Electron diffraction studies of metal phthalocyanines, MPc, where M=Sn, Mg, and Zn (reinvestigation)

Abstract

The structure of two metal phthalocyanines, MPc where M=Sn and Mg, have been determined by gas-phase electron diffraction for the first time; furthermore, the structure of ZnPc established earlier by the same technique has been reanalyzed. The focus of these studies is the position of the metal ion relative to the 16-membered C8N8 ring. Tin(II)phthalocyanine we find to be nonplanar with the Sn(II) ion 1.0(1) Å above the molecular plane in accordance with its structure in crystal established earlier; the two other molecules were found to be planar. Slight nonplanarity of ZnPc found in the previous study is now removed by a new procedure of structural analysis; this is in accordance with the results of ab initio/DFT calculations for this molecule performed by Pulay. From comparisons presented here we can conclude that there is a close structural similarity of metal phthalocyanines in the gas phase and in crystal.

Solvent impact on the planarity and aromaticity of free and monohydrated zinc phthalocyanine: a theoretical study

“…For structures, characterized by d > 0, the ligand molecule is nonplanar. In such case, the Pc molecular fragment is slightly shaped in a form of a cone or saucer [22]. For brevity, the Cartesian coordinates of fully optimized ZnPc and ZnPc•••H 2 O 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.…”

“…In 1999, Fink and co-workers [22] reported on both gas-phase electron diffraction and theoretical DFT studies on the planar equilibrium structure of ZnPc while the BLYP/6-31G* and BLYP/6-31G** data produced a nonplanar molecule with zinc ion about 0.075 Å above the ligand plane [34]. Another experimental electron diffraction and DFT study proposed a planar structure of ZnPc [35].…”

“…For several metal ions, the problem of nonplanarity of their complexes with phthalocyanines was related to the oxidation state of the central atom [22]. Long time ago, the X-ray structure of monohydrated magnesium phthalocyanine (MgPc) [23] showed a significant displacement of metal cation from the molecular plane of the macrocycle (0.496 Å).…”

“…Zinc ion is practically not toxic in doses below 225 mg [19], and ZnPc [20][21][22] (see its general formula in Fig. 1a) is interesting primary due to the fact that Zn(II) ion with d 10 configuration does not contribute directly to the electronic spectra of phthalocyanine, dominated by transitions within their π-electronic system, formed by several conjugated C=N and C=C double bonds.…”

“…Examples of such molecules, showing different structures, are nonplanar tin phthalocyanine (SnPc) and planar MgPc molecules [22], observed by gas electron diffraction. Liao and Scheiner [33] performed theoretical studies on the electronic structure of complexes, formed by several transition metal ions with porphyrins, porphyrazines, and phthalocyanines.…”