Comprehensive comparison between the reaction of N,N'-cyclohexane-1,2-diylidene-bis(4-methoxybenzoylhydrazide) with mercury(II) and copper(II) ions. Synthesis, structure, and kinetics of complex formation

Article abstract of DOI:10.1134/S1070328417020014

Comprehensive comparison between the reaction of N,N'-cyclohexane-1,2-diylidene-bis(4-methoxybenzoylhydrazide) (CHMBH) with HgCl₂ and Cu(NO₃)₂ · 2.5H₂O salts have been investigated, including the synthesis, structure and kinetic of complex formation. The reactions of CHMBH with HgCl₂ or Cu(NO₃)₂ · 2.5H₂O at the same synthetic conditions have been shown to produce completely different type of complexes: [Hg(CHMBH)Cl₂] · CH₃CN (I) and [Cu₃(μ₃-OH)(CTMB)₃(NO₃)₂(CH₃CN)₂] · 5CH₃CN · H₂O (II) (CTMB = cyclohexotriazole-3-(4-methoxybenzamide)). The prepared compounds were characterized using different techniques (NMR, IR, UV-Vis and mass spectroscopies, microelemental analysis, thermogravimetry as well as X-ray powder differection and X-ray single crystal crystallography for I (CIF file CCDC no. 1503398). X-ray crystallography shows that the isolated product of I is a mononuclear complex which contains the [Hg(CHMBH)]²⁺ core. While, the isolated product of II was a trinuclear Cu(II) cluster [Cu₃(μ₃-OH)(CTMB)₃(NO₃)₂(CH₃CN)₂] · 5CH₃CN · H₂O which contains three differently coordinated copper sites. Kinetic studies on the formation of I have been also investigated and compared with that of II. In case of I, the reaction was so slow and exhibits a first-order dependence on the concentration of metal salt and a first-order dependence on the concentration of CHMBH. While in II, the study shows that the reaction is fast and occurs in three distinct phases.

Full text of DOI:10.1134/S1070328417020014

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2017, Vol. 43, No. 2, pp. 113–126. © Pleiades Publishing, Ltd., 2017.
Comprehensive Comparison between the Reaction
of N,N'-Cyclohexane-1,2-Diylidene-Bis(4-
Methoxybenzoylhydrazide) with Mercury(II) and Copper(II) Ions.
Synthesis, Structure, and Kinetics of Complex Formation1
A. J. M. Al-Karawi
Al-Mustansiriya University, College of Science, Department of Chemistry, Baghdad, 46010 Iraq
e-mail: a_jasim2006@yahoo.com
Received November 23, 2015
Abstract—Comprehensive comparison between the reaction of N,N'-cyclohexane-1,2-diylidene-bis(4-
methoxybenzoylhydrazide) (CHMBH) with HgCl2 and Cu(NO3)2 · 2.5H2O salts have been investigated,
including the synthesis, structure and kinetic of complex formation. The reactions of CHMBH with HgCl2
or Cu(NO3)2 · 2.5H2O at the same synthetic conditions have been shown to produce completely different type
of complexes: [Hg(CHMBH)Cl2] · CH3CN (I) and [Cu3(μ3-OH)(CTMB)3(NO3)2(CH3CN)2] · 5CH3CN ·
H2O (II) (CTMB = cyclohexotriazole-3-(4-methoxybenzamide)). The prepared compounds were charac-
terized using different techniques (NMR, IR, UV-Vis and mass spectroscopies, microelemental analysis,
thermogravimetry as well as X-ray powder differection and X-ray single crystal crystallography for I (CIF file
CCDC no. 1503398). X-ray crystallography shows that the isolated product of I is a mononuclear complex
which contains the [Hg(CHMBH)]2+ core. While, the isolated product of II was a trinuclear Cu(II) cluster
[Cu3(μ3-OH)(CTMB)3(NO3)2(CH3CN)2] · 5CH3CN · H2O which contains three differently coordinated
copper sites. Kinetic studies on the formation of I have been also investigated and compared with that of II.
In case of I, the reaction was so slow and exhibits a first-order dependence on the concentration of metal salt
and a first-order dependence on the concentration of CHMBH. While in II, the study shows that the reaction
is fast and occurs in three distinct phases.
Kyewords: bisaroylhydrazones, kinetics of complex formation, mononuclear mercury(II) complexes,
{Cu3(μ3-OH)} core
DOI: 10.1134/S1070328417020014
INTRODUCTION
anti-tubercular, anticancer, and antitumor as well as a
new drug development [11, 12].
In general, there has been an increased interest in
hydrazide and their derivatives, particularly in the last
few years, related to their coordinative and pharmaco-
logical activity as well as their use in analytical chem-
istry as metal-extracting agents [1, 2]. Benzohydrazide
and their derivatives are polyfunctional molecules
(containing multifunctional groups in their structures
Reaction of aroylhydrazide with dialdehyde or
diketone produces bisaroylhydrazones [9, 10].
Bisarnoylhydrazones are known to be a class of versa-
tile ligands, capable of generating different molecular
architectures and coordination polyhedral [13, 14].
Furthermore, bisaroylhydrazones have the potential-
ity of being oxidatively cyclized to 1,2,3,4-tetrazine,
like –CO, –NH–, and –NH2) [3–5]. Due to that, a 1,3,4-oxadiazine or 1,2,3-triazine derivatives [10].
Continuation of our previous studies [15–17], this
work focus on the synthesis and characterization of
N,N'-cyclohexane-1,2-diylidene-bis(4-methoxyben-
zoylhydrazide) (CHMBH). This molecule coordi-
nates to Hg2+ ion and mononuclear complex
[Hg(CHMBH)Cl2] · CH3CN (I) is obtained. X-ray
crystallography shows that the isolated product con-
tains the [Hg(CHMBH)]2+ core in which CHMBH
acts as a planar quadridentate ligand. The remainder
of the coordination sphere comprises anionic ligands
wide range of compounds have been prepared based
on benzohydrazide derivatives [6–10]. Among all of
these, aroylhydrozones (Schiff bases) represent one of
the most known and important compounds. These
compounds possessing an azomethine –NHN=CH–
proton constitutes an important class of compounds
for different biological activities: antimicrobial, anti-
convulsant, analgesic, antiinflammatory, antiplatelet,
1
The article is published in the original.
113

114
AL-KARAWI
(chloride) derived from the parent metal salt. In con- tons—3.84 (OCH3, s., 6H), 10.93 (NH-keto form, s.,
trast, with Cu2+ ion [17] and under the same condi-
tions of preparation, the isolated product was a trinu-
1H), 14.33 (OH-enol form, s., 1H). 13C{1H} NMR
spectrum (δ, ppm): 21.76–34.41 (cyclohexane car-
bons), 56.17 (OCH3), 114.34–131.14 (aromatic car-
bons), 153.17 (C=N), 163.11 (C=O). IR spectrum (ν,
cm–1): 3365 w.m ν(NH); 3059 w ν(C–Har); 2986 w
νas(C–H) of CH3; 2946 w νas(C–H) of CH2); 2873 w
νs(C–H) of CH3; 2833 w νs(C–H) of CH2; 1678 s
ν(C=O); 1602, 1575 m ν(C=Car; 1528 m ν(C=N);
1486 m δ(CH) of CH2; 1364 w δ(CH) of CH3; 1240 v.s
ν(C–O).
clear
Cu(II)
cluster
[Cu3(μ3-
OH)(CTMB)3(NO3)2(CH3CN)2] · 5CH3CN · H2O
(II) (CTMB = cyclohexotriazole-3-(4-methoxyben-
zamide)) which contains three differently coordinated
copper sites.
Kinetic studies on the formation of complexes I
and II suggests the factors that lead to formation of the
two types of products.
Synthesis of I. To a solution of CHMBH (0.15 g,
0.367 mmol) in CH3CN (40 cm3) was added a solution
EXPERIMENTAL
of HgCl2 (0.1 g, 0.367 mmol) in CH3CN (5 cm3). The
solution was not stirred, and after leaving undisturbed
for 1 day, yellow crystals were deposited. The crystals
were removed by filtration, washed with CH3CN and
dried in vacuo. The yield was 0.2 g (78%), m.p. = 214–
216°C.
Materials and methods. All reagents were commer-
cially available and used without further purification,
(1,2-cyclohexanedione 97%, Aldrich Co.), (4-
methoxybenzhyrazide, Aldrich Co.), (acetic acid
100%, Aldrich Co.), (HgCl2 99.5%, Acros Organics
Co.). Solvents used in the syntheses were distilled
from the appropriate drying agent immediately prior
to use. All manipulations in the synthesis of the com-
pounds were performed under air. Infrared spectra
were recorded using a Cary 630 FTIR spectrometer
equipped with an ATR module. 1H and 13C{1H} NMR
spectra were carried out in DMSO-d6 using a Varian
(Agilent) 400 MHz spectrometer. Mass spectrum was
obtained by using a Waters Acquity UPLC with TQD
detector. Elemental analyses (C, H, and N) were car-
ried out on an EuroEA Elemental Analyzer, (Hg) was
performed by the Mikroanalytisches Labor Egmont
Pascher (an der Pulvermühle 3, 53424 Remagen, Ger-
many). Electronic spectra were recorded with a Shi-
madzu UV-3101PC spectrophotometer. X-ray powder
For (C22H24N4O4Cl2Hg)2
anal. calcd., %: C, 38.9; N, 8.2;
Found, %: C, 38.7; N, 8.1;
H, 3.6; Hg, 29.5.
H, 3.8; Hg, 29.1.
1H NMR spectrum (δ, ppm): cyclohexane protons—
1.80 (CH2, m., 4H), 2.91 (CH2, t., 4H, JHH = 3.1 Hz),
aromatic protons—7.09 (CH, d., 4H, JHH = 8.5 Hz),
7.925 (CH, d., 4H, JHH = 8.5 Hz), other protons—
3.86 (OCH3, s., 6H), 11.54 (NH, s., 2H). 13C{1H}
NMR spectrum (δ, ppm): 21.21–32.56 (cyclohexane
carbons), 54.41 (OCH3), 112.66–129.31 (aromatic
carbons), 151.18 (C=N), 161.28 (C=O). IR spectrum
(ν, cm1): 3263 w.m ν(NH); 3071 w ν(C–Har); 2972 w
νas(C–H) of CH3; 2946 w νas(C–H) of CH2; 2879 w
νs(C–H) of CH3; 2840 w νs(C–H) of CH2); 1657 s
ν(C=O); 1598, 1575 m ν(C=Car; 1528 m ν(C=N);
1458 m δ(CH) of CH2); 1353 w δ(CH) of CH3; 1248
v.s ν(C–O).
diffraction patterns were obtained with
a
Shimadzu 6000 diffractometer using CuKα radiation
(λ = 1.54178 Å). Thermogravimetry (TG) and differ-
ential thermogravimetry (DTG) of the compounds (in
the ranges of 20–600°C for I and 30–900°C for II)
were carried out at a heating rate of 10.0 Κ/min by
using (Linseis STA PT-1000) for I and (PerkinElmer
4000) for II.
Synthesis of II [17]. To a solution of CHMBH
(0.15 g, 0.367 mmol) in CH3CN (40 cm3) was added a
solution of Cu(NO3)2 · 2.5H2O (0.085 g, 0.367 mmol)
Synthesis of CHMBH. This compound was pre-
pared according to our previous study [17]. The yield
was 1.7 g (93%), m.p. = 208–210°C.
in CH3CN (5 cm3). The solution was not stirred and
the colour which was initially dark brown, slowly
changed with time through dark brown, dark green,
light green and finally bright green. Leaving the solu-
tion undisturbed produced blue prism crystals after
24 h. The crystals were removed by filtration, washed
with CH3CN and dried in vacuo. The yield was 0.1 g
(57%).
For C22H24N4O4
anal. calcd., %:
Found, %:
C, 64.7;
C, 64.6;
N, 13.7;
N, 13.5;
H, 5.9.
H, 5.8.
1H NMR spectrum (δ, ppm): cyclohexane pro-
tons—1.73 (CH2, m., 4H), 2.61 (CH2, t., 2H, JHH
=
3.1 Hz), 2.81 (CH2, t., 2H, JHH = 3.1Hz), aromatic
protons—7.02 (CH, d., 2H, JHH = 8.9 Hz), 7.07
For C102H127N37O27Cu6
anal. calcd., %: C, 45.6; N, 19.3; H, 4.8; Cu, 14.2.
(CH, d., 2H, JHH = 8.9 Hz), 7.96 (CH, d., 2H, JHH
=
Found, %:
C, 45.4, N, 19.0; H, 4.6; Cu, 13.8.
8.9 Hz), 8.19 (CH, d., 2H, JHH = 7.3 Hz), other pro-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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COMPREHENSIVE COMPARISON BETWEEN THE REACTION
Table 1. Crystallographic data and structure refinements for complex I
115
Chemical moiety
Formula weight
Wavelength, Å
Crystal size, mm
Crystal system
Space group
Unit cell dimensions:
a, Å
(C22H24N4O4Cl2Hg)2(C2H3N)
1400.9
0.71073
0.32 × 0.26 × 0.12
Triclinic
P1
11.2103(15)
11.8606(16)
19.223(3)
86.901(5)
76.165(4)
75.252(4)
2399.9(6)
b, Å
c, Å
α, deg
β, deg
γ, deg
Volume, Å3
Temperature, K
120(2)
51449
Reflections collected
Independent reflections (Rint
)
16148 (0.0268)
13435
Observed reflections with I >2σ(I)
Absorption correction
Trans max/min
Semi-empirical from equivalents
0.5013/0.2238
0.111(11)
Flack parameter
Full-matrix least-squares on F2
R1 = 0.0245; wR2 = 0.0481
R1 = 0.0360; wR2 = 0.0515
1.801 and –1.164
Refinement method
Final R indices I > 2σ(I)
R indices (all data)
Largest diff. peak and hole, e Å–3
IR spectrum (ν, cm–1): 3600–3300 br, ν(OH);
3059 w ν(C–Har); 2989 w νas(C–H) of CH3; 2939 w
νas(C–H) of CH2; 2860 w νs(C–H) of CH3; 2833 w
νs(C–H) of CH2; 1603, 1585 m ν(C=Car); 1510 s
ν(C=N); 1456 w δ(CH) of CH2; 1360 m δ(CH) of
CH3; 1246 v.s ν(C–O).
device. Unit cell constants and orientation matrix were
improved by least-squares refinement of reflections
thresholded from the entire dataset. Integration was
performed with SAINT [20], using this improved unit
cell as a starting point. Precise unit cell constants were
calculated in SAINT from the final merged dataset.
Lorenz and polarization corrections were applied.
Multi-scan absorption corrections were performed
with SADABS [21]. Data were reduced with
SHELXTL [22]. The structure was solved by direct
methods without incident. Hydrogen atoms were
located in idealized positions and were treated with a
riding model. All non-hydrogen atoms were assigned
anisotropic thermal parameters. Refinements contin-
X-ray crystallography. A crystal of I was analyzed
with a Bruker APEX II system using MoKα radiation.
Data collection was carried out using APEX2 software
[18]. Initial cell constants were found by small widely
separated “matrix” runs. The data collection strategy
was determined using COSMO [19]. Scan speed and
scan widths were chosen based on scattering power
and peak rocking curves. Data were collected at –
153°C using an Oxford Cryostream low-temperature ued to convergence, using the recommended weight-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 43 No. 2 2017

116
AL-KARAWI
Table 2. Selected bond lengths in I
Bond
d, Å
Bond
d, Å
Complex A
Complex B
Hg(1)–O(27)
Hg(1)–O(37)
Hg(1)–N(11)
Hg(1)–N(12)
Hg(1)–Cl(1)
Hg(1)–Cl(2)
C(11)–N(11)
C(12)–N(12)
C(27)–N(27)
C(37)–N(37)
C(27)–O(27)
C(37)–O(37)
C(11)–C(12)
C(21)–C(27)
C(31)–C(37)
N(11)–N(27)
N(12)–N(37)
2.674(2)
2.652(2)
2.452(2)
2.446(2)
2.4137(6)
2.3779(6)
1.291(3)
1.281(3)
1.381(3)
1.376(3)
1.211(3)
1.218(3)
1.480(4)
1.487(4)
1.478(4)
1.362(3)
1.365(3)
Hg(2)–O(27)
2.683(2)
2.649(2)
2.449(2)
2.419(2)
2.3830(6)
2.4187(6)
1.280(3)
1.286(3)
1.374(3)
1.375(3)
1.220(3)
1.216(3)
1.493(4)
1.480(4)
1.484(4)
1.371(3)
1.370(3)
Hg(2)–O(37)
Hg(2)–N(11)
Hg(2)–N(12)
Hg(2)–Cl(3)
Hg(2)–Cl(4)
C(11)–N(11)
C(12)–N(12)
C(27)–N(27)
C(37)–N(37)
C(27)–O(27)
C(37)–O(37)
C(11)–C(12)
C(21)–C(27)
C(31)–C(37)
N(11)–N(27)
N(12)–N(37)
ing schemes. The crystallographic data for I are sum- in an excess over the concentration of the metal ion
marized in Table 1. Selected bond lengths are listed in
Table 2.
[23]. The dependence on the concentration of
CHMBH was determined from plots of kobs versus
[CHMBH].
Supplementary material for structure I has been
deposited with the Cambridge Crystallographic Data
Centre (ССDС no. 1503398; deposit@ccdc.
cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
Kinetic studies. Kinetic studies for the reaction of
CHMBH with HgCl2 were performed using a Shi-
madzu UV-3101PC spectrophotometer. The experi-
ments were conducted in air at 25.0°C. The wave-
length used was λ = 410 nm. Stock solutions of HgCl2
and CHMBH were prepared in MeCN (freshly dis-
tilled from CaH2 under an atmosphere of dinitrogen),
and more dilute solutions were prepared from these
stocks. The absorbance-time traces were fitted to
exponential curves using the Applied Photophysics
software. The observed rate constants (kobs) are the
average of at least three experiments. The error bars
presented in the figures show a 10% reproducibility.
All experiments were performed under pseudo first-
CHMBH was prepared by the condensation reac-
tion between 1,2-cyclohexanedione and 4-methoxy-
benzhydrazide in methanol. The reaction of CHMBH
with HgCl2 or Cu(NO3)2 · 2.5H2O in the same condi-
tions have been shown to produce different type of
complexes. The reaction of equimolar amount of
CHMBH and HgCl2 in acetonitrile and ambient con-
ditions produced a mononuclear complex I. While,
the reaction of equimolar amount of CHMBH and
Cu(NO3)2 · 2.5H2O in acetonitrile and ambient condi-
tions proceeds through a variety of colour changes and
the ultimate isolated product is the trinuclear Cu(II)
cluster II [17]. Synthetic routes for I and II are shown
order conditions with the concentration of CHMBH in Scheme 1:
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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COMPREHENSIVE COMPARISON BETWEEN THE REACTION
117
NH
O
N
N
NH
O
O
O
MeCN
RT
HgCl2
⋅
Cu(NO3)2 2.5H2O
MeCN
RT
H
N
H
N
H
N
H
N
N
N
N
N
O
O
O
O
+
Hg1
Hg2
O
O
O
O
Cl
Cl
Cl
Cl
b
a
(I)
O
O
O
O
N
N
N
C
N
C
N
N
NH Cu1
NH Cu4
B
N
N
B
N
N
NH
NH
OH
Cu2
OH
Cu5
N
N
A
A
Cu3
A
Cu6
A
+
O
O
O
O
NH
NH
N
N
N
N
O
O
N
N
O
O
a
b
(II)
A = MeCN, B = NO3 (bridge), C = NO3 (monodentate)
Scheme 1.
coordination of C=O to Hg2+ through oxygen atom.
This was further confirmed by X-ray crystallography.
Mass spectrum of CHMBH showed the parent ion
peak at m/z = 409, which corresponds to M+ (Fig. 1).
In order to study the binding mode of the ligand
CHMBH to the mercury or copper atom, the IR spec-
trum of the free ligand was compared with the spectra
of compounds I and II. The IR spectrum of CHMBH
shows three characteristic bands at (3365, 1678, and
1528 cm–1). These can be assigned to the stretching
vibrations of NH, C=O, and C=N groups, respec-
tively [24]. In the spectra of I and II, the following
aspects have been observed: (i) the ν(C=O) mode at
1678 cm–1 which was observed in the spectrum of
CHMBH is found to shift to lower wave number in the
spectrum of I (1657 cm–1), which may indicats the
The 1H and 13C{1H} NMR spectra of CHMBH and
I displayed signals corresponding to the various proton
and carbon nuclei (see Experimental and Fig. 2).
1
Moreover, in the H NMR spectrum of CHMBH
(Fig. 2a), two singlet signals are observed at 10.93 and
14.33 ppm. These signals are assigned to the protons of
NH and OH groups, respectively, consistent with the
1
keto-enol tautomerism of CHMBH [17]. In the H
NMR spectrum of I (Fig. 2b), the signal belong to the
proton of OH group (enol form) was disappeared. This
observation indicate that no delocalization will further
occur between C=O and C–N groups, because of the coordination of (C=O) to Hg2+ ion; while in the spec-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 43 No. 2 2017

118
AL-KARAWI
409.31
100
Scan ES+
6.80e7
410.32
391.30
411.33
412.31
431.30
447.29465.24
257.22
407.32
230.17
527.37
243.19
202.20
284.24 301.24 329.27 351.32 379.32
491.25 514.35
0
200
240
280
320
360
400
440
480
520
m/z
Fig. 1. Mass spectrum of CHMBH.
trum of II, this mode is completely disappeared, indi- two complexes have almost the same structure). The
cating the enolization of (C=O) followed by deproton- structure clearly shows that CHMBH acts as a qua-
ation and complexation with copper ions; (ii) the dridentate ligand with the two imine nitrogen atoms
ν(C=N) mode of free ligand at 1528 cm–1 is found to
shift to lower wave number in the spectrum of II
(1510 cm–1), while no change in the position was
observed for this mode in the spectrum of I. The
details of the bands and their assignments can be
found in Experimental part.
and two oxygen atoms coordinating to the metal. The
CHMBH ligand is effectively planar, presumably
because of the inflexibility in this ligand due to the
extensive multiple bonding. The overall geometry is
best described as octahedral (Hg is six coordinated)
with the two imine nitrogen atoms and the two oxygen
atoms of the CHMBH ligand occupying the basal
positions and two chloro ligand occupying the apical
site. Previous studies [9] on other Schiff base benzohy-
drazide complexes have reported the X-ray crystal
structures of [Ni(benzohydrazone-2H+)] in which the
Schiff base benzohydrazone ligand (BBH) is depro-
tonated at the hydrazide atoms. BBH has the following
structure:
The spectrum of CHMBH exhibited two absorp-
tion peaks at 274 (νmax = 14200) and 338 nm (νmax
=
7800 dm3 mol–1 cm–1) attributable to the (π–π*) and
(n–π*) transitions, respectively. The spectra of I and
II caused bathochromic shift of ligand band related to
the (π–π*) transition. This band was appeared at 335
(νmax = 18200) and 320 nm (νmax = 18000 dm3 mol–1
cm–1) for I and II, respectively. No band related to (n–
π*) transition could be clearly observed in the spec-
trum of II. The band may be hidden by (π–π*) band.
But in the spectrum of I a shoulder with low intensity
is detected at 430 nm (νmax = 1180 dm3 mol–1 cm–1),
which can be attributed to this transition. The appear-
ance of new medium intensity band at lower wave
Ph
Ph
NH
O
N
N
NH
O
Ph
Ph
BBH =
Thus, in the structure of [Ni(BBH)], the average of
the two C–N hydrazide bond lengths is 1.329 Å and
the average C–O bond length is 1.299 Å. A compari-
son with the analogous bond lengths for
[Hg(CHMBH)Cl2] presented in Table 2 shows that
the C–O distance in the CHMBH complex is signifi-
cantly shorter than in the deprotonated BBH complex.
Similarly, the C–N hydrazide bond length in the
CHMBH complex is appreciably longer than in the
BBH complex. These observations indicate that,
whilst there is delocalisation in the BBH ligand, and
both the C–N and C–O bonds have partial double
numbers 385 (νmax = 11000 and 373 nm (νmax
=
10800 dm3 mol–1 cm–1) for I and II, respectively, were
observed slightly separated from the intraligand (π–
π*) band. These bands were attributed to charge trans-
fer transition. A further broad band with low extinc-
tion coefficient is observed in the visible and near IR
regions (580–1000 nm, νmax = 1600 dm3 mol–1 cm–1)
in the spectrum of II. This broad band was assigned
to ligand field d–d transitions. No ligand field transi-
tions are observed in the spectrum of I because of
filled d-orbital [25–27].
The X-ray structure of I is shown in Fig. 3, which bond character, in the CHMBH ligand, the C–O
consist of two independent complexes: A and B (the bond has more double bond character and the C–N
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COMPREHENSIVE COMPARISON BETWEEN THE REACTION
119
23a, 25a 17a, 19a
1a, 2a, 1b, 2b
6a, 6b
1.91
3a, 3b
1.94
3.96
1.90 1.87
(a)
7.15 7.10 7.05 7.00 6.95
2.8 2.7 2.6
1.75 1.70
16a, 20a
22a, 26a
H
H
2a 1a
H
H
1b
2b
2
1
0.20
0.15
0.10
0.05
0
H
H
6a
3a
3
6
H
H
4
5
H
3b
6b
H
H
H
19a
19 20
20a
22a
22 23
H3C
28
1.78
1.93
N
8
N
N
11
NH
12
23a
7
CH3
30
18
15
9
O
13 21
24
O
27
29
17 16
OH
10
8.25
8.00
26 25
O
14
H
H
H
H
25a
16a
17a
26a
0.77
0.95
6.00
15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
δ, ppm
20a, 22a, 25a, 29a
20a, 22a, 26a, 28a
(b)
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
H
H
7.75
7.50
7.25
7.00
9a 10a
H
H
10
9b
9
10
H
H
8a
8
11 11a
H
H
7
12
H
8b
11b
H
H
H
22a
22 23
23a
25a
25 26
26a
H3C
31
HN
N
6
N
13
NH
5
CH3
14
15 24
33
9a, 9b, 10a, 10b
8a, 8b, 11a, 11b
21
18
4
O
27
O
Hg
30
32
2
20 19
29 28
O
O
1
3
Cl
16
Cl
17
H
H
H
H
28a
19a
20a
29a
1.25
3.64 3.90
6.00 3.84
3.96
15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
δ, ppm
1
Fig. 2. H NMR spectra of CHMBH (a) and I (b).
(hydrazide) bond more single bond character. This tively [17]. But the structure of these molecules is
was further confirmed by 1HNMR spectroscopy.
Similarly, the asymmetric unit of II contains two
independent molecules (Fig. 4)—A and B, respec-
completely different from that of I. The structure of
each molecule comprises a triangle of Cu(II) atoms,
centered around μ3-OH, to form {Cu3(μ3-OH)} motif.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 43 No. 2 2017

120
AL-KARAWI
(a)
C(15)
C(14)
C(13)
C(16)
C(11)
C(22)
C(21)
C(23)
C(12)
O(24)
N(27)
C(32)
N(37)
N(11)
Hg(1)
C(24)
C(25)
N(12)
C(31)
C(38)
C(33)
C(28)
C(27)
O(27)
Cl(2)
C(26)
C(37)
C(36)
C(34)
O(37)
O(34)
Cl(1)
C(35)
(b)
C(26)
C(25)
C(24)
Cl(3)
Cl(4)
O(27)
C(27)
O(24)
C(28)
O(37)
C(35)
Hg(2)
C(38)
C(37)
C(23)
C(34)
C(33)
C(36)
C(21)
N(27)
N(11)
N(37)
C(12)
C(22)
C(31)
N(12)
O(34)
C(11)
C(32)
C(16)
C(13)
C(14)
C(15)
Fig. 3. Ball and stick representation of the two independent complexes A (a) and B (b) in I.
The {Cu3(μ3-OH)} core is supported by three triazole cules. No weight loss could be detected in the ther-
mgram of I at this range of temperatures. These
facts get in agreement with the X-ray single crystal
data for the structures of I and II.
benzamide ligands [17].
The experimental powder diffraction and the cal-
culated pattern from the crystal data of I show a close
correspondence.
Thermal thermograms (TG and DTG) of I and
II are illustrated in Figs. 5a and 5b, respectively.
The curve of II shows significant weight loss at the
range 50–200°C, which revealed to the presence of
Our previous studies on Schiff base thiosemicarba-
zone complexes, [Cd(CHMTSC)(NO3)]+ (III) [15]
and [Cd(PHMTSC-2H+)] (IV) [16] have reported the
kinetics of the reactions of CHMTSC or PHMTSC
hydrate water and coordinated acetonitrle mole- with Cd2+ ion:
H3C
NH
NH
HN
N
N
Cd
NH
N
N
N
N
S
S
Cd
CH3
O
O
S
S
H3C
NH
NH
N
H3C
[Cd(PHMTSC-2H+)]
O
[Cd(CHMTSC)(NO3)]+
The rate constant of the reactions were determined have been proposed. In the current work, the kinetic of
and the mechanism of the formation of the complexes the reaction of CHMBH with Hg2+ has been investi-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
Vol. 43
No. 2
2017

COMPREHENSIVE COMPARISON BETWEEN THE REACTION
(a)
121
O(64)
C(68)
C(64)
C(63)
C(62)
C(65)
C(66)
C(61)
C(16)
C(17)
N(67)
N(53)
O(67)
C(18)
C(15)
C(19)
O(74)
C(67)
C(55)
C(56)
C(57)
C(14)
N(13)
Cu(1)
N(11)
C(54)
N(52)
N(12)
O(71)
O(75)
C(59)
N(51)
O(72)
Cu(3)
O(47)
N(27)
C(27)
N(81)
O(27)
C(58)
O(1)
Cu(2)
C(22)
C(23)
N(83)
C(21)
N(31)
C(39)
C(46)
N(32)
N(33)
C(47)
C(24)
C(45)
C(44)
C(26)
C(25)
C(41)
N(47)
C(42)
C(38)
C(37)
O(24)
C(28)
C(34)
C(35)
O(44)
C(48)
C(43)
C(36)
(b)
C(68)
O(64)
C(64)
C(63)
C(62)
C(65)
C(66)
C(61)
C(17)
C(16)
C(15)
C(67)
O(67)
N(67)
C(54)
C(18)
N(53)
C(55)
C(19)
O(74)
Cu(4)
C(14)
N(13)
N(11)
C(56)
C(57)
N(52)
O(71)
O(2)
C(59)
N(12)
N(27)
C(27)
O(27)
O(75) N(51)
Cu(6)
C(58)
N(81)
O(72)
Cu(5)
C(22)
O(47)
C(47)
C(41)
C(21)
C(46)
N(83)
C(23)
C(24)
N(31)
N(32)
C(45)
C(44)
C(26)
C(39)
O(24)
C(42)
C(43)
C(25)
N(33)
C(35)
C(38)
C(37)
N(47)
C(48)
O(44)
C(28)
C(34)
C(36)
Fig. 4. The structures of the two independent complexes A (a) and B (b) in II.
ditions with [CHMBH] ≥ 10[Hg2+], using UV-Vis
spectrophotometer technique, monitoring the reac-
tion at λ = 410 nm. The experimental trace can be fit-
ted to a single exponential curve (Fig. 6), indicating
gated (Table 3). This study aimed to (i) determine the
rate constant of the reaction; (ii) propose a mecha-
nism of the formation of complex I; (iii) compare the
results with that of our previous studies II–IV. The
reactions were studied under pseudo-first-order con- that the reaction exhibits a first-order dependence on
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 43 No. 2 2017

122
AL-KARAWI
(a)
5
0
–5
0.32
0.28
0.24
0.20
0.16
Mass change –30.8468%
–10
–15
–20
–25
–30
–35
–40
–45
–50
–55
–60
–65
–70
–75
–80
–85
Name: k9
Weight: 20 mg
Measuerment type: TGA DTG
Heating rate: 10 c/min
Mass change –34.6193%
0.12
0.08
0.04
0
–0.04
–0.08
–0.12
–0.16
227.9°C, –0.10 mg/K
290.8°C, –0.16 mg/K
Mass change –21.586%
100
200
300
(b)
400
500
600
120
110
100
90
80
1.5
0
Onset Y = 98.2326%
Onset X = 194.07°C
–2
–4
–6
–8
–10
Onset Y = 99.9070%
Onset X = 65.53°C
Onset Y = 34.6047%
Onset X = 586.42°C
Onset Y = 50.5116%
Onset X = 353.04°C
70
Onset Y = 91.5349%
Onset X = 270.73°C
60
Onset Y = 39.6279%
Onset X = 512.01°C
50
40
30
20
–12
10
–13.41
0
100
200
300
400
500
600
700
800
900
Temperature, °C
Fig. 5. Thermographmetric analyses of I (a) and II (b).
the concentration of Hg2+. This conclusion is con-
firmed in studies where the concentration of Hg2+ was
Consistent with our previous studies [15, 16], the
dependence of kobs on the concentration of CHMBH,
varied in the range 0.2–1.0 mmol dm–3 with exhibiting a first-order dependence on the concentra-
[CHMBH] = 10 mmol dm–3, but the values of the tion of CHMBH, as typified by the plot shown in
observed kobs for each reaction did not change (Table 3).
Fig. 6 and the corresponding rate law in Eq. (1).
–d[Hg2+]/dt = ka[CHMBH][Hg2+],
–d[Hg2+]/dt = k1k2[CHMBH][Hg2+]/k–1[MeCN] + k2[CHMBH],
–d[Hg2+]/dt = k1k2[CHMBH][Hg2+]/k–1[MeCN].
(1)
(2)
(3)
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2017

COMPREHENSIVE COMPARISON BETWEEN THE REACTION
123
A proposed mechanism for the formation of I from consistent with the observed kinetics is shown in
the reaction of Hg2+ with CHMBH in MeCN at 25°C
Scheme 2:
Ar
2+
k1
CHMBH
[Hg(NCMe)6]2+
[Hg(NCMe)5]2+
Hg O
NH
N
(MeCN)5
k2
MeCN
k−1
N
O
NH
Ar
Fast
Ar
O
Ar
Ar
2+
2+
NH
N
O
NH
N
O
NH
N
2Cl−
Cl
Cl
(MeCN)3 Hg
Hg
Hg
N
N
N
O
NH
O
NH
O
NH
Ar
Ar
Ar
Scheme 2.
concept (in case of [Cd(CHMTSC)(NO3)]+ and
As in our previous studies [15, 16] and in line with
other studies on chelate formation [28], the initial
binding of CHMBH to [Hg(NCMe)n]2+ by replace-
ment of one of the coordinated MeCN molecules can
be proposed to be the rate-limiting step of the chelate
formation. The usual intimate mechanism for such a
reaction is dissociative and involves initial dissociation
[Cd(PHMTSC-2H+)], S atom is soft base and Cd2+ is
soft acid, while in case of [Hg(CHMBH)], O atom is
hard base and Hg2+ is soft acid) [29–32].
of a coordinated solvent from [Hg(NCMe)n]2+, gener-
Table 3. Kinetic data for the reaction of Hg2+ and CHMBH
in MeCN at 25°C
2+
ating [M(NCMe)(n – 1)
]
containing a vacant site at
which CHMBH can bind as shown in Scheme 2. The
full rate law for this mechanism is shown in Eq. (2) and
indicates that, over a large concentration range of
CHMBH, the kinetics would exhibit a non-linear
dependence on concentration of CHMBH. However,
when the concentration of CHMBH is small, k–1
[MeCN] > k2 [CHMBH] the rate law would simplify
to that shown in Eq. (3), which is of the same form as
observed experimentally in Eq. (1). For the
reaction studied, the value of ka = k1k2/k–1[MeCN] is
[Hg2+],
[CHMBH],
mmol dm–3
kobs, s–1
mmol dm–3
7.0 × 10–7
10.6 × 10–7
14.5 × 10–7
21.0 × 10–7
23.2 × 10–7
24.1 × 10–7
23.7 × 10–7
0.2
2.0
4.0
6.0
8.0
2.0 × 10–4 dm3 mol–1 s–1, which is 3.1 × 106 times less
than that of [Cd(CHMTSC)(NO3)]+ (III) and
10.0
10.0
10.0
[Cd(PHMTSC-2H+)] (IV) (Table 4); i.e., the reaction
of CHMBH with Hg2+ is 3.1 × 106 times slower than
the reactions of CHMTSC or PHMTSC with Cd2+.
This can be attributed to the Hard–Soft Acid–Base
0.5
1.0
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124
AL-KARAWI
(a)
0.12
0.10
0.08
0.06
0.04
0.02
0
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
Times, h
(b)
0.0000030
0.0000025
0.0000020
0.0000015
0.0000010
0.0000005
0
2
4
6
8
10
12
CHMBH, mmol dm–3
2+
Fig. 6. Typical kinetic data for the reactions of Hg with CHMBH in MeCN at 25°C. (a) A typical experimental absorbance-
2+
–3
–3
......
time curve when [Hg ] = 0.2 mmol dm and [CHMBH] = 2 mmol dm , ((——) is the experimental data and (
) is the fit,
(–t/4.907)+0.115
defined by the equation A = –0.103 e
reproducibility; straight line fit to the data is that defined by the equation k = 2.0 × 10 [CHMBH]).
); (b) the first-order dependence of k on [CHMBH] (error bars show 10%
t
obs
–4
obs
Our previous study [17] reports the kinetisc of the tion occurs in three distinct phases and the kinetics of
reaction of CHMBH with Cu2+. It is evident from the
colour changes observed during its synthesis that II is
formed in a series of steps. Whilst the synthesis is per-
each phase have been determined.
The reaction is characterised by an intial absor-
bance increase (phase 2) followed by an absorbance
decrease (phase 3). Phase 1 has occurred in the dead-
time of the stopped-flow apparatus. Typical stopped-
flow absorbance-time traces are shown in Fig. 7. The
rate constant of the reaction was determined and the
proposed mechanism for the reaction of Cu2+ with
CHMBH in MeCN to form complex II has been given
formed using equimolar amounts of Cu(NO3)2
·
2.5H2O and CHMBH, the kinetic studies have been
performed under a range of conditions ([Cu2+] ≥
[CHMBH] and [CHMBH] > [Cu2+]) using stopped-
flow spectrophotometry, monitoring the reaction at
λ = 410 nm. Irrespective of the conditions, the reac- in Scheme 3:
Table 4. Rate constant details of different reactions in MeCN at 25°C
ka/dm3 mol–1 s–1
Metal ion (M2+
)
Ligand
Reference
2.0 0.5 × 10–4
6.2 0.5 × 102
6.2 0.5 × 102
Hg
Cd
Cd
CHMBH
CHMTSC
PHMTSC
This work
[15]
[16]
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
Vol. 43
No. 2
2017

COMPREHENSIVE COMPARISON BETWEEN THE REACTION
125
+
@
!
?
N
N
N
CuI
N
Intermediate =
Ar
O
C
2+
2+
+
O
O
N
N
N
N
N
O
N
Cu2+
−Cu+
−'ArCO'
Cu2+
HN
Ar
CuII
NH
N
H
N
Ar
N
H
CuII
N
H
Ar
HN
Ar
NH
Ar
N
N
O
Ar
CuI
O
O
Ar
O
CHMBH
A
B
D
O2 oxidation of all Cu(I) to Cu(II)
Fast
and aggregation
[Cu3(μ-OH)(CTMB)3(NO3)2(NCMe)2]
Scheme 3.
The study revealed that the three phases observed
in the formation of II could reasonably correspond to:
(i) the bidentate (or possibly tridentate) coordination
of CHMBH to Cu2+ (phase 1); (ii) chelation of the
bidentate coordinated CHMBH (phase 2) and (iii) the
oxidation of the coordinated hydrazone (by Cu(II)) to
form the triazole (D) and, ultimately, II (phase 3) (for
more details, see reference 17). The comparison shows
that the stories of the formation of I and II are com-
pletely different!
(a)
1.2
1.0
0.8
0.6
0.4
0.2
ACKNOWLEDGMENTS
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4
(b)
The author thanks prof. Richard A. Henderson,
prof. Eric Maatta, Dr. John Desper and Dr. Leila
Maurmann for their help.
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
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2017