Carbon-13 nuclear magnetic resonance study of complexes involving zinc(II) and 2,2′,2″-triaminotriethylamine
Carbon-13 n.m.r. spectra are reported as a function of pH for mixtures of 2,2′,2″-triaminotriethylamine (tren) and zinc nitrate and/or chloride, and of zinc and tren with 1,2-diaminoethane (en), 1,3-diaminopropane (pn), glycine (gly), and L-alanine (ala). Carbon-13 chemical shifts are also reported as a function of pH for tren and L-alanine (carboxylate carbon) alone. The pH profiles have been analysed by computer and the chemical shifts of the methyl, methylene, methine and carboxylate (in the L-alanine complexes only) carbon atoms determined for the following species: tren, Htren+, H2tren2+, H3tren3+, [Zn(tren)(OH)]+, [Zn(tren)(OH2)]2+, [Zn(tren)(en)]2+, [Zn(tren)(pn)]2+, [Zn(tren)(glyO)]+, [Zn(tren)(alaO)]+, [Zn(tren)(Hpn)]3+, and [Zn(tren)(ala)]2+[glyO = glycinate(1–), alaO = alaninate(1–)]. Stability constants have also been determined for the ternary complexes. 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.