A molecular mechanics study of square planar Pt(LI) coordination complexes is reported. Three new ligating atom types which are representative of the sigma-donor ligands prevalent in Pt(II) coordination chemistry-chloride, carboxylate oxygen, and amine nitrogen-are developed to extend the MM2 force field. The newly derived MM force field accurately describes the geometry of both the inner and outer coordination sphere of Pt(II) complexes. Quick and efficient modeling is obtained despite simplifications used in constructing the force field, e.g., neglect of anharmonic corrections to the bond-stretching and angle-bending potentials. The simplifications used in construction of the force field allow accurate structural prediction in a timely manner using readily available software and hardware. Additionally, the new MM force field shows the ability to predict structures, in the absence of a starting guess of the geometry from X-ray crystallography, that are subsequently found to be in good agreement with experimental geometries.