Water-Involved Hydrogen Bonds in Dimeric SupramolecularStructures of Magnesium and Zinc Phthalocyaninato Complexes

摘要

Two dimeric supramolecular structures {MgPc(H2O)·4-methylmorpholine}2—(>1) and {ZnPc(H2O)·4-methylmorpholine}2—(>2) formed from two molecules of magnesium and zinc aquaphthalocyanines in 4-methylmorpholine solution were revealed by single-crystal X-ray diffraction. Coordinated H2O molecules to the metal center of respective Mg or Zn phthalocyanines oriented face-to-face to form two hydrogen bonds, one of them connecting via O–H···N-azamethine atom to form a dimeric structure in the crystals with ring-to-ring distances of 3.412(3) Å in >1 and 3.403(5) Å in >2, whereas the second hydrogen bonds link the solvent 4-methylpholine molecules to form supramolecular dimeric {MgPc(H2O)·4-methylmorpholine}2—(>1) and {ZnPc(H2O)·4-methylmorpholine}2—(>2) structures. The interaction of the metal center of MgPc or ZnPc with O atom of the water molecule results its displacement of ∼0.5 Å from the N4-isonodole plane of the phthalocyaninate(2-) macrocycle that adopts a saucer-shape form. To better understand the interactions leading to the existence of the dimeric structures in the crystals, theoretical calculations of dimer stabilization energy composed of two monomers (MgPcH2O and ZnPcH2O), as well as three-dimensional molecular electrostatic potentials, have been performed using the density functionaltheoretical method. The calculated absorption spectra of both supramolecularmonomers and dimers were compared with the experimental ones in 4-methylmorpholinesolution. The water axial ligation of MgPc and ZnPc and the formationof the monomeric and dimeric supramolecular structures only slightlychange the energy gap between highest occupied molecular orbital andlowest unoccupied molecular orbital levels that is compared with thoseof the parent MgPc and ZnPc pigments.