Abstract
The BF4− anion is characterised by weak Lewis base properties; it is usually classified as a “non-coordinating anion”. The searches through the Cambridge Structural Database (CSD) were performed and it was found that the BF4− anion often occurs in crystal structures and it is involved in numerous intermolecular interactions; hydrogen bonds are the majority of them. The hydrogen bonds involving the BF4− anion as a proton acceptor are closer to linearity with the increase of the strength of interaction that is in line with the tendency known for other hydrogen bonds. However, even for short contacts between the proton and the Lewis base centre, slight deviations from linearity occur. The MP2/aug-cc-pVTZ calculations on the BF4−…HCN complex and on the BF4−…(HCN)4 cluster were also carried out to characterise corresponding C-H…F hydrogen bonds; such interactions often occur in crystal structures.
Highlights
The term ‘non-coordinating anion” was used in earlier [1,2,3,4] and in more recent studies [5] to characterise anions that do not interact with other species
The aim of this study is to check in detail the occurrence of hydrogen bonded arrangements with the BF4 − anion acting as the Lewis base unit; this is based on the Cambridge Structural Database (CSD) searches, including the recent updates of this base
Three CSD searches for the A-H . . . F (A = C, N and O) arrangements were performed here with the F-centre belonging to the BF4 − anion
Summary
The term ‘non-coordinating anion” was used in earlier [1,2,3,4] and in more recent studies [5] to characterise anions that do not interact with other species. It has been described that this term may be misleading since such anions known before as not able to be coordinated reveal properties to interact, at least weakly, with Lewis acid centres [1,4]. The BF4 − species was often mentioned among the other so-called “non-coordinating” or “poorly-coordinating”anions [1]. It was mentioned that numerous crystal structures show the latter anion as a monodentate or bidentate bridging ligand [1]. It has been recognized early that the BF4 − ion is not a completely non-nucleophilic species [7]; its reactivity was analysed recently [8], especially the reactions where the BF4 − ion acts as a nucleophilic fluoride source were discussed in detail
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