DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 2207 Synthesis, multinuclear magnetic resonance spectroscopic studies and crystal structures of mono- and di-selenoether complexes of tin(IV) halides Sandra E. Dann, Anthony R. J. Genge, William Levason and Gillian Reid Department of Chemistry, University of Southampton, Highfield, Southampton, UK SO17 1BJ Reaction of SnX4 (X = Cl or Br) with Me2Se or diselenoether ligands in dry CHCl3 produced white or yellow solids [SnX4L2] in high yield [X = Cl, L2 = MeSe(CH2)nSeMe, PhSe(CH2)nSePh (n = 2 or 3), C6H4(SeMe)2-o or 2Me2Se; X = Br, L2 = MeSe(CH2)nSeMe (n = 2 or 3), C6H4(SeMe)2-o or 2Me2Se].These compounds have been characterised by a combination of variable-temperature 1H, 119Sn-{1H} and 77Se-{1H} NMR, IR spectroscopy and microanalyses. Single-crystal X-ray diffraction studies on trans-[SnX4(SeMe2)2], [SnX4{C6H4(SeMe)2-o}] (X = Cl or Br) and [SnCl4{MeSe(CH2)3SeMe}] confirm distorted octahedral geometry at SnIV in each case, with the bidentate ligands chelating.The C6H4(SeMe)2-o complexes adopt the meso arrangement, while the ligand is in the DL form in [SnCl4{MeSe(CH2)3SeMe}]. The trends in d(Sn]X) and d(Sn]Se) reveal that the trans influence of halide is greater than that of selenium in these systems. In comparable systems d(Sn]Se) is longer in the bromo than in the chloro systems, consistent with the greater Lewis acidity of SnCl4. The NMR studies revealed that pyramidal-inversion and ligand-dissociation processes are facile.In the SeMe2 complexes both cis and trans isomers are present, while in the diselenoether systems the meso and DL forms are both apparent at low temperatures. The co-ordination shifts in the 77Se-{1H} NMR spectra are markedly dependent upon chelate-ring size; the first time this has been observed for complexes of a p-block metal. The co-ordination chemistry of d-block metals has been one of the most active areas of inorganic chemistry in the last fifty years.Although p-block metals also form co-ordination complexes, these lack the characteristic UV/VIS spectra and magnetic properties, which provided much of the early impetus in the d-block work. p-Block metal complexes are often hydrolytically unstable and very labile in solution, which made them difficult to study and less suited to some spectroscopic techniques. The net result is that our knowledge of them is still very limited, although recent applications as precursors for metal chemical vapour deposition (MCVD) synthesis of new electronic materials have stimulated new investigations.In the case of tin(IV), nitrogen- and oxygen-donor ligand complexes have long been known1 and phosphine complexes have recently been studied.2 We recently reported a detailed study of dithioether complexes of tin(IV) halides using 1H and 119Sn-{1H} NMR spectroscopy in solution and 119Sn magic angle spinning (MAS) NMR in the solid state in conjunction with single-crystal X-ray diffraction.3 Here we describe the first systematic study of the synthesis and properties of mono- and di-selenoether complexes of tin(IV) halides.The only prior reports of selenoether complexes are studies of [SnX4(R2Se)2] (X = Cl or Br, R = Me or Me3SiCH2) utilising 1H NMR and vibrational spectroscopy.4,5 Results and Discussion The reaction of SnX4 (X = Cl or Br) with 2 molar equivalents of Me2Se or 1 molar equivalent of diselenoether in dry CHCl3 produced white or yellow solids [SnX4L2] [X = Cl, L2 = MeSe(CH2)nSeMe, PhSe(CH2)nSePh (n = 2 or 3), C6H4(SeMe)2- o or 2Me2Se; X = Br, L2 = MeSe(CH2)nSeMe (n = 2 or 3), C6H4(SeMe)2-o or 2Me2Se]. Attempts to isolate complexes of PhSe(CH2)nSePh (n = 2 or 3) with SnBr4, or SnI4 complexes with any of these ligands, were unsuccessful, although NMR evidence for their formation in situ was obtained in some cases (see below). As we observed previously with dithioethers,3 no interaction between these selenoethers and a suspension of SnF4 in chlorocarbons was apparent.The solid complexes appear indefinitely stable in sealed tubes or in a dry-box, but decompose quickly in moist air, and are very easily hydrolysed by traces of water in solution. The complexes are more hydrolytically unstable than the dithioether analogues,3 and all samples were handled in Schlenk equipment or in a glove-box (water levels < 10 ppm). Samples for solution NMR measurements were made up in rigorously anhydrous solvents in the glove-box, since trace amounts of water lead to some displacement of the neutral ligand.The IR spectra (Experimental section) show the presence of the selenium ligands and for the [SnX4(diselenoether)] complexes show several strong vibrations assignable as n(SnX) (theory 2A1 1 B1 1 B2), and confirm the absence of water. The far-IR spectra of [SnX4- (Me2Se)2] show single strong bands at 312 (X = Cl) and 220 cm21 (X = Br) in agreement with the previous study4 and consistent with the major isomer in the solid state being the trans form.Prior to this study there were no reports of structural data on any tin(IV) selenoether complexes. Therefore, in order to enable comparisons with the thioether derivatives which we reported previously,3 and to establish any trends between the solution NMR behaviour (below) and the solid-state structures, singlecrystal structure analyses were undertaken on trans- [SnX4(Me2Se)2] and cis-[SnX4{C6H4(SeMe)2-o}] (X = Cl or Br).For [SnX4(Me2Se)2] the structures show (X = Cl, Fig. 1, Table 1; X = Br, Fig. 2, Table 2) the central SnIV occupies a crystallographic inversion centre, co-ordinated via four precisely planar X atoms, with two mutually trans SeMe2 ligands completing the slightly distorted octahedral geometry [X = Cl, Sn]X 2.413(2), 2.427(2), Sn]Se 2.7001(9); X = Br, Sn]X 2.576(2), 2.587(2), Sn]Se 2.731(2) Å].In both cases the angles around the central Sn atom are very close to the 90 and 1808 expected for a regular octahedron. The Sn]Se distances in the bromo derivative are significantly longer than in the chloro species, probably a consequence of SnBr4 being a poorer acceptor than SnCl4. McAuliffe and co-workers 6 have reported the structures of the thioether analogues trans- and cis-[SnBr4(SMe2)2]. While the Sn]Br distances in these are very similar to those in trans- [SnBr4(SeMe2)2], the Sn]Se distances in this selenoether species are ca. 0.1 Å longer than d(Sn]S) in trans-[SnBr4(SMe2)2], consistent with the larger radius of Se over S.2208 J.Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 The compounds [SnX4{C6H4(SeMe)2-o}] (X = Cl or Br) both show distorted octahedral co-ordination at SnIV with the diselenoether chelating and adopting the meso arrangement (X = Cl, Fig. 3, Table 3; X = Br, Fig. 4, Table 4) [X = Cl, Sn]X (trans X) 2.389(3), 2.426(3), Sn]X (trans Se) 2.360(3), 2.364(3), Sn]Se 2.749(1), 2.787(2); X = Br, Sn]X (trans X) 2.512(1), 2.547(2), Sn]Br (trans Se) 2.600(2), Sn]Se 2.841(2) Å].The trends apparent in d(Sn]X) with trans ligand parallel those Fig. 1 View of the structure of trans-[SnCl4(Me2Se)2] with the numbering scheme adopted. Ellipsoids are shown at 40% probability and atoms marked with an asterisk are related by a crystallographic inversion centre Fig. 2 View of the structure of trans-[SnBr4(Me2Se)2] with the numbering scheme adopted.Details as in Fig. 1 observed for the thioether compounds,3 i.e. d(Sn]X) trans X are consistently longer than d(Sn]X) trans Se. This suggests that the X ligands exert a greater trans influence than the Se (or S) donors in compounds of this type involving hard tin(IV) centres. Further evidence for this conclusion comes from a comparison of d(Sn]Se) in trans-[SnX4(SeMe2)2] vs. d(Sn]Se) in [SnX4- {C6H4(SeMe)2-o}]. In the former the Se donor atoms are trans to each other, and d(Sn]Se) is noticeably shorter than in the latter where the greater trans influence of the X ligands leads to a significant elongation in d(Sn]Se).As in the Me2Se complexes discussed earlier, the Sn]Se distances in the bromo derivative are longer than in the chloro species, consistent with the relative acceptor strengths of the SnX4 fragments. The angles involved in the chelate ring in [SnX4{C6H4(SeMe)2-o}] are 76.08(4) for X = Cl and 71.60(6)8 for X = Br, reflecting the restricted bite angle of the Se- (o-C6H4)Se linkage. This results in much more distorted overall stereochemistries for the bidentate ligand complexes compared to the monodentate species.Data collection was also undertaken on a poorly diffracting crystal of [SnCl4{MeSe(CH2)3SeMe}] * in an effort to establish whether the diselenoether is chelating or not. While the overall data quality was poor and the residuals rather high, preventing satisfactory refinement, the analysis was sufficient to confirm unambiguously that this compound does contain a chelating diselenoether ligand in the DL arrangement (Fig. 5). While there is no requirement that this structure is retained in solution, the solution NMR parameters suggest that at low temperature the MeSe(CH2)3SeMe compounds are chelated (see below). While the high estimated standard deviations associated with the atomic positions and geometric parameters in this compound preclude any detailed comparisons with structural data on Table 1 Selected bond lengths (Å) and angles (8) for trans- [SnCl4(Me2Se)2] Sn]Se(1) Sn]Cl(1) Sn]Cl(2) Se(1)]Sn]Cl(2) Se(1)]Sn]Cl(1) Sn]Se(1)]C(2) 2.7001(9) 2.413(2) 2.427(2) 91.25(6) 89.40(6) 100.2(3) Se(1)]C(1) Se(1)]C(2) Cl(1)]Sn]Cl(2) Sn]Se(1)]C(1) C(1)]Se(1)]C(2) 1.957(10) 1.952(9) 89.54(8) 100.7(3) 97.3(4) Table 2 Selected bond lengths (Å) and angles (8) for trans- [SnBr4(Me2Se)2] Sn]Br(1) Sn]Br(2) Sn]Se(1) Br(1)]Sn]Br(2) Br(2)]Sn]Se(1) Sn]Se(1)]C(2) 2.576(2) 2.587(2) 2.731(2) 90.47(5) 88.46(5) 102.2(5) Se(1)]C(1) Se(1)]C(2) Br(1)]Sn]Se(1) Sn]Se(1)]C(1) C(1)]Se(1)]C(2) 1.96(2) 1.94(2) 90.63(5) 100.9(4) 96.9(7) * C5H12Cl4Se2Sn, M = 490.6, tetragonal I41/a, a = 10.062(6), c = 25.702(10) Å, U = 2602(3) Å3, Z = 8, Dc = 2.504 g cm23, T = 150 K, colourless prism, 0.25 × 0.24 × 0.15 mm, m = 83.32 cm21, F(000) = 1824; w–2q scans, 1187 unique reflections measured (2qmax = 508), 836 with I > 3s(I) used in all calculations. The structure was solved by Patterson methods7 and refined using iterative cycles of full-matrix least squares 8 which revealed one half [SnCl4{MeSe(CH2)3SeMe}] molecule (with the Sn atom lying on a two-fold axis) in the asymmetric unit. At isotropic convergence the data were corrected for absorption using DIFABS (maximum transmission factor 1.000, minimum 0.662),9 and the Sn, Se and Cl atoms were then refined anisotropically and H atoms were included in fixed, calculated positions.This model refined to R, R9 = 0.106, 0.159 respectively and S = 6.83 for 43 parameters. The final Fourier-difference map showed several residual electron-density peaks of up to 4.5 e Å23. Some of these occurred within 1 Å of the Sn or Se atoms, and attempts to refine the others as partially occupied O atoms (e.g. from H2O solvate molecules) were not successful.J. Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 2209 related compounds, the trends in the bond lengths are similar to those already discussed.Also, it is not surprising that the sixmembered chelate ring in this species, which results in a Se]Sn]Se angle of 85.9(2)8, leads to a considerably less strained octahedral geometry than in the o-phenylene derivatives discussed above. The SnX4/Me2Se (X = Cl or Br) systems have previously been examined by Ruzicka and co-workers 4 via 1H NMR spec- Fig. 3 View of the structure of [SnCl4{C6H4(SeMe)2-o}] with the numbering scheme adopted. 40% Probability ellipsoids are shown Fig. 4 View of the structure of [SnBr4{C6H4(SeMe)2-o}] with the numbering scheme adopted. 40% Probability ellipsoids are shown. Atoms marked with an asterisk are related by a crystallographic mirror plane Table 3 Selected bond lengths (Å) and angles (8) for [SnCl4{C6H4(SeMe)2-o}] Sn]Se(1) Sn]Cl(1) Sn]Cl(3) Se(1)]C(1) Se(2)]C(7) C(2)]C(3) C(2)]C(7) C(3)]C(4) 2.749(1) 2.426(3) 2.360(3) 1.95(1) 1.93(1) 1.39(2) 1.41(2) 1.38(2) Sn]Se(2) Sn]Cl(2) Sn]Cl(4) Se(1)]C(2) Se(2)]C(8) C(4)]C(5) C(5)]C(6) C(6)]C(7) 2.787(2) 2.389(3) 2.364(3) 1.92(1) 1.93(1) 1.38(2) 1.39(2) 1.40(2) Se(1)]Sn]Se(2) Se(1)]Sn]Cl(2) Se(1)]Sn]Cl(4) Se(2)]Sn]Cl(2) Se(2)]Sn]Cl(4) Cl(1)]Sn]Cl(3) Cl(2)]Sn]Cl(3) Cl(3)]Sn]Cl(4) Sn]Se(1)]C(2) Sn]Se(2)]C(7) C(7)]Se(2)]C(8) Se(1)]C(2)]C(7) C(2)]C(3)]C(4) C(4)]C(5)]C(6) C(5)]C(6)]C(7) Se(2)]C(7)]C(6) 76.08(4) 91.27(9) 90.50(9) 87.40(9) 166.37(9) 91.4(1) 93.0(1) 101.7(1) 100.3(3) 98.6(4) 100.2(6) 121.7(9) 120(1) 120(1) 119(1) 119.4(9) Se(1)]Sn]Cl(1) Se(1)]Sn]Cl(3) Se(2)]Sn]Cl(1) Se(2)]Sn]Cl(3) Cl(1)]Sn]Cl(2) Cl(1)]Sn]Cl(4) Cl(2)]Sn]Cl(4) Sn]Se(1)]C(1) C(1)]Se(1)]C(2) Sn]Se(2)]C(8) Se(1)]C(2)]C(3) C(3)]C(2)]C(7) C(3)]C(4)]C(5) Se(2)]C(7)]C(2) C(2)]C(7)]C(6) 82.41(8) 166.60(9) 83.16(8) 91.41(9) 169.7(1) 92.9(1) 95.4(1) 104.2(4) 99.4(5) 103.3(4) 118.7(9) 119(1) 120(1) 120.9(9) 119(1) troscopy.At 300 K in CD2Cl2, [SnCl4(Me2Se)2] exhibits a single d(Me) resonance with no evidence of 119/117Sn satellites, but on cooling to 250 K the resonance splits and ill defined satellites appear.At 180 K two resonances are present (Table 5) in the ratio ca. 1.5 : 1 due to trans and cis isomers, with 119/117Sn couplings of ca. 50–60 Hz. The behaviour of [SnBr4(Me2Se)2] is similar, although the trans : cis ratio is ca. 3 : 1. The 1H NMR spectra of the [SnX4(diselenoether)] complexes are summarised in Table 5. As in our previous study of dithioether complexes,3 NMR studies of the diselenoether complexes were carried out in anhydrous CD2Cl2 solution.The complexes of MeSe(CH2)nSe- Me are poorly soluble in CD2Cl2, especially at low temperatures, resulting in relatively poor quality spectra. Solubilities are higher in tetrahydrofuran or acetone, but the spectra obtained were significantly different and it is probable that these oxygen donors provide alternative ligands for the tin, hence these studies were not pursued. At 180 K the complexes of MeSe(CH2)nSeMe each show two d(Me) resonances (Table 5) due to DL and meso invertomers, which coalesce on warming due to the onset of pyramidal inversion and reversible ligand dissociation.Owing to the very poor solubility, convincing tin satellites were not observable. Resonances due to both invertomers were present in the 1H NMR spectrum of [SnCl4{MeSe(CH2)2SeMe}] below ca. 250 K, and below ca. 225 K in the corresponding spectrum of the bromide. The resonances of the invertomers were observed at lower temperatures for complexes of MeSe(CH2)3SeMe, and for [SnCl4{PhSe(CH2)3SePh}] the expected second-order CH2 resonances were very broad even at 180 K.The complex Fig. 5 View of the structure of [SnCl4{MeSe(CH2)3SeMe}] with the numbering scheme adopted. 40% Probability ellipsoids are shown. Atoms marked with an asterisk are related by a crystallographic twofold operation. Sn]Cl(1) 2.385(9), Sn]Cl(2) 2.427(9), Sn]Se(1) 2.766(4) Å; Se(1)]Sn]Se(1*) 85.9(2)8 Table 4 Selected bond lengths (Å) and angles (8) for [SnBr4{C6H4(SeMe)2-o}] Sn]Br(1) Sn]Br(3) Se(2)]C(1) C(1)]C(1*) C(2)]C(3) 2.600(2) 2.512(1) 1.93(1) 1.36(2) 1.42(2) Sn]Br(2) Sn]Se(2) Se(2)]C(4) C(1)]C(2) C(3)]C(3*) 2.547(2) 2.841(2) 1.95(1) 1.40(2) 1.36(2) Br(1)]Sn]Br(2) Br(2)]Sn]Se(2) Br(3)]Sn]Se(2) Br(3)]Sn]Se(2*) Se(2)]Sn]Se(2*) Sn]Se(2)]C(4) Se(2)]C(1)]C(1*) C(1*)]C(1)]C(2) C(2)]C(3)]C(3*) 169.12(7) 83.38(5) 93.15(4) 164.74(5) 71.60(6) 100.9(4) 120.6(3) 120.0(7) 119.5(7) Br(1)]Sn]Br(3) Br(1)]Sn]Se(2) Br(2)]Sn]Br(3) Br(3)]Sn]Br(3*) Sn]Se(2)]C(1) C(1)]Se(2)]C(4) Se(2)]C(1)]C(2) C(1)]C(2)]C(3) 92.44(5) 87.81(5) 94.40(5) 102.08(7) 96.5(3) 99.8(5) 119.4(8) 120(1)2210 J.Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 Table 5 Proton NMR data a d Complex 300 180 Kb [SnCl4(Me2Se)2] [SnBr4(Me2Se)2] [SnCl4{MeSe(CH2)2SeMe}] [SnBr4{MeSe(CH2)2SeMe}] [SnCl4{MeSe(CH2)3SeMe}] [SnBr4{MeSe(CH2)3SeMe}] [SnCl4{C6H4(SeMe)2-o}] [SnBr4{C6H4(SeMe)2-o}] [SnCl4{PhSe(CH2)2SePh}] [SnCl4{PhSe(CH2)3SePh}] 2.51 2.36 2.48 (3 H), 3.30 (2 H) 2.25 (3 H), 3.15 (2 H) 2.30 (1 H), 2.46 (3 H), 3.2 (2 H) 2.41 (1 H 1 3 H), 3.1 (2 H) 2.83 (3 H), 7.5, 7.65 (2 H) 2.45 (3 H), 7.25, 7.38 (2 H) 3.39 (2 H), 7.2–7.7 (5 H) 2.10 (1 H), 3.25 (2 H), 7.2–7.7 (5 H) 2.44, 2.54 (1 : 1.5) 2.26, 2.40 (1 : 3) 2.40, 2.46, 3.10, 3.40 (1 : 1) 2.21, 2.30, 3.10, 3.30 (2 : 1) 2.40, 2.45, 2.51, 3.11, 3.42 (1 : 5) 2.38, 2.44, 3.05, 3.25 (1 : 3) 2.99, 2.79, 7.55 (5 : 1) 2.76 [2.55 (sh)], 7.47 3.5, 3.8, 7.0–7.8 (1 : 1) Ill defined (see text) a In CD2Cl2 relative to internal SiMe4.b For Me2Se complexes the ratio refers to the relative abundances of the geometric isomers, whereas for the bidentate ligand, it shows the abundances of the invertomers (meso and DL) obtained from integrating Me or CH2 resonances. [SnCl4{C6H4(SeMe)2-o}] was more soluble in CD2Cl2 and at 180 K two sharp methyl resonances with clearly resolved 117/119Sn satellites (3J ca. 40 Hz) were observed, attributable to the expected invertomers, although the relative intensities were quite disparate (>5 : 1). On warming to ca. 210 K the lines coalesced, and above this temperature only a singlet d(Me) resonance was present with no satellites. The corresponding spectrum of [SnBr4{C6H4(SeMe)2-o}] at 180 K contained a broad line at d 2.76 with a weak shoulder at 2.55, suggesting that even at this temperature the low-temperature-limiting spectrum was not achieved.Although the poor spectral quality resulting from the low solubilities, and complications introduced by ligand dissociation, preclude a more detailed treatment of the inversion processes, it is clear that qualitatively inversion barriers decrease in the order Se > S for analogous ligands. The 77Se-{1H} and 119Sn-{1H} NMR spectra of [SnCl4(Me2- Se)2] in CH2Cl2 contained single resonances at 300 K due to fast exchange between the isomers, but on cooling to ca. 250 K separate resonances for the cis and trans isomers are resolved which sharpen on further cooling, and at 180 K clear 1J couplings appear (Table 6). [The g(119Sn) : g(117Sn) ratio is 0.956 : 1 and separate couplings to the two tin isotopes were not resolved.] In contrast, CH2Cl2 solutions of [SnBr4(Me2Se)2] show neither 77Se-{1H} nor 119Sn-{1H} resonances at room temperature, but single resonances appear at ca. 280 K and on further cooling resonances due to the cis and trans isomers are resolved. A solution of [SnCl4(Me2Se)2] containing an excess of Me2Se in CH2Cl2 at 180 K shows sharp 77Se-{1H} resonances for cis and trans isomers and free Me2Se (Fig. 6), showing exchange is slow on the NMR time-scale. On warming to ca. 230 K the resonance of the cis isomer broadens and then disappears, but that of the trans form broadens only near ambient temperatures. Corresponding changes occur in the 119Sn-{1H} spectra as a function of temperature.The NMR spectra of the system [SnBr4(Me2Se)2]–excess Me2Se in CH2Cl2 had generally similar behaviour, but with the onset of exchange at lower temperatures. The behaviour of these complexes is qualitatively similar to that observed in the [SnX4(Me2S)2]–Me2S systems by Knight and Merbach.11 None of the [SnX4(diselenoether)] complexes exhibited a 119Sn-{1H} NMR resonance at 300 K (probably due to reversible ring opening), and only [SnCl4{MeSe(CH2)2SeMe}] exhibited a 77Se-{1H} resonance and even this was very weak and broad.On cooling resonances from both nuclei were observed, initially as single broad peaks which sharpened on cooling and in most cases resolved into two signals by 180 K (Table 6), consistent with the presence of the meso and DL invertomers. Poor solubility of the diselenaalkane complexes (see above) at low temperatures resulted in spectra with relatively poor signal-to-noise ratios even after long accumulations, and prevented identification of satellites and the spectral data in Table 6 should be viewed with these qualifications in mind.Nonetheless the behaviour with X and ligand structure observed in the spectra from the different nuclei (1H, 77Se and 119Sn) are internally consistent. A solution of [SnCl4{C6H4(SeMe)2-o}] containing free C6H4(SeMe)2-o showed separate 77Se-{1H} NMR resonances for the free selenoether and meso and DL forms of the co- Fig. 6 (a) 77Se-{1H} and (b) 119Sn-{1H} NMR spectrum of [SnCl4- (Me2Se)2] containing an excess of Me2Se in CH2Cl2 at 180 KJ.Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 2211 Table 6 77Se-{1H} and 119Sn-{1H} NMR data at 180 K a Complex d(77Se-{1H})b d(119Sn-{1H})c [SnCl4(Me2Se)2] d [SnBr4(Me2Se)2] [SnCl4{MeSe(CH2)2SeMe}] e [SnBr4{MeSe(CH2)2SeMe}] [SnCl4{MeSe(CH2)3SeMe}] [SnBr4{MeSe(CH2)3SeMe}] [SnCl4{C6H4(SeMe)2-o}] [SnBr4{C6H4(SeMe)2-o}] [SnCl4{PhSe(CH2)2SePh}] 185 (460), 204 (490) [1:1] 204 (555), 219 (500) [2:1] 482, 487 [1:1] 493, 496 [2:1] 231, 232 [5:1] 261, 263 [1:2] 323, 338 [1:5] 355 436 2691 (468), 2695 (490) 21296 (500), 21319 (550) 2680, 2682 21283, 21288 2685, 2686.5 21305, 21308 2632, 2635? 21258 (br) — Free selenoether: d(77Se) Me2Se, O; MeSe(CH2)2SeMe, 121; MeSe(CH2)3SeMe, 74; PhSe(CH2)2SePh, 340; C6H4(SeMe)2-o, 202.10 a In anhydrous CH2Cl2–CD2Cl2 containing [Cr(acac)3] (acac = acetylacetonate).b Relative to external neat Me2Se, 1J(77Se]117/119Sn)/Hz in parentheses, approximate ratios in square brackets. c Relative to external neat SnMe4, 1J(77Se–119Sn).d d(77Se-{1H}) 176, d(119Sn-{1H}) 2695 at 300 K. e d(77Se-{1H}) 486 at 300 K. ordinated selenoether at 180 K. The signals were clearly broadened by 220 K and had disappeared by 235 K showing fast ligand exchange at this temperature. The [SnCl4{PhSe(CH2)n- SePh}] (n = 2 or 3) complexes failed to show 119Sn resonances even at 180 K, presumably due to exchange, and only the n = 2 complex exhibited a 77Se resonance at 180 K.A solution of SnI4 in CH2Cl2 containing a large excess of Me2Se exhibited a 77Se-{1H} NMR resonance at d 1 152 at 180 K. This disappeared on warming and was not present unless a large excess of Me2Se was used. It seems likely that this may indicate the formation of a weak adduct {possibly trans- [SnI4(Me2Se)2]} in solution at low temperatures. In contrast, a CH2Cl2 solution of SnI4 containing an excess of MeSe(CH2)2- SeMe showed no evidence for adduct formation over the temperature range 180–300 K.No evidence for complex formation was observed in Ph2Se–SnX4 systems. The SnBr4– PhSe(CH2)2SePh–CH2Cl2 mixtures showed both 119Sn and 77Se resonances at low temperatures indicative of complex formation, but the solid complex could not be isolated. Several consistent trends can be discerned in these data. The 119Sn-{1H} NMR resonances for the complexes show similar patterns of behaviour in cis/trans-[SnX4(Me2E)2] (E = S or Se) and in [SnX4(L]L)] for dithioether and diselenoether analogues with d shifted by 110–150 ppm to low frequency on changing S for Se.In the 77Se-{1H} NMR spectra of [SnX4- (Me2Se)2] large high-frequency co-ordination shifts D ( = dcomplex 2 dligand) are observed of approximately 1200 with the resonance of the cis isomer slightly to high frequency of the trans. For transition-metal complexes containing chelating diselenoether ligands the magnitude of the co-ordination shifts vary greatly with the chelate-ring size.12 Following the approach of Garrou13 first used for diphosphine complexes, one calculates first the co-ordination shift as above, and then the chelate-ring parameter (DR) defined as D(chelate complex) 2 D(equivalent monodentate complex).For our purposes for the complexes of MeSe(CH2)nSeMe, the ‘equivalent monodentate complexes’ are cis-[SnX4(Me2Se)2]. For free MeSe(CH2)2SeMe d 121,10 leading to D 365 for the tin chloride complex and 374 for the bromide and corresponding DR 161 (Cl) and 155 (Br), that is large positive DR values for the five-membered-ring species.In contrast, for MeSe(CH2)3SeMe d 74, D 158 (Cl) and 188 (Br) and DR 246 (Cl) and 231 (Br), i.e. negative DR values for the sixmembered- ring complexes. This is clear evidence for the presence of a chelate-ring-parameter effect in the selenium chemical shift values, and is the first time this has been observed in complexes of a main-group metal. The trends are similar to those established with d-block metal complexes.12 The origin of the chelate-ring effect is unclear even in the much studied diphosphine systems,14 but the observation of such an effect in the tin complexes here, where the metal is behaving as a simple s acceptor, supports the suggestion that it involves the strain in different size rings.10 Since we do not have data for complexes of PhMeSe which would be the ‘equivalent monodentate ligand’ for PhSe(CH2)2- SePh or C6H4(SeMe)2-o, similar calculations of DR cannot be carried out for complexes of these bidentate compounds, although for the latter the substantial co-ordination shifts in themselves strongly suggest that the chelate structures identified by X-ray crystallography for solid [SnX4{C6H4(SeMe)2-o}] are also retained in solution. Experimental Physical measurements were made as described previously.3 The 77Se-{1H} NMR spectra were obtained from anhydrous CH2Cl2–10% CD2Cl2 solutions as described.10 The selenium ligands were made by literature methods.10,15 Syntheses The complexes [SnX4L2] were all made by the same general method. The tin(IV) halides are moisture sensitive, therefore all of the reactions were carried out under an atmosphere of dry nitrogen, using standard Schlenk, vacuum-line and dry-box techniques.[SnCl4(Me2Se)2]. Tin(IV) chloride (0.26 g, 1 mmol) was added to a solution of Me2Se (0.22 g, 2 mmol) in chloroform (10 cm3). The complex formed immediately as a white precipitate which was filtered off and dried in vacuo.Yield 0.44 g, 92% (Found: C, 9.75; H, 2.7. Calc. for C4H12Cl4Se2Sn: C, 10.05; H, 2.5%); n& max/ cm21 (Sn]Cl) 312. [SnBr4(Me2Se)2]. A saturated solution of tin(IV) bromide (0.44 g, 1 mmol) in chloroform (5 cm3) was added dropwise to a solution of Me2Se (0.22 g, 2 mmol) in chloroform (5 cm3). On reducing the volume in vacuo the complex slowly formed as yellow crystals which were filtered off and dried in vacuo.Yield 0.54 g, 82% (Found: C, 7.4; H, 1.9. Calc. for C4H12Br4Se2Sn: C, 7.3; H, 1.85%); n& max/cm21 (Sn]Br) 220. The same general method was used for the synthesis of all of the complexes involving bidentate ligands, and this is detailed for one example of each of X = Cl and X = Br. [SnCl4{MeSe(CH2)2SeMe}]. Tin(IV) chloride (0.26 g, 1 mmol) was added to a solution of the selenoether (0.22 g, 1 mmol) in chloroform (10 cm3). The complex precipitated as a white powder which was filtered off and dried in vacuo.Yield 0.45 g, 72% (Found: C, 10.3; H, 2.5. Calc. for C4H10Cl4Se2Sn: C, 10.1; H, 2.1%); n& max/cm21 (Sn]Cl) 339, 331, 320 and 312. [SnCl4{MeSe(CH2)3SeMe}]. White precipitate. Yield 0.72 g, 93% (Found: C, 12.5; H, 2.6. Calc. for C5H12Cl4Se2Sn: C, 12.25; H, 2.45%); n& max/cm21 (Sn]Cl) 336, 331, 325 and 313. [SnCl4{PhSe(CH2)2SePh}]. Yellow crystalline precipitate. Yield 0.59 g, 81% (Found: C, 27.2; H, 2.5. Calc. for2212 J.Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 Table 7 Crystallographic data Formula M Colour, morphology Crystal dimensions/mm Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 ZF (000) Dc/g cm23 m(Mo-Ka)/cm21 Transmission factors (maximum, minimum) No. of unique observed reflections Rint (based on F2) Unique observed reflections with Io > 2.5s(Io) No. parameters Goodness of fit R(Fo) R9(Fo) Maximum residual peak, trough/e Å23 trans-[SnCl4(Me2Se)2] C4H12Cl4Se2Sn 478.56 Colourless block 0.25 × 0.10 × 0.10 Monoclinic P21/n 6.539(2) 12.610(3) 8.111(2) 107.67(2) 637.2(2) 2 444 2.494 85.04 1.000, 0.694 1189 0.031 925 52 2.29 0.036 0.043 1.19 21.66 trans-[SnBr4(Me2Se)2] C4H12Br4Se2Sn 656.36 Yellow, rhomb 0.45 × 0.40 × 0.20 Monoclinic P21/n 6.768(3) 13.000(3) 8.373(3) 108.47(3) 698.7(4) 2 588 3.119 184.63 1.000, 0.645 1289 0.132 1039 52 4.35 0.050 0.057 1.66 22.15 [SnCl4{C6H4(SeMe)2-o}] C8H10Cl4Se2Sn 524.59 Colourless, block 0.30 × 0.15 × 0.12 Triclinic P1� 8.419(2) 11.323(3) 8.251(1) 90.32(2) 98.17(2) 109.68(2) 731.8(3) 2 488 2.380 73.85 1.000, 0.717 2563 0.028 1763 136 1.97 0.045 0.052 1.33 22.10 [SnBr4{C6H4(SeMe)2-o}] C8H10Br4Se2Sn 702.39 Yellow, block 0.30 × 0.20 × 0.20 Monoclinic P21/m 6.826(3) 11.324(2) 9.936(2) 100.67(2) 754.7(3) 2 632 3.119 184.63 1.000, 0.645 1402 0.043 1143 50 3.49 0.049 0.062 2.49 22.91 R = S(|Fo|i 2 |Fc|i)/S|Fo|i, R9 = [Swi(|Fo|i 2 |Fc|i)2/Swi|Fo|i 2]� �� and w21 = s2(F ).Goodness of fit = [S(|Fo|i 2 |Fc|i 2 |Fc|)/si]/(n 2 m) ª 1 where n = no.of data, m = no. of parameters. C14H14Cl4Se2Sn: C, 28.0; H, 2.35%); n& max/cm21 (Sn]Cl) 330, 324, 319 and 313. [SnCl4{PhSe(CH2)3SePh}]. Orange crystalline precipitate. Yield 0.53 g, 86% (Found: C, 29.5; H, 2.7. Calc. for C15H16Cl4Se2Sn: C, 29.8; H, 2.65%); n& max/cm21 (Sn]Cl) 330, 324, 315 and 304. [SnCl4{C6H4(SeMe)2-o}]. White crystalline precipitate. Yield 0.49 g, 94% (Found: C, 18.35; H, 2.0.Calc. for C8H10Cl4Se2Sn: C, 18.3; H, 1.9%); n& max/cm21 (Sn]Cl) 338, 328, 323 and 317. [SnBr4{MeSe(CH2)2SeMe}]. A saturated solution of tin(IV) bromide (0.44 g, 1 mmol) in chloroform (5 cm3) was added dropwise to a solution of the selenoether (0.22 g, 1 mmol) in chloroform (5 cm3). A pale yellow precipitate formed immediately which was filtered off and dried in vacuo. Yield 0.50 g, 69% (Found: C, 7.5; H, 1.8. Calc. for C4H10Br4Se2Sn: C, 7.35; H, 1.55%); n& max/cm21 (Sn]Br) 220, 218, 216 and 214.[SnBr4{MeSe(CH2)3SeMe}]. Yellow precipitate. Yield 0.48 g, 81% (Found: C, 9.3; H, 1.9. Calc. for C5H12Br4Se2Sn: C, 9.0; H, 1.8%); n& max/cm21 (Sn]Br) 219, 214, 206 and 201. [SnBr4{C6H4(SeMe)2-o}]. Orange crystals. Yield 0.67 g, 86% (Found: C, 13.9; H, 1.7). Calc. for C8H10Br4Se2Sn: C, 13.65; H, 1.4%); n& max/cm21 (Sn]Br) 230, 228, 224 and 222. X-Ray crystallography Single crystals of [SnCl4(Me2Se)2], [SnBr4(Me2Se)2], [SnCl4{C6H4(SeMe)2-o}] and [SnBr4{C6H4(SeMe)2-o}] were obtained from a solution of the appropriate complex in CHCl3.The compounds were extremely sensitive to hydrolysis on exposure to moist air. Therefore, in each case the selected crystal was coated with mineral oil, mounted on a glass fibre using silicone grease as adhesive, and immediately placed in a stream of cold nitrogen gas and cooled to 150 K. Data collection used a Rigaku AFC7S four-circle diffractometer equipped with an Oxford Cryostreams low-temperature attachment, and graphitemonochromated Mo-Ka X-radiation (lmax = 0.710 73 Å); T = 150 K, w–2q scans.The intensities of three standard reflections were monitored every 150. No significant crystal decay or movement was observed. As there were no identifiable faces the raw data for the compounds [SnCl4(Me2Se)2] and [SnCl4{C6H4(SeMe)2-o}] were corrected for absorption using y-scans. The weighting scheme w21 = s2(F) gave satisfactory agreement analyses in each case. Crystallographic data are present in Table 7.All four structures were solved by direct methods,16 and then developed by iterative cycles of full-matrix least-squares refinement (based on F) and Fourier-difference syntheses which located all non-H atoms in the asymmetric unit.8 For [SnBr4(Me2Se)2] and [SnBr4{C6H4(SeMe)2-o}] an empirical absorption correction using DIFABS9 was applied to the raw data at isotropic convergence. All non-H atoms in the structures were refined anisotropically (with the exception of [SnBr4- {C6H4(SeMe)2-o}] for which the C atoms were refined isotropically), and H atoms were placed in fixed, calculated positions with d(C]H) = 0.96 Å.Atomic co-ordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/498. Acknowledgements We thank the University of Southampton and the EPSRC for support, and the latter for a grant to purchase the diffractometer. References 1 I. R. Beattie, Q. Rev. Chem. Soc., 1963, 17, 382. 2 N. C. Norman and N. L. Pickett, Coord. Chem. Rev., 1995, 145, 27.J. Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 2213 3 S. E. Dann, A. R. J. Genge, W. Levason and G. Reid, J. Chem. Soc., Dalton Trans., 1996, 4471. 4 S. J. Ruzicka and A. E. Merbach, Inorg. Chim. Acta., 1976, 20, 221; 1977, 22, 191; S. J. Ruzicka, C. M. P. Favez and A. E. Merbrg. Chim. Acta, 1977, 23, 239. 5 E. W. Abel, S. K. Bhargava, K. G. Orrell and V. Sik, Inorg. Chim. Acta, 1981, 49, 25. 6 N. Bricklebank, S. M. Godfrey, C. A. McAuliffe and R. G. Pritchard, J. Chem. Soc., Chem. Commun., 1994, 695. 7 PATTY, The DIRDIF Program System, P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, S. Garcia-Granda, R. O. Gould, J. M. M. Smits and C. Smykalla, Technical Report of the Crystallography Laboratory, University of Nijmegen, 1992. 8 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corporation, Houston, TX, 1992. 9 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158. 10 D. J. Gulliver, E. G. Hope, W. Levason, S. G. Murray, D. M. Potter and G. L. Marshall, J. Chem. Soc., Perkin Trans 2, 1984, 429. 11 C. T. G. Knight and A. E. Merbach, Inorg. Chem., 1985, 24, 576. 12 E. G. Hope and W. Levason, Coord. Chem. Rev., 1993, 122, 109. 13 P. E. Garrou, Chem. Rev., 1981, 81, 229. 14 J. G. Verkade and L. D. Quin (Editors), Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis, VCH, Deerfield Beach, FL, 1987. 15 E. G. Hope, T. Kemmitt and W. Levason, J. Chem. Soc., Perkin Trans. 2, 1987, 487. 16 G. M. Sheldrick, SHELXS 86, program for crystal structure solution, Acta Crystallogr., Sect. A, 1990, 46, 467. Received 19th February 1997; Paper 7/01181D © Copyright 1997 by the Royal Society of Chemistry