General Method for Determining Redox Potentials without Electrolyte.

A novel method to determine redox potentials without electrolyte is presented. The method is based on a new ability to determine the dissociation constant, K°d, for ion pairs formed between any radical anion and any inert electrolyte counterion. These dissociation constants can be used to determine relative shifts of redox potential as a function of electrolyte concentration, connecting referenced potentials determined with electrochemistry (with 0.1 M electrolyte) to electrolyte-free values. Pulse radiolysis created radical anions enabling determination of equilibrium constants for electron transfer between anions of donor and acceptor molecules as a function of electrolyte concentration in THF. The measurements determined "composite equilibrium constants", KeqC, which contain information about the dissociation constant for the electrolyte cations, X+, with the radical anions of both the donor, K°d(D-•,X+) and the acceptor, K°d(A-•,X+). Dissociation constants were obtained for a selection of radical anions with tetrabutylammonium (TBA+). The electrolyte was found to shift the reduction potentials of small molecules 1-methylpyrene and trans-stilbene by close to +130 mV whereas oligo-fluorenes and polyfluorenes experienced shifts of only (+25 ± 6) mV due to charge delocalization weakening the ion pair. These shifts for reduction of aromatic hydrocarbon molecules are smaller than shifts of +232 and +451 mV seen previously for benzophenone radical anion with TBA+ and Na+ respectively where the charge on the radical anion is localized largely on one C═O bond, thus forming a more tightly bound ion pair.

PolyMOF Nanoparticles: Dual Roles of a Multivalent polyMOF Ligand in Size Control and Surface Functionalization.

Metal-organic framework nanoparticles (MOF NPs) have emerged as an important class of materials that display significantly enhanced performance in many applications compared to bulk MOF materials; their synthesis, however, commonly involves a tedious sequence that controls particle size and surface properties in separate steps. Now, a simple strategy to access functional MOF NPs in one pot is reported that uses a polyMOF ligand possessing a polymer block for surface functionalization and a coordination block with tunable multivalency for size control. This strategy produces uniform polyMOF-5 NPs with sizes down to 20 nm, displaying exceptional structural and colloidal stability upon exposure to ambient conditions. A detailed time-dependent study revealed that the polyMOF NPs were formed following an aggregation-confined crystallization mechanism. Generality was demonstrated through the synthesis of well-defined polyUiO-66 NPs.