Aluminum is an essential part of many important scientific and industrial technologies. For many of these applications, aluminum can be simply described as an electropositive, Lewis acidic metal. However, new characterization tools are needed to support detailed electronic structure models of complex aluminum molecules and materials. Metal K-edge X-ray Absorption Near Edge Spectroscopy (XANES) is an established technique for evaluating electronic structure in bioinorganic and inorganic compounds. Pre-edge peaks in the XANES region correspond to bound state transitions between core and unoccupied orbitals. Therefore, by comparing pre-edge features to established references, information can be gathered on the electronic structure of a system such as oxidation state, ligand environment, and symmetry. However, there is little precedent for the measurement and interpretation of Al K-edge XANES for molecules and materials.Here, we discuss an effort to explore Al K-edge XANES as a unique probe of electronic structure in a well-defined series of aluminum coordination complexes with varying oxidation states and ligand environments. Measurements were conducted in transmission using a Scanning Transmission X-ray Microscope (STXM) on Advanced Light Source Beamline 11.0.2. Initial efforts began with a landmark low-valent aluminum (I) cluster, [(C5Me5)Al]4. The Al K-edge XANES spectra were also compared with Al[{N(Dipp)C(Me)}2CH], which also possesses aluminum in the +1 formal oxidation state but has no Al�Al bonds. Through a combination of molecular orbital and DFT calculations, the spectra of these Al(I) compounds and Al(III) analogues were fully assigned, and the effect of oxidation state was measured. These studies provide a foundation for further analysis of the electronic structure of aluminum compounds through Al K-edge XANES.

X-ray spectroscopic investigations of electronic structure in aluminum coordination complexes

248th National Meeting (2014)

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