Molecular Design of Anionic Phthalocyanines with π–π Stacking Columnar Arrangement. Crystal Structures, Optical, and Magnetic Properties of Salts with the Iron(I) Hexadecachlorophthalocyanine Anions
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Ionic compounds containing iron(I) hexadecachlorophthalocyanine anions have been obtained for the first time as single crystals: (PPN+){[Fe(I)Cl16Pc(−2)]−} (1), (Ph3MeP+)2{[Fe(I)Cl16Pc(−2)]−}(Br–)·C6H4Cl2 (2), and (PPN+)2[Fe(I, II)Cl16Pc(−2)]3(2−)·4C6H4Cl2 (3), where PPN+ is the cation of bis(triphenylphosphoranylidene)ammonium and Ph3MeP+ is the triphenylmethylphosphonium cation. The [Fe(I)Cl16Pc(−2)]− anions form closely packed π–π stacking columns in 1–3. Salts 1 and 2 with integer −1 charge on iron phthalocyanines have uniform and weakly dimerized columns, respectively. Salt 3 has two cations per three iron phthalocyanine molecules which are arranged in trimers within the columns. Different shift of phthalocyanines at the same interplanar distances of 3.33–3.38 Å provides essentially shorter Fe···Fe distances in 3 (3.62–3.84 Å) than those in 1 and 2 (5.07–5.45 Å). Calculations show a strong LUMO–LUMO overlapping between [Fe(I)Cl16Pc(−2)]− in 1–3 with the overlap integrals of 4.1–7.6 × 10–3. Weak signals attributed to the [Fe(II)Cl16Pc(−3)]− species with the delocalization of electron on the phthalocyanine macrocycles are observed in the EPR spectra of 1–3. The content of this admixture is less than 1% in all salts. Nevertheless, static magnetic susceptibility measurements for 3 detected significant magnetization. The effective magnetic moment is 4.05 μB per formula unit at 300 K. It can originate from the spins localized on the iron atoms of [Fe(I)Cl16Pc(−2)]−. The Weiss temperature of −53 K in the 60–300 K range indicates a strong antiferromagnetic interaction of spins which results in the decreases of magnetic moment of 3 with temperature below 220 K down to 2.72 μB at 6 K. Optical spectra of 1–3 show bands ascribed to [Fe(I)Cl16Pc(−2)]− at 339–349, 538–548, 685–691, and 805–821 nm. The bands in the NIR range at 1740–1810 nm were attributed to charge transfer excitations within phthalocyanine columns associated with the unpaired electrons on the iron atoms.
