摘要:
1973 357Nuclear Quadrupole Resonance Investigation of the ComparativeDifferences Between Hexachloro-stannate, -tellurate, and -plumbateresulting from Cationic EffectsBy T. B. Brill * and W. A. Welsh, Department of Chemistry, University of Delaware, Newark, Delaware 1971 1U.S.A.N.q.r. frequencies of 14 salts of SnCls2-, TeC162-, and PbC162- have been recorded in a n effort to observe possibledifferences in anion distortion which could result from the ' inert ' pair electrons of TeIV. There is no evidence ofstereochemical activity of the TeIV ' inert ' pair as might be indicated by an increase in the number of chlorineresonance frequencies and/or anomalous changes in bond ionicity in any of the compounds studied. PbCIG2-appears to be more sensitive to the cation than SnCls2- but the TeCIe2- ion is less sensitive.It is concluded thatanion sensitivity to the cation is not readily predictable on the basis of the size alone.THE tellurium atom in TeCIG2- has seven electron pairsin its valency shell. Vibrationa1,l X-ray,2-4 and n . ~ l . r . ~ . ~data gathered for this ion indicate that it assumes 01,symmetry both in the solid state and in solution.Consequently, it is cited as an exception to the valencyshell electron-pair repulsion (VSEPR) theory advancedby Gillespie and Nyholm.' The VSEPR theory pre-dicts a distorted six-co-ordinate structure for TeClG2-.The seventh electron pair instead becomes ' stereo-chemically inert' (in terms of angular effects) byoccupying the a,, * MO located primarily on the tel-lurium atom.8*9With the exception of vibrational data1 and a pre-liminary report of the crystal structure of pyridiniumhexachlorotellurate(n7) (R = 0.18) and vibrationaldata for (Ph21)zTeC16,1 all structural and spectroscopicinformation known to us deals with compounds in whichthe cation has cubic or spherical symmetry.As aresult the TeClG2- ion lies at a cubic crystal latticesite. I t is not clear how much this high site symmetryinfluences the apparent desire of the TeC162- ion toremain rigorously octahedral.1°In the present investigation TeC1,2- salts were pre-pared in which the counter-ion is of sufficiently lowsymmetry that the anion site will be very distorted,and the 35Cl n.q.r. spectrum of the anion was recorded.N.q.r.spectroscopy is a useful technique in studies ofthis kind because inequivalency in the chlorine atomsis readily revealed by the number of signals observed.In addition, the PbC162- salts were examined because,of the main-group element hexahalogenometallates,the PbC162- ion most closely resembles the TeC162-ion in size. These comparisons enable the importanceof the size difference of the anions to be evaluated as itrelates to the cationic effect. Hereinafter it will be1 D. M. Adams and D. 11. Morris, J- Chein. SOC. ( A ) , 1967,2067; P. J . Hendra and Z. Jovic, ibid., 1968,600; J. A. Creightonand J. H. S. Green, ibid., p. 808.A. C. Hazell, Acta Chem. ScnPzd., 1966, 20, 165; G. Engel,Z. Krist., 1935, 90, 341.E. E. Aynsley and A.C. Hazell, Chern. and Ind., 1963, 611.4 V. A. Angoso, H. Onlren, and H. Hahn, 2. anorg. Chcm.,6 D. Nakamura, K. Ito, and M. Kubo, J . Avner. Chem. SOC.T. L. Brown and L. G. Kent, J . Phys. Chem., 1970, 74,7 R. J. Gillespie and R. S. Nyholm, Quart. Rev., 1957, 11,1964, 328, 225.1962, 84, 163.3572.339.assumed that the cationic effect is any effect that thecation has upon the anion, whether it be an electro-static contribution to the electric-field gradient or astatic polarization of the anion.EXPERIMENTALSIIC~,~- and TeClG2- Salts.-The tin and tellurium com-pounds were prepared in the following general manner.11SnC1,,5H,O (5 g) was dissolved in ~ M - H C ~ (15 ml), or TeO,(5 g) was dissolved in 12h.r-HCl (15 ml). A slight excessof the cation chloride salt was dissolved in the minimumof water, and the two solutions were mixed.Crystallizationoccurred immediately or after slow evaporation. Thecompounds were carefully recrystallized from dilute HC1and dried (P,O,) in a vacuum desiccator. The preparationof K2TeC1, presents a problem because of simultaneousprecipitation of KCl. The following procedure was adopted.TeCl, (10.0 g, 0.037 mol) was dissolved in IM-HC~ (10 ml).KC1 (2-0 g, 0.027 mol) was dissolved in H,O (6 ml). Thesolutions were mixed and allowed t o evaporate very slowlyfor ten days. Pure crystals of K2TeC1, were collectedby use of a glove-bag filled with N,, and dried (P20,).PbCIGa- SuZts.-Lead acetate ( 5 g) was dissolved inconcentrated hydrochloric acid (25 ml) and this was filteredinto a slight excess of the cation chloride solution dissolvedin concentrated hydrochloric acid, and cooled.The yellowprecipitate was filtered off. It was redissolved in boilingconcentrated hydrochloric acid while chlorine was passedinto the solution. Chlorine was passed during cooling,and the crystals were immediately filtered off and dried(NaOH) in a vacuum desiccator.A naZyses.-All compounds were analysed for Te and Sn.Tellurium was determined gravimetrically by convertingthe salts into TeO, according to Vogel's method.12 Tinwas determined gravimetrically as the N-benzoylphenyl-hydroxylamine complex. l3N.q.r. Spectva.-The spectra were recorded as dcscribed9 T. B. Brill, 2. 2. Hugus, jun., and A. F. Schreiner, J .Phys.Chcna., 1970, 74, 2999.10 Another possible means of distorting the anion could beeffected by placing strong electrostatic forces nearby. Com-pounds of TeC1,2- having highly charged cations which coulddistort the TeC1,2- ion have been prepared (A. Catalina, ActaSalamanticensia Sev. Cienc., 1961, 3, 77). In every case, how-ever, the cation remains hydrated in the lattice which effectivelynullifies its polarizing power.11 W. C. Fernelius, Inovg. Syn., 1946, 2, 188.12 A. I. Vogel, ' Quantitative Inorganic Analysis,' John Wileyand Sons, Inc., New York, 1961, p. 509.13 A. I. Vogel, ref. 12, p. 506.D. S. Urch, J . Chem. SOC., 1964, 5775358 J.C.S. Daltonpreviously.14 The error in frequencies can be ca. 0.020MHz if the wrong line of the resonance multiplet has beenchosen as the centre peak.Otherwise it is cu. 0-005 MHz.37Cl signals were observed in several cases to confirmthat 35Cl spectra were being recorded. Many salts did notyield signals unless they were carefully recrystallized.X-Ray Powder Patterns.-Powder patterns were obtainedby use of a Debye-Scherrer camera and Cu-K, radiation.RESULTSN.q.r. Spectra.-Data for the NH,+ 6 and Cs+ salts ofTeC1,2- have been reported previously and are in reasonableagreement with our frequencies. For the K+ salt, thepossibility of a weak resonance near 15-0 MHz has bzenrnenti~ned.~ (Me,N) ,TeCl, was previously investigatedbut no signal was found.5 Many of the SnCl,,- frequencieshave been reported and are in accordance with O U ~ S .~ * ~ ~N.q.r. data for (NH4),PbC1, and Cs,PbCl, also have beenreported.,, l5 Several compounds exhibit some signalasymmetry and this may be due to crystallographicinequivalence of the chlorine atoms. For example, in thepyridinium salts of SnC1,2- and TeCl,,- a single frequencyis reported even though the line is asymmetric. Tworesonances were found in the PbCl,2- salt. From the knowncrystal structure of (pyH) ,TeCl, two crystallographicallyinequivalent C1 atoms would be expected. If severalunresolved signals are present, it is of little consequenceto the interpretation of our results particularly when it isobserved for all three anions.W l N.q.r. frequencies/MHz a t 298 K aCation1 I<+2 Kb+3 Csf4 NH4+5 MeNH,+6 Me,NH+7 Me,N+8 Et,NH,+9 Et,NH+10 (PYH)+11 (2,6-lutH)+12 (4-picH)+13 (4-ClpyH)+14 Mg(H20)62+(pyH)+, pyridinium ;iumTeCl,,-15-13( 18)14.99( 16)1 5.1 4( 7)15.60( 12) d14.98 (25) 815*52( 12)16.29(6)15.91(7)15-48 (6)16.49(7)16.54(4)16-68(10)16- 66(8)16*37(7)15-56(5)35*93(15)15*55(10)SnC1,2-15-06(26) b*15.60(2)16*06(2)15.46(4)15-81 (20) C16.63(10)1&67(5)14*94( 7)1 7- 37( 10)1 7-02 (4)1 7-8 1 (5)17.52( 5)17-32(4)14.9 7 (4)35-92(20)15*83(6)PbCIa2-17.71 d17-06(4) bid1 7-50 (6)18-54(15)15.39(7)19-44( 8)19.30(4)18-76(5)19-87(4)19- 63 (8)1 8.5 8 (8)19.71(8) f15-53(4)36.93(20)(lutH)+ = lutidiiiium; (picH)+ = picolin-a Parenthetical numbers are signal-to-noise ratios.Ref.15. Ref. 9. d Ref. 6. 8 Ref. 5. f Very asymmetric.I Chlorine atom in the pyridinium ring. v(Wl) in 4-chloro-pyridiniurn hydrochloride is 35*32(30) MHz a t 298 K.Structuval Information.-In order validly to compareSnCl,a-, PbCl,,-, and TeC1,a- salts having the same cation,they must be isostructural. The Rb+, Cs+, and NH,+salts of all three anions are known to have the cubic anti-fluorite structure with space-group Fm3m.2 K,SnCl, and(Me,N),SnCl, l6 also have the antifluorite structure. Thel4 T. B. Brill and G. G. Long, J. Phys. Chem., 1971, 75, 1989.lS D. Nakamura, Bull. Chem. SOC. Japan, 1963, 36, 1162.l6 R. W. G. Wyckoff and R. B. Corey, Anaer. J . Sci., 1929, 18,43 7.X-ray powder patterns of (Me4N) ,TeCl, and (Me,N) ,PbCl,are similar to that of the tin salt indicating that all threeare isostructural.(pyH);reCl, is monoclinic3 and its powder pattern issimilar to those of (pyH),SnCl, and (pyH),PbCl,.The(2,4-lutH)+ and [+ClpyH)+ salts of three anions are iso-structural, based on their powder patterns. However,there is no intensity and spacing resemblance among the(4-picH)+ salts of SnCb2-, TeC1,,-, and PbCl,,- and theyprobably have different structures. The MeNH3+ salt ofSnC1,2- is isostructural with PbC1,2- but not TeClG2-.(Et3NH),TeCl, could not be dried sufficiently to obtain apowder pattern, but the SIICI,~- and PbCl,,- salts are ap-parently isostructural. These data are summarized in theFigure.Pb5 TeI ' I 1 I 1 I 1 1'1, I IS.0 10 2026 in degreesPositions and intensities of major peaks in the X-ray powderFor numbers, patterns of SnCl,*-, PbCI,*-, and TeC1,Z- salts.see TableDISCUSSIONGillespie pointed out l 7 that there is little room on thesurface of the TeC162- ion for an extra pair of electronsbased on the C1-C1 contact distances which are nearlytwice the van der Waals radius of C1.The van derWaals radii argument assumes that the C1 atoms arespherical,l* which is doubtful in an MCla2- salt, so thatsome p character could mix with the 5s2 electrons ifthe TeC162- ioii undergoes a static distortion due to thelattice symmetry. A decrease in ionic character (in-crease in n.q.r. frequency) as well as inequivalence in thechlorine atoms would be expected if the ' inert ' pairbecomes stereochemically active.17 According to theTable, none of the TeClG2- compounds behavesl7 R.J. Gillespie, J . Chem. Educ., 1970, 47, 18.la H. A. Bent, Fortschr. Chern. Fovsch., 1970, 14, 11973 359anomalously compared with SnC1,2- and it is reasonableto assume that the electrons occupying the av * MO ofthe TeIV remain ' stereochemically inert ' regardlessof the site symmetry.The results in the Table show that the TeC162- ion isless sensitive to cationic effects than is SnC162-. Thisseems to be abnormal because the TeCb2- ion is largerthan the SnClG2- ion (Sn-C1 = ca. 2-41 A, Te-C1 = ca.2.50 For this reason the PbCb2- ion, which isabout the same size as TeC1,2- (Pb-Cl= ca. 2.50 A),2 wasexamined. As expected PbC162- is much more sensitiveto the cation than SnClG2- and suggests that the sensi-tivity of an MC162- ion to the cation is not predictablesimply on the basis of its size.The (4-ClpyH)+ salts are interesting from the stand-point of 1i.q.r. spectroscopy. Particularly in the caseof tin and lead, there is an unusually large splittingin the signals arising from the anion. Splittings ofthis magnitude do not normally arise from crystallo-graphic inequivalence in the chlorine atoms and acomplete crystal-structure analysis of the SnC1,2-salt has been madel9 in order to reveal the source ofthe effect.We acknowledge financial support from the Universityof Delaware Research Foundation.[2/1282 Receieed, 5th JuwZe, 19721l9 R. Gearhart, W. A. Welsh, T. B. Brill, and R. H. Wood,following paper
ISSN:1477-9226
DOI:10.1039/DT9730000357
出版商:RSC
年代:1973
数据来源: RSC