Radical Cation Salts of N‐Methylpyridone Azines with Halogenido Cuprate Anions

Abstract

AbstractBis(N‐methylpyridone)azine (MPA) and its derivative bis(N‐methyl‐5‐trifluoromethyl‐pyridone)azine (p‐CF3MPA) are investigated concerning their redox behavior. Reactions with copper(II) halides afford via one electron transfer reactions the radical cation salts MPA[CuCl2], MPA[CuBr2] and p‐CF3MPA[CuBr2], all crystallizing as air‐stable dark needles. Cu(II) is reduced to the corresponding cuprate(I) anions [CuX2]− (X=Cl, Br). In the crystal structures, the planar radical cations form stacks with equidistantly arranged molecules. Low temperature data show a significant lattice parameter contraction resulting in denser packing of the radical cations in the stacking direction. MPA[CuBr2] can be further oxidized by CuBr2 to MPA[Cu2Br4] with MPA2+ in the dicationic state. The oxidation states 0, +1, and +2 of the cations are clearly distinguishable by the bond lengths in the central CNNC azine moiety. All compounds are semiconductors with small band gaps between 0.95 and 1.34 eV. The magnetic properties of MPA[CuX2] are dominated by reduced momenta. At temperatures below 50 K, a small magnetic momentum of about 1/3 of one unpaired electron is observed, which probably arise from paramagnetic impurity in form of Cu2+. For T >50 K magnetic momenta turn into a nearly temperature independent paramagnetism. p‐CF3MPA[CuBr2] is mainly paramagnetic with weak antiferromagnetic exchange (TNéel=6 K, J=−2.1 cm−1).