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Transition metal complexes of 1,3-bis(thiomorpholino)propane: crystal structure and dynamic 1H NMR study
Inorganica Chimica Acta 285 (1999) 31±38
Transition metal complexes of 1,3-bis(thiomorpholino)propane: crystal structure and dynamic 1H NMR study Yongxin Lia, Yee-Hing Laia, K.F. Moka,*, Michael G.B. Drewb a
Department of Chemistry, National University of Singapore, Kent Ridge 119260, Singapore Department of Chemistry, The University of Reading, Whiteknights, Reading RG6 6AD, UK
b
Received 22 September 1997; received in revised form 27 March 1998; accepted 12 May 1998
Abstract Complexes of 1,3-bis(thiomorpholino)propane (L) with Zn(II), Pd(II), Pt(II) and Rh(III) of the formula [ZnLCl2], [ML](ClO4)2, (M Pd and Pt), [RhLCl2]Cl4H2O and [RhLCl2]PF6 were prepared and characterised. The molecular structures of [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 were determined by X-ray diffraction. In [ZnLCl2], the ligand acts in a bidentate fashion using its two N atoms while the two S atoms remain free and the coordination structure is a distorted tetrahedron. [PdL](ClO4)2 possesses a distorted square planar coordination geometry with all the four hetero atoms being coordinated. The coordination structure of [RhLCl2]PF6 is a distorted octahedron with the two Cl atoms in trans position and L also acting as a tetradentate ligand. In addition to the crystal structures, the dynamic 1 H NMR behaviour of the three complexes were also investigated. # 1999 Elsevier Science S.A. All rights reserved. Keywords: Crystal structures; Transition metal complexes; Thiomorpholine complexes
1. Introduction
2. Experimental
It is well known that small cyclic ligands, such as piperazine [1±3], morpholine [4] and thiomorpholine [5,6], are able to form complexes with a range of transition metals. Diversity in their coordinating behaviour makes them an interesting family of ligands. However, information in the literature on complexes of such ligands is relatively scarce, especially on that of thiomorpholine [5,6] and its derivatives. Possibly this is because thiomorpholine is not an effective chelating ligand as it prefers the low-energy chair conformation to the boat conformation which is required for the ligand to act in a bidentate fashion. Furthermore, there is much current interest in the use of MN2S2 complexes as structural and spectroscopic models for the coordination environments of active sites in a number of metalloproteins [7±10]. We have recently synthesised and characterised a series of thiomorpholine derivatives and their transition metal complexes [11]. In this paper, we report a thiomorpholine derivative, 1,3-bis(thiomorpholino)propane (L), and its complexes with Zn(II), Pd(II), Pt(II) and Rh(III). Crystal structures have shown that the thiomorpholine moieties of the ligand can adopt both chair and boat conformations upon complex formation, depending on the nature of the metal.
All metal salts were of AR grade and used as received. Thiomorpholine and 1,3-dibromopropane from Aldrich, USA were used without further puri®cation. Melting points were determined using a Thermo-Galen III Hot Stage microscope apparatus. All the proton NMR spectra were measured in CD3CN on a Bruker AMX-500 spectrometer with standard variable-temperature equipment using tetramethylsilane as internal reference. Elemental analyses were performed in the Microanalytical Laboratory of the Department of Chemistry, National University of Singapore. Conductivity measurements were carried out on a STEM 1000 conductivity meter at 308C.
*Corresponding author. Tel.: +65-7722-6589; fax: +65-779-1691.
2.1. 1,3-bis(thiomorpholino)propane (L) A mixture of 1,3-dibromopropane (1.01 g, 5 mmol), thiomorpholine (1.02 g, 10 mmol) and Na2CO3 (1.10 g, 10.4 mmol) in water (7 ml) was heated to re¯ux for 10 h, cooled to room temperature and extracted with chloroform (3 50 ml). The organic layers were combined, dried and the solvent evaporated to give a pale yellow oil. The crude product was dissolved in ethanol (10 ml) and precipitated as hydrochloride salt by adding concentrated HCl (2 ml) to the ethanolic solution. Recrystallisation of the precipitate from
0020-1693/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S0020-1693(98)00260-6
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Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
aqueous ethanol afforded the pure hydrochloride salt as a white powder. The salt was then treated with 10 M NaOH (10 ml) and the solution was extracted with chloroform (3 20 ml). The combined organic layers were dried and the solvent evaporated under reduced pressure to give the ligand as a colourless oil which crystallised slowly upon standing at room temperature (0.75 g, 61%). 1 H NMR: 2.63±2.58 (m, 16H, NCH2CH2S), 2.31 (t, 4H, J 7.3 Hz, 1.56 (quintet, 2H, J 7.3 Hz, CH2CH2CH2), CH2CH2CH2); MS (M): m/z (%) 246 (7), 216 (74), 199 (10), 187 (7), 143 (46), 130 (40), 116 (100), 102 (76), 96 (51), 88 (64), 70 (64), 56 (62), 42 (76); Anal. Calc. for C11H22N2S2 : C, 53.61; H, 9.00; N, 11.37; S, 26.02. Found: C, 53.58; H, 9.13; N, 11.43; S, 26.07%. 2.2. Dichloro(1,3-bis(thiomorpholino)propane)zinc(II) [ZnLCl2] ZnCl2 (34 mg, 0.25 mmol) in methanol (5 ml) was added with stirring to L (62 mg, 0.25 mmol) in methanol (5 ml). Upon standing at room temperature for 1 day, colourless crystals precipitated from the solution. The crystals were ®ltered off, washed with ethanol and diethyl ether and dried under vacuum. Yield: 72 mg (75%); m.p. 284±2868C. 1 H NMR: 3.71 (b, 4H), 3.41 (b, 4H), 2.93 (b, 4H), 2.64 (b, 8H), 1.96 (the signal is overlapped by the solvent peaks); M (CHCl3): negligible. Anal. Calc. for C11H22Cl2N2S2Zn: C, 34.54; H, 5.79; N, 7.32; S, 16.76. Found: C, 34.69; H, 5.87; N, 7.10; S, 16.74%. 2.3. 1,3-bis(thiomorpholino)propanepalladium(II) perchlorate [PdL](ClO4)2 To a solution of PdCl2(CH3CN)2 (31 mg, 0.12 mmol) in CH3CN (4 ml) was added a solution of AgClO4 (50 mg, 0.24 mmol) in CH3CN (4 ml). The mixture was stirred at room temperature for 30 min and the precipitate ®ltered off. The ®ltrate was added dropwise to a solution of L (32 mg, 0.13 mmol) in CH3CN (6 ml) with stirring. After stirring for 1 h, the solution was ®ltered and vapour diffused with diethyl ether at room temperature. Pale yellow crystals precipitated from the solution which were ®ltered off and dried. Yield: 50 mg (76%); m.p. 2408C (decomp). 1 H NMR (298 K): 3.88 (b, 4H), 3.54 (b, 4H), 3.03±2.97 (m, centred at 3.00, 4H), 2.89 (b, 4H), 2.81 (m, 4H), 2.06 (m, 2H); M (CH3CN): 278 (S cm2 molÿ1) (1:2). Anal. Calc. for C11H22Cl2N2O8S2Pd: C, 24.00; H, 4.03; N, 5.09; S, 11.63. Found: C, 23.90; H, 3.90; N, 5.37; S, 11.37%. Caution: perchlorates are hazardous. 2.4. 1,3-bis(thiomorpholino)propaneplatinum(II) perchlorate [PtL](ClO4)2 To a solution of PtCl2(CH3CN)2 (42 mg, 0.12 mmol) in CH3CN (4 ml) was added a solution of AgClO4 (50 mg, 0.24 mmol) in CH3CN (4 ml). The mixture was stirred at
room temperature for 10 h and the precipitate ®ltered off. The ®ltrate was added dropwise to a solution of L (32 mg, 0.13 mmol) in CH3CN (6 ml) with stirring. After stirring for 5 h, the solution was ®ltered and vapour diffused with diethyl ether at room temperature. Colourless crystals precipitated from the solution which were ®ltered off and dried. Yield: 50 mg (65%); m.p. > 2908C (decomp). 1 H NMR: 3.75 (b, 4H), 3.41 (b, 4H), 3.13±3.07 (m, centred at 3.10, 4H), 2.98 (b, 4H), 3.19±2.80 (very broad, 4H), 2.09 (b, 2H); M (CH3CN): 299 (S cm2 molÿ1) (1:2). Anal. Calc. for C11H22Cl2N2O8S2Pt: C, 20.63; H, 3.46; N, 4.37; S, 10.01. Found: C, 20.54; H, 3.41; N, 4.74; S, 10.00%. 2.5. Dichloro-1,3-bis(thiomorpholino)propanerhodium(III) chloride tetrahydrate [RhLCl2]Cl4H2O To a solution of RhCl3 (21 mg, 0.10 mmol) in acetonitrile/ethanol (vol./vol. 1:20, 20 ml) was added a solution of L (27 mg, 0.11 mmol) in acetonitrile (10 ml). The mixture was heated to re¯ux for 10 h until the precipitate formed was dissolved to give a brown solution. After ®ltration to remove the insolubles, the solution was concentrated to about 5 ml and vapour diffused with ether to afford orange ¯aky crystals. Yield: 25 mg (55%); m.p. 110±1138C. 1 H NMR: 4.00 (b, 4H), 3.68 (b, 4H), 3.12 (m, 4H), 2.68 (m, 8H), 2.30 (b, 2H); M (CH3CN): 132 (S cm2 molÿ1) (1:1). Anal. Calc. for C11H30Cl3N2O4RhS2: C, 25.03; H, 5.73; N, 5.31; S, 12.15. Found: C, 25.31; H, 5.63; N, 5.02; S, 12.12%. 2.6. Dichloro-1,3-bis(thiomorpholino)propanerhodium(III) hexafluorophosphate [RhLCl2]PF6 To a solution of [RhLCl2]Cl4H2O (53 mg, 0.10 mmol) in ethanol (8 ml) was added a solution of NH4PF6 (20 mg, 0.12 mmol) in ethanol (8 ml). Orange precipitate, which was formed slowly, was ®ltered off, washed with ethanol and ether and air dried. Yield: 51 mg (90%); m.p. 2358C (decomp). 1 H NMR: 4.00 (b, 4H), 3.68 (b, 4H), 3.12 (m, 4H), 2.68 (b, 8H), 2.30 (b, 2H); M (CH3CN): 140 (S cm2 molÿ1) (1:1). Anal. Calc. for C11H22Cl2F6N2PRhS2: C, 23.38; H, 3.92; N, 4.96; S, 11.35. Found: C, 23.43; H, 3.62; N, 4.79; S, 11.31%. 2.7. Crystallographic analyses Crystals used for X-ray analysis were of approximate dimensions 0.28 0.30 0.15 mm, 0.43 0.33 0.20 mm and 0.28 0.13 0.13 mm for [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 respectively. Data were collected at room temperature on a Siemens SMART diffractometer ®tted with a CCD area detector, using graphite-monochromated Ê ). A hemisphere of data Mo Ka radiation (l 0.71073 A was collected for each complex, at 20±30 s/frame. The data frames were integrated using SAINT [12] program and SADABS [13] was used for absorption effects on a Silicon Graphics Indigo 2 computer. The structures were solved by
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Table 1 Crystal and refinement data for [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 Compound code [ZnLCl2] Formula C11H22Cl2N2S2Zn Crystal system monoclinic Space group P21/c Ê) a (A 10.919(2) Ê) b (A 11.405(1) Ê) c (A 13.846(2) (8) 107.67(1) Ê 3) V (A 1642.9(4) Z 4 Dc (g cmÿ3) 1.547 Dm (g cmÿ3) 1.52 F (000) 792 (mmÿ1) 2.060 h Range ÿ10 to 13 k Range ÿ14 to 14 l Range ÿ16 to 17 Reflection collected 9207 Reflection refined 3342 Goodness of fit 1.048 Ra (observed, all data) 0.0261, 0.0330 wR2b (observed, all data) 0.0646, 0.0671 P P a R jj Fo j ÿ jFo jj= jFo j. P P b wR2 w Fo 2 ÿ Fc 2 2 = w Fo 2 2 1=2 .
[PdL](ClO4)2 C11H22Cl2N2O8PdS2 monoclinic C2/m 27.317(7) 11.504(2) 18.924(3) 98.58(1) 5880(2) 12 1.888 1.82 3368 1.475 ÿ32 to 29 ÿ13 to 13 ÿ21 to 22 15704 5648 1.025 0.0523, 0.0579 0.1460, 0.1516
[RhLCl2]PF6 C11H22Cl2F6N2PRhS2 orthorhombic Cmca 20.064(4) 13.665 (2) 13.246(2) 90.00 3631.8(11) 8 2.067 2.08 2256 1.610 ÿ24 to 21 ÿ13 to 16 ÿ15 to 15 9149 1711 1.036 0.0233, 0.0264 0.0587, 0.0608
3. Results and discussion
the RhCl3 solution was believed to be a neutral complex in which L acts as a bidentate ligand with its two N atoms being coordinated. During the course of re¯ux, one Cl atom was displaced to give the soluble product. The ethanol presumably reduces small quantities of the Rh(III) to Rh(I) to facilitate the substitution reaction, and then atmospheric oxygen reoxidizes the Rh(I) to generate the kinetically inert Rh(III) complex [15±17]. The presence of the four crystalline water molecules was con®rmed by element analysis as well as a very strong and broad band in the high wave number region of its IR spectrum. Two of the three Clÿ ions are coordinated while one is ionic which can be easily replaced by PF± ion in ethanol to give [RhLCl2]PF6. Both rhodium complexes are air-stable and behave as 1:1 electrolytes in acetonitrile.
3.1. Synthesis and general property
3.2. UV±visible spectroscopy
The ligand was readily prepared by the coupling reaction of thiomorpholine and 1,3-dibromopropane in a basic medium. The reaction also works well in toluene with sodium bicarbonate as the acid scavenger. The Zn(II), Pd(II) and Pt(II) complexes were obtained as ®ne crystals from the reaction of L with the corresponding metal salts at room temperature in methanol (for Zn(II)) or acetonitrile. The three complexes are all soluble in acetonitrile and behave as 1:2 electrolytes except for the Zn(II) complex which is a non-electrolyte. They are stable in air in the solid state and their acetonitrile solutions are also stable for several months. [RhLCl2]Cl4H2O could only be prepared at elevated temperature and the reaction medium must contain ethanol [14]. The precipitate formed when L was added to
The d±d transition bands of [PdL](ClO4)2 and [PtL](ClO4)2 were observed at 306 nm (" 2100 Mÿ1 cmÿ1) and 304 nm (" 280 Mÿ1 cmÿ1), respectively. The two rhodium complexes exhibit identical d±d absorption at 352 and 446 nm with " values of 866 and 206 Mÿ1 cmÿ1, respectively; these two bands were assigned 1 to the spin-allowed d±d transitions 1 T1g A1g and 1 1 T2g A1g , and the low intensity of them was consistent with the trans con®guration of the complexes [18,19].
conventional heavy-atom or direct methods with remaining non-hydrogen atoms located from Fourier difference maps. All non-hydrogen atoms were re®ned anisotropically. Hydrogen atoms were placed in calculated positions with ®xed thermal parameters. Re®nements were by full-matrix least-squares method using either SHELXTL [12] for Iris V5.04 or PC SHELXTL [12] V5.04 program. Final re®nements were made on F2 using a weighting scheme of the form w 1=2 Fo 2 aP2 bP where P max Fo 2 2Fc 2 =3. Table 1 lists the crystal parameters and data collection parameters of the three complexes. Selected bond distances and angles are listed in Table 2.
3.3. Crystal structures and dynamic 1H NMR study Crystals of [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 suitable for XRD were grown successfully and their crystal
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Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
Table 2 Ê ) and angles (8) for [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 Selected bond lengths (A [ZnLCl2] Zn±N(1) Zn±Cl(1) N(1)±C(5) S(1)±C(1) S(2)±C(9)
2.093(2) 2.249(1) 1.507(2) 1.792(2) 1.800(2)
Zn±N(2) Zn±Cl(2) N(2)±C(7) S(1)±C(3) S(2)±C(10)
2.098(2) 2.224(1) 1.494(2) 1.802(2) 1.800(2)
N(1)±Zn±N(2) N(1)±Zn±Cl(2) N(2)±Zn±Cl(1) C(2)±N(1)±Zn C(5)±N(1)±Zn C(8)±N(2)±Zn C(1)±S(1)±C(3)
102.32(6) 116.54(4) 102.73(4) 109.67(11) 105.28(11) 108.69(11) 97.35(10)
N(1)±Zn±Cl(1) N(2)±Zn±Cl(2) Cl(1)±Zn±Cl(2) C(4)±N±(1)±Zn C(7)±N±(2)±Zn C(11)±N(2)±Zn C(9)±S(2)±C(10)
103.44(5) 116.57(5) 113.37(3) 116.66(12) 105.27(12) 118.11(11) 97.78(10)
[PdL](ClO4)2a,b Pd(1)±N(1) Pd(1)±S(1) Pd(2)±N(2)
2.073(4) 2.292(2) 2.077(5)
Pd(2)±S(2) Pd(3)±N(3) Pd(3)±S(3)
2.294(2) 2.059(6) 2.244(3)
N(1)±Pd(1)±N(1)* N(1)±Pd(1)±S(1) N(2)±Pd(2)±N(2)* N(2)±Pd(2)±S(2) N(3)±Pd(3)±N(3)* N(3)±Pd(3)±S(3)
102.3(3) 76.31(14) 102.0(3) 76.62(14) 102.2(5) 76.9(3)
S(1)±Pd(1)±S(1)* N(1)±Pd(1)±S(1)* S(2)±Pd(2)±S(2)* N(2)±Pd(2)±S(2)* S(3)±Pd(3)±S(3)* N(3)±Pd(3)±S(3)*
104.41(91) 173.91(13) 104.43(9) 175.51(14) 103.8(3) 176.7(2)
[RhLCl2]PF6a Rh±N(1) Rh±Cl(1) N(1)±C(5) C(1)±S(1)
2.151(2) 2.3642(9) 1.498(3) 1.821(3)
Rh±S(1) Rh±Cl(2) C(5)±C(6) C(4)±S(1)
2.3320(7) 2.3552(9) 1.511(4) 1.813(3)
N(1)±Rh±N(1)* N(1)±Rh±S(1)* N(1)±Rh±Cl(1) N(1)±Rh±Cl(2) Cl(1)±Rh±Cl(2) C(1)±S(1)±Rh
103.82(11) 176.77(6) 93.53(6) 90.13(6) 174.05(3) 97.93(10)
N(1)±Rh±S(1) S(1)±Rh±S(1)* S(1)±Rh±Cl(1) S(1)±Rh±Cl(2) C(1)±S(1)±C(4) C(4)±S(1)±Rh
73.05(6) 110.07(3) 85.92(2) 90.68(2) 91.79(15) 98.01(9)
a b
* is used for symmetry related atoms. Three sets of data are given as there are three distinct molecules in the unit cell.
structures were determined. All of the complexes exhibit broad 1 H NMR signals at ambient temperature (298 K), indicating that the coordinated ligands are not rigidly held. Dynamic NMR studies on selected complexes were, therefore carried out to investigate their behaviour in solution. 3.3.1. [ZnLCl2] This compound was recrystallised from an acetonitrile/ ethanol mixture. An ORTEP [20] diagram of the complex with the atomic numbering scheme is shown in Fig. 1 illustrating 50% probability ellipsoids for the non-hydrogen atoms. The Zn(II) ion is found to sit in a distorted tetrahedral environment, coordinating to two N atoms of the ligand and two Cl atoms. The two S atoms are not coordinated and the two thiomorpholine rings thus adopt energy-favourable
chair conformation as in the free ligand. The chelating ring is also in chair conformation as expected. Ê and The two Zn±N bond distances (2.093(2) A Ê ) are comparable to those found in other tetra2.098(2) A hedral Zn(II) complexes [21]. The two Zn±Cl bond lengths Ê and 2.249(1) A Ê ) are signi®cantly different but (2.224(1) A are also in the normal observed range [22]. Distortion of the coordination geometry from an ideal tetrahedron is signi®cant as the bond angles around the Zn atom range from 102.32(6)8 for angle N(1)±Zn±N(2) to 116.57(5)8 for angle N(2)±Zn±Cl(2). At ambient temperature (298 K), the 1 H NMR spectrum of the complex [ZnLCl2] in CD3CN solution displayed poorly resolved signals and comprised ®ve broad resonances ranging from 1.96 to 3.71. By comparing with
Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
35
Fig. 1. Perspective view of [ZnLCl2] showing the atom numbering scheme; hydrogen atoms have been omitted for clarity.
the well resolved 1 H NMR spectrum of a similar complex, dichloro-1,3-bis(morpholino)propanezinc(II) [4,23], which is isostructural to the present complex, the signals at 1.96 (which is overlapped by the solvent peak) and 2.93 can be assigned to H1 and H2 (for the numbering of H atoms, see Scheme 1), respectively. Two signals at 3.71 and 3.41 were tentatively assigned to the axial and equatorial hydrogen atoms respectively of H3, which are adjacent to the coordinated N atoms and should have higher chemical shifts due to the electron withdrawing effect of the zinc atom. Two overlapped signals at 2.64 and 2.62 were then assigned to H4. On cooling down the solution to 238 K, a further dynamic line broadening of all the signals was observed except the band of H1 which is overlapped by the solvent peaks; the signal due to the equatorial hydrogen atoms of H3 even collapses at 243 K. Unfortunately, the poor solubility of the complex in other low melting point solvents prevents us from further lowering the temperature and a well resolved 1 H NMR spectrum of the complex thus could not be obtained. On raising the NMR probe temperature, the signals due to the thiomorpholine hydrogen atoms broaden owing to the faster conformation change of the rings. At 343 K, only two bands due to H1 and H2 were observed. As a de®nite coalescence temperature as well as a well-resolved spectrum could not be obtained, we are unable to calculate [26] the G6 value for the inversion of the thiomorpholine rings from this variable-temperature 1 H NMR study. 3.3.2. [PdL](ClO4)2 Pale yellow crystals of this complex suitable for X-ray crystallography were obtained by vapour diffusion of ether
Scheme 1. Synthesis of the ligand L with the numbering scheme.
Fig. 2. Perspective view of the cation [PdL]2 showing the atom numbering scheme; hydrogen atoms have been omitted for clarity.
into an acetonitrile solution. Crystals of [PdL](ClO4)2 consist of mononuclear cations and uncoordinated perchlorate anions. Three crystallographically distinct cations and six anions are present in each unit cell; some perchlorate anions are severely distorted and will not be further discussed. For clarity, only one ORTEP [20] diagram of the complex cations is shown in Fig. 2 with its atomic numbering scheme. Unlike in [ZnLCl2], L in this complex acts as a tetradentate chelating ligand and the two thiomorpholine residues are, as required for chelation, in boat conformation. The palladium(II) ion is located on the mirror plane in a distorted square planar environment coordinating to the four hetero atoms of the ligand. The distortion arises mainly from the small bite angle (76.3(1)8 for N(1)±Pd(1)±S(1)) of the chelating thiomorpholine ring. The Pd atom and the N2S2 donor set are strictly coplanar (bond angles around the Pd atom add up to 359.38). The methylene groups of each of the thiomorpholine moieties are not symmetrical to the N2S2 plane and this makes all the eight hydrogen atoms different in chemical environments as observed in the low-temperature 1 H NMR spectrum (see below). The bond distances of Ê ) and Pd±S Pd±N (2.073(4), 2.077(5) and 2.059(6) A Ê (2.292(2), 2.294(2) and 2.244(3) A) of the three isomers are slightly different but are in the normal range [24,25]. The six-membered metal-chelate ring is in half-chair con®guration as expected. At ambient temperature (298 K), the 1 H NMR spectrum of [PdL](ClO4)2 in CD3CN is not well resolved (Fig. 3). The spectrum comprises six signals of the complex; two of them are well resolved multiplets at 3.00 and 2.81 while the other four signals are all broad, indicating the onset of the conformation shift (Scheme 2) at a measurable rate on the NMR timescale. The signal at 2.06 can be unambiguously assigned to H1 by virtue of its intensity and chemical shift. In an NOE experiment, when the resonance at 3.54 was irradiated, enhancements were observed on the signals at 3.88, 3.00 and 2.89, con®rming that the three enhanced signals together with the irradiated one are due to the
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Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
Scheme 3. The labelling of H atoms for [PdL](ClO4)2.
On cooling down the solution, the signals of Hc, Ha and Hb exhibit line broadening and collapse at certain temperatures. At 243 K, a reasonably resolved spectrum was obtained in which each of the above three signals is split into two sets of resonances while Hd displays a multiplet. This spectral feature indicates that, at such a low temperature, the conformation shift becomes slow on the NMR timescale and all the eight protons of each thiomorpholine group are in different chemical environments. By using the line shape analysis method, the G6 value calculated [26] from the coalescence temperature (Tc, 268 K, Fig. 3) and the frequency separation (n, 76.0 Hz at 243 K) of the signals due to Hc is 54.0 kJ molÿ1. This is in accordance with the data (53.9 kJ molÿ1) calculated using Ha as the probe (Tc 266 K; n 64.9 Hz).
1
Fig. 3. Variable temperature H NMR spectra of [PdL](ClO4)2 in CD3CN.
hydrogen atoms of the thiomorpholine rings and the multiplet at 2.81 is then due to H2. On warming the solution, the resonances due to the protons of the thiomorpholine groups display improved resolution. At 338 K, a well resolved spectrum was recorded, showing that at this temperature, the conformation shift is fast on the NMR timescale and the two ethylene groups of each thiomorpholine ring are equivalent. Because the peaks are complex and similar in chemical shift, we could not distinguish them unambiguously. However, based on the analyses of the complex structure and a comparison with the 1 H NMR spectra of two structurally similar complexes, 1,3-bis(piperazino)propanepalladium(II) perchlorate and 1,3-bis(4-methylpiperazino)propanepalladium(II) perchlorate [23], a tentative assignment can be made for the spectrum at 298 K, that is, Hc ( 3.88), Ha ( 3.54), Hd ( 3.00) and Hb ( 2.89) (see Scheme 3 for the labelling of H atoms).
Scheme 2. The conformation shift of [PdL](ClO4)2.
3.3.3. [RhLCl2]PF6 Orange needles of this complex which are suitable for X-ray crystallography were grown by slow evaporation of a mixture of ethanol/acetonitrile solution. A view of the molecule, indicating the atom numbering scheme, is shown in Fig. 4. Molecules of the complex comprise the complex cations and PF6ÿ anions in a ratio of 1:1. The complex cation is symmetrical with a mirror plane passing through the Rh(III) atom, two Cl atoms and the C(6) atom. The Rh(III) atom is positioned in the N2S2 cavity of the complex in a distorted octahedral geometry with two Cl atoms in the
Fig. 4. Perspective view of the cation [RhLCl2] showing the atom numbering scheme; hydrogen atoms have been omitted for clarity.
Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
trans con®guration. The ligand acts again in a tetradentate fashion with the thiomorpholine moieties in boat conformation. The Rh atom and the four coordinating atoms of the ligand are clearly coplanar as the bond angles around the Rh atom within the plane add up to 359.998. The distortion of the coordination sphere from an ideal octahedron arises mainly from the small bite angle (73.05(3)8) of the thiomorpholine moiety. As a result, the angles of N(1)±Rh± N(1A) and S(1)±Rh±S(1A) are opened to 103.82(11)8 and 110.07(3)8, respectively. The Cl(2)±Rh bond is perpendicular to the N2S2 plane (bond angles: Cl(2)±Rh±N(1) 90.13(6)8 and Cl(2)±Rh±S(1) 90.68(2)8) while the bond angles of Cl(1)±Rh±N(1) (93.53(6)8) and Cl(1)±Rh±S(1) (85.92(2)8) deviated signi®cantly from the ideal 908. This may be the result of steric repulsion between Cl(1) atom and C(2) as well as C(2A) atoms (the two ethylene groups of each thiomorpholine moiety are not symmetrical to the N2S2 plane). Chemical models also show that the coordination sphere is crowded. The bond lengths of Cl(1)±Rh Ê ) and Cl(2)±Rh (2.3552(9) A Ê ) are slightly dif(2.3642(9) A ferent but comparable to the data of other octahedral Rh complexes [27,28]. The bond distances of N±Rh Ê ) and S±Rh (2.3320(7) A Ê ) are also in the normal (2.151(2) A range [29]. The 1 H NMR spectrum of [RhLCl2]PF6 in CD3CN at ambient temperature is similar to that of [PdL](ClO4)2. However, the signal positions of the hydrogen atoms of the propylene bridge observed at 3.11 for H2 and 2.30 for H1 are considerably shifted down®eld as compared to the corresponding peaks of the free ligand. On cooling down the solution, resonances due to the thiomorpholine groups were broadened. At 243 K, a reasonably resolved spectrum was recorded. In the spectrum, each of the two broad signals due to Hc and Hb ( 4.00 and 2.68, respectively) at 298 K (the signal of Hb is overlapped by that of Hd; for the tentative assignment, see above analyses for 1 H NMR of [PdL](ClO4)2) is split into two multiplets. Ha and Hd exhibit two multiplets at 3.65 and 2.70, respectively; the latter was overlapped by one of the two multiplets due to Hb. Unlike the case of [PdL](ClO4)2, H1 also shows a set of two multiplets at 2.38 and 2.17 and H2 gives a multiplet ranging from 3.18 to 3.06. This indicates that the propylene bridge is rigid at the temperature and the conformation shift is much slower on the NMR timescale. By using the same line shape analysis method, a G6 value of 55.1 kJ molÿ1 was calculated [26] from the Tc (273 K) and frequency separation (72.5 Hz) of the signals due to Hc. 4. Conclusions The complexes of 1,3-bis(thiomorpholino)propane with Zn(II), Pd(II), Pt(II) and Rh(III) were synthesised and characterised. The ligand can act in both bidentate and tetradentate fashions upon coordination with different metal salts. [ZnLCl2] possesses a slightly distorted tetrahedral
37
coordination sphere while the coordination geometries of [PdL](ClO4)2 and [RhLCl2]PF6 are a distorted square plane and a severely distorted octahedron, respectively. In solution, all the complexes show dynamic properties; at 243 K, one conformer was `frozen' for [PdL](ClO4)2 and [RhLCl2]PF6. 5. Supplementary material Tables of crystal structure data and experimental details, atomic coordinates and equivalent isotropic displacement parameters, calculated hydrogen atom parameters, anisotropic thermal parameters, complete lists of bond lengths and angles of [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 are available from the authors on request. Acknowledgements We thank the National University of Singapore for the support (Research Grant RP950604) and a research studentship to Y.L.
References [1] G. Mann, H.R. Watson, J. Chem. Soc. (1958) 2772. [2] E.J. Tierney, A.D. Sabatelli, J.E. Sarneski, Inorg. Chem. 26 (1987) 617. [3] O. Schlager, K. Wieghardt, A. Rufinska, B. Nuber, J. Chem. Soc., Dalton Trans. (1996) 1659. [4] Mazhar Ul-Haque, M.S. Hussain, J. Ahmed, J. Crystallogr. Spectrosc. Res. 22 (1992) 37. [5] M. Taghiof, D.G. Hendershot, M. Barker, J.P. Oliver, J. Organomet. Chem. 431 (1992) 271. [6] E.J. Tierney, A.D. Sabatelli, J.E. Sarneski, Inorg. Chem. 26 (1987) 617. [7] M. Maroney, Comments Inorg. Chem. 17 (1995) 347. [8] D. Sellman, R. Ruf, F. Knoch, M. Moll, Inorg. Chem. 34 (1995) 4745. [9] G. Peng, J. Nickols, E.A. McCullough Jr., J.T. Spence, Inorg. Chem. 33 (1994) 2857. [10] H. Frydendahl, H. Toftlund, J. Becher, J.C. Dutton, K.S. Murray, L.F. Taylor, O.P. Anderson, R.T. Tiekink, Inorg. Chem. 34 (1995) 4467. [11] Y. Li, Y.H. Lai, K.F. Mok, M.G.B. Drew, Inorg. Chim. Acta 279 (1998) 221. [12] Software package for the SMART system; Siemens Analytical XRay Instruments, Madison, WI, 1996. [13] G.M. Sheldrick, Software for Absorption Correction, University of GoÈttingen, 1996. [14] M. Venkatesh, N. Goswami, W.A. Volkert, E.O. Schlemper, A.R. Ketring, C.L. Barnes, S. Jurisson, Nucl. Med. Biol. 23 (1996) 33. [15] F. Basolo, R.G. Pearson, Mechanisms of Inorganic Reactions, Wiley, New York, 1967. [16] A.W. Addison, R.D. Guillard, H. Vaughan, J. Chem. Soc., Dalton Trans. (1973) 1187. [17] R.D. Gilard, G. Wilkinson, J. Chem. Soc. (1964) 1224. [18] E.J. Bounsall, S.R. Koprich, Can. J. Chem. 48 (1970) 1481. [19] L.S.W.L. Sokol, L.A. Ochrymowycz, D.B. Rorabacher, Inorg. Chem. 20 (1981) 3189.
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[20] K. Johnson, ORTEP II, A Fortran Thermal Ellipsoids Plot Program for Crystal Structure Illustrations, Report ORNL-5138, Oak National Laboratory, Oak Ridge, TN, 1976. [21] S. Htoon, M.F.C. Ladd, J. Cryst. Mol. Struct. 3 (1973) 95. [22] W.J. Wu, D. Barton, S.J. Lippard, J. Am. Chem. Soc. 95 (1973) 1170. [23] Y. Li, Y.H. Lai, K.F. Mok, unpublished results. [24] M. Horike, Y. Kai, N. Kasai, J. Organomet. Chem. 86 (1975) 269.
[25] M. Gupta, R.E. Cramer, K. Ho, C. Pettersen, S. Mishina, J. Belli, C.M. Jensen, Inorg. Chem. 34 (1995) 60. [26] M. Oki, Application of Dynamic NMR Spectroscopy to Organic Chemistry, VCH, Deerfield, FL, 1985. [27] A.C. Skapsi, F.A. Setephens, J. Chem. Soc., Dalton Trans. (1973) 1789. [28] C. Dobinson, R. Mason, D.R. Russell, J. Chem. Soc., Chem. Commun. (1967) 62. [29] N. Goswami, R. Alberto, C.L. Barnes, S. Jurisson, Inorg. Chem. 35 (1996) 7546.
Transition metal complexes of 1,3-bis(thiomorpholino)propane: crystal structure and dynamic 1H NMR study Yongxin Lia, Yee-Hing Laia, K.F. Moka,*, Michael G.B. Drewb a
Department of Chemistry, National University of Singapore, Kent Ridge 119260, Singapore Department of Chemistry, The University of Reading, Whiteknights, Reading RG6 6AD, UK
b
Received 22 September 1997; received in revised form 27 March 1998; accepted 12 May 1998
Abstract Complexes of 1,3-bis(thiomorpholino)propane (L) with Zn(II), Pd(II), Pt(II) and Rh(III) of the formula [ZnLCl2], [ML](ClO4)2, (M Pd and Pt), [RhLCl2]Cl4H2O and [RhLCl2]PF6 were prepared and characterised. The molecular structures of [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 were determined by X-ray diffraction. In [ZnLCl2], the ligand acts in a bidentate fashion using its two N atoms while the two S atoms remain free and the coordination structure is a distorted tetrahedron. [PdL](ClO4)2 possesses a distorted square planar coordination geometry with all the four hetero atoms being coordinated. The coordination structure of [RhLCl2]PF6 is a distorted octahedron with the two Cl atoms in trans position and L also acting as a tetradentate ligand. In addition to the crystal structures, the dynamic 1 H NMR behaviour of the three complexes were also investigated. # 1999 Elsevier Science S.A. All rights reserved. Keywords: Crystal structures; Transition metal complexes; Thiomorpholine complexes
1. Introduction
2. Experimental
It is well known that small cyclic ligands, such as piperazine [1±3], morpholine [4] and thiomorpholine [5,6], are able to form complexes with a range of transition metals. Diversity in their coordinating behaviour makes them an interesting family of ligands. However, information in the literature on complexes of such ligands is relatively scarce, especially on that of thiomorpholine [5,6] and its derivatives. Possibly this is because thiomorpholine is not an effective chelating ligand as it prefers the low-energy chair conformation to the boat conformation which is required for the ligand to act in a bidentate fashion. Furthermore, there is much current interest in the use of MN2S2 complexes as structural and spectroscopic models for the coordination environments of active sites in a number of metalloproteins [7±10]. We have recently synthesised and characterised a series of thiomorpholine derivatives and their transition metal complexes [11]. In this paper, we report a thiomorpholine derivative, 1,3-bis(thiomorpholino)propane (L), and its complexes with Zn(II), Pd(II), Pt(II) and Rh(III). Crystal structures have shown that the thiomorpholine moieties of the ligand can adopt both chair and boat conformations upon complex formation, depending on the nature of the metal.
All metal salts were of AR grade and used as received. Thiomorpholine and 1,3-dibromopropane from Aldrich, USA were used without further puri®cation. Melting points were determined using a Thermo-Galen III Hot Stage microscope apparatus. All the proton NMR spectra were measured in CD3CN on a Bruker AMX-500 spectrometer with standard variable-temperature equipment using tetramethylsilane as internal reference. Elemental analyses were performed in the Microanalytical Laboratory of the Department of Chemistry, National University of Singapore. Conductivity measurements were carried out on a STEM 1000 conductivity meter at 308C.
*Corresponding author. Tel.: +65-7722-6589; fax: +65-779-1691.
2.1. 1,3-bis(thiomorpholino)propane (L) A mixture of 1,3-dibromopropane (1.01 g, 5 mmol), thiomorpholine (1.02 g, 10 mmol) and Na2CO3 (1.10 g, 10.4 mmol) in water (7 ml) was heated to re¯ux for 10 h, cooled to room temperature and extracted with chloroform (3 50 ml). The organic layers were combined, dried and the solvent evaporated to give a pale yellow oil. The crude product was dissolved in ethanol (10 ml) and precipitated as hydrochloride salt by adding concentrated HCl (2 ml) to the ethanolic solution. Recrystallisation of the precipitate from
0020-1693/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S0020-1693(98)00260-6
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Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
aqueous ethanol afforded the pure hydrochloride salt as a white powder. The salt was then treated with 10 M NaOH (10 ml) and the solution was extracted with chloroform (3 20 ml). The combined organic layers were dried and the solvent evaporated under reduced pressure to give the ligand as a colourless oil which crystallised slowly upon standing at room temperature (0.75 g, 61%). 1 H NMR: 2.63±2.58 (m, 16H, NCH2CH2S), 2.31 (t, 4H, J 7.3 Hz, 1.56 (quintet, 2H, J 7.3 Hz, CH2CH2CH2), CH2CH2CH2); MS (M): m/z (%) 246 (7), 216 (74), 199 (10), 187 (7), 143 (46), 130 (40), 116 (100), 102 (76), 96 (51), 88 (64), 70 (64), 56 (62), 42 (76); Anal. Calc. for C11H22N2S2 : C, 53.61; H, 9.00; N, 11.37; S, 26.02. Found: C, 53.58; H, 9.13; N, 11.43; S, 26.07%. 2.2. Dichloro(1,3-bis(thiomorpholino)propane)zinc(II) [ZnLCl2] ZnCl2 (34 mg, 0.25 mmol) in methanol (5 ml) was added with stirring to L (62 mg, 0.25 mmol) in methanol (5 ml). Upon standing at room temperature for 1 day, colourless crystals precipitated from the solution. The crystals were ®ltered off, washed with ethanol and diethyl ether and dried under vacuum. Yield: 72 mg (75%); m.p. 284±2868C. 1 H NMR: 3.71 (b, 4H), 3.41 (b, 4H), 2.93 (b, 4H), 2.64 (b, 8H), 1.96 (the signal is overlapped by the solvent peaks); M (CHCl3): negligible. Anal. Calc. for C11H22Cl2N2S2Zn: C, 34.54; H, 5.79; N, 7.32; S, 16.76. Found: C, 34.69; H, 5.87; N, 7.10; S, 16.74%. 2.3. 1,3-bis(thiomorpholino)propanepalladium(II) perchlorate [PdL](ClO4)2 To a solution of PdCl2(CH3CN)2 (31 mg, 0.12 mmol) in CH3CN (4 ml) was added a solution of AgClO4 (50 mg, 0.24 mmol) in CH3CN (4 ml). The mixture was stirred at room temperature for 30 min and the precipitate ®ltered off. The ®ltrate was added dropwise to a solution of L (32 mg, 0.13 mmol) in CH3CN (6 ml) with stirring. After stirring for 1 h, the solution was ®ltered and vapour diffused with diethyl ether at room temperature. Pale yellow crystals precipitated from the solution which were ®ltered off and dried. Yield: 50 mg (76%); m.p. 2408C (decomp). 1 H NMR (298 K): 3.88 (b, 4H), 3.54 (b, 4H), 3.03±2.97 (m, centred at 3.00, 4H), 2.89 (b, 4H), 2.81 (m, 4H), 2.06 (m, 2H); M (CH3CN): 278 (S cm2 molÿ1) (1:2). Anal. Calc. for C11H22Cl2N2O8S2Pd: C, 24.00; H, 4.03; N, 5.09; S, 11.63. Found: C, 23.90; H, 3.90; N, 5.37; S, 11.37%. Caution: perchlorates are hazardous. 2.4. 1,3-bis(thiomorpholino)propaneplatinum(II) perchlorate [PtL](ClO4)2 To a solution of PtCl2(CH3CN)2 (42 mg, 0.12 mmol) in CH3CN (4 ml) was added a solution of AgClO4 (50 mg, 0.24 mmol) in CH3CN (4 ml). The mixture was stirred at
room temperature for 10 h and the precipitate ®ltered off. The ®ltrate was added dropwise to a solution of L (32 mg, 0.13 mmol) in CH3CN (6 ml) with stirring. After stirring for 5 h, the solution was ®ltered and vapour diffused with diethyl ether at room temperature. Colourless crystals precipitated from the solution which were ®ltered off and dried. Yield: 50 mg (65%); m.p. > 2908C (decomp). 1 H NMR: 3.75 (b, 4H), 3.41 (b, 4H), 3.13±3.07 (m, centred at 3.10, 4H), 2.98 (b, 4H), 3.19±2.80 (very broad, 4H), 2.09 (b, 2H); M (CH3CN): 299 (S cm2 molÿ1) (1:2). Anal. Calc. for C11H22Cl2N2O8S2Pt: C, 20.63; H, 3.46; N, 4.37; S, 10.01. Found: C, 20.54; H, 3.41; N, 4.74; S, 10.00%. 2.5. Dichloro-1,3-bis(thiomorpholino)propanerhodium(III) chloride tetrahydrate [RhLCl2]Cl4H2O To a solution of RhCl3 (21 mg, 0.10 mmol) in acetonitrile/ethanol (vol./vol. 1:20, 20 ml) was added a solution of L (27 mg, 0.11 mmol) in acetonitrile (10 ml). The mixture was heated to re¯ux for 10 h until the precipitate formed was dissolved to give a brown solution. After ®ltration to remove the insolubles, the solution was concentrated to about 5 ml and vapour diffused with ether to afford orange ¯aky crystals. Yield: 25 mg (55%); m.p. 110±1138C. 1 H NMR: 4.00 (b, 4H), 3.68 (b, 4H), 3.12 (m, 4H), 2.68 (m, 8H), 2.30 (b, 2H); M (CH3CN): 132 (S cm2 molÿ1) (1:1). Anal. Calc. for C11H30Cl3N2O4RhS2: C, 25.03; H, 5.73; N, 5.31; S, 12.15. Found: C, 25.31; H, 5.63; N, 5.02; S, 12.12%. 2.6. Dichloro-1,3-bis(thiomorpholino)propanerhodium(III) hexafluorophosphate [RhLCl2]PF6 To a solution of [RhLCl2]Cl4H2O (53 mg, 0.10 mmol) in ethanol (8 ml) was added a solution of NH4PF6 (20 mg, 0.12 mmol) in ethanol (8 ml). Orange precipitate, which was formed slowly, was ®ltered off, washed with ethanol and ether and air dried. Yield: 51 mg (90%); m.p. 2358C (decomp). 1 H NMR: 4.00 (b, 4H), 3.68 (b, 4H), 3.12 (m, 4H), 2.68 (b, 8H), 2.30 (b, 2H); M (CH3CN): 140 (S cm2 molÿ1) (1:1). Anal. Calc. for C11H22Cl2F6N2PRhS2: C, 23.38; H, 3.92; N, 4.96; S, 11.35. Found: C, 23.43; H, 3.62; N, 4.79; S, 11.31%. 2.7. Crystallographic analyses Crystals used for X-ray analysis were of approximate dimensions 0.28 0.30 0.15 mm, 0.43 0.33 0.20 mm and 0.28 0.13 0.13 mm for [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 respectively. Data were collected at room temperature on a Siemens SMART diffractometer ®tted with a CCD area detector, using graphite-monochromated Ê ). A hemisphere of data Mo Ka radiation (l 0.71073 A was collected for each complex, at 20±30 s/frame. The data frames were integrated using SAINT [12] program and SADABS [13] was used for absorption effects on a Silicon Graphics Indigo 2 computer. The structures were solved by
Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
33
Table 1 Crystal and refinement data for [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 Compound code [ZnLCl2] Formula C11H22Cl2N2S2Zn Crystal system monoclinic Space group P21/c Ê) a (A 10.919(2) Ê) b (A 11.405(1) Ê) c (A 13.846(2) (8) 107.67(1) Ê 3) V (A 1642.9(4) Z 4 Dc (g cmÿ3) 1.547 Dm (g cmÿ3) 1.52 F (000) 792 (mmÿ1) 2.060 h Range ÿ10 to 13 k Range ÿ14 to 14 l Range ÿ16 to 17 Reflection collected 9207 Reflection refined 3342 Goodness of fit 1.048 Ra (observed, all data) 0.0261, 0.0330 wR2b (observed, all data) 0.0646, 0.0671 P P a R jj Fo j ÿ jFo jj= jFo j. P P b wR2 w Fo 2 ÿ Fc 2 2 = w Fo 2 2 1=2 .
[PdL](ClO4)2 C11H22Cl2N2O8PdS2 monoclinic C2/m 27.317(7) 11.504(2) 18.924(3) 98.58(1) 5880(2) 12 1.888 1.82 3368 1.475 ÿ32 to 29 ÿ13 to 13 ÿ21 to 22 15704 5648 1.025 0.0523, 0.0579 0.1460, 0.1516
[RhLCl2]PF6 C11H22Cl2F6N2PRhS2 orthorhombic Cmca 20.064(4) 13.665 (2) 13.246(2) 90.00 3631.8(11) 8 2.067 2.08 2256 1.610 ÿ24 to 21 ÿ13 to 16 ÿ15 to 15 9149 1711 1.036 0.0233, 0.0264 0.0587, 0.0608
3. Results and discussion
the RhCl3 solution was believed to be a neutral complex in which L acts as a bidentate ligand with its two N atoms being coordinated. During the course of re¯ux, one Cl atom was displaced to give the soluble product. The ethanol presumably reduces small quantities of the Rh(III) to Rh(I) to facilitate the substitution reaction, and then atmospheric oxygen reoxidizes the Rh(I) to generate the kinetically inert Rh(III) complex [15±17]. The presence of the four crystalline water molecules was con®rmed by element analysis as well as a very strong and broad band in the high wave number region of its IR spectrum. Two of the three Clÿ ions are coordinated while one is ionic which can be easily replaced by PF± ion in ethanol to give [RhLCl2]PF6. Both rhodium complexes are air-stable and behave as 1:1 electrolytes in acetonitrile.
3.1. Synthesis and general property
3.2. UV±visible spectroscopy
The ligand was readily prepared by the coupling reaction of thiomorpholine and 1,3-dibromopropane in a basic medium. The reaction also works well in toluene with sodium bicarbonate as the acid scavenger. The Zn(II), Pd(II) and Pt(II) complexes were obtained as ®ne crystals from the reaction of L with the corresponding metal salts at room temperature in methanol (for Zn(II)) or acetonitrile. The three complexes are all soluble in acetonitrile and behave as 1:2 electrolytes except for the Zn(II) complex which is a non-electrolyte. They are stable in air in the solid state and their acetonitrile solutions are also stable for several months. [RhLCl2]Cl4H2O could only be prepared at elevated temperature and the reaction medium must contain ethanol [14]. The precipitate formed when L was added to
The d±d transition bands of [PdL](ClO4)2 and [PtL](ClO4)2 were observed at 306 nm (" 2100 Mÿ1 cmÿ1) and 304 nm (" 280 Mÿ1 cmÿ1), respectively. The two rhodium complexes exhibit identical d±d absorption at 352 and 446 nm with " values of 866 and 206 Mÿ1 cmÿ1, respectively; these two bands were assigned 1 to the spin-allowed d±d transitions 1 T1g A1g and 1 1 T2g A1g , and the low intensity of them was consistent with the trans con®guration of the complexes [18,19].
conventional heavy-atom or direct methods with remaining non-hydrogen atoms located from Fourier difference maps. All non-hydrogen atoms were re®ned anisotropically. Hydrogen atoms were placed in calculated positions with ®xed thermal parameters. Re®nements were by full-matrix least-squares method using either SHELXTL [12] for Iris V5.04 or PC SHELXTL [12] V5.04 program. Final re®nements were made on F2 using a weighting scheme of the form w 1=2 Fo 2 aP2 bP where P max Fo 2 2Fc 2 =3. Table 1 lists the crystal parameters and data collection parameters of the three complexes. Selected bond distances and angles are listed in Table 2.
3.3. Crystal structures and dynamic 1H NMR study Crystals of [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 suitable for XRD were grown successfully and their crystal
34
Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
Table 2 Ê ) and angles (8) for [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 Selected bond lengths (A [ZnLCl2] Zn±N(1) Zn±Cl(1) N(1)±C(5) S(1)±C(1) S(2)±C(9)
2.093(2) 2.249(1) 1.507(2) 1.792(2) 1.800(2)
Zn±N(2) Zn±Cl(2) N(2)±C(7) S(1)±C(3) S(2)±C(10)
2.098(2) 2.224(1) 1.494(2) 1.802(2) 1.800(2)
N(1)±Zn±N(2) N(1)±Zn±Cl(2) N(2)±Zn±Cl(1) C(2)±N(1)±Zn C(5)±N(1)±Zn C(8)±N(2)±Zn C(1)±S(1)±C(3)
102.32(6) 116.54(4) 102.73(4) 109.67(11) 105.28(11) 108.69(11) 97.35(10)
N(1)±Zn±Cl(1) N(2)±Zn±Cl(2) Cl(1)±Zn±Cl(2) C(4)±N±(1)±Zn C(7)±N±(2)±Zn C(11)±N(2)±Zn C(9)±S(2)±C(10)
103.44(5) 116.57(5) 113.37(3) 116.66(12) 105.27(12) 118.11(11) 97.78(10)
[PdL](ClO4)2a,b Pd(1)±N(1) Pd(1)±S(1) Pd(2)±N(2)
2.073(4) 2.292(2) 2.077(5)
Pd(2)±S(2) Pd(3)±N(3) Pd(3)±S(3)
2.294(2) 2.059(6) 2.244(3)
N(1)±Pd(1)±N(1)* N(1)±Pd(1)±S(1) N(2)±Pd(2)±N(2)* N(2)±Pd(2)±S(2) N(3)±Pd(3)±N(3)* N(3)±Pd(3)±S(3)
102.3(3) 76.31(14) 102.0(3) 76.62(14) 102.2(5) 76.9(3)
S(1)±Pd(1)±S(1)* N(1)±Pd(1)±S(1)* S(2)±Pd(2)±S(2)* N(2)±Pd(2)±S(2)* S(3)±Pd(3)±S(3)* N(3)±Pd(3)±S(3)*
104.41(91) 173.91(13) 104.43(9) 175.51(14) 103.8(3) 176.7(2)
[RhLCl2]PF6a Rh±N(1) Rh±Cl(1) N(1)±C(5) C(1)±S(1)
2.151(2) 2.3642(9) 1.498(3) 1.821(3)
Rh±S(1) Rh±Cl(2) C(5)±C(6) C(4)±S(1)
2.3320(7) 2.3552(9) 1.511(4) 1.813(3)
N(1)±Rh±N(1)* N(1)±Rh±S(1)* N(1)±Rh±Cl(1) N(1)±Rh±Cl(2) Cl(1)±Rh±Cl(2) C(1)±S(1)±Rh
103.82(11) 176.77(6) 93.53(6) 90.13(6) 174.05(3) 97.93(10)
N(1)±Rh±S(1) S(1)±Rh±S(1)* S(1)±Rh±Cl(1) S(1)±Rh±Cl(2) C(1)±S(1)±C(4) C(4)±S(1)±Rh
73.05(6) 110.07(3) 85.92(2) 90.68(2) 91.79(15) 98.01(9)
a b
* is used for symmetry related atoms. Three sets of data are given as there are three distinct molecules in the unit cell.
structures were determined. All of the complexes exhibit broad 1 H NMR signals at ambient temperature (298 K), indicating that the coordinated ligands are not rigidly held. Dynamic NMR studies on selected complexes were, therefore carried out to investigate their behaviour in solution. 3.3.1. [ZnLCl2] This compound was recrystallised from an acetonitrile/ ethanol mixture. An ORTEP [20] diagram of the complex with the atomic numbering scheme is shown in Fig. 1 illustrating 50% probability ellipsoids for the non-hydrogen atoms. The Zn(II) ion is found to sit in a distorted tetrahedral environment, coordinating to two N atoms of the ligand and two Cl atoms. The two S atoms are not coordinated and the two thiomorpholine rings thus adopt energy-favourable
chair conformation as in the free ligand. The chelating ring is also in chair conformation as expected. Ê and The two Zn±N bond distances (2.093(2) A Ê ) are comparable to those found in other tetra2.098(2) A hedral Zn(II) complexes [21]. The two Zn±Cl bond lengths Ê and 2.249(1) A Ê ) are signi®cantly different but (2.224(1) A are also in the normal observed range [22]. Distortion of the coordination geometry from an ideal tetrahedron is signi®cant as the bond angles around the Zn atom range from 102.32(6)8 for angle N(1)±Zn±N(2) to 116.57(5)8 for angle N(2)±Zn±Cl(2). At ambient temperature (298 K), the 1 H NMR spectrum of the complex [ZnLCl2] in CD3CN solution displayed poorly resolved signals and comprised ®ve broad resonances ranging from 1.96 to 3.71. By comparing with
Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
35
Fig. 1. Perspective view of [ZnLCl2] showing the atom numbering scheme; hydrogen atoms have been omitted for clarity.
the well resolved 1 H NMR spectrum of a similar complex, dichloro-1,3-bis(morpholino)propanezinc(II) [4,23], which is isostructural to the present complex, the signals at 1.96 (which is overlapped by the solvent peak) and 2.93 can be assigned to H1 and H2 (for the numbering of H atoms, see Scheme 1), respectively. Two signals at 3.71 and 3.41 were tentatively assigned to the axial and equatorial hydrogen atoms respectively of H3, which are adjacent to the coordinated N atoms and should have higher chemical shifts due to the electron withdrawing effect of the zinc atom. Two overlapped signals at 2.64 and 2.62 were then assigned to H4. On cooling down the solution to 238 K, a further dynamic line broadening of all the signals was observed except the band of H1 which is overlapped by the solvent peaks; the signal due to the equatorial hydrogen atoms of H3 even collapses at 243 K. Unfortunately, the poor solubility of the complex in other low melting point solvents prevents us from further lowering the temperature and a well resolved 1 H NMR spectrum of the complex thus could not be obtained. On raising the NMR probe temperature, the signals due to the thiomorpholine hydrogen atoms broaden owing to the faster conformation change of the rings. At 343 K, only two bands due to H1 and H2 were observed. As a de®nite coalescence temperature as well as a well-resolved spectrum could not be obtained, we are unable to calculate [26] the G6 value for the inversion of the thiomorpholine rings from this variable-temperature 1 H NMR study. 3.3.2. [PdL](ClO4)2 Pale yellow crystals of this complex suitable for X-ray crystallography were obtained by vapour diffusion of ether
Scheme 1. Synthesis of the ligand L with the numbering scheme.
Fig. 2. Perspective view of the cation [PdL]2 showing the atom numbering scheme; hydrogen atoms have been omitted for clarity.
into an acetonitrile solution. Crystals of [PdL](ClO4)2 consist of mononuclear cations and uncoordinated perchlorate anions. Three crystallographically distinct cations and six anions are present in each unit cell; some perchlorate anions are severely distorted and will not be further discussed. For clarity, only one ORTEP [20] diagram of the complex cations is shown in Fig. 2 with its atomic numbering scheme. Unlike in [ZnLCl2], L in this complex acts as a tetradentate chelating ligand and the two thiomorpholine residues are, as required for chelation, in boat conformation. The palladium(II) ion is located on the mirror plane in a distorted square planar environment coordinating to the four hetero atoms of the ligand. The distortion arises mainly from the small bite angle (76.3(1)8 for N(1)±Pd(1)±S(1)) of the chelating thiomorpholine ring. The Pd atom and the N2S2 donor set are strictly coplanar (bond angles around the Pd atom add up to 359.38). The methylene groups of each of the thiomorpholine moieties are not symmetrical to the N2S2 plane and this makes all the eight hydrogen atoms different in chemical environments as observed in the low-temperature 1 H NMR spectrum (see below). The bond distances of Ê ) and Pd±S Pd±N (2.073(4), 2.077(5) and 2.059(6) A Ê (2.292(2), 2.294(2) and 2.244(3) A) of the three isomers are slightly different but are in the normal range [24,25]. The six-membered metal-chelate ring is in half-chair con®guration as expected. At ambient temperature (298 K), the 1 H NMR spectrum of [PdL](ClO4)2 in CD3CN is not well resolved (Fig. 3). The spectrum comprises six signals of the complex; two of them are well resolved multiplets at 3.00 and 2.81 while the other four signals are all broad, indicating the onset of the conformation shift (Scheme 2) at a measurable rate on the NMR timescale. The signal at 2.06 can be unambiguously assigned to H1 by virtue of its intensity and chemical shift. In an NOE experiment, when the resonance at 3.54 was irradiated, enhancements were observed on the signals at 3.88, 3.00 and 2.89, con®rming that the three enhanced signals together with the irradiated one are due to the
36
Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
Scheme 3. The labelling of H atoms for [PdL](ClO4)2.
On cooling down the solution, the signals of Hc, Ha and Hb exhibit line broadening and collapse at certain temperatures. At 243 K, a reasonably resolved spectrum was obtained in which each of the above three signals is split into two sets of resonances while Hd displays a multiplet. This spectral feature indicates that, at such a low temperature, the conformation shift becomes slow on the NMR timescale and all the eight protons of each thiomorpholine group are in different chemical environments. By using the line shape analysis method, the G6 value calculated [26] from the coalescence temperature (Tc, 268 K, Fig. 3) and the frequency separation (n, 76.0 Hz at 243 K) of the signals due to Hc is 54.0 kJ molÿ1. This is in accordance with the data (53.9 kJ molÿ1) calculated using Ha as the probe (Tc 266 K; n 64.9 Hz).
1
Fig. 3. Variable temperature H NMR spectra of [PdL](ClO4)2 in CD3CN.
hydrogen atoms of the thiomorpholine rings and the multiplet at 2.81 is then due to H2. On warming the solution, the resonances due to the protons of the thiomorpholine groups display improved resolution. At 338 K, a well resolved spectrum was recorded, showing that at this temperature, the conformation shift is fast on the NMR timescale and the two ethylene groups of each thiomorpholine ring are equivalent. Because the peaks are complex and similar in chemical shift, we could not distinguish them unambiguously. However, based on the analyses of the complex structure and a comparison with the 1 H NMR spectra of two structurally similar complexes, 1,3-bis(piperazino)propanepalladium(II) perchlorate and 1,3-bis(4-methylpiperazino)propanepalladium(II) perchlorate [23], a tentative assignment can be made for the spectrum at 298 K, that is, Hc ( 3.88), Ha ( 3.54), Hd ( 3.00) and Hb ( 2.89) (see Scheme 3 for the labelling of H atoms).
Scheme 2. The conformation shift of [PdL](ClO4)2.
3.3.3. [RhLCl2]PF6 Orange needles of this complex which are suitable for X-ray crystallography were grown by slow evaporation of a mixture of ethanol/acetonitrile solution. A view of the molecule, indicating the atom numbering scheme, is shown in Fig. 4. Molecules of the complex comprise the complex cations and PF6ÿ anions in a ratio of 1:1. The complex cation is symmetrical with a mirror plane passing through the Rh(III) atom, two Cl atoms and the C(6) atom. The Rh(III) atom is positioned in the N2S2 cavity of the complex in a distorted octahedral geometry with two Cl atoms in the
Fig. 4. Perspective view of the cation [RhLCl2] showing the atom numbering scheme; hydrogen atoms have been omitted for clarity.
Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
trans con®guration. The ligand acts again in a tetradentate fashion with the thiomorpholine moieties in boat conformation. The Rh atom and the four coordinating atoms of the ligand are clearly coplanar as the bond angles around the Rh atom within the plane add up to 359.998. The distortion of the coordination sphere from an ideal octahedron arises mainly from the small bite angle (73.05(3)8) of the thiomorpholine moiety. As a result, the angles of N(1)±Rh± N(1A) and S(1)±Rh±S(1A) are opened to 103.82(11)8 and 110.07(3)8, respectively. The Cl(2)±Rh bond is perpendicular to the N2S2 plane (bond angles: Cl(2)±Rh±N(1) 90.13(6)8 and Cl(2)±Rh±S(1) 90.68(2)8) while the bond angles of Cl(1)±Rh±N(1) (93.53(6)8) and Cl(1)±Rh±S(1) (85.92(2)8) deviated signi®cantly from the ideal 908. This may be the result of steric repulsion between Cl(1) atom and C(2) as well as C(2A) atoms (the two ethylene groups of each thiomorpholine moiety are not symmetrical to the N2S2 plane). Chemical models also show that the coordination sphere is crowded. The bond lengths of Cl(1)±Rh Ê ) and Cl(2)±Rh (2.3552(9) A Ê ) are slightly dif(2.3642(9) A ferent but comparable to the data of other octahedral Rh complexes [27,28]. The bond distances of N±Rh Ê ) and S±Rh (2.3320(7) A Ê ) are also in the normal (2.151(2) A range [29]. The 1 H NMR spectrum of [RhLCl2]PF6 in CD3CN at ambient temperature is similar to that of [PdL](ClO4)2. However, the signal positions of the hydrogen atoms of the propylene bridge observed at 3.11 for H2 and 2.30 for H1 are considerably shifted down®eld as compared to the corresponding peaks of the free ligand. On cooling down the solution, resonances due to the thiomorpholine groups were broadened. At 243 K, a reasonably resolved spectrum was recorded. In the spectrum, each of the two broad signals due to Hc and Hb ( 4.00 and 2.68, respectively) at 298 K (the signal of Hb is overlapped by that of Hd; for the tentative assignment, see above analyses for 1 H NMR of [PdL](ClO4)2) is split into two multiplets. Ha and Hd exhibit two multiplets at 3.65 and 2.70, respectively; the latter was overlapped by one of the two multiplets due to Hb. Unlike the case of [PdL](ClO4)2, H1 also shows a set of two multiplets at 2.38 and 2.17 and H2 gives a multiplet ranging from 3.18 to 3.06. This indicates that the propylene bridge is rigid at the temperature and the conformation shift is much slower on the NMR timescale. By using the same line shape analysis method, a G6 value of 55.1 kJ molÿ1 was calculated [26] from the Tc (273 K) and frequency separation (72.5 Hz) of the signals due to Hc. 4. Conclusions The complexes of 1,3-bis(thiomorpholino)propane with Zn(II), Pd(II), Pt(II) and Rh(III) were synthesised and characterised. The ligand can act in both bidentate and tetradentate fashions upon coordination with different metal salts. [ZnLCl2] possesses a slightly distorted tetrahedral
37
coordination sphere while the coordination geometries of [PdL](ClO4)2 and [RhLCl2]PF6 are a distorted square plane and a severely distorted octahedron, respectively. In solution, all the complexes show dynamic properties; at 243 K, one conformer was `frozen' for [PdL](ClO4)2 and [RhLCl2]PF6. 5. Supplementary material Tables of crystal structure data and experimental details, atomic coordinates and equivalent isotropic displacement parameters, calculated hydrogen atom parameters, anisotropic thermal parameters, complete lists of bond lengths and angles of [ZnLCl2], [PdL](ClO4)2 and [RhLCl2]PF6 are available from the authors on request. Acknowledgements We thank the National University of Singapore for the support (Research Grant RP950604) and a research studentship to Y.L.
References [1] G. Mann, H.R. Watson, J. Chem. Soc. (1958) 2772. [2] E.J. Tierney, A.D. Sabatelli, J.E. Sarneski, Inorg. Chem. 26 (1987) 617. [3] O. Schlager, K. Wieghardt, A. Rufinska, B. Nuber, J. Chem. Soc., Dalton Trans. (1996) 1659. [4] Mazhar Ul-Haque, M.S. Hussain, J. Ahmed, J. Crystallogr. Spectrosc. Res. 22 (1992) 37. [5] M. Taghiof, D.G. Hendershot, M. Barker, J.P. Oliver, J. Organomet. Chem. 431 (1992) 271. [6] E.J. Tierney, A.D. Sabatelli, J.E. Sarneski, Inorg. Chem. 26 (1987) 617. [7] M. Maroney, Comments Inorg. Chem. 17 (1995) 347. [8] D. Sellman, R. Ruf, F. Knoch, M. Moll, Inorg. Chem. 34 (1995) 4745. [9] G. Peng, J. Nickols, E.A. McCullough Jr., J.T. Spence, Inorg. Chem. 33 (1994) 2857. [10] H. Frydendahl, H. Toftlund, J. Becher, J.C. Dutton, K.S. Murray, L.F. Taylor, O.P. Anderson, R.T. Tiekink, Inorg. Chem. 34 (1995) 4467. [11] Y. Li, Y.H. Lai, K.F. Mok, M.G.B. Drew, Inorg. Chim. Acta 279 (1998) 221. [12] Software package for the SMART system; Siemens Analytical XRay Instruments, Madison, WI, 1996. [13] G.M. Sheldrick, Software for Absorption Correction, University of GoÈttingen, 1996. [14] M. Venkatesh, N. Goswami, W.A. Volkert, E.O. Schlemper, A.R. Ketring, C.L. Barnes, S. Jurisson, Nucl. Med. Biol. 23 (1996) 33. [15] F. Basolo, R.G. Pearson, Mechanisms of Inorganic Reactions, Wiley, New York, 1967. [16] A.W. Addison, R.D. Guillard, H. Vaughan, J. Chem. Soc., Dalton Trans. (1973) 1187. [17] R.D. Gilard, G. Wilkinson, J. Chem. Soc. (1964) 1224. [18] E.J. Bounsall, S.R. Koprich, Can. J. Chem. 48 (1970) 1481. [19] L.S.W.L. Sokol, L.A. Ochrymowycz, D.B. Rorabacher, Inorg. Chem. 20 (1981) 3189.
38
Y. Li et al. / Inorganica Chimica Acta 285 (1999) 31±38
[20] K. Johnson, ORTEP II, A Fortran Thermal Ellipsoids Plot Program for Crystal Structure Illustrations, Report ORNL-5138, Oak National Laboratory, Oak Ridge, TN, 1976. [21] S. Htoon, M.F.C. Ladd, J. Cryst. Mol. Struct. 3 (1973) 95. [22] W.J. Wu, D. Barton, S.J. Lippard, J. Am. Chem. Soc. 95 (1973) 1170. [23] Y. Li, Y.H. Lai, K.F. Mok, unpublished results. [24] M. Horike, Y. Kai, N. Kasai, J. Organomet. Chem. 86 (1975) 269.
[25] M. Gupta, R.E. Cramer, K. Ho, C. Pettersen, S. Mishina, J. Belli, C.M. Jensen, Inorg. Chem. 34 (1995) 60. [26] M. Oki, Application of Dynamic NMR Spectroscopy to Organic Chemistry, VCH, Deerfield, FL, 1985. [27] A.C. Skapsi, F.A. Setephens, J. Chem. Soc., Dalton Trans. (1973) 1789. [28] C. Dobinson, R. Mason, D.R. Russell, J. Chem. Soc., Chem. Commun. (1967) 62. [29] N. Goswami, R. Alberto, C.L. Barnes, S. Jurisson, Inorg. Chem. 35 (1996) 7546.