Dillip Kumar Chand

New multinuclear discrete heteroleptic complexes have been synthesized by mixing Pd(II), 2,2′-bipyridine and N,N′-(1,2-phenylene) diisonicotinamide in a single pot as a new approach. A dimeric molecular rhombus and a trimer in equilibrium are obtained where the dimer is the major product. Similar equilibrium is also observed when classical method is employed for the synthesis. The equilibrium is shifted exclusively in favour of the dimer upon addition of benzene. The complexes are characterized by NMR and ESI-MS methods. Crystal structure of the benzene encapsulated rhombus is presented. © 2010 Elsevier Ltd.

A series of binuclear palladium(II)-based self-assembled metallomacrocycles of Pd2L′2L2 type compositions were synthesized by complexation of an imidazole appended non-chelating bidentate ligand L with different cis-protected palladium(II) components (i.e. PdL′). The complexes [Pd2(en)2(L)2](NO3)4, 1, [Pd2(tmeda)2(L)2](NO3)4, 2, [Pd2(bpy)2(L)2](NO3)4, 3, and [Pd2(phen)2(L)2](NO3)4, 4 were characterized by NMR spectroscopy and their nuclearities were established with the help of ESI-MS. Solid state structures of the complexes 2, 3 and [Pd2(phen)2(L)2](OTf)4, 4′ were established by the single-crystal XRD technique. These metallomacrocycles could act as tectons for crystal engineering by using the available π-surface on their architectures. The crystal packing of these molecules revealed the importance of the π-surface on the ligand moiety as well as on the cis-protecting moiety. Utilization of the π-surfaces afforded 1D to 3D supramolecular networks in solid state.

One-pot synthesis of self-assembled heteroleptic complexes of general formula [Pdx(tmeda)x(L)y](NO3) 2x is achieved by combining required amount of tmeda, a chosen ligand L and Pd(NO3)2 under suitable reaction conditions. The strategy is devised using our understanding of a special variety of ligand exchange reactions (LER) around palladium(II) centers as modeled in this work. The one-pot synthesis technique is thus considered as an application of the unique LER. © 2013 Elsevier B.V.

Bis(pyridin-3-ylmethyl) pyridine-3,5-dicarboxylate (L) possessing one internal and two terminal pyridine moieties displayed differential coordination ability when combined with suitable PdIIcomponents. The compound L acted as a bidentate chelating ligand to form mononuclear complexes when combined with cis-[Pd(tmeda)(NO3)2] or Pd(NO3)2in calculated ratios. The combination of Pd(NO3)2with L in a ratio of 3:4, however, afforded the trinuclear “double-decker” cage [(NO3)2⊂Pd3(L)4](NO3)4, in which L acts as a nonchelating tridentate ligand and the counter anion (i.e., NO3–) acts as template. The encapsulated NO3–can be replaced by F–, Cl–, or Br–but not by I–. The F–-encapsulated cage could not be isolated due to its reactivity, whereas the Cl–or Br–encapsulated cages could be isolated. Although anionic guests such as NO3–, Cl–, or Br–stabilized the cages, the presence of excess Cl–or Br–(not NO3–) facilitated decomplexation reactions releasing the ligand. The complexation of Pd(Y)2(Y = BF4–, PF6–, CF3SO3–, or ClO4–) with L afforded the corresponding mononuclear complexes under appropriate conditions. However, these counter anions could not act as templates for the construction of double-decker cages.

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.

Palladium(II) has four coordination sites and forms square planar complexes. Discrete self-assemblies are generated by the combination of a variety of palladium(II) components and ligands ranging from bi- to polydentate. The Pd(II) components used are generally of two varieties: cis-protected Pd(II) and unprotected Pd(II). Most common cis-protecting units (X-X) such as ethylenediamine, 2,2'-bipyridine and 1,3-bis(diphenylphosphino)propane and a few other related chelating systems have been exploited for the complexation reactions. The self-assemblies formed are generally represented as [{cis-Pd(X-X)} x(L) y](monoanion) 2x and [Pd m(L) n](monoanion) 2m when generated from the complexation of a suitable ligand (L) with cis-protected Pd(II) and simple Pd(II) units, respectively. When Pd(solvent) 2Cl 2 is complexed with ligands, the solvent molecules are replaced with the incoming ligands, leading to complexes in which the trans positions are occupied by the chloride anions. © 2012 Elsevier B.V.

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.

Polynuclear self-assembly molecules of general formula [{Pd(en)}x(ligand)y](NO3)2x (A) undergo ligand exchange reaction when heated in DMSO. A mixture of [Pdm(ligand)n](NO3)2m (B) and [Pd(en)2](NO3)2 (C) is generated in this process. The binuclear compound (A) containing a bidentate, non-chelating ligand 1,4-bis(4′-pyridylmethyl)-2,3,5,6-tetrafluorobenzene, is subjected to ligand exchange where upon the compound (A) remains in a dynamic equilibrium with the mixture of ensuing (B) and (C). Combination of separately prepared (B) and (C) also generates (A), thus equilibrium of (A) with (B) and (C) is again observed. We predict [{Pd(bpy)}x(ligand)y](NO3)2x (A′) where 2,2′-bipyridyl (bpy) is the cis-protecting group would not probably undergo ligand exchange. The idea was conceived from the fact that (bpy) is more rigid compared to (en) moreover one of the expected products in the event of ligand exchange [Pd(bpy)2](NO3)2 (C′) is not really very stable unlike (C). In fact, when (A′) is heated in DMSO no ligand exchange is observed at all. More interestingly combination of (B) and (C′) generated (A′) smoothly. Mononuclear complexes obtained from the ligand 4-phenylpyridine are also used for similar study for comparison. It is suggested that (bpy) could serve as a better cis-protecting group for Pd(II)-based self-assembly coordination cage compounds particularly when dissolution of the assemblies in polar solvents and heating of the resultant solution is required. © 2006 Elsevier B.V. All rights reserved.

Abstract: Helical self-assembled coordination complexes are broadly classified under linear and circular helicates. While the number of strands of the ligand units in a molecule of the linear helicates is used for further classifications such as single-stranded, double-stranded and so on, the circular helicates are not classified further. The compositions of helicates are considered as M xL y where the terms x and y stand for the number of metal ion(s) and ligand strands, respectively. However, more than one type of metal centers/ligand in helicates are also known. The linear helicates of a given number of strands are further classified under the number of metal centers such as binuclear, trinuclear and so on. Representative examples are included to exemplify the varieties of helicates. Graphical abstract: Synopsis: Helical self-assembled coordination complexes are broadly classified under linear and circular helicates. While the number of strands of the ligand units in the linear helicates is used for further classifications, the circular helicates are put all under one category. Representative examples are included to exemplify the varieties of helicates. Pictogram:[Figure not available: see fulltext.].

The formation of three examples of a new class of self-assembly Pt(II) cage molecules of general formula [Ptm(ligand)n](NO 3)2m is achieved from Pt(II) and ligands. The compounds are observed in solution state and confirmed from the similarity of their proton NMR behavior as compared with that of reported Pd(II) compounds of the formula [Pdm(ligand)n](NO3)2m. © 2006 Elsevier Ltd. All rights reserved.