To the limit of gas-phase electron diffraction: Molecular structure of magnesium octa(m-trifluoromethylphenyl)porphyrazine

• Molecular structure of MgC72H32N8F24 was studied by combined GED/MS experiment.
• Electronic structure of MgC16H8N8, MgC64H40N8 and MgC72H32N8F24 was studied by DFT.
• π-Systems phenyl rings and macrocycle conjugation defines the conformations.
• Nyquist–Shannon–Kotelnikov theorem is discussed concerning study of large molecules.
• The HOMO–LUMO gap regulation by the substituent is discussed.

The gas-phase molecular structure of the magnesium octa(m-trifluoromethylphenyl)porphyrazine (MgC72H32N8F24) has been studied by a synchronous gas-phase electron diffraction and mass spectrometric experiment at T = 667(10) K in combination with DFT calculations using B3LYP hybrid method and triple-ζ valence basis sets. The molecule has an equilibrium structure of D4 symmetry. The following values of selected internuclear distances have been determined: rh1, Å: r(Mg–N) = 1.979(5), r(N–C) = 1.363(3), r(Nmezo–C) = 1.334(4), r(Cpyr–CPh) = 1.469(3), r(CPh–CF3) = 1.510(5), r(C–F) = 1.349(3), r(Cα–Cβ) = 1.466(3), r(Cβ–Cβ) = 1.380(7). A slight (less than 1 to 2 degrees) twisting deformation of the macrocycle from planarity, caused by the presence of the eight bulky PhCF3 substituents, planes of which are turned by 132.6(9) degrees relative to the adjacent pyrrole rings, has been found. The deviation of phenyl ring planes from 90 degrees orientation is caused by stabilizing donor–acceptor interactions between π-natural orbitals of pyrrole and phenyl moieties. Substitution effects and coordination bonding in magnesium porphyrazine complexes, MgPz, MgPzPh8 and MgPz(CF3Ph)8, are discussed. Sensitivity of GED data to long range interatomic distances of large molecules has been shown.

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