Copper perchlorate catalyzed oxidative cyclisation of a novel bishydrazone ligand, formation of an unusual copper complex and in vitro biological implications

A novel hexadentate bishydrazone ligand, 1,10-bis(di(2-pyridyl)ketone) adipic acid dihydrazone (H2L1) is synthesized and characterized. With copper perchlorate as a catalytic oxidant, the ligand undergoes oxidative cyclisation and resulted in the formation of an unusual copper complex [Cu(L1a)2Cl]ClO4 (1), where L1a is 3-(2-pyridyl)triazolo[1,5-a]-pyridine. The Cu(II) complex was characterized physicochemically, while the molecular structure was confirmed by single crystal X- ray diffraction. In the complex cation, copper(II) is in a distorted trigonal bipyramidal coordination environment, surrounded by two triazolo nitrogen atoms and two pyridyl nitrogen atoms of L1a and a chloride atom. The relevant non covalent intermolecular interactions of the complex quantified using Hirshfeld surface analysis reveals that the O···H/ H···O (27.2%) contacts has the highest contribution. The solution phase bandgaps of the compounds were calculated using Tauc plot, whereas the solid-state band gaps were calculated by Kubelka-Munk model. DFT studies of the compounds indicate that the theoretical calculations corroborate with the experimental data. DPPH antioxidant activity assay of the synthesized compounds showed that the proligand H2L1 has a lower IC50 value (24.1 μM) than that of complex 1 (29.7 μM). The in vitro antibacterial activity was evaluated against Escherichia coli and Staphylococcus aureus, which revealed that complex 1 have excellent activity against E. coli, much as the standard ciprofloxacin. The cytotoxic efficacy investigation of the compounds against A549 (lung) adenocarcinoma cells suggested that H2L1 has more anticancer activity (IC50 value of 149.08 μM) than that of complex 1(IC50 value of 176.70 μM).

Dinuclear lanthanide(III) complexes by metal-ion-assisted hydration of di-2-pyridyl ketone azine

The initial employment of di-2-pyridyl ketone azine in 4f metal chemistry has led to a unique ligand transformation; the resulting anionic ligand is able to bridge two Ln(III) ions, affording neutral and cationic dinuclear complexes with interesting properties.

Synthesis and Coordination Chemistry of Doubly-Tridentate Tripodal Pyridazine and Pyrimidine-Derived Ligands: Structural Interplay Between M2L and M2L2 (M = Ni and Pd) Complexes and Magnetic Properties of Iron(II) Complexes

The coordination chemistry of three bridging doubly-tridentate ligands, including the known compound 3,6-bis(di-2-pyridylmethyl)pyridazine (1), which is structurally similar to 1,4-bis(di-2-pyridylmethyl)phthalazine (2), and two pyrimidine-linked compounds 4,6-bis(di-2-pyridylmethyl)pyrimidine (3), and 4,6-bis(di-2-pyridylamino)pyrimidine (4), was investigated with FeII, NiII, and PdII metal salts. Ligands 3 and 4 were synthesized in one-pot reactions from easily obtained starting materials; compound 3 was synthesized from di-2-pyridylmethane and 4,6-diiodopyrimidine in 48% yield, while ligand 4 was prepared by reacting di-2-pyridylamine with 4,6-dichloropyrimidine in 27% yield. During the synthesis of 4, an additional compound, 4-chloro-6-(di-2-pyridylamino)pyrimidine (5), with only one tridentate binding site was obtained in 30% yield. Reactions of 1, 3, and 4 with FeII or NiII salts gave two types of complexes, either discrete M2L or M2L2 assemblies. The PdII complexes obtained were also characterized as discrete M2L complexes. The compounds were characterized by a combination of NMR and IR spectroscopy, microanalysis and X-ray crystallography. Noticeable differences in the structures obtained for NiII coordination complexes with the carbon-linked (3) and nitrogen-linked (4) ligands were observed, whereby the nitrogen linker adopted a trigonal planar geometry and prevented tridentate facial coordination of the octahedral metal centres. The magnetic properties of dinuclear FeII complexes of 1 were examined to see if they showed spin-crossover effects, a feature recently observed by others in other dinuclear helicate complexes, but the complexes remained high-spin at all temperatures between 300 and 2 K.

Metal complexes formed by metal-assisted solvolysis of di-pyridylketone azine: structures and magnetic properties

A series of metal complexes were achieved from the metal-assisted solvolysis reaction of di-pyridylketone azine (dpka). The tetranuclear nickel cluster , [Ni(2)[dpk(O)(OH)][dpk(O)(OCH(3))](N(3))(2)](2), is centrosymmetric with a central core described as an edge-shared triangle core. Neighboring Ni(II) ions are alternately bridged by (micro(2)-N(3), micro(3)-O) and (micro(2)-O, micro(3)-O) double bridges. Complex , [Cu(4)[dpk(O)(OCH(3))](4)(N(3))(2)](CuCl(2))(2) contains a tetranuclear cluster and two identical [CuCl(2)]M(-) anions. The tetranuclear structure has two crystallographically imposed twofold axes, in which the four copper ions are arranged to be rhombic shape. The neighboring copper(ii) ions along the lateral are bridged by single micro(2)-O from the ligand dpk(O)(OCH(3)) and the short diagonal copper ions are bridged by two symmetric end-on azides. In dinuclear Cu(ii) complex [Cu(2)[dpka(OCH(2)CH(3))]Cl(2)](ClO(4)) (3), the metal centers are coordinated in a planar configuration and bridged by a -N-N- bridge. It is also observed that the Cl atom coordinated to one Cu(II) center is also weakly coordinated to another inversion related Cu(II) to generate a centrosymmetric dimer. The metal centers in one-dimensional polymeric Cu(ii) complex [Cu(2)[dpka(OCH(3))](N(3))(2)(ClO(4))](n) (4), however, are bridged by a -N-N- bridge and an end-to-end azide bridge, alternately. Magnetic susceptibility measurements indicate that shows ferromagnetic interaction within the tetranuclear cluster, and that displays moderately strong antiferromagnetic interaction (J = -56.7 cm(-1)) for the bis(micro-N(3)) bridge. For compound , it shows strong antiferromagnetic coupling (J = -286 cm(-1)) between the intradinuclear Cu(II) ions mediated by the single N-N bridge and negligible magnetic interactions between the adjacent dinuclear Cu(II) ions mediated by the single end-to-end azide bridge. The mechanism of the metal-assisted solvolysis reaction was also discussed.

Tuning the Formation of Cadmium(II) Urocanate Frameworks by Control of Reaction Conditions: Crystal Structure, Properties, and Theoretical Investigation

The reaction of cadmium(II) perchlorate with urocanic acid under different conditions created three novel coordination compounds: [Cd2(L2)2-(L3)2(H2O)8] (1), {[Cd(L)(L2)](H2O)(1/2)}n (2), and {[Cd(L3)2](H2O)(3/2)(EtOH)}n (3), in which L, L2, and L3 are three urocanate tautomers. Complex 1 consists of two separate mononuclear units with different urocanate tautomers, which self-assemble into a 3D hydrogen-bonding network constructed by alternating 2D layers, whereas complexes 2 and 3 self-assemble into 3D alpha-polonium and four-fold interpenetrated diamondoid networks, respectively. The tautomerism of the urocanate ligands and the enormous structural diversity of their complexes are present in this system, which illustrates that the reaction temperature, pressure, and the metal ions themselves act cooperatively to tune the tautomerism of the ligands and the frameworks of their metal coordination compounds. The fluorescence-emission and nitrogen-adsorption properties of these complexes are also investigated.