Atomistic structures and dynamics of prenucleation clusters in MOF-2 and MOF-5 syntheses

Abstract

Chemical reactions in solution almost always take place via a series of minute intermediates that are often in rapid equilibrium with each other, and hence hardly characterizable at the level of atomistic molecular structures. We found that single-molecule atomic-resolution real-time electron microscopic (SMART-EM) video imaging provides a unique methodology for capturing and analyzing the minute reaction intermediates, as illustrated here for single prenucleation clusters (PNCs) in the reaction mixture of metal–organic frameworks (MOFs). Specifically, we found two different types of PNCs are involved in the formation of MOF-2 and MOF-5 from a mixture of zinc nitrate and benzene dicarboxylates at 95 °C and 120 °C, respectively. SMART-EM identified a small amount of 1-nm-sized cube and cube-like PNCs in the MOF-5 synthesis, but not in the MOF-2 synthesis. In the latter, we instead found only linear and square PNCs, suggesting that the MOF-2/-5 bifurcation takes place at the PNC stage.

Cyclodextrins as Surfactants for Solubilization and Purification of Carbon Nanohorn Aggregates

“…We report that as little as 1 wt% of α , β , and γ ‐CD can stably disperse CNHa by selective binding on the tip of the graphitic spikes while glucose and amylose cannot. Direct support for the tip binding was provided visually using single‐molecule atomic resolution real‐time electron microscopic method (SMART‐EM; Figure e), from which we estimated the equilibrium constant of the CD binding to each CNH in CNHa to be about 1 × 10 4 M –1 . This value is similar to values reported for the binding of adamantane derivatives in the cavity of β ‐CD ( K =10 4 −10 5 M –1 ) – a standard system to evaluate the strength of molecular recognition in CDs, and supported our tip‐binding hypothesis of CD molecules .…”

“…Here the SMART‐EM methodology allowed us to study the chemistry of CD molecules bound on CNHs in water at concentration in the order of 10 −8 M, a concentration too low to be quantified by any other analytical methods. Thus, the method offers us a unique possibility to carry out statistical analysis of molecular recognition on a single‐molecule basis . α ‐CD, which binds rather weakly to CNHa, can be easily removed by washing with water, and hence the complexation/decomplexation sequence using α ‐CD provides a method to isolate pure CNHa selectively (Figure c), free of the GB impurity.…”

“…Amino‐CNHa made by treatment of CNHa with NaNH 2 has served as a versatile platform for SMART‐EM . The previous preparation was performed on a sample as received from a commercial source, which contains GB impurity.…”

Nanoarchitectonics for Coordination Asymmetry and Related Chemistry

“…147 Recently, Harano, Nakamura, and co-workers applied single-molecule atomic-resolution real-time electron microscopic (SMART-EM) with video imaging for capturing and observing prenucleation clusters in MOF formation processes ( Figure 29). 148 Two types of prenucleation clusters were identified in formation process of square-lattice MOF and cubic lattice MOF prepared from zinc nitrate and benzene dicarboxylates. Formations of cube-like prenucleation clusters and 1-nm-sized cube were observed in synthetic processes of the cubic lattice MOF.…”

Ultra-Fast Electron Microscopic Imaging of Single Molecules With a Direct Electron Detection Camera and Noise Reduction

“…This method can be used to perform statistical analysis of atomistic structure and dynamics of molecules over several hundred molecules. The in situ kinetic study of chemical reactions (Okada et al, 2017), mechanistic investigation of molecular crystal formation (Harano et al, 2012), and capturing and analyzing minute reaction intermediates (Xing et al, 2019) have illustrated the potential of the SMART-EM methodology in chemistry and nanoscience. This video technology has posed a new challenge of acquiring video images of fast moving or reacting molecules, so that we can visually and quantitatively study the dynamics of the observed chemical events.…”