Magnetic Exchange through the Dianionic Hexaazatrinaphthylene (HATNA) Ligand in {HATNA(Fe^IICl₂)₃}²⁻ Containing Fe^II (S=2) Triangles

Abstract

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.

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)

“…The χ M value in this complex increases down to 1.9 K, showing some degree of spin frustration. [8] On the contrary, a drop of the χ M values is observed in 1 even below 15 K (Figure 2a), indicating antiferromagnetic ordering of the Fe II spins within the assemblies (Figure 2a). One of the reasons for the suppression of spin frustration in the Fe II triangles of 1 can be the reduction of the site symmetry of most part of the {HATA • (FeCl 2 ) 3 } 2À assemblies to 1 at lower temperatures.…”

“…Crystal violet was purchased from Acros. 1,8,9,16,17, by condensation of three equivalents of o-naphthalenediamine with one equivalent of C 6 O 6 • 8H 2 O in glacial acetic acid under reflux in argon atmosphere for 16 h until complete discoloration of the solution and by precipitation of red powder which was washed with acetone and dried. IR spectra and elemental analysis support the formation of HATA.…”

“…This ligand has nongenerated LUMO with a large LUMO-LUMO + 1 gap, and low-lying high-spin triplet (S = 1) and quartet (S = 3/2) states are not available for the dianion and trianion HATNA ligand. [8]…”

“…Recently, the first dianionic {HATNA • (Fe II Cl 2 ) 3 } 2À assembly of HATNA with three high-spin Fe II centers (S = 2) was obtained and studied in our laboratory. [8] Here, it should be noted that other HAT-type ligands are still not investigated in such assemblies.…”

“…[4,13,14] Previously, a synthetic method for the reduction of HATNA with simultaneous coordination of Fe II Cl 2 to the N 2 sites was developed, and this allowed successful preparation and characterization of {HATNA • (Fe II Cl 2 ) 3 } 2À . [8] In this work, this method has been extended for the preparation of dianion and radical-trianion assemblies of HATA and HAT(CN) 6 . Good-quality single crystals suitable for X-ray diffraction analysis are isolated:…”