Stoichiometry-Driven Polymorphism of (Au3Pz3)2Ag Sandwich Clusters Enables Packing-Controlled Photoluminescence.

Abstract

Controlling the photophysical properties of metal clusters without altering their intrinsic cores remains challenging because molecular structure and crystal packing are often strongly coupled in such system. Herein, we show that a cyclic trinuclear gold (I) complex (Au3) can serve as a structurally defined precursor for hierarchical assembly, enabling packing-controlled photoluminescence while changing the metal core composition. By varying the feed ratio of Au3 and AgBF4, two polymorphs, Au6Ag-α and Au6Ag-β, were obtained, both featuring distorted trigonal-prismatic Au3-Ag-Au3 sandwich structures. Despite their identical compositions, they exhibit distinct solid-state emission, with Au6Ag-α showing yellow emission and Au6Ag-β displaying red-shift orange emission with a higher quantum yield. Single-crystal structure analysis and theoretical calculations reveal that Au6Ag-α is governed by a ligand-dominated heptanuclear unit, whereas tighter packing in Au6Ag-β induces intersandwich interactions, giving rise to a stacked decanuclear emissive unit with pronounced ligand-to-metal-metal charge transfer (LMMCT) character. These findings demonstrate that the use of an appropriate cluster precursor enables spatial packing control over compositionally identical clusters, providing a viable route to tune photophysical properties without altering the intrinsic metal core.