Abstract The angle between the g⁄⁄ axis and the copper-copper axis in most parallel planar dimers of the quadridentate salicylaldehyde Schiff base complexes of copper(II) in toluene or xylene has been reconfirmed to be not ≈35°, but ≈17°, by a computer simulation of the dimer ESR spectra at both the K and X-bands. In order to remedy the shortcomings of the so-called point-dipole approximation generally used in the simulation, a delocalization model, in which the delocalization of each unpaired electron on the copper atom and its surrounding four ligand atoms is explicitly taken into consideration, has been discussed in some detail. The delocalization effect has been proven to be highly significant in estimating dimeric structures reliably. An application of this model to the structural estimation of several dimers in solutions has also been made.