Synthesis of Air- and Moisture-Stable Dibenzogallepins: Control of Planarity of Seven-Membered Rings in Solid States by Coordination to Gallium Atoms

Air- and moisture-stable dibenzo­[b,f]­gallepins
with planar seven-membered rings have been designed and synthesized.
From X-ray single-crystal analyses, the effects of the coordination
numbers were evaluated at the gallium atom on the planarity of the
seven-membered rings with a series of the synthesized complexes. Accordingly,
it was shown that the seven-membered ring of dibenzogallepin involving
a three-coordinated gallium atom presented the highest planarity compared
to other dibenzogallepins with four- or five-coordinated gallium atoms.
In addition, from theoretical calculations, it was proposed that the
electronic states of the gallium atom in the complexes contributed
to the energy levels of LUMOs+1.