1,2-Cyclohexanedionedioxime as a useful co-ligand for fabrication of one-dimensional Zn(ii) and Cd(ii) coordination polymers with wheel-and-axle topology and luminescent properties

Abstract

The combination of 1,2-cyclohexanedionedioxime (NioxH₂) and carboxylate-containing ligands resulted in Zn(II) or Cd(II) robust metal building blocks which being coupled with the flexible pyridine ligands fabricated five one-dimensional (1D) coordination polymers {[Cd(CHOO)₂(NioxH₂)(bpe)]·DMF}_∞ (1), [Cd(CHOO)₂(NioxH₂)(dps)]_∞ (2), [Zn(CH₃COO)₂(NioxH₂)(dps)]_∞ (3), [Cd(CH₃COO)₂(NioxH₂)(dps)]_∞ (4), and {[Zn(pyta)₂(NioxH₂)]·DMF}_∞ (5) (where bpe = 4,4′-bipyridine ethane, dps = 4,4′-dipyridylsulfide, Hpyta = (4-pyridylthio)acetic acid, DMF = N,N-dimethylformamide), whose crystal structures were determined by single crystal X-ray diffraction. The stability of compounds 1 and 5 to loss of DMF as a guest has been addressed experimentally, and the crystal-to-crystal transformation observed for 1 resulted in the guest free 1D polymer [Cd(CHOO)₂(NioxH₂)(bpe)]_∞ (1a) which maintains its coordination network with the 10.3% unit cell volume contraction, while compound 5 remains unchangeable under the same conditions. Compounds 1, 5 and the dioxime-free 1D polymer [Cd(pyta)₂(H₂O)]_∞ (6) display blue luminescence upon excitation with ultraviolet light. The emission intensity of the guest-loaded complex 1 is effectively reduced in comparison with the previously reported DMF free analogues [Zn(CH₃COO)₂(NioxH₂)(bpe)(H₂O)]_∞ and [Cd(CH₃COO)₂(bpe)(H₂O)]_∞.