Copper Selenides via Anion Exchange versus Direct Growth – The Role of Diorganyl Diselenides

Anion exchange is a powerful tool for postsynthetic transformation
of nanoparticles that can be coupled with other transformations to
create nanostructures unachievable by direct growth. Previous work
implicated long-chain dialkyl diselenides as drivers of Se2– anion exchange on Cu2–xS, but
it lacked mechanistic details. Here, we examined the reactivity trends
of diphenyl, didodecyl, and dibenzyl diselenides as drivers of anion
exchange to create metastable copper sulfur selenide alloys. We contrasted
these reactivity trends with those of direct synthesis of copper selenide
nanoparticles, demonstrating mechanistic orthogonalities between these
pathways. Dialkyl diselenides were the only species that induced anion
exchange. We rationalized the different reaction outcomes using thermal
decomposition measurements together with MD simulations using a ReaxFF
force field (trained against DFT data). Dialkyl diselenides were shown
to release H2Se, which appears to be critical for achieving
Se2– anion exchange. This demonstrates the utility
of computationally inexpensive atomistic-scale simulations methods
like ReaxFF in the rational design of nanoparticle syntheses. Using
this insight, the dialkyl diselenides were identified as a new class
of selenium exchange reagents based on initial MD simulations of H2Se release. This work provides mechanistic understanding of
nanoparticle anion exchange and insights into decomposition processes
crucial to use of diorganyl diselenides in nanoparticle synthesis.