Synthesis, spectral analysis, and thermodynamic parameters of gold(III) complex in the presence of 4-bromo-2,6-bis(hydroxymethyl)phenol and m-nitroaniline

Article abstract of DOI:10.1007/s00706-019-02498-0

Abstract: In the present study, we synthesized 4-bromo-2,6-bis(hydroxymethyl)phenol (BBHMP), and a gold(III) complex was synthesized in the presence of BBHMP and m-nitroaniline (m-NA). The synthesized complex was characterized using spectral (mass, UV–Vis

Full text of DOI:10.1007/s00706-019-02498-0

Monatshefte für Chemie - Chemical Monthly (2019) 150:1785–1791
https://doi.org/10.1007/s00706-019-02498-0
ORIGINAL PAPER
Synthesis, spectral analysis, and thermodynamic
parameters of gold(III) complex in the presence
of 4‑bromo‑2,6‑bis(hydroxymethyl)phenol and m‑nitroaniline
Özlen Altun · Zeliha Yoruç1
1
Received: 28 March 2019 / Accepted: 20 August 2019 / Published online: 26 September 2019
©
Springer-Verlag GmbH Austria, part of Springer Nature 2019
Abstract
In the present study, we synthesized 4-bromo-2,6-bis(hydroxymethyl)phenol (BBHMP), and a gold(III) complex was syn-
thesized in the presence of BBHMP and m-nitroaniline (m-NA). The synthesized complex was characterized using spectral
1
13
(
mass, UV–Vis, FT-IR, H NMR, C NMR) and thermal measurements (TG–DTA). The results showed that the optimum
3+
conditions for the reactions are pH 7, λ=412 nm and the mole ratio of BBHMP:m-NA:Au is 1:1:1. The reaction of BBHMP
and m-NA with Au(III) was found to be a complexation reaction and one BBHMP molecule and one m-NA molecule react
with one Au(III) molecule. Additionally, the equilibrium constant (K), Gibbs free energy (ΔG), enthalpy (ΔH), and entropy
(
ΔS) were calculated at 298.16 and 313.16 K, respectively. According to the thermodynamic parameters, the reaction was
exothermic because of the decrease in entropy and it was a non-spontaneous process.
Graphic abstract
Keywords Ligand · Au(III) · Structural analysis · Molar composition · Equilibrium constant
Introduction
ligand was synthesized by Chokkanathan and Geetha [2]
using BBHMP and diethylenetriamine with copper(II) pre-
cursors to form copper(II) complexes. In another study [11],
the colorimetric method was deꢀned for naked-eye detection
of ꢁuorine ion in the presence BBHMP which showed a selec-
tive and sensitive ꢁuorescence quenching response towards
ꢁuorine ion among chlorine, bromine and iodine ions.
4
-Bromo-2,6-bis(hydroxymethyl)phenol (BBHMP) is a halo-
genated phenol derivative used for proteomic research and
is obtained from 4-bromophenol, formaldehyde, and NaOH
[1, 2]. Studies on BBHMP date back early 1990s with some
performed more recently [3–10]. For example, a multidentate
m-Nitroaniline (m-NA) [12] is a non-volatile stable solid
with a functional nitro group in meta-position and is used
as a raw material in dyes and as a chemical intermediate
in many synthesis processes [13]. m-NA can enter into
the environment where it undergoes complex transforma-
tions, making the compound a great concern in the ꢀeld
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s00706-019-02498-0) contains
supplementary material, which is available to authorized users.
*
Özlen Altun
ozlenaltun@yahoo.com
1
Department of General and Inorganic Chemistry, Trakya
University, Edirne 22030, Turkey
Vol.:(0
1
123456789)
3

1786
Ö. Altun, Z. Yoruç
of environmental science because of its high toxicity and
suspected carcinogenic role [14, 15].
the absorbance was ꢀxed with pH values above 7 (Fig. 1),
the absorbance value λ=412 nm and the pH value of 7 were
chosen as the working medium [23–27].
There exist a large number of studies involving some
mixed ligand complexes of Au(III) [16–22], but no study
has been performed so far about the complex of Au(III) with
BBHMP and m-NA. In the present study, we synthesized
gold(III) complex in the presence of BBHMP and m-NA,
and determined structural characterization with spectral and
thermal analysis. We also determined reaction conditions,
the composition of the complex and the thermodynamic
parameters using spectral measurements.
Structural analysis of the complex
Elemental analysis of C, H, N, O, and Au is compatible
with the suggested general formula given for BBHMP and
the complex. The molar conductivity of the complex was
calculated with the equation Λm = K/C, where C is the
molar concentration of the complex solution. The Au(III)
complex was dissolved in DMF solvent with a molar con-
−
3
centration of 10 M at 25 °C and used for measurements.
The molar conductivity value of the complex was found
Results and discussion
−
1
−1
2
as 49.6 Ω mol cm . Therefore, this complex can be
regarded as a non-electrolyte complex [28–30]. The mag-
netic moment of the complex was calculated from the cor-
rected magnetic susceptibilities determined at room tem-
perature and was found as 0.00 BM. This result indicates
Determination of the reaction conditions
To determine the wavelength for the reactions, various
solutions with pH values ranging from 1 to 10 of the molar
composition (BBHMP+m-NA) with Au(III) were arranged
8
diamagnetic nature, as expected for low spin d complexes,
3
+
in the mole ratio of 1:1 (Au :BBHMP + m-NA) and the
spectra were recorded at room temperature. The product
produced absorption peaks at λ = 322 and 412 nm. Since
suggesting square–planar geometry for the obtained Au(III)
complex.
The electron impact mass spectrum of gold(III) complex
was used to determine its molecular weight and fragments.
In the mass spectrum of the complex (Fig. 2), the peaks at
m/z = 138.00 (found: 138.14) and 230.12 (found: 230.06)
3,0
2,5
2,0
1,5
1,0
0,5
0,0
+
+
were assigned to [M
] and [M
] , respectively.
m-NA
BBHMP
The peak at m/z = 601.05 (found: 601) is also compatible
+
(
(
λ
λ
)
)
with [M] for the molecular weight of the complex. The
3
22 nm
4
12 nm
overall results of the mass spectrum indicate the presence
of a complexation.
The UV–Vis spectra of the free BBHMP, m-NA and
their Au(III) complex in CHCl revealed absorption peaks
3
between 200 and 500 nm (Fig. 3). The electronic spectra of
the free ligands have two peaks in the UV region for each
ligand [2, 12]. The ꢀrst two peaks at 246 and 247 nm are
assigned to π→π* (phenyl rings) transitions [31], and the
second two peaks at 353 and 358 nm are ascribed to n→π*
because of the long pair electrons of the nitrogen and oxygen
atoms [32]. In the UV–Vis spectrum of the complex, these
transitions are shifted to higher values. The complex has
2
4
6
8
10
pH
Fig. 1 The eꢂect of pH on absorbance
Fig. 2 The mass spectra of the
Au(III) complex
1
3

Synthesis, spectral analysis, and thermodynamic parameters of gold(III) complex in the presence…
1787
4
3
3
2
2
1
1
0
0
,0
,5
,0
,5
,0
,5
,0
,5
,0
Table 1 Thermal analysis data of the Au(III) complex
BBHMP
m-NA
Gold (III) complex
Compound
Steps Tb–Tc/°C Weight loss/℅ Assignments
Au(III) complex 1st
25–200
200–600 45.3
600–900 48.0
6.7
2 H2O
Organic comp.
Au metal
2
3
nd
rd
1
H, C –H and s, 1H, C –H) and –OH (s, 1H, OH) protons,
7 8
1
respectively [2]. The H NMR spectrum of m-NA has pro-
ton signals at 7.52 (s, 1H, C –H), 8.54 (d, 1H, C –H), 7.67
2
4
(
m, 1H, C –H), 8.43 (d, 1H, C –H), and 4.43 ppm (s, 2H,
5 6
1
NH ) [12]. In the H NMR spectra of the Au(III) complex,
2
2
00
250
300
350
400
450
500
the peak observed at 2.41 ppm may be attributed to coordi-
Wavelength/nm
nated water molecules of the complex. The position of the
CH molecules bound to oxygen atoms in the complex is
2
Fig. 3 UV–Vis spectra of the BBHMP, m-NA, and the Au(III) com-
shifted in comparison with that of the free ligand, suggesting
plex
deshielding of the protons of the CH molecules due to its
2
3
+
coordination to Au ion through the ligand oxygen atoms.
Additionally, OH peaks are missing and little shifts are seen
in other values.
three absorption peaks at 412, 322, and 298 nm which are
1
1
1
1
1
1
assigned to A → A , A → B , and A → E transi-
1g
2g
1g
1g
1g
g
1
3
tions, respectively. The peak at 298 nm, corresponding to the
transitional charge transfer from the ligand to the Au(III) ion.
These transitions and assignments show that the complex is
a low spin square–planar complex [33–37].
The C NMR (75 MHz, CDCl ) spectrum of BBHMP
3
shows signals at δ=114.8 (C ), 127.6 (C and C ), 133.3 (C
1
2
6
3
and C ), 156.4 (C ), and 63.2 (C and C ) ppm [2]. For m-
5
4
7
8
1
3
NA, characteristic C NMR signals at 149.3, 121.1, 130.4,
In the FT-IR spectrum of m-NA [12, 32, 38, 39], the
113.9, 148.7, and 108.1 ppm are assigned to C , C , C , C ,
1
2
3
4
−
1
13
peak at 3400 cm due to ν(NH ) stretching vibration was
C , and C , respectively [12]. The C NMR data showed
2
5 6
−
1
obtained at 3434 cm in the complex. The NH stretch-
that the complex was shifted in comparison to BBHMP and
m-NA.
2
ing peak appears to shift to the higher frequencies in the
FT-IR spectrum of complex. The reason for this is that the
The decomposition temperature, percentage mass loss,
and assignments of the complex are presented in Table 1.
In the thermal decomposition of the complex, three decom-
position steps were observed in the temperature range
of 25–900 °C. The first decomposition in the range of
25–200 °C corresponds to the loss of two water molecules
with a mass loss of 6.7%, the second decomposition in the
range 200–600 °C is the decomposition of the organic com-
ponent (45.3%). The remaining compound over 600 °C is
Au (48%). These results show that the complex is in good
agreement with the proposed structure.
3
+
nitrogen atom gives its electrons to Au and makes a coor-
dinated covalent bond. The complex exhibits a broad peak
−
1
at 3400 cm , which was attributed to ν(OH) stretching fre-
quencies of coordinated water molecules [40]. The stretch-
−
1
ing vibrations at 1581, 1247, 2954, and 1347 cm due to
ν(C=C), ν(C–N), ν(CH ), and ν(Ar–NO ), respectively, shift
2
2
to higher wave numbers compared with the free ligands. The
3
+
oxygen atoms in the BBHMP structure that bond with Au
attract electrons of neighboring atoms [2]. This causes the
bonds between neighboring atoms to be more polar. Thus,
functional groups such as ν(C=C), ν(C–N), ν(–CH ), and
2
ν(–NO ) occur at higher frequencies. The occurrence of new
Composition and thermodynamic parameters
of the complex
2
−
1
peaks at 553 and 644 cm in the spectrum of the complex
which may be assigned to ν(Au–N) and ν(Au–O) supports
coordination with the nitrogen and oxygen atoms in the
One maximum for the complex was obtained at diꢂerent
two temperatures from perpetual change graphs using Job’s
method (Fig. 4) [42, 43]. According to Job’s method, the
composition of 1:1 complexes in solution is 0.5. But in our
study, the composition of complex is calculated by extrap-
ν(C–N) and ν(C–O) groups, respectively [41].
1
H NMR (300 MHz, CDCl for BBHMP, m-NA and
3
complex) spectra of free ligands and their Au(III) complex
were recorded to verify the binding of the BBHMP and m-
3
+
3+
3+
NA molecules to the Au ion. For BBHMP, the character-
olation as [Au ]/([Au ] + [BBHMP + m-NA]) ~ 0.471
at 25 °C and ~ 0.492 at 40 °C, respectively. The potential
experimental error may have been caused by laboratory con-
ditions, environmental conditions or UV–Vis device. These
1
istic H NMR signal at δ = 7.13 ppm (s, 1H, C –H and s,
2
1
H, C –H) is assigned to aromatic ring protons. The peaks
6
at 4.20 and 5.64 ppm are attributed to aliphatic –CH (s,
2
1
3

1788
Ö. Altun, Z. Yoruç
(
(
(
(
λ
λ
; 25°C
; 40°C
λ
412 nm, 25 °C
4
4
12 nm
12 nm
y = 0.0744x
0
0
0
0
0
,20
,15
,10
,05
,00
a) 0.4
R² = 0.9981
(
0
0
0
.3
.2
.1
0
1
2
3
4
5
3+
-3
[
Au ] = [BBHMP + m-NA] × 10 /M
λ 412 nm, 40 °C
0
,0
0,2
0,4
3+
0,6
0,8
1,0
(
b) 0.5
y = 0.0762x
R² = 0.9994
3
+
[
Au ]/[Au ] + [BBHMP + m-NA]/M
0
0
0
.4
.3
.2
Fig. 4 The composition of the Au(III) complex
results show that one BBHMP molecule and one m-NA mol-
0.1
0
3
+
ecule react with one molecule of Au ion.
To obtain the equilibrium constant with the help of solu-
tions that give equal absorption, dilution curves were drawn
at the same temperatures. Molar composition (BBHMP+m-
NA) and Au(III) solutions prepared with equal concen-
trations at 25 and 40 °C were diluted at regular intervals
and their absorbances were measured at λ = 412 nm. The
obtained absorbance values of the solutions at diꢂerent
concentrations are shown in Table 2 and Fig. 5. The plots
1
2
3
4
5
3+
-3
[
Au ] = [BBHMP + m-NA] × 10 /M
Fig. 5 The dilution curves for λ412 nm, 25 °C (a) and λ412 nm, 40 °C (b)
3
+
−3
calculated from ([Au ]+[BBHMP+m-NA])=1×10
M
and x shows the concentration of complex formed. The val-
ues of K for the reactions of the mixed ligand with Au(III)
are calculated from the above equations.
3
+
of absorbance (nm) against [Au ]=[BBHMP+m-NA] are
linear.
The equations and the correlation coeꢃcients for 25 and
According to the thermodynamic stability constants,
the values of the changes in ΔG, ΔH, and ΔS were deter-
mined using the following equations:
2
4
0 °C from Fig. 5 were found as y=0.0744 x; R =0.9981
2
and y=0.0762 x; R =0.9994, respectively. In the 1:1 stoi-
chiometric reactions, the equilibrium constant (K) formula
ΔG = −RT ln K,
(2)
[
44] is
ꢀ
ꢁ
ꢀ
ꢁꢀ
ꢁ
ꢀ
ꢁꢀ
ꢁ
K2
K1
T2 − T1
T1 ⋅ T2
ΔH
a1 − x b1 − x
a2 − x b2 − x
ln
=
,
(3)
K =
=
,
(1)
R
x
x
3
+
where a is the concentration of metal ion ([Au ]) which is
1
ΔH − ΔG
3
+
3+
ΔS =
,
(
4)
obtained from [Au ]/([Au ] + [BBHMP + m-NA]), b is
1
T
the concentration of the ligand ([BBHMP+m-NA]) which is
−
1
−1
where R is the gas constant (8.314 J K mol ), T is tem-
perature (K), and K is the equilibrium constant. Thermo-
dynamic parameters for the reaction of the mixed ligand
with Au(III) were recorded using the above equations
(Table 3) [25, 45]. According to Table 3, K and ΔG val-
Table 2 The values of dilution curves of the Au(III) complex
3
+
[
Au ]=[BBHMP+m-
ABS
−
3
NA]×10
−4
−4
ues were calculated as 3.11×10 , 3.10×10 , and 20.019,
λ412, 25 °C
λ412, 40 °C
−
1
2
1.034 kJ mol at 298.16 and 313.16 K, respectively. ΔH
1
2
3
4
5
.66
.66
.66
.66
.66
0.070
0.140
0.222
0.300
0.375
0.075
0.147
0.228
0.307
0.382
−1
and ΔS values of the complex are −0.167 kJ mol , −66.58
−1 −1
and −66.63 J mol
K
at same temperatures, respectively.
1
3

Synthesis, spectral analysis, and thermodynamic parameters of gold(III) complex in the presence…
1789
−
1
Table 3 The thermodynamic parameters of the Au(III) complex
heating rate of 10 °C min . Platinum crucibles with a sam-
ple size of 5–10 mg were used in the analysis.
ΔG/kJ mol−1 ΔH/kJ mol−1 ΔS/J mol−1 K−1
T/K
K
−
−
4
4
2
3
98.16 3.11×10
13.16 3.10×10
20.019
21.034
−0.167
−0.167
−66.58
−66.63
Materials
4
-Bromophenol, formaldehyde, acetic acid, diethyl ether,
m-nitroaniline, and Na[AuCl ]·2H O were obtained from
4
2
Conclusion
Sigma-Aldrich. NaOH, CHCl , and DMF were obtained
3
from Merck and used as supplied.
In the present paper, a gold(III) complex was synthesized
in the presence of 4-bromo-2,6-bis(hydroxymethyl)phenol
4‑Bromo‑2,6‑bis(hydroxymethyl)phenol (1) The reaction
3
(
BBHMP) and m-nitroaniline (m-NA) and characterized
mixture, including an aquatic solution (15 cm ) of 0.04 g
with elemental analysis, magnetic susceptibility, conduc-
NaOH (1 mmol) and 0.173 g 4-bromophenol (1 mmol)
1
13
3
tivity, mass, UV–Vis, FT-IR, H NMR, C NMR, and
TG–DTA. The results of the physical, spectral, and thermal
analysis showed that the reaction of BBHMP and m-NA with
Au(III) is a complex reaction. One molecule of BBHMP and
was stirred for 30 min. Then 30.15 cm formaldehyde (7%,
2 mmol) was added and stirred for 1 week. At the end of
1 week, the product was dissolved in water and concentrated
acetic acid was added dropwise to pH 5 on the magnetic stir-
rer. The obtained white solid precipitate was washed with
water and diethyl ether and dried in vacuum [2] (Scheme 1).
White solid; yield: 0.198 g (85%); m.p.: 152 °C; NMR spec-
tra agree with the ones described in Ref. [2].
3+
one molecule of m-NA react with one molecule of Au ion.
The formula of the complex is predicted to be in the form
of [Au(BBHMP)(m-NA)]·2H O. Considering the thermo-
2
dynamic parameters, the negative value of ΔS and the posi-
tive value of ΔG mean that the process is non-spontaneous
and the negative value of ΔH shows that a certain amount
of energy is released during the reaction. As a result, the
enthalpy contribution changes slightly with temperature and
the reaction is entropy controlled.
4‑Bromo‑2,6‑bis(hydroxymethyl)phenol m‑nitroani‑
line gold(III) dihydrate ([Au(BBHMP)(m‑NA)]∙2H O, 2,
2
C H AuBrN O ) 0233 g BBHMP (1 mmol), 0.12 g NaOH
1
4
16
2 7
(3 mmol), and 0.126 g m-NA (1 mmol) were dissolved in
3
2
5 cm ethanol. Then 0.398 g Na[AuCl ]·2H O (1 mmol)
4
2
was added and reꢁuxed for 5 h at 75–80 °C. A solid, dark
yellow product was obtained, washed with water, and dried.
The complex was soluble in certain organic solvents such
Experimental
as CHCl and DMF. Dark yellow solid; yield: 0.450 g
3
Physical measurements
(75%); m.p.: 141 °C; UV–Vis: λ = 298, 322, 412 nm;
FT-IR (KBr):=3400 (OH), 3434 (NH ), 1581 (C=C), 1247
2
Elemental analysis for C, H, O, and N were carried out with
a Costech ECS 4010 CHNSO elemental analyzer and an
ICP-MS 7700 X (Agilent) analyzer was used for Au metal.
The magnetic moment measurements were recorded using a
MK-1 Sherwood scientiꢀc magnetic susceptibility balance.
Conductivity experiments were completed in DMF with an
Inolab Thermal 740P. pH measurements were made with
a calibrated Metrohm 654 digital pH meter with a Senso-
rex combination pH glass electrode assembly. Mass spectra
were investigated on an AB-SCIEX Triple TOF 4600 Sys-
tem. UV–Vis spectra were determined using a Shimadzu
UV-1700 Pharma spectrophotometer in the wavelength
range of 200–800 nm. FT-IR spectra were measured in trans-
mission mode using a Shimadzu FT-IR-470 spectrometer in
(C–N), 2954 (CH ), 1347 (Ar–NO ), 553 (AuN), 644 (AuO)
2
2
−
1 1
cm ; H NMR (300 MHz, CDCl ): δ=6.77 (s, 1H), 7.42
3
(s, 1H), 7.32 (d, 1H), 6.90 (m, 1H), 6.77 (s, 1H), 7.24 (d,
1
3
1H), 4.36 (s, 2H), 2.41 (s, 2H) ppm; C NMR (75 MHz,
CDCl ): δ = 115.9 and 152.3 (C ), 131.1 and 122.7 (C ),
3
1
2
135.7 and 132.8 (C ), 159.7 and 114.2 (C ), 135.7 and
3
4
150.1 (C ), 131.1 and 107.5 (C ), 69.1 (C ), 69.1 (C )
5
6
7
7
] ,
+
ppm; ESI–MS: m/z = 138.00 (found: 138.14) [M
m-NA
+
230.12 (found: 230.06) [M
] , 601.05 (found: 601)
BBHMP
+
[M] ; magnetic moment: diamagnetic; molar conductivity:
−
1
2
−1
49.6 Ω cm mol ). Accordingly, the reaction as shown in
Scheme 2 was determined.
Composition of the complex
−
1
the wavenumber range of 4000–400 cm . KBr was used
1
13
as the matrix material for pellets. H NMR and C NMR
For the investigation of the composition and equilibrium
constant of the complex, the methods of Job [42, 43] and
Turner & Anderson [44] were used. Various solutions
spectra were determined in CDCl on a Bruker DPX-400
3
spectrometer. TG/DTA curves were obtained with a Seiko
Exstar TG/DTA 6200 thermal analyzer in the temperature
range of 25–1200 °C in static atmosphere of dry air with a
−
3
were prepared with total concentrations of 1 × 10 M,
containing the molar composition (BBHMP + m-NA)
1
3

1790
Ö. Altun, Z. Yoruç
Scheme 1
Scheme 2
3
+
and Au(III) at room temperature and 40 °C. [Au ]/
3. Crane JD, Fenton DE, Latour JM, Smith AJ (1991) J Chem Soc
Dalton Trans 11:2979
3
+
(
[Au ] + [BBHMP + m-NA]) values were calculated and
4
5
.
.
Reim J, Kreb B (1997) J Chem Soc Dalton Trans 20:3793
Yonemura M, Matsumura Y, Furutachi H, Ohba M, Okawa H
(1997) Inorg Chem 36:2711
the absorbances were measured at λ = 412 nm. Then, the
perpetual change graphs for absorbance measurements
3
+
3+
against [Au ]/([Au ]+[BBHMP+m-NA]) were plotted.
Composition of the complex was found from the maximum
values of these graphs.
6. Amudha P, Kandaswamy M, Govindasamy L, Velmurugan D
(
1998) Inorg Chem 37:4486
Amudha P, Akilan P, Kandaswamy M (2000) Polyhedron
9:1769
7
.
1
8
.
Paine RT, Tan YC, Gan XM (2001) Inorg Chem 40:7009
Acknowledgements This study was ꢀnancially supported by Trakya
9. Yonemura M, Arimura K, Inoue K, Usuki N, Ohba M, Okawa
H (2002) Inorg Chem 41:582
University. Research Fund (TUBAP, project # 2016/72).
1
0. Rajendiran TM, Kannappan R, Mahalakshmy R, Rajeswari J,
Venkatesan R, Rao P (2003) Trans Metal Chem 28:447
1. Tavallali H, Deilamy-Rad G, Tabandeh M (2011) Chin Chem
Lett 22:193
1
1
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