Bis(N-methylimidazole)-Substituted Neutral Phthalocyanines {M-III(MeIm)(2)(Pc)(center dot 3)-}(0) (M = Al, Ga) Containing Radical Trianionic Phthalocyanine Macrocycles

摘要

Reduction of aluminium(III) and gallium(III) chloride phthalocyanines (Pc) in the presence of N-methylimidazole (MeIm) by sodium fluorenone ketyl allows the dissolution of phthalocyanines. Slow mixing with n-hexane crystallizes formally neutral compounds [Al-III(MeIm)(2)(Pc)(center dot 3-)](0)center dot MeIm (1) and [Ga-III(MeIm)(2)(Pc)(center dot 3-)](0)center dot 2C(6)H(4)Cl(2) (2), which contain radical trianionic phthalocyanine {Pc center dot 3-} macrocycles. The formation of Pc center dot 3- is confirmed by the appearance of new bands in the NIR range with maxima at 999 (1) and 994 nm (2) and a blueshift of both the Soret and Q-bands of the phthalocyanines. The phthalocyanine macrocycles in 1 and 2 are planar with the central metal atoms positioned exactly in the Pc plane. The average lengths of the M-N(Pc) and M-N(MeIm) bonds in 1 are 1.956(3) and 2.055(2) angstrom, and they are elongated up to 1.987(1) and 2.161(1) angstrom, respectively, in 2. The formation of the 19 pi-electron system of Pc center dot 3- results in partial disruption of the aromaticity with alternation of shorter and longer C-N(imine) bonds belonging to two oppositely located isoindole units in 1 and 2. The presence of unpaired spins on the macrocycles is justified by intense Lorentzian EPR signals with g = 2.0028 and line-width (Delta H) = 0.648 mT in 1 and g = 2.0011 and Delta H = 0.551 mT in 2 at room temperature. The effective magnetic moment of 2 of 1.65 mu(B) at 300 K indicates the contribution of one non-interacting S = 1/2 spin per formula unit, which is weakly antiferromagnetically coupled with a Weiss temperature of -6 K. Weak coupling can be explained by weak pi-pi interaction between the Pc center dot 3- macrocycles in 2.