Synthesis, Physico-Chemical and Biological Properties of Complexes of Cobalt(II) Derived from Hydrazones of Isonicotinic Acid Hydrazide

Isonicotinic Acid Hydrazide의 Hydrazone으로부터 유도된 코발트(II) 착물의 합성, 물리-화학 및 생물학적 성질

Abstract

Hydrazones of isonicotinic acid hydrazide, viz., N-isonicotinamido-furfuralaldimine (INH-FFL), N-isonicotnamido-cinnamalidine (INH-CIN) and N-isonicotnamido-3',4',5'-trimethoxybenzaldimine (INH-TMB) were prepared by reacting isonicotinic acid hydrazide with respective aromatic aldehydes, i.e., furfural, cinnamaldehyde or 3,4,5-trimethoxy-benzaldehyde. A new series of fifteen complexes of cobalt(II) with these new hydrazones, INH-FFL, INH-CIN and INH-TMB, were synthesized by their reaction with cobalt(II) salts. The infrared spectral data reveal that hydrazone ligands behave as a bidentate ligand with N, O donor sequence towards the $Co^{2+}$ ion. The complexes were characterized on the basis of elemental analysis, magnetic susceptibility, conductivity, infrared and electronic spectral measurements. Analytical data reveal that the complexes have general composition [Co($L)_2X_2]\;and\;[Co(L)_3](ClO_4)_2$ where L= INH-FFL, INH-CIN or INH-TMB and X = $Cl^-,{NO_3}-,\;NCS^-\;or\;CH_3COO^-.$ The thermal behaviour of the complexes were studied using thermogravimetrictechnique. Electronic spectral results and magnetic susceptibility measurements are consistent with the adoption of a six-coordinate geometry for the cobalt(II) chelates. The antimicrobial properties of cobalt(II) complexes and few standard drugs have revealed that the complexes have very moderate antibacterial activities.

Isonicotinic acid hydrazid의 Hydrazones, 즉, N-isonicotinamido-furfuralaldimine (INH-FFL), N-isonicotnamido- cinnamalidine (INH-CIN) 및 N-isonicotnamido-3',4',5'-trimethoxybenzaldimine (INH-TMB)를 isonicotinic acid hydrazide와 예를 들면 furfural, cinnamaldehyde 또는 3,4,5-trimethoxy-benzaldehyde 등과 같 은 각각의 방향족 알데히드와의 반응으로부터 제조하였다. INH-FFL, INH-CIN and INH-TMB와 같은 새로운 hydrazones을 코발트(II) 염과 반응시켜 새로운 일련의 15개 코발트(II) 착물을 제조하였다. 적외선 분광 데이타를 통해 hydrazone 리간드들이 $Co^{2+}$ 이온에 대해 N, O 주개원자의 배열을 갖는 두자리 리간드임을 규명하였다. 착물 의 특성은 원소분석, 수자율, 전도도, 적외선 및 전자 스펙트럼 측정을 통해 조사하였다. 분석 데이터로부터 착물은 [$Co(L)_2X_2$] 및 [$Co(L)_3](ClO_4)_2$ (L = INH-FFL, INH-CIN 또는 INH-TMB, 그리고X = $Cl^-,\;{NO_3}^-,\;NCS^-$ 또는 $CH_3COO^-$)의 일반적 조성을 가짐을 알 수 있었다. 열무게법으로부터 착물의 열적 행동을 조사하였다. 전자 스펙 트럼 결과와 자화율 측정으로부터 코발트(II) 킬레이트가 6배위의 기하구조를 이루고 있다는 것을 확인할 수 있었 다. 코발트(II) 착물과 약간의 표준약물에 대한 향균성으로부터 이들 착물이 매우 적합한 향균성질을 가짐을 알 수 있다.

INTRODUCTION

The metal chelates with ligands of biological importance have been playing an important role in the development of new coordination chemistry. Complexes containing chelating ligands, which show promising biological activity, have been recently studied by ourselves1-9 and others.10-20 We have been investigating the synthesis and characterization of cobalt(II),1,2 nickel(II),2,3 oxovanadium(IV)4,5 and platinum(II)6 and some lanthanide (III)7 complexes that contain a range of ancillary ligands such as semicarbazones[7], thiosemicarbazones1,2,4-6 derived from 4-aminoantipyrine and hydrazones3 derived from isonicotinic acid hydrazide. The antibacterial and antifungal properties of the thiosemicarbazone ligands and their cobalt(II),1,2 nickel(II)2 and oxovanadium(IV)4 complexes and nickel(II) complexes with hydrazones3 have also been examined by us.

Isoniazid (isonicotinic acid hydrazide; INH) is a drug of proven therapeutical importance, used against wide spectrum bacterial ailments,viz., tuberculosis. Hydrazones derived from condensation of isoniazid with pyridine aldehydes have been found to show better antitubercular activity than isoniazid.21 We have recently turned our attention to the investigation on transition metal complexes of N and O donor ligands.3,8,9 In this paper we report the synthesis, characterization and biological activities of cobalt(II) complexes of hydrazones derived from isonicotinic acid hydrazide viz., N-isonicotinamido-furfural-2'-aldimine (INH-FFL), N-isonicotinamido cinnamalidine (INH-CIN) and N-isonicotinamido-3',4',5'-trimethoxybenzalaldimine(INH-TMB) (Fig. 1-3).

Fig. 1N-Isonicotinamido-furfuraldimine (INH-FFL)

Fig. 2N-Isonicotinamido-3´,4´,5´-trimethoxybenzaldimine(INH-TMB)

Fig. 3N-Isonicotinamido-cinnamalidene (INH-CIN)

 

EXPERIMENTAL SECTION

Materials

The general experimental techniques have been previously described3,8. CoX2․nH2O (X = Cl–, NO3– or CH3COO–) were obtained from BDH and were used without further purification. Co(NCS)2 was prepared by the reaction of CoCl2 (in ethanol) and ethanolic solution of KNCS in 1:2 molar ratio. The precipitated KCl was filtered off and the filtrate having Co(NCS)2 was used immediately for complex formation with hydrazones viz., INH-FFL, INH-CIN and INH-TMB. Co(ClO4)2 was prepared by the reaction of an ethanolic solution of CoCl2 and NaClO4 in 1:2 molar ratio. The white precipitate of NaCl was filtered off and the filtrate containing Co(ClO4)2 was used as such for complex formation with hydrazones. During the preparation of Co-(NCS)2 and Co(ClO4)2, KNCS and NaClO4 were taken 10% excess.

Synthesis of hydrazones: INH-FFL, INH-TMB and INH-CIN

All the three hydrazones of INH viz., INH-FFL, INH-CIN and INH-TMB were synthesized by method reported by us.3,8,9 INH (0.01 mol) was dissolved in 10 mL of 95% ethanol. To this solution respective aromatic aldehyde i.e. furfural, cinnamaldehyde or 3,4,5-trimethoxybenzaldehyde (0.01mol) in 95% alcohol (10 mL) was added. The reaction mixture was refluxed on a water bath for ~2 hr. The partial removal of solvent on a water bath followed by cooling produced crystalline product of the complexes, which was suction filtered, washed with cold ethanol and dried under vacuum(yd. ~ 80%).

Synthesis of cobalt(II) complexes: [CoX2(L)2] and [Co(L)3](ClO4)2

Depending on nature of anionic ligands (Cl–, NO3–, NCS–, CH3COO– or ClO4–), the cobalt(II) complexes were synthesized by the reaction of warm ethanolic solution of ligand (INH-FFL, INH-TMB or INH-CIN) and metal salts in 1:2 or 1:3 molar ratio. The reaction mixture was refluxed on a water bath for 2-3 hr. It was then concentrated to a small volume on a hot plate at 50 ℃. On cooling the solutions crystals of complexes appeared which were filtered, washed with ethanol and dried in vacuum over P4O10 (yd. 60-75%).

Instrumentation, physical, analytical and antimicrobial studies

The cobalt in the complexes was estimated, spectrophotometrically using 2-nitroso-1-naphthol, after decomposing the complex with conc. H2SO4 and H2O2.22 The chloro content in the complexes was estimated by Volhard’s method.22 The thiocyanate was estimated by titrating slightly acidic solution of the complex with standard AgNO3 solution. The perchlorate was estimated by the methods of Kurz et al.23 The percentage of nitrogen was determined in the laboratory by Kjeldahl method. The molecular weight of the complexes was determined cryoscopically in freezing PhNO2 using a Beckmann thermometer of accuracy ± 0.01℃. The conductivity measurements were carried out using a Toshniwal conductivity bridge and dip type cell operated at 220 volts, AC mains. All the measurements were done at room temperature in PhNO2 as solvent.

The magnetic measurements on powder form of the complexes were carried out at room temperature on Evans magnetic balance (Sherwood Scientific, Cambridge, England) using copper sulphate as calibrant. The infrared spectra of the complexes were recorded on a Perkin Elmer infrared spectrophotometer model 521 in KBr in the range of 4000-200 cm-1. Diffused reflectance spectra of the solid compounds were recorded on a Beckman DK-2A spectrophotometer. Thermogravimetric analyses of the complexes were carried out at IIT Roorkee, India, on a Perkin Elmer Pyris Diamond thermogravimentric analyzer, in static air with open small platinum boat sample holders using the heating rate of 6 ℃ min-1. The antibacterial and antifungal activities of some of the representative cobalt(II) complexes and standard drugs (ampicillin and tetracycline) were screened by following the methods reported else where.1,2

 

RESULTS AND DISCUSSION

The reaction of Co2+ salts with INH-FFL, INH-CIN or INH-TMB on refluxing afforded the complexes of the general composition Co(L)nX2 where X = Cl–, NO3–, NCS– or CH3COO–, n = 2 while X = ClO4–, n = 3 and L = INH-FFL, INH-CIN or INH-TMB. The products were characterized by elemental analysis, magnetic susceptibility, and conductivity, infrared and electronic spectral measurements. The analytical data of these complexes are given in Table 1. All the complexes were quite stable and could be stored for months without any appreciable change. The complexes were soluble in common organic solvents such as dichloromethane, acetone, (CH3)3SO etc. The complexes do not have sharp melting points but decomposed on heating beyond 250 ℃. The molecular weights determined by cryoscopic method in nitrobenzene are given in Table 1. The results are in broad agreement with conductance data. The molar conductance data showed that the chloro, nitrato, isothiocynato and acetato complexes were essentially non-electrolytes in PhNO2, while the perchlorato complexes dissociated in PhNO2 and behaved as 1:2 electrolytes. The magnetic moment data of the complexes reported in Table 1 show that all the cobalt(II) complexes are paramagnetic corresponding to three unpaired electrons indicating a high-spin octahedral configuration. For the present complexes the magnetic moment values lies in the range 4.6-5.7 BM.24

Table 1Analytical, conductivity, molecular weight and magnetic moment data of Co(II) complexes of hydrazones of isoniazid.

Infrared spectra

A study and comparison of the infrared spectra of all the three ligands, viz., INH-FFL, INH-TMB and INH-CIN and their Co(II) complexes, imply that all the ligands are bidentate with azomethine nitrogen and carbonyl-oxygen as two (N, O) coordination sites. The infrared data of all the complexes are provided in Table 2. The infrared frequencies in the present ligands associated with amide group carbonyl-oxygen (C=O), azomethinenitrogen(C=N) and heterocyclic nitrogen are expected to be influenced on complex formation with metal ion. Generally, all amides show two absorption bands: (i) the carbonyl absorption band near 1640 cm–1 known as amide-I band and (ii) strong band in the 1600-1500 cm–1 region, known as amide-II band. The amide-I band in INH-derivatives, however, appears at 1655 cm–1.25,26 In the infrared spectra of the complexes, a considerable negative shift in ν(C = O) is observed indicating a decreased in the stretching force constant of C = O as a consequence of coordination through the carbonyl oxygen atom of the free base. The amide-II band appears at the normal position in the NH- deformation rather than C-N link. In all these ligands the absorptions at 1540-1530 cm–1 have been assigned to amide-II absorptions. The NH stretching absorption in free ligands occurs at ~3300 and 3220cm–1 which remain unaffected after complexation. This observation clearly discards any possibility of coordination through imine-nitrogen atom. Another important band occurs in 1590-1585 cm–1 range is attributed to ν(C = N) (azomethine) mode.27-29 In spectra of all the complexes this band shifted to lower wave number and appeared at 1550-1525cm–1 region, respectively indicating the involvement of N-atom of the azomethine group in coordination with Co2+ ion.27-29 The strong bands observed at 1575-1520 cm–1 and 1080-1000 cm–1 are tentatively assigned to asymmetric and symmetric ν(C = C) + ν(C = N) of pyridine ring30,31 while pyridine ring breathings and deformations remained practically unchanged in frequency and band intensities which clearly revealed non-involvement of pyridine-nitrogen in bonding with Co2+ ion. In far infrared spectral region, the bands in INH-FFL, INH-TMB and INH-CIN were practically unchanged in these complexes. Some new bonds with medium to weak intensities appeared in the regions 450-380 cm–1 for the complexes under study, which are tentatively assigned to ν(Co-N)/ν(Co-O) modes.8,30,31 The overall infrared spectral evidence suggests that the present ligands act as bidentate ligand and coordinate through amide-oxygen and azomethine-nitrogen atoms forming a five membered chelate ring.

Table 2Key infrared bands (cm–1) of Co(II) complexes of hydrazones of isoniazid.

Anions

The pseudo halide NCS– ion is very interesting anion for it may coordinate through the sulfur (thio) or through the nitrogen (isothio) or through both these atoms (bridging). Infrared spectroscopy is very useful in elucidating which type of bonding exists. The various criteria proposed for determining the mode of bonding have been discussed in literature.31 In general the bonding depends on (a) the nature of central atom (b) the nature of other lignads in the coordination sphere and (c) environmental controls and kinetic (mechanistic) controls. The first transition metal series, i.e., Class-A metals form M-N type bonds, whereas metals of second and third transition series, i.e., Class-B metals form the M-S bonds. The C-N stretching frequency (ν1) is generally lower for M-NCS complexes than for M-SCN complexes. Bailey et al. suggested the region near or above 2100 cm–1 for S-bonding below 2100 cm–1 for N-bonding.32 The C-S stretching frequency (ν2) is assigned in the 860-780 cm–1 region for M-NCS and 720-690 cm–1 for M-SCN bonding modes.33,34 The δ(NCS) frequency (ν3) is also different for the two isomers; 490-450 cm–1 for the M-NCS and 440-400 cm–1 for M-SCN bonding.33,34 Bridging thiocyanate usually give higher CN– stretching frequencies than terminal NCS– group.33,34 The three fundamental absorption (C-N) stretching (ν1), (C-S) stretch (ν3) and (N-C-S) bending (ν2) in present complexes were identified at 2040-2035, 845-830 and 470-465 cm–1 region respectively. These frequencies are associated with the terminal N-bonded isothiocyanate ions.33,34

In nitrato (NO3–) complexes, the infrared spectral data indicate the occurrence of two strong absorption bands in the regions 1555-1500 cm–1 and 1310-1295 cm–1 which are attributed to ν4 and ν1 modes of vibrations, of the covalently bonded nitrate groups, respectively. This suggests that nitrate groups are present inside the coordination sphere.35 Distinction between monodentate and bidentate nitrate is usually different. However, by applying Lever’s separation method,36 a separation of 15-25 cm–1 in the combination bands (ν1+ν4) in the 1800-1700 cm–1 region concluded the monodentate nitrate coordination. Other bands appeared at ~1040 (ν2), 810 (ν6) and 7335 cm–1 (ν3/ν5) due to nitrate groups.

The acetate ion (CH3COO–) may coordinate to a metal ion in one of the following modes (a-c):

The νasym(COO–) and νsym(COO–) of free acetate ion are at ~1560 cm–1 and 1416 cm–1 respectively. In the unidentate complex (structure a) ν(C = O) is higher than νasym(COO–) and ν(C-O) is lower than νasym(COO–). As a result the separation between the two ν(CO) is much larger in unidentate complexes than free CH3COO– ion. The opposite trend is observed in the bidentate complexes (structure b) i.e. the separation between two ν(CO) is smaller than that of free CH3COO– ion in this case. In the bridging complexes (structure c), however, two ν(CO) are close to the free ion ν(CO) values. The present complexes show infrared absorption frequency bands corresponding to νasym(COO–) and νsym(COO–) at ~ 1610 and 1370 cm–1 respectively. These observations indicate that both the acetate groups in present complexes are unidentate.2,37

In all the perchlorato complexes, the presence of the ν3(1100-1090 cm–1) and ν4(625-620 cm–1) bands indicates that the tetrahedral symmetry of ClO4– is maintained in all these complexes. Thus it suggested the presence of ClO4– outside the coordination sphere in these complexes.17,38

Electronic spectra

The electronic spectra of all the complexes recorded herein consist of three bands; one in the 7800-8772 cm-1 (ν1), other in the 15400-15500 (ν2), or 18000-18520 cm-1 (ν2), and the third in the 20000-20800 cm-1 (ν3), regions, which clearly indicate the octahedral stereochemistry of the complexes. The energy of ν1 corresponds to 10Dq for weak field and the value of Dq is obtained from it. All the bands, ν1, ν2 and ν3 observed are free from shoulders. So the ligand field parameters, Dq, B and nephelauxetic effect (β) have been calculated using first order perturbation theory from the ligand field spectra of octahedral Co(II) complexes as discussed by Lever39 and Reedijk et al.40 The band maxima, their assignments, the calculated nephelauxetic effect (β) and the ligand field parameters B and Dq for some representative chelate complexes are listed in Tables 3. The appreciable intensity enhancement in all the bands of the Co(II) complexes studied herein clearly shows the existence of distortion from a regular octahedral structure of the present Co(II) complexes. Apart from this, there is no difference in the spectra of regular and pseudo octahedral Co(II) complexes.

Table 3Electronic spectral bands (cm–1) and lignad field parameters of Co(II) complex of hydrazones.

Thermo gravimetric studies Co(II) complexes of INH-TMB and INH-CIN

The results of the thermo gravimetric studies of [Co(INH-TMB)2X2] (X = Cl–, NO3– or NCS–) complexes are presented in Table 4. The thrmo gravimetric data indicate that the complexes are stable upto 150 ℃, which indicates that the complexes are non-hygroscopic in nature and does not have any water molecule. The decomposition and deligation process started above 150 ℃. During 180-360 ℃ both the INH-TMB molecules are lost. Finally at ~605 ℃, the cobalt oxide, Co3O4 formation takes place.

Table 4Thermoanalytical results obtained for Co(II) complexes of INH‐TMB and INH–CIN.

In case of [Co(INH-CIN)2X2] (X = Cl–, NCS– or CH3COO–) complexes the thermo gravimetric curves suggest that in temperature region 190-270℃, the weight loss 37.11-40.26% corresponds to the loss of one molecule of INH-CIN (Table 4). Further heating the [Co(INH-CIN)X2] complexes at temperature range 280-375 ℃, the weight loss (74.06-80.39%) suggests that second molecule of INH-CIN is also evaporated off. Finally at ~666-610 ℃, Co3O4 is formed. The thermal decomposition of Co(II) complexes studied may be represented by the following equations (cf. Table 4):

Biological studies

The antibacterial activities of the cobalt(II) complexes and standard drugs (ampicillin and tetracycline) were screened by agar-disc method in DMF solvent at a concentration of 50 μg mL-1. The organisms used in the present investigations included Bacillus subtilis (B.s.) and Staphylococcus aureous (S.a.) as gram positive bacteria and Escherichia coli (E.c.) and Salmonella typhi (S t.) as gram negative bacteria. The zone of inhibition around each disc containing the test compound was measured accurately. The diameters of zone of inhibition (mm) of the standard drug ampicillin against gram positive bacteria Bacillus subtilis and Staphylococcus aureous and gram negative bacteria Escherichia coli and Salmonella typhi were found to be 24, 22, 17 and 16 respectively, while tetracycline gave 18, 17, 21 and 22 respectively. The results of the antibacterial activities are summarised in Table 5. Under the same conditions, Table 5 shows that all the cobalt(II) complexes of hydrazones studied have moderate antibacterial activities against these bacteria. The cobalt(II) complexes of hydrazones also screened for their antifungal activities against two fungi, Aspergillus niger (A. niger) and Candida albicans (C. albicans). The results are presented in Table 5, which show that almost all the complexes studied showed nearly the same extent of activity but they are less active compared to salicylic acid. These complexes appear to be good antifungal agents.

Table 5Antifungal and antibacterial activities of cobalt(II) complexes of INH–FFL and INH–CIN

 

CONCLUSION

The present study reveals that the hydrazone ligands, INH-FFL, INH-CIN or INH-TMB act as a neutral bidentate ligand coordinating Co2+ ion through N, O-donor sites. The overall experimental evidences reveal that the studied Co(II) complexes display a coordination number six and have distorted octahedral structures. The experimental analyses of the chloro, nitrato, thiocyanato and acetato cobalt(II) complexes of INH-FFL, INH-TMB and INH-CIN suggest that the complexes are nonionic in nature while the perchlorato complexes are 1:2 electrolyte and have general composition as [Co(L)2X2] and [Co(L)3](ClO4)2 (X = Cl–, NO3–, NCS– or CH3COO–; L = INH-FFL, INH-TMB and INH-CIN) respectively.