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An Unprecedented Octanuclear Dy(III) Cluster Exhibiting Single-Molecule Magnet Behavior Thomas Lacelle, Gabriel Brunet, Rebecca J. Holmberg, Bulat Gabidullin, and Muralee Murugesu Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01015 • Publication Date (Web): 18 Sep 2017 Downloaded from http://pubs.acs.org on September 20, 2017

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Crystal Growth & Design

An Unprecedented Octanuclear DyIII Cluster Exhibiting Single-Molecule Magnet Behaviour Thomas Lacelle,‡ Gabriel Brunet,‡ Rebecca J. Holmberg, Bulat Gabidullin, and Muralee Murugesu* Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie, Ottawa, ON, K1N 6N5, Canada.

Abstract: An unprecedented Dy8 cluster, [Dy8(µ4-O)(µ3-OH)8(vht)4(NO3)2(H2O)8](NO3)4, composed of two fused and distorted [Dy4(µ3-OH)4]8+ cubane units is reported. This cluster aggregate exhibits slow relaxation of the magnetization, characteristic of Single-Molecule Magnets (SMMs).

Interest in paramagnetic molecules exhibiting magnet-like behaviour continues to attract much attention, as we achieve increasingly higher energetic barriers to magnetic relaxation (Ueff).1‒3 While much of the recent attention is diverted towards the more simplistic mono- and dinuclear models, clusters of higher nuclearities remain staunch competitors, not only due to their structural aesthetics but also for their significantly higher potential in generating maximal spin ground states,4‒6 one of the key parameters in the synthesis of Single-Molecule Magnets

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(SMMs). In order to further promote intriguing magnetic behaviours, the use of 4f ions, which display inherently large single-ion anisotropies, continues to be a promising avenue to explore. Investigations focused on the intelligent design of molecular magnetic materials inherently coincide with targeting specific structural motifs and/or molecular architectures. Indeed, it is well-established that the magnetic properties of molecular entities are often dictated by their overall structural organization.7‒10 As a result, considerable efforts are directed towards the rational synthesis of polynuclear metal complexes. The prevalent method for exerting such a measure of control on the resulting topology involves careful selection of the organic chelates and synthetic conditions. Both parameters prove to be vital in successfully yielding a desired molecular architecture.11 As part of our recent efforts to elucidate the key underlying components that generate high-performing SMMs, we have developed a plethora of Schiff base ligands that have enabled us to study how minute structural and electronic differences can impact the slow magnetic relaxation,12‒14 characteristic of SMMs. One recent venture has yielded a Schiff base ligand incorporating a tetrazine ring as an integral part of the coordination pocket.15 Thus, despite the oxophilic nature of lanthanide ions, we were able to successfully bridge two metals centres through a tetrazine moiety. In the present work, we have utilized the same ligand building block to obtain a novel cluster arrangement by tuning the reaction conditions. The resulting topology consists of two closed cubane tetramers linked unusually by a µ4-O (oxide) bridge, effectively giving an octanuclear Dy8 cluster. A large number of transition metal-based complexes with cubane-core structures have been reported, illustrating that the specific geometry of the cubane has a significant effect on the nature of the magnetic interactions.16‒18 Similar conclusions have


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been observed in pure lanthanide systems, where greater distortions of the cubane-core have resulted in improved slow relaxation of the magnetization.19‒23 Herein, we report the synthesis, structure and magnetic properties of an unprecedented polynuclear DyIII cluster, namely [Dy8(µ4-O)(µ3-OH)8(vht)4(NO3)2(H2O)8](NO3)4, (1), where vht2‒ is the doubly deprotonated form of (3,6-bis(vanillidenehydrazinyl)-1,2,4,5-tetrazine (Scheme S1). This complex was obtained by the self-assembly of H2vht with Dy(NO3)3, which has previously yielded a tetranuclear compound,15 however upon alteration of the reaction conditions, we have promoted the formation of two linked cubanes. More specifically, a change in solvent from MeOH to EtOH, and of base from NaN3 to Et3N, resulted in a drastic change in topology. This behaviour can be rationalized by the greater basicity of Et3N (evaluated in terms of pKa), when compared to hydrazoic acid, the conjugate acid of the azide anion, which favours the deprotonation of water molecules from either the solvent or the hydrated metal salts. The inclusion of multiple hydroxide and oxide anions in 1, coupled with more sterically bulky EtOH molecules, led to the formation of the cubane-containing Dy8 structure. Single-crystal X-ray diffraction studies were performed on 1, revealing that the complex crystallizes in the monoclinic space group C2/c. Further crystallographic information can be found in Table S1 of the Supporting Information. The DyIII ions are arranged into two [Dy4(µ3OH)4]8+ cubane structures bridged in unique fashion by a µ4-O2‒ (O67) moiety (Figure 1, top). To the best of our knowledge, only two other lanthanide-based compound exhibits a similar type of arrangement, wherein the cubane cores are linked by two µ3-η2-ON‒ or µ-O,O’-carboxylato groups,20,22 rather than a µ4-O2‒ ligand. Also notable is an octanuclear compound in which four lanthanide ions are seen to form a tetrahedra, connected by central µ4-O2‒ ligands, thus giving rise to a distinct molecular architecture.24 In compound 1, however, the µ4-O2‒ moiety connects


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the two halves of the molecule, and form cubane-like structures rather than tetrahedra connected by a central µ4-O2‒ atom.

All four H2vht ligands are doubly deprotonated, through their

phenoxide positions, allowing each ligand to coordinate to two metal centres. The large coordination pockets consist of an imine nitrogen (N11, N20, N41 or N50) a phenoxide oxygen (O9, O28, O39 or O58) and a tetrazine nitrogen (N14, N15, N44 or N55), which act as donor atoms. Furthermore, the vht2‒ ligands adopt a nearly planar conformation, in contrast to our previous work, where half of the ligand molecules would twist severely to give a U-shape geometry, and thus isolate a set of Dy2 units. Within a single cubane, each of the DyIII ions are connected to three other metal centres via three µ3-OH‒ moieties (O64, O65, O66 or O68). It is noteworthy that Dy2 and Dy4 are connected by a µ4-O2‒ group (O67). This type of square motif proves to be common among metal clusters, however, a slight deviation from planarity can be observed, as evidenced by Dy2-O67-Dy2a and Dy4-O67-Dy4a angles of 168 and 164o, respectively. The centre of the cluster resides on a special crystallographic position, where a 2fold rotation axis intercepts O67, and as such, only half of the molecule is symmetrically independent. Additional relevant bond distances and angles can be found in Table S2. The coordination spheres of Dy1 and Dy3 are completed by a terminal bidentate nitrate anion and two water molecules, respectively, while both the coordination spheres Dy2 and Dy4 are completed by one water molecule each (Figure 1, bottom). All DyIII ions are octacoordinate, and their distorted coordination geometries were assessed using SHAPE software.25 The Dy1 and Dy3 metal centres most closely resemble a square antiprism (D4d), however, the triangular dodecahedron (D2d) geometry cannot be definitively ruled out. In the case of Dy2 and Dy4, their significant geometrical distortions best correlate to Johnson gyrofastigium (D2d) and biaugmented trigonal prism (C2v) arrangements, respectively (Table S3). It is also important to


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note that four non-coordinating nitrate anions occupy the lattice to balance the charges. These are stabilized by a number of hydrogen bonds with the vht2‒ ligands.

Figure 1. Polymetallic core (top) and partially labelled molecular structure (bottom) of 1, displaying the two cubanes linked by a µ4‒O2- moiety (shown in black bonds). Colour code: yellow (Dy), red (O), blue (N), grey (C). Hydrogen atoms are omitted for clarity.


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As previously mentioned, the degree of distortion on the lanthanide cubane has been shown to be directly correlated to the observed magnetic behaviour. Of particular interest are the Dy-O-Dy angles that form the cubane-core structure, where the larger the deviation from an ideal 90o, the more pronounced is the slow relaxation of the magnetization. In the present case, the Dy-O-Dy angles vary from 97.2(0) to 112.4(8)°. This upper limit represents the most significant distortion observed among similar cubane-type structures.19‒22,26‒27 Consequently, we were intrigued by the potential of 1, which contains two significantly distorted cubanes bridged by a µ4-O2‒ moiety, to exhibit SMM-like properties. The static (dc) magnetic susceptibility of 1 was probed in the temperature range of 1.9300 K along with an applied dc field of 1000 Oe. The resulting temperature dependence of the

χT curve can be visualized in Figure 2. The room temperature χT value of 112.3 cm3 K mol-1 is in good agreement with the theoretical value of 113.36 cm3 K mol-1 for eight non-interacting DyIII ions (DyIII: 6H15/2, S = 5/2, L = 5, g = 4/3, χT = 14.17 cm3 K mol-1). Upon lowering the temperature, the χT product continuously decreases, and quickly declines below 25 K reaching a value of 80.0 cm3 K mol-1. This decrease can be attributed to the thermal depopulation of excited Stark levels by crystal field splitting and/or antiferromagnetic coupling between the DyIII metal centers. While this behaviour is commonly observed in lanthanide cubane-containing complexes,19‒21,26 there are a few examples of dominant intracluster ferromagnetic interactions.22,27 Thus, even if such interactions are likely to be very weak, the structural distortions of the cubane can influence the magnetic orbital overlap of the Dy ions, resulting in notably different magnetic interactions. In addition to the magnetic susceptibility data, the field dependence of the magnetization was measured at temperatures between 1.8 and 7 K. The M


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versus H plot displays a rapid increase in magnetization up to 1 T where the curves begin to approach saturation (Figure 2, inset). At saturation the curves reach a magnetization value of 40.1 µB which is in strong agreement with the expected value of 41.8 µB for eight uncorrelated DyIII ions. The corresponding M vs. H/T curves deviate from one another, indicating the presence of non-negligible magnetic anisotropy and/or low lying excited states (Figure S1).

Figure 2. Temperature dependence of the χT product at 1000 Oe; Inset: M vs. HT-1 plot from 1.8 to 7 K.

In order to assess the relaxation dynamics of the complex, alternating current (ac) susceptibility measurements were performed with an ac field of 3.78 Oe oscillating at frequencies up to 1488 Hz. We have measured the frequency-dependence of the in-phase (χ′)


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and out-of-phase (χ″) magnetic susceptibilities under zero applied dc fields, where clear peaks are seen to shift to lower frequencies as the temperature is decreased, indicative of slow magnetic relaxation (Figure 3, top). In-phase magnetic susceptibility plots can be found in Figure S2. As an initial investigation into the dynamics of spin reversal, we first fit the shifting peak maxima with an Arrhenius equation (τ = τ0exp(Ueff/kBT), which yielded a small magnetization reversal barrier (Ueff/kB) of 7.8(1) K and a pre-exponential factor (τ0) of 3.842(9) × 10-5 s (Figure S3). The pre-exponential factor is slightly outside the range expected for a typical SMM (10-6-10-10), suggesting that the reversal does not primarily arise from an Orbach mechanism (vide infra). In order to suppress a plausible spin relaxation mechanism occurring via quantum tunnelling of the magnetization, we have also performed frequency-dependent ac magnetic susceptibility measurements between fields of 0 and 2250 Oe to determine the optimal applied dc field, which was found to be Hdc = 1500 Oe (Figure S4). An out-of-phase signal, with shifting of the peak maxima was observed for the resulting data (Figure 3, bottom), and afforded an energy barrier of 20.4(7) K, with τ0 = 6.344(6) × 10-6 s (Figure S5). Performing such a series of measurements in which we observe the χ″ signals under various external dc fields also allows us to evaluate the effect of an applied dc field on the magnetization reversal. Subsequent fitting of this data to a generalized Debye model permits the extraction of the relaxation rate τ-1 which can then be plotted as τ-1 vs. H (Figure S6).28,29 The latter plot exhibits a clear dependence of τ-1 with an applied dc field, and thus suggests the participation of additional relaxation mechanisms such as quantum tunneling and a direct process. The data were analyzed using an equation encompassing terms for the direct process (AH4T), resonance tunneling (B1/1+B2H2) and a constant that includes the terms for thermal relaxation processes (D).28,30 The best fit yielded values of A = 7.19(2) × 10-11 s-1 Oe-4 K-1, B1 = 1.2(8) × 103 s-1, B2 = 1.0(5) × 10-3 Oe-2 and D = 1.1(9) × 103 s-1.


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These results provide an indication that the direct process, even at high fields, contributes minimally to the relaxation, and that quantum tunneling of the magnetization (QTM) is indeed active. Due to the weak barrier, large τ0 values and the minimal contribution from a direct process we have also investigated the possibility of additional relaxation processes, including Raman. By attempting to fit the magnetic data to an equation encompassing all three processes (τ-1 = τ01 kT Ueff

e /

+ CTn + τ-1tunnel), namely Orbach, Raman and QTM, we found that the term accounting

for the thermally-activated Orbach mechanism tended towards very small values and was therefore removed, thereby also avoiding overparameterization. The best fit yielded τtunnel = 4.709(0) × 10-4 s, C = 39.5(2) s-1 K-n, and n = 2.71(7) for the zero field data, and τtunnel = 2.755(3) × 10-3 s, C = 2.0(2) s-1 K-n, and n = 4.31(1) under 1500 Oe (Figure S7). Generally, Kramers ions have a value of n = 9, however n values between 1 and 6 have also been observed.31,32 Moreover, the fit parameters corroborate the fact that QTM is reduced by the application of a static field (1500 Oe), as can be seen in the increase of the relaxation time for quantum tunneling. While the complexity of the octanuclear cluster renders the precise analysis of the relaxation dynamics difficult, it is plausible that Raman and QTM processes account for a significant portion of the relaxation, however a small contribution from thermally-activated and direct relaxation mechanisms cannot be definitively ruled out. Nevertheless, we provide an overview of the dominant pathways responsible for magnetic relaxation, which has been evaluated with difficulty in complexes featuring a [Ln4III] cubane core due to the weak ac behaviour. In the present case, slow magnetic relaxation, while weak, is evident with clear full peaks observed up to 7 K, giving a large range of data to extract key characteristic SMM parameters. The graphical representation of χ″ vs. χ′ (Cole-Cole plot) for 1 under zero applied dc fields was fit using a generalized Debye


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model, and also suggests the possibility of multiples relaxation processes (Figure S8). The extracted values for the α parameter are listed in Table S4.


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Figure 3. Frequency dependence of the out-of-phase, χ″, magnetic susceptibility under applied dc fields of 0 (top) and 1500 Oe (bottom) for complex 1. The solid lines are the best fits to the generalized Debye equation at various temperatures.

While structural distortions can affect the magnetic orbital overlap of the DyIII ions, as previously mentioned, the topological arrangement of the local anisotropy tensors and their relative orientations can also be drastically influenced through changes in the Dy‒OH‒Dy angles. In order to evaluate bulk cluster anisotropy, the alignment of the anisotropy axes was determined using Magellan.33 Electrostatic modelling of the lowest lying Kramers doublets for each DyIII ion reveals that the anisotropy axes of Dy1 and Dy3 align with the most adjacent phenoxide donor atoms, O9 and O39, respectively, while the axes of Dy2 and Dy4 are oriented towards the central O2- bridging ligand (O67) (Figure 4). At first glance, it appears that each vector can potentially be cancelled out, which may explain the relatively weak ac behaviour originating from pure lanthanide cubanes. Upon closer inspection however, we see that two anisotropy axes that appear to be in an antiparallel alignment are in fact slightly tilted from one another, likely giving rise to spin canting. More precisely, the calculated angle between two opposing vectors are in the range of 147‒166o, confirming the overall anisotropy of the system. Thus, we can rationalize that a more significant distortion of the cubane results in improved slow magnetic relaxation due to the lesser degree of antiparallelism in the anisotropy axes.


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Figure 4. Orientation of the magnetic anisotropy of the mj = ±15/2 states of the DyIII ions in 1. We have successfully isolated a novel cluster topology, in which two DyIII cubane cores are linked through an unusual µ4-oxide moiety. The resulting structural distortions induced by this bridging unit lead the largest Dy-O-Dy angles within a [Dy4(OH)4] core. Consequently, we have observed unambiguous frequency-dependent ac magnetic susceptibility in pure a DyIII cubane arrangement, which generally elicits poor slow relaxation of magnetization. We have attempted to fit multiple relaxation processes, however it is clear that Raman and QTM are primary contributors to the magnetization relaxation, rather than a thermally-activated Orbach process. Thus, we were able to clearly ascertain the key parameters that influence the energy barrier to relaxation of the magnetization. This study exemplifies the importance of structure-property relationships for enhancing the performance of SMMs, which becomes increasingly difficult to control in high nuclearity systems, even when considering weak exchange interactions. While the resulting slow magnetic relaxation in 1 is relatively weak, we can apply the underlying principles in this work towards the rational design of highly-performing lanthanide magnetic nanomaterials.


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ASSOCIATED CONTENT Supporting Information Materials and instrumentation, ligand and complex synthesis, single-crystal X-ray crystallography, powder X-ray diffraction, select bond distances and angles, SHAPE constants and additional SQUID magnetometry data.

ACCESSION CODES CCDC 1542459 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Author Contributions ‡T. L. and G. B. contributed equally to this work. Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENT The authors thank the University of Ottawa, NSERC (Discovery, RTI and PGS-D grants) and CFI for their financial support. REFERENCES (1) Guo, F.-S.; Day, B. M.; Chen, Y.-C.; Tong, M.-L.; Mansikkamäki, Layfield, R. A. Angew. Chem., Int. Ed. 2017, 56, DOI: 10.1002/anie.201705426. (2) Chen, Y. C.; Liu, J. L.; Ungur, L.; Liu, J.; Li, Q.-W.; Wang, L.-F.; Ni, Z.-P.; Chibotaru, L. F.; Chen, X.-M.; Tong, M.-L. J. Am. Chem. Soc. 2016, 138, 2829. (3) Meihaus, K. R.; Long, J. R. J. Am. Chem. Soc. 2013, 135, 17952. (4) Larionova, J.; Gross, M.; Pilkington, M.; Andres, H.; Stoeckli-Evans, H; Güdel, H. U; Decurtins, S. Angew. Chem., Int. Ed. 2000, 39, 1605. (5) Ako, A. M.; Hewitt, I. J.; Mereacre, V.; Clérac, R.; Wernsdorfer, W.; Anson C. E.; Powell, A. K. Angew. Chem., Int. Ed. 2006, 118, 5048. (6) Stamataos, T. C.; Abboud, K. A.; Wernsdorfer, W.; Christou, G. Angew. Chem., Int. Ed. 2007, 119, 902. (7) Pedersen, K. S.; Bendix, J.; Clérac, R. Chem. Commun. 2014, 50, 4396. (8) Beltran, L. M. C.; Long, J. R. Acc. Chem. Res. 2005, 38, 325. (9) Zhang, P.; Guo, Y.-N.; Tang, J. Coord. Chem. Rev. 2013, 257, 1728. (10) Kitos, A. A.; Papatriantafyllopoulou, C.; Tasiopoulos, A. J.; Perlepes, S. P.; Escuer, A.; Nastopoulos, V. Dalton Trans. 2017, 46, 3240. (11) Schmitt, W.; Murugesu, M.; Goodwin, J. C.; Hill, J. P.; Mandel, A.; Bhalla, R.; Anson, C. E.; Heath, S. L.; Powell, A. K. Polyhedron 2001, 20, 1687.


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(12) Jiang, Y.; Brunet, G.; Holmberg, R. J.; Habib, F.; Korobkov, I.; Murugesu, M. Dalton Trans. 2016, 45, 16709. (13) Habib, F.; Brunet, G.; Vieru, V.; Korobkov, I.; Chibotaru, L. F.; Murugesu, M. J. Am. Chem. Soc. 2013, 135, 13242. (14) Long, J.; Habib, F.; Lin, P.-H.; Korobkov, I.; Enright, G.; Ungur, L.; Wernsdorfer, W.; Chibotaru, L. F.; Murugesu, M. J. Am. Chem. Soc. 2011, 133, 5319. (15) Lacelle, T.; Brunet, G.; Pialat, A.; Holmberg, R. J.; Lan, Y.; Gabidullin, B.; Korobkov, I.; Wernsdorfer, W.; Murugesu, M. Dalton Trans. 2017, DOI: 10.1039/C6DT04413A. (16) Galloway, K. W.; Whyte, A. M.; Wernsdorfer, W.; Sanchez-Benitez, J.; Kamenev, K. V.; Parkin, A.; Peacock, R. D.; Murrie, M. Inorg. Chem. 2008, 47, 7438. (17) Halcrow, M. A.; Sun, J.; Huffman, J. C.; Christou, G. Inorg. Chem. 1995, 34, 4167. (18) Yang, E.-C.; Wernsdorfer, W.; Hill, S.; Edwards, R. S.; Nakano, M.; Maccagnano, S.; Zakharov, L. N.; Rheingold, A. L.; Christou, G.; Hendrickson, D. N. Polyhedron 2003, 22, 1727. (19) Gao, Y.; Xu, G.-F.; Zhao, L.; Tang, J.; Liu, Z. Inorg. Chem. 2009, 48, 11495. (20) Ke, H.; Gamez, P.; Zhao, L.; Xu, G.-F.; Xue, S.; Tang, J. Inorg. Chem. 2010, 49, 7549. (21) Yi, X.; Bernot, K.; Calvez, G.; Daiguebonne, C.; Guillon, O. Eur. J. Inorg. Chem. 2013, 5879. (22) Miao, Y.-L.; Liu, J.-L.; Li, J.-Y.; Leng, J.-D.; Ou, Y.-C.; Tong, M.-L. Dalton Trans. 2011, 40, 10229. (23) Savard, D.; Lin, P.-H.; Burchell, T. J.; Korobkov, I.; Wernsdorfer, W.; Clérac, R.; Murugesu, M. Inorg. Chem. 2009, 48, 11748. (24) Zhang, J.; Zhang, Z.; Chen, Z.; Zhou, X. Dalton Trans. 2012, 41, 357. (25) Casanova, D.; Llunel, M.; Alemany, P.; Alvarez, S. Chem. ‒ Eur. J. 2005, 11, 1479.


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(26) Liu, C.-M.; Zhang, D.-Q.; Hao, X.; Zhu, D.-B. Cryst. Growth Des. 2012, 12, 2948. (27) Yao, R.-X.; Xu, X.; Zhang, X.-M. RSC Adv. 2014, 4, 53954. (28) Wada, H.; Ooka, S.; Iwasawa, D.; Hasegawa, M.; Kajiwara, T. Magnetochemistry 2016, 2, 43. (29) Amjad, A.; Figuerola, A.; Caneshi, A.; Sorace, L. Magnetochemistry 2016, 2, 27. (30) Abragam, A.; Bleany, B. Electron Paramagnetic Resonance of Transition Metal Ions, Oxford University Press: Oxford, UK, 1970, 60-74 and 555-560. (31) Calahorro, A. J.; Oyarzabal, I.; Fernández, B.; Seco, J. M.; Tian, T.; Fairen-Jimenez, D.; Colacio, E.; Rodríguez-Diéguez, A. Dalton Trans. 2016, 45, 591. (32) Pugh, T.; Chilton, N. F.; Layfield, R. A. Angew. Chem. Int. Ed. 2016, 55, 11082. (33) Chilton, N.; Collison, D.; McInnes, E.; Winpenny, R.; Soncini, A. Nat. Commun. 2013, 4, 2551.

SYNOPSIS We describe the self-assembly of a novel cluster architecture resulting in two DyIII cubanes being linked by a µ4-O2‒ moiety. The dynamic magnetic properties of the crystalline complex reveal single-molecule magnet behaviour without the application of an external field.


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For Table of Contents Use Only

An Unprecedented Octanuclear DyIII cluster Exhibiting Single-Molecule Magnet Behaviour Thomas Lacelle, ‡ Gabriel Brunet, ‡ Rebecca J. Holmberg, Bulat Gabidullin, and Muralee Murugesu* Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie, Ottawa, ON, K1N 6N5, Canada. ‡ Both authors contributed equally to this work.

We report a unique octanuclear DyIII-based cluster, in which two [Dy4(µ3-OH)4]8+ cubanes are linked through a central µ4-O moiety. The resulting distortion of the cubane cores leads to clear slow relaxation of the magnetization under zero applied field; a behaviour which has been observed with difficulty in LnIII-based cubane systems.


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Unprecedented Octanuclear DyIII Cluster ... - University of Ottawa

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