Synthesis, characterization, photophysics, and a ligand rearrangement of CCC-NHC pincer nickel complexes: Colors, polymorphs, emission, and Raman spectra

The metallation/transmetallation strategy has been successfully applied to the preparation of CCC-NHC pincer nickel complexes. Manipulation of the coordination sphere lead to cationic CCC-NHC pincer nickel complexes. These were found to exhibit polymorphism in the solid state with significant differences in the intermolecular distances observed by X-ray crystallography. Three polymorphs were observed for the PF6− salt, and two were observed for the BF4− salt. When BPh4− was the counterion only one morphology was observed, and crystals grown of the triflate salt were too small for analysis. Details of the differences are documented for comparison. Additionally, during crystallization it was found that a rearrangement of the CCC-NHC ligand had occurred, involving coupling of an NHC from two different ligands, which were oxidized.