Electrochemical studies of nickel(II) and cobalt(II) complexes of tetra-azamacrocycles bearing a pyridine functional group and X-ray structures of [NiII(L3)Cl]ClO4 and [NiII(L3)][ClO4]2·H 2O {L3 = meso-2,3,7,11,12-pentamethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1(17), 13,15-triene}

Abstract

The new complexes [NiII(L3)Cl]ClO4 (1), [CoII(L3)(CH3CN)][ClO4]2, and [NiII(L3)][ClO4]2·H 2O (2) {L3 = meso-2,3,7,11,12-pentamethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1 (17),13,15-triene} have been prepared. Their redox chemistry and electrocatalytic behaviour in the CO2 reduction process were studied in comparison with related cobalt(II)-and nickel(II)-tetra-azamacrocyclic systems. The complex cation in (1) [monoclinic, space group P21/n, a = 9.457(4), b = 17.614(3), c = 14.078(4) Å, β = 107.39(2)°, Z = 4, R = 0.065 for 2 812 observed Mo-Kα data] is isostructural with the distorted tetragonal pyramidal CoII analogue. The increased atomic number of the nickel centre is reflected in a significant shortening (by ca. 0.03 Å) of the metal-N bond distances. In (2) [monoclinic, space group P21/c, a = 10.248(1), b = 17.958(4), c = 13.538(3) Å, β = 90.48(2)°, Z = 4, R = 0.076 for 3 310 observed Mo-Kα data] the two independent ClO4 - groups are bridged by the water molecule through hydrogen bonding, and one ClO4 - group is unidentately bound to the 'square-planar' metal atom by a long Ni-O bond of 2.838(7) Å. The macrocyclic L3 ligand adopts different conformations in (1) and (2): the substituted methyl groups at N(2) and N(4) are oriented anti with respect to each other in (1), but bear a syn relationship in (2).