Molecular Structure, Optical and Magnetic Properties of Iron Tetra(2,3-quinoxalino)porphyrazine [(N-MeIm)2FeI{T(2,3-Q)Pz}•3-]}•2- Radical Dianions

Abstract

Iron(II) tetra(2,3-quinoxalino)porphyrazine, Fe II T(2,3-Q)Pz, was obtained using diaminomaleonitrile and o-phenylenediamine as starting materials. Reduction of Fe II T(2,3-Q)Pz by sodium fluorenone ketyl in the presence of cryptand[2.2.2] and N-methylimidazole followed by precipitation of crystals leads to crystalline salt {cryptand[2.2.2](Na +)} 2 ⋅[(N-MeIm) 2 Fe I {T(2,3-Q)Pz} •3-] •2-⋅3C 6 H 4 Cl 2 ⋅2H 2 O (1). Molecular structure and properties of the [(N-MeIm) 2 Fe I {T(2,3-Q)Pz} •3-] •2radical dianions have been studied. Reduction of Fe II T(2,3-Q)Pz is accompanied by strong blue shift of Soret band in spectrum of 1 but Q-band has close position to that in the spectrum of neutral macrocycle. There is an alternation of the C-N meso bonds in the macrocycle in 1, the difference between short and long C-N meso bonds of 0.017 Ȧ supports the formation of radical trianionic T(2,3-Q)Pz •3macrocycle. Coordination of N-methylimidazole molecules to iron (I) atoms with the Fe-N(imidazole) distance of 1.999(7) Ȧ is observed. Both Fe I atom and radical trianionic {T(2,3-Q)Pz} 3•macrocycle contribute to the EPR signal of 1, which is well interpreted as the superposition of Lorentzian shaped lines with g 1 = 2.0917, g 2 = 2.0679, g 3 = 2.0292, g 4 = 1.9991 and g 5 = 1.9922. The lines with higher g-factor (g 1 and g 2) value can be attributed to low spin (S = 1/2) Fe I whereas the lines with lower g-factor (g 4 and g 5) values can be attributed to the radical trianionic {T(2,3-Q)Pz} •3macrocycle. The line with intermediate g-factor value (g 3) can originate from the contribution of both components. The value of effective magnetic moment at 300 K (2.32 µ B) indicates a contribution of two non-interacting S = 1/2 spins from iron(I) atoms and radical trianionic {T(2,3-Q)Pz} •3macrocycle. These spins weakly antiferromagnetically interact with Weiss temperature of-3 K.

Crystalline salts of anionic free-base tetrapyrazinoporphyrazines with alkyl-substituents or an extended π-electron system

“…Sodium fluorenone ketyl ( E redox = −1.3 V vs. SCE 34 ), potassium graphite (KC 8 ), zinc dust ( E redox = −0.762 V vs. SHE 35 ), and fullerene {cryptand(Na + )}(C 60 ˙ − ) salt were successfully used to generate anionic species of TPyzPzs. 14,23–26,31,36…”

“…) salt were successfully used to generate anionic species of TPyzPzs. 14,[23][24][25][26]31,36 In this work, we used zinc dust as a reductant for octamethyl-and octaethyl tetrapyrazinoporphyrazines and tetra-2,3-[5,6-(9,10-phenanthro)pyrazino]porphyrazine in the presence of PPNCl in o-dichlorobenzene. That led to the dissolution of starting macrocycles and the formation of dark purple solutions.…”