Complexation reactions of palladium(II) nitrate with a set of 3-pyridyl appended nonchelating bidentate ligands possessing regioisomeric phenylene-diurea functionalities as spacers were carried out. The ligands utilized in this study are 1,1'-(1,2-phenylene)bis(3-(pyridin-3-yl)urea), L1; 1,1'-(1,3-phenylene)bis(3-(pyridin-3-yl)urea), L2; and 1,1'-(1,4-phenylene)bis(3-(pyridin-3-yl)urea), L3. The complexation reactions of the ligands (L1, L2, and L3) with palladium(II) produced single discrete isomeric cages (1, 2, and 3) of PdL formulation in each case and thereby illustrated ligand-isomerism in coordination cages. All 16 hydrogen atoms of eight urea moieties present in four ligand strands are delineated completely endohedrally in cage 1 and completely exohedrally in cage 3, whereas cage 2 exhibited half of the urea hydrogens in exohedral locations and the remaining half in endohedral locations. In addition to the variable number of solvent molecules, the cavities of cages 1 and 2 lodged four and two nitrate ions, respectively, using the endohedral (H) atoms (i.e., NH groups) as binding sites, whereas the cavity of 3 remained anion free. The abilities of the complexes 1-3 for adsorption of CO gas are demonstrated, and their behaviors are compared.
A series of self-assembled "double saddle"-type trinuclear complexes of [Pd3L'3L2] formulation have been synthesized by complexation of a series of cis-protected palladium(II) components with a slightly divergent "E-shaped" non-chelating tridentate ligand, 1,1'-(pyridine-3,5-diyl)bis(3-(pyridin-3-yl)urea (L). The cis-protecting agents L' employed in the study are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), and 1,10-phenanthroline (phen), for 1, 2, 3, and 4, respectively. The crystal structures of [Pd3(tmeda)3(L)2](NO3)6 (2), [Pd3(bpy)3(L)2](NO3)6 (3), and [Pd3(phen)3(L)2](NO3)6 (4) unequivocally support the new architecture. Two of the "double saddle"-type complexes (3 and 4) are suitably crafted with π surfaces at the strategically located cis-protecting sites to facilitate intermolecular π-π interactions in the solid state. As a consequence, six units of the 3 (or 4) are assembled, by means of six-pairs of π-π stacking interactions, in a circular geometry to form an octadecanuclear molecular ring of [(Pd3L'3L2)6] composition. The overall arrangement of the rings in the crystal packing is equated with the traditional Indian art form rangoli.
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...
Self‐assembled binuclear complexes of Pd2L′2L2 and Pd2L4 type formulations have been achieved by combining the cis‐protected palladium(II) component i. e., [PdL′]2+ (where L′ stands for tmeda) and naked palladium(II) separately with a 3‐pyridyl appended non‐chelating bidentate ligand, L under suitable conditions. Supramolecular fusion of the Pd2L4 and PdL′2 type complexes have been demonstrated that provided the corresponding Pd2L′2L2 type complex. One pot synthesis of the binuclear Pd2L′2L2 type complex is achieved by combining palladium(II), L′ and L at equimolar ratio, however, along with an unidentified trap. The crystal structure of a Pd2L4 type complex confirmed the binuclear architecture of the cage. Intermolecular H‐bonding and π‐π stacking interactions are analyzed from the crystal structure and the extended intermolecular interactions apparently generated a grid pattern.
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