Hexaazatrianthracene (HATA) and hexaazatriphenylenehexacarbonitrile {HAT(CN)6 } are reduced by metallic iron in the presence of crystal violet (CV+ )(Cl- ). Anionic ligands are produced, which simultaneously coordinate three FeII Cl2 to form (CV+ )2 {HATA ⋅ (FeII Cl2 )3 }2- ⋅ 3 C6 H4 Cl2 (1) and (CV+ )3 {HAT(CN)6. (FeII Cl2 )3 }3- ⋅ 0.5CVCl ⋅ 2.5 C6 H4 Cl2 (2). High-spin (S=2) FeII atoms in both structures are arranged in equilateral triangles at a distance of 7 Å. An antiferromagnetic exchange is observed between FeII in {HATA ⋅ (FeII Cl2 )3 }2- (1) with a Weiss temperature (Θ) of -80 K, the PHI estimated exchange interaction (J) is -4.7 cm-1 . The {HAT(CN)6 ⋅ (FeII Cl2 )3 }3- assembly is obtained in 2. The formation of HAT(CN)6 .3- is supported by the appearance of an intense EPR signal with g=2.0037. The magnetic behavior of 2 is described by a strong antiferromagnetic coupling between the FeII and HAT(CN)6 .3- spins with J1 =-164 cm-1 (-2 J formalism) and by a weaker antiferromagnetic coupling between the FeII spins with J2 =-15.4 cm-1 . The stronger coupling results in the spins of the three FeII Cl2 units to be aligned parallel to each other in the assembly. As a result, an increase of the χM T values is observed with the decrease of temperature from 9.82 at 300 K up to 15.06 emu ⋅ K/mol at 6 K, and the Weiss temperature is also positive being at +23 K. Thus, a change in the charge and spin state of the HAT-type ligand to ⋅3- results in ferromagnetic alignment of the FeII spins, yielding a high-spin (S=11/2) system. DFT calculations showed that, due to the high symmetry and nearly degenerated LUMO of both HATA and HAT(CN)6 , their complexes with FeII Cl2 have a variety of closely lying excited high-spin states with multiplicity up to S=15/2.
Keywords: crystal structure; hexaazatrianthracene; hexaazatriphenylenehexacarbonitrile; magnetic properties; reduction; singlet-triplet transitions.
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