Tuning the Crystallinity of a Metal-Organic Coordination Network at the Liquid-Solid Interface

Single layered metal-organic coordination networks (MOCNs) are gaining attention thanks to their unique electronic and magnetic properties. The presence of coordinatively unsaturated metal sites within their structures provides additional binding locations for substrates in catalytic processes. Consequently, MOCNs fabricated on solid surfaces are emerging as promising candidates for use in solution-based heterogeneous applications. The bottom-up synthesis of such surface-supported MOCNs requires a rigorous design by utilizing two-dimensional (2D) crystal engineering. However, a comprehensive description of the factors governing their synthesis at the liquid-solid interface is still missing, resulting in only a few reported examples. In this work, we use scanning tunneling microscopy (STM) at the liquid-solid interface to reveal the effect of the choice of solvent, concentration, and temperature on the structure of a surface-supported MOCN constituted by a tritopic ligand containing pyridyl moieties and trans-protected Pd(II) cations. A quantitative analysis of the network's crystallinity is presented. Furthermore, the impact of the synthetic pathway is investigated and a qualitative description of the growth mechanism is provided. Finally, the porosity of the extended honeycomb network is examined by studying the adsorption of guest molecules in its pores.