Nickel(II) complexes of tricyclic N10-cage ligands

Abstract

Macrocyclic ligands, 2,5,8,10,13,16,17,20,21,24-decaazatricyclo[7.7.4.4]tetracosane (DATT), 2,5,8,10,13,16,17,20,22,26-decaazatricyclo[7.7.5.5]hexacosane (DTCH), 2,5,8,11,14,17,19,22,23,26-decaazatricyclo[8.8.4.49,18]hexacosane (DATH), and 2,5,8,11,14,17,19,23,24,28-decaazatricyclo[8.8.5.59,18]octacosane (DATO), from template condensation of diethylenetriamine with nickel(II) complexes of macrocycles 1,3,6,8-tetraaza-2,2,7,7-tetrachlorocyclodecane (TTCE), 1,3,7,9-tetraaza-2,2,8,8-tetrachlorocyclododecane (TTDE), 1,4,7,10-tetraaza-2,3,8,9-tetrachlorocyclododecane (TTCD), and 1,4,8,11-tetraaza-2,3,9,10-tetrachlorocyclotetradecane (TTTE), respectively, are described. Formulations of the tricyclic cage ligands and their nickel(II) complexes have been confirmed by elemental analyzes, conductivity and potentiometric measurements, and infrared, electronic, 1H-NMR, and mass spectral studies. Highest enhancement of equilibrium constant for nickel(II) complex of DATT (by 1010) over that of the corresponding tetraaza macrocycle of similar planar cavity ([10]-N4) is observed. The cage effect on equilibrium constant decreases rapidly with increase in planar cavity size ([10]-N4 → [14]-N4) of the tricyclic ligand; it can be considered negligible in the DATO system where nickel is well fitted in the planar cavity. A small variation in metal-ligand stability constants (log K = 21–23) indicates that a low value due to poor fitting of the nickel in the planar cavity is compensated by its encapsulation in the small spherical cavity. Thus, high and comparable stability constant values are expected for planar tetraaza and spherical polyaza cavity systems in which nickel ion can be nicely fitted.