Understanding chemical bonding in second row diatomics has been central to elucidating the basics of bonding itself.1 Bond strength and number of bonds are two factors that decide the reactivity of molecules. While bond strengths have been theoretically computed accurately and experimentally determined, the number of bonds has been a more contentious issue especially for complicated multi-reference systems such as C2.2,3 We have developed an experimentally verifiable approach to determine the number of bonds from excited spin state potential energy surfaces. On applying this to a series of hetero-diatomics of the second row, we obtain the surprising phenomena of an inverted charge transfer ionic state after the covalent bonds in the species are broken via higher spin states. These ionic states are ubiquitous in all heterodiatomics and quite contrary to our expectations in non-metallic systems.
Subverting covalency gives rise to ionic bonding in high spin states of heterodiatomics