Ultrashort Mn-Mn Bonds in Organometallic Complexes

Manganese metallocenes larger than the experimentally produced sandwiched MnBz2 compound are studied using several density functional theory methods. First, we show that the lowest energy structures have Mn clusters surrounded by benzene molecules, in so-called rice-ball structures. We then find a strikingly short bond length of 1.8 Å between pairs of Mn atoms, accompanied by magnetism depletion. The ultrashort bond lengths are related to Bz molecules caging a pair of Mn atoms, leading to a Mn-Mn triple bond. This effect is also found when replacing benzenes by other molecules such as borazine or cyclopentadiene. The stability of the Mn-Mn bond for Mn2Bz2 is further investigated using dissociation energy curves. For each spin configuration, the energy versus distance plot shows different spin minima with barriers, which must be overcome to synthesize larger Mn-Bz complexes. © 2017 American Chemical Society.

Benzene; Binary alloys; Bond length; Bond strength (chemical); Density functional theory; Manganese compounds; Molecules; Organometallics; Structure (composition); Synthesis (chemical); Benzene molecules; Cyclopentadienes; Density functional theory methods; Dissociation energies; Lowest energy structure; Organo-metallic complexes; Spin configurations; Triple bonds; Manganese

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