Polymorphism of Au 11 (PR 3 ) 7 Cl 3 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 11 (PR 3 ) 7 Cl 3 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 11 ( p -ClPPh 3 ) 7 Cl 3 ( p -ClPPh 3 = 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 11 ( p -ClPPh 3 ) 7 Cl 3 with a R 3̄ space group. However, the C-H⋯π interaction is the major driving force to form a monoclinic crystal system of Au 11 (PPh 3 ) 7 Cl 3 (PPh 3 = triphenylphosphine) with a P 2(1)/ n space group. Moreover, UV-vis absorption spectra and X-ray photoelectron spectra reveal that the electronic structure of the Au 11 ( p -ClPPh 3 ) 7 Cl 3 nanocluster is greatly influenced by p -ClPPh 3 . 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.