Magnetic Exchange through the Dianionic Hexaazatrinaphthylene (HATNA) Ligand in {HATNA(FeIICl2)3}2− Containing FeII (S=2) Triangles

Herein, a new method for the preparation of anionic hexaazatrinaphthylene (HATNA) coordination complexes was developed. The reduced HATNA coordinated three FeIICl2 units for the formation of (CV+)2{HATNA(FeIICl2)3}2− ⋅ 3.5 C6H4Cl2 (1) (CV+ is a cationic form of crystal violet). The FeII atoms had a high S=2 spin state and were arranged in nearly equilateral triangles at a distance of approximately 7 Å. The χMT value of 1 was 9.70 emu⋅K/mol at 300 K, exceeding the calculated spin‐only value of three independent high‐spin FeII centers (S=2) (9.00 emu⋅K/mol). A strong antiferromagnetic exchange was observed between FeII atoms through the diamagnetic HATNA units since Weiss temperature is −98 K. Magnetic behavior of 1 was modelled by PHI package obtaining the exchange interaction constant J=−4.6 cm−1 and zero‐field splitting parameter D=5.6 cm−1 at g=2.23. Arrangement of magnetic centers in the equilateral triangles supposes that some degree of spin frustration exists in 1. Crystal structures of two phases of pristine HATNA molecule are also reported. New methods to prepare anionic HATNA coordination complexes from iron metal or iron carbonyls yielded (CV+)2{HATNA(FeIICl2)3}2− ⋅ 3.5C6H4Cl2, where CV+ is the crystal violet cation. The FeII atoms have a high S=2 spin state and form equilateral triangles. The exchange interaction constant between high‐spin FeII is J=−4.6 cm−1 indicating antiferromagnetic coupling of spins as well as a rather large zero‐field splitting parameter of D=5.6 cm−1 with a g‐factor of 2.23.