
Research Article


Quantum Mechanical Characterization of MixedLigand Complex of Co(II) Dimethylglyoxime


I.A. Adejoro,
O.O. Adeboye,
B. Akintoye
and
O.F. Akinyele



ABSTRACT

Nonelectrolyte mixedligand complex of the general formula [Co(Hdmg)B], where Hdmg = dimethylgloximato monoanion, B = 2aminophenol(2aph), diethylamine (dea) or malonic acid (MOH) has been synthesized and characterized. The aim of this study is to use quantum mechanical approach to elucidate the geometries and thermodynamic parameters, vibrational frequencies, dipole moments and HOMOLUMO band gaps of the complex with different substituents were carried out. These properties were obtained using the PM3 and DFT with B3LYP at 631G* level. The uv/visble spectrum of CoHdmg(dea)_{2 }showed well resolved absorption bands at 467, 485 nm, these transitions are attributed to metalligand charge transfer transitions while the band at 535 nm is assigned to dd transition within the metal.The uv/visible spectrum of CoHdmg(2aph) presents three distinct bands at 497, 650 nm attributed to metalligand charge transition while the band at 650 nm may account for dd transition with dorbital of the meatal ion. Likewise the three prominent bands in the uv/visible spectrum of CoHdgm(MO) at 451, 463 nm are metalligand charge transfer transitions while the band at 570 nm is attributed to the dd transition within the dorbitals of the metal ion It was observed that the calculated data are in good agreement with experimental data.





Received:
August 30, 2013; Accepted: January 07, 2014;
Published: April 17, 2014 

INTRODUCTION Metal complexes are of great importance in drug design and related areas of life sciences (Bulman, 1994). Efficacies of some therapeutic agents are known to increase upon coordination (Obaleye et al., 2007). Mixedligands complexes are of great importance, they are known to exhibit remarkable activities (Kudirat et al., 1994; Reza et al., 2003; Ogunniran et al., 2007; Shaker et al., 2009). Computational chemistry is a method that is used to investigate materials that are too expensive to buy. It also helps chemists to make predictions before running the actual experiment so that they can be better prepared for making observations (Barden and Schaeffer, 2000). Molecular modeling is an aspect of computational chemistry that gives accurate results compared with experimental results. It is used to account for properties such as bond length, bond angle, dihedrals vibrational frequencies atomic charge distributions etc (Conradie, 2010). Semiempirical calculations were carried out on orotic acid mixed with zinc (II) dehydrate acetate in a neutral medium and it was observed that the calculated results agree well with experimental results (Gloria et al., 2005).

Fig. 1: 
Structure of the complex B= 2aminophenol(2aph) B^{1}
= Hydrogen, B = Diethylamine (dea) B^{1} = Diethylamine(dea), B
= Malonic acid (MOH) B^{1} = Hydrogen 
Theoretical calculations on novel aminopyridino 14ηcyclohexa1, 3diene iron tricarbonyl complexes reveals that the complex is thermodynamically stable (Odiaka et al., 2012). Calculations on novel polymeric Zn (II) complex containing the antimalarial Quinine as ligands gives values that agrees perfectly well with experimental data (Adejoro et al., 2013).
This article studied the quantum mechanical calculation on the experimental results that were carried out on the molecule (Osunlaja et al., 2011). The complex were modelled using Spartan’10 and calculations were carried out on the optimized geometries of the most stable structure (Fig. 1).
MATERIALS AND METHODS Computational methodology: Conformational search was performed on the molecule to locate the structure with the lowest energy. The conformational search was carried out using Molecular Mechanics Force Field (MMFF) which is quite successful in assigning low energy conformers and in providing quantitative estimates of conformational energy differences (Poupaert and Couvreur, 2003). Semiempirical PM3 and Density functional methods was used to carry out molecular calculations on the complexes. The structures were fully optimized and geometric calculations were done to obtain the bond length, bond angle, dihedrals and atomic charge distributions of the complexes. Thermodynamic calculations, vibrational frequencies, heat of formation, dipole moment, EHOMO, ELUMO, band gaps, heat of formation and polarizabilities were carried out (Fig. 2).
RESULTS AND DISCUSSION Geometric calculations were carried out on the most stable structure using PM3 and DFT with B3LYP at 631G* level to obtain the bond length, bond angle, dihedral and atomic charge distribution. The bond length with PM3 method is between 1.92 and 1.49 while with DFT is 1.86 and 1.50. Bond angle is 111.3270.59 with PM3 and 118.27114.73 for Diethylamine dimethylglyoximato cobalt (II). For 2 aminophenol dimethylglyoxime Cobalt(II), the bond length is between 1.591.43 and with DFT it is between 1.43 to 1.49 and the bond angle is between 106.97 and 123.66 with PM3 and 116.83 and 121.23 with DFT. Lastly for Malonic acid dimethylglyoximate cobalt(II) the bond length is between 1.50 and 1.38, the bond angle is 104.04 and 87.24 with PM3 and 128.00 and 82.72. The values obtain for semiempirical and abinitio method differs by an order of magnitude for all the complexes as shown in Table 13.

Fig. 2(ac): 
(a) CoHdmg(dea)_{2}, (b) CoHdmg(2aph) (c) CoHdmg(MO)
and (a, b and c) Structures of the mixed ligands 
Table 1:  Selected bond length, bond angles and dihedrals of diethylamine dimethylglyoximato cobalt (II) (D) angstorom 
 
Table 2:  Selected bonding distance, bonding angles and dihedrals of 2 aminophenol dimethylglyoxime Cobalt(II) (D) angstorom 
 
Table 3:  Selected bonding distances, bonding angles, and dihedrals of malonic acid dimethylglyoximate cobalt(II) (D) angstorom 
 
Table 4:  Electronic properties of the complexes 
 
Table 5: 
Thermodynamic properties of the cobalt(II) complexes 

Electronic properties: The electronic properties of the structures were described by their bands (Young, 2001). The HOMOLUMO band gaps were calculated using PM3 and DFT/B3LYP/631G* method. The value obtained for PM3 is greater than that of DFT/B3LYP/631G*, for all the complexes that is for CoHdmg (2aph) is +7.34 eV, CoHdmg (dea)_{2} is +8.68 eV and CoHdmg (MO) is +7.82 for PM3 and for DFT method, the values are +7.34, +3.82 and +3.19, respectively. This shows that PM3 method predict the electronic properties better than the DFT/B3LYP/631G* method as shown in Table 4. Thermodynamic properties and stabilities: Complexes are thermodynamically stable if ΔG and ΔH are negative. The more negative ΔG and ΔH, the more positive ΔS is and the most stable the complex becomes. From Table 5 negative values of ΔH, ΔG and positive ΔS obtained that is for CoHdmg (2aph) PM3 (2.29 au, 2.35 au, 501.27 J mol^{1} k^{1}) DFT/B3LYP/631G* (2161.65 au, 2161.71 au, 514.59 J mol^{1} k^{1}), CoHdmg(dea) PM3 (2.25 au, 2.32 au, 577.09 J mol^{1} k^{1}), DFT/B3LYP/631G* (2161.65 au, 2161.71 au, 514.59 J mol^{1} k^{1}) and CoHdmg (MO) PM3 (2216.92 au, 2216.98 au, 504.39 J mol^{1} k^{1}), DFT/B3LYP/631G* (2474.57 au, 2474.63 au and 509.21 J mol^{1} k^{1}). Calculation with DFT/B3LYP/631G* basis set better predicts the stability of the Dimethylglyoxime Co(II), complexes.

Fig. 3(ab): 
(a) CoHdmg(dea)_{2} with PM3 and (b) With DFT/B3LYP/631G* 

Fig. 4(ab): 
(a) CoHdmg(2aph) with PM3 and (b) With DFT/B3LYP/631G* 
Vibrational frequencies: The vibrational frequencies obtained from theoretical
calculations were in agreement with the experimental data reported (Osunlaja
et al., 2009) as shown in Table 6 and their corresponding
infra red spectra as shown in Fig. 3a, b,
4a, b and 5a, b.
It was observed that the values obtained from PM3 is closer to experimental
values than the DFT/B3LYP/631G* values. For instance, CoHdmg (2aph) η(NH)_{str
}the experimental result is 3154 cm^{1} while the theoretical
calculation, PM3 (3394 and 3523 cm^{1}), DFT/B3LYP/631G* (35493467
cm^{1}), (OH)_{str} experimental 3381 cm^{1}, theoretical
calculation, PM3(38743886 cm^{1}) and DFT/B3LYP/631G* (35403520
cm^{1}). (CoN), the experimental is 507 cm^{1}, PM3 (643
cm^{1}), DFT/B3LYP/631G* (360 cm^{1}) and for(NO)_{str},
the experimental value is 115 cm^{1} while with PM3 (1869 cm^{1}),
DFT/B3LYP/631G* (1619 cm^{1}).
For CoHdmg(dea)_{2}, (OH)_{str} the experimental value is 3430 cm^{1} while the theoretical calculation, PM3 (3901 cm^{1}), DFT/B3LYP/631G* (3647 cm^{1}),(NH)_{str} the experimental result is 3174 cm^{1} while the theoretical calculation, PM3 is 33203044 cm^{1} and DFT/B3LYP/631G* (34393320 cm^{1}). (C = N)_{str} the experimental data is 1462 cm^{1}, PM3 (1752 cm^{1}), DFT/B3LYP/631G*(1538 cm^{1}). (NO)_{str} experimental is1206 cm^{1}, with PM3 (1668 cm^{1}), DFT/B3LYP/631G*(1449 cm^{1}). (CoN) experimental is 510 cm^{1}, with PM3 (535 cm^{1}), DFT/B3LYP/631G* (563 cm^{1}).
For CoHdmg(MO), (OH)_{str} experimental is 3403 cm^{1} while
theoretical calculation with PM (38583815 cm^{1}) and DFT/B3LYP/631G*
(36473545 cm^{1}). (C = O)_{carboxylic} in the experimental
result is 1591 cm^{1}, theoretical calculation, PM3 (1903 cm^{1}),
DFT/B3LYP/631G* (18751222 cm^{1}).
Table 6:  Experimental and theoretical Infra red data showing absorption bands with their corresponding vibration for the cobalt II cmplexes 
 

Fig. 5(ab): 
(a) CoHdmg(MO) with PM3 and (b) With DFT/B3LYP/631G* 
(NO)_{str}, experimental result is 1080 cm^{1}, PM3 (1937
cm^{1}), DFT/B3LYP/631G* (1617 cm^{1}). (C = O)_{str}
experimental is 1336 cm^{1} and PM3 (2059 cm^{1}), DFT/B3LYP/631G*
(25401875 cm^{1}).
Table 7:  Wavelength and intensity of dethylamine dimethylglyoxime cobalt(II) 
 
 Fig. 6:  UV/visible spectra of Dethylamine Dimethylglyoxime Cobalt (II)with DFT/B3LYP/631G* 

Fig. 7: 
Ultraviolet/visible spectra of 2 aminophenol Dimethylglyoxime
Cobalt (II) with DFT/B3LYP/631G* 
(CoN)_{str} experimental is 510 cm^{1} while PM3 (1422 cm^{1}),
DFT/B3LYP/6 31G* (1002 cm^{1}).
Electronic spectra using Uv/visible: The Uv/visible spectra data (Table
7) showed three major absorption bands. These bands are due to intraligand,
metalligand charge transfer and dd transitions within the metal complexes.
The uv/visble spectrum of CoHdmg (dea)_{2} showed (Fig.
6) well resolved absorption bands at 467, 485 nm, these transitions are
attributed to metalligand charge transfer transitions while the band at 535
nm is assigned to dd transition within the metal.The uv/visible spectrum of
CoHdmg (2aph) (Fig. 7) presents three distinct bands at 497,
650 nm attributed to metalligand charge transition while the band at 650 nm
may account for dd transition with dorbital of the meatal ion.

Fig. 8: 
Ultraviolet/visible spectra of Malonic acid Dimethylglyoxime
Cobalt(II) with DFT/B3LYP/631G* 
Likewise the three prominent bands in the uv/visible spectrum of CoHdgm (MO)
(Fig. 8) at 451, 463 nm are metalligand charge transfer transitions
while the band at 570 nm is attributed to the dd transition within the dorbitals
of the metal ion.
CONCLUSION
The properties of the Complex [Co(II) mixedligand complexes of dimethylglyoxime]
were calculated using Semiempirical PM3 and DFT with B3LYP at 631G* level.
The optimized geometries, dipole moments, geometric parameters, thermodynamics
parameters and vibrational and electronic frequencies were investigated. Computational
method has presented us the opportunity to take a critical look at this mixedligand
complexes of dimethylglyoxime to produce results which compared favourably well
with experimental results. It has also given us the opportunity to compute results
on the properties that cannot be obtained in laboratory experiments. It can
be concluded that in studying and predicting the geometric parameters and vibrational
frequencies of these complexes, the PM3 semiempirical calculation is the best
though it did not account for the chemical shifts which was accounted for by
the DFT/B3LYP/631G*.

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