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

Abstract

Ionic compounds containing iron­(I) hexadecachlorophthalocyanine anions have been obtained for the first time as single crystals: (PPN⁺)­{[Fe­(I)­Cl₁₆Pc­(−2)]⁻} (<b>1</b>), (Ph₃MeP⁺)₂{[Fe­(I)­Cl₁₆Pc­(−2)]⁻}­(Br^–)·C₆H₄Cl₂ (<b>2</b>), and (PPN⁺)₂[Fe­(I, II)­Cl₁₆Pc­(−2)]₃⁽²⁻⁾·4C₆H₄Cl₂ (<b>3</b>), 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 <b>1</b>–<b>3</b>. Salts <b>1</b> and <b>2</b> with integer −1 charge on iron phthalocyanines have uniform and weakly dimerized columns, respectively. Salt <b>3</b> 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 <b>3</b> (3.62–3.84 Å) than those in <b>1</b> and <b>2</b> (5.07–5.45 Å). Calculations show a strong LUMO–LUMO overlapping between [Fe­(I)­Cl₁₆Pc­(−2)]⁻ in <b>1</b>–<b>3</b> 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 <b>1</b>–<b>3</b>. The content of this admixture is less than 1% in all salts. Nevertheless, static magnetic susceptibility measurements for <b>3</b> detected significant magnetization. The effective magnetic moment is 4.05 μ_B 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 <b>3</b> with temperature below 220 K down to 2.72 μ_B at 6 K. Optical spectra of <b>1</b>–<b>3</b> 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