Spontaneous Isomerization [trans-B20H18]2– → [iso-B20H18]2– during Cobalt(II) Complexation with Phenanthroline

Abstract

In this work, the cobalt(II) complexation with 1,10-phenanthroline (Phen) in the presence of the [trans-B20H18]2– anion has been studied. At a Co : Phen = 1 : 2 ratio in acetonitrile, a binuclear cobalt(II) complex with bridging chlorine atoms and the boron cluster anion as a counterion [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18] has been isolated. However, during slow crystallization (within a month), spontaneous isomerization of [trans-B20H18]2– into [iso-B20H18]2– is observed. It has been established by X-ray diffraction analysis that in the crystal of the final compound [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18]1/3[iso-B20H18]2/3, co-crystallization of both isomeric forms of the octadecahydroeicosaborate anion is observed for the first time. The presence of the iso form of the boron cluster anion is also confirmed by IR spectroscopy data: the spectrum of the product shows a band of stretching vibrations of the BHB bridge groups at 1773 cm–1, which is absent in the trans-form of the boron cluster.

Nature of Interactions between Boron Clusters: Extended Delocalization and Retention of Aromaticity post Oxidation

“…24 These undergo further oxidation, generating dianions in two isomeric forms with exohedral rhombic linkage (Figure 1c). The dianions undergo photochemical isomerization [25][26][27][28] where two localized three-centered two-electron (3c-2e) bonds with bridging hydrogen atoms link the B10 clusters (Figure 1d), forming an alternate structural motif. The stable existence of all these systems implies the conservation of their aromatic character irrespective of the charge variations, and they have a rich chemistry of their own.…”

Nature of Interactions between Boron Clusters: Extended Delocalization and Retention of Aromaticity Post-Oxidation

“…The stable existence of all these systems implies the conservation of their aromatic character irrespective of the charge variations, and they have a rich chemistry of their own. ,, Their geometry is duly characterized by single-crystal X-ray diffraction, nuclear magnetic resonance (NMR), and density functional theory (DFT) calculations, − but the basis for these unique structural motifs remains unknown. The localized exohedral 3c–2e bonds are present in the α-rhombohedral allotrope of boron, − while the rhombus motif appears in Na 3 B 20 .…”

“…These undergo further oxidation, generating dianions in two isomeric forms with exohedral rhombic linkage (Figure c). The dianions undergo photochemical isomerization − where two localized three-centered two-electron (3c–2e) bonds with bridging hydrogen atoms link the B 10 clusters (Figure d), forming an alternate structural motif.…”

Extraordinary intense blue Tl+ lone-pair photoluminescence from thallium(i) chloride hydroborate Tl3Cl[B12H12]

“…The previously described salts Tl 2 [B 12 H 12 ] (λ em = 522 nm) and Tl 2 [B 10 H 10 ] (λ em = 510 nm) show significant red shifts for the 6s 1 p 1 → 6s 2 interconfigurational transition of the emission band, which are rather uncommon for Tl + lone-pair luminescence. 9,10 In this study, we present the synthesis and characterisation of previously unknown Tl 3 Cl[B 12 H 12 ]. Much to our own surprise, the title compound not only crystallises with the hexagonal anti-perovskite type structure as the first halide ever, but also shows intense blue radioluminescence from an electronic transition that involves the Tl + lone pair.…”

“…The previously described salts Tl 2 [B 12 H 12 ] ( λ em = 522 nm) and Tl 2 [B 10 H 10 ] ( λ em = 510 nm) show significant red shifts for the 6s 1 p 1 → 6s 2 interconfigurational transition of the emission band, which are rather uncommon for Tl + lone-pair luminescence. 9,10…”