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A new series of lanthanide complexes with the trans-disubstituted Py2[18]aneN6 macrocyclic ligand: synthesis, structures and properties
Polyhedron 160 (2019) 180–188
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Polyhedron journal homepage: www.elsevier.com/locate/poly
A new series of lanthanide complexes with the trans-disubstituted Py2[18]aneN6 macrocyclic ligand: synthesis, structures and properties Rodrigo Lamelas a, Rufina Bastida a, Elena Labisbal a,⇑, Alejandro Macías a,⇑, Teresa Pereira a, Paulo Pérez-Lourido b, Laura Valencia b,⇑, José M. Vila a, Cristina Núñez c a b c
Inorganic Chemistry Department, Faculty of Chemistry, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain Inorganic Chemistry Department, Faculty of Science, University of Vigo, As Lagoas, Marcosende 36310, Pontevedra, Spain Research Unit, Hospital Universitario Lucus Augusti (HULA), Servizo Galego de Saúde (SERGAS), 27002 Lugo, Spain
a r t i c l e
i n f o
Article history: Received 7 September 2018 Accepted 7 December 2018 Available online 25 December 2018 Keywords: trans-Disubstitution Lanthanide complexes N-Alkylated hexaaza-macrocycle X-ray diffraction NMR
a b s t r a c t New lanthanide complexes with the trans-disubstituted macrocyclic ligand Py2[18]aneN6 (denoted as L1) were successfully synthesized. The coordination properties of compound L1 towards different lanthanide metal ions (Ln = La–Yb, except Lu) were explored, and structural studies have been carried out both in the solid state and in aqueous solution. In all cases, complexes with a 1:1 metal:ligand molar ratio were obtained. The crystalline structures of the following compounds: [H4L1](NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3) have been characterized by single crystal X-ray diffraction. In both complexes, the asymmetric unit contains the cation complex [LnL1(NO3)2]+ (Ln = Ce3+, Sm3+) which consist of a mononuclear endomacrocyclic backbone whilst the ten coordination environment is completed by two bidentade nitrate ions. The two five membered chelate rings formed by the ethylenediamine moieties adopt (dd) [or (kk)] conformations and also presented a C2 symmetry (as observed in solution by NMR). Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Magnetic resonance imaging (MRI) is a medical imaging technique consisting of magnetizing body atom nuclei, generally hydrogen nuclei of water molecules, using a very strong magnetic field. This technique measures the random motion of water molecules in tissues, revealing their microarchitecture. For this reason, MRI is frequently used in clinical diagnosis [1]. Gd3+ metal complexes are able of catalytically reducing the time of relaxation of water molecules that are in the vicinity, allowing the obtaining of higher quality images. For this reason, complexes of the element gadolinium (Gd) are the most widely used of all MR contrast agents [2]. However, this metal presents a high toxicity. The ionic radius of Gd3+ and Ca2+ are similar, and as a result it can disrupt Ca2+ mediated signaling, forming strong complexes that can accumulate within the body. For this reason, it is really important to develop novel compounds to be used as contrast agents. They must satisfy the following conditions: contain an effective organic ligand that selectively forms metal complexes, thermodynamically stable and kinetic
⇑ Corresponding authors. E-mail addresses: [email protected] (E. Labisbal), [email protected] (A. Macías), [email protected] (L. Valencia). https://doi.org/10.1016/j.poly.2018.12.006 0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.
alejandroalberto.
inertia. Furthermore, fast renal excretion, stability in aqueous conditions, water solubility, and a low osmotic potential would be also necessary for the clinical application of these compounds in solution [3–5]. On the other hand, macrocyclic derivatives based on 1,4,7, 10-tetraazcyclodecane (cyclen) are among the most broadly used ligands for stable lanthanide complexation in water [1–5]. The easiest synthetic approach is the per substitution, in which all four N-atoms of the macrocycle are alkylated or acylated [1]. The most important representative of this family of ligands is H4DOTA [1,4,7,10-tetraazacyclododecane 1,4,7,10-tetraacetic acid, Chart 1], which forms lanthanide complexes of remarkably high thermodynamic stability and kinetic inertness [6,7]. From the synthetic point of view there is an important challenge, the preparation of mono-, di- or trisubstituted derivatives. The metallic complexes formed between various lanthanide ions and the heptadentate ligand H3DO3A [1,4,7,10-tetraazacyclodecane 1,4,7-triacetic acid, Chart 1] and their derivatives have been also widely studied [8–13]. A feature of the coordination chemistry of lanthanide ions is that it has high coordination rates. In the case of metal complexes with Gd3+ that are used in MRI, they tend to present a coordination index of nine. Typically, the Ln3+ cation occupies the center of the structure of the complex, and is linked to eight heteroatoms of a
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Chart 1.
ligand, while the last coordinating position that remains free is occupied by a molecule of water solvent. Ln3+ complexes with different tetrasubstituted heaazamacrocycles derived from L [Chart 1] have been previously synthesized and studied [14–16]. These ligands are potentially decadentade and for large Ln3+ ions the metal is endomacrocyclic coordinated to all donor atoms, while for the smaller ones, coordination number is in some cases reduced to nine, as in LAc4 [17] [Chart 1]. However, the high number of donor atoms present in these tetrasubstituted macrocycles prevents a water molecule can be incorporated into the first coordination sphere of the Ln3+ ion. In an attempt to obtain a new dipyridine receptor able to form stable Ln3+ complexes with one water molecule in the inner sphere of the ions, we have recently synthesized the new trans-N,N0 methylated hexaazamacrocycle L1 [18], derived from L. This new macrocyclic ligand shows two methylated trans amine groups, and it has been prepared using a similar procedures described for trans-disubstituted cyclen macrocycles [13]. The synthesis of the macrocyclic precursors was achieved following the previously described method [19]. As an extension of our work we report here structural studies, in solid and in solution, of the lanthanide complexes with the ligand trans-N,N0 -methylated hexaazamacrocycle L1, derived from L. This macrocyclic receptor L1 could provide a convenient platform for the design of stable Ln3+ complexes for biological applications. Starting from it, a new receptor can be synthesized by alkylation of the trans secondary amine groups presents in the ligand. Some Ln3+ complexes of L1 have been synthesized and characterized by means of analytical and spectroscopic techniques. The crystal structures of the compound salt [H4L1](NO3)4 showing two trans methyl groups and the metal complexes [CeL1(NO3)2] (NO3) and [SmL1(NO3)2](NO3) have also been characterized by single crystal X-ray crystallography. Also, the structure of the complexes in solution has been studied by NMR. Alkylation of the two remaining secondary amine
groups leads to potentially octadentade macrocyclic receptors as in cyclen derivatives. 2. Experimental 2.1. Chemical and starting materials Pyridine-2,6-dicarbaldehyde [20] and L [21], were achieved following the literature. L1 has been synthesized following the previously mentioned methodology developed in the research group [13]. The remaining reagents employed in the synthesis were purchased from Aldrich/Panreac and were used without further purification. The solvents used were of reagent grade and purified by usual methods. 2.2. Measurements Elemental analyses were performed on a Fisons Instruments EA1108 microanalyzer. Infra-red spectra were recorded as KBr disc on a BIO-RAD FTS 175-C spectrometer. MALDI-TOF were recorded using a Bruker autoflex spectrometer (DCTB matrix). Conductivity measurements were carried out in 103 M acetonitrile solutions at r.t. using a Crison Basic 30 conductimeters. The 1H and 13C NMR spectra were recorded in CDCl3 and CD3CN solutions on a Varian 300 MHz spectrometer. Assignments of the 1H and 13C NMR studies for the lanthanide complexes were based on COSY, DEPT and HSQC experiments. All the measurements were recorded at the Universidad de Santiago de Compostela, in the RIAIDT services. 2.3. General procedure for the preparation of the metal complex of L1 A solution of the appropriate hydrated lanthanide salt (0.4 mmol) in acetonitrile (5 mL) was added dropwise to a stirred solution of the ligand L1 (0.4 mmol) in the same solvent (20 mL).
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The solution was softly heated and stirred for 4 h, and the solvent was partially removed to ca. 5 mL. Diethyl ether was infused into the solution, producing powdery precipitates which were isolated by centrifugation, dried under vacuum and characterized as the hydrated metal complexes of L1. 2.3.1. [LaL1](NO3)37H2O Anal. Calc. for C20H44N9O16La (MW: 805.20): C, 29.8; H, 5.5; N, 15.6. Found: C, 29.1; H, 4.9; N, 16.0%. Yield: 37%. IR (KBr, cm1): 1605, 1463 [m(C@N)py and m(C@C)py], 1485, 1383, 1305, 1031 [m (NO3)]. MALDI-MS (m/z): 617.1 [LaL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 191 (1:1). Color: white. 2.3.2. [CeL1](NO3)37H2O Anal. Calc. for C20H44N9O16Ce (MW: 806.20): C, 29.7; H, 5.5; N, 15.6. Found: C, 29.9; H, 4.8; N, 15.9%. Yield: 39%. IR (KBr, cm1): 3256 [m(NH)], 1601, 1462 [m(C@N)py and m(C@C)py], 1487, 1381, 1037 [m(NO3)]. MALDI-MS (m/z): 618.1 [CeL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 200 (1:1). Color: white. 2.3.3. [PrL1](NO3)37H2O Anal. Calc. for C20H44N9O16Pr (MW:807.20): C, 29.7; H, 5.5; N, 15.6. Found: C, 29.1; H, 5.0; N, 15.3%. Yield: 33%. IR (KBr, cm1): 1605, 1464 [m(C@N)py and m(C@C)py], 1486, 1386, 1038 [m(NO3)]. MALDI-MS (m/z): 618.9 [PrL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 189 (1:1). Color: white. 2.3.4. [NdL1](NO3)37H2O Anal. Calc. for C20H44N9O16Nd (MW: 808.20): C, 29.6; H, 5.5; N, 15.5. Found: C, 29.3; H, 5.1; N, 15.0%. Yield: 41%. IR (KBr, cm1): 1605, 1468 [m(C@N)py and m(C@C)py], 1485, 1383, 1305, 1031 [m(NO3)]. MALDI-MS (m/z): 622.0 [NdL1(NO3)2]+. 1 2 1 KM/X cm mol (in CH3CN): 187 (1:1). Color: white. 2.3.5. [SmL1](NO3)37H2O Anal. Calc. for C20H44N9O16Sm (MW: 818.21): C, 29.4; H, 5.4; N, 15.4. Found: C, 29.7; H, 4.9; N, 16.0%. Yield: 34%. IR (KBr, cm1): 3189 [m(NH)], 1607, 1465 [m(C@N)py and m(C@C)py], 1489, 1342, 1036 [m(NO3)]. MALDI-MS (m/z): 630.0 [SmL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 196 (1:1). Color: white. 2.3.6. [EuL1](NO3)37H2O Anal. Calc. for C20H44N9O16Eu (MW: 819.21): C, 29.3; H, 5.4; N, 15.4. Found: C, 29.1; H, 5.0; N, 14.9%. Yield: 43%. IR (KBr, cm1): 3185 [m(NH)], 1609, 1466 [m(C@N)py and m(C@C)py], 1480, 1384, 1310 [m(NO3)]. MALDI-MS (m/z): 631.1 [EuL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 196 (1:1). Color: white. 2.3.7. [GdL1](NO3)37H2O Anal. Calc. for C20H44N9O16Gd (MW: 824.22): C, 29.1; H, 5.5; N, 15.3. Found: C, 28.9; H, 4.8; N, 15.8%. Yield: 45%. IR (KBr, cm1): 1608, 1468 [m(C@N)py and m(C@C)py], 1480, 1385, 1305 [m(NO3)]. MALDI-MS (m/z): 636.2 [GdL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 198 (1:1). Color: white. 2.3.8. [TbL1](NO3)37H2O Anal. Calc. for C20H44N9O16Tb (MW: 825.22): C, 29.1; H, 5.4; N, 15.3. Found: C, 29.5; H, 4.9; N, 16.1%. Yield: 50%. IR (KBr, cm1): 3014 [m(NH)], 1608, 1467 [m(C@N)py and m(C@C)py], 1481, 1386, 1035 [m(NO3)]. MALDI-MS (m/z): 637.2 [TbL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 210 (between 1:1 and 2:1). Color: white. 2.3.9. [DyL1](NO3)34H2O Anal. Calc. for C20H38N9O13Dy (MW: 771.49): C, 31.0; H, 4.9; N, 16.3. Found: C, 31.5; H, 4.7; N, 16.0%. Yield: 53%. IR (KBr, cm1): 1603, 1466 [m(C@N)py and m(C@C)py], 1481, 1384, 1035 [m(NO3)].
MALDI-MS (m/z): 642.2 [DyL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 202 (between 1:1 and 2:1). Color: white. 2.3.10. [HoL1](NO3)37H2O Anal. Calc. for C20H44N9O16Ho (MW: 831.22): C, 28.9; H, 5.3, N; 15.2. Found: C, 28.5; H, 5.0, N; 14.8%. Yield: 59%. IR (KBr, cm1): 3015 [m(NH)], 1609, 1468 [m(C@N)py and m(C@C)py], 1487, 1386, 1305 [m(NO3)]. MALDI-MS (m/z): 643.2 [HoL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 216 (between 1:1 and 2:1). Color: white. 2.3.11. [ErL1](NO3)35H2O Anal. Calc. for C20H40N9O14Er (MW: 795.51): C, 30.1; H, 5.0, N; 15.8. Found: C, 29.9; H, 4.9, N; 16.0%. Yield: 56%. IR (KBr, cm1): 1603, 1466 [m(C@N)py and m(C@C)py], 1489, 1384, 1036 [m(NO3)]. MALDI-MS (m/z): 644.2 [ErL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 205 (between 1:1 and 2:1). Color: white. 2.3.12. [TmL1](NO3)37H2O Anal. Calc. for C20H44N9O16Tm (MW:835.23): C, 28.7; H, 5.3; N, 15.1. Found: C, 28.4; H, 4.9; N, 14.8%. Yield: 55%. IR (KBr, cm1): 3187 [m(NH)], 1608, 1461 [m(C@N)py and m(C@C)py], 1485, 1386, 1306 [m(NO3)]. MALDI-MS (m/z): 647.0 [TmL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 193 (1:1). Color: white. 2.3.13. [YbL1](NO3)37H2O Anal. Calc. for C20H44N9O16Yb (MW: 840.20): C, 28.6: H, 5.3; N, 15.0, Found: C, 28.3; H, 4.8; N, 14.7%. Yield: 70%. (KBr, cm1): 3242 [m(NH)], 1611, 1469 [m(C@N)py and m(C@C)py], 1483, 1385, 1306, 1034 [m(NO3)]. MALDI-MS (m/z): 652.2 [YbL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 206 (between 1:1 and 2:1). Color: white. 2.4. Crystal structure determinations. Crystals suitable for X-ray diffraction were obtained for [H4L1] (NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3). Measurements were made on a Bruker X8 KappaAPEXII diffractometer. Graphite monochromated Mo Ka was used. All data were correct for Lorentz and polarization effects Empirical absorption corrections were also applied for all the crystal structures obtained [22]. Complex scattering factors were taken from the program package SHELXTL [23]. The structures were solved by directed methods (Patterson for the metal complexes) using SHELX-97 [24] or SIR-92 [25], which revealed the positions pf all mom-hydrogen atoms. All the structures were refined on F2 by a full-matrix least-squares procedure using anisotropic displacement parameters for all non-hydrogen atoms. The hydrogen atoms of the carbons were located in their calculated positions and refined using a riding model. The hydrogen atoms of the amine groups or water molecules were located on a difference Fourier map and refined isotropically. Molecular graphics were obtained with the WebLab ViewerPro [26] and ORTEP-3 [27]. 3. Results and discussion 3.1. Synthesis and characterization of complexes derived from L1 The lanthanide complexes of L1 were synthesized in a 1:1 metal:ligand ratio in acetonitrile, giving rise to compounds of formula [ML1](NO3)3xH2O (M = La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+ and Yb3+) in good yield. All compounds are soluble in DMSO, CH3CN and acetone. The compounds are also soluble in a mixture of DMSO and H2O at 10%.
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N3AH3NA O4N N3AH3NA O6N N2AH2N O3N_$1 N3AH3NA O3N_$1 N3AH3NB O3N_$1 N2AH2N O2N_$2 N2AH2N O3N_$2 N3AH3NB O1N_$2 N3AH3NB O3N_$2
D A
H A
DAH A
3.02(1) 2.80(1) 3.23(1) 2.97(1) 2.972(1) 3.36(1) 2.85(1) 3.23(1) 2.96(1)
2.55(2) 1.96(2) 2.66(2) 2.56(2) 2.58(2) 2.90(2) 2.03(2) 2.63(2) 2.09(2)
114(2) 159(2) 125(2) 110(2) 109(2) 115(2) 159(2) 127(2) 175(2)
$1 x + 1, y + 1, z + 1; $2 x 1, +y, +z.
Table 3 Selected bond lengths (Å) of the metal coordination environment, obtained from the X-ray crystal structures of [Ce(L1)(NO3)2](NO3) and [Sm(L1)(NO3)2](NO3).
LnAN(1) LnAN(2) LnAN(3) LnAN(4) LnAN(5) LnAN(6) LnAO(1N) LnAO(2N) LnAO(5N) LnAO(6N) Fig. 1. X-ray crystal structure of the [H4L1]4+ cation of [H4L1](NO3)4, showing the atomic numbering scheme. The ORTEP plots are the 50% probability level.
The IR spectra were recorded as KBr discs. The bands due to m (C@N) and m(C@C) stretching modes of the pyridine rings on the
[CeL1(NO3)2](NO3)
[SmL1(NO3)2](NO3)
2.713(10) 2.799(8) 2.669(7) 2.631(10) 2.743(8) 2.701(9) 2.560(4) 2.577(5) 2.563(6) 2.586(5)
2.659(12) 2.758(9) 2.647(9) 2.603(13) 2.715(10) 2.671(10) 2.500(8) 2.521(7) 2.517(6) 2.507(5)
complexes of L1 appear displaced when compared with the spectrum of the free ligand (1589, 1460 cm1 in the ligand L1), suggesting the interaction between pyridyl groups and the metal ions [28,29]. The NAH amine stretching vibrations (3312 cm1 in the ligand L1) was shifted to lower frequencies in the spectra of the
Table 1 Crystal data and structure refinement for [H4L1](NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3).
Empirical formula Formula weight T (K) k (Å) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (mg/m3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm) h Range for data collection (°) Index ranges Reflections collected Independent reflections (Rint) Completeness to h (%) Absorption correction Maximum and minimum transmission Refinement method Data/restrains/parameters Absolute structural parameter Godness-of-fit on F2 (GOF) Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)
[H4L1](NO3)4
[CeL1(NO3)2](NO3)
[SmL1(NO3)2](NO3)
C20H34N10O12 606.57 100(2) 0.71073 monoclinic P21/c
C20H30N9O9Ce1 680.62 293(2) 0.71073 orthorombic Pn21a
C20H30N9O9Sm1 690.88 100(2) 0.71073 orthorombic Pn21a
8.756(4) 8.969(4) 16.973(8)
17.515(5) 16.284(5) 8.978(5)
17.478(5) 16.244(5) 8.963(5)
2560.7(18) 4 1.766 1.846 1372 0.22 0.03 0.03 2.33/2.46 0 h 21, 0 k 20, 0 l 11 40,249 2732 [Rint = 0.1072] 99.7% empirical 0.9640 and 0.6869 full-matrix least-squares on F2 2732/1/318 0.04(1) 1.093 R1 = 0.0345; wR2 = 0.0787 R1 = 0.0499; wR2 = 0.1082 1.692 and 1.369
2544.7(18) 4 1.803 2.376 1388 0.30 0.17 0.13 2.33/2.37 0 h 21, 0 k 20, 0 l 11 26,052 2695 [Rint = 0.0610] 100.0% empirical 0.7476 and 0.5358 full-matrix least-squares on F2 2695/1/316 0.04(3) 1.068 R1 = 0.0418; wR2 = 0.1082 R1 = 0.0477; wR2 = 0.1133 2.712 and 1.569
98.741(7) 1317.5(10) 2 1.529 0.127 640 0.27 0.17 0.05 2.35/27.48 11 h 11, 0 k 11, 0 l 22 23,775 3023 [Rint = 0.0717] 100.0% empirical 0.9937 and 0.9665 full-matrix least-squares on F2 3023/0/202 1.032 R1 = 0.0438; wR2 = 0.0965 R1 = 0.0690; wR2 = 0.1087 0.302 and 0.252
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metal complexes, suggesting an interaction between them and the metal ions. In some cases, the band corresponding to the vibration mode of the water, masks the signals of the aminic groups. In all the nitrate complexes several bands in the region associated with nitrate vibrations clearly identify the presence of coordinated nitrate ions [30] whilst an intense band at ca. 1380 cm1 indicates also the presence of ionic nitrate groups [31]. The MALDI mass spectra of the complexes confirmed the formation of the desired lanthanide complexes. In all cases a fragment corresponding to peak [LnL1(NO3)2]+ was observed. The molar conductance values for the complexes of L1, measured in acetonitrile at room temperature, lie in the range reported between 1:1 and 2:1 electrolytes [32]. 3.2. X-ray diffraction Single crystals of [H4L1](NO3)4, suitable for X-ray diffraction, was obtained by slow diffusion of solutions of the ligand and lanthanum nitrate, dissolved in chloroform and acetone respectively. The asymmetric unit is comprised by half molecule of the [H4L1]4+ cation and two nitrate ions. The molecular structure of the [H4L1]4+ cation is shown in Fig. 1. Bond lengths and angles are within the expected values. Crystal data of the compound are collected in Table 1. The ligand shows a nearly plane conformation. The aromatic rings are parallel each other and the intramolecular distance between them is 2.4(1) Å. No inter- or intra-molecular p-stacking interactions have been found in the crystal. Numerous hydrogen bond interactions (Table 2) are observed between nitrate ions and the secondary amine groups of the molecule. Single crystals of [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3) were obtained by slow evaporation of an acetonitrile solution of the corresponding complex and were used for X-ray diffraction analyses. Crystal data of the complexes are collected in the Table 1.
Fig. 2. X-ray crystal structure of the [SmL1(NO3)2]+ cation showing the atomic numbering scheme. Hydrogen atoms are omitted for simplicity. The ortep plots are the 50% probability level.
Selected bond lengths of the lanthanide coordination environments are giving in the Table 3. The Ce3+ and Sm3+ complexes are isostructural, and they crystallize in the orthorhombic, non-centrosymmetric, space group Pn2(1)a. In both complexes, the asymmetric unit contains the cation complex [LnL1(NO3)2]+ (Ln = Ce3+, Sm3+) (see Fig. 2 for the samarium complex) which consist of a mononuclear endomacrocyclic backbone whilst the ten coordination environment is completed by two bidentate nitrate ions. The nitrate groups are located on opposite sides of the best plane defined by the six nitrogen atoms of the ligand. The unit cells of both complexes contain four potential anion-accessible symmetry-related cavities, filled with disordered anions, probably nitrates. The volume of each cavity is ca. 60 Å3. Attempts to model nitrate anions into the solvent cavity did not result in an acceptable model. As an alternative strategy, the SQUEEZE [33] function of PLATON [34] was used to eliminate the contribution of the electron density in the solvent region from the intensity data. The use of this strategy and the subsequent solvent-free model produced better refinement results than the attempt to model the nitrate ions. Therefore, the solvent-free model and intensity data were used for the final results reported here. A total of ca. 34 e was found in each cavity, corresponding approximately to one nitrate per cavity, just the amount necessary to keep the electro neutrality of the compound. Where relevant, the crystal data reported in this paper are given without the contribution of the disordered solvent. The conformation of the macrocycle in the [LnL1(NO3)2]+ cation is almost plane. The dihedral angle between the pyridine units is 17.7° for [CeL1(NO3)2]+, and 19.2° for [SmL1(NO3)2]+ showing that the ligand is slightly twisted and it is practically not folded, with NpyALnANpy angles of 180.0(2) and 179.7(3)° for the Ce3+ and Sm3+ complexes, respectively. The configuration of the nitrogen atoms is SRSR (or RSRS) in both complexes, as the spatial group is centrosymmetric, and the conformation of the two five membered quelate rings due to the coordination of the ethylendiamine fragments to the metal ion is dd (or kk). The trans methyl groups are directed toward the same side of the main macrocyclic hole in an syn conformation. The symmetry of the complexes approaches the C2 group. All the distances decrease in the Ce-Sm direction as expected due to the lanthanide contraction [35]. The LnAO bond lengths are shorter than the LnAN ones, being the LnANPy distances shorter than LnANamine ones.
Fig. 3. Coordination polyhedron in the [CeL1(NO3)2]+ cation.
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Fig. 4. Face to face p,p-intermolecular interactions for [CeL1(NO3)2]+.
Complexes with high number of small-bite ligands are usually close to the 2:6:2 polyhedra such as the tetra decahedron and staggered dodecahedron [36]. The minima S(A) values provided by the SHAPE program for the Ce3+ and Sm3+ complexes belongs to the tetra decahedron with S(A) values of 3.336 and 3.478, respectively (Fig. 3) [37]. The hexagonal plane is clearly comprised by the six nitrogen atom from the ligand. Different intermolecular interactions have been observed in the net. The pyridine fragments from each ligand molecule interact thorough face to face p,p-intermolecular interactions with
adjacent molecules [N1,C1-C5 N4_$1, C10_$1AC14_$1 and N4, C10AC14 N1_$2,C1_$2AC5_$2; Symmetry operations for the Ce3+ complex: $1 x + 2, +y + 1/2, z + 2, $2 x + 2, +y 1/2, z + 2. For the Sm3+ complex: $1 x, +y + 1/2, z, $2 x, +y 1/2, z] giving rise to infinite chains. The distance between planes containing that pyridine rings is 3.7(1) Å or 3.66(6) Å for Ce3+ or Sm3+ complex, respectively, whilst the distance between centroids is 3.95(1) Å, for the Ce3+ complex and 3.94(1) Å for Sm3+ complex. The slipped angles are 20° and 22° for Ce3+ and Sm3+ complexes, respectively (Fig. 4).
Fig. 5. 1H NMR spectrum for [LaL1](NO3)37H2O.
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Table 4 H and 13C data for [LaL1](NO3)37H2O.
1
1
d (ppm)
13
H1 H2 H4(ax) H4(eq) H5(ax) H5(eq) H6(ax) H6(eq) H7(ax) H7(eq) H9 H10 NH
7.94 7.42 3.39 4.69 3.09 2.79 3.09 3.09 4.14 4.26 7.42 2.24 3.22
C1 C2 C3 C4 C5 C6 C7 C8 C9 C10
H
(t,2H) (m,2H) (d,2H) (d,2H) (m,2H) (m,2H) (m,2H) (m,2H) (m,2H) (m,2H) (m,2H) (s, 6H) (a, 2H)
C
d (ppm) 140.7 121.66 160.63 60.33 58.97 46.39 54.79 157.62 122.72 44.31
Structure in solution of the complexes with the lightest Ln3+ ions (Ln = LaAEu). The 1H, 13C, DEPT, COSY and HSQC NMR spectra of the lanthanide ion complexes were recorded in CD3CN. The 1H NMR spectrum of the diamagnetic La3+ complex shows thirteen signals (Fig. 5, Table 4), indicating an effective C2 symmetry in solution, as observed in the crystal structures of the Ce3+ and Sm3+ complexes. The two-dimensional spectra allowed us to identify the geminal protons H4, H5, H6 and H7. Specific assignment H4(ax)/H4(eq), H5 (ax)/H5(eq), H6(ax)/H6(eq) and H7(ax)/H7(eq), was made using the stereochemical dependence of the displacements of the protons as a result of the polarization of the CAH bonds due to the electric field generated by the charge of the cation. This effect normally leads to a disappearance of the protons located in the equatorial position [38].
In the 1H NMR spectrum of the La3+ complex, three signals appear for the pyridine rings: H1 at lower field as a triplet while H2 and H9 collapse in a multiplet at 7.42 ppm. The methylene protons H4 give rise to an AB system with 2J = 14.9 Hz. The signals at 4.26 and 4.13 ppm, which are coupled to each other with 2 J = 15.7 Hz, correspond to the H7 protons, and they appear as ABX systems by coupling with the proton of the NH group. The coupling is greater with H7(ax) 3J = 11.7 Hz, than with H(7eq) 3 J = 4.91 Hz. H6 and H5(ax) give rise to a multiplet at 3.09 ppm. The coupling pattern of the signal at 2.79 ppm indicates that it is an equatorial proton, since the axial protons usually experience a strong coupling between the geminal protons and the neighboring axial protons, while the coupling of the equatorial protons is strong only with the germinal ones [39]. Therefore, this signal was assigned to H5(eq). The signal corresponding to H10 appears as a singlet at 2.24 ppm and the NH groups appear at 3.22 ppm as a broad signal. Also, some small signals reveal the presence of a minority compound. Twelve signals (excluding those of the NH protons), appears also in the 1H NMR spectra of the lighter paramagnetic Ce3+–Eu3+ complexes, in agreement with an effective C2 symmetry of the complexes in solution. (Fig. 6, Table 5), The COSY spectrum of the Ce3+ complex, shows cross peaks between the geminal protons H4(ax)/H4(eq), H5(ax)/H5(eq), H6(ax)/H6 (eq) and H7(ax)/H7(eq). The HSQC spectrum allows us to assign the signal at 49.53 ppm to the NH group. The COSY spectrum shows peaks between the NH group and the protons H(6ax) and H(7ax). The widest signals in the 1H NMR spectrum of the paramagnetic complexes correspond to the axial protons due to the dependence that exists between the distance of these protons to the Ln3+ ion, and the relaxation induced by it. This allows us to identify the axial and equatorial protons. The H4 protons show a single crossed peak by coupling between them while the H5 protons also show peaks crossed with the H6. In the Sm3+ complex, the presence of a crossed peak in the COSY spectrum with the NH group allows us to identify the signals of the protons H6 and H7. H(7ax) gives rise to an AX system with 2 J = 15.2 Hz by coupling with H(7eq), while H(7ax) gives rise to an AXX ’system by further coupling with the proton of the NH group with 3J = 11.6 Hz. The methylene protons H4 give rise to an AX system with 2J = 14.8 Hz. The COSY spectrum also shows a cross-peak between the protons H6 and the H5. The H10 signal appears as a singlet at 0.52 ppm and the signal assignable to the NH groups appears at 14.52 ppm as a broad signal.
Fig. 6. 1H NMR spectrum for [CeL1](NO3)37H2O.
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R. Lamelas et al. / Polyhedron 160 (2019) 180–188 Table 5 H and 13C data for [LnL1](NO3)37H2O.
1
1
Ce3+
Pr3+
Nd3+
Sm3+
Eu3+
H1 H2 H4(ax) H4(eq) H5(ax) H5(eq) H6(ax) H6(eq) H7(ax) H7(eq) H9 H10 NH
8.13 3.45 11.39 5.76 7.21 4.24 13.82 17.09 20.28 21.49 11.88 10.28 49.53
7.97 1.01 28.49 14.00 12.33 7.89 30.06 38.44 41.50 46.84 17.81 24.26 106.20
7.06 1.66 13.23 4.93 13.46 12.90 25.97 23.23 28.40 36.04 13.22 13.84 62.55
7.78 6.48 1.39 1.90 1.67 3.60 3.81 4.91 5.63 7.23 8.05 0.52 14.52
8.52 12.30 23.93 7.94 6.94 14.69 36.86 20.31 37.39 20.86 0.532 15.17 47.35
H
The 1H NMR spectra for the heaviest Ln3+ ions (TbALu) show similar features, but a full assignment of the signals was not possible.
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected].
4. Conclusions References A new trans-disubstituted macrocyclic ligand L1 has been obtained in satisfactory yield and purity. The complexation capability of L1 in a 1:1 metal:ligand molar ratio towards the lanthanide metal ions has been investigated. The ligand L1 probably does not have a large enough cavity to give rise to dinuclear endomacrocyclic complexes with these ions, therefore compounds containing cationic and anionic species were obtained. The crystalline structures of [H4L1](NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3) have been determined. In the Ce3+ and Sm3+ complexes, the metal ions showed a 10-coordinate environment due to the coordination of 2 nitrate ligands in a bidentate fashion. A detailed structural analysis of the [Ln(L1)]3+ complexes based on Ln(III)-induced paramagnetic NMR shifts indicated that in CD3CN they presented an effective C2 symmetry (as observed in the crystal structures of the Ce3+ and Sm3+ complexes). While p,p-stacking interactions have been observed between the pyridine rings of [CeL1(NO3)2] (NO3) and [SmL1(NO3)2](NO3), in the case of [H4L1](NO3)4 only have been observed numerous hydrogen bond interactions. The results reported in this work indicate that the macrocyclic cavity of L1 is well suited for the coordination of lanthanide ions. Acknowledgments
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
This work was made possible thanks to the financial support received from the Xunta de Galicia (Galicia, Spain) under the ‘‘Grupos de Referencia Competitiva” Programme (Project GRC2015/009). The authors are indebted to CACTUS (Universidad de Santiago de Compostela) for the X-ray measurements. C. Núñez acknowledges Miguel Servet I Programme (CP16/00139) from the ‘‘Instituto de Salud Carlos III” (Plan Estatal de I + D + i 2013-2016 and European Development Regional Fund) of the Spanish Ministry of Economy and Competitiveness. Conflicts of interest The authors declare no competing interests.
[20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]
Appendix A. Supplementary data
[31]
CCDC 1852166, 1852164 and 1852165 contains the supplementary crystallographic data for [H4L1](NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3), respectively. These data can be obtained free
[32] [33] [34] [35]
P. Caravan, J.J. Ellison, J. McMurry, L.B. Lauffer, Chem. Rev. 99 (1999) 2293. P. Caravan, Chem. Soc. Rev. 35 (2006) 512. S. Aime, M. Botta, E. Terreno, Adv. Inorg. Chem. 57 (2005) 173. E.M. Surender, S.J. Bradberry, S.A. Bright, C.P. McCoy, D.C. Williams, T. Gunnlaugsson, J. Am. Chem. Soc. 139 (2017) 381. S. Aime, M. Botta, M. Fassano, E. Terreno, Chem. Soc. Rev. 27 (1998) 19. X. Wang, T. Jin, V. Comblin, A. López-Mut, E. Merciny, J.-F. Desreux, Inorg. Chem. 31 (1992) 1095. E. Toth, E. Brucher, I. Lazar, I. Toth, Inorg. Chem. 33 (1994) 4070. K. Kumar, C.A. Chang, L.C. Francesconi, D.D. Dischino, M.F. Malley, J.Z. Gougoutas, M.F. Tweedle, Inorg. Chem. 33 (1994) 3567. K. Kumar, C.A. Chang, M.F. Tweedle, Inorg. Chem. 32 (1993) 587. K. Kumar, M.F. Tweedle, Inorg. Chem. 32 (1993) 4193. C.A. Chang, L.C. Francesconi, M.F. Malley, K. Kumar, J.Z. Gougoutas, M.F. Tweedle, D.W. Lee, L. Wilson, Inorg. Chem. 32 (1993) 3501. D.F. Caffrey, T. Gunnlaugsson, Dalton Trans. 43 (2014) 17964. E.M. Surender, S. Comby, L. Cavanagh, O. Brennan, T.C. Lee, T. Gunlaugsson, Chem 1 (2016) 438. M.C. Fernández-Fernández, R. Bastida, A. Macías, P. Pérez-Lourido, C. PlatasIglesias, L. Valencia, Inorg. Chem. 45 (2006) 4484. C. Núñez, R. Bastida, A. Macías, M. Mato-Iglesias, C. Platas-Iglesias, L. Valencia, Dalton Trans. (2008) 3841. S.W.A. Bligh, N. Choi, C.F.G.C. Geraldes, S. Knoke, M. McParlin, M.J. Sanganee, T. M. Woodrofee, J. Chem. Soc., Dalton Trans. (1997) 4119. L. Valencia, J. Martínez, A. Macías, R. Bastida, R.A. Carvalho, C.F.C.G. Geraldes, Inorg. Chem. 41 (2002) 5300. R. Lamelas, V. García, A. Liñares, R. Bastida, E. Labisbal, A. Fernández-Lodeiro, C. Lodeiro, C. Núñez, L. Valencia, Sens. Actuators B: Chem. 225 (2016) 481. G. Royal, V. Dahaoui-Gindrey, S. Dahaoui, A. Tabard, R. Guilard, P. Pullumbi, C. Lecomte, Eur. J. Org. Chem. (1998) 1971. P. Moore, N.W. Alcook, R.G. Kingston, C. Pierpoint, J. Chem. Soc., Dalton Trans. (1984) 1937. G.L. Rothermel Jr., L. Miao, A.L. Hill, S.C. Jackels, Inorg. Chem. 31 (1992) 4854. G.M. Sheldrick, SADABS. Program of empirical Absorption Correction of Area Detector Data, University of Göttingen, Germany, 1996. shelxtl Versión, An integrated System for Solving and Refining Crystal Structures from Diffraction Data (Revisión 5.1), Bruker AXS LTD. G.M. Sheldrick, SHELX-97 An Integrated System for Solving and Refining Crystal Structures from Diffraction Data, University of Göttingen, Germany, 1997, p. 2. A. Altornare, G. Cascarano, C. Giacovazzo, A. Gualardi, J. Appl. Crystallogr. 26 (1993) 343. WebLab Viewer, Molecular Simulations Inc., 2000. L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565. N.S. Grill, R.H. Nutall, D.E. Scaife, D.W. Sharp, J. Inorg. Nucl. Chem. 18 (1961) 79. S. Aime, M. Botta, U. Casellato, S. Tamburini, P.A. Vigato, Inorg. Chem. 34 (1995) 5825. W.T. Carnall, S. Siegel, J.F. Ferraro, B. Tani, E. Gebert, Inorg. Chem. 12 (1973) 560. P. Guerriero, U. Casellato, S. Tamburini, P.A. Vigato, R. Graziani, Inorg. Chim. Acta 129 (1987) 127. W.J. Geary, Coord. Chem. Rev. 7 (1971) 81. P. van der Sluis, A.L. Spek, Acta Crystallogr., Sect. A 46 (1990) 194. A.L. Spek, PLATON, University of Utrecht, The Netherlands, 2001. M. Seitz, A.G. Oliver, K.N. Raymond, J. Am. Chem. Soc. 129 (2007) 11153.
188
R. Lamelas et al. / Polyhedron 160 (2019) 180–188
[36] A. Ruíz-Martínez, S. Álvarez, Chem. Eur. J. 15 (2009) 7470. [37] M. Llunell, D. Casanova, J. Cirera, P. Alemany, S. Álvarez. S. SHAPE. Program for the Stereochemical Analysis of Molecular Fragments by Means of Continuous Shape Measures and Associated Tools, Version 2.1.
[38] R.K. Harris, Nuclear Magnetic Resonance Spectroscopy: A Physicochemical View, 1983. [39] S. Aime, M. Botta, G. Ermondi, Inorg. Chem. 31 (1992) 4291.
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A new series of lanthanide complexes with the trans-disubstituted Py2[18]aneN6 macrocyclic ligand: synthesis, structures and properties Rodrigo Lamelas a, Rufina Bastida a, Elena Labisbal a,⇑, Alejandro Macías a,⇑, Teresa Pereira a, Paulo Pérez-Lourido b, Laura Valencia b,⇑, José M. Vila a, Cristina Núñez c a b c
Inorganic Chemistry Department, Faculty of Chemistry, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain Inorganic Chemistry Department, Faculty of Science, University of Vigo, As Lagoas, Marcosende 36310, Pontevedra, Spain Research Unit, Hospital Universitario Lucus Augusti (HULA), Servizo Galego de Saúde (SERGAS), 27002 Lugo, Spain
a r t i c l e
i n f o
Article history: Received 7 September 2018 Accepted 7 December 2018 Available online 25 December 2018 Keywords: trans-Disubstitution Lanthanide complexes N-Alkylated hexaaza-macrocycle X-ray diffraction NMR
a b s t r a c t New lanthanide complexes with the trans-disubstituted macrocyclic ligand Py2[18]aneN6 (denoted as L1) were successfully synthesized. The coordination properties of compound L1 towards different lanthanide metal ions (Ln = La–Yb, except Lu) were explored, and structural studies have been carried out both in the solid state and in aqueous solution. In all cases, complexes with a 1:1 metal:ligand molar ratio were obtained. The crystalline structures of the following compounds: [H4L1](NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3) have been characterized by single crystal X-ray diffraction. In both complexes, the asymmetric unit contains the cation complex [LnL1(NO3)2]+ (Ln = Ce3+, Sm3+) which consist of a mononuclear endomacrocyclic backbone whilst the ten coordination environment is completed by two bidentade nitrate ions. The two five membered chelate rings formed by the ethylenediamine moieties adopt (dd) [or (kk)] conformations and also presented a C2 symmetry (as observed in solution by NMR). Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Magnetic resonance imaging (MRI) is a medical imaging technique consisting of magnetizing body atom nuclei, generally hydrogen nuclei of water molecules, using a very strong magnetic field. This technique measures the random motion of water molecules in tissues, revealing their microarchitecture. For this reason, MRI is frequently used in clinical diagnosis [1]. Gd3+ metal complexes are able of catalytically reducing the time of relaxation of water molecules that are in the vicinity, allowing the obtaining of higher quality images. For this reason, complexes of the element gadolinium (Gd) are the most widely used of all MR contrast agents [2]. However, this metal presents a high toxicity. The ionic radius of Gd3+ and Ca2+ are similar, and as a result it can disrupt Ca2+ mediated signaling, forming strong complexes that can accumulate within the body. For this reason, it is really important to develop novel compounds to be used as contrast agents. They must satisfy the following conditions: contain an effective organic ligand that selectively forms metal complexes, thermodynamically stable and kinetic
⇑ Corresponding authors. E-mail addresses: [email protected] (E. Labisbal), [email protected] (A. Macías), [email protected] (L. Valencia). https://doi.org/10.1016/j.poly.2018.12.006 0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.
alejandroalberto.
inertia. Furthermore, fast renal excretion, stability in aqueous conditions, water solubility, and a low osmotic potential would be also necessary for the clinical application of these compounds in solution [3–5]. On the other hand, macrocyclic derivatives based on 1,4,7, 10-tetraazcyclodecane (cyclen) are among the most broadly used ligands for stable lanthanide complexation in water [1–5]. The easiest synthetic approach is the per substitution, in which all four N-atoms of the macrocycle are alkylated or acylated [1]. The most important representative of this family of ligands is H4DOTA [1,4,7,10-tetraazacyclododecane 1,4,7,10-tetraacetic acid, Chart 1], which forms lanthanide complexes of remarkably high thermodynamic stability and kinetic inertness [6,7]. From the synthetic point of view there is an important challenge, the preparation of mono-, di- or trisubstituted derivatives. The metallic complexes formed between various lanthanide ions and the heptadentate ligand H3DO3A [1,4,7,10-tetraazacyclodecane 1,4,7-triacetic acid, Chart 1] and their derivatives have been also widely studied [8–13]. A feature of the coordination chemistry of lanthanide ions is that it has high coordination rates. In the case of metal complexes with Gd3+ that are used in MRI, they tend to present a coordination index of nine. Typically, the Ln3+ cation occupies the center of the structure of the complex, and is linked to eight heteroatoms of a
R. Lamelas et al. / Polyhedron 160 (2019) 180–188
181
Chart 1.
ligand, while the last coordinating position that remains free is occupied by a molecule of water solvent. Ln3+ complexes with different tetrasubstituted heaazamacrocycles derived from L [Chart 1] have been previously synthesized and studied [14–16]. These ligands are potentially decadentade and for large Ln3+ ions the metal is endomacrocyclic coordinated to all donor atoms, while for the smaller ones, coordination number is in some cases reduced to nine, as in LAc4 [17] [Chart 1]. However, the high number of donor atoms present in these tetrasubstituted macrocycles prevents a water molecule can be incorporated into the first coordination sphere of the Ln3+ ion. In an attempt to obtain a new dipyridine receptor able to form stable Ln3+ complexes with one water molecule in the inner sphere of the ions, we have recently synthesized the new trans-N,N0 methylated hexaazamacrocycle L1 [18], derived from L. This new macrocyclic ligand shows two methylated trans amine groups, and it has been prepared using a similar procedures described for trans-disubstituted cyclen macrocycles [13]. The synthesis of the macrocyclic precursors was achieved following the previously described method [19]. As an extension of our work we report here structural studies, in solid and in solution, of the lanthanide complexes with the ligand trans-N,N0 -methylated hexaazamacrocycle L1, derived from L. This macrocyclic receptor L1 could provide a convenient platform for the design of stable Ln3+ complexes for biological applications. Starting from it, a new receptor can be synthesized by alkylation of the trans secondary amine groups presents in the ligand. Some Ln3+ complexes of L1 have been synthesized and characterized by means of analytical and spectroscopic techniques. The crystal structures of the compound salt [H4L1](NO3)4 showing two trans methyl groups and the metal complexes [CeL1(NO3)2] (NO3) and [SmL1(NO3)2](NO3) have also been characterized by single crystal X-ray crystallography. Also, the structure of the complexes in solution has been studied by NMR. Alkylation of the two remaining secondary amine
groups leads to potentially octadentade macrocyclic receptors as in cyclen derivatives. 2. Experimental 2.1. Chemical and starting materials Pyridine-2,6-dicarbaldehyde [20] and L [21], were achieved following the literature. L1 has been synthesized following the previously mentioned methodology developed in the research group [13]. The remaining reagents employed in the synthesis were purchased from Aldrich/Panreac and were used without further purification. The solvents used were of reagent grade and purified by usual methods. 2.2. Measurements Elemental analyses were performed on a Fisons Instruments EA1108 microanalyzer. Infra-red spectra were recorded as KBr disc on a BIO-RAD FTS 175-C spectrometer. MALDI-TOF were recorded using a Bruker autoflex spectrometer (DCTB matrix). Conductivity measurements were carried out in 103 M acetonitrile solutions at r.t. using a Crison Basic 30 conductimeters. The 1H and 13C NMR spectra were recorded in CDCl3 and CD3CN solutions on a Varian 300 MHz spectrometer. Assignments of the 1H and 13C NMR studies for the lanthanide complexes were based on COSY, DEPT and HSQC experiments. All the measurements were recorded at the Universidad de Santiago de Compostela, in the RIAIDT services. 2.3. General procedure for the preparation of the metal complex of L1 A solution of the appropriate hydrated lanthanide salt (0.4 mmol) in acetonitrile (5 mL) was added dropwise to a stirred solution of the ligand L1 (0.4 mmol) in the same solvent (20 mL).
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The solution was softly heated and stirred for 4 h, and the solvent was partially removed to ca. 5 mL. Diethyl ether was infused into the solution, producing powdery precipitates which were isolated by centrifugation, dried under vacuum and characterized as the hydrated metal complexes of L1. 2.3.1. [LaL1](NO3)37H2O Anal. Calc. for C20H44N9O16La (MW: 805.20): C, 29.8; H, 5.5; N, 15.6. Found: C, 29.1; H, 4.9; N, 16.0%. Yield: 37%. IR (KBr, cm1): 1605, 1463 [m(C@N)py and m(C@C)py], 1485, 1383, 1305, 1031 [m (NO3)]. MALDI-MS (m/z): 617.1 [LaL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 191 (1:1). Color: white. 2.3.2. [CeL1](NO3)37H2O Anal. Calc. for C20H44N9O16Ce (MW: 806.20): C, 29.7; H, 5.5; N, 15.6. Found: C, 29.9; H, 4.8; N, 15.9%. Yield: 39%. IR (KBr, cm1): 3256 [m(NH)], 1601, 1462 [m(C@N)py and m(C@C)py], 1487, 1381, 1037 [m(NO3)]. MALDI-MS (m/z): 618.1 [CeL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 200 (1:1). Color: white. 2.3.3. [PrL1](NO3)37H2O Anal. Calc. for C20H44N9O16Pr (MW:807.20): C, 29.7; H, 5.5; N, 15.6. Found: C, 29.1; H, 5.0; N, 15.3%. Yield: 33%. IR (KBr, cm1): 1605, 1464 [m(C@N)py and m(C@C)py], 1486, 1386, 1038 [m(NO3)]. MALDI-MS (m/z): 618.9 [PrL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 189 (1:1). Color: white. 2.3.4. [NdL1](NO3)37H2O Anal. Calc. for C20H44N9O16Nd (MW: 808.20): C, 29.6; H, 5.5; N, 15.5. Found: C, 29.3; H, 5.1; N, 15.0%. Yield: 41%. IR (KBr, cm1): 1605, 1468 [m(C@N)py and m(C@C)py], 1485, 1383, 1305, 1031 [m(NO3)]. MALDI-MS (m/z): 622.0 [NdL1(NO3)2]+. 1 2 1 KM/X cm mol (in CH3CN): 187 (1:1). Color: white. 2.3.5. [SmL1](NO3)37H2O Anal. Calc. for C20H44N9O16Sm (MW: 818.21): C, 29.4; H, 5.4; N, 15.4. Found: C, 29.7; H, 4.9; N, 16.0%. Yield: 34%. IR (KBr, cm1): 3189 [m(NH)], 1607, 1465 [m(C@N)py and m(C@C)py], 1489, 1342, 1036 [m(NO3)]. MALDI-MS (m/z): 630.0 [SmL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 196 (1:1). Color: white. 2.3.6. [EuL1](NO3)37H2O Anal. Calc. for C20H44N9O16Eu (MW: 819.21): C, 29.3; H, 5.4; N, 15.4. Found: C, 29.1; H, 5.0; N, 14.9%. Yield: 43%. IR (KBr, cm1): 3185 [m(NH)], 1609, 1466 [m(C@N)py and m(C@C)py], 1480, 1384, 1310 [m(NO3)]. MALDI-MS (m/z): 631.1 [EuL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 196 (1:1). Color: white. 2.3.7. [GdL1](NO3)37H2O Anal. Calc. for C20H44N9O16Gd (MW: 824.22): C, 29.1; H, 5.5; N, 15.3. Found: C, 28.9; H, 4.8; N, 15.8%. Yield: 45%. IR (KBr, cm1): 1608, 1468 [m(C@N)py and m(C@C)py], 1480, 1385, 1305 [m(NO3)]. MALDI-MS (m/z): 636.2 [GdL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 198 (1:1). Color: white. 2.3.8. [TbL1](NO3)37H2O Anal. Calc. for C20H44N9O16Tb (MW: 825.22): C, 29.1; H, 5.4; N, 15.3. Found: C, 29.5; H, 4.9; N, 16.1%. Yield: 50%. IR (KBr, cm1): 3014 [m(NH)], 1608, 1467 [m(C@N)py and m(C@C)py], 1481, 1386, 1035 [m(NO3)]. MALDI-MS (m/z): 637.2 [TbL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 210 (between 1:1 and 2:1). Color: white. 2.3.9. [DyL1](NO3)34H2O Anal. Calc. for C20H38N9O13Dy (MW: 771.49): C, 31.0; H, 4.9; N, 16.3. Found: C, 31.5; H, 4.7; N, 16.0%. Yield: 53%. IR (KBr, cm1): 1603, 1466 [m(C@N)py and m(C@C)py], 1481, 1384, 1035 [m(NO3)].
MALDI-MS (m/z): 642.2 [DyL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 202 (between 1:1 and 2:1). Color: white. 2.3.10. [HoL1](NO3)37H2O Anal. Calc. for C20H44N9O16Ho (MW: 831.22): C, 28.9; H, 5.3, N; 15.2. Found: C, 28.5; H, 5.0, N; 14.8%. Yield: 59%. IR (KBr, cm1): 3015 [m(NH)], 1609, 1468 [m(C@N)py and m(C@C)py], 1487, 1386, 1305 [m(NO3)]. MALDI-MS (m/z): 643.2 [HoL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 216 (between 1:1 and 2:1). Color: white. 2.3.11. [ErL1](NO3)35H2O Anal. Calc. for C20H40N9O14Er (MW: 795.51): C, 30.1; H, 5.0, N; 15.8. Found: C, 29.9; H, 4.9, N; 16.0%. Yield: 56%. IR (KBr, cm1): 1603, 1466 [m(C@N)py and m(C@C)py], 1489, 1384, 1036 [m(NO3)]. MALDI-MS (m/z): 644.2 [ErL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 205 (between 1:1 and 2:1). Color: white. 2.3.12. [TmL1](NO3)37H2O Anal. Calc. for C20H44N9O16Tm (MW:835.23): C, 28.7; H, 5.3; N, 15.1. Found: C, 28.4; H, 4.9; N, 14.8%. Yield: 55%. IR (KBr, cm1): 3187 [m(NH)], 1608, 1461 [m(C@N)py and m(C@C)py], 1485, 1386, 1306 [m(NO3)]. MALDI-MS (m/z): 647.0 [TmL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 193 (1:1). Color: white. 2.3.13. [YbL1](NO3)37H2O Anal. Calc. for C20H44N9O16Yb (MW: 840.20): C, 28.6: H, 5.3; N, 15.0, Found: C, 28.3; H, 4.8; N, 14.7%. Yield: 70%. (KBr, cm1): 3242 [m(NH)], 1611, 1469 [m(C@N)py and m(C@C)py], 1483, 1385, 1306, 1034 [m(NO3)]. MALDI-MS (m/z): 652.2 [YbL1(NO3)2]+. KM/X1 cm2 mol1 (in CH3CN): 206 (between 1:1 and 2:1). Color: white. 2.4. Crystal structure determinations. Crystals suitable for X-ray diffraction were obtained for [H4L1] (NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3). Measurements were made on a Bruker X8 KappaAPEXII diffractometer. Graphite monochromated Mo Ka was used. All data were correct for Lorentz and polarization effects Empirical absorption corrections were also applied for all the crystal structures obtained [22]. Complex scattering factors were taken from the program package SHELXTL [23]. The structures were solved by directed methods (Patterson for the metal complexes) using SHELX-97 [24] or SIR-92 [25], which revealed the positions pf all mom-hydrogen atoms. All the structures were refined on F2 by a full-matrix least-squares procedure using anisotropic displacement parameters for all non-hydrogen atoms. The hydrogen atoms of the carbons were located in their calculated positions and refined using a riding model. The hydrogen atoms of the amine groups or water molecules were located on a difference Fourier map and refined isotropically. Molecular graphics were obtained with the WebLab ViewerPro [26] and ORTEP-3 [27]. 3. Results and discussion 3.1. Synthesis and characterization of complexes derived from L1 The lanthanide complexes of L1 were synthesized in a 1:1 metal:ligand ratio in acetonitrile, giving rise to compounds of formula [ML1](NO3)3xH2O (M = La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+ and Yb3+) in good yield. All compounds are soluble in DMSO, CH3CN and acetone. The compounds are also soluble in a mixture of DMSO and H2O at 10%.
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N3AH3NA O4N N3AH3NA O6N N2AH2N O3N_$1 N3AH3NA O3N_$1 N3AH3NB O3N_$1 N2AH2N O2N_$2 N2AH2N O3N_$2 N3AH3NB O1N_$2 N3AH3NB O3N_$2
D A
H A
DAH A
3.02(1) 2.80(1) 3.23(1) 2.97(1) 2.972(1) 3.36(1) 2.85(1) 3.23(1) 2.96(1)
2.55(2) 1.96(2) 2.66(2) 2.56(2) 2.58(2) 2.90(2) 2.03(2) 2.63(2) 2.09(2)
114(2) 159(2) 125(2) 110(2) 109(2) 115(2) 159(2) 127(2) 175(2)
$1 x + 1, y + 1, z + 1; $2 x 1, +y, +z.
Table 3 Selected bond lengths (Å) of the metal coordination environment, obtained from the X-ray crystal structures of [Ce(L1)(NO3)2](NO3) and [Sm(L1)(NO3)2](NO3).
LnAN(1) LnAN(2) LnAN(3) LnAN(4) LnAN(5) LnAN(6) LnAO(1N) LnAO(2N) LnAO(5N) LnAO(6N) Fig. 1. X-ray crystal structure of the [H4L1]4+ cation of [H4L1](NO3)4, showing the atomic numbering scheme. The ORTEP plots are the 50% probability level.
The IR spectra were recorded as KBr discs. The bands due to m (C@N) and m(C@C) stretching modes of the pyridine rings on the
[CeL1(NO3)2](NO3)
[SmL1(NO3)2](NO3)
2.713(10) 2.799(8) 2.669(7) 2.631(10) 2.743(8) 2.701(9) 2.560(4) 2.577(5) 2.563(6) 2.586(5)
2.659(12) 2.758(9) 2.647(9) 2.603(13) 2.715(10) 2.671(10) 2.500(8) 2.521(7) 2.517(6) 2.507(5)
complexes of L1 appear displaced when compared with the spectrum of the free ligand (1589, 1460 cm1 in the ligand L1), suggesting the interaction between pyridyl groups and the metal ions [28,29]. The NAH amine stretching vibrations (3312 cm1 in the ligand L1) was shifted to lower frequencies in the spectra of the
Table 1 Crystal data and structure refinement for [H4L1](NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3).
Empirical formula Formula weight T (K) k (Å) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (mg/m3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm) h Range for data collection (°) Index ranges Reflections collected Independent reflections (Rint) Completeness to h (%) Absorption correction Maximum and minimum transmission Refinement method Data/restrains/parameters Absolute structural parameter Godness-of-fit on F2 (GOF) Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)
[H4L1](NO3)4
[CeL1(NO3)2](NO3)
[SmL1(NO3)2](NO3)
C20H34N10O12 606.57 100(2) 0.71073 monoclinic P21/c
C20H30N9O9Ce1 680.62 293(2) 0.71073 orthorombic Pn21a
C20H30N9O9Sm1 690.88 100(2) 0.71073 orthorombic Pn21a
8.756(4) 8.969(4) 16.973(8)
17.515(5) 16.284(5) 8.978(5)
17.478(5) 16.244(5) 8.963(5)
2560.7(18) 4 1.766 1.846 1372 0.22 0.03 0.03 2.33/2.46 0 h 21, 0 k 20, 0 l 11 40,249 2732 [Rint = 0.1072] 99.7% empirical 0.9640 and 0.6869 full-matrix least-squares on F2 2732/1/318 0.04(1) 1.093 R1 = 0.0345; wR2 = 0.0787 R1 = 0.0499; wR2 = 0.1082 1.692 and 1.369
2544.7(18) 4 1.803 2.376 1388 0.30 0.17 0.13 2.33/2.37 0 h 21, 0 k 20, 0 l 11 26,052 2695 [Rint = 0.0610] 100.0% empirical 0.7476 and 0.5358 full-matrix least-squares on F2 2695/1/316 0.04(3) 1.068 R1 = 0.0418; wR2 = 0.1082 R1 = 0.0477; wR2 = 0.1133 2.712 and 1.569
98.741(7) 1317.5(10) 2 1.529 0.127 640 0.27 0.17 0.05 2.35/27.48 11 h 11, 0 k 11, 0 l 22 23,775 3023 [Rint = 0.0717] 100.0% empirical 0.9937 and 0.9665 full-matrix least-squares on F2 3023/0/202 1.032 R1 = 0.0438; wR2 = 0.0965 R1 = 0.0690; wR2 = 0.1087 0.302 and 0.252
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metal complexes, suggesting an interaction between them and the metal ions. In some cases, the band corresponding to the vibration mode of the water, masks the signals of the aminic groups. In all the nitrate complexes several bands in the region associated with nitrate vibrations clearly identify the presence of coordinated nitrate ions [30] whilst an intense band at ca. 1380 cm1 indicates also the presence of ionic nitrate groups [31]. The MALDI mass spectra of the complexes confirmed the formation of the desired lanthanide complexes. In all cases a fragment corresponding to peak [LnL1(NO3)2]+ was observed. The molar conductance values for the complexes of L1, measured in acetonitrile at room temperature, lie in the range reported between 1:1 and 2:1 electrolytes [32]. 3.2. X-ray diffraction Single crystals of [H4L1](NO3)4, suitable for X-ray diffraction, was obtained by slow diffusion of solutions of the ligand and lanthanum nitrate, dissolved in chloroform and acetone respectively. The asymmetric unit is comprised by half molecule of the [H4L1]4+ cation and two nitrate ions. The molecular structure of the [H4L1]4+ cation is shown in Fig. 1. Bond lengths and angles are within the expected values. Crystal data of the compound are collected in Table 1. The ligand shows a nearly plane conformation. The aromatic rings are parallel each other and the intramolecular distance between them is 2.4(1) Å. No inter- or intra-molecular p-stacking interactions have been found in the crystal. Numerous hydrogen bond interactions (Table 2) are observed between nitrate ions and the secondary amine groups of the molecule. Single crystals of [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3) were obtained by slow evaporation of an acetonitrile solution of the corresponding complex and were used for X-ray diffraction analyses. Crystal data of the complexes are collected in the Table 1.
Fig. 2. X-ray crystal structure of the [SmL1(NO3)2]+ cation showing the atomic numbering scheme. Hydrogen atoms are omitted for simplicity. The ortep plots are the 50% probability level.
Selected bond lengths of the lanthanide coordination environments are giving in the Table 3. The Ce3+ and Sm3+ complexes are isostructural, and they crystallize in the orthorhombic, non-centrosymmetric, space group Pn2(1)a. In both complexes, the asymmetric unit contains the cation complex [LnL1(NO3)2]+ (Ln = Ce3+, Sm3+) (see Fig. 2 for the samarium complex) which consist of a mononuclear endomacrocyclic backbone whilst the ten coordination environment is completed by two bidentate nitrate ions. The nitrate groups are located on opposite sides of the best plane defined by the six nitrogen atoms of the ligand. The unit cells of both complexes contain four potential anion-accessible symmetry-related cavities, filled with disordered anions, probably nitrates. The volume of each cavity is ca. 60 Å3. Attempts to model nitrate anions into the solvent cavity did not result in an acceptable model. As an alternative strategy, the SQUEEZE [33] function of PLATON [34] was used to eliminate the contribution of the electron density in the solvent region from the intensity data. The use of this strategy and the subsequent solvent-free model produced better refinement results than the attempt to model the nitrate ions. Therefore, the solvent-free model and intensity data were used for the final results reported here. A total of ca. 34 e was found in each cavity, corresponding approximately to one nitrate per cavity, just the amount necessary to keep the electro neutrality of the compound. Where relevant, the crystal data reported in this paper are given without the contribution of the disordered solvent. The conformation of the macrocycle in the [LnL1(NO3)2]+ cation is almost plane. The dihedral angle between the pyridine units is 17.7° for [CeL1(NO3)2]+, and 19.2° for [SmL1(NO3)2]+ showing that the ligand is slightly twisted and it is practically not folded, with NpyALnANpy angles of 180.0(2) and 179.7(3)° for the Ce3+ and Sm3+ complexes, respectively. The configuration of the nitrogen atoms is SRSR (or RSRS) in both complexes, as the spatial group is centrosymmetric, and the conformation of the two five membered quelate rings due to the coordination of the ethylendiamine fragments to the metal ion is dd (or kk). The trans methyl groups are directed toward the same side of the main macrocyclic hole in an syn conformation. The symmetry of the complexes approaches the C2 group. All the distances decrease in the Ce-Sm direction as expected due to the lanthanide contraction [35]. The LnAO bond lengths are shorter than the LnAN ones, being the LnANPy distances shorter than LnANamine ones.
Fig. 3. Coordination polyhedron in the [CeL1(NO3)2]+ cation.
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185
Fig. 4. Face to face p,p-intermolecular interactions for [CeL1(NO3)2]+.
Complexes with high number of small-bite ligands are usually close to the 2:6:2 polyhedra such as the tetra decahedron and staggered dodecahedron [36]. The minima S(A) values provided by the SHAPE program for the Ce3+ and Sm3+ complexes belongs to the tetra decahedron with S(A) values of 3.336 and 3.478, respectively (Fig. 3) [37]. The hexagonal plane is clearly comprised by the six nitrogen atom from the ligand. Different intermolecular interactions have been observed in the net. The pyridine fragments from each ligand molecule interact thorough face to face p,p-intermolecular interactions with
adjacent molecules [N1,C1-C5 N4_$1, C10_$1AC14_$1 and N4, C10AC14 N1_$2,C1_$2AC5_$2; Symmetry operations for the Ce3+ complex: $1 x + 2, +y + 1/2, z + 2, $2 x + 2, +y 1/2, z + 2. For the Sm3+ complex: $1 x, +y + 1/2, z, $2 x, +y 1/2, z] giving rise to infinite chains. The distance between planes containing that pyridine rings is 3.7(1) Å or 3.66(6) Å for Ce3+ or Sm3+ complex, respectively, whilst the distance between centroids is 3.95(1) Å, for the Ce3+ complex and 3.94(1) Å for Sm3+ complex. The slipped angles are 20° and 22° for Ce3+ and Sm3+ complexes, respectively (Fig. 4).
Fig. 5. 1H NMR spectrum for [LaL1](NO3)37H2O.
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Table 4 H and 13C data for [LaL1](NO3)37H2O.
1
1
d (ppm)
13
H1 H2 H4(ax) H4(eq) H5(ax) H5(eq) H6(ax) H6(eq) H7(ax) H7(eq) H9 H10 NH
7.94 7.42 3.39 4.69 3.09 2.79 3.09 3.09 4.14 4.26 7.42 2.24 3.22
C1 C2 C3 C4 C5 C6 C7 C8 C9 C10
H
(t,2H) (m,2H) (d,2H) (d,2H) (m,2H) (m,2H) (m,2H) (m,2H) (m,2H) (m,2H) (m,2H) (s, 6H) (a, 2H)
C
d (ppm) 140.7 121.66 160.63 60.33 58.97 46.39 54.79 157.62 122.72 44.31
Structure in solution of the complexes with the lightest Ln3+ ions (Ln = LaAEu). The 1H, 13C, DEPT, COSY and HSQC NMR spectra of the lanthanide ion complexes were recorded in CD3CN. The 1H NMR spectrum of the diamagnetic La3+ complex shows thirteen signals (Fig. 5, Table 4), indicating an effective C2 symmetry in solution, as observed in the crystal structures of the Ce3+ and Sm3+ complexes. The two-dimensional spectra allowed us to identify the geminal protons H4, H5, H6 and H7. Specific assignment H4(ax)/H4(eq), H5 (ax)/H5(eq), H6(ax)/H6(eq) and H7(ax)/H7(eq), was made using the stereochemical dependence of the displacements of the protons as a result of the polarization of the CAH bonds due to the electric field generated by the charge of the cation. This effect normally leads to a disappearance of the protons located in the equatorial position [38].
In the 1H NMR spectrum of the La3+ complex, three signals appear for the pyridine rings: H1 at lower field as a triplet while H2 and H9 collapse in a multiplet at 7.42 ppm. The methylene protons H4 give rise to an AB system with 2J = 14.9 Hz. The signals at 4.26 and 4.13 ppm, which are coupled to each other with 2 J = 15.7 Hz, correspond to the H7 protons, and they appear as ABX systems by coupling with the proton of the NH group. The coupling is greater with H7(ax) 3J = 11.7 Hz, than with H(7eq) 3 J = 4.91 Hz. H6 and H5(ax) give rise to a multiplet at 3.09 ppm. The coupling pattern of the signal at 2.79 ppm indicates that it is an equatorial proton, since the axial protons usually experience a strong coupling between the geminal protons and the neighboring axial protons, while the coupling of the equatorial protons is strong only with the germinal ones [39]. Therefore, this signal was assigned to H5(eq). The signal corresponding to H10 appears as a singlet at 2.24 ppm and the NH groups appear at 3.22 ppm as a broad signal. Also, some small signals reveal the presence of a minority compound. Twelve signals (excluding those of the NH protons), appears also in the 1H NMR spectra of the lighter paramagnetic Ce3+–Eu3+ complexes, in agreement with an effective C2 symmetry of the complexes in solution. (Fig. 6, Table 5), The COSY spectrum of the Ce3+ complex, shows cross peaks between the geminal protons H4(ax)/H4(eq), H5(ax)/H5(eq), H6(ax)/H6 (eq) and H7(ax)/H7(eq). The HSQC spectrum allows us to assign the signal at 49.53 ppm to the NH group. The COSY spectrum shows peaks between the NH group and the protons H(6ax) and H(7ax). The widest signals in the 1H NMR spectrum of the paramagnetic complexes correspond to the axial protons due to the dependence that exists between the distance of these protons to the Ln3+ ion, and the relaxation induced by it. This allows us to identify the axial and equatorial protons. The H4 protons show a single crossed peak by coupling between them while the H5 protons also show peaks crossed with the H6. In the Sm3+ complex, the presence of a crossed peak in the COSY spectrum with the NH group allows us to identify the signals of the protons H6 and H7. H(7ax) gives rise to an AX system with 2 J = 15.2 Hz by coupling with H(7eq), while H(7ax) gives rise to an AXX ’system by further coupling with the proton of the NH group with 3J = 11.6 Hz. The methylene protons H4 give rise to an AX system with 2J = 14.8 Hz. The COSY spectrum also shows a cross-peak between the protons H6 and the H5. The H10 signal appears as a singlet at 0.52 ppm and the signal assignable to the NH groups appears at 14.52 ppm as a broad signal.
Fig. 6. 1H NMR spectrum for [CeL1](NO3)37H2O.
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1
1
Ce3+
Pr3+
Nd3+
Sm3+
Eu3+
H1 H2 H4(ax) H4(eq) H5(ax) H5(eq) H6(ax) H6(eq) H7(ax) H7(eq) H9 H10 NH
8.13 3.45 11.39 5.76 7.21 4.24 13.82 17.09 20.28 21.49 11.88 10.28 49.53
7.97 1.01 28.49 14.00 12.33 7.89 30.06 38.44 41.50 46.84 17.81 24.26 106.20
7.06 1.66 13.23 4.93 13.46 12.90 25.97 23.23 28.40 36.04 13.22 13.84 62.55
7.78 6.48 1.39 1.90 1.67 3.60 3.81 4.91 5.63 7.23 8.05 0.52 14.52
8.52 12.30 23.93 7.94 6.94 14.69 36.86 20.31 37.39 20.86 0.532 15.17 47.35
H
The 1H NMR spectra for the heaviest Ln3+ ions (TbALu) show similar features, but a full assignment of the signals was not possible.
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected].
4. Conclusions References A new trans-disubstituted macrocyclic ligand L1 has been obtained in satisfactory yield and purity. The complexation capability of L1 in a 1:1 metal:ligand molar ratio towards the lanthanide metal ions has been investigated. The ligand L1 probably does not have a large enough cavity to give rise to dinuclear endomacrocyclic complexes with these ions, therefore compounds containing cationic and anionic species were obtained. The crystalline structures of [H4L1](NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3) have been determined. In the Ce3+ and Sm3+ complexes, the metal ions showed a 10-coordinate environment due to the coordination of 2 nitrate ligands in a bidentate fashion. A detailed structural analysis of the [Ln(L1)]3+ complexes based on Ln(III)-induced paramagnetic NMR shifts indicated that in CD3CN they presented an effective C2 symmetry (as observed in the crystal structures of the Ce3+ and Sm3+ complexes). While p,p-stacking interactions have been observed between the pyridine rings of [CeL1(NO3)2] (NO3) and [SmL1(NO3)2](NO3), in the case of [H4L1](NO3)4 only have been observed numerous hydrogen bond interactions. The results reported in this work indicate that the macrocyclic cavity of L1 is well suited for the coordination of lanthanide ions. Acknowledgments
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
This work was made possible thanks to the financial support received from the Xunta de Galicia (Galicia, Spain) under the ‘‘Grupos de Referencia Competitiva” Programme (Project GRC2015/009). The authors are indebted to CACTUS (Universidad de Santiago de Compostela) for the X-ray measurements. C. Núñez acknowledges Miguel Servet I Programme (CP16/00139) from the ‘‘Instituto de Salud Carlos III” (Plan Estatal de I + D + i 2013-2016 and European Development Regional Fund) of the Spanish Ministry of Economy and Competitiveness. Conflicts of interest The authors declare no competing interests.
[20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]
Appendix A. Supplementary data
[31]
CCDC 1852166, 1852164 and 1852165 contains the supplementary crystallographic data for [H4L1](NO3)4, [CeL1(NO3)2](NO3) and [SmL1(NO3)2](NO3), respectively. These data can be obtained free
[32] [33] [34] [35]
P. Caravan, J.J. Ellison, J. McMurry, L.B. Lauffer, Chem. Rev. 99 (1999) 2293. P. Caravan, Chem. Soc. Rev. 35 (2006) 512. S. Aime, M. Botta, E. Terreno, Adv. Inorg. Chem. 57 (2005) 173. E.M. Surender, S.J. Bradberry, S.A. Bright, C.P. McCoy, D.C. Williams, T. Gunnlaugsson, J. Am. Chem. Soc. 139 (2017) 381. S. Aime, M. Botta, M. Fassano, E. Terreno, Chem. Soc. Rev. 27 (1998) 19. X. Wang, T. Jin, V. Comblin, A. López-Mut, E. Merciny, J.-F. Desreux, Inorg. Chem. 31 (1992) 1095. E. Toth, E. Brucher, I. Lazar, I. Toth, Inorg. Chem. 33 (1994) 4070. K. Kumar, C.A. Chang, L.C. Francesconi, D.D. Dischino, M.F. Malley, J.Z. Gougoutas, M.F. Tweedle, Inorg. Chem. 33 (1994) 3567. K. Kumar, C.A. Chang, M.F. Tweedle, Inorg. Chem. 32 (1993) 587. K. Kumar, M.F. Tweedle, Inorg. Chem. 32 (1993) 4193. C.A. Chang, L.C. Francesconi, M.F. Malley, K. Kumar, J.Z. Gougoutas, M.F. Tweedle, D.W. Lee, L. Wilson, Inorg. Chem. 32 (1993) 3501. D.F. Caffrey, T. Gunnlaugsson, Dalton Trans. 43 (2014) 17964. E.M. Surender, S. Comby, L. Cavanagh, O. Brennan, T.C. Lee, T. Gunlaugsson, Chem 1 (2016) 438. M.C. Fernández-Fernández, R. Bastida, A. Macías, P. Pérez-Lourido, C. PlatasIglesias, L. Valencia, Inorg. Chem. 45 (2006) 4484. C. Núñez, R. Bastida, A. Macías, M. Mato-Iglesias, C. Platas-Iglesias, L. Valencia, Dalton Trans. (2008) 3841. S.W.A. Bligh, N. Choi, C.F.G.C. Geraldes, S. Knoke, M. McParlin, M.J. Sanganee, T. M. Woodrofee, J. Chem. Soc., Dalton Trans. (1997) 4119. L. Valencia, J. Martínez, A. Macías, R. Bastida, R.A. Carvalho, C.F.C.G. Geraldes, Inorg. Chem. 41 (2002) 5300. R. Lamelas, V. García, A. Liñares, R. Bastida, E. Labisbal, A. Fernández-Lodeiro, C. Lodeiro, C. Núñez, L. Valencia, Sens. Actuators B: Chem. 225 (2016) 481. G. Royal, V. Dahaoui-Gindrey, S. Dahaoui, A. Tabard, R. Guilard, P. Pullumbi, C. Lecomte, Eur. J. Org. Chem. (1998) 1971. P. Moore, N.W. Alcook, R.G. Kingston, C. Pierpoint, J. Chem. Soc., Dalton Trans. (1984) 1937. G.L. Rothermel Jr., L. Miao, A.L. Hill, S.C. Jackels, Inorg. Chem. 31 (1992) 4854. G.M. Sheldrick, SADABS. Program of empirical Absorption Correction of Area Detector Data, University of Göttingen, Germany, 1996. shelxtl Versión, An integrated System for Solving and Refining Crystal Structures from Diffraction Data (Revisión 5.1), Bruker AXS LTD. G.M. Sheldrick, SHELX-97 An Integrated System for Solving and Refining Crystal Structures from Diffraction Data, University of Göttingen, Germany, 1997, p. 2. A. Altornare, G. Cascarano, C. Giacovazzo, A. Gualardi, J. Appl. Crystallogr. 26 (1993) 343. WebLab Viewer, Molecular Simulations Inc., 2000. L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565. N.S. Grill, R.H. Nutall, D.E. Scaife, D.W. Sharp, J. Inorg. Nucl. Chem. 18 (1961) 79. S. Aime, M. Botta, U. Casellato, S. Tamburini, P.A. Vigato, Inorg. Chem. 34 (1995) 5825. W.T. Carnall, S. Siegel, J.F. Ferraro, B. Tani, E. Gebert, Inorg. Chem. 12 (1973) 560. P. Guerriero, U. Casellato, S. Tamburini, P.A. Vigato, R. Graziani, Inorg. Chim. Acta 129 (1987) 127. W.J. Geary, Coord. Chem. Rev. 7 (1971) 81. P. van der Sluis, A.L. Spek, Acta Crystallogr., Sect. A 46 (1990) 194. A.L. Spek, PLATON, University of Utrecht, The Netherlands, 2001. M. Seitz, A.G. Oliver, K.N. Raymond, J. Am. Chem. Soc. 129 (2007) 11153.
188
R. Lamelas et al. / Polyhedron 160 (2019) 180–188
[36] A. Ruíz-Martínez, S. Álvarez, Chem. Eur. J. 15 (2009) 7470. [37] M. Llunell, D. Casanova, J. Cirera, P. Alemany, S. Álvarez. S. SHAPE. Program for the Stereochemical Analysis of Molecular Fragments by Means of Continuous Shape Measures and Associated Tools, Version 2.1.
[38] R.K. Harris, Nuclear Magnetic Resonance Spectroscopy: A Physicochemical View, 1983. [39] S. Aime, M. Botta, G. Ermondi, Inorg. Chem. 31 (1992) 4291.