X-ray crystal structure determinations of two N-methyltriphenylphosphoranimines, Ph 3PN(CH 3)BH 3 ( 1) and [Ph 3PN(CH 3) 2] +BF 4 − ( 2), were carried out to determine the effects of π-bonding between P and N in triphenylphosphoranimines, Ph 3PNR, as a function of formal chargeon the N atom. Crystals of 1 are monoclinic, space group P2 1/n with a = 11.370(2), b = 10.507(2), c = 14.360(4) A ̊ and β = 91.47(2)° with Z = 4. Bond lengths of interest are: PN 1.605(3), NB 1.583(5), NC 1.456(5), average PC(phenyl) 1.805(3) Å. Bond angles of interest are: PNC 124.2(2), PNB 120.7(2), CNB 114.6(3), average CPC 106.8(5), average CPN of 112.0(5)°. Crystals of 2 are monoclinic, space group P2 1/c with a = 16.379(3), b = 16.777(2), c = 14.481(2) A ̊ and β = 94.41(1)° with Z = 8 (2 molecules per asymmetric unit). Average bond lengths of interest are: PN 1.626(4), PC(phenyl) 1.795(7), NC 1.442(13) Å. Average bond angles are: CPC 109(2), CPN 110(2), PNC 123(3), CNC 112.8(4)°. The longer PC distances, the shorter PN distance and smaller CPC angles in 1 compared to 2 are consistent with changes in the s-character around the P atoms.