Protonation and stability constants for Co2+, Ni2+, Cu2+, and Zn2+ of the open-chain polyamine 1-amino-13-(2-pyridyl)-3,6,9,12-tetraazatridecane. Crystal structure of its nickel(II) complex

The new unsymmetric N-6 ligand 1-amino-13-(2-pyridyl)-3,6,9,12-tetraaza (aptatd) containing one pyridyl group has been synthesized and characterized by EA, IR, and NMR. Its proton association constants (log K-H(n)) and stability constants (log K-ML) for Co(II), Ni(II), Cu(II), and Zn(II) ions were determined at 298.1 K and ionic strength 0.100 mol dm(-3) (KNO3) in aqueous solution by potentiometry: log K-H(1)=8.80, log K-H(2)=8.49, log K-H(3)=6.84, log K-H(4)=4.17, log K-H(5)=3.47; log K-ML(Co2+)=18.00, log K-ML(Ni2+)=21.31, log K-ML(Cu2+)=23.62, log K-ML(Zn2+)=15.60. The X-ray structure of its nickel(II) complex [Ni(aptatd)](ClO4)(2) are reported: orthorhombic space group Pbca, a=15.715(1) Angstrom, b=14.280(2) Angstrom, c=19.443(2) Angstrom, V=4363.4 (9) Angstrom(3) with Z=8. The geometry around nickel is a distorted octahedron with the pyridine nitrogen atom being cis to the nitrogen atom of the terminal primary amine.