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 center dot (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 center dot (OTf)(2)), respectively. In contrast to the reaction of 8 center dot (OTf)(2) with NH=C(NHPh)(2), interaction of 8 center dot (OTf)(2) with excess gaseous NH3 leads to formation of the platinum(II) bis(amidine) complex cis-[Pt(tmeda)(NH=C(NH2)Et)(2)][SO3CF3](2) (9 center dot (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 = CH2Ph, Ph) solutions at 20-25 degrees 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 degrees 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 H-1 and C-13{H-1} NMR spectra. The structures of 1, 2, 4, 11, 13, 14, 9 center dot (picrate)(2), and 10 center dot (picrate)(2) were determined by single-crystal X-ray diffraction.