Carolina Estarellas

Very Long-Range Effects: Cooperativity between Anion–π and Hydrogen-Bonding Interactions

The interplay between two important non-covalent interactions involving aromatic rings (namely anion-pi and hydrogen bonding) is investigated. Very interesting cooperativity effects are present in complexes where anion-pi and hydrogen bonding interactions coexist. These effects are found in systems where the distance between the anion and the hydrogen-bond donor/acceptor molecule is as long as approximately 11 A. These effects are studied theoretically using the energetic and geometric features of the complexes, which were computed using ab initio calculations. We use and discuss several criteria to analyze the mutual influence of the non-covalent interactions studied herein. In addition we use Baders theory of atoms-in-molecules to characterize the interactions and to analyze the strengthening or weakening of the interactions depending upon the variation of the charge density at the critical points.

Supramolecular Assembly of Mg(II) Complexes Directed by Associative Lone Pair−π/π−π/π−Anion−π/π−Lone Pair Interactions

Two Mg(II) malonate complexes with protonated 2-aminopyridine and protonated 2-amino-4-picoline as counterions, namely, (C(5)H(7)N(2))(4)[Mg(C(3)H(2)O(4))(2)(H(2)O)(2)](ClO(4))(2) (1) and (C(6)H(8)N(2)H)(2)[Mg(C(3)H(2)O(4))(2)(H(2)O)(2)] x 4 H(2)O (2) [C(5)H(7)N(2) = protonated 2-aminopyridine, C(3)H(4)O(4) = malonic acid, C(6)H(8)N(2)H = protonated 2-amino-4-picoline], have been synthesized from purely aqueous media, and their crystal structures have been determined by single-crystal X-ray diffraction. The role of lone pair...pi interactions in stabilizing the self-assembly process appears to be of great importance in both complexes. Additional weak forces like anion...pi and noncovalent O...O interactions are also found to be operating in 1. A rare combination of lone pair...pi and anion...pi interactions in 1, of the type lone pair...pi/pi...pi/pi...anion...pi/pi...lone pair, is observed, and this unusual supramolecular network is fully described here. An attempt to prepare an analogous complex with 2-amino-4-picoline resulted in 2, which is isomorphous with our recently reported transition-metal complexes of the type (C(6)H(8)N(2)H)(2)[M(C(3)H(2)O(4))(2)(H(2)O)(2)] x 4 H(2)O (M = Ni/Co/Mn). A high-level DFT-D study (RI-B97-D/TZVP) has been used to characterize the different noncovalent interactions present in the solid state. We have also analyzed some crystal fragments to examine energetically some important assemblies that drive the crystal packing. Finally, we have studied the influence of magnesium on some hydrogen-bonding interactions.

Supramolecular assemblies involving anion–π and lone pair–π interactions: experimental observation and theoretical analysis

Two nickel(II) malonate coordination compounds, namely (C5H7N2)4[Ni(C3H2O4)2(H2O)2](ClO4)2 (1) and (C5H7N2)4[Ni(C3H2O4)2(H2O)2](PF6)2 (2) [where C5H7N2 = protonated 2-aminopyridine, C3H4O4 = malonic acid, ClO4− = perchlorate, PF6− = hexafluoridophosphate], have been synthesized from purely aqueous media, and their single-crystal structures have been determined by X-ray diffraction. As anticipated, various weak forces, i.e. lone pair–π, π–π and anion–π interactions, play a key role in stabilizing the self-assembly process observed for both compounds. Intricate combinations of lone pair–π, π–π and anion–π interactions of the type lone pair–π/π–π/π–anion–π/π–lone pair and lone pair–π/π–π/π–anion are observed that are fully described, including by computational methods. The theoretical calculations allow estimating the strength of these π contacts.

Simultaneous Interaction of Tetrafluoroethene with Anions and Hydrogen-Bond Donors: A Cooperativity Study

A computational study of the complexes formed by tetrafluoroethylene, C2F4, with anions has been carried out by means of density functional theory (DFT) and second-order Möller-Plesset (MP2) computational methods, up to MP2/aug-cc-pVTZ level. In addition, the possibility of cooperativity in the interaction of anions and hydrogen-bond donors (FH, ClH, and H2O) when interacting with different faces of the C2F4 molecule has been explored. Electron density of the complexes has been analyzed by means of atoms in molecules (AIM) methodology, while natural bond orbital (NBO) methodology has been used to characterize the orbital interaction. In addition, natural energy decomposition analysis (NEDA) has been applied to analyze the source of the interaction. The energetic results indicate that C2F4 is a weaker anion receptor than C6F6, but in combination with the anions, it became a stronger hydrogen acceptor than C2H4. Cooperativity effects are observed in YH·C2F4·X(-) clusters. In C2F4·X(-) complexes the dominant attractive terms are the electrostatic and polarization ones, while in YH·C2F4·X(-) complexes the charge transfer increases significantly, becoming the most important term for most of the FH and ClH complexes studied here.

Energetic vs synergetic stability: a theoretical study.

The aim of this manuscript is to define a new concept, namely synergetic stability, which can be useful in systems where the interplay of noncovalent interactions is important. Usually, the stability of a noncovalent complex is related to the complexation energy, which is directly proportional to the strength of the noncovalent interactions that are involved in the complex. In ternary complexes characterized by the presence of two different noncovalent interactions, three situations regarding the variation of the strength of the interactions (in comparison to the binary complexes) can be present. The coexistence of the interactions causes, first a strengthening of both interactions, second, a weakening of both, and, third, a strengthening of one interaction at expenses of the weakening of the other. This study deals with ternary complexes where ion-pi and either hydrogen bonding, dihydrogen bonding, or halogen bonding interactions coexist.

Experimental and theoretical study of uracil derivatives: the crucial role of weak fluorine–fluorine noncovalent interactions

We have recently communicated the important role of lone pair–π, π–π and hydrophobic interactions in the solid architecture of 5-fluoro-1-hexyluracil and 1-hexyluracil (CrystEngComm, 2010, 12, 362–365). As a matter of fact, the simple substitution of a hydrogen atom by a fluorine atom has an enormous consequence in the solid state structure. It has been demonstrated that this is due to an increase in the π-acidity of the ring. In this article we extend the study to other uracil derivatives, where we have changed the hydrophobicity of the hexyl chain by introducing hydrophilic groups in the substituent, such as hydroxyl or carboxylic groups. The latter compounds, i.e. (N1-(3-hydroxypropyl)-5-fluorouracil and N1-(4-hydroxycarbonylbutyl)-5-fluorouracil monohydrate present interesting fluorine–fluorine interactions that are very important in determining the crystal packing.

Anion-pi interactions in four-membered rings.

In this study, the importance of anion-pi interactions in four-membered rings has been evidenced. Two kinds of rings have been found to be suitable for participation in anion-pi interactions: first, in different salts of cyclobuten-1,2-dione derivatives and, second, in eta(4)-cyclobutadiene complexes with transition metals.

Lone pair–π vs π–π interactions in 5-fluoro-1-hexyluracil and 1-hexyluracil: a combined crystallographic and computational study

The simple substitution of a hydrogen atom by a fluorine atom in 1-hexyluracil has an enormous consequence on the solid state structure due to the increment in the π-acidity of the ring.

Design of a dual sensing highly selective cyanide chemodosimeter based on pyridinium ring chemistry

A new chemodosimeter, Quino-P, recognizes the strongly nucleophilic cyanide by dual colorimetric and fluorescence ‘off–on’ signalling responses. Noteworthily, several other anions, even in significantly higher concentrations, induce no detectable photophysical perturbations. The chemodosimeter mechanism involves formation of a C4–cyano adduct, which exhibits an uncommon phenomenon of enhanced internal charge transfer interaction.

Can lone pair-π and cation-π interactions coexist? A theoretical study

AbstractThe interplay between two important noncovalent interactions involving different aromatic rings is studied by means of ab initio calculations (MP2/6-31++G**) computing the non-additivity energies. In this study we demonstrate the existence of cooperativity effects when cation-π and lone pair-π interactions coexist in the same system.These effects are studied theoretically using energetic and geometric features of the complexes. In addition we use Bader’s theory of atoms-in-molecules and Molecular Interaction Potential with polarization (MIPp) partition scheme to characterize the interactions. Experimental evidence for this combination of interactions has been obtained from the Cambridge Structural Database.