Search

A theoretical study of the halogen-bondedcomplexes (A–X···C)formed between halogenated derivatives (A–X; A = F, Cl, Br,CN, CCH, CF3, CH3, H; and X = Cl, Br) and anitrogen heterocyclic carbene, 1,3-dimethylimidazole-2-ylidene (MeIC)has been performed using MP2/aug′-cc-pVDZ level of theory.Two types of A–X:MeIC complexes, called here type-I and -II,were found and characterized. The first group is described by longC–X distances and small binding energies (8–54 kJ·mol–1). In general, these complexes show the traditionalbehavior of systems containing halogen-bonding interactions. The secondtype is characterized by short C–X distances and large bindingenergies (148–200 kJ·mol–1), and onthe basis of the topological analysis of the electron density, theycorrespond to ion-pair halogen-bonded complexes. These complexes canbe seen as the interaction between two charged fragments: A–and +[X–CIMe] with a high electrostatic contributionin the binding energy. The charge transfer between lone pair A(LP)to the σ* orbital of C–X bond is also identified as asignificant stabilizing interaction in type-II complexes. [ABSTRACT FROM AUTHOR]

A large set of intramolecular aminoborane-based FLPs was studied employing density functional theory in the H 2 activation process to analyze how the acidity and basicity of boron and nitrogen atoms, respectively, affect the reversibility of the process. Three different linkers were employed, keeping the C-C nature in the connection between both Lewis centers: -CH 2 -CH 2 -, -CH[double bond, length as m-dash]CH-, and -C 6 H 4 -. The results show that significant differences in the Gibbs free energy of the process are found by considering all the combinations of substituents. Of the 75 systems studied, only 9 showed the ability to carry out the process reversibly (Δ G H 2 in the range of -3.5 to 2.0 kcal mol -1 ), where combinations of alkyl/aryl or aryl/alkyl in boron/nitrogen generate systems capable of reaching reversibility. If the alkyl/alkyl or aryl/aryl combination is employed, highly exergonic (non-reversible H 2 activation) and endergonic (unfeasible H 2 activation) reactions are found, respectively. No appreciable differences in the linker were found, allowing us to continue the analysis with the most entropically favorable linker, the -C 6 H 4 - linker. From this, 25 different FLP systems of type 2-[bis(X)boryl]-(Y)aniline (X: H, CF 3 , C 6 F 5 , PF t B, FMes and Y: H, CH 3 , t -but, Ph, Mes) can be formed. By analyzing the electronic properties of each system, we have found that the condensed-to-boron electrophilicity index ω B + is inversely related to the Δ G H 2 . Interestingly, two relationships were found; the first is for alkyl groups (Y: CH 3 and t -but) and the second for aryl groups (Y: H, Ph, and Mes), which is intimately related to the proton affinity of each aniline. In addition, it is quite interesting when the frustration degree, given by B⋯N distance d B-N , is brought together with ω B + , since the quotient has unit energy/length corresponding to unit force; concomitantly, a measure of the FLP strength in H-H bond activation can be defined. With this finding, a rational design of this kind of FLP can be performed by analyzing the acidity of boron through condensed-to-boron electrophilicity and knowing the nature of the substituent of nitrogen according to whether the Y is alkyl or aryl, optimizing the H 2 reversible activation in a rational way, which is crucial to improve the catalytic performance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A new selective fluorogenic chemosensor for Hg 2+ , which combines a calixarene derivative with a BODIPY core as a fluorescent reporter, is described. The remarkable change in its fluorogenic properties in DMSO and CHCl 3 has been analyzed. A study of its spectral properties on dilution, along with molecular modeling studies, allowed us to explain that this behavior involves the formation of a J-dimer, as well as how the sensing mechanism of Hg 2+ proceeds., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)