Synthesis, Crystal Structures and Properties of Two Alkali-Lanthanide Heterometallic Coordination Polymers

Synthesis, structure and properties of two alkali-lanthanide heterometallic coordination polymers with the stoichiometric formula [M-5(OH)(4)(H2O)(14)Ln(NO3)(4)] (where M is Na+ and Ln, Er3+ or Yb3+) are reported. They crystallize in the monoclinic P2(1)/c space group with very similar cell parameters: a = 15.8777(19) a"<<, b = 13.4173(18) a"<<, c = 13.3515(17) a"<<, beta = 93.585(9)A(0), and V = 2838.8(6) a"<<(3) for Er(III) and a = 15.8756(5) a"<<, b = 13.3707(4) a"<<, c = 13.3083(4) a"<<, beta = 93.584(2)A(0), and V = 2819.40(15) a"<<(3) for the Yb(III) polymer. The main findings in the structures of the new compounds are their isomorphism (due to the similarity between erbium and ytterbium ionic radii) and the coexistence in both of highly aqueous coordinated [Na-5(OH)(4)(H2O)(14)](+) and [Ln(NO3)(4)](-) units. The luminescence measurements in the near infrared region after excitation at different wavelengths have confirmed the deleterious effect (quenching) of OH and H2O groups on the emission (intensity and lifetime) of both erbium(III) and ytterbium(III) and the very weak optical absorption of lanthanides. Magnetic measurements show a paramagnetic behavior of the lanthanide centers. Two new isostructural alkali-lanthanide coordination polymers, [Na-5(OH)(4)(H2O)(14)Er(NO3)(4)] and [Na-5(OH)(4)(H2O)(14)Yb(NO3)(4)], have been synthesized and characterized by X-ray diffraction. Their photoluminescent and magnetic properties are presented.