SEMIEMPIRICAL QUANTUM CHEMICAL AND AB INTIO STUDY OF Co(II), Ni(II),Cu(II) AND Zn(II) COMPLEXES WITH THE AZO DYE DERIVED FROM 4-AMINO ANTIPYRINE AND 2,4-DIHYDROXY ACETOPHEONE
https://doi.org/10.53656/nat2021-6.03
Резюме. Semi-empirical quantum chemical calculation was made to study the nucleophilicity of the ligand and to study the mode of bonding between the ligand and the metal ions. The natural atomic charge at different atomic sites of the ligand has been calculated along with the electrostatic potential map to predict the reactive sites for electrophilic and nucleophilic attack. The theoretical spectral data such as IR, NMR and electronic have been calculated and compared with the experimentally generated data.
Ключови думи: Semiempirical study; Chem 3D Ultra; Natural atomic charge; Molecular polarisability
Introduction
Molecular modelling uses theoretical approaches and computational techniques to study molecular systems ranging from small molecular units to large biological molecules (Cornado & Merlin 2003). Molecular modelling provides information of geometrical parameters such as bond lengths, dihedral angles and bond angles along with the spectroscopic data with respect to vibration, electronic and NMR (Leach 2009). In addition to this, Chemical reactivity sites of the ligand and its metal complexes can also be predicted from the natural atomic charge and electrostatic potential map (Ramachandran et al. 2008). The azo dye derived from 4-aminoantipyrine and 2,4-dihydroxyacetophenone as given in fig 1 and its metal complexes as given in fig 4 have been synthesised, characterised and reported (Chaulia 2016). In this study, attempts have been made to predict the reactive sites of the ligand and metal complexes by computing the natural atomic charge and electrostatic potential map. The spectral data such as IR, electronic and NMR of the ligand are calculated and compared with the experimental spectral data.
Figure 1. Optimised geometry of the ligand
Computational Details
The computational calculations were made using Ab Intio and semi empirical methods with Chem 3D Ultra programme (Chem3D Ultra Molecular modelling and Analysis, 2003). The geometry of the ligand and its metal complexes were drawn by using the programme Chem draw present in the same Chem 3D Ultra programme. The geometry of the ligand and its complexes were optimised using molecular mechanics and low lying structures were again optimised using semi empirical quantum chemical methods.
Results and Discussion
The computational study of the ligand and its metal complexes were undertaken and compared with the experimental results.
Natural atomic charge
The natural atomic charges at different atomic sites of the ligand were calculated and presented in the table 1 and fig 2. The natural atomic charge plays important role in determining the electronic properties of a compound such as dipole moment, molecular polarisability and hyperpolarizability (Bejler et al. 1990). The region of highest electron density reflects the potential sites of electrophilic attack. The highest electron densities are concentrated over nitrogen and oxygen atoms, this fact is also supported by the molecular electrostatic potential study in fig 3. Hence, these atoms have the ability to coordinate with the metal ions.
Figure 2. Natural atomic charge of the atoms present in the ligand
Table 1. Natural atomic charges
Molecular electrostatic potential
The Electrostatic potential map gives an idea about the charge distribution and charge related properties of a molecules (Politzer & Murray 1991). The MEP of the investigated compound indicates red colour is concentrated around nitrogen and oxygen atoms and blue colour around some carbon and hydrogen atoms. This observation suggests that the nitrogen and oxygen atoms are rich source of electrons, and the metal ions is coordinating with the ligand through the azo nitrogen and oxygen atoms of the ligand as given in the Fig.3
Figure 3. Electrostatic potential map of the ligand X
Figure 4. Structure of metal complexes
IR spectra
The IR spectra of the ligand and its metal complexes were recorded and the experimental spectral data were compared with the computationally generated spectral data and presented in the fig 5, 8 and table 2 and 3. The IR spectrum of the ligand gives a band at \(1270 \mathrm{~cm}^{-1}\) corresponding (\(\mathrm{C}-\mathrm{O}\) ) vibration but the AM1 (Dewar et al. 1985 ) predicts it at \(1262 \mathrm{~cm}^{-1}\) and the PM3 (Stewart 1989)predicts it at \(1257 \mathrm{~cm}^{-1}\). The experimental frequency for the vibration of \((\mathrm{N}=\mathrm{N})\) appeared at 1493 \(\mathrm{cm}^{-1}\) but the AM1 predicts it at \(1479 \mathrm{~cm}^{-1}\) and the PM3 predicts it at \(1491 \mathrm{~cm}^{-1}\). The computational study indicates the vibrational frequency for (\(\mathrm{C}=\mathrm{O}\) ) is at \(1708 \mathrm{~cm}^{-1}\) according to AM1 and at \(1642 \mathrm{~cm}^{-1}\) according to PM3 but experimental study indicates it at \(1639 \mathrm{~cm}^{-1}\). The correlation coefficient of experimental and computational vibration frequency calculated using AM1 and PM3 is 0.999 as given in fig 6 and 7.
Figure 5. IR spectrum of the ligand(experimental)
Table 2. Experimental and computational vibration frequency data of the ligand
Figure 6. Correlation graph of the ligand
Figure 7. Correlation graph of the ligand
The IR spectrum of metal complex shows a band at \(\sim 1219 \mathrm{~cm}^{-1}\) but in the free ligand, it was at \(1270 \mathrm{~cm}^{-1}\) and missing of peak at \(\sim 3434 \mathrm{~cm}^{-1}\) in the metal complexes that indicates deprotonation of -OH group and formation of bond by the metal atom or ion with the oxygen atom of the -OH group. However, the computational study predicts it at \(1262 \mathrm{~cm}^{-1}\) according to AM1 force field and at 1283 PM3 force field. The spectrum of the complex also shows peak at \(\sim 1454\) \(\mathrm{cm}^{-1}\) but it was at \(1493 \mathrm{~cm}^{-1}\) in the free ligand indicating formation of bond with one of the nitrogen atoms of the azo \(\operatorname{group}(-\mathrm{N}=\mathrm{N}-)\) with the metal atom or ion. The computational generated spectrum indicates this peak at \(1492 \mathrm{~cm}^{-1}\) and 1490 \(\mathrm{cm}^{-1}\) corresponding to AM1 and PM3 force fields. The (\(\mathrm{C}=\mathrm{O}\) ) stretching vibrational frequency of the free ligand is at \(1639 \mathrm{~cm}^{-1}\) but IR spectrum of the complex shows at \(1610 \mathrm{~cm}^{-1}\) that suggests formation of bond of carbonyl oxygen with the metal ion or atom. The computer-generated spectrum data indicates the vibrational frequency at \(1647 \mathrm{~cm}^{-1}\) according to AM1force field but at \(1644 \mathrm{~cm}^{-1}\) according to PM3 force field. The bonding between the metal ion and oxygen atom of the (-OH) group is confirmed by the appearance of peak at \(536 \mathrm{~cm}^{-1}\) in the IR spectrum of the complex \({ }^{7}\) but according to AM1 force field it is at \(561 \mathrm{~cm}^{-1}\) but PM3 predicts it at \(581 \mathrm{~cm}^{-1}\). The bonding between the metal ion and nitrogen atom of the (\(-\mathrm{N}=\mathrm{N}-\) ) group is confirmed by the appearance of peak at \(536 \mathrm{~cm}^{-1}\) in the IR spectrum of the complex but according to AM1 force field it is at \(556 \mathrm{~cm}^{-1}\) but PM3 predicts it at \(522 \mathrm{~cm}^{-1}\). (Sirichote et al. 1998). The correlation coefficient of experimental and computational vibration frequency calculated using AM1 and PM3 is \(\sim 0.997\) as given in fig 9 and 10.
Figure 8. IR spectrum of the ligand(experimental)
Table 3. Experimental and computational vibration frequency data of the \(\operatorname{Co}\) (II) complex
Figure 9. Correlation graph of the Co(II) complex
Figure 10. Correlation graph of the Co(II) complex
Electronic spectra
The semi empirical quantum chemical method find uses in calculating excited states hence to predict UV spectra of chemical compounds effectively. The single point energy calculations were carried out at semi empirical level to predict UV spectra. The computational electronic spectral bands of the ligand and its Co(II), Ni(II), Cu(II) complexes were calculated. The spectral bands of the investigated compounds were calculated by using the ZINDO programme (Zerner 1991).
The ligand and its metal complexes were also characterised by the Electronic spectra. The absorption bands are observed in the UV-Visible region of the electromagnetic spectrum due to transition of electrons between two electronic energy levels when energy difference between two electronic energy levels matches the energy of the incident photon \({ }^{1}\).
\(\Delta E=\tfrac{h c}{\lambda}\) where \(h=\) plank's constant, \(c=\) velocity of light,\(\lambda=\) wavelength of the radiation
The semi empirical quantum chemical method find uses in calculating excited states hence to predict UV spectra of chemical compounds effectively. The single point energy calculations were carried out at semi empirical level to predict UV spectra. The computational electronic spectral bands of the ligand and its \(\operatorname{Co}(\mathrm{II})\), Ni(II), Cu(II) complexes were calculated and given in table. The spectral bands of the investigated compounds were calculated by using the ZINDO programme (Zerner 1991).
The computational study of the Co(II)complex predicts spectral bands at 12987 \(\mathrm{cm}, 16393 \mathrm{~cm}, 22727 \mathrm{~cm}\) corresponding to \({ }^{4} \mathrm{~T}_{1 \mathrm{~g}}(\mathrm{~F}) \rightarrow{ }^{4} \mathrm{~T}_{2 \mathrm{~g}}(\mathrm{~F}),{ }^{4} \mathrm{~T}_{1 \mathrm{~g}}(\mathrm{~F}) \rightarrow{ }^{4} \mathrm{~T}_{2 \mathrm{~g}}(\mathrm{~F})\) and \({ }^{4} \mathrm{~T}_{1 \mathrm{~g}}(\mathrm{~F}) \rightarrow{ }^{4} \mathrm{~T}_{2 \mathrm{~g}}(\mathrm{P})\). T The theoretical spectral bands were compared with the experimental spectral bands which were found at \(14492 \mathrm{~cm}^{-1}, 20449 \mathrm{~cm}^{-1}\) and \(25575 \mathrm{~cm}^{-1}\) respectively as given in table 4. Both experimental and computational values were compared, and the correlation coefficient was found to be 0.954 given in fig 11.
Table 4. Experimental and calculated wavelength of the ligand and its metal complexes
Figure 11. Correlation graph of the Co(II) complex
Similarly, Ni(II) complex predicts spectral bands at \(13157 \mathrm{~cm}^{-1}, 16528 \mathrm{~cm}^{-1}\) and \(23255 \mathrm{~cm}^{-1}\) due to \({ }^{3} \mathrm{~A}_{2 \mathrm{~g}}(\mathrm{~F}) \rightarrow{ }^{3} \mathrm{~T}_{2 \mathrm{~g}}(\mathrm{~F}),{ }^{3} \mathrm{~A}_{2 \mathrm{~g}}(\mathrm{~F}) \rightarrow{ }^{3} \mathrm{~T}_{1 \mathrm{~g}}(\mathrm{~F})\) and \({ }^{3} \mathrm{~A}_{2 \mathrm{~g}}(\mathrm{~F}) \rightarrow{ }^{3} \mathrm{~T}_{1 \mathrm{~g}}(\mathrm{P})\). T2g(F), 3A2g(F) 3T 1g(F) and 3A2g(F) 3T1g(P). The computational study indicated it at \(14084 \mathrm{~cm}^{-1}, 18552 \mathrm{~cm}^{-1}\) and \(24271 \mathrm{~cm}^{-\mathrm{p}}\). A good correlation was obtained between the experimental and calculated data (\(\mathrm{R}^{2}=0.954\) ) given in fig 12 and percentage variation is less than 5. were the following relations and presented in the table no 5
Figure 12. Correlation graph of the Ni(II) com
\(\boldsymbol{D} \boldsymbol{q}=\boldsymbol{\nu} \mathbf{2}-\boldsymbol{\nu} \mathbf{1} / \mathbf{1 0} \ldots \ldots\). Equation 1
\(\boldsymbol{B}=\boldsymbol{\nu} \mathbf{2}+\boldsymbol{\nu} \mathbf{3}-\mathbf{3} \boldsymbol{\nu} \mathbf{1} / \mathbf{1 5} \ldots \ldots\). Equation 2
\(\boldsymbol{\beta} \mathbf{3 5} \boldsymbol{=} \boldsymbol{B} / \mathbf{9 7 1} \quad\)........Equation 3
\(\boldsymbol{\beta} \mathbf{3 5} \%=(\mathbf{1}-\boldsymbol{\beta} \mathbf{3 5}) \times \mathbf{1 0 0} \ldots \ldots\). Equation 4
Similarly, the electronic parameters of Ni(II) metal complex were also calculated by using the following relations and presented in the table no 5
\(\boldsymbol{D} \boldsymbol{q}=\boldsymbol{v} \mathbf{1} / \mathbf{1 0} \ldots \ldots\). Equation 5
\(\boldsymbol{B}=\boldsymbol{\nu} \mathbf{2}+\boldsymbol{\nu} \mathbf{3}-\mathbf{3} \boldsymbol{\nu} \mathbf{1} / \mathbf{1 5} \ldots \ldots\). Equation 6
\(\boldsymbol{\beta} \mathbf{3 5} \boldsymbol{=} \boldsymbol{B} / \mathbf{1 0 4 1} \ldots \ldots .\). Equation 7
\(\boldsymbol{\beta} \mathbf{3 5} \%=(\mathbf{1}-\boldsymbol{\beta} \mathbf{3 5}) \times \mathbf{1 0 0} \ldots \ldots .\). Equation 8
It has been seen that the electronic parameters such as \(\mathrm{B}, \beta_{\Sigma, c}\) and \(v_{2} / v_{1}\) calculated from the computational \(\boldsymbol{\nu} \mathbf{1}, \boldsymbol{\nu} \mathbf{2}\) and \(\boldsymbol{\nu} \mathbf{3} \boldsymbol{1}, \boldsymbol{\nu} \mathbf{2}\) and \(\boldsymbol{\nu} \mathbf{3}\) values for Co and Ni as given in table 6 gives good correlation with the electronic parameters calculated from experimental its values as compared to \(\left[\mathrm{Co}_{2} \mathrm{LCl}_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]\) metal complex.
Table 5. Experimental electronic parameter of the complexes
Table 6. computational Electronic parameter of the complexes
Nuclear magnetic spectra
The Nuclear magnetic resonance spectroscopy has been used for structure elucidations of various complex molecules. The use of experimental and computational data offers powerful techniques to interpret and predict the structure of bulky molecules (Torda & Gunsteren 1992). The gauge independent atomic orbital method has been used for calculating the NMR chemical shifts (Wolinski et al. 1990)
The \({ }^{1} \mathrm{H}\) NMR spectra of the ligand as given in fig 13 and its Zn(II) given in fig 14 complex were recorded experimentally separately. The computational chemical shifts values of the ligand and metal complexes are also collected as given in fig 15 and 16 and these chemical shifts values (\(\delta \exp\) ) were compared with the computational (\(\delta\) calc) \(\delta\) calc \()\) values. The correlation coefficient of both the values was found to be 0.828 as given in fig 17.
Figure 13. Experimental 1H NMR Spectrum of the ligand
Figure 14.
Figure 15. Calculated 1H NMR Spectrum of the ligand
Figure 16. Fig 16. Calculated 1H NMR Spectrum of the Zn(II) complex
Figure 17. Correlation graph of the ligand
The 1H NMR computational data gathered for the ligand are given below
The 1H NMR computational data obtained for the Zn(II) complex are given below
The \({ }^{13} \mathrm{C}\) NMR computational study of the ligand and Zn(II) complex was undertaken to study the nature of bonding between metal ion and donor atoms of the ligand as given in the fig 18 and 19.
Figure 18. 13C NMR spectrum of the ligand
Figure 19. 13C NMR spectrum of the Zn(II) complex
The13C NMR computational data gathered for the ligand are given below
The 13C NMR computational data gathered for the Zn(II) are given below
Conclusion
The tetradentate nature of the ligand is confirmed from the MEP study and the natural atomic charge study of the ligand. The donor atoms of the ligand are found to be azo nitrogen, oxygen atoms of the aromatic hydroxyl group and oxygen atom of the ethanoyl group. The vibration frequencies of various groups of the ligand and its Co(II) complex have been computed under the force fields AM1 and PM3 and the comparison study of the vibration frequencies indicates good correlation coefficient.. The ZINDO program has been used to predict the molecular electronic spectra of Co(II) and Ni(II). The percentage variation between the experimental and computational electronic spectra data is very less. The NMR computational study of \({ }^{1} \mathrm{H}\) spectrum of the ligand and its Zn(II) complex predicts the chemical shifts (\(\delta\) calc) and compared with the experimental \(\delta\) expt spectral data. The \({ }^{13} \mathrm{C}\) NMR spectra of the ligand and its Zn(II) complex are also predicted. All experimental data relating to IR, NMR and electronic agree well with computational generated data of IR, NMR and electronic spectra.
REFERENCES
Bejler, B. H., Merz, K. M., Kollman, P. A., 1990. Atomic charges derived from semi empirical methods. Journal of computational chemistry, 11, 431 – 439.
Chaulia, S. N., 2016. Der pharmacia Letter, 8(21), 55 – 74.
Chem3D Ultra Molecular modelling and Analysis, Cambridge soft Corporation, 1985 – 2003.
Cornard, J. P., Merlin, J. C., 2003. Complexes of Al(III)with isoquercitrin: Spectroscopic characterisation and quantum chemical calculation. Polyhedron, 21, 2801 – 2810.
Dewar, M. J. S, Zoebisch, E. J., Healy, E. F., Stewart, J. J. P., 1985. AM1; A new general purpose quantum mechanical model. Journal of the American Chemical Society, 107, 3902 – 3909.
Leach, Andrew R., 2009. Molecular Modelling Principles and applications. Pearson.
Politzer, P., Murray, J. S., 1991. Molecuar Electrostatic potentials and Reactivity. Reviews in Computational chemistry, New York: VCH Publisher, 273 – 312.
Ramachandran, K. I., Deepa, G., Namboori, K. 2008. Computational Chemistry and Molecular Modelling. Springer.
Sirichote, O. Hansongnern, K., Sudkeaw, P., 1998. Vibrational frequencies and structure of estragole using semiempirical calculations. Journal of sci. Soc. Thai., 24, 65 – 71.
Stewart, J. J. P., 1989. Optimisation of parameters for Semi-empirical Methods I. Journal of computational Chemical Chemistry, 10, 209 – 220.
Torda, A. E. & Gunsteren, W. F., 1992. Molecular modelling using NMR data, Reviews in Computational chemistry, 2. New York: VCH Publisher, 143 – 172.
Wolinski, K., Hinton, J. F., Pulay, F., 1990. Efficient implementation of the gauge atomic orbital method for NMR chemical shifts calculation. J. of Am. Chem. Soc., 112, 8251 – 8260.
Zerner, M. C., 1991. Semi-empirical Molecular orbital methods, Reviews in Computational chemistry, 2. New York: VCH Publisher, 313 – 366.