Abstract
A theoretical investigation on the planarity of molecular structure of zinc phthalocyanine (ZnPc) and its aromaticity has been performed using B3LYP and M06-2X density functionals combined with selected Pople-type basis sets. The effect of the applied calculation method on the optimized structure of ZnPc and ZnPc∙∙∙H2O, both in the gas phase and in the polar solvent, was analyzed. To quantify the aromaticity of the ZnPc and ZnPc∙∙∙H2O complexes, both the geometric and magnetic criteria, i.e., Harmonic Oscillator Model of Aromaticity (HOMA) index and the nucleus-independent chemical shift (NICS) values at the centers or 1 Å above the centers of structural subunits, were calculated. The energies of highest energy occupied molecular orbital (HOMO) and lowest energy unoccupied molecular orbital (LUMO) and energy gaps were also estimated. The results show that the free ZnPC molecule is flat in the gas phase and nonplanar in the polar environments (DMSO and water). ZnPC∙∙∙H2O is nonpolar in the gas phase and polar solvent which is in agreement with recent X-ray reports. Both HOMA and NICS indexes indicate the presence of highly aromatic macrocycle and benzene rings while these parameters for pyrrolic ring are significantly smaller than in free pyrrole. The presence of polar solvents practically does not change aromaticity of the ring subunits of the studied compounds.
Highlights
As a result of accidental discoveries [1, 2], metallophthalocyanines (MPcs) have been known for over a century
In the present theoretical study, we would like to get some insight into the sensitivity of the calculated zinc phthalocyanine (ZnPc) molecular structure, expressed in terms of Zn ion displacement from the plane formed by four nitrogen atoms, in the gas phase and polar solution, to the basis set type and quality
The Cartesian coordinates of fully optimized ZnPc and ZnPc∙∙∙H2O structures at the B3LYP/6-311++G(d,p) and M06-2X/6-311++G(d,p) levels of theory are included in Tables S2–S7 in the supplementary material
Summary
As a result of accidental discoveries [1, 2], metallophthalocyanines (MPcs) have been known for over a century. In the present theoretical study, we would like to get some insight into the sensitivity of the calculated ZnPc molecular structure, expressed in terms of Zn ion displacement from the plane formed by four nitrogen atoms, in the gas phase and polar solution, to the basis set type and quality To achieve this aim, two popular and efficient density functionals, B3LYP [36,37,38] and M06-2X [61, 62], combined with a number of differentquality Pople-type basis sets [63, 64], extended with polarization, diffusion, or both types of additional basis functions, will be applied. The HOMO and LUMO orbitals, as well as the corresponding Eg energies of ZnPc and ZnPc∙∙∙H2O, were directly calculated for the optimized structures
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