Caught in the Act of Substitution: Interadsorbate Effects on an Atomically Precise Fe/Co/Se Nanocluster

Directing groups guide substitution patterns in organic synthetic schemes, but little is known about pathways to control reactivity patterns, such as regioselectivity, in complex inorganic systems such as bioinorganic cofactors or extended surfaces. Interadsorbate effects are known to encode surface reactivity patterns in inorganic materials, modulating the location and binding strength of ligands. However, owing to limited experimental resolution into complex inorganic structures, there is little opportunity to resolve these effects on the atomic scale. Here, we utilize an atomically precise Fe/Co/Se nanocluster platform, [Fe₃(L)₂Co₆Se₈L′₆]⁺ ([1(L)₂]⁺; L = CN^tBu, THF; L′ = Ph₂PN⁽⁻⁾Tol), in which allosteric interadsorbate effects give rise to pronounced site-differentiation. Using a combination of spectroscopic techniques and single-crystal X-ray diffractometry, we discover that coordination of THF at the ligand-free Fe site in [1(CN^tBu)₂]⁺ sets off a domino effect wherein allosteric through-cluster interactions promote the regioselective dissociation of CN^tBu at a neighboring Fe site. Computational analysis reveals that this active site correlation is a result of delocalized Fe···Se···Co···Se covalent interactions that intertwine edge sites on the same cluster face. This study provides an unprecedented atom-scale glimpse into how interfacial metal–support interactions mediate a collective and regiospecific path for substrate exchange across multiple active sites.

Akin to directing groups in organic chemistry, allostery directs reaction chemistry across multiple active sites at the surface of an inorganic cluster.