The self-assembly features of hydrophobic bispyridyldichlorido Pd(II) complexes, equipped with an extended aromatic surface derived from oligophenyleneethynylene (OPE) and polarizable amide functional groups, are reported. The cooperative supramolecular polymerization of these complexes results in bundles of thin fibers in which the monomer units are arranged in a translationally displaced or slipped fashion. Spectroscopic and microscopy studies reveal that these assemblies are held together by simultaneous π-stacking of the OPE moieties and NH···ClPd hydrogen bonds. These unconventional forces are often observed in crystal engineering but remain largely unexploited in supramolecular polymers. Both steric and electronic effects (the presence of bulky and polarizable metal-bound Cl ligands as well as hydrogen bonding donor NH units) prevent the establishment of short Pd-Pd contacts and strongly condition the aggregation mode of the reported complexes, in close analogy to the previously reported amphiphilic Pd(II) complex 4. The results presented herein shed light on the subtle interplay between different noncovalent interactions and their impact on the self-assembly of metallosupramolecular systems.

Supramolecular ring-versus-chain equilibria are ubiquitous in biological and synthetic systems. Understanding the factors that decide whether a system will fall on one side or the other is crucial to the control of molecular self-assembly. This work reports results with two kinds of dinucleoside monomers, in which the balance between closed cycles and open polymers is found to depend on subtle factors that rule conformational equilibria, such as steric hindrance, intramolecular interactions, or π-conjugation pathways.

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Rodlike π‐conjugated molecules in which two OPV fragments are connected through a diacetylene bond self‐assemble in aqueous and organic media. Optical spectroscopy and AFM measurements indicated that, in water, strong hydrophobic interactions between π‐cores promote aggregation into robust, uniform micellar structures. In contrast, in apolar solvents, a fibrilar morphology is obtained by coiling of columnar stacks. These stacks are formed in a nucleation‐elongation process with degrees of cooperativity of 0.006, that is influenced by the low rotation barriers around the σ‐bonds in the diacetylene linker.

Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: Copyright: © 2016 Wiley VCH VerlagEl acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription The Role of Multipoint Hydrogen-bond Symmetry on Chelate Cooperativity in Supramolecular MacrocyclizationsCarlos Montoro-García, [a] Jorge Camacho-García, [a] Ana M. López-Pérez, [a] María J. Mayoral, [a] Nerea Bilbao, [a] and David González-Rodríguez [a] *Abstract: Here, we analyze the intrinsic chelate effect that multipoint H-bonding patterns exert in the overall energy of dinucleoside cyclic systems. Our results indicate that the magnitude of EM is regulated by the symmetry of the H-bonding pattern, which is reduced by about 3 orders of magnitude when going from the unsymmetric ADD-DAA or DDA-AAD patterns to the symmetric DAD-ADA pattern.The supramolecular synthesis [1] of complex nanostructures with a precision analogous to that found in the natural world requires not only an understanding of the noncovalent interactions involved, [2] but also of cooperative and multivalent phenomena that may arise between the individual constituents, since the control of structure and monodispersity depends largely on this issue. [3] A molecule with more than one binding site may assemble into linear (open) or cyclic (closed) structures. Although the size of linear oligomers can be sometimes limited within a certain range, the supramolecular product is commonly a statistical distribution of chain lengths.[4]Therefore, the synthesis of discrete supramolecular structures has normally been focused on closed (multi)macrocyclic systems, where size and structure are dictated by the geometric requirements of the monomer and the binding interaction. [5] The effect that causes the quantitative formation of a particular ring-closed species is defined as chelate cooperativity, and stems from the fact that an intramolecular interaction is favored over an intermolecular one, providing a series of conditions of enthalpic and entropic origin are met. [3] The increased in stability when comparing a linear and a cyclic oligomer of a certain length is given by the product K inter ·EM, where K inter is the intermolecular binding constant and considers the additional association to form the cycle, whereas EM, the key parameter quantifying chelate cooperativity, stands for effective molarity and takes into account that this last binding event is intramolecular (EM = K intra /K inter ). [6] In this context, multipoint H-bonding motifs, constituted by an array of vicinal H-bonding donor (D) and acceptor (A) groups, arise as a relevant noncovalent interaction increasingly used to produce not only discrete cyclic assemblies, but also supramolecular polymers and functional materials.[7] A relevant example is represented by the nucleobases [8] and DNA itself, constituted by combinations of unsymmetric ADD-DAA guaninecytosine and symmetric DA-AD adenine...