Theoretical (in B3LYP/6-3111++G** level), spectroscopic (FT-IR, FT-Raman) and thermogravimetric studies of gentisic acid and sodium, copper(II) and cadmium(II) gentisates

Article abstract of DOI:10.1016/j.saa.2014.04.191

The DFT calculations (B3LYP method with 6-311++G(d,p) mixed with LanL2DZ for transition metals basis sets) for different conformers of 2,5-dihydroxybenzoic acid (gentisic acid), sodium 2,5-dihydroxybenzoate (gentisate) and copper(II) and cadmium(II) genti

Full text of DOI:10.1016/j.saa.2014.04.191

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
ÃÃ
Theoretical (in B3LYP/6-3111++G level), spectroscopic (FT-IR,
FT-Raman) and thermogravimetric studies of gentisic acid and sodium,
copper(II) and cadmium(II) gentisates
a,
⇑
a
b
c
d
d
E. Regulska , M. Kalinowska , S. Wojtulewski , A. Korczak , J. Sienkiewicz-Gromiuk , Z. Rz a˛ czy n´ ska ,
a
a
´
R. Swisłocka , W. Lewandowski
a
Division of Chemistry, Bialystok University of Technology, Zamenhofa 29, 15-435 Bialystok, Poland
Institute of Chemistry, University of Bialystok, Hurtowa 1, 15-399 Bialystok, Poland
Institut des Sciences et Techniques, Université de Valenciennes et du Hainaut-Cambrésis, France
Department of General and Coordination Chemistry, Faculty of Chemistry UMCS, Sq. Maria Curie-Skłodowska 2, Lublin, Poland
b
c
d
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
The formulas of synthesized
complexes were determined.
The monodentate type of
coordination in Cu/Cd gentisates was
established.
ꢀ
ꢀ
The molecular structures were
discussed.
FT-IR and Raman spectra were
studied.
a r t i c l e i n f o
a b s t r a c t
Article history:
The DFT calculations (B3LYP method with 6-311++G(d,p) mixed with LanL2DZ for transition metals basis
sets) for different conformers of 2,5-dihydroxybenzoic acid (gentisic acid), sodium 2,5-dihydroxybenzo-
ate (gentisate) and copper(II) and cadmium(II) gentisates were done. The proposed hydrated structures of
transition metal complexes were based on the results of experimental findings. The theoretical
geometrical parameters and atomic charge distribution were discussed. Moreover Na, Cu(II) and Cd(II)
gentisates were synthesized and the composition of obtained compounds was revealed by means of
elemental and thermogravimetric analyses. The FT-IR and FT-Raman spectra of gentisic acid and
gentisates were registered and the effect of metals on the electronic charge distribution of ligand was
discussed.
Received 24 January 2014
Received in revised form 23 April 2014
Accepted 30 April 2014
Available online 16 May 2014
Keywords:
2
,5-Dihydroxybenzoic acid
Gentisic acid
Metal 2,5-dihydroxybenzoate
DFT calculations
FT-IR
Ó 2014 Elsevier B.V. All rights reserved.
FT-Raman
Introduction
Gentisic acid (2,5-dihydroxybenzoic acid = 2,5-DHBA) belongs
to the group of phenolic acids, substances that naturally occur in
fruit, vegetables, nuts, seeds, flowers and some herb beverages. It
⇑
Corresponding author. Tel.: +48 797 995 975.
E-mail address: e.regulska@pb.edu.pl (E. Regulska).
http://dx.doi.org/10.1016/j.saa.2014.04.191
386-1425/Ó 2014 Elsevier B.V. All rights reserved.
1

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E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
was found in citrus fruits (Citrus spp.), grapes (Vitis vinifera), Jeru-
salem artichoke (Helianthus tuberosus), sesame (Sesamum indicum),
gentians (Gentiana spp.), red sandalwood (Pterocarpus santalinus),
rose gum (Eucalyptus grandis), saxifrage (Saxifraga spp.) and olive
copper, which was described as [Cu(2,5-DHB)
Although Sokolik et al. [11] defined copper gentisate as [Cu(2,5-
DHB) (H O) ] complex. They described the syntheses of copper(II)
2
(H
2
O)
2
]Á2H
2
O.
2
2
4
2,4-, 2,5- and 2,6-dihydroxybenzoates. Presented analytical data of
thermogravimetric analyses, magnetic moments as well as the
electronic and EPR spectra showed that 2,4- and 2,6-dihydroxy-
benzoic acids formed octahydrated complexes with copper(II)
unlike gentisic acid. Furthermore all compounds exhibited higher
anti-inflammatory activities on dextran edema than free carboxylic
acids. Ashidate et al. [6] basing on UV spectra mentioned without
publishing any data that gentisic acid had only minimal copper
chelating activity. According to Micera et al. [12] copper(II) always
displays a different coordination behavior in comparison with Mn,
Co, Ni and Zn divalent ions, which all exhibit very similar coordina-
tion geometries. The authors studied interaction of metal ions with
2,4-, 2,5- and 2,6-dihydoxybenzoic acids and concluded that phe-
nolic groups show a tendency to be involved in hydrogen-bonding
rather than in metal coordination. On the other hand the ligands
have different tendencies when they taking part in the inner
coordination sphere of metal ions. Metal–ligand interactions of
outer-sphere nature are allowed with 2,6-DHBA, whereas for 2,4-
and 2,5-DHBs coordinative properties are more typical for carbox-
ylate ligands. Synthesis and characterization of Mo(VI) complexes
(Olea europaea) [1]. 2,5-DHBA is an active metabolite of salicylic
acid degradation. It shows a broad spectrum of biological activity
such as anti-inflammatory, anti-rheumatic, antioxidant and
antibacterial properties [2,3]. Cunha et al. [4] examined pharmaco-
logical mechanism of relaxation caused by gentisic acid in the
guinea pig trachea. It is believed that gentisic acid has an effective
role in the anticarcinogenetic activity of China-rose hibiscus
(Hibiscus rosa-sinensis) extract [5]. Ashidate et al. [6] report that
gentisic acid inhibits low-density lipoprotein oxidation and the
formation of cholesterol ester hydroperoxides in human plasma.
They also suggest that its antioxidant properties are mainly due
to its radical scavenging activity. A recent study has shown that
gentisic acid is a Fibroblast Growth Factor (FGF) inhibitor [7]. Dihy-
droxybenzoic acids are plant secondary metabolites naturally pres-
ent in almost all plant materials, including food products of plant
origin and other substances such as propolis [8]. In industrial field
they are used as intermediates for production of pharmaceuticals
and other organic chemicals: resins, polyesters, plasticizers, dye-
stuffs, preservatives and rubber chemicals. According to Vraslovic´
et al. [2] gentisic acid acts as a cathodic inhibitor of the Al-2,5Mg
alloy. The inhibitory action of gentisic acid was explained by the
formation of complex molecules with aluminum ions and then pre-
cipitation of these complexes on alloy surface in places where
oxide film was destroyed. Sodium gentisate (Na 2,5-DHB) is known
for its pharmacological properties like anti-inflammatory, analge-
sic and antipyretic drugs [9]. Gentisic acid forms also complexes
with transition metals. Interaction of such metal ions as Mn(II),
Co(II), Ni(II), Cu(II) and Cd(II) with 2,5dihydroxybenzoic acid was
presented by Micera et al. [10]. Crystals suitable for X-ray analysis
they obtained only in the case of Zn complex. It’s crystalline struc-
of 2,3- and 2,5-DHBA as polyoxometallate species having Mo
2 5
O /
MoO core were described by Karaliota et al. [13]. According to
2
Litos et al. [14] gentisic acid acts as tridentate ligand using both
carboxyl oxygen atoms, giving trinuclear oxomolybdenum com-
plex. Each ligand coordinates with three molybdenum atoms. The
hydroxyl-oxygen of the carboxylate group acts as a bridge between
two molybdenum atoms, while the third molybdenum atom coor-
dinates with the carbonyl-oxygen. The two hydroxyl non-bonded
groups of the ligands participate in hydrogen bonding interactions.
This structure was characterized as unusual in contrast to
salicylate (bidentate) coordination type.
ture (Fig. 1) was presented as [Zn(2,5-DHB)
2
(H
2
O)
4
] compound
In the present study the synthesis of sodium, copper(II) and
cadmium(II) gentisates, the evaluation of the their composition
[
10]. Other metals formed similar complexes with exception of
Fig. 1. Crystalline structure of zinc gentisate (the hydrogen bonds are highlighted the dotted lines) [10].

E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
715
and the investigation using vibrational spectroscopy, as well as
quantum-chemical calculations are described.
calculated from the metal oxide residues were also found to be
in good agreement with the results of elemental analysis (Table 1).
The [Cu(C
of 30–150 °C dehydrates and forms an anhydrous complex
Fig. 2a). The relative mass loss calculated from TG curve being
equal to 16.22% corresponds to the loss of four molecules of water
calculated value is 16.31%). In the temperature range of 150–
10 °C the anhydrous gentisate of Cu(II) is finally decomposed to
CuO. Literature data [11] confirmed the one-step dehydration of
four hydrated copper gentisate complex. The tetrahydrate of
gentisate of Cd(II) heated in air is stable up to 30 °C. Above this
temperature, cadmium compound is dehydrated in two steps
losing 2.5 and 1.5 water molecules, respectively (Fig. 2b). The
observed mass loss for total dehydration process is equal 14.48%
7
H
5
O
4
)
2
]Á4H
2
O complex heated in the temperature range
Experimental
(
Sodium 2,5-dihydroxybenzoate was prepared by dissolving the
powder of gentisic acid in the water solution of sodium hydroxide
in a stoichiometric ratio (1:1). Water solution of copper or
cadmium chlorides was added to aqueous solution of sodium gen-
tisate in a stoichiometric ratio (1:2). The obtained precipitates
were filtered off and washed with distilled water and then dried
several hours at about 65 °C. The precipitate of cadmium gentisate
was water-soluble but copper gentisate was insoluble in water.
Elemental analysis for the weight percentages of carbon and
hydrogen was done with Perkin–Elmer 240 equipment. The ther-
mal stability and decomposition of copper and cadmium gentisates
were examined using a Setsys 16/18 (Setaram) thermal analyzer
recording the TG/DSC/DTG curves. The samples (8–9 mg) were
heated in a ceramic crucible between 30–1000 °C [Cd(II) complex]
or 30–750 °C [Cu(II) compound] in flowing air atmosphere with a
heating rate of 5 °C/min. The products of dehydration and decom-
position processes were established on the basis of the TG curves.
FT-IR spectra were recorded with the Equinox 55 Bruker FT-IR
(
4
(
calc. 14.68%). The loss of all water molecules leads to creation of
anhydrous compound, which gradually decomposes to CdO with
formation intermediate, unstable compounds (180–415 °C). In
the case of all investigated complexes, the dehydration process is
endothermic, whereas the combustion of organic ligand is accom-
panied by strong exo-effects seen on the DSC curves. The observed
various ways of thermal decomposition of analyzed 2,5-
dihydroxybenzoates may be a result from the influence of central
ions on properties of complexes.
À1
spectrometer within the range 4000–400 cm . Samples in the
solid state were measured in KBr matrix. Pellets were obtained
with a hydraulic press under 739 MPa pressure. FT-Raman spectra
DFT calculations
of solid samples in capillary tubes were recorded in the range of
Atom assignment for two conformers of gentisic acid and its
sodium, copper and cadmium salts with the values of their energy
and dipole moments are shown in Table 3. The calculations were
performed with use of B3LYP/6-311++G(d,p) method (for Cu and
Cd complexes mixed basis set was used – 6-31++G(d,p)+LANL2DZ).
Fourteen conformers of gentisic acid were taken into account dur-
ing the calculations. No imaginary frequencies were found. The
appropriate structures with the relative energies (in kcal/mol)
are shown in Fig. 3. The conformers that do not have ability to cre-
ate the intramolecular hydrogen bonds between the carboxylic and
hydroxyl groups have the highest energy (nos. IX–XIV). The next
two conformers, VII and VIII, form the intramolecular bonds which
involve the hydrogen atom from the AOH carboxylic group and
oxygen atom from the AOH substituent in the ortho position
À1
4
000–400 cm with a FT-Raman accessory of Bruker MultiRAM.
À1
The resolution of spectrometer was 1 cm
.
The calculations were carried out with the Gaussian09 set of
codes [15]. The B3LYP functional with Pople type basis set (6-
3
11++G(d,p)) was applied. The gentisic acid, sodium salt and its
tautomeric forms were optimized and no imaginary frequencies
were found. In case of copper and cadmium complexes the optimi-
zation were carried out with use of the same DFT method coupled
with mixed basis set: 6-311++G(d,p) for C, O, and H atoms, and
LanL2DZ for transition metals.
Results and discussion
Synthesized complexes composition
(
). The conformers nos. V and VI possess the
intramolecular hydrogen bonds between the carbonyl group and
the hydroxyl substituent ( ) which causes the
The results of elemental and thermogravimetric analyses are
gathered in Table 1. Thermogravimetric analysis was performed
to investigate the thermal stability and to describe the way of
decomposition of copper and cadmium complexes. The results
obtained from their thermal decomposition show that studied gen-
tisates are hydrated salts. The data of thermal decomposition are
listed in Table 2. Thermoanalytical curves of copper and cadmium
complexes (Fig. 2) are presented to indicate that in the case of each
individual complex occurs the various numbers of stages of dehy-
dration process and degradation of organic ligand. The thermal
analysis data show that the number of water molecules is in good
formation of so called quasi-aromatic ring. In the structures of
gentisic acid molecules nos. III and IV the intramolecular
hydrogen bonds exist between the oxygen of the AOH carboxylic
part and the hydrogen atom of the hydroxyl substituent
(
). For the structures with the lowest energy
(I and II) the hydrogen bond is identical as hydrogen bond in
structures V and VI. Depending on the hydrogen atom orientation
in the carboxylic group one can observe the difference between
aforementioned pairs of conformers. In the structures V and VI
agreement with that defined by elemental analysis ([Cu(C
7
5
H O
)
4 2
]Á
4
H
2
O and [Cd(C O). Moreover the metal percentages
7
H
5
O
4
)
2
]Á4H
2
Table 1
The values of weight percentages of carbon, hydrogen and metal in copper and cadmium gentisates.
Formula
Content Ca (%)
Experimental
Content Ha (%)
Experimental
Content Mb (%)
Experimental
Theoretical
Lit. [10]
Theoretical
Lit. [10]
Theoretical
Copper(II) gentisate (C
Cadmium(II) gentisate (C
7
H
5
O
4
)
2
CuÁ4H
2
O
CdÁ4H
37.77–37.90
33.93–33.77
37.68
33.96
37.49
34.79
4.17–4.16
3.74–3.69
4.15
3.74
4.05
3.49
14.97
23.56
14.38
22.92
7
H
5
O
4
)
2
2
O
a
Carbon (C) and hydrogen (H) determined from elemental analysis.
Metal (M) content determined from TG curves.
b

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E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
Table 2
Thermal data of decomposition of Cu(II) and Cd(II) complexes with gentisic acid (air atmosphere).
Complex
D
T
1
(°C)
Mass loss (%)
Calc.
n
T
2
(°C)
Residue (%)
Calc.
Final product of decomposition
Found
Lit. [10]
Found
18.75
CuL
CdL
2
Á4H
2
O
O
30–150
30–140
16.31
9.71
4.97
16.22
9.96
4.52
16.0
14.5
4
2.5
1.5
150–410
180–415
18.01
CuO
CdO
2
Á4H
2
140–180
26.18
26.92
À
L = (C H
7 5
O
4
) .
n – Number of water molecules being lost in dehydration endothermic step.
À Temperature range of dehydration process.
À Temperature range of anhydrous complex decomposition.
DT
1
T
2
Fig. 2. TG and DSC curves of (a) copper gentisate [Cu(C
7
H
5
O
4 2
) ]Á4H
2
O and (b) cadmium gentisate [Cd(C
7
5
H O
4
2
) ]Á4H
2
O.
the hydrogen atom is directed toward the aromatic ring, whereas
in the conformers I and II the hydrogen is directed to the outside
of the molecule.
The difference between structure I and II consists in the spatial
arrangement of hydroxyl substituent located near the aromatic
carbon atom C5. The obtained results clearly show that the
is involved in the inter- and intramolecular hydrogen bonds forma-
tion. Although the intramolecular interactions were included
during the calculations, the intermolecular effects were omitted.
The C7AO2 bond length is lower in the calculated geometry in
comparison with the experimental one by 0.013 Å for both I and
II structures, while C7AO1 and O1AH1 calculated bond lengths
are greater than experimental ones by about 0.032 and 0.058 Å,
respectively. The distance between the O2 and H2 atoms is
ꢁ1.7 Å what suggests quite strong intramolecular hydrogen bond-
ing and therefore stabilization of the structure of gentisic acid. The
differences between the theoretical and experimental angles in the
aromatic ring obtained for the structures of 2,5-dihydroxybenzoic
acid are in the range from À0.92° to +0.96°. Greater changes are
observed for C1AC7AO1 and C1AC7AO2 angles. The first one
decreases by 1.19° and 1.16° in structure I and II, respectively,
while the second one increases by 3.28° and 3.13°, respectively.
Slightly changes are also observed for O1AC7AO2 angle: À2.09°
(structure I) and À1.96° (structure II).
intramolecular hydrogen bonds affect the stability and p-electron
delocalization. The strength of the intramolecular hydrogen bonds
increases with the growth of the electron-donating and electron-
withdrawing capacity of H-bond donor and H-bond acceptor,
respectively. Consequently it leads to an increase of the
delocalization in the quasi-ring.
p-electron
The calculated structural parameters for studied molecules are
gathered in Table 4. To compare the obtained results with the
experimental data the Cambridge Structural Database was
searched for the crystal structures of gentisic acid and gentisates.
Several structures of gentisic acid were found [16–18] but only
the most recent data were taken into account [18]. The quite good
linear correlation between calculated and experimental [18] struc-
tural parameters were obtained. The correlation coefficients R for
the distances between atoms in acid molecule are 0.994 and
Two conformers in case of each metal gentisate molecules were
calculated. The type of hydration and metal bonding for cad-
mium(II) and copper(II) gentisates were assumed on the basis of
the results of elemental and thermogravimetric analyses as well
as the literature data for crystal structure of zinc(II) gentisate
[10]. Comparing the gentisic acid structure with the geometry of
its sodium, copper and cadmium complexes the most visible
changes in the distances between atoms as well as in the angles
between bonds are observed in the region of carboxylic group.
The increase of the oxygenAMetal (OAM) bonds follows the rise
in the ionic radius of metal cations. The high impact of the intra-
molecular hydrogen bonds on the OAM distances was observed.
In the case of sodium gentisate the bidentate structure of the car-
boxylate anion is quite symmetrical (O1AM: 2.215 and 2.212 Å;
O2AM: 2.201 and 2.213 Å). However, in the structure of copper(II)
0
.949, respectively for structures I and II (appropriate values for
angles between the bonds are 0.962 and 0.909). The above data
indicate that the geometrical parameters of structure I (the one
with the lowest energy) are in a better agreement with the
experimentally obtained results. The main differences between
theoretical and experimental bond lengths concern: the C4AH4
distance (the difference between theoretical and experimental val-
ues are
ture II); the C6AH6 and O4AH5 (
= 0.073 Å), the O3AH2 ( = 0.073 Å), the C2AO3 (
and the C5AO4 distances ( = 0.014–0.015 Å). The differences
D
= 0.118 Å for the structure I and
= 0.100–0.104 Å), the C3AH3
= 0.019 Å)
D = 0.120 Å for the struc-
D
(D
D
D
D
between experimental and theoretical bond lengths in the aro-
matic ring of gentisic acid are about ±0.013 Å. The carboxylic group
À
and cadmium(II) gentisates the COO group is monodentate with

E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
717
Table 3
engaged in the intramolecular hydrogen bond formation. The
distance O2AH2 increases in the series of sodium ? cadmium ?
copper gentisates ? gentisic acid (i.e. 1.68 Å ? 1.69–1.71 Å ?
Atom assignments for two conformers of gentisic acid and sodium, copper and
cadmium gentsates with the values of their energy and dipole moments calculated by
B3LYP/6-311++G(d,p). Energy in kcal/mol related to conformation of the structure I of
lowest energy.
1.73 Å ? 1.77 Å). These mean that there is a stronger intramolecular
hydrogen bond in the molecules of metal gentisates than gentisic
acid. Moreover, taking into account the three metal compounds
the strongest intramolecular hydrogen bond exists in the sodium
salt where the ionic type of metal bonding exists. The strength of
the intramolecular hydrogen bond also reflects the calculated
atomic charges gathered on the atoms involved in the quasi-
aromatic ring formation. In the molecule of sodium gentisate the
atomic charge on O2 atom is À0.86e and on H2 atom was 0.22e,
whereas for the structure of gentisic acid the following values
are obtained: À0.65e (O2) and 0.22e (H2). The type of metal
coordination and the presence of the hydrogen bond affects the
oxygen–carbon distances within the carboxylate group. The
difference between the bond lengths of the carboxylate anion,
i.e. C7AO2 and C7AO1 is lower in case of sodium gentisate
(
ꢁ0.03 Å) than copper gentisate (ꢁ0.05 Å). In case of cadmium
gentisate some differences between the bond lengths and angles
of the carboxylate group in the two coordinated ligands are
observed. For example, the difference between the distance of
CAO in the COO group is equal ꢁ0.06 Å in one of the gentisate
À
ligand and ꢁ0.03 Å in the other ligand, or the values of angles
between atoms C7AO2AM: ꢁ69° and ꢁ73° (the same situation
occurs for I and II conformers of cadmium gentisate). Moreover, a
significant increase in the C7AO1AH1/M angles is observed for
gentisates of copper (by 17.18° – structure I and 17.23° – structure
II) and cadmium (by 20.34° and 13.78° for structure I a and b
ligands, respectively) in comparison with gentisic acid. However
for sodium gentisate the decrease is noticed by 17.76° (structure
I) and 17.71° (structure II). Taking into account the experimental
structures of gentisic acid and zinc gentisate the C7AO1AH1/M
angle increases by 22.03° in complex molecule. It confirms the
tendency observed in theoretical data for transition metal com-
plexes. Slightly smaller changes are noticed for O4AC5AC4 and
O4AC5AC6 angles. The first one increases by 5.77° for copper,
5
.71°/5.74° for cadmium (a/b molecules) and 0.37° for sodium salts
if the structure I is taken into account. The second one decreases by
.59°, 5.63°/5.60° and 0.37°, respectively. In experimental structure
5
of zinc gentisate the same tendency is observed: O4AC5AC4 angle
increases by 5.39° and O4AC5AC6 decreases by 5.03°, similarly to
calculated structures of copper and cadmium gentisates. Other
angles change only insignificantly.
The mutual arrangement of ligands in the copper and cadmium
gentisate molecules is very surprising. Namely, in the structure of
copper complex the two coordinated gentisate ligands are in one
line and in the same plane, and the values of the geometrical
parameters as well as atomic charges are identical in both ligands
(
therefore the dipole moment of the molecule is equal 0 D). On the
other hand, in the cadmium complex the ligands are in substan-
tially twisted planes to each other and they are not in lying one
line. Moreover the bond lengths, angles and atomic charges differ
slightly in the two gentisate ligands (the dipole moment of the
structure I is 1.208 D and structure II is 2.286 D). The same type
of metal coordination and the degree of hydration in cadmium
and copper gentisates exist, but finally the kind of metal deter-
mines the spatial structure, geometrical parameters and atomic
charge distribution of molecules.
The bond lengths in the aromatic ring of gentisic acid as well as
its sodium, copper and cadmium salt molecules change very
slightly. The values of the calculated aromatic indices [19] for each
structures (Table 5) let us to draw the following conclusions: (1)
the spatial arrangement of the substituents in the ring influences
on the aromaticity of molecules (higher values of indices were
obtained in case of structures II than I for gentisic acid and sodium
shorter O2AM bond and longer O1AM distance. Bigger differences
between these bond lengths are observed in the case of copper
gentisate than cadmium compound. Moreover, the oxygen O2 is

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E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
Fig. 3. The calculated [B3LYP/6-311++G(d,p)] energies of analyzed conformations of gentisic acid related to the conformation I (with the lowest energy).
gentisate, but for copper and cadmium gentisates the situation was
opposite – structures I possessed higher automaticity indices than
structures II), (2) the aromaticity of complexes varies depending on
the kind of coordinated metal; (3) the gentisate molecules possess
slightly higher aromaticity than gentisic acid. Comparing the val-
ues of indices obtained on the basis of experimental data for gen-
tisic acid [18] and zinc gentisate [10] it is clearly seen that the
aromaticity of metal complex molecule is higher that acid. It
means that zinc cation causes increase in the delocalization of
the electronic charge distribution in the aromatic ring of gentisate
of the COO function (NBO charges on O1/O2 atoms in structure I
of gentisic acid equal À0.679/À0.651e and in sodium salt-structure
I they are À0.799/À0.858e). Atomic charges on the carboxylic oxy-
gen atoms decrease, so electronic density around those atoms
increases. Partial atomic charges on C1 and C6 carbon atoms
increase, while on other carbon atoms in the ring decrease in salt
molecules in comparison with acid. The total charge of aromatic
ring as well as carboxylate group are also calculated and presented
À
in Table 6. The negative values of charge of both COO group and
aromatic ring significantly increase in the following order: gentisic
acid < copper < cadmium < sodium gentisates. As regards to O3 and
O4 oxygen atoms in hydroxyl substituents higher changes are
observed on O3 atom, though around both of them electronic den-
sity increases in comparison with acid structure. The positive
charge on H2 and H5 atoms significantly increases in copper and
cadmium gentisates in comparison with gentisic acid and its
sodium salt. In sodium gentisate molecule lower atomic charges
are observed on H2 and H5 atoms than on those atoms in acid mol-
ecule. The great positive charge is noticed on H4 atom in gentisic
acid as well as in sodium gentisate, but in copper and cadmium
complexes the decrease of this charge by about 0.25e is noticed.
Some differences in atom charges are observed also in water mol-
ecules coordinated to copper and cadmium atoms. In cadmium
gentisate there are four water molecules with different charges
on atoms, each molecule has differ charge distribution. While in
copper salt two molecules of water have the same charges on
atoms and other two also have the same charge distribution, but
differ from the first one. It is interesting to notice that in copper
salt two molecules of gentisate ligand coordinated to Cu(II) atom
have identical charges on atoms, bond lengths and angles between
bonds. However cadmium gentisate contains two different mole-
cules of gentisate ligand.
ligand and therefore higher stabilization of the p-electron system
comparing with the gentisic acid structure. The structural parame-
ters obtained by X-ray measurements of the respective compounds
obtained in the form of crystals are the result of the existing intra-
and intermolecular interactions, including hydrogen bonds. For the
calculated structures the intramolecular interactions can be
included but the intermolecular (especially long-distance) interac-
tions are omitted. This is the reason why the aromaticity indices
obtained for the calculated geometries should be carefully treated
because they do not fully reflect the interactions in real structure.
Moreover, it is interesting that in the case of the theoretically
obtained structure of zinc gentisate with the lowest energy (struc-
ture I) the two hydroxyl substituents in the ring are directed
toward the carboxylate group. Whereas in the experimental struc-
ture of zinc gentisate one of the hydroxyl substituent is directed
À
toward COO anion, but the second one is situated in the opposite
direction because of its involvement in the hydrogen bonding
between the next gentisate ligand (Fig. 1). These intermolecular
interactions are omitted during the calculations what probably
affects the values of the aromaticity indices for theoretical struc-
tures. For the calculated structures the aromaticity increases in
the order: gentisic acid < Cu < Na < Cd gentisates for structure I
(
in the case of BAC indices aromaticity of sodium gentisate is
higher than acid and lower than copper salt molecule); for struc-
ture II all indices show increase of the aromaticity in the following
series: acid < Cu < Cd < Na gentisates.
The changes in distances and angles are due of the replacement
of H atom in carboxylic group by metal atom, which allows a better
distribution of charges in the case of salt molecules. Atomic
charges calculated by NBO method for gentisic acid and for sodium,
copper and cadmium gentisate molecules are presented in Table 6.
The formation of sodium gentisate causes significant changes on
the charge distribution of atoms specially on the oxygen atoms
IR and Raman spectra
The FT-IR and FT-Raman spectra of gentisic acid and sodium,
copper and cadmium gentisates were recorded and the wavenum-
bers, intensities and assignments of selected bands occurring in the
experimental as well as calculated spectra are gathered in Table 7.
Exemplary FT-IR and Raman spectra of cadmium gentisate is pre-
sented in Fig. 4. The bands are numbered along with the notation
used by Varsányi [20]. A good correlation between experimental
and theoretical wavenumbers in IR spectra of gentisic acid as well

E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
719
Table 4
Calculated bond lengths and angles of gentisic acid and sodium, copper and cadmium gentisates.
Atoms
Gentisic acid
Exp. [18]
Sodium gentisate
Theoretical data
Copper gentisate
Theoretical data
Cadmium gentisate
Theoretical data
Zinc gentisate
Theoretical data
Struct. I
Struct. II
Struct. I
Struct. II
Struct. I
Struct. II
Struct. I
Struct. II
Exp. [10]
Bond length (Å)
C1AC2
1.402
1.403
1.376
1.398
1.383
1.407
0.966
1.010
1.366
1.474
0.980
1.387
0.862
0.908
1.238
1.316
0.911
–
1.412
1.402
1.381
1.404
1.381
1.411
1.084
1.083
1.347
1.464
1.084
1.372
0.963
0.980
1.225
1.351
0.969
–
1.415
1.399
1.385
1.402
1.383
1.406
1.086
1.083
1.347
1.467
1.081
1.373
0.962
0.980
1.225
1.348
0.969
–
1.410
1.403
1.385
1.400
1.384
1.405
1.084
1.083
1.351
1.489
1.085
1.379
0.962
0.989
1.291
1.261
2.215
2.210
1.679
1.414
1.399
1.388
1.399
1.385
1.401
1.087
1.083
1.351
1.492
1.082
1.379
0.962
0.989
1.291
1.259
2.212
2.213
1.672
1.414
1.399
1.387
1.400
1.384
1.404
1.086
1.083
1.353
1.486
1.082
1.375
0.962
0.980
1.301
1.251
3.135
1.972
1.728
1.411
1.402
1.383
1.402
1.382
1.408
1.084
1.083
1.352
1.483
1.085
1.374
0.963
0.980
1.300
1.252
3.137
1.971
1.724
1.413a
1
1.410
1.411
1.401
1.402
1.384
1.383
1.400
1.401
1.383
1.383
1.407
1.408
1.084
1.084
1.083
1.083
1.355
1.353
1.490
1.485
1.085
1.085
1.376
1.375
0.963
0.963
0.984
0.983
1.301
1.293
1.247
1.260
3.434
3.261
2.241
2.273
1.707
1.692
1.409
1.409
1.388
1.388
1.386
1.386
1.394
1.394
1.380
1.380
1.392
1.392
0.968
0.968
0.971
0.971
1.369
1.369
1.493
1.493
0.856
0.856
1.384
1.384
0.726
0.726
0.846
0.846
1.295
1.295
1.259
1.259
3.370
3.370
2.051
2.051
1.742
1.742
.414b
C2AC3
C3AC4
C4AC5
C5AC6
C6AC1
C4AH4
C3AH3
C2AO3
C1AC7
C6AH6
C5AO4
O4AH5
O3AH2
C7AO2
C7AO1
O1AH1/M
O2AH1/M
O2AH2
1.398
.399
1.388
.387
1.399
.400
1.385
.385
1.402
.403
1.087
.087
1.083
.083
1.356
.353
1.493
.487
1.082
.082
1.376
.376
0.962
.962
0.984
.983
1.302
.293
1.245
.258
3.430
.253
2.243
.274
1.703
.686
1
1
1
1
1
1
1
1
1
1
1
0
0
1
1
3
2
1.753
1.774
1.771
1
Angle (°)
C1AC2AC3
119.47
120.13
120.49
120.38
119.53
119.99
119.14
120.32
121.56
118.31
122.66
117.81
117.30
123.23
122.08
118.77
120.78
120.61
119.57
120.49
119.79
118.70
120.69
120.99
118.24
120.80
118.72
117.74
123.49
123.53
118.69
120.63
120.77
119.45
120.45
120.02
119.84
119.39
120.97
118.40
119.61
119.94
117.82
123.49
117.87
118.98
120.85
120.26
119.57
120.90
119.44
118.98
120.76
120.82
118.33
121.49
117.62
118.20
122.83
123.14
118.93
120.64
120.48
119.48
120.78
119.69
120.00
119.51
120.84
118.52
120.38
118.84
118.26
122.81
118.01
118.87
120.74
120.52
119.39
120.84
119.64
120.01
119.47
120.86
118.40
120.22
118.94
117.53
123.61
117.94
118.93
120.92
120.34
119.49
120.91
119.41
118.91
120.75
120.86
118.22
121.39
117.71
117.46
123.61
123.38
119.13
19.02
120.64
20.65
120.42
20.65
119.47
19.43
120.89
20.84
119.45
19.55
120.05
20.00
119.53
19.48
120.85
20.86
118.52
18.49
120.22
20.22
118.90
18.94
117.92
17.88
122.95
23.10
117.90
17.93
119.18
119.09
120.83
120.82
120.23
120.33
119.57
119.53
120.98
120.91
119.22
119.32
118.98
118.91
120.79
120.76
120.84
120.86
118.34
118.32
121.36
121.38
117.66
117.71
117.85
117.80
122.97
123.11
123.23
123.34
119.88
119.88
120.65
120.65
119.57
119.57
120.02
120.02
121.15
121.15
118.65
118.65
121.21
121.21
118.98
118.98
125.67
125.67
112.95
112.95
121.26
121.26
117.39
117.39
118.88
118.88
121.26
121.26
117.05
117.05
1
C2AC3AC4
C3AC4AC5
C4AC5AC6
C5AC6AC1
C6AC1AC2
H4AC4AC5
H4AC4AC3
H3AC3AC4
H3AC3AC2
C5AC6AH6
H6AC6AC1
C3AC2AO3
C1AC2AO3
O4AC5AC6
1
1
1
1
1
1
1
1
1
1
1
1
1
1
(
continued on next page)

7
20
E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
Table 4 (continued)
Atoms
Gentisic acid
Exp. [18]
Sodium gentisate
Theoretical data
Copper gentisate
Theoretical data
Cadmium gentisate
Theoretical data
Zinc gentisate
Exp. [10]
Theoretical data
Struct. I
116.91
Struct. II
Struct. I
117.28
Struct. II
Struct. I
122.68
Struct. II
Struct. I
122.62
Struct. II
O4AC5AC4
C2AO3AH2
C2AC1AC7
C7AC1AC6
C1AC7AO1
C1AC7AO2
C7AO2AM
C7AO1AH1/M
O1AC7AO2
C5AO4AH5
117.54
105.63
119.38
120.63
115.93
121.26
–
122.68
107.93
118.82
121.17
114.77
124.39
–
122.52
105.74
121.10
119.20
120.38
117.80
88.44
117.13
106.93
122.40
118.19
116.37
121.04
67.92
117.21
117.13
105.52
106.07
122.26
121.93
118.53
118.75
116.52
117.41
119.92
120.14
68.87
122.93
122.93
104.83
104.83
121.23
121.23
120.11
120.11
116.40
116.40
119.77
119.77
64.61
1
22.65
105.47
06.05
122.05
21.76
118.49
18.69
116.45
17.33
119.96
20.19
69.01
3.47
127.20
20.64
123.59
22.49
109.66
09.73
108.01
118.93
121.28
114.74
124.54
–
105.81
121.32
119.24
120.33
117.87
88.59
106.90
122.22
118.14
116.29
121.07
67.98
1
1
1
1
1
7
73.30
64.61
108.02
122.81
108.19
106.86
120.72
109.92
106.96
120.85
109.94
89.10
89.25
124.04
122.64
109.76
124.19
122.59
109.62
127.42
120.97
123.56
122.45
109.47
109.57
130.05
130.05
123.80
123.80
104.72
104.72
1
121.80
109.20
121.82
109.41
1
1
a
Two molecules of gentisate ligand coordinated to copper(II) or cadmium(II) atom, in copper(II) gentisate there are the same values of distances between atoms and angles
between bonds in a molecules.
b
Two molecules of gentisate ligand coordinated to copper(II) or cadmium(II) atom, in copper(II) gentisate there are the same values of distances between atoms and angles
between bonds in b molecules.
Table 5
Aromaticity indices calculated on the basis of the theoretical as well as the experimental geometries of gentisic acid and sodium, copper, cadmium and zinc gentisates.
Indices
Gentisic acid
Exp.[18]
Sodium gentisate
Theoretical data
Copper gentisate
Theoretical data
Cadmium gentisate
Theoretical data
Zinc gentisate
Theoretical data
Struct. I
0.929
Struct. II
Struct. I
0.950
Struct. II
Struct. I
0.948
Struct. II
Struct. I
Struct. II
Exp. [10]
0.976
HOMA
0.955
0.985
0.844
90.43
0.940
0.985
0.857
90.52
0.953
0.990
0.886
92.09
0.941
0.941
0.985
0.985
0.850
0.850
90.36
90.36
0.955
0.949
0.990
0.989
0.888
0.880
92.28
91.78
0.949
0.942
0.987
0.986
0.866
0.856
91.18
90.60
0
.948
0.988
.988
0.876
.876
91.51
1.51
A
j
0.981
0.827
89.12
0.989
0.874
91.66
0.991
0.883
92.52
0
BAC
0
I
6
9
À1
as its metal complexes were obtained. For example, the correlation
coefficients are equal R = 0.995 and 0.996 for I and II structures of
gentisic acid and R = 0.995 for both structures I and II of sodium
gentisate molecules. Comparing FT-IR spectra of gentisic acid and
its metal complexes one can observed that some bands character-
toward lower wavenumbers in copper salt spectra (880 cm ) as
well as toward higher wavenumbers in the IR spectra of Cd genti-
À1
state (891 cm ). The wavenumbers of band assigned to the sym-
À
metric stretching vibrations of the carboxylate anion
m
s
(COO )
occurs in the IR spectra of sodium, copper and cadmium gentisates
in the range of 1366–1385 cm . The bands assigned to asymmet-
as(COO ) occur in the range 1587–
1566 cm (IR exp.), 1596–1563 (Raman) and the wavenumbers
decrease in the series: Na > Cd > Cu gentisates. In calculated spec-
À1
istic for acid spectra disappeared in the spectra of gentisates,
À1
À
namely:
t
(OH)COOH stretching vibration band at 3130 cm (IR) –
ric stretching vibrations
m
À1
À1
appropriate band in calculated spectra is at 3767 cm (for I and
II structures), the band of b(OH)COOH in-plane deformation at
À1
À1
À1
1
204 cm (in IR exp. spectrum) and at 1284; 1281 cm (in IR
spectrum calculated for I and II structures) and (OH)COOH at
54 cm (IR exp.) and 572; 575 cm (IR calc. I and II structures).
tra this band changes from 1595 to 1560 cm but it is difficult
c
to describe the tendency of the changes, because two ligands in
the cadmium molecule demonstrate two extreme vibration bands
from above mentioned range. The wavenumebrs of the out-of-
À1
À1
8
The bands assigned to the symmetric stretching vibrations
m
(C@O)
À1
À1
À1
À
at 1668 cm (IR exp.), 1664 cm (Raman) and 1730; 1731 cm
plane bending modes of COO are located in the range of 691–
À1
À1
À1
À1
(
7
IR calc.; I and II structures), b(C@O) at 756 cm
(IR exp.),
687 cm
(IR exp.), 693–690 cm
(Raman), 827–813 cm
(IR
À1
À1
51 cm (Raman) and 738; 736 cm (calc. I and II struct.) also
calc.). On the basis of the difference between IR wavenumbers of
decline. On the other hand the appearance of the bands connected
with carboxylate ion is noticed in the spectra of gentisates. The
asymmetric and symmetric stretching vibrations of carboxylate
À
anion [
D
m(COO)] the type of coordination of the COO group by
À
À1
band of bas(COO ) in plane deformations occurs at 598 cm (IR
metal ions in studied gentisates may be analyzed. According to
Zelenak et al. [21] the mode of carboxylate binding can be ionic,
monodentate, bidentate chelating or bridging according the series:
À1
exp.) and at 576 cm (IR calc. for both I and II structures) for Na
gentisate. The increase of wavenumbers of this band is observed
À
in the series Na < Cd < Cu gentisates. The band of b
s
(COO ) in the
D
D
m
(chelating) <
Dm(bridging) 6 Dm(ionic) < Dm(monodentate). The
À1
IR spectra of sodium gentisate occurs at 887 cm and it is shifted
m(COO) for sodium, cadmium and copper gentisates are as

E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
721
Table 6
Data of NBO atomic charge analysis for gentisic acid and sodium, copper and cadmium gentisates.
Atoms
Gentisic acid
Structure I
Sodium gentisate
Copper gentisate
Cadmium gentisate
Structure I
Structure II
Structure I
Structure II
Structure I
Structure II
Structure II
a
b
C1
C2
C3
C4
À0.235
0.361
À0.232
À0.190
0.281
À0.231
0.357
À0.234
À0.224
0.279
À0.218
0.342
À0.238
À0.211
0.273
À0.214
0.340
À0.241
À0.243
0.272
À0.215
0.343
À0.237
À0.232
0.277
À0.215
À0.219
0.346
À0.235
À0.199
0.279
À0.219
0.346
À0.235
À0.199
0.279
À0.216
0.341
À0.238
À0.234
0.276
À0.211
0.335
À0.239
À0.238
0.276
À0.220
0.344
À0.236
À0.200
0.278
À0.214
0.343
À0.237
À0.232
0.277
0.337
À0.237
À0.205
0.278
C5
C6
C7
À0.228
À0.192
À0.230
À0.195
À0.189
À0.189
À0.225
À0.225
À0.190
À0.191
À0.225
À0.226
0.796
0.798
0.776
0.777
0.810
0.810
0.809
0.809
0.810
0.811
0.808
0.810
O1
O2
O3
O4
À0.679
À0.651
À0.673
À0.677
0.223
À0.673
À0.651
À0.675
À0.676
0.223
À0.799
À0.858
À0.697
À0.686
0.215
À0.792
À0.859
À0.698
À0.684
0.214
À0.746
À0.770
À0.686
À0.678
0.504
À0.746
À0.770
À0.686
À0.678
0.504
À0.753
À0.769
À0.685
À0.680
0.504
À0.753
À0.769
À0.685
À0.680
0.504
À0.775
À0.851
À0.692
À0.679
0.502
À0.708
À0.881
À0.699
À0.680
0.500
À0.781
À0.851
À0.690
À0.681
0.501
À0.715
À0.880
À0.697
À0.682
0.499
H2
H3
0.221
0.204
0.214
0.197
0.219
0.219
0.219
0.219
0.218
0.216
0.218
0.217
H4
0.468
0.467
0.46
0.462
0.201
0.201
0.219
0.219
0.201
0.199
0.218
0.217
H5
0.221
0.237
0.222
0.237
0.465
0.465
0.467
0.467
0.464
0.464
0.467
0.467
H6
0.221
0.237
0.222
0.237
0.239
0.239
0.224
0.224
0.238
0.239
0.223
0.224
H1/M
O5
H51
H52
O6
H61
H62
O7
H71
H72
O8
0.489
0.488
0.925
0.925
1.088
1.088
1.554
1.555
À0.914
À0.914
À1.007
À1.007
0.491
0.491
0.484
0.484
0.512
0.512
0.510
0.510
À0.920
À0.920
À0.941
À0.942
0.501
0.501
0.492
0.493
0.482
0.483
0.494
0.495
À0.914
À0.914
À0.973
À0.973
0.512
0.512
0.509
0.508
0.491
0.491
0.486
0.486
À0.920
À0.920
À0.973
À0.972
H81
H82
0.501
0.501
0.487
0.487
0.482
0.483
0.509
0.508
Total atomic charges
Ring
COO
À0.243
À0.245
À0.526
À0.282
À0.881
À0.281
À0.874
À0.253
À0.706
À0.253
À0.706
À0.253
À0.713
À0.253
À0.713
À0.261
À0.816
À0.268
À0.778
À0.259
À0.824
À0.267
À0.785
À0.534
À1
follows: 202, 200 and 187 cm , respectively. The obtained values
are close to each other. Due to the above mentioned rules the
the spectra of acid. Whereas, bands nos. 19a, 19b,
m
(CC)
À1
ꢁ1420 cm , 17b, 11, 12 and 6b are shifted toward lower wave-
obtained values of
D
m
(COO) may indicate bridging chelating mode
numbers in the spectra of gentisates comparing with the spectra
of the carboxylate binding for both cadmium and copper
gentisates, not as expected monodentate binding. The spectro-
of gentisic acid. The stretching vibrations
t
(CC) bands numbered
À1
as 8a, 8b, 19a and 19b occur in the region 1650–1424 cm (IR
À1
À1
scopic criterion must be carefully treated because it was estab-
exp.), 1651–1642 cm (Raman) and 1680–1482 cm (IR calc.).
The first two bands shift to higher values of wavenumbers in the
following series: gentisic acid < sodium < copper < cadmium genti-
sates. The differences between appropriate band in experimental
À
lished on the basis of the wavenumbers of
m
as(COO ) and
À
m
s
(COO ) bands from IR spectra of metal acetates. To be sure of
the type of coordination the crystal structures of the studied com-
pounds should be only discussed. The large discrepancies between
the results of a spectroscopic criterion and the type of metal coor-
dination was demonstrated for differently hydrated structures of
À1
IR spectra of acid and cadmium salt are from 9 to 26 cm for 8a
and 8b, respectively. In the case of 19b and 19a bands the order
is: sodium gentisate < gentisic acid < copper < cadmium gentisates.
À1
À1
the same compound [22]. The values of
D
m(COO) were also calcu-
The shifts equal from 4–15 cm (19b) to 20–32 cm (19a). For 8b
the order of changes is following gentisic acid < sodium <
copper < cadmium gentisates, while for 8a gentisic acid < copper <
lated basing on the theoretical spectra of studied salts. The appro-
priate data amount to 201(I) and 209(II) for Na2,5-DHB; 207(I) and
2
2
15(II) for Cu(2,5-DHB)
12(IIb) cm for cadmium gentisate. The values confirmed the
2
(H
2
O)
4
and 215(Ia), 204(Ib) and 221(IIa),
cadmium < sodium salts. The wavenumbers of the bands connected
À1
À1
with 7a-
t(CH) vibrations are in the range 1252–1238 cm and
established during the calculation monodentate type coordination.
they increase in sodium, copper and cadmium gentisates by
À1
On the other hand according to Micera et al. [12] the value of
10–14 cm in comparison with the gentisic acid spectra, while
À1
À1
D
m(COO) for copper complex with 2,4-DHBA equals 195 cm
that of 11-
c
(CH) occurring in the range 839–814 cm decrease
À1
À1
may indicate non bonding interactions involving the carboxylate
groups distinguish from the Mn, Co, Ni and Zn 2,4-DHBs, which
by 15 cm (for cadmium gentisate) – 25 cm (for copper salt).
The other bands of aromatic ring are placed at about similar
wavenumbers both in the spectrum of acid and salts.
display carboxylate absorption typical for monodentate coordina-
À1
tion (D
m
= 140 cm ). Authors suggested that in the case of Cu
The bands assigned to t(OH) stretching vibrations of the substi-
À1
À1
complex the phenolic groups may be responsible for long intermo-
lecular axial contacts toward the metal ion [12].
tuent in the ring, which occur at (1) 3310 cm (IR), (2) 3073 cm
À1
(IR) and 3073 cm (Raman) in the experimental spectrum of acid,
in the spectra of gentisates are shifted toward higher wavenum-
bers [3483–3194 cm (IR), 3075 cm (Raman)]. It suggest weak-
ening of the intermolecular hydrogen bonding in the metal
complex molecules comparing with acid. In the calculated spectra
The influence of alkali metals on the vibrational structure of
gentisic acid expresses also in the shifts of some other bands in
the spectra of gentisates comparing with the spectra of acid.
Namely, bands nos. 8b, 8a, 14, 7a, 13, 18b, 16a and 6a are located
at higher wavenumbers in the spectra of metal complexes than in
À1
À1
À1
the first band changes only a bit in the range 1–3 cm (structure I)

Table 7
Wavenumbers (cm ), intensities and assignments of selected bands occurring in the experimental and calculated B3LYP/(6-311++G ) FT-IR and Raman spectra of gentisic acid as well as sodium, copper and cadmium gentisates.
À1
ÃÃ
Gentisic acid
Sodium gentisate
Copper gentisate
Raman IR IR calc. (intensity)
Cadmium gentisate
Assignmenta
20]
[
IR
IR calc. (intensity)
Raman IR IR calc. (intensity)
Raman IR IR calc. (intensity)
Raman
exp.
exp.
exp.
Struct. I
Struct. II
Struct. I
Struct. II
Struct. I
Struct. II
Struct. I
Struct. II
3
3
3
310
s
130
s
073
s
3838
(65.0)
3767
(119.9)
3499
(267.2)
3842
(73.1)
3767
(120.0)
3498
(285.4)
3218
(2.2)
3426
s
3841
(53.7)
3844
(58.4)
3422
vs
3839
(122.5)
3843
(156.1)
3483
s
3839 (57.3); 3839
(61.0)
3843 (60.0); 3843
(82.6)
m
m
m
m
m
m
m
m
m
m
m
m
m
(OH)ar
(OH)
(OH)ar
(CH)
3073
m
2985
w
3318
(479.5)
3195
(7.0)
3180
(5.1)
3305
(514.1)
3191
(5.8)
3144
(21.8)
3208
(3.4)
3075
m
2986
m
3490
(1190.5)
3199
(10.1)
3184
(5.7)
3486
(1261.0)
3195
(7.8)
3150
(39.2)
3212
(10.6)
3067 s 3194
s
3431 (472.4); 3411 3424 (513.6); 3401
(740.1)
3198 (5.0); 3197
(5.0)
3184 (3.1); 3183
(3.9)
(771.7)
3194 (4.2); 3193
(4.3)
3149 (18.18); 3148
(19.71)
3212 (4.2); 3212
(4.5)
3
202
2.0)
187
1.1)
185
7.1)
20b
(
3
(
3
3199
(1.9)
(CH)
3152
(13.4)
1731
(385.7)
1671
(48.9)
1625
(44.2)
3171
(10.1)
3177
(24.7)
3176 (10.3); 3175
(10.8)
(CH)
(
1
1
1
668
vs
624
m
595
m
1730
(397.4)
1663
(68.3)
1630
(42.4)
1664 s
(C@O)
(CC)
1632
s
1670
(7.3)
1641
(29.7)
1577
(379.3)
1528
(268.8)
1495
1677
(15.4)
1633
(24.2)
1584
(347.5)
1517
(375.3)
1506
(233.7)
1642
w
1670
(16.7)
1634
(102.8)
1565
(857.5)
1524
(281.9)
1500
(837.5)
1677
(35.6)
1628
(160.3)
1571
(771.4)
1515
(665.2)
1508
(296.5)
1642
m
1611
w
1563
m
1492
vw
1650
sh
1611
sh
1572
s
1487
vs
1673 (5.6); 1671
(8.0)
1641 (21.8); 1639
(7.4)
1590 (637.0); 1560 1595 (611.7); 1566
(366.5) (331.1)
1527 (208.9); 1525 1516 (343.4); 1515
(212.7) (154.5)
1503 (362.0); 1493 1514 (360.2); 1503
1680 (12.2); 1678
(17.6)
1632 (2.9); 1629
(43.3)
1651
vw
8b
8a
1609
m
1614
m
1566
vs
1493
s
1460
vs
(CC)
À
1
587
1596
m
1498
vw
1455
w
as(COO )
(CC)
vs
1491
vs
1462
s
1425
m
1
1
1
1
497
s
472
m
439
vs
377
m
1526
(181.0)
1483
1515
(278.8)
1495
(9.2)
1473
m
1445
w
19b
19a
1459
vw
1462
sh
(CC)
(49.2)
(336.7)
(486.2)
(330.1)
1400
s
1409 s 1401
sh
(CC)
1419
(219.4)
1421
(190.7)
1350
m
1422
(99.9)
1376
(304.1)
1348
(76.3)
1298
(12.8)
1269
(151.3)
1422
(29.0)
1375
(449.5)
1343
(53.8)
1289
(63.5)
1273
(124.5)
1409
(59.7)
1358
(1094.2)
1353
(258.2)
1299
(16.8)
1260
(332.3)
1407
(12.0)
1356
(1666.9)
1348
(22.2)
1290
(222.3)
1264
(262.0)
1420 (86.0); 1415
(61.9)
1375 (383.5); 1356 1374 (501.9); 1354 1390
(624.8)
1352 (84.6); 1351
(73.7)
1299 (12.3); 1298
(6.5)
1265 (164.3); 1260 1269 (124.8); 1265 1254
1420 (15.6); 1415
(19.2)
b(CH)+b(OH)
À
1
s
385
1390
w
1366
vs
1326
sh
1363
m
1330
w
1385
vs
1329
s
m
m
s
(COO )
(862.9)
1346 (83.1); 1345
(23.5)
1290 (69.1); 1289
(122.6)
vw
1325
vw
1
1
1
314
1399
(48.0)
1298
(6.4)
1391
(34.6)
1296
(8.4)
1307 s 1327
m
14
7a
(CC)
w
277
m
1291
sh
1246
w
1286
sh
1248
s
1291 s 1275
m
1287 s 1275
m
m
m
m
CA(OH),
CA(OH)ar
(CH)
240
s
1246
m
1250
s
1249
w
1236
s
(145.9)
(112.3)
vw
1
284
1281
(213.1)
1228
(19.8)
1202
(101.9)
1153
(0.4)
1081
(54.1)
b(OH)
(CH)
(156.6)
1
1
1
190
vs
136
sh
074
m
1236
(14.8)
1192
(345.0)
1146
(18.6)
1199
vs
1131
w
1080
w
1191
sh
1130
w
1078
w
1228
(3.8)
1222
(2.7)
1194
w
1137
w
1083
w
1228
(0.3)
1182
(516.6)
1150
(119.1)
1103
(29.5)
968 (0.7)
1222
(9.2)
1193
(190.7)
1153
(38.5)
1103
(57.8)
945 (7.2)
1196
m
1132
m
1084
w
1230 (3.5); 1230
(1.1)
1184 (43.7); 1183
(414.1)
1149 (43.3); 1148
(58.1)
1101 (2.6); 1101
(18.2)
967 (0.2); 964 (0.2) 943 (3.0) 940 (3.9) 944
vw
955 (20.1); 950
(29.0)
1223 (1.2); 1222
(2.7)
1193 (96.9) 1192
(98.8)
1152 (20.9) 1151
(20.8)
1101 (11.9; 32.1)
13
m
1183
(186.1)
1146
(41.1)
1097
(4.2)
1192
(101.8)
1149
(19.8)
1097
(13.7)
1138
m
1084
s
1141
m
1087
w
1133
vw
1090
vw
18a
18b
b(CH), b(OH)ar
b(CH)
1079
(65.9)
9
51
w
971 (0.2) 951
(26.7)
949 (7.1) 946 (1.4) 939 s
957 w
951
sh
937
m
959 (0.2) 936 (4.1) 942 m 945
m
951
(12.7)
835
(13.8)
948 w
943
m
17b
7b
c
c
(CH)
(CH)
9
34
m
952
(31.9)
835
960
(91.0)
821
960
(143.7)
820
955 (44.4) 950
(53.5)
819 (24.2) 818
(34.9)
À
8
87
880
w
886
vw
891
w
819 (28.9)
s
b (COO )
w
(19.7)
(55.7)
(57.9)

8
8
8
7
76
sh
54
m
39
865
(18.9)
892
(10.6)
878 w
890
(12.0)
906 (7.8)
887
(28.9)
905
(78.1)
890 (12.4); 889
(12.9)
908 (7.1) 908 (8.5)
5
c
c
c
(CH)
(OH)
(CH)
847
(21.1)
829
(33.8)
806
(55.3)
789
(27.8)
736
(20.3)
715
(107.0)
834 w
802 s
822 s 846
(17.3)
787 s 795
847
(87.6)
793
817 vs 816
m
798 w
847
(60.6)
785 s 790
832
(95.0)
789
(311.9)
762
(165.4)
821 m 822 s 848 (46.8); 844
830 (44.6) 826
(50.1)
800 (88.0)
826
vw
11
12
m
(39.7)
785 s
97 s 809
a
(CCC)
(OH),
b(C@O)
(OH)ar
(CCC)
(34.3)
(74.4)
(93.3)
(287.4)
761
(152.7)
784
786 (47.4) 772
(91.1)
788 (44.8) 773
(81.3)
c
c(CH)
(40.9)
7
7
6
56
m
738
(21.7)
751 vs
717
c
(99.9)
21
m
701
vw
702
(14.3)
808 (3.1) 827
(35.1)
700
(12.7)
707
(57.4)
812
704
(63.9)
813
732 w
693 w
702 (8.7)
699 (7.7) 698
(18.3)
818 (34.9) 815
(34.8)
1
a
À
6
m
87
690 m 687
m
691
m
821 (42.9) 813
(59.7)
693
vw
c
c
s
(COO )
(124.1)
(120.1)
79 s
678 w
(C@O)
À
5
98
576
(10.8)
576 (0.4)
627
w
583
(67.6)
699 (6.2)
580 (0.1)
697 (6.1)
614
vw
619
vw
586 (33.5) 576
(13.3)
698 (65.4) 697
(0.3)
586 (15.1) 576
(3.4)
696 (27.8; 48.0)
623
vw
b
as(COO )
(CCC)
(CC)
(OH)
(CC)
(CCC)
(CC)
b(CH)
vw
573
vw
554
m
5
59
sh
50
m
691 (0.1) 692 (0.5) 558 w
697 (0.4) 694 (1.5) 574 m 579
vw
576
16a
6a
a
5
673
(48.3)
673
(49.0)
575
576 (0.4)
552
m
556
m
u
(10.8)
572
c
(102.8)
(113.8)
4
4
4
4
82
sh
539 (2.1) 538 (0.5) 486 s
492
w
461
w
432
w
559
(18.0)
556
(21.0)
492 s
478
w
559
(46.1)
482 (5.6)
557
(53.1)
483
(15.5)
444
(77.8)
416
481 m 494
562 (35.1) 559
(14.0)
484 (1.3); 481 (0.2) 485 (3.9); 482 (1.2)
559 (42.9) 556
(16.4)
498
vw
16b
6b
u
m
463
69 s 478 (0.2) 480 (0.4) 457 s
485 (2.7) 486 (8.0) 466 w
459
w
a
w
431
vw
36
w
423
(23.9)
398
429 (4.6) 442
vw
395 (2.3) 406 w
442 (2.9) 446 (0.7) 443 w
442
(59.9)
419
443 (8.7); 443 (7.1) 446 (8.2); 445 (2.1)
u
05
426
(16.5)
424
(22.2)
435 (26.1); 421
(17.9)
432 (39.0); 418
(24.4)
9b
w
(15.5)
(51.6)
(22.0)
a
m
– stretching vibrations, b – in-plane bending modes,
c
– out-of-plane, u – the aromatic ring out-of-plane bending modes, a – the aromatic ring in-plane bending modes.

7
24
E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
À1
Fig. 4. FT-IR spectra of: (a) gentisic acid, (b) sodium gentisate, (c) copper(II) gentistate, and (d) cadmium(II) gentisate in the range of 1850–400 cm
.
À1
and 1–2 cm (structure II). However the other band appearing at
impact of the intramolecular hydrogen bonds on the OAMetal dis-
À1
3
499 cm in structure I of acid is shifted toward lower wavenum-
bers by 181, 68/88 and 8 cm respectively for sodium, cadmium
a/b ligands) and copper gentisates.
tances was observed. The calculations show that in the molecules
of metal gentisates stronger intramolecular hydrogen bond existed
than in gentisic acid. Moreover, taking into account the three metal
compounds the strongest intramolecular hydrogen bond exists in
the sodium salt where the ionic type of metal bonding exists.
The mutual arrangement of ligands in the copper and cadmium
gentisate molecules is surprising, because in the structure of
copper complex the two coordinated gentisate ligands are in one
line and in the same plane, and the values of the geometrical
parameters as well as atomic charges are identical in both ligands.
But, in the cadmium complex the ligands are in substantially
twisted planes to each other and they are not in lying one line.
Moreover the bond lengths, angles and atomic charges differ
slightly in the two gentisate ligands.
À1
(
Conclusions
The elemental and thermal analyses revealed the formulas of
synthesized complexes of gentisic acid with copper(II) and
cadmium(II), ([Cu(C
7
5
H O
4
)
2 2
]Á4H O
and [Cd(C
7
5
H O
4
)
2
]Á4H
2
O),
ÃÃ
respectively. The successful calculations (in B3LYP/6-311++G
level) for gentisic acid and sodium, cadmium and copper gentisates
were done. The monodentate type of coordination in copper and
cadmium gentisates was established. Different conformations of
molecules were studied in order to obtain the most stable ones.
The orientation of the hydroxyl substituent in the aromatic ring
strongly influence the inter- and intramolecular hydrogen bonds
formation and therefore stabilization of the molecule. The high
The aromatic indices for studied compounds were calculated,
but there is some factors that influence the values of these indices,
inter alia: (1) the spatial arrangement of the substituents in the

E. Regulska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 713–725
[9] G. Levy, T. Tsuchiya, New England J. Med. 287 (9) (1972) 430–432.
725
aromatic and the presence of the inter- and intramolecular hydro-
[
10] G. Micera, L.S. Erre, P. Piu, F. Cariati, G. Ciani, A. Sironi, Inorg. Chim. Acta 107
gen bonding, (2) the kind of coordinated metal, the type of metal
coordination and the degree of hydration.
(
1985) 223–227.
[
11] J. Sokolik, B. Lu cˇ anská, G. Plesch, I. Tumová, A. Valent, P. Švec, J. Krätsmár-
Šmogrovi cˇ , Collect. Czech. Chem. Commun. 58 (1993) 1363–1370.
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13] A. Karaliota, V. Aletras, D. Hatzipanayioti, M. Kamariotaki, M. Potamianou, J.
Mass Spectrom. 37 (2002) 760–763.
The detailed assignment of bands from the FT-IR and Raman
spectra of gentisic acid and metal gentisates were done and the
influence of metal cation on free ligand molecule was discussed.
[
[
[
[
14] C. Litos, A. Terzis, C. Raptopoulou, A. Rontoyianni, A. Karaliota, Polyhedron 25
(
2006) 1337–1347.
Acknowledgements
15] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery, Jr., J.E. Peralta, F. Ogliaro,
M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, Ö. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision D.01, Gaussian Inc.,
Wallingford, CT, 2009.
Scientific work was financed from the budget for science in
2
010–2013 years as a research project of Ministry of Science and
Higher Education No. N N312 427 639.
Calculations by means of the Gaussian 09 set of codes were car-
ried out in Wrocław Centre for Networking and Supercomputing
(http://www.wcss.wroc.pl). Access to HPC machines and licensed
software is gratefully acknowledged.
References
[
[
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