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

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) · 3– ] 0 · MeIm ( 1 ) and [Ga III (MeIm) 2 (Pc) · 3– ] 0 · 2C 6 H 4 Cl 2 ( 2 ), which contain radical trianionic phthalocyanine {Pc · 3– } macrocycles. The formation of Pc · 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) Å, and they are elongated up to 1.987(1) and 2.161(1) Å, respectively, in 2 . The formation of the 19π‐electron system of Pc · 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 linewidth (Δ H ) = 0.648 mT in 1 and g = 2.0011 and Δ H = 0.551 mT in 2 at room temperature. The effective magnetic moment of 2 of 1.65 µ 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 π–π interaction between the Pc · 3– macrocycles in 2 .