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Departments of Chemistry, UniVersity of Oulu, P.O. Box 3000, FI-90014, Finland,. UniVersity of JyVäskylä, P.O. Box 35, FI-40014, Finland, and UniVersi...
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CRYSTAL GROWTH & DESIGN

Isomerism in [MCl2(ERR′)2] (M ) Pd, Pt; E ) S, Se; R, R′ ) Me, Ph)

2006 VOL. 6, NO. 10 2376-2383

Ludmila Vigo,† Maarit Risto,† Esther M. Jahr,† Tom Bajorek,† Raija Oilunkaniemi,*,† Risto S. Laitinen,*,† Manu Lahtinen,‡ and Markku Ahlgre´n§ Departments of Chemistry, UniVersity of Oulu, P.O. Box 3000, FI-90014, Finland, UniVersity of JyVa¨skyla¨, P.O. Box 35, FI-40014, Finland, and UniVersity of Joensuu, P.O. Box 111, FI-80101 Joensuu, Finland ReceiVed June 10, 2006; ReVised Manuscript ReceiVed August 8, 2006

ABSTRACT: A series of thioether and selenoether complexes [MCl2(EPh2)2] and [MCl2(SMePh)2] (M ) Pt, Pd; E ) S, Se) have been prepared and characterized to explore the isomerism of the complexes in solution and in the solid state. The NMR spectroscopic information indicates that only one isomer is present in solution in case of the palladium complexes, while two isomers are formed in the case of most platinum complexes. Single-crystal X-ray structures of trans-[PdCl2(SPh2)2] (1t), trans-[PdCl2(SePh2)2] (2t), cis-[PtCl2(SePh2)2] (4c), trans-[PdCl2(SMePh)2] (5t), and trans-[PtCl2(SMePh)2] (7t) are reported and have been used as starting points for the X-ray powder diffraction structure determinations using simulated annealing method together with Rietveld refinement of the powder diffraction data. The presence of only trans-isomers in the solid phases was deduced in the case of [PdCl2(SPh2)2] and [PdCl2(SePh2)2] (1t and 2t, respectively). By contrast, the Rietveld refinement of the powder X-ray diffraction diagrams of [PtCl2(SPh2)2] and [PtCl2(SePh2)2] indicated the presence of both trans- and cis-isomers (3t, 3c and 4t, 4c, respectively) with mixing ratios that are consistent with NMR spectroscopic information in solution. The density functional theory calculations using [MCl2(EMe2)2] as model complexes indicated that while the trans-isomers of the palladium complexes lie at significantly lower energy than the cis-isomers do, in the case of the platinum complexes the energy difference is smaller and decreases, as the chalcogen atom of the chalcogenoether ligand becomes heavier. Introduction The stereochemistry of chalcogenoether complexes [MX2(ERR′)2] (M ) Pd, Pt; X ) Cl, Br, I; E ) S, Se, Te; R, R′ ) alkyl, aryl) has seen extensive research activity during recent decades (for some selected reviews, see ref 1). It has been shown using 77Se, 125Te, and 195Pt NMR spectroscopy that in the absence of steric and chelating effects, many of the complexes show the presence of both trans- and cis-isomers in solution with the trans/cis ratios increasing Pt < Pd and Cl < Br < I.1d,1e The bonding environment around chalcogen atoms is approximately tetrahedral resulting in further conformational flexibility. Indeed, facile pyramidal inversion has been deduced to take place about the chalcogen center and also has been extensively investigated.2 The isomerism of [MX2(ERR′)2] in the solid state mirrors that in solution. The crystal structures of a number of monodentate [PtX2(SRR′)2] complexes show approximately an even distribution of trans- and cis-isomers.3 In case of some complexes, both isomers have been structurally characterized.3a,3d,3g,3m While information of the corresponding selenoether and telluroether complexes is much sparser, the existence of both transand cis-isomers also has been established.3c,4 By contrast, the single-crystal structure determination of [PdX2(ERR′)2] complexes show mostly trans-isomers,3e,3i,3k,4b,4c,5,6 the sole exceptions being [PdCl2(TeMeR)2] (R ) 2-thienyl, C4H3S, or 2-furyl C4H3O).4c Even these latter two complexes show the presence of both isomers in solution. In this work, we explore the isomerism of [MCl2(EPh2)2] (14) and [MCl2(SMePh)2] (5 and 7) (M ) Pt, Pd; E ) S, Se) * To whom correspondence should be addressed. (R.S.L.) E-mail: [email protected]. Tel. +358-8-553-1611. Fax. +358-8-553-1608. (R.O.) E-mail: [email protected]. Tel. +358-8-553-1686. Fax. +358-8553-1608. † University of Oulu. ‡ University of Jyva ¨ skyla¨. § University of Joensuu.

Table 1. Abbreviated Notation of the [MCl2(ERR′)2] (M ) Pd, Pt; E ) S, Se, R,R′ ) Me, Ph) Isomersa [PdCl2(EPh2)2] [PtCl2(EPh2)2] [PdCl2(EMePh)2] [PtCl2(EMePh)2] S Se

cis

trans

cis

trans

cis

trans

cis

trans

1c 2c

1t 2t

3c 4c

3t 4t

5c 6cb

5t 6tb

7c 8cb

7t 8tb

a The use of only the numeral refers to the composition of the complex without consideration of a specific isomer. b These complexes have been included in the table for completeness, although they have not been considered in this work.

both in solution and in the solid state by NMR spectroscopy and X-ray diffraction (see Table 1 for the abbreviated notation of the different isomers considered in this work). We report the single-crystal X-ray structures of trans-[PdCl2(SPh2)2] (1t), trans-[PdCl2(SePh2)2] (2t), cis-[PtCl2(SePh2)2] (4c), trans[PdCl2(SMePh)2] (5t), and trans-[PtCl2(SMePh)2] (7t).7 Singlecrystal information also has been used as a basis for Rietveld refinement of powder X-ray diffraction data enabling the structural characterization and the determination of the composition of the bulk solid phases. Density functional theory (DFT) calculations using [MCl2(EMe2)2] as model complexes support the experimental work and provide further information on the formation and isomerism of the complexes. Experimental Section General. PdCl2 (Johnson Matthey), PtCl2 (Johnson Matthey), SPh2 (Aldrich), SMePh (Fluka), and SePh2 (Aldrich) were used as purchased. [PdCl2(NCPh)2] and [PtCl2(NCPh)2] were synthesized by modifying the method of Kharasch et al.8 NMR Spectroscopy. 77Se- and 195Pt-{1H}-NMR spectra were recorded on a Bruker DPX400 spectrometer operating at 76.31 and 86.20 MHz, respectively. The typical respective spectral widths were 100.000 and 55.437 kHz, and the pulse widths were 6.7 and 10.0 µs. The pulse delay for selenium was 2.0 s and for platinum was 0.8 s. The saturated D2O solution of selenium dioxide and the D2O solution of [PtCl6]2- were used as external standards. The 195Pt chemical shifts

10.1021/cg060348r CCC: $33.50 © 2006 American Chemical Society Published on Web 09/20/2006

Isomerism in [MCl2(ERR′)2]

Crystal Growth & Design, Vol. 6, No. 10, 2006 2377

Table 2. Details of the Single-Crystal X-ray Structure Determination of Complexes 1t, 2t, 4c, 5t, and 7t 1t empirical formula relative molecular mass crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) T (K) Z F(000) Dc (g cm-3) µ(Mo KR) (mm-1) crystal size (mm) θ range (deg.) no. of reflns collected no. of unique reflns no. of observed reflnsa no. of parameters RINT R1b wR2b R1 (all data) wR2 (all data) GOOF max and min heights in final difference Fourier synthesis (e Å-3) a

2t

4c

C12H10ClPd0.5S 274.91 monoclinic P21/c 5.731(1) 16.985(3) 11.722(2)

C12H10ClPd0.50Se 321.81 monoclinic P21/c 5.646(1) 17.218(3) 11.927(2)

C24H20Cl2PtSe2 732.31 monoclinic P21/n 12.387(3) 13.476(3) 13.778(3)

97.57(3)

96.89(3)

91.64(3)

1131.1(4) 150(2) 4 552 1.614 1.250 0.15 × 0.15 × 0.08 2.12-26.00 13112 2202 2028 134 0.0346 0.0329 0.0877 0.0401 0.1089 1.295 1.586, -0.871

1151.2(4) 120(2) 4 624 1.857 4.209 0.30 × 0.10 × 0.05 3.64-26.00 6537 2220 1950 133 0.0423 0.0338 0.0863 0.0420 0.0915 1.095 1.052, -0.784

2299.1(8) 120(2) 4 1376 2.116 9.511 0.25 × 0.20 × 0.15 2.11-26.00 29924 4517 4232 262 0.0584 0.0301 0.0857 0.0373 0.1097 1.285 1.089, -3.257

5t

7t

C7H8ClPd0.5S 212.84 triclinic P1h 6.845(1) 7.926(2) 8.563(2) 87.86(3) 71.44(3) 65.78(3) 399.4(1) 150(2) 2 212 1.770 1.741 0.25 × 0.25 × 0.15 2.52-25.99 4475 1569 1518 55 0.0367 0.0224 0.0542 0.0233 0.0547 1.057 0.765, -0.641

C7H8ClPt0.5S 257.19 triclinic P1h 6.7442(1) 7.9469(2) 8.6745(2) 88.079(1) 71.727(1) 65.806(1) 400.26(2) 150(2) 2 244 2.134 9.342 0.20 × 0.20 × 0.10 2.83-26.00 6315 1574 1574 55 0.0661 0.0337 0.0866 0.0337 0.0866 1.128 2.569, -3.072

I g 2σ(I). b R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑w(Fo2 - Fc2)2/∑wFo4]1/2.

are reported relative to the external standard and the 77Se chemical shifts relative to neat Me2Se [δ(Me2Se) ) δ(SeO2) + 1302.6].9 All spectra were recorded unlocked. Preparation of [PdCl2(SPh2)2] (1). PdCl2 (1.288 g, 7.26 mmol) and an excess of SPh2 (3.00 mL; 18.2 mmol) were refluxed in 30 mL of benzene for 1 h. Most PdCl2 dissolved during this time. Upon filtering and subsequent cooling of the filtrate slowly to -20 °C, yellow crystals were obtained. They were filtered, washed several times with diethyl ether, and dried. Yield: 3.370 g (85%). Anal. Calcd. for PdCl2S2C24H20: C 52.43; H 3.67; S 11.66%. Found: C 52.10; H 3.52; S 11.32%. Preparation of [PdCl2(SePh2)2] (2). SePh2 (0.30 mL, 1.56 mmol) was added into 5.00 mL of a dichloromethane solution of [PdCl2(NCPh)2] (0.300 g, 0.78 mmol). The reaction mixture was stirred at room temperature for 21/2 h. The dark orange crystals obtained by n-hexane precipitation were filtered, washed twice with n-hexane, and dried. Yield: 0.412 g (82%). Anal. Calcd. for PdCl2Se2C24H20: C 44.78; H 3.13%. Found: C 44.42; H 3.10%. NMR (298 K, CH2Cl2): 77Se δ ) 444 ppm. Preparation of [PtCl2(SPh2)2] (3). PtCl2 (1.123 g, 4.22 mmol) and an excess of SPh2 (3.00 mL; 18.2 mmol) were refluxed in 30 mL of benzene for 1 h. Most PtCl2 dissolved during this time. Upon filtering and subsequent cooling of the filtrate slowly to -20 °C, yellow crystals were obtained and separated by filtration. The filtrate was poured back on the nonreacted PtCl2, and the reaction mixture was further refluxed for 1 h. Upon filtration and slow cooling to -20 °C, a further batch of yellow crystals were obtained. They were filtered, washed several times with diethyl ether, and dried. The two batches of crystals were combined. Yield: 2.675 g (99%). Anal. Calcd. for PtCl2S2C24H20: C 45.15; H 3.19; S 10.04%. Found: C 45.71; H 2.96; S 9.67%. NMR (298 K, CH2Cl2): 195Pt δ ) -3177 and -3306 ppm. Preparation of [PtCl2(SePh2)2] (4). SePh2 (0.30 mL, 1.56 mmol) was added into 5 mL of a CH2Cl2 solution of [PtCl2(NCPh)2] (0.368 g, 0.78 mmol). The reaction mixture was first refluxed for 8 h and then stirred at room temperature overnight. The yellow-orange crystals obtained by n-hexane precipitation were filtered, washed with n-hexane, and dried. Yield: 0.454 g (80%). Anal. Calcd. for PtCl2Se2C24H20: C 39.36; H 2.75%. Found: C 38.69; H 2.40%. NMR (298 K, CH2Cl2): 77 Se δ ) 423 ppm (1JSe-Pt 631 Hz), δ ) 442 ppm (1JSe-Pt 489 Hz); 195 Pt δ ) -3445 and -3678 ppm.

Preparation of [PdCl2(SMePh)2] (5). An excess of SMePh (3.00 mL; 25.5 mmol) was added on 1.015 g (5.72 mmol) of PdCl2. The mixture was warmed in water bath and stirred for 1 h. The dark red solution was cooled slowly, first to room temperature and then to -20 °C. The cold mixture was layered with diethyl ether and left at -20 °C for 2 days with the subsequent formation of dark red crystals. They were filtered, washed several times with diethyl ether, and dried. Yield: 2.390 g (98%). Anal. Calcd. for PdCl2S2C14H16: C 39.50; H 3.79; S 15.06%. Found: C 39.59; H 3.65; S 14.62%. Preparation of [PtCl2(SMePh)2] (7). An excess of SMePh (4.00 mL; 34.0 mmol) was added to 1.030 g (3.87 mmol) of PtCl2 following the same procedure as for the preparation of 5. Orange crystals were obtained. Yield: 1.915 g (96%). Anal. Calcd. for PtCl2S2C14H16: C 32.69; H 3.14; S 12.47%. Found: C 32.77; H 3.00; S 12.46%. NMR (298 K, CH2Cl2): 195Pt δ ) -3177 ppm. X-ray Crystallography. Diffraction data of 1t, 2t, 4c, 5t, and 7t for single-crystal structure determination were collected on a Nonius Kappa-CCD diffractometer using graphite monochromated Mo KR radiation (λ ) 0.71073 Å; 55 kV, 25 mA). Crystal data and the details of structure determinations are given in Table 2. Structures were solved by direct methods using SIR-92 10 or SHELXS-9711a and refined using SHELXL-97.11b After the full-matrix least-squares refinement of the non-hydrogen atoms with anisotropic thermal parameters, the hydrogen atoms were placed in calculated positions in the aromatic rings (C-H ) 0.95 Å) and in the CH3 groups (C-H ) 0.99 Å). In the final refinement, the hydrogen atoms were riding with the carbon atom they were bonded to. The isotropic thermal parameters of the hydrogen atoms were fixed at 1.2 and 1.5 times to that of the corresponding phenyl and methyl carbon atoms, respectively. The scattering factors for the neutral atoms were those incorporated with the programs. The X-ray powder diffraction data of the phases 1-4 were collected at room temperature by Huber imaging plate Guinier camera 670 using germanium monochromated Cu KR1 radiation (λ ) 1.5406 Å; 45 kV, 25 mA). The measurements were carried out in Guinier-type transmission geometry with the angle of incidence 45° to the sample normal. The hand-ground samples were prepared on the vaseline-coated Mylar foil of 3.5 µm thickness, which was mounted on vertical sample holder oscillating horizontally. The X-ray diffraction data were recorded using the curved, position sensitive imaging plate detector in the 2θ angle

2378 Crystal Growth & Design, Vol. 6, No. 10, 2006 range from 4 to 100° with recording time of 120 min and step resolution of 0.005°. The measurement time for each sample was 120 min. The procedure for determining the instrumental resolution and the calibration of the instrument have been described elsewhere.12 The crystal data from powder diagrams and the details of the structure refinements of 1t, 2t, 3t, and 3c are shown in Supporting Information (Table S1). The structure determination of the complexes trans-[PdCl2(SPh2)2] (1t) and trans-[PdCl2(SePh2)2] (2t) from powder X-ray diffraction data including background subtraction,13 peak search, indexing (DICVOL 14), space group analysis and solving of the structure was made by the program DASH v3.0.15 Diffraction range of 5.0-48° (2θ) for 1t and 5.0-44° (2θ) for 2t were used for the structure determination. Three separate structure moieties (Pd, Cl, and SPh2 for 1t, and Pd, Cl, and SePh2 for 2t including the hydrogen atoms in the phenyl rings) were used to solve the structures by simulated annealing method. From preliminary determinations, it was found that the asymmetric unit is formed only by half of the molecule, and thus Pd is lying in a special position. The final iterations in both 1t and 2t revealed four identical structure models, from which the model having the best (lowest) profile chi-value was refined by Rietveld full-matrix full-powder data fitting using the FULLPROF 2000 v3.0 software.16 The data range of 5-70° (2θ) having either 558 or 643 reflections for 1t and 2t, respectively, was used in the Rietveld refinement. The remaining background was fitted by using linear interpolation between a set of fixed points that were provided manually at two degree intervals of 2θ. In the final stage, the background point positions were fixed and the linear interpolation was performed between the points using cubic splines. The peak profiles were modeled using the pseudoVoigt function. Convolution parameter of the Gaussian and Lorentzian portions (η), profile parameters (U, V, W), zero-shift of the pattern, and the coefficients relating to the asymmetry of the profiles were refined as generic variables for all phases. For each phase, independent cell parameters, scale factor and atomic coordinates of all atoms were also refined (in case of the cis-trans mixing ratio, refinement of the hydrogen atoms was omitted from the minor cis-phase). The peakprofiles were calculated as far as 12*fwhm (full-width at halfmaximum). Because of some instabilities observed during the refinements, 46 and 50 soft distance (for 1t and 2t, respectively) and 22 soft angle constraints (σ ) 0.015-0.03 Å and 0.5° for expected bond lengths and angles, respectively) were applied to the phenyl rings to keep their conformation reasonable and to treat the hydrogen atoms as riding atoms on their corresponding carbon atoms. Isotropic temperature factors of hydrogen were set fixed (U ) 0.0443), and a single refinable isotropic temperature factor was set for all the carbon atoms. Anisotropic temperature factors were used for the Pd, Cl, S, and Se atoms (only the three main axes were refined). Finally, a disorder model was introduced in 2t by refining two partial chlorine atoms with occupation factor of 0.5. The structure factors for each atom were calculated using the formal neutral atomic scattering factors incorporated in the FULLPROF program. The structures and the mixing ratio of trans- and cis-isomers of [PtCl2(SPh2)2] (3t and 3c, respectively) were determined by Rietveld refinement using structural models obtained by the single-crystal studies3m as starting points for the refinement. However, while the experimental data could be refined in terms of the 3t, which constitutes the major phase in the solid material, it was discovered that the structure model of the known cis-form could not be fitted. Therefore, several indexing and structure solving tasks were carried out for the remaining diffraction peaks using indexing software package of CRYSFIRE17 and structure determination software DASH.15 The unit cell of 3c which resembled that of the single crystal was found, except that the c-axis was only half of the single-crystal length (see Table S1 in Supporting Information). The space group was searched from the subgroups originating from the space group No. 61 (Pbca). The most promising space group turned out to be No. 19 (P212121). In the suggested structure model, the spacing of the heavy atoms was reasonable, but the location of the phenyl rings was somewhat ambiguous. The hydrogen atoms were omitted from the model.18 The refinement conditions for the trans-phase 3t were similar to those used for 1t and 2t, except that isotropic temperature factors were refined only for Pt, Cl, and S atoms. For carbon and hydrogen atoms, preselected constant values were used throughout the refinement (U ) 0.0317 and 0.0443, respectively). In the case of the 3c, all isotropic temperature factors were kept constant. The Rietveld refinement was

Vigo et al. carried out in three stages, so that at first the parameters of the transphase (3t) were refined, while the parameters of the cis-phase (3c) were kept fixed. Subsequently, the structural parameters of the cis-phase (the profile and global parameters were defined by the trans-phase) were refined by keeping structural parameters of the trans-phase fixed. This was followed by the refinement of all parameters of the trans-phase while keeping those of the cis-phase once again fixed. The refined structure model 3c covered adequately the remaining integrated diffraction intensities and in that respect allowed proper comparison of the weight fractions of cis- and trans-isomers.19 In case of [PtCl2(SePh2)2] (4) evaluation of the mixing ratio of cisand trans-isomers was based only on visual comparison of the diffraction intensities to those of known cis-[PtCl2(SePh2)2] (4c) because of unsuccessful indexing of another isomer whose diffraction peaks severely overlapped with the known cis-phase.

Computational Details The calculations were performed on [MCl2(EMe2)2] (E ) S, Se, Te) model complexes using Gaussian 03 quantum chemical suite of programs.20 All geometry optimizations and frequency calculations were performed using the hybrid DFT theory PBE021 and the Stuttgart relativistic large core effective core potentials (RLC ECP 22-24) basis set for atoms C, S, Se, and Te where the valence orbitals of the double-ζ quality basis set were augmented by two Huzinaga25 polarization functions. The Stuttgart relativistic small core effective core potentials (RSC ECP26,27) basis set was employed for atoms Pd and Pt on which no polarizations were used. The hydrogen atom was treated with the 6-31g(d,p) basis set. Hereafter, the basis sets are referred to as “RC ECP”. The investigation of normal molecular vibrational modes with frequency calculations was used to confirm global and local minima where the absence of imaginary vibrational modes indicated stable geometry. Results and Discussion General. Neat SMePh reacts with PdCl2 and PtCl2 nearly quantitatively to afford [MCl2(SMePh)2] [M ) Pd (5), Pt (7)]. The reaction of SPh2 with PdCl2 and PtCl2 without solvent gave only ca. 15% isolated yields of 1 and 3. With the solvent the yields were almost quantitative. [MCl2(NCPh)2] (M ) Pt, Pd) have turned out to be convenient reagents in the syntheses of chalcogenoether complexes, as exemplified by recent preparations of [MCl2(EMeTh)2] (E ) Se, Te; M ) Pd, Pt; Th ) 2-thienyl, C4H3S)4c and [PtCl2(SMePh)2].3n The reaction of diphenyl selenide with [PdCl2(NCPh)2] in dichloromethane produced trans-[PdCl2(SePh2)2] (2), and the reaction with [PtCl2(NCPh)2] produced a mixture of cis- and trans-[PtCl2(SePh2)2] (4) based on the 77Se and 195Pt{1H}-NMR data. NMR Spectroscopy. In solution, [PdCl2(SePh2)2] (2) exhibits only one 77Se NMR resonance at 444 ppm indicating the presence of one isomer. The crystal structure determination from the single crystal and powder diffraction data demonstrate that the solid material is trans-[PdCl2(SePh2)2] (see below). This isomer is likely also to be retained in solution. The195Pt{1H} NMR spectrum of [PtCl2(SPh2)2] (3) shows two close-lying resonances at -3177 and -3306 ppm with the relative intensities of ca. 85:15. These resonances have been assigned to the trans- and cis-isomers, respectively, based on the quantitative determination of the two isomers in the solid state by the Rietveld refinement of the X-ray powder data that indicate approximately the same ratio between the two isomers (see below). The 77Se NMR spectrum of [PtCl2(SePh2)2] (4) shows two close-lying resonances at 423 ppm (1JSePt ) 631 Hz) and 442

Isomerism in [MCl2(ERR′)2]

Crystal Growth & Design, Vol. 6, No. 10, 2006 2379

Table 3. Selected Bond Lengths (Å) and Angles (°) in 1t, 2t, 4c, 5t, and 7t Based on Single-Crystal X-ray Structure Determination 1t

2t

4c

5t

7t

Pd(1)-S(1) Pd(1)-S(1)a Pd(1)-Cl(1) Pd(1)-Cl(1)a

2.3225(8) 2.3225(8) 2.2859(8) 2.2859(8)

Pd(1)-Se(1) Pd(1)-Se(1)a Pd(1)-Cl(1) Pd(1)-Cl(1)a

2.4245(7) 2.4245(7) 2.288(1) 2.288(1)

Pt(1)-Se(2) Pt(1)-Se(1) Pt(1)-Cl(1) Pt(1)-Cl(2)

2.3900(8) 2.3960(9) 2.305(1) 2.322(2)

Pd(1)-S(1) Pd(1)-S(1)a Pd(1)-Cl(1) Pd(1)-Cl(1)a

2.3181(8) 2.3181(8) 2.292(1) 2.292(1)

Pt(1)-S(1) Pt(1)-S(1)a Pt(1)-Cl(1) Pt(1)-Cl(1)a

2.303(1) 2.303(1) 2.301(1) 2.301(1)

S(1)-Pd(1)-S(1)a S(1)-Pd(1)-Cl(1) S(1)-Pd(1)-Cl(1)a S(1)a-Pd(1)-Cl(1) S(1)a-Pd(1)-Cl(1)a Cl(1)-Pd(1)-Cl(1)a

180.00 84.91(3) 95.09(3) 95.09(3) 84.91(3) 180.00

Se(1)-Pd(1)-Se(1)a Se(1)-Pd(1)-Cl(1) Se(1)-Pd(1)-Cl(1)a Se(1)a-Pd(1)-Cl(1) Se(1)a-Pd(1)-Cl(1)a Cl(1)-Pd(1)-Cl(1)a

180.00 95.71(4) 84.29(4) 84.29(4) 95.71(4) 180.00

Se(1)-Pt(1)-Se(2) Se(1)-Pt(1)-Cl(1) Se(1)-Pt(1)-Cl(2) Se(2)-Pt(1)-Cl(1) Se(2)-Pt(1)-Cl(2) Cl(1)-Pt(1)-Cl(2)

94.27(3) 94.44(4) 174.18(4) 170.12(4) 82.30(4) 89.39(5)

S(1)-Pd(1)-S(1)a S(1)-Pd(1)-Cl(1) S(1)-Pd(1)-Cl(1)a S(1)a-Pd(1)-Cl(1) S(1)a-Pd(1)-Cl(1)a Cl(1)-Pd(1)-Cl(1)a

180.00 94.80(4) 85.20(4) 85.20(4) 94.80(4) 180.00

S(1)-Pt(1)--S(1)a S(1)-Pt(1)-Cl(1) S(1)-Pt(1)-Cl(1)a S(1)a-Pt(1)-Cl(1) S(1)a-Pt(1)-Cl(1)a Cl(1)-Pt(1)-Cl(1)a

180.00 85.14(4) 94.86(4) 94.86(4) 85.14(4) 180.00

a

Symmetry operation: -x, -y, -z.

ppm (1JSePt ) 489 Hz). Two resonances are also found in the 195Pt-{1H}-NMR spectrum at -3445 ppm (1J SePt ) 489 Hz) and -3678 ppm (1JSePt ) 631 Hz). Assignment of these resonances is based on the chemical shifts and coupling constants. It has been reported that the cis-isomers show both the 77Se and 195Pt resonances at lower frequencies and that the 1JSePt coupling constants of the cis-isomers are larger than those of the transisomers due to the higher trans-influence of SeRR′ compared to that of Cl.4c,28 We therefore assign the 77Se chemical shift of 442 ppm and the 195Pt chemical shift of -3445 ppm to trans[PtCl2(SePh2)2] (4t) and the 77Se chemical shift of 423 ppm and the 195Pt chemical shift of -3678 ppm to cis-[PtCl2(SePh2)2] (4c). The resulting intensity ratios of both 77Se and 195Pt resonances imply a trans/cis ratio of ca. 55:45 that is in good agreement with the inference from powder data (see below). We also note that the 77Se chemical shift of trans-[PtCl2(SePh2)2] (4t) is almost identical to that of trans-[PdCl2(SePh2)2] at 444 ppm. The 77Se chemical shifts of the cis- and trans-isomers of 2 and 4 can be compared to the 125Te chemical shifts of analogous tellurium-containing complexes.29 The δ(Te)/δ(Se) ratio is 1.69 for the cis-Pt complexes and 1.65 for the trans-Pt complexes agreeing well with the previously reported δ(Te)/δ(Se) range.32 The195Pt{1H}NMR spectrum of [PtCl2(SMePh)2] (7) shows only one resonance at -3177 ppm that is assigned to the transisomer based on the crystal structure determination.33 It should be noted that this chemical shift is virtually identical with that observed for trans-[PtCl2(SMePh)2] (3c). Single-Crystal X-ray Structures. Selected bond parameters of trans-[PdCl2(SPh2)2] (1t), trans-[PdCl2(SePh2)2] (2t), cis[PtCl2(SePh2)2] (4c), trans-[PdCl2(SMePh)2] (5t), and trans[PtCl2(SMePh)2] (7t) are shown in Table 3. The molecular structures together with the numbering of atoms of isomorphic trans-[PdCl2(SPh2)2] (1t) and trans-[PdCl2(SePh2)2] (2t) are shown in Figure 1, that of cis-[PtCl2(SePh2)2] (4c) is shown in Figure 2, and those of isomorphic trans-[PdCl2(SMePh)2] (5t) and trans-[PtCl2(SMePh)2] (7t) are shown in Figure 3. The coordination environment around the palladium or platinum center is a slightly distorted square-plane in case of each complex. The Pd-S bond lengths in 1t and 5t [2.3225(8) and 2.3181(8) Å, respectively] are typical for single bond lengths (the sum of covalent radii of palladium and sulfur is 2.32 Å 34) and are in agreement with the Pd-S bond lengths in trans[PdCl2(SMe2)2] [2.319(1) Å],5h trans-[PdCl2{S(n-Bu)(pMePh)}2] [2.316(1) Å],5d and trans-[PdCl2{S(n-Bu)(p-t-BuPh)}2] [2.325(1) Å].5f The Pt-S bond lengths of trans-[PtCl2(SMePh)2] (7t) [2.303(1) Å] are also typical for single bond lengths (the sum of covalent radii of platinum and sulfur is 2.33 Å 34) and agree with those reported recently for trans-[PtCl2(SPh2)2] [2.3002(12) Å] and other related complexes (see ref 3m and references therein).

Figure 1. The molecular structure of isomorphic trans-[PdCl2(EPh2)2] [E ) S (1t), Se (2t)] indicating the numbering of atoms. The thermal ellipsoids have been drawn at 50% probability level. The structure in the figure is that of 2t.

Figure 2. The molecular structure of cis-[PtCl2(SePh2)2] (4c) indicating the numbering of atoms. The thermal ellipsoids have been drawn at 50% probability level.

Pd-Se distance in 2t is 2.4245(7) Å and the Pt-Se distances in 4c are 2.3900(8)-2.3960(9) Å agreeing closely with the corresponding bond lengths in trans-[PdCl2(SeEt2)2] [2.424(7) Å],6a trans-[PdCl2(MeSiCH2SeMe)2] and trans-[PtCl2(Me3GeCH2SeMe)2] [2.429(1) and 2.418(2) Å, respectively],4b trans[PdCl2(C4H3SSeMe)2] and trans-[PtCl2(C4H3SSeMe)2] [2.439(2)

2380 Crystal Growth & Design, Vol. 6, No. 10, 2006

Vigo et al.

Figure 3. The molecular structure of isomorphic trans-[MCl2(SMePh)2] [M ) Pd (5t), Pt (7t)] indicating the numbering of atoms. The thermal ellipsoids have been drawn at 50% probability level. The structure in the figure is that of 7t.

Å and 2.411(4) Å, respectively],4c and cis-[PtCl2(PSeZ)2] (PSeZ ) phenoselenazine) [2.376(2), 2.400(2) Å].4a The Pd-Cl bond lengths in 1t, 2t, and 5t range from 2.2859(8) to 2.292(1) Å and are consistent with those in trans[PdCl2(SMe2)2] [2.292(1) Å],5h trans-[PdCl2{S(n-Bu)(pMePh)}2] [2.303(1) Å],5d and trans-[PdCl2{S(n-Bu)(p-t-BuPh)}2] [2.295(1) Å].5f The Pt-Cl distances in 4c are 2.305(1) and 2.322(2) Å and in 7t 2.301(1) Å. They agree well with the average of 14 [PtCl2R2] compounds with mean Pt-Cl bond length of 2.299(5) Å [see ref 3m and references therein]. The Pt-Cl bond lengths in cis-[PtCl2(PSeZ)2] [2.297(4) and 2.3264(4) Å],4a in trans-[PtCl2(Me3GeCH2SeMe)2] [2.305(5) Å]),4b and trans-[PtCl2(C4H3SMe)2] (2.310(1) Å)4c are also consistent with the values determined for 4c and 7t. Weak Cl‚‚‚H hydrogen bonds link all complexes into threedimensional networks. The shortest Cl‚‚‚H distances are 2.713(1), 2.766(1), 2.754(1)-2.878(1), 2.846(1), and 2.862(2) Å for 1t, 2t, 4c, 5t, and 7t, respectively. They do not show halogenchalcogen close contacts by contrast to the telluroether complexes of palladium and platinum that crystallize in dimeric units as a consequence of tellurium-halogen secondary bonding interactions (see ref 4c and references therein). The transcomplexes 1t, 2t, 5t, and 7t crystallize as skewed stacks, as can also be observed for trans-[PtCl2(SPh2)2].3m In the case of cis-complexes, 4c, cis-[PtCl2(SPh2)2],3m and cis-[PtCl2{S(C6H4Cl)2}2],3b no such stacks are apparent. Quantitative Phase Analysis by X-ray Powder Diffraction. The determination of crystal structures and phase compositions by Rietveld refinement of powder X-ray diffraction data were carried out on the phases 1-4 to compare the structures of the bulk material with those determined for the single crystals and to establish the isomer composition of the solid powder samples. The Rietveld refinement of the powder X-ray diffraction diagrams of the phases 1 and 2 showed that they both consist of only one crystalline isomer, viz. trans-[PdCl2(SPh2)2] (1t) and trans-[PdCl2(SePh2)2] (2t) consistent with the single-crystal structural analysis. The selected bond lengths and angles are given in Supporting Information (Table S2), and the final Rietveld refinement plots are shown in Figure 4. The crystal structures of 1t and 2t from X-ray powder diffraction data were similar to the single crystal structures (Figure 5 for the packing of the molecules as determined from the powder diffraction data), and the coordination environments around the metal centers were similarly distorted square-planes. The Pd-S and Pd-Cl bond lengths in 1t are 2.293(4) and 2.315(4) Å,

Figure 4. Final Rietveld refinement plots of (a) 1t and (b) 2t. The red crosses represents experimental diffraction pattern, the black line is the calculated pattern, and the blue line represents the difference yobs - ycalc. The calculated Bragg angles (2θ) are marked by the green vertical bars.

respectively, and the Pd-Se, and Pd-Cl bond lengths in 2t are 2.379(2) and 2.314(2) Å, respectively. The powder data, however, showed that the chlorine atoms in 2t were disordered in two alternative positions on both sides of the square-planar coordination plane of palladium [Cl(1)‚‚‚Cl(1′) ) 0.83(3) Å; Figure 5].35 It can be seen in the low-temperature single-crystal X-ray structure shown in Figure 1 that the thermal ellipsoid of Cl(1) is elongated perpendicular to the square-planar coordination plane suggesting the onset of this disorder. The refinement of the single-crystal data allowing this disorder did not, however, resolve into two different atomic positions. The 195Pt NMR spectrum of the solution of [PtCl2(SPh2)2] (3) indicated the presence of two isomers in the molar ratio of 85:15. Johansson et al.3m have recently reported the singlecrystal structures of both trans- and cis-isomers (3t and 3c, respectively). In the present paper, the presence and mixing ratio of both isomers were evaluated in the powder sample by the Rietveld refinement. The observed and calculated X-ray powder diffraction diagrams based on 3t and 3c are shown in Figure 6. It was established that the weight fractions were ca. 85 and 15% for 3t and 3c, respectively. These results are in excellent agreement with the solution NMR spectrum and verify that the 195Pt chemical shift at -3177 ppm is due to 3t and that at -3306 ppm is due to 3c. The evaluation of the mixing ratio for the isomers of [PtCl2(SePh2)2] (4) was not so straightforward and was based only on visual comparison between the known phase and the

Isomerism in [MCl2(ERR′)2]

Crystal Growth & Design, Vol. 6, No. 10, 2006 2381

Figure 5. The molecular structure of trans-[PdCl2(SePh2)2] (2t) from X-ray powder diffraction data indicating the numbering of atoms and the disorder of the chlorine atoms. The thermal ellipsoids have been drawn at 50% probability level. trans-[PdCl2(SPh2)2] (1t) is isomorphous with 2t, but the chlorine atoms are not disordered.

Figure 6. Final Rietveld fit of the trans-cis mixture of [PtCl2(SPh2)2] (3). The profiles are indicated as follows: red crosses represent experimental diffraction pattern, the black line the calculated pattern, and the blue line represents the difference (yobs - ycalc). The Bragg reflections are shown by the vertical bars for the trans (upper) and for the cis phase (lower).

experimental data since there are reference data only for the cis-isomer (4c). It was assumed that trans-[PtCl2(SePh2)2] (4t) is isomorphic with the analogous palladium complex 2t, but this does not seem to be the case. About 50% of the profile intensities could be fitted to the experimental data based on 4c, but proper Rietveld analysis of the phase mixture could not be carried out due to unsuccessful indexing of the other isomer the diffraction peaks of which were severely overlapped with those of the cis-phase 4c (for experimental and calculated pattern see Figure 7). On the basis of NMR data, it was assumed that the crystallization yielded both trans- and cis-isomers (4t and 4c, respectively) in an analogous manner to [PtCl2(SPh2)2] (3t and 3c). Therefore, both isomers have a weight fraction of ca. 50%. Both the 77Se and 195Pt spectra indicate that the molar

Figure 7. Experimental powder diffraction pattern of the [PtCl2(SePh2)2] phase (4) compared to the calculated powder pattern from the single-crystal structure parameters of cis-[PtCl2(SePh2)2] (4c).

ratio of trans- and cis-isomers is 55:45 in good agreement with the X-ray powder diffraction data. We were unfortunately not able to grow crystals of the trans-isomer suitable for singlecrystal structure determination. Optimized Geometries and Relative Stabilities of transand cis-[MCl2(EMe2)2] (M ) Pd, Pt; E ) S, Se, Te). The selected bond lengths of the PBE0/(RC ECP) optimized geometries of different isomers of the model complexes [MCl2(EMe2)2] (M ) Pd, Pt; E ) S, Se, Te) are shown in Table 4. It can be seen that the calculated bond lengths agree well with the corresponding bond lengths yielded by the X-ray structure determinations (Table 3). The relative PBE0/(RC ECP) energies of the optimized geometries are shown in Figure 8. They are based on the total energies of the molecules and include the zero point vibrational energy correction (ZPVE) (Table S3 in Supporting Information). Both cis- and trans-isomers show two local minima representing two different rotamers of the

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Vigo et al.

Table 4. Selected Bond Lengths (Å) of the PBE0/(RC ECP) Optimized Geometries of Different Isomers of the [MCl2(EMe2)2] (M ) Pd, Pt; E ) S, Se, Te) Model Complexes

E

S

Se

Te

S

Se

Te

S

Se

Te

S

Se

Te

Pd-E Pd-Cl Pt-E PtCl

2.34 2.32 2.33 2.34

2.45 2.32 2.45 2.34

2.62 2.32 2.61 2.34

2.34 2.32 2.32 2.34

2.45 2.32 2.44 2.34

2.60 2.32 2.61 2.34

2.34 2.31 2.32 2.33

2.49 2.34 2.43 2.33

2.61 2.33 2.59 2.35

2.40 2.33 2.31 2.33

2.47 2.34 2.43 2.34

2.58 2.34 2.58 2.34

ligands (Table 4). The rotational barriers about the M-E bonds, however, are below 25 kJ mol-1 in all complexes allowing for free rotation in solution. In crystals, the observed rotamer depends on the packing efficiency. In the case of palladium complexes, the trans-isomers lie significantly lower in energy than the cis-isomers. The energy difference between the trans- and cis-isomers of the platinum complexes is significantly lower and decreases, as the chalcogen becomes heavier. This might well explain why only transisomers have been observed in the case of most palladium complexes, whereas it is possible to isolate both the trans- and cis-isomers of the analogous platinum complexes. Conclusion The [MCl2(ERR′)2] (M ) Pd, Pt; E ) S, Se, Te; R,R′ ) alkyl, aryl) system constitutes a well-explored series of complexes. It has been observed that while most palladium complexes show only the presence of trans-isomers, both transand cis-isomers can be isolated in many analogous platinum systems. In the present contribution, we have explored the isomerism in the solid state. A series of thioether and selenoether complexes [MCl2(EPh2)2] (1-4) and [MCl2(SMePh)2] (5 and 7) (M ) Pt, Pd; E ) S, Se) have been prepared and characterized. The NMR spectroscopic information indicates that only one isomer is present in solution in case of the palladium complexes, while two isomers are formed in case of many platinum complexes. In the solid state, trans-[PdCl2(SPh2)2] (1t), trans-[PdCl2-

(SePh2)2] (2t), cis-[PtCl2(SePh2)2] (4c), trans-[PdCl2(SMePh)2] (5t), and trans-[PtCl2(SMePh)2] (7t) have been identified and structurally characterized by single-crystal X-ray crystallography The powder structure determination using simulating annealing method together with Rietveld refinement of X-ray powder diffraction data has enabled the crystal structures of 1t and 2t to be determined also from the powder data and demonstrate the presence of only the trans-isomer in both cases in the solid phases. Rietveld refinement of the powder X-ray diffraction diagrams of [PtCl2(SPh2)2] and [PtCl2(SePh2)2] indicated the presence of both trans- and cis-isomers (3t, 3c, and 4t, 4c, respectively) with mixing ratios that are consistent with NMR spectroscopic information in solution. DFT calculations using [MCl2(EMe2)2] (M ) Pd, Pt; E ) S, Se, Te) show that the trans-isomers of the palladium complexes lie at significantly lower energy than the cis-isomers. In case of the platinum complexes, the energy difference is smaller and decreases, as the chalcogen atom of the chalcogenoether ligand becomes heavier. Acknowledgment. We thank Ms. Sanna Kantola for her help in part of the synthetic work. Financial support from Academy of Finland and Finnish Cultural Foundation is gratefully acknowledged. Supporting Information Available: Seven X-ray crystallographic files in CIF format (five reporting crystal structures from single-crystal data and two from powder data), two tables containing crystal data of 1t, 2t, 3t, and 3c, as well as selected bond lengths of 1t, and 2t from powder diffraction data, and the total PBE0/(RC ECP) total energies of all [MCl2(EMe2)2] isomers (M ) Pd, Pt; E ) S, Se, Te). This material is available free of charge via the Internet at http://pubs.acs.org.

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Figure 8. Relative PBE0/(RC ECP) energies of the different isomers of [MCl2(EMe2)2] (M ) Pd, Pt; E ) S, Se, Te).

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Crystal Growth & Design, Vol. 6, No. 10, 2006 2383 (17) CRYSFIRE Suite: Shirley, R. 2000, The CRYSFIRE System for Automatic Powder Indexing: User Manual; The Lattice Press: 41 Guildford Park Avenue, Guildford, Surrey GU2 7NL, England. (18) It must be noted that the difficulties in solving the structure of the residual phase 3c originate from the fact that only ∼20% of the intensity gain was caused by this second phase; most of the diffraction peaks were merged partially or completely with the known phase and the weakest diffraction peaks at higher 2θ were missing completely, as they were embedded to the predominant trans-phase 3t. (19) In the mixture of crystalline components, the weight fraction for each phase is given by: Wj ) (SjZjMjV/tj)/[sum(i)(SiZiMiVi/ti)], where Sj is the scale factor of phase j, Zj is the number of formula units per unit cell for phase j, Mj is the mass of the formula unit, Vj is the unit cell volume and tj is the Brindley particle absorption contrast factor for phase j for which the value of 1 was consistently used to all phases. (20) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; AlLaham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.04; Gaussian, Inc.: Wallingford CT, 2004. (21) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV. Lett. 1997, 78, 1396. (22) Kuechle, W.; Dolg, M.; Stoll, H.; Preuss, H. Mol. Phys. 1991, 74, 1245. (23) Bergner, A.; Dolg, M.; Ku¨chle, W.; Stoll, H.; Preuss, H. Mol. Phys. 1993, 80, 1431. (24) Bu¨hl, M.; Thiel, W.; Fleischer, U.; Kutzelnigg, W. J. Phys. Chem. 1995, 99, 4000. (25) Huzinaga, S., Ed. Gaussian Basis Sets for Molecular Calculations; Physical Science Data 16, Elsevier: Amsterdam, 1984. (26) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123. (27) Martin, J. M. L.; Sundermann, A. J. Chem. Phys. 2001, 114, 3408. (28) Kemmitt, T.; Levason, W. Inorg. Chem. 1990, 29, 731. (29) It has been reported that in analogous compounds the 125Te and 77Se chemical shifts bear a constant ratio of 1.6-1.8.30 Kemmitt et al.31 have demonstrated that in metal complexes containing selenium or tellurium donor atoms this ratio spans a range 1.66-2.11. (30) (a) McFarlene, H. C. E.; McFarlene, W. J. Chem. Soc., Dalton Trans. 1973, 2416. (b) O’Brien, D. H.; Dereu, N.; Huang, C.-K.; Irgolic, K. J. Organometallics 1983, 2, 305. (c) Chivers, T.; Laitinen, R. S.; Schmidt, K. J.; Taavitsainen, J. Inorg. Chem. 1993, 32, 337. (31) Kemmitt, T. Levason, W. Webster, M. Inorg. Chem. 1989, 28, 692. (32) [cis-[PtCl2(TePh2)2]: δ(Te) ) 715 ppm, 1JTePt ) 1257 Hz; trans[PtCl2(TePh2)2]: δ(Te) ) 729 ppm, 1JTePt ) 696 Hz.31 (33) It is interesting to note that while in principle the unsymmetrically substituted thioether ligands should give rise to the existence of two diastereoisomers (R*R* and R*S*) in 7t, the small energy barrier for the pyramidal inversion about the chalcogen centre2 indicates that they are interchanging very rapidly in solution. The observation of only one 195Pt resonance is consistent with this inference. It is also likely that the two possible diastereoisomers of 5t are also in fast dynamical equilibrium. (34) Emsley, J. The Elements, 3rd ed.; Wiley: Chichester 1998. (35) The X-ray powder diffraction data of 1t did not indicate disordered chlorine atoms.

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