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Hydrolytic synthesis of novel lanthanide(III) complexes with pyridine-2,6-dicarboxylic acid: Characterization of the structure and the physical properties
Journal of Molecular Structure 1079 (2015) 54–60
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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Hydrolytic synthesis of novel lanthanide(III) complexes with pyridine-2, 6-dicarboxylic acid: Characterization of the structure and the physical properties Nuša Hojnik a,⇑, Matjazˇ Kristl a, Amalija Golobicˇ b, Zvonko Jaglicˇic´ c, Miha Drofenik a,d a
University of Maribor, Faculty of Chemistry and Chemical Engineering, Smetanova 17, SI-2000 Maribor, Slovenia University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškercˇeva 5, SI-1000 Ljubljana, Slovenia Institute of Mathematic, Physics and Mechanics, Jadranska 19, SI-1000 Ljubljana, Slovenia and Faculty of Civil and Geodetic Engineering, Jamova 2, SI-1000 Ljubljana, Slovenia d Jozˇef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia b c
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Two new complexes were
hydrolytically synthesized in aqueous solutions at basic pH. Crystal structures are identified as Na3[Ln(Pydc)3]14H2O. Coordination polyhedron is a tricapped trigonal prism with O atoms in the corners. Mononuclear rare-earth ions display paramagnetic behavior.
a r t i c l e
i n f o
Article history: Received 13 May 2014 Received in revised form 18 July 2014 Accepted 11 September 2014 Available online 21 September 2014 Keywords: Lanthanides Pyridine-2,6-dicarboxylic acid Magnetic properties X-ray structure determination Hydrogen bonds
⇑ Corresponding author. E-mail address: [email protected] (N. Hojnik). http://dx.doi.org/10.1016/j.molstruc.2014.09.029 0022-2860/Ó 2014 Published by Elsevier B.V.
a b s t r a c t The coordination compounds of pyridine-2,6-dicarboxylic acid and two lanthanide(III) ions, Ho3+ and Dy3+, were hydrolytically synthesized in aqueous solutions at a slightly basic pH, and then characterized by thermogravimetric analysis, IR spectroscopy, magnetic measurements as well as X-ray powder and single-crystal diffraction analysis. The elemental analyses were performed to check the purity of the compounds. The formula for these compounds is identified as Na3[Ln(Pydc)3]14H2O (Ln = Ho, 1; Ln = Dy, 2) in agreement with the X-ray structural analysis and all the other experimental data. The absence of the 1709 cm1 band corresponding to m(C@O) in the IR spectra of the compounds evidences the deprotonating of the carboxyl group. The very strong inductive effect of the metal ion that is readily coordinated by the carboxylate group of the zwitterionic ligand is responsible for the formation of the product. The single-crystal X-ray structural analysis revealed that compounds 1 and 2 are isostructural. Their structure can be described as interchanging layers of complex anions [Ln(Pydc)3]3 (Ln = Ho and Dy for 1 and 2, respectively) and layers of hydrated sodium cations. In complex anions the holmium and dysprosium atoms are coordinated by three crystallographically independent pyridinedicarboxylate ligands in tridentate-chelate mode, via one O atom of both carboxylate groups and the ring N atom. The coordination number is nine and the coordination polyhedron is a tricapped trigonal prism with O atoms at the corners. Ó 2014 Published by Elsevier B.V.
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Introduction Pyridinedicarboxylic acid, which can act as a potential scorpionate ligand [1–3], exists in six isomeric forms, i.e., (pyridine-2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-dicarboxylic acid). These isomers can play an important role in building crystal structures. In addition, structural studies of these complex compounds in connection with the chemical systematics of these coordination compounds are potentially valuable in various fields, e.g., in host guest chemistry and crystal engineering, luminescence, catalysis, molecular magnetism, sensors, and nonlinear optics, etc. [4–13]. Here we report on the synthesis and provide a full characterization of newly prepared, mononuclear complexes of pyridine-2,6-dicarboxylic acid (Pydc) and the lanthanide(III) ions Ho3+and Dy3+. The carboxylate groups at the 2- and 6-positions of the pyridine ring can be fully or partially deprotonated for coordination to metals. The carboxylate groups bearing various bridging modes can efficiently induce a magnetic exchange. The geometry of these groups can possess three potential coordinating [N,O,O] donor sites to form stable chelates [14] with various metal ions, functioning as a bidentate [15,16], tridentate [17,18], or bridging ligand [19,20] in complexes. During a more general study we investigated Pydc, which is known to be able to act as a tridentate ligand. The reason for this is probably related to the position of the carboxylate groups, which are sufficiently close to the nitrogen in the pyridinedicarboxylic acid. The control of certain reaction parameters, such as the pH value, the solvent concentration, the molar ratio, and the geometry and flexibility of the ligands, plays a crucial role in the structure-formation processes and the reaction yield [21,22]. A survey of recent literature indicates that a ligand-controlled hydrolysis was successfully used in the structural characterization of water clusters in organic as well as metal-organic compounds. Some of these complexes have great potential for further applications to generate mixed ligands [23–25]. All the compounds described in this paper contain a large number of crystallization water molecules via extensive OAHAO interactions. Similar compounds prepared under low-pH conditions and characterized crystallographically have already been published [26–28].
Experimental part Synthesis All the reactants of A.R. grade were obtained commercially and used without further purification.
Na3[Ho(Pydc)3]14H2O 1 During the two-step synthesis the ligand was first converted, with the addition of NaOH, to its mono-anionic form, the pyridyl and carboxylate groups of which are both capable of metal coordination. The lanthanide salt solution was prepared by dissolving HoCl36H2O (0.5 mmol) in 10 mL of water, and a freshly prepared aqueous solution of NaOH (1.0 M) was added with stirring to the point of precipitation. A ligand solution was prepared by dissolving pyridine-2,6-dicarboxylic acid (1 mmol) in 10 mL of water and adding an aqueous solution of NaOH (1.0 M). The pH of the ligand solution was adjusted to above 8. This solution was then added dropwise to the solution of lanthanide salt. The resulting mixture was stirred at 90 °C for 1 h and then filtered while hot. Brownish-pink single crystals, suitable for analysis, were obtained by the slow evaporation of the solvent over a period of several weeks. Yield: 48%. Elemental analysis (%) calcd. for Na3[Ho(Pydc)3]14H2O (Mr = 981.44): C, 25.53; H, 3.79; N, 4.25. Found: C, 25.70; H, 3.77; N, 4.27.
Na3[Dy(Pydc)3]14H2O 2 This complex was prepared with the procedure described for 1 using Dy(NO3)3xH2O (0.5 mmol) and pyridine-2,6-dicarboxylic acid (1 mmol). Colorless single crystals, suitable for analysis, were obtained. Yield: 45%. Elemental analysis (%) calcd. for Na3[Dy(Pydc)3]14H2O (Mr = 979.01): C, 25.59; H, 3.77; N, 4.26. Found: C, 25.76; H, 3.78; N, 4.29.
Thermal and elemental analysis A thermogravimetric analysis was carried out on a METTLER TGA/SDTA851e system in the temperature range 30–1100 °C in a nitrogen flow (100 mL/min) with a heating rate of 10 K/min using Al2O3 crucibles. Elemental analyses were carried out on a Perkin-Elmer 2400 CHN analyzer at the University of Ljubljana.
XRPD analysis X-ray powder-diffraction data for the products of the thermal decomposition were collected with an AXS-Bruker/Siemens/ D5005 diffractometer using Cu Ka radiation at 293 K. Finely ground samples were placed on a Si single-crystal holder and measured in the range 10° < 2h < 70°. The diffraction data was analyzed using the EVA program and the PDF Datafile.
IR analysis The experimental IR spectra were recorded with a Shimadzu IRAffinty-1 spectrometer in the range 4000–400 cm1 using the KBr pellet method. The data were collected with Shimadzu IRsolution version 1.50. Table 1 Summary of crystallographic data and structure analyses. Compound
1
2
Empirical formula Mr Cell setting, space group Temperature (K) a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dx (Mg m3) Radiation type, wavelength (Å) l (mm1) F(0 0 0) Crystal form, color Crystal size (mm) Absorption correction No. of measured and indep. reflec. No of (F2 > 2.0r(F2)) reflections Rint H range (°) Full-matrix refinement on R[F2 > 2r(F2)], wR(F2), S Dqmax, Dqmin (e Å3) No. of parameters No. of contributing reflections
Na3[Ho(Pydc)3]14H2O 981.44 Triclinic, P-1, No. 2 150(2) 10.2390(3) 10.9385(3) 17.1431(5) 74.429(3) 77.191(3) 72.869(3) 1746.15(9) 2 1.867 Mo Ka, 0.71073
Na3[Dy(Pydc)3]14H2O 979.01 Triclinic, P-1, No. 2 293(2) 10.3188(3) 10.9967(3) 17.2589(4) 74.635(2 77.397(2) 72.735(2) 1782.50(8) 2 1.824 Mo Ka, 0.71073
2.407 984 Prism, brownish pink 0.40 0.35 25 Multiscan 17,475, 9076
2.235 982 Prism, colorless 0.38 0.22 18 Multiscan 17,945, 9249
7777
6748
0.029 2.8–27.5 F2 0.039, 0.092, 1.10 3.46, 1.45 494 9076
0.033 2.7–27.5 F2 0.034, 0.089, 1.07 0.93, 0.87 494 9249
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N. Hojnik et al. / Journal of Molecular Structure 1079 (2015) 54–60
Fig. 1. Mercury drawing of crystal packing of molecules in 1 viewed along the a axis. Hydrogen atoms are omitted for clarity. The red, blue, black, purple and green circles represent the O, N, C, Na and Ho atoms, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Fig. 3. ORTEP drawing of coordination anion of 2. Ellipsoids are represented at the 50% probability level.
Fig. 2. ORTEP drawing of coordination anion of 1. Ellipsoids are represented at the 50% probability level.
Magnetic measurements The magnetic properties of the compounds were measured using a Quantum Design MPMS-XL-5 susceptometer equipped with a SQUID detector. The data were collected between 2 K and 300 K at a magnetic field of 0.1 T. The measured data were corrected for the sample-holder contribution and for the temperature-independent Larmor diamagnetism of the core electrons obtained from Pascal’s tables.
X-ray structure determination Single-crystal diffraction data for both compounds were collected on an Agilent SuperNova dual-source diffractometer with an Atlas detector using Mo Ka radiation. The temperature of the data collection was 150(2) and 293(2) K for 1 and 2, respectively. The data were processed using CrysAlis PRO software [29]. The structure was, in both cases, solved with direct methods using SIR97 [30]. A full-matrix, least-squares refinement on F2 was employed with anisotropic temperature-displacement parameters for the non-hydrogen atoms. The exceptions were the oxygen atoms of disordered water molecules, which were refined with isotropic
Fig. 4. Mercury drawing showing a layer consisting of hydrated sodium cations in 1. Hydrogen atoms are omitted for clarity. The red and purple circles represent the O and Na atoms, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
displacement parameters. The H atoms on the aromatic rings were placed at the calculated positions and treated as riding, with CAH 0.93 Å and Uiso(H) = 1.2Ueq(C). The H atoms of the water molecules coordinated to the Na1, Na2 and Na3 (O13–O18) were located using a difference Fourier map. Their parameters were not refined. The H atoms of the remaining water molecules (coordinated to the disordered sodium cations (Na4 and Na5)) were not located. The Na3, Na5 and O atoms labeled with three digits (from O221 to O262) have an occupancy of 0.5. The description of the disorder is given in the discussion section. The crystal data and the refinement parameters of the compounds 1 and 2 are listed in Table 1. SHELXL97 software [31] was used for the structure refinement and interpretation. Drawings of the structures were produced using ORTEPIII [32] and Mercury [33].
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N. Hojnik et al. / Journal of Molecular Structure 1079 (2015) 54–60 Table 2 Geometrical parameters of hydrogen bonds in 1 and 2. Na3[Ho(Pydc)3]14H2O
Na3[Dy(Pydc)3]14H2O
DAH A
DAH
H A
D A
O13AH131 O231xii O13AH131 O232xii O13AH132 O221vii O13AH132 O222vii O14AH141 O1xi O14AH142 O251xiii O14AH142 O252xiii O15AH151 O261ix O15AH151 O262ix O15AH152 O3vii O16AH162 O241iv O16AH162 O242iv O17AH171 O8vii O17AH172 O9i O18AH181 O2ii O18AH182 O11 O19 O5vii O19 O232vii O20 O7vii O20 O262iii O21 O15v O21 O20iv O221 O19vi O221 O251 O222 O252 O222 O19vi O231 O6 O232 O19viii O241 O10x O241 O12xiv O242 O21 O251 O4iii O251 O6vii O261 O17iii O262 O20iv
0.94 0.94 0.91 0.91 0.87 0.88 0.88 0.82 0.82 0.81 0.91 0.91 0.91 0.78 0.81 0.83
1.88 2.00 1.92 1.88 2.28 1.85 1.97 2.14 1.96 2.12 1.98 1.81 1.86 2.01 1.99 1.93
2.744(11) 2.793(9) 2.760(15) 2.773(11) 3.041(5) 2.706(9) 2.850(1) 2.941(8) 2.752(8) 2.898(4) 2.819(8) 2.704(8) 2.748(4) 2.758(5) 2.767(4) 2.732(4) 2.805(5) 2.875(9) 2.778(5) 2.794(8) 2.818(6) 2.788(6) 2.675(15) 2.722(16) 2.625(14) 2.895(12) 2.895(11) 2.807(9) 2.745(8) 2.894(8) 2.605(8) 2.849(9) 2.866(9) 2.733(8) 2.780(9)
153 142 153 167 146 162 176 166 162 160 154 171 167 161 161 165
DAH
H A
D A
0.99 0.99 0.97 0.97 0.89 0.90 0.90 0.91 0.91 0.87 0.84 0.84 0.92 0.97 0.88 0.95
1.85 2.10 1.83 1.83 2.31 2.02 2.05 2.10 1.92 2.08 2.08 1.94 1.89 1.83 1.92 1.81
2.730(12) 2.887(10) 2.792(18) 2.789(13) 3.088(4) 2.760(13) 2.881(15) 2.980(10) 2.776(9) 2.933(4) 2.853(9) 2.729(9) 2.767(4) 2.783(4) 2.803(4) 2.747(4) 2.815(6) 2.866(10) 2.781(5) 2.806(10) 2.833(6) 2.818(6) 2.700(18) 2.691(19) 2.723(17) 2.906(13) 2.943(11) 2.793(10 2.740(9) 3.009(9) 2.623(9) 2.848(13) 3.043(12) 2.743(10) 2.812(10)
146 135 168 167 146 138 153 162 157 170 153 158 159 166 177 169
Symmetry codes: i x, y + 1, z. ii x, y, z – 1. iii x, 1y, z. iv x 1, y + 1, z. v x 1, y + 1, z. vi x 1, y + 1, z + 1. vii x, y, z. viii x + 1, y 1, z – 1. ix x, y 1, z. x x + 1, y, z. xi x, y 1, z – 1. xii x + 1, y 1, z – 1. xiii x, y 1, z – 1. xiv x + 1, y1, z.
Results and discussions Crystal and molecular structure The compounds 1 and 2 are isostructural. Their structure can be described as interchanging layers of complex anions [Ln(Pydc)3]3 (Ln = Ho and Dy for 1 and 2, respectively) and layers of hydrated sodium cations, stacked along the 0 1 1 direction (diagonal of bc face), as shown in Fig. 1. The anions of 1 and 2 are shown in Figs. 2 and 3, respectively. They are mononuclear complexes where the Ln3+ central ion is nine coordinated by three crystallographically independent pyridinedicarboxylate ligands in tridentate-chelate mode, via one O atom of both the carboxylate group and the ring N atom. The coordination polyhedron is a tricapped trigonal prism with O atoms at the corners. The coordination bond lengths in 1 are slightly shorter, in comparison with 2, which is in accordance with the slightly smaller ionic radius of Ho3+ (1.072 Å) in comparison
with Dy3+ (1.083 Å). The LnAO bond distances are slightly longer than those of the LnAN. Each Pydc ligand is, through another O atom of both carboxylate groups, bonded to sodium cations from the neighboring cationic layer. The O4, O6, O10 and O12 are bonded to two sodium cations as bridges. The O2 and O8 are bonded only to one sodium cation, Table 3 Values of some bands in the IR absorption spectrum of compounds, 1, 2. 1, cm1
2, cm1
Assignment
732(s) 767(m) 1435(s) 1585(m) 1624(s) 2364(m) 3093(m) 3417(m)
732(s) 773(m) 1439(s) 1585(m) 1624(s) 2364(m) 3093(m) 3414(m)
d(CAH) d(OACAO) ms(COO) m(CAC), m(CAN) mas(COO) m(NAH) ms(H2O) mas(H2O)
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Fig. 5. TGA–DTG curves showing the decomposition of Na3[Ho(Pydc)3]14H2O at a heating rate of 10 (K/min) in a nitrogen atmosphere.
Fig. 6. TGA–DTG curves showing the decomposition of Na3[Dy(Pydc)3]14H2O at a heating rate of 10 K/min in a nitrogen atmosphere.
while the other lone pair of electrons are acceptors of the intermolecular OAH O hydrogen bond donated by water molecules (O17 and O18) from the hydrated cationic layer. The layer consisting of hydrated sodium cations is shown in Fig. 4. There are five crystallographically independent sodium cations. All of them are six coordinated with a distorted octahedral coordination. The Na1 and Na2 lie on non-equivalent centers of inversion. On the equatorial positions of the coordination octahedron of the Na1, Na2 and Na3 there are water molecules (O13, O14, O15, O16, O17 and O18) and on the axial positions there are carboxylic O atoms from complex anions (O2, O4, O8 and O10). These octahedrons are, via two bridging water molecules, coordinated at opposite corners, connected in chains along the 0 1 1 direction. Another pair of opposite water molecules (O13 and O15) in the Na1 and Na2 octahedrons are H-bonded to two water molecules. The geometry of the H-bonds is presented in Table 3. The Na4 and Na5 are disordered over two positions with a 0.5 occupancy. They are coordinated with three water molecules and three carboxylic O atoms from three different discrete complexes. The fully occupied O17 and O18 atoms belong to water molecules that are bridges with the Na1 and Na2 octahedrons. On the other hand, the atoms O232, O242, O252 and O262 have a 50% occupancy and correspond to water molecules that are terminally bonded to the Na4 and Na5. They are additionally H-bonded to uncoordinated water molecules (O19, O20, O21, O221 and O222).
In the case of empty sites of Na4 or Na5 there are water molecules with 50% occupied O atoms O231, O241, O251 and O261 (with a different position and H-bonding scheme in comparison to the alternative O232, O242, O252 and O262). From the O O contact distances (Table 2) it can be concluded that they are donors of Hbonds to carboxylate O atoms and not to uncoordinated water molecules. In this way, a quite complicated but electro-neutral and stable structure is built. Thermogravimetric measurements The TGA and DTG curves of the Na3[Ho(Pydc)3]14H2O (Fig. 5) and Na3[Dy(Pydc)3]14H2O (Fig. 6) show that all the obtained complexes of pyridine-2,6-dicarboxylic acid are hydrated compounds that are stable at room temperature. The results for the thermal analysis confirmed the data obtained from the elementary analysis. The complexes of holmium and dysprosium contain 14 molecules of water. The amount of water was determined from the thermogravimetric curves. Under our experimental conditions, each complex is stable up to 40 °C and undergoes two decomposition steps when heating to 1100 °C. In the first step, the loss of crystal water molecules in a one-stage dehydration process is observed in both title compounds between 40 and 200 °C, with a weight loss of (Dmmeas = 25.2%) for complex 1 and (Dmmeas = 25.4%) for complex 2, which is in good agreement with the value calculated
N. Hojnik et al. / Journal of Molecular Structure 1079 (2015) 54–60
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for the release of the water from the coordination sphere (Dmcalc = 25.7%) for the reaction:
Na3 ½LnðPydcÞ3 14ðH2 OÞ ! Na3 ½LnðPydcÞ3 þ 14H2 O ðLn ¼ Ho;DyÞ Anhydrous lanthanide(III) pyridinedicarboxylates are stable up to 450 °C. Above 450 °C both compounds start to decompose through unstable oxocarbonates [34] to appropriate lanthanide oxides and sodium oxide. This behavior is in agreement with previous findings for related coordination compounds [35,36]. The final products are the stable oxides Ho2O3 and Dy2O3, which were characterized by X-ray powder diffraction. In addition, the amorphous sodium oxide was confirmed by flame reaction. The total measured weight losses for the thermal decomposition of both compounds to oxides are comparable with the calculated values for 1 (Dmcalc = 71.3%) and 2 (Dmcalc = 71.5%).
Fig. 7. Molar susceptibility as a function of temperature measured in a magnetic field of 0.1 T. Inset shows an effective magnetic moment as a function of temperature calculated per magnetic ion.
IR assessments Conclusions A set of characteristic frequency bands for the compounds 1 and 2 were compared with each other as well as with the ligand spectrum, and identified with characteristic vibrational modes of the Pydc molecule, which are listed in Table 3. It is clear that the region 400–4000 cm1 contains many characteristic peaks that can be used for the Pydc identification, as found in the literature [37]. At higher frequencies they are connected with stretching ring vibrations, whereas at lower frequencies they are connected with bending m(OAH) vibrations. The characteristic carboxyl vibrations are found at 1709 cm1 as a very strong absorption band of the m(C@O), and at 1411 and 1300 cm1 for which the former is assigned to the m(CAO) and the latter two to the m(CAC) stretching vibrations. Some peaks were also observed below 990 cm1, and bands of various ring vibrations, i.e., stretching, rocking and wagging, are present. The d(OACAO) in-plane deformation vibration that occurs has a strong sharp band at 752 cm1. Magnetic properties The magnetic properties can be explained by the strong coordination of the carboxylate group to the Ln(III) acceptor and the strong paramagnetic character of the rare-earth ions, which are ideal paramagnetic structural probes in supramolecular complexes and in proteins [38]. At high temperatures the effective magnetic moment peff based on the molecular weight of all the compounds exhibits a constant value, indicating paramagnetic behavior. The susceptibility can be well described by the Curie–Weiss formula (Eq. (1)),
v¼
In conclusion, two water-soluble coordination compounds with the general formula Na3[Ln(Pydc)3]14H2O (Ln = Ho, Dy) have been hydrolytically synthesized in aqueous solutions at slightly basic pH. The thermal decomposition of both compounds was studied by thermogravimetric analysis and X-ray powder diffraction, yielding lanthanide oxides as final products, as well as amorphous sodium oxide, which was confirmed by flame reaction. The magnetic properties can be explained by the strong coordination of the carboxylate group to the Ln(III) acceptor and the strong paramagnetic character of the rare-earth ions. Finally, the crystal structure of the novel Ho and Dy compounds has been determined by single-crystal X-ray analysis, revealing a structure by three crystallographically independent pyridinedicarboxylate ligands in the tridentate-chelate mode, via one O atom of both the carboxylate group and the ring N atom and five crystallographically independent sodium cations. The elemental analyses were performed to check the purity of the compounds and all the measurements showed good agreement with the data obtained from the structural analysis. Acknowledgements We gratefully acknowledge the financial support from the Ministry of Higher Education, Science and Technology of the Republic of Slovenia. We also thank the EN-FIST Centre of Excellence (Ljubljana, Slovenia) for the use of the SuperNova diffractometer. Appendix A. Supplementary material
C ðT hÞ
ð1Þ
where C is the Curie constant. For all compounds the measured C values and the corresponding magnetic moments in Table 4 agree satisfactorily with the expected spin-only moments for the free Ho3+ (10.4 BM) and Dy3+ (10.6 BM), calculated with the Russell-Saunders (L–S) coupling scenario [39]. The slight decrease of the effective magnetic moment with a decreasing temperature for all compounds is due to the temperature-dependent spin–orbit coupling (Fig. 7) that is different for (1) and (2) due to the different spin–orbit coupling parameter k and different quantum numbers L and S.
Details of the crystal data, data collection, and refinement parameters for both compounds have also been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 1001193 and 1001194. A copy of the data can be obtained, free of charge, by applying to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44 (0) 1223 336033 or e-mail: [email protected]). Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.molstruc.2014.09.029. References
Table 4 Curie constants and effective magnetic moments of Ln(III). Sample
Ln3+
C (emu K/mol)
peff (BM)
1 2
Ho Dy
13.0 16.7
10.2 11.5
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Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Hydrolytic synthesis of novel lanthanide(III) complexes with pyridine-2, 6-dicarboxylic acid: Characterization of the structure and the physical properties Nuša Hojnik a,⇑, Matjazˇ Kristl a, Amalija Golobicˇ b, Zvonko Jaglicˇic´ c, Miha Drofenik a,d a
University of Maribor, Faculty of Chemistry and Chemical Engineering, Smetanova 17, SI-2000 Maribor, Slovenia University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškercˇeva 5, SI-1000 Ljubljana, Slovenia Institute of Mathematic, Physics and Mechanics, Jadranska 19, SI-1000 Ljubljana, Slovenia and Faculty of Civil and Geodetic Engineering, Jamova 2, SI-1000 Ljubljana, Slovenia d Jozˇef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia b c
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Two new complexes were
hydrolytically synthesized in aqueous solutions at basic pH. Crystal structures are identified as Na3[Ln(Pydc)3]14H2O. Coordination polyhedron is a tricapped trigonal prism with O atoms in the corners. Mononuclear rare-earth ions display paramagnetic behavior.
a r t i c l e
i n f o
Article history: Received 13 May 2014 Received in revised form 18 July 2014 Accepted 11 September 2014 Available online 21 September 2014 Keywords: Lanthanides Pyridine-2,6-dicarboxylic acid Magnetic properties X-ray structure determination Hydrogen bonds
⇑ Corresponding author. E-mail address: [email protected] (N. Hojnik). http://dx.doi.org/10.1016/j.molstruc.2014.09.029 0022-2860/Ó 2014 Published by Elsevier B.V.
a b s t r a c t The coordination compounds of pyridine-2,6-dicarboxylic acid and two lanthanide(III) ions, Ho3+ and Dy3+, were hydrolytically synthesized in aqueous solutions at a slightly basic pH, and then characterized by thermogravimetric analysis, IR spectroscopy, magnetic measurements as well as X-ray powder and single-crystal diffraction analysis. The elemental analyses were performed to check the purity of the compounds. The formula for these compounds is identified as Na3[Ln(Pydc)3]14H2O (Ln = Ho, 1; Ln = Dy, 2) in agreement with the X-ray structural analysis and all the other experimental data. The absence of the 1709 cm1 band corresponding to m(C@O) in the IR spectra of the compounds evidences the deprotonating of the carboxyl group. The very strong inductive effect of the metal ion that is readily coordinated by the carboxylate group of the zwitterionic ligand is responsible for the formation of the product. The single-crystal X-ray structural analysis revealed that compounds 1 and 2 are isostructural. Their structure can be described as interchanging layers of complex anions [Ln(Pydc)3]3 (Ln = Ho and Dy for 1 and 2, respectively) and layers of hydrated sodium cations. In complex anions the holmium and dysprosium atoms are coordinated by three crystallographically independent pyridinedicarboxylate ligands in tridentate-chelate mode, via one O atom of both carboxylate groups and the ring N atom. The coordination number is nine and the coordination polyhedron is a tricapped trigonal prism with O atoms at the corners. Ó 2014 Published by Elsevier B.V.
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Introduction Pyridinedicarboxylic acid, which can act as a potential scorpionate ligand [1–3], exists in six isomeric forms, i.e., (pyridine-2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-dicarboxylic acid). These isomers can play an important role in building crystal structures. In addition, structural studies of these complex compounds in connection with the chemical systematics of these coordination compounds are potentially valuable in various fields, e.g., in host guest chemistry and crystal engineering, luminescence, catalysis, molecular magnetism, sensors, and nonlinear optics, etc. [4–13]. Here we report on the synthesis and provide a full characterization of newly prepared, mononuclear complexes of pyridine-2,6-dicarboxylic acid (Pydc) and the lanthanide(III) ions Ho3+and Dy3+. The carboxylate groups at the 2- and 6-positions of the pyridine ring can be fully or partially deprotonated for coordination to metals. The carboxylate groups bearing various bridging modes can efficiently induce a magnetic exchange. The geometry of these groups can possess three potential coordinating [N,O,O] donor sites to form stable chelates [14] with various metal ions, functioning as a bidentate [15,16], tridentate [17,18], or bridging ligand [19,20] in complexes. During a more general study we investigated Pydc, which is known to be able to act as a tridentate ligand. The reason for this is probably related to the position of the carboxylate groups, which are sufficiently close to the nitrogen in the pyridinedicarboxylic acid. The control of certain reaction parameters, such as the pH value, the solvent concentration, the molar ratio, and the geometry and flexibility of the ligands, plays a crucial role in the structure-formation processes and the reaction yield [21,22]. A survey of recent literature indicates that a ligand-controlled hydrolysis was successfully used in the structural characterization of water clusters in organic as well as metal-organic compounds. Some of these complexes have great potential for further applications to generate mixed ligands [23–25]. All the compounds described in this paper contain a large number of crystallization water molecules via extensive OAHAO interactions. Similar compounds prepared under low-pH conditions and characterized crystallographically have already been published [26–28].
Experimental part Synthesis All the reactants of A.R. grade were obtained commercially and used without further purification.
Na3[Ho(Pydc)3]14H2O 1 During the two-step synthesis the ligand was first converted, with the addition of NaOH, to its mono-anionic form, the pyridyl and carboxylate groups of which are both capable of metal coordination. The lanthanide salt solution was prepared by dissolving HoCl36H2O (0.5 mmol) in 10 mL of water, and a freshly prepared aqueous solution of NaOH (1.0 M) was added with stirring to the point of precipitation. A ligand solution was prepared by dissolving pyridine-2,6-dicarboxylic acid (1 mmol) in 10 mL of water and adding an aqueous solution of NaOH (1.0 M). The pH of the ligand solution was adjusted to above 8. This solution was then added dropwise to the solution of lanthanide salt. The resulting mixture was stirred at 90 °C for 1 h and then filtered while hot. Brownish-pink single crystals, suitable for analysis, were obtained by the slow evaporation of the solvent over a period of several weeks. Yield: 48%. Elemental analysis (%) calcd. for Na3[Ho(Pydc)3]14H2O (Mr = 981.44): C, 25.53; H, 3.79; N, 4.25. Found: C, 25.70; H, 3.77; N, 4.27.
Na3[Dy(Pydc)3]14H2O 2 This complex was prepared with the procedure described for 1 using Dy(NO3)3xH2O (0.5 mmol) and pyridine-2,6-dicarboxylic acid (1 mmol). Colorless single crystals, suitable for analysis, were obtained. Yield: 45%. Elemental analysis (%) calcd. for Na3[Dy(Pydc)3]14H2O (Mr = 979.01): C, 25.59; H, 3.77; N, 4.26. Found: C, 25.76; H, 3.78; N, 4.29.
Thermal and elemental analysis A thermogravimetric analysis was carried out on a METTLER TGA/SDTA851e system in the temperature range 30–1100 °C in a nitrogen flow (100 mL/min) with a heating rate of 10 K/min using Al2O3 crucibles. Elemental analyses were carried out on a Perkin-Elmer 2400 CHN analyzer at the University of Ljubljana.
XRPD analysis X-ray powder-diffraction data for the products of the thermal decomposition were collected with an AXS-Bruker/Siemens/ D5005 diffractometer using Cu Ka radiation at 293 K. Finely ground samples were placed on a Si single-crystal holder and measured in the range 10° < 2h < 70°. The diffraction data was analyzed using the EVA program and the PDF Datafile.
IR analysis The experimental IR spectra were recorded with a Shimadzu IRAffinty-1 spectrometer in the range 4000–400 cm1 using the KBr pellet method. The data were collected with Shimadzu IRsolution version 1.50. Table 1 Summary of crystallographic data and structure analyses. Compound
1
2
Empirical formula Mr Cell setting, space group Temperature (K) a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dx (Mg m3) Radiation type, wavelength (Å) l (mm1) F(0 0 0) Crystal form, color Crystal size (mm) Absorption correction No. of measured and indep. reflec. No of (F2 > 2.0r(F2)) reflections Rint H range (°) Full-matrix refinement on R[F2 > 2r(F2)], wR(F2), S Dqmax, Dqmin (e Å3) No. of parameters No. of contributing reflections
Na3[Ho(Pydc)3]14H2O 981.44 Triclinic, P-1, No. 2 150(2) 10.2390(3) 10.9385(3) 17.1431(5) 74.429(3) 77.191(3) 72.869(3) 1746.15(9) 2 1.867 Mo Ka, 0.71073
Na3[Dy(Pydc)3]14H2O 979.01 Triclinic, P-1, No. 2 293(2) 10.3188(3) 10.9967(3) 17.2589(4) 74.635(2 77.397(2) 72.735(2) 1782.50(8) 2 1.824 Mo Ka, 0.71073
2.407 984 Prism, brownish pink 0.40 0.35 25 Multiscan 17,475, 9076
2.235 982 Prism, colorless 0.38 0.22 18 Multiscan 17,945, 9249
7777
6748
0.029 2.8–27.5 F2 0.039, 0.092, 1.10 3.46, 1.45 494 9076
0.033 2.7–27.5 F2 0.034, 0.089, 1.07 0.93, 0.87 494 9249
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N. Hojnik et al. / Journal of Molecular Structure 1079 (2015) 54–60
Fig. 1. Mercury drawing of crystal packing of molecules in 1 viewed along the a axis. Hydrogen atoms are omitted for clarity. The red, blue, black, purple and green circles represent the O, N, C, Na and Ho atoms, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Fig. 3. ORTEP drawing of coordination anion of 2. Ellipsoids are represented at the 50% probability level.
Fig. 2. ORTEP drawing of coordination anion of 1. Ellipsoids are represented at the 50% probability level.
Magnetic measurements The magnetic properties of the compounds were measured using a Quantum Design MPMS-XL-5 susceptometer equipped with a SQUID detector. The data were collected between 2 K and 300 K at a magnetic field of 0.1 T. The measured data were corrected for the sample-holder contribution and for the temperature-independent Larmor diamagnetism of the core electrons obtained from Pascal’s tables.
X-ray structure determination Single-crystal diffraction data for both compounds were collected on an Agilent SuperNova dual-source diffractometer with an Atlas detector using Mo Ka radiation. The temperature of the data collection was 150(2) and 293(2) K for 1 and 2, respectively. The data were processed using CrysAlis PRO software [29]. The structure was, in both cases, solved with direct methods using SIR97 [30]. A full-matrix, least-squares refinement on F2 was employed with anisotropic temperature-displacement parameters for the non-hydrogen atoms. The exceptions were the oxygen atoms of disordered water molecules, which were refined with isotropic
Fig. 4. Mercury drawing showing a layer consisting of hydrated sodium cations in 1. Hydrogen atoms are omitted for clarity. The red and purple circles represent the O and Na atoms, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
displacement parameters. The H atoms on the aromatic rings were placed at the calculated positions and treated as riding, with CAH 0.93 Å and Uiso(H) = 1.2Ueq(C). The H atoms of the water molecules coordinated to the Na1, Na2 and Na3 (O13–O18) were located using a difference Fourier map. Their parameters were not refined. The H atoms of the remaining water molecules (coordinated to the disordered sodium cations (Na4 and Na5)) were not located. The Na3, Na5 and O atoms labeled with three digits (from O221 to O262) have an occupancy of 0.5. The description of the disorder is given in the discussion section. The crystal data and the refinement parameters of the compounds 1 and 2 are listed in Table 1. SHELXL97 software [31] was used for the structure refinement and interpretation. Drawings of the structures were produced using ORTEPIII [32] and Mercury [33].
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N. Hojnik et al. / Journal of Molecular Structure 1079 (2015) 54–60 Table 2 Geometrical parameters of hydrogen bonds in 1 and 2. Na3[Ho(Pydc)3]14H2O
Na3[Dy(Pydc)3]14H2O
DAH A
DAH
H A
D A
O13AH131 O231xii O13AH131 O232xii O13AH132 O221vii O13AH132 O222vii O14AH141 O1xi O14AH142 O251xiii O14AH142 O252xiii O15AH151 O261ix O15AH151 O262ix O15AH152 O3vii O16AH162 O241iv O16AH162 O242iv O17AH171 O8vii O17AH172 O9i O18AH181 O2ii O18AH182 O11 O19 O5vii O19 O232vii O20 O7vii O20 O262iii O21 O15v O21 O20iv O221 O19vi O221 O251 O222 O252 O222 O19vi O231 O6 O232 O19viii O241 O10x O241 O12xiv O242 O21 O251 O4iii O251 O6vii O261 O17iii O262 O20iv
0.94 0.94 0.91 0.91 0.87 0.88 0.88 0.82 0.82 0.81 0.91 0.91 0.91 0.78 0.81 0.83
1.88 2.00 1.92 1.88 2.28 1.85 1.97 2.14 1.96 2.12 1.98 1.81 1.86 2.01 1.99 1.93
2.744(11) 2.793(9) 2.760(15) 2.773(11) 3.041(5) 2.706(9) 2.850(1) 2.941(8) 2.752(8) 2.898(4) 2.819(8) 2.704(8) 2.748(4) 2.758(5) 2.767(4) 2.732(4) 2.805(5) 2.875(9) 2.778(5) 2.794(8) 2.818(6) 2.788(6) 2.675(15) 2.722(16) 2.625(14) 2.895(12) 2.895(11) 2.807(9) 2.745(8) 2.894(8) 2.605(8) 2.849(9) 2.866(9) 2.733(8) 2.780(9)
153 142 153 167 146 162 176 166 162 160 154 171 167 161 161 165
DAH
H A
D A
0.99 0.99 0.97 0.97 0.89 0.90 0.90 0.91 0.91 0.87 0.84 0.84 0.92 0.97 0.88 0.95
1.85 2.10 1.83 1.83 2.31 2.02 2.05 2.10 1.92 2.08 2.08 1.94 1.89 1.83 1.92 1.81
2.730(12) 2.887(10) 2.792(18) 2.789(13) 3.088(4) 2.760(13) 2.881(15) 2.980(10) 2.776(9) 2.933(4) 2.853(9) 2.729(9) 2.767(4) 2.783(4) 2.803(4) 2.747(4) 2.815(6) 2.866(10) 2.781(5) 2.806(10) 2.833(6) 2.818(6) 2.700(18) 2.691(19) 2.723(17) 2.906(13) 2.943(11) 2.793(10 2.740(9) 3.009(9) 2.623(9) 2.848(13) 3.043(12) 2.743(10) 2.812(10)
146 135 168 167 146 138 153 162 157 170 153 158 159 166 177 169
Symmetry codes: i x, y + 1, z. ii x, y, z – 1. iii x, 1y, z. iv x 1, y + 1, z. v x 1, y + 1, z. vi x 1, y + 1, z + 1. vii x, y, z. viii x + 1, y 1, z – 1. ix x, y 1, z. x x + 1, y, z. xi x, y 1, z – 1. xii x + 1, y 1, z – 1. xiii x, y 1, z – 1. xiv x + 1, y1, z.
Results and discussions Crystal and molecular structure The compounds 1 and 2 are isostructural. Their structure can be described as interchanging layers of complex anions [Ln(Pydc)3]3 (Ln = Ho and Dy for 1 and 2, respectively) and layers of hydrated sodium cations, stacked along the 0 1 1 direction (diagonal of bc face), as shown in Fig. 1. The anions of 1 and 2 are shown in Figs. 2 and 3, respectively. They are mononuclear complexes where the Ln3+ central ion is nine coordinated by three crystallographically independent pyridinedicarboxylate ligands in tridentate-chelate mode, via one O atom of both the carboxylate group and the ring N atom. The coordination polyhedron is a tricapped trigonal prism with O atoms at the corners. The coordination bond lengths in 1 are slightly shorter, in comparison with 2, which is in accordance with the slightly smaller ionic radius of Ho3+ (1.072 Å) in comparison
with Dy3+ (1.083 Å). The LnAO bond distances are slightly longer than those of the LnAN. Each Pydc ligand is, through another O atom of both carboxylate groups, bonded to sodium cations from the neighboring cationic layer. The O4, O6, O10 and O12 are bonded to two sodium cations as bridges. The O2 and O8 are bonded only to one sodium cation, Table 3 Values of some bands in the IR absorption spectrum of compounds, 1, 2. 1, cm1
2, cm1
Assignment
732(s) 767(m) 1435(s) 1585(m) 1624(s) 2364(m) 3093(m) 3417(m)
732(s) 773(m) 1439(s) 1585(m) 1624(s) 2364(m) 3093(m) 3414(m)
d(CAH) d(OACAO) ms(COO) m(CAC), m(CAN) mas(COO) m(NAH) ms(H2O) mas(H2O)
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Fig. 5. TGA–DTG curves showing the decomposition of Na3[Ho(Pydc)3]14H2O at a heating rate of 10 (K/min) in a nitrogen atmosphere.
Fig. 6. TGA–DTG curves showing the decomposition of Na3[Dy(Pydc)3]14H2O at a heating rate of 10 K/min in a nitrogen atmosphere.
while the other lone pair of electrons are acceptors of the intermolecular OAH O hydrogen bond donated by water molecules (O17 and O18) from the hydrated cationic layer. The layer consisting of hydrated sodium cations is shown in Fig. 4. There are five crystallographically independent sodium cations. All of them are six coordinated with a distorted octahedral coordination. The Na1 and Na2 lie on non-equivalent centers of inversion. On the equatorial positions of the coordination octahedron of the Na1, Na2 and Na3 there are water molecules (O13, O14, O15, O16, O17 and O18) and on the axial positions there are carboxylic O atoms from complex anions (O2, O4, O8 and O10). These octahedrons are, via two bridging water molecules, coordinated at opposite corners, connected in chains along the 0 1 1 direction. Another pair of opposite water molecules (O13 and O15) in the Na1 and Na2 octahedrons are H-bonded to two water molecules. The geometry of the H-bonds is presented in Table 3. The Na4 and Na5 are disordered over two positions with a 0.5 occupancy. They are coordinated with three water molecules and three carboxylic O atoms from three different discrete complexes. The fully occupied O17 and O18 atoms belong to water molecules that are bridges with the Na1 and Na2 octahedrons. On the other hand, the atoms O232, O242, O252 and O262 have a 50% occupancy and correspond to water molecules that are terminally bonded to the Na4 and Na5. They are additionally H-bonded to uncoordinated water molecules (O19, O20, O21, O221 and O222).
In the case of empty sites of Na4 or Na5 there are water molecules with 50% occupied O atoms O231, O241, O251 and O261 (with a different position and H-bonding scheme in comparison to the alternative O232, O242, O252 and O262). From the O O contact distances (Table 2) it can be concluded that they are donors of Hbonds to carboxylate O atoms and not to uncoordinated water molecules. In this way, a quite complicated but electro-neutral and stable structure is built. Thermogravimetric measurements The TGA and DTG curves of the Na3[Ho(Pydc)3]14H2O (Fig. 5) and Na3[Dy(Pydc)3]14H2O (Fig. 6) show that all the obtained complexes of pyridine-2,6-dicarboxylic acid are hydrated compounds that are stable at room temperature. The results for the thermal analysis confirmed the data obtained from the elementary analysis. The complexes of holmium and dysprosium contain 14 molecules of water. The amount of water was determined from the thermogravimetric curves. Under our experimental conditions, each complex is stable up to 40 °C and undergoes two decomposition steps when heating to 1100 °C. In the first step, the loss of crystal water molecules in a one-stage dehydration process is observed in both title compounds between 40 and 200 °C, with a weight loss of (Dmmeas = 25.2%) for complex 1 and (Dmmeas = 25.4%) for complex 2, which is in good agreement with the value calculated
N. Hojnik et al. / Journal of Molecular Structure 1079 (2015) 54–60
59
for the release of the water from the coordination sphere (Dmcalc = 25.7%) for the reaction:
Na3 ½LnðPydcÞ3 14ðH2 OÞ ! Na3 ½LnðPydcÞ3 þ 14H2 O ðLn ¼ Ho;DyÞ Anhydrous lanthanide(III) pyridinedicarboxylates are stable up to 450 °C. Above 450 °C both compounds start to decompose through unstable oxocarbonates [34] to appropriate lanthanide oxides and sodium oxide. This behavior is in agreement with previous findings for related coordination compounds [35,36]. The final products are the stable oxides Ho2O3 and Dy2O3, which were characterized by X-ray powder diffraction. In addition, the amorphous sodium oxide was confirmed by flame reaction. The total measured weight losses for the thermal decomposition of both compounds to oxides are comparable with the calculated values for 1 (Dmcalc = 71.3%) and 2 (Dmcalc = 71.5%).
Fig. 7. Molar susceptibility as a function of temperature measured in a magnetic field of 0.1 T. Inset shows an effective magnetic moment as a function of temperature calculated per magnetic ion.
IR assessments Conclusions A set of characteristic frequency bands for the compounds 1 and 2 were compared with each other as well as with the ligand spectrum, and identified with characteristic vibrational modes of the Pydc molecule, which are listed in Table 3. It is clear that the region 400–4000 cm1 contains many characteristic peaks that can be used for the Pydc identification, as found in the literature [37]. At higher frequencies they are connected with stretching ring vibrations, whereas at lower frequencies they are connected with bending m(OAH) vibrations. The characteristic carboxyl vibrations are found at 1709 cm1 as a very strong absorption band of the m(C@O), and at 1411 and 1300 cm1 for which the former is assigned to the m(CAO) and the latter two to the m(CAC) stretching vibrations. Some peaks were also observed below 990 cm1, and bands of various ring vibrations, i.e., stretching, rocking and wagging, are present. The d(OACAO) in-plane deformation vibration that occurs has a strong sharp band at 752 cm1. Magnetic properties The magnetic properties can be explained by the strong coordination of the carboxylate group to the Ln(III) acceptor and the strong paramagnetic character of the rare-earth ions, which are ideal paramagnetic structural probes in supramolecular complexes and in proteins [38]. At high temperatures the effective magnetic moment peff based on the molecular weight of all the compounds exhibits a constant value, indicating paramagnetic behavior. The susceptibility can be well described by the Curie–Weiss formula (Eq. (1)),
v¼
In conclusion, two water-soluble coordination compounds with the general formula Na3[Ln(Pydc)3]14H2O (Ln = Ho, Dy) have been hydrolytically synthesized in aqueous solutions at slightly basic pH. The thermal decomposition of both compounds was studied by thermogravimetric analysis and X-ray powder diffraction, yielding lanthanide oxides as final products, as well as amorphous sodium oxide, which was confirmed by flame reaction. The magnetic properties can be explained by the strong coordination of the carboxylate group to the Ln(III) acceptor and the strong paramagnetic character of the rare-earth ions. Finally, the crystal structure of the novel Ho and Dy compounds has been determined by single-crystal X-ray analysis, revealing a structure by three crystallographically independent pyridinedicarboxylate ligands in the tridentate-chelate mode, via one O atom of both the carboxylate group and the ring N atom and five crystallographically independent sodium cations. The elemental analyses were performed to check the purity of the compounds and all the measurements showed good agreement with the data obtained from the structural analysis. Acknowledgements We gratefully acknowledge the financial support from the Ministry of Higher Education, Science and Technology of the Republic of Slovenia. We also thank the EN-FIST Centre of Excellence (Ljubljana, Slovenia) for the use of the SuperNova diffractometer. Appendix A. Supplementary material
C ðT hÞ
ð1Þ
where C is the Curie constant. For all compounds the measured C values and the corresponding magnetic moments in Table 4 agree satisfactorily with the expected spin-only moments for the free Ho3+ (10.4 BM) and Dy3+ (10.6 BM), calculated with the Russell-Saunders (L–S) coupling scenario [39]. The slight decrease of the effective magnetic moment with a decreasing temperature for all compounds is due to the temperature-dependent spin–orbit coupling (Fig. 7) that is different for (1) and (2) due to the different spin–orbit coupling parameter k and different quantum numbers L and S.
Details of the crystal data, data collection, and refinement parameters for both compounds have also been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 1001193 and 1001194. A copy of the data can be obtained, free of charge, by applying to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44 (0) 1223 336033 or e-mail: [email protected]). Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.molstruc.2014.09.029. References
Table 4 Curie constants and effective magnetic moments of Ln(III). Sample
Ln3+
C (emu K/mol)
peff (BM)
1 2
Ho Dy
13.0 16.7
10.2 11.5
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