Origin of the magnetic couplings for the weak ferromagnet Li plus [TCNE]•- (TCNE = Tetracyanoethylene)

Based upon the 16-K crystal structure, the nearest-neighbor spin couplings (J; H = -2JSa center dot S-b) for the weak ferromagnet (=canted antiferromagnet) Li+[TCNE](center dot-)(TCNE = tetracyanoethylene) (T-c = 21 K), which possesses two interpenetrating diamondoid sublattices with two layers of parallel [TCNE](center dot-)s canted with respect to each other by similar to 60 , are computed at the B3LYP/aug-cc-pV-TZ-level. Li[TCNE] has computed interlattice, through-space interactions that exceed the intralattice, through-bonding to Li+ interactions, that are antiferromagnetic. The interlattice interactions dominate the spin coupling leading to the observed weak ferromagnetic behavior. The computed J's based upon the 50-K structure have the strongest ferromagnetic intralayer interlattice in-teractions increase by 2.9 +/- 0.6% while the antiferromagnetic interlayer interlattice interaction increases by 23% with respect to the 16 K results and are in accord with the observed initial increase and subsequent decrease in the temperature dependence of the canting angle that is a consequence of the these changing opposed in-teractions arising from the change in structure as a function of temperature.

Automated summary

Based on the crystal structure, the study calculated the spin couplings of the weak ferromagnetic Li+[TCNE], finding that through-space interactions were stronger than through-bonding interactions to Li+, dominating the spin coupling and leading to the observed weak ferromagnetic behavior.