Metal-organic frameworks (MOF) have the potential to act as a self-contained, atomistic environment for the systematic exploration of chemical reactions, luminescence, semiconduction, spin-state switching, exciton diffusion, etc. The modular design of these rigid metal-organic materials provides control over molecular structure and orientation, lattice interactions (on multiple length scales), and electronic structure and transitions. Our approach is to 1) delineate and define the metal-organic bonds, using <i>ab initio</i> electron densities, 2) correlate the chemical and structural information to electronic excitation, and 3) translate the electronic structure of the molecular system to the extended framework. Starting with the paddlewheel-shaped metal-organic complex, containing a bimetallic transition-metal complex, we find that the structural parameters depend mostly on the inclusion of diffuse functions in the basis set. The BP86 functional is chosen for its success with transition metal clusters, and the associated errors are compared with those of B3LYP and M06-L. The paddlewheel complex contains two open coordination sites, which, when filled, participate in catalysis and increase electrical conductivity. Understanding how the potential associated with MOF coordination sites is affected by the structure, orientation, and choice of organic component will contribute to illuminating routes for function-oriented design. The photoluminescence of many MOFs results from the decay of the electronic states isolated on the organic linker (ligand) molecules. The energetic position of these excited states, however, depends on the the environment. Our calculations show that the ligand-to-metal charge transfer states are energetically accessible and can particpate in the competing process of electron transfer. By calculating electronic densities directly, we can begin to place molecular calculations on the same computational footing as band structure and begin to realize and assess the semiconducting properties of MOFs in terms of their chemical composition and structure.

Electronic excitation of metal-organic frameworks

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.