Self-Assembly of Ordered Pt Complexes with Bidentate Ligands from Solution onto Graphite Surfaces

Abstract

Metal–ligand coordination offers a versatile platform for programming on-surface nanostructures with well-defined geometries and tunable coordination environments that are directly relevant to the design of ligand-stabilized single-atom catalysts. While numerous studies under ultrahigh vacuum conditions have established the principles governing on-surface metal–ligand coordination on well-defined crystalline substrates, similar coordination systems at the solution/solid interface remain far less explored, despite their direct relevance to solution-phase chemistry and catalytic processes. Here, we investigate the self-assembly structures of 1,10-phenanthroline-5,6-dione (PDO) coordinated to Pt ions on highly oriented pyrolytic graphite (HOPG) using ambient scanning tunneling microscopy (STM). We demonstrate that monolayer assemblies of PDO and/or PDO-Pt complexes can be formed from solution phase PDO and Pt precursor salts. STM analysis reveals that the on-surface assembly structures depend on the ligand-to-metal stoichiometry in the solution during assembly. The PDO ligand without metal self-assembles into an ordered layer. Distinct 1:1 coordination PDO-Pt one-dimensional chains, 2:1 coordination (PDO)₂-Pt assembly, and mixed (PDO)₂-Pt/PDO phases are observed, indicating that Pt coordination geometry and packing order could be programmed through stoichiometric control. These findings provide fundamental insight for designing PDO-based single-site metal centers on support surfaces, thereby offering a model system for understanding on-surface structures of ligand-coordinated metal complexes.