Intermetallic Competition in the Fragmentation of Trimetallic Au-Zn-Alkali Complexes

Cationization is a valuable tool to enable mass spectrometric studies on neutral transition-metal complexes (e.g., homogenous catalysts). However, knowledge of potential impacts on the molecular structure and catalytic reactivity induced by the cationization is indispensable to extract information about the neutral complex. In this study, we cationize a bimetallic complex [AuZnCl3] with alkali metal ions (M+) and investigate the charged adducts [AuZnCl3M](+) by electrospray ionization mass spectrometry (ESI-MS). Infrared multiple photon dissociation (IR-MPD) in combination with density functional theory (DFT) calculations reveal a (3) binding motif of all alkali ions to the three chlorido ligands. The cationization induces a reorientation of the organic backbone. Collision-induced dissociation (CID) studies reveal switches of fragmentation channels by the alkali ion and by the CID amplitude. The Li+ and Na+ adducts prefer the sole loss of ZnCl2, whereas the K+, Rb+, and Cs+ adducts preferably split off MCl2ZnCl. Calculated energetics along the fragmentation coordinate profiles allow us to interpret the experimental findings to a level of subtle details. The Zn2+ cation wins the competition for the nitrogen coordination sites against K+, Rb+, and Cs+ , but it loses against Li+ and Na+ in a remarkable deviation from a naive hard and soft acids and bases (HSAB) concept. The computations indicate expulsion of MCl2ZnCl rather than of MCl and ZnCl2.