Reaction of "cyclamphosphorane" (cyclamPH) with [Pt2Cl4(PEt3)2] yields [PtCl(PEt3)(cyclamPH)]Cl. The complex crystallizes as a dichloromethane solvate in the monoclinic space group P21/n, witha = 13.877(3),b = 23.231(7),c = 8.295(2)Å, β = 91.86(4)°, and an X-ray diffraction study shows square planar platinum coordination in which the labile proton of cyclamPH has transferred from phosphorus to nitrogen and the ligand is attached via simplechelation. The phosphorus istransto chlorine in the platinum coordination plane.The corresponding product,trans-[PtCl2(PEt3)(cyclenPH2)]Cl, derived from reaction of "cyclenphosphorane" (cyclenPH) with [Pt2Cl4(PEt3)2], is shown by NMR studies to have a quite different structure in which the ligand is protonated at two nitrogen sites but not at phosphorus. The phosphorus is pentacoordinate with four attachments to nitrogen atoms and one to platinum. The two chlorine atoms are mutuallytransin the platinum coordination plane.Keywords: crystal structure, cyclenphosphorane reaction, cyclamphosphorane reaction, X-ray diffraction.