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Abstract
A theoretical study and Cambridge Structural Database (CSD) search of dinuclear Ag(I) pyrazolates interactions with Lewis bases were carried out and the effect of the substituents and ligands on the structure and on the aromaticity were analyzed. A relationship between the intramolecular Ag–Ag distance and stability was found in the unsubstituted system, which indicates a destabilization at longer distances compensated by ligands upon complexation. It was also observed that the asymmetrical interaction with phosphines as ligands increases the Ag–Ag distance. This increase is dramatically higher when two simultaneous PH3 ligands are taken into account. The calculated 109Ag chemical shielding shows variation up to 1200 ppm due to the complexation. Calculations showed that six-membered rings possessed non-aromatic character while pyrazole rings do not change their aromatic character significantly upon complexation.
Highlights
Non-covalent interactions (NCIs) are present in complexes formed between two or more Lewis acids and Lewis bases
In this paper we will report the study of nineteen compounds corresponding to the general formula depicted in Scheme 1 and named by a simple code that allows to easy identification: (R-pzAg)2 (L)n
For instance, (4NO2 pzAg)2 (PH3 )4 corresponds to the (4-nitropyrazole:Ag)2 cyclic structure with four phosphines interacting with the silver atoms
Summary
Non-covalent interactions (NCIs) are present in complexes formed between two or more Lewis acids and Lewis bases. A Lewis base (LB) or a LB motif is associated with a region of space where there exists an excess of negative charge (i.e., electron density) in the proximity of an atom or atoms within a molecule This is predominant in anions and in some neutral molecules such as those that exhibit lone pairs (LP: carbenes, amines, phosphines, N-oxides, etc.), multiple bonds (olefins, acetylenes, benzenes and other aromatic molecules), single bonds (alkanes, dihydrogen, etc.), radicals, metals (rarely), etc. A Lewis acid (LA) is associated with a region of space where there is an excess of positive charge (in other words a deficit of negative charge or electron deficiency) in the proximity of an atom or atoms in a molecule This can be found in cations, molecules or atoms exhibiting σ- and π-holes and metals (frequently). It was latter extended to other situations, for example, the π-hole [6,7,8,9,10,11] (positive electrostatic potential perpendicular to an atom of a molecular framework) and lone pair hole (similar to σ-hole but along the atom–lone pair direction) [12,13,14]
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