Selective Coordination Bonding in Metallo‐Supramolecular Systems on Surfaces

The confinement of molecular species in nanoscale environments strongly modifies the interaction pathways compared to homogenous, three-dimensional (bulk) conditions. A new field of chemistry featuring weak interactions, coordination bonding, and covalent chemistry at solid surfaces has recently emerged. In particular, the combination of surface-confined chemistry and scanning probe techniques with subnanometer resolution allows immediate insights into molecular self-organization processes on the nanometer level. Extended monolayers of open, two-dimensional (2D) coordination networks with high organizational periodicity, controlled symmetries, and modular dimensionality have been achieved by using designed, self-instructedmolecular building blocks. The deposition of mixtures of precursor molecules has led to more sophisticated architectures, mainly built on weak intermolecular interactions or weak interactions in combination with coordination bonding, that is, hierarchical motifs. The cooperative assembly of instructed mixtures of molecular bricks enables a high degree of structural control and functionality, for example, the stability and ordering of primary structures can be increased, or the dimensionality and geometry of supramolecular structures can be steered. Observations of molecular-level self-recognition and error correction have demonstrated collective dynamics in surface-confined supramolecular systems. A grand challenge in materials chemistry is the capability to design adaptive materials, that is, to develop systemic methods for tailored structure and function. To exploit the opportunities of systemic chemistry, a detailed understanding of the selectivity in the interaction mechanisms of molecular mixtures, if possible by direct studies at the single-molecule level, is of pivotal interest. Herein, we report on the observation of supramolecular selectivity in the simultaneous coordinative interaction of two different molecular ligands, aromatic bipyrimidines and dicarboxylic acids, with Cu and Fe atoms resulting in a selfsegregation into two distinct, surface-confined coordination network domains. The random mixture of ligands and metals separates into subdomains of pure bipyrimidine–Cu and carboxylate–Fe networks, while heteroleptic ligand combinations, though feasible, are not observed. Each 2D coordination network exhibits a tetragonal geometry with metal atom coordination nodes, but expresses unique molecular composition and spatial organization. The molecular components PBP (5,5’-bis(4-pyridyl)(2,2’bipyrimidine)) and BDA (1,4’-biphenyl-dicarboxylic acid, see Scheme 1) are co-evaporated in a 1:1 number ratio onto a Cu(100) substrate at room temperature under ultra-high vacuum (UHV) conditions. At this temperature, a diffusing copper adatom gas is present at the Cu(100) surface, which has been shown to be available for the formation of extended