Two new types of pyrimidine-bridged Pt(II) complexes, (NR4)(2)[(PtCl3)(2)(mu -pm)] and cis- and trans-{Pt(R2SO)Cl-2}(2)(mu -pm) where pm = pyrimidine, were synthesized and characterized by IR and multinuclear magnetic resonance spectroscopies and by crystallographic methods. Compounds with dimethylsulfoxide, tetramethylenesulfoxide, di-n-propylsulfoxide (DPrSO), di-n-butylsulfoxide (DBuSO), dibenzylsulfoxide (DBzSO), and diphenylsulfoxide were studied. The aqueous reaction of K2PtCl4 with pyrimidine produced the [(PtCl3)(2)(mu -pm)](2)-ions, which can be precipitated with a NR4+ salt. The aqueous reaction of K[Pt(R2SO)Cl-3] with pyrimidine in a 2:1 ratio produced the dinuclear species trans-{Pt(R2SO)Cl-2}(2)(mu -pm). With DBuSO and DBzSO, the analogous cis isomers were also obtained. The Pt-195 NMR resonances of the trans dimeric complexes were observed at higher field (av -3088 ppm) than the cis compounds (av -2948 ppm). The Pt-195 coupling constants with the atoms of pyrimidine (3)J(Pt-195-H-1) and (3)J(Pt-195-C-13) are larger in the cis configuration than in the trans analogues. The crystal structures of two ionic complexes, (NR4)(2)[(PtCl3)(2)(mu -pm)] (R = Me and n-Bu), and of three mixed-ligands dimers, trans-{Pt(R2SO)Cl-2}2(mu -pm) (R2SO = DMSO, DPrSO) and cis-{Pt(DBuSO)Cl-2}(2)(mu -pm), were determined.