Secondary interactions in decachloro-closo-decaborates R2[B10Cl10] (R = Et3NH+, Ph4P+, and [Ag(NH3)2]+): 35Cl NQR, PW-DFT, and X-ray studies

Abstract

Three new salts R2[B10Cl10] (R=Et3NH+, Ph4P+, [Ag(NH3)2]+, 1–3) containing bulky decachloro-closo-decaborate dianion have been synthesized and characterized using the IR, 11B NMR, and 35Cl NQR spectroscopy. Neither IR nor 11B NMR spectra have shown distinctions between compounds 1–3, whereas 35Cl NQR spectra of all the compounds have been split evidencing for crystallographic non-equivalence of chlorine atoms caused by secondary interactions. Crystal structures of 2 and 3 have been studied using X-ray diffraction and periodic DFT calculations, whereas unit cell parameters and space group of 1 have been estimated using powder X-ray diffraction. The 35Cl NQR data supported by analysis of calculated electron density functions within the framework of Bader’s Quantum Theory of Atoms in Molecules (QTAIM) showed that both cation and solvent molecules take part in N–H…Cl and C–H…Cl bonding as strong as 2.5 and 2.1kcal/mol, respectively. The QTAIM study has revealed in 2 a number of p…π interactions between lone pairs of chlorine atoms and delocalized electron density of phenyl rings or CN groups of acetonitrile molecules, and the strongest of them (0.9kcal/mol) has been reflected in the 35Cl NQR spectrum. The results have shown that the halogen-substituted boron clusters can act as tags sensitive to H…Hal and p…π bonding, which can be identified by the NQR spectra even in the absence of structural data.