English

• 1. INTRODUCTION

  The rare earth metals have been paid great attention due to their unique coordinated chemistry characters, f electronic configurations and energetic properties. Therefore, rare earth metal-based materials have presented many fascinating applications including information storage, nonlinear optics, luminescence, proton-conductivity, catalysis, and gas storage^[1-4]. The iodate is interesting in the construction of functional material because of its presence of the stereochemically active lone-pair electrons on iodine atoms, which could also serve as a structure-directing agent^{[5, 6]}. Specially, in the synthesis of nonlinear optical materials, the asymmetric IO₃ or IO₄ groups possessing large hyperpolarizability can lead to the formation of non-centrosymmetric (NCS) structures with wider transparent range (up to 12 μm) and higher optical-damage threshold^[3]. So far, rare earth iodates have been extensively explored, which have illustrated versatile structural motifs ranging from 1-D chains, 2-D layers to 3-D networks built from LnO_x polyhedra (Ln = rare earth elements, x = 7 or 8) and IO_x (x = 3, 4) trigonal pyramids or tetrahedra^[7-10]. Despite of the numerous reported rare earth iodates, there is still a big space for the production of new complexes due to the flexible coordination modes of rare earth ions, and versatile I_xO_y polyiodate anions. Specially, when concerning about their properties, compared with the main attention on their NLO performances, much less attention has been paid to other functions such as luminescence and magnetism^{[4, 11, 12]}. More recently, rare earth metal can also been used as photocatalyt as doping ions in traditional photocatalytic material, in which the rare earth elements serve as upconverter that sum the energies of near-infrared (NIR) quanta to emit a quantum of higher energy^[13-15]. It is significant to investigate the application of rare earth complex in photocatalytic fields, because rare earth elements are diversiform and abundant in the earth, and the rare earth complexes can also absorb UV light. To our knowledge, the study about the photocatalytic performance under UV or Vis lights is still in its infancy^[15]. In this work, a new environmentally friendly 3-D luminescent gadolinium iodate was synthesized, which was directly utilized as a photocatalytic material.

  2. EXPERIMENTAL

  2.1 Materials and methods

  All the reactants including Gd(NO₃)₃·6(H₂O) and I₂O₅ were of reagent grade and used as purchased. FTIR spectrum was recorded as KBr discs on a Shimadzu IR-408 infrared spectrophotometer in the 400~4000 cm^-1 region. X-ray powder diffraction (PXRD) was performed on a Philips X'Pert-MPD diffractometer with CuKα radiation (λ = 1.54056 Å). UV-Vis spectrum was taken on a Shimadzu UV-2101 PC UV-Vis scanning spectrophotomete equipped with an integrating sphere at ambient temperature. Fluorescence spectra were carried out on an Edinburgh FL-FS 920 TCSPC spectrometer.

  2.2 Synthesis of [Gd(H₂O)(IO₃)₂(IO₃H₂O)]_n (1)

  Hydrothermal reaction was executed in the synthesis of 1. In 13 mL deionized water, Gd(NO₃)₃·6(H₂O) (0.451 g, 1 mmol) and I₂O₅ (0.3300 g, 1.0 mmol) were added. The mixture was stirred constantly for 1.5 h and then transferred into a 25 mL Teflon-lined autoclave. The autoclave was heated to 180 ℃, and held at this temperature for 4 d. Then the autoclave was cooled to room temperature in two days. Colorless block crystals can be obtained with the yield of 23.2% (0.1666 g, based on Gd). The product was washed with acetone and distilled water, and dried in air. IR (cm^-1): 3423(s), 3295(s), 1619(s), 838(m), 766(s), 737(m), 574(m), 405(m).

  2.3 Photocatalytic testing

  The photocatalytic activity of the as-synthesized sample 1 was estimated by using RhB aqueous solution as the model dye. A 22 W lamp was used to produce UV light, which was placed at 10 cm away from the sample. In a typical procedure, 80 mg of [Gd(H₂O)(IO₃)₂(IO₃H₂O)]_n was suspended in an RhB solution (100 mL, 20 mg/L) under stirring. Before irradiation, the mixture was stirred in the darkness for 2 h to achieve the equilibrium of the adsorption/desorption equilibrium of the organic contaminants on the catalyst surfaces. At set intervals, about 3 mL aliquots from the beaker were taken out for analysis. The residual concentrations of pollutants in solution were analyzed by recording variations of the organics at the absorption band maximum in the UV-Vis spectra using a UV-Vis spectrophotometer. The percentage of degradation is reported as C/C₀, where C is the absorption of RhB at each irradiated time interval of the main peak of the absorption spectrum at 553 nm, and C₀ is the absorption of the starting concentration when adsorption-desorption equilibrium is achieved.

  2.4 Electronic structure calculation

  The crystallographic data of 1 were used to build the simulated model. During the electronic structure calculation, no further structure optimization was conducted. The DFT calculation was carried out using generalized gradient approximation (GGA)^[16], and the Perdew-Burke-Ernzerhof (PBE) exchange correlation functional was performed in the CASTEP code^[17]. A 3×2×2 Monkhorst-Pack grid with a total number of 6 k points in the irreducible Brillouin zone and 45 empty bands were adopted. The number of plane waves included in the basis was determined by a cutoff energy E_c of 435.4 eV. The pseudoatomic calculations on Gd-4f⁸5s²5p⁶6s², I-5s²5p⁵ and O-2s²2p⁴ were conducted.

  2.5 X-ray crystallography

  The intensity data were collected on a Bruker APEX Ⅱ diffractometer using graphite-monochromated MoKα radiation (λ = 0.71073 Å) at room temperature. The structure was solved by direct methods using SHELXS-97 program^[18] and refined with SHELXL-97^[19] by full-matrix least-squares techniques on F². Non-hydrogen atoms were refined with anisotropic thermal parameters, and hydrogen atoms were assigned with common isotropic displacement factors and included in the final refinement by using geometrical constraints. Crystal data: triclinic, space group P$ \overline 1 $ with M_r = 717.98, a = 7.11710(10), b = 7.42540(10), c = 10.5958(2) Å, α = 95.3050(10), β = 104.9630(10), γ = 110.0210(10)º, V = 498.089(14) ų, Z = 2, D_c = 4.787 g/cm³, F(000) = 630, μ(MoKα) = 16.001 mm^–1, the final R = 0.0197 and wR = 0.0500 (w = 1/[σ²(F_o²) + (0.0166P)² + 6.5492P], where P = (F_o² + 2F_c²)/3), S = 1.036, (Δ/σ)_max = 0.000, (Δρ)_max = 1.019 and (Δρ)_min = –1.490 e/ų. Selected bond lengths and bond angles are given in Table 1. Hydrogen bonds are listed in Table 2.

  Table 1

  

  Table 1.  Selected Bond Lengths (Å) and Bond Angles (º)

  DownLoad: CSV

  Bond	Dist.		Bond	Dist.		Bond	Dist.
  Gd(1)–O(1)	2.378(4)		Gd(1)–O(3)a	2.380(4)		Gd(1)–O(2)b	2.435(5)
  Gd(1)–O(4)	2.397(5)		Gd(1)–O(6)b	2.382(5)		Gd(1)–O(7)c	2.409(4)
  Gd(1)–O(8)	2.384(5)		Gd(1)–O(10)	2.408(5)		I(1)–O(1)	1.796(4)
  I(1)–O(2)	1.817(4)		I(1)–O(3)	1.811(4)		I(1)···O(4)	2.771(5)
  I(1)···O(5)	2.659(6)		I(1)···O(11)	2.796(7)		I(2)–O(4)	1.816(5)
  I(2)–O(5)	1.805(4)		I(2)–O(6)	1.802(4)		I(2)···O(5)b	2.728(6)
  I(3)–O(7)	1.815(5)		I(3)–O(8)	1.807(4)		I(3)–O(9)	1.786(5)
  I(3)···O(3)	2.812(6)
  Angle	(º)		Angle	(º)		Angle	(º)
  O(1)–I(1)–O(3)	99.6(2)		O(1)–I(1)–O(2)	95.7(2)		O(3)–I(1)–O(2)	97.9(2)
  O(6)–I(2)–O(5)	97.6(2)		O(6)–I(2)–O(4)	96.6(2)		O(5)–I(2)–O(4)	97.0(2)
  O(9)–I(3)–O(8)	99.1(2)		O(9)–I(3)–O(7)	101.7(2)		O(8)–I(3)–O(7)	96.2(2)
  Symmetry codes: (a) –x, –y+1, –z+1; (b) –x+1, –y+1, –z+1; (c) –x+1, –y+1, –z+2

  Table 2

  

  Table 2.  Hydrogen Bridging Details of 1

  DownLoad: CSV

  D–H···A	D–H/Å	H···A/Å	D···A/Å	∠(D–H···A)/º	Symmetry codes
  O(10)–H(1W)···O(9)	0.78	2.02	2.760(8)	158	–x+1, –y+2, –z+2
  O(10)–H(2W)···O(5)	0.63	2.37	2.869(7)	138	x, y+1, z
  O(11)–H(3W)···O(8)	1.00	1.97	2.945(8)	164	–x+1, –y+2, –z+1
  O(11)–H(4W)···O(7)	0.81	2.20	2.955(9)	156	x, y, z–1

  3. RESULTS AND DISCUSSION

  3.1 Description of structure

  1 is a quasi-3-D framework constructed from Gd₂O₁₆I₄ dimmer and infinite polyiodate, which is highly different from its previously reported polymorphs^{[4, 11, 20]}. The Gd³⁺ is coordinated to seven O donors from seven IO₃ moieties and one water molecule to give a monocapped trigonal prism geometry, which is commonly observed in rare earth iodate complexes^[3]. The capping site was occupied by O(2) with the longest Y–O bond length. The Gd–O bond distances are in the range of 2.378(4)~2.435(5) Å, and the O–Y–O angles are between 69.06(16) and 151.50(16)º. These values are in good agreement with its polymorphs or the other rare earth iodates^{[4, 7, 11]}. Two GdO₈ monocapped trigonal prisms are bridged by four IO₃ groups to generate a Gd₂O₁₆I₄ dimer with the Gd–Gd distance of 5.305(2) Å, and the distance between two rectangle bottoms of monocapped trigonal prism is 2.701(8) Å (Fig. 1). Adjacent Gd₂O₁₆I₄ dimers are linked into a 1-D chain along the a-axis via a μ₃-I(1)O₃ group. Furthermore, neighboring 1-D chains are connected into a 2-D layer via μ₂-I(3)O₃ groups along the ac-plane (Fig. 1). Consequently, two kinds of linkage modes in IO₃ group can be found: a. I(2)O₃ and I(3)O₃ bind with two Gd centers to present bismondentate μ₂-bridged mode, b. I(1)O₃ coordinates to three Gd ions to give a trimonodentate way (μ₃-bridged, Scheme 1). In iodate groups, the environment of the iodine is surrounded by three strong I–O bonds (mean bond lengths: 1.808(4), 1.808(1) and 1.803(1) Å for I(1), I(2) and I(3), respectively), giving rise to AX₃E configurations. However, in reported polymorph of Gd(IO₃)₃^[4], a chelated/bridged model of iodate was observed due to the absence of coordinated water. Weak I···O bonds are frequently observed in iodate-containing complexes, whose bond lengths are longer than 2.3 Å. If weak I···O bonds are taken into account, the environment of iodine atoms can be divided into two types (Fig. 2): a. I(1) is filled up by additional three weak bonds (bond lengths in the range of 2.659(6)~2.796(7) Å, Table 1), leading to an octahedron in which the iodine atom is displaced off the centre along the ternary axis; b. I(2) and I(3) are weakly bonded by additional one oxygen atom (2.728(6) 2.812(6) Å, Table 1) to give a trigonal bipyramidal geometry. Based on these weak I···O bonds, a 1-D [(IO₃)(IO₃H₂O)]_n chain along the a-axis is generated (Fig. 2d), upon which the neighboring 2-D layers are further linked into a quasi-3-D network (Fig. 3). According to PLATON analysis, no residual solvent accessible void was observed, suggesting small pore size in this 3-D network (about 6.0×3.8 Å). The formation of polyiodates is complicated, which might be involved in excess amounts of iodine precursors, large I/M (M = metal) ratios and strong acid reactive medium. Therefore, only three kinds of isolated iodate polyanions have been reported so far, i. e. I₂O₅, I₃O₈ and I₄O₁₁, in which elongated I–O–I distances can be observed^[3]. To our knowledge, the 1-D [(IO₃)(IO₃H₂O)]_n chain has never been reported. Hydrogen bond between water molecules and IO₃ groups also contribute to the structural stabilization (Table 2).

  Figure 1

  

  Figure 1.  2-D layer constructing from the Gd₂O₁₆I₄ dimmer

  DownLoad: Full-Size Img PowerPoint

  Scheme 1

  

  Scheme 1.  Linkage modes of IO₃: (a) μ₂-bridged and (b) μ₃-bridged

  DownLoad: Full-Size Img PowerPoint

  Figure 2

  

  Figure 2.  Weak I…O bonds around I(1) (a), I(2) (b) and I(3) (c), 1-D [(IO₃)(IO₃H₂O)]_n chain along the a-axis (d)

  DownLoad: Full-Size Img PowerPoint

  Figure 3

  

  Figure 3.  Quasi-3-D network of 1 constructed from weak I…O bonds (blue) and hydrogen bonds (green)

  DownLoad: Full-Size Img PowerPoint

  3.2 PXRD, FTIR, absorption spectrum and optical gap

  Powder X-ray diffraction (PXRD) was conducted to verify its phase purity of as-synthesized sample. As shown in Fig. 4a, the good consistence between experimental curve and simulated one suggests its good purity. The bands at 3423 and 1619 cm^-1 are the stretching and bending modes of the O–H groups in water, and those at 838~574 cm^-1 are the asymmetric and symmetric stretching modes of I–O in iodates^[9]. Besides, the band at 406 cm^-1 could be attributed to the M–O vibration^[9]. The UV-Vis diffuse reflectance spectra executed among 200~1000 nm 1 are given in Fig. 4b, and it is further converted into optical gap by Kubelka-Munk equation^[21]. The strong absorption range (200~320 nm) with peaks at 260 nm can be assigned to the ligand-to-metal charge transfers (CT) from the O-2p orbitals of iodate to Gd ion, which will be further verified by DFT calculation^[22]. This adsorption behavior is consistent with its colorless. The optical gap of 4.15 eV estimated by Kubelka-Munk equation is in good agreement with the calculated value of 4.11 eV (Fig. 5), which is consistent with other metal iodates^[9]. The UV adsorption of 1 hints its UV light-driven photocatalytic property.

  Figure 4

  

  Figure 4.  (a) PXRD pattern and (b) absorbance spectra of 1 (Inset: Tauc plot showing the optical gap)

  DownLoad: Full-Size Img PowerPoint

  Figure 5

  

  Figure 5.  Charge densities in the frontier molecular orbitals (left), band structure (middle) and projected density of states (PDOS, right) for 1

  DownLoad: Full-Size Img PowerPoint

  3.3 Luminescence property

  Luminescent spectrum of 1 was recorded on crystalline samples at room temperature (Fig. 6). 1 can produce yellow emissions centered at 502, 524 and 547 nm (CIE coordinate: x = 0.2568, y = 0.4076, λ_ex = 306 nm). Gd³⁺ possesses the stable half-filled electronic configuration of 4f⁷, leading to the high transfer energy barrier of 32224 cm^-1 from ground state ⁸S_7/2 to the first excited state ⁶P_1/2. Therefore, yellow emissions could not stem from Gd³⁺ ions, but from the electronic transfer in iodate group. And the emission splits might be attributed to their great distortion induced by weak I···O interactions^[23].

  Figure 6

  

  Figure 6.  Solid-state luminescence spectrum of 1 at room temperature (λ_ex = 306 nm)

  DownLoad: Full-Size Img PowerPoint

  3.4 Photocatalytic performance

  The study about the photocatalytic performance of rare earth ideates is limited^[15]. In this work, rhodamine B (RhB) was selected as a model pollutant for the study of photocatalytic performance of 1. Under the UV-light irradiation, the wavelength and absorption intensity changes of RhB with the presence of sample 1 are revealed in Fig. 7a. Blank experiment without the catalyst was also conducted, in which the adsorption peaks change little. But with the presence of 1, the adsorption spectra of RhB decrease gradually and blueshifts can be found with the lengthening of irradiation time, which suggests that the degeneration reactions on RhB have occurred. Fig. 7b shows the degeneration rates in aqueous solutions with or without the presence of 1. After the irradiation time of 210 min, the degradation ratio is about 74.1% (in the presence of 1), 4.0% (no catalyst). These results are slightly higher than that of the non-hydrate Gd(IO₃)₃ (73%)^[15]. The stability of 1 as photocatalyst was verified by PXRD measurement on the recovered sample from reaction system (recovery ratio of catalyst was about 90%). As shown in Fig. 4b, the stability as photocatalyst is good by comparison with the PXRD patterns before and after photocatalytic reaction. The UV light driven photocatalytic process is generally dominated by either hydroxyl radicals (^•OH) or superoxide radicals (^•O^2-)^[24]. In this work, upon UV irradiation, the charge transfers (CT) from the O-2p orbitals of iodate to Gd-4f orbitals might happen, and the holes in iodate may be greatly stabilized due to their delocalization in [(IO₃)(IO₃H₂O)]_n chain. Therefore, the hydroxyl radicals (^•OH) might play an important role in this degeneration process.

  Figure 7

  

  Figure 7.  (a) Absorption spectra changes of the RhB solution with sample 1 under UV light. (b) Photodegradation ratio of RhB with or without the presence of 1

  DownLoad: Full-Size Img PowerPoint

  3.5 Structure/property correlation

  In order to correlate the structure-property in 1, DFT calculation was conducted. And the electronic structure including charge densities in the frontier molecular orbitals, band structure and density of states are shown in Fig. 5. The calculated band gap of 4.11 eV is in good agreement with the experimental value of 4.15 eV. Besides, its band gap is indirect with the top of valence band (VB) and bottom of conductive band (CB) locating at different points. Judged from the PDOS diagram, the top of VB is the main contribution of O-2p orbital of iodate, and the bottom of CB is dominated by I-5p and Gd-4f orbitals, which can be visualized by charge density in the frontier orbitals. The electronic structure verifies the assignments of absorption spectra, which have be assigned to the ligand-to-metal charge transfers (CT) from the O-2p orbitals of iodate to Gd-4f orbitals. Specially, this band structure also suggests that in photocatalytic degeneration reaction, the holes in O and radicals on I might dominate the degeneration process.

  4. CONCLUSION

  A new gadolinium iodate [Gd(H₂O)(IO₃)₂(IO₃H₂O)]_n has been structurally determined, whose quasi-3-D network is generated via weak I···O bonds and hydrogen bonds. Interestingly, its green emission stems from electronic transfer within iodate groups, and its photocatalytic activity for the degradation of rhodamine B was studied. Theoretical calculation was conducted to give structure/property correlation, which will be beneficial for the design of new rare earth-based functional materials.

  
  
• 1. [1]

     Eliseeva, S. V.; Bünzli, J. C. G. Lanthanide luminescence for functional materials and bio-sciences. Chem. Soc. Rev. 2010, 39, 189–227. doi: 10.1039/B905604C

  2. [2]

     Hu, C. L.; Mao, J. G. Recent advances on second-order NLO materials based on metal iodates. Coord. Chem. Rev. 2015, 288, 1–17. doi: 10.1016/j.ccr.2015.01.005

  3. [3]

     Chen, J.; Hu, C. L.; Mao, F. F.; Yang, B. P.; Zhang, X. H.; Mao, J. G. REI₅O₁₄ (RE = Y and Gd): promising SHG materials featuring the semicircle-shaped I₅O₁₄^3- polyiodate anion. Angew. Chem. Int. Ed. 2019, 58, 11666–11669. doi: 10.1002/anie.201904383

  4. [4]

     Sykora, R. E.; Khalifah, P.; Assefa, Z.; Albrecht-Schmitt, T. E.; Haire, R. G. Magnetism and Raman spectroscopy of the dimeric lanthanide iodates Ln(IO₃)₃ (Ln = Gd, Er) and magnetism of Yb(IO₃)₃. J. Solid State Chem. 2008, 181, 1867–1875. doi: 10.1016/j.jssc.2008.04.019

  5. [5]

     Huang, C.; Hu, C. L.; Xu, X.; Yang, B. P.; Mao, J. G. Explorations of a series of second order nonlinear optical materials based on monovalent metal gold(Ⅲ) iodates. Inorg. Chem. 2013, 52, 11551–11562. doi: 10.1021/ic401891f

  6. [6]

     Sun, C. F.; Hu, C. L.; Xu, X.; Yang, B. P.; Mao, J. G. Explorations of new second-order nonlinear optical materials in the potassium vanadyl iodate system. J. Am. Chem. Soc. 2011, 133, 5561–5572. doi: 10.1021/ja200257a

  7. [7]

     Phanon, D.; Mosset, A.; Gautier-Luneau, I. New iodate materials as potential laser matrices. Preparation and characterisation of α-M(IO₃)₃ (M = Y, Dy) and β-M(IO₃)₃ (M = Y, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er). Structural evolution as a function of the Ln³⁺ cationic radius. Solid State Sci. 2007, 9, 496–505. doi: 10.1016/j.solidstatesciences.2007.04.004

  8. [8]

     Assefa, Z.; Ling, J.; Haire, R. G.; Albrecht-Schmittc, T. E.; Sykora, R. E. Syntheses, structures, and vibrational spectroscopy of the two-dimensional iodates Ln(IO₃)₃ and Ln(IO₃)₃(H₂O) (Ln: Yb, Lu). J. Solid State Chem. 2006, 179, 3653–3663. doi: 10.1016/j.jssc.2006.07.042

  9. [9]

     Pan, C. Y.; Mai, H. D.; Chen, W. Z.; Zhao, F. H.; Yang, H. M. Synthesis, structure, and properties of a new Er^Ⅲ iodate. Aust. J. Chem. 2014, 67, 763–767. doi: 10.1071/CH13570

  10. [10]

      Sykora, R. E.; Assefa, Z.; Haire, R. G. Synthesis, structure, and spectroscopic properties of Am(IO₃)₃ and the photoluminescence behavior of Cm(IO₃)₃. Inorg. Chem. 2005, 44, 5667–5676. doi: 10.1021/ic050386k

  11. [11]

      Chai, W.; Lin, J.; Song, L.; Shu, K.; Qin, L.; Shi, H.; Guo, J. A two-dimensional topological structure and a series of corresponding plate-like Ln(IO₃)₃(H₂O)·H₂O (Ln = Nd, Eu, Gd, Tb, Dy) nanomaterials: syntheses, structures and properties. Solid State Sci. 2010, 12, 2100−2105. doi: 10.1016/j.solidstatesciences.2010.09.006

  12. [12]

      Regny, S.; Riporto, J.; Mugnier, Y.; Dantec, R. L.; Kodjikian, S.; Pairis, S.; Gautier-Luneau, I.; Dantell, G. Microwave synthesis and up-conversion properties of SHG-active α-(La, Er)(IO₃)₃ nanocrystals. Inorg. Chem. 2019, 58, 1647−1656. doi: 10.1021/acs.inorgchem.8b03208

  13. [13]

      Li, C.; Wang, F.; Zhu, J.; Yu, J. C. NaYF₄: Yb, Tm/CdS composite as a novel near-infrared-driven photocatalyst. Appl. Catal. B 2010, 100, 433−439. doi: 10.1016/j.apcatb.2010.08.017

  14. [14]

      Qin, W.; Zhang, D.; Zhao, D.; Wang, L.; Zheng, K. Near-infrared photocatalysis based on YF₃: Yb³⁺, Tm³⁺/TiO₂ core/shell nanoparticles. Chem. Commun. 2010, 46, 2304−2306. doi: 10.1039/b924052g

  15. [15]

      Wang, W.; Cheng, H.; Huang, B.; Li, X.; Qin, X.; Zhang, X.; Dai, Y. Ln(IO₃)₃ (Ln = Ce, Nd, Eu, Gd, Er, Yb) polycrystals as novel photocatalysts for efficient decontamination under ultraviolet light irradiation. Inorg. Chem. 2014, 53, 4989−4993. doi: 10.1021/ic500027f

  16. [16]

      Perew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phy. Rev. Lett. 1996, 77, 3865–3868. doi: 10.1103/PhysRevLett.77.3865

  17. [17]

      Segall, M.; Probert, M.; Pickard, C.; Hasnip, P.; Clark, S.; Refson, K.; Payne, M. First principles methods using CASTEP. Z. Krystallogr. 2005, 220, 567–570.

  18. [18]

      Sheldrick, G. M. SHELXS-97: Program for the Solution of Crystal Structures. University of Gottingen, Germany 1997.

  19. [19]

      Sheldrick, G. M. SHELXL-97: Program for the Refinement of Crystal Structures. University of Gottingen, Germany 1997.

  20. [20]

      Douglas, P.; Hector, A. L.; Levason, W.; Light, M. E.; Matthews, M. L.; Webster, M. Hydrothermal synthesis of rare earth iodates from the corresponding periodates: Ⅱ. synthesis and structures of Ln(IO₃)₃ (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er) and Ln(IO₃)₃·2H₂O (Ln = Eu, Gd, Dy, Er, Tm, Yb). Z. Anorg. Allg. Chem. 2004, 630, 479−483. doi: 10.1002/zaac.200300377

  21. [21]

      Kubelka, P.; Munk, F. Z. An article on optics of paint layers. Z. Technol. Phys. 1931, 12, 593−601.

  22. [22]

      Lin, J.; Liu, Q.; Yue, Z.; Diefenbach, K.; Cheng, L.; Lin, Y.; Wang, J. Q. Expansion of the structural diversity of f-element bearing molybdate iodates: synthesis, structures, and optical properties. Dalton Trans. 2019, 48, 4823–4829. doi: 10.1039/C8DT05120H

  23. [23]

      Dong, H.; Sun, L.; Yan, C. Energy transfer in lanthanide upconversion studies for extended optical applications. Chem. Soc. Rev. 2015, 44, 1608−1634. doi: 10.1039/C4CS00188E

  24. [24]

      Huang, H. W.; Tu, S. C.; Zeng, C.; Zhang, T. R.; Reshak, A. H.; Zhang, Y. H. Macroscopic polarization enhancement promoting photo- and piezoelectric-induced charge separation and molecular oxygen activation. Angew. Chem. Int. Ed. 2017, 56, 11860–11864 doi: 10.1002/anie.201706549

• 

  Figure 1  2-D layer constructing from the Gd₂O₁₆I₄ dimmer

  下载: 全尺寸图片 幻灯片
  

  Scheme 1  Linkage modes of IO₃: (a) μ₂-bridged and (b) μ₃-bridged

  下载: 全尺寸图片 幻灯片
  

  Figure 2  Weak I…O bonds around I(1) (a), I(2) (b) and I(3) (c), 1-D [(IO₃)(IO₃H₂O)]_n chain along the a-axis (d)

  下载: 全尺寸图片 幻灯片
  

  Figure 3  Quasi-3-D network of 1 constructed from weak I…O bonds (blue) and hydrogen bonds (green)

  下载: 全尺寸图片 幻灯片
  

  Figure 4  (a) PXRD pattern and (b) absorbance spectra of 1 (Inset: Tauc plot showing the optical gap)

  下载: 全尺寸图片 幻灯片
  

  Figure 5  Charge densities in the frontier molecular orbitals (left), band structure (middle) and projected density of states (PDOS, right) for 1

  下载: 全尺寸图片 幻灯片
  

  Figure 6  Solid-state luminescence spectrum of 1 at room temperature (λ_ex = 306 nm)

  下载: 全尺寸图片 幻灯片
  

  Figure 7  (a) Absorption spectra changes of the RhB solution with sample 1 under UV light. (b) Photodegradation ratio of RhB with or without the presence of 1

  下载: 全尺寸图片 幻灯片

  Table 1.  Selected Bond Lengths (Å) and Bond Angles (º)

  Bond	Dist.		Bond	Dist.		Bond	Dist.
  Gd(1)–O(1)	2.378(4)		Gd(1)–O(3)a	2.380(4)		Gd(1)–O(2)b	2.435(5)
  Gd(1)–O(4)	2.397(5)		Gd(1)–O(6)b	2.382(5)		Gd(1)–O(7)c	2.409(4)
  Gd(1)–O(8)	2.384(5)		Gd(1)–O(10)	2.408(5)		I(1)–O(1)	1.796(4)
  I(1)–O(2)	1.817(4)		I(1)–O(3)	1.811(4)		I(1)···O(4)	2.771(5)
  I(1)···O(5)	2.659(6)		I(1)···O(11)	2.796(7)		I(2)–O(4)	1.816(5)
  I(2)–O(5)	1.805(4)		I(2)–O(6)	1.802(4)		I(2)···O(5)b	2.728(6)
  I(3)–O(7)	1.815(5)		I(3)–O(8)	1.807(4)		I(3)–O(9)	1.786(5)
  I(3)···O(3)	2.812(6)
  Angle	(º)		Angle	(º)		Angle	(º)
  O(1)–I(1)–O(3)	99.6(2)		O(1)–I(1)–O(2)	95.7(2)		O(3)–I(1)–O(2)	97.9(2)
  O(6)–I(2)–O(5)	97.6(2)		O(6)–I(2)–O(4)	96.6(2)		O(5)–I(2)–O(4)	97.0(2)
  O(9)–I(3)–O(8)	99.1(2)		O(9)–I(3)–O(7)	101.7(2)		O(8)–I(3)–O(7)	96.2(2)
  Symmetry codes: (a) –x, –y+1, –z+1; (b) –x+1, –y+1, –z+1; (c) –x+1, –y+1, –z+2

  下载: 导出CSV

  Table 2.  Hydrogen Bridging Details of 1

  D–H···A	D–H/Å	H···A/Å	D···A/Å	∠(D–H···A)/º	Symmetry codes
  O(10)–H(1W)···O(9)	0.78	2.02	2.760(8)	158	–x+1, –y+2, –z+2
  O(10)–H(2W)···O(5)	0.63	2.37	2.869(7)	138	x, y+1, z
  O(11)–H(3W)···O(8)	1.00	1.97	2.945(8)	164	–x+1, –y+2, –z+1
  O(11)–H(4W)···O(7)	0.81	2.20	2.955(9)	156	x, y, z–1

  下载: 导出CSV
•