Dillip Kumar Chand

A pyridine/aniline appended unsymmetrical bidentate ligand N-(4-(4-aminobenzyl)phenyl)nicotinamide, investigated in this work has two well-separated coordination sites. Combination of the ligand with cis-protected palladium(II) (i.e., PdL′) and palladium(II) in separate reactions produced the corresponding Pd2L′2Lun2 and extremely rare Pd2Lun4 type self-assembled binuclear complexes, respectively. Notably, both varieties of complexes are prepared from a common ligand system. Two diastereomers (i.e., (2,0) and (1,1)-forms) are possible for Pd2L′2Lun2 type complex, whereas four diastereomers (i.e., (4,0), (3,1), trans(2,2), and cis(2,2)-forms) can be imagined for the Pd2Lun4 type complex. However, exclusive diastereoselectivity was observed, and the complexes formed belong to (1,1)-Pd2L′2Lun2 and cis(2,2)-Pd2Lun4 forms. The diastereomers are predicted from NMR study in solution and DFT calculations in gas-phase and implicit-solvent media; however, single-crystal structures of both the complexes provided unambiguous support. The rare Pd2Lun4 type complex is studied in further detail. Parameters like counteranion, concentration, temperature, and stoichiometry of metal to ligand did not influence the diastereoselectivity in complex formation. DFT calculations show the cis(2,2) form to be the most stable, followed by the (3,1) isomer. The lowest conformational strain in the bound ligand strands in the cis(2,2)-arrangement along with optimal intermolecular interactions makes it the energetically most stable of all the isomers. Molecular dynamics (MD) simulations were carried out to visualize the self-assembly process toward the formation of Pd2Lun4 type complex and the free energy difference between the cis(2,2) and (3,1) isomers. Snapshots of MD simulation elucidate the step-by-step progress of complexation leading to the cis(2,2)-isomer.

The combination of a flexible pyridine-appended ligand (L1) with 4,4′-bipyridine (L2) and cis-protected Pd(II) units, Pd(L′)(NO3)2, in water yielded a concentration-dependent equilibrium mixture of the corresponding [2]catenanes [Pd2(L′)2(L1)(L2)]2(NO3)8 and their constituent macrocycles [Pd2(L′)2(L1)(L2)](NO3)4. The cis-protecting units (L′) used were ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen). Crystallization of the [2]catenanes via slow evaporation of their CH3CN/H2O (1:1) solutions yielded a single crystalline form in the case of [Pd2(2,2′-bpy)2(L1)(L2)]2(NO3)8 and two concomitant crystalline forms (solvates) in the case of [Pd2(phen)2(L1)(L2)]2(NO3)8. The formation of the [2]catenane is facilitated by noncovalent interactions such as N-H···O, C-H···O, and C-H···πcontacts and π···πstacking. The solvates of [Pd2(phen)2(L1)(L2)]2(NO3)8 revealed differences in the orientation of the amide carbonyl group and conformational differences in the ligands and phen units in the macrocycles and may thus be termed conformational solvatomorphs. The molecular packing in all the structures was found to be driven by intermolecular π···πstacking interactions between the aromatic rings in their cis-protected Pd(II) units. However, because of the awkward shape of the molecules, the closest 2,2′-bpy and phen units in all the structures overlap differently rather than the commonly observed "head-to-tail"or "head-to-head"modes.

Double-decker shaped conjoined-cages of Pd3L4 formulation are prepared via self-assembly of Pd(ii) with a set of three regioisomeric tridentate ligands. Alongside the targeted double-decker cage, unprecedented hour-glass shaped conjoined-cages of Pd3L4 formulation are also formed in two cases. The double-decker cage prepared from one ligand system and the hour-glass from another (but with a regioisomeric ligand) are structurally well suited to exemplify configurational ligand isomerism.

Three new cobalt(II) complexes [Co(µ2-L)]3(ClO4)3.2H2O, 1, [Co(L)(NO3)], 2 and {[Co(µ2-L)(MeOH)](BPh4).(MeOH)}n, 3 are prepared where L stands for 2-(bis(pyridin-2-ylmethyl)amino)acetate. Single crystal X-ray diffraction analysis confirmed the trinuclear core for 1, and 1-D polymeric structure for 3. It is proposed that these complexes are largely mononuclear in solution state. Reactivity of the complexes with aerial dioxygen, in presence of Et3N, invariably produced a common complexed cation [Co(L)(pic)]+ where pic stands for picolinate. The novelty of the finding is in terms of the presence of both intact ligand (i.e L) and a fragment of the ligand (i.e. pic) in the same complex. Crystal structures of the isolated complexes [Co(L)(pic)](ClO4), 4a and [Co(L)(pic)](NO3), 4b confirmed the solid state structures. The Co(II) center of a complex is oxidized to Co(III) and the bound ligand moiety afforded a picolinate unit (due to oxidative Cpicolyl-Namine bond cleavage). The picolinate unit then connects with another molecule of a Co(III) complex containing L in its original form. Oxidation of a representative complex using H2O2 also resulted [Co(L)(pic)]+, but a stable binuclear dihydroxo bridged Co(III) complex [Co(L)(µ2-OH)]2(ClO4)2, 5 was formed when controlled amount of H2O2 (1 equiv) was employed. Graphical abstract: [Figure not available: see fulltext.] Synopsis: Three new Co(II) complexes of 2-(bis(pyridin-2-ylmethyl)amino)acetate (L) are prepared. Reactivity of the complexes with aerial dioxygen, in presence of Et3N, invariably produced Co(III) complexes having the common complexed cation [Co(L)(picolinate)]+. Picolinate is generated due to the oxidative cleavage of bound L.

Selective binding of chloride over the other most abundant anions in living organisms is pivotal due to its essential role in physiological functions. Herein, we report a template-free Pd2L4 cage exhibiting high selectivity for medium-sized halides (i. e., Cl−, Br−) in water owing to the size-discriminatory nature of the cage cavity. In pure water, this cage displays high selectivity and micromolar affinity for chloride. The cage shows no binding towards other biologically more abundant essential anions such as phosphates, carboxylates, or bicarbonate. This cage shows an unprecedented nanomolar affinity with 1 : 1 binding stoichiometry for chloride in aqueous-DMSO media. This high affinity was achieved with the best use of traditional hydrogen bonding and electrostatic interactions, as confirmed by single-crystal X-ray diffraction analysis. This well-defined cage sequestrates F− by cleaving a B−F bond in BF4− in a facile manner in a nonpolar solvent or in the presence of excess ligand. This cage also demonstrates capture of the sub-ppm chloride level that is present in commercial D2O samples.

Binuclear Pd(II) self-assemblies with composition [Pd2(bpy)2(L)2](NO3)4, 1 and [Pd2(phen)2(L)2](NO3)4, 2 were synthesized by equimolar combination of the multi-dentate ligand N, Nʹ-di(pyridin-3-yl)pyridine-2,6-dicarboxamide, L with suitable cis-protected palladium(II) units. Complexes 1 and 2 were characterized by 1H NMR, 13C NMR, COSY, HSQC and ESI-MS. The molecular structure of complexes 1 and 2 were determined by single crystal X-ray diffraction technique. Solid state structure for complex 1 displays a unique three dimensional array of molecules which resembles an “egg tray” through inter molecular π-π- stacking using the strategically located π-surfaces of the cis-protecting units as well as the ligand. Molecular docking study shows excellent interaction of complexes 1 and 2 at the active site of Protein-Arginine-N Methyltransferase 1 with binding energy -9.34 and -9.73 kcal/mol, respectively.

A self-assembled coordination cage usually possesses one well-defined three-dimensional (3D) cavity whereas infinite number of 3D-cavities are crafted in a designer metal-organic framework. Construction of a discrete coordination cage possessing multiple number of 3D-cavities is a challenging task. Here we report the peripheral decoration of a trinuclear [Pd3L6] core with one, two and three units of a [Pd2L4] entity for the preparation of multi-3D-cavity conjoined-cages of [Pd4(La)2(Lb)4], [Pd5(Lb)4(Lc)2] and [Pd6(Lc)6] formulations, respectively. Formation of the tetranuclear and pentanuclear complexes is attributed to the favorable integrative self-sorting of the participating components. Cage-fusion reactions and ligand-displacement-induced cage-to-cage transformation reactions are carried out using appropriately chosen ligand components and cages prepared in this work. The smaller [Pd2L4] cavity selectively binds one unit of NO3−, F−, Cl− or Br− while the larger [Pd3L6] cavity accommodates up to four DMSO molecules. Designing aspects of our conjoined-cages possess enough potential to inspire construction of exotic molecular architectures.

The title compound Nitro(4′-(2-pyridyl)-2,2′:6′,2″-terpyridyl) palladium(II) nitrate, 1 consists of a terpyridyl derivative 4′-(2-pyridyl)-2,2′:6′,2″-terpyridyl, (terpy) L bonded to a Pd(II) unit through Pd-N coordinate bond. The complex 1 is characterized by 1H, 13C NMR, H-H COSY, C-H COSY and by single crystal X-ray diffraction technique. The NMR data of complex shows the diamagnetic shielding of the signal due to terpy α-proton. The crystal structure of the compound shows that the fourth coordination site of palladium is occupied by a nitrate ion. The electrical neutrality of the complex is maintained by another nitrate ion present outside of the coordination sphere. The core structure of the terpyridine moiety lies almost co-planar and the substituted pyridine group is slightly twisted with respect to the core structure. The dihedral angle between the substituted pyridine group and the mean plane passing through the core terpyridine unit is found to be approximately 12°. Further analysis of the crystal structure show one molecule of the complex cation 1 is linked to two other molecules (one on either side) by inter molecular π-π stacking interaction and forms a one dimensional π-polymer. Several of these π-polymers engaged in further π-π stacking to form the three dimensional array. The complex 1 shows the ability to bind to B-DNA. Molecular docking studies show that complex 1 binds to the minor grove of B-DNA with an attractive van der Waals energy of −7.48 kcal/mol.

Abstract: A procedure for the expedient synthesis of well-characterized Cu(I) oxide nanoparticles (Cu2ONPs) from Cu(II) salts by employing Rice (Oryza sativa) as a cheap and ready source of reducing as well as stabilizing agent has been demonstrated. The judicious choice of rice as a catalyst has helped in the symbiotic combination of two events: viz., acidic hydrolysis of starch to form glucose and the subsequent formal reduction of Cu2+ by the in-situ generated monosaccharide reducing sugar (glucose) under the alkaline condition to produce Cu2O. Further, rice was also found to be effectively stabilizing the nanoparticles from agglomeration. Optical and microscopic techniques were suitably employed for the characterization of the nanoparticles of approximately 10 nm size. Furthermore, the specifically generated nanoparticles were found to be active catalysts in an aqueous medium for Azide-alkyne Huisgen cycloaddition (Click reaction) under base free condition via one-pot multi-component addition for the synthesis of mono-, bis- and tris-1,2,3-triazoles in good to excellent yields. Graphic abstract: Cu2ONPs synthesized using hydrolysed Rice, an active catalyst for synthesis of mono-, bis- and tris-1,4-disubstituted 1,2,3-triazoles via one pot multicomponent reactions in water.[Figure not available: see fulltext.].

A pyridine/aniline appended unsymmetrical bis-monodentate ligand N-(3-aminophenyl)nicotinamide, Lun is synthesized via condensation of nicotinic acid with excess m-phenylene diamine. A low-symmetry binuclear complex of the Pd2L′2Lun2 type and an extremely rare trinuclear complex of the Pd3Lun6 type are produced by self-assembly of the ligand Lun with cis-protected palladium(ii) (i.e., PdL′) and palladium(ii), respectively. Two isomers (i.e. [(2,0), (2,0)] and [(1,1), (1,1)]-forms) are theoretically possible for the Pd2L′2Lun2-type complex whereas nine isomers can be envisaged in the case of the Pd3Lun6-type arrangement. However, one of the isomers of the Pd2L′2Lun2-type complex as well as the one for the Pd3Lun6-type complex are experimentally obtained. The exclusive formation of specific isomers could be predicted from the 1D/2D NMR study in the solution state and the DFT calculations in the gas phase/implicit solvent media. The formation of the predicted all-(1,1)-[Pd2(en)2Lun2](NO3)4 has been confirmed by a single-crystal XRD study. DFT calculations for the isomers of the Pd3Lun6-type arrangement show that a [cis(2,2), cis(2,2), cis(2,2)] isomer is energetically favourable than the alternatively predicted [trans(2,2), trans(2,2), trans(2,2)] isomer. Conformational changes within the build of the exclusively formed isomers are proposed on the basis of NMR study.