Synthesis, Characterization and Biological Evaluation of Mixed Ligand Complexes of Pt(IV), Pt(II) and Pd(II) Ions Containing Dibasic Acids and Heterocyclic Amines

Abstract

Mixed ligand complexes of dibasic acid and heterocyclic amine with transition metal ions have been synthesized and characterized. Research was devoted to the synthesis and characterization of mixed ligand complexes of Pt(II), Pt(IV) and Pd(II) ions with some dibasic acid (viz., malonic acid, oxalic acid and phthalic acid) as primary and heterocyclic bases, (viz., quinoline (Q), iso-quinoline (IQ), pyridine (Py), 2-aminopyridine (2apy) and 4-picoline (4-pico) as secondary ligands. The general formula of the complexes are as follows; [MLL1] (where M = Pt(IV) (1-8), Pt(II) (13), Pd(II) (9-12,14-17); L=2C3H2O4, malonato (1-4), 2C2O4, oxalato (5-8), C8H4O4, phthalato (9-13), oxalato C2O4(14-17); and L1 =2C9H7N, quinoline (1, 5, 9, 14), 2C9H7N, iso-quinoline (2, 6, 10,15), 2C5H5N, pyridine (3, 7, 11, 16) , 2C6H7N, 4-picoline (4, 8, 13), C5H6N2, 2-aminopyridine (12, 17)). Complexes were characterized by elemental analysis, conductivity, magnetic measurement, infrared and electronic spectroscopic studies. All the complexes were isolated in the ethanolic solution as amorphous solid. All the synthesized complexes are colored. The complexes, all were slightly soluble in water and methanol but are readily soluble in DMF and DMSO. Single crystal of the complexes could not be isolated from any solution. The conductance values of the complexes were in the range (10.35-12.85) Ω-1 cm2 mol-1 indicated that these complexes were non-electrolyte in nature. Melting points of the complexes were in the range 240 to 270(± 5°C) while those of the ligands were -15 to 211 (± 5°C) which indicate the strong indication of coordination of the ligands and formation of the complexes. The ν(OCO)asym mode of Pt(IV), Pt(II) and Pd(II) complexes of oxalato, malonato & phthalato is found as a very strong-to-strong band at 1575.7-1708.9 cm-1, and the corresponding ν(OCO)sym one is exhibited at 1363.6-1410.9 cm-1 Two ν(OCO) stretching symmetrical and asymmetrical lie lower than the free ion values and the frequency difference between these two modes is 198-317 cm-1. From the frequency difference it is evident that the carboxylate group acts as a monodentate ligand. Further, the presence of MO (O = Oxygen in deprotonated dibasic acid) bonding is evident from the appearance of vM-O modes at 500.0-557.4 cm-1 in the spectra of the complexes. The presence of M-N bonding in the complexes is evident from the appearance of VM-N modes at 421.4-476.4 cm-1. Shifting of infrared spectra of aminopyridine to ~3320.2-3345.3 cm-1 and 3056.0-3061.8 cm-1 in the mixed ligand complexes is indicated the coordination through amino nitrogen to the metal ions. By comparing the data of elemental analysis, magnetic moment, spectroscopic analysis the proposed empirical formula of the synthesized complexes can be following: [Pt(MA)2(Q)2](1), [11t(MA)2(IQ)2](2). [Pt(MA)2(Py)210)), [Pt(N4A)(4-pico)2](4), [Pt(OX)2(Q)21(5), [Pt(OX)2(IQ)2](6), [1't(OX)2(Py)21(7), [Pt(OX)2(4-pico)2](8), [Pd(Ph)(Q)2](9), [Pd(Ph)(1Q)]( 10), [Pd(Ph)(Py)21( 11), [Pd(I'h)(2-apy)J( 12), [Pt(Ph)(4-pico)21( 13), [Pd(OX)(Q)2J( 14), [Pd(OX)( IQ)21( 15), [Pd(OX)(Py)21( 16) and [Pd(OX)(2-apy)](17) where, MA = Deprotonated malonic acid, OX = Deprotonated oxalic acid, Ph = Deprotonated phthalic acid, Q = quinoline, IQ = iso-quinoline, Py = pyridine, 4-pico = 4-picoline, 2-apy = 2-aminopyridine. The magnetic moment values of the complexes indicated that these complexes are diamagnetic. This diamagnetism is supported by the small negative values obtained for their magnetic susceptibility. The electronic spectra of the Pt(IV) complex gave three bands at 36,000, 39,650 and 41,000 cm-1 corresponding to the transitions 1Aig → 1Tig1g, 1Aig1g → 3T1g and 1A1g → 1T2g. In addition to the d-d transitions, the Pt (IV) complexes obtained two charge transfer bands at 39000 and 50000 cm-1 The electronic spectra of the Pd (II) complex showed three spin allowed d-d transitions and two charge transfer bands. The bands were obtained at 22203-23055, 28155-28500, 3 1000-31350, 34500-35005 and 40000-40205 cm-1 corresponding to the transitions 1A1g → 1A2g, 1A1g → 1B1g, 1A1g → 1Eg, 1A1g → 1A2u and 1A1g → 1Eu respectively. The Pt(II) complex gave three bands at 36000, 39650 and 41000 cm-1 corresponding to the transitions 1A1g → 1B1u, 1A1g → 1Eu, and 1A1g → 1A2u respectively. Electronic spectra and magnetic measurement confirmed that Pt (IV) (1-8) complexes are octahedral structure and Pt (II) (13) & Pd (II) (9-12, 14-17) complexes are square planar structure. From the antibacterial screening it is seen that all complexes have antibacterial activity against Gram-positive (Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis) and Gram-negative (Pseudornonas aeruginosa, Salmonella bovismorbificans, Salmonella typhi, Escherichia coli) bacteria through disc diffusion method. Complexes [Pt(MA)2(4-pico)2} showed the highest antibacterial activity against all bacteria tested. The complexes 1, 6 and 11 showed the lowest inhibition zones against Staphylococcus aureus, Listeria monocytogenes & Enterococcusfaecalis corresponding to zone sizes of 8, 11 and 10 mm respectively. The complexes 2, 7 & ii exhibited no zone inhibition against Staphylococcus aureus, Salmonella typhi and Salmonella bovismorbificans. All the synthesized complexes have shown mild to moderate antibacterial activity. The highest and the lowest activities were found in complex 4 and complex 11 respectively.