Tuning the Electrochemical Potential of Perfunctionalized Dodecaborate Clusters Through Vertex Differentiation

Abstract

We report a new class of redox-­‐active vertex-­‐differentiated dodecaborate clusters featuring pentafluoroaryl groups. These [B12(OR)11NO2] clusters share several unique photophysical properties with their [B12(OR)12] analogues, while exhibiting significantly higher (+0.5 V) redox potentials. This work describes the synthesis, characterization, and isolation of [B12(O-­‐CH2C6F5)11NO2] clusters in all 3 oxidation states (dianion, radical, and neutral). Reactivity to post-­‐functionalization with thiol species via SNAr on the pentafluoroaryl groups is also demonstated.

A Super-Oxidized Radical Cationic Icosahedral Boron Cluster

“…The broadness of this signal is due to extensive and overlapping hyperfine splitting patterns that result from the delocalization of a single electron across all twelve boron nuclei of the cluster core. 17,19 The signal broadness and isotropic g-factor of this species are consistent with EPR data of hypocloso-dodecaborate radical anion analogues that our group [23][24][25] and others [16][17][18][19] have previously reported, and further support the presence of an unpaired electron that is delocalized throughout the B 12 core.…”

“…The boron 1s binding energies observed for 1 and [1] 2of 189.4 and 188.5 eV, respectively, agree well with the values reported for other hypercloso and closo cluster derivatives. 21,[23][24][25] As previously reported, sequential oxidation of colorless closo-[B 12 (OR) 12 ] 2species to the hypercloso form leads to the formation of intensely colored solutions marked by diagnostic electronic absorption bands observed by UV-vis spectroscopy. 12,20,24,25 For the present system, the colorless [Na(Et 2 O)] 2 [1] salt displayed negligible absorptions across the visible region, while the UV-vis spectrum of 1 exhibits an absorption located at λ max 466 nm that is attributed to charge transfer from the peripheral oxygen atoms of the alkoxy substituents to the B 12 core.…”

“…Closo- [ X-ray photoelectron spectroscopy (XPS) has proven to be a valuable tool for assessing the charge state of molecular and extended network boron cluster systems based on predictable trends in boron 1s binding energies. 21,[23][24][25] The XPS measurements of [1] •+ , 1, and [1] 2-( Figure 3C) feature boron 1s regions that display the presence of intact molecular clusters with increasing binding energies that are consistent with the corresponding increased redox state of the clusters. The highest binding energy was observed for [1] •+ (190.3 eV), and suggests that this cluster is the most oxidized of the series, further substantiating the electron-deficient nature of the B 12 core, and our formulation of this species as a radical cation.…”

“…This redox boundary poses critical questions concerning the oxidation limit of icosahedral boron clusters, which is not only of fundamental interest, but could also have implications in the use of B 12 -based materials for energy storage and other applications. 2,[21][22][23] As previously established, 2,12,20,21,24,25 the redox potential of alkoxy and benzyloxy-substituted B 12 clusters ([B 12 (OR) 12 ]) can be rationally tuned as a function of their substituents by greater than 1 V for the same redox event. With this in mind, in addition to the high chemical, electrochemical, and 2,12,20,21,24,25 and this work, which introduces a third, reversible redox event for the B 12 (O-3-methylbutyl) 12 (1) derivative.…”

Cross-linking dots on metal oxides

“…This endeavor would combine practical implications along with a fundamental approach of probing these materials at the molecular level to control material properties, such as solubility and redox potential, or even impart new dimensions by employing innovative cross-linkers, such as metal complexes to generate favorable magnetic, plasmonic, or catalytic behavior. [17][18][19][20] This information can guide researchers to make predictable modifications of metal oxides using well-defined cross-linkers to continually improve metal oxides. Predicting how factors influence the properties of hybrid metal oxides is paramount for shaping their tunability, especially in evaluating different metal oxides for exclusive applications.…”