Radical anion and dianion salts of titanyl macrocycles with acceptor substituents or an extended π-system

Abstract

Crystalline anionic salts of titanyl macrocycles with acceptor substituents or an extended π-system have been obtained for the first time: (PPN⁺)₂{OTi^IV(PcCl₈⁴⁻)}²⁻ (1), (PPN⁺){OTi^IV(Nc˙³⁻)}˙⁻·2C₆H₄Cl₂ (2) and (PPN⁺)₂{OTi^IV(AceTPrzPz⁴⁻)}²⁻·1.3C₆H₄Cl₂·0.8C₆H₅CN (3) where PPN⁺ is the bis(triphenylphosphoranylidene)ammonium cation, PcCl₈ – 2,3,9,10,16,17,23,24-octachlorophthalocyanine; Nc – 2,3-naphthalocyanine, AceTPrzPz – tetra(acenaphthenopyrazino)porphyrazine. Salts 1–3 were obtained in the reduction of the parent titanyl macrocycles by fluorenone ketyl in the presence of an excess of PPNCl in o-dichlorobenzene with following precipitation of crystals with n-hexane. Reduction of macrocycles in 1–3 is accompanied by the appearance of intense NIR bands in the solid spectra at 963–1159 nm. It has been found that the extended π-system with linear annulation in {OTi^IV(Nc˙³⁻)}˙⁻ provides the shift of the NIR band to smaller energies (1159 nm) in comparison with those in the spectra of {OTi^IV(Pc˙³⁻)}˙⁻ (995–998 nm). Reduction of macrocycles leads also to the alternation of C–N_imine bonds due to partial disruption of their aromaticity. The disruption is higher for the dianions in 1 and 3 in comparison with the radical anions in 2. One-dimensional π–π stacking chains and layers are formed in 1 and 3 with diamagnetic {OTi^IV(PcCl₈⁴⁻)}²⁻ and {OTi^IV(AceTPrzPz⁴⁻)}²⁻ dianions, respectively. Salt 2 contains nearly isolated [{OTi^IV(Nc˙³⁻)}˙⁻]₂ dimers with a strong π–π interaction between paramagnetic radical anion macrocycles. As a result, a transition from the triplet to singlet state with antiparallel ordering of spins within the dimers is observed in 2 below 200 K.