Synthesis of a new Cd(II)–Ni(II) hetero-metallic coordination polymer base on citric acid ligand. X-ray structure, thermal stability, XPS and fluorescence studies

• A new heterometallic polymer, NiCd(cit)(H2O) (cit = citrate), was synthesized under hydrothermal conditions.
• Six-coordinated Cd2+ form infinite chains linked by carboxylate which generate 2D structures through NiO6 bridges.
• The TG-MS and DSC results show that this compound is thermally stable up to 250 °C.
• The spectral information from XPS and fluorescence is consistent with the citrate coordination to Cd2+ and Ni2+ cations.

A new hetero-metallic polymer, NiCd(cit)(H2O) (cit = citrate), was synthesized under hydrothermal conditions. The structural analysis indicates the formation of a 2D structure, bridged by the cit4− group. This compound crystallizes in the monoclinic P21/c space group, with lattice parameters: a = 6.0817(3) Å, b = 14.9725(6) Å, c = 9.6817(5) Å, β = 101.353(5)°. Full characterization by powder diffraction analysis, thermocalorimetry and scanning electron microscopy, XPS and fluorescence have been carried out. The TG-MS and DSC results show that this compound is thermally stable up to 250 °C and the DSC profile shows a medium-intense endotherm centred at approximately 300 °C. The distances of Cd–O are in the range of 2.169(4)–2.647(4) Å, similar to pure cadmium(II)−citrate aqueous complex Cd(C6H6O7)(H2O). The six-coordinated Cd2+ is linked by carboxylate groups to form an infinite chain, which is further connected through NiO6 octahedral bridges to generate 2D structure in the bc plane.

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