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Rare earth thiocyanate complexes with 18-crown-6 co-ligands
Polyhedron 52 (2013) 560–564
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Rare earth thiocyanate complexes with 18-crown-6 co-ligands Jacinta M. Bakker, Glen B. Deacon, Peter C. Junk ⇑ School of Chemistry, Monash University, Clayton, Vic. 3800, Australia
a r t i c l e
i n f o
Article history: Available online 24 August 2012 Dedicated to Alfred Werner on the 100th Anniversary of his Nobel prize in Chemistry in 1913.
a b s t r a c t Reaction of [Ln(NCS)3(THF)4]2 or [Yb(NCS)3(THF)4] with 18-crown-6 yields the moisture-stable [Ln(NCS)3(18-crown-6)] (Ln = La, Nd, Dy, Yb) complexes. Although the Ln contraction does not affect the coordination number, the crown ether is decreasingly folded with decreasing ion size. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Lanthanoids Rare earths Thiocyanates Crown ethers
1. Introduction Building on earlier interest in complexes of lanthanoid(II/III) thiocyanates with tetrahydrofuran (THF) and 1,2-dimethoxyethane (dme) [1–6], we have recently published a comprehensive study of their syntheses from the commercially available Hg(SCN)2 by redox transmetallation, and the structures of a wide range of [Ln(NCS)3 (L)n] and [Ln(NCS)2(L)n] (L = THF or dme) complexes [7]. All were highly moisture sensitive. However, it is apparent that multidentate ligands can give water-stable complexes. For example, [Ln(NCS)3 (tetg)(H2O)] (Ln = Sm or Ce; tetg = tetramethylene glycol) species are isolated as aqua complexes, which are nine coordinate [8a,b]. 2,20 -60 ,200 -Terpyridine complexes are also moisture stable [8c]. With the same intention, a miscellaneous range of Ln(NCS)3 complexes with an N-p-chlorophenyl-aza-15-crown-5 ligand [9], with diaza-18-crown-6 ligands [10,11], hexa-aza-18-crown-6 [12], dibenzo-30-crown-10 [13], and dibenzo-18-crown-6 [14] have been structurally characterised. However, only one X-ray crystal structure of a Ln(NCS)3 complex with 18-crown-6 has been reported, namely 10-coordinate [La(NCS)3(18-crown-6)(Me2NCHO)] [15]. Other complexes have been prepared but their structures have not been determined [16]. We now report the synthesis and structures of [Ln(NCS)3(18-crown-6)] complexes with a wide variation in Ln3+ ionic radius. Previous LnII/III(NCS)n (n = 2, 3) complexes with THF and dme show several different structural responses to the lanthanoid contraction [7]. Complexes between LnCl3 and 18-crown-6 show considerable variety [17]. There is a change from [LnCl2(H2O) ⇑ Corresponding author. Present address: School of Pharmacy & Molecular Sciences, James Cook University, Townsville, Qld. 4811, Australia. E-mail addresses: [email protected], [email protected] (P.C. Junk). 0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2012.08.028
(18-crown-6)]Cl for Ln = La, Ce to [LnCl(H2O)2(18-crown-6)]Cl2 for Ln = Pr–Tb, though all are nine-coordinate [17a] and there are variations in associated water of crystallisation for Ln = La, Ce. Variation in crystallisation conditions lead to anhydrous [LaCl3(18-crown-6)] [17a], [Ln(H2O)7(MeOH)][LnCl(OH)2(18-crown-6)]2Cl7 (Ln = Tb, Dy) with eight coordination for the complex cations without the crown ether [17b], or even expulsion of the crown from the coordination sphere in [Dy(H2O)8]Cl318-crown-64H2O [17c]. 2. Results and discussion Treatment of [Ln(NCS)3(THF)4]2 (Ln = La, Nd, Dy) and [Yb(NCS)3(THF)4] [7] with dried 18-crown-6 in THF gave complexes 1a–1d.
1=x½LnðNCSÞ3 ðTHFÞ4 x þ 18-crown-6 THF
! ½LnðNCSÞ3 ð18-crown-6Þ yTHF
(Ln = La (1a), x = 2, y = 0; Ln = Nd (1b), Dy (1c), x = 2, y = 1; Ln = Yb (1d), x = 1, y = 1). Single crystals were obtained of 1b–1d, and microanalyses or metal analyses on the crystals were in agreement with the single crystal composition. On the other hand, 1a deposited as a powder under the same conditions that gave single crystals of 1b–1d, and was isolated without THF of crystallisation, as indicated by microanalysis. The X-ray powder diffractogram of 1a was in agreement with that of powdered 1b and both differed from the X-ray powder diffractogram generated from single crystal data for 1b. In addition, the IR spectra of all four compounds after grinding to powders for Nujol mulls were similar and showed no clear evidence for the presence of tetrahydrofuran. Thus, it appears from both X-ray
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powder and IR data that the THF of crystallisation of 1b–1d is lost on grinding the crystals into a powder. The complexes were all air (moisture)-stable in contrast to the THF complexes used as reagents. Thus, a Nujol mull of 1a was exposed to the atmosphere for three days without significant change in the IR spectrum. From 1a to 1d, m(CN) [18] increases progressively from 2038 to 2057 cm1 attributable to increased Lewis acidity of Ln3+ as the ionic radius contracts, whilst m(CS) is observed near 835 cm1 as expected for an isothiocyanato complex [18].
2.1. Structures of complexes 1b–1d X-ray structure determinations showed that they were isostructural and isomorphous, with the composition [Ln(NCS)3(18-crown6)]THF. The lanthanoid metal atoms are nine-coordinate (commonly observed for Ln halide crown ether complexes [17,19]), bonding to three isothiocyanate ligands and six oxygen donor atoms from the 18-crown-6 which is bonded in an in cavity fashion (Fig. 1a). The THF molecule resides in the lattice. The 18-crown-6 molecule was disordered in (1d) and successfully modelled over two positions. The stereochemistry of the metal centres for compounds (1b– 1d) is distorted monocapped square antiprismatic, where the capping atom is O(4) (Fig. 1b) [20,21]. From the bond length data (Table 1), hLn–Ni decreases by more than expected from ionic radius differences [22], whereas hLn–Oi decreases by less than expected, indicating that the steric strain imposed by the lanthanoid contraction is borne by the 18-crown-6 O–Ln binding. However, unlike THF and dme complexes of Ln(NCS)3, there is no change in coordination number/stereochemistry from Nd to Yb, nor is there any displacement of NCS from the coordination sphere by the donor solvent (THF) as observed in LnCl3/18-crown-6 complexes [17]. Reported nine-coordinate Nd complexes, [Nd(NCS)3(DD18C6)] (DD18C6 = dibenzyldiaza-18-crown-6), [11b] [Nd(terpy)2(NCS)3]xEtOH (terpy = 2,20 :60 ,200 -terpyridine; x = 0 or 2) [8c] and [Nd(phen)3(NCS)3]EtOH (phen = 1,10-phenanthroline) [8c] display Nd–N(NCS) bond lengths ranging between 2.466(1)–2.522(2), 2.498(2)–2.580(2) and 2.488(4)–2.498(4) Å respectively. These are somewhat larger, and the first two cover a larger range than those of (1b) (Table 1), indicating that the steric demands of 18-crown-6 are less than for DD18C6, 2 terpy or 3 phen ligands because of greater flexibility of 18-crown-6. [Dy(NCS)3(dibenzo-30-crown10)(H2O)2]H2OMeCN displays Dy–N bond lengths ranging between 2.26(1) and 2.402(9) Å encompassing the much narrower range for (1c) [13a]. The average length of Dy–N bonds in eight coordinate [Dy(NCS)3(dme)2(l-dme)0.5] is 2.35 Å [7], which is relatively
Fig. 1a. The structure of (1c), isostructural with (1b) and (1d). Ellipsoids shown at 50% probability, hydrogen atoms omitted for clarity.
Fig. 1b. The donor atom geometry about the metal centres in (1b–1d).
Table 1 Selected bond lengths (Å) and angles (°) for complexes (1b–1d). (1b)
(1c)
(1d)
Bond lengths Ln(1)–N(1) Ln(1)–N(2) Ln(1)–N(3) Ln–N(av) Ln(1)–O(1) Ln(1)–O(2) Ln(1)–O(3) Ln(1)–O(4) Ln(1)–O(5) Ln(1)–O(6) Ln–O(av) N(1)–C(1) N(2)–C(2) N(3)–C(3) S(1)–C(1) S(2)–C(2) S(3)–C(3)
2.460(5) 2.469(5) 2.471(5) 2.47 2.579(4) 2.564(4) 2.579(4) 2.585(4) 2.550(4) 2.593(4) 2.58 1.171(7) 1.177(7) 1.151(7) 1.619(6) 1.625(6) 1.636(6)
2.367(3) 2.351(3) 2.381(3) 2.37 2.512(2) 2.517(2) 2.527(2) 2.519(2) 2.487(2) 2.539(2) 2.52 1.158(4) 1.162(4) 1.158(4) 1.615(3) 1.617(3) 1.629(3)
2.320(5) 2.312(5) 2.335(5) 2.32 2.476(5) 2.466(5) 2.499(4) 2.487(5) 2.477(5) 2.507(5) 2.49 1.154(7) 1.148(8) 1.171(7) 1.617(6) 1.626(7) 1.631(6)
Bond angles N(1)–Ln(1)–N(2) N(2)–Ln(1)–N(3) N(1)–Ln(1)–N(3) Ln(1)–N(1)–C(1) Ln(1)–N(2)–C(2) Ln(1)–N(3)–C(3)
142.0(2) 75.8(2) 142.0(2) 136.2(4) 165.7(5) 173.4(4)
141.69(9) 76.59(9) 140.66(9) 174.3(2) 170.0(2) 174.9(2)
143.2(2) 76.1(2) 140.6(2) 165.7(5) 172.8(5) 170.2(5)
slightly longer compared with the average Dy–N bond length in (1c) after consideration of the effects of the different coordination numbers [22]. The nine-coordinate Yb complex [Yb(NCS)3(TDCO)] (TDCO = 1,7,10,16-tetraoxa-4,13-diazacyclooctadecane) displays Yb–N(NCS) bond lengths (2.351(9)–2.385(9) Å) [10] which are longer than in (1d) perhaps indicating extra steric crowding in the former complex because of reduced flexibility from inclusion of two N-donor atoms in the crown host. By contrast with Nd–N bond lengths of (1b), the Nd–O bond lengths are somewhat longer than those of [Nd(NCS)3(DD18C6)] (2.546(1)–2.571(3) Å) [11b] but within the range for [Nd(NCS)3 (dme)3] (2.518(2)–2.642(2) Å) [7], though the difference in Nd–N values is much more than in Nd–O data. Comparable Dy–O(ether) bond lengths are found between (1c) and [Dy(Hoda)3]H2odaH2O (oda = oxydiacetate) [23]. Nine-coordinate [Yb(NCS)3(TDCO)] exhibits an average Yb–O bond length of 2.52 Å [10] which is slightly longer than in (1d) (2.49 Å), but again the effect is much less marked than differences in Yb–N bond lengths.
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Table 2 The fold in the 18-crown-6 molecule for complexes (1b–1d). The values are the angle between the planes O(1)O(2)O(3)O(4) and O(4)O(5)O(6)O(1). Complex
Angle between planes (°)
(1b) (1c) (1d)
59.7(1) 66.88(9) 70.2(2)
other forming an oval involving six of the [Ln(NCS)3(18-crown-6)] molecules around two lattice THF molecules. Possibly (1a) has holes too large to retain THF of crystallisation, and hence failure to form single crystals. In addition, THF may be too weak a donor to bind to [La(NCS)3(18-crown-6)] thereby raising the coordination number as observed in the structurally characterised [La(NCS)3(18crown-6)(Me2NCHO)] [15]. 3. Conclusions
The N@C and C@S bond distances are comparable in all thiocyanate ligands of (1b–1d). The N–Ln–N angles in the three crystal structures of (1b–1d) (Table 1) were similar with a distorted Y-shaped geometry (Fig. 1b). The nine-coordinate complex, [LaCl3(18-crown-6)], displays similar Cl–La–Cl angles (142°, 140° and 78°) [17a] and [Yb(NCS)3(TDCO)] has N(NCS)–Yb–N(NCS) angles of 143°, 138° and 76° [10]. Upon coordination to metal ions, the ideal D3h 18-crown-6 conformation [24] is often disturbed as the host molecule manipulates itself to accommodate the guest. The 18-crown-6 molecules in complexes (1b) and (1c) display a C2(A+) (gauche angle sequence g, g+, g+, g, g+, g+) [24] geometry. In (1d) it is difficult to unequivocally decipher which parts of the disorder should be combined together. Of the four possible combinations of gauche sequences, only two are commonly observed: C2(A–) (g+, g, g, g+, g, g) or S2 (g+, g+, g, g+, g, g) [24]. The C2(A–) conformation is more likely to be correct as it is also observed in [LaCl3(18-crown-6)] [17a]. Torsion angles are given in Table S1. Comparison of the angle between the relevant planes surrounding O1 and O4 in complexes (1b–1d) shows decreased strain on the 18-crown-6 molecule in the sequence 1b–1d (Table 2 and Fig. S1). In (1b–1d), two thiocyanate ligands (containing N(2) and N(3)) coordinate to the metal cation on the less crowded side of the crown ether while the other thiocyanate (N(1)) ligand coordinates on the concave side of the crown ether (Fig. 1a). The importance of the lattice THF molecule is illustrated when viewing the packing of complexes (1b–1d) along the a-axis (C2) (Fig. 2), where the monomeric structures pack directly behind each
In contrast to the trivalent rare earth thiocyanate complexes with dme and THF [7], the lanthanoid contraction does not cause structural changes in the rare earth thiocyanate 18-crown-6 series for Nd, Dy and Yb (1b–1d) derivatives, as all analogues display nine coordinate monomeric structures [Ln(NCS)3(18-crown-6)]THF with distorted monocapped square antiprismatic stereochemistry. Although the La derivative (1a) could not be obtained as single crystals suitable for single crystal X-ray crystallography, powder XRD, elemental analyses and IR spectroscopy suggest a similar structure, but the increased size of La3+ may account for lack of THF of crystallisation. The fold between the planes of atoms O(1)O(2)O(3)O(4) and O(4)O(5)O(6)O(1) of the 18-crown-6 host becomes more obtuse as the metal guest becomes smaller. All complexes are air/moisture stable once isolated in contrast to the THF complexed precursors. 4. Experimental 4.1. General All manipulations were carried out under an inert atmosphere of purified nitrogen using conventional glove box and Schlenk techniques owing to the air and moisture sensitivity of the reactants. Tetrahydrofuran (THF) was distilled from sodium benzophenone ketyl over sodium wire, and toluene and hexane were distilled from sodium wire into dry storage flasks equipped with Teflon taps and stored under nitrogen. 18-Crown-6 (Sigma–Aldrich) was dried under vacuum and stored in the dry box. IR spectra were recorded
Fig. 2. Packing of complexes (1b–1d) when viewed down the a-axis illustrating the lattice THF molecules filling the cavities in between six monomeric crown complexes.
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between 4000 and 650 cm1 as Nujol mulls between NaCl plates with a Perkin-Elmer 1600 FTIR instrument. Melting points were determined in sealed glass capillaries under nitrogen and are uncalibrated. Samples were sent in sealed glass pipettes under nitrogen to Campbell Microanalytical Laboratory, Chemistry Department, University of Otago Dunedin, New Zealand for microanalyses (C, H, N). Rare earth metal analyses were determined by titration of the undigested sample against a standardised Na2H2edta solution using Xylenol orange as the indicator and hexamethylenetetramine as the buffer. X-ray powder diffraction measurements were run on a Phillips powder diffractometer using a Cu anode at 1.54059 Å and a carbon monochromator. The pictogram was measured in 0.2° steps at a rate of 2°/min. 4.2. Syntheses of complexes (1a–1d) General: [RE(NCS)3(THF)4]2 (RE = La, Nd, Dy) and [Yb(NCS)3 (THF)4] were prepared in an inert atmosphere by redox transmetallation reactions or by the oxidation of [Yb(NCS)2(THF)4] (synthesised by redox transmetallation [5]) with 0.5 equiv of Hg(SCN)2 respectively [7]. The dinuclear rare earth thiocyanate complexes and monomeric [Yb(NCS)3(THF)4] were combined with 2.2 and 1.1 stoichiometric equivalents respectively of 18-crown-6 in a Schlenk flask which was subsequently charged with THF. The reaction mixture was stirred for a number of days (below) at room temperature and contained a significant amount of precipitate. Filtration through a filter cannula and concentration of the filtrate, gave crystals of 1b–1d. The precipitated powder from the initial reaction mixture was washed with toluene to remove excess 18crown-6 and dried under reduced pressure before being characterised (IR identical with that of single crystals). To determine yields, the reactions were repeated, the reaction mixture was evaporated to dryness, and the solid product washed thoroughly with toluene and characterised by IR spectra, which were identical with those of single crystals. 4.2.1. [La(NCS)3(18-crown-6)] (1a) [La(NCS)3(THF)4]2 powder (0.85 g, 0.71 mmol) and 18-crown-6 (0.40 g, 1.52 mmol) in THF (60 ml) were stirred for 4 days at ambient temperature. The filtrate was separated and concentrated to crystallisation, but a fine white precipitate deposited instead of single crystals. Yield: 0.78 g, 95%; mp 228 °C (dec.); IR (Nujol cm1): m = 2063 sh, 2053 sh, 2042 vs 1348 m, 1290 m, 1250 w, 1239 w, 1105 m, 1082 s, 1069 s, 1032 m, 969 m, 926 vw, 879 vw, 835 m, 805 vw. Anal. Calc. for C15H24N3O6S3La (577.47 no lattice THF): C, 31.20; H, 4.19; N, 7.28. Found: C, 31.67; H, 4.29; N, 7.02%. Powder XRD data: d-spacings and relative intensities: 9.14 (47), 8.92 (35), 8.16 (47), 7.57 (100), 6.14 (41), 6.08 (35), 5.91 (59), 5.85 (41), 5.82 (35), 5.45 (35), 5.06 (35), 5.02 (35), 4.88 (41), 4.84 (41), 4.78 (41), 4.55 (41), 4.29 (47). 4.2.2. [Nd(NCS)3(18-crown-6)]THF (1b) [Nd(NCS)3(THF)4]2 (0.25 g, 0.21 mmol) and 18-crown-6 (0.12 g, 0.45 mmol) in THF (30 ml) were stirred for 1 week at ambient temperature. The filtrate was separated, concentrated to 5 ml and allowed to stand at room temperature until a mixture of powder and a small amount of single needle shaped crystals suitable for X-ray crystallography were deposited. Yield: 0.31 g, 93%; mp 228 (dec.) °C; IR (Nujol cm1): m = 2045 vs 1351 w, 1289 w, 1247 w, 1106 m, 1078 s, 1065 sh, 1030 w, 964 m, 878 vw, 835 w, 816 vw, 801 vw, 742 w, 699 vw. Anal. Calc. for C19H32NdN3O7S3, (654.91): C, 34.84; H, 4.92; N, 6.42. Found: C, 35.30; H, 5.28; N, 5.09%. Powder XRD data: d-spacings and relative intensities: 9.14 (47), 8.99 (40), 8.12 (47), 7.58 (100), 6.13 (47), 6.09 (47), 5.88 (47), 5.84 (40), 5.78 (40), 5.50 (33), 5.18 (33), 5.03 (40), 4.99 (40), 4.92 (47), 4.83 (40), 4.76 (33), 4.59 (33), 4.27 (53). Simulated PXRD
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data from the single crystal structure determination: d-spacings and relative intensities: 12.70 (20), 11.65 (30), 9.25 (100), 7.58 (24), 7.20 (46), 6.96 (62), 5.89 (28), 5.54 (19), 5.14 (18), 4.89 (54), 4.22 (12). 4.2.3. [Dy(NCS)3(18-crown-6)]THF (1c) [Dy(NCS)3(THF)4]2 (0.10 g, 0.08 mmol) and 18-crown-6 (0.05 g, 0.18 mmol) in THF (30 ml) were stirred for 2 days at ambient temperature. The filtrate was separated and concentrated to ca. 3 ml causing a small number of rod shaped colourless crystals suitable for X-ray crystallography to deposit. Yield: 0.08 g, 72%; mp 314– 318 °C (dec); IR (Nujol cm1): m = 2054 vs 1600 w, 1352 m, 1288 m, 1243 m, 1111 s, 1080 vs, 1070 sh, 1031 sh, 963 vs, 932 sh, 880 w, 838 m, 804 w, 742s, 699 m. Anal. Calc. for C19H32DyN3O7S3 (673.16): Dy 24.14. Found: Dy 23.34%. 4.2.4. [Yb(NCS)3(18-crown-6)]THF (1d) [Yb(NCS)3(THF)4] (0.20 g, 0.31 mmol) and 18-crown-6 (0.09 g, 0.35 mmol) in THF (30 ml) were stirred overnight at ambient temperature. The filtrate was separated and concentrated to ca. 3 ml causing bright yellow crystalline needles suitable for X-ray crystallography to deposit after 3 days. Yield: 0.17 g, 79%; mp 279– 284 °C; IR (Nujol cm1): m = 2057 vs 1351 w, 1291 w, 1249 w, 1239 sh, 1110 sh, 1071 s, 1062 sh, 964 m, 881 vw, 835 w, 804 vw, 701 vw. Anal. Calc. for C19H32N3O7S3Yb (683.70): Yb 25.31. Found: Yb 25.19%. 4.3. X-ray crystallography experimental Crystalline samples of (1c–1d) were mounted on glass fibres in viscous hydrocarbon oil at 123 K. Data were collected on a Bruker X8 ApexII diffractometer (with monochromated Mo Ka radiation (k = 0.71073 Å)) processed by using the SAINT [25] and SADABS [26] package (Bruker). The structures were solved by direct methods, and all reflections were used in least squares refinement on F2, with anisotropic thermal parameters refined for non-hydrogen atoms. Hydrogen atoms were placed in calculated positions using a riding model. Structural solution and refinement were carried out using the SHELX suite of programs [27,28] with the graphical interface X-seed [29]. 4.3.1. [Nd(NCS)3(18-crown-6)]THF (1b) C19H32N3NdO7S3, M = 654.90, blue rod, 0.07 0.06 0.04 mm3, monoclinic, space group P21/c (No. 14), a = 7.3387(2), b = 23.3454(6), c = 15.2641(4) Å, b = 96.1730(10)°, V = 2599.96(12) Å3, Z = 4, Dcalc = 1.673 g/cm3, F000 = 1324, 2hmax = 47.8°, 18854 reflections collected, 4021 unique (Rint = 0.0527). Final Goodness-of-fit = 1.268, R1 = 0.0420, wR2 = 0.0730, R indices based on 3682 reflections with I > 2r(I) (refinement on F2), 298 parameters, 0 restraints. Lp and absorption corrections applied, l = 2.280 mm1. 4.3.2. [Dy(NCS)3(18-crown-6)]THF (1c) C19H32DyN3O7S3, M = 673.16, colourless rod, 0.25 0.10 0.10 mm3, monoclinic, space group P21/c (No. 14), a = 7.6376(2), b = 22.4489(7), c = 15.1010(5) Å, b = 93.381(2)°, V = 2584.65(14) Å3, Z = 4, Dcalc = 1.730 g/cm3, F000 = 1348, 2hmax = 55.0°, 28 412 reflections collected, 5929 unique (Rint = 0.0341). Final Goodnessof-fit = 1.219, R1 = 0.0284, wR2 = 0.0504, R indices based on 5562 reflections with I > 2r(I) (refinement on F2), 299 parameters, 0 restraints. Lp and absorption corrections applied, l = 3.176 mm1. 4.3.3. [Yb(NCS)3(18-crown-6)]THF (1d) C19H32N3O7S3Yb, M = 683.70, yellow block, 0.27 0.25 0.12 mm3, monoclinic, space group P21/c (No. 14), a = 7.8734(4), b = 21.7805(9), c = 14.9885(6) Å, b = 92.6740(10)°, V = 2567.5(2) Å3, Z = 4, Dcalc = 1.769 g/cm3, F000 = 1364, 2hmax = 55.0°, 12 249
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reflections collected, 5895 unique (Rint = 0.0309). Final Goodnessof-fit = 1.130, R1 = 0.0456, wR2 = 0.0955, R indices based on 5041 reflections with I > 2r(I) (refinement on F2), 341 parameters, 21 restraints. Lp and absorption corrections applied, l = 3.929 mm1. 4.3.4. Details Some carbon atoms (C5A C5B; C15A C15B; C13A C13B; C14A C14B) in the 18-crown-6 molecule were disordered over two positions and were modelled and refined to be reasonable. S2 was also disordered and modelled over two positions. Further restraints were added for the anisotropic refinement of the disordered atoms. The lattice THF molecule was refined isotropically and is disordered over four positions, two of which are related by symmetry. Appendix A. Supplementary data CCDC 882177–882179 contain the supplementary crystallographic data for this paper. These data can be obtained free 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]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.poly.2012.08.028. References [1] [2] [3] [4] [5] [6] [7]
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[8] (a) A.N. Zhao, X. Cheng, Chin. Chem. Lett. 3 (1992) 1025; (b) N. Zhao-Ai, L. Feng, X. Cheng, Chem. J. Chin. Univ. 13 (1992) 1349; (c) S.A. Cotton, V. Frankevicius, R.E. How, B. Ahrens, L.L. Ooi, M.F. Mahon, P.R. Raithby, S.J. Teat, Polyhedron 22 (2003) 1489. [9] L. Luo, M.-L. Wei, S.-P. Yan, G.-L. Wang, H.-G. Wang, X.-K. Yao, Chem. J. Chin. Univ. (Chin. Ed.) 13 (1992) 1201. [10] F. Benetollo, G. Bombieri, G. Depaoli, M.R. Truter, Inorg. Chim. Acta 245 (1996) 223. [11] (a) M.I. Saleh, A. Salhin, B. Saad, S.M. Zain, Z. Arifin, J. Mol. Struct. 415 (1997) 71; (b) M.I. Saleh, A. Salhin, B. Saad, H.-K. Fun, J. Mol. Struct. 475 (1999) 93. [12] (a) G. Bombieri, F. Benetollo, A. Polo, L. De Cola, W.T. Hawkins, L.M. Vallarino, Polyhedron 8 (1989) 2157; (b) F. Benetollo, G. Bombieri, W.A. Gootee, K.K. Fonda, K.M. Samaria, L.M. Vallarino, Polyhedron 17 (1998) 3633; (c) F. Benetollo, G. Bombieri, K.M. Samaria, L.M. Vallarino, J. Chem. Crystallogr. 26 (1996) 9. [13] (a) S. Yan, S. Jiang, D. Liao, G. Wang, R. Wang, H. Wang, X. Yao, J. Inclusion Phenom. Mol. Recognit. Chem. 15 (1993) 159; (b) S. Yan, G. Wang, H. Wang, X. Yao, Polyhedron 10 (1991) 1869. [14] Z. Xu, Y. Gu, Q. Zheng, F. Shen, C. Yao, S. Yan, G. Wang, Wuli Xuebao 31 (1982) 956. [15] J.G. Mao, Z.S. Jin, J.Z. Ni, Jiegou Huaxue 13 (1994) 329. [16] A. Cassol, A. Seminaro, G. De Paoli, Inorg. Nucl. Chem. Lett. 9 (1973) 1163. [17] (a) R.D. Rogers, A.N. Rollins, R.D. Etzenhouser, E.J. Voss, C.B. Bauer, Inorg. Chem. 32 (1993) 3451; (b) R.D. Rogers, L.K. Kurihara, E.J. Voss, Inorg. Chem. 26 (1987) 2360; (c) R.D. Rogers, Inorg. Chim. Acta 133 (1987) 347. [18] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds: Part B: Applications in Coordination, Organometallic and Bioinorganic Chemistry, sixth ed., Wiley, 2008. p121. [19] G. Meyer, J. Alloys Compd. 300–301 (2000) 113. [20] M. Johnson, J.C. Taylor, G.W. Cox, J. Appl. Crystallogr. 13 (1980) 188. [21] M.C. Favas, D.L. Kepert, Prog. Inorg. Chem. 28 (1981) 309. [22] R.D. Shannon, Acta Crystallogr., Sect. A 32 (1976) 751. [23] R. Baggio, M. Perec, M.T. Garland, Acta Crystallogr., Sect. E 59 (2003) m994. [24] T.M. Fyles, R.D. Gandour, J. Inclusion Phenom. 12 (1992) 313. [25] SAINT and SADABS are part of the ApexII software package, Bruker AXS, Madison, WI, USA. [26] R.H. Blessing, Acta Crystallogr., Sect. E 51 (1995) 33. [27] G.M. Sheldrick, SHELXL-97, University of Göttingen, Germany, 1997. [28] G.M. Sheldrick, SHELXS-97, University of Göttingen, Germany, 1997. [29] L.J. Barbour, J. Supramol. Chem. 1 (2003) 189.
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Rare earth thiocyanate complexes with 18-crown-6 co-ligands Jacinta M. Bakker, Glen B. Deacon, Peter C. Junk ⇑ School of Chemistry, Monash University, Clayton, Vic. 3800, Australia
a r t i c l e
i n f o
Article history: Available online 24 August 2012 Dedicated to Alfred Werner on the 100th Anniversary of his Nobel prize in Chemistry in 1913.
a b s t r a c t Reaction of [Ln(NCS)3(THF)4]2 or [Yb(NCS)3(THF)4] with 18-crown-6 yields the moisture-stable [Ln(NCS)3(18-crown-6)] (Ln = La, Nd, Dy, Yb) complexes. Although the Ln contraction does not affect the coordination number, the crown ether is decreasingly folded with decreasing ion size. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Lanthanoids Rare earths Thiocyanates Crown ethers
1. Introduction Building on earlier interest in complexes of lanthanoid(II/III) thiocyanates with tetrahydrofuran (THF) and 1,2-dimethoxyethane (dme) [1–6], we have recently published a comprehensive study of their syntheses from the commercially available Hg(SCN)2 by redox transmetallation, and the structures of a wide range of [Ln(NCS)3 (L)n] and [Ln(NCS)2(L)n] (L = THF or dme) complexes [7]. All were highly moisture sensitive. However, it is apparent that multidentate ligands can give water-stable complexes. For example, [Ln(NCS)3 (tetg)(H2O)] (Ln = Sm or Ce; tetg = tetramethylene glycol) species are isolated as aqua complexes, which are nine coordinate [8a,b]. 2,20 -60 ,200 -Terpyridine complexes are also moisture stable [8c]. With the same intention, a miscellaneous range of Ln(NCS)3 complexes with an N-p-chlorophenyl-aza-15-crown-5 ligand [9], with diaza-18-crown-6 ligands [10,11], hexa-aza-18-crown-6 [12], dibenzo-30-crown-10 [13], and dibenzo-18-crown-6 [14] have been structurally characterised. However, only one X-ray crystal structure of a Ln(NCS)3 complex with 18-crown-6 has been reported, namely 10-coordinate [La(NCS)3(18-crown-6)(Me2NCHO)] [15]. Other complexes have been prepared but their structures have not been determined [16]. We now report the synthesis and structures of [Ln(NCS)3(18-crown-6)] complexes with a wide variation in Ln3+ ionic radius. Previous LnII/III(NCS)n (n = 2, 3) complexes with THF and dme show several different structural responses to the lanthanoid contraction [7]. Complexes between LnCl3 and 18-crown-6 show considerable variety [17]. There is a change from [LnCl2(H2O) ⇑ Corresponding author. Present address: School of Pharmacy & Molecular Sciences, James Cook University, Townsville, Qld. 4811, Australia. E-mail addresses: [email protected], [email protected] (P.C. Junk). 0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2012.08.028
(18-crown-6)]Cl for Ln = La, Ce to [LnCl(H2O)2(18-crown-6)]Cl2 for Ln = Pr–Tb, though all are nine-coordinate [17a] and there are variations in associated water of crystallisation for Ln = La, Ce. Variation in crystallisation conditions lead to anhydrous [LaCl3(18-crown-6)] [17a], [Ln(H2O)7(MeOH)][LnCl(OH)2(18-crown-6)]2Cl7 (Ln = Tb, Dy) with eight coordination for the complex cations without the crown ether [17b], or even expulsion of the crown from the coordination sphere in [Dy(H2O)8]Cl318-crown-64H2O [17c]. 2. Results and discussion Treatment of [Ln(NCS)3(THF)4]2 (Ln = La, Nd, Dy) and [Yb(NCS)3(THF)4] [7] with dried 18-crown-6 in THF gave complexes 1a–1d.
1=x½LnðNCSÞ3 ðTHFÞ4 x þ 18-crown-6 THF
! ½LnðNCSÞ3 ð18-crown-6Þ yTHF
(Ln = La (1a), x = 2, y = 0; Ln = Nd (1b), Dy (1c), x = 2, y = 1; Ln = Yb (1d), x = 1, y = 1). Single crystals were obtained of 1b–1d, and microanalyses or metal analyses on the crystals were in agreement with the single crystal composition. On the other hand, 1a deposited as a powder under the same conditions that gave single crystals of 1b–1d, and was isolated without THF of crystallisation, as indicated by microanalysis. The X-ray powder diffractogram of 1a was in agreement with that of powdered 1b and both differed from the X-ray powder diffractogram generated from single crystal data for 1b. In addition, the IR spectra of all four compounds after grinding to powders for Nujol mulls were similar and showed no clear evidence for the presence of tetrahydrofuran. Thus, it appears from both X-ray
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powder and IR data that the THF of crystallisation of 1b–1d is lost on grinding the crystals into a powder. The complexes were all air (moisture)-stable in contrast to the THF complexes used as reagents. Thus, a Nujol mull of 1a was exposed to the atmosphere for three days without significant change in the IR spectrum. From 1a to 1d, m(CN) [18] increases progressively from 2038 to 2057 cm1 attributable to increased Lewis acidity of Ln3+ as the ionic radius contracts, whilst m(CS) is observed near 835 cm1 as expected for an isothiocyanato complex [18].
2.1. Structures of complexes 1b–1d X-ray structure determinations showed that they were isostructural and isomorphous, with the composition [Ln(NCS)3(18-crown6)]THF. The lanthanoid metal atoms are nine-coordinate (commonly observed for Ln halide crown ether complexes [17,19]), bonding to three isothiocyanate ligands and six oxygen donor atoms from the 18-crown-6 which is bonded in an in cavity fashion (Fig. 1a). The THF molecule resides in the lattice. The 18-crown-6 molecule was disordered in (1d) and successfully modelled over two positions. The stereochemistry of the metal centres for compounds (1b– 1d) is distorted monocapped square antiprismatic, where the capping atom is O(4) (Fig. 1b) [20,21]. From the bond length data (Table 1), hLn–Ni decreases by more than expected from ionic radius differences [22], whereas hLn–Oi decreases by less than expected, indicating that the steric strain imposed by the lanthanoid contraction is borne by the 18-crown-6 O–Ln binding. However, unlike THF and dme complexes of Ln(NCS)3, there is no change in coordination number/stereochemistry from Nd to Yb, nor is there any displacement of NCS from the coordination sphere by the donor solvent (THF) as observed in LnCl3/18-crown-6 complexes [17]. Reported nine-coordinate Nd complexes, [Nd(NCS)3(DD18C6)] (DD18C6 = dibenzyldiaza-18-crown-6), [11b] [Nd(terpy)2(NCS)3]xEtOH (terpy = 2,20 :60 ,200 -terpyridine; x = 0 or 2) [8c] and [Nd(phen)3(NCS)3]EtOH (phen = 1,10-phenanthroline) [8c] display Nd–N(NCS) bond lengths ranging between 2.466(1)–2.522(2), 2.498(2)–2.580(2) and 2.488(4)–2.498(4) Å respectively. These are somewhat larger, and the first two cover a larger range than those of (1b) (Table 1), indicating that the steric demands of 18-crown-6 are less than for DD18C6, 2 terpy or 3 phen ligands because of greater flexibility of 18-crown-6. [Dy(NCS)3(dibenzo-30-crown10)(H2O)2]H2OMeCN displays Dy–N bond lengths ranging between 2.26(1) and 2.402(9) Å encompassing the much narrower range for (1c) [13a]. The average length of Dy–N bonds in eight coordinate [Dy(NCS)3(dme)2(l-dme)0.5] is 2.35 Å [7], which is relatively
Fig. 1a. The structure of (1c), isostructural with (1b) and (1d). Ellipsoids shown at 50% probability, hydrogen atoms omitted for clarity.
Fig. 1b. The donor atom geometry about the metal centres in (1b–1d).
Table 1 Selected bond lengths (Å) and angles (°) for complexes (1b–1d). (1b)
(1c)
(1d)
Bond lengths Ln(1)–N(1) Ln(1)–N(2) Ln(1)–N(3) Ln–N(av) Ln(1)–O(1) Ln(1)–O(2) Ln(1)–O(3) Ln(1)–O(4) Ln(1)–O(5) Ln(1)–O(6) Ln–O(av) N(1)–C(1) N(2)–C(2) N(3)–C(3) S(1)–C(1) S(2)–C(2) S(3)–C(3)
2.460(5) 2.469(5) 2.471(5) 2.47 2.579(4) 2.564(4) 2.579(4) 2.585(4) 2.550(4) 2.593(4) 2.58 1.171(7) 1.177(7) 1.151(7) 1.619(6) 1.625(6) 1.636(6)
2.367(3) 2.351(3) 2.381(3) 2.37 2.512(2) 2.517(2) 2.527(2) 2.519(2) 2.487(2) 2.539(2) 2.52 1.158(4) 1.162(4) 1.158(4) 1.615(3) 1.617(3) 1.629(3)
2.320(5) 2.312(5) 2.335(5) 2.32 2.476(5) 2.466(5) 2.499(4) 2.487(5) 2.477(5) 2.507(5) 2.49 1.154(7) 1.148(8) 1.171(7) 1.617(6) 1.626(7) 1.631(6)
Bond angles N(1)–Ln(1)–N(2) N(2)–Ln(1)–N(3) N(1)–Ln(1)–N(3) Ln(1)–N(1)–C(1) Ln(1)–N(2)–C(2) Ln(1)–N(3)–C(3)
142.0(2) 75.8(2) 142.0(2) 136.2(4) 165.7(5) 173.4(4)
141.69(9) 76.59(9) 140.66(9) 174.3(2) 170.0(2) 174.9(2)
143.2(2) 76.1(2) 140.6(2) 165.7(5) 172.8(5) 170.2(5)
slightly longer compared with the average Dy–N bond length in (1c) after consideration of the effects of the different coordination numbers [22]. The nine-coordinate Yb complex [Yb(NCS)3(TDCO)] (TDCO = 1,7,10,16-tetraoxa-4,13-diazacyclooctadecane) displays Yb–N(NCS) bond lengths (2.351(9)–2.385(9) Å) [10] which are longer than in (1d) perhaps indicating extra steric crowding in the former complex because of reduced flexibility from inclusion of two N-donor atoms in the crown host. By contrast with Nd–N bond lengths of (1b), the Nd–O bond lengths are somewhat longer than those of [Nd(NCS)3(DD18C6)] (2.546(1)–2.571(3) Å) [11b] but within the range for [Nd(NCS)3 (dme)3] (2.518(2)–2.642(2) Å) [7], though the difference in Nd–N values is much more than in Nd–O data. Comparable Dy–O(ether) bond lengths are found between (1c) and [Dy(Hoda)3]H2odaH2O (oda = oxydiacetate) [23]. Nine-coordinate [Yb(NCS)3(TDCO)] exhibits an average Yb–O bond length of 2.52 Å [10] which is slightly longer than in (1d) (2.49 Å), but again the effect is much less marked than differences in Yb–N bond lengths.
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Table 2 The fold in the 18-crown-6 molecule for complexes (1b–1d). The values are the angle between the planes O(1)O(2)O(3)O(4) and O(4)O(5)O(6)O(1). Complex
Angle between planes (°)
(1b) (1c) (1d)
59.7(1) 66.88(9) 70.2(2)
other forming an oval involving six of the [Ln(NCS)3(18-crown-6)] molecules around two lattice THF molecules. Possibly (1a) has holes too large to retain THF of crystallisation, and hence failure to form single crystals. In addition, THF may be too weak a donor to bind to [La(NCS)3(18-crown-6)] thereby raising the coordination number as observed in the structurally characterised [La(NCS)3(18crown-6)(Me2NCHO)] [15]. 3. Conclusions
The N@C and C@S bond distances are comparable in all thiocyanate ligands of (1b–1d). The N–Ln–N angles in the three crystal structures of (1b–1d) (Table 1) were similar with a distorted Y-shaped geometry (Fig. 1b). The nine-coordinate complex, [LaCl3(18-crown-6)], displays similar Cl–La–Cl angles (142°, 140° and 78°) [17a] and [Yb(NCS)3(TDCO)] has N(NCS)–Yb–N(NCS) angles of 143°, 138° and 76° [10]. Upon coordination to metal ions, the ideal D3h 18-crown-6 conformation [24] is often disturbed as the host molecule manipulates itself to accommodate the guest. The 18-crown-6 molecules in complexes (1b) and (1c) display a C2(A+) (gauche angle sequence g, g+, g+, g, g+, g+) [24] geometry. In (1d) it is difficult to unequivocally decipher which parts of the disorder should be combined together. Of the four possible combinations of gauche sequences, only two are commonly observed: C2(A–) (g+, g, g, g+, g, g) or S2 (g+, g+, g, g+, g, g) [24]. The C2(A–) conformation is more likely to be correct as it is also observed in [LaCl3(18-crown-6)] [17a]. Torsion angles are given in Table S1. Comparison of the angle between the relevant planes surrounding O1 and O4 in complexes (1b–1d) shows decreased strain on the 18-crown-6 molecule in the sequence 1b–1d (Table 2 and Fig. S1). In (1b–1d), two thiocyanate ligands (containing N(2) and N(3)) coordinate to the metal cation on the less crowded side of the crown ether while the other thiocyanate (N(1)) ligand coordinates on the concave side of the crown ether (Fig. 1a). The importance of the lattice THF molecule is illustrated when viewing the packing of complexes (1b–1d) along the a-axis (C2) (Fig. 2), where the monomeric structures pack directly behind each
In contrast to the trivalent rare earth thiocyanate complexes with dme and THF [7], the lanthanoid contraction does not cause structural changes in the rare earth thiocyanate 18-crown-6 series for Nd, Dy and Yb (1b–1d) derivatives, as all analogues display nine coordinate monomeric structures [Ln(NCS)3(18-crown-6)]THF with distorted monocapped square antiprismatic stereochemistry. Although the La derivative (1a) could not be obtained as single crystals suitable for single crystal X-ray crystallography, powder XRD, elemental analyses and IR spectroscopy suggest a similar structure, but the increased size of La3+ may account for lack of THF of crystallisation. The fold between the planes of atoms O(1)O(2)O(3)O(4) and O(4)O(5)O(6)O(1) of the 18-crown-6 host becomes more obtuse as the metal guest becomes smaller. All complexes are air/moisture stable once isolated in contrast to the THF complexed precursors. 4. Experimental 4.1. General All manipulations were carried out under an inert atmosphere of purified nitrogen using conventional glove box and Schlenk techniques owing to the air and moisture sensitivity of the reactants. Tetrahydrofuran (THF) was distilled from sodium benzophenone ketyl over sodium wire, and toluene and hexane were distilled from sodium wire into dry storage flasks equipped with Teflon taps and stored under nitrogen. 18-Crown-6 (Sigma–Aldrich) was dried under vacuum and stored in the dry box. IR spectra were recorded
Fig. 2. Packing of complexes (1b–1d) when viewed down the a-axis illustrating the lattice THF molecules filling the cavities in between six monomeric crown complexes.
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between 4000 and 650 cm1 as Nujol mulls between NaCl plates with a Perkin-Elmer 1600 FTIR instrument. Melting points were determined in sealed glass capillaries under nitrogen and are uncalibrated. Samples were sent in sealed glass pipettes under nitrogen to Campbell Microanalytical Laboratory, Chemistry Department, University of Otago Dunedin, New Zealand for microanalyses (C, H, N). Rare earth metal analyses were determined by titration of the undigested sample against a standardised Na2H2edta solution using Xylenol orange as the indicator and hexamethylenetetramine as the buffer. X-ray powder diffraction measurements were run on a Phillips powder diffractometer using a Cu anode at 1.54059 Å and a carbon monochromator. The pictogram was measured in 0.2° steps at a rate of 2°/min. 4.2. Syntheses of complexes (1a–1d) General: [RE(NCS)3(THF)4]2 (RE = La, Nd, Dy) and [Yb(NCS)3 (THF)4] were prepared in an inert atmosphere by redox transmetallation reactions or by the oxidation of [Yb(NCS)2(THF)4] (synthesised by redox transmetallation [5]) with 0.5 equiv of Hg(SCN)2 respectively [7]. The dinuclear rare earth thiocyanate complexes and monomeric [Yb(NCS)3(THF)4] were combined with 2.2 and 1.1 stoichiometric equivalents respectively of 18-crown-6 in a Schlenk flask which was subsequently charged with THF. The reaction mixture was stirred for a number of days (below) at room temperature and contained a significant amount of precipitate. Filtration through a filter cannula and concentration of the filtrate, gave crystals of 1b–1d. The precipitated powder from the initial reaction mixture was washed with toluene to remove excess 18crown-6 and dried under reduced pressure before being characterised (IR identical with that of single crystals). To determine yields, the reactions were repeated, the reaction mixture was evaporated to dryness, and the solid product washed thoroughly with toluene and characterised by IR spectra, which were identical with those of single crystals. 4.2.1. [La(NCS)3(18-crown-6)] (1a) [La(NCS)3(THF)4]2 powder (0.85 g, 0.71 mmol) and 18-crown-6 (0.40 g, 1.52 mmol) in THF (60 ml) were stirred for 4 days at ambient temperature. The filtrate was separated and concentrated to crystallisation, but a fine white precipitate deposited instead of single crystals. Yield: 0.78 g, 95%; mp 228 °C (dec.); IR (Nujol cm1): m = 2063 sh, 2053 sh, 2042 vs 1348 m, 1290 m, 1250 w, 1239 w, 1105 m, 1082 s, 1069 s, 1032 m, 969 m, 926 vw, 879 vw, 835 m, 805 vw. Anal. Calc. for C15H24N3O6S3La (577.47 no lattice THF): C, 31.20; H, 4.19; N, 7.28. Found: C, 31.67; H, 4.29; N, 7.02%. Powder XRD data: d-spacings and relative intensities: 9.14 (47), 8.92 (35), 8.16 (47), 7.57 (100), 6.14 (41), 6.08 (35), 5.91 (59), 5.85 (41), 5.82 (35), 5.45 (35), 5.06 (35), 5.02 (35), 4.88 (41), 4.84 (41), 4.78 (41), 4.55 (41), 4.29 (47). 4.2.2. [Nd(NCS)3(18-crown-6)]THF (1b) [Nd(NCS)3(THF)4]2 (0.25 g, 0.21 mmol) and 18-crown-6 (0.12 g, 0.45 mmol) in THF (30 ml) were stirred for 1 week at ambient temperature. The filtrate was separated, concentrated to 5 ml and allowed to stand at room temperature until a mixture of powder and a small amount of single needle shaped crystals suitable for X-ray crystallography were deposited. Yield: 0.31 g, 93%; mp 228 (dec.) °C; IR (Nujol cm1): m = 2045 vs 1351 w, 1289 w, 1247 w, 1106 m, 1078 s, 1065 sh, 1030 w, 964 m, 878 vw, 835 w, 816 vw, 801 vw, 742 w, 699 vw. Anal. Calc. for C19H32NdN3O7S3, (654.91): C, 34.84; H, 4.92; N, 6.42. Found: C, 35.30; H, 5.28; N, 5.09%. Powder XRD data: d-spacings and relative intensities: 9.14 (47), 8.99 (40), 8.12 (47), 7.58 (100), 6.13 (47), 6.09 (47), 5.88 (47), 5.84 (40), 5.78 (40), 5.50 (33), 5.18 (33), 5.03 (40), 4.99 (40), 4.92 (47), 4.83 (40), 4.76 (33), 4.59 (33), 4.27 (53). Simulated PXRD
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data from the single crystal structure determination: d-spacings and relative intensities: 12.70 (20), 11.65 (30), 9.25 (100), 7.58 (24), 7.20 (46), 6.96 (62), 5.89 (28), 5.54 (19), 5.14 (18), 4.89 (54), 4.22 (12). 4.2.3. [Dy(NCS)3(18-crown-6)]THF (1c) [Dy(NCS)3(THF)4]2 (0.10 g, 0.08 mmol) and 18-crown-6 (0.05 g, 0.18 mmol) in THF (30 ml) were stirred for 2 days at ambient temperature. The filtrate was separated and concentrated to ca. 3 ml causing a small number of rod shaped colourless crystals suitable for X-ray crystallography to deposit. Yield: 0.08 g, 72%; mp 314– 318 °C (dec); IR (Nujol cm1): m = 2054 vs 1600 w, 1352 m, 1288 m, 1243 m, 1111 s, 1080 vs, 1070 sh, 1031 sh, 963 vs, 932 sh, 880 w, 838 m, 804 w, 742s, 699 m. Anal. Calc. for C19H32DyN3O7S3 (673.16): Dy 24.14. Found: Dy 23.34%. 4.2.4. [Yb(NCS)3(18-crown-6)]THF (1d) [Yb(NCS)3(THF)4] (0.20 g, 0.31 mmol) and 18-crown-6 (0.09 g, 0.35 mmol) in THF (30 ml) were stirred overnight at ambient temperature. The filtrate was separated and concentrated to ca. 3 ml causing bright yellow crystalline needles suitable for X-ray crystallography to deposit after 3 days. Yield: 0.17 g, 79%; mp 279– 284 °C; IR (Nujol cm1): m = 2057 vs 1351 w, 1291 w, 1249 w, 1239 sh, 1110 sh, 1071 s, 1062 sh, 964 m, 881 vw, 835 w, 804 vw, 701 vw. Anal. Calc. for C19H32N3O7S3Yb (683.70): Yb 25.31. Found: Yb 25.19%. 4.3. X-ray crystallography experimental Crystalline samples of (1c–1d) were mounted on glass fibres in viscous hydrocarbon oil at 123 K. Data were collected on a Bruker X8 ApexII diffractometer (with monochromated Mo Ka radiation (k = 0.71073 Å)) processed by using the SAINT [25] and SADABS [26] package (Bruker). The structures were solved by direct methods, and all reflections were used in least squares refinement on F2, with anisotropic thermal parameters refined for non-hydrogen atoms. Hydrogen atoms were placed in calculated positions using a riding model. Structural solution and refinement were carried out using the SHELX suite of programs [27,28] with the graphical interface X-seed [29]. 4.3.1. [Nd(NCS)3(18-crown-6)]THF (1b) C19H32N3NdO7S3, M = 654.90, blue rod, 0.07 0.06 0.04 mm3, monoclinic, space group P21/c (No. 14), a = 7.3387(2), b = 23.3454(6), c = 15.2641(4) Å, b = 96.1730(10)°, V = 2599.96(12) Å3, Z = 4, Dcalc = 1.673 g/cm3, F000 = 1324, 2hmax = 47.8°, 18854 reflections collected, 4021 unique (Rint = 0.0527). Final Goodness-of-fit = 1.268, R1 = 0.0420, wR2 = 0.0730, R indices based on 3682 reflections with I > 2r(I) (refinement on F2), 298 parameters, 0 restraints. Lp and absorption corrections applied, l = 2.280 mm1. 4.3.2. [Dy(NCS)3(18-crown-6)]THF (1c) C19H32DyN3O7S3, M = 673.16, colourless rod, 0.25 0.10 0.10 mm3, monoclinic, space group P21/c (No. 14), a = 7.6376(2), b = 22.4489(7), c = 15.1010(5) Å, b = 93.381(2)°, V = 2584.65(14) Å3, Z = 4, Dcalc = 1.730 g/cm3, F000 = 1348, 2hmax = 55.0°, 28 412 reflections collected, 5929 unique (Rint = 0.0341). Final Goodnessof-fit = 1.219, R1 = 0.0284, wR2 = 0.0504, R indices based on 5562 reflections with I > 2r(I) (refinement on F2), 299 parameters, 0 restraints. Lp and absorption corrections applied, l = 3.176 mm1. 4.3.3. [Yb(NCS)3(18-crown-6)]THF (1d) C19H32N3O7S3Yb, M = 683.70, yellow block, 0.27 0.25 0.12 mm3, monoclinic, space group P21/c (No. 14), a = 7.8734(4), b = 21.7805(9), c = 14.9885(6) Å, b = 92.6740(10)°, V = 2567.5(2) Å3, Z = 4, Dcalc = 1.769 g/cm3, F000 = 1364, 2hmax = 55.0°, 12 249
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reflections collected, 5895 unique (Rint = 0.0309). Final Goodnessof-fit = 1.130, R1 = 0.0456, wR2 = 0.0955, R indices based on 5041 reflections with I > 2r(I) (refinement on F2), 341 parameters, 21 restraints. Lp and absorption corrections applied, l = 3.929 mm1. 4.3.4. Details Some carbon atoms (C5A C5B; C15A C15B; C13A C13B; C14A C14B) in the 18-crown-6 molecule were disordered over two positions and were modelled and refined to be reasonable. S2 was also disordered and modelled over two positions. Further restraints were added for the anisotropic refinement of the disordered atoms. The lattice THF molecule was refined isotropically and is disordered over four positions, two of which are related by symmetry. Appendix A. Supplementary data CCDC 882177–882179 contain the supplementary crystallographic data for this paper. These data can be obtained free 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]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.poly.2012.08.028. References [1] [2] [3] [4] [5] [6] [7]
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