Molecular and crystal structure of 9-[α-(9H-fluoren-9-ylidene)-4-chlorobenzyl]-9H-fluoren-9-yl; an organic antiferromagnet with TN= 3.25 K

Abstract

The crystal structure of the title radical has been determined by X-ray diffraction at ambient temperature. The crystal system is monoclinic with a space group of Cc: a= 33.204(4), b= 9.391(1), c= 15.290(1)Å, β= 101.223(7)°, Z= 8. The final R factor is 0.035 for 2623 observed reflections. There are two crystallographically independent molecules constituting a pair of atropisomers. Two fluoren-9-yl groups and a chlorophenyl moiety are arranged in a propeller shape. The range of the torsion angles of the fluorenyl blades is 25°∼ 33°, and that of the chlorophenyl blades is 55°∼ 59°. The electron-spin exchange pathways are discussed based on the McConnell's spin-density Hamiltonian. The exchange-coupled neighbours are estimated to be z= 6, to which the highest T_N among organic radicals can be attributed.