Self-Assembly of Molecular Trefoil Knots Featuring Pentadecanuclear Homoleptic AuI-, AuI/AgI-, or AuI/CuI-Alkynyl Coordination

Abstract

Metal-free and metal-containing molecular trefoil knots are fascinating ensembles that are usually covalently assembled, the latter requiring the rational design of di- or multidentate/multipodal ligands as connectors. In this work, we describe the self-assembly of pentadecanuclear AuI trefoil knots [Au15(C≡CR)15] from monoalkynes HC≡CR (R=9,9-X2-fluorenyl with X=nBu, n-hexyl) and [AuI(THT)Cl]. Hetero-bimetallic counterparts [Au9M6(C≡CR)15] (M=Cu/Ag) were self-assembled by reactions of [Au15(C≡CR)15] with [Cu(MeCN)4]+/AgNO3 and HC≡CR. The type of pentadecanuclear trefoil knots described herein is characterized by X-ray crystallography, 2D NMR and HR-ESI-MS. [Au9Cu6(C≡CR)15] is relatively stable in hexane; its excited state properties were investigated. DFT calculations revealed that non-covalent metal–metal and metal–ligand interactions, together with longer alkyl chain-strengthened inter-ligand dispersion interactions, govern the stability of the trefoil knot structures.