Abstract
The singlet-triplet splitting energy gap ΔES-T=ES-ET is calculated for the ortho-, meta-, and para-xylylenes and their heteroatomic analogous by means of AM1-CI approach. It is shown that when the radical centers\(R^. (R^. = H_2 C^. - ,H_2 N^{. + } - or HN^. - )\) are twisted sufficiently far out of conjugation with the benzene ring, ΔES-T tends to zero or is negative, i.e. ortho-, meta-, and para-phenylenes turn into weak ferromagnetic or antiferromagnetic coupling unit, while they are strong ferromagnetic (meta-isomers) or antiferromagnetic (ortho-, para-isomers) coupling units under planar conformation. It is suggested that serious twisted conformation is not recommended candidate for the design of novel high-spin molecules with stable high-spin ground states by ortho- or para-phenylene coupling unit.
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Zhang, J., Zhang, H., Wang, L. et al. Effect of configuration and conformation on the spin multiplicity in xylylene type biradicals. Sc. China Ser. B-Chem. 43, 524–530 (2000). https://doi.org/10.1007/BF02969498
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DOI: https://doi.org/10.1007/BF02969498