Structure and NMR Behavior of Cobalt(III) Polyamine Complexes of α,ω-Alkylenediamine-N,N,N′,N′-tetramethylenetetraphosphonate in Aqueous Solution

The complex formation of α,ω-diaminopolyphosphonates (ethylenediamine- [H8edtmp], trimethylenediamine- [H8tdtmp] and hexamethylenediamine-N,N,N′,N′-tetramethylenetetraphosphonate [H8hdtmp]) with cobalt(III) polyamine complexes has been investigated by means of 31P NMR spectroscopy. The formation and protonation constants of the complexes and the 31P NMR chemical shifts of each protonated species were determined from the pH dependence of the 31P NMR signals. In any complexes, the nitrogen atom of the ligand is not coordinated to CoIII. The complex cis-[CoCl(en)2(NH3)]2+ forms a mononuclear O-monodentate complex and two types of binuclear bis(O-monodentate) complexes by a reaction with edtmp and tdtmp, and forms a mononuclear O-monodentate complex and a dinuclear bis(O-monodentate) complex with hdtmp. The complex cis-[CoCl2(en)2]+ forms a mononuclear O-monodentate complex and a mononuclear O,O-bidentate complex having an eight-membered chelate ring with edtmp and tdtmp, and forms a mononuclear O,O-bidentate...