Ag ₃₂ Cu ₁₂ (SR) ₃₀ ⁴⁻ : A New Alloy Cluster Through Intercluster Reaction

Heteroatom alloying in atomically precise clusters without changing the overall structure over a wide range of composition is often challenging. In the case of a multilayer cluster core, it is even more so because of the heavy distortion due to the mismatched bond lengths and bond angles, leading to the lowering of symmetry. Here, we report high-level mixing of Cu into the [Ag₄₄(4-FTP)₃₀]⁴⁻ (4-FTP: 4-fluorothiophenol) system, leading to the formation of a new Ag-Cu alloy [Ag₃₂Cu₁₂(4-FTP)₃₀]⁴⁻ following an intercluster reaction pathway with Cu₁₂S₆(DPPPT)₄ cluster. Interestingly, [Ag₃₁Cu₁₃(4-FTP)₃₀]⁴⁻ was also observed, although at lower intensity, suggesting the possibility of multilayer alloying in the Ag₄₄ system, which was not seen before during alloying with Au. A detailed study based on UV-vis absorption, electrospray mass spectrometry (ESI MS), trapped ion mobility spectrometry (TIMS), and density functional theory (DFT) calculation suggests that the Cu atoms prefer to occupy the outer staple position compared to the core. However, the presence of a second isomer and a dynamic equilibrium between two isomeric species from TIMS analysis suggests the possibility of interlayer migration of Cu atoms within the cluster. In the future, such unusual alloying can be studied with different heteroatoms.