Mapping metal sequences in MOFs Most metal-organic frameworks (MOFs) contain just one type of metal in the nodes connecting the organic linkers. Multivariate MOFs containing multiple metals can offer greater selectivity in sorption and catalytic properties, but determining the arrangement of metals in these materials is challenging. Ji et al. found that atom-probe tomography can reveal sequences of metals for MOF-74 single crystals containing combinations of cobalt, cadmium, lead, and manganese ions. In this MOF, the metals form oxide rods that are connected by the organic linker into a honeycomb lattice. The obtained sequences, which were tuned by varying the proportion of metals and synthesis temperature, could be random, short and long duplicates, and single metal insertions. Science , this issue p. 674