Protonation and stability constants for Co2+, Ni2+, Cu2+ and Zn2+ of two open-chain hexadentate N6 ligands containing two pyridyl groups:: Crystal structures of their Ni(II) complexes

Two open-chain hexadentate N-6 ligands containing two pyridyl groups, 1,13-bis(2-pyridyl)-2,5,9,12-tetraazatridecane (bpytd) and 1,14-bis(2-pyridyl)-2,6,9,13-tetraazatetradecane (bpytt), have been synthesized as their tetrahydrochloride salts and their proton association constants and stability constants of Co(II), Ni(II), Cu(II) and Zn(II) chelates have been determined by potentiometry. The stability constants are higher than those for analogous hexadentate N-6 ligands containing one pyridyl moiety, which are in turn higher than those for analogous aliphatic N-6 ligands. The Ni(II) complexes [Ni(bpytd)](ClO4)(2) . H2O (1) and [Ni (bpytt)](ClO4)(2) (2) have been synthesized and their structures have been determined by three-dimensional Xray diffraction methods. Their geometries at nickel are six-coordinate pseudo-octahedra, with pyridyl nitrogen atoms being mutually cis for 1 and trans for 2. (C) 1998 Elsevier Science Ltd. All rights reserved.