Structure of Amorphous Selenium by 2D ⁷⁷Se NMR Spectroscopy: An End to the Dilemma of Chain versus Ring

Abstract

Amorphous selenium, owing to its tremendous technological importance and perhaps to its chemical simplicity, has been studied for nearly a century and yet an unequivocal structural description of this material remains lacking to date. The primary controversy regarding the structure of amorphous Se relates to the relative fraction of Se atoms residing in ∞1Se chains versus in Se₈ rings. Herein we present the results of a two-dimensional solid-state ⁷⁷ Se nuclear magnetic resonance (NMR) spectroscopic study of the chain and ring crystalline allotropes of Se as well as of amorphous Se to unequivocally demonstrate that 1) the Se₈ rings and the ∞1Se chains are characterized by their unique ⁷⁷ Se NMR signatures and 2) the structure of amorphous Se consists exclusively of ∞1Se chains.