Theoretical Study on the Gas Phase Reaction of Au + with CS2

29卷9期结构化学( TEGOU HUAYUE)Vol. 29. No 92010.91347~1352Theoretical study on theGas Phase reaction of Au with CS,LI Tao-Hong YU Shi-WenLIU Xiang-Yi XIE Xiao-Guang(Faculty of Chemistry, Southwest Forestry College, Kunming 650224, China)b(Department of Chemistry, Qujing Normal University, Qujing 650011, china)(Department of Chemistry, Yunnan University, Kunming 650091, China)ABSTRACT The reaction of Au('S, D) with CSz has been investigated at the B3LYP andCCSD(T) levels of theory. The identified reaction pathways revealed that the experimentallyobserved products, AuS and AuCS, can be produced by the insertion of Au into C-S bond.Thecalculated energetics shows that the reactions on singlet surface lead to excited-state productsAus('2)+'CS and AuCS'('2)+'s, and have notable energy barriers, whereas the reactions ontriplet surface producing the ground state products of Aus ('2)+CS and AuCS* 2)+3s areenergetically much more favorable. This result suggests that the minor formations of AuS andAucs observed in the previous experiment under room-temperature condition should result fromthe reactions of excited-state Au(D)with CS]. Further, the possibility for singlet-triplet surfacecrossing was also discussed by approximately determining the crossing region.Keywords: gold cation, carbon disulfide, insertion, theoretical study1 INTRODUCTIONmetal cations, such as Sc, y and La, whereas theThe chemistry of transition-metal sulfur systems products for late metal cations like Cu, Ag and auhas been an active area due to their significance in Recently, we have performed a theoretical study onindustrial catalysis, biology systems and material the reaction of early 5d transition metal cation, Lascience!-. CS2 is an important sulfur-transfer rea- (F, ' S), with CS2 16). The spin-allowed reaction, latgent and it is well suited for the study of metal- CS,- LaSt+'CS, which produces thesulfur interactions because they can achieve several excited-state product was calculated to be highlynodes of coordination and undergo a variety of sul- endothermic by around 120 k/mol. At room tem-fur-transfer reactions. Recently, D. K. Bohme re- perature, this reaction is almost impossible. In cosearch group have surveyed the reactions of 46 trast, the spin-forbidden reaction, La+ CS2atomic cations with CS2 using(ICP/SIFT)tandem Las+ CS, which yields the ground-state productmass spectrometer at room temperaturel). The was calculated to be exothermic by about 70 kJ/molresults show that the metal sulfides MS are the The favorableness of the spin-forbidden reactionprimary products for early 3d, 4d and 5d transition indicates that at low-energy condition the formation中国煤化工Received 13 July 2009: accepted 2 November 2009O Supported by the General Program of the Applied Basic Research of Science and TechnolCNMHG(No 2008ZC095), the Scientific Research Fund of Yunnan Provincial Education Department(No. 08Y0195), and partially supportedby the Key Laboratory of Forest Resources Conservation and Use in the Southwest Mountains of China(Southwest Forestry University)2comespondingauthor.E-mail:xgxie@ynu.edu.cnLIT. H et al. Theoretical Study on the Gas Phase Reaction of Au with CSNo 9of singlet ground state product Las from triplet point vibrational energies were used to correct all theground state ' La involves spin-inversion(SI) and relative energies. To ensure that the lowest-energymust proceed through a triplet-singlet surface cros- electronic states were found, the Stable keyword wassing. Such behavior of transition metal cations has used to test the stability of dFT wave functions. allbeen previously defined as two-state reactivity connectivities of minima and transition states were(TSR)I. Why do the late Sd transition metal cations, verified by intrinsic reaction coordinate(IRC)calcu-such as Au, appear to be inert toward CS2? Does the lations. Our previous studies 6, 13-15 have shown thattwo-state reactivity of these cations like Au play an the present theoretical method and basis sets canimportant role in the reactions with CS2? To answer provide reasonable and satisfactory accuracy in dea-these questions, herein we present a theoretical study ling with the transition metal-containing systemson the reaction of Au('s, ' D)with CS2. In this Based on the geometries of B3LYP/BS1, additionalreactions). the Au-CS2 adduct Au( CS2)was found single point calculations were performed employingto be the dominant product(91%), and only minor CCSD(T) 6, I7) method with SDD basis set for Auformation of Aus(1%)and AuCS(4%)was obser- and the standard basis set 6-311+G"8, 19)was usedved(CS2 accounts for 4%). This indicates that Au for C and S. This theoretical level is denoted byis somewhat reactive toward CSz, but notable energy CCSD(T)/BS2barriers exist on the potential energy surfaces(PESs)of this reaction. Theoretical investigations on the 3 RESULTS AND DISCUSSIONreaction mechanism and PES will be helpful forunderstanding the low reactivity of AuThe geometries of the stationary points on bothsinglet and triplet surfaces are shown in Fig. 1.The2 CALCULATION METHODScorresponding potential energy diagram is given inFig. 2. The calculated energies at B3LYP/BSI andGeometry optimizations were carried out at density CCSD(T)/BS2 levels are collected in Tablefunctional theory(DFT)level employing the hybrid shown in Table 1, theS-'D excitation energy of Aufunctional B3LYPl8 as implemented in GAUS. was calculated to be 222. 6 kJ/mol at the b3LYPSIAN98 program package. All electron basis sets level, which almost reproduced the experimentalTZVP of Ahlrichs et al. were used for C and S. value of 220.7 kJ/mol/ 20). In contrast, CCSDT)For Au the Stuttgart/Dresden relativistic effective slightly overestimated the energy of the triplet statecore potential(RECP)basis set SDD2 was applied, of Au*, giving this excitation energy as 2326kJ/molwith a [8s7p6d/6s p3d basis set for 5s5p5d6s Consequently, CCSD(T)/BS2 presented highervalence electrons. The combination of B3LYP with relative energies for some of the singlet and tripletthe above basis sets is denoted as B3LYP/BSI. species. Nevertheless, the PESs described by the twoHarmonic vibrational analysis was caried out at the levels are similar. In the following discussionsame level to characterize thpoints as a local minimum or a transition state. Zero- refer to those obtained at the b3LYP/BSI levelEnergies(Ere, kJ/mon) and Imaginary Frequencies(cm )for Transition States'An'+ ',-969953954YH坐196-970.030955200.6968.0464571-1703288121396793471642010Vol.29F(JIEGOU HUAXUE)Chinese134916096993715796796454679678566468-967.88734152226-969968278-967980681896991272-9679328306121.5-96801581961779967906806'AuCS+s9699072847118496794049880-956 00_0oMI,C.'Asc.’AD2C,1Fig. 1. Optimized geometries at the B3LYP/BSI level(bond lengths in a and bond angles in degree)20 TMFig.2. Potential energy diagram for the reaction of Aut ('s, 'D)with CS, at the B3LYP/BS1 level3. 1 Singlet surfaceto IMl. As the complete rupture of the activatedC-SAs shown in Fig. 1, on the singlet surface, the bond, the insertion intermediate IM2 is produced.reaction is initiated by the formation of a collision IM2 has a linear structure and lies above thecomplex,IMl, which locates below the reactants by reactants by 42.1 kJ/mol. This insertion intermediate200.6 k/mol. In this complex, Au coordinates with is also different from the angular-shape speciesone of the sulfur atoms in CS2 and significantly resulting from the La CSz reaction. The disso-stretches the corresponding C-S bond. This S-bound ciation of Af hond in TM one lead to 'Aus*+complex is structurally different from the C-s CS中国煤化bond is also abridged complex formed in the reaction of La with possiblCNMH GS to AucS.+CS26. After IMI, Au inserts into the C-S bond via s. One may expect that the formation of Aucs++TS, with an energy barrier of 321. 9 k/mol relative S is also possible, according to the concept of spir1350LTHeal:Theeti:siuyonthedasPhaseReacionofAt'wihcs2No9conservation. In fact, we did locate a triplet state It can be seen in Fig. 2 that 'TS has activation ener-AuCS, but this species lies above its singlet gy of 121.3 J/mol, relative to the reactants. On thespecies by 389.1 kJ/mol. Further, it is not a real local other hand, the formations of Aus and areminimum, but a first order point with one imaginary highly endothermic by 312.0 and 2802k J/molfrequency which corresponds to its dissociation into respectively. Therefore, it can be concluded that theAu and CS. Thus, we speculate that the triplet two products can not be formed on this surfaceexcitedAuCS may not exist.under room-temperature condition.Nea iea ordinateFig 3. Potcntial energies along the IRC of TS -IM13. 2 Triplet surfacereaction of ground-state Au with CS, leads toDifferent from the reaction on the singlet surface, excited-state products, whereas that of excited-statethe initial complex (IMI)formed on the triplet sur- Au with CS2 produces ground-state products. As aface is a T-shape carbon-coordinated complex with result, the formations of the products on singlet sur-symmetry. Relative to the triplet reactants, IMI face are highly endothermic, while the reactions onis stabilized by 261.2 kJ/mol. Interestingly, the si- triplet surface are exothermic. As shown in Fig. 2,milar species was also located in the reaction of LaTS lies above the singlet-state reactants by 103.3with CS2, but it is in the singlet state 6. with the kJ/mol and the formations of 'Aus*+'cs andbending of Au-c-S bond angle, via TS which lies ' AuCS.+'s are endothermic by 312.0 and 280.2below the triplet reactants by 119.6 kJ/mol, Au also kJ/mol, respectively. Apparently, the formations ofinserts into one of the C-S bonds through TS, for- Aus*and aucs* on the singlet surface under roomming the triplet insertion intermediate, TM2. The temperature condition are almost impossible. In con-energy barrier of this step is 141.9 kJ/mol relative to trast, the reactions on triplet surfaces are barrierlessIMI. IM2 also has a linear structure and our relative to the triplet reactantslculation indicates that it is more stable than"IM2 Two possibilities may explain the experimental re-by 133. 2 kJ/mol. Thus, the triplet sate should be the sult that minor formations of Aus* and Aucs* wereground state of the insertion intermediate. The break observed at room temperature. The first pos-of Au-C and Au-S bonds of IM2 can lead to 'Aus sibility is that the triplet excited cations Au(D)+'CS and AuCS*+s, respectively. As listed in contributed to the formations of Aus* and aucs+Table 1, both B3LYP/BSl and CCSD(T)BS2 pre- As中国煤化工fmordicted that Aus is significantly more stable than Aus*Aus, which indicates that the triplet state('z)is surfaHHCNMHS. Bohme et althe ground state of aushave confirmed that small population of tripletBased on the above discussions, we know that the excited-state Au'(<10%)cations was generated2010 Vol结构化学( JIEGOU HUAXUE) Chinese J struct.Chemthe ion source and they might be involved in the ted by Yoshzawa et al 21, for approximately loca-reactions'5).Another possibility is that singlet-triplet ting the crossing points of the two PESs of differentintersystem crossing occurred in the reaction. The multiplicities. The main idea of this approach isfacts that Au has a singlet ground state, while the perform a series of single point calculations of oneinsertion intermediate and products have triplet spin state along the IRC of the other spin state 22)ground state indicate that surface-crossing between Starting from the singlet insertion transition state,the low-and high-spin states is possible. If singlet- TS, along the IRC of TS - IMI, a series of sintriplet surface crossing happens, the reaction on the gle-point calculations (20 points along the IRC)singlet surface will lead to the energetically more were carried out with triplet spin state at thefavorable triplet surface through the crossing region. B3LYP/BSI level, and the triplet potential energyHowever, even though this is true, the spin-forbid. curve was obtained. It can be seen in Fig. 3 that theden reaction Au('S)+'CS2-Aus('2)+'CS is two curves cross into each other indeed. It should bealso impossible under room temperature because it noted that this does not mean the crossing betweenhas high activation energy barrier(103 3 kJ/mol)and two iRC curves but that between the two surfaces. Init is highly endothermic (177.9 kJ/mol). Similar other words, at this point the triplet and singlet statessituation can be found for the Au('s)+CS2of this system have the same energy and geometAuCS(2)+'s reaction. Combining the experiment The crossing point locates at IRC=0., with relativewith our calculations, the formations of AuS and energy=115.0 kJ/mol(without ZPE correction).TheAuCs in the experiment of Bohme et al. can be geometry of this point is also shown in Fig 3. Thesafely assigned to the reaction of Au ( D)with CS2. activated C-s bond length is 2.660 A, which isThe more exothermic feature of AuCS rationalizes longer than that of TS (2.463 A)and shorterthat the formation of AuCS(4%)is more efficient that of TS(2.831 A). This indicates thatthan that of Aus ( 1%)51crossing region is approximately located betweenAlthough the two-state reactivity of Au may not TS and TS. Moreover, the crossing point locatedplay an important role in the room-temperature here is not definitely the energy-minimum crossingexperiment of Bohme et al. 5), the possibility of the point between the singlet and triplet surfaces, butoccurrence of surface-crossing under higher energy only a possible point in this region. In fact,condition can not be ruled out. Therefore, we carried marked in Fig. 3, surface-crossing may occur atout additional calculations to provide some infor- another point in this region with lower energy, wheremation for this issuethe mix or strong interaction between different3. 3 Singlet-triplet surface crossingelectronic configurations with the same symmetryAs discussed above, the energetically favorable re- may lead to the inversion of spinaction Au('S)+'CS2-Aus' ('2)+'CS is spin. It can be seen in Fig. 2 that the spin-conservingThis reaction involves a change of spin reactions Au' 'S)+'CS2-Aus' (2)+and must proceed through singlet-triplet surface Aucs* ( z)+'s are endothermic by 312.0 and 280.2crossing. The aim of the following calculations is to kJ/mol, respectively, whereas the spin-forbiddendetermine the region where the surface crossing may reactions, Au'd's)+CS2+ Aus'('z)+'cs andoccurAuCS(2)+'S, are endothermic by 177.9 andBy analyzing the structural similarities of the inser- 118.4if the spintion transition states, TS and TS, we speculate that forb中国煤化工ermthe crossing point(CP)should be located inCNMH Ghs of Aust andITS and after 3TS. To locateAuCs would be significantly lowered. As thecrossing point, we chose a simple approach sugges- reaction goes on, the reaction system should changel352LIT. H. et al. Theoretical Study on the Gas Phase Reaction of Au with CSits spin state from singlet to triplet state in the should be addressed here that the above discussionscrossing region and move to the triplet PES which on the issue of surface-crossing are based on ourprovides a lower energy pathway to the triplet gro- qualitative calculations More accurate results for theund-state insertion intermediate IM2, leading to the related issues, such as the probability for the occur-ground-state products. This pathway can be descry- rence of spin inversion, requires more complicatedbed as Au('s)+CS2→lMl→CP→3M2→ calculations at higher theoretical levels, and this isAuS*(2)+CS or AuCs"('z)+>s. Finally, it beyond the scope of this workREFERENCES( Rodriguez J. A Kuhn, M. HrBek, J.J. Phys. Chem. 1996, 100, 15494-155022)Holm,R.H. Chen, rev1996,%6,2237-3042.B)Kaim, W. Schwederski, B, Bioinorganic Chemistry: Inorganic Elements in the Chemistry of Life, Wiley, New York 1994(4) Almond, M Cockayne, B; Cooke, S. 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