ΔGcalc > 20 kJ•mol -1 per dimer unit could not be prepared (Supplementary Fig. ), a single mixing level could be accessed selectively even if competing arrangements were close to isoenergetic, resulting in excellent fidelity. The Rh distribution appeared homogeneous in EDX maps of both mixing levels 2 and 3, but the structomers' catalytic performance in propene hydrogenation displayed substantial differences with Rh0.50Cu0.50-kofo-2 << Rh0.50Cu0.50-kofo-3 and Rh0.50Cu0.50-KOFO-2 >> Rh0.50Cu0.50-KOFO-3. Crucially, structural differences between Rh environments in level 2 and level 3 structomers only appear at a distance of 8 or more chemical bonds, so that they would commonly be regarded as isolated sites . Selective access to a particular structomer can thus ensure that the measured catalytic activity is not a weighted average of the performance of active sites in different spatial environments, which may vary substantially. Going forward, an in-depth analysis will be carried out to understand the mechanistic origin of the observed reactivity differences in olefin hydrogenation and facilitate a translation of structomer-based performance optimization to catalyst systems of increased practical relevance. A variety of structurally distinct metal dimers, clusters and cages have been reported, so that an extension of mobility-tuned synthesis to optimize the spatial correlation for other metal centers and coordination geometries can readily be envisaged . The EPR-based characterization approach we developed not only permits facile distinction of different metal arrangements, but also provides direct feedback on the degree of interaction between electron spins present in different structomers. In addition to the choice of metal arrangement, the electronic communication could be varied via the choice of L2, which was used to tune the interaction between distant Cu centers independently from the interactions between proximal Cu centers.