Scheme 1. Dependence of particle sizes on metal-to-linker solution stoichiometry. (a) In the proposed seesaw model of MOF nanocrystal growth (solid line), particle sizes minimize at maximally imbalanced metal-to-linker ratios and at low proton concentrations (ε). The seesaw arises from acidic ligands acting as capping agents in region I and as acids in region II. Conversely, rates of bulk ionic crystal growth (dashed line) maximizes at monomer solution stoichiometries that match the bulk crystal (σ). (b) Observation of the seesaw relationship between NH2-MIL-125 particle sizes and modulator equivalents, reproduced from ref. 19.
