Molecular structures of [PCl2N]3-MCl3 adducts, M=B, Al, Ga, In, Tl, have been studied employing HF, B3LYP*, B3LYP , PW91, BLYP, OLYP, BP and LDA methods using DZP basis set (as defined in Amsterdam Density Functional, ADF, package). Some aspects of adduct formation like considering the difference between Front and Back dihedral angles and also ring puckering showed that the [PCl2N]3-AlCl3 is the most stable adduct comparing the others. Based on the comparison between the X-ray and theoretical geometrical parameters of [NPCl2]3(AlCl3) and [NPCl2]3(GaCl3), the LDA method and BP, PW91 and OLYP functionals combined with DZP basis set were found to yield the most satisfactory agreement. Results showed that with surprise, the LDA(DZP) method has the maximum matching with experimental data, comparing the others.