Two types of novel tetra-iron substituted sandwich-type arsenotungastates with supporting lanthanide pendants

Two classes of novel tetra-iron substituted sandwich-type arsenotungastates (ATs) with supporting lanthanide (Ln) pendants KNa2 [Ln(H2O)(7)][Fe-4(H2O)(10)(B-beta-AsW9O33)(2)]center dot 21H(2)O [Ln = La-III (1), Pr-III (2), Nd-III (3), Sm-III (4)] and [Ln(H2O)(8)](2)[Fe-4(H2O)(8)(L-thr)(2)(B-beta-AsW9O33)(2)]center dot 20H(2)O [Ln = La-III (5), Pr-III (6), Nd-III (7), Sm-III (8), Eu-III (9), Gd-III (10), Tb-III (11), Dy-III (12), Er-III (13)] (L-thr = L-threonine) have been synthesized by the hydrothermal reaction of the [As2W19O67(H2O)](14-) precursor with Fe3+ cations and Ln(3+) cations in the presence of L-thr or L-leucine and L-alanine, and further characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction. Structural analyses indicate that 1-4 display the inorganic 2-D sheet architecture constructed from tetra-iron sandwiched AT [Fe-4(H2O)(10)(B-beta-AsW9O33)(2)](6-) fragments by bridging [Ln(H2O)(7)](3+) cations whereas the molecular structures of the isostructural 5-13 consist of an organic-inorganic hybrid tetra-iron substituted sandwich-type AT [Fe-4(H2O)(8)(L-thr)(2)(B-beta-AsW9O33)(2)](6-) fragment and two pendant [Ln(H2O)(8)](3+) cations. As far as we know, 1-4 represent the rare inorganic 2-D extended ATs based on transition-metal substituted sandwich-type polyoxometalate units and Ln linkers and 5-13 are the first Fe-Ln heterometallic ATs with amino acid ligands. The solid state photoluminescence (PL) measurements of 9 and 11 have been performed at room temperature. The PL emission of 9 is mainly derived from the characteristic D-5(0) -> F-7(2) (J = 4-0) transitions of the Eu-III cations whereas the PL behavior of 11 stems from the common contribution of the D-5(4) -> F-7(J) (J = 5-3) transitions of the Tb-III ions and oxygen-to-metal (O -> W) charge-transfer transitions of AT segments. The thermo-gravimetric (TG) analyses of 1-4 and 6-12 have been investigated.