Very strong antiferromagnetic coupling interaction in (TCNQ) ₂^2- spin dimers H-bonding molecular magnetic compound

An ion-pair type of hydrogen bonding molecular magnetic compound was prepared by means of combining the paramagnetic TCNQ^- (TCNQ=7,7,8,8-tetracyanoquinodimethane) and nonmagnetic 4-aminopyridinium. The single crystal structure of the title compound shows two TCNQ^- anions form an isolated -type (TCNQ)₂^2- dimer, and the adjacent (TCNQ)₂^2- dimers are connected by 4-aminopyridinium via strong hydrogen-bonding. The variable temperature magnetic susceptibility measurement in the temperature range of 2∼ 400 K indicates diamagnetism characteristics of the compound. The magnetic coupling constants between the neighboring TCNQ^- anions were evaluated by the broken-symmetry approach in the density functional theory (DFT) framework. The results reveal that the strong antiferromagnetic coupling interaction (J/k_B ≈ 1805 K) within the π-type (TCNQ)₂^2- dimer gives rise to the diamagnetism behavior for this ion-pair compound.