Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of Fe II (S=2) Spins in Differently Charged {HAT ⋅ (Fe II Cl 2 ) 3 } n (n=2- and 3-) Assemblies of Hexaazatriphenylenes (HAT).

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 Fe II Cl 2 to form (CV + ) 2 {HATA ⋅ (Fe II Cl 2 ) 3 } 2-  ⋅ 3 C 6 H 4 Cl 2 (1) and (CV + ) 3 {HAT(CN) 6. (Fe II Cl 2 ) 3 } 3-  ⋅ 0.5CVCl ⋅ 2.5 C 6 H 4 Cl 2 (2). High-spin (S=2) Fe II atoms in both structures are arranged in equilateral triangles at a distance of 7 Å. An antiferromagnetic exchange is observed between Fe II in {HATA ⋅ (Fe II Cl 2 ) 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  ⋅ (Fe II Cl 2 ) 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 Fe II and HAT(CN) 6 .3- spins with J 1 =-164 cm -1 (-2 J formalism) and by a weaker antiferromagnetic coupling between the Fe II spins with J 2 =-15.4 cm -1 . The stronger coupling results in the spins of the three Fe II Cl 2 units to be aligned parallel to each other in the assembly. As a result, an increase of the χ M 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 Fe II 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 Fe II Cl 2 have a variety of closely lying excited high-spin states with multiplicity up to S=15/2.