Mechanistic\nInsight into the Formation and Deposition\nof Conductive, Layered Metal–Organic Framework Nanocrystals

This\npaper describes the use of the layered conductive metal–organic\nframework (MOF) (nickel)<sub>3</sub>-(hexahydroxytriphenylene)<sub>2</sub> [Ni<sub>3</sub>(HHTP)<sub>2</sub>] as a model system for\nunderstanding the process of self-assembly within this class of materials.\nWe confirm and quantify experimentally the role of the oxidant in\nthe synthetic process. Monitoring the deposition of Ni<sub>3</sub>(HHTP)<sub>2</sub> with <i>in situ</i> infrared spectroscopy\nrevealed that MOF formation is characterized by an initial induction\nperiod, followed by linear growth with respect to time. The presence\nand identity of oxidizing agents is critical for the coordination-driven\nself-assembly of these materials and impacts both the length of the\ninduction period and the observed rate of MOF growth. A large excess\nof hydrogen peroxide results in a 2× increase in the observed\ndeposition rate (9.6 ± 6.8 × 10<sup>–4</sup> vs 5.0\n± 2.8 × 10<sup>–4</sup> min<sup>–1</sup>)\nover standard reaction conditions, but leads to the formation of large,\nirregularly shaped particles. Slower deposition rates in the presence\nof oxygen favor the formation of uniformly sized nanorods (98 ±\n38 × 25 ± 6 nm). These quantitative insights into the mechanism\nof HHTP-based MOF formation provide valuable information about the\nfundamental aspects of coordination and polymerization that are critical\nfor nanoscale crystal engineering of structure–property relationships\nin this class of materials.