Polymorphism of [Cu(PhCHCHS)(PPh)][BF] and Double-Helical Assembly of [CuH(PhCHCHS)(PPh)Cl]: Origin of Two Chiral Nanoclusters with Triple-Helical Core from Intermediates.

Here, we report the solvent-induced polymorphism in [Cu(PET)(TPP)]BF (TPP = triphenylphosphine, PET = 2-phenylethanthiol), and double-helical assembly of the [CuH(PET)(TPP)Cl] (Cu) nanocluster (NC) from reaction intermediates. Both copper NCs have an intrinsically chiral triple-stranded helicate metal core, unlike traditional copper NCs with a polyhedral-based kernel. The chiral structure of Cu resembles an enantiomeric pair in the unit cell. Moreover, Cu has a three-layered 3D chirality of a sandwich constructed of sulfur-bridged copper NCs aligned in a top-middle-down configuration. Furthermore, the Cu NC self-hierarchically assembles into a complex double-stranded helix secondary structure sustained by noncovalent interactions. Electrospray ionization mass spectrometry (ESI-MS), density functional theory (DFT), and X-ray photoelectron spectroscopy (XPS) were utilized to validate the single-crystal X-ray diffraction (SCXRD) data. Overall, this study provides an interesting example of polymorphism, chirality, and hierarchical double-helical assembly of NCs, allowing for extensive understanding of complicated structures at the atomic level.