Hexaborate Cluster Radical Anions [B₆Hal_n Hal'_6-n]^.- and [B₆Hal₅R]^.-(Hai, Hal' = CI, Br, I; R = H, alkyl). Chemical or Electrochemical Generation, Vibrational, UV-Vis and EPR Spectroscopy

Abstract

Paramagnetic hexaborate clusters with mixed halide, halide/alkyl or halide/hydride substi tution were prepared from oxidizable dianionic precursors and were characterized by cyclic voltammetry, EPR, vibrational and UV-VIS spectroscopy. The EPR studies reveal increasing g anisotropy and EPR linewidths on replacing Cl by Br and especially by I substituents; on the other hand, the replacement of one halide by one alkyl (CH3 or CFFCN) or hydride substituent in [BftHalsR]*-causes decreasing radical persistence and g anisotropy. These results indicate a fairly uniform participation of the cluster core and the substituent sphere in the spin distribution as a major factor for the stability of these non-7r radicals.

Metal-Free Peralkylation of the closo-Hexaborate Anion

“…Solutions of 1a , b in anhydrous CH 3 CN display apparent irreversible one-electron-oxidation waves at 0.32 and 0.46 V vs Fc/Fc + , respectively (see Figure A and the Supporting Information). The observed redox irreversibility is consistent with previous reports of hexaborate cluster decomposition under oxidizing conditions ( vide infra ). , The anodic shift in the oxidative peak potential between 1a and 1b is likely due to the slightly more electron withdrawing nature of the benzyl substituents in 1b ; similar substituent effects have been observed in hexaborate and dodecaborate systems …”

“…Perhalogentated clusters B 6 X 6 2– (X = Cl, Br, I), mixed halogen clusters B 6 X n X′ 6– n 2– (X = F, Cl, Br, I; for X = F, n = 1), and B 6 X 5 R 2– (R = alkyl) were previously shown to exhibit redox behavior . To determine the electrochemical behavior of 1a , b , cyclic voltammetry (CV) studies were conducted.…”

Multidimensional potential of boron-containing molecules in functional materials

“…X = H, n = 8). 43,44 Several theoretical studies have appeared later for species with X = H 45,46 and the attention was also extended to perhalide compounds (X = Hal, n = 6, 8, 9, 10), [47][48][49][50][51][52][53][54][55][56] to peralkylated species such as [B 12 Me 12 ] •-, 57 and to related OR substituted derivatives (R = CH 2 Ph, H). [58][59][60] The substituted 'hypercloso' compounds, typically generated by one-electron oxidation from dianionic closo precursors, are stabilized with electronegative substituents because neither Hal + nor R + or RO + are good leaving groups such as H + .…”

Boratome als Spinträger in zwei‐ und dreidimensionalen Systemen

“…Die Rechnungen zeigten außerdem eine ausgeglichene Spinverteilung von etwa 1 = 12 für jedes der Bor-und Iodatome in [B 6 I 6 ]C À (Abbildung 4). [24] Mit den leichteren Halogensubstituenten Brom und Chlor ist die g-Anisotropie schwächer ausgeprägt, [49,50] nicht nur wegen der wesentlich kleineren Spin-Bahn-Kopplungskonstante dieser Atome, sondern auch wegen der verringerten Spinübertra-gung auf die peripheren Halogenide (z. B.…”

“…[24] 6 Hal n Hal' 6Àn ]C À in isomeren Formen (cis, trans) sowie der Halogenid/Hydrid-und Halogenid/Alkyl-Verbindungen bestätigt die wesentlichen Beiträge der Substituenten zum einfach besetzten Clusterorbital experimentell. [49,50] Der starke Substituenteneffekt scheint zuerst überraschend, wenn man den großen Elektronegativitätsunterschied zwischen Halogen-und Boratomen betrachtet. Allerdings sind, wie durch Rechnungen an [B 6 I 6 ]C À bestätigt wurde, [24] freie Elektronenpaare der Halogenidsubstituenten an der Spinverteilung beteiligt.…”