Two new types of pyrimidine-bridged Pt(II) complexes, (NR4)2(PtCl3)2(μ-pm) and cis- and trans-{Pt(R2SO)Cl2}2(μ-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(μ-pm)2- ions, which can be precipitated with a NR4 + salt. The aqueous reaction of KPt(R2SO)Cl3 with pyrimidine in a 2:1 ratio produced the dinuclear species trans-{Pt(R2SO)Cl2}2(μ-pm). With DBuSO and DBzSO, the analogous cis isomers were also obtained. The 195Pt NMR resonances of the trans dimeric complexes were observed at higher field (av −3088 ppm) than the cis compounds (av −2948 ppm). The 195Pt coupling constants with the atoms of pyrimidine 3 J(195Pt−1H) and 3 J(195Pt−13C) are larger in the cis configuration than in the trans analogues. The crystal structures of two ionic complexes, (NR4)2(PtCl3)2(μ-pm) (R = Me and n-Bu), and of three mixed-ligands dimers, trans-{Pt(R2SO)Cl2}2(μ-pm) (R2SO = DMSO, DPrSO) and cis-{Pt(DBuSO)Cl2}2(μ-pm), were determined.