Structural Changes in Metal Chalcogenide Nanoclusters Associated with Single Heteroatom Incorporation

Atomically
precise nanoclusters (NCs) are promising building blocks
for designing materials and interfaces with unique properties. By
incorporating heteroatoms into the core, the electronic and magnetic
properties of NCs can be precisely tuned. To accurately predict these
properties, density functional theory (DFT) is often employed, making
the rigorous benchmarking of DFT results particularly important. In
this study, we present a benchmarking approach based on metal chalcogenide
NCs as a model system. We synthesized a series of bimetallic, iron–cobalt
chalcogenide NCs [Co6–xFexS8(PEt3)6]+ (x = 0–6) (PEt = triethyl phosphine) and
investigated the effect of heteroatoms in the octahedral metal chalcogenide
core on their size and electronic properties. Using ion mobility-mass
spectrometry (IM-MS), we observed a gradual increase in the collision
cross section (CCS) with an increase in the number of Fe atoms in
the core. DFT calculations combined with trajectory method CCS simulations
successfully reproduced this trend, revealing that the increase in
cluster size is primarily due to changes in metal–ligand bond
lengths, while the electronic properties of the core remain largely
unchanged. Moreover, this method allowed us to exclude certain multiplicity
states of the NCs, as their CCS values were significantly different
from those predicted for the lowest-energy structures. This study
demonstrates that gas-phase IM-MS is a powerful technique for detecting
subtle size differences in atomically precise NCs, which are often
challenging to observe using conventional NC characterization methods.
Accurate CCS measurements are established as a benchmark for comparison
with theoretical calculations. The excellent correspondence between
experimental data and theoretical predictions establishes a robust
foundation for investigating structural changes of transition metal
NCs of interest to a broad range of applications.