Structures and photoluminescence of another crown-typed polyoxotungstoeuropate [H2O⊂{Eu(H2O)4}2{Eu(H2O)2(AsW9O33)}4]x- in the presence of Na+ or Ca2+

Two novel polyoxotungstoeuropates [H2O subset of{EunNa1-n(H2O)(2)}(2){Eu(H2O)(2)(AsW9O33)}(4)](21-) (n = 1/4) la and [H2O subset of{EunCa1-n(H2O)(4)}(2) {EunCa1-n(H2O)(2)(AsW9O33)}(4)](20-) (n = 2/3) 2a were formed by the reaction of alpha-B-[AsW9O33](9-) and Eu3+ wit h Na2+ or Ca2+ as the counter cation. Na18H3[H2O subset of{EunNa1-n(H2O)(2)}(2){Eu(H2O)(2)(AsW9O33)}(4)]center dot 48H(2)O (n = 1/4) 1 crystallized in the tetragonal space group P4/ncc, with a = 28.82(2) (A) over circle, c = 26.45(2) (A) over circle, V = 2 1974(23) (A) over circle (3) and Z = 4, while Ca9Na2[H2O subset of{EunCa1-n(H2O)(4)}(2){EunCa1-n(H2O)(2)(AsW9O33)}(4)]center dot 63H(2)O (n = 2/3) 2 crystallized in the triclinic space group P1, with a = 14.27(1) (A) over circle, b = 20.26(2) (A) over circle, c = 20.54(2) (A) over circle, alpha = 81.69(3)degrees, beta = 86.10(3)degrees, y = 72.93(3)degrees, V = 5613(7) (A) over circle (3) and Z = 1. These anion Structures consisted of tetramer of L-shaped units [Eu(H2O)(2)(AsW9O33)](6-) with water molecules encapsulated in the center. Interestingly, these tetramers also contained an apical attachment of two square-antiprismatic Eu3+ centers each of which is coordinated by one bridging O atom for each [AsW9O33](9-) ligand and four aqua molecules. These apical Eu atoms had different coordination environments from Eu atom in L-shaped Unit, and were disordered together with Na atoms with a quarter occupancy of Eu for 1, while all the Eu atoms together with Ca atoms with a 2/3 occupancy of Eu for 2. The photouminescence spectra, excitation spectra and lifetimes for these two complexes Were discussed based on crystal Structures. Notably, for 1 the emission from two different sites of Eu3+ was isolated in photoluminescence spectra under two different F-7(0) -> D-5(0) excitation wavelengths at 579.8 and 580.5 nm. (c) 2005 Elsevier B.V. All rights reserved.