Noncovalent synthesis of donor/acceptor stacks

Supramolecular arrays composed of alternating tetracyanoethylene acceptors (A) and 1,4-dioxybenzene-based donors (D) self-assemble spontaneously in the solid state. Infinite one-dimensional […A…D…A…D…] stacks are formed by co-crystallizing tetracyanoethylene and 1,4-dimethoxybenzene. When bis- p-phenylene-34-crown-10, possessing two 1,4-dioxybenzene donors (D-D) bridged by polyether chains, is employed, infinite one-dimensional […A…D-D…A…D-D…] arrays are formed with the cavities of macrocyclic polyethers of adjacent stacks perfectly in register to afford channels — occupied by MeCN molecules — along one crystallographic direction. Graphi

Linkage Isomerism in Square-Planar Complexes of Platinum and Palladium with Histidine and Derivatives

Reactions of three histidine-containing ligands (L-histidine, iV-acetyl-L-histidine, glycyl-L-histidine) with monofunctional Pdand Pt (M) species ((dien)M, (trpy)M, cis-(NH)Pt(l-MeU)(HO)], cis-[(NH)Pt(l-MeC)-(HO)], trans-[(NHCH)Pt(l-MeC)(HO)]) have been studied by applying primarily H NMR and occasionally Pt NMR spectroscopy. Depending on reaction conditions (pH; M:ligand ratio), different products are formed which, in the case of N-acetylhistidine and (dien)Pt, for example, include monodentate coordination through N1 of imidazole (3a), N3 of imidazole (4a), and O of carboxylate (5a) or bidentate bridging via N1, O (6a), N3, O (7a) and N1, N3 (8a). With L-histidine and (dien)Pt, in addition, formation of an isomer with coordination through the amino group is observed (13), which takes place by a migration process from the initially favored O site (12). In the case of the ternary nucleobase/N-acetylhistidine complexes of Pt, N1 and N3 linkage isomers have been separated using HPLC and isolated in a few cases (16-18) and their acid/base equilibria determined. The formation of N1 and N3 linkage isomers, which correspond to the metallated forms of the respective tautomers, is the outstanding feature of this study. The differentiation of tautomers of the Pt compounds in many cases is straightforward in spectra recorded at low magnetic field (80-100 MHz) when Pt-H (imidazole) couplings are observable. In addition, the methine resonances of the two isomers differ, with those of the N3 isomers downfield relative to those of the N1 isomer. On the basis of published data on the tautomer distribution and the measured distribution of (dien)Pd over the two imidazole sites, it is estimated that Pd complex formation with N1 is slightly favored over N3 in the case of N-acetylhistidine, but substantially more so in the case of L-histidine. As for (dien)Pt, the distribution of imidazole-bound isomers reflects primarily kinetic rather than thermodynamic factors

interactions as a control element in supramolecular complexes: experimental and theoretical evaluation of receptor affinities for the binding of bipyridinium-based guests by catenated hosts

Academi

The template-directed synthesis of cyclobis(paraquat-4,4′-biphenylene)

The self-assembly of a π-electron deficient bipyridinium-based cyclophane around a π-electron rich ferrocene-based polyether as template provides a relatively simple method of self-assembling, in preparative yields, an organic molecular square-namely, cyclobis(paraquat-4,4′-biphenylene)-that is able to recognise and bind π-electron rich guests