Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of FeII (S=2) Spins in Differently Charged HAT ⋅ (FeIICl2) 3n (n=2‐ and 3‐) Assemblies of Hexaazatriphenylenes (HAT)

Abstract 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.