Dataset for Linker Conformational Flexibility in the Assembly of Hafnium Metal–Organic Layers

Reticular chemistry provides a powerful way to select building units for desired network topology. It does not, however, tell a synthetic chemist which concentrations of metal precursor, linker, water, acid, and base will produce that network as a crystalline material. Linker conformation may be one source of consideration. Conformational flexibility makes the required connecting orientation accessible, but the same flexibility also increases chances of unwanted linkage that asks for more reversible error-correcting linking conditions. We tested the relationship between framework synthetic accessibility and conformational flexibility of the linkers in hafnium metal–organic layers (MOLs) assembled from six-connected Hf6(μ3-O)4(μ3-OH)4 nodes and four tritopic linkers: benzene-1,3,5-tricarboxylic acid (H3BTC), 4,4′,4″-nitrilotribenzoic acid (H3NTB), 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB), and 1,3,5-tris(4′-carboxy[1,1′-biphenyl]-4-yl)benzene (H3BBC). The linkers have different torsional pathways to reach the required carboxylate orientation. Automated synthesis and powder X-ray diffraction supplied 201 BTC, 148 NTB, 148 BTB, and 134 BBC outcomes while five reagent concentrations were varied. Machine learning on the datasets established phase diagrams that show 92.7%, 68.3%, and 3.3% fractions of the synthetic space yield MOL formation for NTB, BTB, and BBC, respectively, at a probability cutoff of 0.5; none of the Hf–BTC formulations led to MOL formation. Torsional profiles show that NTB and BTB reach the node-imposed angle by a single low-energy C‒C bond rotation, while BBC must distribute the rotation across two serial bonds, and BTC requires a higher energy terminal-group rotation. The combined synthesis map and molecular calculations show the importance of linker conformation to form the designed geometry.