Pentacoordinate hypervalent boron compounds 4a and 4b with a newly prepared 1,8-dimethoxy-10-methylacridinyl ligand were synthesized. X-ray crystallography revealed that the distances between the central boron and both oxygen atoms; of the tridentate ligand were in the range of 2.37-2.53 angstrom, showing the pentacoordinate structure. Cyclic voltammetry of 4b showed that the potential of the reduction (E-1/2 = -0.57 V in CH2Cl2, vs. SCE) is much lower than that of the corresponding Gabbai's system 5 (-0.28 V), probably due to the difference in coplanarity between the boryl group and the acridinyl skeleton in 4b and 5 (twist angle = 44.8 degrees in 5 and 88.2 degrees in 4b).