Rational syntheses, structure, and properties of the first bismuth(II) carboxylate

Article abstract of DOI:10.1021/ic049937h

Bismuth(II) trifluoroacetate (1), the first inorganic salt of bismuth in oxidation state +2, has been obtained in its pure, unstabilized form. Several synthetic routes suggested for the isolation of the new compound include (i) mild oxidation of elemental bismuth with some metal trifluoroacetates, e.g., Ag^I and Hg^II; (ii) mild reduction of bismuth-(III) trifluoroacetate with metals, such as Zn; (iii) comproportionation reaction between Bi and Bi(O₂CCF₃)₃. The last approach gives the title compound 1 in quantitative yield as a sole product. Bismuth(II) trifluoroacetate has been characterized by NMR, IR, and UV-vis spectroscopy as well as by single-crystal X-ray diffraction. Crystallographic study reveals the dinuclear paddle-wheel structure for diamagnetic molecules Bi₂(O ₂CCF₃)₄. The Bi-Bi bond distances in dimetal units of 1 are averaged to 2.9462(3) A, and there are no axial intermolecular contacts between these units in the solid state. The compound is volatile and exists in vapor phase up to 220 °C when it disproportionates back to Bi⁰ and Bi^III species, i.e., by the reverse of the synthetic route iii. In contrast, the solution chemistry is quite limited: the bismuth(II) trifluoroacetate is decomposed by the majority of common solvents, but it can be stabilized by aromatic systems. The dibismuth unit has been shown to be preserved in the latter solvents and can be crystallized out in a form of π-adducts with arenes. Two such adducts, Bi₂(O ₂CCF₃)₄·(C₆H₅Me) (2) and Bi₂(O₂CCF₃)₄· (1,4-C₆H₄Me₂)₂ (3), have been isolated as single crystals and characterized by X-ray diffraction techniques. In the structures of both 2 and 3, the bismuth(II) centers exhibit weak η⁶-coordination to aromatic rings.

Full text of DOI:10.1021/ic049937h

Inorg. Chem. 2004, 43, 3461−3466
Rational Syntheses, Structure, and Properties of the First Bismuth(II)
Carboxylate
Evgeny V. Dikarev* and Bo Li
Department of Chemistry, UniVersity at Albany, Albany, New York 12222
Received January 14, 2004
Bismuth(II) trifluoroacetate (1), the first inorganic salt of bismuth in oxidation state +2, has been obtained in its
pure, unstabilized form. Several synthetic routes suggested for the isolation of the new compound include (i) mild
I
II
oxidation of elemental bismuth with some metal trifluoroacetates, e.g., Ag and Hg ; (ii) mild reduction of bismuth-
(III) trifluoroacetate with metals, such as Zn; (iii) comproportionation reaction between Bi and Bi(O CCF ) . The last
2
3 3
approach gives the title compound 1 in quantitative yield as a sole product. Bismuth(II) trifluoroacetate has been
characterized by NMR, IR, and UV−vis spectroscopy as well as by single-crystal X-ray diffraction. Crystallographic
study reveals the dinuclear paddle-wheel structure for diamagnetic molecules Bi2(O CCF ) . The Bi−Bi bond distances
2
3 4
in dimetal units of 1 are averaged to 2.9462(3) Å, and there are no axial intermolecular contacts between these
units in the solid state. The compound is volatile and exists in vapor phase up to 220 °C when it disproportionates
back to Bi0 and BiIII species, i.e., by the reverse of the synthetic route iii. In contrast, the solution chemistry is quite
limited: the bismuth(II) trifluoroacetate is decomposed by the majority of common solvents, but it can be stabilized
by aromatic systems. The dibismuth unit has been shown to be preserved in the latter solvents and can be crystallized
out in a form of π-adducts with arenes. Two such adducts, Bi2(O CCF ) ‚(C H Me) (2) and Bi2(O CCF ) ‚(1,4-
2
3 4
6
5
2
3 4
C H Me2)2 (3), have been isolated as single crystals and characterized by X-ray diffraction techniques. In the
6
4
structures of both 2 and 3, the bismuth(II) centers exhibit weak η6-coordination to aromatic rings.
Chart 1
Introduction
Low-valent dibismuth organometallic compounds (Chart
1, A and B) can be synthesized in solution by reduction of
Bi(III) species with alkali metals,1 lithium alumohydride,2
or cobaltocene.3 On the other hand, binary inorganic
compounds with homonuclear Bi-Bi bonds can be obtained
in the solid state by reduction of bismuth(III) salts with
metallic bismuth. The latter technique has been successfully
applied for the isolation of various bismuth subhalides BimXn
* Corresponding author. Tel: (518) 442-4401. Fax: (518) 442-3462.
E-mail: dikarev@albany.edu.
(1) (a) Ashe, A. J., III; Kampf, J. W.; Puranik, D. B.; Al-Taweel, S. M.
Organometallics 1992, 11, 2743-2745. (b) Twamley, B.; Sofield, C.
D.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1999, 121,
3357-3367. (c) Calderazzo, F.; Morvillo, A.; Pelizzi, G.; Poli, R. J.
Chem. Soc., Chem. Commun. 1983, 507-508. (d) Calderazzo, F.; Poli,
R.; Pelizzi, G. J. Chem. Soc., Dalton Trans. 1984, 2365-2369. (e)
Wieber, M.; Rudolph, K. Z. Naturforsch. 1988, B43, 739-743. (f)
Wieber, M.; Sauer, I. Z. Z. Naturforsch. 1987, B42, 695-698. (g)
Ashe, A. J., III; Kausch, C. M.; Eisenstein, O. Organometallics 1987,
6, 1185-1188.
(2) Balazs, G.; Breunig, H. J.; Lork, E. Organometallics 2002, 21, 2584-
2586.
(m:n ) 6:7, X ) Cl,4 Br;5 4:4 (C), X ) Br,5 I;6 14:4,7 18:4,8
X ) I). We attempted to extend this synthetic approach for
(3) Calderazzo, F.; Morvillo, A.; Pelizzi, G.; Poli, R.; Ungari, F. Inorg.
Chem. 1988, 27, 3730-3733.
10.1021/ic049937h CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/28/2004
Inorganic Chemistry, Vol. 43, No. 11, 2004 3461

Dikarev and Li
1668s, 1645s, 1435m, 1187s, 1153s, 846m, 792m, 726s, 522m. IR
(CHCl3, cm-1): 1660s, 1644s, 1443m, 1190s, 1156s, 849w, 793w,
726m. The cyclic voltammogram of 1 in CH2Cl2 exhibits a series
of irreversible redox couples at E1/2 ) +0.41, +1.15, -0.61, and
-0.86 V. +ESI-MS (CHCl3, m/z) 757 ([Bi2(O2CCF3)3]+).
Reaction of Bi(O2CCF3)3 with Zn. A mixture of bismuth(III)
trifluoroacetate (0.055 g, 0.10 mmol) and activated zinc (0.020 g,
0.31 mmol) was evacuated and sealed in a glass ampule. A few
orange crystals of 1 could be seen in the cold zone after the ampule
was heated at 105 °C for 2 days.
Reaction of Bi with Ag(O2CCF3). Bismuth powder (0.021 g,
0.10 mmol) and silver(I) trifluoroacetate (0.044 g, 0.20 mmol) were
sealed in an evacuated Pyrex ampule and placed in a furnace at a
temperature of 110 °C in the reaction zone. Crystals of 1 were
formed in the cold and middle sections of the container. The yield
after 4 days was ca. 40%. A silver mirror was also observed in the
ampule.
Reaction of Bi with Hg(O2CCF3)2. A mixture of metallic
bismuth (0.042 g, 0.20 mmol) and mercury(II) trifluoroacetate
(0.085 g, 0.20 mmol) was sealed under vacuum in a glass ampule.
The reaction conditions were as those in the previous procedure
with Ag(O2CCF3). Orange crystals of 1 appeared in the cold zone
of the tube along with drops of metallic mercury. The yield was
about 70% (collected) after 4 days.
Crystal Growth. Crystals of the toluene adduct (2) were obtained
by dissolving compound 1 (5 mg) in neat toluene (1 mL). A sealed
NMR tube with yellow solution was placed in the freezer at -50
°C. Orange crystals of 2 accumulated at the bottom of the tube
after 3 days. When open in air the crystals tend to lose solvent
followed by their decomposition. Orange crystals of p-xylene adduct
(3) were grown by a similar approach in the refrigerator at a
temperature of ca. 10 °C.
X-ray Crystallographic Procedures. A single crystal of 1
selected from the solid state reaction of Bi(O2CCF3)3 with Bi was
used for structural determination. Crystals of 2 and 3 were obtained
as described above. The X-ray intensity data were measured for 1
at 90(2) and 173(2) K and for 2 and 3 at 173(2) K (Bruker KRYO-
FLEX) on a Bruker SMART APEX CCD-based X-ray diffracto-
meter system equipped with a Mo-target X-ray tube (λ ) 0.71073
Å) operated at 1800 W power. The crystals were mounted on a
goniometer head with silicone grease. The detector was placed at
a distance of 6.140 cm from the crystal. For each experiment a
total of 1850 frames were collected with a scan width of 0.3° in ω
and an exposure time of 20 s/frame. The frames were integrated
with the Bruker SAINT software package using a narrow-frame
integration algorithm to a maximum 2θ angle of 56.54° (0.75 Å
resolution). The final cell constants are based upon the refinement
of the XYZ-centroids of several thousand reflections above 20σ(I).
Analysis of the data showed negligible decay during data collection.
Data were corrected for absorption effects using the empirical
method (SADABS).
The structures were solved and refined by full-matrix least-
squares procedures on |F2| using the Bruker SHELXTL (version
6.12) software package. The coordinates of bismuth atoms for the
structures were found in direct method E maps. The remaining
atoms were located after an alternative series of least-squares cycles
and difference Fourier maps. Aromatic hydrogen atoms in 3 were
located and refined independently. All other hydrogen atoms were
included in idealized positions for structure factor calculations. In
the structure of 2 the methyl group of toluene was found to be
disordered in two opposite directions. The fluorine atoms of most
of the CF3 groups in experiments at 173 K appeared to be disordered
over three rotational orientations. No disorder of trifluoromethyl
the preparation of other classes of low-valent bismuth
compounds, in particular for carboxylates. Reduced bismuth
carboxylates were unknown until recently,9 when Frank et
al. demonstrated that bismuth(II) trifluoroacetate exists, at
least in the vapor phase, and may be stabilized in the form
of a one-dimensional coordination copolymer with hexa-
methylbenzene (D). Here we report for the first time several
synthetic approaches to bismuth(II) trifluoroacetate (1) in
pure, unstabilized form. The title compound has been
obtained in the solid state in quantitative yield and fully
characterized by NMR, UV-vis, and IR spectroscopy as well
as by single-crystal X-ray diffraction.
Experimental Section
General Data. All of the manipulations were carried out in a
dry, oxygen-free, dinitrogen or argon atmosphere by employing
standard ampule and Schlenk techniques. Bismuth powder
(99.99+%), zinc powder, bismuth(III) oxide, mercury(II) trifluo-
roacetate, and silver(I) trifluoroacetate were purchased from Aldrich
and used as received. Bismuth(III) trifluoroacetate was prepared
in 82% yield according to the literature procedure10 and dried under
vacuum for 24 h at room temperature and then for 48 h at 70 °C.
UV-vis spectra were acquired using a Hewlett-Packard 8452A
diode array spectrophotometer. IR spectra were recorded on a
Nicolet Magna 550 FTIR spectrometer using KBr pellets and on a
Perkin-Elmer spectrum RX I FT-IR system in chloroform solution.
NMR spectra were obtained using a Varian Gemini 300 spectrom-
eter at 282.2 MHz for 19F and 75.4 MHz for 13C. Chemical shifts
are reported in ppm relative to TMS for 13C and CFCl3 for 19F. All
13C and 19F NMR spectra were acquired in the proton-decoupled
mode. X-band ESR measurements were recorded both on solid
samples and in toluene solution at room temperature with a
frequency of 9.4 GHz on an IBM-200D-SRC ESR spectrometer.
Cyclic voltammograms were performed with a computer controlled
CHI-620A (CH Instruments) in nitrogen-saturated CH2Cl2 solutions
with tetrabutylammonium hexafluorophosphate (TBAH, 0.1 mol)
as a supporting electrolyte.
Syntheses. Reaction of Bi(O2CCF3)3 with Bi. A stoichiometric
mixture of finely divided bismuth (0.021 g, 0.10 mmol) and
bismuth(III) trifluoroacetate (0.109 g, 0.20 mmol) was sealed in
an evacuated glass ampule. The container was then placed in an
electric furnace having a temperature gradient along the length of
the tube. The ampule was kept at 110 °C for 2 days to allow orange
(red when heated) crystals of 1 to be quantitatively deposited in
the coldest end of the tube where the temperature was set ca. 6-7
°C lower. UV-vis (C7H8, 22 °C) λmax, nm (ꢀ, M-1‚cm-1): 282
(sh, 970), 296 (1893), 422 (br., 657). UV-vis (CHCl3, 22 °C) λmax
,
nm (ꢀ, M-1‚cm-1): 246 (2234), 270 (2471), 350 (sh, 526), 388
(1086). 19F NMR (C7D8, 22 °C): δ -74.73 (s, CF3), (CD2Cl2, 22
°C): δ -73.24 (s, CF3). 13C NMR (C7D8, 22 °C): δ 113.1 (q, JCF
) 284.9 Hz, CF3), 175.4 (q, JCF ) 40.3 Hz, OCO). IR (KBr, cm-1):
(4) Friedman, R. M.; Corbett, J. D. Inorg. Chim. Acta 1973, 7, 525-527.
(5) Von Benda, H.; Simon, A.; Bauhofer, W. Z. Anorg. Allg. Chem. 1978,
438, 53-67.
(6) Von Schnering, H. G.; Von Benda, H.; Kalveram, C. Z. Anorg. Allg.
Chem. 1978, 438, 37-52.
(7) Dikarev, E. V.; Popovkin, B. A.; Shevelkov, A. V. Z. Anorg. Allg.
Chem. 1992, 612, 118-122.
(8) Dikarev, E. V.; Popovkin, B. A. Dokl. Phys. Chem. 1990, 310, 4-6.
(9) Frank, W.; Reiland, V.; Reiss, G. J. Angew. Chem., Int. Ed. 1998, 37,
2984-2985.
(10) Reiss, G. J.; Frank, W.; Schneider, J. Main Group Met. Chem. 1995,
18, 287-294.
3462 Inorganic Chemistry, Vol. 43, No. 11, 2004

The First Bismuth(II) Carboxylate
Table 1. Crystallographic Data for Bi2(O2CCF3)4 (1),
[Bi2(O2CCF3)4‚(C6H5Me)]∞ (2), and Bi2(O2CCF3)4‚(1,4-C6H4Me2)2 (3)
We have also attempted the reduction of Bi(O2CCF3)3 by
metallic bismuth in refluxing toluene solution, but did not
observe any color change indicative of a reaction even after
several days. Activated zinc can be used instead of metallic
bismuth to provide the reductive power for bismuth(III)
trifluoroacetate in the solid state. However, the yield of 1
was far from quantitative in this case. In addition, there was
a problem of separation of the product from zinc trifluoro-
acetate. As an alternative approach, we have demonstrated
that metallic bismuth can be mildly oxidized to BiII by 2
equiv of silver(I) trifluoroacetate with 40% yield:
1
2
3
formula
fw
Bi2O8C8F12
870.04
Bi2O8C15F12H8
962.17
Bi2O8C24F12H20
1082.36
triclinic
P1h
9.0356(5)
9.6154(6)
9.9363(6)
78.1150(10)
821.42(8)
1
crystal system monoclinic
monoclinic
C2/c
space group
a (Å)
b (Å)
P21/n
8.1792(6)
14.8836(12)
21.7639(17)
98.4100(10)
2621.0(4)
6
11.8730(9)
14.4229(10)
13.7818(10)
90.4510(10)
2360.0(3)
4
c (Å)
â (deg)
V (Å3)
Z
F
calcd (g‚cm3)
3.307
20.276
2.708
15.027
2.188
10.806
µ (mm-1
)
Bi + 2Ag(O2CCF3) f Bi(O2CCF3)2 + 2Ag
(2)
radiation (λ, Å) Mo KR (0.71073) Mo KR (0.71073) Mo KR (0.71073)
transm factors 0.1065-0.2938
temp (K) 90(2)
0.1972-0.2657
173(2)
0.2211-0.6718
173(2)
3684/ 18/235
Similarly, an equimolar amount of mercury(II) trifluoro-
acetate can be used for the preparation of 1 from elemental
bismuth:
data/restraints/ 6141/ 0/406
params
2779/ 36/196
R1,a wR2b
I > 2σ(I)
0.0236, 0.0560
0.0286, 0.0575
0.0481, 0.0881
0.0549, 0.0903
1.232
0.0230, 0.0544
0.0258, 0.0554
1.045
all data
Bi + Hg(O2CCF3)2 f Bi(O2CCF3)2 + Hg
(3)
quality-of-fitc 1.042
2
2
2
a R1 ) ∑||Fo| - |Fc|/∑|Fo|. b wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
The yield of 1 in this reaction is relatively high; however,
the required separation from mercury makes this method less
advantageous than comproportionation process 1.
c Quality-of-fit ) [∑[w(Fo2 - Fc )2]/(Nobs - Nparams)]1/2, based on all data.
2
Bismuth(II) trifluoroacetate has been obtained previously9
only in a form of coordination copolymer with hexameth-
ylbenzene in low (ca. 20%) yield by an unclarified ther-
molysis of bismuth(III) trifluoroacetate in the presence of
arene. In that case, either the partial reduction of Bi(O2CCF3)3
by C6Me6 takes place or disproportionation of BiIII to BiII
and higher oxidation states of bismuth (BiIV and/or BiV)
occurs. In our attempts to clarify the mechanism of the above
reaction, the arene complex of 1 was always a minor product
(<10%). The major product was always an unreduced BiIII
trifluoroacetate coordination complex with hexamethylben-
zene. Some of our observations support the idea of at least
partial thermal disproportionation of Bi(O2CCF3)3. Thus,
when neat BiIII trifluoroacetate is heated at 110 °C in a sealed
vessel, a few orange blocks of 1 can be detected in the cold
section of the tube along with small colorless crystals.
Properties. Bismuth(II) trifluoroacetate is highly volatile
and starts to sublime at about 60 °C. It shows fair thermal
stability in a sealed ampule until it decomposes back to
bismuth(0) and BiIII trifluoroacetate around 220 °C. It is
worth noting that decomposition of 1 takes place in the vapor
phase and produces well-shaped rhombohedral crystals of
metallic bismuth in different parts of the ampule. In open
air, the crystals of 1 immediately turn red and rapidly
degrade, leaving a colorless liquid containing fine black
powder (metallic bismuth). Bismuth(II) trifluoroacetate is
groups was encountered in the structure of 1 at 90 K. Anisotropic
displacement parameters were assigned to all non-hydrogen atoms,
except the disordered fluorines. Relevant crystallographic data for
all compounds are summarized in Table 1. Selected bond lengths
and angles are given in Table 2.
Results and Discussion
Synthesis. In general, bismuth(II) trifluoroacetate (1) can
be obtained either by mild reduction of bismuth(III) trifluo-
roacetate or by mild oxidation of metallic bismuth with metal
trifluoroacetates. The title compound has been synthesized
in quantitative yield as the only product of the compropor-
tionation reaction:
Bi + 2Bi(O2CCF3)3 f 3 Bi(O2CCF3)2
(1)
The reaction was carried out in a sealed Pyrex ampule at
110 °C, and the product 1 was deposited in the cold zone of
the tube in the form of large prismatic orange crystals. The
completion of the reaction and mass transfer takes about 2
days, and the product may be collected in pure form, free of
any impurities. This process is very similar to the preparation
of crystalline bismuth subhalides5-8 BinX4 (X ) Br, n ) 4;
X ) I, n ) 4, 14, 18), but it requires lower temperatures
due to higher volatility of the trifluoroacetate compared to
the subhalides.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Bi2(O2CCF3)4 (1), [Bi2(O2CCF3)4‚(C6H5Me)]∞ (2), Bi2(O2CCF3)4‚(1,4-C6H4Me2)2 (3), and
[Bi2(O2CCF3)4‚(C6Me6)]∞ (4)
1
2
3
4c
Bi-Bi
Bi-O
2.9516(3),a 2.9407(3)b
2.378(4)-2.409(3)a
2.348(4)-2.432(4)b
2.9395(6)
2.375(7)-2.404(8)
2.9635(3)
2.380(3)-2.416(3)
2.9466(11)
2.387(6)-2.417(7)
Bi‚‚‚C
3.427(10)-3.537(9)
81.6(2)
88.9(3), 163.1(2)
3.307(5)-3.464(5)
81.35(8)
88.70(13), 162.64(11)
3.354(4)-3.358(3)
81.4(2)
88.8(3), 162.8(4)
Bi-Bi-Od
O-Bi-Od
81.47(8)
88.74(14), 163.12(12)
a For centrosymmetric molecule. b For noncentrosymmetric molecule. c From ref 9. d Averaged values.
Inorganic Chemistry, Vol. 43, No. 11, 2004 3463

Dikarev and Li
Figure 1. A perspective drawing of a centrosymmetric molecule in the
crystal structure of bismuth(II) trifluoroacetate (1). Atoms are represented
by thermal ellipsoids at the 40% probability level.
soluble in anhydrous, deoxygenated benzene, xylene, and
toluene and can be kept in the latter solvent for a long time,
especially at low temperatures. Traces of water obviously
initiate the disproportionation of 1, even in aromatic solvents,
which can be followed by UV-vis observations. Compound
1 is also soluble in dichloromethane and chloroform, but
cannot be preserved in these solvents for more than several
minutes. The color of the solutions gradually turns pale, and
traces of precipitating bismuth can be seen. The crystals of
1 are practically insoluble in hexanes and pyridine, while
they are immediately decomposed by a majority of common
solvents, such as THF, ether, acetone, alcohols, acetonitrile,
and water. It is so sensitive toward these solvents that even
handling the compound in dinitrogen or argon gloveboxes
requires the absence of any solvent vapors.
Figure 2. Packing diagram showing six discrete molecules of Bi2(O2-
CCF3)4 in the unit cell of the structure 1.
Chart 2
(Chart 2) due to axial coordination of the metal center to a
carboxylate oxygen of a neighboring unit (Table 3).
Structure. The structure of 1 consists of two crystallo-
graphically independent dimetal tetrabridged Bi2(O2CCF3)4
units located in the unit cell at an angle of 74° to each other.
Only one of these units resides on an inversion center.
Bismuth(II) trifluoroacetate in its pure form indeed maintains
a paddle-wheel structure (Figure 1) similar to the one that
has been observed9 in its coordination copolymer with
hexamethylbenzene. This behavior is in contrast to what we
have recently reported11 for mercury(II) trifluoroacetate that
reveals dimeric tetrabridged structure in the complex [Hg2(O2-
CCF3)4‚C6Me6]∞,12 but which exhibits a very complex layered
network built on monomeric Hg(O2CCF3)2 units in its
unligated form. The major structural feature of 1 is the total
absence of any kind of axial interactions between dibismuth
units (Figure 2). Each bismuth atom maintains a slightly
distorted square pyramidal coordination composed of one
Bi and four O atoms. The closest contacts to the open
coordination site on bismuth are fluorine atoms from
neighboring units at distances of longer than 3.3 Å. The
presence of discrete dibismuth units makes the bismuth(II)
trifluoroacetate structure unique among other dimetal(II)
tetra(trifluoroacetates) bearing no exogenous ligands. The
latter are known13-16 to maintain a 1D polymeric structure
There is a single bond between two bismuth atoms in 1
in accord with the fact that it is diamagnetic in the solid
state. The bismuth-bismuth distances are 2.9516(3) Å and
2.9407(3) Å for centrosymmetric and noncentrosymmetric
units, respectively. The Bi-Bi bond has almost the same
length as that in the bismuth(II) trifluoroacetate complexes
with hexamethylbenzene,9 toluene, and xylene (Table 4). The
shortening effect of bridging ligands can be clearly seen when
we compare the Bi-Bi bond in 1 with those in nonbridged
dibismuth organometallic compounds Bi2R4 (2.983-3.053
Å, Table 4) and in metallic bismuth.17 On the other hand,
the Bi-Bi bonding in 1 is longer than a double BidBi bond
found in BiI organometallic compounds Bi2R2 with bulky
2-
R-substituents, as well as in the “naked” Bi2 anion.18
Bismuth(II) trifluoroacetate does not exhibit any phase
transition during cooling down to -183 °C. The crystals of
(13) Cotton, F. A.; Norman, J. G., Jr. J. Coord. Chem. 1972, 1, 161-71.
(14) Dikarev, E. V. Manuscript is in preparation.
(15) Cotton, F. A.; Dikarev, E. V.; Feng, X. Inorg. Chim. Acta 1995, 237,
19-26.
(16) (a)Karpova, E. V.; Boltalin, A. I.; Korenev, Yu. M.; Troyanov, S. I.
Russ. J. Coord. Chem. 2000, 26, 361-366. (b) Cotton, F. A.; Dikarev,
E. V.; Petrukhina, M. A. Inorg. Chem. 2000, 39, 6072-6079.
(17) Cucka, P.; Barrett, C. S. Acta Crystallogr. 1962, 15, 865-872.
(18) (a) Tokitoh, N.; Arai, Y.; Okazaki, R.; Nagase, S. Science 1997, 277,
78-80. (b) Sasamori, T.; Arai, Y.; Takeda, N.; Okazaki, R.; Furukawa,
Y.; Kimura, M.; Nagase, S.; Tokitoh, N. Bull. Chem. Soc. Jpn. 2002,
75, 661-675. (c) Xu, L.; Bobev, S.; El-Bahraoui, J.; Sevov, S. C. J.
Am. Chem. Soc. 2002, 122, 1838-1839.
(11) Dikarev, E. V.; Li, B. Abstracts of Papers, 226th National Meeting
of the American Chemical Society, New York, NY; American
Chemical Society: Washington, DC, 2003; INOR-190.
(12) Lau, W.; Huffman, J. C.; Kochi, J. K. J. Am. Chem. Soc. 1982, 104,
5515-5517.
3464 Inorganic Chemistry, Vol. 43, No. 11, 2004

The First Bismuth(II) Carboxylate
Table 3. Characteristic Structural Parameters for Dimetal(II) Tetra(trifluoroacetates)
metal
M-M (Å)
bond
single
quadruple
double
single
M-O (Å)
2.386(4)
2.057(8)
2.066(3)
2.047(3)
1.922(6), 2.419(5)
M-M-O (deg)
M‚‚‚O (Å)
M-M‚‚‚O (deg)
ref
Bi
2.9462(3)
2.090(4)
2.2645(6)
2.3813(8)
3.086(2)
81.47(8)
92.1(2)
89.63(9)
88.2(1)
this work
Mo
Ru
Rh
Cua
2.72(1)
161.0(2)
167.49(8)
169.3(1)
143.8(2)
13
14
15
16
2.375(3)
2.337(4)
2.054(5)
none
67.4(1)-92.0(2)
a Cu2(O2CCF3)4 maintains a different structure with intermolecular Cu-O interactions being short and one of the intramolecular Cu-O contacts being
long.
Table 4. The Bi-Bi Bond Lengths in Dibismuth Complexes
complex
Bi-Bi (Å)
ref
Bi2(O2CCF3)4
2.9407(3), 2.9516(3)
2.9395(6)
2.947(1)
2.9635(3)
2.983(1)
this work
this work
9
this work
19a
Bi2(O2CCF3)4‚C6H5Me
Bi2(O2CCF3)4‚C6Me6
Bi2(O2CCF3)4‚(1,4-C6H4Me2)2
[Bi2Et4][AlBut3]2
[Bi2Et4][GaBut3]2
2.984(1)
19a
Bi2Ph4
2.984(2), 2.988(1),
2.990(2)
2.990(2)
3.035(3)
3.053(1)
3.045(3)
3.072
2.8327(14)
2.8206(8)
2.8699(6)
2.8377(7)
1c,d, 19c
Figure 3. A fragment showing the alternating arrangement of Bi2(O2-
CCF3)4 and toluene molecules in the chain structure of monoadduct 2. Only
one orientation of the disordered CF3 and CH3 groups is depicted.
Bi2(2,2′,5,5′-tetramethyldibismole)
Bi2(SiMe3)4
Bi2[CH(SiMe3)2]4
Bi2[Ge(C6F5)2]4
R-Bi (metal)
Bi2(2,6-Mes2H3C6)2
1a
19b
2
19d
17
1b
18a
18b
18c
a
Bi2Tbt2
b
Bi2Bbt2
2-
Bi2
a Tbt ) 2,4,6-[(Me3Si)2CH]3C6H2. b Bbt ) 2,6-[(Me3Si)2CH]2-4-[(Me3-
Si)3C]C6H2.
1 show relatively high thermal compressibility: 1.9 vol %
on going from -100 to -183 °C. That behavior is similar
to that of some other metal trifluoroacetates; e.g., ruthenium-
(II) trifluoroacetate shrinks 1.9% in the same temperature
range. Such “shrinkage” might be attributed to the changes
in orientational disorder of carboxylate CF3 groups. While
trifluoromethyl groups are severely disordered at higher
temperatures, this disorder essentially disappears at lower
temperatures, allowing the dimetal units to come closer to
each other.
Compound 1 was found to be diamagnetic, and no ESR
signals were observed at room temperature in toluene
solution, thus suggesting no tendency for Bi-Bi bond
cleavage under these conditions. Bismuth(II) trifluoroacetate
can be crystallized from toluene solution in a form of 1:1
coordination copolymer (2). The structure consists of infinite
chains [Bi2(O2CCF3)4‚(C6H5Me)]∞ (Figure 3) running in two
almost perpendicular directions within the unit cell. The
coordination of bismuth to aromatic rings in 2 can be
described as η6 (Table 2) with the distance from metal to
the center of the ring being 3.23 Å. The aromatic planes,
however, are not perpendicular to the Bi-Bi vector, with
the angle between the latter and the normal to the plane being
18.5°.
Figure 4. A perspective drawing of the Bi2(O2CCF3)4 bis-adduct with
p-xylene (3). Fluorine and hydrogen atoms are shown as spheres of arbitrary
radii. Only bismuth atoms are labeled for clarity.
From solution of 1 in neat p-xylene, yet a different type
of adduct, Bi2(O2CCF3)4‚(1,4-C6H4Me2)2 (3), has been crys-
tallized. Bis-adduct 3 exhibits a discrete structure (Figure
4) with the dibismuth unit flanked by two arene molecules
at axial positions. The η6-coordination of an arene molecule
to only one bismuth atom in 3 is slightly tighter, but
otherwise very similar to that in 2 with the 3.10 Å Bi-to-
ring center distance and 15.8° deviation from perpendicular-
ity. The length of the Bi-Bi bond and other dimensions of
the dimetal unit in the adducts 2 and 3 vary slightly compared
to the characteristics of pure bismuth(II) trifluoroacetate (1).
That implies that interaction of the bismuth atom with the
aromatic system in arenes is relatively weak and does not
disturb the dimetal unit. It is worth noting that hexameth-
ylbenzene tremendously enhances the stability of 1, so that
the crystals of the adduct are stable in open air for days. At
the same time, the crystals of adducts with toluene (2) and
p-xylene (3) are still vulnerable when exposed to open
atmosphere, but to a lesser degree than pure trifluoroacetate.
Conclusions. New bismuth(II) trifluoroacetate is the first
“inorganic” salt of bismuth in oxidation state +2 that has
been obtained in pure form with quantitative yield. The fact
that this compound remains intact in aromatic solvents and
in the vapor phase makes it attractive to study its chemistry
(19) (a) Kuczkowski, A.; Schulz, S.; Nieger, M. Angew. Chem., Int. Ed.
2001, 40, 4222-4225. (b) Mundt, O.; Becker, G.; Roessler, M.;
Witthauer, C. Z. Anorg. Allg. Chem. 1983, 506, 42-58. (c) Whitmire,
K. H.; Cassidy, J. M. Acta Crystallogr. 1992, C48, 917-919. (d)
Pankratov, L. V.; Zakharov, L. N.; Bochkova, R. I.; Fukin, G. K.;
Struchkov, Yu. T. Russ. Chem. Bull. 1994, 43, 867-870. (e) Silvestru,
C.; Breunig, H. J.; Althaus, H. Chem. ReV. 1999, 99, 3277-3327.
Inorganic Chemistry, Vol. 43, No. 11, 2004 3465

Dikarev and Li
using both solution and solid state approaches. Our prelimi-
nary results indicate an intriguing reactivity of 1 toward
various transition metal complexes and electron-deficient
molecules, as well as some organic substrates. We shall
report these new findings shortly.
Science Foundation for funding the CCD diffractometer
(CHE-0130985) at the University at Albany.
Supporting Information Available: Four X-ray crystallo-
graphic files, in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to the University at
Albany for support of this work. We thank the National
IC049937H
3466 Inorganic Chemistry, Vol. 43, No. 11, 2004