Synthesis, characterization, and photophysical properties of 2-hydroxybenzaldehyde [(1E)-1-pyridin-2-ylethylidene]hydrazone and its rhenium(I) complexes

Article abstract of DOI:10.1002/ejic.200701199

The 2-hydroxybenzaldehyde [(1E)-1-pyridin-2-ylethylidene] hydrazone (HL²) ligand was prepared and its rhenium(I) complexes [ReX(CO) ₃(HL²)] were obtained by reaction with fac-[ReX(CO) ₃(CH₃CN)₂] (X = Cl, Br) in chloroform. The compounds were characterized by elemental analysis, mass spectrometry, and IR, UV/Vis, and ¹H NMR spectroscopy. Furthermore, the structures were also established by X-ray diffraction. The aromatic rings are almost coplanar in the ligand structure, and the configuration around the hydrazone group is strongly dominated by the presence of an intramolecular hydrogen bond between the OH group and the hydrazinic nitrogen atom N1. The rhenium center is coordinated through the pyridine and hydrazinic nitrogen atoms to give a five-membered chelate ring. In addition, the free ligand shows interesting luminescence properties. The effect of the metal coordination on the photophysical behavior of the resulting complex was also studied. ? Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701199

FULL PAPER
DOI: 10.1002/ejic.200701199
Synthesis, Characterization, and Photophysical Properties of
2-Hydroxybenzaldehyde [(1E)-1-pyridin-2-ylethylidene]hydrazone and Its
Rhenium(I) Complexes
Paula Barbazán,[a] Rosa Carballo,[a] Berta Covelo,[a,b] Carlos Lodeiro,[c]
João Carlos Lima,[c] and Ezequiel M. Vázquez-López*[a]
Keywords: Rhenium / Hydrazones / Carbonyl ligands / Luminescence
The 2-hydroxybenzaldehyde [(1E)-1-pyridin-2-ylethylid-
lecular hydrogen bond between the OH group and the hy-
ene]hydrazone (HL2) ligand was prepared and its rhenium(I) drazinic nitrogen atom N1. The rhenium center is coordi-
complexes [ReX(CO)3(HL2)] were obtained by reaction with
fac-[ReX(CO)3(CH3CN)2] (X = Cl, Br) in chloroform. The
compounds were characterized by elemental analysis, mass
spectrometry, and IR, UV/Vis, and 1H NMR spectroscopy.
Furthermore, the structures were also established by X-ray
diffraction. The aromatic rings are almost coplanar in the li-
gand structure, and the configuration around the hydrazone
group is strongly dominated by the presence of an intramo-
nated through the pyridine and hydrazinic nitrogen atoms to
give a five-membered chelate ring. In addition, the free li-
gand shows interesting luminescence properties. The effect
of the metal coordination on the photophysical behavior of
the resulting complex was also studied.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
energy levels of the metal-centered dπ orbitals and/or by
using functional groups that modulate the electron-donor
or -acceptor properties of the ligands.[8] Modifications may
yield complexes that are no longer luminescent owing to
the low energy of the MLCT states (energy-gap law[9]), al-
though in such cases other promising applications such as,
for example, nonlinear optical properties may result.[10]
We, in collaboration with other groups, have initiated a
research program aimed at the synthesis and characteriza-
tion of rhenium(I) complexes of different Schiff base deriva-
tives like thiosemicarbazones[11–13] and, more recently, hy-
drazone derivatives.[14] Both series of ligands are versatile
systems that can coordinate as neutral ligands or in their
deprotonated form. In addition, different coordination
groups can be easily added to the general framework in the
search for different properties, such as those outlined above,
or different coordinative behavior. For instance, HL1
(Scheme 1) forms very stable complexes with the fragment
fac-{ReX(CO)3} (X = Br, H2O) by N,NЈ-coordination.[15]
The substitution of the 2-acetylpyridine fragment by a for-
myl ferrocene group [H(Fc)L1 in Scheme 1] gives rise to,[16]
as a result of the N,O-coordination mode, significant spec-
troscopic differences that may become suitable tools for co-
ordinative diagnosis in the chemistry of hydrazone ligands.
We present here the synthesis and characterization of an
isomer of HL1, 2-hydroxybenzaldehyde [(1E)-1-pyridin-2-
ylethylidene]hydrazone (HL2 in Scheme 1), for which ap-
propriate photophysical properties derived from the salicyl-
aldimine group[17] are expected, despite the presence of the
same donor groups as those in HL1.
Introduction
The study of rhenium(I) complexes with N,NЈ-chelate
rings has two main aims. Firstly, the complexes of {Re(CO)3}+
with N,NЈ-chelate ligands, in which one or both substitu-
ents are aromatic heterocycles, are exceptionally stable.
There are numerous reports on complexes of this type as
models for the design of 188Re or 99mTc systems for thera-
peutic applications[1] or labeling of targeting biomolec-
ules.[2–6] In the latter application, the selected ligand re-
quires a second group for conjugation to a biomolecule.
The kinetic inertness and chemical robustness of the com-
plexes are also desirable properties for such applications. A
second aspect of interest concerns the luminescent proper-
ties of the diimine complexes. Indeed, complexes of the type
[ReCl(diimine)(CO)3] with polypyridyls such as 2,2Ј-bipyr-
idine as diimine ligands are generally luminescent.[7] The
emission originates from 3MLCT (triplet metal-to-ligand
charge transfer excited states). Control of the photophysical
properties of these complexes can be achieved by using a
coligand with different ligand field strength to adjust the
[a] Departamento de Química Inorgánica, Universidade de Vigo,
Facultade de Química,
36310 Vigo, Galicia, Spain
Fax: +34-986-812556
E-mail: ezequiel@uvigo.es
[b] Unidade de Determinación Estructural e Proteómica, CACTI,
Universidade de Vigo,
36310 Vigo, Spain
[c] REQUIMTE-CQFB, Departamento de Química, Faculdade de
Ciências e Tecnologia, Universidade Nova de Lisboa,
2829-516 Monte de Caparica, Portugal
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E. M. Vázquez-López et al.
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uct in some instances. The formation of this unexpected
compound was proved by spectroscopic studies (IR, NMR,
mass spectrometry, and X-ray diffraction)[19] and can only
be avoided by following path i.
The formation of H2L3 (Scheme 3) from salicylaldehyde
hydrazone in the presence of [W(CO)6] was described be-
fore.[20] The authors propose the formation of a dimer by
attack of a molecule of salicylaldehyde hydrazone on its
tungsten complex. The tetracyclic intermediate, N–NH2–
NH2–N, yields the bis(2-hydroxybenzaldehyde)hydrazone
through decomposition of the metal complex after release
of hydrazine. Although this mechanism is probably correct,
our observation of the formation of H2L3 in the synthesis
of HL2 provides evidence against the catalytic role attrib-
uted to [W(CO)6] or other metals. In fact, the rhenium(I)
complexes were obtained in good yield and the formation
of H2L3 from its solutions was not observed in any case
(see below).
Scheme 1.
Results and Discussion
Synthesis and Spectroscopic Characterization
Ligand HL2 was readily obtained by reaction of the pre-
viously prepared 2-acetylpyridine hydrazone with salicylal-
dehyde as described previously (Scheme 2, path i).[18] Ele-
mental analysis and spectroscopic characterization support
the formation of the ligand. X-ray quality crystals of the
free ligands were obtained by slow evaporation of the
mother liquor.
Scheme 3. Mechanism of excited-state intramolecular proton trans-
fer (ESIPT) responsible for the fluorescence in HL2.
The fac-[ReX(HL2)(CO)3] (1, X = Cl; 2, X = Br) com-
plexes were obtained as reddish-brown solids in high yield
by reaction of 1:1 mixtures of HL2 and fac-[ReX(CO)3-
(CH3CN)2] in refluxing chloroform. We attempted to ob-
tain the complexes from the corresponding 2-acetylpyridine
rhenium complex by following a similar method to that re-
ported by Alberto et al.[21] for the synthesis of rhenium(I)
complexes of different Schiff base ligands, but the title com-
pounds were not detected. Elemental analysis and mass
spectrometry confirmed the stoichiometry. A facial geome-
try around the rhenium atom is suggested by the three
strong ν(CO) IR bands in the range 1901–2036 cm–1.
In the 1H NMR spectra of both isolated rhenium(I) com-
plexes in [D6]DMSO, the C–H proton signals are generally
Scheme 2.
Another possible path (Scheme 2, path ii) for the synthe- shifted to lower field with respect to that of the free ligand
sis of the target compound from commercial salicylalde- (HL2). This effect of rhenium coordination was also ob-
hyde hydrazone was also explored. In this case, the ligand served in other hydrazine-based ligands such as thiosemi-
was obtained in very low yield, which did not increase upon carbazones.[11–15] However, metalation has the opposite ef-
use of other solvents or reaction conditions (ethanol, tolu- fect on the H–O signal. Bearing in mind that the hydrogen
ene, or catalytic amounts of sulfuric or hydrochloric acids bond is probably responsible for the strong displacement (δ
or by using water-trapping systems, such as a Dean–Stark = 11.40 ppm) of the H–O signal in free HL2 with respect to
receiver). Interestingly, we observed the formation of bis(2- the usual position for an aromatic alcohol, the chemical
hydroxybenzaldehyde)hydrazone (H2L3, Scheme 2) in reac- shift observed in the complexes (δ = 10.50 ppm) suggests a
tions through path ii, and in fact, this was the major prod- different electronic distribution on the hydroxybenzylidene
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A Hydrazone Derivative and Its Rhenium(I) Complexes
hydrazone fragment induced by the metal fragment. How- Table 1. Main interatomic distances [Å] and angles [°] in HL2,
[ReCl(CO)3(HL2)] (1), and [ReBr(CO)3(HL2)] (2).
1
ever, conclusions based on the differences in the H chemi-
HL2
1
2
cal-shift data for the hydroxy group between the ligand and
its complexes are unreliable, because although the reso-
nances of the hydroxy protons involved in the hydrogen
O1–C3
N2–C8
1.351(4)
1.278(4)
1.408(4)
1.268(4)
1.473(5)
1.449(5)
1.356(8)
1.280(9)
1.402(7)
1.298(9)
1.475(9)
1.439(9)
2.152(6)
2.222(6)
2.493(2)
1.346(12)
1.323(13)
1.387(10)
1.289(13)
1.457(14)
1.447(13)
2.154(9)
bonds tend to be shifted downfield, they are subject to nu- N2–N1
merous effects that are hard to predict.[22] In contrast, the
N1–C1
C8–C9
dδ/dT values of hydroxy groups do provide some infor-
C2–C1
mation about intramolecular hydrogen bonding. Strongly
Re–N3
Re–N2
Re–Cl
hydrogen-bonded hydroxy groups show little change with
temperature, because the interaction with solvents that are
hydrogen-bond acceptors is small. Conversely, the chemical
shifts of hydroxy protons hydrogen bonded to the solvent
do show a marked temperature dependence due to changes
2.203(9)
Re–Br
2.6257(11)
111.8(9)
115.4(9)
116.6(9)
122.5(10)
122.1(9)
73.8(3)
116.5(7)
131.6(7)
118.2(7)
114.8(10)
C8–N2–N1
C1–N1–N2
N2–C8–C9
113.4(3)
113.9(3)
116.5(3)
125.4(4)
123.0(4)
113.3(6)
117.2(6)
117.1(7)
123.8(7)
122.4(7)
73.3(2)
in mobility of the solvent molecules.[23] The dδ/dT values N2–C8–C14
for the rhenium complexes (6ϫ10–3 ppm) are almost twice
N1–C1–C2
N3–Re–N2
the value of the free ligand (4ϫ10–3 ppm), but they suggest
C8–N2–Re
117.6(5)
129.1(4)
118.4(5)
113.5(6)
that, although the hydrogen bond is probably weakened,
N1–N2–Re
C9–N3–Re
N3–C9–C8
the hydroxy proton is mainly involved in the intramolecular
interaction Ϫ a situation consistent with solid-state results
(see below).
116.3(4)
The two aromatic rings in the structure of the HL2 ligand
are practically coplanar. The configurations of the bonds
involved in the hydrazone group are strongly dominated by
the hydrogen bonding between the OH group and the nitro-
gen N1 atom. This interaction yields a very stable six-mem-
bered ring,[24] which is also observed in the two rhenium
complex structures and, in addition, is responsible for the
E configuration of the C1=N1 bonds in the three com-
pounds. The configuration of the N2=N1 and C8=N2
bonds is also E in HL2.
X-ray Studies
The molecular structures and the numbering scheme of
the free ligand and the rhenium complexes included in the
present work are shown in Figure 1. Selected bond lengths
and angles are included in Table 1. Details about the data
collection and refinement are included in the Experimental
Section.
The coordination polyhedron around the rhenium atom
can be described as a distorted octahedron formed by coor-
dination of the two nitrogen atoms of the HL2 ligand, N2
and N3, by the three carbonyl carbon atoms and the halo-
gen atoms. The main distortion from the ideal octahedral
geometry is imposed by the formation of a chelate ring, as
can be seen by the N2–Re–N3 angle (Table 1). The Re–N
and Re–X distances are similar to those found in complexes
of the fragment fac-“ReX(CO)3” with hydrazone-based li-
gands,[25] for example, [ReBr(CO)3(HL1)] (2.158 and
2.167 Å).[15]
The phenyl and pyridine rings are also coplanar after
coordination, as can be deduced from angle between the
root mean square planes of 15.4(3) and 13.6(3)° for com-
pounds 1 and 2, respectively [3.0(1)° for HL2]. The coordi-
nation of the rhenium to the N2 and N3 atoms and, conse-
quently, the formation of the five-membered chelate ring,
lead to rotation of the pyridine ring with respect to that in
HL2 (where the N3 atom is oriented towards the methyl
group C14). In terms of the bond lengths in the hydrazone
arm, there are only statistical differences between the values
Figure 1. Molecular structure of HL2 (A) and [ReBr(CO)3(HL2)]
(B).
The structure of HL2 was obtained from single crystals observed in free ligand and its complex.
formed from the mother liquor. The study by X-ray diffrac-
An interesting parameter that highlights differences be-
tion of red single crystals of the compounds [ReX(CO)3- tween the free ligand and its complexes is the intramolecu-
{HL2}] showed them to be isotypic and confirmed the lar hydrogen bond. We allowed the hydroxy hydrogen atom
metal configuration inferred from the spectroscopic data.
to refine freely in order to obtain more metric information
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E. M. Vázquez-López et al.
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on the D–H···A values. Although the differences between
the O1–H and H···N1 distances and the O1–H···N1 angle
are not significant due to the high value of the standard
deviation associated with them, the lengthening of the
O1···N1 distance is reliable (Table 2). In the free ligand, the
O1–H···N1 parameters indicate a significant hydrogen-
bonding interaction. The O1···N1 distance is borderline be-
tween a strong and normal (moderate) hydrogen bond.[26]
However, the quality of the crystals of the complexes and,
consequently, the high values of the standard deviation did
not allow precise information to be obtained on the H···N1
and O1–H···N1 distances and angles. Once again, the
O1···N1 distance, although longer than that observed in the
free ligand, indicates a moderate hydrogen bond. The angle
between the plane defined by the atoms C8–N2–N1 and the
phenoxy group plane is almost negligible in HL2 (1.3°) but
increases to 19.5° in 1 and 17.2° in 2.
Table 2. Structural parameters describing intramolecular and inter-
molecular moderate and nonconventional hydrogen bonds.[a]
D–H···A
d(D–H) [Å] d(H···A) [Å] d(D···A) [Å] Ͻ(DHA) [°]
HL2
O1–H1···N1
0.98(3)
0.93
0.93
1.69(3)
2.60
2.75
2.598(2)
3.462(3)
3.589(3)
153(2)
155.4
151.3
C1–H2···O1#1
C11–H11···N3#2
1
O1–H1···N1
0.84(8)
0.95
0.95
1.97(9)
2.85
2.466
2.635(7)
3.754(8)
3.384(10)
135(8)
161.8
175.3
C10–H10···Cl#3
C11–H11···O1#4
2
O1–H1···N1
0.70(10)
0.93
0.93
2.17(11)
2.96
2.42
2.645(11)
3.858(11)
3.347(15)
126(12)
163.8
172.5
C10–H10···Br#3
C11–H11···O1#4
[a] Symmetry code #1 x – 1/2,–y + 1/2, –z + 1; #2 x – 1/2, y, –z +
1/2; #3 1 – x, –y, –z; #4 1 – x, 1/2 + y, –1/2 – z.
The intermolecular association in the structures of the
HL2 ligand and the two rhenium complexes is shown in
Figure 2. As outlined above, the OH group is prevented
from establishing hydrogen-donor intermolecular interac-
tions, because of the strong intramolecular interaction with
the N1 atom, although it can interact with H atoms of C–
H aromatic groups to link the molecules into chains (Fig-
ure 2a). In the structure of HL2, these chains are associated
through weak zig-zag C–H···N or Cmethyl–H···π interactions
in the characteristic herringbone arrangement usually ob-
served when the latter kind of interaction is present in aro-
matic molecules.[27] This type of arrangement gives rise to
zig-zag sheets (Figure 2b).
The intermolecular associations in the structures of com-
plexes 1 and 2 can be described in two steps. Firstly, the
molecules are associated in centrosymmetric dimers
through C10–H···X#3 interactions. Although the C–H···X
distances are slightly longer than those usually reported,[28]
they are shorter than the sum of the van der Waals radii. In
Figure 2. Intermolecular associations in the structure of HL2 (a),
(b) and 1 and 2 (c), (d).
addition, the distances reported previously were observed rameters in M–X groups has yet to be carried out. Sec-
in systems with interactions between organic fragments and ondly, the dimers are associated in a brick-wall arrange-
anionic Cl– or Br–. In fact, a systematic study of these pa- ment through C11–H···O1#4 interactions (Figure 2c and d).
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A Hydrazone Derivative and Its Rhenium(I) Complexes
Note that the C–H···O intermolecular interaction is rein- are due to π–π* transitions of the hydrazone group. The
forced in the complexes with respect to the free ligand absorption spectra of both complexes (Figure 3b) are iden-
(Table 2). However, it does not seem to be responsible of tical and show broader bands that are redshifted relative to
the lengthening of the intramolecular interaction N···H–O. those in the free ligand: ca. 373 nm (shoulder) and 301 nm.
The NMR spectroscopic solution studies, where the C–H···O The longest wavelength band has a tail up to around
interaction is absent, suggest that the last interaction is 450 nm and this is responsible for the orange coloration of
weaker in the complexes than in HL2.
both complexes.
The free ligand has fluorescent properties that are appar-
ent under a UV lamp (λ = 365 nm). The emission spectra
of the HL2 ligand (CHCl3 solution and solid state at room
temperature) are shown in Figure 3a. The maximum of the
emission band in chloroform presents an exceptionally large
Stokes’ shift (11.027 cm–1 = 31.5 kcal/mol) similar to those
found in other molecules with the salicylaldimine group and
usually assigned to an excited-state intramolecular proton
transfer state (ESIPT) present in these molecules.[29] The
intensity of the fluorescence emission of HL2 decreases con-
siderably when a protic solvent such as methanol is added
to the chloroform solution (Figure 3b; Table 3) with no no-
ticeable change in the emission maximum. This is due to
the competition for intermolecular hydrogen bonding from
the solvent, which destabilizes the intramolecular hydrogen
bond in the molecule Ϫ a feature that is necessary for the
occurrence of intramolecular proton transfer. Both aspects
confirm that the emission is due to de-excitation of an ex-
cited state of the keto form of the salicylaldimine group
(Scheme 3).[17]
UV/Vis Absorption and Emission Spectra
The free-ligand UV/Vis absorption spectrum (Figure 3a)
is characterized by two bands at 342 and 295 nm, which
Table 3. UV/Vis absorption data for the free ligand and its rheni-
um(I) complexes.
Compound Solvent
λ [nm] (ε [L/molcm])
HL2
CHCl3
MeOH
CHCl3
MeOH
CHCl3
MeOH
342 (14148), 295 (23646)
344 (16500), 296 (27300)
301 (21487), 373 (37526)
352 (19100), 284 (27100)
304 (8900), 378 (15081)
368 (53433), 276 (89130)
1
2
Both rhenium(I) complexes are nonemissive at room
temperature. The increase in intersystem crossing due to the
presence of the metal deactivates efficiently the singlet ex-
cited state and fluorescence is no longer observed. Triplet
emission is also strongly quenched at room temperature. In
contrast, when dichloromethane solutions of [ReBr(CO)3-
(HL2)] are cooled to 77 K, a weak redshifted emission with
vibrational structure (maxima at 630 at 670 nm) is detected
(Figure 3b) and is assigned to a triplet state.
Conclusions
The photophysical properties of the studied compounds
are of interest. The mechanism shown in Scheme 3 for the
fluorescence of HL2 has been proposed for other lumines-
cent systems based on Schiff bases of salicylaldehyde with
amines,[29] and the luminescent behavior of these systems is
very sensible to changes in the N···H–O interactions such
as electron density on the hydrogen-bonding acceptor or
the planarity of the molecule. Both factors are affected by
Figure 3. (a) Absorption (– - –) and emission (– – –) of HL2 in
chloroform solution ([HL2] = 2.1 10–5 , 25 °C, λexc = 345 nm),
emission spectra of HL2 in the solid state (----), and excitation spec-
tra collecting at λem = 560 nm (–––); (b) fluorescence emission spec-
tra of HL2 in chloroform (–––), methanol (– - –), and 50:50 v/v
mixture chloroform/methanol (– – –) solutions. ([L] = 2.1 10–5 ,
25 °C, λexc = 345 nm); (c) absorption spectra of complex 2 in chlo-
roform (2.1 10–5 , λexc = 370 nm) at 25 °C (–––), and emission
spectra at 77 K for complex 2 in chloroform (····).
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E. M. Vázquez-López et al.
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ments were also recorded in the solid state by using an optical fiber
device connected to the spectrofluorimeter. The decay times of the
compounds were too fast for the equipment time resolution
(Ͻ100 ps). The quantum yields were also very low (Յ1.5ϫ10–3)
and with significant error.
rhenium coordination, as observed in the solid state (X-ray
studies) and dδ/dT values of NMR hydroxy signals suggest
similar behavior in solution, and contribute to the deactiva-
tion of ESIPT mechanism in the complexes. Thus, the be-
havior observed in 2 involves emission at low temperature
and at wavelengths higher than in the fluorescence spec-
trum of the free ligand, and furthermore, the emission band
presents vibration resolution Ϫ an observation consistent
with an emission process from a low-energy triplet state (a
summary of the processes is illustrated in Scheme 4). Sim-
ilar behavior was observed in other rhenium(I) com-
plexes.[30] As in those cases, collisions with solvent mole-
cules at room temperature favor de-excitation by vibrational
relaxation as opposed to radiative decay from the forbidden
T1ǞS0 transition. When the former path is deactivated (low
temperature and/or rigid medium), then phosphorescence
can be observed.
X-ray Crystallography: Crystallographic data collection and refine-
ment parameters are listed in Table 4. All crystallographic measure-
ments were performed with a Bruker Smart CCD apparatus at
CACTI (University of Vigo) at room temperature [293(2) K] by
using graphite monochromated Mo-Kα radiation (λ = 0.71073 Å).
The data were corrected for absorption effects by using the SAD-
ABS program.[33] Structure analyses were carried out by direct
methods.[34] Least-squares full-matrix refinements on F2 were per-
formed by using the SHELXL97 program. Atomic scattering fac-
tors and anomalous dispersion corrections for all atoms were taken
from International Tables for Crystallography.[35] All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were refined
as riders except O1–H, which was refined isotropically at positions
previously identified in the corresponding Fourier map. Graphics
were obtained with PLATON[36] and MERCURY.[37]
Table 4. Crystal data collection and structure refinement data.
Compound
HL2
1
2
Formula
Mr
C14H13N3O
239.27
C17H13ClN3O4ReC17H13BrN3O4Re
544.95
589.41
Crystal system
Space group
a [Å]
b [Å]
c [Å]
orthorhombic
Pbca
12.375(3)
13.306(3)
15.091(3)
monoclinic
P21/c
monoclinic
P21/c
14.8520(16)
16.5924(18)
7.0420(7)
93.779(2)
1731.6(3)
4
14.915(2)
16.541(2)
6.9455(9)
92.838(2)
1711.4(4)
4
β [°]
Scheme 4. Energy-level diagram for the emitting state of HL2 (dot-
ted box) and its rhenium(I) complexes. Ligand emission is derived
from an excited-state intramolecular proton transfer (ESIPT) state,
whereas the complex emission (only observed at 77 K) is derived
from a ligand-centered triplet state.
V [Å3]
Z
2485.1(10)
8
Dc
1.274
0.784
0.0491
0.0836
2.090
0.801
0.0398
0.0691
2.288
0.811
0.0501
0.0780
S[a]
R[b,c]
wR2[b,d]
Max./min. peaks
[eÅ–3]
0.222/–0.284
1.316/–1.418
1.573/–2.271
[a] Goodness-of-fit on F2. [b] Observation criterion IϾ2σ(I). [c] R
Experimental Section
2
2 2
= Σ||Fo| – |Fc||/Σ||Fo|. [d] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
General: All operations performed in the synthesis and isolation of
the compounds were carried out under an atmosphere of dry ar-
gon. All solvents were dried with appropriate drying agents, de-
gassed by using a vacuum line, and distilled under an Ar atmo-
sphere. [ReX(CO)5][31] and [ReX(CO)3(CH3CN)2][32] were prepared
as previously reported. 2-Acetylpyridine, hydrazine hydrate, and
salicylaldehyde were purchased from Aldrich. Elemental analyses
were carried out with a Fisons EA-1108. Although the microanaly-
sis results for rhenium compounds are clearly enhanced by addition
of combustion catalyst (V2O5), the carbon results are without
Ϯ0.4%. However, inspection of the 13C NMR spectra shows exclu-
sively signals attributed to the compounds. Melting points were
determined with a Gallenkamp MFB-595 apparatus and are uncor-
rected. Mass spectra were recorded with a Hewlett–Packard 5989A
spectrometer operating under FAB conditions (nitrobenzyl alcohol
matrix). IR spectra were recorded from KBr pellets with a Bruker
Vector 22FT. 1H NMR spectra were obtained with a Bruker AMX
400 spectrometer from [D6]DMSO solutions. UV/Vis spectra were
obtained with a CARY 100 BIO (Varian) spectrophotometer from
MeOH and CHCl3 solutions. Fluorescence emission spectra were
CCDC-666491 (for HL2), -666492 (for 1), and -666493 (for 2) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of HL2: 2-Acetylpyridine hydrazone was synthesized by
following the method reported by Sandbhor et al.[38] with a slight
modification as follows: to a solution of hydrazine hydrate (7.8 mL,
8026 mg) in methanol (25 mL) was added 2-acetylpyridine
(1.12 mL, 1209.6 mg), and the solution was stirred at 0 °C for 2 h.
The pale-yellow solution was stored in the refrigerator overnight.
The solvent was removed in vacuo to 10 mL, and the pale-yellow
precipitate was filtered off and dried under vacuum over CaCl2/
KOH. A solution of salicylaldehyde (0.03 mL, 34.38 mg) in meth-
anol (5 mL) was added dropwise to a solution of the crude material
(100 mg) in methanol (10 mL). The yellow solution was heated (30–
40 °C) for 2 h. The yellow precipitate was filtered off and dried
under vacuum over CaCl2/KOH. Single crystals of HL2 were ob-
tained from the mother liquor. Yield: 76 mg (86%). M.p. 140 °C.
measured with a Horiba-Jobin–Yvon SPEX Fluorolog 3.22 spec- 1H NMR: δ = 11.40 (s, 1 H, O1-H), 8.90 (s, 1 H, C1-H), 8.70 (d,
trofluorimeter with a spectral band width of 5.0 nm for excitation
and emission spectra. Steady-state fluorescence emission measure-
J = 4.090 Hz, 1 H, C13-H), 8.20 (d, J = 7.998 Hz, 1 H, C10-H),
7.90 (t, J = 7.737 Hz, 1 H, C11-H), 7.70 (d, J = 7.602 Hz, 1 H, C7-
2718
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Eur. J. Inorg. Chem. 2008, 2713–2720

A Hydrazone Derivative and Its Rhenium(I) Complexes
[4] N. Metzler-Nolte, Angew. Chem. Int. Ed. 2001, 40, 1040–1043.
[5] R. Schibli, R. La Bella, R. Alberto, E. García-Garayoa, K.
Ortner, U. Abram, P. A. Schubiger, Bioconjugate Chem. 2000,
11, 345–351.
[6] R. Waibel, R. Alberto, J. Willuda, R. Finnern, R. Schibli, A.
Stichelberger, A. Egli, U. Abram, J. Mach, A. Plückthun, P. A.
Schubiger, Nat. Biotechnol. 1999, 17, 897–901.
[7] G. Knör, M. Leirer, A. Vogler, J. Organomet. Chem. 2000, 610,
16–19.
[8] A. Albertino, C. Garino, S. Ghiani, R. Gobetto, C. Nervi, L.
Salassa, E. Rosenberg, A. Sharmin, G. Viscardi, R. Buscaino,
G. Croce, M. Milanesio, J. Organomet. Chem. 2007, 692, 1377–
1391.
[9] J. V. Caspar, T. J. Meyer, J. Phys. Chem. 1983, 87, 952–957.
[10] B. J. Coe, S. Houbrechts, I. Asselberghs, A. Persoons, Angew.
Chem. Int. Ed. 1999, 38, 366–369.
[11] R. Carballo, J. S. Casas, E. García-Martínez, G. Pereiras-Ga-
bián, A. Sanchez, J. Sordo, E. M. Vázquez-López, Inorg. Chem.
2003, 42, 6395–6403.
[12] R. Carballo, J. S. Casas, E. García-Martínez, G. Pereiras-Ga-
bián, A. Sánchez, J. Sordo, E. M. Vázquez-López, J. C. Garcia-
Monteagudo, J. Organomet. Chem. 2002, 656, 1–10.
[13] R. Carballo, J. S. Casas, E. Garcia-Martínez, G. Pereiras-Ga-
bián, A. Sánchez, U. Abram, E. M. Vázquez-López, Crys-
tEngComm 2005, 7, 113–120.
H), 7.50 (t, J = 6.041 Hz, 1 H, C12-H), 7.40 (t, J = 7.727 Hz, 1 H,
C5-H), 7.00 (m, 2 H, C4,6-H), 2.52 (s, 3 H, C14-H) ppm. 13C
RMN: δ = 165.72 (C3), 161.04 (C1), 158.69 (C8), 154.43 (C9),
148.91 (C13), 136.68 (C11), 133.02 (C5), 131.05 (C7), 125.07 (C12),
120.87 (C10), 119.46 (C6), 118.39 (C2), 116.36 (C4), 13.67 (C14)
ppm. IR: ν = 3444 [s, br. ν(OH)], 1618 (s), 1547 (w), 1462 [m
˜
ν(C=N) + ν(C=C)], 1272–1029 [m, w δ(C–H)] cm–1. MS: m/z (%)
= 240.01 (100) [M]+. C14H13N3O (239.28): calcd. C 70.28, H 5.48,
N 17.56; found C 70.05, H 5.46, N 17.61.
Synthesis of the [ReX(CO)3(HL2)] (1, X = Cl; 2, X = Br) Complexes:
To a solution of HL2 (31.0 mg X = Cl or 27.2 mg X = Br) in CHCl3
(10 mL) was added the corresponding equimolecular amount of
fac-[ReX(CO)3(CH3CN)2] (50.4 mg X = Cl, 49.0 mg X = Br), and
the red solution/mixture was heated under reflux for 2 h. The red-
dish-brown precipitate was filtered off and dried under vacuum.
Single crystals suitable for X-ray studies were obtained by slow
evaporation of ethyl acetate (for 1) or chloroform (for 2) solutions.
Data for 1: Yield: 47.1 mg (66.7%). M.p. 261 °C. 1H NMR: δ =
10.50 (s, 1 H, O1-H), 9.20 (s, 1 H, C1-H), 9.00 (d, J = 5.226 Hz, 1
H, C13-H), 8.40 (m, 2 H, C10,11-H), 8.00 (d, J = 7.831 Hz, 1 H,
C7-H), 7.80 (t, J = 6.308 Hz, 1 H, C12-H), 7.45 (t, J = 8.539 Hz,
1 H, C5-H), 7.00 (m, 2 H, C4,6-H), 2.60 (s, 3 H, C14-H) ppm. 13
C
RMN: δ = 197.32, 196.82 (C15,17), 187.83 (C16), 168.88 (C3),
158.63 (C1), 157.74 (C8), 154.86 (C9), 152.98 (C13), 140.18 (C11),
134.39 (C5), 128.85 (C7), 127.59 (C12), 127.32 (C10), 119.61 (C6),
[14] P. Barbazán, R. Carballo, J. S. Casas, E. García-Martínez, G.
Pereiras-Gabián, A. Sánchez, E. M. Vázquez-López, Inorg.
Chem. 2006, 45, 7323–7330.
[15] J. Grewe, A. Hagenbach, B. Stromburg, R. Alberto, E.
Vázquez-López, U. Abram, Z. Anorg. Allg. Chem. 2003, 629,
303–311.
[16] G. Pereiras-Gabián, E. M. Vázquez-López, H. Braband, U.
Abram, Inorg. Chem. 2005, 44, 834–836.
117.94 (C2), 116.59 (C4), 15.59 (C14) ppm. IR: ν = 3446 [m, br.
˜
ν(OH)], 2034 (m), 1902 [s ν(COfac)], 1623 (w), 1603 (w), 1568 (w),
1537 (w), 1484 [w ν(C=N) + ν(C=C)], 1267–1039 [w δ (C–H)] cm–1.
MS: m/z (%) = 544.92 (21.41) [M]+, 509.95 (29.42) [M – Cl]+,
425.97 (3.51) [M – 3CO]+. C17H13ClN3O4Re (544.97): calcd. C
37.47, H 2.40, N 7.71; found C 36.87, H 2.31, N 7.53. Data 2:
[17] M. D. Cohen, G. M. J. Schmidt, S. Flavian, J. Chem. Soc. 1964,
2041–2051.
1
Yield: 49.6 mg (74.2%). M.p. 289 °C. H NMR: δ = 10.50 (s, 1 H,
[18] F. Chen-jie, D. Chun-ying, M. Hong, H. Cheng, M. Qing-jin,
L. Yong-jiang, M. Yu-hua, W. Zhe-ming, Organometallics
2001, 20, 2525–2532.
[19] X. Xu, X. You, Z. Sun, X. Wang, H. Liu, Acta Crystallogr.,
Sect. C 1994, 50, 1169–1171.
O1-H), 9.20 (s, 1 H, C1-H), 9.00 (d, J = 5.221 Hz, 1 H, C13-H),
8.40 (d, J = 7.980 Hz, 1 H, C10-H), 8.30 (t, J = 5.2720 Hz, 1 H,
C11-H), 8.00 (d, J = 7.707 Hz, 1 H, C7-H), 7.80 (t, J = 5.8925 Hz,
1 H, C12-H), 7.40 (t, J = 8.0475 Hz, 1 H, C5-H), 7.00 (m, 2 H,
C4,6-H), 2.70 (s, 3 H, C14-H) ppm. 13C RMN: δ = 196.83, 196.35
(C15,17), 187.17 (C16), 168.76 (C3), 158.63 (C1), 157.80 (C8),
154.84 (C9), 153.17 (C13), 140.08 (C11), 134.40 (C5), 128.74 (C7),
127.66 (C12), 127.35 (C10), 119.61 (C6), 117.92 (C2), 116.60 (C4),
[20] W. Wang, B. Spingler, R. Alberto, Inorg. Chim. Acta 2003, 355,
386–393.
[21]
B. R. Leeflang, J. F. G. Vliegenthart, L. M. J. Kroon-Baten-
burg, B. P. van Eijck, J. A. Kroon, Carbohydr. Res. 1992/6/4,
230, 41–61.
M. C. Etter, Acc. Chem. Res. 1990, 23, 120–126.
R. Alberto, R. Schibli, R. Waibel, U. Abram, A. P. Schubiger,
Coord. Chem. Rev. 1999, 190–192, 901–919.
15.63 (C14) ppm. IR: ν = 3448 [vs, br. ν(OH)], 2036 (m), 1925 (s),
˜
[22]
[23]
1901 [s ν(COfac)], 1626 (m), 1600 (sh.), 1566 (w), 1458 [w ν(C=N)
+ ν(C=C)], 1270–1038 [w δ(C–H)] cm–1. MS: m/z (%) = 588.96
(1.26) [M]+, 510.05 (1.63) [M – Br]+. C17H13BrN3O4Re (589.42):
calcd. C 34.64, H 2.22, N 7.13; found C 35.20, H 2.03, N 6.88.
[24]
G. Desiraju, T. Steiner in International Union of Crystallogra-
phy Monographs on Crystallography, Number 9: The Weak Hy-
drogen Bond In Structural Chemistry and Biology, Oxford Uni-
versity Press, Oxford, 2001, p. 480.
Acknowledgments
[25]
[26]
[27]
[28]
[29]
[30]
G. R. Desiraju, A. Gavezzoti, J. Chem. Soc., Chem. Commun.
1989, 621–623.
E. Hadjoudis, I. M. Mavridis, Chem. Soc. Rev. 2004, 33, 579–
588.
This research was supported by the European Rural Development
Fund, the Directorates General for Research of the Galician
Government, and the Spanish Ministry of Education and
S. M. El-Medani, M. M. Aboaly, H. H. Abdalla, R. M. Rama-
dan, Spectrosc. Lett. 2004, 37, 619–632.
G. A. Jeffrey in An Introduction to Hydrogen Bonding, Oxford
University Press, New York, 1997, p. 303.
M. St.-Jacques, P. R. Sundararajan, K. J. Taylor, R. H. Mar-
chessault, J. Am. Chem. Soc. 1976, 98, 4386–4391.
a) A. Vogler, H. Kunkely, Coord. Chem. Rev. 2000, 200–202,
991–1008; b) B. D. Rossenaar, D. J. Stufkens, A. Vlcek Jr, Inorg.
Chem 1996, 35, 2902–2909; c) G. J. Stor, F. Hartl, J. W. M.
Van Outersterp, D. J. Stufkens, Organometallics 1995, 14, 115–
1131.
Science
through
projects
CTQ2006-05642/BQU
and
PGIDIT06PXIB314373PR, and by the Portuguese Foundation for
Science and Technology (POCI/QUI/55519/2004 FCT/FEDER and
PDTC/QUI/66250/2006).
[1] R. Schibli, R. Schwarzbach, R. Alberto, K. Ortner, H.
Schmalle, C. Dumas, A. Egli, P. A. Schubiger, Bioconjugate
Chem. 2002, 13, 750–756.
[2] R. Alberto, K. Ortner, N. Wheatley, R. Schibli, A. P. Schubiger,
J. Am. Chem. Soc. 2001, 123, 3135–3136.
[3] J. Wald, R. Alberto, K. Ortner, L. Candreia, Angew. Chem. Int.
Ed. 2001, 40, 3062–3066.
[31]
[32]
S. P. Schmidt, W. C. Trogler, F. Basolo, Inorg. Synth. 1990, 28,
160.
M. F. Farona, K. F. Kraus, Inorg. Chem. 1970, 9, 1700–1704.
Eur. J. Inorg. Chem. 2008, 2713–2720
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2719

E. M. Vázquez-López et al.
[33] G. M. Sheldrick, SADABS, University of Göttingen, Germany, [37] I. J. Bruno, J. C. Cole, P. R. Edgington, M. K. Kessler, C. F.
FULL PAPER
1996.
Macrae, P. McCabe, J. Pearson, R. Taylor, Acta Crystallogr.,
Sect. B 2002, 58, 389–397.
[38] U. Sandbhor, S. Padhye, D. Billington, D. Rathbone, S.
Franzblau, C. E. Anson, A. K. Powell, J. Inorg. Biochem. 2002,
90, 127–136.
[34] G. M. Sheldrick, SHELX-97: Program for the Solution and Re-
finement of Crystal Structures, version 2, University of
Göttingen, Germany, 1997.
[35] IUCr (Ed.: A. J. C. Wilson), International Tables for Crystal-
lography, Kluwer, Dordrecht, 1992, vol. C.
[36] A. L. Spek, PLATON: A Multipurpose Crystallographic Tool,
version 21.08.03 for LINUX, Utrecht University, Utrecht, The
Netherlands, 2006.
Received: November 7, 2007
Published Online: April 30, 2008
2720
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2713–2720