Carbon-13 nuclear magnetic resonance study of the zinc(II) complexes of 3,7-diazanonane-1,9-diamine and 1,2-diaminoethane

Abstract

Carbon-13 n.m.r. spectra are reported as a function of pH for 3,7-diazanonane-1,9-diamine (dadn), for mixtures of dadn or 1,2-diaminoethane (en) and zinc nitrate, and for mixtures of zinc and dadn with en, 1,3-diaminopropane (pn), acetate, glycine (gly), and L-alanine (ala). The pH profiles have been analysed by computer and invidual chemical shifts determined for the following species: dadn, Hdadn⁺, H₂dadn²⁺, H₃dadn³⁺, H₄dadn⁴⁺, [Zn(dadn)]²⁺, [Zn(dadn)(OH)]⁺, [Zn(dadn)(en)]²⁺, [Zn(dadn)(pn)]²⁺, [Zn(dadn)(MeCO₂)]⁺, [Zn(dadn)(glyO)]⁺, [Zn(dadn)(alaO)]⁺, [Zn(dadn)(Hpn)]³⁺, [{Zn(dadn)}₂(pn)]⁴⁺, [Zn(dadn)(gly)]²⁺, [zn(dadn)(glyO)₂], [Zn(dadn)(ala)]²⁺, [Zn(en)]²⁺, [Zn(en)₂]²⁺, and [Zn(en)₃]²⁺. Acid dissociation constants have also been determined for the protonated dadn species and stability constants for the ternary and en complexes. Proposals are made concerning the co-ordination geometries of zinc–dadn complexes and possible generalisations are considered.