A new N6 hexadentate ligand and a novel heptacoordinated N 6O-type Fe(III) compounds: Synthesis, characterization and structure of [Fe(dimpyen)(OH)](A)2 (A = PF6- or ClO 4-)

Article abstract of DOI:10.1016/j.ica.2011.05.008

In this contribution, we report the syntheses of a novel N₆ donor set ligand, dimpyen = N1,N2-di[(1-methyl-1H-2-imidazolyl) methyl]-N1,N2-di(2-pyridilmethyl)-1,2-ethanediamine. This type of ligand was designed to modulate the properties of the metal ions bound to it. The reaction with Fe(II) gives off a new heptacoordinated iron(III) complex. We study the spectroscopic (UV-Vis), magnetic and electrochemical behavior and also made the structural determination with X-ray diffraction at 134 K and a heptacoordinated N₆O-type derivative of Fe(III) is reported as well. This complex crystallize as perchlorate or hexafluorophosphate and the formula of these derivatives are [Fe(dimpyen)(OH)](PF₆)₂ (1) and [Fe(dimpyen)(OH)](ClO₄)₂ (2) which both crystallize with an intermediate geometry, between pentagonal bipyramidal and monocapped octahedral. The UV-Vis spectra in CH₃CN solution show a shoulder at 306 nm assigned to one ligand-metal charge-transfer (LMCT) transition, in addition, a weaker and wide band assigned to the charge transfer HO-Fe transition (λ_max at 404 nm with an extinction coefficient of 818 cm^-1 M^-1) is also observed. The magnetic studies corroborate a high-spin iron (III) species in all the temperature range considered. Measurements of cyclic voltammetric confirm a reversible system Fe(III) species, with E_1/2 = -0.380 V/Fc⁺-Fc, this low potential value explains the high stability of the Fe(III) and the easy oxidation of Fe(II) by atmospheric O₂(g) reaction.

Full text of DOI:10.1016/j.ica.2011.05.008

Inorganica Chimica Acta 375 (2011) 213–219
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
A new N6 hexadentate ligand and a novel heptacoordinated N6O-type Fe(III)
compouꢀnds: Synthesis, characterization and structure of [Fe(dimpyen)(OH)](A)2
ꢀ
(A = PF6 or ClO4 )
Norma Ortega-Villar a, Víctor M. Ugalde-Saldívar a, Blas Flores-Pérez a, Marcos Flores-Alamo a, J.A. Real b,
Rafael Moreno-Esparza a,
⇑
a Facultad de Química, Universidad Nacional Autónoma de México, México DF 04510, Mexico
b Instituto de Ciencia Molecular (ICMol), Universidad de Valencia C/Catedrático José Beltrán Martínez, 2, Paterna, 46071 Valencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
In this contribution, we report the syntheses of a novel N6 donor set ligand, dimpyen = N1,N2-di[
(1-methyl-1H-2-imidazolyl) methyl]-N1,N2-di(2-pyridilmethyl)-1,2-ethanediamine. This type of ligand
was designed to modulate the properties of the metal ions bound to it. The reaction with Fe(II) gives
off a new heptacoordinated iron(III) complex. We study the spectroscopic (UV–Vis), magnetic and elec-
trochemical behavior and also made the structural determination with X-ray diffraction at 134 K and a
heptacoordinated N6O-type derivative of Fe(III) is reported as well. This complex crystallize as perchlo-
rate or hexafluorophosphate and the formula of these derivatives are [Fe(dimpyen)(OH)](PF6)2 (1) and
[Fe(dimpyen)(OH)](ClO4)2 (2) which both crystallize with an intermediate geometry, between pentago-
nal bipyramidal and monocapped octahedral. The UV–Vis spectra in CH3CN solution show a shoulder
at 306 nm assigned to one ligand–metal charge-transfer (LMCT) transition, in addition, a weaker and
wide band assigned to the charge transfer HO–Fe transition (kmax at 404 nm with an extinction coefficient
of 818 cmꢀ1 Mꢀ1) is also observed. The magnetic studies corroborate a high-spin iron (III) species in all
the temperature range considered. Measurements of cyclic voltammetric confirm a reversible system
Fe(III) species, with E1/2 = ꢀ0.380 V/Fc+–Fc, this low potential value explains the high stability of the
Fe(III) and the easy oxidation of Fe(II) by atmospheric O2(g) reaction.
Received 21 December 2010
Received in revised form 29 April 2011
Accepted 6 May 2011
Available online 17 May 2011
Keywords:
Iron (III) complexes
Hexadentate ligand
Heptacoordination
Redox properties
Magnetic properties
Crystal structure
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
in different proportions, which should allow for easy identification
of the stereochemistry through NMR spectroscopy in solution or by
In recent years, considerable effort has been focused on the syn-
thesis of molecular materials with Fe that exhibit physical proper-
ties that may be switched in a controlled manner, especially in the
magnetochemical area, because they are potentially good candi-
dates for signal generation and processing [1]. Such behavior is
modulated with the type of ligand bound to either Fe(II) or Fe(III).
Our group is involved with the design of new ligands to do this [2].
On the other hand, seven-coordination is not common in transi-
tion-metal chemistry: an estimate based on the number of transi-
tion-metal sigma-bonded complexes found in the Cambridge
Structural Database reveals that heptacoordinate complexes repre-
sent only 1.8% of the total number of structures reported [3]. Being
seven an odd coordination number, no regular polyhedron can de-
scribe the coordination sphere around the metal atom. The most
common polyhedra have the pentagonal bipyramid or either the
capped octahedron or the capped trigonal prism, types of vertices
infrared spectroscopy in the solid state [4]. However very often, it
is possible to observe solution spectra consistent with seven equiv-
alent ligands due to the existence of low energy barrier fluxional
processes. These geometries are receiving more attention as they
can be identified as intermediates in associated reactions of vari-
ous six-coordinated complexes [5,6]. It is clear that single crystal
X-ray crystallography should be better adapted to fully character-
ize the stereochemistry of a given heptacoordinate molecule.
Then heptacoordination is a well-known coordination mode,
although examples with iron(II) or (III) are rather rare. Some are re-
ported in compounds with iron(II), observed with pentadentate li-
gands maintaining five coordination sites in one plane and
allowing two axial coordinations [7]. There are very few structural
reports of an heptacoordinated Fe(III) [8].
Furthermore, the study of compounds with this geometry is
also of interest from another point of view, since it has been found
that Fe(III) PBP complexes with aza-ligands exhibit an excellent
superoxide dismutase (SOD) activity and offer considerable prom-
ise as SOD catalysts for pharmaceutical applications. In these
⇑
Corresponding author. Tel.: +52 (55) 56223793; fax: +52 (55) 56162019.
E-mail address: moresp@servidor.unam.mx (R. Moreno-Esparza).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.05.008

214
N. Ortega-Villar et al. / Inorganica Chimica Acta 375 (2011) 213–219
systems, the [Fe(N5)(H2O)OH] form of the complex is responsible
for the catalytic properties, and a condition for the high activity
of the complexes is their existence in mostly this form under phys-
iological pH conditions [9,10].
Although several reviews on this subject have been published
lately, the ongoing study of these systems does not fail to provide
novel and interesting information.
The analysis of such parameters as electrochemical behavior
and UV–Vis spectroscopy should render more arguments to estab-
lish a relationship between the studied properties and the chemi-
cal behavior of these complexes [11].
In light of the aforementioned facts, we report the syntheses
of a new N6 donor set ligand dimpyen = N1,N2-di[(1-methyl-1H-
2-imidazolyl)methyl]-N1,N2-di(2-pyridilmethyl)-1,2-ethanedi-
amine, and the syntheses, spectroscopic (UV–Vis), magnetic and
structural characterization of a novel heptacoordinated N6O-type
iron(III) complex with an intermediate geometry between pen-
tagonal bipyramid and capped octahedron.
from the reaction vessel. Diffraction experiments were performed
on an Atlas (Gemini Mo) area detector diffractometer and analyzed
using Mo Ka X-ray radiation (k = 0.71073 Å). The dimensions of
the analyzed crystals were; 0.40 ꢂ 0.37 ꢂ 0.18 mm for 1 and
0.45 ꢂ 0.18 ꢂ 0.06 mm for 2. Only random fluctuations of less than
2% in the intensities of three standard reflectionswere observed dur-
ing the course of data collection. Neutral atom scattering factors and
anomalous dispersion corrections were taken from International Ta-
bles for Crystallography [13]. The data were corrected for absorption
effects using the analytical numeric absorption correction using a
multifaceted crystal model based on expressions derived by Clark
and Reid [14]. The structure was solved by direct methods using
the program SIR-2004 [15] combined with Fourier difference synthe-
ses and refined against F2, least-squares refinement based on F2 was
carried out by full-matrix method with SHELXL-97-2 [16]. All non-
hydrogen atoms were refined anisotropically successfully, while
hydrogen atoms were included at calculated positions by using the
riding model. The crystal data for the analyzed compounds with
other pertinent details for the structure determination are reported
in Table 1 while the selected bond length and angles of the com-
pound are presented in Table 2. Complete listings of bond lengths,
bond angles, and anisotropic thermal parameters are supplied as
supplementary material. The molecular structure drawings were
generated using ORTEP for windows [17].
2. Materials and methods
2.1. Reagents and solvents
Starting reagents and solvents were purchased from commer-
cial sources and used as received.
3. Experimental
2.2. Physical measurements
3.1. Synthesis of the ligand dimpyen
Infrared spectra were recorded on a Perkin–Elmer/1600 FT IR
spectrometer on KBr pellets in the 4000–450 cmꢀ1 range. Elemen-
tal analyses were done on a Fissons elemental micro analyzer mod-
el EA 1108, CHNS-O. 1H NMR spectroscopic measurements were
done on Varian 300 NMR Unity-Inova spectrometer using TMS as
internal standard. Mass spectroscopy (FAB+), was done in a JEOL
JMS-SX spectrometer, 102 A. UV–visible spectra were recorded
on a Diode array HP 8493A spectrophotometer at 293 K on
1.0 cm quartz cell.
The synthetic route of this new ligand is presented in the
Scheme 1, and each stage of the procedure is presented below.
3.1.1. 1-Methyl-1H-imidazole-2-carbaldehyde (A)
1-Methyl-imidazole (3 mL, 0.038 mol) was dissolved in 25 mL
of dry THF, under N2 atmosphere, the system is cooled to ꢀ78 °C
and stirred for 10 min, to this is added slowly 6.6 mL of butyl-lith-
ium (0.146 mol, 2.5 M in hexane) keeping the temperature below
ꢀ73 °C, after 5 min, 5.3 mL (0.076 mol) of dimethylformamide
was added. This solution is stirred during 1 h at ꢀ73 °C and then
allowed to reach room temperature while stirring 40 min more.
After this period, 189 mL HCl 2 N are added and stirred 1 h at room
temperature. The mixture is then neutralized to pH 10 with 40%
NaOH and then extracted with dichloromethane (3 ꢂ 60 mL). All
organic extracts are collected and dried over Na2SO4 at reduced
pressure. After distillation a colorless solid is obtained yielding
4.117 g (98.5%).
2.2.1. Magnetic studies
The variable-temperature (1.8–300 K) magnetic susceptibility
measurements for each Fe(III) derivative were recorded with a
Quantum Design MPMS2SQUID susceptometer and calibrated with
(NH4)2Mn(SO4)2ꢁ12H2O. In all cases the vM values have been cor-
rected for diamagnetism.
2.2.2. Electrochemical measurements
All experiments were performed with an EG&G-PAR 263 A
potenciostat-galvanostat in acetonitrile solution containing 0.1 M
N-tetrabutylammonium hexafluorophosphate, (C4H9)4NPF6, as
the supporting electrolyte. A typical three-electrode array was em-
ployed for all electrochemical measurements: glass carbon micro-
disk (C, 7.1 mm2) as working electrode, Pt wire as counter
electrode, and a pseudoreference electrode of AgBr(s)–Ag(wire)
immersed in an acetonitrile 0.1 M (C4H9)4NBr solution. All solu-
tions were deoxygenated with N2 before each measurement. All
voltammograms were started from the current null potential
(Ei=0) of each solution and were scanned in both directions. In
agreement with IUPAC convention [12], the voltammogram of
the ferricinium/ferrocene (Fc+/Fc) system, used as reference, was
obtained to establish the values of half wave potentials (E1/2) for
each experiment from the expression E1/2 = (Eap + Ecp)/2.
3.1.2. [(E)-[(1-Methyl-1H-imidazol-2-yl) methylidene]amino]
ethyl})amine (B)
500 mg (4.54 mmol) of (A), 1.09 g (9.10 mmol) of MgSO4 and
5 mL of dichloromethane were stirred under N2. To this mixture
0.151 mL (136.2 mg; 2.27 mmol) of ethylenediamine were dis-
solved in 1 mL of dichloromethane, and stirred overnight at room
temperature. The mixture was filtered over cellite and washed
with dichloromethane (3 x 10 mL) and dried in vacuum, obtaining
400 mg (72.7%) of a colorless solid.
3.1.3. [(1-Methyl-4,5-dihydro-1H-imidazol-2-yl)methyl](2-{[(1-
methyl-4,5-dihydro-1H-imidazol-2-yl)methyl]amino}ethyl) amine (C)
200 mg (0.819 mmol) of (B) were dissolved in 15 mL of metha-
nol, cooled in an ice bath and stirred. Then 0.062 mg (1.64 mmol)
of sodium borohydride was added. After the solid dissolves the
mixture is allowed to reach room temperature and stirred six more
hours. After this period, NaCl saturated solution is added until pre-
cipitation and then extracted with chloroform (4 ꢂ 60 mL), the
2.2.3. Single crystal X-ray diffraction
X-ray data collection, structure solution and refinement were
made from crystals of the complex suitable for diffraction obtained

N. Ortega-Villar et al. / Inorganica Chimica Acta 375 (2011) 213–219
215
Table 1
Crystal data and structure refinement for 1 and 2.
Complex
1
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C24 H31 F12 Fe N8 O P2
793.36
134(2)
C24 H31 Cl2 Fe N8 O9
702.32
134(2)
0.71073
0.71073
triclinic
triclinic
ꢀ
ꢀ
P1
P1
9.7670(10)
12.7260(10)
13.3260(10)
76.354(4)
74.751(4)
81.120(4)
1545.4(2)
2
9.3300(10)
12.7310(10)
12.9760(10)
77.961(5)
72.203(6)
81.945(6)
1430.4(2)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(0 0 0)
1.705
0.7
806
1.631
0.782
726
)
Crystal size (mm3)
0.40 ꢂ 0.37 ꢂ 0.18
0.45 ꢂ 0.18 ꢂ 0.06
h Range for data collection (°)
Index ranges
Reflections collected
3.2–27.08
3.19–27.11
ꢀ12 6 h 6 12, ꢀ13 6 k 6 16, ꢀ17 6 l 6 16
12396
ꢀ11 6 h 6 10, ꢀ16 6 k 6 13, ꢀ16 6 l 6 16
12278
Independent reflections
Completeness to h = 27.08°
Absorption correction
6668 [R(int) = 0.0192]
98.1%
analytical
6141 [R(int) = 0.0370]
97.2%
analytical
Maximum and minimum transmission
Refinement method
0.909 and 0.835
full-matrix least-squares on F2
6668/42/490
0.961 and 0.815
full-matrix least-squares on F2
6141/2/400
Data/restraints/parameters
Goodness-of-fit on F2
1.098
1.085
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0389, wR2 = 0.1072
R1 = 0.0498, wR2 = 0.1108
0.641 and ꢀ0.663
R1 = 0.0595, wR2 = 0.1742
R1 = 0.0781, wR2 = 0.1864
0.770 and ꢀ1.273
Largest diff. peak and hole (e Åꢀ3
)
resulting colorless solid is dried over Na2SO4 at reduced pressure
with 67% yield (135 mg).
Table 2
Selected bond lengths [Å] and angles [°] for 1 and 2.
1
2
3.1.4. N1,N2-Di[(1-metil-1H-2-imidazolil)metil]-N1,N2-di(2-piridil-
metil)-1,2-etanodiamina (dimpyen)
Fe(1)–O(1)
Fe(1)–N(5)
Fe(1)–N(6)
Fe(1)–N(4)
Fe(1)–N(3)
Fe(1)–N(1)
Fe(1)–N(2)
1.852(1)
2.094(2)
2.095(2)
2.263(2)
2.272(2)
2.381(2)
2.394(2)
Fe(1)–O(1)
Fe(1)–N(6)
Fe(1)–N(5)
Fe(1)–N(4)
Fe(1)–N(3)
Fe(1)–N(2)
Fe(1)–N(1)
1.865(2)
2.078(3)
2.087(3)
2.266(3)
2.289(3)
2.380(3)
2.385(3)
In a round bottom flask a mixture 100 mg (0.403 mmol) of (C),
132.2 mg (0.806 mmol) of picolyl chloride, 10 mL of toluene and
322 mg (8.05 mmol) of a NaOH in 5 mL water solution was re-
fluxed 48 h. Then, the mixture was cooled in an ice bath were a
slightly yellow precipitate was obtained. The precipitate was fil-
tered and washed with water (3 ꢂ 10 mL) and methanol
(3 ꢂ 10 mL) and dried at reduced pressure. The light yellow solid
was separated by column chromatography (SiO2/CHCl3, CH3OH,
NH4OH (60:6:0.6)) yielding 80% (141 mg).
O(1)–Fe(1)–N(5)
O(1)–Fe(1)–N(6)
N(5)–Fe(1)–N(6)
O(1)–Fe(1)–N(4)
N(5)–Fe(1)–N(4)
N(6)–Fe(1)–N(4)
O(1)–Fe(1)–N(3)
N(5)–Fe(1)–N(3)
N(6)–Fe(1)–N(3)
N(4)–Fe(1)–N(3)
O(1)–Fe(1)–N(1)
N(5)–Fe(1)–N(1)
N(6)–Fe(1)–N(1)
N(4)–Fe(1)–N(1)
N(3)–Fe(1)–N(1)
O(1)–Fe(1)–N(2)
N(5)–Fe(1)–N(2)
N(6)–Fe(1)–N(2)
N(4)–Fe(1)–N(2)
N(3)–Fe(1)–N(2)
N(1)–Fe(1)–N(2)
94.04(7)
95.21(7)
170.60(7)
79.89(7)
83.80(7)
99.46(7)
80.48(7)
98.53(7)
81.39(7)
160.35(7)
143.32(7)
100.46(7)
72.88(7)
68.56(7)
129.40(7)
143.95(7)
73.13(7)
98.27(7)
129.89(7)
68.79(7)
72.73(6)
O(1)–Fe(1)–N(6)
O(1)–Fe(1)–N(5)
N(6)–Fe(1)–N(5)
O(1)–Fe(1)–N(4)
N(6)–Fe(1)–N(4)
N(5)–Fe(1)–N(4)
O(1)–Fe(1)–N(3)
N(6)–Fe(1)–N(3)
N(5)–Fe(1)–N(3)
N(4)–Fe(1)–N(3)
O(1)–Fe(1)–N(2)
N(6)–Fe(1)–N(2)
N(5)–Fe(1)–N(2)
N(4)–Fe(1)–N(2)
N(3)–Fe(1)–N(2)
O(1)–Fe(1)–N(1)
N(6)–Fe(1)–N(1)
N(5)–Fe(1)–N(1)
N(4)–Fe(1)–N(1)
N(3)–Fe(1)–N(1)
N(2)–Fe(1)–N(1)
93.29(10)
96.38(10)
170.24(11)
79.80(9)
84.90(11)
98.08(10)
79.23(9)
99.55(10)
81.05(10)
158.77(10)
144.51(9)
99.22(10)
73.50(10)
68.51(10)
130.25(10)
142.22(9)
73.39(10)
97.98(10)
131.88(10)
68.83(10)
73.26(9)
1H NMR (300 MHz, CDCl3) see Scheme 2: 8.51 (1H, d, J2–3 = 6 Hz,
H2), 7.60 (1H, dd, J4–3 = 6 Hz, J4–5 = 6 Hz, H4), 7.29 (1H, d,
J5–4 = 6 Hz, H5), 7.15 (1H, dd, J3–2 = 6 Hz, J3–4 = 6 Hz, H3), 6.88
(1H, s, H12), 6.77 (1H, s, H11), 3.69 (2H, s, H9), 3.67 (2H, s, H7),
3.51 (3H, s, H13), 2.65 (2H, s, H8).
3.2. Preparation of the coordination compounds
The synthesis of the reported complexes is achieved irrespec-
tive of either if Fe(II) or Fe(III) are used as starting material.
3.2.1. Synthesis with Fe(II) salt
The synthetic procedure starting with Fe(II) is as follow:
h
i
FeIIðBF4Þ ꢁ 6H2O þ dimpyen ! FeIIIðdimpyenÞðOHÞ ðBF4Þ
2
2
where Xꢀ = ClO4 or PF6
.
ꢀ
ꢀ
h
i
To a mixture of 0.0393 g (0.116 mmol) of Fe(BF4)2ꢁ6H2O in meth-
anol (10 mL) a solution of 0.05 g of dimpyen (0.116 mmol) was
added drop-wise. The resulting orange solution was stirred
30 min, then slowly added 20 mL of methanol either with 0.057 g
FeIIIðdimpyenÞðOHÞ ðBF4Þ þ XðexcessÞ
2
h
i
!
FeIIIðdimpyenÞðOHÞ X2 þ NaBF4 or NH4BF4

216
N. Ortega-Villar et al. / Inorganica Chimica Acta 375 (2011) 213–219
Scheme 1. Synthetic route of the hexadendate ligand dimpyen.
To a mixture of 0.016 g (0.058 mmol) of FeCl3ꢁ6H2O in 10 mL of
methanol was added drop-wise a solution of 0.025 g of dimpyen
(0.058 mmol). The resulting orange solution was stirred 30 min
then was slowly added 20 mL of methanol with 0.03 g
(0.184 mmol) of NH4PF6.
The final red solution was left at reduced pressure for a week
and orange single crystals were filtered off from an orange solution
and washed with water.
IR and MS data are essentially the same for both counteranions.
IR: 3448 cmꢀ1 (O–H), 3086 cmꢀ1 (CH aromatic ring) 2950 and
2892 cmꢀ1 (C–H of CH3 and CH2), 1610 cmꢀ1 (aromatic ring defor-
mation), 1597 and 1572 cmꢀ1 (imidazolic rings), 838 and 557 cmꢀ1
ꢀ
(PF6 counterion).
4. Results and discussion
Scheme 2. 1H NMR chemical shifts of ligand dimpyen.
4.1. N1,N2-Di[(1-methyl-1H-2-imidazolyl)methyl]-N1,N2-di(2-
pyridilmethyl)-1,2-ethanediamine) ligand
(0.349 mmol) of NH4PF6 for 1 or 0.05 g (0.35 mmol) of NaClO4ꢁH2O
for 2.
This type of ligand was designed to modulate the properties of
the metal ions bound to it. Due to the fact that the hexacoordinated
tetrakis(2-pyridil-methyl)-1,2-ethanediamine iron (II) complex
presents spin-crossover, a similar ligand with one pyridine ex-
changed with a benzyl substituent, produce Fe(II) complexes with
very different properties but no spin-crossover, when these com-
plexes are coupled to form a dimer with dicyanamide the obtained
complex shows again the spin crossover-behavior [2]. The studied
ligand has two pyridine rings exchanged by two methyl–imidazol
rings in order to modify the character of the donor atom. A route
with four steps has been envisioned to synthesize this new ligand,
characterizing each intermediate. The global yield for the ligand
was around 40% (see experimental).
The final orange solution was left resting for 3 days and orange
single crystals suitable for X-ray analysis were filtered off from the
solution in both cases. A change in the oxidation state of the Fe(II)
ion is observed, and a Fe(III) complex is obtained in both cases.
3.2.1.1. [FeIII(dimpyen)(OH)](PF6)2 (1). Yield: 0.050 g, 54%. Orange
crystals. FAB + MS: m/z 793 (M)+, 486 (Mꢀ2PF6ꢀOH+eꢀ)+, 648
(MꢀPF6)+. Anal. Calc. for C24H31N8OP2F12Fe: C, 36.34; N, 14.12; H,
3.94. Found: C, 37.31; N, 13.50; H, 3.53%. MW : 793.33 g/mol.
3.2.1.2. [FeIII(dimpyen)(OH)](ClO4)2 (2). Yield: 0.044 g, 54%. Orange
crystals. FAB+MS: m/z 702 (M)+, 486 (Mꢀ2ClO4ꢀOH+eꢀ)+, 602
(MꢀClO4)+. Anal. Calc. for C24H31N8O9Cl2Fe: C, 41.02; N, 15.95; H,
4.42. Found: C, 41.57; N, 15.85; H, 4.25%. MW: 702.30 g/mol.
4.2. Crystal structure of (N1,N2-di[(1-methyl-1H-2-imidazolyl)
methyl]-N1,N2-di(2-pyridilmethyl)-1,2-ethanediamine)hydroxo iron
(III) hexafluorophosphate (1) and perchlorate (2)
3.2.2. Synthesis with the Fe(III) salt
Using the Fe(III) salt gives the same complex. The synthetic pro-
cedure starting from the Fe(III) salt is depicted below:
h
i
The first point to note in the structure of both salts is that the
Fe(III) ion, instead of being a regular hexacoordinated octahedron,
has a quite rare heptacoordinated geometry. Additionally for the
synthesis made starting from the iron (III) salt, the unit cell deter-
mined has the same values as the derivative obtained starting from
the Fe(II) salt.
FeCl3 ꢁ 6H2O þ dimpyen ! FeIIIðdimpyenÞðOHÞ ðClÞ2
h
i
FeIIIðdimpyenÞðOHÞ ðClÞ þ NH4PF6 ðexcessÞ
! FeIII ðdimpyenÞ ðOHÞꢃðPF6Þ þ 2NH4Cl
2
2

N. Ortega-Villar et al. / Inorganica Chimica Acta 375 (2011) 213–219
217
It is important to notice that there are very few examples of this
geometry for Fe complexes and a search in the Cambridge Crystal-
lographic Database results in only one example (a dimer) of the
N6O coordination system surrounding the Fe(III) center [18].
The structures consists of the [Fe(dimpyen)OH]2+ cation units
that comprise iron(III) centers coordinated to the hexadentate li-
gand dimpyen with one hydroxide in the coordination sphere.
The Fe atom is heptacoordinated with N6O environment by virtue
of the six nitrogen atoms (N1, N2, N3, N4, N5 and N6) from chelat-
ing dimpyen ligand and an oxygen atom (O1) from hydroxide,
forming a coordination polyhedron that can be described as a dis-
torted pentagonal bipyramid. In general these heptadentate com-
plexes can adopt any of three geometrical configurations,
pentagonal bipyramidal, capped trigonal prism or capped octahe-
dron. Since these geometries are energetically very similar it often
acquires an intermediate geometry, as is this case [3]. A view of the
perchlorate salt of the complex with atom numbering scheme is
shown in Fig. 1.
Selectedbondlengthsandanglesare summarizedin Table2. Con-
sidering the axis of the pentagonal bipyramid that with the largest
angle, and the equatorial positions those nearest to the mean plane,
it is observed that the two axial distances are shorter than the equa-
torial Fe-N bond, being N3 and N4 the pyridine, N5 and N6 the imid-
azole and N1 and N2 the olefinic nitrogen atoms, all of them more or
less comparable to similar systems [19]. The Fe–O hydroxide bond
length is the shortest of them all, as expected for this kind of bond.
Fe1 is 0.010(1) Å for 1 and 0.014(1) for 2 out of the best equatorial
plane defined by N1, N2, N3, N4 and O1 (the deviations from the
mean plane are N1 = 0.544 (7), N2 = 0.548 (8), N3 = 0.331(8),
The unit cell consists of two [Fe(dimpyen)OH]+2 units facing each
ꢀ
other trough the hydroxide, accompanied by two PF6ꢀ or two ClO4
anions for 1 and 2, respectively (Fig. S1, unit cell of the perchlorate
complex supplementary material). The Fe distances between near-
est neighbors are 7.1416(7), 10.8778(8) and 16.109(1) Å for the
hexafluorophosphate complex 1, however although not very large
there are differences for the perchlorate complex 2, being the dis-
tances of the same neighbors at 6.8877(9), 9.104(1) and
9.330(1) Å. There are no true hydrogen bonds observed neither in
1 nor in 2, and this explains the observed disorder in both the per-
chlorate and hexafluorophosphate moieties.
4.3. UV–Vis spectra of complexes 1 and 2
Both compounds are soluble either in methanol or acetonitrile.
The UV–Vis spectra of both complexes in acetonitrile solution were
as expected virtually identical (see Fig. 2). The spectrum of 1 shows
bands at 209 nm and at 258 nm which, by comparison with the
spectrum of the free ligand dimpyen, are assigned to pyridinic
and imidazolic rings
p ?
p⁄ transitions, additionally the shoulder
at 306 nm is assigned to a ligand–metal charge-transfer (LMCT)
transition. In addition, a weaker and wide band is also observed
and assigned to the charge transfer HO–Fe transition (kmax at
404 nm with an extinction coefficient of 818 cmꢀ1 Mꢀ1). No bands
at higher wavelengths are detected in the visible region.
The stability of the complex in solution is demonstrated by the
unchanged absorbance along several hours for all the studied com-
pounds, in spite that in general terms, the heptacoordinate 3d me-
tal complexes are usually more labile than their corresponding
octahedral species [20].
N4 = 0.314 (8) and O1 = 0.013(8) Å for
1 and N1 = 0.505(7),
N2 = 0.539(8), N3 = 0.354(8), N4 = 0.269(8) and O1 = 0.052(8) Å for
2). The deviation from ideal pentagonal-bipyramidal geometry is
indicated by the difference in the basal angles, which varies from
68.6(1)° to 80.5(1)° for 1 and 68.5(1)° to 79.8(1)° for 2, while the axial
sites are occupied by the nitrogen atoms from the imidazol moiety of
the ligand yielding N5–Fe1–N6 as the trans-axial angle (170.61(8)°)
for 1 and 170.2(1)° for 2. The coordination polyhedron is shown in
Fig. S2 (supplementary material).
4.4. Magnetic properties of 1 and 2
Compounds 1 (17 mg) and 2 (22 mg) are paramagnetic in all the
studied temperature range. The magnetic behavior expressed as
versus T, being the molar magnetic susceptibility and T the tem-
perature, is shown in Fig. 3 for both compounds. The MT product
obtained at 300 K is nearly constant for both complexes within the
vT
v
v
Fig. 1. ORTEP diagram of [Fe(dimpyen)OH](ClO4)2 (2) at 134 K with the corresponding atom numbering scheme. Displacement ellipsoids are shown at 50% probability levels.

218
N. Ortega-Villar et al. / Inorganica Chimica Acta 375 (2011) 213–219
Fig. 2. UV–Vis spectra for [Fe(dimpyen) (OH)](PF6)2 (1) in CH3CN solutions at 290 K
obtained from 800 to 350 nm; concentration 1.6 mM.
Fig. 4. Typical cyclic voltammograms of [Fe(dimpyen)(OH)](PF6)2 (1), obtained on
carbon glass electrode in 0.1 M Bu4NPF6 CH3CN solutions; recorded in (a) positive
direction (anodic sweep) and (b) negative direction (cathodic sweep).
temperature range explored, showing that the iron(III) remains
presented for similar complexes (0.576, 0.356, 0.350 V/Fc+–Fc) [2]
and can explain the reactivity of the Fe(II) in the coordination com-
pound towards the molecular oxygen. The reason for this, stems
from the fact that as the hydroxo complex is formed, the pH solu-
tion decrease as a result of the hydrolysis of the water bound to the
Fe(II) at the same time, as the pH decrease the redox potential of
the of the O2/H2O pair increases, this favors the oxidation of Fe(II)
to Fe(III). As the Fe(III) is formed, the hydrolysis of the water mol-
ecule is favored due to the higher acidity of Fe(III). As a conse-
quence of this, the stability of the hydroxo complex of Fe(III) is
enhanced and the redox potential of the Fe(III)/Fe(II) pair decrease,
favoring symbiotically the global oxidation process. This can be ob-
served in the reported E1/2 value (ꢀ0.38 V/Fc+–Fc) of this system.
high-spin (S = 5/2). The values obtained are 4.39 cm3 K molꢀ1 for
1 and 4.34 cm3 K molꢀ1 for 2, with
leff = 5.9 BM for both, which
is in the range of the spin-only value, as expected for a Fe(III) ion
[21].
4.5. Electrochemical properties
A typical volammogram of the compounds is shown in Fig. 4,
and presents a reversible signal at E1/2 = ꢀ0.38 V/Fc+–Fc, which
can be attributed to a monoelectronic exchange process for the
system Fe(III)/Fe(II). Additionally there is an irreversible signal at
Ecp = ꢀ1.45 V/Fc+–Fc, that has been assigned to the reduction of
the coordinated ligand dimpyen. The anodic sweep does not show
any oxidation processes above ꢀ0.38 V/Fc+–Fc, while the cathodic
sweep shows a reduction signal at Ecp = ꢀ0.35 V that can be as-
signed to the reduction from Fe(III) to Fe(II) in the coordination
compound. This observation is consistent with the observed oxida-
tion state of the metallic center in both compounds.
5. Conclusions
This paper shows the synthesis of a novel N6 ligand and a rather
rare heptacoordinated complex of Fe(III), in fact the only example
to our knowledge of a simple Fe(III)N6O complex. Even though the
complex synthesis was started either with Fe(II) or Fe(III) salts, the
end result was always the Fe(III) complex. This can be explained in
terms of the ligand environment affecting the E1/2 of the iron ion
reacting with the molecular oxygen. Although the spin-crossover
behavior was not observed, a small variation on the ligand, give
off, a very important change in the redox properties of the system,
promoting the formation of the Fe(III) heptadentate complex.
The half wave potential value for the Fe(III)/Fe(II) is
E1/2 = ꢀ0.38 V/Fc+–Fc. This value is very small compared with those
5
4
Acknowledgments
3
2
1
0
Compund 1
Compund 2
We are grateful to M. en C. Margarita Romero for her invaluable
support on the characterization of the ligand, to Q. Marisela Gut-
ierrez Franco for the IR spectra, to Georgina Duarte Lisci for the
MS spectra and Nayeli López Balbiaux for the elemental analysis.
Appendix A. Supplementary material
CCDC 760507 and 760508 contain the supplementary crystallo-
graphic data for complexes 1 and 2, respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2011.05.008.
0
50
100
150
200
250
300
T / K
Fig. 3. Plot of vMT vs. T data for (a) 1 and (b) 2 compounds (rate of measurements:
1 K/min).

N. Ortega-Villar et al. / Inorganica Chimica Acta 375 (2011) 213–219
219
[10] M.V. Cherrier, L. Martin, C. Cavazza, L. Jacquamet, D. Lemaire, J. Gaillard, J.C.
Fontecilla-Camps, J. Am. Chem. Soc. 28 (2005) 10075. 10082.
[11] G. Guisado-Barrios, Y. Li, A.M.Z. Slawin, D.T. Richens, I.A. Gass, P.R. Murray, L.J.
Yellowlees, E.K. Brechin, Dalton Trans. (2008) 551.
References
[1] P. Gütlich, Y. Garcia, H.A. Goodwin, Chem. Soc. Rev. 29 (2000) 419.
[2] (a) N. Ortega-Villar, V.M. Ugalde-Saldivar, M.C. Muñoz, L.A. Ortiz-Frade, J.G.
Alvarado-Rodriguez, J.A. Real, R. Moreno-Esparza, Inorg. Chem. 46 (2007)
7285;
[12] G. Gritzner, J. Küta, Pure Appl. Chem. 4 (1984) 462.
[13] A.J.C. Wilson (Ed.), International Tables for Crystallography, Volume C, Kluwer
Academic Publishers, Dordrecht, The Netherlands, 1995.
[14] R.C. Clark, J.S. Reid, Acta Crystallogr., Sect. A 51 (1995) 887.
[15] C. Giacovazzo, M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L.
Cascarano, L. De Caro, G. Polidori, R. Spagna, SIR-2004 (v 1.0) A Program for
Automatic Solution and Refinement of Crystal Structures, 2004.
[16] (a) G.M. Sheldrick, SHELX97, Programs for Crystal Structure Analysis, Release 97-
2, Institüt für Anorganische Chemie der Universität, Göttingen, Germany,
1998;
(b) G.M. Sheldrick, Acta. Crystallogr., Sect. A 64 (2008) 112.
[17] L. Farrugia, ORTEP3 for Windows, J. Appl. Crystallogr. 30 (1997) 565.
[18] F.H. Allen, Acta Crystallogr., Sect. B 58 (2002) 380.
[19] (a) J.M.D. Vera, J.S. Varela, I.B. Maimoun, E. Colacio, Eur. J. Inorg. Chem. (2005)
1907;
(b) N. Ortega-Villar, A.L. Thompson, M.C. Muñoz, V.M. Ugalde-Saldivar, A.E.
Goeta, R. Moreno-Esparza, J.A. Real, Chem. Eur. J. 11 (2005) 5721;
(c) X. Solans, L. Ruiz-Ramirez, R. Moreno-Esparza, M. Labrador, A. Escuer, J.
Solid State Chem. 109 (1994) 315.
[3] D. Casanova, P. Alemany, J.M. Bofill, S. Alvarez, Chem. Eur. J. 6 (2003) 1281.
[4] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds. Part B: Applications in Coordination, Organometallic and
Bioinorganic Chemistry, vol. 19, John Wiley, New York, 1997, p. 292.
[5] J.R. Atwood, Inorganic and Organometallic Reaction Mechanisms, Wiley-VCH,
New York, 1997.
[6] (a) T. Schneppensieper, S. Seibig, A. Zahl, P. Tregloan, R. van Eldik, Inorg. Chem.
40 (2001) 3670;
(b) F.P. Rotzinger, Chem. Rev. 105 (2005) 2003.
[7] (a) X.H. Bu, W. Chen, Z.H. Zhang, R.H. Zhang, S.M. Kuang, T. Clifford, Inorg.
Chim. Acta 310 (2000) 110;
(b) D.S. Marlin, M.M. Olmstead, P.K. Mascharak, Inorg. Chem. 42 (2003) 1681;
(c) S.L. Jain, A.M.Z. Slawin, J.D. Woollins, P. Bhattacharyya, Eur. J. Inorg. Chem.
(2005) 721;
(d) A. Majumder, C.R. Choudhury, S. Mitra, C. Marschner, J. Baumgartner, Z.
Naturforsch. 60b (2005) 99;
(e) X. Wang, S. Wang, L. Li, E.B. Sundberg, G.P. Gacho, Inorg. Chem. 42 (2003)
7799;
(f) J.D. Lee, M.H. Lee, J. Ind. Eng. Chem. 7 (2001) 137.
(b) P. Laine, A. Gourdon, J. Launay, J. Tuchagues, Inorg. Chem. 21 (1995) 5150;
(c) I. Morgenstern-Badarau, F. Lambert, J.P. Renault, M. Cesario, J.D. Marechal,
F. Maseras, Inorg. Chim. Acta (1–2) (2000) 338;
(d) C.P. Raptopoulou, Y. Sanakis, A. Boudalis, Eur. J. Inorg. Chem. 36 (2008)
5632;
(e) F. Bonadio, M.C. Senna, J. Ensling, A. Sieber, A. Neels, H. Stoeckli-Evans, S.
Decurtins, Inorg. Chem. 4 (2005) 969.
[20] I. Ivanovic´-Burmazovic´, M.S.A. Hamza, R. van Eldik, Inorg. Chem. Commun. 11
(2002) 937.
[8] A. Majumder, G. Pilet, M.S.E. Fallah, J. Ribas, S. Mitra, Inorg. Chim. Acta 7 (2007)
2307.
[21] O. Kahn, Molecular Magnetism, VCH, Weinheim, 1993.
[9] D. Zhang, D.H. Busch, P.L. Lennon, R.H. Weiss, W.L. Neumann, D.P. Riley, Inorg.
Chem. 5 (1998) 956. 963.