Complexes of d‐ and f‐metal Ions with Redox‐Active and Highly Symmetric Truxenone Ligand: Effect of Cations and Coordination on Distortions of Radical Anions and Singlet–Triplet Transition in Dianions

European Journal of Inorganic Chemistry. 2025. Vol. 28. No. 14. Article e202400760.

Krivenko K., Shestakov A., Maxim A. Faraonov, Alexey V. Kuzmin, Khasanov S., Otsuka A., Yamochi H., Kitagawa H., Konarev D.

Truxenone (Tr) with high C3h symmetry forms crystalline radical anion and dianion salts. The {Bu3MeP+}(Tr⋅−) (1) and {Cp*2Co+)}(Tr⋅−)⋅2 C6H4Cl2 (2) show intense low‐energy absorption up to 2000 nm. Calculations predict Jahn–Teller distortions for Tr⋅−, which are enhanced by the asymmetric approach of cations to Tr⋅−, leading to C=O bond length alternation and EPR signal asymmetry in 2. Two cesium ions form short contacts of 3.07–3.45 Å with oxygen atoms of Tr2‐ in {Cryptand[2.2.2](Cs+)}2(Tr2‐) (3), linking the dianion into a 1D polymer. Calculations suggest a triplet state for the dianion, but the unsymmetric approach of Cs+ to the oxygen atoms of Tr2‐ stabilizes the singlet ground state. The triplet state is populated above 100 K. An estimated singlet–triplet energy gap is 344 ± 7 K. Radical anions of Tr⋅− coordinate with one d‐ or f‐metal, forming {Cp*2Co+}{TbIII(TMHD)3⋅Tr}‐⋅1.5 C7H8 (4) and {Cp*2Co+}{MnII(acac)2⋅Tr}‐⋅2.4 C6H4Cl2 (5) (TMHD is 2,2,6,6‐tetramethyl‐3,5‐heptanedionate; acac is acetylacetonate). Antiferromagnetic TbIII–Tr⋅− coupling is observed in 4. The χMT value of 3.32 emu⋅K/mol at 300 K for 5 with high‐spin MnII is lower than expected. That indicates a spin state of S=2 owing to the antiparallel alignment of MnII and Tr⋅− spins. Strong MnII–Tr⋅− coupling arises from the spin density localization on the oxygen coordinated to Mn(II). Complexes with metals demonstrate low‐energy absorption with maxima at 1504–1740 nm.

Keywords: Truxenone, труксенон