Structure, Stereochemistry and Novel 'Hydrogen Bonding' in Two Bipyridinium Salts of the B₁₀H₁₀^2- Anion

Abstract

Crystal structure determinations of (LH)₂(B₁₀H₁₀), (1), and (LH₂)(B₁₀H₁₀), (2), L = 2,2'- bipyridine , have been carried out by single-crystal X-ray diffraction methods at 295 K, being refined by full-matrix least squares to residuals of 0.041, 0.047 for 1758, 1771 'observed' independent reflections respectively. Crystals of (1) are monoclinic, P2₁/n, a 12.040(7), b 17.71(1), c 11.142(4) Å, β 101.78(4)º, Z 4. Crystals of (2) are monoclinic, P2₁/c, a 9.937(4), b 10.837(3), c 14.856(5) Å, β 109 2l(3)º, Z 4. The colour of the compounds is accounted for by charge-transfer interactions of a novel type, namely between the positively charged cationic acid hydrogen atoms and the negatively charged non-apical hydrogen atoms of the anion. In yellow (1), these distances are 2.26(5) Å, while in red (2), they are much shorter, being 1.89(4), 1.97(3) Å.