Synthesis, Characterization, Photoluminescence, and Simulations of a CCC-NHC-Supported Pt2Ag2 Mixed-Metal Cluster Containing a PtAg2 Metallacyclopropane

The pincer CCC-bis(NHC)-supported Pt(II) complex 2, (1,3-bis( N -((trimethylsilyl)methyl)imidazol-2-ylidene)-2-phenylene)chloroplatinum(II), was prepared and was reacted with excess or stoichiometric silver(I) trifluoroacetate. The reaction with excess yielded the Pt 2 Ag 2 cluster 3, which to our knowledge contains the first unsymmetrically substituted example of a PtAg 2 metallacyclopropane, as revealed by X-ray crystallography. A distorted-octahedral configuration was also found in the coordination sphere of one of the silver atoms. Multiple weak hydrogen bonds (WHB) including C–H···O, C–H···F, and C–F···π interactions were identified in the lattice of cluster 3 . The unique structure of cluster 3 was simulated using density functional theory (DFT), which revealed that it was thermodynamically favored over the more expected configurations. The stoichiometric reaction with Ag(OCCF 3 ) afforded the simple ligand exchange product (1,3-bis( N -((trimethylsilyl)methyl)imidazol-2-ylidene)-2-phenylene)(trifluoroacetato)platinum(II) ( 4 ). The reaction of stoichiometric or excess AgOAc afforded only the monomeric product of simple ligand metathesis, (1,3-bis( N -((trimethylsilyl)methyl)imidazol-2-ylidene)-2-phenylene)(acetato)platinum(II) ( 5 ). This observation is consistent with the hypothesis that the weak hydrogen bond network and the increased Lewis acidity of Ag(OCCF 3 ) are significant contributors to the structure of cluster 3 . The photophysical properties of complexes 2 – 5 have been investigated. The emission color of the solution of cluster 3 was found to be concentration dependent.