Quantum-chemical calculations, tautomeric, thermodynamic, spectroscopic and X-ray studies of 3-(4-fluorophenylhydrazone)pentane-2,4-dione

Article abstract of DOI:10.1016/j.dyepig.2009.09.003

The structural and tautomeric characteristics of 3-(4-fluorophenylhydrazone)pentane-2,4-dione were studied using IR, ¹H and ¹³C NMR spectroscopy, X-ray diffraction analysis and quantum-chemical calculations. Crystallographic data shows that the compound has a hydrazone structure that contains intramolecular H-bonds assisted by resonance, with a N-O distance of 2.5872?A?. The effective atomic charges in the tautomeric forms of the colorant (enol-azo, keto-azo and hydrazone), was calculated using an MO LCAO quantum-chemical method employing the Hu?ckel approximation; the compound was stabilized in the hydrazone form and displayed high reactivity. The thermodynamic functions of the proton dissociation constant of the colorant were determined by potentiometry; the dissociation process was unspontaneous, endothermic and entropically unfavorable. The findings reveal that the colorant has the same structure in both DMSO solution and the solid state.

Full text of DOI:10.1016/j.dyepig.2009.09.003

Dyes and Pigments 85 (2010) 1–6
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Quantum-chemical calculations, tautomeric, thermodynamic, spectroscopic
and X-ray studies of 3-(4-fluorophenylhydrazone)pentane-2,4-dione
Abel M. Maharramov, Rafiga A. Aliyeva, Ismayil A. Aliyev, Faig H. Pashaev, Arzuman G. Gasanov,
*
Saida I. Azimova, Rizvan K. Askerov, Atash V. Kurbanov, Kamran T. Mahmudov
Department of Chemistry, Baku State University, Az 1148, Baku street, Z.Khalilov 23, Azerbaijan
a r t i c l e i n f o
a b s t r a c t
Article history:
The structural and tautomeric characteristics of 3-(4-fluorophenylhydrazone)pentane-2,4-dione were
studied using IR, 1H and 13C NMR spectroscopy, X-ray diffraction analysis and quantum-chemical
calculations. Crystallographic data shows that the compound has a hydrazone structure that contains
intramolecular H-bonds assisted by resonance, with a N–O distance of 2.5872 Å. The effective atomic
charges in the tautomeric forms of the colorant (enol-azo, keto-azo and hydrazone), was calculated using
an MO LCAO quantum-chemical method employing the Hu¨ckel approximation; the compound was
stabilized in the hydrazone form and displayed high reactivity. The thermodynamic functions of the
proton dissociation constant of the colorant were determined by potentiometry; the dissociation process
was unspontaneous, endothermic and entropically unfavorable. The findings reveal that the colorant has
the same structure in both DMSO solution and the solid state.
Received 22 June 2009
Received in revised form
30 August 2009
Accepted 6 September 2009
Available online 11 September 2009
Keywords:
3-(4-Fluorophenylhydrazone)
pentane-2,4-dione
Hydrogen bonding
Hydrazone dyes
Tautomeric studies
ꢀ 2009 Elsevier Ltd. All rights reserved.
X-ray characterization
Thermodynamic parameters
Quantum-chemical calculations
1. Introduction
hydrogen bonds within compounds that contain a b-diketo-enol
fragment. The current authors [8] have reported the crystal
structures and spectroscopic data of five, ADB’s derived from
dibenzoylmethane and showed that the interplay between the
The coupling of aryldiazonium salts with
compounds results in the formation of a series of azoderivatives of
-diketones (ADB) that have been shown to exist as intra-
b-dicarbonyl
b
N–O H-bond strength and p-delocalization was a general
moleculary H-bonded arylhydrazone tautomers (Scheme 1) [1–5]:
In recent years, much attention has been devoted to structural
studies of heterodienic systems that form strong intramolecular
hydrogen bonds, N–H$$$O, which are assisted by resonance
(RAHB) and which, inter alia, may offer potential technological
applications as bistate molecular switches [6–11]. ADB’s enjoy
manifold applications, that include its use as a semiconductor
[12], an analytical reagent for spectrophotometric determination
of metal ions [13–15], high-density recordable optical storage
[16], spin-coating films [17] liquid crystals [18], self-assembled
layers [19] and organic synthesis [20]. The RAHB model [21] was
employed to interpret both the intra- and inter-molecular
phenomenon. In a furthet study using six, ADB’s derived from
benzoylacetone or acetylacetone of the nature of the intra-
molecular hydrogen bond formed by the HN–N]C–C]O moiety
in these compounds [9], the same authors showed that the
magnitude of this strong H-bond was determined by the degree
of
p-delocalization within the ketohydrazone hetero conjugated
system and was modulated by all other factors which can influ-
ence the degree of conjugation, including inductive effects and
non-bonded inter-molecular interactions.
This paper concerns the precise nature of the products formed
by this coupling reaction. F-4-C6H4NHN]C(COCH3)2 (HL) was
prepared using the method described [22] and both structural and
tautomeric studies were undertaken using IR, 1H and 13C NMR
spectroscopy, as well as thermodynamic and quantum-chemical
calculations. The crystalline and molecular structures of HL
obtained using X-ray diffraction analysis were also determined.
* Corresponding author.
E-mail address: kamran_chem@mail.ru (K.T. Mahmudov).
0143-7208/$ – see front matter ꢀ 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.09.003

2
A.M. Maharramov et al. / Dyes and Pigments 85 (2010) 1–6
. ..
CH3
CH3
O
C
H
N
F
N
F
N
F
O
C
O
C
H3C
C
H
C
N
C H
N
N
.
.
.
O
C
O
C
O
C
E-enol-azo
keto-azo
hydrazone
CH3
CH3
CH3
H
O
.
.
.
N
F
H3C
C
C
N
O
C
Z-enol-azo
CH3
Scheme 1. Possible tautomeric equilibria in HL.
2. Experimental
2.1. Materials and methods
The identification of the HL was demonstrated by element
analysis, IR and 1H and 13C NMR spectrometry.
Elemental analysis: C11H11F1N2O2 (M ¼ 222.03); C 59.38 (calc.
59.45); H 4.90 (4.99); N 12.57 (12.61) %. IR (KBr): 3436 n(NH), 1670
The synthetic work was performed in air and at room tempera-
ture. All chemicals were obtained from commercial sources and
were used as received. 1H and l3C NMR spectra were recorded on
a Bruccer 300 spectrometer using tetramethylsilane as the internal
reference. The infrared spectrum (4000–400 cmꢀ1) was recorded on
a Nicolet FT-IR Nexus spectrophotometer on KBr pellets. The acidity
of the solutions was measured using an I-130 potentiometer with an
ESL-43-07 glass electrode and an EVL-1M3.1 silver–silver chloride
electrode adjusted by standard buffer solutions. The pH-metric
titration was carried out in aqueous-ethanol with consideration of
the Bates correction [23] at different temperatures 298 ꢁ 0.5,
308 ꢁ 0.5, and 318 ꢁ 0.5 K. A constant temperature was maintained
to within 0.5 K by using an ultrathermostat (Neslab 2 RTE 220).
n
(C]O), 1626
internal TMS,
in H-bond), 7.45–7.56 (m, 2 H, Ar–H), 7.24–7.28 (m, 2 H, Ar–H),
14.56 (s, 1 H, N–H). 13C NMR in DMSO, internal TMS,
(ppm): 26.14
n
(C]O–H), 1587
n .
(C]N) cmꢀ1 1H NMR in DMSO,
d
(ppm): 2.51 (s, 3 H, free CH3CO), 2.62 (s, 3 H, CH3CO
d
(CH3), 30.05 (CH3), 111.34 (Ar–H), 113.11 (Ar–H), 115.20 (Ar–H),
117.18 (Ar–H), 133.44 (C]N), 144.22 (Ar–NH–N), 157.23 (Ar–F),
195.45 (C]O), 196.12 (C]O).
2.3. Data collection
Highly redundant single crystal X-ray diffraction data sets were
collected at 150 K up to a max 2
SMART APEX CCD diffractometer using monochromatic MoK
radiation,
0.71073 Å, and a 0.5ꢂ separation between frames. Data
q
of ca. 58.84ꢂ on a Bruccer AXS
a
l
2.2. Synthesis of the 3-(4-fluorophenylhydrazone)
pentane-2,4-dione
integration was performed using SAINT program in the diffrac-
tometer package [24]. The structures were solved by direct
methods and Fourier’s difference, and refined by least squares on F2
with anisotropic displacement parameters for non-H atoms. All
hydrogen atoms were located from difference Fourier maps and
refined isotropically. All calculations to solve the structures, to
refine the model proposed and to obtain results were carried out
with the computer programs SHELXS-97 and SHELXL-97 and
SHELXTL/PC [24–27]. Crystallographic data (excluding structure
factors) for the structure reported in this paper have been depos-
ited with the Cambridge Crystallographic Data Centre as supple-
mentary publication, CCDC 716531 Registered in England No.
2155347, Registered Charity No. 800579 for compound HL. Copies
of this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK. Fax: þ44
1223 336 033. E-mail: data_request@ccdc.cam.ac.uk. Web page:
http://www.ccdc.cam.ac.uk.
The free arylhydrazone ligand of HL was synthesized via the
Japp–Klingemann reaction [22] of the aromatic diazonium salt of 4-
fluoroaniline and pentane-2,4-dione, in an ethanolic solution
containing sodium acetate.
2.2.1. Diazotization
A 2.40 mL (0.025 mol) portion of 4-fluoroaniline (caution:
highly toxic; combustible liquid and vapour; incompatible with
acids, acid chlorides, strong oxidizing agents, acid anhydrides,
chloroformates) was dissolved in 50 mL of water and 1 g of crys-
talline KOH was added. The ensuing solution was cooled in an ice
bath to 273 K and 1.725 g (0.025 mol) of NaNO2 added; 5 mL HCl
was then added in portions over 40 min. The temperature of the
mixture should not exceed 278 K.
2.2.2. Azocoupling
8 g CH3COONa were added to a mixture of 2.43 mL (0.025 mol)
pentane-2,4-dione and 50 mL of ethanol. The resulting solution was
cooled in an ice bath and a suspension of 4-fluoroaniline diazonium
was added in three portions. In the diazocoupling, the pH should be
maintained in the range of 8–10; crystalline CH3COONa may be
added if needed.
2.4. Potentiometric measurements
The following mixtures, (i)–(ii), were prepared and titrated
potentiometrically against standard 0.005 M KOH in 40/60% (v/v)
water-ethanol mixture at 298 K.
Yield 81% (based on pentane-2,4-dione), yellow powder is
soluble in DMSO, methanol, ethanol and acetone but insoluble in
water.
(i) 5 mL 0.001 M HCl þ 5 mL 1 M KCl þ 30 mL ethanol;
(ii) 5 mL 0.001 M HCl þ 5 mL 1 M KCl þ 25 mL ethanol þ 5 mL
0.00l M ligand;

A.M. Maharramov et al. / Dyes and Pigments 85 (2010) 1–6
3
Table 1
For each mixture, the volume was made up to 50 mL with
bidistilled water before the titration process. These titrations were
also repeated at temperatures of 308 and 318 K.
Crystal data, experimental parameters and selected details of the refinement
calculations of compounds HL.
Empirical formula
Formula weight
Crystal system
Space group
a, Å
C11H11F1N2O2
222.03
Monoclinic
C2/c
18.827(3)
12.839(2)
3. Results and discussion
3.1. Synthesis of HL and spectroscopic study
b, Å
c, Å
26.425(5)
90
104.834(2)
90
HL was synthesized via the Japp–Klingemann reaction [22]
between 4-fluoroaniline and acetylacetone in an ethanolic solution
containing sodium acetate. The 1H NMR spectrum of HL in dime-
thylsulfoxide-d6 solution at room temperature shows a signal at
a
, deg
, deg
b
g
, deg
Z
16
Volume, Å3
F(000)
6186.1(18)
2808
1.438
0.112
d
14.56 which is assigned to the proton of the protonated nitrogen
Dc, g cmꢀ3
atom adjacent to the aryl unit (]N–NH– hydrazone form). The two
methyl groups of the pentane-2,4-dione moiety yield separate
singlets in the proton spectrum. These data support the predomi-
nance of the hydrazone form (Scheme 1) with a six-membered
H-bonded ring involving one of the carbonyl groups and the
protonated nitrogen moiety of the hydrazone structure. The IR
m
, mmꢀ1
Index ranges
Theta range for data collection
Reflections collected
Independent reflections
Completeness to theta ¼ 29.42ꢂ
Absorption correction
Max. and min. transmission
Refinement method
ꢀ24 ꢃ h ꢃ 25, ꢀ17 ꢃ k ꢃ 17, ꢀ34 ꢃ l ꢃ 27
1.99–29.42ꢂ
19 416
7748 [R(int) ¼ 0.0253]
90.6%
Semi-empirical from equivalents
0.9779 and 0.9671
Full-matrix least-squares on F2
7748/0/433
spectrum of the isolated compound shows
n
(NH) vibration at
3436 cmꢀ1, while
n(C]O), n(C]O–H) and n(C]N) are observed at
1670, 1626 and 1587 cmꢀ1, correspondingly, also supporting the
existence of the H-bonded hydrazone structure in the solid state.
Data/restraints/parameters
Goodness-of-fit on F2
0.931
Final R indices [I > 2
R indices (all data)
Largest diff. peak and hole
s
(I)]
R1 ¼ 0.0459, wR2 ¼ 0.1435
R1 ¼ 0.0559, wR2 ¼ 0.1548
0.375 and ꢀ0.833 e.Åꢀ3
3.2. X-Ray study
Fig. 1 presents the molecular diagram of HL, while Table 1
provides a survey of crystallographic and refinement data; Table 2
shows bond distances and Table 3 the intra and inter-molecular
H-bonding interactions stabilizing the structure (hydrazone form).
center, may be causing an efficient shortening of the N–H
distance. The two remaining inter-molecular H-contacts, Table 3,
is of C–H/O type. The one involving H(3) defines chains parallel
to the b-axis, while the other involving H(2), links chains together
into a weakly connected 3D network. As it can be expected, the
lengths of free C(8)–O(1) 1.2245(15) Å and H-bonded C(10)–O(2)
1.2375(15) Å carbonyl groups are not equal. The six-membered
cycle H(2N)–N(2)–N(1)–C(9)–C(10)–O(2) is hexahedra with
mutual angles N(2)–N(1)–C(9) and C(9)–C(10)–O(2) equal to
122.01(11)ꢂ and 119.87(11)ꢂ respectively, but the angles O(2)–
H(2N)–N(2) 129.16(12)ꢂ and N(1)–C(9)–C(10) 123.50(11)ꢂ are not
equal with connected H-bond.
The structure has been well refined with final indices, [I > 2
of R1 ¼ 0.0459 and wR2 ¼ 0.1435, Table 1. The relevant charac-
teristics, Fig. 1 are (i) the presence of the -diketohydrazone core,
s(I)],
b
confirming the route followed by the coupling reaction and the
tautomerization process [1–5]; (ii) the presence of one HN–N]C–
C]O heterodienic system with the ideal geometry to form the
heteronuclear N(2)–H(2N)/O(2) RAHB, Fig.
1 that may be
considered fairly weak, Table 3 (vide infra); and (iii) the molecule
is basically planar, (Table 2), the main deviations being due to
slight rotations around the C(4)–F(1), C(9)–C(10) and C(8)–C(9)
bonds (Table 2).
Here, it is possible to see that N–H/O, H-bond found in HL,
with N/O distance, 2.5872(12) Å, falls in the middle of the N/O
distances range, 2.538–2.597 Å, as observed in previous studies
3.3. Quantum-chemical calculations of the tautomeric forms of HL
It is known that the development of procedures for direct
analysis depends on the sensitivity of the method, which is
determined by the sensitivity of both the selected procedure and
the organic reagent to the analyte. The synthesis of these reagents
and the revelation of correlations between their structure, selec-
tivity, and other properties are important problems in using of
organic reagents. The selectivity of organic reagents is improved
by doubling the number of functional analytical groups, intro-
ducing a substituent into the reagent molecule, and modifying
with surface-active substances, nonaqueous, aqueous-organic, and
organized media [29–32]. We modified organic reagents (using
the example of ADB) based on the theory of shifting the tauto-
meric equilibrium, to improve the sensitivity and selectivity of the
reagents. The study of the effect of the structure of the reagents
on their analytical characteristics and the properties of the
complexes and the use of the effect of the functional groups for
developing direct photometric procedures without element pre-
separation are important analytical problems [5,15]. To determine
the reactivity of tautomers of HL and the specific character of
deprotonation of their functional groups, we performed quantum-
chemical calculations using the Hu¨ckel method (MOLCAO)
on
b-diketo-arylhydrazones [28]. Comparatively, this suggests
that the 4-F group, sp ¼ 0.06, located far from the N–H/O
Fig. 1. Molecular structure of HL.

4
A.M. Maharramov et al. / Dyes and Pigments 85 (2010) 1–6
Table 2
Structural parameters (distances Å, anglesꢂ, torsion anglesꢂ) of compound HL.
Bond
Length (Å)
Torsion angle
Length (ꢂ)
F(1)–C(4)
O(1)–C(8)
O(2)–C(10)
N(1)–N(2)
N(1)–C(9)
N(2)–C(1)
C(1)–C(6)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
Angle
N(2)–N(1)–C(9)
N(1)–N(2)–C(1)
C(6)–C(1)–C(2)
C(6)–C(1)–N(2)
C(2)–C(1)–N(2)
C(1)–C(2)–C(3)
C(4)–C(3)–C(2)
F(1)–C(4)–C(3)
F(1)–C(4)–C(5)
O(1)–C(8)–C(9)
O(1)–C(8)–C(7)
N(1)–C(9)–C(10)
N(1)–C(9)–C(8)
O(2)–C(10)–C(9)
O(2)–C(10)–C(11)
1.3606(14)
1.2245(15)
1.2375(15)
1.3040(14)
1.3207(15)
1.4130(16)
1.3878(18)
1.3913(17)
1.3930(17)
1.3756(19)
1.3798(19)
1.3891(18)
1.5020(18)
1.4930(16)
1.4709(18)
1.5001(17)
Length (ꢂ)
122.01(11)
118.95(10)
120.93(12)
121.18(11)
117.89(11)
119.74(12)
118.18(12)
118.72(12)
118.24(12)
121.14(12)
120.39(11)
123.50(11)
112.65(11)
119.87(11)
119.75(12)
C(9)–N(1)–N(2)–C(1)
N(1)–N(2)–C(1)–C(6)
N(1)–N(2)–C(1)–C(2)
C(6)–C(1)–C(2)–C(3)
N(2)–C(1)–C(2)–C(3)
C(1)–C(2)–C(3)–C(4)
C(2)–C(3)–C(4)–F(1)
C(2)–C(3)–C(4)–C(5)
F(1)–C(4)–C(5)–C(6)
C(3)–C(4)–C(5)–C(6)
C(2)–C(1)–C(6)–C(5)
N(2)–C(1)–C(6)–C(5)
C(4)–C(5)–C(6)–C(1)
N(2)–N(1)–C(9)–C(10)
N(2)–N(1)–C(9)–C(8)
O(1)–C(8)–C(9)–N(1)
C(7)–C(8)–C(9)–N(1)
O(1)–C(8)–C(9)–C(10)
C(7)–C(8)–C(9)–C(10)
N(1)–C(9)–C(10)–O(2)
C(8)–C(9)–C(10)–O(2)
N(1)–C(9)–C(10)–C(11)
C(8)–C(9)–C(10)–C(11)
179.24(11)
8.36(18)
ꢀ172.24(11)
ꢀ0.52(19)
ꢀ179.93(11)
ꢀ0.31(18)
ꢀ178.14(11)
0.9(2)
178.42(11)
ꢀ0.6(2)
0.80(19)
ꢀ179.81(11)
ꢀ0.3(2)
ꢀ1.59(18)
ꢀ179.29(10)
ꢀ171.21(11)
8.75(16)
11.10(18)
ꢀ168.95(11)
3.46(19)
ꢀ179.09(11)
ꢀ175.48(11)
1.97(18)
[33–37]. The Hu¨ckel method involves a
the molecular orbitals are written as a linear combination of the
p
-electron approximation:
orbitals cp and cq. The system of equations (2) has nontrivial
solutions if the determinant of the coefficients Cqi is zero:
atomic orbitals of
atoms, etc.):
p
-electrons (2pzorbitals of the C, O, and N
H11 ꢀ ES11 H12 ꢀ ES12 ,,, H1m ꢀ ES1m
H21 ꢀ ES21 H22 ꢀ ES22,,,H2m ꢀ ES2m
j
j
¼ 0
(5)
m
X
ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ
4i
¼
C
q cqð2pzÞ
(1)
i
Hm1 ꢀ ESm1 Hm2 ꢀ ESm2,,,Hmm ꢀ ESmm
Opening of this determinant leads to an m-order equation with
respect to E. Solution of this equation gives m real roots E1, E2, .. Em
called the orbital energies of the molecule in the
q ¼ 1
where Cqi are unknown coefficients determined by solving a system
of equations in the simple version of MO LCAO:
p-electron
X
ꢀ
ꢁ
approximation. Each of these roots Ei is substituted into Eq. (2) to
determine the ratios of the coefficients Cqi and the numerical values
of these coefficients are found from the normalization condition for
Hpq ꢀ ESpq Cq ¼ 0; p ¼ 1; m
(2)
i
q
the molecular orbitals 4i
:
where the following definitions are introduced:
Z
Z
Z
b
X
2
*
Ui*UidV ¼
jUij dV ¼
C C Sqq ¼ 1
(6)
cp*
H
cqdV;
(3)
(4)
i
i
qi
qi
Hpq
¼
q;qi
Z
Thus, for solution of the system of equations (2) (i.e., for deter-
Spq
¼
c*pcqdV;
mination of the orbital energies Ei and the corresponding sets of
coefficients Cqi), one must know numerical Hpq and Spq values.
However, Hpq values cannot be calculated exactly because the explicit
The Hpq values are the matrix elements of the effective Hamil-
tonian for a -electron moving in an effective field with no regard
-electrons; Spq are the overlap integrals for the atomic
b
¨ckel method, H
p
expression for the operator H is unknown. In the Hu
pq
and Spq are estimated from the Hu¨ckel approximations [35].
to other
p
Table 3
Distances/Å and angles/ꢂ of hydrogen bond interactions.
D–H/A
Symmetry
Distances
D–H
Angles
D–H/A
D/A
H/A
N(2)–H(N2)/O(2)
C(2)–H(2)/O(2)
C(3)–H(3)/O(1)
x, y, z
0.9070(13)
0.9492(14)
0.9510(13)
2.5872(12)
3.4474(17)
3.3632(15)
1.9160(13)
2.5380(14)
2.4464(13)
129.16(12)
160.10(12)
162.05(11)
ꢀx, 1ꢀy, ꢀz
x þ 0.5,ꢀy þ 1.5, z ꢀ 0.5

A.M. Maharramov et al. / Dyes and Pigments 85 (2010) 1–6
5
0.403
C
0.733
0.447
C
C
0.915
0.749
-0.350
O
0.091
C
0.005
0.129 C
O
0.201 C
O
0.218
C
C
C
C
C
0.270
0.202
-0.960
C
C
-0.354
N
C
C
-0.433
0.145
0.242
0.307
C
F
N
C
0.248
0.201
O
O
0.198
0.749
0.687
O
C
C
C
C
-0.643
0.091
0.005
0.513
0.447
(enol-azo)
enol
ketone
0.704
0.766
0.764
C
C
C
C
-0.624
0.095
0.005
-0.604
O
0.086
C
0.008
C
C
0.328
C
C
O
0.344
0.244
-0.421
N
-0.338
-0.958
F
C
0.14C8
-0.415
N
-0.430 0.160
-0.958
0.227 C
0.328C
C
N
C
F
N
C
0.204
0.202
O
C
C
0.344 C
O
C
C
-0.624
0.005
-0.604
0.095
0.086
0.008
C
(keto-azo)
(hydrazone)
0.766
0.764
Scheme 2. Effective
p-electron charges in the tautomeric forms of pentane-2,4-dione and HL.
The numerical values of coefficients Cqi allow one to determine
the effective charge qA (au) of an atom A in the molecule according
to the MO method by the formula [37]:
of KCl. The dissociation constants of HL at different temperatures
were calculated by the equation [30]:
ꢀlogKdis ¼ pH þ log½HLꢄ ꢀ log½Lꢀꢄ; ꢀ logKdis ¼ pK:
X
X
2
qA ¼ n0A ꢀ
ni
jcq j
(7)
i
The dissociation constants of the reagent was pK ¼ 8.12 ꢁ 0.01.
As follows from the molecular diagrams of the reagent tautomeric
forms, upon potentiometric titration in groups, where a proton is
detached (from ꢀOH (enol-azo) and from ]N–NH (hydrazone), the
i
q˛A
where n0A is the positive charge of the nuclear core of the atom A (in
the Hu¨ckel method, n0A ¼ 1 for all atoms), ni is the number of
electrons in the ith molecular orbital; summation for i is performed
over the occupied molecular orbitals. We designed a program for
Hu¨ckel computations and determined the numerical values of
coefficients Cqi in Eq. (1). Using formula (7), we calculated the
effective atomic charges for molecule HL under study and con-
structed its molecular diagrams (Scheme 2).
The molecular diagrams show that the introduction of func-
tional groups (]N–NH–Ar) into a molecule of pentane-2,4-dione
changes the reaction centers. Because absolute values of the atoms
ꢀ0N:430 and ꢀ0O:604 are greater (hydrazone) than ꢀ0O:350 and ꢀ0O:643
absolute effective charges at the atoms are greater
N
ꢀ0:430 than at the
atoms of ꢀ0O:350. Therefore, we believe that the proton is detached
from a hydrazone form.
The dissociation constant has been evaluated at 298, 308 and
318 K and it is given in Table 4. The slope of the plot (pK versus 1/T)
was utilized to evaluate the enthalpy change ð
D
Hꢂ Þ for the disso-
ciation process. From the Gibbs energy change ð
D
Gꢂ Þ and ð
D
Hꢂ Þ
values one can deduce the entropy change ð
D
Sꢂ Þ using the well
known relationships [33]:
(enol-azo). Also we can report that hydrogen migrated from enol-
D
Gꢂ ¼ 2:303RTpK;
D
Sꢂ ¼ ð
D
Hꢂ ꢀ
D
Gꢂ Þ=T
azo ðꢀ0:350
O
Þ to hydrazone ðꢀ0:430
Þ.
N
All thermodynamic parameters of the dissociation process of HL
are recorded in Table 4.
Inspection of these values reveals that [38–42]: i The pL values
decrease with increasing temperature revealing that its acidity
3.4. Determination of thermodynamic functions of the dissociation
processes of reagent
increases with increasing temperature; ii A positive value of
indicates that its dissociation is accompanied by adsorption of heat
and the process is endothermic; iii A large positive value of
Go
indicates that the dissociation process is not spontaneous; iv A
negative value of
So is obtained due to increased order as a result
D
Ho
To determine the dissociation constants of the reagents, we used
pH-metric titration in aqueous-ethanol media. The ionic strength
was maintained constant (I ¼ 0.1 M) by adding a calculated amount
D
D
of solvation processes.
Table 4
Thermodynamic characteristics process dissociation HL in aqueous-ethanol
solution.
4. Conclusions
T, K
pK
D
Gꢂ , kJ molꢀ1
D
Hꢂ , kJ molꢀ1
D
Sꢂ , J molꢀ1 Kꢀ1
ꢀ48.72 ꢁ 1.76
298 ꢁ 0.5 8.12 ꢁ 0.01 46.33 ꢁ 0.09
308 ꢁ 0.5 7.95 ꢁ 0.03
The novel compound, 3-(4-fluorophenylhydrazone)pentane-
2,4-dione (HL) dye was synthesized via the Japp–Klingemann
reaction between the aromatic diazonium salt 4-fluoroaniline and
31.81 ꢁ 1.67
318 ꢁ 0.5 7.77 ꢁ 0.05

6
A.M. Maharramov et al. / Dyes and Pigments 85 (2010) 1–6
[13] Aliyeva RA, Chyragov FM, Mahmudov KT. Journal of Analytical Chemistry
2005;50:137–40.
[14] Gadjieva SR, Mursalov TM, Mahmudov KT, Pashaev FH, Chyragov FM. Journal
of Analytical Chemistry 2006;61:550–5.
[15] Mahmudov KT, Aliyeva RA, Gadjieva SR, Chyragov FM. Journal of Analytical
Chemistry 2008;63:435–8.
[16] Chen ZM, Huang FX, Wu YQ, Gu DH, Gan FX. Inorganic Chemistry Commu-
nications 2006;9:21–4.
pentane-2,4-dione in an ethanolic solution containing sodium
acetate. The results of MO LCAO quantum-chemical calculations
was showed that HL stabilized in hydrazone form (hydrogen
migrated from enol-azo to hydrazone) and this form has high
reactivity. In addition, the proton is detached from a hydrazone
form (dissociation process). The dissociation process is unsponta-
neous, endothermic and entropically unfavorable, which showed
by potentiometric titration. The X-ray diffraction, IR and NMR show
that the studied compound presents in the same hydrazone
structure in solid phases and in DMSO solution. The presence of one
heterodienic system, HN–N]C–C]O, forming a fairly weak het-
eronuclear RAHB, N–H/O, has been supported by crystallographic
data, and length of this distance N/O 2.5872(12) Å falls in the
middle of the N/O distances range, 2.538–2.597 Å, as observed in
[17] Chen ZM, Wu YQ, Gu DH, Gan FX. Spectrochimica Acta Part
68:918–26.
A 2007;
[18] Jeong MJ, Park JH, Lee C, Chang JY. Organic Letters 2006;8:2221–4.
[19] Marten J, Erbe A, Critchley K, Bramble JP, Weber E, Evans SD. Langmuir
2008;24:2479–86.
[20] Shchegolkov EV, Burgart YaV, Khudina OG, Saloutin VI, Chupakhin ON. Russian
Chemical Bulletin, International Edition 2004;53:2584–90.
[21] Bertolassi V, Gilli P, Ferretti V, Gilli G. Journal of the American Chemical Society
1991;113:4917–25.
[22] Japp FR, Klingemann F. Liebigs Annalen der Chemie 1888;247:190–225.
[23] Bates RG. Determination of pH: theory and practice. New York: Wiley; 1973.
[24] Brucer. APEX2 & SAINT. Madison, Wisconsin, USA: Brucer, AXS Inc.; 2004.
[25] Sheldrick GM. Acta Crystallographica Section A 1990;46:467–73.
[26] Sheldrick GM. Acta Crystallographica Section A 2008;64:112–22.
[27] Farrugia LJ. Journal of Applied Crystallography 1999;32:837–8.
[28] Marten J, Seichter W, Weber E, Bohme U. Journal of Physical Organic Chem-
istry 2007;20:716–31.
previous studies on b-diketo-arylhydrazones [28]. This might be
useful in the design of functional materials attributed to smart
hydrogen bonding [6–11], photo-triggered structural switching
[43], and targeted metal ion complexes [1–5,13–15].
[29] Christian GD. Analytical chemistry. New York: Phoenix Color Corp; 1994.
[30] Harvey D. Modern analytical chemistry. New York: Wiley; 2000.
[31] Vogel AI. Textbook of macro and semimicro qualitative inorganic analysis.
New York: Bungay; 1979.
References
[32] Chow Chan Chung, editor. Analytical method validation and instrument
performance verification. New York: Wiley; 2004.
[1] Gadjieva SR, Mahmudov KT. Russian Journal of Inorganic Chemistry
2004;49:1291–4.
[33] Atkins P, Paula De J. Physical chemistry, Oxford: Oxford Univ., p. 1150.
[34] Levin Ira N. Physical chemistry. New Delhi: Pashupati Printers Pvt. Ltd.; 2002.
[35] Streitwieser A. Molecular orbital theory for organic chemists. New York:
Wiley; 1961.
[2] Aliyeva RA, Chyragov FM, Mahmudov KT. Russian Journal of Inorganic
Chemistry 2004;49:1458–60.
[3] Aliyeva RA, Chyragov FM, Babanly IM, Mahmudov KT, Babanly MB. Russian
Journal of Inorganic Chemistry 2004;49:1461–4.
[36] Khigasi K, Baba H, Rembaum A. Quantum organic chemistry. New York: Wiley;
1965.
[4] Aliyeva RA, Chyragov FM, Mahmudov KT, Babanly MB. Russian Journal of
Inorganic Chemistry 2005;50:131–4.
[37] Dmitriev IS. Elektron glazami khimika (electron as chemists see it). Leningrad:
Khimiya; 1986.
[38] Gadjieva SR, Mursalov TM, Mahmudov KT, Chyragov FM. Russian Journal of
Coordination Chemistry 2006;32:304–8.
[39] Gadjieva SR, Pashaev FH, Chyragov FM, Gasanov AG, Mahmudov KT. Russian
Journal of Inorganic Chemistry 2007;52:640–4.
[5] K.T. Mahmudov. Cand. Sci. (Chem.) Dissertation, Baku, 2006.
[6] Olivieri AC, Wilson RB, Paul IC, Curtin DY. Journal of the American Chemical
Society 1989;111:5525–32.
[7] Inabe T. New Journal of Chemistry 1991;15:129–36.
[8] Bertolasi V, Ferretti V, Gilli P, Gilli G, Issa YM, Sherif OE. Journal of the Chemical
Society, Perkin Transactions 2 1993;11:2223–8.
[40] Gadjieva SR, Mahmudov KT, Pashaev FH, Gasanov AG, Chyragov FM. Russian
Journal of Coordination Chemistry 2008;34:534–8.
[9] Bertolasi V, Nanni L, Gilli G, Ferretti V, Gilli P, Issa YM, et al. New Journal of
Chemistry 1994;18:251–61.
[41] Aliyeva RA, Pashaev FH, Gasanov AG, Mahmudov KT. Russian Journal of
Coordination Chemistry 2009;35:241–6.
[10] Bertolasi V, Gilli P, Ferretti V, Gilli G. Acta Crystallographica Section
1994;50:617–25.
B
[42] Aliyeva RA, Pashaev FH, Gasanov AG, Mahmudov KT. Russian Journal of
Inorganic Chemistry 2009;54:1407–11.
[43] McVie J, Alastair D, Sinclair RS, Truscott RG. Journal of the Chemical Society,
Perkin Transactions 2 1980;2:286–90.
[11] Krygowski TM, Wozniak K, Anulewics R, Pawlak D, Kolodziejski W, Grech E,
et al. Journal of Physical Chemistry A 1997;101:9399–404.
[12] Hassib HB, Issa YM, Mohamed WS. Journal of Thermal Analysis and Calo-
rimetry 2008;92:775–82.