Synthesis, Crystal Structure, Magnetic Susceptibility, and Single-Crystal EPR Studies of Bis(Diazafluorenone)Dichlorocopper(II): A Novel Cu(NN)₂X₂ System with an Unusual Distortion

The crystal structure of Cu(dafone)₂Cl₂(dafone = 4, 5-diazafluoren-9-one) was determined (monoclinic, space group P2₁/n with a = 6.5911 (6) Å, b = 13.0712 (5) Å, c = 11.4813 (9) Å, β = 95.575 (4)°, and Z = 2). This structure represents the first crystallographic example in a family of Cu(NN)₂X₂chromophores (NN = 2, 2'-bipyridine, 1, 10-phenanthroline, or bis(2-pyridyl)amine, and X is an anion) that has retained its octahedral coordination through trans ligation, in spite of the steric effects. The room-temperature magnetic moment is 1.74_μB, and it shows little variation down to 5 K. An exchange-averaged EPR spectrum is observed at X-band frequency while the analysis of line shape at Q-band frequency gave a value of |J| = 0.005 (3) cm^-1. The solid complex has electronic spectral bands at 14.29 kK and 16.95 kK. The molecular g tensor with g_x= 2.070, g_y= 2.066, g_z= 2.206 corresponds to a |x²-y²) ground state.