The Structure of Alkali Metal Derivatives of Azoles: N-sigma versus pi Structures
High level ab initio calculations have been used to study the relative stability of N−σ and π configurations of the neutral alkaline derivatives of azoles. The N−σ structure is the one normally expected for nonionized azolate salts. However, the results show that in the case of the pyrrole and imidazole the π configuration is more stable than the N−σ one. The preference of the N−σ vs π configurations is related to the presence or the absence of two contiguous nitrogen atoms in the azole ring. A search in the CSD shows that some pyrrolate and imidazolate salts exist in solid phase in the π configuration.