Mechanistic Insight into the Formation and Deposition of Conductive, Layered Metal–Organic Framework Nanocrystals

This paper describes the use of the layered conductive metal-organic framework (MOF) (nickel)₃-(hexahydroxytriphenylene)₂ [Ni₃(HHTP)₂] as a model system for understanding the process of self-assembly within this class of materials. We confirm and quantify experimentally the role of the oxidant in the synthetic process. Monitoring the deposition of Ni₃(HHTP)₂ with <i>in situ</i> infrared spectroscopy revealed that MOF formation is characterized by an initial induction period, followed by linear growth with respect to time. The presence and identity of oxidizing agents is critical for the coordination-driven self-assembly of these materials and impacts both the length of the induction period and the observed rate of MOF growth. A large excess of hydrogen peroxide results in a 2× increase in the observed deposition rate (9.6 ± 6.8 × 10^-4 vs 5.0 ± 2.8 × 10^-4 min^-1) over standard reaction conditions, but leads to the formation of large, irregularly shaped particles. Slower deposition rates in the presence of oxygen favor the formation of uniformly sized nanorods (98 ± 38 × 25 ± 6 nm). These quantitative insights into the mechanism of HHTP-based MOF formation provide valuable information about the fundamental aspects of coordination and polymerization that are critical for nanoscale crystal engineering of structure-property relationships in this class of materials.