SYNTHESIS AND CRYSTALLOGRAPHIC CHARACTERIZATION OF [Eu(C₁₈H₁₈N₆)(OAc)₂⁺][Cl⁻] · 7H₂O, A TEN-COORDINATE Eu(III) COMPLEX WITH A CLOSE-TO-PLANAR HEXADENTATE C₁₈H₁₈N₆ LIGAND: AN INTERESTING CASE OF A STRUCTURE WITH MULTIPLE DISORDER PROBLEMS

Abstract

The title compound crystallizes in the centrosymmetric triclinic space group Pl (No. 2) with a = 8.7080(18) Å, b = 9.2777(14) Å, c = 10.2707(22) Å, α = 77.762(14)°, β = 77.482(17)°, γ = 84.735(15)°, V = 790.7(3) ų and Z = 1. The structure was solved and refined to R = 2.37% and wR = 3.19% for all 2073 independent reflections. The structure is disordered, with overlapping images of two enantiomeric [Eu(C₁₈H₁₈N₆)(OAc)⁺ ₂] ions surrounding an inversion center on which lies a Eu(III) cation. These two images correspond to isomers with λλ and ΔΔ conformations of their N-CH₂—CH₂—N moieties. The ten-coordinate europium(III) cation has a staggered 2:6:2 coordination geometry, with six equatorial Eu-N bonds to the hexadentate macrocyclic ligand and two quasi-axial Eu-O bonds to each of the two bidentate acetate ligands. Further manifestations of disorder occur for the acetate ligands and for H₂O/CI⁻ sites in the crystal lattice.

Key Words:

• Europium(III)
• ten-coordination
• macrocyclic C₁₈H₁₈N₆ ligand
• Schiff base
• crystal structure
• disorder