Abstract
The isotopically enriched cyanide anion, (13C≡15N)−, has a great potential as the NMR probe of non-covalent interactions. However, hydrogen cyanide is highly toxic and can decompose explosively. It is therefore desirable to be able to theoretically estimate any valuable results of certain experiments in advance in order to carry out experimental studies only for the most suitable molecular systems. We report the effect of hydrogen bonding on NMR properties of 15N≡13CH···X and 13C≡15NH···X hydrogen bonding complexes in solution, where X = 19F, 15N, and O=31P, calculated at the ωB97XD/def2tzvp and the polarizable continuum model (PCM) approximations. In many cases, the isotropic 13C and 15N chemical shieldings of the cyanide anion are not the most informative NMR properties of such complexes. Instead, the anisotropy of these chemical shieldings and the values of scalar coupling constants, including those across hydrogen bonds, can be used to characterize the geometry of such complexes in solids and solutions. 1J(15N13C) strongly correlates with the length of the N≡C bond.
Highlights
The opposite situation is observed for complexes with pyridine-4-amine and 1-azabicyclo[2.2.2]octane, Figure 1e,f. This result is associated with the fact that the energy of hydrogen cyanide is 65 kJ/mol lower than the energy of hydrogen isocyanide, Figure 1a
One can say that the binding energy of the CNH···X form is much higher [89], and this form may be stable if the carbon atom participates in another covalent or non-covalent interaction [43,90,91,92]
The analysis of the energetically most favorable structures with the hydrogen bonded cyanide anion at different conditions is beyond the scope of this study
Summary
Hydrogen cyanide and cyanide salts are ubiquitous compounds. They can be both the starting ingredients of life [1,2] and the reason for its end [3,4,5]. The most distinctive feature of the cyanide anion is that its two ends are capable of almost equal non-covalent interactions [6]. Its orientation in crystalline cyanide salts is often disordered [7,8,9,10,11]
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