ChemInform Abstract: Recent Investigations on Short‐lived Organosilicon Molecules and Molecular Ions

MNDO Calculations as a valuable tool for structure evaluation of contact ion pairs

“…In general, the structural characterization of carefully grown single crystals of organic salts [39] is of current interest for several reasons: Novel bondings possibilities, such as the intramolecular Na@ sandwich, are discovered and hints concerning microscopic pathways of complex redox reactions in solution, especially via contact ion pairs, are obtained [8,9,39,48,49]. Here, the additional attempt has been made to convince the preparative chemist that approximate calculations using Michael's Noble Donation to Organic Chemistry are indeed a valuable tool to shed more light into the depths of the ocean of known alkali metal compounds with often surprising structures, where numerous details of their formation and their bonding are still hidden.…”

“…The investigations concerning other contact ion pairs of 2,5-bis(trimethylsilyl)-p-benzosemiquinone with larger and, therefore, more loosely coordinated counter cations [6,9] such as K@ (rKe = 138 pm), have also been accompanied by approximate energy hypersurface calculations, simulating-back in 1984 for the sake of CPU-time-the K@ countercation by a sparkle of unit charge (cf. Section 11).…”

“…1: cv (--)). Both the cv and ESR/ENDOR data for 2,5-bis(trimethylsilyl)-p-benzoquinone [6,9], together with the quantum chemical energy hypersurface calculations reported here, provide some insight into the pathway of a consecutive two-electron reduction, although solvent effects are still largely neglected. In general, the partially dynamic contact ion pairs could be of interest both bioinorganically because of their carrier properties and industrially as molecular switches [ll].…”

“…As an introductory example, for which we first performed MNDO calculations [6,9] as reported in Section 111, 2,5-bis(trimethylsilyl)-p-benzoquinone is presented (Fig. 1).…”

“…In solution, these include contact ion pairs formed as intermediates within the multidimensional network of electron transfer, ion complexation, and ion solvation equilibria that are investigated advantageously by a combination of cyclovoltammetric and ESR/ ENDOR measurements [6,9]. More recently, the first radical contact ion dimer has been isolated as single crystals and structurally characterized [ 101.…”