N‐σ versus π configuration in mono‐ and bis‐pyrrole and imidazole derivatives of alkaline earth metals

A theoretical study of the preferred N‐σ or π configuration of the mono‐ and bis‐pyrrole and imidazole derivatives of alkaline earth metals has been carried by means of DFT and ab initio methods, up to G2 computational level. The energetic results show that the beryllium derivatives prefer the N‐σ configuration while the calcium ones prefer the π one. In the case of magnesium, both configurations present similar stability. The calculated dissociation enthalpies correspond to the fact that the metallic atom is strongly bonded to the azoles in both configurations. The NBO analysis shows that the systems can be considered as formed by the azolates interacting with the charged metallic atom and thus the Natural Energy Decomposition Analysis (NEDA) indicates that the main attractive force is the electrostatic. Copyright © 2009 John Wiley & Sons, Ltd.