Absorption- and Excitation-Modulated Luminescence of Pr3+, Nd3+

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Article Cite This: ACS Omega 2019, 4, 2669−2675

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Absorption- and Excitation-Modulated Luminescence of Pr3+, Nd3+, and Lu3+ Compounds with Dianions of Tetrafluoroterephthalic and Camphoric Acids Elena A. Mikhalyova,† Olena V. Khomenko,‡ Konstantin S. Gavrilenko,§,∥ Vladimir P. Dotsenko,‡ Anthony W. Addison,*,⊥ and Vitaly V. Pavlishchuk*,†

ACS Omega 2019.4:2669-2675. Downloaded from pubs.acs.org by 193.56.73.173 on 02/06/19. For personal use only.

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L. V. Pisarzhevskii Institute of Physical Chemistry of the National Academy of Sciences of the Ukraine, Prospekt Nauki 31, 03028 Kiev, Ukraine ‡ A. V. Bogatsky Physico-Chemical Institute of the National Academy of Sciences of the Ukraine, 86 Lustdorfskaya doroga, 65080 Odessa, Ukraine § Chembiocenter of Taras Shevchenko National University of Kiev, 67 Chervonotkatska Street, 02094 Kiev, Ukraine ∥ Enamine Ltd, 78 Chervonotkatska Street, 02094 Kiev, Ukraine ⊥ Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104-2816, United States S Supporting Information *

ABSTRACT: The luminescence of coordination polymers of Pr3+, Nd3+, and Lu3+ with tetrafluoroterephthalate and camphorate, [Ln2(Fbdc)3(DMF)2(H2O)]2 (Ln = Pr, Nd, Lu) and [Ln2(Camph)2(NO3)2(MeOH)]4 (Ln = Pr, Nd, Lu), was studied. Ligand-centered and/or metal-centered emissions appear, which depend on the excitation wavelength, ultimately allowing the emitted light color to be adjusted. Low-efficiency ligand-to-metal energy transfer leads to a difference between the excitation spectra of the tetrafluoroterephthalate- and camphorate-Pr3+ compounds, arising from a primary filtering effect on the ligand-centered excitation, by Pr3+ absorption. A secondary inner filter effect significantly changes the shape of the luminescence band, allowing a wide variation in the emission color, producing, for instance, a purple color, which is not the normal spectral emission. The low-efficiency energy transfer renders tetrafluoroterephthalate and camphorate ineffective as traditional “antenna” ligands for Pr3+ and Nd3+.

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INTRODUCTION Elevated current interest in luminescent lanthanide complexes results from their emission characteristics, i.e., the high purity and reproducibility of their emission colors, which are necessary for the potential application of these compounds as materials for sensors, biological markers, solid-state lasers, components of luminescent films, and markers for protection of documents against falsification.1 Lanthanide−organic frameworks (LnOFs) constitute one of the most promising classes of luminescent compounds.1−3 LnOFs usually contain at least two potential light-emitting centers: an organic ligand and the Ln3+ ion. The occurrence and intensity of luminescence arising from the linker ligand or metal ion depends on their ability to absorb excitation energy, the probabilities of ligand-to-metal and metal-to-ligand energy transfers, and the possibility of radiationless deactivation of excited states. The relative efficiencies of these processes and, hence, the emission quantum yields are strongly dependent on the electronic structures of the organic ligand and the Ln3+ ion and govern the luminescence spectrum of the compound. This allows such compounds to cover almost the full visible spectral range of emission color by appropriate combination of different ligands and metals in the LnOFs. However, the prediction of © 2019 American Chemical Society

luminescence characteristics (intensity and color) of such compounds is as yet far from facile. The stability of Ln3+-ion complexes with O-donor ligands, combined with the wide variety of available carboxylates, has led to the generation of a large number of LnOFs with aromatic carboxylates,4−6 terephthalate being a typical component of many known luminescent LnOFs, such as {[Tb(bdc)1.5(H2O)]·(DMF)(H2O)}n (bdc2− = terephthalate dianion),7 [Eu2(bdc)3(H2O)4]n,8 and [Ln2(bdc)3(H2O)(DMF)3]n (Ln = Pr, Nd, Sm, Eu).9 These complexes, including [Pr2(bdc)3(H2O)(DMF)3]n and [Nd2(bdc)3(H2O)(DMF)3]n, possess intense metal-centered emission, while bdc2− has a triplet state energy of 23 300 cm−1 and plays the role of an antenna ligand in these compounds.9 For this work, two different carboxylates were chosen on the basis of the following points. It has been shown10,11 that, generally, substitution of C−H by C−F in ligands leads to an enhancement of the luminescence intensity, so tetrafluoroterephthalate (Fbdc2−) is used as a counterion in this study. As Received: September 14, 2018 Accepted: January 10, 2019 Published: February 5, 2019 2669

DOI: 10.1021/acsomega.8b02388 ACS Omega 2019, 4, 2669−2675

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Figure 1. Diffuse reflectance spectra of (a) Gd3+-carboxylates13 and (b, c) LnFbdc and LnCamph. Band assignments were made by comparison of the spectra with known ones for Pr3+ and Nd3+ compounds.21−25

ligand-centered emission; (ii) the consequent inner filter effects caused by Pr3+ and Nd3+ will noticeably change the luminescence color range; (iii) use of tetrafluoroterephthalate, rather than its nonfluorinated analogue, will enhance the metal-centered emission because of suppression of the vibrational relaxation associated with C−H bonds. Therefore, the aims of this work are to describe the luminescence of Pr3+, Nd3+, and Lu3+ coordination polymers with tetrafluoroterephthalate and camphorate, [Ln2(Fbdc)3(DMF)2(H2O)]2 (LnFbdc, Ln = Pr, Nd, Lu) and [Ln2(Camph)2(NO3)2(MeOH)]4 (LnCamph, Ln = Pr, Nd, Lu), to provide an implicit contrast with the known Eu and Tb systems,13 and to detect any influence of the Ln3+ ions’ absorption in these compounds on their ligand-centered emission and the color of the emitted light.

the electronic structures of aliphatic and aromatic ligands differ significantly, the emission properties of their Ln3+ complexes thus also vary.3,12 The main reason for choosing camphorate (Camph2−) was that its triplet state energy is 23 700 cm−1,13 which is very close to the respective value for bdc2−.9 The triplet state energies of tetrafluoroterephthalate (24 700 cm−1)13 and camphorate (23 700 cm−1)13 are both higher than the energies of emission levels of most lanthanides, which display emission in the visible and NIR regions; so camphoric acid, with its rigid cyclic structure, can be considered in this sense as an appropriate aliphatic analogue of tetrafluoroterephthalic acid. Moreover, lanthanide complexes with these ligands, namely, [Pr(Fbdc) 3 (DMF) 2 (H 2 O)] 2 1 4 and [Nd2(Camph)2(NO3)2(MeOH)]4,15 possess similar crystal structures, with two-dimensional polymers formed by dinuclear “building blocks” linked by −O2C−R−CO2− bridges in two directions (type 2B2 according to the classification in ref 14), arranged in almost “grid”-like layers. This provides an additional resemblance between the tetrafluoroterephthalate and camphorate dianions. On the other hand, the lanthanide compounds possessing luminescence in the visible region, which have been most studied so far, are those of Tb3+ and Eu3+, with green or red metal-centered emission, respectively.1,16,17 To extend the luminescence color range by increasing the likelihood of the additional appearance of ligand-centered emission, which may lead to the production of different colors, longer-wavelength emitting Pr3+ and Nd3+ and nonemitting Lu3+ ions have been chosen from the lanthanide row for this work. The logic of such a choice is based on (i) the probable ligand-centered emission of Lu3+ compounds, which acts as a luminescence reference and (ii) the characteristic near-infrared (NIR) luminescence of compounds of Pr3+ and Nd3+ and their just weak (if any) metal-centered emission in the visible range, which potentially leads to the appearance of ligand-centered luminescence.10,16,17 Moreover, amongst lanthanide ions, Pr3+ and Nd3+ have the most intense absorption due to their Laporte-forbidden f−f transitions,18 and in different spectral ranges: i.e., Pr3+ absorbs blue and orange light, and Nd3+ absorbs in the green and orange regions. Thus, partial absorption of ligand emission by Pr3+ and Nd3+ (i.e., inner filter effects) may broaden the color range of ligand-centered emission. Hence this work is based on the hypotheses/ideas that (i) the use of longer-wavelength emitting Pr3+ and Nd3+ and the nonemitting (reference 4f10) Lu3+ will lead to significant

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RESULTS AND DISCUSSION Electronic Spectra of LnFbdc and LnCamph. Broad bands in the UV region appear in all the complexes’ electronic spectra (Figure 1b). These bands are similar within each ligand’s series of metal complexes and are assigned to absorption by the organic ligands (Figure 1a). For the LnFbdc complexes, ligand absorption (Fbdc2−) is due to aromatic π → π* transitions,13,19 with a maximum around 280 nm, whereas for the LnCamph complexes, the Camph2− absorption13,20 displays three resolved components at 220, 260, and 290 nm, assignable to the carboxylate π → π*, n → σ*, and n → π* transitions, respectively.19 Sharp bands characteristic of Pr3+ and Nd3+ f−f transitions are present in the spectra of the complexes with these metals (Figure 1b,c). The positions and shapes of these bands are as commonly seen in the electronic spectra of Pr3+ and Nd3+ compounds;21−24 the bands’ assignments are given in Figure 1b,c. Photoluminescence Properties. The luminescence properties of Ln3+ compounds depend substantially on the relative positions of the ligand triplet level and the excited state of the Ln3+ ion.1,4,17 The Fbdc2− and Camph2− triplet level energies have been determined earlier as 24 700(100) and 23 700(300) cm−1,13 respectively. These values are higher than the excited level energies of Pr3+ (3P0, near 20 700 cm−1, 3P1, near 21 200 cm−1 and 1D2, near 16 400 cm−1)9,10,25 and of Nd3+ (4F3/2, near 11 300 cm−1);10,23 therefore, ligand-to-Ln3+ energy transfer should be anticipated. In the case of Pr3+, this transfer is associated with levels of the same multiplicity and 2670


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Figure 2. (a) Excitation spectrum monitored for λem = 640 nm (green), emission spectrum excited with λex = 445 nm (red), and diffuse reflectance spectrum (black) of PrFbdc. (b) Excitation spectrum monitored for λem = 642 nm (green), emission spectrum excited with λex = 445 nm (red), and diffuse reflectance spectrum (black) of PrCamph.

In the excitation spectra (Figure 2) of PrFbdc and PrCamph measured at the 3P0 → 3F2 transition emission maximum of Pr3+ ions (λem = 640 and 642 nm for PrFbdc and PrCamph, respectively), broad bands are observed in the UV region. These are assigned to (i) the edge of the ligand absorption for Fbdc2− or Camph2− 13 (for PrFbdc or PrCamph, respectively) and (ii) the Pr 3+ 5d → 4f transitions.27,28 Although the excitation spectra of PrFbdc and PrCamph were measured for wavelengths related to Pr3+centered emission, no Pr3+-centered luminescence was observed upon excitation at wavelengths of the maxima in the excitation spectra, i.e., λex = 317 and 370 nm for PrFbdc and λex = 367 nm PrCamph, vide infra. This is a consequence of the ineffectuality of energy transfer from the ligand to Pr3+ and the overlapping of Pr3+-centered and ligand-centered emission, so that the excitation spectrum is the result of a simple superposition of Pr3+ and ligand excitation spectra. The excitation spectra of PrFbdc and PrCamph are somewhat dissimilar in the region typical of Pr3+ absorption (440−500 nm): three minima are found in the excitation spectrum of PrFbdc, whereas three maxima appear at the corresponding wavelengths in the spectrum of PrCamph. The positions of these extrema coincide with the positions of the f− f bands in the absorption spectrum (Figure 2).21,22,25 The presence of local minima in an excitation spectrum in what is normally an absorption region is unusual. Their nature can be accounted for by the interplay of two effects: (i) the lower intensity of ligand-centered emission caused by a primary filtering effect of the Pr3+ ion: i.e., Pr3+ f−f transitions absorb significantly in that same region where the ligand absorption is of relatively low intensity29,30 and (ii) the normal maxima in the excitation spectrum for a Ln3+ ion associated with its absorption.21,25 This rationalization is supported by (i) the absence of Pr3+ emission by excitation with λex less than 440 nm, and (ii) by the broadening of the minima in the excitation spectrum. Metal-centered emission is observed for both NdFbdc and NdCamph (Figure 4). Three bands near 895, 1060 and 1330 nm, which can be assigned to the 4F3/2 → 4I9/2, 4F3/2 → 4I11/2, and 4F3/2 → 4I13/2 transitions (Figure 4), respectively, are seen in the luminescence spectra of these complexes.31,32 In the excitation spectra of NdFbdc and NdCamph (monitored for

hence is allowed. It might be noted that reverse energy transfer from Pr3+ to ligand would also be allowed. PrFbdc, NdFbdc, PrCamph, and NdCamph MetalCentered Emission. Metal-centered emission is observed for PrFbdc, NdFbdc, PrCamph, and NdCamph. For the Pr3+ complexes, this emission arises by excitation at 445 nm, corresponding to the Pr3+-centered 3H4 → 3P2 transition (Figure 2). Since the Pr3+ ion possesses three emissive states, the interpretation of its luminescence spectrum is hardly straightforward, but tentative assignments may be made (Figure 3). The emission spectra of PrFbdc and PrCamph

Figure 3. Energy-level scheme for Pr3+ and Nd3+ compounds illustrating excitation and emission processes. Wavy lines indicate nonradiative transitions.

are similar (Figure 2) and display several Pr3+-centered bands near 525, 610, and 640 nm corresponding to the 3P1 → 3H5, 3 P0 → 3H6, and 3P0 → 3F2 transitions, respectively.25,26 In the spectrum of PrCamph, additional bands at 486 and 542 nm attributed to 3P0 → 3H4 and 3P0 → 3H5 are observed.25,26 The apparent absence of these bands in the emission spectrum of PrFbdc can be accounted for by their being overwhelmed by the more intense ligand luminescence, which dominates this region. The Pr3+ emission’s sharp lines contrast with the broad ligand emission bands. No NIR (850−1500 nm) emission is observed for PrFbdc or PrCamph. 2671


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Figure 4. (a) Excitation spectrum monitored for λem = 1057 nm (green), emission spectrum excited with λex = 310 nm (red), and diffuse reflectance spectrum (black) of NdFbdc. (b) Excitation spectrum monitored for λem = 1062 nm (green), emission spectrum excited with λex = 305 nm (red), and diffuse reflectance spectrum (black) of NdCamph.

Figure 5. Ligand-centered emission spectra of PrFbdc (green), NdFbdc (red), and LuFbdc (black) with (a) λex = 317 nm and (b) λex = 370 nm.

F3/2 → 4I11/2 emission), several sharp bands appear, attributable to Nd3+ absorption.23,33 It should be noted that the energy gaps between the lowest potentially emissive state and the highest spin−orbit (J) level of the nonfluorescent state are just 3900 cm−1 (3P0 → 1D2) or 6950 cm−1 (1D2 → 1G4) for Pr3+ and 5400 cm−1 (4F3/2 → 4 I15/2) for Nd3+ ions.11,34 These energy gaps are close to the first ligand O−H and C−H vibrational overtone frequencies (6800 and 6000 cm−1 respectively),35 which usually leads to efficient nonradiative deactivation processes.11,15,34 Although the Ln3+ in LnFbdc has a coordinated water molecule, and in LnCamph a methanol molecule is coordinated, all Pr3+ and Nd3+ complexes studied here, nonetheless, display metalcentered emission. LnFbdc and LnCamph Ligand-Centered Emission. LnFbdc and LnCamph (Ln = Pr3+, Nd3+, Lu3+) display a broad emission band (Δν1/2 > 3000 cm−1) in the 320−550 nm region, attributed to ligand-centered UV-excited luminescence (Figures 5 and 6). Indeed, for the Lu3+ complexes, no sharp minima or maxima are observed in conjunction with these bands (Figures 5 and 6); the corresponding emission band shape for the Pr3+ and Nd3+ compounds is similar. This ligandbased emission assignment is supported by the fact that Ln3+ f−f transitions have narrow bands (Δν1/2 < 500 cm−1);18 nearUV/visible region charge-transfer transitions are unusual for these ions, and these observed bands appear in the same energy region within each ligand’s metal complexes. The appearance of ligand-centered bands in the emission spectrum 4

Figure 6. Ligand-centered emission spectra of PrCamph (green), NdCamph (red), and LuCamph (black) with λex = 367 nm.

indicates that ligand-to-metal energy transfer is ineffective. The different positions of the emission bands in the spectra of LnFbdc with λex = 317 nm (λem = 350 nm) and 370 nm (λem = 450 nm) may be caused by dominant emission from the S1 and T1 excited states of Fbdc2−, which also agrees with the estimated energies for these levels.13 Sharp minima are observed on the ligand-centered emission bands in the spectra of the Pr3+ and Nd3+ compounds, which probably correspond to reabsorption of emitted light by Ln3+ ions, followed by deactivation of their excited statei.e., a 2672


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Figure 7. Colorimetric coordinates for emission of LnFbdc (a) and LnCamph (b). 1Ln = Pr, 2Ln = Nd, 3Lu, aλex = 317 nm (a) or 367 nm (b), bλex = 370 nm, cλex = 445 nm.

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secondary inner filter effect.30,36,37 This may be observed when a compound’s emission overlaps with some other moiety’s absorption and the emission and absorption process probabilities are comparable. Since absorption by Ln3+ ions is usually caused by Laporte-forbidden f−f transitions and is not intense, only a minority of lanthanide ions exhibit this effect,1,29,31,36−44 and usually it appears when organic species and lanthanide ions are not chemically bonded (mechanical mixtures, doped diureasils, or xerogels).1,29,37,40−44 To the best of our knowledge, there are only a few examples where this effect has been observed in coordination compounds.31,36,38,39 Moreover, the inner filter effect caused by Ln3+ ions usually appears as small dips on the organic fragment’s emission, and little attention has been paid to their influence on the perceived emission color. Nevertheless, if emission and absorption process probabilities are comparable, the inner filter effect can significantly change the shape of an emission band and, hence, the color of the emitted light, and this may allow the production of colors, such as purple, which are otherwise normally absent in the spectrum but obtainable by combining red and blue, as an alternative to its production by additive combination of emission wavelengths from two different, unconnected luminophores. The colorimetric coordinates have been estimated for all spectra in this work (Figure 7). These coordinates differ significantly among the ligand-centered emission of the Pr3+, Nd3+, and Lu3+ compounds as a result of “tuning” of the color by partial absorption of the emitted light. The emission color of NdFbdc depends significantly on the excitation wavelength, and in the case of λex = 370 nm, it is purple, due to absorption of green wavelengths by Nd 3+ f−f transitions. The luminescence colors of PrFbdc and PrCamph also vary with excitation wavelength, which is attributed to the changeover from ligand-centered emission (λex = 317 or 370 nm) to a metal-centered one (λex = 445 nm), as the spectra reveal. So for lanthanide compounds with Fbdc2− and Camph2− in this work, the emission color can be tuned over a wide range by changing the metal ion and excitation wavelength.

CONCLUSIONS The luminescence properties of Pr3+ and Nd3+ coordination polymers with tetrafluoroterephthalic and camphoric acid anions have been studied. The Pr3+ and Nd3+ compounds possess ligand-centered or metal-centered emission that depends on the excitation wavelength and allows controllable changes in the color of the emitted light. This is enabled by low-efficiency ligand-to-metal energy transfer and shows that Fbdc2− and Camph2− are not very effective as traditional “antenna” ligands for Pr3+ and Nd3+. In addition, an inner filter effect appears in the ligand-centered emission for PrFbdc, NdFbdc, PrCamph, and NdCamph, which significantly changes the shape of the emission band and allows variation of the emission color over a wide range, producing a color (purple), which is not based on the normal spectral emission. The excitation spectra of the tetrafluoroterephthalate- and camphorate-Pr3+ compounds are significantly different, which may arise from a primary filtering effect of Pr3+ absorption on the ligand-centered emission.

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EXPERIMENTAL SECTION Materials and Methods. Commercially available reagents and solvents (Aldrich and UkrReaChim) were used without further purification. Camphoric acid (H2Camph) and tetrafluoroterephthalic acid (H2Fbdc) were purchased from Acros Organics and lanthanide nitrates from Aldrich. C, H, Nmicroanalyses were performed with a Carlo Erba 1106 analyzer. X-ray powder diffraction data were collected on a Bruker X9 diffractometer (Cu Kα radiation). Diffuse reflectance spectra were measured on a Specord M-40 at room temperature and were recalculated to absorption using the Kubelka−Munk function.45,46 The photoluminescence measurements were performed for solid samples of pure compounds at room temperature with a Horiba Jobin-Yvon Inc. Fluorolog FL 3-22 luminescence spectrometer. Synthesis and Crystalline Constitution. [Ln2(Fbdc)3(DMF)2(H2O)]2 (LnFbdc, Ln = Pr, Nd, Lu) were prepared as described previously,20 whereas the 2673


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with high potential porosity and luminescence properties. J. Mol. Struct. 2015, 1086, 34−42. (8) Xu, H.; Liu, F.; Cui, Y.; Chen, B.; Qian, G. A luminescent nanoscale metal-organic framework for sensing of nitroaromatic explosives. Chem. Commun. 2011, 47, 3153−3155. (9) Decadt, R.; Hecke, K. V.; Depla, D.; Leus, K.; Weinberger, D.; Van Driessche, I.; Van Der Voort, P.; Van Deun, R. Synthesis, Crystal Structures, and Luminescence Properties of Carboxylate Based RareEarth Coordination Polymers. Inorg. Chem. 2012, 51, 11623−11634. (10) Hasegawa, Y.; Wada, Y.; Yanagida, S. Strategies for the design of luminescent lanthanide(III) complexes and their photonic applications. J. Photochem. Photobiol., C 2004, 5, 183−202. (11) Stein, G.; Würzberg, E. Energy gap law in the solvent isotope effect on radiationless transitions of rare earth ions. J. Chem. Phys. 1975, 62, 208−213. (12) Mikhalyova, E. A.; Yakovenko, A. V.; Zeller, M.; Gavrilenko, K. S.; Kiskin, M. A.; Smola, S. S.; Dotsenko, V. P.; Eremenko, I. L.; Addison, A. W.; Pavlishchuk, V. V. Crystal structures and intense luminescence of tris(3-(2′-pyridyl)-pyrazolyl)borate Tb3+ and Eu3+ complexes with carboxylate co-ligands. Dalton Trans. 2017, 46, 3457− 3469. (13) Mikhalyova, E. A.; Smola, S. S.; Gavrilenko, K. S.; Dotsenko, V. P.; Eremenko, I. L.; Pavlishchuk, V. V. Metal-Centered Photoluminescence of Eu3+ and Tb3+ Coordination Polymers with Dianions of Camphoric and Tetrafluoroterephthalic Acids. Theor. Exp. Chem. 2015, 51, 30−36. (14) Mikhalyova, E. A.; Kolotilov, S. V.; Zeller, M.; Thompson, L. K.; Addison, A. W.; Pavlishchuk, V. V.; Hunter, A. D. Synthesis, structure and magnetic properties of Nd3+ and Pr3+ 2D polymers with tetrafluoro-p-phthalate. Dalton Trans. 2011, 40, 10989−10996. (15) Wu, H.-C.; Jhu, Z.-R.; Lee, G.-H.; Peng, S.-M.; Yang, C.-I.; Kuei, C.-H. Lanthanide coordination polymers based on Ln2 cluster: Syntheses, crystal structures photoluminescence and magnetic properties. Polyhedron 2013, 66, 34−38. (16) Bünzli, J.-C. G.; Piguet, C. Taking advantage of luminescent lanthanide ions. Chem. Soc. Rev. 2005, 34, 1048−1077. (17) Bünzli, J.-C. G. On the design of highly luminescent lanthanide complexes. Coord. Chem. Rev. 2015, 293−294, 19−47. (18) Carnall, W. T. The Absorption and Fluorescence Spectra of Rare Earth Ions in Solution. In Handbook on the Physics and Chemistry of Rare Earths, 1979; Chapter 24, Vol. 3, pp 171−208. (19) Barltrop, J. A.; Coyle, J. D. Excited States in Organic Chemistry; John Wiley and Sons: London, 1975. (20) Jiang, Z.-Q.; Jiang, G.-Y.; Zhao, Z.; Hou, D.-C.; Zou, M.; Kang, Y. A rare homochiral lanthanium(sic)(III)-camphorate coordination polymer with 4-connected sql topology. Inorg. Chem. Commun. 2012, 22, 26−28. (21) Oczko, G.; Starynowicz, P. Crystal structure and absorption spectroscopy of Ln(HF2CCOO)3·3H2O (Ln = Pr, Er) single crystals. J. Mol. Struct. 2000, 523, 79−91. (22) Huskowska, E.; Porcher, P.; Legendziewicz, J. Electronic spectroscopy (Pr3+) and crystal field parameter calculations (Eu3+) for complexes of formula [Ln(2,2′-bipyridine-1,1′-dioxide)4](ClO4)3. J. Alloys Compd. 2002, 341, 187−192. (23) Mondry, A.; Starynowicz, P. Optical spectroscopy of neodymium(III) complexes with diethylenetriaminepentaacetic acid in solution and in [C(NH2)3]2[Nd(dtpa)(H2O)]·7H2O single crystal. Polyhedron 2000, 19, 771−777. (24) Legendziewicz, J. Spectroscopy and structure of selected lanthanide polymeric and monomeric systems. J. Alloys Compd. 2000, 300−301, 71−87. (25) Rai, A.; Sengupta, S. K.; Pandey, O. P. Lanthanum(III) and praseodymium(III) derivatives with dithiocarbamates derived from αamino acids. Spectrochim. Acta, Part A 2006, 64, 789−794. (26) Zhang, R.; Liu, Y.; Ren, J.; Chen, G. Visible and near infrared photoluminescence of Pr3+ doped oxy-chalcohalide glasses. Chem. Phys. Lett. 2013, 568−569, 80−83.

compounds, [Ln2(Camph)2(NO3)2(MeOH)]4 (LnCamph, Ln = Pr, Nd, Lu), were obtained similarly to the complexes with Ln = Eu, Gd, Tb.13 Crystal structures of LnFbdc and LnCamph have been described previously.14,15 The isomorphism of our LnFbdc and LnCamph with those calculated for the known coordination polymers, PrFbdc14 and NdCamph,15 was confirmed by coincidence of their X-ray powder patterns (Figure S1, Supporting Information) using the Mercury 3.8 software.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b02388.

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Synthesis of the complexes and X-ray powder diffraction data for LnCamph and LnFbdc (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Tel: 1-(215)-895-2646. Fax: 1(215)-895-3525. (A.W.A.). *E-mail: [email protected] (V.V.P.). ORCID

Anthony W. Addison: 0000-0002-0706-7377 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partially supported by a joint project of Trilateral Partnerships between researchers of Ukraine, Russia, and Germany of VolkswagenStiftung (ref No. 90343) and the National Academy of Sciences of Ukraine Program of Fundamental Research “New Functional Substances and Materials for Chemical Engineering” (contracts Nos. 9-17 and 9-18). The authors acknowledge the research agreement between the Pisarzhevskii Institute and the College of Arts & Sciences of Drexel University. E.A.M. thanks a President of Ukraine’s Grant for competitive projects (F75/28960) of the State Fund for Fundamental Research for partial financial support and this publication partially contains the results of studies conducted thereunder.

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REFERENCES

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Absorption- and Excitation-Modulated Luminescence of Pr3+, Nd3+

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