Self-Assembly of a Family of Isopolytungstates Induced by the Synergistic Effect of the Nature of Lanthanoids and the pH Variation in the Reaction Process: Syntheses, Structures, and Properties
2016-01-06T00:00:00Z (GMT) by
Three types of new lanthanoid(Ln)-containing isopolyoxotungstates [H2N(CH3)2]6Na6[Ln4(H2O)22W28O94H2]2·113H2O [Ln = Pr3+ (1), Nd3+ (2), Sm3+ (3)], Na2[Eu(H2O)7]2[Eu(H2O)5]2[W22O74H2]·20H2O (4), and Na3H2[Ln(H2O)4][Ln (H2O)5]2[W22O74H2]·36H2O [Ln = Gd3+ (5), Tb3+ (6), Er3+ (7), Tm3+ (8), Yb3+ (9), Lu3+ (10)] have been obtained by reacting Na2WO4·2H2O with Ln(NO3)3·6H2O in the presence of dimethylamine hydrochloride in the acidic aqueous solution and structurally characterized by elemental analyses, IR spectroscopy, UV spectroscopy, electrospray ionization mass spectrometry (ESI–MS), thermogravimetric (TG) analyses, and single-crystal X-ray diffraction. 1, 2, and 3 are isostructural and display a one-dimensional (1-D) chain-like alignment built by hexameric Ln8-comprising [Ln4(H2O)22W28O94H2]212– entities via [Ln(H2O)5]3+ connectors. The [Ln4(H2O)22W28O94H2]212– entity consists of two [Ln4(H2O)22W28O94H2]6– subunits connected by two W–O–Ln–O–W linkers. Intriguingly, the rare λ-shaped octacosatungstate [W28O94H2]18– moiety observed in the [Ln4(H2O)22W28O94H2]6– subunit is composed of two undecatungstate [W11O38H]9– fragments joined through a hexatungstate [W6O22]8– fragment by sharing four μ2-O atoms. In 4, 22-isopolytungstate [W22O74H2]14– anions are interlinked together by four W–O–Eu1–O–W linkers giving rise to the 1-D chain motif, and then adjacent 1-D chains are further bridged through multiple W–O–Eu2–O–W connectors to engender the two-dimensional extended sheet structure with the 4-connected topology. The isomorphic 5–10 demonstrate the discrete structure consisting of a [Ln(H2O)4][Ln (H2O)5]2[W22O74H2]8– unit. The pH ranges in which 3, 4, and 9 are stable in aqueous solution have been examined by virtue of UV and ESI–MS spectra. The solid-state luminescent properties of 3, 4, and 6 have been probed at room temperature. 3 displays the pink emission derived from characteristic emission bands of the Sm3+ cations that correspond to transitions from the 4G5/2 excited-state to lower 6HJ (J = 5/2, 7/2, 9/2, 11/2) levels, 4 emits the red light that mainly results from the 5D0 → 7F2 transition of the Eu3+ cations, and 6 manifests the green luminescence mainly originating from the 5D4 → 7F5 transition of the Tb3+ cations. Their lifetime decay curves all conform to the single exponential function, affording their lifetimes of 8094.19 ns, 149.00 μs and 384.89 μs, respectively.