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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
journal contribution
posted on 2016-01-06, 00:00 authored by Hailou Li, Wen Yang, Xiuhua Wang, Lijuan Chen, Jianru Ma, Liwei Zheng, Junwei ZhaoThree 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.
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pH rangesPropertiesThree typesUV spectroscopydimethylamine hydrochlorideNa 3HReaction ProcessNa 2WOlifetime decay curves149.00 μsheet structureIsopolytungstates InducedIR spectroscopyW 28O moietypH VariationH 2O unit6 manifestsH 2NH 2O3 displaysW 6O fragment8094.19 nsSynergistic EffectLnW 11O fragments384.89 μTG6 HJW 22O anionsESIelectrospray ionization mass spectrometryroom temperatureemission bands
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