Electronic Structure of Superoxidized Radical Cationic Dodecaborate-Based Clusters

Abstract

The expanding field of boron clusters has attracted continuous theoretical efforts to understand their diverse structures and unique bonding. We recently discovered a new reversible redox event of B 12 (O-3-methylbutyl) 12 in which the superoxidized radical cationic form [B 12 (O-3-methylbutyl) 12 ] •+ was identified and isolated for the first time. Herein, comprehensive (TD-)DFT studies in tandem with electrochemical experiments were employed to demonstrate the generality of the reported behavior across perfunctionalized B 12 (OR) 12 clusters (R = aryl or alkyl). While the spin density of radical cationic clusters is delocalized in the core region, the oxidation brings about notable gains of positive partial charges on the supporting groups whose electronics can readily tune the redox potential of the 0/•+ couple. The underlying changes of frontier orbitals were elucidated, and the resulting [B 12 (OR) 12 ] •+ species manifest a general diagnostic absorption as a consequence of mixed local/chargetransfer excitations.

Electrochemical Cycling of Redox-Active Boron Cluster-Based Materials in the Solid State

“…The packing motif of B 12 (OCH 3 ) 12 as a powder (Figure B) shows ample interstitial space (∼3 Å cavities between clusters; Figure S32), suggesting the possibility of metal-ion insertion. Furthermore, this cluster also shows access to multiple oxidation states in solution (Figure C), as well as a radical cationic state, a phenomenon recently observed , by our group for many other B 12 (OR) 12 clusters. B 12 (OCH 3 ) 12 shows redox activity over a wide voltage window in solution, with half-wave potentials ( E 1/2 ) spanning a range of more than 1 V, from −0.79 V vs Fc/Fc + (2 – → 1 – ) up to +0.89 V (0 → 1 + ), in good agreement with previous observations of the effect of the R substituent on the redox potentials of B 12 (OR) 12 clusters. ,,, Elucidation of the atomic-level structure of B 12 (OCH 3 ) 12 , in combination with the rich redox behavior in solution, further prompted us to test our original hypothesis and explore whether this material would be a viable candidate for a solid-state electrochemical cell.…”

“…B 12 (OCH 3 ) 12 shows redox activity over a wide voltage window in solution, with half-wave potentials (E 1/2 ) spanning a range of more than 1 V, from −0.79 V vs Fc/Fc + (2 − → 1 − ) up to +0.89 V (0 → 1 + ), in good agreement with previous observations of the effect of the R substituent on the redox potentials of B 12 (OR) 12 clusters. 96,97,102,107 Elucidation of the atomic-level structure of B 12 (OCH 3 ) 12 , in combination with the rich redox behavior in solution, further prompted us to test our original hypothesis and explore whether this material would be a viable candidate for a solid-state electrochemical cell.…”

“…Recent advances in boron cluster chemistry ,,− show that judicious exopolyhedral modifications of these species can result in the emergence of boron-centered redox events in solution, which in many cases can be tunable. In particular, ether-functionalized dodecaborate clusters [B 12 (OR) 12 ; R = alkyl, aryl] demonstrate the richest solution-based redox behavior exhibited by boron clusters studied to date. ,− ,− Due to the enhanced electronic stabilization provided by the ether groups, the majority of these boron clusters have access to four stable oxidation states in solution (Figure A). Their redox potentials can be tuned over a wide voltage range through simple modification of the electron-donating or -withdrawing nature of the carbon-based substituent (Figure B).…”

Electrochemical Cycling of Redox-Active Boron Cluster-Based Materials in the Solid State

“…Despite this, the structure determined via refinement of the powder data shows excellent agreement with the single crystal structure (Figure 3; SI, Figure S27 and Table S1- The packing motif of B 12 (OCH 3 ) 12 as a powder (Figure 3B) shows ample interstitial space (~3 Å cavities between clusters; SI, Figure S29), suggesting the possibility of metal ion insertion. Furthermore, this cluster also shows access to multiple oxidation states in solution (Figure 2C), as well as a radical cationic state, a phenomenon recently observed 102,107 by our group for many other B 12 (OR) 12 clusters. B 12 (OCH 3 ) 12 shows redox activity over a wide voltage window in solution, with half-wave potentials (E 1/2 ) spanning a range of more than 1 V, from -0.79 V vs Fc/Fc + (2à 1-) up to +0.89 V (0 à 1+), in good agreement with previous observations of the effect of the R substituent on the redox potentials of B 12 (OR) 12 clusters.…”

“…In particular, ether-functionalized dodecaborate clusters [B 12 (OR) 12 ; R = alkyl, aryl] demonstrate the richest solution-based redox behavior exhibited by boron clusters studied to date. 14,[95][96][97][99][100][101][102][103][104][105][106][107][108][109][110][111][112] Due to the enhanced electronic stabilization provided by the ether groups, the majority of these boron clusters have access to four stable oxidation states in solution (Figure 1A). Their redox potentials can be tuned over a wide voltage range through simple modification of the electron-donating or withdrawing nature of the carbonbased substituent (Figure 1B).…”