Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of Fe<sup>II</sup> (<i>S</i>=2) Spins in Differently Charged {HAT ⋅ (Fe<sup>II</sup>Cl<sub>2</sub>)<sub>3</sub>}<sup><i>n</i></sup> (<i>n</i>=2‐ and 3‐) Assemblies of Hexaazatriphenylenes (HAT)
Maxim V. Mikhailenko, Salavat S. Khasanov, Alexader F. Shestakov, Alexey V. Kuźmin, Akihiro Otsuka, Hideki Yamochi, Hiroshi Kitagawa, Dmitri V. Konarev
Abstract
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.