Lewis Base Mediated Polymorph Selectivity of Pyrite CuSe2 through Atom Transfer in Solid-State Metathesis

Abstract

Preparation of metastable solid-state materials is often hindered by the limitations of traditional solid-state chemistry, namely the high temperatures required to induce solid-state diffusion. Here, we present the formation of the metastable pyrite polymorph of CuSe2 through a metathesis reaction mediated by the Lewis base, triphenylphosphine (Ph3P). The Ph3P added to the double salt-exchange reaction CuCl2 + Na2Se2 abstracts selenium from the precursor and promotes the reaction at 130–150 °C, rather than 300 °C required for the neat reaction mixture. Powder X-ray diffraction experiments indicate that substoichiometric amounts of added phosphine yield pyrite CuSe2; infrared and nuclear magnetic resonance spectroscopies as well as mass spectrometry corroborate the formation of Ph3PSe and Cu(Ph3P)n+ adducts, which implicates the Lewis base in facilitating atom-transfer reactions, thus lowering the activation barrier to forming the metastable pyrite polymorph of CuSe2. These results provide an example of a ...