Biomimetic complexes of Cd(II), Mn(II), and Zn(II) with 1,1-diaminobutane–Schiff base. EGA/MS study of the thermally induced decomposition

Article abstract of DOI:10.1134/S107036321703029X

Frequently, in addition to X-ray and spectroscopic approaches, thermal analysis is the method of choice for comprehensive characterization of precipitated metal complexes. However, thermogravimetry itself is not sufficient enough for explaining complex de

Full text of DOI:10.1134/S107036321703029X

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 3, pp. 564–568. © Pleiades Publishing, Ltd., 2017.
Biomimetic Complexes of Cd(II), Mn(II), and Zn(II)
with 1,1-Diaminobutane–Schiff Base. EGA/MS Study
1
of the Thermally Induced Decomposition
a
a
a
b
a
R. Risoluti , M. A. Fabiano , G. Gullifa , L. W. Wo , and S. Materazzi *
a
Department of Chemistry, Sapienza University of Rome, Aldo Moro Sq. 5, Rome, 00185 Italy
*
e-mail: stefano.materazzi@uniroma1.it
b
Department of Chemistry, Illinois State University, S. School Street 251, Normal IL, 61761 USA
Received Janury 8, 2017
Abstract—Frequently, in addition to X-ray and spectroscopic approaches, thermal analysis is the method of
choice for comprehensive characterization of precipitated metal complexes. However, thermogravimetry itself
is not sufficient enough for explaining complex decomposition or releasing steps. For correct elucidation of the
decomposition mechanism of biomimetic Cd(II), Mn(II), and Zn(II) complexes with 1,1-diaminobutane–Schiff
base, evolved gas analysis by mass spectrometry (EGA/MS) was used to define the thermally induced steps.
Those were synthesized and characterized by hyphenated thermogravimetry-mass spectrometry (TG–MS) that
allowed to interpret the decomposition steps.
Keywords: 1,1-diaminobutane–Schiff base, biomimetic complexes, cadmium complexes, manganese
complexes, zinc complexes, evolved gas analysis, EGA/MS, TG–MS
DOI: 10.1134/S107036321703029X
INTRODUCTION
The growing antimicrobial resistance (AMR) presents
major threats to public health because it reduces the
effectiveness of antimicrobial treatment leading to
higher mortality and health care expenditure [13, 14].
Thus, recent studies pay high attention to new Schiff
bases containing SNO donor atoms and their pharma-
cologically active complexes.
Complexes containing Shiff base ligands and
transition metal ions are intensively studied due to
their versatile structures, biomimetic potential
modelling and wide industrial applications. Schiff
bases are able to form coordination bonds with many
metal ions via the azomethine or phenolic groups. Due
to their easy formation and strong metal-binding
ability, those have been used for synthesis of various
metal complexes. Over the recent years coordination
compounds of biologically active ligands [1–4] have
received close attention.
Besides X-ray and spectroscopic methods, a thermo-
analytical characterization was highly efficient in
making the more complete approach to thermally
induced decomposition mechanisms [15–17]. Ho-
wever, thermogravimetry (TG) itself is no longer
sufficient to explain complex releasing steps. The
experience of our group demonstrated high efficiency
of thermoanalytical data combined with FTIR and/or
MS spectroscopies. The hyphenation allows to charac-
terize correctly releasing or decomposition steps
[18–22] and to propose decomposition mechanisms for
precipitated complexes [23–30].
Due to significant influence of chelation upon bio-
logical properties of compounds, the Schiff bases
complexes potential applications have been tested
[
5, 6] and their antibacterial, antifungal, anticancer,
and herbicidal activities [7–12] were detected. The
ability of microorganisms to become resistant to major
therapies used against them has long been recognized
and became more pronounced. Recently, the number
of diseases, caused by multidrug resistant gram-positive
microorganisms, has been continuously increasing.
In a recent study several complexes with N,N'-bis-
(2-hydroxybenzylidene)-1,1-diaminobutane
ligand
(
BHBDAB) were precipitated and characterized [31].
This was followed by synthesis of similar or new
complexes by the same method [31]. Evolved Gas
Analysis by Mass spectrometry (EGA/MS) was
1
The text was submitted by the authors in English.
5
64

BIOMIMETIC COMPLEXES OF Cd(II), Mn(II), AND Zn(II)
565
Scheme 1. Synthesis of the complexes.
O
O
NEt3
O
H
H
NH NO
N
N
4
3
+
+
CH3
OH
HO
OH
HO
H C
3
MCl2
N
N
M
O
O
H O
OH2
2
applied to prove the thermally induced behavior. The
precipitated compounds were characterized by
hyphenated TG–MS that allowed to describe each
thermally induced step.
internal standard (Yttrium 100 µg/L at a wavelength
371.030 nm) was used.
Thermoanalytical curves were recorded on a Perkin-
Elmer TGA7 instrument. The samples, ca. 7–8 mg,
were heated in platinum crucibles within temperature
range 20–850°C, in the atmosphere of Ar or air
(mixture of N with O , 80 and 20%, v/v, respectively)
EXPERIMENTAL
Cd(II), Mn(II) and Zn(II) chlorides, ammonium
nitrate, salicylaldehyde, and butanal were supplied by
Aldrich and Fluka. The solvents were purchased from
Merck and used without further purification. The
earlier study [31] approach was applied to the
synthesis of the ligand and precipitation of the
complexes of general formula M(BHBDAB)(H O) ,
2
2
at a flow rate of 100 mL/min and a scanning rate of
5 deg/min (best resolution rate).
MS of the gases evolved in the course of the
thermoanalytical experiments were recorded by a STD
2
960 simultaneous DTA–TGA instrument (TA Instru-
2
2
ments Inc., USA) using sealed crucibles with a pinhole
on the top. The gaseous species were analyzed on a
ThermoStar GDS 200 (Balzers Instrument) quadrupole
Mass Spectrometer equipped with Chaneltron detector
(EI, 70eV), by passing those through a heated 100%
methyl deactivated fused silica capillary tubing. Two
different TG instruments recorded overlapped curves,
so ensuring the reproducibility of the thermo-analytical
experiments. Such experimental approach was constantly
applied to achieve comparable data, with the aim of
proposing decomposition characteristic behavior among
complexes with similar ligand structures [32–36].
where M = Cd(II), Mn(II) or Zn(II) (Scheme 1).
Precipitation of the complexes was followed by
elemental analysis on a VarioEl III CHN Analyzer.
FTIR spectra were recorded on a Perkin Elmer 1760X
spectrophotometer. The metal concentration was
determined by ICP-OES (Varian ICP/VISTA MPX)
equipped with an ultrasonic nebulizer (U 5000 AT+,
Cetac Technologies Inc.). Analytical blanks were
performed. A subtraction of blanks (calculated as the
mean value of six replicated measurements) was
applied in all cases. To control nebulizer efficiency, an
Table 1. Elemental analysis data for the precipitated complexes
Found, %
Calculated, %
Complex
a
C
H
N
M
C
H
N
25.3
14.1
16.5
16.5
Cd(BHBDAB)(H
Mn(BHBDAB)(H
Zn(BHBDAB)(H
2
O)
O)
O)
2
48.3
56.2
54.3
4.7
5.6
5.6
6.0
7.1
7.1
25.0
14.2
16.3
48.9
56.2
54.7
4.9
5.7
5.6
6.3
7.3
7.1
2
2
2
2
a
Cd, Mn and Zn (M) were determined by ICP-OES.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 3 2017

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RISOLUTI et al.
(
a)
(b)
(c)
(d)
Weight, %
00
1
st thermally
induces loss
nd thermally
induces loss
1
1
2
3
rd thermally
8
6
4
2
0
0
0
0
0
induces loss
2
3
2
1
final
decomposition
3
4
5
2
0
200
400
600
800
Temperature, °C
0
100
200
300
400
Temperature, °C
Fig. 2. EGA/MS m/z traces for the (a) first, (b) second,
c) third, and (d) final thermal decomposition steps of com-
(
+
Fig. 1. Thermoanalytical curves of (1) cadmium(II), (2)
manganese(II), and (3) zinc(II) chloride complexes; air flow
rate 100 mL/min, heating rate 5 deg/min.
plexes as functions of temperature. (1) m/z = 29, H C=NH ,
2
+
(2) m/z = 18, H O, (3) m/z = 17, HO , (4) m/z = 28,
2
+
2
CH =CH , (5) m/z = 42, CH CH=CH .
2
3
2
RESULTS AND DISCUSSION
Actually, there were recorded same decomposition
steps but different thermal stability. Similar thermal
behavior has been reported earlier by our research
group [24, 28, 37–39].
According to the elemental analysis (Table 1), the
complexes did not contain two external water
molecules even upon the experimental conditions of
the previous report [31] being strictly followed. It
could be due to the drying process that removed all
unstructured water molecules. Such result did not
come as a surprise because in the earlier study [31] the
thermogravimetric curves exhibited incongruence with
the calculated weight loss. Probably Alaghaz [31]
obtained different complexes in the course of
preparing crystals for X-ray powder diffraction.
The percent weight loss (Table 1) was probably due
to the first release of two coordinated water molecules
followed by the tail of the ligand. This hypothesis was
based on the calculated molecular weight loss and the
absence of nitrogen-containing fragments in the mass
spectra of the evolved gas.
EGA/MS confirmed the release of two water
molecules (fragments at m/z = 17 and 18 accompanied
by the tail m/z = 28) (Fig. 2). Such pattern was not
influenced by the gas flow (air or Ar). Consequently,
the release of CO could be excluded because m/z = 28
was also detected under inert flow conditions which
supported the proposed decomposition path.
FTIR spectra confirmed the complex formation by
the shift of the main common absorption bands (KBr),
–
1
ν, cm : 1560, 1316 and 1265, whereas in the study
–
1
[
(
31], the bands at 1373–1380 cm for all complexes
CH stretching and the aliphatic protons) were not
3
affected by complexation.
The third releasing process was deduced from
purging the analyzer furnace with N . The recorded
fragments at m/z = 28 and 29 (Fig. 2) and calculated
percent weight loss indicated rupture of the ligand ring
Decomposition mechanism of the precipitated com-
plexes was elucidated on the basis of thermally induced
releasing steps studied comparatively by EGA/MS
coupled with TG. In Fig. 1, the thermoanalytical
profiles of the complexes are overlapped to compare
the releasing steps when the purging flow was air.
2
(
Fig. 3), and the temporary consequent rearrangement.
The fourth thermally induced step led to complete
decomposition of the residual compound and forma-
tion of the metal oxide. This step demonstrated MS
fragments related to water, nitrogen and carbon
dioxides upon purging the furnace by the air. Inert gas
The thermal decomposition proceeded via four
main steps that were similar for all complexes and did
not depend on the nature of coordinated metals.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 3 2017

BIOMIMETIC COMPLEXES OF Cd(II), Mn(II), AND Zn(II)
567
Table 2. Temperature range of the main thermal steps and the corresponding percent weight loss
TG weigt loss, %
Complex
found, %
calculated, %
1
st step
9.0
2nd step 3rd step 4th step 1st step 2nd step 3rd step 4th step
Cd(BHBDAB)(H
2
O)
O)
O)
2
10.0
10.2
10.4
25.0
25.1
25.0
35.8
35.5
34.6
9.2
9.2
9.1
10.8
10.8
10.6
25.2
25.2
24.8
35.6
35.6
34.9
Mn(BHBDAB)(H
Zn(BHBDAB)(H
2
2
9.2
2
2
9.0
2
nd TGA loss
4. Drabent, K., Bialoska, A., and Ciunik, Z., Inorg. Chem.
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j.inoche.2003.11.008
H C
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. Perrino, C., Marconi, E., Tofful, L., Farao, C.,
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j.atmosenv.2012.02.07
3rd
N
N
TGA loss
3rd
TGA loss
M
O
O
6. Arion, V.B., Reisner, E., Fremuth, M., Jokupec, M.A.,
Keppler, B.K., Kukushkin, V.Y., and Pombeiro, A.J.L.,
J. Inorg. Biochem., 2003, vol. 96, p. 95. doi 10.1016/
S0162-0134(03)80556-1
H O OH2
2
1st TGA loss
7
. Liu, Y., Kravtsov, V., Walsh, R.D., Poddar, P.,
Srikanthc, H., and Eddaoudi, M., Chem. Commun.,
Fig. 3. General decomposition mechanism
2
004, p. 2806. doi 10.1039/B409502B
flow (N or Ar) did not lead to a constant final residue
at 800°C.
2
8
. Aiello, D., Materazzi, S., Risoluti, R., Thangavel, H., Di
Donna, L., Mazzotti, F., Casadonte, F., Siciliano, C.,
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The proposed decomposition mechanism was
supported by correlation between the MS
fragmentation and the calculated and experimental
percent weight loss data (Table 2).
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1
The thermally induced decomposition mechanism
of Cd(II), Mn(II) and Zn(II) complexes with N,N'-bis(2-
hydroxybenzylidene)-1,1-diaminobutane was studied
by on-line coupling mass spectrometer to
a
13. Ashley, D. and Brindle, M., J. Clin. Pathol., 1960,
vol. 13, p. 336.
thermogravimetric analyzer. The resulting weight loss
and the m/z traces from the EGA/MS allowed to
propose the decomposition path and confirmed the
thermally induced mechanism.
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