Structural effect of the competition of 4-picoline and water molecules to form complexes with Be, Mg and Zn phthalocyanines

Abstract

The BePc(4-Mepy), MgPc(4-Mepy) 2 were recrystallised from wet 4-picoline and the aqua M((II) phthalocyaninato complexes, BePcH 2O · (4-Mepy) ( Ia), (MgPcH 2O · (4-Mepy)) 2 ( IIa) and (MgPcH 2O · (4-Mepy) 2) · (4-Mepy) ( IIb), have been obtained. Recrystallisation of ZnPc(4-Mepy) in wet 4-picoline yields the β-ZnPc in microcrystalline form. The Ia, IIa and IIb complexes were obtained in crystalline form. The composition of the Mg complexes ( IIa and IIb) depends on the crystallisation temperature. The BePcH 2O · (4-Mepy) compound crystallises in the centrosymmetric space group of the triclinic system, while both Mg complexes crystallise in the P2 1/ n space group of the monoclinic system. In all crystals the central M(II) atom (Be and Mg) is 4 + 1 coordinated, equatorially by four N-isoindole atoms of Pc macrocycle and axially by O atom of water molecule. Interaction of the central M atom of MgPc with axially ligated water molecule leads to the saucer-shape of the Pc ring and deviates the central M(II) atom from the N 4-isondole plane by 0.308(2), 0.482(2) and 0.537(2) Å in Ia, IIa and IIb, respectively. The molecules in the Ia and IIa crystals are linked together by a pair of O–H⋯N hydrogen bonds between the H atom of water molecule and the azamethine N atom of the other Pc into a dimeric structure, and the 4-picoline molecules are linked to the (MPcH 2O) 2 dimeric structure. In IIb crystal the MgPcH 2O molecule is linked by O–H⋯N hydrogen bonds with two 4-picoline molecules, while the third 4-picoline molecule interacts only by the van der Waals forces. The O–H⋯N hydrogen bonding system and the π–π interactions between the aromatic Pc macrocyles are the key for the molecular arrangement and stabilisation of the structure. The stability of the solid-state complexes was analysed by thermogravimetric measurements. Only the solid-state spectrum of IIa complex exhibits an intense near IR absorption band. The spectra of IIa and IIb in solution are identical, the Q band is blue shifted in O-donor solvents comparing with the spectrum in N-donor solvents.