Weak ferromagnetism below 12 K in a lithium tetrafluorotetracyanoquinodimethanide salt

The spin interaction between TCNQF4−. molecules in the Li+, Na+, K+, Rb+, Cs+ and NMe4+ salts was investigated in the temperature range of 2 to 300 K. The other salts than Li+·TCNQF4−. exhibited almost temperature-independent small susceptibilities, indicating disappearance of the free radical moments. On the other hand, the susceptibility of the Li+ salt obeyed a Curie-Weiss law above 50 K with a Curie constant of 0.36(1) emu K mol−1 and an asymptotic Curie temperature of −30(2) K. A sudden enhancement of the susceptibility was observed at 12 K. These results suggest an antiferromagnetic ordering of the radical anions accompanied with spin cantings (weak ferromagnetism) in the Li+ salt below 12 K.