Synthesis and reactivity of haloacetato derivatives of iron(II) including the crystal and the molecular structure of [Fe(CF3COOH) 2(μ-CF3COO)2]n

Article abstract of DOI:10.1021/ic061903h

The syntheses of haloacetates of iron(II) and their reactivity are described. The compound Fe(CF₃COO)₂, 1, crystallizes from CF₃COOH/(CF₃CO)₂O solution as the polynuclear [Fe(CF₃COO)₂(CF₃COOH)₂] _n, 2, which contains bridging trifluoroacetates and monodentate trifluoroacetic acid groups. Fe(CF₃COO)₂(DMF)_x, as obtained from Fe(CO)₅ and CF₃COOH/(CF ₃CO)₂O in DMF, reacts with dioxygen at room temperature to give two μ₃-oxo compounds, namely, [Fe₃(μ ₃-O)(CF₃COO)₆(DMF)₃], 3, a Fe ^(II)-Fe^(III)-Fe^(III) derivative, and [Fe ₄(μ₃-O)₂(μ₂-CF ₃COO)₆(CF₃COO)₂(DMF)₄], 4, containing Fe(III) atoms only, which have been characterized by X-ray diffraction methods. Iron(II) chloro- and bromoacetates can be isolated by exchange reactions of iron(II) acetate with chloro- and bromo-substituted acetic acids in moderate to good yields. The stability of iron(II) haloacetates decreases on increasing the atomic weight and the number of halogens on the α-carbon atom. The species Fe(CX₃COO)₂ (X = Cl, 7; Br, 8), in THF solution, slowly convert into [Fe₃(μ₃-O) (CCl₃COO)₆(THF)₃], 11, or [Fe ₃(μ₃-O)(CBr₃COO)₆(THF) ₃][FeBr₄], 10, respectively. Likewise, when iron(II) acetate (or trifluoroacetate) is left for several hours in the presence of a variety of haloacetic acids in THF, selective formation of different species, depending on the nature of the starting compound and of the acid employed, is observed. The formation of these products is the result of C-X bond activation (X = Cl, Br) and haloacetato decomposition, which occurs with concomitant oxidation at the metal centers. Carboxylic acid degradation species (CH ₂XCOOH, CX₄, CX₃H, CX₂H₂, X = Cl, Br) have been observed by GC-MS.

Full text of DOI:10.1021/ic061903h

Inorg. Chem. 2007, 46, 3378−3384
Synthesis and Reactivity of Haloacetato Derivatives of Iron(II) Including
the Crystal and the Molecular Structure of [Fe(CF3COOH)2(µ-CF3COO)2]n
|
Fabio Marchetti,†,§ Fabio Marchetti,†, Bernardo Melai,† Guido Pampaloni,*,† and Stefano Zacchini‡
Dipartimento di Chimica e Chimica Industriale, UniVersita` di Pisa, Via del Risorgimento 35,
I-56126 Pisa, Italy, and Dipartimento di Chimica Fisica e Inorganica, UniVersita` di Bologna,
Viale Risorgimento 4, I-40136 Bologna, Italy
Received October 5, 2006
The syntheses of haloacetates of iron(II) and their reactivity are described. The compound Fe(CF3COO)2, 1, crystallizes
from CF3COOH/(CF3CO)2O solution as the polynuclear [Fe(CF3COO)2(CF3COOH)2]n, 2, which contains bridging
trifluoroacetates and monodentate trifluoroacetic acid groups. Fe(CF3COO)2(DMF)x, as obtained from Fe(CO)5 and
CF3COOH/(CF3CO)2O in DMF, reacts with dioxygen at room temperature to give two
µ3-oxo compounds, namely,
[Fe3( 3-O)2( 2-CF3COO)6(CF3COO)2(DMF)4],
µ
3-O)(CF3COO)6(DMF)3], 3, a Fe(II) Fe(III) Fe(III) derivative, and [Fe4(
−
−
µ
µ
4, containing Fe(III) atoms only, which have been characterized by X-ray diffraction methods. Iron(II) chloro- and
bromoacetates can be isolated by exchange reactions of iron(II) acetate with chloro- and bromo-substituted acetic
acids in moderate to good yields. The stability of iron(II) haloacetates decreases on increasing the atomic weight
and the number of halogens on the
R
-carbon atom. The species Fe(CX3COO)2 (X
) Cl, 7; Br, 8), in THF solution,
slowly convert into [Fe3( 3-O)(CCl3COO)6(THF)3], 11, or [Fe3(
µ
µ
3-O)(CBr3COO)6(THF)3][FeBr4], 10, respectively.
Likewise, when iron(II) acetate (or trifluoroacetate) is left for several hours in the presence of a variety of haloacetic
acids in THF, selective formation of different species, depending on the nature of the starting compound and of the
acid employed, is observed. The formation of these products is the result of C
haloacetato decomposition, which occurs with concomitant oxidation at the metal centers. Carboxylic acid degradation
species (CH2XCOOH, CX4, CX3H, CX2H2, X Cl, Br) have been observed by GC-MS.
−X bond activation (X ) Cl, Br) and
)
Introduction
been studied extensively,4 and it has been found that the
nature of the compounds depends on the haloacetate (by
operating under the same experimental conditions in the
presence of excess (RCO2)O, anhydrous (Cu(CH2XCOO)2,
X ) Cl, Br) or aquo derivatives (Cu(CHX2COO)2(H2O), X
) Cl, Br) were obtained) or on the presence of Lewis bases
(according to IR spectroscopy, different coordination
modes of the haloacetatessbridging monodentate, bridging
bidentate, and bidentateswere observed). Moreover, the
stability of copper(I) haloacetates with respect to oxidation
to copper(II) decreases on increasing the number of halides
on the R-carbon atom and on the atomic weight of the
halogen.
Trifluoroacetato derivatives of transition metals are used
in catalysis1 due to the higher solubility of the precursors
with respect to simple acetates and due to the fact that, being
[CF3COO]- ligands and Lewis bases weaker than hydrogen-
substituted acetates, they can be easily displaced or change
their coordination from bi- to monodentate, according to the
electronic and steric requirements of the central metal atom.
In the framework of our research on carboxylato deriva-
tives of transition metals, we have recently reported on the
syntheses and the properties of vanadium,2 manganese,3 and
copper4 trihaloacetato derivatives. Copper haloacetates have
* To whom correspondence should be addressed. E-mail: pampa@
dcci.unipi.it. Tel: int. code + 39 050 2219 219. Fax: int. code + 39 050
2219 246.
(2) Calderazzo, F.; De Benedetto, G. E.; Detti, S.; Pampaloni, G. J. Chem.
Soc., Dalton Trans. 1997, 3319.
(3) Calderazzo, F.; Englert, U.; Pampaloni, G.; Passarelli, V.; Serni, G.;
Wang, R. Can. J. Chem. 2001, 79, 495.
(4) (a) Belli Dell’Amico, D.; Alessio, R.; Calderazzo, F.; Della Pina, F.;
Englert, U.; Pampaloni, G.; Passarelli, V. J. Chem. Soc., Dalton Trans.
2000, 2067. (b) Calderazzo, F.; Donati, N.; Englert, U.; Marchetti,
F.; Pampaloni, G.; Passarelli, V. Inorg. Chim. Acta 2003, 100, 346.
† Universita` di Pisa.
‡ Universita` di Bologna.
§ Born in 1950 in Castelfiorentino (FI), Italy.
| Born in 1974 in Bologna, Italy.
(1) Gardner, C. D.; Hughes, B. AdV. Inorg. Chem. Radiochem. 1975, 17,
1. Sommazzi, A.; Garbassi, F. Prog. Polym. Sci. 1997, 22, 1547.
3378 Inorganic Chemistry, Vol. 46, No. 8, 2007
10.1021/ic061903h CCC: $37.00
© 2007 American Chemical Society
Published on Web 03/13/2007

Haloacetate DeriWatiWes of Iron(II)
suspension was filtered and the solid was washed with THF (3 ×
10 mL) and dried in vacuo affording 1‚DMF7 (32.5 g, 62% yield)
as a microcrystalline colorless solid. Anal. Calcd for C7H7F6-
FeNO5: C, 23.7; H, 2.0; N, 3.9. Found: C, 23.5; H, 1.8; N, 3.6.
IR (Nujol and polychlorotrifluoroethylene mull): 1671vs (νas-
(COO)), 1649vs, 1459s (νs(COO)), 1210vs (νas(CF3)), 1147s (νs-
These facts, together with the recently reported synthesis
of iron(II) trifluoroacetate,3 prompted us to extend our studies
to iron, and in this paper we wish to report on the preparation
of halocarboxylato derivatives of iron(II), as obtained by
exchange reaction, and the identification of halide transfer
reactions mainly involving [CCl3COO]- or [CBr3COO]-
anions.
Moreover, the crystal and molecular structure of the CF3-
COOH adduct of iron(II) trifluoroacetate is reported, repre-
senting an addition to the rather restricted family of
coordination compounds containing the carboxylate and its
conjugated acid as ligands at the same time.4a,5
(CF3)), 846m-s, 795m-s, 725m-s, 666w cm-1
.
Reaction of 1‚DMF with O2 in THF: Preparation of 3 and
4. A colorless solution of 1‚DMF (1.93 g, 5.44 mmol) in THF (40
mL) was saturated with dry oxygen and stirred at room temperature
for 3 h. The volume of the dark red solution was reduced to ca. 15
mL, and heptane was added (20 mL) to form two layers. After 6
days, well formed red and black crystals were filtered, dried briefly
in vacuo, and separated under the microscope. No attempt was made
to increase the yields of the two products.
Experimental Section
The black crystals (0.10 g, 2%) corresponded to 3. Anal. Calcd
for C21H21F18Fe3N3O16: C, 23.3; H, 2.0; N, 3.9. Found: C, 24.3;
H, 2.4; N, 3.4. IR (Nujol and polychlorotrifluoroethylene mull):
1703s, 1651vs, 1501m-w, 1462s, 1369s, 1229s, 1201, 1158s,
All operations were carried out using standard Schlenk-tube
techniques, under an atmosphere of prepurified dinitrogen. The
reaction vessels were dried in an oven prior to use. Solvents were
dried by conventional methods. Elemental analyses were performed
by a Carlo Erba model 1106 elemental analyzer. Infrared spectra
were recorded by a Perkin-Elmer model FT 1725X instrument on
Nujol and polychlorotrifluoroethylene mulls under exclusion of
moisture and oxygen or by a FTIR spectrometer equipped with a
Perkin-Elmer UATR sampling accessory. Photochemical reactions
were performed in a quartz apparatus equipped with a 150 W
mercury lamp.
Commercially available Fe(CO)5 (Fluka) was used without
further purification. Iron(II) acetate was obtained by reaction of
Fe(CO)5 with CH3COOH/(CH3CO)2O in DMF at 140 °C.6 Trif-
luoroacetic acid, CF3COOH (Aldrich), and trifluoroacetic anhydride
were used as received. The carboxylic acids, CX3COOH, CHX2-
COOH, and CH2XCOOH, X ) Cl, Br, were dried overnight in
vacuo at room temperature. N,N-Dimethylformamide, DMF, was
stirred overnight over BaO, filtered under inert atmosphere, and
distilled under reduced pressure.
Preparation of Fe(CF3COO)2(DMF), 1‚DMF. A solution of
CF3COOH (24.0 mL, 312 mmol) in DMF (200 mL) was treated
with Fe(CO)5 (20.0 mL, 148 mmol) and heated at ca. 140 °C. After
3 h, gas evolution had ceased and no iron carbonyl derivative was
detected in solution (IR spectrum). The colorless solution was
evaporated in vacuo at 110 °C, thus obtaining a colorless solid
residue. After the addition of toluene (300 mL), the suspension
was filtered, washed with toluene (4 × 10 mL), and dried in vacuo
at room temperature. The solid residue was treated with THF (100
mL) and, after 14 h of stirring at room temperature, the resulting
853m, 795m, 727s, 692m, 670m-w cm-1
.
The red crystals (0.060 g, 3% yield) were identified as 4. Anal.
Calcd for C28H28F24Fe4N4O21: C, 23.4; H, 2.0; N, 3.9. Found: C,
23.3; H, 2.2; N, 3.6. IR (Nujol and polychlorotrifluoroethylene
mull): 1713m-w, 1691m-w, 1637vs, 1466m, 1416m-w, 1377m,
1204vs, 1166m, 1157m, 1146m, 853m-w, 797m-w, 727m, 649m
cm-1
.
A gas-volumetric control of the reaction showed that 3.37 mmol
of 1‚DMF in THF (25 mL) absorbed dioxygen at 21.7 °C up to a
O2/Fe molar ratio of 0.22 in 3 h.
1. Preparation of Fe(CH3-nXnCOO)2 Complexes. 1A. Fe-
(CF3COO)2‚THF, 1‚THF. A solution of CF3COOH (19.5 mmol)
in THF (50 mL) was treated with Fe(CH3COO)2, 5 (1.69 g, 9.72
mmol). The solid slowly dissolved, and a colorless solution was
obtained after ca. 2 h of stirring at room temperature. The volume
of the solution was reduced to ca. 5 mL in vacuo at room
temperature; addition of heptane (30 mL) caused the separation of
a colorless solid which was recovered by filtration and identified
(after drying in vacuo for 2 h) as 1‚THF (2.47 g, 85% yield, IR
and elemental analysis).
The treatment of 1‚DMF with 2 equiv of CH3COOH in THF
under the experimental conditions described above did not produce
appreciable amounts of 5, and unreacted 1‚DMF was recovered in
almost quantitative yields.
1B. Fe(CHCl2COO)2(THF), 6. A solution of CHCl2COOH (19.4
mmol) in THF (50 mL) was treated with 5 (1.49 g, 8.57 mmol).
The colorless suspension was stirred at room temperature for 3 days.
The colorless solid was recovered by filtration, washed with THF
(2 × 2 mL), and dried in vacuo at room temperature (2 h), affording
6 (3.16 g, 96% yield) as a microcrystalline, colorless, air-sensitive
solid. Anal. Calcd for C8H10Cl4FeO5: C, 25.0; H, 2.6. Found: C,
25.2; H, 2.8. IR (Nujol and polychlorotrifluoroethylene mull):
2897w, 1631vs (νas(COO)), 1461s, 1402vs (νs(COO)), 1378m-s,
1367m-s, 1296mw, 1223m-s, 1042s (νas(C-O-C), THF), 921w,
882m-w (νas(C-O-C), THF), 827m-s, 771m-s, 718s, 666m-s
(5) (a) [TiCl2(RCOO)(RCOOH)]2O, R ) Et: Barrow, H.; Brown, D. A.;
Alcock, N. W.; Errington, W.; Wallbridge, M. G. H. J. Chem. Soc.,
Dalton Trans. 1994, 3533. R ) But: Barrow, H.; Brown, D. A.;
Alcock, N. W.; Clase, H. J.; Wallbridge, M. G. H. J. Chem. Soc.,
Dalton Trans. 1994, 195. (b) Ti2Cl7(RCOO)(RCOOH), R ) p-ClC6H4,
CH ) CHMe: Alcock, N. W.; Brown, D. A.; Illson, T. F.; Roe, S.
M.; Wallbridge, M. G. H. J. Chem. Soc., Dalton Trans. 1991, 873.
(c) MM′(C6H5COO)4(C6H5COOH)2, M ) M′ ) Cr: Cotton, F. A.;
Extine M. W.; Rice, G. W. Inorg. Chem. 1978, 17, 176. M ) M′ )
Ru: Spohn, M.; Stra¨hle, J.; Hiller, W. Z. Naturforsch. 1986, B41,
541. M ) Cu, M′ ) Ni: Spohn, M. Ph.D. Thesis, Universita¨t
Tu¨bingen, 1986. (d) [V3(µ3-Ã)(CH3COO)6(CH3COOH)2(THF)][VCl4-
(CH3COOH)2]: Cotton, F., A.; Lewis, G. E.; Mott, G. N. Inorg. Chem.
1982, 21, 3316. (e) Ru2(CH3COO)4(CH3COOH)2‚0.7H2O: Cotton, F.
A.; Makutz, M.; Zhong, B. Inorg. Chem. 1988, 27, 4368. (f) Cr2(CH3-
COO)4(CH3COOH)2: Cotton, F. A.; Rice, G. W. Inorg. Chem. 1978,
17, 2004. (g) Cu2(CH3COO)4(CH3COOH)2: Rao, V. M.; Sathya-
narayana, D. N.; Manohar, H. J. Chem. Soc., Dalton Trans. 1983,
2167.
cm-1
.
1C. Fe(CCl3COO)2(THF), 7. A solution of CCl3COOH (2.92
g, 17.8 mmol) in THF (50 mL) was treated with 5 (1.53 g, 8.79
mmol). The initially colorless suspension turned red-orange after
2 h of stirring at room temperature; the solid isolated consisted of
(7) The amount of DMF retained by the compound depends on the drying
conditions: in our experiments the DMF/Fe molar ratio ranged from
1.6 to 0.5.
(6) Calderazzo, F.; Floriani, C.; Henzi, R.; L’Eplattenier, F. J. Chem. Soc.
A 1969, 1378.
Inorganic Chemistry, Vol. 46, No. 8, 2007 3379

Marchetti et al.
a mixture of iron(II) trichloroacetate and acetate (IR spectrum on
a solid sample). A qualitative test (Ag+ in aqueous acidic solution)
on the surnatant liquid was positive for chloride ion. After 90 h of
stirring at room temperature, the colorless solid was recovered by
filtration, washed with THF (2 × 2 mL), and dried in vacuo at
room temperature (2 h), affording 7 (2.66 g, 67% yield) as a
microcrystalline, colorless, air-sensitive solid. Anal. Calcd for C8H8-
Cl6FeO5: C, 21.2; H, 1.8. Found: C, 21.0; H, 1.7. IR (Nujol and
polychlorotrifluoroethylene mull): 2897w, 1651vs,br (νas(COO)),
1513m-w, 1462m-s (νs(COO)), 1377m-s, 1026m-w (νas(C-
O-C), THF), 885m,w,sh (νs(C-O-C), THF), 837m-s 739s, 683s
CBr4, CBr3H, CBr2H2, and CH2BrCOOH. The solvent was removed
in vacuo, and the residue was dissolved in THF (5 mL). The solution
was layered with heptane, obtaining 12 (0.275 g, 50% yield) as a
microcrystalline orange powder after standing at room temperature
for 2 days. Anal. Calcd for C24H39Br7Fe4O16: C, 21.1; H, 2.9.
Found: C, 20.7; H, 2.7. IR (solid state): 2984w, 1588vs (νas(COO)),
1439vs (νs(COO)), 1411vs (νs(COO)), 1343m-s, 1045m, 1024m-s
(νas(C-O-C), THF), 870s (νs(C-O-C), THF), 655ms cm-1
.
2D. Preparation of Fe3(µ3-O)(CCl3COO)6(DMF)(THF)2, 13.
To a solution of CCl3COOH (1.31 g, 8.02 mmol) in THF (20 mL),
1‚DMF (0.950 g, 2.68 mmol) was added. The mixture was stirred
for 18 h at room temperature. A GC-MS analysis of the solution
revealed the presence of CF3COOH, CCl3COOH (unreacted), CCl4,
CCl3H, CCl2H2, and CHCl2COOH. The solvent was removed in
vacuo, and the residue was dissolved in CH2Cl2 (5 mL). The
solution was layered with diethyl ether and pentane, obtaining 13
(0.630 g, 51% yield) as a microcrystalline red powder after standing
at ca. -20 °C for 3 days. Anal. Calcd for C23H23Cl18Fe3NO16: C,
20.1; H, 1.7; N, 1.0. Found: C, 19.7; H, 2.9; N, 0.9. IR (solid
state): 2982w, 2891w, 1704m, 1678s (νas(C-O), DMF), 1650vs
(νas(COO)), 1488w, 1429w, 1359vs (νs(COO)), 1259w, 1114w,
1027m (νas(C-O-C), THF), 963w, 918w, 872m (νs(C-O-C),
cm-1
.
1D. Fe(CBr3COO)2(THF)2, 8. A solution of CBr3COOH (6.01
g, 20.2 mmol) in THF (50 mL) was treated with 5 (1.530 g, 8.80
mmol). The initially colorless suspension quickly turned red-orange
and a qualitative test (Ag+ in aqueous acidic solution) on the
surnatant liquid was positive for bromide ion. The colorless solid
was recovered by filtration, washed with THF (2 × 2 mL), and
dried in vacuo at room temperature (1 h), affording 8 (3.44 g, 49%
yield) as a microcrystalline, colorless, air-sensitive solid. Anal.
Calcd for C12H16Br6FeO6: C, 18.2; H, 2.0. Found: C, 18.1; H,
2.2. IR (solid state): 3016w, 2973w, 2879w, 1618vs (νas(COO)),
1406m, 1374 m-s (νs(COO)), 1193m, 1159m, 1039s (νas(C-O-
C), THF), 918w, 881m (νs(C-O-C), THF), 700s, 691s cm-1
1E. Fe(CHBr2COO)2(THF), 9. Experimental procedures as in
section 1D; reaction time 20 h. Compound was a microcrystalline,
colorless, air-sensitive solid (74% yield from CHBr2COOH and 5).
Anal. Calcd for C8H10Br4FeO5: C, 17.1; H, 1.8. Found: C, 17.6;
H, 2.1. IR (solid state): 3019w, 2964w, 2889w, 1616vs (νas(COO)),
1405m, 1372m-s (νs(COO)), 1194m, 1159m, 1036s (νas(C-O-
THF), 848vs, 834vs, 741s, 676vs cm-1
.
2E. Preparation of [Fe3(µ3-O)(CH2BrCOO)6(THF)3][FeBr4],
14. Experimental procedures as in section 2C; reaction time 7 days.
Orange microcrystalline powder was obtained by layering the final
reaction mixture with heptane, at room temperature (28% yield from
5 and excess CH2BrCOOH). GC-MS analysis of the reaction
mixture: CH3COOH, CH2BrCOOH (unreacted), CBr4, CBr3H,
CBr2H2. Anal. Calcd for C24H36Br10Fe4O16: C, 18.0; H, 2.3.
Found: C, 18.3; H, 2.0. IR (solid state): 3012w, 2962w, 1615s
(νas(COO)), 1552sh,m, 1537sh,m, 1398sh,vs, 1372vs (νs(COO)),
1259w, 1191m-w, 1114w, 1025w (νas(C-O-C), THF), 950w,
C), THF), 918w, 877m (νs(C-O-C), THF), 807m, 690vs cm-1
.
2. Reactivity of Fe(CH3-nXnCOO)2 Complexes. 2A. Prepara-
tion of [Fe3(µ3-O)(CBr3COO)6(THF)3][FeBr4], 10. A solution of
8 (0.80 g, 1.0 mmol) in THF (40 mL) was stirred for 48 h at room
temperature. A GC-MS analysis was carried out on an aliquot of
the final reaction mixture; the analysis revealed the presence of
CH2BrCOOH, CBr4, CBr3H, and CBr2H2. The volume of the
remaining solution was reduced to ca. 5 mL in vacuo at room
temperature; addition of heptane (30 mL) allowed the isolation of
10 (0.18 g, 39% yield) as an orange microcrystalline solid which
could be recrystallized from CH2Cl2 layered with diethyl ether, at
room temperature. Anal. Calcd for C24H24Br22Fe4O16: C, 11.3; H,
0.9. Found: C, 11.5; H, 1.1. IR (solid state): 2420w, 1631s (νas-
(COO)), 1400s (νs(COO)), 1230m, 1226m-s, 1091m, 1023m-s
(νas(C-O-C), THF), 938m, 876m (νs(C-O-C), THF), 841vs,
859m (νs(C-O-C), THF), 796m-w, 689vs, 661s cm-1
.
2F. Preparation of cis-[Fe(DMF)4(THF)2][FeBr4]2, 15. Ex-
perimental procedure as in section 2C; reaction time 18 h. A
microcrystalline red solid (53% yield from 1‚DMF and excess CBr3-
COOH) was obtained. Crystals suitable for X-ray analysis were
obtained at room temperature from a THF solution layered with
diethyl ether. GC-MS analysis of the reaction mixture: CF3COOH,
CBr3COOH (unreacted), CBr4, CBr3H, CBr2H2. Anal. Calcd for
C20H44Br8Fe3N4O6: C, 19.3; H, 3.6. Found: C, 18.7; H, 3.4. IR
(solid state): 2964w, 2936w, 2890w, 1672s,sh (νas(C-O), DMF),
1644vs (νas(COO)), 1493w, 1434m-w, 1362m (νs(COO)), 1260m,
1110m, 1028m-s (νas(C-O-C), THF), 872m-w (νs(C-O-C),
THF), 798m-s, 685m cm-1
.
726s, 679vs cm-1
.
X-ray Crystallography. Relevant crystal parameters and details
of structure solutions of [Fe(CF3COOH)2(µ-CF3COO)2]n, 2, and
cis-[Fe(DMF)4(THF)2][FeBr4]2, 15, are listed in Table 1. The
diffraction experiments were carried out on a Bruker Apex II
diffractometer, equipped with a CCD detector using Mo KR
radiation. Data were corrected for Lorentz polarization and absorp-
tion effects (empirical absorption correction SADABS).8 The
structures were solved by direct methods and refined by full-matrix
least-squares based on all data using F2.9 Non-hydrogen atoms were
refined anisotropically, unless otherwise stated. H atoms were placed
in calculated positions and refined by a riding model. Crystals of
2 show some nonmerohedral twinning. Despite different attempts
to take this into account during data processing, the R values for
2B. Preparation of Fe3(µ3-O)(CCl3COO)6(THF)3, 11. Experi-
mental procedures as in section 2A; reaction time 72 h. Compound
was a microcrystalline red solid (40% yield from 7). GC-MS
analysis: CCl4, CCl3H, CH2Cl2. Crystals suitable for X-ray analysis
were obtained at room temperature from a THF solution layered
with diethyl ether. Anal. Calcd for C24H24Cl18Fe3O16: C, 21.0; H,
1.8. Found: C, 20.8; H, 2.0. IR (solid state): 2394w, 2901vw, 1657s
(νas(COO)), 1396vs (νs(COO)), 1261m, 1226m-s, 1091m, 1023m-s
(νas(C-O-C), THF), 957w-m, 873m (νs(C-O-C), THF), 819s,
795s, 711s, 674vs cm-1
.
The same product was obtained by reaction of 5 with excess
CCl3COOH in THF solution.
2C. Preparation of [Fe3(µ3-O)(CH3COO)5(CBr3COO)(THF)3]-
[FeBr4], 12. To a solution of CBr3COOH (1.21 g, 4.07 mmol) in
THF (15 mL), 5 (0.280 g, 1.61 mmol) was added. The mixture
was stirred for 12 h at room temperature. A GC-MS analysis of
the final solution revealed the presence of CBr3COOH (unreacted),
(8) Sheldrick, G. M. SADABS, Program for empirical absorption correc-
tion; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(9) Sheldrick, G. M. SHELX97, Program for crystal structure determina-
tion; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
3380 Inorganic Chemistry, Vol. 46, No. 8, 2007

Haloacetate DeriWatiWes of Iron(II)
Table 1. Crystal Data and Details of the Structure Refinement for
Compounds 2 and 15a
compound
2
15
formula
mol wt
T, K
C8H2F12FeO8
509.95
100(2)
C20H44Br8Fe3N4O6
1243.42
293(2)
radiation
cryst syst
space group (no.)
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Mo KR
triclinic
P1h (No. 2)
8.5335(17)
9.829(2)
11.004(2)
114.74(3)
98.09(3)
90.31(3)
827.9(3)
2
monoclinic
C2/c (No. 15)
20.253(2)
12.0930(13)
35.505(4)
91.396(2)
Figure 1. View of the polynuclear chain of 2. Thermal ellipsoids are at
30% probability. The CF3 groups have been omitted for clarity.
8693.4(17)
8
1.900
Z
F
Table 2. Selected Bond Distances (Å) and Angles (deg) for 2
calc, g cm-3
2.046
1.078
µ, mm-1
8.374
Fe(1)-O(1)
Fe(1)-O(3)
Fe(1)-O(5)
2.219(8)
2.210(8)
2.123(7)
Fe(1)-O(6)
Fe(1)-O(7)
Fe(1)-O(8)
2.072(8)
2.116(7)
2.092(8)
data/restr/params
R(Fo) [I > 2σ(I)]
2865/132/262
0.1123
0.2997
6033/482/358
0.0988
0.2675
1.029
2
Rw(Fo )
O(6)-Fe(1)-O(8)
O(6)-Fe(1)-O(7)
O(8)-Fe(1)-O(7)
O(6)-Fe(1)-O(5)
O(8)-Fe(1)-O(5)
O(7)-Fe(1)-O(5)
O(6)-Fe(1)-O(3)
O(8)-Fe(1)-O(3)
90.8(4)
89.8(3)
100.4(3)
100.9(3)
89.6(3)
165.3(3)
174.0(3)
90.6(3)
O(7)-Fe(1)-O(3)
O(5)-Fe(1)-O(3)
O(6)-Fe(1)-O(1)
O(8)-Fe(1)-O(1)
O(7)-Fe(1)-O(1)
O(5)-Fe(1)-O(1)
O(3)-Fe(1)-O(1)
84.2(3)
84.9(3)
90.1(3)
174.2(3)
85.3(3)
84.6(3)
89.1(3)
GOF
1.051
a R(Fo) ) ∑||Fo| - |Fc||/∑|Fo|; Rw(Fo2) ) [∑[w(Fo - Fc )2]/
2
2
2
2
2
∑[w(Fo )2]]1/2; GOF ) [∑[w(Fo - Fc )2]/(N - P)]1/2, where N and P are
the number of observations and parameters, respectively.
this structure remain quite large. The two THF and two of the four
DMF ligands in 15 are disordered. Disordered atomic positions were
split and refined using one occupancy parameter per disordered
group.
1.262(14) and C(3)-O(3) 1.217(14) Å) and a longer one
corresponding to the C(1)-O(2) and C(3)-O(4) single bonds
(1.303(14) and 1.323(14) Å, respectively). Intramolecular
hydrogen bonds exist between the hydroxyl group of
coordinated CF3COOH and the oxygen atoms of the bridging
[CF3COO]- anions, the distances of O(2)‚‚‚O(7) and O(4)‚
‚‚O(5) being 2.685(11) and 2.656(11) Å, respectively. Similar
distances (2.734, 2.62, 2.642(5), 2.614, and 2.632 Å) were
observed in Cu2(CX3COO)4(CX3COOH)2, X ) Cl,4a H;5g
M(RCOO)4(RCOOH)2, M ) Cr, R ) CH3;5f M ) Ru, R )
C6H5;5c M ) Ru, R ) C6H5.5c The elongation of the Fe-
(1)-O(5) and Fe(1)-O(7) bonds (2.119 Å, mean value) with
respect to Fe(1)-O(6) and of the Fe(1)-O(8) bond (2.082
Å, mean value) is probably a consequence of the cited
hydrogen bond.
Due to the easy loss of DMF followed by crystal
breakdown, we have not been able to study the DMF adduct
by X-ray crystallography. Nevertheless, on the basis of the
solubility data (the compound is very soluble in DMF,
slightly soluble in THF, and almost insoluble in toluene) and
the molecular structure of the trifluoroacetic acid adduct, the
hypothesis has been put forward that Fe(CF3COO)2(DMF)n
is a polynuclear compound containing bridging trifluoroac-
etates and axial DMF groups.
Results and Discussion
Being interested in studying the reactivity of iron(II)
halocarboxylates, we decided to use the recently described
trifluoroacetate Fe(CF3COO)2, which can be prepared3 as the
trifluoroacetic acid adduct, Fe(CF3COO)2(CF3COOH)x, by
photolysis of Fe(CO)5 in CF3COOH/(CF3CO)2O mixtures at
room temperature. Alternatively, Fe(CF3COO)2(DMF)n is
obtained by thermal treatment of Fe(CO)5 in DMF, in the
presence of a slight excess of CF3COOH.3 The photochemi-
cal reaction was used at the beginning of the research, but
later we moved to the thermal reaction due to the fact that
the latter allowed the preparation of larger amounts of
product: 35-40 g of Fe(CF3COO)2(DMF)n can generally
be obtained in one run.
While preparing the iron(II) trifluoroacetate by the pho-
tochemical approach, we obtained single crystals of com-
pound 2 directly from the mother liquor; the crystal structure
has been solved and a view of the structure is reported in
Figure 1. Compound 2 is polynuclear; the infinite polymer
contains distorted octahedral iron atoms (Fe‚‚‚Fe distance,
4.762(4) Å), each coordinated to two monodentate CF3-
COOH (mean value of the Fe-O distance, 2.214 Å) and
four bridging [CF3COO]- ligands (mean value of the Fe-O
distance, 2.101 Å). The two CF3COOH groups are in relative
cis-position and, as a consequence, the polymeric chain
contains nearly orthogonal Fe2(µ-CF3COO)2 eight-membered
rings connected by the iron atoms. Table 2 reports a selection
of bond distance and angles.
During the large scale, thermal preparations of iron(II)
trifluoroacetate, we obtained variable yields (depending on
the reaction conditions) of another iron(II) derivative, prob-
ably a polynuclear compound at present under study, which
can be separated from Fe(CF3COO)2(DMF)n by washing the
raw material with THF (see Experimental Section).
Iron(II) trifluoroacetate is rather air sensitive: when a
colorless solution of 1‚DMF in THF is exposed to dry O2,
red and black crystals are obtained by layering the solution
Within the coordinated CF3COOH ligands, two different
C-O bond distances are present: a shorter one (C(1)-O(1)
Inorganic Chemistry, Vol. 46, No. 8, 2007 3381

Marchetti et al.
with heptane. These were carefully separated under a
microscope and characterized analytically, spectroscopically,
and by X-ray diffraction (see Supporting Information). The
black crystals consist of the trinuclear compound Fe3(µ3-
O)(CF3COO)6(DMF)3, 3, and the red crystals are the tetra-
nuclear Fe4(µ3-O)2(µ2-CF3COO)6(CF3COO)2(DMF)4 deriva-
tive, 4, both of them possessing several similar structural
types in the literature.10-12 According to gas-volumetric
results (a dioxygen uptake up to a O2/Fe molar ratio of 0.22
was observed within 3 h), the oxidation of Fe(CF3COO)2‚
DMF is quantitative and likely to proceed according to eq
1.
Although reactions using trifluoroacetates as starting
materials have been used for the preparation of haloacetates
of copper(I),4b the experimental observation in the case of
iron(II) can be explained when considering that the driving
force of the reaction is probably the O-H bond energy of
the acid product and that the acid strength of the carboxylic
acids in water increases on increasing the electronegativity
of the halo substituents on the R-position.14 It has to be noted
that Zn(CF3SO3)2(DME)2 was prepared from Zn(CF3COO)2-
(DME)2 and the stoichiometric amount of CF3SO3H.15
The less soluble but still largely available iron(II) acetate,
Fe(CH3COO)2, 5,6 was then used as starting material. Due
to its 3D extended structure,16 iron(II) acetate is less soluble
in THF than the trifluoroacetate, but it is still reactive to
undergo full exchange (see eq 3) after some hours of stirring
at room temperature in the presence of the appropriate
haloacetic acid.
14Fe(CF3COO)2‚DMF + 3O2 f
2Fe3(µ3-O)(CF3COO)6(DMF)3
+
3
2Fe4(µ3-O)2(µ2-CF3COO)6(CF3COO)2(DMF)4
(1)
4
Fe(CH3COO)2 + 2CX3COOH f
Fe(CX3COO)2 + 2CH3COOH (3)
In agreement with the existence of two types of trifluo-
roacetato ligands (monodentate and bidentate bridging) in
4, the IR spectrum shows two COO asymmetric stretching
vibrations at 1713 (monodentate) and 1637 cm-1 (bridging
bidentate).1,13 The two bands at 1466 and 1416 cm-1 can be
attributed to the COO symmetric stretching vibrations.
Carboxylato Exchange Reactions. Due to the large
availability of Fe(CF3COO)2(DMF)n, it was decided to use
this compound as starting material for the preparation of other
halocarboxylates of iron(II). Unfortunately, the reaction
reported in eq 2 gives only low conversion to the exchange
product, which is gained if the reaction mixture is evaporated
in vacuo to remove the volatile CF3COOH eventually formed
in the reaction.
CX3 ) CF3, CHCl2, CCl3, CBr3, CHBr2
The haloacetates of iron(II) are colorless crystalline solids,
sensitive to air in the solid state, and slowly decompose on
standing in solution at room temperature, this decomposition
being faster on increasing the number and the atomic weight
of the halogen in the R-position, vide infra. IR spectra are
characterized by the strong CdO stretching absorptions in
the 1700-1600 cm-1 region, assigned to the carboxylate
asymmetric vibration and the medium-to-strong CdO sym-
metric bands in the 1460-1370 cm-1 region, thus suggesting
the presence of bidentate carboxylates.13 Bands typical of
the CH3-nXn (X ) F, Cl, Br) groups are observed in the
low region of the spectrum, their positions dependent on the
atomic weight of the halogen, together with the asymmetric
and symmetric absorptions due to coordinated THF.
Fe(CF3COO)2(DMF)n + 2CX3COOH f
Fe(CX3COO)2 + 2CF3COOH + nDMF (2)
X ) H, Cl
It is interesting to note that the solid haloacetates have
been isolated with variable amounts of THF, as suggested
by elemental analyses: generally we found a THF/Fe molar
ratio of 1:1 in the microcrystalline solids after 2 h of drying
in vacuo at room temperature. In one occasion, the solid
compound was dried for a shorter time and the bis-THF
adduct Fe(CBr3COO)2(THF)2, 8, was obtained. By taking
into consideration that the solid structure of 2 shows two
bridging acetates and two axially coordinated trifluoroacetic
acid groups, we propose that the solid haloacetates have the
Fe(CX3COO)2(THF)2 composition; the axial THF can be
partially lost during the drying procedure.
As a confirmation of this observation, iron(II) trifluoroacetate
is easily obtained by the reverse of the reaction reported in
eq 2, i.e., the reaction of iron(II) acetate 5 with trifluoroacetic
acid.
(10) Cannon, R. D.; White, R. P. Prog. Inorg. Chem. 1988, 36, 195.
(11) (a) Yan, B.; Chen, Z.-D. Inorg. Chem. Commun. 2001, 4, 138. (b)
Wemple, M. W.; Coggin, D. K.; Vincent, J. B.; Mc Cusker, J. K.;
Streib, W. E.; Huffman, J. C.; Hendrickson, D. N.; Christou, G. J.
Chem. Soc., Dalton Trans. 1998, 719. (c) Armstrong, W. H.; Roth,
M. E.; Lippard, S. J. J. Am. Chem. Soc. 1987, 109, 6318. (d)
Chaudhuri, P.; Winter, M.; Fleischhauer, P.; Haase, W.; Flo¨rke, U.;
Haupt, H.-J. Inorg. Chim. Acta 1993, 212, 241. (e) Wu, L.; Pressprich,
P.; Coppens, P.; De, Marco, M. Acta Crystallogr., Sect. C 1993, 49,
1255. (f) Reynolds, R. A., III; Dunham, W. R.; Coucouvanis, D. Inorg.
Chem. 1998, 37, 1232. (g) C¸ elenligil-C¸ etin, R.; Staples, R. J.;
Stavropoulos, P. Inorg. Chem. 2000, 39, 5838. (h) Overgaard, J.; Hibbs,
D. E.; Rentschler, E.; Timco, G. A.; Larsen, F. K. Inorg. Chem. 2003,
42, 7593.
Reactivity of Iron(II) Chloro- and Bromoacetates.
Compounds 6-9 are not stable in THF: their colorless
solutions turn deep red with kinetics dependent on the
temperature (the reaction is faster at the boiling point of the
(12) (a) Boudalis, A. K.; Lalioti, N.; Spyroulias, G. A.; Raptopoulou, C.
P.; Terzis, A.; Bousseksou, A.; Tangoulis, V.; Tuchagues, J.-P.;
Perlepes, S. P. Inorg. Chem. 2002, 41, 6474. (b) Bacsa, J.; Zhao, H.;
Dunbar, K. R. Acta Crystallogr., Sect. C: Cryst. Struct. Commun.
2003, 59, m561.
(14) Kortu¨m, G.; Vogel, W.; Andrussov, K. Dissociation Constants of
Organic Acids; Butterworth: London, 1961.
(13) (a) Deacon, G. B.; Phillips, R. J. Coord. Chem. ReV. 1980, 33, 227.
(b) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 5th ed.; J. Wiley: New York, 1997; Part
B, p 59.
(15) Belli Dell’Amico, D.; Boschi, D.; Calderazzo, F.; Labella, L.;
Marchetti, F. Inorg. Chim. Acta 2002, 330, 149.
(16) Alcala´, R.; Garc´ıa Ferna´ndez, J. ReV. Acad. Cienc. Exactas, Fis., Quim.
Nat. Zaragoza 1973, 28, 303.
3382 Inorganic Chemistry, Vol. 46, No. 8, 2007

Haloacetate DeriWatiWes of Iron(II)
Scheme 1
Scheme 2
Figure 2. View of the structure of 15. Only one [FeBr4]- anion has been
reported. Thermal ellipsoids are at 20% probability.
route to the synthesis, although in lower yields, of mixed-
valence, tri-iron, oxo-centered compounds, analogous to that
reported in the previous section, which is prepared by direct
oxidation of iron(II) trifluoroacetate with dioxygen.
To investigate this point further, we decided to consider
the reaction of the acetate 5 or, alternatively, of the
trifluoroacetate, 1‚DMF, with a slight excess of CX3COOH
(CX3 ) CCl3, CBr3, CH2Br), in THF solution over longer
periods of time.
By operating under these conditions, we have found that
5 reacts with CCl3COOH or CBr3COOH, yielding 11 or
[Fe3(µ3-O)(CH3COO)5(CBr3COO)(THF)3][FeBr4], 12, re-
spectively (see Scheme 2), coherent with results found for
the decomposition of 7 and 8. The presence of two types of
carboxylates in 12 is proposed on the basis of the IR
spectrum in the 1800-1500 cm-1 region, which contains
bands assigned to the asymmetric and symmetric vibrations
of the two [RCOO]- groups. The reactions of 1‚DMF with
CCl3COOH and of 5 with CH2BrCOOH give similar
outcomes, resulting in formation of the trinuclear complexes
[Fe3(µ3-O)(CCl3COO)6(DMF)(THF)2], 13, and [Fe3(µ3-
O)(CH2BrCOO)6(THF)3][FeBr4], 14, respectively, character-
ized by IR spectroscopy and elemental analysis.
mixture rather than at room temperature), the nature of the
halogen (compound 8 decomposes faster than 9), the number
of halogens (the rate of decomposition increases according
to the sequence CH3 < CH2X < CHX2 , CX3), and the
quantity of residual acid employed in the synthesis (the
decomposition reaction is accelerated by the presence of
excess acid). Reactions are accompanied by formation of
CX4, CX3H, CX2H2 (X ) Cl, Br), and of CH2BrCOOH or
CHCl2COOH in the case of CX3 ) CBr3, CCl3, respectively,
which have been detected by GC-MS analyses carried out
on the reaction mixtures.
Dark red solid residues have been obtained upon removal
of the solvent. Although complicated mixtures of products
have been obtained from 6 and 9, the compounds Fe3(µ3-
O)(CCl3COO)6(THF)3, 11, and [Fe3(µ3-O)(CBr3COO)6(THF)3]-
[FeBr4], 10, have been isolated in satisfactory yields (Scheme
1) and characterized by elemental analysis, IR spectroscopy,
and X-ray diffraction17 (the crystal structure of compound
11 is reported as Supporting Information) in the cases of 7
and 8.
The experimental evidence described above points out that
the degradation of iron(II) chloro- and bromoacetates is a
complicated process which includes C-X bond activation,
redox exchanges involving the metal centers (see the
formation of the [FeBr4]- anion and the presence of Fe(III)
in the final products), and decomposition of the haloacetate
ions (see formation of organohalides). The latter process is
likely to supply the oxygen atom required for the formation
of the µ-oxo-centered products.18 It is noticeable that
decomposition of CX3COOH (X ) Br, Cl) occurs at
considerable rates, in solution, only at high temperatures.19
In other words, the degradation of iron(II) chloro- and
bromoacetates, in inert atmosphere, represents an alternative
Surprisingly, the reaction of 1‚DMF with excess CBr3-
COOH affords a compound not containing carboxylates. It
has been identified by X-ray diffraction as the ionic Fe(II)/
Fe(III) derivative cis-[Fe(DMF)4(THF)2][FeBr4]2, 15 (see
Figure 2); a selection of bond distances and angles is reported
in Table 3. The compound consists of two nearly tetrahedral
[FeBr4]- anions and one cis-[Fe(DMF)4(THF)2]2+ dication,
which possesses a slightly distorted octahedral geometry
(Oaxial-Fe-Oequatorial, 90.7°, mean value; Oequatorial-Fe-
Oequatorial, 175.9°). The ligands coordinated to the dication
are disordered around their Fe-O bonding vector and, in
particular, both the THF ligands and two of the four DMF
ligands have been split into two positions. Rotational disorder
is also displayed by the two [FeBr4]- anions for which the
bromide ligands show high thermal ellipsoids. Two sets of
significantly different Fe-O bond distances are observed:
(17) Low quality crystals have been obtained for the product obtained from
10 in THF. Crystal data: rhombohedral, R3, a ) 15.86(2) Å, c )
14.14(4) Å. Due to the low quality of the diffraction pattern, it has
not been possible to fully solve and refine the structure. Nonetheless,
there is evidence for the presence in the unit cell of three [FeBr4]-
anions and three [Fe3(µ3-O)(CX3COO)6L3]+ cations. The nature of X
and L has not been determined.
(18) Cotton, F. A.; Extine, M. W.; Falvello, L. R.; Beck, Lewis, D.; Lewis,
G. E.; Murillo, C. A.; Schwotzer, W.; Tomas, M.; Troup, J. M. Inorg.
Chem. 1986, 25, 3505.
(19) Howe, R. Carbonic Acid and Its DeriVatiVes in Rodd’s Chemistry of
Carbon Compounds, 2nd ed.; Coffey, S., Ed.; Elsevier Publishing
Company: Amsterdam, 1965; Vol I, Part C, p 268. Grignard, V.;
Dupont, G.; Locquin, R; Baud, P. Traite´ de Chimie Organique; Masson
et Cie: Paris, 1948; p 244.
Inorganic Chemistry, Vol. 46, No. 8, 2007 3383

Marchetti et al.
Table 3. Selected Bond Distances (Å) and Angles (deg) for 15
Conclusions
Fe(1)-O(1)
Fe(1)-O(2)
Fe(1)-O(3)
Fe(2)-Br(1)
Fe(2)-Br(2)
Fe(3)-Br(5)
Fe(3)-Br(6)
2.101(13)
2.105(13)
2.076(12)
2.307(4)
2.319(5)
2.306(4)
2.314(4)
Fe(1)-O(4)
Fe(1)-O(5)
Fe(1)-O(6)
Fe(2)-Br(3)
Fe(2)-Br(4)
Fe(3)-Br(7)
Fe(3)-Br(8)
2.061(13)
2.177(12)
2.146(12)
2.285(6)
2.292(5)
2.327(4)
2.309(4)
By crystallization from CF3COOH/(CF3CO)2O, the poly-
mer [Fe(CF3COO)2(CF3COOH)2]n has been isolated and
characterized by X-ray diffraction: it contains bridging
trifluoroacetates and monodentate trifluoroacetic acid groups
and adds to the restricted family of structurally characterized
compounds containing both a coordinated carboxylic acid
and its conjugate base.4,5
Iron(II) acetates are good starting material for the prepara-
tion of different halocarboxylates by exchange reactions. The
resulting species are not stable in THF solution and
decompose affording, inter alia, mononuclear and trinuclear
µ3-oxo complexes. Although the differences in the product
types, i.e., mononuclear or trinuclear, cationic or neutral, are
not easy to rationalize, the experimental results evidence
the low tendency of the tribromoacetate anion to act as a
ligand and the fact that extensive oxidation of the metal
centers is favored by those haloacetates containing the
heavier halide.
Analogous results can be achieved by reacting iron(II)
acetate (or trifluoroacetate) with haloacetic acids. All of these
reactions are accelerated upon increasing the following
parameters of (i) temperature, (ii) atomic weight of the
halogen on the R-carbon atom, (iii) number of halogens (CH3
< CH2X < CHX2 , CX3), and (iv) quantity of acid
employed. The nature of the isolated compounds strongly
suggests that the decompositions occur via C-X bond
activation and haloacetato degradation and that these pro-
cesses are accompanied by concomitant oxidation at the
metal centers. This hypothesis is confirmed by the detection
of various organohalide species in the final solutions. Similar
arguments were invoked to explain the instability of some
copper(I) haloacetates.4
O(4)-Fe(1)-O(3)
O(4)-Fe(1)-O(1)
O(3)-Fe(1)-O(1)
O(4)-Fe(1)-O(2)
O(3)-Fe(1)-O(2)
O(1)-Fe(1)-O(2)
O(4)-Fe(1)-O(6)
O(3)-Fe(1)-O(6)
O(1)-Fe(1)-O(6)
O(2)-Fe(1)-O(6)
O(4)-Fe(1)-O(5)
O(3)-Fe(1)-O(5)
O(1)-Fe(1)-O(5)
O(2)-Fe(1)-O(5)
173.9(6)
92.8(6)
91.2(5)
91.4(6)
92.8(6)
93.4(5)
86.8(5)
88.8(5)
88.3(5)
177.6(5)
89.5(6)
86.3(5)
176.9(5)
88.6(5)
O(6)-Fe(1)-O(5)
Br(3)-Fe(2)-Br(4)
Br(3)-Fe(2)-Br(1)
Br(4)-Fe(2)-Br(1)
Br(3)-Fe(2)-Br(2)
Br(4)-Fe(2)-Br(2)
Br(1)-Fe(2)-Br(2)
Br(5)-Fe(3)-Br(8)
Br(5)-Fe(3)-Br(6)
Br(8)-Fe(3)-Br(6)
Br(5)-Fe(3)-Br(7)
Br(8)-Fe(3)-Br(7)
Br(6)-Fe(3)-Br(7)
89.8(5)
109.5(3)
111.9(2)
108.86(19)
106.1(2)
110.8(2)
109.62(19)
109.56(19)
108.20(17)
110.33(18)
111.35(17)
109.37(18)
108.02(17)
the Fe-OTHF distance is 2.161 Å (mean value) compared
with the Fe-ODMF distance of 2.085 Å (mean value). The
overall geometry of the [Fe(DMF)4(THF)2]2+ cation re-
sembles that reported in the literature for iron(II) cations of
general formula [FeL6]2+, which are well-known for L )
DMF20 and L ) THF.21
As far as the [FeBr4]- anion is concerned, the mean value
of the Fe-Br distances (2.307 Å) is in the same range
observed for [p-EtC5H5NH][FeBr4],22 [(N,N′-CH3)2C4H8]]-
[FeBr4]2,23 [Fe(η5-C5H5)2][FeBr4],24 [(Ph3PO)2H][FeBr4],25
and [Mo(η5-C6H6)2][FeBr4].26
A GC-MS control, performed on solutions at the end of
each reaction, indicated the presence of CX3COOH (X )
H, F). This fact suggests that acetate (or trifluoroacetate)
exchange has probably occurred, followed by degradation
of the formed iron(II) haloacetate. GC-MS detection of the
organohalides CX4, CX3H, and CX2H2 (X ) Br, Cl),
oxidation of the iron atoms, and C-X bond activation are
in agreement with this hypothesis.
Acknowledgment. The authors wish to thank the Min-
istero dell’ Istruzione, dell’ Universita` e della Ricerca
(MIUR, Roma), Programma di Ricerca Scientifica di Notev-
ole Interesse Nazionale 2004-5 for financial support. Prof.
M. Monari, University of Bologna, is gratefully acknowl-
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11.
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Supporting Information Available: Crystallographic informa-
tion files (CIF) for the crystal structures of compounds 2, 3, 4, 11,
and 15. This material is available free of charge via the Internet at
http://pubs.acs.org. Crystallographic data of compounds 2 (CCDC
634719), 3 (CCDC 634718), 4 (CCDC 634717), 11 (CCDC
634716), and 15 (CCDC 634715) have been deposited with the
Cambridge Crystallographic Data Centre. Copies can be obtained
free of charge from: The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (Fax, 441223336033; e-mail, deposit@
ccdc.cam.ac.uk; or WWW, http://www.ccdc.cam.ac.uk).
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3384 Inorganic Chemistry, Vol. 46, No. 8, 2007