Luminescence and magnetocaloric effect of Ln(4) clusters (Ln = Eu, Gd, Tb, Er) bridged by CO32- deriving from the spontaneous fixation of carbon dioxide in the atmosphere

The synthesis and characterization of a new family of neutral tetranuclear Ln(III) complexes, [Eu4L4(CO3) (acac)(2)(H2O)(2)(CH3OH)(2)]center dot 5H(2)O center dot 2CH(3)OH(1), [Gd4L4(CO3)(acac)(2) (CH3OH)(4)]center dot 2CH(3)OH center dot CH2Cl2 (2), [Tb4L4(CO3)(acac)(2)(H2O)(2)(CH3OH)(2)]center dot 3H(2)O center dot CH3OH (3), and [Er4L4(CO3)(acac)(2)(H2O)(2)(CH3OH)(DMF)]center dot H2O center dot CH3OH (4) (where acac-is acetylacetonate, H2L is 2-(hydroxyimino)-2-[(5-methyl-2-hydroxyphenyl) methylene] hydrazide and DMF = N, N-dimethyl formamide) are reported. For complexes 1-4, by absorbing and fixing CO2 spontaneously under atmospheric conditions, with CO32- as a bridging tetradentate ligand, the four Ln(III) ions are bridged by two mu(2)-O oxygen atoms from CO32- to form a Ln(4) cluster. X-ray diffraction data reveal that the non-centrosymmetric (1, 3 and 4) or centrosymmetric (2) unit has two distinct Ln(III) ions, nine-coordinated Ln(III) ions in distorted spherical capped square antiprism geometry and eight-coordinated Ln(III) ions in distorted triangular dodecahedron geometry. Magnetic study indicates that complex 2 can act as a cryogenic magnetic refrigerant and the magnetocaloric effect (MCE) was detected with the magnetic entropy change of -Delta S-m = 21.43 J kg(-1) K-1 at Delta H = 7 T and 5 K. Furthermore, the fluorescence properties of complexes 1 and 3 were also investigated. The results prove that complex 3 can show Tb-III characteristic emission peaks, while for complex 1, Eu-III typical emission peaks were not observed.