The thiocyanate anion as a polydentate halogen bond acceptor

Pascal Cauliez (1) , Victor Polo (2) , Thierry Roisnel (1) , Rosa Llhusar (2) , Marc Fourmigué (1)

1 ISCR - Institut des Sciences Chimiques de Rennes
2 Departament of Quimica Fisica i Analitica

Co-crystallisation of the Et4N+ or n-Bu4N+ salts of the thiocyanate anion with o-, m- and p-diodoperfluorobenzene or the sym-trifluorotriiodobenzene allowed for the isolation of six different salts which were structurally characterized by single crystal X-ray diffraction. Halogen bonding interactions are observed between the neutral iodinated molecules acting as halogen bond donors and the S or N ends of the thiocyanate anion, with a variety of bonding modes (terminal as well as bridging), and characterised by short I(N,S) contacts and linear C-I(N,S) motifs. On the other hand, the IN≡C angles present deviations from linearity (145-170°) while the IS-C angles are close to 90°, revealing a type II halogen bond interaction with the S atom acting as pseudo halogen. The observation of structures where only the S or the N atom are engaged in halogen bonding suggests that the two coordination modes are close in energy, as confirmed by DFT calculations and ELF analysis which give also a rationale for the observed structural preferences. This bidentate nature of the SCN− anion in halogen bonding interactions is reminiscent of its various coordination modes with the Cd2+ cation, best understood in terms of the hard-soft acid-base concept.

Domaines: Chimie organique

Pascal Cauliez, Victor Polo, Thierry Roisnel, Rosa Llhusar, Marc Fourmigué. The thiocyanate anion as a polydentate halogen bond acceptor. CrystEngComm, 2010, 12, pp.558-566. ⟨10.1039/b913559f⟩. ⟨hal-00468289⟩