Cadmium(II) coordination polymers based on substituted malonic acid: Synthesis, characterization and photoluminescence properties

  • Déniz M
  • Pasán J
  • Rasines B
 et al. 
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© The Partner Organisations. Four novel complexes of cadmium(ii) with alkyl/aryl-substituted malonate ligands of formulae {[Cd(Memal)(H 2 O)] 6 ·0.5H 2 O} n (1), [Cd(Etmal)(H 2 O)] n (2), [Cd(Butmal)(H 2 O)] n (3) and [Cd(Bzmal)(H 2 O)] n (4), (Memal = methylmalonate, Etmal = ethylmalonate, Butmal = butylmalonate and Bzmal = benzylmalonate) have been prepared and characterized by single crystal X-ray analysis. Their luminescence, UV-Vis absorption properties and thermal behaviour were also investigated. Complex 1 is a three-dimensional compound where each metal centre is connected to four other ones leading to a sodalite network with the point symbol {4 2 ·6 4 }. Each cadmium(ii) ion in 1 is seven-coordinate with a water molecule and six oxygen atoms from three Memal ligands building a somewhat distorted pentagonal bipyramidal surrounding. The Memal ligand in 1 adopts a μ 3 -κO:κ 2 O′:κ 2 O′′:κO′′′ coordination mode. 2-4 are isomorphous compounds with a two-dimensional structure where centrosymmetric double oxo(carboxylate-substituted malonate)-bridged dicadmium(ii) units are linked to four other dinuclear entities through anti-anti and anti-syn carboxylate bridges to form a Shubnikov tetragonal layered [4 4 6 2 ]-sql net. Each cadmium(ii) ion in 2-4 is six-coordinate in a distorted octahedral environment with four carboxylate-oxygen atoms building the basal plane and a water molecule plus another carboxylate-oxygen atom in the axial positions. The substituted malonate ligands in 2-4 exhibit the μ 4 -κO:κ 2 O′:κ 2 O′′:κO′′′ coordination mode. The tests of the emission spectra of 1-4 show that the length of the side chain influences the photoluminescence properties of the complexes. Finally, the decays of the luminescence of 1-4 and the respective free substituted malonic acids reveal that the same value of the average life time is observed for 1 (H 2 Memal), whereas in the case of 2-4, they are greater than that of 1 and those of their corresponding acids. The longer decay rates in 2-4 are consistent with the lack of water molecules in the environment of the cadmium(ii) ion in these complexes, indicating that the sheet-like structure of 2-4 provides a chemical surrounding with less non-radiative relaxation processes.

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  • M. Déniz

  • J. Pasán

  • B. Rasines

  • P. Lorenzo-Luis

  • F. Lahoz

  • C. Vera-Gonzales

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