Structure of bromotrinitrosyl iron, [Fe(NO)3Br], and DFT calculations of the structures of [Fe(NO)3X] (X = Cl, Br, I)

Article abstract of DOI:10.1002/zaac.200500415

Bromotrinitrosyl iron was prepared by passing a stream of nitrogen monoxide over a mixture of iron dibromide and iron powder at elevated temperatures. It readily loses NO to give [(ON)₂Fe(μ-Br)Fe(CO)₂]. The structure of freshly obtained [Fe(NO)₃Br] was determined by X-ray diffraction at 200 K and shows (distorted) tetrahedral coordination with N-Fe-N and N-Fe-Br angles of 107.9(2)° and 111.0(2)° and bent Fe-N-O groups (162.5(6)°). The DFT calculations in the series [Fe(NO)₃X] (X = Cl, Br, I) reproduce well the experimental structural parameters and vibrational frequencies.

Full text of DOI:10.1002/zaac.200500415

DOI: 10.1002/zaac.200500415
Structure of Bromotrinitrosyl Iron, [Fe(NO) Br], and DFT Calculations of the
3
Structures of [Fe(NO) X] (X ؍ Cl, Br, I)
3
Wolfgang Beck*, Thomas M. Klapötke* and Peter Mayer
Munich, Department of Chemistry and Biochemistry, Ludwig-Maximilian Universität
Received October 19th, 2005.
Dedicated to the Memory of Professor Reinhard Nast (1912Ϫ2004)
Abstract. Bromotrinitrosyl iron was prepared by passing a stream
of nitrogen monoxide over a mixture of iron dibromide and iron
powder at elevated temperatures. It readily loses NO to give
3
groups (162.5(6)°). The DFT calculations in the series [Fe(NO) X]
(X ϭ Cl, Br, I) reproduce well the experimental structural para-
meters and vibrational frequencies.
[(ON)
2
2
Fe(µ-Br)Fe(CO) ]. The structure of freshly obtained
[
Fe(NO)
3
Br] was determined by X-ray diffraction at 200 K and
shows (distorted) tetrahedral coordination with NϪFeϪN and
NϪFeϪBr angles of 107.9(2)° and 111.0(2)° and bent FeϪNϪO
Keywords: Nitrosyl; Iron; Bromide; Halide; Crystal structure;
DFT calculations
Introduction
The halo bridged dimers, [(ON) Fe(µ-X) Fe(NO) ] (X ϭ
Cl, I) with an FeϪFe bond which often has been used for
2
2
2
various reactions and as catalysts (see ref. [1]) have been
Recently, the interesting history and development of the
chemistry of nitrosyl iron halides was reviewed [1] and the
prepared in good yields from FeX /Fe and NO and sub-
2
sequent sublimation in vacuo [6Ϫ8].
structures of the trinitrosyl iron complexes [Fe(NO) Cl] [2]
3
and [Fe(NO) I] [1] were determined by X-ray diffraction.
3
In the following we report on the formation and structural
Results and Discussion
characterization of [Fe(NO) Br]. DFT theoretical studies
3
were carried out in order to compare the structural para-
The title complex was obtained by leading a stream of puri-
fied nitrogen monoxide over a mixture of anhydrous iron
dibromide and iron powder at ϳ150 °C. Fine black needles
sublimed in a slow NO stream and were immediately used
for X-ray structural determination and for IR spectra.
meters in the series [Fe(NO) X] (X ϭ Cl, Br, I). The first
3
evidence for the existence of the unstable trinitrosyl iron
bromide was observed by Fischer [3] by passing nitrogen
monoxide over solid, anhydrous FeBr and the product con-
2
tained clearly more than 2 mol NO per mol Fe. The com-
plex [Fe(NO) Br] was isolated from the reaction of
3
[
Fe(CO) Br ] and NO as black fine needles, which sublime
4 2
in an NO stream and easily lose nitrogen monoxide [4].
Similarly, the iodo and chloro complexes are formed from
tetracarbonyldihalo iron [Fe(CO) X ], and NO ([4] and ex-
4
2
perimental part). In this work we used a mixture of an-
hydrous FeBr and Fe powder as starting materials for the
2
reaction with NO. Firstly, Nast [5] succeeded in isolating
chlorotrinitrosyl iron, [Fe(NO) Cl], by passing NO over a
3
mixture of anhydrous FeCl and Fe powder at elevated tem-
2
peratures.
*
*
Prof. Dr. Wolfgang Beck,
Prof. Dr. Thomas M. Klapötke,
Department Chemie und Biochemie LMU München
Butenandtstr. 5Ϫ13
D-81377 München
E-mail: wolfgang.beck@cup.uni-muenchen.de
thomas.m.klapoetke@cup.uni-muenchen.de
3
Figure 1 Molecular structure of [Fe(NO) Br] in the crystal
Z. Anorg. Allg. Chem. 2006, 632, 417Ϫ420
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
417

W. Beck, Th. M. Klapötke, P. Mayer
FeBr
2
ϩ Fe ϩ 6 NO Ǟ 2[Fe(NO)
3
Br]
tetrahedral coordination (Fig.1). In the series Cl Ǟ Br Ǟ I,
with increasing FeϪX bond lengths the FeϪNϪO and
NϪFeϪN angles become larger and the NϪFeϪX angles
become smaller. The environment at the Fe atom in the
iodo complex is closer to tetrahedral geometry. The bending
of the FeϪNϪO groups (Table 1) which were also found
in [(ON) Fe(µ-I) Fe(NO) ] [6] was verified by theoretical
2[Fe(NO)
3
Br] Ǟ [(ON) Fe(µ-Br) Fe(NO) ] ϩ 2 NO
2
2
2
The IR spectra (CH Cl solution) clearly showed the two
ν˜ NO absorptions of [Fe(NO) Br] at 1899 cm (A ) and at
2
2
Ϫ1
3
1
Ϫ1
1794 cm (E). The ratio of the intensities of the two NO
2
2
2
absorptions (1/7.9) is typical for a tetrahedral M(NO)3
group [9] and an angle between the NO groups of 109 °C
can be calculated from this ratio (assuming linear FeϪNϪO
groups [10]. Besides the ν˜ NO absorptions of [Fe(NO) Br]
two additional NO absorptions at 1817 and 1766 cm ap-
considerations [2, 13, 14].
Summerville and Hoffmann [13] noticed for nitrosyl com-
plexes
MϪNϪO bending which is also observed in the
Fe(NO) X] series. With decreasing NϪFeϪN angles an in-
a correlation between NϪMϪN angles and
3
Ϫ1
[
3
peared which can be attributed to the dimer [(ON) Fe-
2
crease of FeϪNϪO bending is found (Table 1). For a large
series of dinitrosyl complexes a distinct linear correlation
between the non bonding O···M···O angles and the
NϪMϪN bond angles has been demonstrated [14] and this
(µ-Br) Fe(NO) ] [11] which is easily formed by the loss of
2 2
NO from [Fe(NO) Br] as was also observed by
Kramolowsky [12] in the reaction of [Fe(NO) Br] witch
PPh3 which gives the dinitrosyl complex [Fe(NO)2-
3
3
trend is observed also for [Fe(NO) X] (X ϭ Br, I) (Table 1).
3
(PPh )Br], OPPh and N O. Solid [Fe(NO) Br] can only be
3 3 2 3
DFT calculations by Legzdins et al. [2] on [(ON) FeFBF ] con-
3
3
stored without decomposition for some days under an at-
mosphere of NO.
The title complex crystallizes in the same trigonal space
group P6 mc (Table 2) as do [Fe(NO) Cl] [2] and
firm, that bent FeϪNϪO links have an electronic origin
and can be explained by MO theory.
3
3
[
Fe(NO) I] [1]. The crystallographically imposed 3-fold axis
DFT Calculations on [Fe(NO) X] (X ؍ Cl, Br, I)
3
3
makes all three FeϪNϪO groups equivalent. The cell vol-
ume and the structural parameters of [Fe(NO) Br] lie be-
tween those of [Fe(NO) X] (X ϭ Cl, I) (Table 1). The
[
The DFT calculations carried out in this work showed very
good agreement with the experimental structural data, es-
pecially for the FeϪX bond length (Table 3). Moreover, the
trends in the series Cl Ǟ Br Ǟ I are well reproduced for
3
3
Fe(NO) X] molecules (X ϭ Cl, Br, I) show (distorted)
3
˚
˚
3
Table 1 Bond lengths /A and angles /° and cell volumes /A of
Fe(NO) X]
[
3
3
Table 3 Experimental and computational data for [Fe(NO) X]
X
N-O
Fe-N
Fe-X
Fe-N-O N-Fe-N N-Fe-X O···Fe···O V
Cl
Br
I
p.g.
C
3ν
C
3ν
C
3ν
Cl 1.152(5) 1.702(4) 2.252(2) 161.5(4) 106.5(2) 112.3(2) Ϫ
Br 1.154(7) 1.705(5) 2.388(2) 162.5(6) 107.9(2) 111.0(2) 99.6(2) 288.20(3)
1.145(6) 1.706(4) 2.588(2) 165.5(6) 110.3(2) 108.6(2) 104.6 (1) 317.66(5)
268.9(1)
˚
d(Fe-X) / A
exptl.
B3LYP/ECP
2.252(2)
2.256
2.388(2)
2.4047
2.588(2)
2.615
I
a
a
a
a
˚
d(Fe-N) / A
exptl.
B3LYP/ECP
1.702(4)
1.661
1.705(5)
1.659
1.706(4)
1.657
3
Table 2 Crystallographic Data of [Fe(NO) Br]
˚
d(N-O) / A
exptl.
B3LYP/ECP
formula
BrFeN
225.77
200(2)
3 3
O
1.152(5)
1.143
1.154(7)
1.143
1.145(6)
1.143
formula weight
temperature / K
crystal system
space group
hexagonal
P6 mc
<
exptl.
(Fe-N-O) /°
3
161.5(4)
167.6
162.5(6)
170.4
166.5(6)
174.5
˚
a /A
7.2950(4)
7.2950(4)
6.2533(3)
288.20(3)
2
9.470
2.602
B3LYP/ECP
˚
b /A
˚
<(N-Fe-N) /°
exptl.
B3LYP/ECP
c /A
˚
3
106.5(2)
111.1
107.9(2)
112.7
110.3(2)
115.0
volume /A
z
absorption coefficient/min
density calc./Mg/m3
F(000)
a
Ϫ1
<
exptl.
(N-Fe-X) /°
112.3(2)
107.8
111.0(2)
106.0
108.6(2)
103.1
212
a
B3LYP/ECP
range (theta)/°
index ranges
3.22 Ϫ 27.43
Ϫ 8 Յ h Յ 9, Ϫ9 Յ k Յ k, Ϫ7 Յ l Յ 7
reflections collected
reflections unique
data / restraints / parameters
GOOF
3097
ν(N-O), E / cm1
265 [R(intl ϭ 0.0927]
265/1/20
1.102
0.0319
0.0720
0.0280
0.0699
1
1
789
893 (3030)
1794
1899 (3100)
1798
1901(3140)
R
1
(all data)
wR (all data)
[I > 2 σ (I)]
wR (I > 2 σ (I)]
absolute structure parameter
ν (N-O), A
l
/ cm1
2
1898
1993 (398)
1899
1993 (412)
1895
1991 (475)
R
1
2
zpe / kcal molϪ1
-EB3LYP / a.u.
15.8
15.8
15.9
0.51(3)(racemic twin refinement)
0.539 and Ϫ0.307
˚
Ϫ3
largest diff. peak and hole / e·A
974.096588
527.261044
525.300853
418
zaac.wiley-vch.de
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 417Ϫ420

3
Structure of Bromotrinitrosyl Iron, [Fe(NO) Br]
the FeϪN bond length and also for the FeϪNϪO,
NϪFeϪN and NϪFeϪX bond angles. The calculated ν˜ NO
wavenumbers are by ϳ100 cm higher than the experimen-
tal values and agree well if a linear scaling factor of 0.95
is applied.
B3LYP level of theory, using Becke’s three parameter functional
where the local and non-local correlation is provided by the LYP
(the correlation functional of Lee, Yang, Parr) expression [19Ϫ21].
For N, O and Cl a polarized valence triple-zeta basis set of the type
Ϫ1
6-311G(2df) was used.
For iron, bromine and iodine energy-consistent pseudopotentials
were used [22]. The energy-consistent pseudopotentials of the
Stuttgart/Cologne group are semi-local pseudopotentials adjusted
to reproduce atomic valence-energy spectra. The adjustment of the
pseudopotential parameters has been done in fully numerical calcu-
lations, valence basis sets have been generated a-posteriori via en-
ergy optimization. In this study we used quasirelativistic multielec-
tron-fit Wood-Boring (MWB) pseudopotentials for bromine
Experimental Section
3 2 3
[Fe(NO) Br] from FeBr /Fe and NO [Fe(NO) Br] was synthesized
using the apparatus described earlier [5, 15]. A slow stream of puri-
fied (using 50 % KOH solution and solid NaOH) nitrogen monox-
ide (Aldrich) was passed through a glass tube over a ceramic con-
2
tainer with a mixture of ϳ 2g anhydrous, sublimed FeBr and
excess Fe powder (Aldrich). The electric oven was heated to
ϳ150 °C and then allowed to cool down to ϳ100 °C within 3 h.
Black fine needles sublimed to the colder part of the tube which
were collected under NO atmosphere and immediately used for
X-ray structure determination and IR spectra.
(
ECP28MWB) [23] and iodine (ECP46MWB) [23] and a relativistic
multielectron-fit Dirac-Fock (MDF) potential for iron
ECP10MDF) [24].
(
The bromine (7), iodine (7) and iron (16) valence electrons were
treated with valence basis sets of the following contraction: Br,
(14s10p2d1f)/[3s3p2d1f]; [25]; I,(14s10p3d1f)/[3s3p2d1f] [8]; Fe,
IR spectra (Perkin Elmer Spectrum One, CH
899 w ([Fe(NO) Br]); 1766 w, 1817 w ([Fe (NO)
cm (decomposition product?).
2
Cl
2
): νNO ϭ 1794 vs,
1
3
2
4
Br ]); 1735 w-m,
2
Ϫ1
(
8s7p6d1f)/[6s5p3d1f] [24].
[
Fe(NO) Br] from [Fe(CO) Br ] and NO (see [4])
Acknowledgements. We are grateful to the Ludwig-Maximilian
University Munich and to Wacker-Chemie, München for support.
We thank Dr. Armin Enzmann and Gunnar Spiess for valuable help.
3
4
2
A slow stream of purified NO (from NaNO
Kipp apparatus was passed over a vessel with a mixture of ϳ1 g
Fe(CO) Br ] [16] and excess iron powder (from Fe(CO) ) in a glass
2 2 4
and 50 % H SO in a
[
4
2
5
tube which was heated to 60 °C. NO is consumed. If the heating is
made to quickly, sudden reaction with glowing of the solid may
occur. When the consumption of NO is finished the temperature is
raised to 115 °C. After 6 h bright, 1Ϫ2 cm long, black needles were
sublimed to the colder part of the tube in a slow stream of NO.
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Z. Anorg. Allg. Chem. 2006, 417Ϫ420