How do weak Z–X–X and stronger X–Z–X interactions affect NMR chemical shifts of chalcogenide dihalides, R2Z·X2? Theoretical background on the structural prediction of R2Z·X2 through chemical shifts in solutions

Abstract

AbstractThe mechanism is clarified for the high applicability of criteria to distinguish molecular complexes (MC) from pseudo‐trigonal bipyramidal adducts (TBP) of chalcogenide dihalogens in solutions, based on the NMR chemical shifts. The criteria are theoretically investigated employing MC and TBP of MeSeMe (1), EtSeEt (3), PhSePh (7), PhSPh (8), and PhSeH (22) with chlorine and/or bromine. The adducts of (CH2CH)2Se (26), H2C(CHCH)2Se (27), and H2C(CHCH)2S (28) are also investigated. Behaviors of total absolute magnetic tensors (σt) for the atoms in question are analyzed separately by the diamagnetic and paramagnetic terms, which well support the observed NMR chemical shifts of the MC and TBP adducts in solutions. As a result, the criteria are thoroughly supported on the basis of theoretical background and the mechanism of criteria is clarified with the diamagnetic and paramagnetic terms. The results shed light on the specific effect of weak ZXX and stronger XZX interactions on the NMR chemical shifts of the adducts, R2Z·X2. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:446–456, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20707