Optical, electrochemical and structural studies of the first rhenium compound of di-2-pyridylketone benzoylhydrazone (dpkbz) fac-Re(CO) 3(dpkbh)Cl

Article abstract of DOI:10.1016/S0020-1693(03)00324-4

The reaction between Re(CO)₅Cl and di-2-pyridylketone benzoylhydrazone (dpkbh) in refluxing toluene gave fac-Re(CO) ₃(dpkbh)Cl in good yield. Spectroscopic and electrochemical measurements on fac-Re(CO)₃(dpkbh)Cl revealed strong solvent-solute interaction, as manifested by the sensitivity of its reduction potentials and electronic absorption spectra to solvent variations. Spectroscopic and thermo-optical measurements in polar solvents in the presence of NaBH ₄ and NaBF_4, or NaOH and citric acid reveal reversible interconversion between the low- and high-energy electronic states of fac-Re(CO)₃(dpkbh)Cl at 440 and 318 nm. Electrochemical measurements on fac-Re(CO)₃(dpkbh)Cl show irreversible redox processes pointing to electrochemical transformations following the first electronic transfer(s). Crystals of fac-Re(CO)₃(dpkbh)Cl obtained from an acetonitrile solution of fac-Re(CO)₃(dpkbh)Cl are centric and crystals of fac-Re(CO)₃(dpkbh)Cl·dmso obtained from a dmso solutions of fac-Re(CO)₃(dpkbh)Cl are acentric. Structural studies show non-identical twins of fac-Re(CO)₃(dpkbh)Cl and fac-Re(CO) ₃(dpkbh)Cl·dmso with distorted octahedral coordination about rhenium and the conformation about the amide group is syn- in fac-Re(CO) ₃(dpkbh)Cl and anti- in fac-Re(CO)₃(dpkbh)Cl·dmso. The packing of molecules shows a web of hydrogen bonds that may account for the stability of different conformations observed in the solid state.

Full text of DOI:10.1016/S0020-1693(03)00324-4

Inorganica Chimica Acta 353 (2003) 89ꢀ98
/
www.elsevier.com/locate/ica
Optical, electrochemical and structural studies of the first rhenium
compound of di-2-pyridylketone benzoylhydrazone (dpkbz) fac-
Re(CO)3(dpkbh)Cl
Mohammed Bakir *, Ordel Brown
Department of Chemistry, The University of the West Indies, Mona Campus, Kingston 7, Jamaica
Received 21 October 2002; accepted 2 April 2003
Abstract
The reaction between Re(CO)5Cl and di-2-pyridylketone benzoylhydrazone (dpkbh) in refluxing toluene gave fac-
Re(CO)3(dpkbh)Cl in good yield. Spectroscopic and electrochemical measurements on fac-Re(CO)3(dpkbh)Cl revealed strong
solventꢀsolute interaction, as manifested by the sensitivity of its reduction potentials and electronic absorption spectra to solvent
/
variations. Spectroscopic and thermo-optical measurements in polar solvents in the presence of NaBH4 and NaBF4, or NaOH and
citric acid reveal reversible interconversion between the low- and high-energy electronic states of fac-Re(CO)3(dpkbh)Cl at 440 and
318 nm. Electrochemical measurements on fac-Re(CO)3(dpkbh)Cl show irreversible redox processes pointing to electrochemical
transformations following the first electronic transfer(s). Crystals of fac-Re(CO)3(dpkbh)Cl obtained from an acetonitrile solution
of fac-Re(CO)3(dpkbh)Cl are centric and crystals of fac-Re(CO)3(dpkbh)Cl×
Re(CO)3(dpkbh)Cl are acentric. Structural studies show non-identical twins of fac-Re(CO)3(dpkbh)Cl and fac-Re(CO)3(dpkbh)Cl×
dmso with distorted octahedral coordination about rhenium and the conformation about the amide group is syn- in fac-
Re(CO)3(dpkbh)Cl and anti- in fac-Re(CO)3(dpkbh)Cl×dmso. The packing of molecules shows a web of hydrogen bonds that may
/dmso obtained from a dmso solutions of fac-
/
/
account for the stability of different conformations observed in the solid state.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Rhenium; Di-2-pyridyl ketone; Hydrazone; Optosensing
1. Introduction
is hydroxydi(2-pyridyl)methoxide and tridentate
through the nitrogen atoms of the pyridine rings and
the oxygen atom of the methoxide moiety of dpkO,OH
Di-2-pyridyl ketone (dpk), its oxime (dpkoxime), and
hydrazone (dpkhydrazone) derivatives are of interest for
their physico-chemical properties, reactivity patterns
and applications in many processes that include mole-
as in fac-Re(CO)3(dpkO,OH) [6ꢀ8,11].
/
We have been interested in the chemistry of di-2-pyridyl-
like ligands and have described the synthesis, optical,
electrochemical and structures of a variety of dpk
cular recognition and catalysis [1ꢀ10]. Several coordina-
/
derivatives and their metal compounds [11ꢀ24]. Optical
/
tion modes were reported for dpk and its derivatives
that include monodentate binding through an N atom of
one pyridyl ring, as in [Ag(dpkoxime)]NO2, bidentate
binding through the N atoms of the pyridyl rings as in
fac-Re(CO)3(dpk)Cl or through an N atom of one
pyridine ring and the N atom of the backbone as in
and thermodynamic measurements on dpk hydrazones
that include di-2-pyridylketone benzoylhydrazone
(dpkbh) in polar non-aqueous solvents revealed rever-
sible interconversion between two interlocked electronic
states due to different conformational forms of the
hydrazone backbone resulted from intermolecular inter-
action between these species and their surroundings
[15,20,21]. The high values for the extinction coefficients
and low values for the activation parameters for the
interconversion between the low- and high-energy
[Co(dpkO,OH)(dpkoxime)]NO2×
/
H2O where dpkO,OH
* Corresponding author. Tel.: ꢁ
/
876-935-8164; fax: ꢁ876-977-1835.
/
E-mail address: mohammed.bakir@uwimona.edu.jm (M. Bakir).
0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00324-4

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M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ98
/
electronic states of dpk hydrazones in polar non-
aqueous solvents allowed for the use of these systems
(dpk hydrazones and surrounding molecules) as mole-
cular sensors for a variety of chemical stimuli that
include metal ions and biomolecules [15,20,21]. X-ray
structural analysis on a series of dpk hydrazones
revealed the presence of a web of non-covalent interac-
2. Experimental
2.1. Reagents and reaction procedures
Solvents were reagent grade and thoroughly deox-
ygenated prior to use. All other reagents were obtained
from commercial sources and used without further
tions that include solventꢀ
/
solute, soluteꢀsolute, and p-
/
purification. The ligand dpkbh, melting point 141ꢀ
/
stacking, which may account for their interlocked
charge-transfer bands and molecular sensitivity
142 8C was prepared by refluxing a mixture of dpk,
benzhydrazide, EtOH, and two drops of HCl using a
standard procedure as described previously for the
synthesis of several dpk hydrazones that include dpkbh
[21]. All reactions were performed under a nitrogen
atmosphere.
[17,19,21ꢀ24]. Although, dpkbh is widely used as a
/
sensitive analytical reagent for the optical determination
of trace amounts of metal ions, and in a recent report,
we described its optosensing behavior in non-aqueous
media, to our knowledge there has been no report on the
isolation of any of its metal compounds [21].
2.2. Preparation of fac-Re(dpkbh)(CO)3Cl
A mixture of Re(CO)5Cl (200 mg, 0.55 mmol), dpkbh
(220 mg, 0.73 mmol) and toluene (50 ml) was refluxed
for 10 h. The resulting reaction mixture was allowed to
cool to room temperature and reduced in volume to ꢀ
/
25 ml. An off-yellow solid was filtered off, washed with
hexane, diethyl ether, and dried; yield 240 mg (72%)
(Found: C, 41.18; H, 2.37; Cl, 8.99. C21H14Cl N4O4Re
requires C, 41.48; H, 2.32; Cl, 9.22%). Infrared data
(KBr disk, cmꢂ1): n(Cꢀ
/
O) 2016, 1907, 1870; n(Cꢁ
/
O)
1655 and n(Nꢂ
/
H) 3156, 3130, 3067, 3035 and n(Cꢂ
/H)
2883. 1H NMR (d ppm): in dmso-d6 12.08 (s, 1H, NH),
9.02 (d, 1H, dpk), 8.90 (d, 1H, dpk), 8.24 (overlapped
t’s, 2H dpk), 8.11 (d, 1H, dpk), 7.97 (d, 1H, dpk)), 7.74
In this report, we describe the synthesis of the first metal
carbonyl compound of dpkbh along with its optical,
electrochemical and structural properties. Studies of this
nature are important as a variety of hydrazones are used
in non-linear optics and molecular recognition and
solvent variations and the presence of organized non-
covalent hydrogen bonds in materials was recognized by
many authors to lead to the formation of polar chains
and their appropriate packing may lead to the genera-
tion of acentric crystals required for non-linear optical
(m, 4H, ph), 7.50 (m, 3H, 1H ph, and 2H dpk). UVꢀ
/
Vis
2000).
{CH2Cl2, l (nm), (o, cmꢂ1 Mꢂ1)}: 310 (24 8409
/
2.3. Physical measurements
Electronic absorption spectra were recorded on a
PerkinꢀElmer Lambda 19 UVꢀVisꢀNIR spectrometer.
/
/
/
1
Solution H NMR spectra were recorded on a Bruker
ACE 200-MHz Fourier-transform spectrometer and
referenced to the residual protons in the incompletely
responses, e.g. second harmonic generation [25ꢀ28].
/

M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ
/98
91
deuteriated solvent. Infrared spectra were recorded as
KBr pellets on a PerkinꢀElmer Spectrum 1000 FT-IR
Table 1
Crystal data and structure refinement for fac-Re(CO)3(dpkbh)Cl and
/
fac-Re(CO)3(dpkbh)Cl×
/
dmso
Spectrometer. Electrochemical measurements were per-
formed with the use of a Princeton Applied Research
(PAR) Model 173 potentiostat/galvanostat and Model
276 interface in conjunction with a 286 PC. Data were
acquired with the EG&G PARC Headstart program
and manipulated using the Microsoft Excel Program.
Measurements were performed in solutions that were 0.1
Compound
fac-
fac-
Re(CO)3(dpkbz)Cl Re(CO)3(dpkbz)Cl×
/
dmso
Empirical formula
Formula weight
Crystal system
C21H14ClN4O4Re
608.01
triclinic
C23H20ClN4O5SRe
686.14
triclinic
¯
P/1
¯
P1
Space group
/
M in [N(n-Bu)4](PF6). The Ep,a, Ep,c and Epꢃ
/(Ep,a
ꢁ
/
Unit cell dimensions
˚
Ep,c)/2 values were referenced to the potassium chloride
saturated calomel electrode (SCE), at room temperature
and are uncorrected for junction potentials. The number
of electrons on the redox waves was determined using
the oxidative peak current of the reversible one-electron
couple of FeCp2/FeCp2ꢀ couple as an internal standard.
Electrochemical cells were of conventional design based
on scintillation vials or H-cells. A glassy-carbon disc was
used as the working electrode and Pt-wire as a counter
electrode.
a (A)
˚
12.17(9)
13.42(17)
13.75(10)
106.37(9)
90.00(4)
90.00(9)
2154.8(4)
4
9.04(12)
12.14(14)
12.25(10)
80.17(8)
75.56(9)
86.53(11)
1282.3(2)
2
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
V (A )
˚
Z
Dcalc (mg mꢂ3
)
1.874
1.777
4.964
Absorption coefficient 5.799
(mmꢂ1
F(0 0 0)
u Range for data col- 2.28ꢀ
)
1168
668
/19.99
2.23ꢀ
4098/4098
[Rint 0.0000]
/
22.50
2.4. X-ray crystallography
lection (8)
Reflections collected/
unique
2788/2682
Yellow crystals of fac-Re(CO)3(dpkbh)Cl and fac-
[Rint
19.99 (66.6%)
ꢃ/0.0119]
ꢃ
/
Re(CO)3(dpkbh)Cl×/dmso were obtained from acetoni-
Completeness to u
Absorption correction empirical
22.50 (99.7%)
none
trile and dmso solutions of fac-Re(CO)3(dpkbh)Cl when
allowed to stand at room temperature for several days.
Single crystals were selected and mounted on glass fibers
with epoxy cement. A Brucker AXS with a Mo Ka
radiation and a graphite monochromator was used for
data collection and the SHELXTL software package
version 5.1 was used for structure solution [29,30]. Cell
parameters and other crystallographic information are
given in Table 1 along with additional details concerning
data collection.
Max/min transmission 0.5603 and 0.2303
Data/restraints/para-
meters
2682/0/530
4098/4/421
1.355
Goodness-of-fit on F2 1.036
Final R indices [I ꢁ
/
R1ꢃ/0.0356
R1ꢃ0.0543
/
2s(I)]
wR2ꢃ
R1ꢃ0.0410
wR2ꢃ0.1158
/
0.1086
wR2ꢃ
R1ꢃ0.0551
wR2ꢃ0.1413
/
0.1375
R indices (all data)
/
/
/
/
Absolute structure
parameter
Extinction coefficient
0.127(18)
2.5. Analytical procedures
0.0016(3)
0.0005(7)
Largest difference peak 0.791 and ꢂ
/
0.789
2.970 and ꢂ4.051
/
and hole (e Aꢂ3
)
Elemental microanalyses were performed by MEDAC
Ltd, Department of Chemistry, Brunel University, Ux-
bridge, United Kingdom.
Temperatureꢃ
/
298(2) K, wavelengthꢃ0.71073 A, refinement meth-
/
od, full-matrix least-squares on F2.
3. Results and discussion
Re(CO)3(dpknph)Cl where dpknph is dpk p-nitophe-
nylhydrazone and other related compounds [19,22]. In
the IR spectrum of fac-Re(CO)3(dpkbh)Cl, three strong
When Re(CO)5Cl was allowed to react with dpkbh in
refluxing toluene, fac-Re(CO)3(dpkbh)Cl was isolated
in good yield. This reaction is similar to those reported
for the synthesis of rhenium tricarbonyl compounds of
bands appeared in the n(Cꢀ/O) stretching region similar
to those reported for the carbonyl groups in fac-
Re(CO)3(dpknph)Cl and other tricarbonylhalorhe-
nium(I) compounds containing a-diimine ligands of
the type fac-Re(CO)3(L-L)Cl, and they confirmed the
the type fac-Re(CO)3(L-L)Cl where L-Lꢃbidentate a-
/
diimine ligand from the reaction between Re(CO)5Cl
and L-L in refluxing toluene [11,14]. The formulation of
the isolated rhenium-carbonyl compound as fac-
Re(CO)3(dpkbh)Cl is based on the results of a number
of spectroscopic measurements and a comparison of
these results with those reported for fac-
assigned fac-geometry [11,14,19]. The n(Cꢁ
/
N) of the
hydrazone moiety and the combined n(CꢁC) and n(Cꢁ
/
/
N) of the pyridine vibrations are normal and in the same
region as in fac-Re(CO)3(dpknph)Cl [19].

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M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ98
/
ppm and a series of resonances consistent with the
coordinated dpkbh. No evidence of paramagnetic line
broadening or unusual shifts of resonances appeared in
the spectra of this compound confirming its diamagnetic
character.
The electronic absorption spectra of fac-
Re(CO)3(dpkbh)Cl in different solvents are shown in
Fig. 1. These spectra show sensitivity of the absorption
bands of fac-Re(CO)3(dpkbh)Cl to solvent variations as
apparent from the change in position and intensity of
A strong and sharp stretching mode appeared at 1654
cmꢂ1 due to the ketonic group of N,N-coordinated
the low energy (ꢀ
nm) absorption bands in different solvents and point to
solventꢀsolute interactions. In non-polar solvents such
as CH2Cl2, a single absorption band with extinction
coefficient of 24 8409
2000 Mꢂ1 cmꢂ1 appeared at 310
nm, and in polar hydrogen bonding solvents such as
dmf, two absorption bands appeared at 440 and 318. A
plot of the absorbance of the low and high-energy
absorption bands at 440 and 318 nm versus total
concentration in dmf is non-linear pointing to deviation
from Beers’ Law. As the concentration of fac-
Re(CO)3(dpkbh)Cl decreases, the ratio of the low- and
high-energy absorption bands increases, pointing to
/
440 nm) and high-energy (ꢀ
/
320ꢀ310
/
dpkbh. This band appeared at higher energy (ꢀ30
/
/
cmꢂ1) compared to the ketonic stretching mode of
dpkbh and is consistent with the decrease in electron
density of the ketonic group upon N,N-coordination of
dpkbh, hints to enhanced p-back bonding as a result of
electron/charge delocalization across the metallocyclic
ring and backbone of the hydrazone moiety, and is
similar to those observed for the N,N-coordination of
/
dpk [11]. In the n(NH) and n(Cꢂ/H) stretching region of
fac-Re(CO)3(dpkbh)Cl, a series of weak and broad
bands appeared between 3200 and 2800 cmꢂ1 and for
the free ligand, a sharp band appeared at 3060 cmꢂ1
and a broad band appeared at 2920 cmꢂ1. The broad
direct solventꢀsolute interaction and confirming the
/
spectral results observed in Fig. 1. These spectral
features are similar to those reported for dpkbh, fac-
Re(CO)3(dpkphh)Cl where dpkphh is dpk phenylhydra-
zone and other related compounds although subtle
difference are worth noting [21,22]. Compared to fac-
character of these bands and their appearance at 53200
/
cmꢂ1 point to possible participation of these groups in
1
hydrogen bonding [31]. The H NMR spectra of fac-
Re(CO)3(dpkbh)Cl in dmso-d6 shows d(Nꢂ
/
H) at 12.08
Fig. 2. Electronic absorption spectra of 1.00ꢄ
Re(CO)3(dpkbh)Cl and 2.2ꢄ
10ꢂ1 M NaBF4 in dmso in the presence
of 1.80ꢄ
10ꢂ4 M (1), 2.2ꢄ10ꢂ4M (2), 2.5ꢄ10ꢂ5 M (3), 5.0ꢄ10ꢂ3
M (4) and 1.20ꢄ
10ꢂ2 M (5) NaBH4 in dmso at 298 K.
/
10ꢂ5
M fac-
Fig. 1. Electronic absorption of fac-Re(CO)3(dpkbh)Cl in (1) dmso
(2.00ꢄ
10ꢂ5 M), (2) dmf (2.00ꢄ10ꢂ5 M), (3) CH3CN (2.60ꢄ10ꢂ5
M) and (4) CH2Cl2 (3.10ꢄ
10ꢂ5 M).
/
/
/
/
/
/
/
/
/
/

M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ
/98
93
Re(CO)3(dpkbh)Cl and allowed calculations of its
thermodynamic activation parameters.1 A plot of
ln(A440/A318) versus 1/T ꢄ
with a slope of ꢂ494920 per decade with intercept of
1.059
0.05 that gave changes in enthalpy (DHf) of ꢁ
4.109 8.2390.45 kJ
0.20 kJ molꢂ1, entropy (DSf) of ꢁ
molꢂ1 and free energy (DGf) of ꢁ 0.20 kJ molꢂ1
1.669
/
103 Kꢂ1 gave a straight line
/
/
ꢁ
/
/
/
/
/
/
/
/
in dmso. The reversible interconversion between the
high and low electronic states of fac-Re(CO)3(dpkbh)Cl
and its low activation parameters and high value for the
extinction coefficient of the electronic states allow for
the use of these systems (fac-Re(CO)3(dpkbh)Cl and
surrounding molecules) as molecular sensors for variety
of species in procedures similar to those we reported for
the optosensing behavior of dpkbh [21]. The spectra of
fac-Re(CO)3(dpkbh)Cl in dmso in the presence and
absence of Mg(ClO4)2×
/
nH2O are shown in Figs. 3 and 4
shows plot of the absorbance of fac-
a
Re(CO)3(dpkbh)Cl in dmso in the presence of NaOH
and citric acid versus their concentration. When a dmso
solution of NaOH was added to a dmso solution of the
fac-Re(CO)3(dpkbh)Cl or a dmso solution of fac-
Re(CO)3(dpkbh)Cl containing citric acid, the low-en-
ergy absorption band became favorable and when a
dmso solution of citric acid was added to the dmso
solution of fac-Re(CO)3(dpkbh)Cl or a dmso solution of
fac-Re(CO)3(dpkbh)Cl containing NaOH, the high-
energy absorption band became favorable. These results
further confirm the reversible interconversion between
the low- and high-energy electronic states of fac-
Re(CO)3(dpkbh)Cl in polar solvents and reveal that
Fig. 3. Electronic absorption spectra of 3.00ꢄ
Re(CO)3(dpkbh)Cl in dmso (1) in the presence 1ꢄ
10ꢂ9 M (2), 2ꢄ
10ꢂ9 M (3), 5ꢄ10ꢂ9 M (4), 1ꢄ10ꢂ8 M (5), 2ꢄ10ꢂ8 M (6) and 5ꢄ
10ꢂ8 M (7) in Mg(ClO4)2.
/
10ꢂ5
M fac-
/
/
/
/
/
/
Re(CO)3(dpkphh)Cl, the low energy absorption bands
of fac-Re(CO)3(dpkbh)Cl significantly shift to high [22].
For example, in dmso, the low- and high-energy
absorption bands of fac-Re(CO)3(dpkphh)Cl were ob-
served at 506 and 398 nm. In the case of dpkbh, the low-
and high-energy absorption bands appeared at 400 and
328 nm in dmso [21]. When a solution of NaBH4 was
added to a solution of fac-Re(CO)3(dpkbh)Cl in a polar
solvent in the presence and absence of NaBF4, the
intensity of the low energy band increased and the
intensity of the high-energy band decreased (see Fig. 2).
The reverse was observed when a solution of NaBF4 was
added to a solution of fac-Re(CO)3(dpkbh)Cl or solu-
tion of fac-Re(CO)3(dpkbh)Cl containing NaBH4. This
allowed calculations of the extinction coefficients of fac-
Re(CO)3(dpkbh)Cl in polar solvents and gave o440 and
chemical species in concentration as low as 1.00ꢄ
10ꢂ9
/
M can be detected and determined using the molecular
sensor fac-Re(CO)3(dpkbh)Cl in dmso. A comparison
of the optosensing behavior of fac-Re(CO)3(dpkbh)Cl
with those we reported for dpkbh in non-aqueous media
reveal that under the present conditions fac-
Re(CO)3(dpkbh)Cl is 100 times more sensitive than
1
For the following interconversion:
b-fac-Re(CO)3(dpkbh)Cl?a-fac-Re(CO)3(dpkbh)Cl (1)
Application of Beer’s Law gives:
o318 values of 26 9309
Mꢂ1, respectively, in dmso. Following a similar proce-
dure, extinction coefficients of 23 07092000 and
22 4509
2000 cmꢂ1 Mꢂ1 were calculated at 440 and
/
2000 and 27 0609
2000 cmꢂ1
/
Aa=Ab ꢃoaca=obcb (2)
and
/
ln(Aa=Ab)ꢃln(oa=ob)ꢁln K (3)
/
The equilibrium constant is related to the thermodynamic parameters
as shown in Eq. (4):
318 nm, respectively, in dmf. The electronic absorption
spectra of fac-Re(CO)3(dpkbh)Cl in polar solvents are
temperature dependent, as the temperature increases,
the ratio of A440/A318 increases, and the reverse was
observed when the temperature was allowed to decrease.
These results confirmed the reversible interconversion
between the high- and low-electronic states of fac-
ln KꢃDSø=RꢂDHø=RT (4)
and substitution of Eq. (4) into Eq. (3) gives:
ln(Aa=Ab)ꢃln(ob=ob)ꢁDSø=RꢂDHø=RT (5)
A plot of ln(Aa/Ab) versus 1/T gives a straight line with a gradient of
ꢂ/
DHø/R and an intercept of {ln(oa/ob)ꢁDSø/R}.
/

94
M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ98
/
dpkbh toward metal ions [21]. Further the N,N-
coordination of dpkbh in fac-Re(CO)3(dpkbh)Cl con-
firm that the optosensing behavior of dpk hydrazones is
due to the conformational changes of the hydrazone
backbone associated with the solventꢀ
tion.
The
/
solute interac-
electrochemical
properties of fac-
Re(CO)3(dpkbh)Cl in non-aqueous media were investi-
gated using voltammetric techniques. Cyclic voltammo-
grams of fac-Re(CO)3(dpkbh)Cl in CH2Cl2, CH3CN
and dmf are shown in Fig. 5. On reductively initiated
scans, irreversible one electron reduction appeared at
Ep,c
generated product waves at Ep,a
0.84 V and reversible one electron oxidations at E1/2
1.55 and ꢁ1.54 V in CH2Cl2 and CH3CN, respec-
tively. In dmf, two irreversible reductions appeared at
Ep,c 1.36 and ꢂ1.92 V, reductively generated pro-
duct waves appeared at Ep,a 0.5 and ꢂ0.92 V, and
an irreversible oxidation appeared at Ep,a 1.87 V. On
ꢃ
/
ꢂ
/
1.50 and ꢂ
/
1.43 followed by electrochemically
ꢃ
/
ꢁ
/
0.85, ꢂ0.54 and ꢁ
/
/
ꢃ
/
ꢁ
/
/
ꢃ
/
ꢂ
/
/
ꢃ
/
ꢂ
/
/
ꢃ
/
oxidatively initiated scans, the reductively generated
product waves disappeared and new oxidatively gener-
ated product waves appeared in dmf at Ep,c
ꢃ
/
ꢂ0.64
/
and ꢂ1.15 V. These voltammograms reveal the sensi-
/
tivity of fac-Re(CO)3(dpkbh)Cl to solvent variations
and in accord with the electronic absorption spectral
properties observed in these solvents. The first reduction
wave is assigned to the ReI/0 couple and the oxidation
wave is assigned to the ReI/II couple, as they fall in the
potential observed for these couple in a variety of
rhenium carbonyl compounds of polypyridyl-like li-
Fig. 4. A plot of A440 (1 and 2) and A318 of 3.00ꢄ
10ꢂ5 M fac-
Re(CO)3(dpkbh)Cl in dmso versus concentration of NaOH (1,2) and
/
citric acid (3,4).
gands of the type fac-Re(CO)3(L-L)Cl where L-Lꢃ
dpk, dpkoxime, dpknph and others [12,14,19,22]. For
example, in the voltammograms of fac-
Re(CO)3(dpkphh)Cl an irreversible reduction assigned
to ReI/0 appeared at Ep,c
1.75 V in CH2Cl2. The
/
ꢃ
/
ꢂ
/
irreversibility of the first electronic reduction and
oxidation in dmf and appearance of electrochemically
generated product waves hint to rich electrochemical
behavior and studies are in progress to explore the
electrochemical behavior of fac-Re(CO)3(dpkbh)Cl in
various media in the presence/absence of various sub-
strates and elucidate the mechanism for the redox
decomposition of fac-Re(CO)3(dpkbh)Cl [22].
Single crystals of fac-Re(CO)3(dpkbh)Cl grown from
an acetonitrile solution of fac-Re(CO)3(dpkbh)Cl are
¯
1 and single crystals of fac-
centric in the space group P
Re(CO)3(dpkbh)Cl×dmso obtained from a dmso solu-
tion of fac-Re(CO)3(dpkbh)Cl are acentric in the space
/
/
¯
group P
/
1: These results confirm the solventꢀsolute
/
interactions noticed in our solution measurements.
Structural analysis revealed the presence of twins of
fac-Re(CO)3(dpkbh)Cl and fac-Re(CO)3(dpkbh)Cl×
dmso. ORTEP drawings of fac-Re(CO)3(dpkbh)Cl and
fac-Re(CO)3(dpkbh)Cl×dmso are shown in Fig. 6 and
selected bond distances and angles are given in Table 2.
/
Fig. 5. Cyclic voltammograms of fac-Re(CO)3(dpkbh)Cl in CH2Cl2 (a
and b), CH3CN (c and d) and DMF (e and f) solutions 0.1 M in [N(n-
Bu)4](PF6) at a glassy carbon working electrode at a scan rate of 400
mV sꢂ1 versus SCE.
/

M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ
/98
95
Table 2
Bond lengths (A) and angles (8) for fac-Re(CO)3(dpkbh)Cl and fac-Re(CO)3(dpkbh)Cl×
˚
/dmso
fac-Re(CO)3(dpkbh)Cl
fac-Re(CO)3(dpkbh)Cl×dmso
/
Bond lengths
Re(1)ꢂ
Re(1)ꢂ
Re(1)ꢂ
Re(1)ꢂ
Re(1)ꢂ
Re(1)ꢂ
Re(1?)ꢂ
Re(1?)ꢂ
Re(1?)ꢂ
Re(1?)ꢂ
Re(1?)ꢂ
Re(1?)ꢂ
/
C(1)
C(2)
C(3)
N(1)
N(2)
Cl(1)
1.901(11)
1.909(10)
1.900(18)
2.209(7)
2.189(7)
2.457(4)
1.938(15)
1.930(18)
1.946(9)
2.221(10)
2.149(11)
2.455(2)
1.258(16)
1.374(11)
1.37(2)
1.93(2)
/
1.926(14)
1.904(9)
2.20(2)
/
/
/
2.154(19)
2.485(7)
1.93(3)
/
/
C(1?)
C(2?)
C(3?)
N(1?)
N(2?)
Cl(1?)
/
1.910(9)
1.910(9)
2.210(15)
2.242(18)
2.459(7)
1.21(3)
/
/
/
/
N(3)ꢂ
N(3)ꢂ
N(4)ꢂ
C(5)ꢂ
N(3?)ꢂ
N(3?)ꢂ
N(4?)ꢂ
C(5?)ꢂ
S(1)ꢂO(6)
S(1?)ꢂO(6?)
/
C(4)
N(4)
C(5)
/
1.41(2)
/
1.47(3)
/O(4)
1.230(15)
1.283(11)
1.368(10)
1.347(15)
1.236(14)
1.14(3)
1.33(2)
1.29(3)
/
C(4?)
N(4?)
C(5?)
/
/
1.38(4)
/O(4?)
1.29(3)
1.49(3)
/
/
1.36(2)
Bond angles
C(3)ꢂRe(1)ꢂ
C(1)ꢂRe(1)ꢂ
C(3)ꢂRe(1)ꢂ
C(1)ꢂRe(1)ꢂ
C(2)ꢂRe(1)ꢂ
C(3)ꢂRe(1)ꢂ
N(2)ꢂRe(1)ꢂ
C(3)ꢂRe(1)ꢂ
N(1)ꢂRe(1)ꢂ
C(2?)ꢂRe(1?)ꢂ
C(1?)ꢂRe(1?)ꢂ
C(2?)ꢂRe(1?)ꢂ
C(1?)ꢂRe(1?)ꢂ
C(3?)ꢂRe(1?)ꢂ
C(2?)ꢂRe(1?)ꢂ
C(1?)ꢂRe(1?)ꢂ
C(3?)ꢂRe(1?)ꢂ
N(2?)ꢂRe(1?)ꢂ
C(3?)ꢂRe(1?)ꢂCl(1?)
N(1?)ꢂRe(1?)ꢂCl(1?)
C(4)ꢂN(3)ꢂN(4)
N(3)ꢂN(4)ꢂC(5)
O(4)ꢂC(5)ꢂN(4)
N(4?)ꢂN(3?)ꢂC(4?)
N(3?)ꢂN(4?)ꢂC(5?)
O(4?)ꢂC(5?)ꢂN(4?)
/
/
C(1)
C(2)
N(2)
N(2)
N(2)
N(1)
90.2(6)
87.8(4)
91.6(4)
91.9(10)
91.9(9)
92.1(9)
/
/
/
/
/
/
95.9(4)
92.8(8)
/
/
176.2(3)
93.1(4)
83.4(3)
173.8(8)
94.4(10)
81.7(8)
/
/
/
/
N(1)
/
/
Cl(1)
175.5(3)
84.3(3)
177.1(9)
83.2(6)
/
/
Cl(1)
/
/
C(1?)
C(3?)
N(2?)
N(2?)
N(2?)
N(1?)
N(1?)
N(1?)
87.8(7)
90.1(5)
85.8 (10)
87.2(11)
173.7(7)
92.4(10)
93.8(10)
97.7(7)
/
/
/
/
176.1(4)
95.6(6)
/
/
/
/
92.5(4)
/
/
93.0(5)
/
/
176.6(3)
93.1(4)
176.5(11)
93.2(9)
/
/
/
/N(1?)
83.5(4)
84.0(6)
175.9(10)
85.8(4)
/
/
175.8(4)
84.32(19)
121.4(10)
121.0(10)
118.2(13)
120.7(7)
120.4(8)
120.0(11)
/
/
/
/
116.1(19)
110.2(15)
127.6(19)
117.2(16)
123.1(18)
/
/
/
/
/
/
/
/
/
/
115(2)
The bond distances and angles are normal and similar to
those we reported for fac-Re(CO)3(dpknph)Cl×dmso,
fac-Re(CO)3(dpkphh)Cl×CH3CN, dpkbh and other re-
lated compounds [16ꢀ19,21ꢀ24]. The coordination
about rhenium is distorted octahedral with the N,N-
bidentate dpkbh forming a six membered (Rex ꢂN1x ꢂ
C15x ꢂC00x ꢂC25x ꢂN2x where xꢃ1,1?, 2 or 2?) me-
tallocyclic ring with the pyriding rings in a butterfly (L)
formation. The NꢂN bite angles [ꢃN(1)x ꢂRex ꢂ
N(2)x] (see Table 2) are of the same order as the 81.68
and 84.68 bite angles observed for the same bit angles in
fac-Re(CO)3(dpkO,OH) [18] and ReOCl2(dpkO,OH)
[32], respectively, and is larger than those reported for
a variety of rhenium compounds of a-diimine ligands of
/
/
/
/
/
/
/
/
/
/
/
/
/
/

96
M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ98
/
Fig. 7. Packing diagrams of (a) fac-Re(CO)3(dpkbh)Cl and (b) fac-
dmso. Non-covalent bonds are denoted by dashed
line.
Re(CO)3(dpkbh)Cl×
/
Fig. 6. ORTEP drawings of (a) fac-Re(CO)3(dpkbh)Cl and (b) fac-
Re(CO)3(dpkbh)Cl×
/
dmso. The thermal ellipsoides are drawn at the
30% probability level.
Table 3
˚
Bond lengths (A) and angles (8) for fac-Re(CO)3(dpkbh)Cl and fac-
Re(CO)3(dpkbh)Cl×dmso
the type fac-Re(CO)3(L-L)Cl [33ꢀ
fac-Re(CO)3(bipy)(OPOF2) has
/
38], for example, in
a
/
ꢃ
/
N(1)ꢂRe1ꢂ
/
/
N(1A)ꢃ74.38 [37]. These results confirm that the six
/
Dꢂ
/
H
/
Á Á Á
/
A
d(Dꢂ
/
H) d(H
/
Á Á Á
/
A) d(D
/
Á Á Á
/
A)
B/(DHA)
membered metallocyclic ring in rhenium compounds of
polypyridyl-like ligands is more stable than the five-
membered metallocyclic ring in rhenium compounds of
a-diimine ligands. The amide NH and CO groups of the
hydrazone moiety in fac-Re(CO)3(dpkbh)Cl are in anti-
position and the hydrazone moiety is non-planar while
fac-Re(CO)3(dpkbh)Cl
N(4?)ꢂH(4?)Á Á Á
O(4?)1
N(4)ꢂH(4)Á Á Á
O(4)2
C(14?)ꢂ
C(22?)ꢂ
C(32)ꢂH(32)
C32?ꢂH(32?)Á Á Á
/
/
/
0.86
0.86
0.93
2.08
2.11
2.83
2.60
2.45
2.47
2.85(1)
2.87(1)
3.53(1)
3.27(1)
2.86(2)
2.88(1)
147.23
145.38
133.50
129.58
106.96
106.73
/
/
/
/
H(14?)Á Á Á
/Cl(1)
/
H(22?)
/
/Á Á Á O(3)3 0.93
/
/
Á Á Á
/
N(3)
0.93
0.93
/
/
/
N(3?)
in fac-Re(CO)3(dpkbh)Cl×
/
dmso the amide NH and CO
fac-Re(CO)3(dpkbh)Cl×
N(4)ꢂH(4)Á Á ÁO(5)
N(4?)ꢂH(4?)Á Á Á
C(11?)ꢂH(11?)
C(14)ꢂH(14)Á Á Á
C(22)ꢂH(22)Á Á Á
C(22?)ꢂH(22?)
C(33)ꢂH(33)Á Á Á
C(36)ꢂH(36)Á Á Á
/
dmso
0.86
0.86
0.93
0.93
0.93
0.93
0.93
0.93
groups of are in syn position and the hydrazone moiety
is semi-planar (see Fig. 6). These results confirm the
/
/
/
1.98
2.20
2.82
2.43
2.50
2.39
2.57
2.42
2.78(3)
3.00(3)
3.66(3)
3.31(3)
3.17(3)
3.11(3)
3.41(3)
3.16(3)
154.81
155.82
150.26
159.48
129.46
134.51
151.51
135.70
/
/
/
O(5?)
proposed conformational changes due to solventꢀsolute
interactions noticed in our solution measurements and
reveal that the low energy electronic state is due to the
/
/
/
Á Á Á
/
Cl(1)4
O(2)4
/
/
/
/
/
/
O(4?)5
/
/
Á Á Á
/
O(4)6
syn conformation associated with the solventꢀsolute
/
/
/
/
O(3?)7
interaction and the high-energy electronic state is due to
the anti-conformation due to solvent free interaction.
This is consistent with our optical measurements as in
non-polar solvent such as CH2Cl2 a high-energy electro-
/
/
/
O(5)
Symmetry transformations used to generate equivalent atoms: 1ꢃ
1ꢂx, 1ꢂy, ꢂz, 2ꢃ1ꢂx, 2ꢂy, ꢂz, 3ꢃ x, 1ꢂy, ꢂz, 4ꢃ1ꢁx, y,
z, 5ꢃx, y, 1ꢁz, 6ꢃx, y, ꢂ1ꢁz and 7ꢃx, ꢂ1ꢁy, 1ꢁz.
/
/
/
/
/
/
/
/
/
ꢂ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
nic state appeared at ꢀ
ing solvent two electronic states appeared at ꢀ
318 nm (Fig. 6).
/
310 nm and in polar coordinat-
/440 and
Re(CO)3(dpkbh)Cl×
/dmso units interlocked via a web
ꢀ
/
of hydrogen bonds (see Table 3 and Figs. 7 and 8). The
crystallized dmso molecules are not equivalent, in
The packing of molecules (Fig. 7) reveals stacks of
non-helical fac-Re(CO)3(dpkbh)Cl and helical fac-

M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ
/98
97
Fig. 8. Views of the hydrogen bonding in fac-Re(CO)3(dpkbh)Cl (a and b) and fac-Re(CO)3(dpkbh)Cl×
/dmso (c and d). Non-covalent bonds are
denoted by dashed line.
residue fac-Re(CO)3(dpkbh)Cl×
/
dmso a three centered
4. Conclusion
bifurcated hydrogen bond is formed between dmso
oxygen atom and amide N4 and aromatic C36 protons
(see Table 3 and Fig. 8(c)) and in residue [fac-
The isolation of fac-Re(CO)3(dpkbh)Cl marks the
first instance a metal compound of N,N-bidentate
dpkbh has been reported. Spectroscopic and electro-
chemical measurements on fac-Re(CO)3(dpkbh)Cl re-
(Re(CO)3(dpkbh)Cl×
/
dmso]? two centered linear hydro-
H4)
gen bond is formed between O5 and the amide (N4ꢂ
/
proton of the hydrazone moiety (see Table 3 and Fig.
8(d)). The hydrogen bond between the hydrazone N3 of
fac-Re(CO)3(dpkbh)Cl and aromatic C32 proton ap-
pears to reinforce the syn conformation of the hydra-
zone amide moiety and the hydrogen bond between the
carbonyl group and the aromatic C22 proton of the
pyridyl ring appears to reinforce the anti-conformation
of the amide moiety of the hydrazone backbone. The
bond distances and angles of the hydrogen bonds are
normal and similar to those reported for a variety of
vealed strong solventꢀ
studies on fac-Re(CO)3(dpkbh)Cl
Re(CO)3(dpkbh)Cl×dmso reveal octahedral coordina-
tion about rhenium and different conformations about
the amide of the hydrazone moiety. The packing of
molecules reveals a web of hydrogen bonds that may
account for the different conformational forms in the
solid state.
/
solute interaction and structural
and fac-
/
compounds containing such interactions [16ꢀ
/
19,21ꢀ
/
24,39ꢀ42].
/
Acknowledgements
Owing their convenient synthesis, rich physico-che-
mical properties, potential use in non-linear optics and
molecular sensing work is in progress to isolate a variety
of metal compounds of polypyridyl-like ligands to
explore their electro-optical properties, solid state struc-
tures and conformations.
I acknowledge funding from The University of the
West Indies (UWI) and Inter-America Development
Bank (IDB) for funds to establish the X-ray Laboratory
at UWI-Mona.

98
M. Bakir, O. Brown / Inorganica Chimica Acta 353 (2003) 89ꢀ98
/
[23] M. Bakir, O. Green, Acta Crystallogr. Sect. C 58 (2002) 0263.
[24] M. Bakir, O. Brown, J. Mol. Struct. 641 (2002) 183.
[25] J. Ellena, G. Punte, B.E. Rivero, J. Chem. Crystallogr. 26 (1996)
319.
References
[1] Z.E. Serna, R. Corte´s, M.K. Urtiaga, M.G. Barandika, L.
Lezama, M.I. Arriortua, T. Rojo, Eur. J. Inorg. Chem. (2001)
865.
[26] M.C. Etter, Acc. Chem. Res. 23 (1990) 120.
[27] F. Pan, C. Bosshard, M.S. Wong, C. Serbutoviez, K. Schenk, V.
Gramlich, P. Gunter, Chem. Mater. 9 (1997) 1328.
[28] C. Bosshard, K. Sutter, P. Pretre, J. Hullinger, M. Florsheimer, P.
Kaatz, P. Gunter, Organic Nonlinear Optical Materials, Gor-don
and Breach Science Publishers, Amsterdam, 1995.
[29] Bruker-SHELXTL, Software version 5.1, Brucker AXS, Madison,
Wisconsin, USA, 1997.
[2] G. Yang, S.-L. Zheng, X.-M. Chen, H.K. Lee, Z.-Y. Zhou,
T.C.W. Mak, Inorg. Chim. Acta 303 (2000) 86.
[3] H. Bock, T.T.H. Van, H. Schodel, R. Dienelt, Eur. J. Org. Chem.
¨
(1998) 585.
[4] S.R. Breeze, S. Wang, J.E. Greedan, N.P. Raju, Inorg. Chem. 35
(1996) 6944.
[5] H.-L. Kwong, L.-S. Cheng, W.-S. Lee, W.-L. Wong, W.-T. Wong,
Eur. J. Inorg. Chem. (2000) 1997.
[30] G.M. Sheldrick, SHELX97 and SHELXL97, University of Gottin-
¨
gen, Germany, 1997.
[6] M.A.S. Goher, F.A. Mautner, Polyhedron 18 (1999) 3425.
[7] S.O. Sommerer, C.E. MacBeth, A.J. Jircitano, K.A. Abboud,
Acta Crystallogr. Sect. C 53 (1997) 1551.
[31] F.L. Boschke, W. Fresenius, J.F.K. Huber, E. Pungor, G.A.
Rechnitz, W. Simon, Th.S. West (Eds.), Tables of Spectral data
for Structure Determination of Organic, Springer, Berlin, Heidel-
berg, 1983.
[8] S.O. Sommerer, B.L. Westcott, A.J. Jircitano, K.A. Abboud,
Inorg. Chim. Acta 238 (1995) 149.
[32] T.I.A. Gerber, H.J. Kemp, J.G.H. du Preez, G. Bandoli, J. Coord.
Chem. 28 (1993) 329.
[9] L.H.S.A. Terra, M.C. Da Cunha Areias, I. Gaubeur, M.E.V.
Suarez-Iha, Spectrosc. Lett. 32 (1999) 257.
[33] V.W.-W. Yam, K.K.-W. Lo, K.-K. Cheung, R.Y.-C. Kong, J.
Chem. Soc., Chem. Commun. (1995) 1191.
[10] M. Carcelli, C. Pelizzi, G. Pelizzi, P. Mazza, F. Zani, Franca, J.
Organomet. Chem. 488 (1995) 55.
[34] D.H. Gibson, B.A. Sleadd, X. Yin, A. Vij, Organometallics 17
(1998) 2689.
[11] M. Bakir, J.A.M. McKenzie, J. Chem. Soc., Dalton Trans. (1997)
3571.
[35] V.W.-W. Yam, K.-Z. Wang, C.-R. Wang, Y. Yang, K.-K.
Cheung, Organometallics 17 (1998) 2440.
[12] M. Bakir, J.A.M. McKenzie, Electroanal. Chem. 425 (1997) 61.
[13] M. Bakir, J. Electroanal. Chem. 466 (1999) 60.
[14] M. Bakir, K. Abdur-Rashid, Trans. Metal Chem. 24 (1999) 384.
[15] M. Bakir, K. Abdur-Rashid, W.H. Mulder, Talanta 51 (2000)
735.
[36] V.W.-W. Yam, V.C.-Y. Lau, K.-K. Cheung, Organometallics 14
(1995) 2749.
[37] E. Horn, M.R. Snow, Aust. J. Chem. 33 (1980) 2369.
[38] J.C. Calabrese, W. Tam, Chem. Phys. Lett. 133 (1987) 244.
[39] D. Braga, F. Grepioni, G.R. Desiraju, Chem. Rev. 98 (1998)
1375.
[16] M. Bakir, Acta Crystallogr. Sect. C 57 (2001) 1154.
[17] M. Bakir, Acta Crystallogr. Sect. C 57 (2001) 1371.
[18] M. Bakir, Acta Crystallogr. Sect. C 58 (2002) m74.
[19] M. Bakir, Eur. J. Inorg. Chem. (2002) 481.
[20] M. Bakir, C. Gyles, Talanta 56 (2002) 1117.
[21] M. Bakir, O. Brown, J. Mol. Struct. 609 (2002) 129.
[22] M. Bakir, Inorg. Chim. Acta 332 (2002) 1.
[40] J.P. Glusker, M. Lewis, M. Rossi, Crystal Structure Analysis for
Chemists and Biologists, Wiley-VCH, New York, 1994.
[41] J.H. Williams, Acc. Chem. Res. 26 (1993) 593.
[42] G.R. Desiraju, Crystal Engineering, Elsevier, New York, 1989.