Molecular sensing behavior of the first Mn(I)-compound of di-2-pyridylketone-p-nitrophenylhydrazone (dpknph), fac-[Mn(CO) 3(dpknph)Br]

Article abstract of DOI:10.1016/j.ica.2004.12.050

The reaction between [Mn(CO)₅Br] and di-2-pyridylketone-p- nitrophenylhydrazone (dpknph) in diethyl ether under ultrasonic conditions gave fac-[Mn(CO)₃(dpknph)Br] in good yield. Optical and thermodynamic measurements on fac-[Mn(CO)₃(dpknph)Br] in non-aqueous polar solvents revealed reversible interconversion between two intense charge transfer absorption bands due to π-π* (dpk), followed by dpk → nitro intraligand charge transfer transition (ILCT), mixed with metal ligand charge transfer transition (MLCT) due to dπ(Mn)→π_(dpk). In non-polar solvents, a single absorption band appeared. Extinction coefficients of 46 200 ± 2000 and 28 400 ± 2000 M^-1 cm^-1 were calculated in DMSO for the low- and high-energy electronic states of fac-[Mn(CO)₃(dpknph)Br] using excess NaBF₄. Changes in enthalpy (ΔH^?) of +14.0 and -12.1 kJ mol^-1, entropy (ΔS^?) of +28.65 and -64.30 J mol^-1 K^-1, and free energy (ΔG^?) of +5.48 and +7.08 kJ mol^-1 at 298 K were calculated for the interconversion between the high and low energy electronic states of fac-[Mn(CO)₃(dpknph)Br]. These results allow for the use of these systems (fac-[Mn(CO) ₃(dpknph)Br] and surrounding solvent or solute molecules) as optical sensors for a variety of physical and chemical stimuli that include metal ions. Group 12 metal ions in concentrations as low as 1.00 × 10^-9 M can be detected and determined using fac-[Mn(CO)₃(dpknph)Br] in dmso in the presence and absence of NaBH₄.

Full text of DOI:10.1016/j.ica.2004.12.050

Inorganica Chimica Acta 358 (2005) 1835–1840
www.elsevier.com/locate/ica
Molecular sensing behavior of the first Mn(I)-compound of
di-2-pyridylketone-p-nitrophenylhydrazone (dpknph),
fac-[Mn(CO)3(dpknph)Br]
*
Mohammed Bakir , Orville Green, Colin Gyles
Department of Chemistry, The University of the West Indies, Mona Campus, Kingston 7, WI, Jamaica
Received 8 July 2004; accepted 30 December 2004
Available online 11 February 2005
Abstract
The reaction between [Mn(CO)5Br] and di-2-pyridylketone-p-nitrophenylhydrazone (dpknph) in diethyl ether under ultrasonic
conditions gave fac-[Mn(CO)3(dpknph)Br] in good yield. Optical and thermodynamic measurements on fac-[Mn(CO)3(dpknph)Br]
in non-aqueous polar solvents revealed reversible interconversion between two intense charge transfer absorption bands due to p–p*
(dpk), followed by dpk ! nitro intraligand charge transfer transition (ILCT), mixed with metal ligand charge transfer transition
(MLCT) due to dp
! pꢀðdpkÞ. In non-polar solvents, a single absorption band appeared. Extinction coefficients of
ðMnÞ
46200 2000 and 28400 2000 Mꢁ1 cmꢁ1 were calculated in DMSO for the low- and high-energy electronic states of fac-
[Mn(CO)3(dpknph)Br] using excess NaBF4. Changes in enthalpy (DHø) of +14.0 and ꢁ12.1 kJ molꢁ1, entropy (DSø) of +28.65
and ꢁ64.30 J molꢁ1 Kꢁ1, and free energy (DGø) of +5.48 and +7.08 kJ molꢁ1 at 298 K were calculated for the interconversion
between the high and low energy electronic states of fac-[Mn(CO)3(dpknph)Br]. These results allow for the use of these systems
(fac-[Mn(CO)3(dpknph)Br] and surrounding solvent or solute molecules) as optical sensors for a variety of physical and chemical
stimuli that include metal ions. Group 12 metal ions in concentrations as low as 1.00 · 10ꢁ9 M can be detected and determined using
fac-[Mn(CO)3(dpknph)Br] in dmso in the presence and absence of NaBH4.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Manganese; Carbonyl; Hydrazones; Sensors; Di-2-pyridyl ketone
RH
1. Introduction
O
N
H
H
N
O
N
Manganese carbonyl compounds are of interest in
part because of their rich physico-chemical properties,
reactivity patterns and applications in many important
chemical processes [1–10]. We have been interested in
the chemistry of di-2-pyridyl ketone and its oxime and
hydrazone derivatives (see below) and their metal com-
pounds and reported on the synthesis and characteriza-
tion of a variety of polypyridyl-like ligands and their
metal compounds [11–25].
N
N
N
N
N
N
dpk
dpk.oxime
dpkhydrazone
The electrochemical behavior of fac-[Re-(CO)3-
(dpk)Cl] in the presence and absence of different sub-
strates that include CO2 and Groups I and II metal ions
shows high sensitivity to solvent and substrate concen-
tration and the use of fac-Re(CO)3(dpk)Cl as an electro-
chemical sensor for Groups I and II metal ions [17,18]. In
the case of CO2, electrochemical reactions at metal and
ligand sites of fac-Re(CO)3(dpk)Cl were envisaged and
*
Corresponding author. Tel.: +1 876 935 8164; fax: +1 876 977
1835.
E-mail address: mohammed.bakir@uwimona.edu.jm (M. Bakir).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.12.050

1836
M. Bakir et al. / Inorganica Chimica Acta 358 (2005) 1835–1840
the electrochemical response of fac-Re-(CO)3 (dpk)Cl in
the presence of metal ions depends on the polarizing
power of the cation, i.e., charge density of cation, and
cations with a large charge to radius ratio show the high-
est perturbation [17,18,22]. Electrochemical measure-
ments on fac-Re(CO)3(dpk Æ oxime)Cl show the oxime
moiety to act as an electron sink/reservoir and its first
reduction potential dpk Æ oxime/dpk Æ oximeÅꢁ in non-
aqueous media is solvent dependent and controlled by
the proton-accepting ability of the solvent [19]. Plausible
mechanisms for the reduction and oxidation of fac-Re-
(CO)3(dpk Æ oxime)Cl to fac-Re(CO)3(dpkH Æ NH2)Cl
and fac-Re(CO)3(dpk)Cl were proposed and consistent
with the observed electrochemical transformations [19].
Spectroscopic and electrochemical measurements on
solutions of fac-Re(CO)3(dpknph)Cl and free dpknph
show the metal complex to undergo faster electron trans-
fer than the free ligand and the use of fac-
Re- (CO)3(dpknph)Cl as an optical sensor for metal
ions [20,21]. X-ray crystallographic analysis on rhenium
compounds of di-2-pyridyl ketone hydrazones revealed
the presence of a web of non-covalent interactions
that include solvent–solute and solute–solute interac-
tions [11,14,15,24]. In a recent report, we described the
synthesis and electrochemical behavior of manganese
tricarbonyl compounds of N,N-bidentate di-2-pyridylke-
tone (dpk), fac-[Mn(CO)3- (dpk)Br] and its N,O,N-
tridentate hydroxybis(2-pyridyl)methanolato anion
(dpkO,OHꢁ), fac-[Mn(CO)3- (dpk,O,OH))], and here
we report on the synthesis and optosensing behavior of
the first manganese compound of di-2-pyridyl ketone-4-
nitrophenylhydrazone (dpkn-ph), fac-[Mn(CO)3 (dpknph)-
Br] [12].
1949 s and 1922 s m(NO2) st as 1599, m(NO2) st sy
1334 and m(NO2) c 760 cmꢁ1
.
2.3. Physical measurements
Electronic absorption spectra were recorded on a Per-
kin–Elmer Lambda 19 UV/VIS/NIR spectrometer or
HP-8452A spectrophotometer. Infrared spectra were re-
corded as KBr pellets on a Perkin–Elmer Spectrum 1000
FT-IR Spectrometer. A Lauda-Brinkmann RM6 Circu-
lar Bath was used for temperature control.
2.4. Optical sensing studies
A stock solution of fac-[Mn(CO)3(dpknph)Br] in
DMSO and stock solutions of chemical stimulus
(NaBH4, NaBF4 or Group 12 salts) in DMSO were pre-
pared separately. Optical changes (electronic absorption
spectral changes) were measured on a solution prepared
by mixing appropriated volumes of fac-[Mn(CO)3-
(dpknph)Br] and stimulus solutions to prepare the de-
sired solution (see figure captions for details). With the
exception of the thermodynamic studies, all measure-
ments were made at room temperature.
2.5. Analytical procedures
Elemental microanalyses were performed by ME-
DAC Ltd., Department of Chemistry, Brunel Univer-
sity, Uxbridge; UK.
3. Results and discussion
The first manganese compound of dpknph, fac-
[Mn(CO)3(dpknph)Br], was prepared in good yield from
the reaction between [Mn(CO)5Br] and dpknph in diethyl
ether under ultrasonic conditions. This reaction is similar
to those reported for the synthesis of fac-[Mn(CO)3-
(dpk)Br] from the reaction between [Mn(CO)5Br] and
dpk in diethyl ether under ultrasonic conditions [12].
The formulation of (1) as fac-[Mn(CO)3(dpknph)Br]
was based on its elemental analysis and confirmed from
its infrared spectrum that confirmed its facial geometry
and coordination of dpknph (see Section 2).
2. Experimental
2.1. Reagents and reaction procedures
Solvents were of reagent grade and thoroughly deox-
ygenated prior to use. The compound dpknph was pre-
pared as described previously [20]. All other reagents
were obtained from commercial sources and used with-
out further purification.
2.2. Preparation of fac-[Mn(CO)3(dpknph)Br]
O-
N+
H
A mixture of Mn(CO)5Br (200 mg, 0.41 mmol),
dpknph (200 mg, 0.60 mmol) and diethyl ether
(100 mL) was allowed to stand in an ultrasonic bath
for 0.5 h. The resulting orange precipitate was filtered
off, washed with hexane, diethyl ether and dried; yield
150 mg (56%). Anal. Calc. for C20H13BrN5O5Mn: C,
44.63; H, 2.43; N, 13.00. Found: C, 44.75; H, 2.73; N,
12.88%. IR (KBr disk): m(NH) 3200, m(C„O 2027 s,
CO
N
N
N
O
Br
CO
CO
Mn
N
fac-[Mn(CO) (dpknph)Br]
3

M. Bakir et al. / Inorganica Chimica Acta 358 (2005) 1835–1840
1837
The electronic absorption spectra of fac-
[Mn(CO)3(dpknph)Br] in different solvents are shown
in Fig. 1. These spectra show sensitivity to solvents and
hint to strong solvent–complex interactions. In non-oxy-
gen containing solvents such as CH2Cl2 or CH3CN, a
highly intense absorption band appeared at 415 and
405 nm, respectively, with extinction coefficient of
32000 2000 Mꢁ1 cmꢁ1. In oxygen containing solvents,
two absorption bands appeared at 582 and 420 nm and
582 and 417 nm in DMSO and DMF, respectively. These
absorption bands are due to p ! p*(dpk) followed by
(dpk) ! (nitro) intra-ligand charge transfer transition
(ILCT), mixed with metal–ligand charge transfer transi-
tions (MLCT) due to dp(Mn) ! p*(dpk) similar to those
reported for fac-[Re(CO)3(dpknph)Cl] [20,21]. A com-
parison of the electronic absorption spectral properties
of fac-[Mn(CO)3(dpknph)Br] with those of fac-[Re-
(CO)3(dpknph)Cl] and dpknph in DMSO (see Table 1)
shows the low energy absorption band to be sensitive to
metal variations and the high energy absorption band
to be insensitive to metal variations. The blue shift
(26 nm) of the low energy absorption band of
fac-[Mn(CO)3(dpknph)Br] compared to fac-[Re-
(CO)3(dpknph)Cl] is consistent with the electron rich
character of the manganese bromide moiety compared
to rhenium chloride moiety.
centration of DMSO increases (see Fig. 2). This points
to the interconversion between the high- and low-energy
electronic states of fac-[Mn(CO)3(dpknph)Br], confirms
the high sensitivity of the electronic transitions to their
surroundings and hints to the possible use of fac-
[Mn(CO)3(dpknph)Br] as a molecular optical sensor.
In DMSO or DMF, the electronic absorption spectra
of fac-[Mn(CO)3(dpknph)Br] are concentration-depen-
dent. As the concentration of fac-[Mn(CO)3(dpknph)Br]
decreases, the ratio of the absorption of the low- to high-
energy electronic states increases and a plot of absor-
bance of the high and low energy electronic states versus
concentration is non-linear, pointing to deviation from
Beerꢀs law and consistence with solvent–complex inter-
action, hinting to the possible use of these systems
(fac-Mn(CO)3(dpknph)Br plus surrounding solvent
molecules) as optical sensors for a variety of substrates.
The electronic absorption spectra of fac-
[Mn(CO)3(dpknph)Br] in DMSO are sensitive to the
nature and concentration of NaBX4 salts, where X = F
or H (see Figs. 3 and 4). In the presence of excess
NaBF4, the low-energy absorption band at 583 nm
Table 1
The low and high energy absorption bands of dpknph and its rhenium
and manganese carbonyl compounds
In a binary DMSO/CH2Cl2 co-solvent system, the
electronic absorption spectra of fac-[Mn(CO)3-
(dpknph)Br] show that the intensity of the low-energy
electronic transition increases and the intensity of the
high energy electronic transition decreases as the con-
Compound
k1/nm (e/Mꢁ1cmꢁ1
)
k2/nm (e/Mꢁ1cmꢁ1
)
fac-[Mn(CO)3(dpknph)Br] 582(46200)
600(87000)
580(91000)
420(28400)
422(35000)
420(35000)
fac-Re(CO)3[(dpknph)Cl]
Dpknph
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0.80
At 417 nm
CH3CN
CH2Cl
0.60
DMF
DMSO
0.40
0.20
DMSO
At 583 nm
DMF
0.00
20.00
40.00
60.00
80.00
100.00
0.00
300.00
400.00
500.00
600.00
700.00
Volume % DMSO/CH2Cl2
Wavelength, nm
Fig. 2. A plot of the absorbance at 581 and 417 nm of fac-
[Mn(CO)3(dpknph)Br] vs. volume % of binary DMSO/CH2Cl2 co-
solvent.
Fig. 1. Electronic absorption spectra of fac-[Mn(CO)3(dpknph)Br]
2.000 · 10ꢁ5 M measured in different solvents.

1838
M. Bakir et al. / Inorganica Chimica Acta 358 (2005) 1835–1840
disappeared and the intensity of the high-energy absorp-
tion band at 417 nm increased. This allowed calculations
of the extinction coefficients of fac-[Mn(CO)3-
(dpknph)Br] and gave extinction coefficients of
46200 2000 and 28400 2000 mꢁ1cmꢁ1 for the low-
and high-energy electronic states, respectively. The mag-
nitude of the extinction coefficient of the high-energy
electronic state fac-[Mn(CO)3(dpknph)Br] is 0.81 that
of the high-energy electronic state of fac-[Re(-
CO)3(dpknph)Cl] (e412 = 35000 2000 mꢁ1cmꢁ1) and
the magnitude of the extinction coefficient of the low-en-
ergy electronic state of fac-[Mn(CO)3(dpknph)Br] is
ꢂ0.53 of that reported for the optical sensor fac-[Re-
(CO)3(dpknph)Cl] (e608 = 87000 2000 mꢁ1cmꢁ1). These
results show that NaBX4 salts in concentrations as low
as 1.00 · 10ꢁ5 M can be detected and determined using
fac-[Mn(CO)3(dpknph)Br].
0.60
0.40
0.20
0.00
With NaBF4
Without NaBF4
Thermo-optical
measurement
on
fac-
[Mn(CO)3(dpknph)Br] in DMSO and DMF confirmed
the reversible interconversion between the high- and
low-energy electronic states of fac-[Mn(CO)3- (dpknph)-
Br]. A plot of ln(A583/A417) versus 1/T is shown in
300.00
400.00
500.00
600.00
700.00
Wavelength, nm
Fig. 3. Electronic absorption spectra of fac-[Mn(CO)3(dpknph)Br]
2.00 · 10ꢁ5 M in DMSO in the presence and absence of NaBF4
1.00 · 10ꢁ3 M.
1
Fig. 5. Straight lines were obtained with slopes of
ꢁ1.685 · 103 and ꢁ1.453 · 103 K per decade that gave
thermodynamic parameters for the interconversion be-
tween the high and low energy electronic states of
fac-[Mn(CO)3(dpknph)Br] as shown in Table 2. The free
energy of these reactions is in the range observed for the
interconversion between high- and low-energy confor-
mations of fac-[Re(CO)3(dpknph)Cl] in non-aqueous
solvents [17]. The low values for the activation parame-
ters confirm the facile interconversion between the
high- and low-energy electronic states of fac-[Mn(CO)3-
(dpknph)Br] and point to possible use of these systems
as molecular sensors for a variety of species in proce-
dures similar to those reported for the optosensing of
fac-Re(CO)3(dpknph)Cl toward metal ions and biomol-
ecules [16,21].
0.50
1
2
0.40
0.30
0.20
0.10
0.00
8
8
7
6
5
4
3
1
For the following interconversion:
2
1
b fac-½MnðCOÞ ðdpknphÞBrꢃ ¢ a fac-½MnðCOÞ ðdpknphÞBrꢃ
ð1Þ
ð2Þ
3
3
Application of Beerꢀs Law gives:
Aa=Ab ¼ eaca=ebcb
300.00
400.00
500.00
600.00
700.00
and
Wavelength, nm
lnðAa=AbÞ ¼ lnðea=ebÞ þ ln K:
ð3Þ
Fig. 4. Electronic absorption spectra of
a mixture of fac-
[Mn(CO)3(dpknph)Br] 2.00 · 10ꢁ5 M and NaBF4 1.75 · 10ꢁ5 M in
DMSO in the presence of (1) 0.00, (2) 1.00 · 10ꢁ6, (3) 2.00 · 10ꢁ6, (4)
3.00 · 10ꢁ6, (5) 4.00 · 10ꢁ6, (6) 5.00 · 10ꢁ6, (7) 2.0 · 10ꢁ5 and (8)
5.00 · 10ꢁ5 M NaBH4.
The equilibrium constant is related to the thermodynamic parameters
as shown in Eq. (4):
ln K ¼ DSø=R ꢁ DHø=RT
ð4Þ
ð5Þ
and substitution of (4) into (3) gives:
lnðAa=AbÞ ¼ lnðea=ebÞ þ DSø=R ꢁ DHø=RT:
Optosensing measurements of group 12 metal ions
using fac-[Mn(CO)3(dpknph)Br] in DMSO in the pres-
ence and absence of NaBH4 show high sensitivity of

M. Bakir et al. / Inorganica Chimica Acta 358 (2005) 1835–1840
1839
0.70
the low and high energy electronic transitions of
fac-[Mn(CO)3(dpknph)Br] to slight variations in the
concentration of group 12 metal ions. The electronic
absorption spectra of fac-[Mn(CO)3(dpknph)Br] in
DMSO in the presence of stoichiometric amounts of
HgCl2 are shown in Fig. 6 and Fig. 7 shows the same
in the presence of NaBH4. These spectra show that
HgCl2 in concentration less than 1.00 · 10ꢁ9 M can be
detected and determined using fac-[Mn(CO)3 (dpknph)-
Br] in DMSO in the presence or absence of NaBH4. Sim-
ilar results were obtained using ZnCl2 and CdCl2. A plot
of the absorbance of fac-[Mn(CO)3(dpknph)Br] in
DMSO in the presence of NaBH4 versus concentration
of group 12 metal ions is shown in Fig. 8. These results
show that fac-[Mn(CO)3(dpknph)Br] in the presence or
absence of NaBH4 can differentiate between group 12
metal ions, and the addition of NaBH4 enhances the
optosensing behavior of fac-[Mn(CO)3(dpknph)Br].
The addition of NaBH4 to a DMSO solution of fac-
[Mn(CO)3(dpknph)Br] perturbs the equilibrium distri-
bution of the high and low energy electronic states of
fac-[Mn(CO)3(dpknph)Br] in DMSO and enhances the
absorbance of the low energy absorption band. This in-
creases the optical range for optosensing studies, en-
hances the sensitivity of the system, and allows for
lower detection limits. In previous studies on fac-[Re-
(CO)3(dpknph)Cl] towards group 12 metal ions, a detec-
tion limit of 1 · 10ꢁ5 M was reported [21].
0.60
0.50
0.40
0.30
0.20
0.10
0.00
5
1
1
2
3
4
300.00
400.00
500.00
600.00
700.00
Wavelength, nm
Fig. 6. Electronic absorption spectra of fac-[Mn(CO)3(dpknph)Br]
2.00 · 10ꢁ5 M in DMSO in the presence of (1) 0.00, (2) 1.00 · 10ꢁ9, (3)
2.50 · 10ꢁ9, (4) 5.00 · 10ꢁ9, and (5) 1.00 · 10ꢁ8 M HgCl2.
0.80
1
0.60
8
2
5
4
-0.50
3
0.40
3
DMSO
2
4
0.20
-1.50
1
5
6
7
8
0.00
300.00
400.00
500.00
600.00
700.00
DMF
-2.50
Wavelength, nm
Fig. 7. Electronic absorption spectra of a mixture of fac-[Mn(CO)3-
(dpknph)Br] 2.00 · 10ꢁ5 M and NaBH4 2.00 · 10ꢁ3 M in DMSO in
the presence of (1) 0.00, (2) 1.00 · 10ꢁ9, (3) 2.50 · 10ꢁ9, (4) 5.00 · 10ꢁ9
,
(5) 1.00 · 10ꢁ8, (6) 2.00 · 10ꢁ8, (7) 4.00 · 10ꢁ8 and (8) 8.00 · 10ꢁ8 M
HgCl2.
-3.50
2.70
2.90
3.10
3.30
3.50
Due to its convenient synthesis, coupled with its rich
physico-chemical properties and current interest in
developing molecular sensors, this system is currently
under extensive investigation.
1/T-x103, K-1
Fig. 5. A plot of ln(Aa/Ab) vs. 1/T · 103 Kꢁ1 of DMSO and DMF
solutions of fac-[Mn(CO)3(dpknph)Br] 2.00 · 10ꢁ5 M.

1840
M. Bakir et al. / Inorganica Chimica Acta 358 (2005) 1835–1840
Table 2
Thermodynamic parameters for the interconversion between the high-
and low-energy electronic states of fac-[Mn(CO)3(dpknph)Br]
reported by us for the optical sensor fac-[Re(CO)3-
(dpknph)Cl].
Solvent DHø (kJ molꢁ1
)
DSø (J molꢁ1
)
DGø (kJ molꢁ1
)
K
DMSO +14.0
DMF
+28.65
ꢁ64.30
+5.47
+7.08
+0.11
+0.06
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Fig. 8. A plot of the absorbance of fac-[Mn(CO)3(dpknph)Br]
2.00 · 10ꢁ5 M in the presence of 2.0 · 10ꢁ4 M NaBH4 vs. concentra-
tion of ZnCl2, CdCl2 and HgCl2 in DMSO.
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4. Conclusion
[22] M. Bakir, in: B. Bryskins (Ed.), Rhenium and Rhenium Alloys,
TMS Publication, 1997, p. 231.
[23] M. Bakir, Acta Cryst. C57 (2001) 1154.
A new manganese-based optical sensor of dpknph is
reported and shows higher sensitivity and a higher
detection limit towards metal ions of group 12 than that
[24] M. Bakir, Acta Cryst. C57 (2001) 1371.
[25] M. Bakir, Acta Cryst. C58 (2002) m74.