Quantum mechanical density functional theory (DFT) and coupled DFT/molecular mechanics (QMMM) studies of the compounds (H3P)(3)M(eta(1)-SO2) and (MenPh3-nP) M-3(eta(1)-SO2) (M = Ni, Pd, Pt; n = 0-3) model the experimental data well, particularly the planar/pyramidal geometries at sulfur. Bond dissociation energy (BDE) calculations confirm that Pd/Pt systems with pyramidal SO2 ligands exhibit M-S BDEs smaller by 30-50% than Ni systems with planar SO2. However, scans of the potential energy surfaces show that flexing the planar/pyramidal torsion angle within ranges of 20-30degrees requires little energy. Bond energy decomposition calculations indicate that the electrostatic DeltaE(elstat) term determines the BDE for Pd/Pt molecules where the sulfur is pyramidal, whereas all three terms matter when the sulfur is planar, as for Ni compounds. However, this accounts only for a fraction of the BDE differences; orbital energy matching accounts for the balance.