Icosahedral Carboranes

Geometries of 11‐Vertex Carborane Monoanion Radicals with 2n+3 Skeletal Electron Counts

“…Spin EPR calculations were also carried out on [1] ·and [2] ·using B3LYP/EPR-II with the SMD solvation model and tetrahydrofuran as solvent. The EPR spectra for both [1] ·and [2] ·were simulated ( Figure 4) and are indeed similar to the observed EPR spectra depicted in the literature with experimental line widths of 25 G for [1] ·and 28 G for [2] ·in the solid-state EPR spectra. The unpaired electron is mainly located at the cluster carbon atoms with calculated Fermi coupling constants of 35.5-38.5 G and with minor occupancies at the boron atoms (B3, B6) attached to both cluster carbon atoms with calculated coupling constants of around 7 G ( Table 2).…”

“…Carborane clusters are generally governed by the skeletal electron-counting rules: closed clusters contain 2n+2 skeletal electrons (SEs) and open clusters contain 2n+4 SEs. [1,2] Both 2n+2 SE and 2n+4 SE clusters, usually classified as closo and nido clusters, respectively, are prevalent in carborane chemistry, whereas 2n+3 SE clusters remain relatively rare. The first 2n+3 carborane radical was prepared in 1965 by chemical reduction of 1-phenyl-ortho-carborane (1-Ph-1,2-C 2 B 10 H 11 ) and detected by electron paramagnetic resonance spectroscopy (EPR), but this species is not considered stable partly due to the facile cleavage of the cluster carbon-hydrogen bond on reduction.…”

“…[10] Cyclic voltammetry (CV) studies reported fully reversible reduction waves, which show both species to be remarkably stable. [11][12][13][14][15][16][17] In 2007, a combined spectroelectrochemical, EPR, and computational study on radical [1] ·showed the 2n+3 geometry to contain a long cluster-C-cluster-C distance of 2.39 Å, in contrast to the corresponding C-C distance of 1.76 Å in 1. [12] The geometry of the diamagnetic dianion [1] 2was determined later by a combined NMR spectroscopic and computational study.…”

“…ture [12,19] gave us the opportunity to compare these experimental findings with predicted energy and EPR spectroscopic data on 1 and 2 from various model chemistries. Computations on 1,2-diphenyl-ortho-carborane 1 have been explored in several studies but only one study in 2015 calculated the Gibbs free energy differences of the 2n+3 monoanion radical [1] ·relative to neutral 1 and dianion [1] 2in the form of ΔG solv1 and ΔG solv2 , respectively. [22] The reported model chemistry was B3LYP-GD3BJ/6-311++G(d,p) with CPCM/UKAS solvation model using acetonitrile as solvent.…”

Metallacarboranes on the Road to Anticancer Therapies: Cellular Uptake, DNA Interaction, and Biological Evaluation of Cobaltabisdicarbollide [COSAN]−

“…[9][10][11] In this direction, towards the designa nd development of high-boron-containing compounds, some of us have been interested in the development of anionic sandwich metallacarboranes ([3,3'-M(1,2-closo-C 2 B 9 H 11 ) 2 ] À )i nw hich the central metal ion, commonly Co III (cobaltabisdicarbollide, [COSAN] À )o r Fe III (ferrabisdicarbollide, [FESAN] À )i sh 5 -bonded to two [C 2 B 9 H 11 ] 2À moieties. [12] [COSAN] À ,has three accessible redox reversible processes, [13] formally Co 2 + / + ,C o 3 + /2 + ,a nd Co 4 + /3 + at À2.64, À1.75, and 1.22 V, respectively,v ersus Fc + /Fc, although the Co 3 + /2 + is the one more readily observeda nd studied. In addition, previous work demonstratedt hat, in aqueouss olution, H[COSAN] produces monolayerv esicles at ac oncentration < 13 mm that transform into micelles [14] when the concentration increases, with the ability to readily cross biological membranes even if they are negatively charged [15] and accumulate inside living cells with no appreciable effect on cell viability.…”