4+1 Complexes of zinc phthalocyanine with pyridine derivative ligands

• Axially ligated by pyridine derivatives of ZnPc complexes are obtained.
• Two polymorphic forms of ZnPc(3,4-Dimepy) and one form of ZnPc(4-Etpy) are reported.
• UV–Vis spectra of ZnPcL dyes show that Pc π-system is not perturbed by the axial L.
• The ZnPcL dyes are about 3–4 times more soluble than the parent ZnPc pigment.
• 3D MESP maps are helpful for understand the interaction of ZnPc with pyridine derivatives.

Two complexes of zinc phthalocyanine monoaxially ligated by 3,4-dimethylpyridine (1) and 4-ethylpyridine (2) were obtained in crystalline forms. Compound 1 depending on the crystallisation condition crystallises in two crystalline modifications, i.e. monoclinic (P21/c, 1m) and orthorhombic (Pccn, 1o), whereas compound 2 crystallises only in one orthorhombic form (Pccn space system). Structures 1o and 2 are isotypic; an explanation of that behaviour was proposed. Each structure contains the zinc phthalocyanine and the ligand molecules in molar ratio 1:1, which was confirmed by X-ray single diffraction and thermogravimetric analysis. Ligation of the ZnPc by N-ring aromatic ligands with formation of complexes 1 and 2 does not change the colouring properties, but increases their solubility in the organic solvents comparing to the parent ZnPc pigment.

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