Characterizations of novel binuclear alkaline-earth metallocenes: M2(n ⁵-E₅)2 (M = Be, Mg and Ca; E = P and As)

A series of novel binuclear alkaline-earth metallocenes M2(5-E5)2 (M = Be, Mg and Ca; E = P and As) have been studied at the B3LYP/6-311G* and BP86/6-311G* levels of density functional theory. The bonding between the two alkaline earth metal atoms and the bonding between the alkaline earth metal and the five-membered ring are investigated. Natural Bonding Orbital (NBO) analysis shows that the bonding between the metal atom and the five-membered ring is predominantly ionic and each metal atom is in its +1 oxidation state. The lighter alkaline earth metal has stronger bonding in both M2(5-P5)2 and M2(5-As5)2. A single metal-metal bonding exists between the two metal atoms. For the same alkaline earth metal, the metal-metal bond in M2(5-As5)2 is weaker than that in M2(5-P5). Nucleus independent chemical shift (NICS) values confirm that the planar [image omitted] exhibits characteristics of aromaticity in these M2(n-E5)2 species. The NICS values M2(5-P5)2 are larger than those of the M2(5-As5)2 analogues. The NICS(0.0) and NICS(1.0), values are in the order of Be2(5-E5)2 Mg2(5-E5)2 Ca2(5-E5)2.