Interplay between Electronic, Magnetic, and Transport Properties in Metal Organic–Radical Frameworks

The
development of modern electronic and spintronic technologies
depends in large part on the ability to design materials exhibiting
switchable magnetic and electrical properties. Here, motivated by
the successful demonstration of reversible redox switching of magnetic
order and electrical conductivity in two-dimensional metal–organic
frameworks (MOFs) based on benzoquinoid linkers, we perform hybrid
density functional theory calculations to investigate this phenomenon
at the atomistic level. Electronic, magnetic, and charge transport
properties have been systematically investigated for oxidized and
reduced forms of Mn and Fe benzoquinoid frameworks (i.e., (Me4N)2[Mn2L3], (Me4N)2[Fe2L3] and Na3(Me4N)2[Mn2L3], Na­(Me4N)2[Fe2L3], respectively, with deprotonated
chloranilic acid as L). We demonstrate that the experimentally observed
large increase in electronic conductivity upon ligand-centered reduction
in the Mn MOF (109 S·cm–1) is due
to cooperative effects arising from band gap reduction and the presence
of electrons with lower effective mass. Superior conductivity (by
at least 3 orders of magnitude) of the redox pair of the Fe benzoquinoid
framework as compared to the Mn analogue stems from similar factors
and, notably, a large increase in electron delocalization for the
reduced Fe compound.