with Chiral Structure: Matrix Infrared Spectra and Theoretical

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A: Spectroscopy, Molecular Structure, and Quantum Chemistry 2

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The OMS, OM(#-SO), and OM(#-SO)(#-OS) Molecules (M = Ce, Th) with Chiral Structure: Matrix Infrared Spectra and Theoretical Calculations Tengfei Huang, Qiang Wang, Wenjie Yu, Xuefeng Wang, and Lester Andrews J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b03731 • Publication Date (Web): 30 May 2018 Downloaded from http://pubs.acs.org on May 30, 2018

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The Journal of Physical Chemistry

The OMS, OM(η2-SO), and OM(η2-SO)(η2-O2S) Molecules (M = Ce, Th) with Chiral Structure: Matrix Infrared Spectra and Theoretical Calculations Tengfei Huang,† Qiang Wang,†,‡ Wenjie Yu,† Xuefeng Wang,*,† and Lester Andrews*,§ †

School of Chemical Science and Engineering, Tongji University, Shanghai 200092, P. R. China

‡

State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of

Sciences, Taiyuan 030001, Shanxi, China §

Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States

ABSTRACT: Infrared absorptions of the matrix isolated OMS, OM(η2-SO), and OM(η2-SO)(η2-O2S) (M = Ce, Th) molecules were observed following reactions of laser-ablated Ce and Th metal atoms with SO2 during condensation in excess argon and neon. Band assignments for the main vibrational modes were confirmed by appropriate

34

SO2 and S18O2 isotopic shifts. B3LYP, BPW91 density functional and

CASSCF/CASPT2 calculations were performed to characterize these new reaction products and to explore the admixture of f orbitals into the bonding giving stronger M ≡O triple bonds. It is very interesting that both OM(η2-SO) and OM(η2-SO)(η2-O2S) molecules show chiral structure.

1

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The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

INTRODUCTION The coordination chemistry of SO2 and activation of the S–O bond in SO2 have attracted much attention from the standpoint of environmental protection and resource utilization.1−3 Oxidation of SO2 to form SO3 catalyzed by certain transition metal oxides is an important issue for the sulfuric industry.4-6 The first metal atom reactions with SO2 involved

Group 1 (alkali metals), and formed ion pair (M+)(SO2−)

species.7 Recently, the researches of the laser-ablated Group 2 (Be, Mg),8,9 Group 4 (Ti, Zr, Hf),10 Group 5 (V, Nb, Ta),11 Group 6 (Cr, Mo, W) and U,12,13 Group 11(Cu, Ag, Au),14 Group 12 (Zn, Cd),15 and Group 14 (Pb)16 metal atom reactions with SO2 in inert matrices have been carried out. Novel complexes such as NgBeSO2 (Ng = Ne, Ar, Kr, Xe), M(η2-O2S) (M = Mg, Cu, Zn, Cd, Pb), M(η2-O2S)2 and M2(η2-O2S) (M = Mg, Pb) and OM(η2-SO) (M = Ti, Zr, Hf, V) have been identified in low-temperature matrices employing IR spectroscopy. It is interesting to note for U atom reaction with SO2 forms SUO2 and the f electrons are fully involved in bonding. However, to the best of our knowledge, no study has been reported on the reactions of lanthanoid metal atoms with SO2. Herein, we present a matrix infrared spectroscopic investigation of laser-ablated cerium and thorium atom reactions with SO2 in excess argon and neon. The new metal oxide complex OM(η2-SO) and its SO2 adduct OM(η2-SO)(η2-O2S), and the simple triatomic molecule OMS (M = Ce, Th) are identified from matrix isolation infrared spectroscopy with isotopic substitution and theoretical vibrational frequency calculations. Additional wave function based calculations were performed to describe 2


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the f electron involved multiple bonding in the OMS and OM(η2-SO) molecules in detail. EXPERIMENTAL AND COMPUTATIONAL METHODS Laser-ablated Ce or Th atoms reacted with SO2 in excess argon or neon during condensation at 4 K using apparatus and methods described in our previous papers.8,9,17,18 The Nd:YAG laser fundamental (1064 nm, 10 Hz repetition rate with 10 ns pulse width) was focused onto a rotating metal target, which provided a bright plume of metal atomic emissions spreading uniformly to the cold CsI window. The cerium or thorium target was polished to remove oxide coating and immediately placed in the vacuum chamber. Sulfur dioxide was condensed and evacuated before dilution with research grade argon or neon. A mixture of S18O2 and S16,18O2 with a trace of S16O2 was prepared by ignition of sulfur powder (99.5%, Alfa Aesar) in 18O2 (>99%, Shanghai Research Institute of Chemical Industry) and purified by freeze-pump-thaw cycle. The sample of 34SO2 was similarly prepared from sulfur-34 (98.8% 34S, Cambridge Isotope Laboratories) reaction with oxygen (99.999%, British Oxygen Company). The laser output energy was varied about 10−20 mJ/pulse. FTIR spectra were recorded at 0.5 cm−1 resolution on a Bruker Vertex 80 V spectrometer with 0.1 cm−1 accuracy using a MCT range B detector. Matrix samples were annealed at different temperatures and selected samples were subjected to photolysis by a medium pressure mercury arc lamp (Philips, 175W) with the globe removed. Supporting density functional theory (DFT) calculations were performed using the Gaussian 09 program package19 with the hybrid B3LYP20,21 and pure BPW9122−24 3



density functionals, the 6-311+G(3df) basis set25 for sulfur and oxygen atoms, and the SDD pseudopotential for cerium and thorium.26,27 All of the geometrical parameters were fully optimized and the harmonic vibrational frequencies were obtained analytically at the optimized structures. Natural Bond Orbital (NBO) analysis was performed using NBO 3.1 embedded in Gaussian 09 program package.28 Additional wave function based calculations were performed using CASSCF/CASPT2 and the ANO-RCC-VTZP basis set with the MOLCAS 8.0 software in order to describe the multiconfigurational nature of OMS and OM(η2-SO) and to analyze the M=O/S bonding in detail.29−33 The active space used to describe OMS comprised two σ and four π bonding/antibonding orbitals pairs (12,12), which was similar with that employed in previous paper.34 For OM(η2-SO), an active space composed of 12 electrons in 12 orbitals (12,12) was chosen, which contained one σ and two π bonding/antibonding pairs mainly localized on M=O, two σ and two σ* orbitals centered on M(η2-SO), and one σ bonding/antibonding pair on the S−O moiety included to stabilize this active space. Calculations of Mulliken charges were also performed employing this program.35 The active molecular orbitals were visualized using the Gabedit 2.4.10 package.36 Molecular orbital composition analysis was carried out using the Ros-Schuit method for active orbitals obtained from the CASSCF/CASPT2 calculations.37,38

RESULTS AND DISCUSSION Infrared spectra of laser ablated cerium and thorium atom reaction products with 4


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SO2, S18O2, or

34

SO2 in excess argon or neon during condensation at 4 K will be

presented in turn. Density functional theory and CASSCF/CASPT2 calculations were performed to characterize new reaction products and investigate the multiple bonding. The calculated vibrational frequencies were compared to support product identification. Absorptions for common species in these experiments, such as SO,39,40 SO2−,40 SOO,41 SO3,42 cerium oxides CeO and CeO2,43−45 and thorium oxides ThO and ThO2,44,46,47 have been identified in previous studies. Ce + SO2. Infrared spectra of laser-ablated cerium atoms codeposited with SO2 in argon are illustrated in Figure 1 and absorptions for new products are listed in Table 1. The strong peak at 783.5 cm−1 in the Ce−O stretching region and the medium intensity band at 696.4 cm−1 were observed after deposition. These bands increased on annealing to 20 K by 20% and decreased with full-arc irradiation. Further annealing to 35 K increased these bands markedly, which, in addition, generated a new absorption at 778.4 cm−1 in the same region. Another five bands were observed at 981.1, 968.9, 902.2, 788.7, and 534.3 cm−1 after deposition, which showed little changes on annealing, whereas they increased dramatically at the expense of bands at 783.5 and 696.4 cm−1 on irradiation. A medium intensity band at 808.4 cm−1 is due to CeO, and the strong peak at 736.7 cm−1 and weak peak at 758.4 cm−1 to CeO2 because the Ce18O (767.4 cm-1) and Ce18O2 (701.7 cm-1) counterparts were also observed.43−45 Analogous experiments were done when neon was used as the host matrix, and the results are exhibited in Figure 2 and listed in Table 1. Th + SO2. Figures 3 and 4 show laser-ablated Th atom reactions with SO2 in 5



solid argon and neon, respectively. New absorption was observed centered at 800.6 cm-1 in the Th=O stretching region on deposition in argon matrix. This band increased observably on annealing to 20K, decreased on full-arc irradiation, and further increased on annealing to 35 K. Furthermore, a photosensitive peak at 806.6 cm−1 was detected as well. Vibrational bands of ThO (878.9 and 876.6 cm−1) and ThO2 (787.1 and 735.1 cm−1) were produced by the codeposition since their isotopic counterparts were also detected.44,46 New bands were found at 979.6, 966.5, 832.5, 769.7, and 586.0 cm−1 for similar reactions in excess neon, which increased on >220 nm irradiation while the 818.9 and 660.0 cm−1 peaks exhibited marked decrease. These absorptions are given in Table 1. Calculations. Density functional computations and CASPT2 optimizations were performed for new reaction products, to assist in the identification of the various IR absorptions and to explore multiple bonding in the new molecules. As shown in Figure 5, the structures obtained for the insertion products OMS and OM(η2-SO), formed by coordination of the S−O subunit to the metal center of M−O (M = Ce, Th), were optimized to singlet ground states by two different density functionals, B3LYP and BPW91, and the CASPT2 wave function based method. Isomers, SM(η2-O2), were optimized, which are 55.8 kcal/mol (Ce) or 51.6 kcal/mol (Th) higher in energy than OM(η2-SO) based on B3LYP calculation. From cerium to thorium, the M=O and M=S bond lengths for these molecules increase, whereas both the OMS bond angles for OMS molecules and OMO bond angles for OM(η2-SO) molecules markedly decrease. Calculations were also done for 6


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the OM(η2-SO)(η2-O2S) adducts, which were generated by the binding of another SO2 molecule to the metal center of OM(η2-SO) through two O atoms, employing DFT methods to help assign new product bands. These calculated geometries are very similar to the analogous group 4 metal-containing molecules identified in the previous studies.9,48−52 Calculated frequencies of these new products are summarized in Tables 2, 3, and 4, respectively. Active orbitals obtained from the CASSCF/CASPT2 calculations for these molecules are given in Figures 6 and S1-S5. OM(η2-SO) (M = Ce, Th) Identification. As shown in Figure 1, the strong band at 783.5 cm−1 and medium band at 696.4 cm−1 were observed in the reactions of laser-ablated cerium atoms with SO2 diluted in argon. These two absorptions exhibited the same tendencies on deposition, annealing, irradiations, and further annealing, indicating that they are due to the same molecule. Our theoretical calculations predicted these two modes to be separated by similar wavenumbers. A 34

SO2 experiment gave the same strong band without shift, which reveals no

participation of sulfur in this mode, but the 696.4 cm−1 band shifted to 690.5 cm−1, suggesting that this vibration involves the S atom. Through B3LYP calculations, the Ce-O stretching vibration has no 34S shift but the S−O mode shows a redshift of about 6.2 cm−1 with 34S substitution. For the

18

O enriched sample, the counterpart peaks at

743.4 and 669.4 cm−1 were observed with isotopic 16O/18O frequency ratios of 1.0539 and 1.0403, respectively, which are close to the 1.0542 and 1.0403 ratios of calculated frequencies. In addition, the sample contained about 10% SO2, 25% S16,18O2, and 65% S18O2, and doublet oxygen isotopic distributions were detected for these two 7



Page 8 of 35

absorptions, indicating that only one oxygen atom was involved in each vibrational mode. Thus, the strong band at 783.5 cm−1 in solid argon is assigned to the Ce−O stretching mode while the medium band at 696.4 cm−1 is appropriate for the S−O stretching vibration. These two bond stretching vibrational modes are characteristic of the OCe(η2-SO) molecule. As illustrated in Figure 2, in the neon matrix, the Ce−O and S−O stretching modes for the OCe(η2-SO) molecule are detected at 799.2 and 697.3 cm−1, respectively. The Ce−O argon-neon matrix shift is near to that observed for cerium oxides.43 These absorptions were predicted at 815.4 and 702.7 cm-1 by our theoretical

calculation

at

the

B3LYP/6-311+G(3df)/SDD

level,

which

are

overestimated by 2.0 and 0.8%. Similarly, using 18O enriched sample, the Ce−O mode showed a red shift to 758.6 cm−1 (the S−O mode was not observed), but in the 34SO2 experiment, no shift was observed for the Ce−O stretching mode while the S−O stretching mode shifted to 691.3 cm−1. The CASPT2 stretching frequencies for OCe(η2-SO) were 883.7 and 766.6 cm−1, which match experimental values reasonably. The reactions of Th atoms with SO2 in an argon matrix gave a weak peak at 800.6 cm−1 in the Th−O stretching region (Figure 3). In solid neon, this peak blue-shifted to 818.9 cm−1, and another one weak peak was observed at 660.0 cm−1 in the S−O stretching region (Figure 4). These two absorptions showed the same trends on codeposition, >320 nm irradiation, and further irradiation (>220 nm), and thus they are assigned to the OTh(η2-SO) molecule. The B3LYP functional predicted the Th−O stretching mode at 820.4 cm−1 and the S−O stretching mode at 663.1 cm-1, which are 8


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0.2 and 0.5% above the observed neon matrix value, and the BPW91 calculation gave lower peaks for the same modes at 806.8 and 658.8 cm-1, which are only underestimated by 1.5% (Ne) and 0.2% (Ne). With 34SO2 sample in argon, the Th−O mode was still at 800.6 cm−1, and in excess neon, the 818.9 cm−1 band exhibited no shift as well, but the 660.0 cm−1 band showed a 5.5 cm−1 isotopic shift. In

18

O

enriched sample in solid argon, the Th−O stretching band had a shift of 42.9 cm−1, which agrees very well with the B3LYP functional calculated redshifts of 44.1 cm−1 for the ThO isotopic molecule. The Th−O and S−O stretching modes for the

18

O

substitution were detected at 773.8 and 638.6 cm−1 employing neon as the matrix. The stretching frequencies calculated by CASSCF/CASPT2 for OTh(η2-SO) were 803.2 and 684.3 cm−1, indicating the close agreement of the two different density functional frequency calculations. Energy changes provide useful evidence for the expected reactions. The insertion reactions of M (M = Ce, Th) atoms into SO2 to form OM(η2-SO) are exothermic by 133 kcal/mol (Ce) and 183 kcal/mol (Th), respectively, based on B3LYP calculations for reaction (1). M + SO2 → OM(η2-SO)

(1)

OMS (M = Ce, Th) Identification. As shown in Figure 1, another Ce−O stretching mode at 778.4 cm−1 was generated during the reactions of laser-ablated cerium atom with SO2 in solid argon. This peak was too weak to observe on codeposition but increased dramatically on annealing to 35 K, showed no shift with 34

S substitution while had a red shift about 39.3 cm−1 with 18O enriched sample giving 9



Page 10 of 35

1.0532 16O/18O isotopic frequency ratio. Therefore, this band is assigned to the Ce−O stretching mode of the OCeS molecule, and the analogous assignment has been done in our previous paper.9 In solid neon the strong peak at 790.8 cm−1 is appropriate absorption for the Ce−O stretching mode of OCeS, and the

34

S and

18

O counterparts

were observed at 790.8 and 749.7 cm−1 (Figure 2). DFT calculations support these OCeS assignments. The B3LYP functional predicted a somewhat higher frequency at 821.1 cm−1 for the Ce−O stretching mode, and with Cs symmetry imposed, the CASPT2 stretching frequency was 844.9 cm−1 for the Ce−O stretching mode, so it is reasonable to predict that the gas phase frequency of Ce−O in OCeS is 800 ± 10 cm−1. The weak band at 797.6 cm−1 in an argon matrix increased markedly on annealing to 35 K, which is the Th−O stretching mode of the OThS molecule (Figure 3). This assignment was demonstrated by further isotopic experiments. With S18O2 sample, this peak shifted to 754.8 cm−1 resulting in the isotopic ratio of 1.0567, whereas this band had no shift in

34

16

O/18O frequency

SO2 experiment. B3LYP

calculation was performed for OThS: one strong Th−O stretching mode was calculated at 817.0 cm−1, and with defining a 1.0566

16

18

O substitution, this peak shifted to 773.2 cm−1

O/18O isotopic frequency ratio, which is very close to the

observed value. Complementary experiments were done in neon, and the weak absorption for the Th−O stretching mode of OThS was observed at 812.2 cm−1, the 34

S counterpart at 812.2 cm−1 and

18

O counterpart at 766.7 cm−1 (Figure 4). With

CASPT2 the Th−O stretching mode was calculated at 818.5 cm−1, which agrees well. OM(η2-SO)(η2-O2S) (M = Ce, Th) Identification. Another group of new bands 10


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was found at 981.1, 968.9, 902.2, 788.7, and 534.3 cm−1 in laser-ablated Ce atom reactions with SO2 diluted in argon. These bands gained at the expense of the bands due to OCe(η2-SO) at 783.5 and 696.4 cm−1 on broadband irradiation (Figure 1). With 34

S substituted sample, the 981.1, 968.9, 902.2, and 534.3 cm−1 bands shifted to 970.6,

958.2, 889.9, and 531.9 cm−1 giving 1.0108, 1.0112, 1.0138, and 1.0045

32

S/34S

isotopic frequency ratios, whereas no shift was observed for the 788.7 cm−1 peak in the Ce−O stretching region. In the S18O2 experiment, these new peaks shifted to 947.1, 933.4, 864.7, 748.5, and 525.1 cm−1 resulting in

16

O/18O isotopic vibrational

frequency ratios 1.0359, 1.0380, 1.0434, 1.0537, and 1.0175, respectively. Obviously, the 788.7 cm−1 band exhibited the largest isotopic

16

O/18O ratio (1.0537), which

suggests a typical transition metal=O stretching vibration mode. The remaining peaks with smaller 16O/18O isotopic ratios supply clues of S=O/S−O stretching and O=S=O bending modes. Additionally, with the sample mixed by about 8% SO2, 23% S16,18O2, and 69% S18O2, the oxygen isotopic distribution for the 788.7 cm−1 band showed a doublet at 788.7 and 748.5 cm−1 suggesting that just one oxygen atom is involved in this mode. Therefore, it is reasonable to assign these new bands to the OCe(η2-SO)(η2-O2S) adduct: specifically speaking, the 788.7 cm−1 band is assigned to the Ce=O stretching mode, the 981.1 and 968.9 cm−1 bands are due to S=O stretching modes while the 534.3 cm−1 band corresponds to a O=S=O bending mode. The last 902.2 cm−1 peak is attributed to the S−O stretching mode, which is analogous to the assignments given in our earlier investigation.9 DFT calculations support these assignments. The B3LYP calculation for the OCe(η2-SO)(η2-O2S) molecule predicted 11



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S=O stretching modes at 981.3 and 962.0 cm−1, S−O stretching vibration at 914.6 cm−1 (as found in our experiments, the calculated intensity of this mode is also very weak), Ce−O stretching mode at 847.5 cm−1, and O=S=O bending mode at 550.3 cm−1, which match the observed trends very well. Furthermore, the detected

16

O/18O

isotopic ratios for S=O, S−O, and Ce−O stretching vibration modes are very close to the theoretical values (1.0363, 1.0398, 1.0398, and 1.0542 cm−1) computed by B3LYP functional. In a neon matrix, new bands at 994.1, 977.5, and 547.4 cm−1 increased on full-arc irradiation, which are assigned to the OCe(η2-SO)(η2-O2S) adduct. New peaks at 806.6 and 586.2 cm−1 were observed in the reactions of laser-ablated thorium atom with SO2 in solid argon (Figure 3), which can be assigned to the OTh(η2-SO)(η2-O2S) adduct. The peak at 806.6 cm−1 having the 1.0566 16O/18O isotopic ratio is appropriate for the absorption of a Th−O stretching mode. In the neon matrix, five new bands at 979.6, 966.5, 832.5, 769.7, and 586.0 cm−1 were observed for the OTh(η2-SO)(η2-O2S) molecule (Figure 4). The IR spectra of

18

O and

34

S

substitution experiments are similar to that of the cerium case, so the analogous assignments are made for this molecule. The 832.5 cm−1 peak is attributed to the Th−O stretching mode, and the 979.6 and 966.5 cm−1 absorptions correspond to S=O stretching modes while the 586.0 cm−1 band is due to the O=S=O bending vibration, and the 769.7 cm−1 band is assigned to the S−O stretching mode. The OM(η2-SO)(η2-O2S) molecules can in principle be produced by the addition of SO2 to OM(η2-SO), which are exothermic by 27.8 kcal/mol (Ce) and 35.7 kcal/mol (Th) (B3LYP). It is interesting that the optimized OM(η2-SO)(η2-O2S) molecules have 12


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triplet ground states, which are more stable than the corresponding singlet states by energies of 16.2 kcal/mol (Ce) and 20.7 kcal/mol (Th) (B3LYP). ୦௩

OM(η2-SO) + SO2 ሱሮ OM(η2-SO)(η2-O2S)

(2)

Bonding. The Ce−O stretching modes for OCeS, OCe(η2-SO), and OCe(η2-SO)(η2-O2S) molecules were observed at 778.4, 783.5, and 788.7 cm-1 in solid argon, respectively, suggesting that Ce−O bonding is enhanced in this sequence. Recall that the antisymmetric and symmetric Ce−O stretching modes for CeO2 were measured at 736.7 and 757.3 cm-1 in the argon matrix.45 To further confirm these oxo bonding schemes, benchmark level CASPT2 calculations were performed. As shown in Figures S1-S3, the molecular orbitals reveal that the Ce−O bonding can be described by one σ bond and two π bonds. The Ce−O bond length is calculated at 1.786 Å (OCeS), 1.784 Å for OCe(η2-SO), and 1.770 Å for OCe(η2-SO)(η2-O2S) as presented in Figure 5, which are shorter than the diatomic CeO bond distance (1.84 Å) proposed from tabulated atomic radii,53 and the triple CeO bond distance (1.816 Å, CASPT2) for the OCeO molecule. Additionally based on CASSCF/CASPT2 calculations (Figure 6), the average f atomic orbital component for the Ce−O bond is 4.78% for OCeO, 5.21% for OCeS, and 5.31% for OCe(SO), respectively, suggesting more admixture of f orbitals into the bonding gives a stronger Ce≡O triple bond. At the CASPT2 level the Th-O bond distance is calculated at 1.916 Å (OThO), 1.890 Å (OThS), and 1.895 Å [OTh(η2-SO)], respectively. As shown in Figures S4 and S5, it is reasonable to conclude that the Th-O bonds in these molecules have considerable triple bond character. In addition, the average f orbital component for a 13



Th−O bond is 5.07% for OThO, 5.34% for OThS, and 5.48% for OTh(η2-SO) (Figure 6). Interestedly the calculated charge distribution for the metal center is decreased from Ce to Th ( for example, CASSCF Mulliken partial charges are -0.53O +1.10Ce -0.57S and

-0.45

O

+0.89

Th

-0.43

S, respectively), reflecting more p electrons of ligands O and S

are engaging in donation to metal center and hence more covalent M−O/M−S bonds are formed. As listed in Tables S1 and S2 the calculated B3LYP NBO analysis for OMS, OM(η2-SO), and OM(η2-SO)(η2-O2S) shows that for Ce−O/ Ce−S π bonds over 98% p character is on the O or S to the Ce or Th. The cases of dative electron donation were also reported in our earlier papers.54−57 It is very interesting that both OM(η2-SO) and OM(η2-SO)(η2-O2S) molecules show chirality. The optimized molecules are enantiomers with chiral metal centers, as illustrated in Figure 7. The insertion reaction of metal atom to SO2 from different orientations produced different OM(η2-SO) molecules, which can be viewed as the origins of such enantiotopic molecules.9 The doublets shown in Figure 2 might be the same vibration mode absorptions of two enantiomers trapped in different sites in solid neon. The above mentioned mechanism for the generation of enantiotopic adducts may be involved in one of the necessary processes in enantioselective synthesis, asymmetric catalysis, and many other related domains using catalysts containing cerium and thorium

atoms.

CONCLUSIONS Laser-ablated Ce or Th atoms reacted with SO2 in excess argon or neon during 14


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condensation at 4 K to generate the new products OMS, OM(η2-SO), and OM(η2-SO)(η2-O2S) (M = Ce, Th), which were observed by infrared absorptions and confirmed by appropriate isotopic shifts, and DFT and CASSCF/CASPT2 frequency calculations.

The

Ce−O

stretching

modes

for

OCeS,

OCe(η2-SO),

and

OCe(η2-SO)(η2-O2S) molecules were observed at 778.4, 783.5, and 788.7 cm-1 in solid argon, which are higher than antisymmetric and symmetric Ce−O stretching modes were measured at 736.7 and 757.3 cm-1. Based on CASSCF/CASPT2 calculations, the average f atomic orbital component for Ce−O bond is 4.78% for OCeO, 5.21% for OCeS, and 5.31% for OCe(SO), respectively, suggesting more admixture of f orbitals into the bonding gives stronger Ce≡O triple bond. Similar Th-O bonding character was found in the new products.

ASSOCIATED CONTENT Supporting Information Active orbitals obtained from the CASSCF/CASPT2 calculations for OMO, OMS, OM(η2-SO), (M = Ce, Th) and OCe(η2-SO)(η2-O2S) molecules are given in Figures S1-S5.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (X.W.), [email protected] (L.A.). Notes 15



The authors declare no competing financial interest.

ACKNOWLEDGMENTS There are no conflicts of interest to declare. This work was supported by the National Natural Science Foundation of China Grant (No.21503252) and the Ministry of Science and Technology of China Grant (No. 2012YQ220113-7). We also acknowledge financial support from the (U.S.) Department of Energy Grant No. DE-SC0001034 to L. A.

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(54) Gong, Y.; Wang, X. F.; Andrews, L.; Schloder, T.; Riedel, S. Infrared Spectroscopic and Theoretical Investigations of the OUF2 and OThF2 Molecules with Triple Oxo Bond Character. Inorg. Chem. 2012, 51 (12), 6983−6991. (55) Wang, X. F.; Andrews, L.; Thanthiriwatte, K. S.; Dixon, D. A. Infrared Spectra of H2ThS and H2US in Noble Gas Matrixes: Enhanced H-An-S Covalent Bonding. Inorg. Chem. 2013, 52 (18), 10275−10285. (56) Mikulas, T.; Chen, M. Y.; Dixon, D. A.; Peterson, K. A.; Gong, Y.; Andrews, L. Reactions of Lanthanide Atoms with Oxygen Difluoride and the Role of the Ln Oxidation State. Inorg. Chem. 2014, 53 (1), 446−456. (57) Vent-Schmidt, T.; Andrews, L.; Thanthiriwatte, K. S.; Dixon, D. A.; Riedel, S. Reaction of Laser-Ablated Uranium and Thorium Atoms with H2Se: A Rare Example of Selenium Multiple Bonding. Inorg. Chem. 2015, 54 (20), 9761−9769.

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Table 1. Infrared Absorptions (cm−1) Observed for Products of the Reactions of Ce and Th Atoms with SO2 Molecules SO2/Ar

S18O2/Ar

34

SO2/Ar

S18O2/Ne

SO2/Ne

34

SO2/Ne

assignment

_______Ce_____ 778.4

739.1

778.4

790.8

749.7

790.8

OCeS

783.5

743.4

783.5

799.2(795.8)

758.6(755.3)

799.2(795.8)

OCe(η2-SO)

696.4

669.4

690.5

697.3(688.7)

691.3(683.0)

OCe(η2-SO)

981.1

947.1

970.6

994.1

960.3

982.8

OCe(η2-SO)(η2-O2S)

968.9

933.4

958.2

977.5

939.7

968.6


902.2

864.7

889.9


788.7

748.5

788.7


534.3

525.1

531.9

547.4 ______

525.8

545.6


Th_______

797.6

754.8

797.6

812.2

766.7

812.2

OThS

800.6

757.7

800.6

818.9

773.8

818.9

OTh(η2-SO)

660.0

638.6

654.5

OTh(η2-SO)

979.6

968.5

OTh(η2-SO)(η2-O2S)

903.2

966.5

957.6


806.6

832.5

802.7

832.5


769.7

731.8

765.3


586.0

566.4

585.9


631.4(627.7)

806.6 586.2

763.4

24


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Table 2. Calculated Frequencies for the OM(η2-SO) (1A) Molecules (M = Ce and Th)a B3LYP 16−32

18−32

BPW91 16−34

16−32

18−32

CASPT2 16−34

16−32

mode assignment

91.8(19) 122.3(29) 318.2(44) 538.2(104) 766.6(65) 883.7(358)

S−Ce=O bend O−Ce=O bend Ce−SO str Ce−O str S−O str Ce=O str

99.8(20) 132.3(32) 354.5(57) 547.7(109) 684.3(69) 803.2(274)

S−Th=O bend O−Th=O bend Th−SO str Th−O str S−O str Th=O str

2

OCe(η -SO) 44.2(21) 42.9(19) 43.5(21) 64.1(17) 61.2(16) 64.0(17) 101.2(33) 96.7(30) 101.1(33) 93.1(29) 88.8(26) 93.1(29) 286.4(29) 284.1(28) 280.2(29) 281.8(21) 279.9(20) 275.7(20) 483.3(49) 460.0(45) 482.7(48) 460.7(33) 438.0(31) 460.4(33) 702.7(73) 675.5(65) 696.5(72) 710.3(61) 682.8(55) 703.9(60) 815.4(364) 773.5(332) 815.4(365) 774.7(304) 735.0(276) 774.7(305) OTh(η2-SO) 109.6(15) 104.8(13) 108.9(14) 106.8(13) 102.0(11) 106.2(13) 142.9(31) 135.5(28) 142.8(31) 140.5(26) 133.3(23) 140.4(26) 306.1(36) 304.1(35) 299.0(35) 311.9(33) 310.0(32) 304.6(32) 524.1(87) 497.7(80) 523.3(86) 515.8(71) 489.9(66) 514.9(71) 663.1(59) 636.8(51) 657.6(60) 658.8(50) 632.4(44) 653.4(52) 820.4(282) 776.3(255) 820.4(282) 806.8(246) 763.4(223) 806.7(246) a Frequencies and intensities (in parentheses) are in cm−1 and km mol−1, respectively.

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Page 26 of 35

Table 3. Calculated Frequencies for the OM(η2-SO)(η2-O2S) (3A) Molecules (M = Ce and Th)a

16−32

B3LYP 18−32

BPW91 18−32

16−34

16−32 16−34 2 OCe(η -SO)(η -O2S) 246.8(60) 241.9(56) 244.2(59) 228.6(28) 225.4(24) 225.6(28) 356.9(96) 339.9(93) 356.8(96) 335.4(58) 319.1(55) 335.3(58) 550.3(117) 523.5(100) 547.9(120) 519.4(69) 494.6(60) 516.8(70) 847.5(323) 803.9(295) 847.5(323) 795.3(269) 754.4(244) 795.3(269) 914.6(35) 879.6(33) 905.8(35) 891.3(10) 857.3(8) 882.8(10) 962.0(92) 925.2(83) 952.9(92) 897.6(31) 863.2(29) 889.1(30) 981.3(165) 946.9(155) 970.4(159) 944.9(143) 912.2(133) 934.1(141) 2 2 OTh(η -SO)(η -O2S) 240.8(43) 234.4(64) 239.5(28) 236.9(38) 233.6(40) 236.0(14) 360.6(104) 341.9(97) 360.6(104) 353.3(89) 334.8(83) 353.2(89) 550.4(103) 523.4(87) 548.0(106) 521.2(84) 495.5(71) 519.0(86) 834.3(314) 789.4(283) 834.2(314) 817.7(278) 773.8(250) 817.6(278) 901.2(39) 866.8(35) 892.5(39) 872.5(29) 839.2(26) 864.1(28) 964.0(149) 927.9(132) 954.2(150) 911.2(101) 876.7(89) 902.2(102) 976.9(157) 941.7(152) 966.7(149) 925.9(134) 893.1(128) 915.8(127) a −1 −1 Frequencies and intensities (in parentheses) are in cm and km mol , respectively.

mode assignment

2

26


Ce−SO str Ce−O str O=S=O bend Ce=O str S−O str S=O str S=O str Th−SO str Th−O str O=S=O bend Th=O str S−O str S=O str S=O str

Page 27 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


Table 4. Calculated Frequencies for the OMS (1A′) Molecules (M = Ce and Th)a B3LYP 16−32

18−32

CASPT2b

BPW91 16−34

16−32

18−32

16−34

16−32

mode assignment

OCeS 86.6(30)

83.2(28)

86.2(29)

84.4(26)

81.4(25)

83.9(26)

94.6(19)

O=Ce=S bend

422.7(95)

422.6(93)

412.5(90)

406.4(72)

406.2(70)

396.5(68)

442.7(126)

Ce=S str

821.1(360)

778.9(328)

821.1(361)

781.5(294)

741.4(268)

781.5(294)

844.9(373)

Ce=O str

OThS 146.4(14)

140.0(13)

145.7(14)

140.8(11)

134.7(11)

140.2(11)

146.0(12)

O=Th=S bend

422.2(84)

422.2(84)

411.3(80)

420.6(72)

420.5(72)

409.7(69)

434.3(107)

Th=S str

818.5(267)

Th=O str

817.0(259) 773.2(233) 816.9(260) 800.0(222) 757.2(199) 800.0(222) Frequencies and intensities (in parentheses) are in cm−1 and km mol−1, respectively. b CASPT2 values with Cs symmetry imposed. a

27



Page 28 of 35

Figure 1. Infrared spectra for the cerium atom and SO2 reaction products in solid argon at 4 K. (a) Ce + SO2 deposition for 60 min; (b) after annealing to 20 K; (c) after >220 nm irradiation; (d) after annealing to 35 K; (e) Ce +

34

SO2 deposition for

60 min; (f) after annealing to 20 K; (g) after >220 nm irradiation; (h) after annealing to 35 K; (i) Ce + S16,18O2 deposition for 60 min; (j) after annealing to 20 K; (k) after >220 nm irradiation; (l) after annealing to 35 K.

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Figure 2. Infrared spectra for the cerium atom and SO2 reaction products in solid neon at 4 K. (a) Ce + SO2 deposition for 60 min; (b) after annealing to 8 K; (c) after >220 nm irradiation; (d) after annealing to 10 K; (e) Ce +

34

SO2 deposition for

60 min; (f) after annealing to 8 K; (g) after >220 nm irradiation; (h) after annealing to 10 K; (i) Ce + S16,18O2 deposition for 60 min; (j) after annealing to 8 K; (k) after >220 nm irradiation; (l) after annealing to 10 K.

29



Page 30 of 35

Figure 3. Infrared spectra for the thorium atom and SO2 reaction products in solid argon at 4 K. (a) Th + SO2 deposition for 60 min; (b) after annealing to 20 K; (c) after >220 nm irradiation; (d) after annealing to 35 K; (e) Th +

34

SO2 deposition for

60 min; (f) after annealing to 20 K; (g) after annealing to 30 K; (h) after annealing to 35 K; (i) Th + S16,18O2 deposition for 60 min; (j) after annealing to 20 K; (k) after >220 nm irradiation; (l) after annealing to 35 K.

30


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Figure 4. Infrared spectra for the thorium atom and SO2 reaction products in solid neon at 4 K. (a) Th + SO2 deposition for 60 min; (b) after >320 nm irradiation; (c) after >220 nm irradiation; (d) Th +

34

SO2 deposition for 60 min; (e) after >320 nm

irradiation; (f) after >220 nm irradiation; (g) Th + S16,18O2 deposition for 60 min; (h) after annealing to 8 K; (i) after >320 nm irradiation; (j) after annealing to 10 K; (k) after annealing to 12 K.

31



Figure 5. Optimized geometries (bond lengths in angstrom) for OMS, OM(η2-SO), and OM(η2-SO)(η2-O2S) molecules, respectively, obtained with CASPT2 (italic type), BPW91 (normal type), and B3LYP calculations (bold type).

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Figure 6. Active orbitals obtained from the (6,6) CASSCF/CASPT2 calculations for OMO, OMS, and OM(η2-SO).

33



Figure 7. OM(η2-SO) reacted with SO2 (after >220 nm irradiation) producing chiral OM(η2-SO)(η2-O2S) molecules (M = Ce, Th).

34


Page 34 of 35

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TOC Graphic

35


with Chiral Structure: Matrix Infrared Spectra and Theoretical

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