The Schiff base ligands benzylidene­(4-tert-butylphenyl)­amine 4-methyl ester (L1), (4-nitrobenzylidene)­(4-tert-butylphenyl)­amine (L2), and (4-cyanobenzylidene)­(4-tert-butylphenyl)­amine (L3) and the new series of cyclometalated mononuclear piano-stool complexes [(η5-C5Me5)­RhCl­(L1)] (1), [(η5-C5Me5)­RhCl­(L2)] (2), [(η5-C5Me5)­RhCl­(L3)] (3), [(η5-C5Me5)­IrCl­(L1)] (4), [(η5-C5Me5)­IrCl­(L2)] (5), and [(η5-C5Me5)­IrCl­(L3)] (6) have been synthesized. The ligands L1–L3 and complexes 1–6 have been thoroughly characterized by satisfactory elemental analyses, spectral studies (ESI-MS, IR, 1H and 13C NMR, UV–vis), and structures of 1–3 authenticated by X-ray single-crystal analyses. Efficient binding of 1–6 with calf thymus DNA (CT DNA) have been established by UV–vis and emission spectroscopic studies. Protein binding (bovine serum albumin, BSA) has been investigated by UV–vis, fluorescence, synchronous, and 3D fluorescence spectroscopy. Binding of the complexes with DNA through minor groove and hydrophobic interaction with proteins via sub domain IIA cavity has been substantiated by molecular docking studies. The complexes exhibited significant cytotoxicity against the human lung cancer cell line (A549), and 1 and 2 showed better activity than cisplatin. The cytotoxicity, morphological changes, and apoptosis have been assessed by MTT assay, Hoechst 33342/PI staining, cell cycle analysis by fluorescence-activated cell sorting (FACS), and reactive oxygen species (ROS) generation by DCFH-DA dye. The complexes 1–6 induce apoptosis in the order 2 > 1 > 4 > 3 > 5 > 6.

Three new lanthanide metal–organic frameworks IRHs-(1–3) supported by cyamelurate linkers have been synthesized and structurally characterized. The incorporation of numerous heteroatoms (N and O) into the pore walls and the relatively small microchannels of these porous solids enhance bonding force of the host–guest interactions, thus promoting the adsorption of carbon dioxide (CO2) over methane (CH4). The nonpolar covalent bonds in methane also favor the less uptake due to the hydrophilic walls of these frameworks. Grand canonical Monte Carlo simulations were performed to determine the origin of the adsorption. The density isocontour surfaces show that CO2 is mainly adsorbed on the walls composed of organic linkers and around the metal sites, whereas no specific adsorption site is observed for CH4, which indicates weak interactions between the framework and the adsorbed gas. As expected, the simulations show that CH4 is not observed around the metal center due to the presence of H2O molecules. The excellent selectivity of CO2/CH4 binary mixture was predicted by the ideal adsorbed solution theory (IAST) via correlating pure component adsorption isotherms with the Toth model. At 25 °C and 1 bar, the CO2 and CH4 uptakes for IRH-3 were 2.7 and 0.07 mol/kg, respectively, and the IAST predicated selectivity for CO2/CH4 (1:1) reached 27, which is among the best value for MOF materials.

A new synthetic route was carried out via a one-pot reaction to prepare a novel series of amidine/amidinate cobalt complexes 8−10 by mixing ligand 2 (6-pyridin-2-yl-[1,3,5]triazine-2,4-diamine) with Co(II) in acetonitrile or benzonitrile. We observed that a change of solvent from methanol (used in complex 7, previously reported) to nitrile solvents (MeCN and PhCN) led to the in situ incorporation of the amidine group, ultimately forming 8−10. So far, this is a unique method reported to introduce amidine/amidinate groups into a pyridinyl-substituted diaminotriazine complex. Remarkably, the single crystal X-ray diffraction study (SCXRD) of these new compounds reveals associations involving Janus DATamidine and Janus DATamidinate. A mechanism is proposed to explain the formation of amidine/ amidinate groups by investigating the single crystal structures of the possible intermediates 11 and 12 where the cobalt ion acts as a template. These amidine/amidinate cobalt complexes were used as a model to assess the photocatalytic activity for the hydrogen evolution reaction (HER). Complexes 9 and 10 show a 74% and 86% enhancement, respectively, of the catalytic activity towards the HER compared to complex 7. This highlights the structure−property relationship. By examining the novel cobalt complexes described here, we discovered the following: (i) a method to introduce an amidine group into a pyridine DAT-based complex, (ii) the efficiency of amidine complexes to form multiple hydrogen bonds to direct the molecular organization, (iii) the plausible mechanism of formation of amidines based on the SCXRD study, (iv) the modification of the final structure and hence the final properties by varying the reaction conditions, and (v) the utility of amidine complexes towards photocatalytic HER activity.

Two new ligands N,N,N′,N′-tetraisopropyl/tetraisobutyl-3,4-pyridinedicarboxamide L1-L2 and six of their Hg(II)X 2 complexes (where X= Cl -, Br -and I -) have been synthesized and characterized. Single crystal X-ray structures of three complexes of L1 (1-3) with HgCl 2 /Br 2 / I 2 and two complexes of L2 (4-5) with HgCl 2 /Br 2 , show that these are 2D coordination polymers, with three different (one new) topologies and five coordinated Hg(II) ions, in square pyramidal coordination. Complex 6, of L2 with HgI 2 , is a dimer with a four coordinated tetrahedral Hg(II) ion. The ligands behave as 2-or 3-connecting linkers for forming CPs but only 1-connector in the dimer. Various types of H-bonding and other noncovalent interactions have been calculated, analyzed and discussed for all the complexes and the ligand L1. Though large size and soft character of iodide coupled with the steric effects of large isobutyl groups, are mainly responsible for a change in the primary structure of 6, but a significant role of the semilocalized LP···π and C-H···O non-covalent interactions into this has also been found. The latter transform this dimer to a stable 2D H-bonded network instead of a coordination polymer. The unique halide bridged 2D structure of 1 forms 1D zig-zag chains of metal ions owing to the mercurophilic interactions. Weaker interactions of the same kind further extend along the basic skeleton of 2D CP and are facilitated by LP···π, strong C-H···Cl and C-H···N(py) interactions.

A wide range of 4,6-diarylated/heterylated pyridin-2(1H)-one derivatives were synthesized in good to excellent yields from 1,3-diarylated/heterylated-2-propen-1-ones (chalcones) in one pot under metal and base-free conditions. This domino reaction suggests a novel mechanism comprising of Michael addition followed by amination, subsequent intramolecular amidation and finally dehydronitrosation. The usefulness of the designed 4,6-diarylated/heterylated pyridin-2(1H)-one derivatives has further been demonstrated by synthesizing medicinally important 2,4,6-triaryl/heteryl pyridines via Pd-catalyzed cross-coupling reaction.