Gas-phase structures of hemiporphyrazine and dicarbahemiporphyrazine: Key role of interactions inside coordination cavity

Abstract

The structures of free hemiporphyrazine and dicarbahemiporphyrazine molecules were determined by gas-phase electron diffraction and DFT calculations. Distance corrections (re – ra) were calculated using two different approaches: commonly applied Sipachev's algorithm and a recently developed technique based on molecular dynamics simulations. Both approaches examined against each other for the first time in the refinement of a relatively large (52 atoms) structure were found to result in almost the same final structural parameters. Gas-phase structures of hemiporphyrazine and dicarbahemiporphyrazine are saddle distorted, in contrast to the planar structure previously found for the solid-state hemiporphyrazine. Doubly charged anionic form of hemiporphyrazine was calculated to be significantly saddle distorted, while the anion of dicarbahemiporphyrazine was determined to possess a planar equilibrium structure. Structural features of the molecules and their doubly charged anionic forms are discussed in terms of AIM and NBO analyses.