Carbon-13 nuclear magnetic resonance study of ternary complexes involving zinc(II) and triethylenetetramine
The 13C n.m.r. spectra are reported as a function of pH for mixtures of triethylenetetramine (trien) and zinc nitrate with acetic acid, glycine (gly), L-alanine (ala), 1,2-diaminoethane (en), and 1,3-diaminopropane (pn) and for pn alone. The pH profiles for these rapidly-exchanging systems have been analysed by computer, and the chemical shifts of the methyl, methylene, and methine carbon atoms and the stability constants determined for the following species: [Zn(trien)(MeCO2)]+, [Zn(trien)(gly)]2+, [Zn(trien)(ala)]2+, [Zn(trien)(Hen)]3+, [Zn(trien)(Hpn)]3+, [Zn(trien)(glyO)]+, [Zn(trien)(alaO)]+, [Zn(trien)(en)]2+, and [Zn(trien)(pn)]2+[glyO = glycinate(1–), alaO =L-alaninate(1–)]. The implications of the results as to the co-ordination geometry of zinc in these complexes and the extent of transmission of inductive effects through the metal are discussed.