Comparative study of beryllium,magnesium and zinc phthalocyanine complexes with 4-picoline

Three new Be(II), Mg(II) and Zn(II) phthalocyaninato(2-) complexes with 4-picoline (4-Mepy) in the crystalline form have been obtained by recrystallization of the respective M(II)Pc in 4-picoline under water-free conditions. BePc and ZnPc in 4-picoline solution form 4 + 1 coordinated complexes, while the 4-Mepy molecules biaxially ligate MgPc. The planar phthalocyaninato(2-) macroring of BePc and ZnPc upon mono-axial ligation by the 4-Mepy molecule adopts the saucer-shape form. The interaction of the central M(II) with the ligated 4-Mepy molecule leads to a deviation of the metal from the centre cavity by ∼0.31 Å and ∼0.35 Å in the Be and Zn phthalocyaninato complexes, respectively. In MgPc, the Pc ring upon biaxial ligation retains a planar configuration. The axial M(II)–N(4-Mepy) bond is longer than the four equatorial M(II)–N_iso bonds in Mg and Zn phthalocyaninato complexes, while in the Be complex the opposite relation between the axial and equatorial Be–N bonds is observed. Thermogravimetric analysis for all these compounds exhibits only one slope down, due to the loss of 4-Mepy molecules from the complexes, which transform finally into the respective M(II)Pc complexes in the β-form.