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This paper reports a simple approach for the synthesis of three pairs of novel mononuclear β -diketonate complexes of copper(II), zinc(II) and palladium(II) from monobasic O^O donor ligands 3-phenyl-4-fluorobenzolyl-5-isoxazolone (HL 1 ) and 3-phenyl-4-toluyl-5-isxoazolone (HL 2 ). The synthesized compounds are characterized by FT-IR, ESI/FAB mass, 1 H NMR, UV–visible and thermogravimetric analyses. The free ligand HL 1 and the copper(II) complex, [Cu(L 2 ) 2 (CH 3 OH) 2 ] are unambiguously characterized by single crystal X-ray diffraction studies. The free ligand HL 1 has adopted orthorhombic crystal system with P 2(1) space group and the unit cell parameters are a = 8.1552(3), b = 10.1169(4), c = 17.0819(6) A, and α = β = γ = 90°. The crystal structure of the complex, [Cu(L 2 ) 2 (CH 3 OH) 2 ] is monoclinic with P 2(1)/ c space group and the unit cell parameters are a = 10.2571(2), b = 16.2640(3), c = 20.1717(3) A, and α = 90, β = 99.56 and γ = 90°. The copper(II) complex has adopted distorted octahedral geometry where the z -axis is occupied by two solvent methanol molecules according to the crystal data. While the EPR spectra of both the Cu(II) complexes display a strong axial signal with g || ≈ 2.2 and g ⊥ ≈ 2.0, which obviously suggests the square planar geometry around the copper(II) ion. The interaction of the complexes with calf thymus DNA (CT-DNA) was investigated using UV–visible and fluorescence spectroscopic techniques. Anticancer activity of the complexes revealed their potential towards inhibiting the growth of human breast cancer cell lines, MDA-MB-231. The palladium complexes of both the ligands are found to be good in exhibiting apoptosis. Moreover, the complexes of fluoro-substituted ligand are better antimicrobial agents when compared with those of methyl substituted ligand.

Three pincer type palladium(II) complexes (1–3) were synthesised from the reactions of PdCl2 with thiosemicarbazone ligands (L1–L3), and characterized by elemental analyses and UV Visible, FT-IR, 1H & 13C NMR spectroscopic techniques. The molecular structure of 2 was confirmed by single crystal X-ray crystallography. The X-ray diffraction study of complex 2 revealed the pincer type tridentate SNO coordination of N-substituted isatin thiosemicarnbazone with the palladium ion. The binding affinity and mode of the palladium(II) complexes (1–3) toward calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) were determined by UV–Visible and fluorescence spectrophotometric methods. Spectral evidences showed intercalative mode of DNA binding with the palladium(II) complexes. The magnitude of hypochromism is in the order of 3 > 2 > 1, which reflects the DNA binding efficacy of the complexes. The binding mode was further confirmed by CD spectra which indicate the non-groove mode of binding; hence the intercalative mode of binding is proposed. The alterations in the secondary structure of the protein by the complexes were confirmed by synchronous fluorescence spectroscopic studies. Spectral evidences also showed good binding property of the complexes with the protein. Complexes (1–3) cleaved the pUC19 plasmid DNA in the absence of an external agent. The complexes were found to possess significant in vitro cytotoxicity against human breast (MCF7) and lung (A549) cancer cell lines.

N-ethyl-2-(phenyl(pyridin-2-yl)methylene)hydrazinecarbothioamide (HBpyeTsc) was obtained from 4-ethyl-3-thiosemicarbazide and 2-benzoylpyridine. The complexes (CuBpyeTscCl) and Ni[BpyeTsc]2Cl2 were synthesized from HBpyeTsc and [CuCl2·2H2O]/[NiCl2·6H2O]. The synthesized ligand and complexes were characterized by analytical and various spectroscopic techniques. The molecular structure of the ligand and complexes was determined by single crystal X-ray diffraction method. The single crystal X-ray diffraction revealed that CuBpyeTscCl and Ni[BpyeTsc]2Cl2 exhibited square planar and distorted octahedral geometry respectively. All of the synthesized compounds HBpyeTsc, CuBpyeTscCl and Ni[BpyeTsc]2Cl2 were studied for their interaction with calf thymus DNA (CT DNA) and bovine serum albumin (BSA). A DNA cleavage study showed that the complexes cleaved DNA without any external agent. The alterations in the secondary structure of the protein by the ligand and complexes were confirmed by synchronous fluorescence spectroscopic studies. Spectral evidences also showed good binding property of the complexes with the protein. An in vitro cytotoxicity study of the complexes found significant activity against lung cancer cell lines (A549) and less toxicity toward the normal cell lines (L929). The best results for the copper(II) and nickel(II) complexes are the IC50 values of 56.07 and 80.10 μM respectively.

Six square planar Ni(II) complexes of 3,3-dialkyl/aryl-1-benzoylthiourea derivatives have been synthesized and characterized by elemental analyses, and electronic, FT-IR and NMR spectroscopic techniques. A cis-O2S2 disposition in complexes 3, 4 and 5 was confirmed by single crystal X-ray crystallography. The cytotoxicity of the 3,3-dialkyl/aryl-1-benzoylthiourea molecules and their complexes was measured against human ductal breast carcinoma cell line (T47D). Cytotoxicity increased after the complexation of the ligands to nickel(II). In particular, the study showed that complexes 3 and 4 are the most cytotoxic against T47D cell lines while they did not affect the normal human dermal fibroblast cell line (HDF).

Square planar palladium(II) complexes of the type [Pd(L)(PPh3)] (1–6) (where L is the dianion of N-(2-mercaptophenyl)salicylideneimine or 5-substituted-N-(2-mercaptophenyl)salicylideneimine or N-(2-mercaptophenyl)naphthylideneimine) have been synthesised from the reactions between [Pd(PPh3)4] and H2L in dichloromethane–ethanol mixture. The new complexes have been characterized by analytical and spectral (electronic, IR, 1H, 13C{1H} and 31P{1H} NMR spectroscopy) techniques. The structures of three complexes (1, 2 and 6) have been solved by single-crystal X-ray diffraction experiments which indicate square planar coordination geometries around palladium(II) by O, N, S and P donor atoms. The palladium(II) complexes (1–6) exhibited good catalytic activity in Suzuki–Miyaura cross-coupling reaction between phenylboronic acid and 4-bromotoluene in N,N-dimethylacetamide at 100 °C. Complex 3 (1 mol%) was found to be the most active and hence was used for probing the scope of possible substrates. Heterocyclic boronic acid and heterocyclic aryl bromides have also been used as substrates to provide heterocyclic biaryls.

The synthesis and characterization of Pd(II) complexes with the general formula cis-[Pd(L-O,S)2] (HL = N,N-diethyl-N′-benzoylthiourea, N,N-diisobutyl-N′-benzoylthiourea or N,N-dibenzyl-N′-benzoylthiourea) and trans-[PdCl2(HL-S)2] (HL = N,N-diphenyl-N′-benzoylthiourea, N,N-di-n-butyl-N′-benzoylthiourea or N,N-diisopropyl-N′-benzoylthiourea) are reported. These complexes were formed from the reaction between PdCl2 and N,N-di(alky/aryl)-N′-benzoylthiourea in acetonitrile with the formulation dependent on the nature of HL. The new Pd(II) complexes have been characterized by analytical and spectral (FT-IR, UV–Vis, 1H NMR and 13C NMR, Mass) techniques. The molecular structures of two of the complexes (1 and 5) have been conformed by X-ray crystallography. Complex 1 shows cytotoxicity against human breast cancer cells.

New Ni(II) thiosemicarbazone complexes containing triphenylphosphine namely [Ni(Sal-mtsc)(PPh3)](2) and [Ni(Nap-mtsc)(PPh3)] (3) (where Sal-mtsc = salicylaldehyde-N(4)-methylthiosemicarbazone and Nap-mtsc = 2-hydroxy-1-naphthaldehyde-N(4)-methylthiosemicarbazone) have been synthesised and characterized by elemental analysis, IR, electronic and 1H NMR spectroscopy. The crystal structures of the complexes have been determined by single crystal X-ray diffraction technique. In all the complexes the thiosemicarbazone ligand coordinated to nickel through ONS mode. The electrochemical behavior of the complexes has been investigated by using cyclic voltammetry in acetonitrile. The new complexes were subjected to test their DNA topoisomerase II inhibition efficiency. The complex [Ni(Nap-mtsc)(PPh3)] (3) showed 95% inhibition. The observed inhibition activity was found to be more potent than the activity of conventional standard Nalidixic acid.

The coordination behaviour of ferrocenylthiosemicarbazone was investigated in a trinuclear [Ni(Fctsc)2] complex. The structure of the complex has been studied by X-ray crystallography. The complex crystallizes in rhombohedral space group R 3 ¯ c with six molecules per unit cell has the dimensions of a = 28.8042(2) A, b = 28.8042(2) A and c = 19.5131(3) A, α = 90°, β = 90°, γ = 120°. The electronic communication between the metal centers has been studied by cyclic voltammetry.

New thiosemicarbazone nickel(II) complex, derived from salicylaldehyde-N-phenylthiosemicarbazone, was synthesized and characterized by means of IR, electronic, and mass spectral techniques. Its two different types of crystal structures were also characterized by single crystal X-ray diffraction technique and reported here. In type A, the complex crystallizes in the monoclinic space group P21/c with four molecules per cell and has the dimensions of a = 9.2066(7), b = 19.1090(13), c = 18.589(2) A, β = 92.87 (1)°. In type B, the complex crystallizes in the triclinic space group P 1 ¯ with two molecules per cell and has the dimensions of a = 10.406(4), b = 10.876(4), c = 14.614(5) A, α = 64.81(1), β = 74.07(2), γ = 70.85(2)°.