IS CN- SIGNIFICANTLY ANISOTROPIC? COMPARISON OF CN- VS Cl-: CLUSTERING WITH HCN AND CONDENSED-PHASE THERMOCHEMISTRY

Article abstract of DOI:10.1021/j100321a009

Pulsed high-pressure mass spectrometry shows that the clustering thermochemistry of the CN^- anion with HCN behaves in a fashion quite similar to Cl^-, Br^-, and I^-, indicating CN^- acts very much like a spherical ion with radius slightly larger than Cl^-.The falloff of binding energy with increasing number of HCN molecules provides no evidence of any significant shell structure.Ab initio calculations support the low degree of anisotropy of CN^-.While the most stable complex with HCN is CN^-..HCN, there is little loss of stability when CN^- and HCN do not form a linear complex.The central CN^- may rotate almost freely in clusters with two or three molecules of HCN, suggesting a nearly spherical character for the anion within these complexes.The calculations also confirm the lack of shell structure since complexes of the type CN^-..HCN..HCN are nearly equal in energy to NCH..CN^-..HCN.The behavior of CN^- as a nearly spherical anion is further supportedby a survey of condensed-phase thermochemistry wherein properties such as lattice energies and solvation energies are closely matched by Cl^-.