Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of FeII (S=2) Spins in Differently Charged {HAT. (FeIICl2)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 (FeCl2)-Cl-II to form (CV+)(2){HATA . ((FeCl2)-Cl-II)(3)}(2-) . 3 C6H4Cl2 (1) and (CV+)(3){HAT(CN)(6)(.) ((FeCl2)-Cl-II)(3)}(3-) . 0.5CVCl . 2.5 C6H4Cl2 (2). High-spin (S=2) Fe-II atoms in both structures are arranged in equilateral triangles at a distance of 7 angstrom. An antiferromagnetic exchange is observed between Fe-II in {HATA . ((FeCl2)-Cl-II)(3)}(2-) (1) with a Weiss temperature (Theta) of -80 K, the PHI estimated exchange interaction (J) is -4.7 cm(-1). The {HAT(CN)(6) . ((FeCl2)-Cl-II)(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 (FeCl2)-Cl-II units to be aligned parallel to each other in the assembly. As a result, an increase of the chi T-M 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 (FeCl2)-Cl-II have a variety of closely lying excited high-spin states with multiplicity up to S=15/2.

Automated summary

The synthesis of two new complexes through the reduction of metallic iron and their magnetic behaviors were studied. The results revealed that changes in the charge and spin state of the ligand can affect the spin arrangement of the iron ions.