Photoluminescent 3D Lanthanide−Organic Frameworks with 2,5

CRYSTAL GROWTH & DESIGN

Photoluminescent 3D Lanthanide-Organic Frameworks with 2,5-Pyridinedicarboxylic and 1,4-Phenylenediacetic Acids

2008 VOL. 8, NO. 7 2505–2516

Paula C. R. Soares-Santos,† Luı´s Cunha-Silva,† Filipe A. Almeida Paz,† Rute A. Sa´ Ferreira,‡ Joaõ Rocha,† Tito Trindade,† Luı´s D. Carlos,*,‡ and Helena I. S. Nogueira*,† Department of Chemistry, CICECO, UniVersity of AVeiro, 3810-193 AVeiro, Portugal, and Department of Physics, CICECO, UniVersity of AVeiro, 3810-193 AVeiro, Portugal ReceiVed February 8, 2008; ReVised Manuscript ReceiVed March 31, 2008

ABSTRACT: Novel three-dimensional lanthanide-organic frameworks with 2,5-pyridinedicarboxylic (2,5-H2pdc) and 1,4phenylenediacetic acids (1,4-H2pda) were synthesized by hydrothermal synthesis, and characterized structurally using single-crystal and powder X-ray diffraction, elemental and thermogravimetric analyses, FT-IR and photoluminescence spectroscopies, and diffuse reflectance. The structural details of [Ln2(2,5-pdc)2(1,4-pda)(H2O)2] [where Ln3+ ) Eu3+, Tb3+, (Eu0.2Tb0.8)3+ and (Eu0.1Tb0.9)3+] and the dehydrated [Eu2(2,5-pdc)2(1,4-pda)] phase were unveiled by single-crystal X-ray diffraction. Photoluminescence measurements performed for the Eu3+ and Tb3+ compounds show emission at room temperature. Energy transfer from Tb3+ to Eu3+ has been observed for the Eu3+/Tb3+ mixed materials. Introduction Crystalline polymeric materials, in particular those threedimensionally connected and exhibiting permanent porosity, have been the subject of intensive worldwide research over the last two decades. Much of this attention is particularly focused in the field of crystal engineering dealing with the design, synthesis and detailed structural characterization of metal-organic frameworks (MOFs), which belong to the more general class of coordination polymers (encompassing all possible dimensionalities of the materials: 1D, 2D and 3D). The versatility inherent to the employed coordination chemistry principles led to an explosive growth in the number of new and fascinating structural architectures, in some of the cases closely allied with potential applications in functional materials.1 Remarkably, the vast majority of the reported compounds are based on d-block transition metal centers. However, due to their potential interesting application in optical devices and fascinating topological architectures which can be achieved by their high numbers of coordination, lanthanide centers have recently attracted the attention of crystal engineers.2,3 One of the current technological main challenges to the display and lighting industry concerns the development of new full-color emitting devices exhibiting red-green-and-blue (RGB) emission. This purpose can be achieved by incorporation of Eu3+, Pr3+ or Sm3+ for red, of Tb3+ or Er3+ for green and of Tm3+ or Ce3+ for blue. It is thus not surprising why the preparation of stoichiometric mixed-lanthanide silicates4,5 or MOFs based on mixed-lanthanide metallic centers6 has attracted a considerable amount of attention in recent years. Following our ongoing research efforts toward the isolation of novel multidimensional coordination polymers,7 we have recently reported a series of 1D functional materials having Sm3+, Eu3+ and Tb3+ bound to aromatic ambidentate ligands * Corresponding authors: Dr. Helena Isabel Seguro Nogueira, Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal. Phone: 351-234 370727. Fax: 351-234 370084. E-mail: [email protected]. Dr. Luı´s Antońio Dias Carlos, Department of Physics, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal. Phone: 351-234 370946. Fax: 351-234 424965. E-mail: [email protected]. † Department of Chemistry. ‡ Department of Physics.

which can act as optical antenna.8–10 We are currently interested in employing the same design principles toward functional materials but with the final objective of increasing the overall dimensionality of the networks. 2,5-Pyridinedicarboxylic (2,5H2pdc) and 1,4-phenylenediacetic (1,4-H2pda) acids are precursors of bridging ligands which can coordinate to lanthanides through a number of different coordination fashions. Moreover, these molecules are also good candidates to act as antennae and transfer the absorbed energy to the metallic centers, thus improving the photoluminescent properties of the isolated materials.11 Here, we wish to report a series of novel 3D lanthanide-organic frameworks (LnOFs), [Ln2(2,5-pdc)2(1,4pda)(H2O)2], in which lanthanide centers [Eu3+ (1), Tb3+ (2), Er3+ (3), (Eu0.2Tb0.8)3+ (4) and (Eu0.1Tb0.9)3+ (5)] are coordinated to residues of 2,5-H2pdc and 1,4-H2pda. The compounds were synthesized hydrothermally and characterized by vibrational and photoluminescence spectroscopies, diffuse reflectance, and elemental and thermogravimetric analysis. The crystal structures of compounds 1, 2, 4 and 5 and the dehydrated phase of the Eu3+ material (1-dehyd) were determined by singlecrystal X-ray diffraction. We also report on the photoluminescent properties of this series of functional materials. Experimental Section Synthesis of [Ln2(2,5-pdc)2(1,4-pda)(H2O)2]. All reagents were purchased from Aldrich and used without further purification. An aqueous solution (ca. 2 mL) of LnCl3 · nH2O [1 mmol; Ln3+ ) Eu3+, Tb3+, Er3+, (Eu0.2Tb0.8)3+ and (Eu0.1Tb0.9)3+] was added to another aqueous solution (ca. 10 mL) of 2,5-pyridinedicarboxylic acid (2,5H2pdc, 0.167 g, 1 mmol), 1,4-phenylenediacetic acid (1,4-H2pda, 0.097 g, 0.5 mmol) and NH3 (25%, 0.21 mL, 2.75 mmol). After stirring for 1 h at room temperature, the mixture was transferred to a Parr Teflonlined reaction vessel (ca. 25 mL) and placed inside a preheated oven at 403 K for 5 days. After the reaction, the vessel was allowed to cool slowly to room temperature yielding crystalline materials (white for 1, 2, 4 and 5, and pink for 3). A small quantity of crystals for each solid was preserved in a portion of the mother solution for the single-crystal X-ray diffraction studies. Instrumentation. FT-IR spectra were obtained as KBr pellets using a Mattson 7000 FT instrument. Elemental analyses for C, H and N were performed with a CHNS-932 elemental analyzer in the Microanalysis Laboratory of the University of Aveiro. The lanthanide content for each compound was obtained by ICP (inductively coupled

10.1021/cg800153a CCC: $40.75  2008 American Chemical Society Published on Web 06/06/2008

2506 Crystal Growth & Design, Vol. 8, No. 7, 2008

Soares-Santos et al.

Table 1. Crystal and Structure Refinement Details for [Ln2(2,5-pdc)2(1,4-pda)(H2O)2] [Where Ln3+ ) Eu3+ (1), Tb3+ (2), (Eu0.2Tb0.8)3+ (4) and (Eu0.1Tb0.9)3+ (5)] and [Eu2(2,5-pdc)2(1,4-pda)] (1-dehyd) formula formula weight crystal system space group a/Å b/Å c/Å β/° volume/Å3 Z Dc/g cm-3 µ(Mo KR)/mm-1 crystal size/mm crystal type θ range index ranges

reflections collected independent reflections data completeness final R indices [I > 2σ(I)]a,b final R indices (all data)a,b largest diff peak and hole CCDC No. a

1

1-dehyd

2

4

5

C12H9EuNO7 431.16 monoclinic P21/c 9.1666(5) 15.5309(8) 8.5327(4) 102.874(2) 1184.23(10) 4 2.418 5.334 0.18 × 0.07 × 0.02 colorless plates 3.59 to 29.13 -11 e h e 12 -20 e k e 21 -8 e l e 11 33338 3143 (Rint ) 0.0254) to θ ) 29.13°, 98.7% R1 ) 0.0150 wR2 ) 0.0324 R1 ) 0.0183 wR2 ) 0.0335 0.616 and -0.627 e Å-3 664124

C12H7EuNO6 413.15 monoclinic P21/c 9.0090(5) 16.2579(9) 8.0584(4) 99.408(2) 1164.42(11) 4 2.357 5.413 0.20 × 0.10 × 0.02 colorless plates 3.58 to 29.13 -12 e h e 12 -22 e k e 19 -11 e l e 11 20495 3111 (Rint ) 0.0247) to θ ) 29.13°, 99.6% R1 ) 0.0148 wR2 ) 0.0306 R1 ) 0.0184 wR2 ) 0.0314 0.664 and -0.592 e Å-3 664123

C12H9NO7Tb 438.12 monoclinic P21/c 9.1376(5) 15.4194(9) 8.5106(5) 102.660(3) 1169.96(12) 4 2.487 6.083 0.20 × 0.10 × 0.02 colorless plates 3.61 to 29.13 -12 e h e 12 -21 e k e 21 -11 e l e 10 30681 3062 (Rint ) 0.0314) to θ ) 29.13°, 97.4% R1 ) 0.0149 wR2 ) 0.0352 R1 ) 0.0183 wR2 ) 0.0364 0.495 and -0.481 e Å-3 664125

C12H9Eu0.20NO7Tb0.80 436.73 monoclinic P21/c 9.1431(6) 15.4335(10) 8.5173(6) 102.739(3) 1172.29(14) 4 2.474 5.934 0.26 × 0.10 × 0.02 colorless plates 3.60 to 29.12 -12 e h e 12 -19 e k e 21 -10 e l e 11 22642 3095 (Rint ) 0.0270) to θ ) 29.12°, 98.3% R1 ) 0.0136 wR2 ) 0.0316 R1 ) 0.0151 wR2 ) 0.0323 0.594 and -0.416 e Å-3 664126

C12H9Eu0.10NO7Tb0.90 437.43 monoclinic P21/c 9.1341(4) 15.4387(6) 8.5095(3) 102.735(2) 1170.48(8) 4 2.482 6.011 0.22 × 0.12 × 0.05 colorless plates 3.60 to 29.11 -12 e h e 12 -21 e k e 21 -11 e l e 11 25849 3138 (Rint ) 0.0306) to θ ) 29.11°, 99.8% R1 ) 0.0139 wR2 ) 0.0331 R1 ) 0.0156 wR2 ) 0.0340 0.683 and -0.540 e Å-3 664127

R1 ) ∑||Fo| - |Fc||/∑ |Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}.

Table 2. Selected Bond Lengths (in Angstroms) and Angles (in Degrees) for the Eu3+ Coordination Environment Present in [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1)a Eu(1)-O(1) Eu(1)-O(2) Eu(1)-O(2)i Eu(1)-O(3) Eu(1)-O(4)iv Eu(1)-O(5)ii Eu(1)-O(6)iii Eu(1)-O(1W) Eu(1)-N(1) O(1)-Eu(1)-O(2) O(1)-Eu(1)-O(2)i O(1)-Eu(1)-O(3) O(1)-Eu(1)-O(4)iv O(1)-Eu(1)-O(5)ii O(1)-Eu(1)-O(6)iii O(1)-Eu(1)-O(1W) O(1)-Eu(1)-N(1) O(2)-Eu(1)-O(2)i O(2)-Eu(1)-O(3) O(2)-Eu(1)-O(4)iv O(2)-Eu(1)-O(5)ii O(2)-Eu(1)-O(6)iii

2.5498(14) 2.5952(13) 2.3804(13) 2.3956(13) 2.4755(13) 2.3998(13) 2.4072(14) 2.4446(14) 2.6592(16) 50.36(4) 122.57(4) 143.16(5) 75.11(5) 78.93(5) 97.14(5) 72.63(5) 135.54(5) 73.77(5) 139.83(4) 121.89(4) 74.52(4) 71.21(5)

O(2)-Eu(1)-O(1W) O(2)-Eu(1)-N(1) O(2)i-Eu(1)-O(3) O(2)i-Eu(1)-O(4)iv O(2)i-Eu(1)-O(5)ii O(2)i-Eu(1)-O(6)iii O(2)i-Eu(1)-O(1W) O(2)i-Eu(1)-N(1) O(3)-Eu(1)-O(4)iv O(3)-Eu(1)-O(5)ii O(3)-Eu(1)-O(6)iii O(3)-Eu(1)-O(1W) O(3)-Eu(1)-N(1) O(4)iv-Eu(1)-O(5)ii O(4)iv-Eu(1)-O(6)iii O(4)iv-Eu(1)-O(1W) O(4)iv-Eu(1)-N(1) O(5)ii-Eu(1)-O(6)iii O(5)ii-Eu(1)-O(1W) O(5)ii-Eu(1)-N(1) O(6)iii-Eu(1)-O(1W) O(6)iii-Eu(1)-N(1) O(1W)-Eu(1)-N(1)

102.88(5) 146.03(4) 87.37(5) 141.37(4) 73.96(5) 73.22(5) 141.40(5) 83.64(5) 95.03(5) 134.27(5) 69.46(5) 70.53(5) 61.43(5) 77.12(5) 143.16(5) 73.83(5) 64.38(5) 137.68(4) 143.48(5) 75.04(5) 69.53(5) 126.20(5) 110.54(5)

a Symmetry transformations used to generate equivalent atoms: (i) -x, -y, -z + 1; (ii) -x + 1, -y, -z + 1; (iii) x - 1, y, z; (iv) x, -y + 1/2, z - 1/2.

plasma) analysis on an ICP-AES Jobin Yvon model 70+ at the Central Analytical Laboratory of the University of Aveiro. Thermogravimetric analyses (TGA) were carried out using a Shimadzu TGA 50, with a heating rate of 10 °C/min, under a continuous air stream with a flow rate of 10 cm3/min. Diffuse reflectance spectra were measured on a JASCO V-560 instrument. Photoluminescence Spectroscopy. Photoluminescence spectra were recorded in the solid state between room temperature and 14 K with a modular double grating excitation spectrofluorimeter with a TRIAX 320 emission monochromator (Fluorolog-3, Jobin Yvon-Spex) coupled to a R928 Hamamatsu photomultiplier, using the front face acquisition mode. The excitation source was a 450 W Xe arc lamp. Excitation spectra were corrected from 240 to 580 nm for the spectral distribution of the lamp intensity using a photodiode reference detector. Emission spectra were corrected for the spectral response of the

Table 3. Selected bond lengths (in Angstroms) and Angles (in Degrees) for the Eu3+ Coordination Environment Present in [Eu2(2,5-pdc)2(1,4-pda)] (1-dehyd)a Eu(1)-O(1) Eu(1)-O(2) Eu(1)-O(2)ii Eu(1)-O(3) Eu(1)-O(4)iv Eu(1)-O(5)v Eu(1)-O(6)iii Eu(1)-N(1) O(1)-Eu(1)-O(2) O(1)-Eu(1)-O(2)ii O(1)-Eu(1)-O(3) O(1)-Eu(1)-O(4)iv O(1)-Eu(1)-O(5)v O(1)-Eu(1)-O(6)iii O(1)-Eu(1)-N(1) O(2)-Eu(1)-O(2)ii O(2)-Eu(1)-O(3) O(2)-Eu(1)-O(4)iv

2.4140(15) 2.6399(14) 2.2798(13) 2.3321(14) 2.3375(14) 2.3574(13) 2.3405(14) 2.5991(16) 51.09(4) 126.55(5) 125.25(5) 76.36(5) 88.65(5) 81.35(5) 142.42(5) 75.74(5) 144.45(4) 121.56(5)

O(2)-Eu(1)-O(5)v O(2)-Eu(1)-O(6)iii O(2)-Eu(1)-N(1) O(2)ii-Eu(1)-O(3) O(2)ii-Eu(1)-O(4)iv O(2)ii-Eu(1)-O(5)v O(2)ii-Eu(1)-O(6)iii O(2)ii-Eu(1)-N(1) O(3)-Eu(1)-O(4)iv O(3)-Eu(1)-O(5)v O(3)-Eu(1)-O(6)iii O(3)-Eu(1)-N(1) O(4)iv-Eu(1)-O(5)v O(4)iv-Eu(1)-O(6)iii O(4)iv-Eu(1)-N(1) O(5)v-Eu(1)-O(6)iii O(5)v-Eu(1)-N(1) O(6)iii-Eu(1)-N(1)

70.76(4) 71.41(5) 144.54(5) 93.56(5) 150.73(5) 77.35(5) 76.54(5) 84.09(5) 83.84(5) 140.71(5) 73.14(5) 64.40(5) 86.28(5) 129.47(5) 68.45(5) 138.11(5) 76.59(5) 131.76(5)

a Symmetry transformations used to generate equivalent atoms: (ii) -x + 1, -y, -z + 1; (iii) x - 1, y, z; (iv) x, -y + 1/2, z - 1/2; (v) -x + 2, -y, -z + 1.

monochromators and the detector, using typical correction spectra provided by the manufacturer. The lifetime measurements were acquired with the setup described for the luminescence spectra using a pulsed Xe-Hg lamp (6 µs pulse at half-width and 20-30 µs tail). The radiance measurements and the CIE (Commission Internationale de L’Eclairage) (x,y) emission color coordinates were obtained using a telescope optical probe (TOP 100 DTS140-111, Instrument Systems). The excitation source was a Xe arc lamp (150 W) coupled to a Jobin Yvon-Spex monochromator (TRIAX 180). The width of the rectangular excitation spot was set to 2 mm and the diameter used to collect the emission intensity to 0.5 mm, thus ensuring that the entire sample was illuminated. As a reference, the emission color coordinates and the radiance of the standard red phosphor Y2O3:Eu and green phosphor Gd2O2S:Tb (Phosphor Technology) were also measured. Since the radiance will depend on the surface density of the emitting centers, care was taken in the preparation of the samples; pellets with a thickness around 0.30-0.35 mm containing the same amount and compaction degree were made. The radiance values were corrected for the spectral

Photoluminescent 3D Lanthanide-Organic Frameworks

Crystal Growth & Design, Vol. 8, No. 7, 2008 2507

Figure 1. Schematic representation of the Eu3+ coordination environments present in (a) [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1) and (b) [Eu2(2,5pdc)2(1,4-pda)] (1-dehyd), showing the labelling scheme of all non-hydrogen atoms. Thermal ellipsoids are draw at the 80% probability level. Atoms composing the asymmetric unit of each material are connected by black-filled bonds. For selected bond lengths (in Å) and angles (in deg) see Tables 2 and 3. Symmetry operations used to generate equivalent atoms: (i) -x, -y, -z + 1; (ii) -x + 1, -y, -z + 1; (iii) x - 1, y, z; (iv) x, -y + 1/2, z - 1/2; (v) -x + 2, -y, -z + 1; (vi) -x - 1, -y, -z; (vii) -x, -y, -z. distribution of the lamp intensity. The absolute emission quantum yields were measured at room temperature using a Quantum Yield Measurement System C9920-02 from Hamamatsu with a 150 W xenon lamp coupled to a monochromator for wavelength discrimination, an integrating sphere as sample chamber and a multi-channel analyzer for signal detection. Single-Crystal X-ray Diffraction Studies. Suitable single crystals of [Ln2(2,5-pdc)2(1,4-pda)(H2O)2] [where Ln3+ ) Eu3+ (1), Tb3+ (2), (Eu0.2Tb0.8)3+ (4) and (Eu0.1Tb0.9)3+ (5)] were manually harvested and mounted on Hampton Research CryoLoops using FOMBLIN Y perfluoropolyether vacuum oil (LVAC 25/6) purchased from Aldrich with the help of a Stemi 2000 stereomicroscope equipped with Carl Zeiss lenses.12 The preparation of the fully dehydrated form of the Eu3+containing material (1-dehyd) required special experimental conditions: as-synthesized 1 was placed inside an oven at 573 K over a period of 15 h and, while maintained at this temperature, the crystals were immediately immersed in a highly viscous FOMBLIN Y perfluoropolyether vacuum oil (LVAC 140/13) which, on the one hand, prevented the absorption of water molecules from the surrounding environment and, on the other, was used for crystal handling (selection and mounting for single-crystal data collection). Complete single-crystal data sets were collected at 150(2) K on a Bruker X8 Kappa APEX II charge-coupled device (CCD) area-detector diffractometer (Mo KR graphite-monochromated radiation, λ ) 0.71073 Å) controlled by the APEX2 software package,13 and equipped with an Oxford Cryosystems Series 700 cryostream monitored remotely using the software interface Cryopad.14 Images were processed using the software package SAINT+,15 and data were corrected for absorption by the multiscan semiempirical method implemented in SADABS.16 Structures were solved using the direct methods implemented in SHELXS-97,17 which allowed the immediate location of the majority of the atoms composing the framework backbone. All remaining non-hydrogen atoms were directly located from difference Fourier maps calculated from successive full-matrix least-squares refinement cycles on F2 using SHELXL-97.18 Non-

hydrogen atoms of all materials were successfully refined using anisotropic displacement parameters. Hydrogen atoms bound to carbon were located at their idealized positions using appropriate HFIX instructions in SHELXL (43 for the aromatic carbon atoms belonging to the phenyl groups and 23 for the -CH2- moieties) and included in subsequent refinement cycles in riding-motion approximation with isotropic thermal displacements parameters (Uiso) fixed at 1.2 times Ueq of the carbon atom to which they are attached. Hydrogen atoms associated with the coordinated water molecules were markedly visible from difference Fourier maps. The atoms were included in the final structural models with the O-H and H · · · H distances restrained to 0.95(1) and 1.45(1) Å, respectively (in order to ensure a chemically reasonable geometry for these molecules), and by assuming a riding-motion approximation with an isotropic thermal displacement parameter fixed at 1.5 times Ueq of the oxygen atom to which they are attached. In the mixed-lanthanide materials 4 and 5, the crystallographically independent Tb3+ and Eu3+ centers were constrained to share the same crystallographic position and identical anisotropic displacements parameters. The Eu3+:Tb3+ rates of occupancy were fixed 2:8 and 1:9 for 4 and 5, respectively. The last difference Fourier map synthesis showed: for 1, the highest peak (0.616 eÅ-3) and deepest hole (-0.627 eÅ-3) located at 0.80 Å and 1.16 Å from Eu(1), respectively; for 1-dehyd, the highest peak (0.664 eÅ-3) and deepest hole (-0.592 eÅ-3) located at 0.85 Å and 0.82 Å from Eu(1), respectively; for 2, the highest peak (0.495 eÅ-3) and deepest hole (-0.481 eÅ-3) located at 0.53 Å from O(2) and 1.50 Å from C(12), respectively; for 4, the highest peak (0.594 eÅ-3) and deepest hole (-0.416 eÅ-3) located at 0.68 Å from C(10) and 0.30 Å from Eu(1), respectively; for 5, the highest peak (0.683 eÅ-3) and deepest hole (-0.540 eÅ-3) located at 0.86 Å from Eu(1) and 0.29 Å from H(1W), respectively. Information concerning crystallographic data collection and structure refinement details is summarized in Table 1. Selected bond lengths



Figure 2. Schematic representation of the centrosymmetric dimeric SBUs present in (a) [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1) and (b) [Eu2(2,5pdc)2(1,4-pda)] (1-dehyd), showing the labelling scheme for all atoms composing the Eu3+ coordination environment. Carbon atoms belonging to the anionic 1,4-pda2- bridging ligand are represented in light-blue, and hydrogen atoms bound to carbon were omitted for clarity. Symmetry operations used to generate equivalent atoms: (i) -x, -y, -z + 1; (ii) -x + 1, -y, -z + 1; (iii) x - 1, y, z; (iv) x, -y + 1/2, z - 1/2; (v) -x + 2, -y, -z + 1. and angles for the Eu3+ coordination environments of 1 and 1-dehyd are collected in Tables 2 and 3, respectively. Structural drawings have been prepared using the software package Crystal Diamond.19 Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre (deposition numbers are given in Table 1). Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 2EZ, U.K. Fax: (+44) 1223 336033. E-mail: [email protected]. Variable Temperature Powder X-ray Diffraction Studies. Variable-temperature powder X-ray diffraction data for [Eu2(2,5-pdc)2(1,4pda)(H2O)2] (1) and [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)(H2O)2] (4) were collected on an X’Pert MPD Philips diffractometer (Cu KR X-radiation, λ ) 1.54060 Å), equipped with an X’Celerator detector, a curved graphite-monochromated radiation, a flat-plate sample holder in a Bragg-Brentano para-focusing optics configuration (40 kV, 50 mA), and a high-temperature Antoon Parr HKL 16 chamber controlled by a

Antoon Parr 100 TCU unit. Intensity data were collected in the step mode (0.05°, 1 s per step) in the range ca. 8° e 2θ e 38°. Data were collected between ambient temperature and 400 °C for the two compounds. For 4, after reaching the maximum temperature of 400 °C, the sample was allowed to cool slowly to ambient while inside the chamber, after which two powder patterns were collected with an interval of 12 h.

Results and Discussion Crystal Structure Description of [Ln2(2,5-pdc)2(1,4-pda)(H2O)2]. A series of 3D LnOFs were isolated using hydrothermal synthetic approaches (see Experimental Section) and ultimately formulated as [Ln2(2,5-pdc)2(1,4-pda)(H2O)2] [where Ln3+ ) Eu3+ (1), Tb3+ (2), (Eu0.2Tb0.8)3+ (4) and (Eu0.1Tb0.9)3+ (5)] on the basis of single-crystal X-ray diffraction studies (Table


Figure 3. Coordination modes of the (a) 2,5-pdc2- and (b) 1,4pda2-anionic ligands in the neutral 3∞[Eu2(2,5-pdc)2(1,4-pda)(H2O)2] 3D LnOF.

1) in combination with thermoanalytical investigations (see next section) and CHN elemental analysis. Phase purity and homogeneity of the bulk samples, plus the unequivocal phase identification of [Er2(2,5-pdc)2(1,4-pda)(H2O)2] (3) as being isostructural with the remaining compounds, were further


confirmed from Le Bail whole-powder-diffraction-pattern profile fittings (see Supporting Information). Remarkably, systematic searches in the literature and in the Cambridge Structural Database (CSD, Version 5.28 with three updatessAugust 2007)20 reveal that these materials constitute the first examples of MOFs simultaneously containing anionic residues of 2,5H2pdc and 1,4-H2pda. Even though 2,5-H2pdc has been largely employed in the preparation of multidimensional MOFs21 (the latest version of the CSD contains a total of 78 entries), only a handful of materials with 1,4-H2pda are known to date. Indeed, among the nine MOFs deposited with the CSD having residues of this last ligand, only those recently reported by Pan et al. contain lanthanide centers as the network nodes, [La2(pda)3(H2O)] · 2H2O and [Er2(pda)3(H2O)] · 2H2O.3 3D LnOFs belonging to the [Ln2(2,5-pdc)2(1,4-pda)(H2O)2] family were found to be isostructural, crystallizing in the monoclinic P21/c space group. Even though crystal structures at 150(2) K have been fully determined and refined for almost all materials (see Table 1), the crystallographic description will be focused on [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1), and its dehydrated form, [Eu2(2,5-pdc)2(1,4-pda)] (1-dehyd), for which the structural details have also been unveiled using single-crystal X-ray diffraction. Therefore, the structural features emphasized for 1 and 1-dehyd are valid, unless otherwise stated, for all the remaining members of this series of LnOFs. The as-synthesized (“hydrated”: 1) and the dehydrated (1-dehyd) forms of the Eu3+containing material have a single crystallographically indepen-

Figure 4. Mixed polyhedra (in purple) and ball-and-stick representation of the crystal packing of 1 (a and b) and 1-dehyd (c and d) viewed in perspective along the (a and c) [100] and (b and d) [001] crystallographic directions. Carbon atoms belonging to 1,4-pda2- are colored in light-blue, and hydrogen bonds are represented as dashed green lines. Hydrogen atoms belonging to the organic ligands have been omitted for clarity purposes.



Figure 5. Mixed ball-and-stick and polyhedral representation of a portion of the neutral ∞3 [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] 3D LnOF emphasizing the hydrogen bonds involving the coordinated water molecules. Carbon atoms belonging to 1,4-pda2- are colored in light-blue, and hydrogen bonds are represented as dashed green lines. Hydrogen atoms belonging to the organic ligands have been omitted for clarity purposes. Symmetry operations used to generate equivalent atoms: (i) x, - y + 1/2, z - 1/2; (ii) x, -y + 1/2, z + 1/2.

dent lanthanide center. In compound 1, Eu3+ is coordinated to one water molecule, four O atoms and one nitrogen from four symmetry-related 2,5-pdc2- residues, plus another three O atoms belonging to two symmetry-related 1,4-pda2- residues, totally describing a nine-coordination coordination sphere, {EuNO8}, which resembles a highly distorted tricapped trigonal prism (Figures 1a, 2a and S8a in the Supporting Information): indeed, on the one hand, the Eu-O bond distances are found in the rather large 2.3804(13)-2.5952(13) Å range and, on the other, the Eu-N(1) bond length is even longer, 2.6592(16) Å; moreover, the O-Eu-O and O-Eu-N bond angles can be found in the 50.36(4)-143.48(5)° and 61.43(5)-146.03(5)° ranges, respectively (see Table 2). When heated at 573 K, 1 releases the coordinated water molecule in a typical singlecrystal-to-single-crystal phase transformation to 1-dehyd. In this material the eight-coordinated lanthanide center, {EuNO7}, appears with an overall coordination geometry even more distorted, faintly resembling a distorted dodecahedron (Figures 2b, 3b and S8b in the Supporting Information): when compared to 1, even though the Eu-N(1) distance becomes slightly smaller [2.5991(16) Å], the range for the Eu-O distances increases quite significantly to 2.2798(13)-2.6399(13) Å; for this material, the O-Eu-O and O-Eu-N bond angles are now found in the 51.09(4)-150.73(5)° and 68.45(5)-144.54(5)° ranges, respectively (Table 3). It is of considerable importance to emphasize that the release of the coordinated water molecule produces significant changes in the geometry of the coordination spheres of Eu3+, even though the overall connectivity features of the anionic 2,5-pdc2and 1,4-pda2- residues are retained. The crystallographically independent anionic 2,5-pdc2- ligand is connected to four symmetry-related Eu3+ optical centers, ultimately appearing in the crystal structures as a pentadentate ligand (Figure 3a): the carboxylate groups are coordinated through typical syn-unidentate coordination fashions (mode I) to three Eu3+, with one group establishing a close syn,syn-bridge between adjacent centers; the heteroatom of the aromatic ring forms with the adjacent carboxylate group a typical N,O-chelate (mode II′), with the observed bite angles being 61.43(5)° and 64.40(5)° for 1 and 1-dehyd, respectively. The anionic 1,4-pda2- residue,

structurally located at an inversion center, is also bound to four symmetry-related optical centers but, due to the bidentate chelation to Eu3+ (mode II) coupled to the anti-unidentate mode (I′), it acts instead as a hexadentate ligand (Figure 3b). The intermetallic connectivity through the anionic ligands described above leads to the formation of edge-shared centrosymmetric dimeric units (Figure 2), which can also be envisaged as pseudo-secondary building units (SBUs) for the hypothetical construction of the 3D frameworks (see below): two Eu3+ optical centers are bring together by the cooperative coordination of two µ2-bridging O(2) atoms plus two syn,synbridging carboxylate chelates (in a typical half-paddlewheellike motif) arising from, respectively, two symmetry-related anionic 1,4-pda2- and 2,5-pdc2- ligands. The intermetallic Eu · · · Eui/ii distances within the SBU for 1 and 1-dehyd are 3.9819(2) Å and 3.8898(2) Å, respectively [symmetry codes: (i) -x, -y, 1 - z; (ii) 1 - x, -y, 1 - z]. Neighboring optical centrosymmetric {Eu2O12N2(H2O)2} (in 1) and {Eu2O12N2} (in 1-dehyd) cores (see Figure S9 in the Supporting Information) are physically interconnected via the syn,anti-bridge of the O(3)-O(4) carboxylate group belonging to 2,5-pdc2-, which leads to a brick-wall-like distribution of the SBUs in the bc plane (Figure 4). Noteworthy, for 1, these inter-SBU connections are further strengthened by strong and highly directional O-H · · · O hydrogen bonds involving the coordinated water molecule (bifurcated donor) of one centrosymmetric dimeric SBU and neighboring carboxylate groups (green dashed bonds in Figures 4a and 5): O(1W)-H(1W) · · · O(3)iv with d(D · · · A) ) 2.632(2) Å and ∠(DHA) ) 159(2)°; O(1W)-H(2W) · · · O(1)vi with d(D · · · A) ) 2.858(2) Å and ∠(DHA) ) 172.2(19)° [symmetry codes: (iv) x, -y + 1/2, z - 1/2; (vi) x, - y + 1/2, z + 1/2]. The undulated brick-wall-like layers placed in the bc plane of the unit cell are bridged along the [100] crystallographic direction by both 2,5-pdc2- and 1,4-pda2-, ultimately leading to the formation of the neutral 3D frameworks: ∞3 [Eu2(2,5pdc)2(1,4-pda)(H2O)2] for 1 and ∞3 [Eu2(2,5-pdc)2(1,4-pda)] for 1-dehyd. A more systematic description of the neutral ∞3 [Eu2(2,5pdc)2(1,4-pda)(H2O)2] and 3∞[Eu2(2,5-pdc)2(1,4-pda)] frameworks


Figure 6. Schematic representation of the (a) 12-connected node and (b) topological view of the 3∞[Eu2(2,5-pdc)2(1,4-pda)(H2O)2] and 3∞[Eu2(2,5pdc)2(1,4-pda)] uninodal frameworks with total Scha¨fli symbol of 312.448.55.6: the center of mass of the centrosymmetric SBU was taken as the node (in green); connections between nodes through 2,5-pdc2and 1,4-pda2- were replaced by a rod. Internodal distances: 13.415(5) Å, 11.044(5) Å, 9.167(5) Å and 8.860(4) Å.

can be achieved using a typical topological approach, i.e., reducing the crystal structures to connecting nodes (for simplicity the center of mass of the centrosymmetric dimeric SBUs; see Figure 6a) and bridging rods (direct connections between nodes through the 2,5-pdc2- and 1,4-pda2- anionic ligands).22 This procedure, based on purely mathematical concepts applied to crystal chemistry, allows the immediate taxonomy of the isolated networks. Topological studies performed using the software package TOPOS23 revealed that the hydrated and dehydrated frameworks share the same topological description, being 12-connected unidodal nets with a total Scha¨fli symbol of 312.448.55.6 (Figure 6b). To the best of our knowledge this topology is unique, as confirmed by TOPOS23 in conjunction with systematic searches in the literature and in the Reticular Chemistry Structure Resource (RCSR).24 Moreover, a search in the EPINET25 further reveals that this topology has not yet been enumerated. Variable Temperature Powder X-ray Diffraction Studies. In order to assess the thermal integrity of the crystalline [Ln2(2,5-pdc)2(1,4-pda)(H2O)2] frameworks and their transformation into the respective dehydrated phases, representative


amounts of [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1) and the mixedlanthanide [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)(H2O)2] (4) materials were studied in situ by powder X-ray diffraction between ambient temperature and 400 °C (Figure 7). Despite the notable decrease in the overall crystallinity of the products, the dehydrated materials [Eu2(2,5-pdc)2(1,4-pda)] (1-dehyd) and [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)] (4-dehyd) could clearly be isolated at 400 °C. Indeed, on the one hand, the collected patterns were clearly indexed with unit cell metrics very close to those obtained for 1-dehyd from single-crystal X-ray diffraction measurements and, on the other, Le Bail whole-powderdiffraction-pattern profile fittings for these two dehydrated materials unequivocally confirm the homogeneity of the bulk dehydrated samples (Table 1 and Figures S6 and S7 in Supporting Information). It is also important to emphasize that, based upon the in situ studies for [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)] (4-dehyd) (see Figure 7b), it is also possible to infer that after the release of all water molecules the material does not immediately transform into the original phase, with the dehydrated material maintaining its crystallinity for, at least, 12 h. Thermal Properties. The thermograms for the [Ln2(2,5pdc)2(1,4-pda)(H2O)2] family (Figure S10 in the Supporting Information) are similar, showing weight losses occurring in two distinct stages. The first weight loss corresponds to the release of the two coordinated water molecules and occurs between 20 and 245-270 °C. The dehydrated phases are thermally stable up to 400 °C. The second weight loss is attributed to thermal decomposition of the organic components, leading to the formation of the stoichiometric amount of Ln2O3 around 660-795 °C. Infrared Spectroscopy. Table 4 gathers for the 3D LnOFs [Ln2(2,5-pdc)2(1,4-pda)(H2O)2] family the diagnostic FT-IR vibrational bands sensitive to metal coordination, the CHN content and the molecular formulas, which are in accordance with the crystallographic studies, and the lanthanide content obtained by ICP, whose values are in agreement with the calculated ones. FT-IR bands have been tentatively assigned for the free ligands and their lanthanide compounds.3,26,27 The infrared spectra of all compounds show two very strong bands at 1639 and 1604 cm-1, assigned to the asymmetric modes νas(CO2) and which are shifted to lower wavenumbers when compared with the free ligands (1731 cm-1 for 2,5-H2pdc and 1697 cm-1 for 1,4-H2pda). The symmetric modes νs(CO2) give rise to the very strong bands centered at 1398 and 1371 cm-1, showing small shifts relatively to the free ligands (1384 cm-1 for 2,5-H2pdc and 1341 cm-1 for 1,4-H2pda). All these shifts produce ∆ values which are in good agreement with the described coordination modes of the organic components. Photoluminescent Studies. The photoluminescence of compounds 1, 2, 4 and 5 was investigated between room temperature and 14 K. The room temperature diffuse reflectance spectra (Figure S11 in the Supporting Information) of 1, 2, 4 and 5 are similar and consist of a large broad absorption band in the UV region, approximately at 240-350 nm, and of intra-4fn transitions of Eu3+ and Tb3+. A similar large broad absorption band in the UV region (ca. 240-400 nm) is observed for the 2,5H2pdc ligand, whereas the 1,4-H2pda ligand exhibits a slightly narrower absorption band approximately at 245-275 nm, with the maximum occurring at about 260 nm. Therefore we may assume that the referenced large broad absorption band observed in the spectra of compounds 1, 2, 4 and 5 is due to the contribution of both coordinating ligands. The excitation spectra of 2 (Tb3+), shown in Figure 8A at (a) 14 and (b) 300 K monitored at 544 nm, are very similar and



Figure 7. Variable-temperature powder X-ray diffraction data showing the thermal stability of (a) [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1) and (b) [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)(H2O)2] (4) up to ca. 400 °C and their transformation into the respective dehydrated phases. Phase identification of the in situ generated dehydrated phases at 400 °C, [Eu2(2,5-pdc)2(1,4-pda)] (1-dehyd) and [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)] (4-dehyd), through Le Bail whole-powder-diffraction-pattern profile fittings are provided as Supporting Information (Figures S6 and S7). Table 4. Analytical and Spectroscopic Data for LnOFs 1-5 and the Free Ligands vibrational spectrab (cm-1)

analysisa (%) compound 2,5-pyridinedicarboxylic acid 1,4-phenylenediacetic acid [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1) [Tb2(2,5-pdc)2(1,4-pda)(H2O)2] (2) [Er2(2,5-pdc)2(1,4-pda)(H2O)2] (3) [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)(H2O)2] (4) [Eu0.2Tb1.8(2,5-pdc)2(1,4-pda)(H2O)2] (5) a

C

32.13 (33.43) 32.16 (32.90) 30.92 (32.03) 31.56 (33.00) 31.83 (32.95)

N

3.19 (3.25) 3.24 (3.20) 3.44 (3.14) 3.23 (3.21) 3.22 (3.20)

H

2.12 (2.10) 2.40 (2.07) 2.35 (2.03) 2.45 (2.08) 2.45 (2.07)

Ln

35.94 (35.24) 36.02 (36.27) 38.13 (36.01) 7.43; 29.37c (6.96; 29.11)c 3.73; 33.22c (3.47; 32.70)c

νas(CO2)

ν(CN), ν(CC)

νs(CO2)

1731 vs 1697 vs 1639 vs, 1604 vs

1596 s, 1536 m 1589 vs, 1538 s

1384 vs 1341 m 1398 vs, 1371 vs

1639 vs, 1602 vs

1581 vs, 1540 s

1398 vs, 1371 vs

1639 vs, 1604 vs

1590 vs, 1542 m

1398 vs, 1371 vs

1639 vs, 1604 vs

1590 vs, 1540 s

1398 vs, 1371 vs

1639 vs, 1604 vs

1590 vs, 1540 s

1398 vs, 1371 vs

Calculated values in parentheses. b Infrared data; vs, very strong; s, strong; m, medium. c Eu; Tb.

composed of a large broad band between 240 and 350 nm (in agreement with the diffuse reflectance data) and a series of sharp lines characteristic of the Tb3+ energy levels. This large broad band (intensity maximum at ca. 255 nm) exhibits a continuous absorption along approximately 100 nm although, at lower temperature, two components peaking around 250 and 300 nm are distinguishable and may be ascribed to the excited levels of the ligands.8,9 The component peaking at lower wavelength has possibly the contribution of the 1,4-H2pda ligand since the diffuse reflectance of this molecule shows an absorption band with a maximum at about 260 nm. Figure 9A shows the emission spectra of 2 (Tb3+) at (a) 14 and (b) 300 K excited at 305-310 nm and displays the intra4f8 5D4 f 7F6-0 transitions. Comparing the two spectra, changes are observed in the relative intensities of the 5D4 f 7F6,4-0

transitions relatively to 5D4 f 7F5, in the number and full-widthat-half-maximum of the Stark components. The 5D4 f 7F0 transition (14 K and excited at 305 nm) has at least three distinguishable Stark components (inset of Figure 9A) with relative energies in agreement with published data.28 Since the Tb3+ ions lie in the same average local site symmetry (in agreement with the X-ray diffraction studies) and the 7F0 is a nondegenerated level, the detection of more than one component in the 5D4 f 7F0 transition points to thermal population of the upper 5D4 levels. Even at 14 K the emission from such levels, usually termed as hot lines, is not quenched rendering the emission spectra quite intricate.28 The excitation spectra of 1 (Eu3+), monitored at 615 nm, are given in Figure 8B at (a) 14 and (b) 300 K. The spectrum at room temperature is composed of a large broad band in the



Figure 8. Excitation spectra of (A) [Tb2(2,5-pdc)2(1,4-pda)(H2O)2] (2) and (B) [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1) monitored at 544 and 615 nm, respectively, collected at (a) 14 K and (b) room temperature (* vibronic Stokes-line).

Figure 10. Room temperature excitation spectra of (A) [Eu0.4Tb1.6(2,5pdc)2(1,4-pda)(H2O)2] (4) and (B) [Eu0.2Tb1.8(2,5-pdc)2(1,4-pda)(H2O)2] (5) monitored at (a) 544 and (b) 697 nm.

Figure 9. Emission spectra of (A) [Tb2(2,5-pdc)2(1,4-pda)(H2O)2] (2) at (a) 14 K excited at 305 nm, and at (b) room temperature excited at 310 nm, and of (B) [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1) excited at 320 nm at (a) 14 K and at (b) room temperature. The inset in (A) shows a detailed view of the 5D4 f 7F0 transition at 14 K excited at 305 nm.

Figure 11. 14 K emission spectra of (A) [Eu0.4Tb1.6(2,5-pdc)2(1,4pda)(H2O)2] (4) and (B) [Eu0.2Tb1.8(2,5-pdc)2(1,4-pda)(H2O)2] (5) excited at (a) 464 and (b) 377 nm.

same region as that observed for 2, and a series of sharp lines characteristic of the Eu3+ energy levels. The large broad band is composed by two clearly distinguishable components, peaking at ca. 250 and 300 nm, which may be ascribed to the excited levels of the ligands.8,9 At 14 K the transitions from the 7F1 level disappear because this energy level is not populated at this temperature. Additionally, the spectrum at low temperature shows a new band at about 430 nm ascribed to a vibronic Stokes-line (marked with an asterisk in Figure 8B) in the sideband of the 7F0 f 5D2 transition.29 The vibration frequency of this satellite line occurs around 1540 cm-1, and according to infrared data it might be assigned to the C-C and C-N stretches (see Table 4). Figure 9B collects the (a) 14 and (b) 300 K emission spectra of 1 (Eu3+) excited at 320 nm, showing the intra-4f6 5D0 f 7 F0-4 transitions. No changes are detected in the emission spectra by varying the excitation wavelength (255, 320 and 395 nm, Figure S12 in the Supporting Information), neither at room temperature nor at 14 K. The abnormal high intensities of the 5 D0 f 7F4 lines relative to the magnetic dipole-allowed 5D0 f 7 F1 transition are likely due to the distortion of the Eu3+ local

symmetry group toward a pure inversion center environment, as it was recently addressed in the Na9[EuW10O36] · 14H2O polyoxometalate.30 Consider now the photoluminescent studies of the Eu3+/ Tb3+mixed-lanthanide materials, namely, 4 (2Eu3+:8Tb3+) and 5 (Eu3+:9Tb3+), and the corresponding Tb3+-to-Eu3+ energy transfer mechanisms. Figure 10 compares the room temperature excitation spectra of 4 (A) and 5 (B), monitored within the 5D4 f 7F5 [Tb3+, 544 nm, (a)] and 5D0 f 7F4 [Eu3+, 697 nm, (b)] transitions. The spectra monitored within the 5D0 f 7F4 transition exhibit the 5D4-2, 5L9,10 and 5G6-4 Tb3+ levels, a clear evidence of the occurrence of Tb3+-to-Eu3+ energy transfer. The relative intensity of the Tb3+ levels with respect to those of Eu3+ is higher for 5 than for 4 (Figure 10B), because the Tb3+ quantity in the former material is higher. Lowering the temperature to 14 K (Figure S13 in the Supporting Information) the spectra of 4 and 5 are more structured, with the band at about 430 nm appearing in the spectra monitored within the 3+ 5 Eu D0 f 7F4 (697 nm) transition, as previously observed in the excitation spectrum of 1 at 14 K (Figure 8B) and ascribed to a vibronic Stokes-line. The 14 K emission spectra of 4 (A) and 5 (B) excited in the Eu3+ 5D2 [464 nm, (a)] and Tb3+ 5D3 [377 nm, (b)] levels are



Table 5. Room Temperature Radiance and CIE (x,y) Color Coordinates, Absolute Emission Quantum Yield and Lifetimes for 1, 2, 4 and 5a compound [Eu2(2,5-pdc)2(1,4-pda)(H2O)2] (1) [Tb2(2,5-pdc)2(1,4-pda)(H2O)2] (2) [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)(H2O)2] (4)

[Eu0.2Tb1.8(2,5-pdc)2(1,4-pda)(H2O)2] (5)

a

excitation wavelength (nm) 395 311 260 377 311 270 489 395 377 311

(x,y)

radiance (µW/cm2 sr)

(0.66, 0.34) (0.66, 0.34)

0.55

(0.34, 0.58) (0.35, 0.58)

2.22

(0.66, 0.34)

(0.59, 0.38)

260

(0.54, 0.42)

0.11 0.21 0.13 0.07 0.45 0.38 0.08 0.08 0.30

(0.61, 0.38)

260 489 395 377 311

absolute emission quantum yield

1.32

(0.66, 0.34)

0.23 0.08 0.09 0.35

(0.56, 0.42) 1.13

τ (ms) 0.605 ( 0.003 (5D0) 1.035 ( 0.006 (5D4) 0.653 ( 0.006 (5D0)b 0.644 ( 0.007 (5D0)b 0.657 ( 0.004 (5D0)b 0.130 ( 0.004 (5D4)c 0.678 ( 0.007 (5D0)b 0.627 ( 0.006 (5D0)b 0.659 ( 0.006 (5D0)b 0.246 ( 0.002 (5D4)c

0.26

The experimental errors of radiance and absolute emission quantum yield are 5%. Emission wavelength 694 nm. c Emission wavelength 489 nm.

Figure 12. Partial CIE chromaticity diagram (1931) showing the (x,y) color coordinates of the room-temperature emission of [Eu2(2,5pdc)2(1,4-pda)(H2O)2] (1), [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)(H2O)2] (4) and [Eu0.2Tb1.8(2,5-pdc)2(1,4-pda)(H2O)2] (5) excited at 260 nm, and of [Tb2(2,5-pdc)2(1,4-pda)(H2O)2] (2) excited at 270 nm. Photographs of the compounds processed as thin pellets under UV excitation (ca. 250 nm) are given on the right part of the figure.

given in Figure 11. The spectra excited within the Tb3+ level (Figure 11b) show the typical Eu3+ and Tb3+ lines (see Figures 9A for 2 and 9B for 1), clearly supporting the above-mentioned Tb3+-to-Eu3+ energy transfer. Excitations within the large broad band (255 and 310 nm) produce similar spectra (Figure S14 in the Supporting Information) to those obtained under direct Tb3+ excitation, suggesting that ligand-to-Tb3+, ligand-to-Eu3+, and Tb3+-to-Eu3+ energy transfer occurs in the mixed-lanthanide materials. On the contrary, excitation within the Eu3+ level only show the typical Eu3+ lines (Figure 11a). The abnormal higher intensity of the 5D0 f 7F4 transition with respect to the magnetic dipole-allowed 5D0 f 7F1 transition already reported for 1 is also observed in the emission spectra of the Eu3+-containing materials (4 and 5).30 The radiance and the CIE (x,y) emission color coordinates of 1 (Eu3+), 2 (Tb3+), and mixed-lanthanide materials 4 (2Eu3+: 8Tb3+) and 5 (Eu3+:9Tb3+) were measured and compared to

b

Figure 13. Room temperature decay curves of (A) [Eu0.4Tb1.6(2,5pdc)2(1,4-pda)(H2O)2] (4) (+, λem ) 694 nm, λexc ) 395 nm; g, λem ) 489 nm, λexc ) 311 nm), and (B) (∆, λem ) 694 nm, λexc ) 311 nm; / (in blue), λem ) 694 nm, λexc ) 489 nm). The solid lines represent the best fits (r > 0.99) to the data considering a single-exponential behavior. The inset shows the “grow-in” component of the emission decay profile of [Eu0.4Tb1.6(2,5-pdc)2(1,4-pda)(H2O)2] (4) (∆, λem ) 694 nm, λexc ) 311 nm).

red (Y2O3:Eu) and green (Gd2O2S:Tb) standard phosphors (Table 5 and Figure 12). The radiance measurements were made under the same experimental conditions for the prepared materials and for the commercial standard phosphors. Radiances of 1 and 2 (0.55 and 2.22 µW/cm2 sr, respectively) are smaller (about 33 times for 1 and 4 times for 2) than those obtained for the standard phosphors (2.52 and 1.36 µW/cm2 sr for Y2O3:Eu and Gd2O2S:Tb, respectively). However, one must also consider the higher concentration of the emitting centers in 1 and 2 (approximately 7 times higher) when compared with the standard phosphors. The radiances of 4 and 5 (1.32 and 1.13 µW/cm2 sr, respectively), although smaller (about 14 times for 4 and 16 times for 5) than the radiance of the Y2O3:Eu, increased more than double when compared with 1. This fact, together with the decrease of the radiance with respect to compound 2, supports the existence of an effective room temperature Tb3+to-Eu3+ energy transfer in compounds 4 and 5. Clearly, the (x,y) emission color coordinates of 1 and 2 (Figure 12) are similar to Y2O3:Eu (0.65, 0.35) and Gd2O2S:Tb (0.36, 0.54), respectively. Although the coordinates of 4 and 5 lie within the red region of


the chromaticity diagram, the observed shift toward the yellow with respect to the Eu3+ (1) sample reflects the contribution of the Tb3+ emission to the overall emission (Figure 12). Room temperature lifetimes values of the excited states, 5D0 (Eu3+) and 5D4 (Tb3+) for compounds 1, 2, 4 and 5 are given in Table 5, and the corresponding decay curves for 4 are displayed in Figure 13 (see Figure S15 for 1 and 2 and Figures S16, S17B and S18 for 5 in the Supporting Information). For compounds 1 and 2, the lifetimes were monitored within the more intense line of the 5D0 f 7F2 and 5D4 f 7F5 transitions, respectively, and excited at 311 nm. The emission decay curves of compounds 1 (Eu3+) and 2 (Tb3+) (Figure S15 in the Supporting Information) reveal a single-exponential behavior yielding to lifetime values of 0.605 ( 0.003 and 1.035 ( 0.006 ms, respectively. The lifetimes of the mixed-lanthanide materials 4 (2Eu3+:8Tb3+) and 5 (Eu3+: 9Tb3+) were monitored within both the 5D0 f 7F4 (694 nm) and 5 D4 f 7F6 (489 nm) transitions, thus avoiding spectral overlap. The 5D0, when excited via the intra-4f6 (at 395 nm), and 5D4, when excited at 311 nm, decay curves of 4 (Figure 13A) and 5 (Figure S16A in the Supporting Information) also reveal typical singleexponential behavior, yielding higher 5D0 lifetime values for the 5 D0 when compared to compound 1, and significantly lower lifetimes for 5D4 when compared to compound 2 (see Table 5). The single-exponential behavior of the 5D4 decay curves is also observed upon excitation at 250 or 395 nm (Figure S17 in the Supporting Information). The 5D0 lifetime measurements for 4 (Figure 13B) and 5 (Figure S16B in the Supporting Information), acquired at ca. 311 or 489 nm, yielded closer lifetimes values, even though they are higher than that obtained for the pure Eu3+ sample (1) (Table 5). Noteworthy, for shorter times the decay curves of the mixed-lanthanide materials 4 (Figure 13B) and 5 (Figure S16B), when excited at 311 or 489 nm (or 250 nm, Figure S18 in the Supporting Information) and detected at 694 nm, exhibit a nonexponential behavior. Subtracting the 5D0 single-exponential component from the measured intensity in the time range 0-0.30 ms, a “grow-in” behavior (or risetime) is discerned (inset of Figure 13B), which indicates that the decay curves have a contribution from a ligand-to-Tb3+/ligand-to-Eu3+ (excitation at 250 and 311 nm) or Tb3+-to-Eu3+ (excitation at 489 nm) energy transfer pathway. A similar effect was already observed in other Eu3+/ Tb3+ mixed materials, and it has been attributed to the Tb3+-toEu3+ energy transfer pathway.5,31 Indeed, for time values larger than 0.35 ms for 4 (Figure 13B) and 0.55 (when exciting at 489 nm) or 0.7 ms (when exciting at 311 nm) for 5 (Figure S16 B in the Supporting Information) the curves are well fitted by a singleexponential function. All these results clearly indicate the existence of room temperature Tb3+-to-Eu3+ energy transfer mechanism. The absolute emission quantum yields, η, as a function of the excitation wavelength, are gathered in Table 5. For all the samples, maximum values are measured for excitation at 311 nm (2,5-H2pdc ligand absorption). The emission quantum yields decrease between 16 and 38%, for excitation within the broad absorption of the 1,4H2pda ligand (261 nm), and between 48 and 84%, for intra-4f excitation, 5L6 (395 nm) for the Eu3+ samples and 5D3 (377 nm) for the Tb3+ ones. The increase of the measured absolute emission quantum yield values for the mixed-lanthanide samples, when compared with the values obtained for the Eu3+ one, supports the previous conclusion concerning the existence of an effective room temperature Tb3+-to-Eu3+ energy transfer. The 5D0 radiative (kr) and nonradiative (knr) transition probabilities and the 5D0 quantum efficiency (q) [q ) kr/(kr + knr) and η e q] can be estimated based on the emission spectrum and 5D0 lifetime.8,32 Due to the Tb3+-to-Eu3+ energy transfer this is only possible for compound 1 whose radiative contribu-


tion may be calculated from the relative intensities of the 5D0 f 7F0-4 transitions (the 5D0 f 7F5,6 branching ratios are neglected due to their poor relative intensity with respect to that of the remaining 5D0 f 7F0-4 lines). The 5D0 f 7F1 transition does not depend on the local ligand field and thus may be used as a reference for the whole spectrum, in vacuum A0-1 ) 14.65 s-1.33 An effective refractive index of 1.5 was used leading to A(5D0 f 7F1) ≈ 50 s-1. The values found for q are 0.20 (kr ) 0.337 ms-1) and 0.22 (kr ) 0.364 ms-1), for 311 and 395 nm, respectively. Conclusions A series of 3D LnOFs [Ln2(2,5-pdc)2(1,4-pda)(H2O)2] [Ln ) Eu3+, Tb3+, Er3+, (Eu0.2Tb0.8)3+ and (Eu0.1Tb0.9)3+] has been prepared using hydrothermal synthesis. These materials, on the one hand, constitute the first examples of MOFs simultaneously containing anionic residues of 2,5-H2pdc and 1,4-H2pda and, on the other, are some of the few stoichiometric mixedlanthanide MOF materials reported in the literature. Singlecrystal and powder X-ray diffraction studies, spectroscopy results and CHN elemental analysis clearly support the assumption that all prepared compounds (1 to 5) are isostructural. Single-crystal X-ray diffraction for the dehydrated form of the Eu3+-containing material (1-dehyd) showed that the release of the coordinated water molecule produces significant changes in the geometry of the coordination spheres of Eu3+, however the overall connectivity features of the anionic 2,5-pdc2- and 1,4-pda2- residues in the framework are retained. The dehydrated materials are thermally stable up to 400 °C, and retain their crystallinity for, at least, 12 h (observed for 4-dehyd). The existence of an effective room temperature Tb3+-to-Eu3+ energy transfer on compounds 4 and 5 is sustained by the photoluminescence studies, particularly by the excitation spectra, the 5D0 (Eu3+) and 5D4 (Tb3+) lifetimes, the absolute emission quantum yield values, and clearly indicates that the Eu3+ and the Tb3+ ions are in close spatial proximity and no clustering of a given Ln3+ exists in a separate material domain. Acknowledgment. We are grateful to the Fundaçaõ para a Cieˆncia e a Tecnologia (FCT, Portugal) for their general financial support (POCI/QUI/58887/2004 and POCI-PPCDT/QUI/58377/ 2004 supported by FEDER), the postdoctoral scholarships No. SFRH/BPD/14954/2004 (to P.C.R.S.-S.) and SFRH/BPD/14410/ 2003 (to L.C.-S.), and for financial support toward the purchase of the single-crystal diffractometer. Supporting Information Available: X-ray crystallographic information (CIF format files) for compounds 1, 1-dehyd, 2, 4 and 5. Additional structural figures and Le Bail whole-powder-diffractionpattern profile fittings for compounds 1 to 5, 1-dehyd and 4-dehyd; thermograms between ambient temperature and 800 °C for 1 to 5; diffuse reflectance spectra of compounds 1, 2, 4 and 5, 2,5-H2pdc and 1,4-H2pda; room temperature decay curves of 1, 2 and 5. This material is available free of charge via the Internet at http://pubs.acs.org.

References (1) (a) Champness, N. R. Making Coordination Frameworks. In Making Crystals by Design - Methods, Techniques and Applications, 1st ed.; Braga, D.; Grepioni, F., Eds. Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2007; pp 193-208. (b) Kepert, C. J. Chem. Commun. 2006, 695–700. (c) Uemura, K.; Matsuda, R.; Kitagawa, S. J. Solid State Chem. 2005, 178, 2420–2429. (d) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F. Acc. Chem. Res. 2005, 38, 217–225. (e) Hill, R. J.; Long, D. L.; Champness, N. R.; Hubberstey, P.; Schroder, M. Acc. Chem. Res. 2005, 38, 335–348. (f) Hill, R. J.; Long, D. L.; Hubberstey, P.; Schroder, M.; Champness, N. R. J. Solid State Chem. 2005, 178, 2414–2419. (g) Kitagawa, S.; Uemura, K. Chem. Soc. ReV.


(2)

(3) (4)

(5) (6) (7)

2005, 34, 109–119. (h) Ye, B. H.; Tong, M. L.; Chen, X. M. Coord. Chem. ReV. 2005, 249, 545–565. (i) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334–2375. (j) Rao, C. N. R.; Natarajan, S.; Vaidhyanathan, R. Angew. Chem., Int. Ed. 2004, 43, 1466–1496. (k) James, S. L. Chem. Soc. ReV. 2003, 32, 276–288. (l) Janiak, C. Dalton Trans. 2003, 2781–2804. (m) Eddaoudi, M.; Moler, D. B.; Li, H. L.; Chen, B. L.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319–330. (n) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629–1658. (o) Ferey, G. Chem. Mater. 2001, 13, 3084–3098. (p) Zaworotko, M. J. Chem. Commun. 2001, 1–9. (q) Hagrman, P. J.; Hagrman, D.; Zubieta, J. Angew. Chem., Int. Ed. 1999, 38, 2639–2684. (a) Chelebaeva, E.; Larionova, J.; Guari, Y.; Sa´ Ferreira, R. A.; Carlos, L. D.; Paz, F. A. A.; Trifonov, A.; Gue´rin, C. Inorg. Chem. 2008, 47, 775–777. (b) Surble, S.; Serre, C.; Millange, F.; Pelle, F.; Ferey, G. Solid State Sci. 2007, 9, 131–136. (c) de Lill, D. T.; Cahill, C. L. Cryst. Growth Des. 2007, 7, 2390–2393. (d) Wang, H. S.; Zhao, B.; Zhai, B.; Shi, W.; Cheng, P.; Liao, D. Z.; Yan, S. P. Cryst. Growth Des. 2007, 7, 1851–1857. (e) Zhang, X. J.; Xing, Y. H.; Sun, Z.; Han, J.; Zhang, Y. H.; Ge, M. F.; Niu, S. Y. Cryst. Growth Des. 2007, 7, 2041–2046. (f) Hu, D. X.; Luo, F.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2007, 7, 1733–1737. (g) Gu, X. J.; Xue, D. F. Inorg. Chem. 2007, 46, 5349–5353. (h) Zaleski, C. M.; Noord, A.; Kampf, J. W.; Pecoraro, V. L. Cryst. Growth Des. 2007, 7, 1098–1105. (i) Luo, F.; Hu, D. X.; Xue, L.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2007, 7, 851–853. (j) Navarro, J. A. R.; Barea, E.; Salas, J. M.; Masciocchi, N.; Galli, S.; Sironi, A. Inorg. Chem. 2007, 46, 2988– 2997. (k) Zhang, L. Z.; Gu, W.; Li, B.; Liu, X.; Liao, D. Z. Inorg. Chem. 2007, 46, 622–624. (l) Li, B.; Gu, W.; Zhang, L. Z.; Qu, J.; Ma, Z. P.; Liu, X.; Liao, D. Z. Inorg. Chem. 2006, 45, 10425–10427. (m) Guillou, O.; Daiguebonne, C. Lanthanide-containing Coordination Polymers. In Handbook on the Physics and Chemistry of Rare Earths; Gschneidner, K. A., Bunzli, J.-C. G., Pecharsky, V. K., Eds.; Elsevier B. V.: Amsterdam, 2005; Vol. 34, pp 359-404. (n) He, Z.; Gao, E. Q.; Wang, Z. M.; Yan, C. H.; Kurmoo, M. Inorg. Chem. 2005, 44, 862– 874. (o) Liu, C. B.; Sun, C. Y.; Jin, L. P.; Lu, S. Z. New J. Chem. 2004, 28, 1019–1026. (p) Millange, F.; Serre, C.; Marrot, J.; Gardant, N.; Pelle, F.; Ferey, G. J. Mater. Chem. 2004, 14, 642–645. (q) Zheng, X. J.; Wang, Z. M.; Gao, S.; Liao, F. H.; Yan, C. H.; Jin, L. P. Eur. J. Inorg. Chem. 2004, 2968–2973. (r) Cao, R.; Sun, D. F.; Liang, Y. C.; Hong, M. C.; Tatsumi, K.; Shi, Q. Inorg. Chem. 2002, 41, 2087– 2094. (s) Wang, Z.; Jin, C. M.; Shao, T.; Li, Y. Z.; Zhang, K. L.; Zhang, H. T.; You, X. Z. Inorg. Chem. Commun. 2002, 5, 642–648. Pan, L.; Adams, K. M.; Hernandez, H. E.; Wang, X. T.; Zheng, C.; Hattori, Y.; Kaneko, K. J. Am. Chem. Soc. 2003, 125, 3062–3067. (a) Ananias, D.; Paz, F. A. A.; Carlos, L. D.; Geraldes, C.; Rocha, J. Angew. Chem., Int. Ed. 2006, 45, 7938–7942. (b) Ananias, D.; Carlos, L. D.; Rocha, J. Opt. Mater. 2006, 28, 582–586. (c) Kostova, M. H.; Ferreira, R. A. S.; Ananias, D.; Carlos, L. D.; Rocha, J. J. Phys. Chem. B 2006, 110, 15312–15316. (d) Ferreira, A.; Ananias, D.; Carlos, L. D.; Morais, C. M.; Rocha, J. J. Am. Chem. Soc. 2003, 125, 14573–14579. Ananias, D.; Kostova, M.; Paz, F. A. A.; Ferreira, A.; Carlos, L. D.; Klinowski, J.; Rocha, J. J. Am. Chem. Soc. 2004, 126, 10410–10417. (a) de Lill, D. T.; de Bettencourt-Dias, A.; Cahill, C. L. Inorg. Chem. 2007, 46, 3960–3965. (b) Sendor, D.; Hilder, M.; Juestel, T.; Junk, P. C.; Kynast, U. H. New J. Chem. 2003, 27, 1070–1077. (a) Shi, F.-N.; Cunha-Silva, L.; Sa´ Ferreira, R. A.; Mafra, L.; Trindade, T.; Carlos, L. D.; Paz, F. A. A.; Rocha, J. J. Am. Chem. Soc. 2008, 130, 150–167. (b) Cunha-Silva, L.; Mafra, L.; Ananias, D.; Carlos, L. D.; Rocha, J.; Paz, F. A. A. Chem. Mater. 2007, 19, 3527–3538. (c) Girginova, P. I.; Paz, F. A. A.; Soares-Santos, P. C. R.; Ferreira, R. A. S.; Carlos, L. D.; Amaral, V. S.; Klinowski, J.; Nogueira, H. I. S.; Trindade, T. Eur. J. Inorg. Chem. 2007, 4238–4246. (d) Paz, F. A. A.; Klinowski, J. Pure Appl. Chem. 2007, 79, 1097–1110. (e) Shi, F. N.; Paz, F. A. A.; Girginova, P.; Rocha, J.; Amaral, V. S.; Klinowski, J.; Trindade, T. J. Mol. Struct. 2006, 789, 200–208. (f) Paz, F. A.; Klinowski, J. Chem. Ind. 2006, 21–23. (g) Shi, F. N.; Paz, F. A. A.; Girginova, P. I.; Mafra, L.; Amaral, V. S.; Rocha, J.; Makal, A.; Wozniak, K.; Klinowski, J.; Trindade, T. J. Mol. Struct. 2005, 754, 51–60. (h) Girginova, P. I.; Paz, F. A. A.; Nogueira, H. I. S.; Silva, N. J. O.; Amaral, V. S.; Klinowski, J.; Trindade, T. J. Mol. Struct. 2005, 737, 221–229. (i) Paz, F. A. A.; Klinowski, J. J. Solid State Chem. 2004, 177, 3423–3432. (j) Paz, F. A. A.; Shi, F. N.; Klinowski, J.; Rocha, J.; Trindade, T. Eur. J. Inorg. Chem. 2004, 2759–2768. (k) Paz, F. A. A.; Klinowski, J. Inorg. Chem. 2004, 43, 3882–3893. (l) Paz, F. A. A.; Klinowski, J. Inorg. Chem. 2004, 43, 3948–3954. (m) Paz, F. A. A.; Klinowski, J. Chem. Commun. 2003, 1484–1485. (n) Paz, F. A. A.; Bond, A. D.; Khimyak, Y. Z.; Klinowski, J. Acta


(8)

(9)

(10)

(11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)

(22) (23)

(24) (25) (26) (27) (28) (29)

(30) (31)

(32)

(33)

Crystallogr. E 2002, 58, M691–M693. (o) Paz, F. A. A.; Khimyak, Y. Z.; Bond, A. D.; Rocha, J.; Klinowski, J. Eur. J. Inorg. Chem. 2002, 2823–2828. Soares-Santos, P. C. R.; Nogueira, H. I. S.; Felix, V.; Drew, M. G. B.; Ferreira, R. A. S.; Carlos, L. D.; Trindade, T. Chem. Mater. 2003, 15, 100–108. Soares-Santos, P. C. R.; Nogueira, H. I. S.; Rocha, J.; Felix, V.; Drew, M. G. B.; Ferreira, R. A. S.; Carlos, L. D.; Trindade, T. Polyhedron 2003, 22, 3529–3539. (a) Soares-Santos, P. C. R.; Paz, F. A. A.; Ferreira, R. A. S.; Klinowski, J.; Carlos, L. D.; Trindade, T.; Nogueira, H. I. S. Polyhedron 2006, 25, 2471–2482. (b) Cunha-Silva, L.; Soares-Santos, P. C. R.; Nogueira, H. I. S.; Trindade, T.; Klinowski, J.; Rocha, J.; Paz, F. A. A. Acta Crystallogr. E 2008,E64,m529–m530. Lehn, J. M. Angew. Chem., Int. Ed. 1990, 29, 1304–1319. Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615–619. APEX2. Data Collection Software Version 2.1-RC13; Bruker AXS: Delft, The Netherlands 2006. Cryopad. Remote monitoring and control, Version 1.451; Oxford Cryosystems: Oxford, United Kingdom, 2006. SAINT+. Data Integration Engine V. 7.23a; Bruker AXS: Madison, WI, 1997-2005. Sheldrick, G. M. SADABS V.2.01, Bruker/Siemens Area Detector Absorption Correction Program; Bruker AXS: Madison, WI, 1998. Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Solution; University of Go¨ttingen: Go¨ttingen, 1997. Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; University of Go¨ttingen: Go¨ttingen, 1997. Brandenburg, K. DIAMOND, Version 3.1e; Crystal Impact GbR: Bonn, Germany, 2006. (a) Allen, F. H. Acta Crystallogr. B 2002, 58, 380–388. (b) Allen, F. H.; Motherwell, W. D. S. Acta Crystallogr. B 2002, 58, 407–422. (a) Huang, Y. G.; Wu, B. L.; Yuan, D. Q.; Xu, Y. Q.; Jiang, F. L.; Hong, M. C. Inorg. Chem. 2007, 46, 1171–1176. (b) Wen, L. L.; Lu, Z. D.; Lin, J. G.; Tian, Z. F.; Zhu, H. H.; Meng, Q. J. Cryst. Growth Des. 2007, 7, 93–99. (c) Sun, L. P.; Niu, S. Y.; Jin, J.; Yang, G. D.; Ye, L. Eur. J. Inorg. Chem. 2006, 5130–5137. (d) Garcia-Zarracino, R.; Hopfl, H. J. Am. Chem. Soc. 2005, 127, 3120–3130. (e) Liu, Y. L.; Kravtsov, V. C.; Beauchamp, D. A.; Eubank, J. F.; Eddaoudi, M. J. Am. Chem. Soc. 2005, 127, 7266–7267. (f) Qin, C.; Wang, X. L.; Wang, E. B.; Su, Z. M. Inorg. Chem. 2005, 44, 7122–7129. (g) Wei, Y. L.; Hou, H. W.; Li, L. K.; Fan, Y. T.; Zhu, Y. Cryst. Growth Des. 2005, 5, 1405–1413. (h) Garcia-Zarracino, R.; Hopfl, H. Angew. Chem., Int. Ed. 2004, 43, 1507–1511. (i) Liang, Y. C.; Hong, M. C.; Su, W. P.; Cao, R.; Zhang, W. J. Inorg. Chem. 2001, 40, 4574–4582. (j) Liang, Y. C.; Cao, R.; Su, W. P.; Hong, M. C.; Zhang, W. J. Angew. Chem., Int. Ed. 2000, 39, 3304–3307. Wells, A. F. Structural Inorganic Chemistry, 4th ed.; Clarendon Oxford University Press: New York, 1975. (a) Blatov, V. A.; Shevchenko, A. P. TOPOS - Version 4.0 Professional (beta eValuation); Samara State University: Samara, Russia, 2006. (b) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. J. Appl. Crystallogr. 2000, 33, 1193. RCSR (Reticular Chemistry Structure Resource). Website: http:// okeeffe-ws1.la.asu.edu/RCSR/home.htm. EPINET. Website: http://epinet.anu.edu.au. Kopel, P.; Sindelar, Z.; Klicka, R. Transition Met. Chem. 1998, 23, 139–142. Song, Y. S.; Yan, B.; Chen, Z. X. J. Mol. Struct. 2005, 750, 101–108. Faucher, M. D.; Morlotti, R.; Moune, O. K. J. Lumin. 2002, 96, 37–49. Soares-Santos, P. C. R.; Trindade, T.; Tome, A. C.; Rocha, J.; Ferreira, R. A. S.; Carlos, L. D.; Paz, F. A. A.; Klinowski, J.; Nogueira, H. I. S. New J. Chem. 2004, 28, 1352–1358. Ferreira, R. A. S.; Nobre, S. S.; Granadeiro, C. M.; Nogueira, H. I. S.; Carlos, L. D.; Malta, O. L. J. Lumin. 2006, 121, 561–567. Braga, S. S.; Ferreira, R. A. S.; Goncalves, I. S.; Pillinger, M.; Rocha, J.; Teixeira-Dias, J. J. C.; Carlos, L. D. J. Phys. Chem. B 2002, 106, 11430–11437. (a) Fernandes, J. A.; Ferreira, R. A. S.; Pillinger, M.; Carlos, L. D.; Jepsen, J.; Hazell, A.; Ribeiro-Claro, P.; Goncalves, I. S. J. Lumin. 2005, 113, 50–63. (b) Carlos, L. D.; Messaddeq, Y.; Brito, H. F.; Ferreira, R. A. S.; Bermudez, V. D.; Ribeiro, S. J. L. AdV. Mater. 2000, 12, 594–598. Werts, M. H. V.; Jukes, R. T. F.; Verhoeven, J. W. Phys. Chem. Chem. Phys. 2002, 4, 1542–1548.

CG800153A

Photoluminescent 3D Lanthanide−Organic Frameworks with 2,5

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