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

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.