Synthesis and crystal structure of cobalt(II) Schiff base precursor for cobalt oxide thin film by thermal chemical vapor deposition

Article abstract of DOI:10.1016/j.poly.2015.12.033

The tetrahedral Schiff base complex bis(N-isopropylsalicylaldimine)cobalt(II) [Co(saliprn)₂] (CSI) was prepared by template method. The complex was characterized by FT-IR, mass spectroscopy, TG/DTA and single crystal X-ray structure determination analysis. The dynamic TG analysis showed that the complex is completely volatile. The equilibrium vapor pressure of the complex was studied by non-isothermal and isothermal thermogravimetric transpiration techniques over the temperature range of 474-514 K. The E_a (48.4 kJ mol^-1) and ΔH_sub (111.54 kJ mol^-1) for the complex and expression for temperature dependence of vapor pressure (P_e) were obtained. The thermal behavior of the cobalt(II) complex was studied by thermogravimetry techniques using different non-isothermal heating rates under nitrogen atmosphere. The complex was found to be volatile and used in thermal chemical vapor deposition for the development of nanocrystalline cobalt oxide thin films over silica substrates. These nanocrystalline thin films were analyzed by XRD and SEM confirmed the presence of Co₃O₄ phase with almost nil carbon.

Full text of DOI:10.1016/j.poly.2015.12.033

Accepted Manuscript
Synthesis and Crystal Structure of Cobalt (II) Schiff Base Precursor for Cobalt
Oxide Thin Film by Thermal Chemical Vapor Deposition
P. Sravanthi, C. Chandrakala, M.G. Johnson, S. Arokiasamy, K.S. Nagaraja, B.
Jeyaraj
PII:
S0277-5387(15)00783-4
DOI:
http://dx.doi.org/10.1016/j.poly.2015.12.033
POLY 11732
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
27 September 2015
17 December 2015
Please cite this article as: P. Sravanthi, C. Chandrakala, M.G. Johnson, S. Arokiasamy, K.S. Nagaraja, B. Jeyaraj,
Synthesis and Crystal Structure of Cobalt (II) Schiff Base Precursor for Cobalt Oxide Thin Film by Thermal
Chemical Vapor Deposition, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.12.033
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Synthesis and Crystal Structure of Cobalt (II) Schiff Base Precursor for Cobalt Oxide Thin
Film by Thermal Chemical Vapor Deposition
P. Sravanthi a, C. Chandrakala a, M. G. Johnson a, S. Arokiasamy b, K. S. Nagaraja a, B. Jeyaraj
a*
a Department of Chemistry, Loyola Institute of Frontier Energy (LIFE), Loyola College, Chennai
– 34, India
b Department of Chemistry, VIT University, Chennai – 127, India
*Corresponding author. Tel.:+91 8056029860
E-mail: psravanthireddy1@gmail.com, Jeyaraj.boniface@gmail.com
Abstract
The tetrahedral Schiff base complex bis(N-isopropylsalicylaldimine)cobalt(II)
[Co(saliprn)2] (CSI) was prepared by template method. The complex was characterized by FT-
IR, mass spectroscopy, TG/DTA and single crystal X-ray structure determination analysis. The
dynamic TG analysis showed that the complex is completely volatile. The equilibrium vapor
pressure of the complex was studied by non-isothermal and isothermal thermogravimetric
transpiration techniques over the temperature range of 474 K – 514 K. The Ea (48.4 kJmol-1) and
∆Hsub (111.54 kJmol-1) for the complex and expression for temperature dependence of vapour
pressure (Pe) obtained. The thermal behavior of the cobalt(II) complex was studied by
thermogravimetry techniques using different non-isothermal heating rates under nitrogen
atmosphere. The complex was found to be volatile and used in thermal chemical vapour
deposition for the development of nanocrystalline cobalt oxide thin films over silica substrates.
These nanocrystalline thin films were analyzed by XRD and SEM confirmed the presence of
Co3O4 phase with almost nil carbon.
Keywords: Cobalt complex; thermo gravimetric analysis; Vapor pressure and kinetics; Cobalt
Oxide Thin films; SEM and XRD.
1. Introduction:
Metal oxide thin films have attracted a lot of attention due to their importance in the material
science, microelectronics, heterogeneous catalysis and also utilized as spacer layers on
electrotransparent model systems [1-5]. The inorganic materials are formed from molecular
metal-organic precursors by chemical vapor deposition, molecular beam epitaxy and sol-gel have
advantages over solid-state synthesis [6]. The majority of the chemical vapor deposition activity
has focused on fabrication of cobalt oxide thin film layers for magento-optic applications,
1

electrochemical transparent properties of semiconducting oxides, strong electron interactions in
solids, glass industry for colouration, and chemical process as catalytic activator in oxidation
sites [7-10].
Chemical vapor deposition requires the metal complexes which should meet general
conditions such as sublime without decomposition, easy handling, low or no toxicity for the
material deposited and/or the substrate used [11]. The vapor pressure of the precursor as a
function of temperature influences the choice of precursor in chemical vapor deposition and
related processes [12]. Several techniques such as ebulliometric, static, manometric measurement
and Knudsen cell techniques are currently used for the measurement of the vapor pressure of a
pure substance [13, 14]. Several studies [15] have shown that thermogravimetry is a rapid and
convenient technique for the determination of vapor pressure curves, enthalpy of sublimation and
vaporization, solid state kinetics of chemical reactions for volatile compounds. Among several
methods for vapor pressure measurements transpiration technique also known as gas-
entertainment technique is more versatile and enables vapor pressure over a wide range of
temperature [16]. Thermochemical properties of Schiff bases have attracted our attention in their
ability to coordinate metal ions, acting as bidentate or tetradentate ligand to give metal chelates
[17].
We hereby report the reaction of Schiff base ligands with Co2+ which led to potential
precursors for producing cobalt oxide thin films for technological applications [18] by thermal
chemical vapour deposition technique. This includes synthesis, crystal structure determination
and thermogravimetric analysis. The differential and integral iso-conversional methods [17] were
used for the evaluation of the activation energy from non-isothermal data. The vapor pressure of
bis(N-isopropylsalicylaldimine)cobalt(II) was measured by thermogravimetry based transpiration
technique [19, 20].
2. Experimental:
2.1.Materials:
Cobalt acetate tetrahydrate [Merck, 97%], and isopropylamine [Aldrich, 98%] were used
as such in the synthesis of cobalt complexes. Methanol, acetone, dichloromethane and ethanol
were used after distillation.
2

2.2.Synthesis of bis(N-isopropylsalicylaldimine)cobalt(II):
An ethanolic solution of salicylaldehyde (6 moles) and isopropyl amine (6 moles) were added to
the aqueous solution of cobalt(II) acetate (7 moles) with constant stirring which was refluxed for
3-4 h at 323K and left for overnight in an ambient temperature. The obtained brick red
precipitate was filtered and dried in a vacuum desiccator containing fused calcium chloride. The
compound was recrystallised using dichloromethane which forms hexagonal crystals (Fig: 1) and
dried over fused calcium chloride.
2.3.Characterization techniques:
The FT-IR spectrum for the complexes was recorded in KBr medium to infer the various
stretching frequencies using Perkin Elmer FTIR spectrometer in the range of 4000-400 cm-1. The
Electronic Ionization - Mass Spectrum (EI-MS) was recorded by YOKUDELNA_ES+_2000
model at an accelerating voltage of 32V at ambient temperature. The thermogram was carried
out with Perkin Elmer Pyris-Diamond TG-DTA. The purge gas was high purity nitrogen dried by
passing through refrigerated molecular sieves (Linde 4A) at a flow rate 12 dm3h-1. The single
crystal XRD data was collected using a Bruker Apex – II CCD diffractometer with omega and
phi scan mode with Mo-Kα (λ=0.71073 Å) radiation at room temperature (T=296.3 K). The
ORTEP view of the molecule was drawn at 50% probability thermal displacement ellipsoids
with the atom numbering scheme. SEM for the cobalt oxide thin films was analysed by FEI
Quanta FEG 200 instrument. The powder X-Ray diffraction measurements were performed with
Bruker XPERT-PRO Spectrometer with a copper tube (λ=1.54060 Å).
2.4.Preparation of Thin film:
The thin films of cobalt oxide were coated by using the atmospheric thermal metallo-
organic chemical vapour deposition (TMOCVD) where alumina served as a deposition chamber.
Prior to each deposition, the silica substrate was sonicated for 30 min on an ultrasound sonicator
and the reaction chamber was cleaned by acetone. This process was done to ensure that the
deposition surfaces were free from contamination and defects.
For the deposition of cobalt oxide thin film, the cleaned surface of silica substrates and
fine powder of the precursor were kept in a quartz boat which was kept in a working chamber.
3

This chamber was maintained at 550°C in a digitally controlled furnace. On getting to the hot
zone, the precursor kept in the quartz boat sublimed before it thermally decomposed resulting in
the coating on the substrates. The whole process was left for 2 h at the deposition temperature of
550°C. After cooling, the coated films were characterized by SEM/EDAX and XRD to analyze
the phases.
3. Result and discussion:
3.1.Characterization:
The IR spectral studies (Fig: 2) suggested the band at 1605 cm-1 correspond to υ(C=N)
upon complexation indicating the involvement of azomethine groups in the coordination and the
band at 1330 cm-1 due to υ(phenolic C-O). The bands observed at 426 cm-1 and 528 cm-1 were
assigned to υ(Co-N) and υ(Co-O) respectively [21]. The isotopic cluster peaks of the complex
(Fig: 3) at m/z =384 is identified as the molecular ion peak. The cluster peaks at m/z=222
correspond to the species including metal. The peak at m/z = 164 corresponds to the ligand
without the metal atom. The stereochemistry of the Co(II) complex was given by the magnetic
moment 3.87 BM corresponding to three unpaired electrons which suggests four co-ordinate
tetrahedral arrangement.
3.2.Non-Isothermal Thermogravimetry (TG) study:
Bis(N-isopropylsalicylaldimine)cobalt(II) complex undergoes single smooth step weight
loss on heating between 474 - 514 K with nil residue (Fig:4). It is interesting to note that the
enhanced thermal stability and volatility is due to expulsion of two water molecules and
coordination of azomethine nitrogen (-CH=NH) with Co instead of carbonyl oxygen as in
bis(salicylaldehydato)cobalt(II) dihydrate. It was decided to substitute H of =NH (Fig: 1) by
alkyl chains thereby tuning the volatilization behavior depending upon the length of the alkyl
chain. The single step weight loss gives a wide temperature window for volatilization as the
melting point is the important requirement for potential precursor for CVD applications [22, 23].
Non-isothermal TG runs of CSI at different heating rates revealed that the complex was
thermally stable upto 514 K. The temperature dependent equilibrium vapor pressure derived
from Dalton’s law of partial pressures for a mixture of ideal gas is calculated as:
ꢀ = ꢂꢃꢄ /ꢆꢇ
ꢁ
ꢅ
ꢈ
4

Where W is the mass loss at various isothermal temperatures, Vc is the flow of carrier gas, R is
the universal gas constant, M is the molecular mass of the monomeric precursor vapor species,
Tc is the temperature of the carrier gas. The vapor pressure Pe at each saturation temperature was
calculated from the mass loss of the sample within a definite period. Attainment of equilibrium
conditions was evident from the mass loss plots at all the isothermal steps as seen from the
straight line plots passing through the origin (Fig: 5a), showing equal masses are vaporized in
equal intervals of time. The least-square expressions for the complex derived from the
corresponding vapor pressure data plotted as log Pe vs 1/T (Fig: 5b) .The temperature
dependence of Pe could be represented by the expression
ꢀ
ꢊꢀꢋ
−58,284 ± 981
ꢁ
ꢐ ꢒ
+ 18 ± 0.2ꢏ 474 − 514ꢑ
ln ꢉ
ꢌ =
ꢍ
ꢎ
The enthalpy of vaporization was calculated by multiplying the slope of the equation with -2.303
R, a value of 111.54 K J mol-1 was derived for the standard enthalpy of sublimation (∆subH) [15,
24, 25].
3.3.Determination of activation energy:
The rate constant k for the vaporization enthalpy of the complexes was determined for every 10
% weight loss of the complex. The expression for k is given by
ꢔꢕ
ꢓ =
ꢔꢖ
Where dα/dt is the derivative of the fraction vaporized with respect to time and k is the rate
constant of vaporization, whereas degree of conversion (α) is calculated in terms of mass loss.
ꢗꢘ − ꢗꢙ
ꢕ =
ꢗꢘ − ꢗꢚ
Where wt is the weight at any time, wi and wf are the initial and final weights. The Arrhenius
expression is represented as
ꢝꢞ
ꢟ
ꢠꢡ
ꢓ = ꢛꢜ
The plot of ln k versus 1000/T (Fig: 6a) was found to be linear. The activation energy (Ea) for the
vaporization of the complexes was calculated from the slope. The activation energy values for
5

different heating rates of 2, 4, 6, 8, 10 and 12 K min-1are obtained as 111 0.4, 110 0.4, 109 0.4,
113 0.4, 116 0.4 and 115 0.4 kJmol-1. However, due to complexity of the kinetic description
concerning the solid state reaction processes, it is usually assumed that the apparent activation
energy is not a constant value but depends on α. Therefore, the kinetic procedure adopted in this
work was first based on two multi-heating rate methods. Both approaches determine the
activation energy using thermal analysis data carried out at different fixed heating rates. The
activation energy for the non-isothermal sublimation of CSI was calculated using Kissinger
expression:
ꢐ
ꢒꢪꢫꢬ
ꢛꢃ
ꢭꢮ
ꢣ
ꢨ 1 − ꢕꢤ
ꢭꢮ
ꢃꢄꢤ
ꢩ
ꢯ
− ꢢ
lnꢏ ꢢ ꢦ = ꢧꢨ
ꢄꢤꢥ
ꢦ
Where Tm and αm are the absolute temperature and weight loss at the maximum weight-loss rate
(dα/dt)m. From the slope of ln(β/T2 ) against 1/Tm (Fig: 6b) the activation energy was found to
m
be 123 1kJmol-1. The activation energy values for different conversion levels were also
determined by Flynn-Wall-Ozawa technique [26] with the expression:
ꢛꢭꢮ
ꢃ
ꢭꢮ
ꢃꢄ
ꢐ ꢒ
ꢧꢨ ꢣ = ꢧꢨ ꢢ
ꢰ ꢐ ꢒꢲ
ꢦ − ꢧꢨ ꢱ ꢕ −
The straight lines obtained from the plots of heating rates against temperature (Fig: 6c) gave a
mean Ea value 107 0.7kJmol-1. Kissinger-Akahira-Sunrose method [27, 28] similar to Kissinger
method, but thermodynamic temperature for the maximum weight loss was replaced by
thermodynamic temperature adequate for a certain level of conversion of the complex is
expressed by the equation as
ꢣ
ꢛꢃ
ꢐ ꢒ
ꢭꢳ ꢴ
ꢭ
ꢃꢄ
ꢧꢨ ꢢ ꢦ = ꢧꢨ ꢢ
ꢄꢥ
ꢦ −
The plot ln(β/T2) against 1/T (Fig: 6d) gave a straight line with apparent activation energy as
98 0.7 kJmol-1. The activation energy by Friedman method (Fig: 6e) [29] from the following
expression yielded a value 93.8 1.3 kJmol-1.
ꢔꢕ
ꢧꢨ ꢢꢣ ꢉ ꢌꢦ = ꢧꢨ ꢛꢵ ꢕ −
ꢔꢄ
ꢭꢮ
ꢃꢄ
ꢰ
ꢐ ꢒꢲ
6

The model fitting analysis of the non-isothermal data (Table 1) suggest that the sublimation
kinetics follow the models. The experimentally determined value suggests that the thermal
signification occurs predominantly via congruent sublimation as a single step process.
3.4.Structural description of Compound:
The crystal structure was solved by a direct method with the SHELXS- 97 program [29, 30]. The
single crystal data (Table 2) of the bis(N-isopropylsalicylaldimine)cobalt(II) complex (CCDC
No: 1012524) revealed that it crystallizes in the orthorhombic space group Pbac. The unique
metal center (Co) is surrounded by two Schiff base ligands (Fig.7) forming a distorted
tetrahedron. The ligand is bidentate with one phenolato – O and one imine – N as the donor sites.
The basal plane of the cobalt(II) is formed by two imine nitrogen and two phenolato oxygen
atoms which are in the axial positions from the two Schiff base ligands giving CoN2O2, with
exception of the isopropyl groups the complex shows almost perfect C2 symmetry. The bond
lengths (Table 3) of C(7) – N(1) [1.289Å ] and C(17) – N(2) [1.272 Å] confirm the presence of
double bonds and are comparable to those in other Schiff base complex [31]. The co-ordination
of the nitrogen to the cobalt metal caused the reduction of bond lengths of Co(1) – O(1)[1.9020
Å] of the isopropyl substituted complex from 1.921Å in the parent compound Co(sal)2. The co-
ordination by nitrogen which replaces oxygen in Co(sal)2 increased the covalent nature and
volatility. The bond angle Co(1) – N(2) – C(17) is 120.69°and the rotational motion of the alkyl
groups shield the cobalt atom from the approach of water molecule [32].
3.5.Scanning Electron Microscope and EDAX of cobalt oxide coated thin films:
The cobalt oxide thin films were prepared by atmospheric thermal CVD method on silica
substrate using the present complex as MOCVD precursor. The surface morphology of the thin
film (Fig: 8) was determined by the rate of precursor transport, decomposition reaction, surface
diffusion and lattice incorporation during the deposition process. The surface morphology of the
deposited films revealed a progressive grain growth with increasing temperature. The SEM
micrographs of cobalt oxide films exhibit uniform dense microstructure grown at 550 °C over
silica substrate. Energy Dispersion X-Ray (EDX) analysis was carried out on as deposited cobalt
oxide films indicating the peaks corresponding to cobalt and oxygen. No sizeable carbon
contamination could be detected supporting the purity of the film by thermal chemical vapour
deposition. In our previous work, the deposition of CrN/Ni by Plasma Assisted Metallo Organic
CVD using precursors like [Cr(acac)3] and [Ni(acac)2en] small amounts of carbon deposition
7

was observed. This was rectified by using certain catalysts like ammonium biflouride [33]. In the
present work EDAX indicated the absence of carbon.
The powder cobalt oxide from thin films deposited at 550 °C on a Si(100) substrate have
shining blackish grey colour which was found to be crystalline with (311) orientation (JCPDS
No 78:1969) revealing the presence of face centered cubic plane by powder XRD. It was
observed that the films deposited in the oxygen atmosphere comprised of Co3O4 phase without
carbon contamination. The detection limit for carbon is greater than 5% in XRD. According to
the XRD data (311) is the strongest reflection in the polycrystalline Co3O4, being as strong as
(111) reflection. The preference for (111) over (220) and (400) is also observed (Fig: 9). XRD
study of the crystallite reduced form of different cobalt oxides have been investigated by X-Ray
diffraction and the peaks indexed for each type of cobalt oxide [34]. Cobalt oxide thin films have
also been developed using Co(acac)3 as MOCVD precursor and obtained CoO an Co2O3 phases
under N2 atmosphere with slight amount of carbon [10]. In the present study as it being
atmospheric chemical vapour deposition we obtained Co3O4 as a major phase and no CoO phase
could be detected. The average grain size of the powder Co3O4 obtained from the thin film
deposition was calculated using Debye-Scherrer’s equation.
0.9ꢷ
ꢶ =
ꢗ cos ꢸ
Where D is the grain size, λ is the x-ray wavelength, θ is the Bragg angle, w is the full
width at half maximum of diffraction peak. The average grain size is observed at 5.89 nm at
lattice constant of 5.17 Å [35].
4. Conclusion:
The coordination complexes of several transition metals have been extensively used as
precursors for the production of the metallic or metal oxide films by TCVD process. Hence a
systematic approach for the development of volatile precursor using aromatic based ligand
resulted a promising vapour source of cobalt. This complex is a better precursor for thermal
CVD owing to the high volatility of imine (-CH=NH) based complex. The vapor pressure (Pe)
and sublimation enthalpies (∆Hsub) were evaluated for bis(N-isopropylsalicylaldimine)cobalt(II)
complex by TG based transpiration technique in which activation energy was found to agree with
enthalpy of isothermal sublimation process. The activation energy values for non-isothermal
8

sublimation processes agree with each other. The SEM images confirm the uniform coating of
the complex over silica substrate, with the incorporation of cobalt and oxygen with almost nil
carbon residues.
Supplementary material
Crystallographic data of bis(N-isopropylsalicylaldimine)cobalt(II) complex has been deposited
with the Cambridge Crystallographic Data Centre [CCDC No. 1012524]. Copies of the data can
be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 0
1223 336 033; email: deposit@ccdc.cam.ac.uk.
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Figure Titles:
1. Fig 1: Reaction Scheme of bis(N-isopropylsalicylaldimine)cobalt(II)
2. Fig 2: FT-IR spectrum of bis(N-isopropylsalicylaldimine)cobalt(II)
3. Fig 3: EI-Mass spectrum of bis(N-isopropylsalicylaldimine)cobalt(II)
4. Fig 4: TG/DTA of bis(N-isopropylsalicylaldimine)cobalt(II) in N2 atmosphere at a
heating rate of 10°C min-1.
5. Fig 5: (a) Mass loss against time isothermal plots and (b) Clausius-Clapeyron plot.
6. Fig 6: Non-isothermal plots (a) Arrhenius Plots of ln k vs 1/T (b) Kissinger Plot of
ln(β/T2 ) vs 1/Tm (c) Flynn – Wall of ln β vs 1/T (d) Kissinger-Akahira-Sunrose (KAS)
m
Plot of ln(β/T2) vs 1/T (e) Friedman Plots of lnβ*(dα/dT) vs 1/T of bis(N-
isopropylsalicylaldimine)cobalt(II) at different heating rates (°C min-1).
7. Fig 7: ORTEP and packing diagram of bis(N-isopropylsalicylaldimine)cobalt(II) with
50% probability.
8. Fig 8: SEM and EDAX images of the cobalt oxide coating obtained on silica substrate
using bis(N-isopropylsalicylaldimine)cobalt(II) complex as precursor.
9. Fig 9: X-ray Diffraction of the powder cobalt oxide collected from the thin film coatings
over silica substrate.
12

H
C
H3C
O
CH3
Ethanol
Reflux for 5-6h
+
+
(CH3COO)2 Co. 4H2O
CH
NH2
OH
Isopropylamine
Salicylaldehyde
H3C
CH3
CH
H
C
N
O
Co
O
N
C
H
CH
H3C
CH3
Fig 1: Reaction Scheme of bis(N-isopropylsalicylaldimine)cobalt(II)
100.0
95
90
85
2358.42
80
75
70
65
60
55
50
3780.63
3547.17
426.68
1868.03
2243.98
2492.64
528.75
795.97
%T
937.06
45
40
35
30
25
20
15
10
5
2825.81
902.82741.56
1076.81
3293.53
3255.63
3015.17
701.05
1153.50
1492.50
1605.04
1567.66 1423.79
1268.56
1330.79
0.0
4000.0 3600 3200
2800 2400 2000
1800
1600
1400
1200 1000
800
600
400.0
cm-1
Fig 2: FT-IR spectrum of bis(N-isopropylsalicylaldimine)cobalt(II)
13

Fig 3: EI-Mass spectrum of bis(N-isopropylsalicylaldimine)cobalt(II)
2500
25
2000
1500
1000
500
0
20
15
10
5
0
-5
-10
-15
-500
0
50
100 150 200 250 300 350 400 450
Temp, °C
Fig 4: TG/DTA of bis(N-isopropylsalicylaldimine)cobalt(II) in N2 atmosphere at a heating
rate of 10°C min-1
14

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
474 K
484 K
494 K
504 K
514 K
0
10
20
30
40
50
60
Time/min
(a)
7.0
6.5
6.0
5.5
5.0
4.5
1.90 1.95 2.00 2.05 2.10 2.15 2.20 2.25 2.30
1000/T
(b)
Fig 5: (a) Mass loss against time isothermal plots and (b) Clausius-Clapeyron plot.
15

-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
(a)
2°C
4°C
6°C
8°C
10°C
12°C
1.76 1.78 1.80 1.82 1.84 1.86 1.88 1.90
1000/T, K
-9.2
-9.4
-9.6
(b)
-9.8
-10.0
-10.2
-10.4
-10.6
-10.8
-11.0
1.66
1.68
1.70
1.72
1.74
1.76
1.78
1000/T ,K
m
16

10
20
30
40
50
60
70
80
(C)
2.5
2.0
1.5
1.0
0.5
1.65
1.70
1.75
1.80
1.85
1.90
1000/T, K
-10.0
-10.4
-10.8
-11.2
-11.6
-12.0
10
20
30
40
50
60
70
80
(d)
1.64
1.68
1.72
1.76
1.80
1.84
1.88
1000/T, K
17

-1.4
-1.6
-1.8
-2.0
-2.2
-2.4
-2.6
-2.8
-3.0
-3.2
(e)
1.68 1.70 1.72 1.74 1.76 1.78 1.80 1.82 1.84
1000/T
Fig 6: Non-isothermal plots (a) Arrhenius Plots of ln k vs 1/T (b) Kissinger Plot of ln(β/T2 )
m
vs 1/Tm (c) Flynn – Wall of ln β vs 1/T (d) Kissinger-Akahira-Sunrose (KAS) Plot of
ln(β/T2) vs 1/T (e) Friedman Plots of lnβ*(dα/dT) vs 1/T of bis(N-
isopropylsalicylaldimine)cobalt(II) at different heating rates °C (min-1).
18

Fig 7: ORTEP and packing diagram of bis(N-isopropylsalicylaldimine)cobalt(II) with 50%
probability.
19

Fig 8: SEM and EDAX images of the cobalt oxide coating obtained on silica substrate using
bis(N-isopropylsalicylaldimine)cobalt(II) complex as precursor.
250
200
150
100
50
(311)
(220)
(440)
(511)
(111)
(222)
0
0
10
20
30
40
50
60
70
80
90
2θ (Deg.)
Fig 9: X-ray Diffraction of the powder cobalt oxide collected from the thin film coatings
over silica substrate.
20

Table Titles:
1. Table 1:Non-isothermal sublimation kinetics of bis(N-isopropylsalicylaldimine)cobalt(II)
2. Table 2:Experimental crystal data for bis(N-isopropylsalicylaldimine)cobalt(II).
3. Table 3:Selected interatomic distances (Å) and angles (°) for bis(N-
isopropylsalicylaldimine)cobalt(II)
21

Table 1:
Non-isothermal sublimation kinetics of bis(N-isopropylsalicylaldimine)cobalt(II).
Non-isoconvertional methods
Ea , kJmol-1
Arrhenius method
111 0.4, 110 0.4, 109 0.4, 113 0.4, 116 0.4
and 115 0.4
123 1
Flynn Wall Ozawa method
Kissinger method
107 0.7
98 0.7
Kissinger-Akahira-Sunrose method
Friedman method
93.8 1.3
22

Table 2:
Experimental crystal data for bis(N-isopropylsalicylaldimine)cobalt(II).
Empirical Formula
Formulae weight
C20H25CoN2O2
384.35
Temperature
296(2) K
Crystal System, Space group
a(Å)
Orthorhombic, Pbca
15.1638(7)
b(Å)
13.1829(6)
c(Å)
19.3931(9)
α(°)
90
β(°)
90
γ(°)
90
Volume (Å3)
3876.7(3)
Z, Calculated density (Dcalc ) (mg/m3)
Absorption coefficient (mm-1)
F(000)
Z: 8, 1.317
0.900
1616
Crystal Size
0.40 x 0.30 x 0.30 mm
2.30 to 29.58
Theta range for data collection (°)
Limiting indices
-22≤ h ≤ 21, -18 ≤ K ≤ 16, -26 ≤ l ≤ 26
71880 / 5399 [R(int) = 0.0317]
29.58 99.3 %
Semi-empirical from equivalents
0.801 and 0.682
Full-matrix least-squares on F^2
5399 / 0 / 230
Reflections collected / unique (Rint)
Completeness to theta
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R Indices (all data)
Largest diff. peak and hole
1.110
R1 = 0.0345, wR2 = 0.0857
R1 = 0.0629, wR2 = 0.1050
0.360 and -0.356 e.A^-3
23

Table 3:
Selected interatomic distances (Å), angles (°) for bis(N-isopropylsalicylaldimine)cobalt(II).
C(7)-N(1)
C(8)-N(1)
1.289(2)
1.474(2)
N(1)-C(7)-C(6)
N(1)-C(8)-C(9)
127.55(16)
109.85(16)
C(11)-O(2)
C(1)-O(1)
1.308(2)
1.308(2)
1.405(3)
1.420(2)
1.436(2)
1.289(2)
1.474(2)
1.308(2)
1.406(3)
1.416(3)
1.416(3)
1.440(3)
1.282(2)
1.484(3)
1.9979(14)
1.9868(15)
1.9020(13)
1.9082(13)
N(1)-C(8)-C(10)
N(2)-C(17)-C(16)
N(2)-C(18)-C(19)
N(2)-C(18)-C(20)
C(7)-N(1)-C(8)
109.89(18)
127.71(18)
110.13(17)
108.27(19)
118.00(15
120.59(12)
121.39(12)
120.69(14)
121.95(12)
125.57(11)
125.12(13)
118.43(6)
112.10(7)
96.28(6)
C(1)-C(2)
C(1)-C(6)
C(6)-C(7)
C(7)-N(1)
C(7)-N(1)-Co(1)
C(8)-N(1)-Co(1)
C(17)-N(2)-Co(1)
C(18)-N(2)-Co(1)
C(1)-O(1)-Co(1)
C(11)-O(2)-Co(1)
O(1)-Co(1)-O(2)
O(1)-Co(1)-N(2)
O(2)-Co(1)-N(2)
O(1)-Co(1)-N(1)
O(2)-Co(1)-N(1)
N(2)-Co(1)-N(1)
C(8)-N(1)
C(11)-O(2)
C(11)-C(12)
C(11)-C(16)
C(11)-C(16)
C(16)-C(17)
C(17)-N(2)
C(18)-N(2)
N(1)-Co(1)
N(2)-Co(1)
O(1)-Co(1)
O(2)-Co(1)
96.45(6)
112.83(6)
122.42(6)
Selected geometric parameters (Å, °).
Co(1)—O(2)
Co(1)—O(1)
1.909 (3)
1.921 (3)
O2i—Co1—O2
O2i—Co1—O1
O2—Co1—O1
O1—Co1—O1i
180
87.27 (13)
92.73 (13)
180
24

Graphical Abstract Pictogram
Bis(N-isopropylsalicylaldimine)cobalt(II)

Graphical Abstract Synopsis
A metallo-organic CVD precursor bis(N-isopropylsalicylaldimine)cobalt(II) was synthesized by
template method showing orthorhombic space group Pbac. In the crystal structure cobalt(II) is
surrounded by two Schiff base ligands forming a distorted tetrahedron. The complex was found
to be volatile and used in Thermal Chemical Vapor Deposition (TCVD) for the development of
nanocrystalline cobalt oxide thin films.