The synthesis, characterization, and emission properties of a series of Pt(diphosphine)(dithiolate) complexes are reported. Diphosphine ligands include 1,2-bis(diphenylphosphino)ethane (dppe), 1,2-bis(diphenylphosphino)ethylene (dppv), 1,2-bis(diphenylphosphino)benzene (dppb), 1,2-bis(dicyclohexylphosphino)ethane (chpe), bis(diphenylphosphino)methane (dppm), 1,2-bis(dimethoxyphosphino) ethane (pompom), triphenylphosphine (PPh(3)), dimethylphenylphosphine (PMe(2)Ph), tricyclohexylphosphine (PCy(3)), triphenyl phosphite (P(OPh)(3)), and triisopropyl phosphite (P(O-i-Pr)(3)). Dithiolate ligands include maleonitriledithiolate (mnt) and 1-(ethoxycarbonyl)-1-cyanoethylene-2,2-dithiolate (ecda). The complexes are readily synthesized by the addition of the diphosphine ligand to Pt-(COD) (dithiolate). On the basis of characterizations using NMR and infrared spectroscopies, all of the complexes are assigned square planar coordination geometries with varying degrees of distortion determined by ligand steric; and electronic effects. The assignment of square planar coordination is confirmed by single crystal structure determinations of Pt(dppe)(mnt) (la) and Pt(dppb)(mnt) (3a). Pink crystals of Pt(dppe)(mnt) (la) (C30H24N2P2-PtS2) are monoclinic, space group P2(1)/n (No. 14), with a 11.491(4) Angstrom, b = 12.484(2) Angstrom, c = 19.822(7) Angstrom, beta = 91.34(1)degrees, V = 2842.90 Angstrom(3), Z = 4, and final R = 0.029 (R(w) = 0.031) for 4793 unique reflections. Orange crystals of Pt(dppb)(mnt) (3a) (C34H24N2P2PtS2) are monoclinic,:space group P2(1)/n (No. 14), with a 10.050(7) Angstrom, b = 19.301(3)K c, = 15.800(6) Angstrom, beta = 94.36(6)degrees, V = 3056.28 degrees(3), Z = 4, and final R = 0.030 (R(w) = 0.036) for 5576 unique reflections. The average Pt-S (2.299(7) Angstrom for la and 2.301(2) Angstrom for 3a) and Pt-P (2.257(2) Angstrom for 1a and 2,256(7) Angstrom for 3a) bond distances in each structure agree well with previously reported structural results. The metrical parameters of the mnt chelate ring indicate some degree of metal-ligand delocalization in both structures. The P-31 NMR spectra of the phosphines resonances for all of the complexes show platinum satellites ((1)J(Pt-P) = 1100-2500 Hz). In addition, the ecda complexes exhibit complex second-order coupling patterns, arising from the asymmetry of the ecda ligand. All of the complexes exhibit strong emission in the solid state and in frozen glasses at 77 K. Emission spectra are structured for the mnt complexes and broad and featureless for the ecda complexes. Solid-state emission lifetimes at 77 K are in the microsecond range.