Crystalline salts of metal phthalocyanine radical anions [M(Pc˙3−)]˙− (M = CuII, PbII, VIVO, SnIVCl2) with cryptand(Na+) cations: structure, optical and magnetic properties

Abstract

Radical anion salts of metal phthalocyanines {cryptand[2,2,2](Na⁺)}[M(Pc˙³⁻)]˙⁻·C₆H₄Cl₂ (M = Cu^II (1), Pb^II (2), V^IVO (3) and Sn^IVCl₂ (4)) and {cryptand[2,2,1](Na⁺)}[Sn^IVCl₂(Pc˙³⁻)]˙⁻·C₆H₄Cl₂ (5) have been obtained as single crystals. Phthalocyanine planes form channels to accommodate the cryptand[2,2,2](Na⁺) cations and solvent C₆H₄Cl₂ molecules in 1–3. Nearly square phthalocyanine layers are formed in salts 4 and 5, which are parallel to the ac plane and have an effective π–π interaction between the Pc˙³⁻ macrocycles. The using of smaller cryptand[2,2,1](Na⁺) cations in 5, instead of larger cryptand[2,2,2](Na⁺) cations in 4, allows one to obtain more closely packed Pc layers. Reduction in the salts was centered on the Pc macrocycles, providing alternation of the C–N (imine) bonds in Pc due to partial loss of aromaticity. New bands were also observed in the NIR spectra at 946–1006 nm and the Soret and Q-bands were essentially blue-shifted in the spectra of the salts. The [Cu^II(Pc˙³⁻)]˙⁻ and [V^IVO(Pc˙³⁻)]˙⁻ radical anions contain paramagnetic Cu^II and V^IVO centers and the Pc˙³⁻ radical trianions, both having a S = 1/2 spin state. These radical anions were nearly isolated in the salts. Weak antiferromagnetic coupling with a Weiss temperature (θ) of −2 K was observed in 1. The magnetic behavior of 3 was described by a modified singlet–triplet model with a ferromagnetic exchange coupling of J/k_B = 7.7 K within [V^IVO(Pc˙³⁻)]˙⁻ and θ = −1.3 K. The stronger antiferromagnetic coupling with a Weiss temperature of θ = −64 K was observed in 4 and was accompanied by the decrease of molar magnetic susceptibility below 35 K due to antiferromagnetic ordering of spins. The magnetic behavior of 4 was described using the Heisenberg model for quasi-square two-dimensional antiferromagnetic coupling between spins with an exchange interaction of J/k_B = −18 K.