Crystalline salts of metal phthalocyanine radical anions [M(Pc3-)]- (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(Pc3-)]-·C6H4Cl2 (M = CuII (1), PbII (2), VIVO (3) and SnIVCl2 (4)) and {cryptand[2,2,1](Na+)}[SnIVCl2(Pc3-)]-·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 Pc3- 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 [CuII(Pc3-)]- and [VIVO(Pc3-)]- radical anions contain paramagnetic CuII and VIVO centers and the Pc3- 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/kB = 7.7 K within [VIVO(Pc3-)]- 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/kB = -18 K.