Novel carbonyl iron-bismuth clusters - Synthesis, structure, CO2 insertion and potential as molecular precursors for BiFeO3

Article abstract of DOI:10.1016/j.jorganchem.2011.01.028

The reaction of Fe₂(CO)₉ with Bi(OSiMe ₂^tBu)₃ gave soluble [(CO) ₄FeBi(OSiMe₂^tBu)]₂ (1) in moderate yield whereas in case of Bi(O^tBu)₃ used as starting material both [(CO)₄FeBi(O^tBu)]_n (2) and the bismuth-iron cluster [(CO)₃FeBi₃(O^tBu) ₄{OCO(O^tBu)}]₂ (3) were isolated. The latter forms upon insertion of CO₂, released during reaction of diiron nonacarbonyl with bismuth tert-butoxide, into a Bi-O^tBu bond. The compounds were characterized by IR and ¹H NMR spectroscopy as well as thermogravimetric analyses. Additionally, the molecular structures of compounds 1 and 3 were elucidated by single crystal X-ray diffraction. The core structure of [(CO)₄FeBi(OSiMe₂^tBu)]₂ (1) is build up by a four-membered Bi₂Fe₂ ring whereas [(CO) ₃FeBi₃(O^tBu)₄{OCO(O ^tBu)}]₂ (3) is composed of two tetrahedral FeBi ₃ cluster cores that dimerise via bridging -OCO(O^tBu) ligands. Analysis of the TGA residues by PXRD revealed that compound 2 is the best precursor for multiferroic BiFeO₃ among the compounds studied here, although Bi₂₅FeO₃₉ was detected as minor impurity.

Full text of DOI:10.1016/j.jorganchem.2011.01.028

Journal of Organometallic Chemistry 696 (2011) 1647e1651
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Novel carbonyl ironebismuth clusters e synthesis, structure, CO2 insertion and
potential as molecular precursors for BiFeO3
,
Katarzyna Wójcik a, Tobias Rüffer a, Heinrich Lang a, Alexander A. Auer b, Michael Mehring a
*
a Institut für Chemie, Technische Universität Chemnitz, Straße der Nationen 62, D-09111 Chemnitz, Germany
b Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, D-40237 Düsseldorf, Germany
a r t i c l e i n f o
a b s t r a c t
The reaction of Fe2(CO)9 with Bi(OSiMet2Bu)3 gave soluble [(CO)4FeBi(OSiMe2t Bu)]2 (1) in moderate yield
whereas in case of Bi(OtBu)3 used as starting material both [(CO)4FeBi(OtBu)]n (2) and the bismutheiron
cluster [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3) were isolated. The latter forms upon insertion of CO2,
released during reaction of diiron nonacarbonyl with bismuth tert-butoxide, into a BieOtBu bond. The
compounds were characterized by IR and 1H NMR spectroscopy as well as thermogravimetric analyses.
Additionally, the molecular structures of compounds 1 and 3 were elucidated by single crystal X-ray
diffraction. The core structure of [(CO)4FeBi(OSiMet2Bu)]2 (1) is build up by a four-membered Bi2Fe2 ring
whereas [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3) is composed of two tetrahedral FeBi3 cluster cores that
dimerise via bridging eOCO(OtBu) ligands. Analysis of the TGA residues by PXRD revealed that
compound 2 is the best precursor for multiferroic BiFeO3 among the compounds studied here, although
Bi25FeO39 was detected as minor impurity.
Article history:
Received 29 October 2010
Received in revised form
23 January 2011
Accepted 25 January 2011
Keywords:
Bismuth alkoxide
Iron carbonyl
Bismuth cluster
BiFeO3
CO2 insertion
Ó 2011 Published by Elsevier B.V.
1. Introduction
C5Ht3Bu2) were also investigated [16]. Quite a large number of
compounds with transition metalebismuth bonds is known to date
Currently, there is great interest in multiferroic perovskite-type
BiFeO3 (BFO), which offers great potential for ferroelectric, piezo-
electric, magnetoelectric and spintronics applications [1,2].
Although BFO has been in the focus of several research groups, the
synthesis of phase-pure BFO of uniform size and morphology is still
a challenge and applications of BFO materials are restricted so far
due to significant leakage current which has been attributed to the
presence of additional oxide phases and defects [2]. To overcome
these problems several approaches were focused on developing
novel synthetic procedures for BiFeO3 starting from a variety of
inorganic and organometallic compounds [3e6]. Our interest stems
from recent work on heterobimetallic bismuth alkoxides as
molecular single source precursors [7], whichdin combination
with irondhave not been studied so far. However, bismutheiron
carbonyl clusters are well known and a variety of complexes such as
Bi2Fe3(CO)9, [Bi{Fe(CO)4}4]3ꢀ, [BiFe3(CO)10]ꢀ, [BiFe3(CO)9(COMe)],
[17] and the first attempt to prepare the organobismutheiron
complex (CO)4FeBiPh3 by the reaction of Ph3Bi with Fe(CO)5 was
reported already in 1941.[18] However, several decades later it was
shown that the postulated compound (CO)4FeBiPh3 does not form
upon reaction of Ph3Bi with either Fe(CO)5 or Fe2(CO)9, but that
similar molecules such as (CO)4FeBiR3 (R ¼ Et, Pr, nBu, tBu)d
prepared starting from Fe2(CO)9 and triorganobismuthanesdare
accessible including single crystals for X-ray diffraction analysis in
case of (CO)4FeBitBu3 [19,20]. Breunig and coworkers also reported
several complexes that were obtained in the reaction of dibismu-
thanes or cyclobismuthanes with metal carbonyls [21]. For
example, the reaction of tetra(neopentyl)dibismuthane with
[Fe2(CO)9] in toluene gave [(CO)4Fe{Bi(CH2CMe3)2}2] which after
elimination of one molecule R3Bi was converted into dimeric
[(CO)4FeBiCH2CMe3]2. The analogue trimethyl silylmethyl bismuth
complex [(CO)4FeBiCH2SiMe3]2 was obtained in the reaction of
cyclo-(Me3SiCH2Bi)n (nd3, 5) with [Fe2(CO)9]. Noteworthy, in case
of R ¼ nBu a 1D chain of [(CO)4FeBiR]N was observed instead of
a cluster upon reaction of [Et4N]3[Bi{Fe(CO)4}4] with nBuBr [22].
However, similar Fe-containing compounds with alkoxides or
related ligands were not reported so far.
2ꢀ
and [Bi2Fe3(CO)9]2ꢀ have been
[Bi2Fe4(CO)13
]
2ꢀ, [Bi4Fe4(CO)13
]
reported previously [8e14]. Recently, an even larger anionic cluster
4ꢀ
[15], and
composed of twelve metal atoms, [Bi4Fe8(CO)28
]
formerly, compounds such as [{Fe3(CO)9{BiFe(CO)2Cp00}] (Cp00 ¼ h5
-
The aim of current research in our group is the synthesis of
heterobimetallic bismuth alkoxides with potential for the prepa-
ration of oxides such as BiFeO3. Thus, the reaction of Fe2(CO)9 with
* Corresponding author.
E-mail address: michael.mehring@chemie.tu-chemnitz.de (M. Mehring).
0022-328X/$ e see front matter Ó 2011 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2011.01.028

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K. Wójcik et al. / Journal of Organometallic Chemistry 696 (2011) 1647e1651
Bi(OtBu)3 and with Bi(OSiMe2t Bu)3 was investigated. The synthesis,
structures and properties of the products [(CO)4FeBi(OSiMet2Bu)]2
(1), [(CO)4FeBi(OtBu)]n (2) and [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3)
are discussed here.
Table 1
Crystallographic data collection and refinement for compounds 1 and 3.
Compound
[(CO)4FeBi(OSiMet2Bu)]2
(1)
[(CO)3FeBi3(OtBu)4
(OCO(OtBu)]2 (3)
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
a (Å)
C
20H30Bi2Fe2O10Si2
C24H45Bi3FeO10
1176.39
105 K
1.54184 Å
Triclinic
Pꢀ1
1016.28
105 K
1.54184 Å
Triclinic
Pꢀ1
2. Results and discussion
2.1. Reaction of Fe2(CO)9 with Bi(OSiMet2Bu)3
The reaction of Bi(OSiMe2t Bu)3 with diiron nonacarbonyl was
carried out at room temperature in n-pentane. The colour of the
reaction mixture changed after 1 h from orange-gold to brown.
After 16 h the solvent together with volatile Fe(CO)5 was removed
in vacuo and the oily residue was redissolved in n-pentane. Crys-
tallization from n-pentane at ꢀ20 ꢁC resulted in red needles of
[(CO)4FeBi(OSiMet2Bu)]2 (1) suitable for single crystal X-ray
diffraction analysis. Further crystallization gave a small fraction of
crystalline Fe3(CO)12 [23]. The bismuth compound [(CO)4FeBi(OSi-
Met2Bu)]2 (1) is soluble in polar and non-polar solvents. Elemental
analysis of compound 1 is in good agreement with calculated
values, the IR spectrum shows, as expected, two strong absorption
bands in the carbonyl region at 2052 and 1981 cmꢀ1 and in the 1H
6.9148 (3)
15.6242 (10)
15.9589 (9)
66.221 (6)
86.664 (4)
87.923 (4)
574.97 (15)
2
10.6591 (5)
11.8086 (6)
15.1464 (7)
101.810 (4)
94.931 (4)
93.187 (4)
1853.96 (15)
2
b (Å)
c (Å)
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Z
Density (calculated)
2.143 Mg/m3
2.107 Mg/m3
30.867 mmꢀ1
1088
0.3 ꢂ 0.15 ꢂ 0.1 mm
4.17e61.98ꢁ
11,679
Absorption coefficient 29.892 mmꢀ1
F(000)
Crystal size
Theta range
Reflections collected
Independent reflections 4788
952
0.4 ꢂ 0.1 ꢂ 0.03 mm
3.09e61.91ꢁ
11,620
5727
[R(int) ¼ 0.0339]
[R(int) ¼ 0.0385]
NMR spectrum a singlet at
d
0.92 assigned to the C(CH3)3 group and
Max. and min.
Transmission
Data/param/restr
Goof on F2
1.00000 and 0.22692
4788/124/325
1.004
1.00000 and 0.18342
5731/48/343
1.041
R1 ¼ 0.0400,
wR2 ¼ 0.1066
R1 ¼ 0.0416,
wR2 ¼ 0.1031
a singlet at 0.10 assigned to Si(CH3)2 are observed. For compounds
d
of the general type [(CO)4FeBiR]2 (e.g. R ¼ Me, Et, PhCH2, i-Pr, nBu)
[24,25] it was shown that after dissolution of crystals composed of
trans-isomers a second series of signals occurred in the 1H NMR
spectrum suggesting cisetrans isomerisation in solution. However,
for compound 1 exclusively broadening of the 1H NMR signals at
low temperature instead of a second series of signals was observed.
Crystals of 1 are sensitive to air and moisture and decompose
slowly in solution to give Fe3(CO)12 [23] and Bi2Fe3(CO)9 [12] as was
confirmed by single crystal X-ray diffraction analysis. Similarly, it
was observed previously that [(CO)4FeBiCH2CMe3]2 [21] and
[(CO)4FeBiMe]2 [24] decompose to give Bi2Fe3(CO)9. The compound
[(CO)4FeBi(OSiMet2Bu)]2 (1) crystallizes in the space group Pꢀ1
with two formula units. Crystal data and structure refinement
details are summarized in Table 1 and the molecular structure is
shown in Fig. 1. The unit cell of 1 contains two crystallographically
independent but similar centrosymmetric dimers 1a and 1b. As
expected these two molecules do not show significant differences
of related bond lengths and only minor differences of up to 3% for
related bond angles. Therefore, only compound 1a is discussed
here. The molecular structure of 1a is composed of a Fe2Bi2 paral-
lelogram that lies on a crystallographic inversion centre. In the solid
state the OSiMet2Bu groups are oriented trans to each other with
R1, wR2
R1 ¼ 0.0761,
wR2 ¼ 0.2151
R1 ¼ 0.0902,
wR2 ¼ 0.2274
R indices (all data)
Largest diff. hole
and peak
10.776[46] and ꢀ1.839 e Åꢀ3 3.088 and ꢀ2.143 e Åꢀ3
1949 cmꢀ1 typical for compounds of the type [(CO)4FeBiR]2
(R ¼ Me, Et; 2036 and 1981 cmꢀ1; R ¼ CH2CMe3, 2037, 1983 and
1958 cmꢀ1). From the recovered solution the n-pentane together
with volatile products was removed to give a brown precipitate.
respect to the Fe2Bi2 ring. The two Fe atoms are linked via m-BiO-
SiMet2Bu groups. The geometry at the bismuth atoms is best
described as pyramidal. The BieFe distances are 2.748 (3) Å and
2.765 (3) Å, and are comparable with BieFe distances in
compounds of the type [(CO)4FeBiR]2 (R ¼ alkyl) [21,24,26]. In the
Fe2Bi2 parallelogram the BieBi distance amounts to 3.6400 (12) Å
and is considered non-bonding. In the lattice no interactions
between the dimers are observed.
2.2. Reaction of Fe2(CO)9 with Bi(OtBu)3
Reaction of Fe2(CO)9 with Bi(OtBu)3 was carried out in n-
pentane at room temperature in a similar way as for Bi(OSiMet2Bu)3.
After 15 h n-pentane and volatile Fe(CO)5 were collected, the brown
residue was extracted with n-pentane and the suspension filtered.
A dark brown and moisture sensitive precipitate that is not soluble
in common organic solvents was obtained in 35% yield. On the basis
of IR data formation of [(CO)4FeBi(OtBu)]n (2) is suggested. The IR
spectrum shows characteristic absorptions bands at 2037, 1984 and
Fig. 1. Ortep diagram (50% probability level) of the molecular structure of [(CO)4FeBi
(OSiMet2Bu)]2 (1) and selected bond lengths (Å) and angles (ꢁ). H atoms are omitted for
0
clarity. Symmetry transformations used: ¼ ꢀx, ꢀy þ 1, ꢀz þ 1. Bi1eFe1 2.748 (3),
Bi10eFe1 2.765 (3), Bi10eBi1 3.6400 (12), O5eBi1 2.104 (13), O5eSi1 1.625 (13), C1eFe1
1.83 (2), C1eO11.13 (3), C2eFe11.788 (18), C2eO2 1.16 (2), C3eFe11.79 (2), C3eO3 1.15
(3), C4eFe1 1.83 (2), C4eO4 1.13 (2); O5eBi1eFe1 96.4 (4), O5eBi1eFe10 98.7 (4),
O5eBi1eBi10 101.5 (4), Fe1eBi1eFe10 97.36 (8), Fe1eBi1eBi10 48.89 (6), Fe10eBi1eBi10
48.47 (6).

K. Wójcik et al. / Journal of Organometallic Chemistry 696 (2011) 1647e1651
1649
Crystallization of this material at ꢀ20 ꢁC in n-pentane afforded red-
gold crystals of [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3) in yield 30%.
Compound 3 is poorly soluble in organic solvents, sensitive towards
air and moisture, respectively, and starts to decompose at
temperatures slightly above 30 ꢁC. The infrared spectrum of
compound 3 reveals two strong absorption bands in the carbonyl
region at 1995 and 1934 cmꢀ1 quite different from compound 2.
The single crystal X-ray diffraction analysis of 3 revealed an
unexpected result. Obviously, under the reaction conditions
employed starting from Bi(OtBu)3 and Fe2(CO)9, carbon dioxide is
formed and inserts into a BieOR bond to finally yield reproducibly
the organometallic bismuth carbonate [(CO)3FeBi3(OtBu)4{OCO
(OtBu)}]2 (3). Addition of CO2 to the flask prior to crystallization did
not enhance the yield. The formation of CO2 by reaction of an
alkoxide with iron pentacarbonyl was reported earlier and does
explain the reaction pathway to give compound 3 as reported here
[27]. Noteworthy, the first examples of CO2 fixation by organome-
tallic bismuth compounds to give carbonates were reported only
recently by Breunig et al. and Yin et al. [28,29]. Currently there is
some interest in bismuth-containing catalysts for cycloaddition of
CO2 to epoxides [30]. However, due to its low stability we were not
able to study the reversibility of CO2 fixation or the catalytic
properties of the heterobimetallic alkoxido cluster 3. The latter
crystallizes in the space group Pꢀ1 with two formula units. Bond
lengths and angles are presented together with the molecular
structure (Fig. 2), and information on data collection and refine-
ment data are given in Table 1. The single crystal X-ray structure
analysis reveals that [(CO)3FeBi3(OtBu)4{OCO(OtBu)}] (3) is
comprised of two dimers of tetranuclear bimetallic bismutheiron
clusters which are connected by two bidentate bridging eOCO
(OtBu) ligands. The monomers consist of three bismuth atoms
which form a Bi3-ring coordinated by three bridging OtBu groups
and connected with one terminal OtBu and one OCO(OtBu) ligand. A
Fe(CO)3 fragment is m3-coordinated to the Bi-ring. The BieBi
distances in the Bi3-ring are in the range from 3.385 Å to 3.470 Å
(Fig. 3). These distances are longer than typical BieBi bonds in
bismuth clusters (dBieBi 3.0e3.1 Å) [31], but comparable to BieBi
Fig. 3. Representation of the Bi3Fe unit in [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3).
bond lengths in the complexes [Ru2Bi17
[32], [NEt4]2[Bi4Fe4(CO)13
(dBieBi 3.47 Å) [14], [NnBu4]
(m
-Bi)4]5þ(dBieBi 3.42 Å)
]
[Bi4Fe8(CO)28] (dBieBi 3.41 Å) [15], and in the Zintl ion Bi35þ (dBieBi
3.31 Å) [33]. In the literature only a few examples based on Bi3-rings
such as the heteroatomic Zintl clusters [InBi3]2ꢀ and [GeBi3]2ꢀ were
reported. [34] The six MeM distances in these tetrahedral clusters
are in range from 2.99 Å to 3.04 Å and thus are significantly shorter
than in the Bi3Fe unit of compound 3. In conclusion, residual BieBi
bonding is expected to occur in the cluster 3 based on the literature
survey of BieBi bond lengths.
In order to verify that the bismuth atoms in compound 3 are in
a partially reduced oxidation state, quantum chemical calculations
have been carried out. For this purpose a model compound 3a has
been used in which all methyl groups of compound 3 have been
replaced by hydrogen atoms followed by optimization of the
hydrogen atoms positions at the B3-LYP/TZVP level of theory
[35e37]. The positions of all other atoms were taken from the X-ray
structure analysis and were fixed during the optimization. The
Fig. 2. Ortep diagram (50% probability level) of the molecular structure of [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3) and selected bond lengths (Å) and angles (ꢁ). H atoms are omitted for
clarity. Symmetry transformations used: 0 ¼ x þ 2, ꢀy, ꢀz. Bi1eBi2 3.4553 (5), Bi1-Bi3 3.3852 (5), Bi2eBi3 3.4699 (5), Bi1eFe1 2.6093 (13), Bi2eFe1 2.6208 (14), Bi3eFe1 2.6503 (13),
Bi1eO4 2.178 (6), Bi1eO5 2.262 (6), Bi1eO90 2.648 (7), Bi2eO4 2.518 (6), Bi2eO6 2.183 (6), Bi2eO8 2.427 (6), Bi3eO5 2.389 (7), Bi3eO6 2.517 (7), Bi3eO7 2.122 (7), C1eFe1 1.803
(10), C1eO1 1.144 (12), C2eFe1 1.782 (9), C2eO2 1.169 (11), C3eFe1 1.805 (11), C3eO3 1.136 (13), Bi1eBi2eBi3 58.526 (10), Bi1eBi3eBi2 60.521 (10), Bi3eBi1eBi2 60.953 (10),
Fe1eBi1eBi2 48.79 (3), Fe1eBi1eBi3 50.47 (3), Fe1eBi2eBi1 48.51 (3), Fe1eBi2eBi3 49.20 (3), Fe1eBi3eBi1 49.41 (3), Fe1eBi3eBi2 48.46 (3), Bi1eFe1eBi2 82.67 (4), Bi2eFe1eBi3
82.34 (4), Bi1eFe1eBi3 80.12 (4).

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K. Wójcik et al. / Journal of Organometallic Chemistry 696 (2011) 1647e1651
3. Conclusion
We have studied the reaction on Fe2(CO)9 with Bi(OSiMet2Bu)3
and Bi(OtBu)3, respectively, with the aim to prepare molecular
precursors for the synthesis of multiferroic BiFeO3. The reaction
starting from Bi(OSiMet2Bu)3 (1) gave the novel heterobimetallic
cluster [(CO)4FeBi(OSiMet2Bu)]2 (1) which shows an iron to bismuth
ratio that perfectly matches the ratio required for BiFeO3. However,
pyrolysis studies showed that a mixture of different ironebismuth
oxides and bismuth silicates was formed. Upon reaction of Fe2(CO)9
with Bi(OtBu)3 followed by crystallization from n-pentane the novel
bismutheiron cluster [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3) was
isolated. This is an interesting example that demonstrates the
capability of bismuth compounds to insert CO2, but which is not
suitable as precursor for BiFeO3. The most promising precursor,
[(CO)4FeBi(OtBu)]n (2), was also obtained from the reaction of
Fe2(CO)9 with Bi(OtBu)3 as a compound of low solubility and
stability. Pyrolysis studies show that BiFeO3 is obtained as major
crystalline phase with only a minor impurity of Bi25FeO39. This
observation demonstrates that in contrast to silanolates hetero-
bimetallic bismuth alkoxides such as [(CO)4FeBi(OtBu)]n (2) hold
potential as molecular precursors for BiFeO3. However, other
alkoxide ligands have to be introduced to increase solubility and/or
stability which is required for materials processing via solution or
gas phase.
Fig. 4. XRPD of the residue after decomposition of [(CO)4FeBiOtBu]n (2) under inert
atmosphere.
results of the NBO analysis [38,39] based on the resulting geometry
verify the assumption of a reduced oxidation state of the bismuth
atoms and residual BieBi bonding. The NPA charges at the bismuth
atoms are in the range from þ1.265 to þ1.356 which is in accor-
dance with the NPA charge of the bismuth atoms in the cluster
4. Experimental section
[Bi4Fe8(CO)28
]
4ꢀ (QNPA þ 1.285) [15]. Also the Wiberg bond indices
for the BieBi bonds in both compounds are comparable (3: WBIBieBi
0.108e0.118; [Bi4Fe8(CO)28
ence in the overall charge of both clusters the NPA charge on the m3
4.1. General methods
]
4ꢀ: WBIBieBi 0.112). Due to the differ-
-
All reactions were carried out using standard Schlenk tech-
niques under an atmosphere of nitrogen or argon [40]. Solvents
were distilled from appropriate drying agents prior to use.
[Fe2(CO)9] (Aldrich) was used as received. BiCl3 (Aldrich) was
purified with SOCl2. Bi(OSiMet2Bu)3 was prepared according to
a literature method [41]. For the synthesis of Bi(OtBu)3 an improved
synthetic protocol, adapted from the literature [42,43], was devel-
oped. Infrared spectra with 4 cmꢀ1 resolution were recorded on
a Nicolet “FTIR-200” spectrophotometer as KBr pellets. NMR
spectra were recorded on a Bruker spectrometer (Typ Avance III
500) at room temperature. CHN-analyses were carried out with
a CHN-Analysator Type FlashAE 1112 (Co. Thermo). However,
compounds 2 and 3 start to decompose slowly even under inert
conditions and thus no satisfying elemental analyses were
obtained. TGA analyses were made using a “Pyris 1 TGA 7” (Co.
PerkineElmer). X-ray diffraction data collection was carried out on
coordinated Fe atoms differ significantly as do the Wiberg bond
indices for the Biem3Fe bonds (3: QNPA(Fe) þ 0.090, WBIBie
m
3Fe
0.500e0.545; [Bi4Fe8(CO)28
]
4ꢀ: QNPA(Fe) ꢀ2.244, WBIBie 3Fe 0.615).
m
The BieFe bonds are mainly built by p-type orbitals of the bismuth
atoms and the doubly occupied non-bonded bismuth atoms lone
pairs show approximately 90% s-type orbital character.
The thermal decomposition of the complexes [(CO)4FeBi(OSi-
Me2t Bu)]2 (1), [(CO)4FeBi(OtBu)]n (2) and [(CO)3FeBi3(OtBu)4{OCO
(OtBu)}]2 (3) was studied by thermogravimetric analysis (TGA).
Thermal decomposition of compound 1 under helium proceeds in
a single step between 100 ꢁC and 270 ꢁC showing a mass loss of
48.3% which is significantly higher than expected for the formation
of BiFeO3. Thus, volatile metal containing decomposition products
were eliminated. Noteworthy, the PXRD of the final residue reveals
formation of BiFeO3, Bi4(SiO4)3 and Bi2Fe4O9. Under air complex 1
starts to decompose at approximately 30 ꢁC and shows a total mass
loss of 36.6% after heating to 600 ꢁC. The final material is composed
of Bi4(SiO4)3 as the main crystalline phase accompanied by traces of
Bi2Fe4O9.
The thermal decomposition under helium of both [(CO)4FeBi
(OtBu)]n (2) and [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3) proceeds in
two steps starting at approximately 30 ꢁC. In case of compound 3
between 30 ꢁC and 400 ꢁC a mass loss of 14.0% and second mass loss
of 4.7% in the range from 400 ꢁC to 600 ꢁC was observed, which is
significantly lower than calculated for the formation of Fe2O3/
3Bi2O3 (33.8%) and indicates incomplete thermal degradation.
PXRD of the final residue reveals formation of the crystalline phases
Bi25FeO39 and BiFeO3. Compound 2 reveals the first mass loss (6.2%)
between 30 ꢁC and 400 ꢁC and a second mass loss of 2.3% in the
range from 400 ꢁC to 700 ꢁC. These values are in good agreement
with the calculated mass loss of 8.2% that is required for the
conversion of the precursor [(CO)4FeBiOtBu]n (2) into BiFeO3. The
PXRD shows formation of BiFeO3 as the main crystalline phase,
however, containing minor impurities of Bi25FeO39 (Fig. 4).
an Oxford diffractometer (Type Gemini S) using Cu-Ka radiation.
The structures were solved by direct methods using SHELXS-97
[44] and refined by full-matrix least-square procedures on F2 using
SHELXL-97 [45]. In case of compound 1 high residual electron
density peaks were observed close to the Bi atoms [46].
4.2. Experimental procedures
4.2.1. [Bi(OtBu)3]
To a suspension of BiCl3 (20.52 g, 65.08 mmol) in THF (250 ml)
was added a THF solution (250 ml) of KOtBu (21.91 g, 195.23 mmol)
at room temperature. The suspension is stirred overnight and the
solvent removed in vacuo. The solid residue was extracted for 6 h
with 500 ml n-pentane using a Soxhlet extractor. The amount of
solvent is reduced at 5 ꢁC until a cloudy solution is obtained. At
room temperature the solid material dissolves and the solution is
kept at ꢀ20 ꢁC overnight to give 19.24 g (69%) Bi(OtBu)3 as col-
ourless or slightly yellow crystals.

K. Wójcik et al. / Journal of Organometallic Chemistry 696 (2011) 1647e1651
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1651
4.2.2. [(CO)4FeBi(OSiMet2Bu)]2 (1)
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To a gold coloured suspension of [Fe2(CO)9] (1.00 g, 2.74 mmol)
in 100 ml n-pentane was added Bi(OSiMet2Bu)3 (1.65 g, 2.74 mmol)
and the mixture was stirred overnight. The colour changed after 2 h
from gold to dark brown. The solution was filtered and the solvent
was removed in vacuo to give an oily product. Single crystals of
[(CO)4FeBi(OSiMet2Bu)]2 (1) (0.42 g, 30% based on Bi) were obtained
from n-pentane solution at ꢀ20 ꢁC.
Dec. 120 ꢁC, Anal. Calcd: C10H15BiFeO5Si (507.98) requires C,
23.64 H, 2.98% Found: C, 24.04; H 2.8% 1H NMR (CDCl3):
d 0.92 (s),
0.10 (s) IR/KBr [cmꢀ1]: 2962 (s), 2925 (s); 2051 (s); 1978 (s); 1947
(w), 16,257 (s); 1260 (s); 1095 (s); 1028 (s); 888 (s); 588 (m).
4.2.3. [(CO)4FeBi(OtBu)]n (2) and [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2
(3)
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To a gold coloured suspension of [Fe2(CO)9] (1.00 g, 2.74 mmol) in
100 ml n-pentane was added Bi(OtBu)3 (1.18 g, 2.74 mmol) as a solid
and the mixture was stirred overnight. The colour changed after 2 h
from gold to dark brown. The solvent was removed in vacuo, the
solid was extracted with n-pentane and was filtered off to give
[(CO)4FeBi(OtBu)]n (2) (0.41 g, 30% based on Bi). Single crystals of
[(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3) suitable for single crystal X-ray
diffraction analysis were obtained repeatedly from n-pentane
solution (0.36 g, 35% based on Bi) at ꢀ30 ꢁC. TG-diagrams of freshly
prepared 2 and 3 demonstrate that both compounds start to
decompose at approximately 30 ꢁC. [(CO)4FeBi(OtBu)] (2)IR/KBr
[cmꢀ1]: 2037 (s); 1985 (s); 1949 (s); 1458 (m); 1356 (m); 1261 (w);
1176 (w); 195 (w); 917 (w); 802 (w); 585 (s). [(CO)3Fe-
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Bi3(OtBu)4{OCO(OtBu)}]2 (3)Dec. < 40 ꢁC, 1H NMR (CDCl3):
d 1.26 (s)
IR/KBr [cmꢀ1]: 1993 (s); 1932 (s); 1637 (s); 1458 (s)-1321 (s); 1102
(w); 1021 (w); 1022 (s); 802 (m); 571-474 (s).
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(1994) 7535 ) for Bi) have been used as supplied in the NWChem package.
[39] The NBO analysis has been carried out using the NBO package ( A.E. Reed,
L.A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988) 899 ) as interfaced to NWChem
Acknowledgement
We are grateful to the Deutsche Forschungsgemeinschaft for
financial support.
(NWChem,
A Computational Chemistry Package for Parallel Computers,
Version 5.1; Pacific Northwest National Laboratory: Richland, WA, 2007).
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Appendix A. Supplementary material
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39 (2010) 3219.
CCDC 787059 (compound 3) and 787060 (compound 1) contain
the supplementary crystallographic data. These data can be
obtained free of charge from the Cambridge Crystallographic Data
centre via www.ccdc.cam.ac.uk/data_request/cif.
[44] G.M. Sheldrick, Acta Crystallogr., A 46 (1990) 467.
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References
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1.41 ÅeBi2 (Q1 10.78 e Åꢀ3), 1.28 ÅeBi1 (Q2 10.53 e Åꢀ3), 1.29 ÅeBi2 (Q3
10.13 e Åꢀ3) and 1.25 ÅeBi1 (Q4 9.99 e Åꢀ3). Acoording to W. Massa (Kris-
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ca. 10% of the electron density of the heavy atom are expected at distances
between 0.6 and 1.2 Å. In addition, these unrefined electron density peaks
might be attributed to large absorption effects. Repeated measurements of 1
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