Comparison of Rh24L124 with a physical mixture of Rh24(L1)24 and Cu24(L1)24 confirmed that spatially separated Cu2 PWs showed no perceptible influence on the performance of Rh2 PWs in propene hydrogenation (Supplementary Fig. ). We observed a clear difference, however, in the performance of Rh0.50Cu0.50-kofo-4, which was prepared via mechanochemical synthesis, and a 1:1 physical mixture of Rh24(L1)24 and Cu24(L1)24. A batch of Rh0.50Cu0.50-kofo-4 in which the grinding time was reduced led to a propene hydrogenation rate intermediate between kofo-4 and the physical mixture, which is consistent with the activity of Rh2 centers changing as a function of intermixing with Cu2 centers (Supplementary Fig. ). To test the synthetic reproducibility and the effect of surface area variations, we synthesized a second batch of all MOP samples and subjected them to distinct activation protocols prior to evaluation in propene hydrogenation (Supplementary Figs. ). An identical trend for the relative hydrogenation performance (kofo-4 > kofo-3 > kofo-2) was again obtained (Supplementary Fig. ) even though the non-optimized activation protocol led to notable variations in the surface areas of different structomers. The spatial arrangement of Rh2 PWs was thus a better predictor of the materials' efficiency in promoting propene hydrogenation than the surface area (Supplementary Figs. ). We next extended our studies to Rh0.50Cu0.50 MOF structomers. To provide a reference point, we compared pure rhodium MOP and MOFs with L1 = BDC-OH and L2 = bipy or dabco, which showed that the dabco-containing MOF led to the fastest propene conversion, followed by the MOP, and finally the bipy-containing MOF (Supplementary Fig. ). Only structomers with level 4 mixing reproduced the relative activity trend observed with pure Rh samples, while other structomers showed notably disparate activity trends of RhCu-KOFO-2-dabco > RhCu-KOFO-2-bipy >> RhCu-kofo-2, and RhCu-KOFO-3dabco > RhCu-KOFO-3-bipy ~ RhCu-kofo-3.When comparing the two series of compositionally identical materials, Rh0.50Cu0.50-KOFO-x-bipy (x = 2, 3, 4) and Rh0.50Cu0.50-KOFO-x-dabco (x = 2, 3, 4), we found that the reaction rates increased in the order KOFO-3 < KOFO-4 < KOFO-2.