The nucleophilic addition of N,N'-diphenylguanidine, HN=C(NHPh)(2) (DPG), to two adjacent dialkylcyanamide ligands \in cis-[PtCl2(NCNR2)(2)] (R = Me; R-2 = C5H10, C4H8O) gives unusual eight-membered chelates [PtCl2{NH=C-(NR2)N(Ph)C(=NH)N(Ph)C(NR2)=AH}] (1-3) with trisguanidine as the cyclic ligand, in which the central guanidine =NH group remains uncoordinated. Treatment of trans-[PtCl2(NCNR2)(2)] (R = R = Me; R-2 = C5H10, C4H8O) with 1 equiv of HN=C(NHPh)(2) in a solution (R = R = Me; R-2 = C5H10) or in a suspension (R-2 = C4H8O) of CHCl3 or MeNO2 at 20-25 degrees C for 20 h results in the generation of the 1,3,5-triazapentadiene monochelates [PtCl{NH=C(NR2)N(Ph)C(NH2)=NPh}(NCNR2)](CI) (4-6). When any of trans-[PtCl2(NCNR2)(2)] reacts with 2 equiv of DPG at 20-25 degrees C for 1-2 days or 4-6 are treated with 1 equiv more of HN=C(NHPh)(2) at the same temperature, the complexes bearing two chelate rings [Pt{NH=C(NR2)N(Ph)C(NH2)=NPh}(2)](Cl)(2) (7-9) are formed. The formulation of the obtained complexes was supported by satisfactory C, H, and N elemental analyses, agreeable ESI+-MS, IR and H-1 and C-13{H-1} NMR spectroscopies; the structures of 1 and 2 were determined by the single-crystal X-ray diffraction. Theoretical studies (at the B3LYP level of theory) revealed that the alkylnitrile eight-membered product is significantly less stable than the corresponding cyanamide species 1-3, and this fact, at least partially, explains why the former was not detected in the reaction between cis-dinitrileplatinum(II) complexes and DPG.