Manganese(ii) complexes of hexaazatrinaphthylene and hexaazatrianthracene: synthesis, structure and properties

Abstract

Complexes of high-spin (S = 5/2) manganese(II) with hexaazatrinaphthylene (HATNA) and hexaazatrianthracene (HATA) dianions and radical trianions have been obtained in a crystalline form. Neutral HATNA is coordinated with only one Mn^II(dedtc)₂ fragment (dedtc: diethyldithiocarbamate) in [{Mn^II(dedtc)₂}(HATNA)]⁰ (1) with long Mn^II–N(HATNA) bonds of 2.390(5) Å. The HATNA dianions are coordinated with three Mn^II(dedtc)₂ or Mn^II(acac)₂ units in {(K⁺)(crypt)}₂[{Mn^II(dedtc)₂}]₃{(HATNA)}²⁻·2C₆H₄Cl₂ (2) and {(K⁺)(crypt)}₂[{Mn^II(acac)₂}₃{(HATNA)}]²⁻·2C₆H₄Cl₂·C₆H₁₄ (3) (crypt is cryptand[2.2.2]) with shorter Mn^II–N(HATNA) bonds of 2.252(3) and 2.287(4) Å length, respectively. The Mn^II–N(HATA or HATNA) bonds are shortened to 2.160(4) and 2.110(4) Å in dianionic (CV⁺)₂[(Mn^IICl₂)]₃{(HATA)}²⁻·4C₆H₄Cl₂ (4) and trianionic {(K⁺)(crypt)}₃ {(Mn^III₂)₃(HATNA)}³⁻·5C₆H₄Cl₂ (5) complexes, respectively (CV⁺ is a crystal violet cation). It is shown that the Mn^II–N bonds in 1–5 are longer in comparison with the Fe^II–N and especially Co^II–N bonds. Weak antiferromagnetic Mn^II–Mn^II coupling with J values of −1.98 and −2.70 cm⁻¹ is observed for diamagnetic ligands in 2 and 4. The paramagnetic HATNA˙³⁻ ligand (S = 1/2) leads to the additional antiferromagnetic Mn^II–HATNA˙³⁻ coupling with a J value of −6.6 cm⁻¹ in 5, which coexists with weaker Mn^II–Mn^II coupling with a J value of −0.6 cm⁻¹. As a result, the χ_MT value in 5 only weakly depends on temperature. Thus, the Mn^II–HATNA˙³⁻ and Mn^II–Mn^II couplings are noticeably smaller than those in previously studied Co^II and Fe^II assemblies. Zero-field splitting parameter D is rather high for manganese(II) ions in 2, 4 and 5 being −3.1 to −4.6 cm⁻¹. Weaker exchange coupling allows the observation of both EPR signals from Mn^II and the paramagnetic ligand. An isotropic EPR signal from Mn^II with a g-factor of 2.03–2.04 is observed in 2 in the whole studied temperature range. An isotropic EPR signal is also observed in 4 with g = 2.0346 at 295 K. This signal shifts to a lower g-factor at 100 K, whereas low-field components appear only at 4.5 K. The contribution from HATNA˙³⁻ in 5 probably decreases the g-factor to 2.0017 at 295 K. Zero-field splitting of the EPR signal for Mn^II is manifested at 4.2 K.