Molecular structure, optical and magnetic properties of metal-free phthalocyanineradical anions in crystalline salts (H2Pc˙−)(cryptand[2,2,2][Na+])·1.5C6H4Cl2 and (H2Pc˙−)(TOA+)·C6H4Cl2 (TOA+ is tetraoctylammonium cation)

Abstract

Ionic compounds containing radical anions of metal-free phthalocyanine (H₂Pc˙⁻): (H₂Pc˙⁻)(cryptand[2,2,2][Na⁺])·1.5C₆H₄Cl₂ (1) and (H₂Pc˙⁻)(TOA⁺)·C₆H₄Cl₂ (2) have been obtained as single crystals for the first time. Their crystal structures have been determined, and optical and magnetic properties have been investigated. The H₂Pc˙⁻ radical anions have a slightly bowl-like shape with four pyrrole nitrogen atoms located below the molecular plane, while four phenylene substituents are located above this plane. Changes in the average length of N–C and C–C bonds in H₂Pc˙⁻ in comparison with those in neutral H₂Pc indicate that negative charge is mainly delocalized over the 24-atom phthalocyanine ring rather than the phenylene substituents. The H₂Pc˙⁻ formation is accompanied by a shift of up to 10 cm⁻¹ and disappearance of some intense IR-active bands whereas the band of the N–H stretching mode is shifted by 21–27 cm⁻¹ to larger wavenumbers. New bands attributed to H₂Pc˙⁻ appear in the NIR spectra of the salts with maxima at 1033 and 1028 nm for 1 and 2, respectively. The formation of H₂Pc˙⁻ is accompanied by the splitting of the Soret and Q-bands of H₂Pc into several bands and their blue-shift up to 32 nm. Narrow EPR signals with g = 2.0033 and linewidth of 0.16–0.24 mT at room temperature in the spectra of the salts were attributed to the H₂Pc˙⁻ radical anions. According to SQUID measurements they have S = 1/2 spin states with effective magnetic moments of 1.73 (1) and 1.78 (2) μ_B at 300 K. Magnetic behavior of 1 and 2 follows the Curie–Weiss law with negative Weiss temperatures of −0.9 and −0.5 K, respectively, indicating weak antiferromagnetic interactions of spins. The EPR signal splits into two lines below 120 and 80 K for 1 and 2, respectively and these lines are noticeably broadened below 25 K.