Synthesis, characterization, and crystal structure analysis of pentane-2,4-dionato(1,4,7,10-tetra-azacyclododecane)cobalt(III) diperchlorate monohydrate and its brominated complex (3-bromopentane-2,4-dionato)(1,4,7,10-tetra-azacyclododecane)cobalt(III) diperchlorate hemihydrate

Abstract

Pentane-2,4-dionato(1,4,7,10-tetra-azacyclododecane)cobalt(III) diperchlorate (1) reacts with N-bromosuccinimide to give its brominated complex, (3-bromopentane-2,4-dionato)(1,4,7,10-tetra-azacyclododecane)cobalt(III) diperchlorate (2). The complexes have been characterized by elemental analyses, electrical conductivity measurements, i.r., ¹H n.m.r., and electronic spectra. The three-dimentional X-ray crystallographic structure determination of the title complexes confirmed the completion of bromination at the 3-position of the pentane-2,4-dionato-moiety without altering the stereochemistry of the co-ordination sphere and macrocyclic ligand. The parent (1) crystallizes in the space group Pna2₁, with a= 18.974(6), b= 13.403(4), c= 8.928(2)Å, and Z= 4, while complex (2) crystallizes in the space group Pbca, with a= 15.138(4), b= 21.360(5), c= 14.066(7)Å, and Z= 8. The structures were solved by the heavy-atom method to give R= 0.0499 and 0.0635 for (1) and (2), respectively. The cobalt ion is co-ordinated in a distorted octahedral fashion with the four nitrogen atoms of the 12-membered macrocyclic ligand and two oxygen atoms of the pentane-2,4-dionato-moiety in a cis position, in which the distortion from the regular octahedron is found in the donor nitrogen atoms of the macrocyclic ligand. The six-membered chelate ring consisting of the 3-bromopentane-2,4-dionato group and the cobalt ion slightly deviates from the overall planarity, with deviations of 0.19 and 0.18 Å for the Co and Br atoms, while the planarity of the corresponding chelate ring of (1) is preserved within ±0.04 Å. The cation of (1) exhibits a mirror plane passing through the pentane-2,4-dionato-moiety, Co, and two nitrogen atoms in a cis position, while for the brominated complex (2) the symmetry is not preserved due to the deviation from overall planarity of the chelate ring.