Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of copper(II) and zinc(II)

Article abstract of DOI:10.1007/s10973-016-5805-z

Some new carbamates, viz. M(MorphcbmH)₂X₂ (MorphcbmH?=?morpholinecarbamic acid, M?=?Cu, X?=?Cl, ClO₄,NO₃; M?=?Zn, X?=?Cl, ClO₄, NO₃, CH₃COO and X₂?=?SO₄), h

Full text of DOI:10.1007/s10973-016-5805-z

J Therm Anal Calorim
DOI 10.1007/s10973-016-5805-z
Experimental investigations of thermal stability of some
morpholinecarbamic acid complexes of copper(II) and zinc(II)
Shashi B. Kalia1 Rajesh Kumar1 Monika Bharti1 J. Christopher2
•
•
•
Received: 17 July 2015 / Accepted: 29 August 2016
´
´
Ó Akademiai Kiado, Budapest, Hungary 2016
Abstract Some new carbamates, viz. M(MorphcbmH)2X2
(MorphcbmH = morpholinecarbamic acid, M = Cu,
X = Cl, ClO4,NO3; M = Zn, X = Cl, ClO4, NO3,
CH3COO and X2 = SO4), have been synthesized and
investigated. Compounds were characterized by elemental
analysis, molar conductance, FT infrared, fluorescence,
NMR (1H and 13C) and solution electronic absorption
spectral studies. Room temperature field-dependent mag-
netic susceptibility measurements, PXRD spectral and
cyclic voltametric studies were also conducted. Chelating
bidentate mode of coordination of ligand, MorphcbmH
with four coordination around metal ion has been proposed.
Ligand and its compounds have also been studied using
non-isothermal thermogravimetric analysis and differential
scanning calorimetric analytical techniques which inferred
formation of metal oxide/MCO3 as final thermal decom-
position products. Compounds were screened against the
lipase enzyme for assaying their enzyme activity and were
found to retard the lipase activity from 48.16 to
Keywords Morpholinecarbamic acid (MorphcbmH) Á
Copper(II) Á Zinc(II) Á TG/DSC Á Fluorescence
spectroscopy Á Cyclic voltammetry
Introduction
Carbamate compounds with general formula -O2CNR2, R
being H, an alkyl or an aryl group are of particular interest
due to their applications in polymer industry [1–3], as
agrochemicals [1–5] and pharmaceuticals [1–3]. Decom-
position of carbamates has been reported to be a fairly slow
process, and to speed up the reaction, use of catalysts has
been proposed. Generally, carbamates thermally decom-
pose to give various products such as amine, alkene, carbon
dioxide, alcohol and isocyanate depending upon their alkyl/
aryl ester derivative carbamate [6, 7]. However, thermal
investigations on metal carbamates are scanty [8]. Since
carbamate compounds have insecticidal applications and
are less toxic and are biodegradable in nature, it becomes
important to study their thermal stability for accounting
nature of residues in environment particularly in soil and
water bodies. In view of this, thermogravimetric (TG) and
differential scanning calorimetric (DSC) analytical tech-
niques have been used to investigate thermal stability and
decomposition patterns of free ligand, morpholinecarbamic
acid (MorphcbmH) and some of its complexes.
0.044 lmol mL-1 min-1
.
Experimental
Materials
& Shashi B. Kalia
shashibalakalia@rediffmail.com
1
2
Department of Chemistry, Himachal Pradesh University,
Shimla 171005, India
All the chemicals used were purchased from Fluka and
without further purification.
Indian Oil Corporation, R&D, Faridabad, Haryana, India
123

S. B. Kalia et al.
Synthesis of ligand and complexes
Cu(MorphcbmH)2(NO3)2 Analysis found: C 26.72, H
4.02, N 12.47, Cu 14.10 %; Calculated for CuC10H18
N4O12: C 26.69, H 4.00, N 12.45, Cu 14.12 %. Reaction
yield 91 %. Decomposition temperature: 142 °C.
MorphcbmH
Dry carbon dioxide gas was passed for about 5 min through
continuously stirred solution of morpholine (1 ml, 1000 ll)
in hexane (3–5 ml). White-colored product separated out
immediately. It was filtered, washed with hexane, dried in
air and finally in a calcium chloride desiccator.
Zn(MorphcbmH)2Cl2 Analysis found: C 30.18, H 4.50,
N 7.06, Zn 16.30, Cl 17.80 %; Calculated for ZnC10H18
N2O6Cl2: C 30.15, H 4.52, N 7.03, Zn 16.33, Cl 17.83 %.
Reaction yield 88 %. Decomposition temperature: 165 °C.
Zn(MorphcbmH)2(ClO4)2 Analysis found: C 22.85, H
3.45, N 5.30, Zn 12.31, Cl 13.45 %; Calculated for ZnC10H18
N2O14Cl2: C 22.81, H 3.42, N 5.32, Zn 12.35, Cl 13.49 %.
Reaction yield 90 %. Decomposition temperature: 136 °C.
Zn(MorphcbmH)2(NO3)2 Analysis found: C 26.55, H
3.97, N 12.40, Zn 14.45 %; Calculated for ZnC10H18
N4O12: C 26.60, H 3.99, N 12.41, Zn 14.41 % Reaction
yield 91 %. Decomposition temperature: 154 °C.
Zn(MorphcbmH)2(CH3COO)2 Analysis found: C 37.78,
H 5.40, N 6.31, Zn 14.62, CH3COO 26.55 %; Calculated
for ZnC14H24 N2O10: C 37.75, H 5.39, N 6.29, Zn 14.60,
CH3COO 26.51 % Reaction yield 90 %. Decomposition
temperature: 147 °C.
Cu(MorphcbmH)2X2 ((M = Cu, X = Cl, ClO4,NO3)
and Zn(MorphcbmH)2X2 (X = Cl, ClO4, NO3, CH3COO
and X2 = SO4)
CuX2ÁxH2O, 0.382 mmol (65.06 mg for X = Cl, x = 2;
92.21 mg for X = NO3, x = 3 and 141.22 mg for X =
ClO4, x = 6) and ZnX2ÁxH2O, 0.382 mmol (52.01 mg for
X = Cl, x = 0; 141.62 mg for X = ClO4, x = 6;
72.13 mg for X = NO3, x = 0; 75.44 mg for X =
CH3COO, x = 1 and 109.75 mg for X = SO4, x = 7) were
dissolved in ethanol (5 ml). To this solution was added
solid morpholinecarbamic acid (100 mg, 0.764 mmol,) in
small portions (10 mg) with stirring after successive
intervals of 15–20 min in a total period of about 3 h. The
reaction was carried out at room temperature (25–30 °C).
Complex separates out within an hour after addition of
complete acid, yet reaction mixture was stirred for another
2–3 h to ensure completion of reaction. The solid product
(for copper compounds, yellow when X = Cl, sky blue
when X = NO3 and bluish green when X = ClO4 and for
zinc compounds, white when X = Cl, ClO4, NO3,
CH3COO and X2 = SO4) was then centrifuged, washed
with ethanol using centrifugation technique and dried in
air. Final drying was done in a calcium chloride desiccator.
Zn(MorphcbmH)2SO4 Analysis found: C 28.40, H 4.22,
N 6.63, S 7.58, Zn 15.34 %; Calculated for ZnC10H18 N2
SO10: C 28.36, H 4.25, N 6.61, S 7.56, Zn 15.36 %
Reaction yield 85 %. Decomposition temperature: 152 °C.
Physical measurements
Room temperature molar conductance measurements (10-3
M DMSO solutions) were taken by using Elico conductivity
bridge type CM-82T. Thermal analyses of the complexes
were carried out by using thermogravimetric analyzer (TGA)-
Model 2950 and differential scanning calorimeter (DSC)-
Model 2920, Make-TA Instruments, USA. Thermocouple Pt/
Pt–Rh (10 %) with temperature range of 20–800 °C was
employed. Sample (5–10 mg) in a Pt crucible under static air
atmosphere was heated at a rate of 10 °C min-1. TGA
instrument was calibrated periodically using Al2O3 as stan-
dard reference. Nicolet 5700 FTIR spectrophotometer was
used to record infrared spectra of complexes as KBr pellets in
4000–600 cm-1 region and as NaCl plates as windows in
region 600–200 cm-1. Perkin Elmer LS 55 spectrometer with
scanning range 200–900 nm was used to measure fluores-
cence emission spectra of compounds (10-3 M DMSO
Analysis and techniques
Carbon, hydrogen, nitrogen and sulfur analyses were per-
formed using Elemental Analyzer Vario EL-III. Copper
and zinc were determined volumetrically by EDTA using
Pyrocatechol violet and Eriochrome Black T (EBT) as
indicators, respectively.
MorphcbmH Analysis found: C 45.84, H 6.90, N 10.72 %;
Calculated for C5H9NO3: C 45.80, H 6.87, N 10.68 %.
Reaction yield 96 %. Decomposition temperature: 65 °C.
Cu(MorphcbmH)2Cl2 Analysis found: C 30.30, H 4.49,
N 7.10, Cu 15.98, Cl 17.92 %; Calculated for CuC10H18
N2O6Cl2: C 30.26, H 4.53, N 7.06, Cu 16.01, Cl 17.90 %.
Reaction yield 90 %. Decomposition temperature: 110 °C.
Cu(MorphcbmH)2(ClO4)2 Analysis found: C 22.90, H
3.45, N 5.35, Cu 12.12, Cl 13.55 %; Calculated for CuC10H18
N2O14Cl2: C 22.87, H 3.43, N 5.33, Cu 12.10, Cl 13.53 %.
Reaction yield 89 %. Decomposition temperature: 142 °C.
1
solution). H NMR spectra of complexes were recorded on
JEOL JNM PMX60 SI/DRX-300 MHz Bruker spectropho-
tometers using (CD3)2SO as solvent and TMS as an internal
standard, while 13C NMR spectra were recorded on DRX-
300 MHz Bruker spectrophotometer using same solvent.
Magnetic susceptibilities of the samples were measured on
vibrating sample magnetometer PAR-155 (model-152). The
instrument was calibrated with Cu(OOCCH3)2ÁH2O, whose
magnetic susceptibility at room temperature is known. Cary
123

Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of…
100 Bio UV–Visible recording Spectrophotometer (range
200–900 nm) was used to record solution (DMSO) electronic
absorption spectra of complexes, with solvent as reference, in
quartz glass cells. PXRD patterns were obtained using Bruker
AXSd8 advance X-ray diffractometer with Mo-Ka
incubated at 45 °C on water bath for 10, 30, 50 and 70 min,
respectively. All the experiments were performed in triplicate.
In another one clean and dry test tube, 10 ll of steapsin lipase
enzyme was taken and to it added the solution of test tube
marked A. Then, again incubated the test tube in water bath at
45 °C for 10 min. The enzyme activity was arrested by
keeping the reaction mixture at -80 °C for about 5 min.
Then, A410 nm of the solution was measured. Added the
solutions of test tubes B, C, D, E into test tubes 1, 2, 3, 4 after
10, 30, 50 and 70 min, respectively. Test tubes were incu-
bated in water bath at 45 °C for 10 min. The enzyme activity
was arrested by keeping the reaction mixture at -80 °C for
about 5 min. Then, A410 of the solution was measured. The
activity of enzyme was calculated with the help of formula.
˚
˚
(k = 0.7107 A) and Cu-Ka (k = 1.54184 A) radiation sour-
ces and [XPERT-PRO] diffractometer with Cu-Ka
˚
(k = 1.54184 A) radiation source. The measurements were
taken at a temperature of 25 °C (RT) and a 2h angle range of
10°–80°. A step resolution of 0.019° was used with a step
time of 19.2 s. Cyclic voltammograms of compounds in
DMSO solution (10-3 M) were recorded on Autolab Poten-
tiostat 128 N Electrochemical Analyzer using KCl/NaClO4
(10-1 M) as supporting electrolyte in the potential range -2
to ?2 V at a scan rate of 100 mV s-1
.
TestðtÞÀControlðCÞ
Activity of enzyme ¼
OD of Standard
Lipase enzyme activity
1
 Conc: of standard Â
10
Compounds were also investigated for the lipase enzyme
inhibition (steapsin) activity at different incubation times, i.e.,
10, 30, 50 and 70 min along with control. Experiments were
performed in triplicate. In six dry and clean test tubes labeled
A, B, C, D, E and F, tris buffer gum acacia solution (2.90 mL,
0.05 M, pH 8.5) was taken. These were incubated in water
bath at 45 °C for 10 min, removed from the water bath and
cooled to room temperature. Eighty microliter (80 ll) of
p-nitrophenylpalmitate (p-NPP) substrate solution was added
to each test tube which was again incubated in water bath at
 Dilution factor
1
Â
Molecular weight of p À NPP
Results and discussion
Free ligand, MorphcbmH (Eq. 1) and its copper(II) and zinc(II)
complexes were synthesized according to the reaction (Eq. 2):
O
O
OH
N
C
or
-
N
C
δ
Hexane
+
O
O
N
H
δ
CO2
+
O
O
ð1Þ
ð2Þ
H
(MorphcbmH)
(Morph)
Synthesis of 4-MorphcbmH
O
C
N
xH2O
M(MorphcbmH)2X 2
-
+
δ
2
MX2.xH2O
+
+
O
δ
O
H
MorphcbmH
Synthesis of metal complexes
45 °C for another 10 min. In another set of four clean and dry
test tubes was taken 1 mg of solid compound under study and
added 10 ll of steapsin lipase enzyme in each of these test
tubes. The test tubes were numbered as 1, 2, 3 and 4 and were
where (M = Cu, X = Cl, x = 2; X = NO3, x = 3 and
X = ClO4, x = 6 and M = Zn, X = Cl, NO3 and x = 0;
X = ClO4, x = 6; X = CH3COO, x = 1 and X2 = SO4,
x = 7)
123

S. B. Kalia et al.
These complexes do not melt but decompose between
110 and 165 °C and are sparingly soluble in methanol but
are fairly soluble in DMSO.
a.u. A dramatic decrease in emission intensities on com-
plex formation for M(MorphcbmH)2X2 (M = Cu, X = Cl,
ClO4, NO3; M = Zn, X = Cl, ClO4, NO3, and X2 = SO4)
has been observed to fall at 47–230 a.u., whereas there is
increase in emission intensity on complex formation for
Zn(MorphcbmH)2(CH3COO)2 lying at 330 a.u. Further-
Molar conductance studies
more, an increase in excitation intensity (Iex) for above
ex
complexes, i.e., 180–954 a.u. at k
observed as compared to that for free ligand, i.e., Mor-
= 370 nm, has been
The 10-3 M DMSO solution of complexes M(MorphcbmH)2-
X2 (M = Cu, X = Cl, ClO4, NO3; M = Zn, X = Cl, ClO4,
NO3, CH3COO) exhibited molar conductance values,
136–179 ohm-1cm2 mol-1 thatsupported their1:2electrolytic
behavior [9], whereas Zn(MorphcbmH)2SO4 has molar con-
ductance value 15 ohm-1 cm2 mol-1 suggesting its non-
electrolytic nature.
max
ex
max
phcbmH: Iex = 171 a.u. at k
= 290 nm. Degree of
fluorescence quenching increases upon complex formation
with metal ions [13] and is explained by processes, mag-
netic perturbation, redox-activity, and electronic energy
transfer.
Infrared spectral studies
1H NMR spectra
FTIR spectra of MorphcbmH and its complexes, viz.
M(MorphcbmH)2X2 (M = Cu, X = Cl, ClO4, NO3;
M = Zn, X = Cl, ClO4, NO3, CH3COO and X2 = SO4),
exhibit a new relatively broad and strong band at
3415–3431 cm-1 due to m O–H stretching vibration that
points to the formation of O–H bond supporting the
presence of carbamate ligand as a Zwitterion. Observa-
tion of this band at higher wave number than the usual
values of 3400–3200 cm-1 infers that interaction of lone
electron pair on oxygen with positively charged hydro-
gen is stronger than normal O–H interaction. Peculiar
infrared spectral absorptions in the regions 1570–1633
and 1544–1565 cm-1 due to m(CO2) and m(C=N) corre-
sponding to [NCO2 moiety of MorphcbmH ligand and
its complexes are informative of bridging bidentate
binding mode of ligand in all metal-carbamic acid
complexes under present investigations. This kind of
binding is further supported by Calderazzo et al. [10].
Appearance of additional bands in the region
361–420 cm-1 due to m(M–O) in complexes as compared
to free carbamic acid ligand reveals the formation of
metal–oxygen bond [11].
1H NMR spectra of MorphcbmH and Zn(MorphcbmH)2X2
(X = Cl and X2 = SO4) have also been performed. Hete-
rocyclic secondary amine, i.e., Morph exhibits resonance
signal due to O–H proton, d 1.65; –CH2– protons, 2,6- and
3,5-protons, d 2.54–2.57 and d 3.63–3.66; [N-CH3 pro-
1
tons, d nil ppm. H NMR spectrum of free acid ligand,
MorphcbmH (Fig. 1), shows the resonance signals as two
triplets for 2,6 and 3,5-methylene protons: d 2.91; d
3.71.(Table 1). The signal due to [N–H proton of free
Morph was not observed suggesting thereby formation of
MorphcbmH ligand on reaction with carbon dioxide, while
appearance of new signal at d 3.44 ppm has been attributed
to proton resonance of O–H as a result of formation of new
O–H bond as shown below:
O
5
6
C
N
O
O
H
3
2
Zwitterionic form of MorphcbmH
Appearance of this downfield signal further suggests
presence of positive charge on oxygen atom (deshielding
the proton) as a result of proton binding with oxygen
atom of O\ group yielding Zwitterionic form of acid
ligand.
Fluorescence spectroscopy studies
The fluorescent spectra of MorphcbmH and its complexes
exhibit maximum emission wavelengths (kemmax) at 352 nm
and 407–470 nm, respectively, corresponding to blue light
emission, the excitation wavelength being 290 nm for
ligand and 370 nm for all compounds. A red shift in
emission peak kemmax values upon incorporation of metal ion
into ligand moiety has been observed [12]. The fluorescent
emission intensity (Iem) for free ligand MorphcbmH is 309
For complexes, viz. Zn(MorphcbmH)2X2 (X = Cl and
X2 = SO4) (Figs. 2, 3), separate triplets due to 2,6-
methylene (d 3.73 ppm) and (d 3.50 ppm) and 3,5-
methylene (d 2.97 ppm), and (d 2.81 ppm) protons have
been observed on the downfield and upfield side, respec-
tively, in comparison with corresponding free ligand
(Table 1). Observation of single triplet instead of two
123

Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of…
Fig. 1 1H NMR Spectrum of
MorphcbmH
12
11
10
9
8
7
6
5
4
3
2
1
0
–1 ppm
Table 1 1H NMR spectral data, d (ppm) for Morph and MorphcbmH and its zinc(II) complexes
Sr. no.
Compound
NH/O–H
(2,6-) CH2
(3,5-) CH2
1.
2.
3.
4.
Morph
1.65(s, 1H)
3.44(s, 1H)
3.40(s, 1H)
3.30(s, 1H)
2.54–2.57 (t, 4H)
2.91(t, 4H)
3.63–3.66(t, 4H)
3.71(t, 4H)
MorphcbmH
Zn(MorphcbmH)2Cl2
Zn(MorphcbmH)2SO4
3.73(t, 4H)
2.97(t, 4H)
3.50(t, 4H)
2.81(t, 4H)
Fig. 2 1HNMR Spectrum of
Zn(MorphcbmH)2Cl2
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
ppm
triplets for 2,6-methylene proton in all complexes under
study in comparison with free acid ligand may result either
frequency and chemical shift values—deshielding of
N-bonded methylene protons upon coordination through
oxygen atoms to the central metal ion—has been observed,
i.e., Zn(MorphcbmH)2Cl2 (m NCO2 = 1621 cm-1) \
Zn(MorphcbmH)2SO4 (m NCO2 = 1625 cm-1) [14, 15], d
3.73 [ d 3.50 ppm.
C
N
group of Mor-
because of hindered rotation of O2
phcbmH ligand or because of accidental degeneracy
attributed to high local symmetry of NCO2M moiety [11].
A
direct relationship between [NCO2 vibrational
123

S. B. Kalia et al.
Fig. 3 1H NMR Spectrum of
Zn(MorphcbmH)2SO4
10
9
8
7
6
5
4
3
2
1
0
ppm
11
13C NMR spectra
NMR spectra of zinc(II) complexes of MorphcbmH, viz.
Zn(MorphcbmH)2Cl2 and Zn(MorphcbmH)2SO4, show
(Figs. 5, 6) signals: 2,6 –CH2, d 77.93–78.59 and d
78.06–78.71 ppm; 3,5 –CH2, d 70.75 and d 67.06 ppm;
[NCO2, d 172 and d 180 ppm, respectively (Table 2).
13C NMR spectrum of free ligand MorphcbmH (Fig. 4)
shows signals: 2,6–CH2, d 76.75–77.39 ppm; 3,5 –CH2, d
67.02–67.62 ppm and [NCO2, d 170 ppm (Table 2). 13C
Fig. 4 13C NMR Spectrum of
MorphcbmH
200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 ppm
Table 2 13C NMR spectral data, d (ppm) for MorphcbmH and its zinc(II) complexes
Sr. no.
Compound
(2,6-) CH2
(3,5-) CH2
[NCO2
1.
2.
3.
MorphcbmH
76.75–77.39
77.93–78.59
78.06–78.71
67.02–67.62
70.75
170
172
180
Zn(MorphcbmH)2Cl2
Zn(MorphcbmH)2SO4
67.06
123

Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of…
Fig. 5 13C NMR Spectrum of
Zn(MorphcbmH)2Cl2
200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
Fig. 6 13C NMR Spectrum of
Zn(MorphcbmH)2SO4
200 190 180 170 160 150 140 130 120 110 100 90
80
70
60
50
40
30
20 ppm
That all 13C d values have been observed at higher numbers
as compared to free ligand indicate greater deshielding of
carbon atoms plausibly due to higher electronegativity of
oxygen atom at 4th position of MorphcbmH ligand.
per copper(II) ion. Due to spin–orbit coupling, magnetic
moment values are higher than the spin-only value. Room
temperature variation of magnetization with field (-10,000
to 10,000 G) and observation of hysteresis loops for cop-
per(II) complexes, viz. Cu(MorphcbmH)2X2 (X = Cl,
ClO4, NO3), have revealed them to attain saturation mag-
netization in the applied field strength—typical of ferro-
magnetic materials. The values of magnetic parameters,
i.e., MS(saturation magnetization); HC(coercivity); and
MR(remanence magnetization), calculated from the hys-
teresis loops lie in the range 1.9–25 9 10-4 emu/g;
Magnetic study
For copper(II) complexes, viz. Cu(MorphcbmH)2X2
(X = Cl, ClO4,NO3) room temperature magnetic moment
values, have been observed to lie in the range 2.40–1.79
B.M. indicative of the presence of one unpaired electron
123

S. B. Kalia et al.
2600–5800 G; and 0.6–11 9 10-4 emu/g, respectively.
Range of parameters is compatible with the literature data.
Calculated MR/MS values for these complexes lie in the
range 0.31–0.46. Higher the value of MR/MS ratio greater is
the softness behavior of the substance [16]. Zinc(II) car-
bamate complexes Zn(MorphcbmH)2X2 (X = Cl, ClO4,
NO3, CH3COO and X2 = SO4,) exhibit room temperature
magnetic moment values in the range 0.2–0.05 B.M.
indicating their diamagnetic behavior.
1000
800
600
400
200
0
Electronic spectra
Electronic absorption spectra of MorphcbmH complexes of
copper(II), viz. Cu(MorphcbmH)2X2 (X = Cl, ClO4, NO3)
in DMSO solution, exhibit two bands in the regions: Band
0
10
20
30
40
50
60
70
80
2θ-/Scale
I, 11,990–13,927 to 13,888–14,598 cm-1 is considered to
Fig. 7 Powder XRD of MorphcbmH
2
contain electronic transitions dxy ? d2x - and (dxz,
y
2
dyz) ? d2x - for copper(II) ion in tetragonally distorted
y
120
100
80
60
40
20
0
octahedral environments. Band II, 28,571–29,325 cm-1 is
assigned to L ? M charge transfer transition 2pp ?
2
(d2x - ). For zinc(II) complexes, viz. Zn(MorphcbmH)2X2
y
(X = Cl, ClO4,NO3,CH3COO and X2 = SO4), electronic
spectral bands have been observed to lie in the range,
27,173–28,735 cm-1. On the basis of the literature reports,
zinc(II) carbamate complexes can have dimeric structures
as shown below (Scheme 1) with (ZnO4X) (X = Cl, ClO4,
CH3COO, NO3) and ZnO4X2 (X2 = SO4) chromophores.
Dimeric/tetrameric nature of complexes finds support from
the literature due to Tang et al. [17].
X-ray diffraction studies
0
10
20
30
40
50
60
70
80
2θ-/Scale
PXRD patterns of MorphcbmH and its complexes, viz.
Cu(MorphcbmH)2Cl2, and Zn(MorphcbmH)2X2 (X = Cl,
NO3), exhibit sharp XRD peaks (Figs. 7, 8) with low value
of full width at half maximum (FWHM) thus indicating
their crystalline nature [18, 19]. By using Debye–Scherrer
equation [18, 19], XRD crystallite sizes corresponding to a
value of full width at half maximum (FWHM) for six peaks
of high intensity at respective h values were calculated.
Tables 3 and 5 show the d spacing, 2h, relative intensity,
FWHM and crystallite size of these complexes. The mean
particle sizes calculated using the Debye–Scherrer equation
Fig. 8 Powder XRD of Zn(MorphcbmH)2Cl2
from the line broadening in the diffractograms are found to
be 10.43 and 8.97, 8.88, and 103.21 nm for free ligand
MorphcbmH
and
Cu(MorphcbmH)2Cl2,
Zn(Mor-
phcbmH)2Cl2, and Zn(MorphcbmH)2(NO3)2 complexes,
respectively. The data (Tables 3–5) show that larger the
crystallite size of the sample, the sharper is the peak, i.e.
decrease in FWHM on the XRD pattern. The tabular data
for copper(II) complexes of MorphcbmH is in good
agreement with that for the reported crystalline complexes,
carbamates and agriculturally active organic compounds
[20] (Table 4).
Cl
H
O
C
Cl
H
N
O
C
O
O
O
O
O
O
Zn
C
N
Zn
N
O
O
Cyclic voltammetric study
C
O
H
N
Cl
O
Figures 9–11 show cyclic voltammograms of MorphcbmH,
Cu(MorphcbmH)2Cl2 and Zn(MorphcbmH)2(NO3)2. CV
data of MorphcbmH ligand revealed a reversible couple
Cl
H
Scheme 1 Proposed structure of Zn(MorphcbmH)2Cl2
123

Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of…
Table 3 XRD data of Morpholinecarbamic acid
Morpholinecarbamic acid
Sr. no.
d Spacing
2h
Relative intensity/%
FWHM
Dp/nm
1.
2.
3.
4.
5.
6.
3.924
5.147
4.653
4.839
2.697
3.193
22.656
17.227
19.072
18.331
33.217
27.939
50.22
46.89
43.20
37.35
36.41
34.54
0.1476
0.1968
0.0984
0.0984
0.1968
0.1968
10.06
7.44
14.93
14.92
7.68
7.59
Table 4 XRD data of Cu(MorphcbmH)2Cl2 and Cu(MorphcbmH)2(CH3COO)2
Cu(MorphcbmH)2Cl2 Cu(MorphcbmH)2(CH3COO)2
Sr. no.
d Spacing
2h
Relative
intensity/%
FWHM
Dp/nm
Sr. no.
d Spacing
2h
Relative
intensity/%
FWHM
Dp/nm
1.
2.
3.
4.
5.
6.
2.032
1.983
2.072
2.148
1.960
1.857
44.572
45.734
43.678
42.054
46.264
49.057
14.29
12.72
12.11
10.77
9.95
0.1476
0.1476
0.0984
0.3936
0.1800
0.3936
10.61
10.66
15.87
3.94
1.
2.
3.
4.
5.
6.
5.529
3.305
4.757
3.979
2.764
3.696
16.029
26.973
18.651
22.342
32.386
24.077
93.82
70.19
49.99
49.15
42.51
37.19
0.344
0.196
0.295
0.246
0.196
0.393
4.24
7.58
4.97
6.00
7.70
3.77
8.75
9.49
4.04
Table 5 XRD Data of Zn(MorphcbmH)2Cl2 and Zn(MorphcbmH)2(NO3)2
Zn(MorphcbmH)2Cl2 Zn(MorphcbmH)2(NO3)2
Sr. no.
d Spacing
2h
Relative
intensity/%
FWHM
Dp/nm
Sr. no.
d Spacing
2h
Relative
intensity/%
FWHM
Dp/nm
1.
2.
3.
4.
5.
6.
3.734
6.399
7.708
8.160
5.000
4.123
23.830
13.839
11.479
10.842
17.735
21.552
100
0.2952
0.0984
0.0984
0.2952
0.1968
0.2460
5.03
14.93
14.93
4.94
1.
2.
3.
4.
5.
6.
4.435
4.067
3.787
3.622
3.356
3.188
20.001
21.835
23.469
24.554
26.538
27.957
69.2
100
0.020
0.025
0.015
0.014
0.012
0.011
76.26
60.37
80.91
80.23
78.37
71.21
65.44
54.7
53.6
53.0
49.4
103.5
111.46
131.72
136.69
7.45
6.01
1.0
5.0
0.0
5.0
0.0
–5.0
–1.0
–1.5
–5.0
–1.0
–2
–1
0
1
2
–2
–1
0
1
2
Applied potential/V
Applied potential/V
Fig. 9 Cyclic Voltammogram of MorphcpmH
Fig. 10 Cyclic Voltammogram of Cu(MorphcpmH)2Cl2
123

S. B. Kalia et al.
1.5
1.0
electron processes. Ratio of Ipa/Ipc for two reduction as well
as two oxidation processes exhibited involvement of one-
electron change. Range of potential values of copper(II)
and zinc(II) complexes is well in agreement with that of the
literature data [22].
5.0
Thermal studies
0.0
TG curve of free ligand, MorphcbmH (Fig. 12a), shows it
to be stable up to 60 °C. It exhibits single-step 100 %
decomposition without leaving any residue in the crucible.
DSC curves have revealed an endothermic peak at 83 °C
(Fig. 12b). This is ascribed to sublimation followed by
decomposition to volatile products such as amine, mor-
pholine and carbon dioxide. Endothermic degradation of
MorphcbmH ligand is analogous to that for
4-methylpiperazine-1-carbodithioc acid (4-MPipzcdtH)
[23]. A total mass loss of 100 % in temperature range of
60–140 °C is in agreement with decomposition path for
free MorphcbmH ligand (Eq. 3).
–5.0
–1.0
–2
–1
0
1
2
Applied potential/V
Fig. 11 Cyclic Voltammogram of Zn(MorphcpmH)2(NO3)2
with Epa = 1.50 V and Epc = 1.30 V, DE = 0.20 V.
Corresponding Ipa and Ipc values are 4 and 3.6 A, respec-
tively, with Ipa/Ipc = 1.11. The complexes Cu(Mor-
phcbmH)2X2 (X = Cl, ClO4,NO3) show well-defined
O
N
H
N
C
CO2
OH
+
O
O
ð3Þ
Morph
MorphcbmH
Decomposition of MorphcbmH
redox process corresponding to the formation of the Cu(II)/
Cu(III) couple with anodic peak in the range
Epa = 0.53–0.65 V and the associated cathodic peak in
range Epc = 0.75–0.88 V. This couple is found to be
reversible with DE = -0.23 to -0.19 V and the ratio of
anodic to cathodic peak currents Ipa/Ipc = 0.75–1.0 corre-
sponding to a simple one-electron process [21].
Thermal decomposition of Cu(MorphcbmH)2Cl2 com-
plex follows four-step pathway (Fig. 12c). First step occurs
between 40 and 70 °C with mass loss of 9.12 % corre-
sponding to loss of one mole of hydrochloric acid
(Table 6). Second step occurs between 70 and 160 °C with
mass loss of 9.15 % due to loss of another mole of
hydrochloric acid. Third step involves evolution of carbon
dioxide along with one mole of morpholine in temperature
range 160–355 °C with 32.95 % mass loss. The fourth step
occurs at a temperature of 470–670 °C with mass loss of
29.00 % which corresponds to evolution of one mole of
carbon monoxide and amine, i.e., morpholine leaving
residual species CuO having 20.05 mass percent. DSC
curve of complex exhibits three exothermic peaks at tem-
peratures 43, 157 and 290 °C for first, second and third
steps, respectively (Fig. 12d).
Cyclic voltametric measurements for complexes of
zinc(II), viz. Zn(MorphcbmH)2X2 (X = Cl, ClO4, NO3,
CH3COO and X2 = SO4) gave: two anodic waves lying in
potential range between Epa = (i) 0.63–0.90 V, (ii) -0.68
to -0.62 V and two cathodic waves lying in potential
range between Epc = (i) 0.77–0.93 V, (ii) -1.10 to
-0.40 V. Respective DEs lie in the range (i) -0.30 to
-0.03 V and (ii) -0.28 to 0.44 V with corresponding Ipa/
Ipc = (i) 0.82–1 and (ii) 0.83–0.96. Data of CV study of
Zn(II) complexes revealed two cathodic reduction peaks,
which are attributed to reduction of Zn(II) ? Zn(I) and
Zn(I) ? Zn(0), respectively, while two anodic oxidation
peaks are attributed to oxidation of Zn(0) ? Zn(I) and
Zn(I) ? Zn(II), respectively, indicating reversible one-
That Cu(MorphcbmH)2 was first-stage intermediate of
thermal decomposition of [Cu(MorphcbmH)2]Cl2 at
157 °C has been supported by measuring the FTIR of
residue species. This has been done by stopping the heat-
ing, cooling the residue and measuring its FTIR. FTIR
123

Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of…
spectrum of proposed species, i.e., Cu(MorphcbmH)2,
exhibited peculiar vibrational modes at 1628, 1450, 657
and 418 cm-1 due to characteristic absorptions of m(CO2),
m(C=N) of NCO2, d(NCO2) and m(Cu–O) moieties of
MorphcbmH ligand, respectively [8, 10, 24] (Fig. 13).
Thermal decomposition of Cu(MorphcbmH)2(ClO4)2
occurs in three steps (Fig. 12e). First step involves a mass
loss of 24.50 % at a temperature of 40–160 °C which may
correspond to loss of four moles of O2 (oxidation/reduction
process). Elimination of two moles of hydrochloric acid and
two moles of amine, i.e., morpholine with total mass loss of
46.95 % at a temperature of 160–345 °C, occurs in second
step, while third step occurs at a temperature of 345–605 °C
with mass loss of 13.98 % corresponding to elimination of
one mole each of CO2 and CO. Mass percent 15.17 %
remained as CuO residue (Table 6). DSC curve shows an
endothermic peak at 136 °C for first step and two exother-
mic peaks at 221 and 370 °C for second and third steps,
respectively (Fig. 12f). An intramolecular solid phase redox
reaction has been proposed to be responsible for appearance
of endothermic peak at 136 °C most plausibly attributed to
simultaneous presence of both oxidizing (perchlorate) and
reducing (morpholine) moieties in a same complex molecule
[25]. Final TG residue, CuO was cooled, collected and
estimated for copper by EDTA titration. CuO Analysis
found: Cu 79.41 %; Calculated: 79.87 %.
Fig. 12 TG/DSC curves of:
a, b MorphcbmH;
c, d Cu(MorphcbmH)2Cl2;
e, f Cu(MorphcbmH)2(ClO4)2;
g, h Zn(MorphcbmH)2Cl2;
i, j Zn(MorphcbmH)2(ClO4)2;
k, l Zn(MorphcbmH)2(NO3)2
and m, n Zn(MorphcbmH)2
(CH3COO)2
123

S. B. Kalia et al.
Fig. 12 continued
TG/DSC curve of Zn(MorphcbmH)2Cl2 complex
(Fig. 12g, h) shows that it has decomposed in three stages.
First stage involves elimination of two moles of
hydrochloric acid and one mole of morpholine at a tem-
perature of 130–385 °C with mass loss of 40.07 %. Second
step occurs at a temperature of 425–540 °C with mass loss
of 32.95 % corresponding to loss one mole each of mor-
pholine and carbon dioxide. Last step involves elimination
of carbon monoxide molecule with a mass loss of 7.25 %
between 540 and 650 °C leaving ZnO as final residue with
20.06 mass percent. DSC curve of complex exhibits one
endothermic and one exothermic peak at 127 and 328 °C,
respectively, for first step and one exothermic peak at
483 °C for second step (Table 6).
Thermal decomposition of Zn(MorphcbmH)2(ClO4)2
(Fig. 12i) occurs in three steps. First step involves mass
loss of 38.30 % at a temperature of 50–170 °C corre-
sponding to loss of two moles of perchloric acid. Elimi-
nation (oxidative/reductive: since oxidation process is not
independent of reduction process) of one mole of oxygen
and one mole of ethylene with a mass loss of 11.50 % at a
temperature of 200–300 °C occurs in second step. While
the third step occurring at temperature of 300–305 °C with
a mass loss of 35 % corresponding to elimination of one
mole of CO2, one mole of CO, one mole of nitrogen and
three moles of ethylene corresponds well with oxidative
decomposition of the intermediate to yield ZnO (15.41 %)
as final residue. DSC curve (Fig. 12j) exhibits two
endothermic peaks at 137 and 186 °C for first and second
steps, respectively, while third step exhibits exothermic
peak at 303 °C.
The fact that ZnO was final residue of thermal decom-
position of [Zn(4-MorphcbmH)2](ClO4)2 has been inferred
from its PXRD pattern (Fig. 14). PXRD pattern exhibited
peaks at 2h values of 31.74°, 34.37°, 36.20°, 47.45°,
56.55°, 62.80° and 67.96° corresponding to planes (100),
(002), (101), (102), (110), (103) and (112), respectively.
Similar PXRD pattern for ZnO has earlier been reported in
the literature [26].
TG/DSC curves of Zn(MorphcbmH)2(NO3)2 and
Zn(MorphcbmH)2(CH3COO)2 complexes show them to
decompose in two steps (Table 6). The first step involving
elimination of two moles of nitric acid and two moles of
acetic acid at a temperature of 40–205 and 45–150 °C with
mass loss of 28 % and 27 %, respectively(Fig. 12k, m).
The second step occurs at a temperature of 205–385 °C
with mass loss of 44.40 % corresponding to decomposition
of intermediate to loss of one mole of carbon monoxide and
two moles of amine, i.e., morpholine in former complex,
while in latter complex, it occurs at a temperature of
150–310 °C with mass loss of 55 % corresponding to loss
two moles of amine, i.e., morpholine, one mole of carbon
123

Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of…
123

S. B. Kalia et al.
50
40
30
20
10
0
418
657
1628
1388
571
1450
1258
1106
882
1800 1600 1400 1200 1000
800
600
400
200
wavenumber/cm–1
Fig. 13 FTIR spectrum of first-stage intermediate Cu(4-Mor-
phcbmH)2 of thermal decomposition of Cu(4-MorphcbmH)2]Cl2
1200
1000
1 0 0
002
800
2
2
0
1
600
400
200
1
1
20
30
40
50
2θ
60
70
80
Fig. 14 Powder XRD of final residue (ZnO)
monoxide and one mole of carbon dioxide. Residue left
corresponds to ZnCO3 in former case and ZnO in latter
case with 27.73 and 18.21 % mass percent, respectively.
The DSC curve of Zn(MorphcbmH)2(NO3)2(Fig. 12l)
shows two endothermic peaks at a temperature of 122 and
147 °C, while second step shows two exothermic peaks at
194 and 212 °C. DSC curve of Zn(MorphcbmH)2(CH3-
COO)2 (Fig. 12n) shows three endothermic peaks at 51,
117 and 148 °C for first step and one endothermic peak at a
temperature of 214 °C for second step.
Thermal decomposition patterns for carbamate com-
pounds, viz. [Zn(MorphcbmH)2]Cl2, [Zn(MorphcbmH)2]
(CH3COO2)2 and [Zn(MorphcbmH)2](NO3)2, i.e., with
monovalent counter anions, were not observed to be com-
parable. In these particular cases, the anion effect may most
plausibly contribute to a combination of factors related to
123

Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of…
Table 7 Effect of MorphcbmH and some of its copper(II) and zinc(II) compounds on lipase activity (l mol mL-1 min-1
)
Chemical compound
Lipase activity
0 min
Lipase activity
10 min
Lipase activity
30 min
Lipase activity
50 min
Lipase activity
70 min
MorphcbmH
28.58
31.86
27.51
32.03
43.16
48.16
34.97
30.30
38.41
2.712
3.022
2.677
3.169
4.096
5.070
3.458
3.122
3.012
0.898
0.869
0.865
1.043
1.362
1.187
1.148
0.901
1.012
0.564
0.464
0.514
0.605
0.651
0.623
0.685
0.565
0.563
0.403
0.186
0.357
0.420
0.446
0.341
0.044
0.345
0.401
Cu(MorphcbmH)2Cl2
Cu(MorphcbmH)2(ClO4)2
Cu(MorphcbmH)2(NO3)2
Zn(MorphcbmH)2Cl2
Zn(MorphcbmH)2(ClO4)2
Zn(MorphcbmH)2(NO3)2
Zn(MorphcbmH)2(CH3COO)2
Zn(MorphcbmH)2SO4
crystal lattice, e.g., mismatching of ion size, shape and
imbalance of attractive power while TG/DSC curves for
[Zn(4-MorphcbmH)2](ClO4)2 and [Zn(4-MorphcbmH)2]
(NO3)2 have exhibited similar exothermic one and two
decomposition steps with single broad exotherm for former
and two sharp exotherms for latter complex. However, final
residue percentage of 15.41 and 27.73 % for two complexes,
respectively, as well as of 15.17 % for [Cu(Mor-
phcbmH)2](CIO4)2 has revealed non-explosive nature of
complexes with perchlorate and nitrate as counter anions.
It has been observed that for TG/DSC patterns for the
complexes under investigation experimental percent mass
loss matches with the corresponding theoretical percent
mass loss (Table 6) for their various stages of thermal
decomposition which supports present thermal decompo-
sition pattern is in relevance to the literature reports [23].
Conclusions
Morpholinecarbamic acid and its copper(II) and zinc(II)
complexes were synthesized and investigated by FTIR,
fluorescence, UV–visible and 1H NMR spectroscopy,
magnetic studies which support four coordination around
copper(II) and zinc(II). Thermal study of MorphcbmH and
its complexes indicated their low thermal stability, IDT
values 40–80 °C with the exception of Zn(Mor-
phcbmH)Cl2 (IDT = 130 °C). TG curves exhibit two or
more than two steps of decomposition patterns. The final
product of thermal decomposition is MO or MCO3
(M = Cu, Zn). All complexes gave increase in lipase
enzyme inhibition activity (48.16–0.044 lmol mL-1 min-1
with increase in time due to their ability to block the active
site of the lipase enzyme.
)
Lipase enzyme activity
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