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.