Aromaticity of pentafulvene's complexes with alkaline metal atoms

Geometry of pentafulvene's complexes with the atoms of the first group of Periodic Table (Li, Na, K, Rb, and Cs) are optimized at the B3LYP/6-311 ++G(d, p) level of theory. Two kinds of complexes are considered: (1) those which are in equilibrium geometry, and (2) complexes which are formed by gradual change in the distance between the metal atom and penta-fulvene ring. Aromaticities of the considered complexes in their equilibrium geometries are investigated using different indices included geometry-based (HOMA), magnetism-based (NICS, NICS(1), and NICS(1)zz), pi-electron count-based (pEDA), and electronic-based (Shannon Aromaticity; (SA)) indices. All indices are well correlated to each other and to some local (atomic charges) and global (binding-energy) properties, with one exception-HOMA. The same regularity is observed for non-equilibrium complexes.