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Issue 6, 2008
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Towards understanding of magnetic interactions within a series of tetrathiafulvalene–π conjugated-verdazyl diradical cation system: a density functional theory study

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Abstract

The intramolecular magnetic exchange coupling constants (J) for a series of tetrathiafulvalene (TTF) and verdazyl diradical cations connected by a range of π conjugated linkers have been investigated by means of methodology based on unrestricted density functional theory. The magnetic interaction between radicals is transmitted via π–electron conjugation for all considered compounds. The calculation of J yields strong or medium ferromagnetic coupling interactions (in the range of 56 and 300 K) for diradical cations connected by linkers with an even number of carbon atoms that are able to provide a spin polarization pathway, while antiferromagnetic coupling is predicted when linkers with an odd number of carbon atoms are employed. The topological analysis of spin density distributions have been used to reveal the effects of the spin polarization on both linkers and spin carriers. The absence of heteroatoms that impede the spin polarization pathway, and the existence of a unique spin polarization path instead of several possible competitive routes are factors which contribute to large positive J values favoring ferromagnetic interactions between the two terminal π-radicals. The magnitude of J depends strongly on the planarity of the molecular structure of the diradical cation since a more effective orbital overlap between the two π-systems can be achieved. Hence, the dependence of J on the torsion angle (θ) of each spin carrier has been analyzed. In this respect, our findings show that this geometrical distortion reduces largely the calculated J values for ferromagnetic couplings, leading to weak antiferromagnetic interactions for a torsion angle of 90°.

Graphical abstract: Towards understanding of magnetic interactions within a series of tetrathiafulvalene–π conjugated-verdazyl diradical cation system: a density functional theory study

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Publication details

The article was received on 04 Oct 2007, accepted on 14 Nov 2007 and first published on 23 Nov 2007


Article type: Paper
DOI: 10.1039/B715315E
Phys. Chem. Chem. Phys., 2008,10, 857-864

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    Towards understanding of magnetic interactions within a series of tetrathiafulvalene–π conjugated-verdazyl diradical cation system: a density functional theory study

    V. Polo, A. Alberola, J. Andres, J. Anthony and M. Pilkington, Phys. Chem. Chem. Phys., 2008, 10, 857
    DOI: 10.1039/B715315E

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