# Directing Cation Coordination and Phase in Nickel Sulfide Nanocrystals through the Addition of Phosphines

## TL;DR

This paper shows how adding phosphine ligands can control the structure of nickel sulfide nanocrystals by influencing nickel coordination.

## Contribution

The study introduces a new method using coordination chemistry to selectively produce specific nickel sulfide phases.

## Key findings

- Phosphine ligands with different steric bulk affect nickel coordination and nanocrystal phase.
- Bulky phosphines destabilize surfaces with highly coordinated nickel atoms.
- Selective synthesis of millerite, heazlewoodite, and godlevskite phases was achieved.

## Abstract

In nanocrystal syntheses,
multiple routes to achieve phase control
have been explored, such as precursor reactivity and cation exchange.
While these routes have opened doors to phase manipulation, the former
does not directly target the product structure and the latter has
limitations on which structures can be formed. Here, we combine both
ideas, focusing on the structure and also influencing precursor reactivity.
For the first time, we intentionally used concepts from coordination
chemistry to influence the metal in solution and, in turn, affect
the interstitial sites that the cation fills in the solid. Through
the addition of bidentate and monodentate phosphine ligands of varying
bite angles, steric bulk, and electron donation ability, we were able
to influence the coordination around the nickel ion and thus the product
nickel sulfide phase. We discovered that the steric bulk of the phosphine
had the biggest influence on the resulting product by destabilizing
surfaces with highly coordinated nickel atoms by occupying coordination
sites on the metal. By varying which phosphine ligand was added, we
were able to selectively target pure millerite (NiS), heazlewoodite
(Ni3S2), and godlevskite (Ni9S8).