Polymorphism of Au(PR)Cl clusters: understanding C-H⋯π interaction and C-H⋯Cl-C van der Waals interaction on cluster assembly by surface modification.

The C-H⋯π interaction and the C-H⋯Cl-C van der Waals interaction play a crucial role in the crystallization of nanoclusters. In this paper, we present an example of a crystal system transformation of Au(PR)Cl from monoclinic (M) to trigonal (T) by surface modification. Atomically-resolved gold nanoclusters containing tris(4-chlorophenyl)phosphine and chloride ligands were synthesized and determined to be Au(-ClPPh)Cl (-ClPPh = tris(4-chlorophenyl)phosphine) by X-ray crystallography. Crystal data demonstrated that the C-H⋯Cl-C interaction is dominant in a trigonal crystal system of Au(-ClPPh)Cl with a 3̄ space group. However, the C-H⋯π interaction is the major driving force to form a monoclinic crystal system of Au(PPh)Cl (PPh = triphenylphosphine) with a 2(1)/ space group. Moreover, UV-vis absorption spectra and X-ray photoelectron spectra reveal that the electronic structure of the Au(-ClPPh)Cl nanocluster is greatly influenced by -ClPPh. This work provides critical implications for the crystallization of metal nanoclusters, as well as a better understanding of the non-covalent interaction on the nanocluster assembly and the crystal engineering by surface modification.