).
DTF Calculationsa
In the literature some related molecular rhenium cluster
complexes with PPh2(CH2)6PPh2 (dpph), PPh2CH2PPh2 (dppm),
PPh2(CH2)2POPh2 (dppeO), PPh2(CH2)4POPh2 (dppbO), and
PEt3 ligands are described. The structures of compounds trans-
[Re6Se8(µ2-dpph)2I2];26 trans-[Re6Se8I2(η1-dppm)4], trans-[Re6-
Se8I2(η1-dppeO)4], and trans-[Re6Se8I2(η1-dppbO)4];27 and trans-
[Re6Se8(PEt3)4I2]5 are similar to those found in compounds 1
and 2. Every dpph ligand in the complex trans-[Re6Se8(µ2-
dpph)2I2] is coordinated to two neighboring Re atoms of the
same cluster in a bridge-chelate manner, whereas dppm, dppeO,
dppbO, and PEt3 ligands in corresponding complexes are
monodentate. Organic P-donor ligands in these complexes are
coordinated to four Re atoms in the equatorial plane of the
rhenium octahedron. Two remaining Re atoms in trans-positions
are coordinated by iodine atoms.
a Bold lines correspond to the upper part of octahedral complex
[{Re6S7Br}Br6]3-. supposed scheme of substitution of terminal Br ligands
by PPh3 is indicated by arrows. Sulfur atoms are omitted for clarity.
analogue. This hypothesis is in agreement with the yields of
compounds 5 and 6. The low content of the third isomer d did
not allow us to isolate it from the reaction mixture.
In this work the reactivity of the octahedral rhenium cluster
chalcobromide complexes with three types of cluster cores,
namely, {Re6Q8}, {Re6Q7Br}, and {Re6S6Br2}, have been
studied. The isolation of two isomeric compounds containing
{Re6S6Br2} cluster cores was successful. All compounds
synthesized are molecular complexes. It was estimated that in
the conditions studied the number of neutral terminal PPh3
ligands depends on the composition of the cluster core. The
Re-L (L ) Brterminal, PPh3) distances depend on a nature of
the chalcogen atoms: selenium containing compounds have
longer Re-L average distances than their sulfur analogues
(Table 2). For all compounds the Re-L distances are in a good
agreement with literature data.10,12,13,33 This is the main differ-
ence from the compounds containing 3,5-Me2pzH ligands where
all six terminal ligands were substituted by organic molecules.8,9
It was also shown earlier that reactions between mixed-ligand
cluster complexes [{Re6Q7Br}Br6]3- (Q ) S, Se) and molten
3,5-Me2pzH resulted in substitution of µ3-Br ligand in the cluster
core by oxygen with formation of cationic cluster complexes
In conclusion, six novel octahedral rhenium cluster complexes
with the general formula [{Re6(µ3-Q)8-n(µ3-Br)n}(PPh3)4-n
-
Brn+2] (Q ) S, n ) 0, 1, 2; Q ) Se, n ) 0, 1) have been
synthesized by reaction of cluster rhenium chalcobromides with
molten triphenylphosphine. The compounds were characterized
by single-crystal X-ray diffraction and elemental analysis, 31P-
{1H} NMR spectroscopy, luminescent measurements, and
quantum-chemical calculations. It was shown that compounds
1, 2, and 4 exhibit broad emission spectra in the range of 600-
850 nm. The interesting feature of structures 3-6 is the ligand
ordering in mixed chalcohalide cluster cores. By the example
of compounds 5 and 6 the possibility of preparation and isolation
of isomeric complexes containing cluster cores of composition
{Re6S6Br2}4+ has been demonstrated.
2+
8
6
[{Re Q7O}(3,5-Me2pzH)6]
in addition to substitution of
terminal bromine ligands by molecules of 3,5-Me2pzH.
Only one other example of a Re6 cluster complex with ordered
arrangement of the µ3 ligands in mixed-ligand chalcohalide
cluster core has been reported to date, cis-[{Re6Te6Cl2}(TeCl2)2-
Cl4].35 It is interesting to note that the TeCl2 ligands are
coordinated to the Re atoms that are bonded only by µ3-Te
ligands. Our new compounds make a good addition to the family
of octahedral rhenium clusters with an atomic ordering in the
cluster core.
We believe that the atomic ordering in the cluster core is
controlled by the preference by PPh3 ligands to coordinate with
rhenium atoms which are bonded exclusively with µ3-Q atoms
(Q ) S, Se) as seen in the structures of compounds described
here. DFT calculations of rhenium atomic charges in mixed-
ligand chalcobromide complexes used as starting compounds
confirm our hypothesis (see the table in the Supporting
Information). For example, in the cluster anion [{Re6S7Br}Br6]3-
Acknowledgment. This research was supported by the
Russian Foundation for Basic Research (Grants 05-03-32123,
05-03-32745, and 05-03-08090) and by the Bundesministerium
fu¨r Bildung and Forschung (WTZ-Projekt RUS 01/241). We
are indebted to Dr. Dmitry Y. Naumov, Nikolaev Institute of
Inorganic Chemistry of SB RAS, for collection of X-ray
intensities through the use of the Bruker Nonius X8Apex
diffractometer.
Supporting Information Available: X-ray crystallographic
data (CIF) and a table with calculated rhenium atomic charges
in starting complexes [{Re6Q7Br}Br6]3- and [{Re6S6Br2}Br6]2-
.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JA0668062
9
J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3721