New Re(I) tricarbonyl-diimine complexes with N,N′-bis(substituted benzaldehyde)-1,2-diiminoethane Schiff base ligands: Synthesis, spectroscopic and electrochemical studies and crystal structures

Article abstract of DOI:10.1016/j.poly.2010.01.035

The syntheses, structures and spectroscopic properties of tricarbonylrhenium(I) complexes with N,N′-bis(2-bromo, 4-bromo, 4-chloro and 3-methoxybenzaldehyde)-1,2-diiminoethane Schiff base ligands have been investigated in this paper. Characterization of t

Full text of DOI:10.1016/j.poly.2010.01.035

Polyhedron 29 (2010) 1600–1606
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
New Re(I) tricarbonyl-diimine complexes with N,N0-bis(substituted
benzaldehyde)-1,2-diiminoethane Schiff base ligands: Synthesis,
spectroscopic and electrochemical studies and crystal structures
Valiollah Mirkhani a, , Reza Kia b, ,1,2, Akbar Rostami Vartooni a, Hoong-Kun Fun c
*
*
a Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
b Department of Chemistry, Science and Research Branch, Islamic Azad University, Poonak, Tehran, Iran
c X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, USM, 11800 Penang, Malaysia
a r t i c l e i n f o
a b s t r a c t
The syntheses, structures and spectroscopic properties of tricarbonylrhenium(I) complexes with N,N0-
bis(2-bromo, 4-bromo, 4-chloro and 3-methoxybenzaldehyde)-1,2-diiminoethane Schiff base ligands
have been investigated in this paper. Characterization of these complexes was carried out with FTIR,
NMR, UV–Vis spectroscopy, elemental analysis and X-ray crystallography. The electrochemical behavior
of the investigated complexes has been studied by cyclic voltammetry. The crystal structures of the 4-
chloro, 4-bromo and 4-methoxy substituted complexes are stabilized by intermolecular C–Hꢀ ꢀ ꢀCl and
C–Hꢀ ꢀ ꢀO hydrogen bonds. The remarkable features of the 2-bromo, 4-bromo and 4-chloro substituted
complexes are short intermolecular halogen–oxygen contacts. In the 4-bromo complex, short intermolec-
ular Brꢀ ꢀ ꢀO and Oꢀ ꢀ ꢀO contacts link neighboring molecules along the [1 0 0] direction, which are further
Article history:
Received 25 August 2009
Accepted 28 January 2010
Available online 8 February 2010
Keywords:
Tricarbonylrhenium(I) complexes
Diimine ligands
X-ray crystallography
stabilized by short intermolecular
p
ꢀ ꢀ ꢀ interactions. In 2-bromo complex, intermolecular Brꢀ ꢀ ꢀO interac-
p
tions link neighboring molecules into 1D extended chains along the [0 1 0] and [0 0 1] directions, forming
a 2D network which is parallel to the bc-plane.
Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.
1. Introduction
are, depending on their structure and environment, promising sen-
sitizers, luminophores, photocatalysts, radical photoinitiators and
The fac-[Re(CO)3(L)X]0/+ complexes, where L is a bi-functional
Schiff base ligand and X is a halogen atom or another ligand approx-
imately axial to the aromatic rings plane, have aroused recent atten-
tion [1,2]. Their ease of synthesis, multi-denticity, combination of
donor atoms and stability have made Schiff bases the preferred li-
gand system for use as radiopharmaceuticals [3], in catalysis [4]
and as model systems for biological macromolecules [5].
luminescent probes or sensors. Their potential function depends
on the character and properties of their lowest excited state, and
hence control of the excited state resulting from a MLCT transition
and the redox properties of the [Re(CO)3(L)X] complexes through
structural and electronic modification in the axial or diimine ligands
can be a way of improving the photo- and electro-catalytic proper-
ties of these compounds.
Unique photophysical and physicochemical properties of Re(I)
tricarbonyl-diimine complexes are connected with the existence
of energetically low-lying charge transfer excited states with large
electron density shift from the metal to the diimine ligand (MLCT
state). Because of the powerful reductive and/or oxidative proper-
ties in the MLCT state, such complexes can be considered as photo-
sensitizer, e.g., in photovoltaic cells [6,7]. Their photochemical
properties have been utilized for the electrocatalytic and photocat-
alytic reduction [8,9] of CO2 to CO. Several tricarbonylrhenium(I)
complexes have been used as electroluminescent materials in
OLED-type devices [10,11]. Rhenium carbonyl-diimine complexes
In this work, we report the synthesis, characterization, electro-
chemistry and the crystal structures of [Re(CO)3(4-cbzen)Cl] (1),
[Re(CO)3(4-bbzen)Cl] (2), [Re(CO)3(2-bbzen)Cl] (3) and [Re(CO)3-
(3-mbzen)Cl] (4), in which 4-cbzen = N,N0-bis(4-chlorobenzalde-
hyde)-1,2-diiminoethane, 4-bbzen = N,N0-bis(4-bromobenzalde-
hyde)-1,2-diiminoethane, 2-bbzen = N,N0-bis(2-bromobenzalde-
hyde)-1,2-diiminoethane and 3-mbzen = N,N0-bis(3-methoxy-
benzaldehyde)-1,2-diiminoethane.
2. Experimental
2.1. General
* Corresponding authors. Tel.: +98 3117932713; fax: +98 3116689732.
E-mail address: zsrkk@yahoo.com (R. Kia).
All chemicals were of reagent grade and were used without fur-
ther purification. The solvents were dried before use with the
appropriate drying reagents.
1
Thomson Reuters Researcher ID: A-5471-2009.
2
Postdoctoral fellow, USM, Malaysia.
0277-5387/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.01.035

V. Mirkhani et al. / Polyhedron 29 (2010) 1600–1606
1601
Table 1
Crystal data and structure refinement parameters for complexes 1–4.
Complex
1
2
3
4
Formula
C19H14Cl3N2O3Re
610.87
C19H14Br2ClN2O3Re
699.79
C19H14Br2ClN2O3Re
699.79
0.41 ꢂ 0.40 ꢂ 0.29
colourless
monoclinic
P21/c
C21H20ClN2O5Re
602.04
0.21 ꢂ 0.15 ꢂ 0.14
pale-yellow
monoclinic
P21/n
Formula weight
Crystal size (mm)
Colour
Crystal system
Space group
hmax (°)
0.34 ꢂ 0.19 ꢂ 0.17
0.70 ꢂ 0.21 ꢂ 0.11
colourless
colourless
triclinic
triclinic
ꢀ
ꢀ
P1
P1
32.5
37.5
40
32.3
a (Å)
b (Å)
c (Å)
7.1111(1)
10.0136(1)
14.6812(1)
73.50(1)
83.72(1)
77.58(2)
977.598(18)
2
7.1532(8)
10.2750(12)
14.7417(17)
73.097(6)
84.124(6)
77.064(6)
1009.6(2)
2
16.3744(3)
9.7068(2)
13.8832(3)
90
111.288(1)
90
2056.07(7)
4
2.261
13.7332(3)
10.6295(2)
14.6455(2)
90
93.380(1)
90
2134.19(7)
4
1.874
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
2.075
6.65
2.302
10.13
l
(mmꢁ1
)
9.95
5.85
F (0 0 0)
584
656
1312
1168
Index ranges
ꢁ10 6 h 6 10
ꢁ15 6 k 6 15
ꢁ22 6 l 6 21
37 585
ꢁ12 6 h 6 12
ꢁ17 6 k 6 17
ꢁ25 6 l 6 25
47 946
ꢁ28 6 h 6 28
ꢁ17 6 k 6 17
ꢁ24 6 l 6 25
85 299
ꢁ17 6 h 6 20
ꢁ14 6 k 6 15
ꢁ21 6 l 6 21
31 765
Number of measured reflections
Number of independent reflections (Rint
)
6699/0.026
6675
253
1.03
0.016
10 572/0.042
9294
253
1.05
0.0308
12 645/0.049
10 524
253
1.04
0.0403
7510/0.055
5241
273
0.97
0.0374
Number of observed reflections [I > 2
Number of parameters
Goodness-of-fit (GOF) on F2
R1 (observed data)
r(I)]
wR2 (all data)a
0.0348
0.0766
0.1083
0.0789
2
2
2
2
w ¼ 1=½r2ðF2o Þ þ ð0:0127PÞ þ 0:7305Pꢃ for 1; w ¼ 1=½r2ðFo2Þ þ ð0:0381PÞ þ 0:7477Pꢃ for 2; w ¼ 1=½r2ðFo2Þ þ ð0:0703PÞ þ 0:8024Pꢃ for 3 and w ¼ 1=½r2ðFo2Þ þ ð0:0351PÞ ꢃ
a
for 4; where P ¼ ðF2o þ 2Fc2Þ=3:
Elemental analyses were performed on a Leco, CHNS-932 ana-
2.3. Synthesis of the ligands
lyzer. IR spectra were recorded on an IRPrestige-21 Shimadzu FTIR
instrument in KBr pellets. NMR spectra were obtained on a Brucker
Avance 500 MHz spectrometer. Electronic spectra were recorded
on a Shimadzu UV-160 spectrophotometer. Emission spectra were
recorded on a RF-5000 Shimadzu spectrofluophotometer at room
temperature from solution samples in CH2Cl2. Cyclic voltammetry
(CV) was done using a three-electrode cell containing Ag/AgNO3 in
CH3CN reference electrode, a Pt wire counter electrode and a glassy
carbon (GC) working electrode. These measurements were per-
formed in CH2Cl2 containing 0.02 M Bu4NClO4 (TBAP) as a support-
ing electrolyte.
2.3.1. N,N0-Bis(4-chlorobenzaldehyde)-1,2-diiminoethane (4-cbzen)
In a 50 mL round-bottomed flask, 3 mmol (0.2 mL) of ethylendi-
amine was added to a CH2Cl2 solution of 6 mmol of 4-chlorobenz-
aldehyde (0.84 g). After stirring at room temperature for 3 h, the
solution was filtered and the resulting solid was recrystallized
from ethanol. FTIR (KBr, cmꢁ1): mmax 1643 (C@N). 1H NMR (d6-
DMSO, dppm): 4.00 (s, 4H, –CH2–CH2–); 7.39–7.67 (m, 8H, aromatic
hydrogens); 8.27 (s, 2H, iminic hydrogens).
2.3.2. N,N0-Bis(4-bromobenzaldehyde)-1,2-diiminoethane (4-bbzen)
This ligand was prepared by a procedure similar to 4-cbzen
ligand, but using 4-boromobenzaldehyde (1.11 g). The solid was
collected by filtration and recrystallized from ethanol. FTIR (KBr,
cmꢁ1): mmax 1643 (C@N). 1H NMR (d6-DMSO, dppm): 3.88 (s, 4H,
–CH2–CH2–); 7.62–7.67 (m, 8H, aromatic hydrogens); 8.33 (s, 2H,
iminic hydrogens).
2.2. Crystal structure determination
Single crystals of [Re(CO)3(4-cbzen)Cl] (1), [Re(CO)3(4-bbzen)-
Cl] (2), [Re(CO)3(2-bbzen)Cl] (3) and [Re(CO)3(3-mbzen)Cl] (4),
suitable for X-ray diffraction analysis, were grown by slow evapo-
ration of a solution of complexes dissolved in CH2Cl2 and toluene
(2:1). The crystallographic data and refinement parameters of the
complexes are listed in Table 1. Data were collected on a Bruker
2.3.3. N,N0-Bis(2-bromobenzaldehyde)-1,2-diiminoethane (2-bbzen)
This ligand was prepared by a procedure similar to that for
4-cbzen ligand, except that 0.7 mL of 2-bromobenzaldehyde was
used. The solution was filtered and the resulting solid was recrys-
tallized from ethanol. FTIR (KBr, cmꢁ1): mmax 1632 (C@N). 1H NMR
(d6-DMSO, dppm): 3.96 (s, 4H, –CH2–CH2–); 7.36–7.94 (m, 8H, aro-
matic hydrogens); 8.56 (s, 2H, iminic hydrogens).
SMART APEXII CCD area detector diffractometer with Mo Ka radi-
ation (k = 0.71073 Å) equipped with an Oxford cryo-system Cobra
low temperature attachment. Cell parameters were retrieved using
SMART [12] software and refined using SAINT [13] on all observed
reflections. Data reduction and correction for Lp (Lorentz-polariza-
tion) and decay were performed using SAINT PLUS software. Absorp-
tion corrections were applied using SADABS [14]. The structure was
solved by direct methods and refined by the least squares method
on F2 using the SHELXTL program package [15]. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were posi-
tioned geometrically and refined with a riding model approxima-
tion with their parameters constrained to the parent atom with
Uiso (H) = 1.2 or 1.5 Ueq (C).
2.3.4. N,N0-Bis(3-methoxybenzaldehyde)-1,2-diiminoethane (3-mbzen)
This ligand was prepared by a procedure similar to that for
4-cbzen ligand, except that 0.73 mL of 3-methoxybenzaldehyde
was used. The solution was filtered and the resulting solid was
recrystallized from ethanol. FTIR (KBr, cm-1): mmax 1645 (C@N).
1H NMR (d6-DMSO, dppm): 3.76 (s, 6H, methoxy hydrogens), 3.88

1602
V. Mirkhani et al. / Polyhedron 29 (2010) 1600–1606
Cl
R1
N
R1
R1
N
R1
N
N
Toluene/CH 2Cl2
Reflux
Re
CO
+ Re(CO)5Cl
R2
R2
R2
R2
OC
CO
R3
R3
R3
R3
4-cbzen: R1=H, R2=H, R3=Cl
4-bbzen: R1=H, R2=H, R3=Br
2-bbzen: R1=Br, R2=H, R3=H
3-mbzen: R1=H, R2=OCH3, R3=H
[Re(CO)3(4-cbzen)Cl] (1)
[Re(CO)3(4-bbzen)Cl] (2)
[Re(CO)3(2-bbzen)Cl] (3)
[Re(CO)3(3-mbzen)Cl] (4)
Scheme 1. Preparation of the characterized Re(I) tricarbonyl-diimine complexes.
2.4. Synthesis of the rhenium complexes
Table 2
UV–Vis spectral data of the ligands and complexes 1–4 in CH2Cl2 (4 ꢂ 10ꢁ5 M).
2.4.1. [Re(CO)3(4-cbzen)Cl] (1)
Compound
kmax (nm) [e )
] (Mꢁ1 cmꢁ1
To a 50 mL round-bottom flask containing 0.55 mmol (0.17 g) of
4-cbzen dissolved in 20 mL of degassed CH2Cl2 and toluene (1:2),
was added an equimolar amount of Re(CO)5Cl (0.2 g). The mixture
was heated at reflux for 4 h. The solution was concentrated to half
volume and n-hexane was added to precipitate the complex. Anal.
Calc. for C19H14ClN4O7Re: C, 37.36; H, 2.29; N, 4.58. Found: C,
37.29; H, 2.34; N, 4.51%. FTIR (KBr, cmꢁ1): mmax 2021, 1916 and
1889 (CO); 1626 (C@N). 1H NMR (d6-DMSO, dppm): 4.09–4.13 and
4.23–4.25 (two sets of multiples, 4H, –CH2–CH2–); 7.62–7.89 (m,
8H, aromatic hydrogens); 9.19 (s, 2H, iminic hydrogens). 13C{1H}
NMR (d6-DMSO, dppm): 65.42 (–CH2–CH2–); 129.56, 131.52,
135.29, 136.81 (aromatic carbons); 174.22 (iminic carbons);
192.47 (CO); 195.60 (2CO).
4-cbzen
4-bbzen
2-bbzen
245 [26 750], 290 [9500]
252 [39 450], 292 [5000]
250 [27 720], 291 [3275]
245 [14 333], 300 [6500]
3-mbzena
Complex 1
Complex 2
Complex 3
Complex 4
235 [15 025], 261 [32 500], 373 [1825]b
233 [12 750], 261 [28 750], 370 [1800]b
233 [13 250], 257 [17 950], 366 [1712]b
238 [19 833], 258 [21 966], 369[1770]b
C = 12 ꢂ 10ꢁ5
C = 1 ꢂ 10ꢁ3
M
a
b
2.4.2. [Re(CO)3(4-bbzen)Cl] (2)
This complex was synthesized by a procedure similar to 1, but
using the 4-bbzen ligand (0.22 g). Anal. Calc. for C19H14ClN4O7Re:
C, 32.62; H, 2.00; N, 4.00. Found: C, 32.53; H, 1.97; N, 3.99%. FTIR
(KBr, cmꢁ1): mmax 2019, 1913 and 1886 (CO); 1630 (C@N). 1H
NMR (d6-DMSO, dppm): 4.09–4.12 and 4.22–4.25 (two sets of mul-
tiples, 4H, –CH2–CH2–); 7.76–7.81, (m, 8H, aromatic hydrogens);
9.17 (s, 2H, iminic hydrogens). 13C{1H} NMR (d6-DMSO, dppm):
65.42 (–CH2–CH2–); 125.96, 131.63, 132.47, 135.64 (aromatic car-
bons); 174.31 (iminic carbons); 192.46 (CO); 195.6 (2CO).
2.4.3. [Re(CO)3(2-bbzen)Cl] (3)
This complex was prepared by a procedure similar to that for 1,
but using the 2-bbzen ligand (0.22 g). Anal. Calc. for
C19H14ClN4O7Re: C, 32.62; H, 2.00; N, 4.00. Found: C, 32.45; H,
1.86; N, 3.95%. FTIR (KBr, cmꢁ1): mmax 1900 (broad) and 2017
(CO); 1625 (C@N). 1H NMR (d6-DMSO, dppm): 4.15–4.19 and
4.38–4.42 (two sets of multiples, 4H, –CH2–CH2–); 7.45–7.79 (8H,
aromatic hydrogens); 9.16 (s, 2H, iminic hydrogens). 13C{1H}
NMR (d6-DMSO, dppm): 64.38 (–CH2–CH2–); 121.67, 128.63,
131.58, 133.07, 133.27, 137.59 (aromatic carbons); 173.94 (iminic
carbons); 192.17 (CO); 194.93 (2CO).
Fig. 1. Cyclic voltammograms of [Re(CO)3(2-bbzen)Cl] (a), [Re(CO)3(4-cbzen)Cl] (b),
[Re(CO)3(4-bbzen)Cl] (c) and [Re(CO)3(3-mbzen)Cl] (d) in CH2Cl2 at 298 K (scan rate
=100 mV/s, C = 2 ꢂ 10-4 M).
2.4.4. [Re(CO)3(3-mbzen)Cl] (4)
This complex was prepared by a procedure similar to that for 1,
but using the 3-mbzen ligand (0.16 g). Anal. Calc. for
C19H14ClN4O7Re: C, 41.91; H, 3.32; N, 4.65. Found: C, 41.25; H,
3.36; N, 4.65%. FTIR (KBr, cmꢁ1): mmax 2019, 1921 and 1889 (CO);
1630 (C@N). 1H NMR (d6-DMSO, dppm): 3.82 (s, 6H, methoxy hydro-
gens), 4.11–4.13 and 4.23–4.25 (two sets of multiples, 4H, –CH2–
CH2–); 7.10–7.62 (m, 8H, aromatic hydrogens); 9.18 (s, 2H, iminic
hydrogens). 13C{1H} NMR (d6-DMSO, dppm): 65.5 (–CH2–CH2–);
114.51, 118.37, 122.09, 130.69, 137.47, 159.97 (aromatic carbons);
174.76 (iminic carbons); 192.8 (CO); 195.68 (2CO).
Fig. 2. The molecular structure of complex 1, showing 50% probability displace-
ment ellipsoids and the atomic numbering.
(s, 4H, –CH2–CH2–); 6.96–7.44 (m, 8H, aromatic hydrogens); 8.31
(s, 2H, iminic hydrogens).

V. Mirkhani et al. / Polyhedron 29 (2010) 1600–1606
1603
Fig. 3. The crystal packing of complex 1, viewed down the a-axis showing intermolecular Clꢀ ꢀ ꢀO interactions.
Fig. 4. The crystal packing of complex 2, viewed down the a-axis showing intermolecular Brꢀ ꢀ ꢀO interactions.
Fig. 5. The crystal packing of complex 3, viewed down the b-axis showing short intermolecular Brꢀ ꢀ ꢀO contacts, forming1D extended chains along the c-axis.

1604
V. Mirkhani et al. / Polyhedron 29 (2010) 1600–1606
3. Results and discussion
3.1. General characterization
The synthetic routes of complexes 1–4 are outlined in Scheme 1.
The new complexes are stable in the solid and solution states, and
they were characterized by the usual spectroscopic techniques.
The IR spectra of the complexes show three or two (one peak is
broad) strong bands in the carbonyl region (1880–2010 cmꢁ1
)
which arise from a facial conformation around a hexa-coordinated
rhenium. The -donor character of the chlorine atom increases the
Re–CO back-bonding, which decreases the energy of (CO). Coordi-
(C@N)
p
m
nation of the diimine ligands are indicated by the shifts of
m
from 1643 cmꢁ1 in the free ligand to 1626 cmꢁ1 in 1, from 1643 to
1620 cmꢁ1 in 2, from 1632 to 1625 cmꢁ1 in 3 and from 1645 to
1630 cmꢁ1 in 4.
In the 1H NMR spectra of complexes 1–4, which are presented
in the experimental section, the signals are shifted to the low-field
region with respect to the free ligands, as a result of ligand coordi-
nation. The chemical shifts observed at d 9.19 for 1, at d 9.17 for 2,
at d 9.16 for 3 and at d 9.18 for 4 are assigned to the proton of
azomethine (–CH@N–) as a singlet. The signals of the –CH2–CH2–
protons appear as two sets of multiples in the complexes, but ap-
peared as a singlet (at 3.76–4 ppm) in the free ligands, indicating
that the methylene protons of the complexes are magnetically
non-equivalent. The 13C NMR spectra of the complexes show two
signals with an integral of 2:1 in the range 192–196 ppm, and
the downfield peaks are ascribed to the two carbonyl groups cis
to the chloride while the upfield resonance is assigned to the car-
bonyl trans to the chloride.
The UV–Vis spectroscopic data for the ligands and complexes
are given in Table 2. The bands of the diimine ligands are due to
the
p?p p
* and n ? * transitions [16]. In general, the electronic
absorption spectra of rhenium(I) diimine complexes show intense
high-energy absorption bands at ca. 230–330 nm and low-energy
absorption bands at ca. 400 nm [17,18]. The former, which are also
found in the free ligands, are assigned as
p
?
p
* transitions and the
*
p (diimine) metal-to-
later are tentatively assigned as d (Re)?
p
ligand charge transfer (MLCT) transitions. The spectral positions
*
of the p?p bands in the complexes are red-shifted in comparison
to the ligand, due to the coordination of the heavy metal core.
The complexes 1–4 do not show emission in CH2Cl2 at room
temperature. Fig. 1 shows cyclic voltammograms of the complexes
in CH2Cl2 under a nitrogen atmosphere. Complexes 1–4 show a
quasi-reversible Re(I/II) redox couple with E1/2 values of 1.11,
1.12, 1.11 and 1.12 V versus Ag/AgNO3 (in CH3CN), respectively.
Fig. 6. The crystal packing of complex 4, viewed down the b-axis showing linking of
molecules by intermolecular interactions. Only the H atoms involved the interac-
tion are shown.
In the cyclic voltammogram, peak to peak separations (
D
Tp) of
) of
90, 90, 100 and 160 mV were observed at a scan rate (
m
100 mV/s for complexes 1–4, respectively.
and 77.73(11)° for 4 slightly deviate from the expected ideal 90°
for an octahedron. As can be seen in Table 3, the trans angles at
the Re(I) site are in the range 172.88(6)–176.23(9)°, showing a
slight deviation from an ideal octahedral arrangement. Hydrogen
bonding interactions in complexes 1, 2 and 4, C–Hꢀ ꢀ ꢀX (X = O and
Cl), are listed in Table 4, which stabilize the crystal structures.
Complex 3 does not show any classic hydrogen bonds. The inter-
esting features of complexes 1, 2 and 3 are the short intermolecular
Clꢀ ꢀ ꢀO, Brꢀ ꢀ ꢀO, Oꢀ ꢀ ꢀO, and Brꢀ ꢀ ꢀO contacts, respectively, which are
listed in Table 5. In complex 1, the short intermolecular Clꢀ ꢀ ꢀO con-
tacts link neighboring molecules into individual dimers which are
further connected by C–Hꢀ ꢀ ꢀCl hydrogen bonds (Fig. 3). In complex
2, the short intermolecular Brꢀ ꢀ ꢀO and Oꢀ ꢀ ꢀO contacts link neigh-
boring molecules into a chain along the [1 0 0] direction (Fig. 4).
These contacts are shorter than the sum of the van der Waals radii
of these atoms. Complex 2 is further stabilized by intermolecular
3.2. Structural characterization
The perspective drawing of complex 1 and the crystal packing of
complexes 1–4 are shown in Figs. 2–6. In general, the coordination
geometries of the prepared complexes are distorted octahedral,
due to the chelating effect of the rigid diimine ligands. The three
terminal CO ligands coordinated with the Re are arranged in a fa-
cial fashion, which is similar to those found in other related rhe-
nium systems [19–21]. Selected bond lengths and bond angles of
the complexes are presented in Table 3. The Re–N bond lengths
in these complexes are in the range of reported for other previously
synthesized complexes [22,23]. Due to the
p-donor character of
the chloride ligand, the length of the axial Re–C bonds is slightly
shorter than the values of the equatorial Re–C bonds. The diimine
ligands bite angles of 78.52(5)° for 1, 78.15(8)° for 2, 77.35(8)° for 3

V. Mirkhani et al. / Polyhedron 29 (2010) 1600–1606
1605
Table 3
The attractive nature of these interactions is mainly due to elec-
trostatic effects, but polarization, charge-transfer and dispersion
contributions all play an important role [24]. The Xꢀꢀ ꢀEl (X = Halogen,
El = Electronegative atom) interactions, or in general non-bonded
interactions, are capable of affecting the realized crystalline
architecture of solid compounds decisively and they may thus
be used as tools in molecular designs, crystal engineering and
supramolecular chemistry [25].
Selected bond distances (Å) and angles (°).
Complex 1
Re(1)–Cl(1)
Re(1)–N(1)
Re(1)–N(2)
Re(1)–C(17)
Re(1)–C(18)
Re(1)–C(19)
2.4886(4)
2.2237(16)
2.1859(14)
1.9163(18)
1.9321(15)
1.910(2)
N(1)–Re(1)–N(2)
N(1)–Re–C(18)
N(2)–Re–C(19)
C(17)–Re–C(18)
C(17)–Re–C(19)
C(17)–Re(1)–Cl(1)
78.52(5)
98.36(7)
98.58(6)
92.36(7)
87.30(8)
172.88(6)
Complex 2
Re(1)–Cl(1)
Re(1)–N(1)
Re(1)–N(2)
Re(1)–C(17)
Re(1)–C(18)
Re(1)–C(19)
2.4929(7)
2.188(2)
2.225(2)
1.913(3)
1.918(3)
1.937(3)
N(1)–Re(1)–N(2)
N(1)–Re–C(17)
N(2)–Re–C(19)
C(18)–Re–C(17)
C(18)–Re–C(19)
C(18)–Re(1)–Cl(1)
78.15(8)
4. Conclusion
98.62(10)
98.14(11)
86.86(12)
92.08(11)
173.53(9)
This work describes the synthesis and characterization of sev-
eral Re(I)–tricarbonyl complexes with diimine ligands. The ligands
were obtained by the condensation of benzaldehyde derivatives
with ethylendiamine. All the complexes have been fully character-
ized by FTIR, 1H, 13C NMR and UV–Vis spectroscopy, elemental
analysis and X-ray diffraction analysis. The presence of three
strong IR absorptions in the region of CO stretching vibrations is
consistent with a facial coordination of the three carbonyl ligands.
The molecular units of the complexes are stabilized by intermolec-
ular hydrogen bonds and short intermolecular halogen–oxygen
and oxygen–oxygen interactions.
Complex 3
Re(1)–Cl(1)
Re(1)–N(1)
Re(1)–N(2)
Re(1)–C(17)
Re(1)–C(18)
Re(1)–C(19)
2.4884(7)
2.186(3)
2.193(2)
1.921(3)
1.911(3)
1.909(3)
N(1)–Re(1)–N(2)
N(1)–Re–C(18)
N(2)–Re–C(17)
C(19)–Re–C(17)
C(19)–Re–C(18)
C(19)–Re(1)–Cl(1)
77.35(8)
98.82(10)
98.39(10)
90.02(12)
86.48(12)
176.23(9)
Complex 4
Re(1)–Cl(1)
Re(1)–N(1)
Re(1)–N(2)
Re(1)–C(19)
Re(1)–C(20)
Re(1)–C(21)
2.4835(10)
2.195(3)
2.199(3)
1.912(4)
1.913(4)
1.929(4)
N(1)–Re(1)–N(2)
N(1)–Re–C(19)
N(2)–Re–C(21)
C(20)–Re–C(19)
C(20)–Re–C(21)
C(20)–Re(1)–Cl(1)
77.73(11)
99.48(15)
97.17(15)
86.58(18)
90.87(18)
175.83(13)
5. Supplementary material
CCDC 694693–694696 contain the supplementary crystallo-
graphic data for complexes 1–4, respectively. These data can be ob-
tained
free
of
charge
via
www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
Table 4
Parameters of hydrogen bonding interactions in complexes 1-4.
D–Hꢀ ꢀ ꢀA
Hꢀ ꢀ ꢀA (Å)
Dꢀ ꢀ ꢀA (Å)
D–Hꢀ ꢀ ꢀA (°)
Complex 1
Acknowledgements
C(10)–H(10A)ꢀ ꢀ ꢀCl(1)i
C(12)–H(12A)ꢀ ꢀ ꢀCl(1)
2.7300
2.7900
3.5910(16)
3.6529(18)
155.00
155.00
This work was supported by the University of Isfahan and the
Universiti Sains Malaysia (USM). The authors are grateful for their
support. Dr. R. Kia thanks USM for a post-doctoral research fellow-
ship. Dr. E. Shams is acknowledged for helpful discussions about
the CV measurements.
Complex 2
C(1)–H(1A)ꢀ ꢀ ꢀCl(1)
2.7800
2.7500
3.654(3)
3.616(3)
156.00
155.00
C(7)–H(7A)ꢀ ꢀ ꢀCl(1)i
Complex 4
C(5)–H(5A)ꢀ ꢀ ꢀCl(1)
C(7)–H(7A)ꢀ ꢀ ꢀO(5)ii
C(18)–H(18A)ꢀ ꢀ ꢀCl(1)iii
2.6200
2.6000
2.6500
3.505(4)
3.426(5)
3.526(4)
158.00
148.00
151.00
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