American Journal of Analytical Chemistry
Vol.06 No.02(2015), Article ID:53393,8 pages

Kinetics and Vapor Pressure Studies of bis(N-alkyl-2-hydroxonapthaldimine)nickel (II) (N-R = methyl to pentyl) Complexes

Maria Francis George Johnson1, Thevabakthi Siluvai Muthu Arul Jeevan2*, Sebastian Arockiasamy3, Karachalacheruvu Seetharamaiah Nagaraja1

1Department of Chemistry, Loyola Institute of Frontier Energy (LIFE), Loyola College, Chennai, India

2Department of Chemistry, College of Natural and Computational Sciences, University of Gondar, Gondar, Ethiopia

3Department of Chemistry, School of Advanced Sciences (SAS), VIT University Chennai Campus, Chennai, India

Email: *

Copyright © 2015 by authors and Scientific Research Publishing Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY).

Received 29 December 2014; accepted 16 January 2015; published 20 January 2015


The complexes of bis[N-alkyl-2-hydroxonapthaldimine]nickel(II) (N-alkyl = methyl, ethyl, propyl, butyl or pentyl) were synthesized and their volatilization in N2 atmosphere was demonstrated by the TG-based transpiration technique. The equilibrium vapor pressure of the complexes over a temperature span of 470 - 590 K was determined by adapting a horizontal dual arm single furnace thermoanalyser as a transpiration apparatus. It yielded as 153.1 (±1.9), 122.9 (±0.3), 147.6 (±10.7), 151.8 (±10.9) and 114.7 (±5.3) k∙Jmol−1 respectively. The entropies of vaporization for these complexes as calculated from the intercept of the linear fit expressions were found to be 319.7 (±3.9), 229.9 (±5.8), 317.8 (±17.2), 319.7 (±19.1) and 254.6 (±9.6) Jmol−1∙K−1 respectively. The non-isothermal vaporization activation energy was determined from Arrhenius and Coats-Redfern methods.


Volatile Nickel Complexes, Thermal Properties, Vapor Pressure, Transpiration Technique, Enthalpy and Entropy of Vaporization, Vaporization Kinetics

1. Introduction

Success of the metallo-organic chemical vapor deposition (MOCVD) technique for preparing thin films rests mainly on the availability of completely volatile precursors. Therefore, development of stable, non-toxic and completely volatile solid metallo-organic precursors for use in CVD of metallic nickel has attracted intensive research [1] -[7] . Many publications warned the use of highly toxic Ni(CO)4 as a precursor [8] [9] , which was first used by Mond in 1885. Other precursors used in MOCVD of Ni films are Ni(acac)2en [1] , Ni(tfacim)2 (tfacim = triflouroacetylacetone-imine) [3] [4] , Ni(L)2 [L= dimethylglyoxime [10] , diethylglyoxime, dipropylglyoxime [6] ], Ni(η5-C5H5)2 [7] , Ni(L)2 [L = acetylacetone (acac) [11] , hexafluoroacetylacetone (hfac) [12] and tetramethylheptanedione (tmhd) [13] ]. Ni(tmhd)2 [14] and Ni[(acac)2en] [1] met the requirements of an ideal precursors in CVD applications. It is essential to synthesize new precursors with mixed O and N environment around Ni employing aromatic ligands for better volatility. This paper describes the synthesis and characterization of nickel complexes by using Schiff base ligands. These complexes are characterized by elemental analyses, FT-IR, FABMS, TG/DTA, vaporization kinetics and vapor pressure measurement by the TG-based transpiration technique.

2. Experimental

NiCl2∙6H2O, 2-hydroxynaphthal (Aldrich), methylamine, ethylamine, propylamine, butylamine, pentylamine (Loba Chemie, India), liquor ammonia and methanol (S. D. Fine, India) were used as procured.

2.1. Synthesis of the Complexes

2.1.1. Synthesis of bis(2-hydroxonapthaldehydato)nickel(II) [Ni(2-hydroxynapthal)2]

NiCl2∙6H2O (9.48 g) was dissolved in water (20 cm3) to which 2-hydroxynaphthal (10 cm3) was added drop- wise under constant stirring. To this reaction mixture, liquor ammonia (12 cm3) was added drop-wise by continuously monitoring the formation of a greenish yellow precipitate. This precipitate was digested at 333 K over a water bath for 0.5 h, which was filtered, washed with ethanol and dried under vacuum [15] . Yield: 76%.

2.1.2. Syntheses of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II) complexes [N-alkyl = methyl to pentyl]

The syntheses of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II), where N-alkyl = methyl to pentyl complexes were carried out by treating the appropriate primary amines with the hot alcoholic suspension of Ni(2-hydrox- onapthal)2. The resulting olive green solution was refluxed for about 0.5 h and the crystals formed were filtered, washed with ethanol and dried under vacuum. The compound was recrystallized from methanol. Yield: 56% - 82%.

2.2. Characterization

The C, H and N analyses were performed on a CARBO-ERBA-11008 rapid elemental analyzer. IR spectra were recorded as KBr pellets on a Perkin-Elmer FT-IR spectrometer (RX1, FT-IR) in the region of 4000 - 450 cm−1. Fast atom bombardment mass spectra (FABMS) of the nickel complexes were recorded by employing a JEOL SX 102/DA-6000 spectrometer using argon as the FAB gas with an accelerating voltage of 10 kV and the spectra were recorded at room temperature. M-nitrobenzyl alcohol (NBA) was used as the matrix unless specified otherwise. The thermal analyses were carried out using Perkin-Elmer, Pyris Diamond TG/DTA at a linear heating rate of 0.17 Ks−1. High purity nitrogen (purity > 99.99%) dried by passing through refrigerated molecular sieves (Linde 4A) was used as the purge gas at a flow rate of 12 dm3∙h−1.

2.3. Vapor Pressure Measurement Studies

A horizontal thermal analyzer was adapted as a transpiration setup for vapor pressure measurements. The configuration of the horizontal dual arm with a single narrow furnace chamber minimizes errors arising from convection, buoyancy, thermo molecular and electrostatic charge effects. The arms of the thermo balance served as the temperature-cum-DTA sensors.

The block diagram of the thermal analyzer, modification for its functioning in the transpiration mode, including precise flow calibration for the carrier gas using a capillary glass flow meter and corrections for apparent weight losses in isothermal mode were the same as reported [15] [16] . The choice of 6 dm3∙h−1 for N2 gas was made for the isothermal equilibrium vaporization on the basis of the existence of a plateau in the plot of the equilibrium vapor pressure against the flow rate. The vapor pressure measurements were carried out by rapid heating 0.17 Ks−1 and after allowing for temperature stabilization, subsequent changes in isothermal steps were done at a heating rate of 0.03 Ks−1. It turned out that the vapor pressure derived from the TG-based transpiration method was reliable to 10% accuracy [15] [16] .

2.4. Vaporization Kinetics

Experiments were performed under non-isothermal conditions at a programmed linear heating rate of 10˚C∙min−1 for methyl to pentyl homologues. Among the various methods for the kinetics evaluation of TG weight loss data, Arrhenius method was followed in the present investigation to study the vaporization kinetics.

3. Results and Discussion

3.1. Thermal Analyses

The elemental analyses and their composition are presented in Table 1. The melting point endotherms (Figure 1) were calculated accurately using the built-in Pyris software and the values 280˚C, 271˚C, 205˚C, 176˚C and 175˚C for methyl to pentyl homologues respectively which exhibited a decreasing trend with increasing length of the alkyl chain. The non-isothermal TG curves (Figure 2) of bis(2-hydroxonapthaldehydato)nickel(II) indicated a 37.8% residue at 700 K making it unsuitable for CVD applications. The TG curves of bis(N-alkyl-2-hy- droxonapthaldimine)nickel(II) homologues (where N-alkyl = methyl to pentyl) showed a single step weight loss commencing from 700 K, leading to a negligible amount of residue qualifying themselves as precursors for CVD.

3.2. Spectral Characterization

The relevant frequencies such as, , and (Table 2) support the struc-

ture. The FABMS patterns (Table 3) of bis[N-alkyl-2-hydroxonapthaldimine)]nickel(II) (where N-alkyl = methyl to pentyl) complexes revealed the molecular masses (M) of the complexes and their fragmentation pattern. The values of molecular ion peaks were observed at (Da) = 430, 454, 483, 510 and 539 respectively, for methyl to pentyl homologues as clusters due to the isotopic abundances of natural nickel (58Ni: 67.76%, 60Ni: 26.16%, 61Ni: 1.25%, 62Ni: 3.66%, 64Ni: 1.16%).

3.3. Vapor Pressure Measurements

Effective control of the process of any type of CVD and to monitor the composition, thickness and microstructure of thin films, relevant information on precursor chemistry, possible fragmentation pattern by the decomposition of precursors and vapor pressures are needed. Therefore vapor pressure measurement was deemed as essential for these complexes to be used for MOCVD.

If W is the mass loss of the sample (Table 4) at the isothermal temperature caused by the flow of dm3 of the carrier gas (measured at), the vapor pressure could be calculated using Dalton’s law of partial pressure for ideal gas mixtures as


where is the molar mass of the complexes, and are the temperature and volume of the carrier gas respectively. The molecular mass of the congruently vaporizing species was obtained from FABMS. The observed mass loss and the calculated (using Equation (1)) (Table 4) and versus 1000/T (K) are shown in Figure 3. The values of slope and intercept of the Clausius-Clapeyron equation obtained from the plot for the nickel homologues (Table 5) along with the values of enthalpy of vaporization and entropy of vaporization are given.


Table 1. Elemental analyses and melting points of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II) complexes.

Table 2. Relevant IR frequencies of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II).

Table 3. Assignment of peaks in FAB mass spectra of bis(N-alkyl-(2-hydroxonapthal)nickel(II) complexes; N-alkyl = methyl (a) to pentyl (e) respectively.

Table 4. Mass loss (for 60 min) and for equilibrium solid vaporization of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II) homologues by TG-based transpiration method.

Table 5. Clausius-Clapeyron parameters for bis(N-alkyl-2-hydroxonapthaldimine)nickel(II).

Figure 1. DTA traces of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II).

Figure 2. Non-isothermal TG curves of nickel complexes.

Figure 3. Clausius-Clapeyron plots for bis(N-alkyl-2-hydroxonapthaldimine)nickel(II) homologues.

Enthalpy of vaporization is obtained by multiplying the slope in Equation (2) with −2.303 R. The least- square expressions from the plots are included in Table 5 along with the temperature ranges of their experimental measurements employing the TG-based transpiration technique. The values as calculated from the slope of the curve were found to be 153.1 (±1.9), 122.9 (±0.3), 147.6 (±10.7), 151.8 (±10.9) and 114.7 (±5.3) k∙Jmol−1

respectively. The entropies of vaporization for these complexes as calculated from the intercept of the

linear fit expression were found to be 319.7 (±3.9), 229.9 (±5.8), 317.8 (±17.2), 319.7 (±19.1) and 254.6 (±9.6) Jmol−1∙K−1. The vapor pressure of the complexes will be helpful for fixing the metal organic chemical vapor deposition (MOCVD) process parameters for getting the desired phase and rate of deposition of nickel and composite materials.

3.4. Determination of Activation Energy

The rate constant for the vaporization enthalpy of the complexes was determined in the temperature range of 400 - 680 K for every 10% weight loss of the complex. The expression (3) for is given by


where is the derivative of the fraction vaporized with respect to time and is the rate constant of va- porization. For every 10% weight loss, was calculated by the expression (4) as


where is the per cent weight at any time and and respectively, are the initial and final percent sample weights [17] . The Arrhenius expression (5) is


And the plot of versus 1000/T (K) (Figure 4) is found to be linear. From the slope, the activation energy for the vaporization of the complexes was calculated. The activation energy values were found to be 106 ± 4, 111 ± 6, 114 ± 7, 115 ± 7 and 121 ± 4 k∙Jmol−1 respectively for methyl to pentyl homologues.

The kinetics of the complexes was followed by employing the Coats-Redfern approximation which gives the expression (6).


A plot of versus 1000/T (K) gives (Figure 5) a straight line when the correct func-

tion is used in the equation. The function describes the mechanism of the reaction [18] . Straight lines with high-correlation coefficient and low standard deviation were selected to represent the possible controlling mechanism. The corresponding kinetic parameters were then calculated and are shown in Table 6. The best fit for the methyl complex is obtained using A3 Avrami-Erofe’ev Equation (3). For the ethyl and pentyl complexes, best fit was obtained with R2, contracting area model. For the propyl and butyl complexes, best fit was obtained with A2, two dimensional Avrami-Erofe’ev Equations (2) model. The activation energy values were found to be 112 (±5), 115 (±5), 105 (±6), 108 (±10) and 126 (±5) k∙Jmol−1 respectively for methyl to pentyl homologues. Analysis of these data show that the activation energies which are in good agreement with that obtained using Arrhenius’s method.

Figure 4. Arrhenius plots of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II).

Figure 5. Plots of versus 1000/T (K); where (a); (b); and (c).

Table 6. Activation energies obtained using the Coats-Redfern method for several solid state processes at heating rate of 10˚C∙min−1 for methyl to pentyl.

4. Conclusion

The thermodynamic and kinetic decomposition of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II) (N-alkyl = me- thyl, ethyl, propyl, butyl or pentyl) complexes were carried out. The molecular masses of the homologous series of the nickel complexes were obtained from FABMS. The TG-based transpiration technique was used to eva- luate the vapor pressure data of bis(N-alkyl-2-hydroxonapthaldimine)nickel(II) homologues. The standard en- thalpies of vaporization and entropies of vaporization of the complexes have been evaluated. The non-isothermal vaporization activation energy values were determined by Arrhenius and Coats-Redfern methods.


This work received financial support from the Department of Science and Technology (DST), India, through Grant No. SR/S3/ME/03/2005-SERC-Engg. The authors thank the Central Drug Research Institute, Lucknow, for recording the mass spectra and C, H and N analyses.


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