Scanning probe microscopy of metal–organic coordination systems: characterization of monolayers, single crystals, discrete architectures

Metal–organic coordination is omnipresent in a number of functional materials. Such systems are highly diverse in terms of their composition, complexity, and dimensionality. They include two-dimensional (2D) and three-dimensional (3D) structures ranging from monolayers of metal–organic coordination networks (MOCNs) physisorbed on solid surfaces, to crystalline metal–organic frameworks (MOFs), to discrete metallosupramolecular architectures (DMSAs). The use of these metal–organic materials in a wide variety of applications has been demonstrated, showing promise for their incorporation into emerging technologies. Several design strategies have been developed for the fabrication of MOCNs, MOFs, and DMSAs exhibiting a diverse array of structures, enabling precise control over their functional properties. As these strategies are designed at the molecular level, there has been considerable interest in the nanoscale resolution imaging of metal–organic coordination systems across different length scales. This review provides a glimpse of recent progress in the nanoscale characterization of metal–organic coordination systems using scanning probe microscopy (SPM). Systems ranging from surface-confined MOCN monolayers, to MOF thin films, surfaces of MOF single crystals, and DMSAs are discussed. Specifically, we discuss the contribution of scanning tunneling microscopy (STM), atomic force microscopy (AFM), and techniques that combine SPM with spectroscopic methods to obtain high-resolution chemical information, toward the nanoscale structural characterization of multinuclear metal–organic assemblies.