Square Planar Cobalt (II) complexes of chloro-substituted hydroxy-imino ligands containing sulphur

 

Dilip C. Sawant*, R.G. Deshmukh

Department of Chemistry, Konkan Gyanpeeth Karjat College of Arts, Science and Commerce

Karjat, Raigad, Maharashtra, INDIA

*Corresponding Author E-mail: dcsawant@rediffmail.com, ravideshmukh@vsnl.net

A mononuclear cobalt (II) complexes were synthesized from chloro-substituted benzaldehyde derivatives of (N”-[(1Z,2E)-(hydroxyimino)-1-phenylpropylidene]thiocarbonohydrazide (HPTCHOPD) and characterized by magnetic, spectroscopic and electrochemical techniques and by powdered x-ray diffraction. The ligand HPTCHOPD has been reported to give complexes with various metal ions known to coordinate through the oxygen or nitrogen atoms of oximino function andthe imino atoms of the thiocarbohydrazide moiety in this ligand. Whereas thione sulfur of HPTCHOPD is not takes part in coordination with metal ion and found ligand is in thiol form. The aim being to investigate the behaviour of thione sulfur coordination in chloro-substituted benzaldehyde derivatives of HPTCHOPD.The infrared and electronic spectra indicates non-involvement of thione sulfur coordination with Co(II) ion. The molecular weight determination, infrared spectra, electronic spectra, and room temperature magnetic susceptibility measurements proposedmonomeric square planar geometry.The powdered X-ray crystallography study reveals orthorhombic crystal system for these complexes. The energy optimised structures are proposed using the semi empirical quantum mechanical calculations in Argust Lab programme.

 

 

INTRODUCTION:

Studies on metal complexes of Schiff base ligands containing N, O, and S-donor atoms have attracted much more in previous years due to their novel stereo-chemical feature, broad biological activities and their importance in catalysis. In a recent years, sulfur containing ligands such as thiosemicarbazones, thiocarbazones and their transition metal complexes have received more attention in the area of medicinal chemistry due to their pharmacological properties such as antimicrobial, anticancer, anti- HIV activities.^[1-7]

Received on 04.12.2017         Modified on 20.12.2017

Accepted on 28.01.2018         © AJRC All right reserved

Cobalt(II) complexes with the N, O, S-donor ligands are investigated due to their structural properties (ability to occur as cis and trans isomers) and potential application are attractive in studies of magnetism or magnetic exchange ions^[8]. Inour previous studies^[9-11], we have reported that ligand prepared from isonitrosopropiophenone and thiocarbohydrazide, HPTCHOPD [IUPAC name (N”-[(1Z,2E)-(hydroxyimino)-1-phenylpropylidene]thiocarbono hydrazide)], exist as thione and thiol tautomer’s. Therefore, there has been considerable interest in studying the coordination properties of various binding modes of the ligand.  In continuation of our work^[12-13] new ligands of HPTCHOPD were prepared by reacting with choro-substituted benzaldehydes 2-chlorobenzaldehyde and 4-chlorobenzaldehyde. These electron withdrawing substituents on benzaldehyde yield interesting cobalt(II) complexes. The interest in coordination chemistry of these ligands is primarily because of thus ambientacy. Some of these compounds are found to possess antibacterial and antifungal activity. The nature of these substituents groups like steric properties, electronic properties and the geometric properties affect the metal orbitals and thus affect its properties. In catalytic system in electron donating property of the ligand or the size of the substituents on the ligand play an important role in enantioselectivity and efficiency of a ligand or its complex^[14]. In the present work we report the synthesis and characterization of Co(II) complexes of chloro-substituted benzaldehyde of schiff base HPTCHOPD.

 

 

 

General Scheme:

 

R=Cl, R₁=H; HL⁴: N''-[(1Z)-(2-chlorophenyl)methylene]-N’’’-[(1Z,2E)-(2-hydroxyimino)-1-phenylpropylidene]thiocarbonohydrazide

R=H, R₁=Cl; HL⁵: N''-[(1Z)-(4-chlorophenyl)methylene]-N’’’-[(1Z,2E)-(2-hydroxyimino)-1-phenylpropylidene]thiocarbonohydrazide

 

 

 

 

MATERIALS AND METHODS:

Physical Measurements:

The elemental analyses were carried by standard methods.^[15]Infrared spectra were recorded on a Jasco FTIR 4600 spectrophotometer in the spectral range of 4000-400cm-1. Electronic spectra were measured on Equiptronic EQ-824 spectrophotometerin dimethyl formamide solution at KGKC Karjat. The molar conductance measurements of the complexes in dimethyl formamide (DMF) were obtained using an Equiptronic EQ-660 conductivity meter. Magnetic susceptibility measurements were carried out by employing Gouy’s balance using Hg(Co(SCN)₄] as calibrant at Institute of Science Mumbai. The effective magnetic moments were calculated after diamagnetic correction for ligand component using Pascal’s constants. The powdered XRD pattern of all Co(II) complexes recorded in the 2q range of 10 to 80° at a wavelength 1.5406 A° using Cuka radiation source by MiniFlex II desktop X-ray Diffractometer at TIFR Mumbai.

 

Synthesis:

Synthesis of ligands:                                    

The schiff base HPTCHOPD was synthesized as described in our previous paper.^[9-11]

 

 

Preparation of electron withdrawing chloro-substituted benzaldehyde ligands HL⁴and HL⁵

 

Synthesis of Schiff base N''-[(1Z)-(2-chlorophenyl)methylene]-N’’’-[(1Z,2E)-(2-hydroxyimino)-1-phenylpropylidene] thiocarbonohydrazide (HL⁴): 

2-chlorobenzaldehyde (4.305g, 0.030M) in ethanol (25cm3) was added to an ethanol solution (75 cm³) of HPTCHOPD (5.011g, 0.020M) and 5cm³ conc. HCl at 50°C. The mixture refluxed for 3hrs and kept overnight, whence, a yellow solid product was obtained which was filtered, washed with ethanol and dried. Crystallization from hot ethanol gave product, melted at 259°C. The purity of product was monitored by TLC using silica gel as well as by High Performance Liquid Chromatography (HPLC). The yield of a product was 5.0g, 67.13% of the theoretical.

 

Synthesis of Schiff base N''-[(1Z)-(4-chlorophenyl)methylene]-N’’’-[(1Z,2E)-(2-hydroxyimino)-1-phenylpropylidene]thiocarbonohydrazide (HL⁵): 

4-chlorobenzaldehyde (4.301g, 0.030M) in ethanol (25cm³) was added to an ethanol solution (75 cm³) of HPTCHOPD (5.020g, 0.020M) and 5cm³ conc. HCl at 50°C. The mixture refluxed for 3hrs and kept overnight, whence, a yellow solid product was obtained which was filtered, washed with ethanol and dried. Crystallization from hot ethanol gave product, melted at 243°C. The purity of product was monitored by TLC using silica gel as well as by HPLC method. The yield of a product was 3.61g, 39.44% of the theoretical.

 

Both the productsare insoluble in water and dilute hydrochloric acid and organic solvent like chloroform, acetonitrile, benzene and glacial acetic acid. The products arepartially soluble in aqueous solution of 0.5M sodium hydroxide and organic solvents like methanol, ethanol and soluble in DMF, DMSO.

 

 

Synthesis of metal complexes:

A general method was adopted for the synthesis of Co(II) complexes of HL⁴and HL⁵ was as follows:

An excess ethanol solution of two moles ligand was reacted with ethanol solution of one mole CoCl₂.6H₂O. The reaction mixture was refluxed for 3 hours, cooled, filtered, washed with ethanol and neutralized with excess hot water, dried and recrystallized to give a desired Co(II) complex. 

 

Typical procedure for preparation of Co(II) complex of 4-methoxy substituted benzaldehyde, Co(L⁴)₂:

An ethanol solution (10cm³) containing 1.002g (0.0042M) of CoCl₂.6H₂O was treated with ethanol solution (50cm³) of 3.251g (0.0087M) ligand HL². The reddish-brown precipitate obtained, was shake well for 10-15minutes at room temperature and digest at refluxed temperature for 3hours. Further cooled to room temperature, filtered, washed with ethanol and neutralized with excess hot water, dried at 110ºC and re-crystallised from chloroform.

 

 

 

Results:

Table I: Analytical data and Physical properties of ligands

ID	Molecular Formula	FWT	Yield %	Colour	D. Pt. ºC	Elemental analysis [Found(Expected)]				Molar Conductance
						%C	%H	%N	%S	Scm2/mol
HPTCHOPD	C10H13N5OS	251.30	59.60	Yellow	150	47.70 (47.81)	5.22 (5.18)	28.02 (27.89)	13.05 (12.75)	0.018
HL4	C17H16ClN5OS	373.86	54.38	Yellow	259	55.06 (54.56)	4.17 (4.28)	19.15 (18.72)	8.26 (8.56)	5.92
HL5	C17H16ClN5OS	373.86	38.94	Yellow	243	55.08 (54.56)	4.16 (4.28)	19.26 (18.72)	8.88 (8.56)	1.88

 

Table II: Analytical data and Physical properties of Co(II) complexes

ID	Molecular Formula	FWT	Yield %	Colour	D. Pt. ºC	Elemental analysis [Found(Expected)]
						%Co	%C	%H	%N	%S	%Cl
Co(L4)2	C34H30Cl2Co N10O2S2	804.6	67.74	Light brown	240	7.05 (7.32)	50.23 (50.71)	4.02 (3.85)	17.66 (17.40)	7.96 (7.95)	8.32 (8.82)
Co(L5)2	C34H30Cl2Co N10O2S2	804.6	74.25	Green-brown	240	7.11 (7.32)	50.18 (50.71)	3.90 (3.85)	17.50 (17.40)	7.61 (7.95)	8.03 (8.82)

 

Table II: Cont….

                                                                                                                                                                                                                                                        

Table III: selected ir bands for ligands and its Co(II) complexes

Compounds	Ir bands (cm-1)
	n(O-H) oxime	n(N-H)	n(C=N) (azomethine)	n(C=N) (oxime)	n(HC=N) imino	n(C-N) C=NOH	>N-C=S C=S + C=C
HPTCHOPD	3269	3304, 3170	1619	-	-	1487	1284
HL4	3260	3180, 2973	1617	1561	1518	1487	1285
Co(L4)2	3260	disappear, 2973	1590	-	1518	1487	1280
HL5	3312	3189, 2911	1594	1564	1518	1487	1285
Co(L5)2	3312	3180, disappear	1590	-	1519	1489	1287

 

                                                                                                                                                                                                                                                        

 

 

 

 

 

 

Table III: Cont…..

Compounds	Ir bands (cm-1)
	n(N=N) new	n(N-O) C=NOH	d(C=S) >N-C=S	(Cu-N)	(Cu-S)	(Cu-O)
HPTCHOPD	-	1001	752	-	-	-
HL4	-	1000	757	-	-	-
Co(L4)2	1360	1008	757	564	-	505
HL5	-	1008	767	-	-	-
Co(L5)2	1377	1008	767	566	-	504

 

 

Table IV: Electronic spectral data of Co(II)complexes

Complexes	Charge transfer S® Cu(II)	Charge Transfer Azomethine N à Cu(II)	2A1gà2B2g
Co(L4)2	-	22222 cm-1 (e=6302)	17544 cm-1(e=3273)
Co(L5)2	-	22989 cm-1 (e=7084)	17699cm-1(e=3042)

 

 

 

Table V: Crystallographic data for Co(II) complexes

	Co(L4)2	Co(L5)2
Molecular formula	C34H30Cl2Co N10O2S2	C34H30Cl2Co N10O2S2
Crystal system	Orthorhombic	Orthorhombic
Space group	Pbmn	Pbmn
l (A°)	1.5406	1.5406
Reflections	15	19
2q (deg) maxima	19.142	19.719
‘d’ (A°) maxima	4.632	4.498
Unit cell dimensions
a (A°)	11.2161	12.5511
b (A°)	10.9729	12.8269
c (A°)	11.2964	12.1171
A (A°)	0.00472	0.00377
B (A°)	0.00493	0.00361
C (A°)	0.00465	0.00404
α (°)	90	90
b (°)	90	90
g (°)	90	90
Unit cell Volume, V (A°3)	1390.28	1950.74
Density, d (g/cm3)	1.921	1.369
Particle size (nm)	1.597	1.681
q ranges °	13-41	12-76
Intensity (Arb. unit)	26-241	10-204

 

DISCUSSIONS:

Compositional and NMR studies

Analytical and spectroscopic data for ligands and its Co(II) complexes are summarized in Tables (I), (II) and (III). The elemental analysis indicates cobalt complexes possess 1:2 metal to ligand composition and can be formulated as mononuclear complex for HL⁴ and HL⁵. The high decomposition temperatures (>200°C) of the complexes indicates stronger metal-ligand bonding. The ligands are soluble in dilute alkali and insoluble in dilute hydrochloric acid indicating acidic nature of oximino proton and absence of protonable free -NH₂ group of parent molecule HPTCHOPD respectively. The ¹H NMR spectra of ligand HL⁴ to HL⁵ shows three sharp singlet at ~d10.6ppm, d12.0ppm and d12.4ppm due to the imino –CH=N, azomethine N-H and oximino O-H proton of respectively.^[9-11] Since these protons expected to be rather acidic and therefore the weakest shielded proton in the molecule support by disappearance of the signal in D₂O shaking ¹H NMR spectra. The spectra also exhibited two singlet and one multiplet at d1.5ppm, d8.0ppm and d7.0-7.7ppm due to methyl –CH₃, -NH and phenyl moiety respectively.

 

Molar conductance studies

The molar conductivity was measured in DMF at 10^-3M concentration. The observed conductance values of the Co(II) complexes of ligands HL⁴ to HL⁵is 12.15 and 9.05 mho.cm².mol^-1. These values are less than the values reported for 1:1 electrolytes (Table II) indicating non-electrolytes in nature.

 

Infrared studies

The significant IR bands with their assignments of the Co(II) complexes in the region 4000-500cm^-1 are presented in Table (III). The reported schiff base ligands HL⁴ to HL⁵ are act as a tridentate ligand. The possible coordination sites being azomethine nitrogen, oximino oxygen and/or nitrogen and thione sulfur. The three types of C=N linkages present in ligand HL⁴ to HL⁵, appears in range 1512-1617cm^-1 assigned to azomethine C=N, imino HC=N of benzaldehyde moiety and oximino C=NOH. The appearance of a new band 1520-1530cm^-1 due to the HC=N group confirms the successful derivatization. This band is not altered and shown at its usual position in spectra of Co(II) complexes of HL⁴ to HL⁵ indicating non-involvement of imino HCH=N group in coordination with metal ion. The azomethine and oximino n(C=N) modes are seen between 1500 and 1620cm^-1 in ligands.^[4,16] Of these, the one at ~1617cm^-1 and 1594cm-1 in ligand  HL⁴ and HL⁵ respectively, assigned to azomethine moiety shifted to lowering frequencies of 27 and 4cm^-1 in present Co(II) complexes of HL⁴ and HL⁵ respectively indicated the co-ordination through the azomethine nitrogen.^[17-21]While the band assigned to oximino C=NOH at ~1560cm-1 in parent ligands are weak shoulder or merged with neighbouring band indicates the co-ordination through oximino oxygen and/or oximino nitrogen.^[17] The bonding of the azomethine nitrogen as one of the coordination site is further confirmed with the presence of a band in the range of 560-577cm^-1 assigned to a n(Cu-N) vibration for these complexes^[4]. The nN-H band of the free ligand HL⁴ and HL⁵ shown at 3180, 2973 and 3189, 2911 respectively. Out of these two band one band is absent and another will be shifted towards downwards in the spectra of the complexes supporting deprotonation of the ligands during coordination with metal ion.^[22] The deprotonation of the azomethine amino –NH group confirmed by formation of new band at 1360 and 1377cm^-1 assigned –N=N- group^[23]. The new band observed at 2068cm-1 in Co(II) complexes of HL⁵ supports the formation  –N=N group.^[20]  The coordination mode of oximino (C=NOH) group to the metal ion via either oxygen or nitrogen or both oxygen and nitrogen atom appears interesting spectral feature. The oximino –OH stretching vibration is observed in free ligand HL⁴ and HL⁵ at 3260and 3312cm^-1 respectively, lower down from the usual nO-H vibration around 3500cm^-1 an account of strong inter and/or intra molecular hydrogen bonding of nO-H of the oxime groups with the imino-nitrogen atoms.^[24] In Co(II) complexes of HL⁴ and HL⁵ the oximino band is observed at its usual position but in weak intensity. This may be due to coordinate bond formation through oxygen of hydroxyl group.^[25]The mode of coordination of oximino function with metal ion via oximino oxygen and/or nitrogen shows shifting of oxygen bonded band nN–O observed at around 1000cm^-1 and formed new nitrogen bonded nNàO band in region 1200-1250cm^-1. In Co(II) complexes of  HL⁴ and HL⁵ only one medium intense band observed at ~1008cm^-1 due to oxygen bonded nN–O atom indicates MN₂O₂ chromophore with an symmetrical structure with six-membered rings involving bonding through oxime oxygen atom.^[15] The thiocarbonyl (C=S) absorption at 1285, 757 and 1285, 767cm^-1 is found in ligand HL⁴ and HL⁵ respectively are not altered and shown as its usual position indicates thione sulfur is not participate in coordination with respected Co(II) ion. Thus, the analytical and spectral data shows monomeric Co(II) complexes of  HL⁴ and  HL⁵ coordinates through two azomethine nitrogen and two oximino oxygen.

 

Magnetic properties

The effect of substituent of benzaldehydes on the electronic and magnetic properties of the complexes were detected by its electronic spectra and magnetic susceptibility measurements, are presented in Table (IV) and (II) respectively. The observed m_eff of Co(II) complexes is the characteristics of the stereochemistry around the metal ion. The low-spin square planar complexes will have m_eff values in the range of 2.1-2.9B.M.^[26-32] This arise from one unpaired electron and also orbital contribution. The orbital contribution is large in the case of square planar Co(II)complexes.^[33]

 

The molar magnetic susceptibilities at room temperature for the present Co(II) complexes of ligands HL⁴ and HL⁵ is 2.56 and 2.16BM respectively. The magnetic moments correspond to one unpaired electron per cobalt atom, suggesting the low spin square-planar geometry for the complex.

 

The electronic spectra                                                          

The electronic spectra of the complexes in DMF solution are given Table IV. It is known that Co(II) complexes having tetrahedral configuration possess a characteristic intense multicomponent band in the region 12000-16000cm^-1, associated with ⁴A₂(F) à⁴T₁(P) transition (n₃).^[34] The spectra of present complexes in DMF, no multicomponent band in the above region, suggesting that the complexes may not possess tetrahedral configuration. Low spin square planar cobalt(II) complexes exhibit  a narrow band near 8500cm^-1 and a second stronger and broader band near 20000cm^{-1 [35-36]}. Few investigators ^[37-38] without studying the near infrared region, have suggested that the square-planar cobalt(II) complexes exhibit a band near 20000cm^-1. In the present investigation exhibit absorption at 17544 and 17699cm^-1 respectively, which may be assigned to ²A_1gà²B_2g transition. Near infrared studies could not be made due to limitation of the instrumental facility. The spectrum resembles those of reported complexes and the effective magnetic moments corresponding to the low spin square planar stereochemistry around d⁷ Co(II) ion.^[26-29] In addition of these bands, a bands in the range 22222-23810cm^-1 observed which is attributed to a charge transfer transition indicating nitrogen-to-cobalt NàCu charge transfer bands. The band expected above 24000cm^-1 for sulfur-to-cobalt SàCu charge transfer^[3] is not observed, supporting non-involvement of thione sulfur in coordination with central Co(II) ion.

 

Powder X-ray diffraction studies

The x-ray diffractogram of Co(II) complexes of HL⁴ and HL⁵ was scanned in the range 20-80° at wavelength 1.543 Å. The diffractogram and associated data depict the 2θ value for each peak, relative intensity and inter-planar spacing (d-values). All the reflection has been indexed for h, k, l values using methods reported in the literature. ^[39-42]The diffractogram of Co(II) complex of HL⁴ had fifteen reflections with maxima at 2θ = 19.14° corresponding to d value 4.63Å. The diffractogram of Co(II) complex of HL⁵ had nineteen reflections with maxima at 2θ = 19.71° corresponding to d value 4.493Å. The x-ray diffraction pattern of these complexes with respect to major peaks of relative intensity greater than 10% has been indexed by using computer programme WinPloter^[39]. The above indexing method also yields Miller indices (hkl), unit cell parameters and unit cell volume. The unit cell of Co(II) complex of HL⁴ yielded values of lattice constants, a=11.21 Å, b=10.97 Å, c = 11.29 Å and unit cell volumeV=1390.28 ų. The unit cell of Co(II) complex of HL⁵ yielded values of lattice constants, a=12.55 Å, b=12.82 Å, c = 12.11 Å and unit cell volume V=1950.74 ų. In concurrence with these cell parameters, the condition such as a = b = c and α = β= γ=90° required for sample to be Orthorhombic were tested and found to be satisfactory. Hence it can be concluded that Co(II) complexes of HL⁴ and HL⁵ has Orthorhombic crystal system^[40]. The number of formula units per unit cell (n) is calculated from the relation n=dNV/M, where d= density of the compound, N=Avogadro’s number, V=Volume of the unit cell and M=Molecular weight of the complex.The density of the compound is calculated based BCC unit cell (there are two atoms per unit cell). The experimental density of Co(II) complex of HL⁴ and HL⁵ is 1.921 and 1.369g/cm³ respectively. The Scherrer equation in X-ray diffraction and crystallography is a formula which relates the size of the crystallites in a solid to the broadening of a peak in a diffraction pattern. The Debye–Scherrer equation is B =kl/s.cosq; where ‘S’ is Crystallite size, l is wavelength of X-ray radiation (Cu Ka= 1.54060 A˚), k constant taken as 0.94, q is diffraction angle and B=Full width at half maximum height. The crystallite size of the Co(II) complex of HL⁴ and HL⁵ is  1.597nm and 1.681nm suggesting that the complexes are nanocrystalline.

 

Molecular Modelling studies of ligands

Molecular modelling of the ligand and metal complexes of Co(II) have been carried out using molecular mechanics and Hartree-Fock (HF) Quantum methods. The Universal Force Field (UFF) and AM1 (Austin Model 1) approximation is used for molecular mechanics calculations in ArgusLab 4.0.1 programme^[40,43-44]. The ligand and its metal complexes were built and geometry optimization was done using this software. The molecular modelling picture are shown below:

 

 

The molecule was built and geometry optimization was done using quantum mechanics, molecular orbital calculations were performed with AM1 (Austin Model 1) approximation, for thesynthesized ligand^[44]. The Self consistent field (SCF) energy value and heat of formation for the optimized geometry are reported below.

 

 

Table VI: The computational study of ligand and its Co(II) complexes: energy

Energy	HL4	Co(L4)2		HL5	Co(L5)2
		Five membered ring	Six membered ring		Five membered ring	Six membered ring
Final SCF Energy (kcal/mol)	82358.037	-248624.909	-2487080.430	70733.6542	-248648.950	-248702.489
Final Geom Energy (kcal/mol)	51.7267	145.195	167.610	88.3229	134.780	151.806
Heat of Formation (kcal/mol)	182644.8982	-	-	168567.082	-	-

 

Table VII: The computational study of Co(II) complexes: Bond length

 

Table VII: The computational study of Co(II) complexes: bond angles

Finding of these computed works are in good agreement with the experimental results. The selected bond lengths, bond angles of the complexes are given in table VII. In the Co(II) complex of HL⁴, the metal ion may be bonded to N(12) and N(37) nitrogen atoms of azomethine group and N(11) and N(36) nitrogen atoms of the oximino group, they form a five membered ring. Whereas Co(II) complex of HL⁵, the metal ion may be bonded to N(12) and N(36) nitrogen atoms of azomethine group and N(11) and N(35) nitrogen atoms of the oximino group, they form a five membered ring.But when the metal ions coordinate with N(12) and N(37) nitrogen atoms of azomethine group and O(4) and O(18) oxygen atoms of the oximino group in Co(II) complex of HL⁴, they form a six membered ring. Similarly when the metal ions coordinate with N(12) and N(36) nitrogen atoms of azomethine group and O(4) and O(18) oxygen atoms of the oximino group in Co(II) complex of HL⁵, they form a six membered ring. The total Geometric energies of five membered ring Co(II) complex of HL⁴ and HL⁵ is found to be 145.195kcal/mol and 134.78kcal/mol respectively. The total energies of both the complexes have increased to 167.610kcal/mol and 151.806kcal/mol respectively, when they formed six membered ring. From this energy difference it is concluded that both the complexes formed a five membered ring with azomethine nitrogen and oximino oxygen atom.^[40]

 

Computational electronic spectra of Co(L⁴)₂ and Co(L⁵)₂

The computational electronic data show a pattern similar to the theoretical spectrum^[44], even though the some of the peaks do not match exactly. According to the calculations, Co(II) complexes of HL⁴ and HL⁵ maximum absorption observed at 17964cm^-1and 17681cm^-1 respectively. However experimental values of these complexes are 17544cm^-1 and 17699cm^-1 respectively. As we discussed earlier experimental near infrared studies could not be made due to limitation of the instrument. In computational study, found band at 9806cm^-1 and 8240cm^-1 well within the range of square planar geometry.

 

 

Table VIII: The computational study of Co(II) complexes: bond angles

 

CONCLUSION:

The analytical and physico-chemical analyses confirm the composition and the structure of the newly obtained ligands and its Co(II) complexes.The molecular weight determination, infrared spectra, electronic spectra, and room temperature magnetic susceptibility measurements proposed mononuclear square planar geometry.The powdered X-ray crystallography study reveals orthorhombic crystal system for these complexes. The infrared and electronic spectra indicates non-involvement of thione sulfur coordination with Co(II) ion. This could have been due to the greater probability of the thiol contribution in the thione-thiol resonance prevalent in the ligand, thereby making perhaps the sulfur atom less available for coordination. The computational study suggested that both the complexes formed a five membered ring with azomethine nitrogen and oximino oxygen atom

 

 

ACKNOWLEDGEMENTS:

The Authors wish to thank Department of Chemistry, Konkan Gyanpeeth Karjat College of Arts, Science and Commerce teaching and non-teaching staff, Niraj Bahuguni for encouraging and support. Also thank to Dr.P.D.Babu from UGC-DAE, BARC Mumbai for VSM data, Dr.N.Kulkarni from TIFR Mumbai and Dr.Malge from Institute of Science Mumbai for powdered XRD data, Dr.R.M.Patil from Institute of Science for magnetic susceptibility and his guidance. Also thankful to SAIF, IIT Mumbai for the PMR, ESR, TGA-DTA data.

 

CONFLICT OF INTEREST:

The authors,Dilip C. Sawant and R.G.Deshmukh,certify that we have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.i.e.We, the authors declares that we have no conflict of interest.

 

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Received on 12.12.2017         Modified on 20.01.2018

Accepted on 21.02.2018         © AJRC All right reserved