The tailoring reaction of the two adjacent nitrile ligands in cis-[PtCl₂(RCN)₂] (R = Me, Et, CH₂Ph, Ph) and [Pt(tmeda)(EtCN)₂][SO₃CF₃]₂ (8·(OTf)₂; tmeda = N,N,N′,N′- tetramethylethylenediamine) upon their interplay with N,N′- diphenylguanidine (DPG; NH=C(NHPh)₂), in a 1:2 molar ratio gives the 1,3,5-triazapentadiene complexes [PtCl₂{NHC(R)NHC(R)=NH}] (1-4) and [Pt(tmeda){NHC(Et)NHC(Et)NH}][SO₃CF₃]₂ (10·(OTf)₂), respectively. In contrast to the reaction of 8·(OTf)₂ with NH=C(NHPh)₂, interaction of 8·(OTf)₂ with excess gaseous NH₃ leads to formation of the platinum(II) bis(amidine) complex cis-[Pt(tmeda){NH=C(NH ₂)Et}₂][SO₃CF₃]₂ (9·(OTf)₂). Treatment of trans-[PtCl₂(RCN) ₂] (R = Et, CH₂Ph, Ph) with 2 equiv of NH=C(NHPh) ₂ in EtCN (R = Et) and CH₂Cl₂ (R = CH ₂Ph, Ph) solutions at 20-25°C leads to [PtCl{NH=C(R)NC(NHPh)=NPh} (RCN)] (11-13). When any of the trans-[PtCl₂(RCN)₂] (R = Et, CH₂Ph, Ph) complexes reacts in the corresponding nitrile RCN with 4 equiv of DPG at prolonged reaction time (75°C, 1-2 days), complexes containing two bidentate 1,3,5-triazapentadiene ligands, i.e. [Pt{NH=C(R)NC(NHPh)=NPh}₂] (14-16), are formed. Complexes 14-16 exhibit strong phosphorescence in the solid state, with quantum yields (peak wavelengths) of 0.39 (530 nm), 0.61 (460 nm), and 0.74 (530 nm), respectively. The formulation of the obtained complexes was supported by satisfactory C, H, and N elemental analyses, in agreement with FAB-MS, ESI-MS, IR, and ¹H and ¹³C{¹H} NMR spectra. The structures of 1, 2, 4, 11, 13, 14, 9· (picrate)₂, and 10·(picrate) ₂ were determined by single-crystal X-ray diffraction.