X-ray crystallographic, spectroscopic and molecular sensing properties of fac-tricarbonylchloro(di-2-pyridylketonebenzoylhydrazone)rhenium(I) dimethylformamide solvate

Article abstract of DOI:10.1016/j.molstruc.2003.12.038

The molecular sensor fac-[Re(CO)₃(dpkbh)Cl]·DMF (1) where DMF=N,N-dimethyl formamide and dpkbh=di-2-pyridylketonebenzoylhydrazone crystallized in the acentric triclinic space group P1. Structural analysis shows two units of (1) with rhenium in distorted octahedral geometry, the carbonyl groups are in facial positions with an average C-Re-C angle of 90° and the N,N-bidentate dpkbh forms six-membered metallocyclic ring with rhenium in a boat conformation. The molecular packing shows the binding of DMF to fac-[Re(CO)₃(dpkbh)Cl] and helical strands of (1) interlocked via a network of hydrogen bonds. Optical measurements on fac-[Re(CO) ₃(dpkbh)Cl] in DMF show the presence of two interlocked charge transfer bands at 440 and 318 nm that are highly sensitive to slight variations in their surroundings. As the concentration decreases, the intensity of the low energy absorption band at 440 nm increases and the reverse is observed when the concentration increases. Thermo-optical measurements on fac-[Re(CO) ₃(dpkbh)Cl] in DMF established the reversible interconversion between the high and low energy electronic states of fac-Re(CO) ₃(dpkbh)Cl and changes in enthalpy (ΔH^?) of+17.44±0.40kJmol^-1, entropy (ΔS^?) of +37.45±0.50 J mol^-1 and free energy (ΔG ^?) of +6.27±0.30 kJ mol^-1 in DMF were calculated. Acids or bases in concentration as low as 1.0×10 ^-9M can be detected and determined using fac-[Re(CO) ₃(dpkbh)Cl] in DMF. ¹H-NMR measurements on fac-[Re(CO)₃(dpkbh)Cl] in DMF in non-aqueous media reveal high sensitivity to solvent and temperature variations and points to strong solvent-complex interactions. The amide protons and solvate protons show high sensitivity to temperature variations than the aromatic protons pointing to the participation of the amide proton in solvate-complex hydrogen bonds in non-aqueous solutions of fac-[Re(CO)₃(dpkbh)Cl].

Full text of DOI:10.1016/j.molstruc.2003.12.038

Journal of Molecular Structure 691 (2004) 265–272
www.elsevier.com/locate/molstruc
X-ray crystallographic, spectroscopic and molecular sensing properties
of fac-tricarbonylchloro(di-2-pyridylketonebenzoylhydrazone)rhenium(I)
dimethylformamide solvate
*
Mohammed Bakir , Ordel Brown, Toni Johnson
Department of Chemistry, The University of the West Indies, Mona Campus, Kingston, WI 7, Jamaica
Received 1 December 2003; revised 19 December 2003; accepted 22 December 2003
Abstract
The molecular sensor fac-[Re(CO)3(dpkbh)Cl]·DMF (1) where DMF ¼ N,N-dimethyl formamide and dpkbh ¼ di-2-pyridylketone-
benzoylhydrazone crystallized in the acentric triclinic space group P1. Structural analysis shows two units of (1) with rhenium in
distorted octahedral geometry, the carbonyl groups are in facial positions with an average C–Re–C angle of 908 and the N,N-
bidentate dpkbh forms six-membered metallocyclic ring with rhenium in a boat conformation. The molecular packing shows the
binding of DMF to fac-[Re(CO)3(dpkbh)Cl] and helical strands of (1) interlocked via
a network of hydrogen bonds.
Optical measurements on fac-[Re(CO)3(dpkbh)Cl] in DMF show the presence of two interlocked charge transfer bands at 440 and
318 nm that are highly sensitive to slight variations in their surroundings. As the concentration decreases, the intensity of the low
energy absorption band at 440 nm increases and the reverse is observed when the concentration increases. Thermo-optical
measurements on fac-[Re(CO)3(dpkbh)Cl] in DMF established the reversible interconversion between the high and low energy
electronic states of fac-Re(CO)3(dpkbh)Cl and changes in enthalpy ðDHBÞ of þ 17.44 ^ 0.40 kJmol21
,
entropy ðDSBÞ of
þ37.45 ^ 0.50 J mol21 and free energy ðDGBÞ of þ6.27 ^ 0.30 kJ mol21 in DMF were calculated. Acids or bases in concentration
as low as 1.0 £ 1029 M can be detected and determined using fac-[Re(CO)3(dpkbh)Cl] in DMF. 1H-NMR measurements on fac-
[Re(CO)3(dpkbh)Cl] in DMF in non-aqueous media reveal high sensitivity to solvent and temperature variations and points to strong
solvent-complex interactions. The amide protons and solvate protons show high sensitivity to temperature variations than
the aromatic protons pointing to the participation of the amide proton in solvate-complex hydrogen bonds in non-aqueous solutions of
fac-[Re(CO)3(dpkbh)Cl].
q 2004 Elsevier B.V. All rights reserved.
Keywords: Sensors; Di-2-pyridyl ketonebenzoylhydrazone; Rhenium; X-ray crystallography
1. Introduction
conformational) is important for molecular recognition as
the interconversion between states allows to probe their
structural relaxation and interactions with their surround-
ings [8]. The presence of organized non-covalent
hydrogen bonds in materials was suggested by many
authors to form polar chains and their appropriate
packing may lead to the generation of acentric crystals
required for non-linear optical responses, e.g. second
harmonic generation [9,10]. We have been interested in
the chemistry of di-2-pyridyl ketone (dpk) and its oxime
and hydrazone derivatives (see below) because of their
The development of molecular systems sensitive to
their surrounding has attracted a flurry of research
activities in recent years for their use in part as sensitive
reagents for the determination of trace amounts of
biological and industrial substrates [1–7]. Bistability,
i.e. the ability the systems (sensor plus surrounding
molecules) to exist in two different states (electronic or
*
Corresponding author. Tel.: þ876-935-8164; fax: þ876-977-1835.
E-mail address: mohammed.bakir@uwimona.edu.jm (M. Bakir).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2003.12.038

266
M. Bakir et al. / Journal of Molecular Structure 691 (2004) 265–272
rich physico-chemical properties, reactivity patterns and
applications in molecular recognition, catalysis and others
[11–19].
Table 1
Crystal data and structure refinement for fac-[Re(CO)3(dpkbh)Cl]·DMF
Empirical formula
Formula weight
C24H21ClN5O5Re
681.11
Temperature
298(2) K
˚
0.71073 A
Wavelength
Crystal system, space group
Unit cell dimensions
Triclinic, P1
˚
a ¼ 9:1300ð10Þ A a ¼ 80:685ð7Þ8
˚
b ¼ 12:1673ð11Þ A b ¼ 81:978ð10Þ8
˚
c ¼ 12:4555ð15Þ A g ¼ 75:235ð7Þ8
3
˚
Volume
1313.3(2) A
Z; Calculated density
Absorption coefficient
Fð000Þ
2, 1.722 mg/m3
4.771 mm21
664
0.6 £ 0.8 £ 0.7 mm3
Crystal size
Theta range for data collection
Limiting indices
2.25–25.008
210 # h # 1; 214 # k # 14;
214 # l # 14
In recent reports we described the synthesis of a series of
di-2-pyridyl ketone hydrazones and reported on their
optosensing behavior toward biomolecules and metal ions
[17–22]. Metal ions in concentrations as low as 1028 M can
be detected and determined using di-2-pyridyl ketone
hydrazones [19–21]. Structural studies on dpkbh (2), fac-
[Re(CO)3(dpkbh)Cl] (3) where dpkbh ¼ di-2-pyridylketo-
nebenzoylhydrazone and fac-[Re(CO)3(dpkbh)Cl]·DMSO
(4) where DMSO is dimethyl sulfoxide, revealed the
presence of infinite one dimensional chains of non-coplanar
pyridine rings in dpkbh, and centric and acentric units of (3)
and (4), respectively [21–23]. The isolation of solvent free
and DMSO solvated crystals of (3) confirms the high
sensitivity of (3) to its surrounding and here the structure of
DMF solvated fac-[Re(CO)3(dpkbh)Cl] along with its
solution optosensing and proton nuclear magnetic resonance
properties are reported.
Reflections collected/unique
Completeness to theta ¼ 25.00
Absorption correction
5545/5545 ½RðintÞ ¼ 0:0000Š
99.6%
Empirical
Max. and min. transmission
Refinement method
0.3873 and 0.3135
Full-matrix least-squares on F2
5545/7/651
Data/restraints/parameters
Goodness-of-fit on F2
1.011
Final R indices ½I . 2sigmaðIފ
R indices (all data)
R1 ¼ 0:0231; wR2 ¼ 0:0691
R1 ¼ 0:0236; wR2 ¼ 0:0697
0.106(12)
Absolute structure parameter
Extinction coefficient
0.0034(4)
˚
0.923 and 20.901 eA
23
Largest diff. peak and hole
along with additional details concerning data collection. All
non-hydrogen atoms were refined with anisotropic thermal
parameters.
2.3. Optical sensing studies
2. Experimental
A stock solution of fac-[Re(CO)3(dpkbh)Cl]·DMF in
DMF and stock solutions of stimulus (NaOH, NaBH4,
NaBF4 or citric acid) in DMF were prepared separately.
Optical changes (electronic absorption spectral changes)
were measured on solutions of fac-[Re(CO)3(dpkbh)Cl] in
the absence and presence of stimulus solutions in DMF (see
figure captions for details). With the exception of thermo-
optical measurements, all measurements were made at room
temperature.
2.1. Reagents
Solvents were reagent grade and thoroughly deoxyge-
nated prior to use. All other reagents were obtained from
commercial sources and used without further purification.
fac-[Re(CO)3(dpkbh)Cl] was prepared from the
reaction between Re(CO)5Cl and dpkbh in refluxing
toluene as described in the literature [23]. Crystals of
fac-[Re(CO)3(dpkbh)Cl]·DMF were obtained from a DMF
solution of fac-[Re(CO)3(dpkbh)Cl] when allowed to stand
at room temperature for several days.
2.4. Physical measurements
Electronic absorption spectra were recorded on a HP-
8452A spectrophotometer or a Perkin–Elmer UV/VIS/NIR
spectrometer l-19. Baseline corrections on blank solvents
were recorded prior to measurements. A Lauda-Brinkmann
RM6 circular bath was used for temperature control.
Solution 1H NMR spectra were recorded on a Bruker
AVANCE 500-MHz Fourier-transform spectrometer and
referenced to the residual protons in the incompletely
deuteriated solvent.
2.2. X-ray crystallography
A single crystal isolated from a DMF solution of fac-
[Re(CO)3(dpkbh)Cl] was selected and mounted on a glass
fiber with epoxy cement. A Bruker 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 [24,25]. Cell parameters and
other crystallographic information are given in Table 1

M. Bakir et al. / Journal of Molecular Structure 691 (2004) 265–272
267
3. Results and discussion
possible to assign the high energy electronic state of
fac-[Re(CO)3(dpkbh)Cl]·DMF in non-polar solvents
(310 nm in CH2Cl2) to the syn-conformation and the low
energy electronic state in hydrogen binding solvent (440 nm
in DMF) to the anti-conformation. Although the hydrazone
(CyN–NH–CO) moiety is semi-planar, the total hydrazone
backbone (CyN–NH–CO–Ph) is not planar and is similar
to those reported for (3) and (4).
The packing of molecules (Fig. 2) shows stacks of (1)
interlocked via a network of hydrogen bonds (Table 3).
This confirms the strong solvate-complex and complex-
complex interactions in the solid state. The bond distances
and angles of the hydrogen-bonds are of the same order as
those observed in (4), fac-[Re(CO)3(dpkphh)Cl]·CH3CN
and other related compounds [17,18,23]. For example,
hydrogen-bond parameters of 1.98, 2.78 and 154.52; and
2.20, 3.00 and 156.02 were reported for d(H· · ·A), D(D· · ·A)
and /DHA were reported for the N–H· · ·O hydrogen bonds
in (4) [23].
3.1. Structural studies
A view of the molecular structure offac-[Re(CO)3(dpkbh)Cl]·DMF
is shown in Fig. 1 and selected bond distances and angles are
given in Table 2. Two well separated units of
fac-[Re(CO)3(dpkbh)Cl]·DMF were observed with two
nitrogen atoms from the pyridyl rings, three carbon atoms
from the carbonyl groups, and one chloride atom occupying
the pseudo octahedral coordinated sites of rhenium atoms.
The N–N bidentate dpkbh forms a six membered
metallocyclic ring with rhenium in a boat conformation
and the pyridine rings in a butterfly (L) formation. This is
similar to that reported for a variety of N,N-bidentate
binding of di-2-pyridyl ketone and its oxime and hydrazone
derivatives of rhenium tricarbonyl moiety [17,18,23].
The bond distances and angles are normal and similar to
those reported for (2), (3), (4) and other related compounds
although slight variations were noted, especially those
related to the hydrazone backbone (CyN–NH–CO)
(see Table 2) [23]. The amide (NH) and the acyl (CO)
moiety are in anti conformation with torsional angles of
175.8 and 2178.98 for H4–N4–C5–O4 and H40 –N40 –
C50 –O40, respectively. These angles are of similar order as
the 175.9 and 173.08 observed for the same angles in (4) and
are significantly different than the –15.8 and 13.48 observed
in (3). These results reveal that the anti-conformation is
favored in hydrogen bonding solvent and the syn-confor-
mation is favored in solvent free crystals. These results are
consistent with the spectroscopic and electrochemical
behavior of these systems in non-aqueous media where
two interlocked electronic states were observed in hydrogen
bonding solvents and a single electronic state was
observed in non-coordinating solvents [23]. Thus it is
3.2. Spectroscopic properties
In previous reports we described the electronic absorp-
tion properties of dpkbh and fac-[Re(CO)3(dpkbh)Cl] in
non-aqueous solvents and revealed the presence of bistable
charge transfer absorption bands [21,23]. For the free
uncoordinated dpkbh, these bands are intra-ligand charge
transfer (ILCT) assigned to dpk p to pp transition followed
by dpk to benzoyl charge transfer. In the case of fac-
[Re(CO)3(dpkbh)Cl], although these transitions are ligand
dominated, the high energy electronic transition may be
mixed with a MLCT transition due to dp(Re) to pp (dpk) as
a variety of Re(I)-carbonyl compounds of the type fac-
[Re(CO)3(L–L)Cl], where L–L ¼ a-diimine ligand, have
their MLCT band reported in the same vicinity observed for
Fig. 1. The molecular structure of fac-[Re(CO)3(dpkbh)Cl]·DMF. The thermal ellipsoids are drawn at the 30% probability level and H atoms are shown as small
spheres of arbitrary radii.

268
M. Bakir et al. / Journal of Molecular Structure 691 (2004) 265–272
Table 2
calculated for dpkbh at 392 and 324 nm, respectively in
the presence and absence of NaOH or citric acid. For
fac-[Re(CO)3(dpkbh)Cl], extinction coefficients of
23,709 ^ 2000 and 22,450 ^ 2000 cm21 M21 were calcu-
lated at 440 and 318 nm, respectively, using NaBH4 and
NaBF4 to push the electronic states to the low and high
energy forms. Although we reported the optical properties
of fac-[Re(CO)3(dpkbh)Cl] in DMSO, here we report on the
optical behavior of fac-[Re(CO)3(dpkbh)Cl] in DMF [23].
The electronic absorption spectra of fac-[Re(CO)3(dpkbh)Cl]
is concentration dependent. As the concentration decreases,
the low energy electronic state at 440 nm becomes favorable
and the reverse is observed when the concentration of fac-
[Re(CO)3(dpkbh)Cl] increases. These results point to
solvent-complex interactions and hint to reversible inter-
conversion between the high and low energy electronic
states of fac-[Re(CO)3(dpkbh)Cl] in DMF. When the
temperature was allowed to increase on a DMF solution
of fac-[Re(CO)3(dpkbh)Cl], the ratio of the absorbance of
low energy to high energy electronic states increases and
when the temperature was allowed to decrease, the reverse
was observed. These results confirm the reversible inter-
conversion between the low and high energy electronic
states of fac-[Re(CO)3(dpkbh)Cl] and allowed for
calculations of the thermodynamic parameters for the
interconversion between the high and low energy electronic
states of fac-[Re(CO)3(dpkbh)Cl] in DMF. A plot of
lnðA440=A318Þ versus 1=T £ 103; K21 (see Fig. 3) gave a
straight line with a slope of 22.10 ^ 0.32 per unit decade
and an intercept of þ4.56 ^ 0.04 that gave changes
in enthalpy ðDHBÞ of þ17.44 ^ 0.40 kJ mol21, entropy
ðDSBÞ of þ 37.45 ^ 0.50 J mol21 and free energy ðDGBÞ
of þ6.27 ^ 0.30 kJ mol21 in DMF.
˚
Bond lengths (A) and angles (8) for fac-[Re(CO)3(dpkbh)Cl], fac-
[Re(CO)3(dpkbh)Cl]·DMSO and fac-[Re(CO)3(dpkbh)Cl]·DMF
fac-[Re(CO)3 fac-[Re(CO)3
fac-[Re(CO)3
(dpkbh)Cl]
(dpkbh)Cl]·DMSO (dpkbh)Cl]·DMF
Bond distances
Re(1)–C(1)
Re(1)–C(2)
Re(1)–C(3)
Re(1)–N(1)
Re(1)–N(2)
Re(1)–Cl(1)
Re(10)–C(10)
Re(10)–C(20)
Re(10)–C(30)
Re(10)–N(10)
Re(10)–N(20)
Re(10)–Cl(10)
N(3)–C(4)
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)
1.832(13)
1.928(12)
1.938(18)
2.220(12)
2.308(13)
2.468(5)
2.025(14)
1.83(2)
1.926(14)
1.904(9)
2.20(2)
2.154(19)
2.485(7)
1.93(3)
1.910(9)
1.910(9)
2.210(15)
2.242(18)
2.459(7)
1.21(3)
1.848(18)
2.177(15)
2.084(12)
2.482(4)
1.287(19)
1.354(15)
1.348(19)
1.151(16)
1.296(14)
1.357(13)
1.43(2)
N(3)–N(4)
1.41(2)
N(4)–C(5)
1.47(3)
C(5)–O(4)
1.230(15)
1.283(11)
1.368(10)
1.347(15)
1.236(14)
1.14(3)
N(30)–C(40)
N(30)–N(40)
N(40)–C(50)
C(50)–O(40)
1.33(2)
1.29(3)
1.38(4)
1.29(3)
1.24(2)
Bond angles
C(3)–Re(1)–C(1)
C(1)–Re(1)–C(2)
C(3)–Re(1)–N(2)
C(1)–Re(1)–N(2)
90.2(6)
87.8(4)
91.6(4)
95.9(4)
91.9(10)
91.9(9)
91.1(6)
87.6(6)
90.7(5)
97.8(5)
174.5(6)
95.4(5)
82.0(4)
174.1(5)
80.2(3)
90.2(8)
80.9(7)
173.3(9)
93.4(5)
95.8(6)
92.1(9)
92.8(8)
C(2)–Re(1)–N(2) 176.2(3)
173.8(8)
94.4(10)
81.7(8)
C(3)–Re(1)–N(1)
N(2)–Re(1)–N(1)
93.1(4)
83.4(3)
C(3)–Re(1)–Cl(1) 175.5(3)
177.1(9)
83.2(6)
N(1)–Re(1)–Cl(1) 84.3(3)
C(20)–Re(10)–C(10) 87.8(7)
C(10)–Re(10)–C(30) 90.1(5)
C(20)–Re(10)–N(20) 176.1(4)
C(10)–Re(10)–N(20) 95.6(6)
C(30)–Re(10)–N(20) 92.5(4)
C(20)–Re(10)–N(10) 93.0(5)
C(10)–Re(10)–N(10) 176.6(3)
C(30)–Re(10)–N(10) 93.1(4)
N(20)–Re(10)–N(10) 83.5(4)
C(30)–Re(10)–Cl(10) 175.8(4)
N(10)–Re(10)–Cl(10) 84.32(19)
85.8(10)
87.2(11)
173.7(7)
92.4(10)
93.8(10)
97.7(7)
For the following interconversion:
b 2 fac-½ReðCOÞ3ðdpkbhÞClŠ
Y a 2 fac-½ReðCOÞ3ðdpkbhÞClŠ
ð1Þ
176.5(11)
93.2(9)
174.8(6)
94.4(7)
where b is the conformation at high energy (318 nm) and a
is the conformation at low energy (440 nm)
Application of Beer’s Law gives:
84.0(6)
85.0(5)
175.9(10)
85.8(4)
178.0(6)
87.6(3)
Aa=Ab ¼ 1aca=1bcb
and
ð2Þ
C(4)–N(3)–N(4)
N(3)–N(4)–C(5)
O(4)–C(5)–N(4)
N(40)–N(30)–C(40) 120.7(7)
N(30)–N(40)–C(50) 120.4(8)
O(40)–C(50)–N(40) 120.0(11)
121.4(10)
121.0(10)
118.2(13)
116.1(19)
110.2(15)
127.6(19)
117.2(16)
123.1(18)
115(2)
115.2(11)
116.6(11)
126(3)
120.4(9)
118.6(10)
100.1(19)
lnðAa=AbÞ ¼ lnð1a=1bÞ þ ln K
ð3Þ
The equilibrium constant is related to the thermodynamic
parameters as shown in Eq. (4):
ln K ¼ DSB=R 2 DHB=RT
and substitution of Eq. (4) into Eq. (3) gives:
ð4Þ
the high energy ILCT band [21,23]. Manipulation of the
equilibrium distribution of the electronic states allowed
calculations of the extinction coefficients of dpkbh and fac-
[Re(CO)3(dpkbh)Cl] in non-aqueous media by the addition
of a substrate that pushes the equilibrium into one favorable
electronic state. In DMF extinction coefficients of
45,000 ^ 2000 and 15,000 ^ 2000 M21 cm21 were
lnðAa=AbÞ ¼ lnð1a=1bÞ þ DSB=R 2 DHB=RT
A plot of lnðAa=AbÞ versus 1=T gives a straight line with a
gradient of 2DHB=R and an intercept of {lnð1a=1bÞ þ
DSB=R}:
ð5Þ

M. Bakir et al. / Journal of Molecular Structure 691 (2004) 265–272
269
Fig. 2. A view of the packing of fac-[Re(CO)3(dpkbh)Cl]·DMF.
In DMSO changes in enthalpy ðDHBÞ of
þ4.10 ^ 0.20 kJ mol21, entropy ðDSBÞ of þ8.23 ^ 0.45 J mol21
and free energy ðDGBÞ of þ1.66 ^ 0.20 kJ mol21 were reported
[23]. These results reveal that the high to low energy
electronic state conversion is more favorable in DMSO
than DMF.
The electronic absorption spectra of fac-[Re(CO)3(dpkbh)Cl]
in DMF in the presence or absence of a stimuli are sensitive
Table 3
˚
Hydrogen bonds for fac-[Re(CO)3(dpkbh)Cl]·DMF (A and 8)
D–H· · ·A
d(D–H)
d(H· · ·A)
d(D· · ·A)
/(DHA)
Inter
N4-H4· · ·O5
N40 –H40· · ·O50
0.86
0.86
2.13
2.05
2.88
2.81
145.93
147.11
Intra
C70 –H70A· · ·O50
C70 –H70C· · ·O10
C12–H12· · ·O40
C120 –H120· · ·O4
C24–H24· · ·O1
C21–H21· · ·Cl10
C210 –H210· · ·Cl1
0.96
0.96
0.93
0.93
0.93
0.93
0.93
2.40
2.57
2.59
2.43
2.53
2.88
2.83
2.81
3.37
3.24
3.08
3.41
3.62
3.68
105.61
141.66
127.41
126.88
156.47
145.30
144.20
Fig. 3. A plot of lnðA440=A318Þ versus 1=T £ 103; K21 of 1.5 £ 1025 M fac-
[Re(CO)3(dpkbh)Cl] in DMF.

270
M. Bakir et al. / Journal of Molecular Structure 691 (2004) 265–272
Fig. 4. Electronic absorption spectra of a mixture of 2.50 £ 1025 M fac-
[Re(CO)3(dpkbh)Cl] and 1.00 £ 1023 M NaOH in DMF (1) in the presence
1.00 £ 1029 (2), 2.00 £ 1029 (3), 5.00 £ 1029 (4), 1.00 £ 1028 (5),
5.00 £ 1028 (6), 2.00 £ 1027 (7) and 1.00 £ 1026 (8) M citric acid in DMF.
Fig. 5. A plot of A440 (1 and 3) and A318 (2 and 4) of 2.50 £ 1025 M fac-
[Re(CO)3(dpkbh)Cl] in DMF in the absence of NaOH (1 and 4) and in the
presence of 1.00 £ 1023 M NaOH (2 and 3) versus concentration of citric
acid.
to variations in acid or base concentration. Fig. 4 shows the
electronic absorption spectra of
possible use of this system ( fac-[Re(CO)3(dpkbh)Cl] and
surrounding solvent molecules) as a magnetosensor for a
a
mixture of
fac-[Re(CO)3(dpkbh)Cl] and NaOH in DMF in the
presence of increasing amounts of citric acid.
Similar results were obtained in the absence of NaOH
and in both cases citric acid in concentrations as low as
1.0 £ 1029 M can be detected and determined using fac-
[Re(CO)3(dpkbh)Cl] in DMF. In the presence of NaOH,
the absorbance of the low energy electronic state of fac-
[Re(CO)3(dpkbh)Cl] increases compared to the absorbance
in the absence of NaOH and hence increases the optical
window that can be utilized for optosensing
measurements and hence improves the accuracy and
sensitivity of these systems. A plot of the absorbance of
fac-[Re(CO)3(dpkbh)Cl] in DMF in the presence and
absence of NaOH versus concentration of citric acid is
shown in Fig. 5 and reveals that citric acid in concen-
trations as low as 1 £ 1029 M can be detected and
determined using fac-[Re(CO)3(dpkbh)Cl] in the presence
and absence of NaOH. The reverse was done when
excess acid was added to a DMF solution of fac-
[Re(CO)3(dpkbh)Cl] and the resulting solution was titrated
with NaOH solution in DMF.
1
variety of stimuli. The H-NMR spectra of fac-[Re(CO)3
(dpkbh)Cl] are sensitive to temperature variations and the
spectra in d6-DMSO and CDCl3 measured at different
temperatures are shown in Figs. 7 and 8. From these
spectra it is apparent that the chemical shifts of the amide
The 1H-NMR spectra of fac-[Re(CO)3(dpkbh)Cl] in
different solvents are shown in Fig. 6. These spectra
reveal high sensitivity to solvent variations as apparent
from the chemical shift variations of the amide (N–H)
signal between 13 and 9 ppm, aromatic signals between
10 and 7 ppm and the solvate protons ,4 ppm. These
results hint to strong solvate-complex interactions and
Fig. 6. 1H-NMR spectra of fac-[Re(CO)3(dpkbh)Cl]·DMF measured in d6-
DMSO, d7-DMF, CDCl3 and d6-ACETONE at 30 8C.

M. Bakir et al. / Journal of Molecular Structure 691 (2004) 265–272
271
Fig. 7. 1H-NMR spectra of fac-[Re(CO)3(dpkbh)Cl] measured in d6-DMSO
at 30, 40, 50 and 60 8C.
Fig. 9. A plot of chemical shift ðdÞ of the amide proton of fac-
[Re(CO)3(dpkbh)Cl] in different solvents versus 1=T £ 103; K21
.
and solvate protons are more sensitive to temperature
variations than the chemical shifts of the aromatic protons.
A plot of the chemical shift of the amide and solvate
protons versus 1=T £ 103; K21 (see Figs. 9 and 10) gave
straight lines that gave slopes of 20.64 ^ 0.05,
20.40 ^ 0.04, 20.60 ^ 0.02 and 0.34 ^ 0.05 for the
amide protons (see Fig. 9) and -0.76 ^ 0.05,
20.72 ^ 0.05, 20.68 ^ 0.02 and 0.28 ^ 0.05 for the
solvate protons (see Fig. 10) in DMF, DMSO, (CD3)2CO
and CDCl3. The higher is the slope, the more sensitive the
proton to temperature variation and points to the shielding
of proton through inter- or intra-molecular hydrogen
bonds from its surroundings. These results reveal that
the amide proton in DMF, DMSO and (CD3)2CO is more
shielded from its surrounding through a classic hydrogen
Fig. 8. 1H-NMR spectra of fac-[Re(CO)3(dpkbh)Cl] measured in CDCl3 at
30, 40, 50 and 60 8C.
Fig. 10. A plot of chemical shift ðdÞ of the solvent proton of fac-
[Re(CO)3(dpkbh)Cl] in different solvents versus 1=T £ 103; K21
.

272
M. Bakir et al. / Journal of Molecular Structure 691 (2004) 265–272
bond of the type N–H· · ·O than in CDCl3. The aromatic
protons show low sensitivity to temperature variations and
no hydrogen bond analysis was done in this study. These
results confirm the solvate-complex interactions and are in
accord with the optical and structural results obtained in
this study.
References
˝
[1] C.v. Bu¨ltzingslowen, A.K. McEvoy, C. McDonagh, B.D. MacCraith,
Anal. Chim. Acta 480 (2003) 275.
[2] M.-a. Haga, T. Takasugi, A. Tomie, M. Ishizuya, T. Yamada, M.D.
Hossain, M. MiyaoInoue, J. Chem. Soc., Dalton Trans. (2003) 2069.
[3] A.G. Philip, Coord. Chem. Rev. 240 (2003) 191.
[4] C.W. Rogers, M.O. Wolf, Coord. Chem. Rev. 233–234 (2002) 341.
[5] C.J. Ward, P. Patel, T.D. James, Org. Lett. (Communication) 4
(2002) 477.
Owing the convenient synthesis of polypyridyl-like
ligands and their metal compounds coupled with their rich
physico-chemical properties, together with our continued
interest in the development of molecular sensors, the
coordination chemistry and sensing behavior of poly-
pyridyl-like ligands and their metal compounds toward a
variety of stimuli, including biomolecules and metal ions
remains under investigation in our laboratories.
[6] K.-H. Wong, M.C.-W. Chan, C.-W. Che, Chem.—Eur. J. 5
(1999) 2845.
`
[7] V.V. Vasilev, S.M. Borisov, Sensors Actuators B: Chem. 82
(2002) 272.
[8] O. Kahn, Chem. Br. (1999) 24.
[9] J. Ellena, G. Punte, B.E. Rivero, J. Chem. Crystallogr. 26 (1996) 319.
[10] M.C. Etter, Acc. Chem. Res. 23 (1990) 120.
[11] H. Kumagai, M. Endo, M. Kondo, S. Kawata, S. Kitagawa, Coord.
Chem. Rev. 237 (2003) 197.
[12] V. Camel, Spectrochim. Acta Part B 58 (2003) 1177.
[13] C.J. Milios, E. Kefalloniti, C.P. Raptopoulou, A. Terzis, R. Vicente,
N. Lalioti, A. Escuer, S.P. Perlepes, Chem. Commun. (2003) 819.
[14] M. Bakir, J.A.M. McKenzie, J. Chem. Soc. Dalton Trans. (1997) 3571.
[15] M. Bakir, J. Electroanal. Chem. 466 (1999) 60.
[16] M. Bakir, I. Hassan, O. Green, J. Mol. Struct. 657 (2003) 75.
[17] M. Bakir, Eur. J. Inorg. Chem. (2002) 481.
4. Conclusion
X-ray structural studies of fac-[Re(CO)3(dpkbh)Cl]·DMF have
revealed helical strands of fac-[Re(CO)3(dpkbh)Cl]·DMF and a
network of hydrogen bonds that include solvate-complex
and complex–complex interactions. The electronic absorp-
tion spectra of fac-[Re(CO)3(dpkbh)Cl]·DMF are sensitive
to slight variations in their surrounding and substrates in
concentrations as low as 1029 M can be detected and
determined using fac-[Re(CO)3(dpkbh)Cl] in DMF.
1H-NMR measurements reveal high sensitivity of the
amide and solvate protons to solvent and temperature
variations, point to strong solvate-complex interactions and
are in accord with the optical and structural studies reported
in this study.
[18] M. Bakir, Inorg. Chim. Acta 332 (2002) 1.
[19] M. Bakir, K. Abdur-Rashid, C. Gyles, Spectrochim. Acta Part A 59
(2003) 2123.
[20] M. Bakir, C. Gyles, J. Mol. Struct. 649 (2003) 133.
[21] M. Bakir, O. Brown, J. Mol. Struct. 609 (2002) 129.
[22] M. Bakir, C. Gyles, Talanta 56 (2002) 1117.
[23] M. Bakir, O. Brown, Inorg. Chim. Acta 353 (2003) 89.
[24] Bruker-SHELXTL, Software Version 5.1. Bruker AXS, Inc.,
Madison, WI, USA, 1997.
¨
[25] G. M. Sheldrick, SHELX97 and SHELXL97, University of Gottingen,
Germany, 1997.