Ligand Isomerism in Coordination Cages.

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 Pd2L4 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)urea 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 CO2 gas are demonstrated, and their behaviors are compared.

Crystal structure of bis-(2-amino-anilinium) hydrogen phosphate.

The asymmetric unit of the title compound, 2C6H9N2 (+)·HPO4 (2-), comprises two 2-amino-anilinium cations and one hydrogen phosphate dianion. In the crystal, the HPO4 (2-) dianions are linked by O-H⋯O hydrogen bonds into chains along [100]. The inorganic anionic chains and organic cations are linked by N-H⋯O and N-H⋯N hydrogen bonds, forming a two-dimensional supra-molecular network extending parallel to (001).

Hypoelectronic 8-11-Vertex Irida- and Rhodaboranes.

A series of novel isocloso-diiridaboranes [(Cp*Ir)2B6H6], 1, 2; [1,7-(Cp*Ir)2B8H8], 4; [1,4-(Cp*Ir)2B8H8], 5; [(Cp*Ir)2B9H9], 8; isonido-[(Cp*Ir)2B7H7], 3; and 10-vertex cluster [5,7-(Cp*Ir)2B8H12], 6 (Cp* = η(5)-C5Me5) have been isolated and structurally characterized from the pyrolysis of [Cp*IrCl2]2 and BH3·thf. On the other hand, the corresponding rhodium system afforded 10- and 11-vertices clusters [5-(Cp*Rh)B9H13)], 7, and [(Cp*Rh)2B9H9], 9, respectively. Clusters 1 and 2 are topological isomers. The geometry of 1 is dodecahedral, similar to that of its parent borane [B8H8](2-), in which two of the [BH] vertices are replaced by two [Cp*Ir] fragments. The geometry of 2 can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. Compounds 4 and 5 are 10-vertex isocloso clusters based on a 10-vertex bicapped square antiprism structure. The only difference between them is the presence of a metal-metal bond in 5. The solid-state structures of 8 and 9 attain an 11-vertex geometry in which a unique six-membered B6H6 moiety is bonded to the metal center. In addition, quantum-chemical calculations have been used to provide further insight into the electronic structure and stability of the clusters. All the compounds have been characterized by IR and (1)H, (11)B, and (13)C NMR spectroscopy in solution, and the solid-state structures were established by X-ray crystallographic analysis.

Gallium and indium complexes containing the bis(imino)phenoxide ligand: synthesis, structural characterization and polymerization studies.

A series of gallium and indium complexes containing a bis(imino)phenolate ligand framework were synthesized and completely characterized with different spectroscopic techniques. The molecular structures of a few complexes were determined using single crystal X-ray diffraction studies. These compounds were found to be extremely active towards the bulk ring opening polymerization (ROP) of lactides yielding polymers with high number average molecular weight (Mn) and controlled molecular weight distributions (MWDs). The neutral complexes produce isotactic enriched poly(lactic acid) (PLA) from rac-lactide (rac-LA) under melt conditions, whereas the ionic complex produces atactic PLA. The polymerizations are controlled, as evidenced by the narrow molecular distribution (MWDs) of the isolated polymers in addition to the linear nature of number average molecular weight (Mn) versus conversion plots with variations in monomer to catalyst ratios. The kinetic and mechanistic studies associated with these polymerizations have been performed.

Octadecanuclear gear wheels by self-assembly of self-assembled "double saddle"-type coordination entities: molecular "rangoli".

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.