Single-site transition metal centers at surfaces are of growing interest in developing new chemical functionality. We study a redox assembly approach using a metal-organic coordination strategy to achieve greater complexity. Here, we report new results in which some structural order is exchanged for variation in electronic character of the metal sites. A tetrazine with two electron withdrawing pyrimidinyl substituents was co-deposited with platinum metal on the Au(100) surface. In a 2:1 metal:ligand ratio, only half of the platinum is oxidized to the +2 oxidation state, with the remainder coordinating to the ligand without charge transfer, as Pt0. The resultant Pt0/PtII mixed valence structure is thought to form due to the aversion of the ligand towards a four-electron reduction and the strong preference of Pt towards 0 and +2 oxidation states. Scanning tunneling microscopy reveals irregular chain structures that are attributed to the mixture of Pt valence states, each with distinct local coordination geometries. Tetraethyltetra-aza-anthraquinone (EtTAAQ), utilizes a quinone backbone with adjacent pyrazine rings to generate four symmetric binding pockets. EtTAAQ has the capacity for up to a four-electron reduction, enabling the possibility for bimetallic sites between ligands. Surface studies conducted on the Au(111) surface demonstrate TAAQ complexation with Fe at different stoichiometric ratios of Fe:TAAQ as Fe 2p core level shifts. The formation of a surface structure seen in STM images also provides evidence that metal-ligand complexation has occurred, even though multiple binding motifs are present, which produce meandering chain structures. These studies advance our understanding of metal-organic complexation in surface environments toward greater complexity and chemical functionality.

Complexity in metal-organic redox assembly at surfaces: Bimetallic sites and redox isomer surface structures

2019 Spring National Meeting

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