Molecular Decomposition Routes of Diaryl Diselenide Precursors in Relation to the Phase Determination of Copper Selenides

Abstract

1H nuclear magnetic resonance (NMR), 77Se NMR, and powder X-ray diffraction (XRD) were used to monitor the thermal decomposition of diphenyl and dibenzyl diselenide precursors toward the synthesis of copper selenides. Copper was found to promote the decomposition of both precursors. The inorganic nanocrystals and organic byproducts were sensitive to the specific diaryl diselenides and the presence of oleylamine and copper. Molecular mechanistic routes are proposed. Berzelianite (Cu1.8Se), klockmannite (CuSe), umangite (Cu3Se2), and both petřı́čekite (m-CuSe2) and krutaite (p-CuSe2) were identified as products. Multistep transformations between phases were discovered through reactions with the organoselenium precursors, and organic decomposition products are proposed.

Predictive Synthesis of Copper Selenides Using a Multidimensional Phase Map Constructed with a Data-Driven Classifier

“…49−53 The utility of these precursors stems from their programmable reactivity as a function of C−Se bond strength, which depends upon the identity of the functional group, as first proposed by Vela and co-workers. 54 However, it has been shown by Macdonald and co-workers that this reactivity, along with the mechanisms of precursor conversion, concurrently depends upon the presence of Cu(oleate) 2 and oleylamine, 42 which is a C18 primary amine that acts as both a high-temperature solvent and reducing agent. 55,56 This illustrates the high-dimensional nature of the chemistry, which complicates rational phase determination.…”

“…The variables initially chosen for this investigation were: ( 60 The volumetric ratio of oleylamine to ODE was chosen because of the known influence of oleylamine on the decomposition mechanism of the diselenide precursors, in addition to its ability to act as a reducing agent for copper. 42,56 This allows the amount of oleylamine to be varied continuously, while keeping the overall reaction concentration constant. Time and temperature were chosen due to their direct influence on the kinetics and thermodynamics of the reaction.…”

“…Diorganyl diselenides (R–Se−Se−R, where R = alkyl, allyl, benzyl, or phenyl) have emerged over the past 15 years as versatile precursors for the kinetically controlled synthesis of metal selenides. − The utility of these precursors stems from their programmable reactivity as a function of C–Se bond strength, which depends upon the identity of the functional group, as first proposed by Vela and co-workers . However, it has been shown by Macdonald and co-workers that this reactivity, along with the mechanisms of precursor conversion, concurrently depends upon the presence of Cu­(oleate) 2 and oleylamine, which is a C18 primary amine that acts as both a high-temperature solvent and reducing agent. , This illustrates the high-dimensional nature of the chemistry, which complicates rational phase determination. We use a classification algorithm that identifies patterns in the reaction data to subsequently predict the copper selenide phase, or a combination of phases, for a given set of experimental variables.…”

“…Despite this, the Ph 2 Se 2 precursor facilitates a much richer Cu–Se phase space, which is exemplified by the nine phase combinations achieved using this precursor versus the four phase combinations achieved with the Bn 2 Se 2 precursor. This suggests that the various metastable copper selenides themselves may have a high activation barrier to conversion to the more thermodynamically stable copper selenides and that the Ph 2 Se 2 precursor has a distinctive decomposition mechanism that leads to these metastable species, rather than just a difference in activation barrier …”

“…That is, the targeted synthesis of a single material can be difficult because of the large number of variables that must be controlled to obtain the phase purity. Consequently, chimie douce materials syntheses are traditionally developed via fragmented empirical knowledge of the underlying consequences of experimental variables. , For this reason, achieving phase control in such syntheses can be tedious and laborious.…”