摘要:
J . CHEM. SOC. DALTON TRANS. 1994 2919Structures, Energies and Vibrational Spectra of FourIsomers of HydrogendioxothiosuIfate(1v) Anion (HS,O,-)and of the Related Anion CISO,-: an ab-initioMolecular-orbital StudyKarol Miaskiewicza and Ralf Steudel * r ba Biology and Chemistry Department, Pacific Northwest Laboratory, Richland, WA 99352, USABerlin, Germanylnstitut fur Anorganische und Analytische Chemie, Technische Universitat Berlin, Sekr. C 2, D - I0623The ground-state geometries, energies, atomic charges and vibrational wavenumbers of four isomericforms of the HS,O,- anion as well as of the related CIS0,- anion have been calculated at theHF/6-311 G** and HF/6-311 ++G** levels. Electron correlation has been taken into account accordingto second order Msller-Plesset perturbation theory (MP2).The most stable isomer of HS,O,- isHSS0,- 1 the formation of which from SO, and H S - is exothermic by ca. 108 kJ mol-l (calculatedreaction energy). The analogous formation of CIS0,- from SO, and CI- is exothermic by 79 kJ mol-'.Slightly less stable than 1 are HOS(S)O- 2 and HS(S)O,- 4 and least stable is the isomer HOSSO-3. Anions 1-3 are of C, symmetry and 4 as well as CIS0,- are of C, symmetry. The likelyintermediates of the reaction between H,S and SO, in its early stage are discussed. The calculatedwavenumbers of the fundamental modes of CIS0,- agree well with experimental data.The reaction of sulfur dioxide with hydrogen sulfide accordingto equation ( 1 ) is one of the most important industrial processessince more than 25 million tons of elemental sulfur annually areproduced in this way.'*2 The technical process is carried out atelevated temperatures using alumina- or titanium dioxide-basedcatalysts.However, the two gases react also without catalystsboth in the vapour and liquid phases as well as in organicsolvents, but it seems that traces of moisture are needed in thesecases.3The mechanism and possible intermediates of reaction (1) arenot known with certainty. Most likely the primary product inthe vapour phase is the van der Waals complex H2S-S02 whichhas been structurally characterized by microwave spectro-scopy: the two molecules are aligned on top of each other withtheir two-fold rotation axes almost parallel but their dipolevectors antiparallel. The S S distance of 345 pm correspondsto the van der Waals distance. This adduct may then rearrangeby a proton shift from sulfur to oxygen to form dihydrogendioxothiosulfate(Iv), HS-S02H.This molecule has never beenobserved but ub-initio molecular-orbital (MO) calculationshave shown that it is the most stable structure of all possibleisomers of composition H,S,O,. According to a massspectroscopic study the chain-like isomer HO-S-S-OH can beproduced by electron-impact-induced decomposition of itsdiisopropyl ester followed by collision-induced neutralization ofthe cation to give the neutralWhile the various isomers of H2S202 are well characterizedtheir anions are not. Owing to the formation of water in reaction( 1 ) and since water seems to be required to initiate it undernon-catalytic conditions, the formation of HS202 - accordingto equation (2) has to be taken into account.CompoundsH2S202 + H,O- H30+ + HS,O,- (2)containing the hydrogendioxothiosulfate(1v) anion HS,O, -are unknown and no information whatsoever is available aboutthis species. Therefore, we have carried out a detailed ub-initioMO study on four isomers of HS,O,- to determine theirstructures, energies and vibrational spectra. The HS,O, -anion is isoelectronic with the well known hydrogensulfiteanion HS0,- and with the less well studied chlorosulfite anionCISO, - (also known as chlorosulfinate anion). Salt-likecompounds apparently containing the ClSO, - ion have been~ r e p a r e d , ~ but besides their optical and vibrational spectra littleis known about their properties.For this reason the ClSO, - ionwas included in the present MO calculation to elucidate itsstructure and to compare the calculated and experimentalvibrational spectra.CalculationsAll quantum-chemical calculations were performed with theGAUSSIAN 92 program package' for ab-initio MO calcul-ations. Molecular structures were fully optimized at theHartree-Fock level with the 6-3 1 1 G** and 6-3 1 1 + + G** basissets. Single-point calculations at the MP2 levels were done onthe optimized structures. Zero-point vibrational energies werecalculated from the wavenumbers (scaled by 0.89) obtainedfrom the optimized structures.The vibrational wavenumbers given in the Tables have beenscaled by a factor of 0.89 according to the suggestion by Popleet al.' For each of the isomers of HS,O,- the optimizationswere performed with different starting geometries towardsrotation around S-SH and S-OH bonds.The most stablerotamers were taken into consideration and are presented here.The thermochemical properties were calculated by standardmethods. loResults and DiscussionThe Hydrogendioxosulfate(1v) Anion.-Since H ,S20, mayexist as different isomers5 the same is to be expected for itsmonoanion HS,O, - . Therefore, four different connectivitieshave been considered; these correspond to the five most stablestructures of the parent compound H2S202. Regardless of th2920 J. CHEM. SOC. DALTON TRANS. 1994Table 1corresponding zero-point vibrational energies scaled by 0.89 (in kJ mol-')Total energies (in Eh = 4.36 x lo-'* J) of four HS,O,- isomers, of ClSO,-, Cl-., HS- and SO, obtained with different basis sets, andZero-point Zero-pointIon/Molecule HF/6-31 lG** energy MP2//6-3 1 1 G* * HF/6-3 1 1 + + G** energy MP2//6-3 1 1 + + G**1 HSS0,-2 HOS(S)O3 HOSSO-4 HS(S)O,-ClSO, -SO,c1-HS--945.388 305 45 39.5-945.396 576 13 50.0-945.347 686 69 46.3-945.383 151 07 52.0- 1006.814 234 3 21.0-459.564 047 0 -- 398.134 262 9 14.7- 547.225 081 9 18.8- 946.070 742 42- 946.062 672 37-946.01 3 853 36- 946.050 809 38- 1007.493 629 2-459.700 263 8- 398.270 955 0-547.767 141 2-945.402 366 41 40.4-945.410 413 56 49.8-945.374 169 38 46.3- 945.392 284 76 5 1.421 .O - 1006.823 398 4-459.565 425 1 -- 398.135 594 6 14.8-547.231 447 7 18.6- 946.096 463 65-946.089 526 83- 946.056 137 86- 946.072 085 65- 1007.514 446 5-459.703 570 2-398.273 506 6- 547.779 818 813 4Fig.1of atomsStructures of four isomers of the HS,O,- anion and numberingSHS-SO- HO-SO- HO-SS-0- HSO-0 S 01 2 3 4starting geometry only one conformation each was found for theanions 1-4; in other words, no rotational isomers were stableenough to have their geometries optimized. The stable struc-tures are shown in Fig. 1, the total energies in Table 1 , therelative stabilities in Table 2, the geometrical parameters inTable 3 and the atomic charges in Table 4. At the HF/6-311 G**and HF/6-3 11 + + G** levels of theory isomer 2 is the moststable, but the energy difference between it and 1 is only ca.1 1 kJmol-' . When electron correlation according to the second-orderMdler-Plessert perturbation theory is taken into accountisomer 1 becomes most stable both with and without diffusefunctions included. It should be noted that this isomer is alsofavoured by its low zero-point energy (see Table 1). At the MP2level isomer 4 is less stable than 1 by ca. 76 kJ mol-' and isomer3 by more than 1 10 kJ mol-'.The geometrical parameters of the HS,O,- anions are mostinteresting (Table 3). While isomers 1-3 are of C, symmetry, 4 isof C, symmetry. The HSS02- ion is related to thehydrogenthiosulfate ion HSSO, - which has been isolated asNH4HS20, '' and treated by ab-initio MO methods.12 Themost striking feature of HSS0,- 1 is the extremely long S-Sbond of 241.4 pm. This value may be compared to thatcalculated for the related dithionite anion S2042 - (21 6.9 pm),13while d(S-S) = 215.5 pm has been obtained for HS,0,-.12 TheS-S bond length of 1 is quite sensitive to the kind of basis setapplied: at the HF/6-311G** level it was optimized at 259.7 pm.Another unusual feature of 1 is the fact that the molecule is notof C, symmetry.The two non-bonding distances H 0 are301 and 389 pm (HF/6-311+ +G**). In other words, thehydrogen atom is leaning towards one of the terminal oxygens[0(1)] rather than towards the centre of charge of the twooxygen atoms; as a consequence the bond length d[S-O( l)] =144.8 pm is slightly larger than d[S-0(2)] = 144.7 pm and thetwo angles S-S-0 are different: a[S-SO(l)] = 100.5 anda[S-S-O(2)] = 102.3".The calculated structure of HSS0,- israther similar to the structure of the most stable isomer ofhydrogensulfite HOS0,-. This anion is also not of C,symmetry but the hydrogen atom is closer to one of the terminaloxygen atoms than to the other.I4 The structure of isomer 1may be considered as an adduct between the Lewis base HS-and the Lewis acid SO, [equation (3)].(3) HS- + SO, - HSS0,-The thermodynamics of this adduct formation will bediscussed below. However, it is interesting that in other SO,adducts with Lewis bases D similar long bonds D-S have beenreported. For example, for H20 SO, d(S 0) = 282pmI5 and for C5H,N SO, d(S N) = 261 pm l6 havebeen observed by microwave spectroscopy of the gaseouscompounds.The ion HSS02 - is isoelectronic with ClSO, - forwhich d(S-Cl) = 274.7 pm has been calculated (see below). Itmay also be compared with the SO, adduct of thiocyanate ion[NCS SO2]-, which has been isolated with the cation[K( 18-crown-6)] + (1 8-crown-6 = 1,4,7,10,13,16-hexaoxacyclo-octadecane). An X-ray diffraction analysis of the yellow crystalsshowed the anion to be of C, symmetry with an S-S bonddistance of 273.6 pm. ''The HOS(S)O- anion 2 has a similar conformation to that ofisomer 1; in this case the hydrogen atom is closer to the terminalsulfur (268 pm) than to the terminal oxygen atom (280 pm) butthe difference between these two non-bonded contacts is small.The terminal sulfur has in fact a slightly larger atomic charge(-0.64) than that of the terminal oxygen (-0.55); see Table 4.All geometrical parameters of 2 have normal values, and itsstructure corresponds to the most stable conformer of thehydrogensulfite isomer HOSO, - .I 4The five-atomic chain HOSSO- 3 should form ondeprotonation of the experimentally observed unchargeddihydroxydisulfane molecule, HOSSOH.6 However, 3 is theleast stable of the various HS,O, - isomers. Obviously thoseisomers are favoured which have both oxygen atoms linked tJ. CHEM. SOC. DALTON TRANS. 1994 292 1Table 2HF calculations have been taken into accountEnergies (kJ mol-') of the four isomeric structures of HS20,- in relation to the energy of isomer 1.The zero-point energies obtained by theIsomer HF/6-3 1 1 G** MP2//6-3 1 1 G** HF/6-3 1 1 + + G** MP2//6-31 I + + G**1 0 0 0 02 - 11.2 31.8 - 11.6 27.73 113.5 156.3 80.0 111.84 25.4 64.2 38.3 75.8Table 3 Bond distances d/pm, valence angles a/" and torsion angles .r/"of four isomers of HS,O,- (HF/6-311+ +G** level). Species 1-3 areof C , and 4 is of C, symmetryd(S-S)d (S-a)d (S-0 H )d(S-H)d(0-H)x( s-s-0)x( s-s-0, )a( 0-S-0)a( S-S-H)a(0-S-H)a(S-O-H) cwS(S0)1241.4144.71133.4100.511 14.094.8--~-~-161.12203.544.8 147.1165.094.702.3 111.099.8105.4---108.635.2-3205.0154.2169.094.2110.0106.7----107.465.8- 80.74199.4144.6134.4113.7115.6103.0104.5------the same sulfur atom.This then results in stronger S-0 bondsas can be seen from the corresponding bond distances (Table 3).The interesting features of isomer 3 are the two torsional angles~(0-S-S-0) = -80.7 and z(H-0-S-S) = 65.8'. Normallythese angles adopt values close to +80°;6*'8 the somewhatsmaller angle at the S-0 bond may be a result of the attractionbetween the hydrogen atom and the terminal oxygen atom(H 0 338 pm). The Mulliken charges of these atoms arelisted in Table 4.The structure of isomer 4, HS(S)O,-, corresponds to thealternative structure (C,, symmetry) of the hydrogensulfite ion,HS03-, as observed in solid CsHSO,." It is interesting thatthe S-0 and S-S bonds of 4 are shorter (stronger) than in theother three isomers and nevertheless it is not the most stableHS,O,- anion.All the geometrical parameters of 4 havenormal values. These may be compared to the results of anX-ray diffraction analysis of MeS(S)0,Na.H,0.20 TheMeS( S)O, - anion 5 is the simplest possible organic derivativeof anion 4. In 5 the bond lengths and valence angles are asfollows: d(S-S) = 198, d(S-0) = 145, d(S-C) = 177 pm;a(S-S-0) = 110.8,a(O-S-O) = 115.4,anda(S-S-C) = 108.4'.There is very close agreement between these results and thosefor the structure calculated for HS(S)O, - (Table 3).To support further work directed towards the identificationof HS20, - in reaction mixtures or the preparation of salts withthis anion, we have calculated the wavenumbers of the normalmodes of isomers 1 4 as well as their infrared and Ramanintensities (Table 5).The assignments given are based on theatomic displacements but should be considered as tentativesince the low molecular symmetries result in strong vibrationalcouplings between various types of motions.The Chlorosulfite Anion.-Salts with the anion ClSO, - havebeen prepared and characterized by optical and vibrationalspectroscopy 7.21 , 2 2 but no experimental structure determin-ations have been published. An ab-initio MO study apparentlyassuming C,, symmetry for ClSO, - and applying a 6-21 G basisset has resulted in the structural parameters23 d(S-Cl) = 329pm, d(S-0) = 154 pm, and a(0-S-Cl) = 124.9'; no furtherdetails were given.The ClSO, - ion forms on addition of SO, tochloride ions [equation (4)], a process believed to occur evenc1- + so, __+ ClSO, - (4)in the earth's atm~sphere.,~ Solid chlorosulfites easily looseSO, indicating the weakness of the S-Cl bond. According toseveral experimental studies reaction (4) is exothermic in thevapour phase. The reaction enthalpy has been estimated fromhigh-pressure mass spectrometric measurements as - 91.2 kJmol-' .25 On the other hand a value of - 79.9 kJ mol has beenderived from the dissociation energy of Cl(H,O)- and the freeenthalpy of the displacement reaction ( 5 ) in the vapour phase at23 0C.24SO, + Cl(H,O)- --+ ClS0,- + H,O (5)In solution the equilibrium between the solvated speciesdepends on the solvent (solv), equation (6).The equilibriumC1-(solv), + SO,(solv), ClSO,-(solv), + nsolv (6)constant K was determined as 2000 k 600 in 1,2-dichloro-ethane,7 365 k 6 in a ~ e t o n i t r i l e ~ ~ , ~ ~ , ~ ~ and 26 in dimethylsulfoxide at 25 'C., ' Calorimetric measurements have resultedin a reaction enthalpy of - 17.2 kJ mol-' in acetonitrile and of- 2.9 kJ mol-' in dimethyl sulfoxide at 25 'C.,,In this study the structure of ClSO, - was optimized with the6-31 1G** and 6-31 1 + + G** basis sets; the results are shownin Table 6. The absolute energies of ClS0,- and of speciesrelated to HS,O,- and CEO,- are given in Table 1. TheClS0,- ion is of C, symmetry and similar in geometry to theHSS0,- ion 1; see Table 3. Comparison of the parameters ofClS0,- with those calculated for SO, using the same basis set(HF/6-3 11 + + G**) shows that the S-0 bond lengths of SO,(140.8 pm) increase on chloride ion addition (to 142.2 pm inClSO,-). The 0-S-0 angle expectedly decreases from 1 18.7" inSO, to 115.1' in ClSO,-.(Table 7)may be compared to the Raman spectrum of tetraalkyl-ammonium chlorosulfites which have been recorded bothfor solid and dissolved sample^.^ As the data in Table 7demonstrate there is a very satisfactory agreement betweencalculated (scaled by 0.89) and observed wavenumbers for fourof the six fundamental modes of ClSO,-.The two lowest-energy modes also fit two weak Raman lines if the publishedassignment of these two lines is reversed. The close agreementthen reached demonstrates the reliability of the calculationprocedure applied.Comparison of the ClS0,- and HSS0,- spectra with thevibrational modes of SO, demonstrates the impact of thedonor (Cl-, HS-) on the bonding in the SO, unit.For SO, thescaled wavenumbers are v1 1203, v, 531 and v3 1378 cm-'(HF/6-3 1 1 + + G** level). The data in Tables 5 and 7 show thatthe symmetric and asymmetric SO stretching modes are shiftedto considerably lower wavenumbers on adduct formation. Incontrast, the SO, bending mode is practically not affected and iscalculated to occur at 522-540 cm-' for all three species(ClSO, - , HSSO, - , SO,).The calculated vibrational spectrum of ClSO,Thermodynamic Considerations.-To determine the energychange of the gas-phase reactions (3) and (4) the total energies ofthe anions HS-, C1- and of SO, were calculated applying th2922 J.CHEM. SOC. DALTON TRANS. 1994Table 4 Mulliken charges of four isomers of HS,O,- and of CISO, ~ calculated with the 6-31 1 + + G** basis set. For atom numbering see Fig. 1Atom HSSO, - HOS(S)O - HOSSO- HS(S)O, - CISO, -W) -0.39 - 0.64 -0.12 -0.51 +0.68S(2) + 0.50 + 0.36 -0.10 + 0.5 I -O(1) -0.54 - 0.45 - 0.37 - 0.48 - 0.46O(2) -0.54 -0.55 - 0.67 - 0.48 - 0.46HjCl - 0.03 + 0.28 + 0.27 - 0.03 -0.77Table 5 Wavenumbers (cm-I) of the nine fundamental vibrations of the four HS,O, - isomers calculated with the HF/6-3 1 1 + + G** basis set.Relative (infrared, Raman) intensities are given in parentheses. Wavenumbers have been scaled by a factor of 0.89 (v = stretching, F = bending,z = torsional mode)HSSO, - HOS(S)O - HOSSO- HS(S)O, --2525 (7, 100)587 (93, 5)--1181 (100,21)1051 (6, 5)--150 (10, 3)522 (44, 1)383 (1, 1)215 (26,20)133 (8,4)-3635 (1 7, 100)11 17 (31, 5)-----1031 (100, 16)691 (64, 10)507 (35,29)446 (1 7,4)367 (1 1, 10)321 (4, 10)209 (12,6)-3698 (30, 100)1108 (30, 11)----__840 (100,42)666 (78, 50)426 (1, 24)339 (64, 3)316(1, 18)228 (10,8)118 (7, 5)--2416 (36, 100)11 14 (5,6)1071 (57, 7)1181 (100,4)1043 (86,4)---557 (36, 7)516 (14, I )381 (2, 5)311 (1,2).--Table 6anion calculated with and without diffuse functions in the basis setBond distances d/pm and valence angles XI" of the CISO,HF/6-31 lG** HF/6-311+ +G**d(S-CI) 288.0 247.7d (S-0) 141.8 142.2x(CI-S-0) 103.4 102.7a(0-S-0) 11 5.6 115.1Table 7 Wavenumbers (cm-') of the six fundamental vibrations of theCISO, - anion calculated with the HF/6-3 1 1 + + G** basis set andscaled by a factor of 0.89.Relative (infrared, Raman) intensities aregiven in parentheses. The vibrational wavenumbers observed for solidand dissolved (liquid SO,) [NR,][CISO,] (R = Me or Et) are also givenMode Symmetry Calculated solid solutionv(S0) A' 1155(50, 100) 1120 11236(SO,) A' 540 (I 7,2) 535 527v(SC1) A' 282 (25, 6) 215 214S(OSC1) A' 93 (16, 1) - 103*v(S0) A" 1293 (100,9) 1290 1314S(0SCl) A" 147 (1,2) - 172** In ref. 7 the assignment of these weak Raman lines is reversed.HF/6-3 1 1G** and HF/6-3 1 1 + + G** approximations andtaking electron correlation into account.The results are given inTable 1. The molecular parameters of HS- are as follows:d(SH) = 133.9 pm; v(SH) 2774 cm-' (unscaled); atomic chargesS -0.925, H -0.075 (all calculated by HF/6-311+ +G**).From the data in Table 1 the energy change for reaction (3) iscalculated as - 113.2 kJ mol-l, and for reaction (4) -81.5 kJmol-' is obtained (MP2/6-3 1 1 + + G** basis). If the zero-pointenergies of the species involved are taken into account thereaction energies are - 105.3 kJ mol-' [(3)] and -78.8 kJ molk'[(4)]. Using the heat capacities the reaction energies at 298.1 5 Kwere obtained as - 108.2 kJ mol-' for (3) and -79.2 kJ mol-'for (4).The latter value is in excellent agreement with theexperimental enthalpy data mentioned above. Finally, it shouldbe mentioned that the electron affinities of Cl, SH and SO, areall positive.28 In other words, the anions Cl-, SH- and SO,-are stable with regard to electron loss. We therefore expect thesame for the more complex anions HS2O2 - and ClSO, - .Summarizing it may be stated that the most stable isomer ofthe still hypothetical hydrogendioxothiosulfate(1v) anion issimilar in geometry and in its energy of formation from SO, tothe experimentally proven chlorosulfite ion. It therefore can beexpected that HS,O,- isomers play a role in the reactionbetween H,S and SO, and in other redox reactions of sulfurcorn pound^.^^ Furthermore it seems likely that salts with theHS,O, - anion will be prepared in the future.The reaction ofSO2 with ionic hydrogensulfides M'HS- under mildconditions (to avoid redox reactions) may be a suitable route tosuch species. The further reactions of H,S2O2 and HS,O,-with either SO, or H,S will be dealt with in a separatepublication.AcknowledgementsThis work was supported by the Deutsche Forschungsgemein-schaft.References1 H. Fischer, in Ullmanns Enzyklopadie der technischen Chemie, VCH,Weinheim, 1982, vol. 21, pp. 8-25; J. R. West, in Kirk-OthmerEncyclopedia of Chemical Technology, Wiley, New York, 1983, vol.22, pp. 267-297.2 B. G. Goar, J. A. Lagas, J. Borsboom and G. Hejkoop, Sulphur, 1992,222,44; Anonymous, Sulphur, 1991,211,27; 1993,229,25 (StatisticalSupplement).3 P.W. Schenk and R. Steudel, Angew. Chem., 1965, 77, 437;I. K. 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ISSN:1477-9226
DOI:10.1039/DT9940002919
出版商:RSC
年代:1994
数据来源: RSC