The reaction between mu-eta(2):eta(2)-dibridging peroxodicopper complex of bis[3-(2-hydroxybenzylideneamino)phenyl]sulfone and phenol are investigated by performing paired interacting orbitals (PIO) analysis proposed by Fujimoto et al. Perusal of the contour maps and overlap populations of main PIOs suggested that formation of mono-phenoxo complex is easy; however di-phenoxo complex formation is difficult because of the non-flexibility of the SO2-bridged ligand. This result supplies the reason why poly (phenylene oxide) was not formed in our system. (c) 2005 Elsevier B.V. All tights reserved.