Structural and Antifungal Evaluation of Palladium(II) Complexes Ligated by Triphenyl Phosphine and Isomeric 1-substituted phenyl tetrazoline-5-thione

Introduction

The relationship between structural and biological properties of metal complexes with thioamide ligands has been reviewed by West et.al.¹ Several Palladium (II) complexes having thioamide ligands are reported to be potential anti-tumor activity^2-3 and significant antifungal activity⁴. Cowper and Co-workers⁵ have examined the antimicrobial activity of some 1,2,3,4-Tetrazole having thioamide group. The present paper aims at structural and biological evaluation of some Palladium (II) complexes ligated by 1-substituted phenyl- tetrazoline-5-thione. The phenyl ring was substituted at various locations with methyl and chloro groups to correlate the electronic effect of such substituents on the magnitude of the bio-activities.

The identification of all Palladium (II) complexes have been established on the basis of elemental analysis, Magnetic, conductivity, IR, UV-vis and ¹H NMR spectral data.

Experimental

All the chemicals used were of AR grade or CP grade. The ligand, 1-substituted tetrazoline-5-thione⁶ and complexes⁷ were prepared by the method reported in literature. Elemental analysis, magnetic measurements, IR, UV-vis and ¹H NMR spectral data were obtained as reported in our previous paper.⁸

ANALYSIS

Sl. No. 1 : [Pd(Pf₃)₂(P-CH₃-L)₂]Cl₂ (Yellow) :

Calculated (%) for C₅₂H₄₆N₈P₂S₂Cl₂Pd : C, 57.51; H, 4.23; N, 10.32; Pd, 9.76;

Found (%) : C, 57.46; H, 4.33; N, 10.52; Pd, 10.02;

Sl. No. 2 : [Pd(Pf₃)(H₂O)(P-CH₃-L)₂](NO₃)₂ (Yellow) :

Calculated (%) for C₃₄H₃₃N₁₀O₇S₂P.Pd : C, 45.63; H, 3.69; N, 15.65; Pd, 11.85; Found (%) : C, 45.83; H, 3.70; N, 15.50; Pd, 12.01;

Sl. No. 3 : [Pd(Pf₃)₂(P-Cl-L)₂]Cl₂ (Yellow) :

Calculated (%) for C₅₀H₄₀N₈P₂S₂Cl₄Pd : C, 53.28; H, 3.55; N, 9.94; Pd, 9.41;

Found (%) : C, 53.25; H, 3,56; N, 10.10; Pd, 9.45;

Sl. No. 4 : [Pd(Pf₃)₂(O-Cl-L)₂](NO₃)₂ (Yellow) 

Calculated (%) for C₅₀H₄₀N₁₀O₆P₂S₂Pd : C, 50.89; H, 3.39; N, 11.87; Pd, 8.99;

Found (%) : C, 50.91; H, 3.41; N, 11.88; Pd, 8.88;

Sl. No. 5 : [Pd(Pf₃)(H₂O)(P-Cl-L)₂](NO₃)₂ (Yellow) :

Calculated (%) for C₃₂H₂₇N₁₀O₇S₂Cl₂P.Pd : C, 41.06; H, 2.88; N, 14.97; Pd, 11.33; Found (%) : C, 41.26; H, 2.98; N, 14.63; Pd, 11.35;

Sl. No. 6 : [Pd(Pf₃)₂(P-Cl-L)₂]Cl₂ (Yellow) :

Calculated (%) for C₅₀H₄₀N₈P₂S₂Cl₄Pd : C, 53.28; H, 3.55; N, 9.94; Pd, 9.41;

Found (%) : C, 53.33; H, 3.58; N, 10.20; Pd, 9.48;

Sl. No. 7 : [Pd(Pf₃)₂(M-CH₃-L)₂]Cl₂ (Yellow) :

Calculated (%) for C₅₂H₄₆N₈P₂S₂Cl₂Pd : C, 57.51; H, 4.23; N, 10.32; Pd, 9.76;

Found (%) : C, 57.66; H, 4.42; N, 10.35; Pd, 10.02;

Sl. No. 8 : [Pd(Pf₃)₂(O-CH₃-L)₂]Cl₂ (Yellow) :

Calculated (%) for C₅₂H₄₆N₈P₂S₂Cl₂Pd : C, 57.52; H, 4.23; N, 10.32; Pd, 9.76;

Found (%) : C, 57.62; H, 4.40; N, 10.52; Pd, 10.02;

Sl. No. 9 : [Pd(Pf₃)(H₂O)(O-Cl-L)₂](NO₃)₂ (Yellow) :

Calculated (%) for C₃₂H₂₇N₁₀O₇S₂Cl₂PPd : C, 41.06; H, 2.88; N, 14.97; Pd, 11.33; Found (%) : C, 41.22; H, 2.80; N, 14.96; Pd, 11.50;

Results And  Discussion

The analytical data of complexes are consistent with proposed stiochiometries. The molar conductance of complexes was measured in DMF (10^-3 M) which indicate them uni-bivalent electrolyte and value was found between 170-181.5 Ù^-1cm²mol^-1. This indicates the presence of ionic chloride and ionic nitrate in complexes. The chemical analysis of sodium extract solution of complexes and infrared spectra further confirmed the presence of anions in the outer sphere of all complexes.

The d – d transition bands in the electronic spectra of complexes at 26980 – 27770 cm^-1 (¹A_1g ® ¹E_g), 22600 – 23820 cm^-1 (¹A_1g ® ¹B_1g) and at 21670 – 21690 (¹A_1g ® ¹A_2g) are in agreement with the transition suggested for four coordinated Palladium (II) complexes having square planar structure^9-10. The diamagnetic behavior of complexes also supports the square planar structure of complexes. The other bands in ultra-violet region are assigned to intra-ligand charge transfer.

Ir Spectra

Considering thioamide function of ligands and complexes (table 1) and nature of shift of thioamide bands indicates thioamide-sulphur coordination^11-13. Thioamide band IV with high n_CS character red shift to lower frequency on complexation^13-15. Further evidence in support of the coordination of thione sulphur of thioamide moiety is provided by presence of new Pd – S stretching vibration in the low-frequency IR spectra. The single n_{Pd – S} bands at 320 – 325 cm^-1 confirms two thioamide ligands at their trans disposition in square planar geometry^16-17. The presence single Pd – P stretching mode also supports two Pf₃ ligands are at Trans in square planar structure.

The presence of ionic nature of nitrate anion in complexes (Sl. No. 2, 4, 5 & 9) is indicated by non-ligand bands at 1360 cm^-1 and 795 cm^-1 and presence of coordinated water molecule in complexes (Sl. No. 2, 5 & 9) at 3440 cm-1 (nH₂O), 1605 cm-1 (dH₂O), 790 cm^-1 (pH₂O) and 480 cm^-1 (n_Pd-O).  These assignments are consistent with our previous report¹⁰.

¹h Nmr Spectra

The ¹H NMR spectra of ligands and complexes were recorded in CDCl₃/TMS to substantiate further mode of metal-ligand bonding. All the complexes showed broad signals in the range d8.22 – 8.85 PPM range due to aromatic protons of Pf₃ molecule¹⁸. The broad multiplet in the region 7.30 – 7.84 PPM due to phenyl protons of both ligands and complexes. The broad nature of peak may be due to the presence of four nitrogen atoms which display large quadrupole resonance broadening effect¹⁹.  The methyl protons and imino protons of ligands are observed almost at the same positions at d2.40 – 2.94 PPM and d1.25 – 1.42 PPM respectively. This indicates that imino proton is intact and deprotonation has not occurred on complexation and coordination occurs only through thione sulphur. This is consistent with IR spectral results.

Antifungal Activity

All Palladium (II) complexes were screened for their antifungal activity against Aspergllus flavus, a common fungicide using cup-plate method reported in literature²⁰. The solvent used was DMSO. The inhibition zone formed around each filter paper at room temperature for about 96 hrs. inhibition²¹ was measured. The standard fungicide carbendazim was used for comparison. The results are shown in table 2.

The antifungal activity of complexes increases with increase in concentration.  The complex [Pd(Pf₃)₂(P-Cl-L)₂](NO₃)₂ proved to be the most active antifungal agent in the study. A close examination of the structures of the active compounds reveal that antifungal activity was more confined to ligands substituted at para-position of 1-phenyl-tetrazoline-5-thione rather than other substitution position, ortho and meta. The structure activity correlation of these complexes showed that para substituted phenyl ring with either electron donating or electron withdrawing functions exhibit maximum activity and in general the presence of nitrate group increased the magnitude of the activity.

Table 1: Major IR and ¹H NMR Spectral data of ligands and Palladium (II) complexes.

Compounds	IR (cm-1) Thioamide Bands						1H NMR (PPM)
	Band I	Band II	Band III	Band IV	nPd-S/ (nPd-P)	nPd-O	Imino proton	Methyl proton	Phenyl proton
O-CH3-L (ligand)	1500 (m)	1290 (m)	1025 (m)	810 (m)	¾ (-)	¾	1.25	2.40	7.30 – 7.85
Complex (Sl. No. 8)	1510 (m)	1285 (m)	1005 (m)	780 (m)	320 w (430 m)	480 (m)	1.23 1.52	2.94	7.45
M-CH3-L (ligand)	1500 (s)	1280 (ms)	1060 (m)	790 (m)	¾ (-)	¾	1.20	2.26	7.50
Complex (Sl. No. 7)	1515 (m)	1270 (s)	1035	780 (m)	310 w (425 m)	485 (m)	1.21 2.53	2.94	7.46
P-CH3-L (ligand)	1500 (ms)	1280 (s)	1044 (m)	810 (m)	¾ (-)	¾	1.25	2.40	7.31 – 7.82
Complex (Sl. No. 9)	1510 (m)	1290 (m)	1030 (m)	750 (m)	325 w (430 m)	480 (m)	1.42 1.72	2.85	7.65
Complex (Sl. No. 2)	1515 (m)	1295 (m)	1020 (m)	765 (m)	330 w (435 m)	485 (m)	1.50 2.20	2.88	7.65
P-Cl-L (ligand)	1498 (m)	1280 (s)	1055 (m)	780 (m)	¾ (-)	¾	1.28	¾	7.40 – 8.30
Complex (Sl. No. 3)	1500 (m)	1295 (m)	1030 (m)	750 (m)	335 w (430 m)	480 (m)	1.45	¾	7.28 – 7.85
Complex (Sl. No. 4)	1510 (m)	1280 (s)	1020 (m)	755 (m)	330 w (435 m)	482 (m)	1.42	¾	7.45 – 7.82
Complex (Sl. No. 5)	1515 (m)	1285 (m)	1025 (m)	760 (m)	335 w (440 m)	480 (m)	1.45	¾	7.45 – 7.84
O-Cl-L (ligand)	1500 (m)	1290 (m)	1025 (m)	810 (m)	¾ (-)	¾	1.25	¾	7.50 – 9.68
Complex (Sl. No. 6)	1510 (m)	1295 (m)	1015 (m)	780 (m)	332 w (425 m)	485 (m)	1.22 2.53	¾	7.52 – 8.95

Table 2: Fungicidal activity and electronic spectral data of complexes. 

Complex	AV % inhibition  A. Flavus (PPM)			Electronic Spectral Bands (d – d Transition) (cm-1)
	1000	100	10
[Pd(Pf3)2(P-CH3-L)2]Cl2	47.4	26.3	20.5	22600 (1A1g ® 1B1g) 27770 (1A1g ® 1Eg) 30030 (1A1g ® 1A2g)
[Pd(Pf3)(P-CH3-L)2](NO3)2	60.0	50.7	43.2	19450 (1A1g ® 1B1g) 27770 (1A1g ® 1Eg) 37740 (CT Band)
[Pd(Pf3)2(P-Cl-L)2]Cl2	80.8	70.5	65.6	27700 (1A1g ® 1Eg) 23820 (1A1g ® 1B1g) 21770 (1A1g ® 1A2g)
[Pd(Pf3)2(P-Cl-L)2](NO3)2	89.3	76.6	65.3	27780 (1A1g ® 1Eg) 23850 (1A1g ® 1B1g) 21670 (1A1g ® 1A2g)
[Pd(Pf3)2(O-Cl-L)2]Cl2	55.9	39.2	20.5	27760 (1A1g ® 1Eg) 23890 (1A1g ® 1Eg) 21770 (1A1g ® 1A2g)
[Pd(Pf3)2(O-CH3-L)2]Cl2	35.6	28.5	19.5	27680 (1A1g ® 1Eg) 23810 (1A1g ® 1B1g) 21690 (1A1g ® 1A2g)
[Pd(Pf3)2(m-CH3-L)2]Cl2	37.2	28.2	20.5	26980 (1A1g ® 1Eg) 23690 (1A1g ® 1B1g) 21660 (1A1g ® 1A2g)
[Pd(Pf3)(H2O)(P-Cl-L)2]Cl2	88.2	73.6	55.6	18450 (1A1g ® 1B1g) 27725 (1A1g ® 1Eg) 37690 (CT Band)
Carbendazim (stand)	98.7	88.2	80.5	———-

References

1. West D.X., Liberta A.E., Padhye S.B., Chikate R.C., Sonawane P,B., Kumbhar A.S. and Yerande R.G.. Coord. Chem. Rev. 123, 49 (1993).
2. Quiroga A.G., Perez J.M., Montero E.I., Masaguer J.R., Alonso C., Navarro-Ranninger C., J. Inorg. Biochem., 70, 117 (1998).
3. Quiroga A.G., Perez J.M., Lopez-Solera I., Montero E.I., Masaguer J.R., Alonso C and Navarro-Ranninger C., J. Inorg. Biochem. 69, 275 (1998).
4. Campo R., Criado J.J., Garcia E., Hermose M.R., Montc E. and Sanz F., J. Inorg. Biochem. 89, 74 (2002).
5. Cowper A.J., Astik R.R. and Thaker K.A., J. Indian Chem. Soc. 58, 1087 (1981).
6. Lieber E. and Chandran J.R., Can J. Chem. 37, 101 (1959).
7. Pandey R.N. and Kumar Sheo Shankar, J. Ultra Chem. Vol 7(2), 271 (2011).
8. Pandey R.N., Kumari Gunjan, Nag A.K. and Renu Bala, Rasayan J. Chem. Vol 2(4), 886 (2009).
9. Mehta B.H., Pawanoji A.A. and Shaikh J.A., J. Indian Chem. Soc. 87, 779 (2010).
10. Pandey R.N. and Kumar Sheo Shankar, J. Ultra Chem. Vol 8(3), 355 (2012).
11. Beukeleer S.De and Desseyn H.O., Spectrochim. Acta A51, 1617 (1995).
12. Hereygers M.L.B.F., Desseyn H.O., Verhulst K.A.F., Lenstra A.T.H. and Perlepes S.P., Polyhedron, 15, 3437 (1966).
13. Singh B, Singh R, Choudhary R.V. and Thakur K.P., Indian J. Chem. 11, 174 (1973)
14. Desseyn H.O., Van der Veken B.J. and Herman M.A., Appl. Spectrosc. 32, 101 (1978).
15. Rao C.N.R., Venkataraghavan R. and Kasturi T,R., Can. J. Chem. 42, 36 (1964).
16. Jacobs P., Dimitrou K., Perlepes S.P., Plakatouras J. and Desseyn H.O., Bull. Soc. Chim. Belg. 98, 901 (1989).
17. Kovala-Demertzi D., Perlepes S.P. and Lazaras G., Bull. Soc. Chim. Belg. 98, 503 (1989).
18. Kanchana Devi S., Balasubramanian K.P., Chinusamy V., Karvembu R. and Nataranjan K., Trans. Met. Chem. 30, 330 (2005).
19. Pandey R.N., Singh R.K. and Sinha R.J., Acta Gencia Indica, Vol. 35(C), 505 (2009).
20. Hanna W.G. and Manwad M.M., Trans. Met. Chem. 26, 644 (2001).
21. Hesse B. and Hiopka, Pesticides, 8, 37 (1974).

---

This work is licensed under a Creative Commons Attribution 4.0 International License.