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  • Title: Radical anion and dianion salts of titanyl macrocycles with acceptor substituents or an extended π-system.
    Author: Faraonov MA, Konarev DV, Fatalov AM, Khasanov SS, Troyanov SI, Lyubovskaya RN.
    Journal: Dalton Trans; 2017 Mar 14; 46(11):3547-3555. PubMed ID: 28240750.
    Abstract:
    Crystalline anionic salts of titanyl macrocycles with acceptor substituents or an extended π-system have been obtained for the first time: (PPN+)2{O[double bond, length as m-dash]TiIV(PcCl84-)}2- (1), (PPN+){O[double bond, length as m-dash]TiIV(Nc˙3-)}˙-·2C6H4Cl2 (2) and (PPN+)2{O[double bond, length as m-dash]TiIV(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 {O[double bond, length as m-dash]TiIV(Nc˙3-)}˙- provides the shift of the NIR band to smaller energies (1159 nm) in comparison with those in the spectra of {O[double bond, length as m-dash]TiIV(Pc˙3-)}˙- (995-998 nm). Reduction of macrocycles leads also to the alternation of C-Nimine 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[double bond, length as m-dash]TiIV(PcCl84-)}2- and {O[double bond, length as m-dash]TiIV(AceTPrzPz4-)}2- dianions, respectively. Salt 2 contains nearly isolated [{O[double bond, length as m-dash]TiIV(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.
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