Insight into the Oriented Growth of Surface-Attached Metal-Organic Frameworks: Surface Functionality, Deposition Temperature, and First Layer Order

The layer-by-layer growth of a surface-attached metal-organic framework (SURMOF), [Cu₂(F₄bdc)₂(dabco)] (F₄bdc = tetrafluorobenzene-1,4-dicarboxylate and dabco = 1,4-diazabicyclo-[2.2.2]octane), on carboxylate- and pyridine-terminated surfaces has been investigated by various surface characterization techniques. Particular attention was paid to the dependency of the crystal orientation and morphology on surface functionality, deposition temperature, and first layer order. For the fully oriented deposition of SURMOFs, not only a suitable surface chemistry but also the appropriate temperature has to be chosen. In the case of carboxylate-terminated surfaces, the expected [100] oriented [Cu₂(F₄bdc)₂(dabco)] SURMOF can be achieved at low temperatures (5°C). In contrast, the predicted [001] oriented SURMOF on pyridine-terminated surface was obtained only at high deposition temperatures (60°C). Interestingly, we found that rearrangement processes in the very first layer determine the final orientation (distribution) of the growing crystals. These effects could be explained by a surprisingly hampered substitution at the apical position of the Cu₂-paddle wheel units, which requires significant thermal activation, as supported by quantum-chemical calculations. (Figure Presented).