Next Article in Journal
Comparative Volatilomic Profile of Three Finger Lime (Citrus australasica) Cultivars Based on Chemometrics Analysis of HS-SPME/GC–MS Data
Next Article in Special Issue
Highly Luminescent Crystalline Sponge: Sensing Properties and Direct X-ray Visualization of the Substrates
Previous Article in Journal
Enhanced Performance of Camphorsulfonic Acid-Doped Perovskite Solar Cells
Previous Article in Special Issue
Trapping of Ag+ into a Perfect Six-Coordinated Environment: Structural Analysis, Quantum Chemical Calculations and Electrochemistry
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:

Variable Dimensionality of Europium(III) and Terbium(III) Coordination Compounds with a Flexible Hexacarboxylate Ligand

Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3 Lavrentiev Ave., 630090 Novosibirsk, Russia
Department of Natural Sciences, Novosibirsk State University, 2 Pirogov Str., 630090 Novosibirsk, Russia
Authors to whom correspondence should be addressed.
Molecules 2022, 27(22), 7849;
Submission received: 25 October 2022 / Revised: 11 November 2022 / Accepted: 12 November 2022 / Published: 14 November 2022


A reaction between 4,4′,4″-(benzene-1,3,5-triyltris(oxy))triphthalic acid (H6L) and lanthanide(III) nitrates (Ln = Eu3+, Tb3+) in water under the same conditions gave a molecular coordination compound [Tb(H4.5L)2(H2O)5]∙6H2O in the case of terbium(III) and a one-dimensional linear coordination polymer {[Eu2(H3L)2(H2O)6]∙8H2O}n in the case of europium(III). The crystal structures of both compounds were established by single-crystal X-ray diffraction, and they were further characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. The compounds demonstrated characteristic lanthanide-centered photoluminescence. The lanthanide-dependent dimensionality of the synthesized compounds, which are the first examples of the coordination compounds of hexacarboxylic acid H6L demonstrates its potential as a linker for new coordination polymers.

Graphical Abstract

1. Introduction

Aromatic polycarboxylic acids are important building blocks for the construction of metal–organic frameworks (MOFs), since the carboxylate groups are able to form strong coordination bonds with most metal cations [1,2,3,4]. Rigid di-, tri- and tetracarboxylic acids were successfully used for the preparation of robust MOFs [5,6,7]. In recent years, an increasing amount of attention has been paid to flexible MOFs, which are able to expand or contract their networks upon external stimuli, such as temperature, pressure or electromagnetic irradiation [8,9,10,11,12,13]. The flexibility of MOFs can be induced by the conformational flexibility of their organic linkers; the latter may be achieved by introducing ether groups into their structures [14,15,16,17]. Increasing the number of the carboxylic groups in MOF linkers may leave some of them uncoordinated by the metal nodes and improve the functional properties of the resulting MOF, such as proton conductivity, adsorption selectivity for gases from their mixtures or metal ions from solutions [18].
In this work, we explore the coordination chemistry of an ether-bridged hexa-carboxylate ligand, 4,4’,4’’-(benzene-1,3,5-triyltris(oxy))triphthalic acid (H6L, Scheme 1), for which no coordination compounds have been reported before, although the compound itself was first prepared two decades ago and used for the synthesis of hyperbranched organic polymers [19]. Two lanthanide metals, europium(III) and terbium(III), were chosen as the central ions for the synthesis of coordination compounds because of their potential luminescent properties [20,21,22,23,24,25,26,27], possible applications as catalytic platforms [28,29], proton-conductive or magnetic materials [30]. In addition, flexible polycarboxylate ligands are especially suitable for the formation of lanthanide coordination polymers because of their ability to form strong metal-oxygen bonds and saturate the high lanthanide coordination numbers [31,32].

2. Results and Discussion

2.1. Synthesis of the Coordination Compounds

Terbium(III) and europium(III) coordination compounds were prepared as single crystals by the reaction between H6L and metal nitrate hexahydrates (1:1 molar ratio) in an aqueous solution under hydrothermal conditions (Scheme 1). It was found that specific pH conditions are necessary for the formation of the products. Thus, 3 equivalents (relative to the amount of the metal salt) of the base (KOH) were necessary to carry out the reaction at 90 °C, followed by neutralization with HNO3 (2.5 equivalents) and prolonged crystallization at room temperature. Numerous attempts to carry out the reaction under other conditions (no acid of base added, only acid or base added, variable temperature) did not result in the formation of any solid product. When the amounts of acid or base used were different from the ones indicated above, only amorphous solids were obtained that were not further characterized. It is interesting to note that under identical synthetic conditions, Tb3+ formed a molecular complex with a 1:2 M:L ratio, while Eu3+ gave a linear coordination polymer of a 1:1 M:L composition. Other M:L ratios from 6:1 to 1:6 were tested as well, but they gave no solid products or only amorphous precipitates.

2.2. Crystal Structure of the Coordination Compounds

Single-crystal X-ray diffraction analysis revealed that compound 1 crystallizes in a monoclinic crystal system, space group C2/c. The compound is a molecular complex, consisting of one Tb3+ ion, five coordinated water molecules, two crystallographically equivalent ligand molecules and six lattice water molecules (Figure 1a). Each Tb3+ ion coordinates nine oxygen atoms, four of which are from the carboxylic groups of two organic ligands and the remaining five are from the coordinated water molecules. According to the Shape 2.1 software package [33], the coordination environment is best described by a muffin configuration (MFF) [34] (Figure 1b, Table S1). The Tb-O distances are 2.397(2) and 2.547(2) Å for the carboxylate ligand and vary from 2.330(2) Å to 2.418(2) Å for the coordinated water molecules, which are typical values for such types of coordination. The proton of the carboxylic group at the ortho-position to the coordinated carboxylate group participates in an intramolecular hydrogen bond (d(D···A) = 2.394(3) Å, d(H···A) = 1.25(4) Å, d(D–H) = 1.14(4) Å, ∠(D–H···A) = 174(3)°) and is disordered over two equivalent positions in two anionic ligands (Figure S1). To achieve electroneutrality, the terbium(III) coordination sphere should therefore be composed as [Tb(H4.5L)2(H2O)5]. The benzene rings in compound 1 participate in intermolecular π-π stacking interactions with the centroid-to-centroid separation of 3.791 Å (the angle between the benzene ring planes is 10.9°, Figure S2), and the water molecules are involved in multipoint hydrogen bonds (Table S2), which connect the molecules of compound 1 into a three-dimensional supramolecular framework (Figure 1c).
Although the Eu-compound 2 was synthesized by the same method as the Tb-compound 1, the single crystal X-ray diffraction analysis of compound 2 reveals a completely different crystal structure. Compound 2 crystallizes in a triclinic crystal system with space group P-1; the asymmetric unit contains one Eu3+ ion, one H3L3- ligand, three coordinated water molecules and four lattice water molecules (Figure 2a). Similarly to compound 1, the coordination polyhedron of Eu3+ is close to the muffin shape (Table S1), but in contrast to the Tb-compound 1, two Eu3+ cations are joined by the bridging carboxylate groups into binuclear 8-connected [Eu2] secondary building units (Figure 2b), which are connected by two H3L3- linkers into 1D infinite chains parallel to the ac-plane (Figure 2c). The Eu–O distances for the coordinated carboxylate groups are 2.385(2) Å and 2.526(2) Å, typical for europium(III) carboxylate compounds. Further, a 3D supramolecular structure is formed between one-dimensional chains through the hydrogen bonding interactions, involving the coordinated carboxylate and the uncoordinated carboxylic groups (Table S3, Figure 2d and Figure S3).
Different coordination behaviors of Tb3+ and Eu3+ towards H6L ligand under the same conditions may be attributed to the known lanthanide contraction effect. Despite a weak monotonic change of the ionic radii in the lanthanide series, for a certain Ln3+ ion, a structure may cease to be stable due to the increased steric hindrance in the ever-shrinking coordination sphere of the metal ion. This can lead to a change in the ligand connectivity, including a change in dimensionality and topology. Gadolinium, which stands between the europium and terbium in the lanthanide series, often appears to be a breaking point in such alternations and one product is formed for lanthanides lighter than Gd and a different product is obtained for heavier lanthanides [35,36,37].
The conformational flexibility of the potentially hexacarboxylate ligand H6L is evident from the variability of the dihedral angles between the benzene rings connected by ether bonds in Tb-compound 1 and Eu-compound 2 from 61.5° to 88.8° (Figure 3).

2.3. X-ray Powder Diffraction, IR Spectroscopy and Thermogravimetric Analysys

The phase purity of compounds 1 and 2 was confirmed by powder X-ray diffraction. As shown in Figure S4, the experimental diffractograms recorded at room temperature and the simulated patterns obtained from single crystal data are in good agreement.
The IR spectra of the H6L ligand, Tb-compound 1 and Eu-compound 2 are shown in Figure S5. The IR spectrum of Tb-compound 1 features an absorption peak near 3037 cm−1, which is attributed to the C–H stretching vibrations of the aromatic ring. The benzene ring vibration bands were observed at 1582 cm−1 and 1549 cm−1. In addition, the spectrum of Tb-compound 1 demonstrates a wide O-H stretching vibration peak near 3390 cm−1 from water molecules and protonated carboxylate groups involved in hydrogen bonding. The characteristic peaks at 1737 cm−1 and 1711 cm−1 may be assigned to the stretching vibrations of the protonated carboxyl groups, in accordance with incomplete deprotonation of the H6L ligand. The strong bands at 1582 cm−1, 1549 cm−1, 1455 cm−1 and 1425 cm−1 correspond to the asymmetric and symmetric stretching vibrations of the carboxylate groups. The IR spectrum of Eu-compound 2 demonstrated features similar to the spectrum of Tb-compound 1. Thus, the peaks near 3080 cm−1 and 3390 cm−1 were attributed to C–H and O–H stretching vibrations, and correspondingly, the benzene ring vibrations were observed at 1596 cm−1 and 1431 cm−1. The band at 1721 cm−1 corresponds to the C = O carbonyl stretching of COOH groups, while the bands near 1596 cm−1, 1554 cm−1 and 1431 cm−1 were assigned to the asymmetric and symmetric stretching vibrations of the carboxylate groups.
The TG curve of Tb-compound 1 exhibited a weight loss of 14.3%, which occurred in two steps within 30–200 °C (Figure S6). The first step in the range of 30–150 °C is due to the removal of free water molecules (found: 7.4%, calc.: 6.8%), and the second step at 150–200 °C is due to the removal of coordinated water molecules (found: 6.9%, calc.: 5.7%). After dehydration, Tb-compound 1 remains stable up to 360 °C, indicative of good thermal stability.

2.4. Luminescent Properties of the Ligand and the Coordinaion Compounds

The solid-state luminescent spectra of H6L ligand, Tb-compound 1 and Eu-compound 2 were measured for the powdered samples at room temperature. As shown in Figure S7, the H6L ligand showed a broad emission peak with a maximum of 456 nm (λex = 370 nm). The excitation spectra of both Tb-compound 1 and Eu-compound 2 showed broad bands with maxima near 300 nm (Figure S8), suggesting ligand-centered absorption. When excited at 300 nm, the Tb-compound 1 exhibited the following four characteristic emission peaks from the Tb3+ ion: 490, 545, 584 and 622 nm, attributed to 5D47F6, 5D47F5, 5D47F4, 5D47F3 transitions [38], respectively (Figure 4a). Likewise, upon excitation at 310 nm, the Eu-compound 2 exhibited the following four characteristic emission peaks from the Eu3+ ion: 593, 615, 649 and 694 nm, attributed to 5D07F1, 5D07F2, 5D07F3, 5D07F4 transitions [39], respectively (Figure 4b). The luminescence lifetime of the Tb-compound 1 obeys a single exponential equation (characteristic lifetime of 0.68 ms), which indicates that a single coordination environment exists for Tb3+ ion (Figure 4c). The luminescence lifetime of the Eu-compound 2 was 0.28 ms (Figure 4c). The quantum yields of the Tb-compound 1 and the Eu-compound 2 were 8% and 2%, respectively. Relatively low quantum yields may be due to the conformational flexibility of the ligand, leading to vibrational non-radiative energy dissipation, often observed for lanthanide coordination polymers with flexible ligands [40,41]. In addition, the presence of five or three coordinated water molecules in the lanthanide coordination sphere in compounds 1 and 2 also leads to deactivation through O–H vibrations [42].
As shown in Figure 4d, the emission of compounds 1 and 2 is characterized by the chromaticity coordinates (0.3318, 0.5769) and (0.6425, 0.3464). The color temperature of the green emission of Tb-compound 1 was 5600 K, and the red emission of the Eu-compound 2 had a color temperature of 8870 K, both of which correspond to the cool colors (>5000 K are called cool colors).
In order to gain insight into the photoluminescence mechanism, TD-DFT calculations for the H6L ligand and its triply deprotonated form (as lithium salt, Li3H3L) were carried out. In the optimized structure of the Li3H3L model, the dihedral angles corresponding to the rotation of the phthalate rings are in good agreement with the values obtained from the X-ray crystal structure of compound 2, suggesting that the predicted conformation of the anionic ligand is approximately the same as in the structure of compound 2 (Figure S9, Table S4). Therefore, the obtained geometry of Li3H3L may be used for further calculations of the photophysical properties. According to TD-DFT calculations, the UV-Vis absorption of H6L is associated with the S0→S1 excitation; the calculated maximum is 302 nm. The S0→S1 excitation is accompanied by the following three major electron transitions: HOMO→LUMO (contribution 49%), HOMO-1→LUMO (contribution 41%), HOMO-2→LUMO (contribution 10%). As one can see from the localization of the molecular orbitals, the S0→S1 excitation is a π→π* transition with the charge transfer between the aromatic rings of H6L (Figure S10).
The calculated position of the absorption maximum of Li3H3L is 316 nm, which is in reasonable agreement with the experimentally observed value of 308 nm for compound 2. The S0→S1 excitation is characterized by the following two major electronic transitions: HOMO→LUMO (68%) and HOMO-1→LUMO (32%). The charge transfer accompanying the π→π* excitation in Li3H3L is even more pronounced compared to the protonated ligand H6L (Figure 5).
Relatively long luminescence lifetimes of the coordination compounds 1 and 2 suggest an emission due to f-f lanthanide transitions. At the same time, the broad absorption bands near 310 nm suggest a ligand-centered excitation; therefore, an intersystem crossing S1-T1 process must be assumed, followed by an energy transfer from the T1 state to 5D0 or 5D4 states of Eu3+ or Tb3+ ions. A comparison of the energies of these states indicates that in both cases, such transitions are energetically favorable (Figure 6).

3. Materials and Methods

3.1. Starting Materials and Synthetic Procedures

All reagents were commercially available and used without further purification. The ligand 4,4′,4″-(benzene-1,3,5-triyltris(oxy))triphthalic acid (H6L) was obtained from Jinan Henghua Sci. & Tec. Co. Ltd. (Jinan, China) and used as received.

3.1.1. Synthesis of Compound [Tb(H4.5L)2(H2O)5]∙6H2O (1)

A mixture containing Tb(NO3)3∙6H2O (3.6 mg, 0.008 mmol), H6L (5 mg, 0.008 mmol) were dissolved in H2O (2 mL) and then 24 μL of 1 M KOH solution was added. The solution was sealed in a screw-cap vial and heated at 90 °C for 48 h, gradually cooled to room temperature and 20 μL of 1 M HNO3 solution were added. The resulting clear solution was heated at 100 °C for 24 h, gradually cooled to room temperature again and allowed to stand for 2 weeks to obtain pale yellow flaky crystals. Yield: 47% (based on H6L). Elemental analysis calcd. (%) for C60H55O41Tb: C, 45.3; H, 3.5. Found (%) C, 45.3; H, 3.2. IR (cm−1, KBr): 3390 (m), 3073 (m), 2929 (m), 2612 (w), 2144 (w), 1737 (m), 1711 (m), 1662 (m), 1582 (s), 1549 (s), 1455 (s), 1425 (s), 1374 (s), 1329 (m), 1307 (m), 1264 (m), 1223 (s), 1128 (m), 1064 (m), 1010 (m), 924 (w), 883 (w), 857 (w), 795 (w), 774 (w), 743 (w), 711 (w), 670 (w), 638 (w), 533 (w), 473 (w), 439 (w).

3.1.2. Synthesis of Compound {[Eu2(H3L)2(H2O)6]∙8H2O}n (2)

Compound 2 was synthesized in the same way as compound 1, except that Tb(NO3)3∙6H2O was replaced by Eu(NO3)3∙6H2O (3.6 mg, 0.008 mmol). Yield: 52% (based on H6L). Elemental analysis calcd. (%) for C60H50Eu2O40: C, 42.0; H, 2.9. Found (%) C, 42.2; H, 2.9. IR (cm−1, KBr): 3386 (m), 3082 (m), 2925 (w), 1721 (m), 1674 (m), 1596 (s), 1554 (s), 1431 (s), 1385 (s), 1322 (m), 1267 (m), 1221 (s), 1142 (m), 1118 (m), 1069 (w), 1008 (m), 922 (w), 850 (w), 836 (w), 821 (w), 804 (w), 781 (w), 710 (w), 680 (w), 656 (w), 637 (w), 610 (w), 572 (w), 458 (w).

3.2. Physical Methods of Analysis

Powder X-ray diffraction (PXRD) measurements were carried out using a Bruker D8 ADVANCE diffractometer (Bruker Corporation, Billerica, MA, USA), Cu-Kα radiation, λ = 1.5406 Å, 2θ range 3–40°. Elemental analyses for C and H were performed using a Vario MICRO Cube analyzer (Elementar Analysensysteme GmbH, Langenselbold, Germany). Thermogravimetric analysis (TGA) was carried on a NETZSCH TG 209 F1 Iris Thermo Microbalance (Erich NETZSCH GmbH & Co. Holding KG, Selb, Germany) heated from 30 to 850 °C under helium atmosphere with the heating rate of 10 °C/min. IR spectra were recorded on a Bruker Scimitar FTS 2000 spectrometer (Bruker Corporation, Billerica, MA, USA) in the range 4000–400 cm−1. Luminescence spectra, luminescence lifetimes and quantum yields were obtained on Horiba Jobin Yvon Fluorolog 3 (HORIBA Jobin Yvon SAS, Edison, NJ, USA) photoluminescence spectrometer equipped with 450W ozone-free Xe-lamp, a cooled photon detection module and an integrating sphere.

3.3. Single-Crystal X-ray Diffraction

Diffraction data for single crystals compounds 1 and 2 were collected with a Bruker D8 Venture diffractometer with a CMOS PHOTON III detector and IμS 3.0 source (mirror optics, λ (CuKα) = 1.54178 Å). The φ-and ω-scanning techniques were employed to measure the intensities. The crystal structures were solved and refined by means of the SHELXT [43] and SHELXL [44] programs using OLEX2 GUI [45]. Atomic displacement parameters for non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed geometrically and refined in the riding model. The crystallographic parameters and the details of the diffraction experiment are given in Table 1. The bond lengths and bond angles for the Tb-compound 1 and Eu-compound 2 are provided in Tables S5 and S6.

3.4. Computational Chemistry Details

The calculations were performed using Gaussian 09 package [46]. The isolated H6L molecule was used to model the free ligand, while a triply deprotonated form (balanced by three lithium cations, Li3H3L) was used to represent the anionic ligand in compound 2. Singlet ground state geometry optimizations of H6L were carried out in the gas phase at the DFT level of theory employing the three-parameter hybrid B3LYP functional [47,48,49,50] and 6–31 + G(d) basis set [51,52,53,54]. An empirical dispersion correction was applied using the D3 version of Grimme’s empirical dispersion with Becke-Johnson damping [55]. The frequency calculations in a harmonic approximation were performed for the optimized geometries in order to establish the nature of the stationary points, lack of imaginary vibration modes for the optimized structures indicates that the stationary points found corresponded to minima on the potential energy surface. The first singlet and triplet exited states of H6L and Li3H3L were computed at time-dependent DFT (TD-DFT) level, using the optimized ground state geometry and the same functional and basis set used for the ground state calculations.

4. Conclusions

In summary, the coordination chemistry of a flexible aromatic triether-bridged hexacarboxylate ligand (4,4′,4″-(benzene-1,3,5-triyltris(oxy))triphthalic acid) was studied for the first time, and two new lanthanide coordination compounds were prepared and characterized. It was found that the nature of the lanthanide affects the dimensionality of the compounds formed. Thus, in identical reaction conditions, Tb3+ forms a discrete coordination compound, while Eu3+ yields a 1D coordination polymer. Both compounds demonstrated characteristic lanthanide-centered emission and ligand-centered excitation, in accordance with the experimental absorption spectra and TD-DFT calculations. Therefore, the aromatic ligand acts as an antenna for lanthanide excitation and further studies of its coordination chemistry may lead to the preparation of efficient light emitters. It should also be noted that the observed difference in the reactivity of Eu3+ and Tb3+ may contribute to solving the problem of lanthanide separation.

Supplementary Materials

The following supporting information can be downloaded at:, Figure S1. Fragment of the molecular structure of compound 1 showing a hydrogen bond between the coordinated and un-coordinated carboxylic groups; Figure S2. Fragment of the crystal structure of compound 1 showing π-π interaction between the benzene rings of two molecules (green dashed line); Figure S3. Fragment of the crystal structure of compound 2 showing hydrogen bonds between the coordinated carboxylate and uncoordinated carboxylic groups in two different coordination polymer chains; Figure S4. Calculated and experimental PXRD patterns of the compounds 1 (a) and 2 (b); Figure S5. FT-IR spectra of H6L ligand, compound 1 and compound 2; Figure S6. Thermogravimetric analysis curve for the compound 1; Figure S7. The solid-state excitation (λem = 450 nm) and emission (λex = 370 nm) spectra of H6L at room temperature; Figure S8. The solid-state excitation spectra of the compounds 1em = 545 nm) and 2 (λem = 615 nm) at room temperature; Figure S9. Optimized geometry of H6L obtained at B3LYP[GD3BJ] 6–31 + G(d) level of theory; Figure S10. Isosurfaces (at 0.02 e/Bohr3) of the molecular orbitals of H6L ground state calculated at B3LYP[GD3BJ] 6–31 + G(d) level of theory; Table S1. Continuous shape measures criteria (S) for nine-coordinated metal centers in the compounds 1 and 2; Table S2. Geometrical parameters of the hydrogen bonds in compound 1; Table S3. Geometrical parameters of the hydrogen bonds in compound 2; Table S4. Calculated and experimental geometrical parameters of H3L3–; Table S5. Selected bond distances (d) and angles (φ) for compound 1; Table S6. Selected bond distances (d) and angles (φ) for the compound 1; CIF files and CheckCIF reports for the compounds 1 and 2.

Author Contributions

Conceptualization, A.S.P. and V.P.F.; methodology, A.S.P.; investigation, X.Y., D.I.P., A.A.R.; writing—original draft preparation, X.Y.; writing—review and editing, A.S.P.; supervision, V.P.F.; project administration, V.P.F.; funding acquisition, V.P.F. All authors have read and agreed to the published version of the manuscript.


The research was supported by the Ministry of Science and Higher Education of the Russian Federation, project number 121031700321-3. Yu Xiaolin gratefully appreciates the financial support of China Scholarship Council (CSC, grant No. 202008090088).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Experimental data associated with this research are available from the authors. Crystallographic data for the structural analysis were deposited at the Cambridge Crystallographic Data Centre, CCDC No. 2214908 for compound 1, 2214910 for compound 2. Copies of the data can be obtained free of charge from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336-033;


The Siberian Branch of the Russian Academy of Sciences (SB RAS) Siberian Supercomputer Centre is gratefully acknowledged for providing supercomputer facilities. The authors thank the XRD facilities of NIIC for collecting the diffraction data.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Sample Availability

Samples of the compounds 1 and 2 are available from the authors.


  1. Butova, V.V.; Soldatov, M.A.; Guda, A.A.; Lomachenko, K.A.; Lamberti, C. Metal-organic frameworks: Structure, properties, synthesis and characterization. Russ. Chem. Rev. 2016, 85, 280–307. [Google Scholar] [CrossRef]
  2. Belousov, Y.A.; Drozdov, A.A.; Taydakov, I.V.; Marchetti, F.; Pettinari, R.; Pettinari, C. Lanthanide azolecarboxylate compounds: Structure, luminescent properties and applications. Coord. Chem. Rev. 2021, 445, 214084. [Google Scholar] [CrossRef]
  3. Kalmutzki, M.J.; Hanikel, N.; Yaghi, O.M. Secondary building units as the turning point in the development of the reticular chemistry of MOFs. Sci. Adv. 2022, 4, eaat9180. [Google Scholar] [CrossRef] [Green Version]
  4. Liu, Z.-Q.; Zhao, Y.; Zhang, X.-D.; Kang, Y.-S.; Lu, Q.-Y.; Azam, M.; Al-Resayes, S.I.; Sun, W.-Y. Metal–organic frameworks with 1,4-di(1H-imidazol-4-yl)benzene and varied carboxylate ligands for selectively sensing Fe(III) ions and ketone molecules. Dalton Trans. 2017, 46, 13943–13951. [Google Scholar] [CrossRef] [PubMed]
  5. Yaghi, O.M.; O’Keeffe, M.; Ockwig, N.W.; Chae, H.K.; Eddaoudi, M.; Kim, J. Reticular synthesis and the design of new materials. Nature 2003, 423, 705–714. [Google Scholar] [CrossRef] [PubMed]
  6. Guillerm, V.; Eddaoudi, M. The Importance of Highly Connected Building Units in Reticular Chemistry: Thoughtful Design of Metal–Organic Frameworks. Acc. Chem. Res. 2021, 54, 3298–3312. [Google Scholar] [CrossRef]
  7. Cheng, X.; Guo, L.; Wang, H.; Gu, J.; Yang, Y.; Kirillova, M.V.; Kirillov, A.M. Coordination Polymers from Biphenyl-Dicarboxylate Linkers: Synthesis, Structural Diversity, Interpenetration, and Catalytic Properties. Inorg. Chem. 2022, 61, 12577–12590. [Google Scholar] [CrossRef]
  8. Elsaidi, S.K.; Mohamed, M.H.; Banerjee, D.; Thallapally, P.K. Flexibility in Metal–Organic Frameworks: A fundamental understanding. Coord. Chem. Rev. 2018, 358, 125–152. [Google Scholar] [CrossRef]
  9. Murdock, C.R.; Lu, Z.; Jenkins, D.M. Effects of Solvation on the Framework of a Breathing Copper MOF Employing a Semirigid Linker. Inorg. Chem. 2013, 52, 2182–2187. [Google Scholar] [CrossRef]
  10. Bigdeli, F.; Lollar, C.T.; Morsali, A.; Zhou, H.-C. Switching in Metal–Organic Frameworks. Angew. Chemie Int. Ed. 2020, 59, 4652–4669. [Google Scholar] [CrossRef]
  11. Demakov, P.A.; Poryvaev, A.S.; Kovalenko, K.A.; Samsonenko, D.G.; Fedin, M.V.; Fedin, V.P.; Dybtsev, D.N. Structural Dynamics and Adsorption Properties of the Breathing Microporous Aliphatic Metal–Organic Framework. Inorg. Chem. 2020, 59, 15724–15732. [Google Scholar] [CrossRef] [PubMed]
  12. Albalad, J.; Peralta, R.A.; Huxley, M.T.; Tsoukatos, S.; Shi, Z.; Zhang, Y.-B.; Evans, J.D.; Sumby, C.J.; Doonan, C.J. Coordination modulated on-off switching of flexibility in a metal–organic framework. Chem. Sci. 2021, 12, 14893–14900. [Google Scholar] [CrossRef] [PubMed]
  13. Liu, Z.-Q.; Zhao, Y.; Wang, P.; Kang, Y.-S.; Azam, M.; Al-Resayes, S.I.; Liu, X.-H.; Lu, Q.-Y.; Sun, W.-Y. Fluorescent sensing and selective adsorption properties of metal–organic frameworks with mixed tricarboxylate and 1H-imidazol-4-yl-containing ligands. Dalton Trans. 2017, 46, 9022–9029. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  14. Gu, W.-J.; Gu, J.-Z.; Kirillova, M.V.; Kirillov, A.M. Zn(II) metal–organic architectures from ether-bridged tetracarboxylate linkers: Assembly, structural variety and catalytic features. CrystEngComm 2022, 24, 5297–5306. [Google Scholar] [CrossRef]
  15. Gu, J.; Wen, M.; Liang, X.; Shi, Z.; Kirillova, M.; Kirillov, A. Multifunctional Aromatic Carboxylic Acids as Versatile Building Blocks for Hydrothermal Design of Coordination Polymers. Crystals 2018, 8, 83. [Google Scholar] [CrossRef] [Green Version]
  16. Gu, J.-Z.; Liang, X.-X.; Cui, Y.-H.; Wu, J.; Shi, Z.-F.; Kirillov, A.M. Introducing 2-(2-carboxyphenoxy)terephthalic acid as a new versatile building block for design of diverse coordination polymers: Synthesis, structural features, luminescence sensing, and magnetism. CrystEngComm 2017, 19, 2570–2588. [Google Scholar] [CrossRef]
  17. Chen, J.; Li, Y.; Gu, J.; Kirillova, M.V.; Kirillov, A.M. Introducing a flexible tetracarboxylic acid linker into functional coordination polymers: Synthesis, structural traits, and photocatalytic dye degradation. New J. Chem. 2020, 44, 16082–16091. [Google Scholar] [CrossRef]
  18. Bhadra, B.N.; Ahmed, I.; Lee, H.J.; Jhung, S.H. Metal-organic frameworks bearing free carboxylic acids: Preparation, modification, and applications. Coord. Chem. Rev. 2022, 450, 214237. [Google Scholar] [CrossRef]
  19. Hao, J.; Jikei, M.; Kakimoto, M. Preparation of Hyperbranched Aromatic Polyimides via A2 + B3 Approach. Macromolecules 2002, 35, 5372–5381. [Google Scholar] [CrossRef]
  20. Sahoo, S.; Mondal, S.; Sarma, D. Luminescent Lanthanide Metal Organic Frameworks (LnMOFs): A Versatile Platform towards Organomolecule Sensing. Coord. Chem. Rev. 2022, 470, 214707. [Google Scholar] [CrossRef]
  21. Wu, S.; Min, H.; Shi, W.; Cheng, P. Multicenter Metal–Organic Framework-Based Ratiometric Fluorescent Sensors. Adv. Mater. 2020, 32, 1805871. [Google Scholar] [CrossRef]
  22. Lunev, A.M.; Belousov, Y.A. Luminescent sensor materials based on rare-earth element complexes for detecting cations, anions, and small molecules. Russ. Chem. Bull. 2022, 71, 825–857. [Google Scholar] [CrossRef]
  23. Song, D.; Ji, X.; Li, Y.; Chen, S.; Wu, S.; Zhang, Y.; Gao, E.; Zhu, M. A terbium-based coordination polymer for sensitive ratiometric fluorescence detection of lamotrigine. J. Lumin. 2022, 251, 119129. [Google Scholar] [CrossRef]
  24. Ma, Y.; Zhu, M.; Zhang, Y.; Sun, Y.; Wu, S. A water-stable Eu-MOF as multi-responsive luminescent sensor for high-efficiency detection of Fe3+, MnO4− ions and nicosulfuron in aqueous solution. J. Solid State Chem. 2022, 316, 123598. [Google Scholar] [CrossRef]
  25. Demakov, P.A.; Ryadun, A.A.; Dorovatovskii, P.V.; Lazarenko, V.A.; Samsonenko, D.G.; Brylev, K.A.; Fedin, V.P.; Dybtsev, D.N. Intense multi-colored luminescence in a series of rare-earth metal-organic frameworks with aliphatic linkers. Dalton Trans. 2021, 50, 11899–11908. [Google Scholar] [CrossRef] [PubMed]
  26. Smirnova, K.S.; Ivanova, E.A.; Pozdnyakov, I.P.; Russkikh, A.A.; Eltsov, I.V.; Dotsenko, V.V.; Lider, E.V. 2D polymeric lanthanide(III) compounds based on novel bright green emitting enaminoneligand. Inorg. Chim. Acta 2022, 542, 121107. [Google Scholar] [CrossRef]
  27. Khistiaeva, V.V.; Melnikov, A.S.; Slavova, S.O.; Sizov, V.V.; Starova, G.L.; Koshevoy, I.O.; Grachova, E.V. Heteroleptic β-diketonate Ln(iii) complexes decorated with pyridyl substituted pyridazine ligands: Synthesis, structure and luminescence properties. Inorg. Chem. Front. 2018, 5, 3015–3027. [Google Scholar] [CrossRef]
  28. Shi, X.; Cao, B.; Liu, J.; Zhang, J.; Du, Y. Rare-Earth-Based Metal–Organic Frameworks as Multifunctional Platforms for Catalytic Conversion. Small 2021, 17, 2005371. [Google Scholar] [CrossRef]
  29. Zhang, Y.; Liu, S.; Zhao, Z.-S.; Wang, Z.; Zhang, R.; Liu, L.; Han, Z.-B. Recent progress in lanthanide metal–organic frameworks and their derivatives in catalytic applications. Inorg. Chem. Front. 2021, 8, 590–619. [Google Scholar] [CrossRef]
  30. Biswas, S.; Neugebauer, P. Lanthanide-Based Metal-Organic-Frameworks for Proton Conduction and Magnetic Properties. Eur. J. Inorg. Chem. 2021, 2021, 4610–4618. [Google Scholar] [CrossRef]
  31. Feng, L.; Wang, H.-S.; Xu, H.-L.; Huang, W.-T.; Zeng, T.-Y.; Cheng, Q.-R.; Pan, Z.-Q.; Zhou, H. A water stable layered Tb(III) polycarboxylate with high proton conductivity over 10−2 S cm−1 in a wide temperature range. Chem. Commun. 2019, 55, 1762–1765. [Google Scholar] [CrossRef]
  32. Yang, L.; Zhang, S.; Qu, X.; Yang, Q.; Liu, X.; Wei, Q.; Xie, G.; Chen, S. Synthesis, crystal structure and photoluminescence property of Eu/Tb MOFs with mixed polycarboxylate ligands. J. Solid State Chem. 2015, 231, 223–229. [Google Scholar] [CrossRef]
  33. Alemany, P.; Casanova, D.; Alvarez, S.; Dryzun, C.; Avnir, D. Continuous Symmetry Measures: A New Tool in Quantum Chemistry. Rev. Comput. Chem. 2017, 30, 289–352. [Google Scholar]
  34. Ruiz-Martínez, A.; Casanova, D.; Alvarez, S. Polyhedral Structures with an Odd Number of Vertices: Nine-Coordinate Metal Compounds. Chem. A Eur. J. 2008, 14, 1291–1303. [Google Scholar] [CrossRef] [PubMed]
  35. Demakov, P.A.; Ryadun, A.A.; Fedin, V.P. Aliphatic-Bridged Early Lanthanide Metal–Organic Frameworks: Topological Polymorphism and Excitation-Dependent Luminescence. Inorganics 2022, 10, 163. [Google Scholar]
  36. Demakov, P.A.; Sapchenko, S.A.; Samsonenko, D.G.; Dybtsev, D.N.; Fedin, V.P. Gadolinium Break in a Series of Three-Dimensional trans-1,4-Cyclohexane Dicarboxylates of Rare Earth Elements. J. Struct. Chem. 2019, 60, 815–822. [Google Scholar] [CrossRef]
  37. Tan, X.-F.; Zhou, J.; Zou, H.-H.; Fu, L.; Tang, Q.; Wang, P. A series of lanthanide glutarates: Lanthanide contraction effect on crystal frameworks of lanthanide glutarates. RSC Adv. 2017, 7, 17934–17940. [Google Scholar] [CrossRef] [Green Version]
  38. Heffern, M.C.; Matosziuk, L.M.; Meade, T.J. Lanthanide Probes for Bioresponsive Imaging. Chem. Rev. 2014, 114, 4496–4539. [Google Scholar] [CrossRef] [Green Version]
  39. Binnemans, K. Interpretation of europium(III) spectra. Coord. Chem. Rev. 2015, 295, 1–45. [Google Scholar] [CrossRef] [Green Version]
  40. Alzakhem, N.; Bischof, C.; Seitz, M. Dependence of the Photophysical Properties on the Number of 2,2′-Bipyridine Units in a Series of Luminescent Europium and Terbium Cryptates. Inorg. Chem. 2012, 51, 9343–9349. [Google Scholar] [CrossRef]
  41. Huang, Y.; Zhu, Q.; Sheng, T.; Hu, S.; Fu, R.; Shen, C.; Tan, C.; Wen, Y.; Bai, S.; Wu, X. Lanthanide coordination polymers assembled from triazine-based flexible polycarboxylate ligands and their luminescent properties. CrystEngComm 2013, 15, 3560–3567. [Google Scholar] [CrossRef]
  42. Gai, Y.; Jiang, F.; Chen, L.; Wu, M.; Su, K.; Pan, J.; Wan, X.; Hong, M. Europium and Terbium Coordination Polymers Assembled from Hexacarboxylate Ligands: Structures and Luminescent Properties. Cryst. Growth Des. 2014, 14, 1010–1017. [Google Scholar] [CrossRef]
  43. Sheldrick, G.M. SHELXT—Integrated space-group and crystal-structure determination. Acta Crystallogr. Sect. A 2015, 71, 3–8. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  44. Sheldrick, G.M. Crystal structure refinement with SHELXL. Acta Crystallogr. Sect. C 2015, 71, 3–8. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  45. Dolomanov, O.V.; Bourhis, L.J.; Gildea, R.J.; Howard, J.A.K.; Puschmann, H. OLEX2: A complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 2009, 42, 339–341. [Google Scholar] [CrossRef]
  46. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G.A.; et al. Gaussian 09, Rev. D.01; Gaussian, Inc.: Wallingford, CT, USA, 2013. [Google Scholar]
  47. Becke, A.D. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A 1988, 38, 3098–3100. [Google Scholar] [CrossRef]
  48. Lee, C.; Yang, W.; Parr, R.G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785–789. [Google Scholar] [CrossRef] [Green Version]
  49. Vosko, S.H.; Wilk, L.; Nusair, M. Accurate spin-dependent electron liquid correlation energies for local spin density calculations: A critical analysis. Can. J. Phys. 1980, 58, 1200–1211. [Google Scholar] [CrossRef] [Green Version]
  50. Stephens, P.J.; Devlin, F.J.; Chabalowski, C.F.; Frisch, M.J. Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J. Phys. Chem. 1994, 98, 11623–11627. [Google Scholar] [CrossRef]
  51. McLean, A.D.; Chandler, G.S. Contracted Gaussian basis sets for molecular calculations. I. Second row atoms, Z = 11–18. J. Chem. Phys. 1980, 72, 5639–5648. [Google Scholar] [CrossRef]
  52. Krishnan, R.; Binkley, J.S.; Seeger, R.; Pople, J.A. Self-consistent molecular orbital methods. XX. A basis set for correlated wave functions. J. Chem. Phys. 1980, 72, 650–654. [Google Scholar] [CrossRef]
  53. Clark, T.; Chandrasekhar, J.; Spitznagel, G.W.; Schleyer, P.V.R. Efficient diffuse function-augmented basis sets for anion calculations. III. The 3-21+G basis set for first-row elements, Li–F. J. Comput. Chem. 1983, 4, 294–301. [Google Scholar] [CrossRef]
  54. Frisch, M.J.; Pople, J.A.; Binkley, J.S. Self-consistent molecular orbital methods 25. Supplementary functions for Gaussian basis sets. J. Chem. Phys. 1984, 80, 3265–3269. [Google Scholar] [CrossRef]
  55. Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 2011, 32, 1456–1465. [Google Scholar] [CrossRef]
Scheme 1. Synthesis of Tb(III) and Eu(III) coordination compounds 1 and 2.
Scheme 1. Synthesis of Tb(III) and Eu(III) coordination compounds 1 and 2.
Molecules 27 07849 sch001
Figure 1. X-ray crystal structure of the compound 1: (a) molecular structure (both positions of the disordered carboxylic proton are shown); (b) coordination polyhedron of Tb3+ cation; (c) 3D supramolecular structure formed as a result of hydrogen bonding (purple dotted lines) and π-π stacking (black dotted lines).
Figure 1. X-ray crystal structure of the compound 1: (a) molecular structure (both positions of the disordered carboxylic proton are shown); (b) coordination polyhedron of Tb3+ cation; (c) 3D supramolecular structure formed as a result of hydrogen bonding (purple dotted lines) and π-π stacking (black dotted lines).
Molecules 27 07849 g001
Figure 2. X-ray crystal structure of the compound 2: (a) elementary unit of the coordination polymer; (b) binuclear secondary building unit; (c) linear chain of the coordination polymer; (d) supramolecular interactions between the chains (two separate chains are colored blue and green).
Figure 2. X-ray crystal structure of the compound 2: (a) elementary unit of the coordination polymer; (b) binuclear secondary building unit; (c) linear chain of the coordination polymer; (d) supramolecular interactions between the chains (two separate chains are colored blue and green).
Molecules 27 07849 g002
Figure 3. Dihedral angles between the central benzene ring and the phenoxy rings in H3L3- ligand in the structure of the compounds 1 (a) and 2 (b).
Figure 3. Dihedral angles between the central benzene ring and the phenoxy rings in H3L3- ligand in the structure of the compounds 1 (a) and 2 (b).
Molecules 27 07849 g003
Figure 4. Photophysical profiles of the compounds 1 and 2: (a) emission spectrum of the compound 1; (b) emission spectrum of the compound 2; (c) luminescence decay curves for the compounds 1 and 2; (d) CIE 1931 diagram for the emission of the compounds 1 and 2 (points corresponding to emission colors are indicated by stars).
Figure 4. Photophysical profiles of the compounds 1 and 2: (a) emission spectrum of the compound 1; (b) emission spectrum of the compound 2; (c) luminescence decay curves for the compounds 1 and 2; (d) CIE 1931 diagram for the emission of the compounds 1 and 2 (points corresponding to emission colors are indicated by stars).
Molecules 27 07849 g004
Figure 5. Isosurfaces (at 0.02 e/Bohr3) of the molecular orbitals of Li3H3L ground state calculated at B3LYP[GD3BJ] 6–31 + G(d) level of theory.
Figure 5. Isosurfaces (at 0.02 e/Bohr3) of the molecular orbitals of Li3H3L ground state calculated at B3LYP[GD3BJ] 6–31 + G(d) level of theory.
Molecules 27 07849 g005
Figure 6. Energy diagram showing the calculated S0, S1 and T1 states of Li3H3L model (at TD-DFT B3LYP 6–31 + G(d) level of theory) and energy levels of Eu3+ and Tb3+ ions.
Figure 6. Energy diagram showing the calculated S0, S1 and T1 states of Li3H3L model (at TD-DFT B3LYP 6–31 + G(d) level of theory) and energy levels of Eu3+ and Tb3+ ions.
Molecules 27 07849 g006
Table 1. Crystallographic data and details of the structure refinement for the compounds 1 and 2.
Table 1. Crystallographic data and details of the structure refinement for the compounds 1 and 2.
ParameterCompound 1Compound 2
Molecular formulaC60H43O35TbC30H29EuO22
Formula weight, g∙mol−11481.85893.49
Temperature, K150(2)150.00
Crystal systemMonoclinicTriclinic
Space groupC2/cP-1
a, Å38.585(2)8.66180(10)
b, Å13.1992(7)10.0305(2)
c, Å11.9356(7)19.2763(3)
β, °106.289(2)80.1830(10)
Cell volume, Å5834.6(6)1647.66(5)
ρcalc, g/cm31.6871.801
μ, mm−11.3202.000
Independent reflections9710 [Rint = 0.0508, Rsigma = 0.0445]5809 [Rint = 0.0405, Rsigma = 0.0402]
Goodness-of-fit on F21.0611.036
Final R indexes [I ≥ 2σ(I)]R1 = 0.0353, wR2 = 0.0756R1 = 0.0263, wR2 = 0.0547
Final R indexes [all data]R1 = 0.0458, wR2 = 0.0786R1 = 0.0295, wR2 = 0.0565
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Yu, X.; Pavlov, D.I.; Ryadun, A.A.; Potapov, A.S.; Fedin, V.P. Variable Dimensionality of Europium(III) and Terbium(III) Coordination Compounds with a Flexible Hexacarboxylate Ligand. Molecules 2022, 27, 7849.

AMA Style

Yu X, Pavlov DI, Ryadun AA, Potapov AS, Fedin VP. Variable Dimensionality of Europium(III) and Terbium(III) Coordination Compounds with a Flexible Hexacarboxylate Ligand. Molecules. 2022; 27(22):7849.

Chicago/Turabian Style

Yu, Xiaolin, Dmitry I. Pavlov, Alexey A. Ryadun, Andrei S. Potapov, and Vladimir P. Fedin. 2022. "Variable Dimensionality of Europium(III) and Terbium(III) Coordination Compounds with a Flexible Hexacarboxylate Ligand" Molecules 27, no. 22: 7849.

Article Metrics

Back to TopTop