Diamagnetic to paramagnetic transition in trisdimethylaminocyclopropenium tetracyanoquinodimethanide (TDAC-TCNQ)

Radhakrishnan, T. P. ; Van Engen, D. ; Soos, Z. G. (1987) Diamagnetic to paramagnetic transition in trisdimethylaminocyclopropenium tetracyanoquinodimethanide (TDAC-TCNQ) Molecular Crystals and Liquid Crystals, 150 (1). pp. 473-492. ISSN 1542-1406

Full text not available from this repository.

Official URL: http://www.tandfonline.com/doi/abs/10.1080/0026894...

Related URL: http://dx.doi.org/10.1080/00268948708074815


Two crystalline forms of TDAC-TCNQ obtained under different crystallization conditions are both stable at room temperature. The diamagnetic yellow form belongs to the triclinic space group P1̅, with unit cell parameters a=7.030(2), b=8.791(2), c=17.306(6) Å, α=94.23(3)°, β=101.24(3)°, γ=90.95(2)°, V=1045.7(6) Å3 and Z=1 (Rw=0.073); it also has a long [sgrave]-bond between TCNQ- in adjacent stacks, but shows no thermally activated triplets. The paramagnetic black form belongs to the monoclinic space group P2l/c, with unit cell parameters a = 17.536(4), b = 7.272(2), c = 17.776(4) Å, β=113.36(2)°, V = 2081.2(9) Å3 and Z=4 (Rw = 0.058); it corresponds to a mixed stack of closed shell TDAC+ ions and TCNQ- ion-radicals. Heating the yellow crystal above 79±3°C converts it to the black form. Subsequent cooling below -50±10°C regains the yellow form with paramagnetic TCNQ- defects. The hysteresis is interpreted in terms of a high activation barrier for the large (>2Å) molecular motion of each TCNQ-, in contrast to the unactivated, small amplitude (<0.2 Å) motions associated with spin-Peierls transitions.

Item Type:Article
Source:Copyright of this article belongs to Taylor and Francis Group.
Keywords:TCNQ Complexes; Magneto-structural Transition
ID Code:78125
Deposited On:17 Jan 2012 11:43
Last Modified:17 Jan 2012 11:43

Repository Staff Only: item control page