TRANSITION-METAL DIATOMICS - MN-2, MN-2+, CRMN

The Mn2 molecule, exhibiting antiferromagnetic exchange coupling between the 3d5 electrons on each atom, has been investigated further in cyclopropane matrices at temperatures ranging from 12 to 110 K. This allowed electron-spin-resonance spectra to be observed in the higher spin states S = 4 and 5 and confirmed the previous deduction of van der Waals bonding with r≅3.4 Å. In addition, the derived anisotropic parameters D s suggest that exchange striction (as previously observed in solids) is occurring such that r varies from about 3.2 to 3.6 Å in the S = 0 to S = 5 states, with a corresponding variation in the exchange coupling constant J in these states. The removal of one electron to produce Mn2 + results in the formation of a single σ bond and high-spin coupling among the remaining 11 unpaired electrons to yield a 12Σ; ground state. In contrast, its isoelectronic counterpart CrMn is found to have a 4Σ ground state and multiple bonding, more in accord with expectations for a diatomic between Cr2 and Mn2. © 1990 American Institute of Physics.