Symmetrical and asymmetrical surface structure expansions of silver nanoclusters with atomic precision

Abstract

Controlling symmetrical or asymmetrical growth has allowed a series of novel nanomaterials with prominent physicochemical properties to be produced. However, precise and continuous size growth based on a preserved template has long been a challenging pursuit, yet little has been achieved in terms of manipulation at the atomic level. Here, a correlated silver cluster series has been established, enabling atomically precise manipulation of symmetrical and asymmetrical surface structure expansions of metal nanoclusters. Specifically, the C₃-axisymmetric Ag₂₉(BDTA)₁₂(PPh₃)₄ nanocluster underwent symmetrical and asymmetrical surface structure expansions via an acid-mediated synthetic procedure, giving rise to C₃-axisymmetric Ag₃₂(BDTA)₁₂(PPh₃)₁₀ and C₁-axisymmetric Ag₃₃(BDTA)₁₂(PPh₃)₁₁, respectively. In addition, structural transformations, including structural degradation from Ag₃₂ to Ag₂₉ and asymmetrical structural expansion from Ag₃₂ to Ag₃₃, were rationalized theoretically. More importantly, the asymmetrically structured Ag₃₃ nanoclusters followed a chiral crystallization mode, and their crystals displayed high optical activity, derived from CD and CPL characterization. This work not only provides an important model for unlocking the symmetrical/asymmetrical size growth mechanism at the atomic level but also pioneers a promising approach to activate the optical activity of cluster-based nanomaterials.