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

Article abstract of DOI:10.1039/c6dt04896j

Crystalline anionic salts of titanyl macrocycles with acceptor substituents or an extended π-system have been obtained for the first time: (PPN⁺)₂{O=Ti^IV(PcCl₈^4?)}^2? (1), (PPN⁺){O=Ti^IV(Nc^?3?)}^??·2C₆H₄Cl₂ (2) and (PPN⁺)₂{O=Ti^IV(AceTPrzPz^4?)}^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 {O=Ti^IV(Nc^?3?)}^?? provides the shift of the NIR band to smaller energies (1159 nm) in comparison with those in the spectra of {O=Ti^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 {O=Ti^IV(PcCl₈^4?)}^2? and {O=Ti^IV(AceTPrzPz^4?)}^2? dianions, respectively. Salt 2 contains nearly isolated [{O=Ti^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.