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Synthesis, structure, and luminescence of a two-dimensional lanthanide(III)-suberate coordination polymer resulting from dimeric secondary building units
Inorganic Chemistry Communications 12 (2009) 191–194
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, structure, and luminescence of a two-dimensional lanthanide(III)-suberate coordination polymer resulting from dimeric secondary building units Daniel T. de Lill a, Andrew M. Tareila a, Christopher L. Cahill a,b,* a b
The George Washington University, Chemistry, 725 21st St NW, Washington, DC 20052, United States The Carnegie Institution of Washington, Geophysical Laboratory, DC 20015, United States
a r t i c l e
i n f o
Article history: Received 23 July 2008 Accepted 29 November 2008 Available online 10 December 2008
a b s t r a c t A two-dimensional lanthanide-suberate has been synthesized via hydrothermal methods. This structure is composed of dimeric secondary building units that are extended into sheets by suberate anions. Direct photoexcitation of the lanthanide center (Eu(III) and Tb(III)) show typical emission characteristics. Ó 2009 Elsevier B.V. All rights reserved.
Keywords: Lanthanide Luminescence Coordination polymer Hydrothermal synthesis
Coordination polymers (CPs) are a class of solid-state materials in which metal centers are tethered together through organic linkers to create a multi-dimensional structure [1–12]. With physical attributes similar to earlier solid-state predecessors such as zeolites or AlPOs, CPs have become expanded beyond these materials in that they allow for the element of design [13–16]. Crystal engineering is a term commonly used to refer to the ability to deliberately control CP systems in order to fabricate specific topologies of interest through a combination of predictable metal coordination geometries and linker binding preferences [17,18]. Once synthesized, the metal center and its first sphere of coordination are typically regarded as the primary building unit [19]. Subsequent polymerization into a secondary building unit can occur and ultimately forms multi-dimensional structures once linked together through an organic species. In lanthanide containing CPs, higher dimensional SBUs such as chains (one-dimensional) or slabs (two-dimensional) are arguably the most common [5]. Zerodimensional (or monomeric) units such as dimers are less common, perhaps due to the higher coordination preferences of the lanthanide ion that are partially satisfied via self-polymerization. Herein we report the synthesis, structure, and luminescent properties of a new two-dimensional lanthanide-suberate (Ln = Sm3+, Eu3+, Gd3+, Tb3+, and Dy3+) resulting from dimeric SBUs (see Fig. 1). The title compound (compound 1, [Eu2(C8H12O4)3(H2O)4]) was synthesized hydrothermally over three days at 120 °C. EuCl3, sub* Corresponding author. Address: The George Washington University, Chemistry, 725 21st St NW, Washington, DC 20052, United States. E-mail address: [email protected] (C.L. Cahill). 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.11.033
eric acid, and 1,2-bis(4-pyridyl)ethane (DPE) were combined in a 23 mL Teflon-lined Parr bomb with the relative molar ratios of 1:2:1 (90 mg, 85 mg, 44 mg) in 1.5 mL of water, and the pH was adjusted to 6.0 using concentrated ammonium hydroxide solution. After cooling to room temperature over approximately 2 h, a clear light yellow solution was decanted from clear colorless crystals. The crystals were washed several times with both water and ethanol, and allowed to air dry at room temperature. Elemental analysis was performed and show good agreement (found/calculated): C (31.90%, 32.30%); H (4.75%, 4.97%). The compound was successfully synthesized without the addition of DPE as well and subsequent reactions with the chloride or nitrate salts of trivalent Sm, Gd, Tb, and Dy led to the formation of materials isostructural to the title compound as demonstrated by powder X-ray diffraction. Single crystal data of the Tb3+ structure was also collected, and elemental analysis of this compound also shows good agreement (found/calculated): C (31.66%, 31.80%); H (4.56%, 4.89%). Structure 1 (Fig. 1, Eu-analogue) [20] is a two-dimensional material where EuO9 polyhedra are edge-shared to form dimers that are tethered together by suberate anions down the [1 0 0] and [0 0 1] direction to form 2D sheets. The Eu2O16 dimers are connected by edge-sharing through two bridging tridentate oxygen atoms, O8 (one crystallographically unique, one related through symmetry). The remaining carboxylic oxygen atoms, O1, O2, O3, O4, and O5 are bound to the metal center in a bidentate fashion. The last two oxygen atoms, O6 and O7 are bound water molecules. The sheets are stacked in an alternating ABAB fashion. This staggered motif is stabilized by the presence of strong hydrogen bonds between the bound water molecules and adipate oxygen atoms.
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Daniel T. de Lill et al. / Inorganic Chemistry Communications 12 (2009) 191–194
Fig. 1. Title compound as viewed down the [1 0 0] direction. The polyhedra represent (LnO9)2 dimers, the secondary building unit, that is polymerized into two-dimensional sheets via suberate anions (black lines). The inset figure is of the sheet as viewed down the [0 1 0] direction.
One water ligand, O6, is hydrogen bound to both O1 (donor–acceptor distance of 2.709 Å) and O5 (donor–acceptor distance of 2.671 Å). The other water ligand, O7, is also bound to two adipate oxygen atoms, O4 (donor–acceptor distance of 2.700 Å) and O2 (donor–acceptor distance of 2.778 Å.) Though formally considered two-dimensional, one may regard the structure as three-dimensional based on the strength of the hydrogen bonds present. Crystal data and selected bond lengths and angles for both compounds (Eu and Tb) can be found in Tables 1 and 2. CCDC 700675 and 700676 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. A compound previously synthesized by our laboratory, Dy2(C6H8O4)3(H2O)4 (a Dy-adipate) [21] holds many structural similarities to compound 1. Both compounds were synthesized hydrothermally under nearly identical reaction conditions. Both exist as two-dimensional coordination polymers with dimeric building units, Dy2O16 and Eu2O16 linked by adipate and suberate anions, respectively in a bridging tridentate fashion through carboxylate oxygen atoms. The coordination sphere around each compound is identical, as described above for compound 1. Stacking and hydrogen bonding motifs are identical as well. Further similarities include identical space group (P21/c) and nearly identical cell
dimensions, with the difference along a attributed to the increased length of the suberate anion as compared with adipate. Table 3 compares several attributes of each compound. Thermogravimetric analysis of the title compound (Tb3+ structure) resulted in the following observations. At approximately 110 °C, the compound loses 5.5% of its mass attributed to the loss of two of the four bound water molecules. At 160 °C, the compound loses the other two bound water molecules. The loss of the suberate from the compounds occurs in three distinct steps, one for each suberate in the compound. The first occurs at 260 °C, the second at 385 °C, and the third at 430 °C. The end product at 550 °C was Tb4O7 as determined from PXRD (PDF# 13-0387), indicating that half the Tb3+ was oxidized to Tb4+ during the thermal treatment. Luminescence spectroscopy was conducted on the Tb and Eu structures since both compounds display typical green and red emission (respectively) when excited with a hand-held UV lamp. Though lanthanide photoluminescence often requires the aid of a conjugated organic compound to sensitize emission, Tb3+ and Eu3+ can sometimes be excited directly, as believed to be the case here. Spectra from both compounds display sharp absorption bands typical of f–f transitions within lanthanide ions. By contrast, organic absorption and energy transfer are typically seen as broad undefined charge transfer bands in the UV portion of the spectrum.
Table 2 Selected bond lengths and angles for title compound. Table 1 Crystallographic details for title compound.
Molecular formula a (Å) b (Å) c (Å) a () b () c () Crystal system Space group Z Rint R1 wR2
Eu2(C8H12O4)3(H2O)4
Tb2(C8H12O4)3(H2O)4
EuC12H22O8 13.8309(8) 13.8903(8) 9.0690(5) 90.00 107.3710(10) 90.00 Monoclinic P21/c 4 0.0584 0.0246 0.0511
TbC12H22O8 13.8081(5) 13.8334(5) 9.0577(3) 90.00 107.4200(10) 90.00 Monoclinic P21/c 4 0.0872 0.0324 0.0546
Eu2(C8H12O4)3(H2O)4 Eu1–O1 2.468(3) Å Eu1–O2 2.497(3) Å Eu1–O3 2.438(3) Å Eu1–O4 2.469(3) Å Eu1–O5 2.506(3) Å Eu1–O6 2.372(3) Å Tb2(C8H12O4)3(H2O)4 Tb1–O1 2.418(4) Å Tb1–O2 2.451(4) Å Tb1–O3 2.444(4) Å Tb1–O4 2.477(4) Å Tb1–O5 2.373(4) Å Tb1–O6 2.488(4) Å
Eu1–O7 Eu1–O8 Eu1–O8 [1] O6–Eu1–O7 O8–Eu1–O8 Eu1–O8–Eu1 [1]
2.378(3) Å 2.405(2) Å 2.562(2) Å 81.81(13)° 66.35(9)° 113.65(9)°
Tb1–O7 Tb1–O8 Tb1–O8 [2] O7–Tb1–O5 O8 [2]–Tb1–O8 Tb1 [2]–O8–Tb1
2.368(4) Å 2.539(3) Å 2.383(4) Å 81.52(13)° 66.10(14)° 113.90(14)°
Superscript indicates the following symmetry operations: (1) x + 1, y + 2, z + 2.
x + 1,
y + 1,
z; (2)
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Daniel T. de Lill et al. / Inorganic Chemistry Communications 12 (2009) 191–194 Table 3 Comparison of title compound with previously reported dy-adipate.
Linker Space group Unit cell dimensions a b c b SBU Dimensionality Hydrogen bondinga Ow1–O Ow2–O
Eu2(C8H12O4)3(H2O)4
Tb2(C8H12O4)3(H2O)4
Dy2(C6H8O4)3(H2O)4
Suberic acid P21/c
Suberic acid P21/c
Adipic acid P21/c
13.8309(8) Å 13.8903(8) Å 9.0690(5) Å 107.3710(10)° Dimer 2D, 3D with H-bonding
13.8081(5) Å 13.8334(5) Å 9.0577(3) Å 107.4200(10)° Dimer 2D, 3D with H-bonding
11.651(2) Å 13.942 (2) Å 8.981 (2) Å 110.837(3)° Dimer 2D, 3D with H-bonding
2.671 Å, 2.709 Å 2.700 Å, 2.778 Å
2.651 Å, 2.707 Å 2.692 Å, 2.784 Å
2.645 Å, 2.689 Å 2.687 Å, 2.740 Å
a The hydrogen bonding is reported as Donor–Acceptor distance. Ow represents a bound water molecule, and O is a carboxylic oxygen atom to which it is hydrogen bound, as described in more detail in the text in reference to Eu2(C8H12O4)3(H2O)4.
Though these excitation bands are in the UV, they are sharp rather than broad. This coupled with the fact that there is no precedent for energy transfer from non-aromatic (i.e., aliphatic) ligands or linkers in the literature lead us to believe that these are wavelengths for direct lanthanide excitation rather than ligand-to-lanthanide energy transfer for sensitized emission. Excitation spectra were taken from 250–500 nm while monitoring emission at 545 nm (for Tb3+) and 615 nm (for Eu3+) using appropriate slit widths and filters. From this, excitation wavelengths of 285 nm
(for Tb3+) and 309 nm (for Eu3+) were selected for emission studies. Excitation and emission spectra for these compounds can be seen in Figs. 2 and 3. The Tb structure produced a typical excitation and emission spectra for this ion, with major emission transitions labeled in Fig. 2. The emission from the Eu structure was very weak, as also observed with the hand-held UV lamp. Though the Tb compound was a vibrant green, the Eu compound had very pale red emission. As such, the excitation spectrum of Eu was also weak and believed
Fig. 2. Excitation (left) and emission spectra (right) of the Tb-analogue of the title compound.
Fig. 3. Excitation (left, note scale) and emission spectra (right) of the Eu-analogue of the title compound.
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essentially to be lost to the background. There was one observable transition at 309 nm, believed to belong to either the 7F0 ? 5F4 or 7 F0 ? 5I8 transition. Regarding the emission spectrum, the 5 D0 ? 7F1 and 5D0 ? 7F2 transitions are the only ones observable [22–24]. The peak centered around 720 nm is attributed to emission from the Xe lamp used as the excitation source. This was retained in the figure for comparison (scale) to the weak Eu emission. Though no quantitative measurements were conducted (quantum yields, lifetimes), it can be deduced that they would be unremarkable in that direct excitation of these ions is inefficient owing to their low molar absorptivities. The title compound is an interesting development in the exploration of lanthanide containing coordination polymers. Due to the lanthanide ion’s preference for high coordination numbers, polymerization of the metal center into infinite building units is common. Presented here is a zero-dimensional, dimeric building unit that coordinates through suberate ions to form a two-dimensional structure. The compound has low thermal stability where mass loss begins at 110 °C. The Tb3+ and Eu3+ compounds emit visible radiation when excited directly, and their structures bear a resemblance to a previously synthesized compound constructed from adipic rather than suberic acid. Acknowledgement The authors gratefully acknowledge the National Science Foundation for their generous support (NSF-CAREER Grant to C.L.C. (DMR-0348982) and NSF-MRI Grant for single crystal diffractometer (DMR-0419754)). References [1] S.L. James, Chem. Soc. Rev. 32 (2003) 276. [2] N.R. Champness, Dalton Trans. (2006) 877.
[3] N.L. Rosi, M. Eddaoudi, J. Kim, M. O’Keeffe, O.M. Yaghi, Cryst. Eng. Comm. 4 (2002) 401. [4] M.J. Rosseinsky, Micropor. Mesopor. Mater. 73 (2004) 15. [5] D.T. de Lill, C.L. Cahill, Prog. Inorg. Chem. 55 (2007) 143. [6] C.L. Cahill, D.T. de Lill, M. Frisch, Cryst. Eng. Comm. 9 (2007) 15. [7] D.T. de Lill, C.L. Cahill, Cryst. Growth Des. 7 (2007) 2390. [8] U. Mueller, M. Schubert, F. Teich, H. Puetter, K. Schierle-Arndt, J. Pastre, J. Mater. Chem. 16 (2006) 626. [9] C. Janiak, Dalton Trans. (2003) 2781. [10] X. Lin, J. Jia, P. Hubberstey, M. Schroeder, N.R. Champness, Cryst. Eng. Comm. 9 (2007) 438. [11] C.J. Kepert, Chem. Comm. (2006) 695. [12] A. Dimos, D. Tsaousis, A. Michaelides, S. Skoulika, S. Gohlen, L. Ouahab, C. Didierjean, A. Aubry, Chem. Mater. 14 (2002) 2616. [13] C.S. Cundy, P.A. Cox, Chem. Rev. 103 (2003) 663. [14] C.N.R. Rao, S. Natarajan, R. Vaidhyanathan, Angew. Chem. Int. Ed. 43 (2004) 1466. [15] S.T. Wilson, B.M. Lok, C.A. Messina, T.R. Cannan, E.M. Flanigen, ACS Symp. Series 218 (1983) 79. [16] B.M. Lok, C.A. Messina, R.L. Patton, R.T. Gajek, T.R. Cannan, E.M. Flanigen, J. Am. Chem. Soc. 106 (1984) 6092. [17] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T.M. Reineke, M. O’Keefe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319. [18] S. Kitagawa, S. Noro, T. Nakamura, Chem. Comm. (2006) 701. [19] G. Ferey, J. Solid State Chem. 152 (2000) 37. [20] Intensity data were collected at room temperature on a Bruker SMART diffractometer with an APEX II CCD detector using omega and psi scans. The structure was solved with direct methods and refined with SHELXL-97 in the P-1 space group within the WINGX software system. Powder X-ray diffraction data were collected on a Scintag XDS 2000 (Cu Ka, 3–60°, 0.05° step, 1.0 s/ step). The calculated powder patterns were compared to the single crystal data and show excellent agreement, confirming phase purity. [21] D.T. de Lill, W.W. Brennessel, L.A. Borkowski, N.S. Gunning, C.L. Cahill, Acta Crystallogr. Sec E: Struct. Rep. Online E61 (2005) m1343. [22] Solid State Luminescence: Theory, Materials, and Devices, Chapman & Hall, London, New York, 1993. [23] Lanthanide Probes in Life, Chemical, and Earth Sciences: Theory and Practice, Elsevier, Amsterdam, New York, 1989. [24] D.T. de Lill, A. de Bettencourt-Dias, C.L. Cahill, Inorg. Chem. 46 (2007) 3960– 3965.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, structure, and luminescence of a two-dimensional lanthanide(III)-suberate coordination polymer resulting from dimeric secondary building units Daniel T. de Lill a, Andrew M. Tareila a, Christopher L. Cahill a,b,* a b
The George Washington University, Chemistry, 725 21st St NW, Washington, DC 20052, United States The Carnegie Institution of Washington, Geophysical Laboratory, DC 20015, United States
a r t i c l e
i n f o
Article history: Received 23 July 2008 Accepted 29 November 2008 Available online 10 December 2008
a b s t r a c t A two-dimensional lanthanide-suberate has been synthesized via hydrothermal methods. This structure is composed of dimeric secondary building units that are extended into sheets by suberate anions. Direct photoexcitation of the lanthanide center (Eu(III) and Tb(III)) show typical emission characteristics. Ó 2009 Elsevier B.V. All rights reserved.
Keywords: Lanthanide Luminescence Coordination polymer Hydrothermal synthesis
Coordination polymers (CPs) are a class of solid-state materials in which metal centers are tethered together through organic linkers to create a multi-dimensional structure [1–12]. With physical attributes similar to earlier solid-state predecessors such as zeolites or AlPOs, CPs have become expanded beyond these materials in that they allow for the element of design [13–16]. Crystal engineering is a term commonly used to refer to the ability to deliberately control CP systems in order to fabricate specific topologies of interest through a combination of predictable metal coordination geometries and linker binding preferences [17,18]. Once synthesized, the metal center and its first sphere of coordination are typically regarded as the primary building unit [19]. Subsequent polymerization into a secondary building unit can occur and ultimately forms multi-dimensional structures once linked together through an organic species. In lanthanide containing CPs, higher dimensional SBUs such as chains (one-dimensional) or slabs (two-dimensional) are arguably the most common [5]. Zerodimensional (or monomeric) units such as dimers are less common, perhaps due to the higher coordination preferences of the lanthanide ion that are partially satisfied via self-polymerization. Herein we report the synthesis, structure, and luminescent properties of a new two-dimensional lanthanide-suberate (Ln = Sm3+, Eu3+, Gd3+, Tb3+, and Dy3+) resulting from dimeric SBUs (see Fig. 1). The title compound (compound 1, [Eu2(C8H12O4)3(H2O)4]) was synthesized hydrothermally over three days at 120 °C. EuCl3, sub* Corresponding author. Address: The George Washington University, Chemistry, 725 21st St NW, Washington, DC 20052, United States. E-mail address: [email protected] (C.L. Cahill). 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.11.033
eric acid, and 1,2-bis(4-pyridyl)ethane (DPE) were combined in a 23 mL Teflon-lined Parr bomb with the relative molar ratios of 1:2:1 (90 mg, 85 mg, 44 mg) in 1.5 mL of water, and the pH was adjusted to 6.0 using concentrated ammonium hydroxide solution. After cooling to room temperature over approximately 2 h, a clear light yellow solution was decanted from clear colorless crystals. The crystals were washed several times with both water and ethanol, and allowed to air dry at room temperature. Elemental analysis was performed and show good agreement (found/calculated): C (31.90%, 32.30%); H (4.75%, 4.97%). The compound was successfully synthesized without the addition of DPE as well and subsequent reactions with the chloride or nitrate salts of trivalent Sm, Gd, Tb, and Dy led to the formation of materials isostructural to the title compound as demonstrated by powder X-ray diffraction. Single crystal data of the Tb3+ structure was also collected, and elemental analysis of this compound also shows good agreement (found/calculated): C (31.66%, 31.80%); H (4.56%, 4.89%). Structure 1 (Fig. 1, Eu-analogue) [20] is a two-dimensional material where EuO9 polyhedra are edge-shared to form dimers that are tethered together by suberate anions down the [1 0 0] and [0 0 1] direction to form 2D sheets. The Eu2O16 dimers are connected by edge-sharing through two bridging tridentate oxygen atoms, O8 (one crystallographically unique, one related through symmetry). The remaining carboxylic oxygen atoms, O1, O2, O3, O4, and O5 are bound to the metal center in a bidentate fashion. The last two oxygen atoms, O6 and O7 are bound water molecules. The sheets are stacked in an alternating ABAB fashion. This staggered motif is stabilized by the presence of strong hydrogen bonds between the bound water molecules and adipate oxygen atoms.
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Fig. 1. Title compound as viewed down the [1 0 0] direction. The polyhedra represent (LnO9)2 dimers, the secondary building unit, that is polymerized into two-dimensional sheets via suberate anions (black lines). The inset figure is of the sheet as viewed down the [0 1 0] direction.
One water ligand, O6, is hydrogen bound to both O1 (donor–acceptor distance of 2.709 Å) and O5 (donor–acceptor distance of 2.671 Å). The other water ligand, O7, is also bound to two adipate oxygen atoms, O4 (donor–acceptor distance of 2.700 Å) and O2 (donor–acceptor distance of 2.778 Å.) Though formally considered two-dimensional, one may regard the structure as three-dimensional based on the strength of the hydrogen bonds present. Crystal data and selected bond lengths and angles for both compounds (Eu and Tb) can be found in Tables 1 and 2. CCDC 700675 and 700676 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. A compound previously synthesized by our laboratory, Dy2(C6H8O4)3(H2O)4 (a Dy-adipate) [21] holds many structural similarities to compound 1. Both compounds were synthesized hydrothermally under nearly identical reaction conditions. Both exist as two-dimensional coordination polymers with dimeric building units, Dy2O16 and Eu2O16 linked by adipate and suberate anions, respectively in a bridging tridentate fashion through carboxylate oxygen atoms. The coordination sphere around each compound is identical, as described above for compound 1. Stacking and hydrogen bonding motifs are identical as well. Further similarities include identical space group (P21/c) and nearly identical cell
dimensions, with the difference along a attributed to the increased length of the suberate anion as compared with adipate. Table 3 compares several attributes of each compound. Thermogravimetric analysis of the title compound (Tb3+ structure) resulted in the following observations. At approximately 110 °C, the compound loses 5.5% of its mass attributed to the loss of two of the four bound water molecules. At 160 °C, the compound loses the other two bound water molecules. The loss of the suberate from the compounds occurs in three distinct steps, one for each suberate in the compound. The first occurs at 260 °C, the second at 385 °C, and the third at 430 °C. The end product at 550 °C was Tb4O7 as determined from PXRD (PDF# 13-0387), indicating that half the Tb3+ was oxidized to Tb4+ during the thermal treatment. Luminescence spectroscopy was conducted on the Tb and Eu structures since both compounds display typical green and red emission (respectively) when excited with a hand-held UV lamp. Though lanthanide photoluminescence often requires the aid of a conjugated organic compound to sensitize emission, Tb3+ and Eu3+ can sometimes be excited directly, as believed to be the case here. Spectra from both compounds display sharp absorption bands typical of f–f transitions within lanthanide ions. By contrast, organic absorption and energy transfer are typically seen as broad undefined charge transfer bands in the UV portion of the spectrum.
Table 2 Selected bond lengths and angles for title compound. Table 1 Crystallographic details for title compound.
Molecular formula a (Å) b (Å) c (Å) a () b () c () Crystal system Space group Z Rint R1 wR2
Eu2(C8H12O4)3(H2O)4
Tb2(C8H12O4)3(H2O)4
EuC12H22O8 13.8309(8) 13.8903(8) 9.0690(5) 90.00 107.3710(10) 90.00 Monoclinic P21/c 4 0.0584 0.0246 0.0511
TbC12H22O8 13.8081(5) 13.8334(5) 9.0577(3) 90.00 107.4200(10) 90.00 Monoclinic P21/c 4 0.0872 0.0324 0.0546
Eu2(C8H12O4)3(H2O)4 Eu1–O1 2.468(3) Å Eu1–O2 2.497(3) Å Eu1–O3 2.438(3) Å Eu1–O4 2.469(3) Å Eu1–O5 2.506(3) Å Eu1–O6 2.372(3) Å Tb2(C8H12O4)3(H2O)4 Tb1–O1 2.418(4) Å Tb1–O2 2.451(4) Å Tb1–O3 2.444(4) Å Tb1–O4 2.477(4) Å Tb1–O5 2.373(4) Å Tb1–O6 2.488(4) Å
Eu1–O7 Eu1–O8 Eu1–O8 [1] O6–Eu1–O7 O8–Eu1–O8 Eu1–O8–Eu1 [1]
2.378(3) Å 2.405(2) Å 2.562(2) Å 81.81(13)° 66.35(9)° 113.65(9)°
Tb1–O7 Tb1–O8 Tb1–O8 [2] O7–Tb1–O5 O8 [2]–Tb1–O8 Tb1 [2]–O8–Tb1
2.368(4) Å 2.539(3) Å 2.383(4) Å 81.52(13)° 66.10(14)° 113.90(14)°
Superscript indicates the following symmetry operations: (1) x + 1, y + 2, z + 2.
x + 1,
y + 1,
z; (2)
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Daniel T. de Lill et al. / Inorganic Chemistry Communications 12 (2009) 191–194 Table 3 Comparison of title compound with previously reported dy-adipate.
Linker Space group Unit cell dimensions a b c b SBU Dimensionality Hydrogen bondinga Ow1–O Ow2–O
Eu2(C8H12O4)3(H2O)4
Tb2(C8H12O4)3(H2O)4
Dy2(C6H8O4)3(H2O)4
Suberic acid P21/c
Suberic acid P21/c
Adipic acid P21/c
13.8309(8) Å 13.8903(8) Å 9.0690(5) Å 107.3710(10)° Dimer 2D, 3D with H-bonding
13.8081(5) Å 13.8334(5) Å 9.0577(3) Å 107.4200(10)° Dimer 2D, 3D with H-bonding
11.651(2) Å 13.942 (2) Å 8.981 (2) Å 110.837(3)° Dimer 2D, 3D with H-bonding
2.671 Å, 2.709 Å 2.700 Å, 2.778 Å
2.651 Å, 2.707 Å 2.692 Å, 2.784 Å
2.645 Å, 2.689 Å 2.687 Å, 2.740 Å
a The hydrogen bonding is reported as Donor–Acceptor distance. Ow represents a bound water molecule, and O is a carboxylic oxygen atom to which it is hydrogen bound, as described in more detail in the text in reference to Eu2(C8H12O4)3(H2O)4.
Though these excitation bands are in the UV, they are sharp rather than broad. This coupled with the fact that there is no precedent for energy transfer from non-aromatic (i.e., aliphatic) ligands or linkers in the literature lead us to believe that these are wavelengths for direct lanthanide excitation rather than ligand-to-lanthanide energy transfer for sensitized emission. Excitation spectra were taken from 250–500 nm while monitoring emission at 545 nm (for Tb3+) and 615 nm (for Eu3+) using appropriate slit widths and filters. From this, excitation wavelengths of 285 nm
(for Tb3+) and 309 nm (for Eu3+) were selected for emission studies. Excitation and emission spectra for these compounds can be seen in Figs. 2 and 3. The Tb structure produced a typical excitation and emission spectra for this ion, with major emission transitions labeled in Fig. 2. The emission from the Eu structure was very weak, as also observed with the hand-held UV lamp. Though the Tb compound was a vibrant green, the Eu compound had very pale red emission. As such, the excitation spectrum of Eu was also weak and believed
Fig. 2. Excitation (left) and emission spectra (right) of the Tb-analogue of the title compound.
Fig. 3. Excitation (left, note scale) and emission spectra (right) of the Eu-analogue of the title compound.
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essentially to be lost to the background. There was one observable transition at 309 nm, believed to belong to either the 7F0 ? 5F4 or 7 F0 ? 5I8 transition. Regarding the emission spectrum, the 5 D0 ? 7F1 and 5D0 ? 7F2 transitions are the only ones observable [22–24]. The peak centered around 720 nm is attributed to emission from the Xe lamp used as the excitation source. This was retained in the figure for comparison (scale) to the weak Eu emission. Though no quantitative measurements were conducted (quantum yields, lifetimes), it can be deduced that they would be unremarkable in that direct excitation of these ions is inefficient owing to their low molar absorptivities. The title compound is an interesting development in the exploration of lanthanide containing coordination polymers. Due to the lanthanide ion’s preference for high coordination numbers, polymerization of the metal center into infinite building units is common. Presented here is a zero-dimensional, dimeric building unit that coordinates through suberate ions to form a two-dimensional structure. The compound has low thermal stability where mass loss begins at 110 °C. The Tb3+ and Eu3+ compounds emit visible radiation when excited directly, and their structures bear a resemblance to a previously synthesized compound constructed from adipic rather than suberic acid. Acknowledgement The authors gratefully acknowledge the National Science Foundation for their generous support (NSF-CAREER Grant to C.L.C. (DMR-0348982) and NSF-MRI Grant for single crystal diffractometer (DMR-0419754)). References [1] S.L. James, Chem. Soc. Rev. 32 (2003) 276. [2] N.R. Champness, Dalton Trans. (2006) 877.
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