Strikingly Long C···C Distances in 1,2-Disubstitutedortho-Carboranes and Their Dianions

Abstract

Neutral and especially dianionic 6-and 12-vertex closo ortho-carboranes (o-carboranes) 1,2-R2-1,2-C2BnHn (R ) H, CH3, NH2, OH, F, SiH3, PH2, SH, Cl, as well as e -, CH2 -, NH -, O -, SiH2 -, PH -, and S -) exhibit extremely large variations (over 1 Å!) of the cage CC distances, from 1.626 to 2.638 Å, at the B3LYP/6-31G*//B3LYP/6-31G* DFT level. These CC "bond lengths," among the longest ever reported, generally are greater in the icosahedral than those in the corresponding octahedral systems and depend strongly on the substituents. While 1,2-(NH2)2-1,2-C2B10H10 has the longest Cc‚‚‚Cc separation in neutral species (1.860 Å), Cc‚‚‚Cc distances can be much larger in the corresponding dianions. These range fromRemarkably, there is no abrupt discontinuity over the entire range of CC lengths. Consequently, the relationship between the gradual changes in the distances and the nature of the bonding was analyzed by means of the form of the Kohn-Sham orbitals, the Wiberg Cc‚‚‚Cc bond indices, and Bader AIM method. Cluster carboranes, and possibly other heteroboranes, thus appear to offer unique opportunities for modulating Cc‚‚‚Cc distances.

New synthetic and structural studies on nitroso-ortho-carboranes RCB10H10CNO and bis(ortho-carboranyl)amines (RCB10H10C)2NH (R=Ph or Me)

“…These findings have been supplemented by computational studies on XCb o X systems by Oliva et al [10]. Related studies by Teixidor and Viñas on thiolato and phosphino derivatives of ortho-carboranes also showed similar C1-C2 distance lengthening attributed to exo-C-S or C-P -bonding as well as steric effects [11].…”

Synthesis, Crystal Structure and Photoluminescence of 1,2-Bis(phenylselenyl)-1,2-dicarba-closo-dodecaborane(12)

“…It is believed that the significant elongation of the C cage -C cage distance in 1 compared with that in closo-C 2 B 10 H 12 is the result of both electronic and steric effects as described for its sulfur analogs [15,19], and the difference (from that in compound 2) may be attributed to the difference in electronegtivity between sulfur (2.58) and selenium (2.55, both Pauling scale) atoms.…”

“…have received much current interest. On the other hand, o-carborane has been shown to be a good system to modulate the C-C distance [15,16]. Depending on the steric and electronic nature of the C-substituents, the carbon-carbon distances within the C 2 B 10 clusters can vary from 1.629(4)Å in closo-C 2 B 10 H 12 [17] to 2.156(4)Å in a sterically crowded ferrocenyl derivative reported recently [18].…”

Study on the Reactivity of Amino Acid Chemosensor, NPFNP, with Ethanol: Structural Elucidation through Single Crystal XRD and DFT Calculations

“…The sum of the three angles around N2 atom is 350 o , which clearly indicates the pyramidal disposition of the bonds at the atom N2. The C-C bond distances in its aromatic rings are in the normal range of 1.32-1.45 Å, which is characteristic of delocalized aromatic rings [19]. The selected bond length, bond angles and torsion angles are presented in Table 2.…”