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Radical anion and dianion salts of titanyl macrocycles with acceptor substituents or an extended π-system†
Maxim A. Faraonov,Dmitri V. Konarev,Salavat S. Khasanov,Sergey I. Troyanov,Rimma N. Lyubovskaya
Dalton Transactions Pub Date : 02/16/2017 00:00:00 , DOI:10.1039/C6DT04896J
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.

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