Diffusion of ammonia into CH2Cl2 solutions of the dialkylcyanamide complexes cis- or trans-[PtCl2(RCN)2] (R = NMe2, NEt2, NC5H10) at 20–25 °C leads to metal-mediated cyanamide–ammonia coupling to furnish, depending on reaction time, one or another type of novel bisguanidine compound, i.e. the molecular cis- or trans-[PtCl2{NH
C(NH2)R}2] (cis-1–3 and trans-1–3) and the cationic cis- or trans-[Pt(NH3)2{NH
C(NH2)R}2](Cl)2 (cis-4–6 and trans-4–6) complexes. Compounds cis-1–3 or trans-1–3 were converted to cis-4–6 or trans-4–6, accordingly, upon prolonged treatment with NH3 in CH2Cl2. The ammination of the relevant nitrile complexes cis- or trans-[PtCl2(RCN)2] (R = Et, CH2Ph, Ph) in CH2Cl2 solutions affords only the cationic compounds cis- or trans-[Pt(NH3)2{NH
C(NH2)R}2](Cl)2 (cis-7–9 and trans-7–9). The formulation of 1–9 was supported by satisfactory C, H and N elemental analyses, agreeable ESI+-MS (or FAB+-MS), IR, 1H and 13C NMR spectroscopies. The structures of trans-1, trans-3, cis-4, trans-4, cis-7, and cis-9 were determined by single-crystal X-ray diffraction disclosing structural features and showing that the ammination gives ligated guanidines and amidines in the E- and Z-forms, respectively, where both correspond to the trans-addition of NH3 to the nitrile species.