Modeling Covalency with Molecular Analogues of Conductive Metal-Organic Frameworks

2-D metal-organic frameworks (MOFs) with metallic or semiconductor charge mobilities continue to expand with ever increasing diversity in their molecular composition and hence orbital interactions. Predicting the charge transport behavior emerging from these structures presents many challenges, such as the need for plane-wave calculations rather than molecular intuition. To evaluate the utility of a local, molecular orbital perspective in rationalizing 2-D MOF conductivity, here we report that molecular analogues of common building blocks of metal-organic frameworks were modeled using density functional theory (DFT) and Atoms-In-Molecules analysis. Delocalization index, Löwdin spin population, Mayer bond order and nucleus-independent chemical shift (NICS) values were compared across all models, revealing increased electronic delocalization of sulfur-based molecular systems versus their oxygen analogues. The models corresponding to extended frameworks with high reported experimental conductivities, Cu 3 (BHT) and Ni 3 (BHT) 2 , demonstrated a closer match in delocalization index, well-distributed spin population and increased bond orders relative to their oxygen analogues. NICS analysis showed a partial decrease in the aromaticity of sulfur-based systems, rather than either the preservation or total disruption of aromaticity observed in oxygen-based models. These computational metrics were applied to N-heterocyclic benzimidazolium dithiocarboxylate ligands as a predictor of conductivity in a novel framework material. These findings predict strong covalency and hence conductivity in a potential copper-based NHC-BICS 2 extended framework.