Cr(III)-HMC (HMC = 5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane) Alkynyl Complexes: Preparation and Emission Properties

Presented here is the chemistry of Cr^III alkynyl complexes based on the rac-HMC and meso-HMC ligands (HMC = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Thus far, two pairs of cis/trans-[Cr­(rac/meso-HMC)­(C₂R)₂]Cl (R = Ph, C₂H/C₂SiMe₃) complexes have been synthesized from reactions between cis/trans-[Cr­(rac/meso-HMC)­Cl₂]Cl and LiC₂R. These complexes were characterized using single crystal X-ray diffraction, UV–vis spectroscopy, FT-IR spectroscopy, and fluorimetry. Single crystal X-ray diffraction studies revealed that these complexes adopt a pseudo-octahedral geometry. The electronic spectra of both the cis- and trans-[Cr­(rac/meso-HMC)­(C₄R′)₂]Cl (R′ = H or SiMe₃) complexes exhibit d–d bands with pronounced vibronic progression associated with the asymmetric stretch of the Cr-bound CC bonds. All of these complexes are phosphorescent and show structured emissions originating from the ligand field excited states.