Pyridylmethylamines as ligands in iron halide complexes - Coordination behaviour depending on the halide, the denticity of the amino ligand and the oxidation state of iron

Article abstract of DOI:10.1002/zaac.200600200

2-Pyridylmethylamine (amp) and 8-aminochinoline (ach) readily form the following complexes with iron halides in methanol: [(amp)₂FeCl ₂] (1a), [(amp)₂FeBr₂] (1b), [(ach) ₂Fe(MeOH)₂]Br₂ (1c), and [(amp)FeCl ₂(μ-OMe)]₂ (2). Methanol was chosen as a solvent because these reactions are rather complex in ether. For example, FeCl ₃ forms the ionic complex pair [(dme)₂FeCl₂] [FeCl₄] (3) with 1,2-dimethoxyethane (dme). The reaction of FeBr ₂ with tridentate di(2-pyridylmethyl)amine (dpa) and tetradentate 1,2-dipyridyl-1,2-diaminoethane (dpdae) yields the complexes [(dpa) ₂Fe]Br₂·2 MeOH (4) and [(dpdae)₂Fe] [FeBr₄] (5), respectively. Crystallographic and magnetochemical investigations show the high-spin configuration for the complexes 1 and 2, whereas the short Fe-N distances of 4 clearly indicate a low-spin state. Compound 2 exhibits an antiferromagnetic exchange interaction with a coupling constant J = -29.4cm^-1 (H;af = -J S;af_A·S;af _B).

Full text of DOI:10.1002/zaac.200600200

DOI: 10.1002/zaac.200600200
Pyridylmethylamines as Ligands in Iron Halide Complexes ؊ Coordination
Behaviour Depending on the Halide, the Denticity of the Amino Ligand and the
Oxidation State of Iron
Astrid Malassa, Helmar Görls, Axel Buchholz, Winfried Plass, and Matthias Westerhausen*
Jena, Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität
Received June 28th, 2006.
Abstract. 2-Pyridylmethylamine (amp) and 8-aminochinoline (ach)
readily form the following complexes with iron halides in methanol:
[(amp)2FeCl2] (1a), [(amp)2FeBr2] (1b), [(ach)2Fe(MeOH)2]Br2 (1c),
and [(amp)FeCl2(µ-OMe)]2 (2). Methanol was chosen as a solvent
because these reactions are rather complex in ether. For example,
FeCl3 forms the ionic complex pair [(dme)2FeCl2] [FeCl4] (3) with
1,2-dimethoxyethane (dme). The reaction of FeBr2 with tridentate
di(2-pyridylmethyl)amine (dpa) and tetradentate 1,2-dipyridyl-1,2-
diaminoethane (dpdae) yields the complexes [(dpa)2Fe]Br2·2
MeOH (4) and [(dpdae)2Fe] [FeBr4] (5), respectively. Crystallo-
graphic and magnetochemical investigations show the high-spin
configuration for the complexes 1 and 2, whereas the short Fe-N
distances of 4 clearly indicate a low-spin state. Compound 2
exhibits an antiferromagnetic exchange interaction with a coupling
constant J ϭ Ϫ29.4 cmϪ1 (H;af ϭ ϪJ S;afA·S;afB).
Keywords: Iron; Pyridyl complexes; Amino complexes; Pyridyl-
methylamines
Introduction
These halide anions can also be substituted by nitrate if a
stoichiometric amount of NaNO3 is added to a methanol
solution of (H2O)2FeCl2 [5].
Iron plays a key role in many metalloenzymes such as
lipoxygenases and methane monooxygenases. These non-
hem iron enzymes are able to oxidize unsaturated fatty ac-
ids or methane with oxygen after activation of the appropri-
ate C-H bonds. Furthermore, iron enzymes such as hemer-
ythrin are responsible for the transport of oxygen. In all
these metalloenzymes, the iron atoms are in an octahedral
environment and partly coordinated by histidine groups.
Therefore, in many biomimetic complexes, pyridine ligands
are employed to mimic the reactivity of these iron enzymes.
Iron(II) readily forms the octahedral tris(2-pyridyl-
methylamine)iron(II) cation with couterions such as halide,
perchlorate, or hexafluorophosphate [1]. These complexes
show magnetic isomerism: With raising temperature the
low-spin state changes into the high-spin state. Last year,
Törnroos et al. [2] published the neutral complex dichloro-
bis(2-pyridylmethylamine)iron(II). The complexes with cis
and the trans arrangement of the chloro substituents
cocrystallized from 1-butanol. Other alcohols such as meth-
anol [3], ethanol [4], propanol, tert-butyl alcohol and allyl
alcohol lead to a substitution of the chloride ligands [3].
The tridentate ligand di(2-pyridylmethyl)amine forms the
solvent-separated ion pair dichloro-bis(2-pyridylmethyl)-
amine]iron(II) [6], the iron atom shows low-spin configura-
tion of the iron(II) center. A coordination at iron(III) leads
only to an addition of this ligand and the formation of
trichloro(2-pyridylmethyl)amine]iron(III) [7]. Iron(III) is
also able to oxidize C-N bonds of the similar ligand N-(2-
pyridyl)methyl]pyridine-2-carboxamide [8]. It is well-known
since decades that alkylamides of the late transition metals
are not very stable [9]. Due to the oxidation force of iron
there are also only very few examples of amides. An excep-
tion are the trialkylsilyl substituted amides. Thus, only the
bis(trimethylsilyl)amides of iron(II) and iron(III) [10, 11] as
well as the extremely reactive (2-pyridylmethyl)(trialkyl-
silyl)amides of iron(II) [12] are well-known. In order to
compare the 2-pyridylmethylamides with the corresponding
amines we prepared a series of compounds with bidentate
2-pyridylmethylamine, tridentate di(2-pyridylmethyl)amine
and 1,2-dipyridyl-1,2-diaminoethane.
Results and Discussion
* Prof. Dr. M. Westerhausen
Institut für Anorganische und Analytische Chemie
Friedrich-Schiller-Universität Jena
August-Bebel-Str. 2
D-07743 Jena, Germany
Tel.: ϩ49 (0) 3641 948110
Synthesis
The THF adducts of FeCl2 and FeBr2 reacted with 2-
pyridylmethylamine (amp) in methanol to give the bis(amp)
complexes with the halide ligands in trans arrangement ac-
cording to equation 1. The complexes [(amp)2FeX2] with
X ϭ Cl (1a) and Br (1b) formed regardless of the chosen
Fax: ϩ49 (0) 3641 948102
e-mail: m.we@uni-jena.de
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A. Malassa, H. Görls, A. Buchholz, W. Plass, M. Westerhausen
stoichiometry of the starting materials in the shape of
yellow cuboids and yellow-green platelets, respectively. A
similar reaction of [(thf)2FeBr2] with less flexible 8-amino-
chinoline (ach) led also to the 1:2 complex 1c, however, the
bromide ions were substituted by the solvent molecules,
giving an ion triple with the [(ach)2(MeOH)2Fe]2ϩ cation.
Formula 2
[(dpdae)2Fe]2ϩ [FeBr4]2Ϫ (5) in the shape of orange-red
platelets, regardless of the stoichiometry of the starting
materials. The iron(II) ion of the cation is in a distorted
octahedral environment whereas the the anion forms a
[FeBr4]2Ϫ tetrahedron.
Formula 1
Molecular Structures
The reaction of FeCl3 with Amp in methanol gave the
dimeric complex 2 with the methanolate anions in the
bridging positions. The single crystals appeared to be light
brown, in pulverized form they were yellow. A powder dif-
fractogram confirmed that these substances were identical.
If the solvent was changed to an ether the reaction of FeCl3
with Amp gives no pure products but an inseparable mix-
ture. In order to understand the difficulties arising from the
solvent change, the ether adduct was investigated. Anhy-
drous iron(III) chloride was dissolved in hot 1,2-dimethoxy-
ethane (dme). During cooling to room temperature, orange
platelets of [(dme)2FeCl2]ϩ [FeCl4]Ϫ (3) precipitated.
Whereas FeCl3 formed a 1:1 complex with di(2-pyridyl-
methyl)amine (dpa) [7], FeCl2 and dpa yielded the 1:2 com-
pound [6]. The reaction of [(thf)2FeBr2] with Dpa gave the
1:2 complex 4 according to equation 2 regardless of the
stoichiometry of the starting materials. This compound pre-
cipitated in the shape of red platelets. The crystalline com-
pound contains methanol molecules in the cavities between
the iron(II) complexes.
The compounds of the type (amp)2FeX2 with X as Cl (1a)
and Br (1b) show the same molecular inversion symmetry,
however, they crystallize in different space groups. Data of
these complexes are listed in Table 1 together with those
of [(ach)2Fe(MeOH)2]Br2 (1c) in comparison to well-known
compounds [2, 5]. The compounds 1a, 1b and 1c are rep-
resented in Figures 1, 2 and 3, respectively.
The centrosymmetric compounds of the type
[(amp)2FeX2] are very similar: The bite angle N1-Fe-N2 of
all of these compounds is very small and varies between
75.7° and 79.6°. Due to these small angles, the octahedral
geometry at the iron centers is distorted. The Fe-N bonds
vary between 215 and 220 pm for the amino group as well
as for the pyridyl ligand. The data of the 8-aminochinoline
complex 1c fit very well into this scheme. For the C2-sym-
metric cis-[(amp)2FeCl2], the Fe-N bond lengths are slightly
elongated but here the Fe-Cl distances are smaller [2]. An
exception is the nitrate [(amp)2Fe(NO3)2] [5], which shows
very short Fe-N bonds. On the other hand, the Fe-O dis-
tances to the monodentate nitrate anion are extremely large
despite an electrostatic attraction. Even the neutral meth-
anol molecule in 1c shows a closer contact to the iron(II)
center (214.1(2) pm) than the nitrate with a value of
Due to steric strain the tetradentate ligand 1,2-dipyridyl-
1,2-diaminoethane (dpdae) cannot bind with all of the ni-
trogen donor atoms to a single metal atom. The reaction of
[(THF)2FeBr2] with dpdae yielded the ion pair
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Pyridylmethylamines as Ligands in Iron Halide Complexes
Table 1 Selected bond lengths/pm and angles/° of [(Amp)2FeX2] and related complexes in comparison to literature data.
[(amp)2FeX2]
[(amp)2FeX2]
[(amp)2FeX2]
[(amp)2FeX2]
[(amp)2FeX2]
[(ach)2FeX2]
X
Fe-X
Fe-N1
Fe-N2
N1-Fe-N2
N1-Fe-X
Cl (1a)
Br (1b)
Cl (trans) [2]
249.39(4)
217.5(1)
219.7(1)
77.13(5)
Cl (cis) [2]
246.13(5)
222.0(1)
222.7(1)
75.68(5)
91.76(4)
99.68(4)
91.94(5)
89.77(4)
167.06(4)
NO3 [5]
229.7(4)
212.8(6)
207.6(5)
79.6(2)
MeOH (1c)
214.1(2)
219.4(2)
218.6(2)
76.77(8)
93.20(7)
250.08(6)
218.5(2)
218.9(2)
76.57(8)
90.25(5)
273.86(4)
215.1(3)
217.2(3)
77.9(1)
87.08(7)
89.57(4)
88.8(2)
N1-Fe-N2 Ј
N2-Fe-X
103.43(8)
89.19(6)
102.2(1)
92.04(9)
102.87(5)
91.35(4)
100.4(2)
94.2(2)
103.23(8)
93.14(8)
Fig. 1 Molecular structure of [(amp)2FeCl2] (1a). The ellipsoids
represent a probability of 30 %. The N-bound hydrogen atoms are
represented with arbitrary radii, all other H atoms are neglected
for clarity reasons.
Fig. 3 Molecular structure of [(ach)2Fe(MeOH)2]Br2 (1c). The
ellipsoids represent a probability of 30 %. The N- and O-bound
hydrogen atoms are drawn with arbitrary radii, all other H atoms
are neglected for clarity reasons.
Fig. 4 Molecular structure of [(dme)2FeCl2] [FeCl4] (3). The ellip-
soids represent a probability of 30 %. The H atoms are neglected
for clarity reasons.
Selected bond lengths/pm: Fe1-Cl1 222.26(8), Fe1-O1 212.7(2),
Fe1-O2 207.4(2), Fe2-Cl2 220.0(1), Fe2-Cl3 219.7(1), Fe2-Cl4
218.95(9); angles/°: O1-Fe-O2 78.07(7), Cl1-Fe1-Cl1A 100.85(5).
Fig. 2 Molecular structure of [(amp)2FeBr2] (1b). The ellipsoids
represent a probability of 30 %. The N-bound hydrogen atoms are
shown with arbitrary radii, all C-bound H atoms are omitted for
clarity reasons.
229.7(4) pm [5]. These Fe-N bond lengths show a character-
istic elongation of approximately 20 pm compared with
low-spin complexes. For example, the octahedral complex
[Fe(Py-C(O)-N-C6H4-S-CH2)2] shows average Fe-N dis-
tances of 196.8 pm for the pyridyl unit and of 197.3 pm for
the amido fragment [13].
lengths of approximately 220 pm whereas those of the octa-
hedral cation (Fe1-Cl1) are slightly increased. Due to the
high-spin configuration no distortion can be expected for
the anion. The cation shows two different Fe1-O distances
to the ether ligand (207.4(2) and 212.7(2) pm). Due to the
higher oxidation state of the iron atom, these values are
smaller than for the methanol-iron contact in 1c.
Figure 4 shows the molecular structure of [(dme)2FeCl2]ϩ
[FeCl4]Ϫ (3) as well as selected structural parameters. The
tetrahedral tetrachloroferrate(III) anion shows Fe2-Cl bond
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A. Malassa, H. Görls, A. Buchholz, W. Plass, M. Westerhausen
Fig. 7 Molecular structure of [(dpdae)2Fe] [FeBr4] (5). The ellip-
soids represent a probability of 30 %. The N-bound hydrogen
atoms are drawn with arbitrary radii, all C-bound H atoms are
neglected for clarity reasons.
Selected bond lengths/pm: FeA-N1A 206.6(6), FeA-N3A 207.8(6),
FeA-N4A 210.5(6), Fe-Br1 240.3(1), Fe-Br2 238.7(1), Fe-Br3
242.7(1), Fe-Br4 246.0(1); angles/°: N1A-FeA-N3A 80.7(2), N1A-
FeA-N4A 82.9(2), N3a-FeA-N4A 79.0(2).
Fig. 5 Molecular structure of [(amp)2FeCl2(µ-OMe)]2 (2). The el-
lipsoids represent a probability of 30 %. The N-bound hydrogen
atoms are represented with arbitrary radii, all other H atoms are
neglected for clarity reasons.
Selected bond lengths/pm: Fe-Cl1 236.69(8), Fe-Cl2 230.37(7), Fe-
N1 216.4(2), Fe-N2 217.4(2), Fe-O1M 195.5(2), Fe-O1MA
203.3(2); angles/°: N1-Fe-N2 75.69(9), N1-Fe-Cl1 93.27(6), N1-Fe-
Cl2 95.20(5), Fe-O1M-FeA 104.44(7).
nuclear unit the Fe3ϩ ions are symmetrically bridged by two
methanolate groups with Fe-O bond lengths of 195.5(2) and
203.3(2) pm, which are within the usually observed range
[14, 15]. Moreover, also the bond angle at the bridging oxy-
gen atom with 104.44(7)° is found within the expected
range. The Fe-N bonds are only slightly shortened com-
pared to the iron(II) derivatives discussed earlier. The two
chlorine atoms are in a cis-arrangement and show distances
to the iron center of 230.37(7) and 236.69(8) pm, which are
drastically smaller than those listed in Table 1 for iron(II)
complexes.
The molecular structure of [(dpa)2Fe]Br2·2 MeOH (4) is
represented in Figure 6 and is very similar to the structure
of the corresponding chloride complex which was described
earlier by Davies et al. [6]. The Fe-N bond lengths of 4 lie at
199 and 203 pm for the pyridyl unit and the amino moiety,
respectively. The smaller distance to the pyridyl groups re-
sults from a higher s-orbital participation at the nitrogen
atom. The magnetic measurements confirm the low-spin
state of this complex in agreement with the investigations
of Davies et al. [6].
Figure 7 shows the molecular structure of [(dpdae)2Fe]2ϩ
[FeBr4]2Ϫ (5). The Fe-N bonds lengths show values of
206.6(6) pm for the pyridyl fragment and 207.8(6) and
210.5(6) pm for the amino functions. The fused five-mem-
bered metallacycles induce intramolecular strain and lead
to the variation of these values. Due to this fact, small bite
angles N-Fe-N between 79 and 83° are observed and reflect
the deviation from an octahedral geometry at the iron
center.
The tetrahedral tetrabromoferrate(II) anion displays an
average Fe-Br distance of 241.9 pm which is smaller than in
the octahedral complex 1b. A comparison with the very few
literature-known tetrabromoferrate(II) (average Fe-Br
244 pm [16] and 245 pm [17]) and the very common tetra-
bromoferrate(III) anions (average Fe-Br bond length
232 pm, min./max. Fe-Br distances 228/238 pm) allows an
Fig. 6 Molecular structure of the centrosymmetric [(dpa)2Fe]2ϩ
cation of 4. The ellipsoids represent a probability of 30 %. The N-
bound hydrogen atoms are represented with arbitrary radii, all
other H atoms are neglected for clarity reasons.
Selected bond lengths/pm: Fe-N1 199.2(4), Fe-N2 203.1(4), Fe-N3
199.5(4); angles/°: N1-Fe-N2 83.4(2), N1-Fe-N3
, N2-Fe-N3
82.9(2), N1-Fe-N2A 96.6(2), N1-Fe-N3A 94.4(2), N2-Fe-N3A.
The molecular structure of the centrosymmetric di-
nuclear complex 2 is represented in Figure 5. In the di-
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Pyridylmethylamines as Ligands in Iron Halide Complexes
is illustrated in Figure 8 and corresponds to a coefficient of
determination of r2 ϭ 0.99997.
The observed antiferromagnetic interaction between the
high-spin iron(III) ions is consistent with the usually ob-
served superexchange through alcoholate bridges [14, 19].
Moreover, for dinuclear iron(III) units bridged by ligand
oxygen atoms (oxo, hydroxo, alkoxo, etc.) a magnetostruc-
tural correlation has been established between the magnetic
coupling and the shortest superexchange pathway between
the iron(III) ions [15]. For 2 this shortest average length of
the coupling pathway is <Fe-O> ϭ 199.4 pm, leading to a
predicted coupling constant of J ϭ Ϫ19 cmϪ1. It is worth
noting here that the observed experimental value is well
within the predictive range of the reported relationship.
This is corroborated by the fact that other alcoholate
bridged dinuclear iron(III) complexes with only slightly
smaller values for the shortest average length of the ex-
change pathway of 199.1 and 198.9 pm exhibit coupling
constants of Ϫ30.8 and 32.6 cmϪ1, respectively [14, 19].
Fig. 8 Plot of χM and χMT vs. T for complex 2 at an applied field
of 2 kOe. The corresponding fit functions are drawn as solid lines
(for parameters see text).
unambiguous assignment of the oxidation state and con-
firms that the anion of 5 contains an iron(II) ion.
Summary and Perspectives
Magnetochemical Investigations of 2
Selected physical data of iron complexes with pyridyl-
methylamino ligands are given in Table 2. The oxidation
state of the iron atom shows only a minor influence on the
Fe-N bond lengths. However, the spin state strongly affects
The magnetic properties of compound 2 were determined
by magnetic susceptibility measurements of polycrystalline
samples with a SQUID-susceptometer as a function of tem-
perature in the range from 2 to 300 K. The χM and χMT
plots of the obtained data are given in Figure 8. At room
temperature complex 2 exhibits a nearly paramagnetic be-
havior with χMT values of about 6.0 cm3 K molϪ1, which
approaches the theoretical spin-only value for two indepen-
dent S ϭ 5/2 centers per molecule expected for the high
temperature limit [18]. Upon lowering the temperature com-
plex 2 shows an antiferromagnetic coupling of the two
iron(III) ions, leading to a decrease of the χMT values. The
sharp increase of the χM values at very low temperatures is
indicative for the presence of paramagnetic impurities.
A quantitative analysis of the susceptibility data has been
performed with the assumption of an isotropic interaction
by using the Heisenberg-Dirac-Van Vleck Hamiltonian
ˆ
ˆ
ˆ
H ϭ ϪJ SA·SB with SA ϭ SB ϭ 5/2. The least-squares fit
was carried out including a term representing possible para-
magnetic impurities. A good fit to the data was obtained
with a coupling constant J ϭ Ϫ29.4 cmϪ1, g ϭ 2.085 and
a fraction of paramagnetic impurities of ρ ϭ 0.018. This fit
Formula 3
Table 2 Comparison of selected characterization data of the compounds 1, 2, 4, and 5.
[(amp)2FeCl2]
[(amp)2FeBr2]
[(ach)2Fe(MeOH)2]2ϩ
[(amp)FeCl2(µ-OMe)]2
[(dpa)2Fe]Br2·2 MeOH
[(dpdae)2Fe]2ϩ
X
1a
2
1b
2
1c
2
2
3
4
2
5
2
a)
n(Fenϩ
)
Fe-N(pyridyl)
Fe-N(amine)
Spin
218.5
218.9
h.s.
215.1
217.2
h.s.
219.4
218.6
h.s.
216.4
217.4
h.s.
199.2, 199.5
203.1
l.s.
206.6
207.8, 210.5
h.s.
b)
ν(NH)
3337, 3233
3277, 3228
3157 (broad)
3302, 3245
3346 (broad)
3277, 3247
a) Oxidation state of the iron center; b) high spin h.s., low spin l.s.
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A. Malassa, H. Görls, A. Buchholz, W. Plass, M. Westerhausen
(1.0 mmol, 87 %). M.p. 110 °C (dec.). Elemental analysis
(C20H24Br2FeO2N4, 568.08 g molϪ1): calcd.: C 41.97, H 4.09, N
9.84; found: C 42.29, H 4.26, N 9.86 %.
IR/cmϪ1: 3157 br, vs, 2752 m, 2488 w, 1999 w, 1947 w, 1885 w, 1816 w,
1743 w, 1678 w, 1622 m, 1592 m, 1576 s, 1503 vs, 1425 m, 1406 m, 1320 s,
1264 w, 1248 w, 1223 m, 1196 w, 1174 w, 1134 m, 1075 vs, 1061 s, 1030 m,
1001 vs, 895 m, 831 vs, 793 s, 769 vs, 668 br, w, 633 m, 580 m, 566 m, 525 m,
500 w, 491 m, 466 w. MS (DEI, m/z): only the fragmentation pattern of the
ligand was observed, 144 ([ach]ϩ, 100 %), 117 ([ach-NH2-CH]ϩ, 52 %).
the Fe-N distances. The low-spin configuration leads to a
shortening of the Fe-N bonds of nearly 20 pm.
Trialkylsilyl substituted 2-pyridylmethylamines can easily
be deprotonated (A) and oxidized (B) by tin(II) and at elev-
ated temperatures by zinc(II) compounds. These reactions
lead to a C-C coupling and after protonation to the forma-
tion of 1,2-dipyridyl-1,2-bis(trialkylsilylamino)ethane (C).
The reaction sequence is illustrated in equation 3. The
standard potentials E0(Fe2ϩ/Fe3ϩ) of ϩ0.77 V, E0(Fe/Fe2ϩ
)
[(amp)FeCl2(µ-OMe)]2 (2): A solution of 0.80 g of anhydrous
FeCl3 (4.9 mmol) in 10 ml of methanol was prepared. Within 10
minutes a solution of 0.53 g of 2-aminomethylpyridine (amp,
4.9 mmol) was added. A yellow-brown microcrystalline solid of 2
(1.29 g, 4.8 mmol, 99 %) precipitated. M.p. 180 °C (dec.). Elemen-
tal analysis (C14H22Cl4Fe2O2N4, 531.85 g molϪ1): calcd.: C 31.66,
H 4.14, N 10.37; found: C 31.62, H 4.17, N 10.53 %.
IR/cmϪ1: 3302 s, 3245 m, 3155 w, 3078 w, 1601 m, 1569 w, 1483 m, 1521 w,
1282 m, 1164 m, 1111 w, 1080 s, 1035 vs, 1023 vs, 977 w, 930 m, 889 w, 815 w,
770 s, 653 m, 643 m , 586 m, 509 s. MS (DEI, m/z): only the fragmentation
of amp was observed, 107 ([amp-H]ϩ, 100 %), 79 ([py]ϩ, 93 %).
of Ϫ0.44 V and E0(Fe/Fe3ϩ) of Ϫ0.04 V offer a broad win-
dow for electron transfer reactions. In order to perform the
C-C coupling reaction, a deprotonation of the amino group
is required as the first reaction step. Therefore, the 2-pyrid-
ylmethylamides of iron [12] are far less stable than these
amine complexes. Future investigations are in progress in
order to show to what extent these complexes can serve as
precursors for the C-C coupling reactions.
[(dme)2FeCl2] [FeCl4] (3): Anhydrous FeCl3 was dissolved in
boiling 1,2-dimethoxyethane (dme). Cooling to r.t. afforded quanti-
tatively the precipitation of orange platelets. M.p. 194 °C (dec.).
Elemental analysis (C8H20O4Cl8Fe2, 504.65 g molϪ1): calcd.: C
19.04, H 3.99; found: C 19.16, H 4.08 %.
Experimental Section
General procedure: All manipulations were carried out in an anhy-
drous argon atmosphere and the solvents were thoroughly dried.
Starting 1,2-dipyridyl-1,2-bis(tert-butyldimethylsilylamino)ethane
was prepared according to a literature procedure [20].
IR/cmϪ1
: 3422 br, m, 2991 w, 2943 m, 2842 w, 1617 w, 1450 s, 1438 m,
1287 m, 1243 m, 1204 w, 1184 m, 1113 m, 1065 s, 1016 vs, 979 m, 859 m,
847 vs, 803 m, 552 s.
[(amp)2FeCl2] (1a): On a solution of 0.07 g of (thf)1.5FeCl2
(0.3 mmol) in 20 ml of THF a second solution of 0.07 g of
2-aminomethylpyridin (amp, 0.6 mmol) in 2 ml of methanol was
layered.Within 4 days the first crystals formed. Now the mixture
was stored at 5 °C and 0.03 g of yellow cuboids of 1 (0.1 mmol,
29 %) precipitated. M.p. 219 °C (dec.).
IR/cmϪ1: 3337 s, 3233 s, 3149 m, 3014 m, 1603 s, 1568 m, 1491 m, 1331 w,
1290 m, 1254 w, 1212 w, 1152 m, 1104 w, 1060 m, 1013 s, 979 w, 921 m,
896 w, 810 w, 766 s, 730 m, 646 w, 633 m, 552 m, 474 w. MS (DEI, m/z): 234
([Fe(amp)Cl2]ϩ, 1 %), 199 ([Fe(amp)Cl]ϩ, 2 %), 108 ([amp]ϩ, 100 %), 79
([py]ϩ, 88 %).
[(dpa)2Fe]Br2·2 MeOH (4): A solution of 0.70 g of bis(2-pyridyl-
methyl)amine (dpa, 3.6 mmol) in 3 ml of methanol was added to a
stirred solution of 0.63 g of (thf)2FeBr2 (1.8 mmol) in 5 ml of meth-
anol. A red solid of 4 (0.86 g, 1.3 mmol, 72 %) precipitated from
this brown solution. M.p. 250 °C (dec.). Elemental analysis
(C26H34Br2FeO2N6, 678.24 g molϪ1): calcd.: C 46.04, H 5.05, N
13.39; found: C 45.66, H 5.03, N 12.18 %.
IR/cmϪ1: 3346 br, s, 3131 vs, 3017 m, 1608 m, 1569 w, 1485 m, 1312 m,
1248 w, 1155 m, 1120 m, 1070 m, 1027 s, 911 m, 820 w, 781 m, 792 s, 565 br,
w, 492 w, 458 w. MS (DEI, m/z): 415 ([Fe(dpa)Br2-H]ϩ, 0,3 %), 336
([Fe(dpa)Br)]ϩ, 6 %), 200 ([dpaϩH]ϩ, 17 %), 107 ([amp-H]ϩ, 59 %), 93
([picolyl]ϩ, 100 %), 78 ([py-H]ϩ, 14 %).
[(amp)2FeBr2] (1b): A solution of 0.34 g of 2-aminomethylpyridin
(3.2 mmol) in 2 ml of methanol was added dropwise to a solution
of 0.57 g of (thf)2FeBr2 (1.6 mmol) in 5 ml of methanol. A yellow-
brown solution formed and already after 30 minutes, the crystalli-
zation of began. Within 17 hours yellow-green microcrystalline 2
precipitated. This solid was collected, the volume of the mother
liquor reduced and another crop of crystals were obtained. Recrys-
tallization from hot methanol gave 0.51 g of 2 (1.2 mmol, 75 %) in
the shape of yellow-green platelets. M.p. 260 °C (dec.). Elemental
analysis (C12H16Br2FeN4; 431.94 g molϪ1): calcd.: C 33.37, H 3.73,
N 12.97; found: C 33.37, H 3.82, N 13.08 %.
[(dpdae)2Fe] [FeBr4] (5): 1,2-Dipyridyl-1,2-bis(tert-butyldimeth-
ylsilylamino)ethane (0.28 g, 0.63 mmol) was dissolved in 2 ml of
methanol which yielded quantitatively the formation of MeOSit-
BuMe2 and 1,2-dipyridyl-1,2-diaminoethane (dpdae). This solution
was layered on the solution of 0.23 g of (thf)2FeBr2 (0.63 mmol) in
5 ml of methanol. At the border of these two solutions a red ring
formed. Within 4 days orange-red platelets precipitated from this
mixture. After reduction of the volume and storage of the mother
liquor at 5 °C afforded another crop of orange-red crystals. M.p.
148 °C (dec.).
IR/cmϪ1: 3277 vs, 3228 vs, 3149 s, 3055 w, 2026 w, 1944 w, 1653 w, 1602 vs,
1568 m, 1481 s, 1283 m, 1189 w, 1144 s, 1106 s, 1093 s, 1051 w, 1019 vs, 973 w,
932 m, 809 w, 771 vs, 668 w, 645 w, 630 m, 551 m, 476 m. MS (DEI, m/z):
324 ([Fe(amp)Br2]ϩ, 1 %), 243 ([Fe(amp)Br]ϩ, 3 %), 108 ([amp]ϩ, 100 %), 80
([pyϩH]ϩ, 97 %).
IR/cmϪ1: 3277 m, 3247 m, 1607 w, 1591 m, 1572 w, 1302 w, 1160 w, 1012 m,
799 w, 756 m, 632 w. MS (DEI, m/z): 448 ([2dpdaeϩFe-2NH3]ϩ, 1 %), 429
([dpdaeϩFeϩ2Br-H]ϩ, 2 %), 289 ([dpdaeϩFeϩNH3-H]ϩ, 100 %), 196
([dpdae-NH3-H]ϩ, 36 %), 108 ([amp]ϩ, 84 %), 79 ([py]ϩ, 44 %).
[(ach)2Fe(MeOH)2]Br2 (1c): A solution of 0.32 g of 2-aminochin-
oline (2.22 mmol) in 7 ml of methanol was dropped at r.t. to a
solution of 0.40 g of (thf)2FeBr2 (1.11 mmol) in 3 ml of methanol.
The reaction mixture turned red immediately. Storage at 5 °C
afforded the precipitation of a microcrystalline powder of 1c.
Reduction of the volume of the mother liquor and storage at 5 °C
yielded another crop of crystals of 1c. Recrystallization from boil-
ing methanol gave 0.54 g of orange-brown platelets of 1c
Magnetic measurements
The magnetic susceptibility data were measured on a MPMSR-5S-
SQUID magnetometer from Quantum Design in the range from 2
to 400 K at an applied magnetic field of 2 kOe. Diamagnetic correc-
tions were estimated according to Pascal’s constants. The suscepti-
2360
www.zaac.wiley-vch.de
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 2355Ϫ2362

Pyridylmethylamines as Ligands in Iron Halide Complexes
Table 3 Crystal data and refinement details for the X-ray structure determinations
Compound
1a
1b
1c
2
3
4
5
Formula
C12H16Cl2FeN4 C12H16Br2FeN4 C20H24Br2FeN4O2 C14H22Cl4Fe2N4O2 C8H20Cl6Fe2O4 C24H26Br2FeN6 * 2 CH4O C24H28Br4Fe2N8
fw /g·molϪ1
T/°C
343.04
Ϫ90(2)
monoclinic
P21/c
431.96
Ϫ90(2)
triclinic
568.10
Ϫ90(2)
monoclinic
P21/c
531.86
Ϫ90(2)
monoclinic
P21/c
504.64
Ϫ90(2)
orthorhombic triclinic
Pbcm
678.26
Ϫ90(2)
859.88
Ϫ90(2)
triclinic
crystal system
space group
¯
¯
P1
¯
P1
P1
˚
a/ A
6.1016(5)
12.8559(10)
9.3085(6)
6.6820(5)
7.0774(3)
8.5467(5)
112.255(3)
96.085(3)
96.600(4)
366.65(4)
1
9.4902(4)
13.0177(9)
9.7133(7)
11.0055(6)
8.1195(3)
12.2240(8)
6.775(2)
14.9714(7)
19.3557(9)
8.7387(6)
9.2175(9)
9.7053(9)
76.643(4)
84.627(6)
67.888(5)
704.64(11)
1
9.9256(6)
11.0407(8)
15.9915(10)
74.469(4)
74.956(4)
64.936(4)
1507.87(17)
2
˚
b/ A
˚
c/ A
Ͱ /°
β/°
98.552(5)
105.242(4)
108.920(3)
γ/°
3
˚
V/A
722.05(9)
2
1157.78(13)
2
1033.31(10)
2
1963.3(7)
4
Z
ρ (g·cmϪ3
)
1.578
14.05
4639
1413
1640
1.956
64.68
2588
1528
1.630
41.25
7975
2193
2637
0.0750
0.0306
1.041
1.709
19.37
7128
1763
2363
0.0801
0.0329
0.989
1.707
22.99
11975
1568
1.598
34.05
4731
2423
1.894
62.91
10495
4822
6810
0.1582
0.0578
1.024
µ (cmϪ1
)
measured data
data with I > 2σ(I)
unique data (Rint
)
1662
2319
3070
wR2 (all data, on F2)a) 0.0951
0.0806
0.0308
1.093
0.0815
0.0350
1.033
0.1617
0.0576
1.070
R1 (I > 2σ(I))a)
0.0353
1.135
sb)
Ϫ3
˚
Res. dens./e·A
Absorpt. method
0.399/Ϫ0.431 0.652/Ϫ0.862 0.643/Ϫ0.608
multi-scan multi-scan multi-scan
0.305/Ϫ0.373
multi-scan
0.7305/0.7701
611360
0.417/Ϫ0.416 1.296/Ϫ0.710
multi-scan multi-scan
0.6228/0.7769 0.4923/0.6800
611361 611362
1.947/Ϫ1.274
multi-scan
0.3669/0.4580
611363
absorpt corr T min/max 0.7884/0.8475 0.5888/0.8075 0.4703/0.5089
CCDC No. 611357 611358 611359
a) Definition of the R indices: R1 ϭ (ΣʈFoΗ-ΗFcʈ)/ΣΗFoΗ wR2 ϭ {Σ[w(Fo2-Fc2)2]/Σ[w(Fo2)2]}1/2 with wϪ1 ϭ σ2(Fo2) ϩ (aP)2.
b) s ϭ {Σ[w(Fo2-Fc2)2]/(No-Np)}1/2
.
bility data were further corrected for the presence of paramagnetic
impurity. For details see refs. [21, 22].
[3] M. Hostettler, K. W. Törnroos, D. Chernyshov, B. Vangdal,
H.-B. Bürgi, Angew. Chem. 2004, 116, 4689Ϫ4695; Angew.
Chem. Int. Ed. 2004, 43, 4589Ϫ4594.
[4] D. Chernyshov, M. Hostettler, K. W. Törnroos, H.-B. Bürgi,
Angew. Chem. 2003, 115, 3955Ϫ3960; Angew. Chem. Int. Ed.
2003, 42, 3825Ϫ3830.
[5] G. Chen, Y.-X. Sun, M. Sun, W. Qi, Acta Crystallogr. 2004,
E60, m1547Ϫm1549.
[6] C. J. Davies, G. A. Solan, J. Fawcett, Polyhedron 2004, 23,
3105Ϫ3114.
[7] N. M. F. Carvalho, A. Horn, A. J. Bortoluzzi, V. Drago, O. A.
C. Antunes, Inorg. Chim. Acta 2006, 359, 90Ϫ98.
[8] S. Zhu, W. W. Brennessel, R. G. Harrison, L. Que, Inorg.
Chim. Acta 2002, 337, 32Ϫ38.
X-ray structure determinations
The intensity data were collected on a Nonius Kappa CCD dif-
fractometer using graphite-monochromated Mo-Kα radiation (λ ϭ
˚
0.71073 A). Data were corrected for Lorentz polarization and for
absorption effects [23Ϫ25]. The crystal data and refinement details
are summarized in Table 3. The structures were solved by direct
methods (SHELXS [26]) and refined by full-matrix least squares
2
techniques against Fo (SHELXL-97 [27]).
Supporting Information available: Crystallographic data (excluding
structure factors) have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication CCDC-
611357 for 1a, CCDC-611358 for 1b, CCDC-611359 for 1c, CCDC-
611360 for 2, CCDC-611361 for 3, CCDC-611362 for 4, and
CCDC-611363 for 5. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [E- mail: deposit@ccdc.cam.ac.uk].
[9] D. C. Bradley, M. H. Chisholm, Acc. Chem. Res. 1976, 9,
273Ϫ280.
[10] R. A. Andersen, K. Faegri, J. C. Green, A. Haaland, M. F.
Lappert, W. P. Leung, K. Rypdal, Inorg. Chem. 1988, 27,
1782Ϫ1786.
[11] M. M. Olmstead, P. P. Power, S. C. Shoner, Inorg. Chem. 1991,
30, 2547Ϫ2551.
[12] C. Koch, A. Malassa, C. Agthe, H. Görls, R. Biedermann, H.
Krautscheid, M. Westerhausen, Z. Anorg. Allg. Chem., in
preparation.
Acknowledgement. This work was supported in the collaborative
research center of the DFG (SFB 436) and we thank the Deutsche
Forschungsgemeinschaft (DFG, Bonn-Bad Godesberg, Germany)
for generous funding.
[13] A. K. Singh, R. Mukherjee, Inorg. Chem. 2005, 44,
5813Ϫ5819.
[14] B. Chiari, O. Piovesana, T. Tarantelli, P. F. Zanazzi, Inorg.
Chem. 1982, 21, 1396Ϫ1402.
[15] S. M. Gorun, S. J. Lippard, Inorg. Chem. 1991, 30, 1625Ϫ1630.
[16] G. Schmid, G. Barbenheim, R. Boese, Z. Naturforsch. 1985,
40b, 787Ϫ793.
References
[1] L. Wiehl, G. Kiel, C. P. Köhler, H. Spiering, P. Gütlich, Inorg.
Chem. 1986, 25, 1565Ϫ1571.
[17] W. Pohl, I.-P. Lorenz, H. Nöth, M. Schmidt, Z. Naturforsch.
1995, 50b, 1485Ϫ1493.
[2] K. W. Törnroos, D. Chernyshov, M. Hostettler, H.-B. Bürgi,
Acta Crystallogr. 2005, C61, m450Ϫm452.
[18] O. Kahn, Molecular Magnetism, VCH Publishers, New
York, 1993.
Z. Anorg. Allg. Chem. 2006, 2355Ϫ2362
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
2361

A. Malassa, H. Görls, A. Buchholz, W. Plass, M. Westerhausen
[19] B. Chiari, O. Piovesana, T. Tarantelli, P. F. Zanazzi, Inorg.
Chem. 1984, 23, 3398Ϫ3404.
[20] M. Westerhausen, T. Bollwein, K. Karaghiosoff, S. Schneider-
bauer, M. Vogt, H. Nöth, Organometallics 2002, 21, 906Ϫ
911.
[24] “Processing of X-Ray Diffraction Data Collected in Oscil-
lation Mode”: Z. Otwinowski, W. Minor, in C. W. Carter, R.
M. Sweet (eds.): Methods in Enzymology, Vol. 276, Macromole-
cular Crystallography, Part A, pp. 307Ϫ326, Academic Press
1997.
[21] W. Plass, Inorg. Chem. 1997, 36, 2200Ϫ2205.
[22] W. Plass, Eur. J. Inorg. Chem. 1998, 799Ϫ805.
[23] COLLECT, Data Collection Software; Nonius B. V., Nether-
lands, 1998.
[25] SORTAV, R. H. Blessing, Acta Crystallogr. 1995, A51, 33Ϫ38.
[26] G. M. Sheldrick, Acta Crystallogr. 1990, A46, 467Ϫ473.
[27] G. M. Sheldrick, SHELXL-97 (Release 97-2), University of
Göttingen, Germany, 1997.
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 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 2355Ϫ2362