Infrared Spectroscopic And Theoretical Studies Of Metal-sulfur Oxide Complexes

Metal-sulfur oxide complexes are important species in a series of chemical processes such as catalytic oxidation of sulfur oxides and biological assimilation of inorganic sulfur to sulfur-containing amino acids.Fundamental studies on the geometric and electronic structures of these complexes help understand their roles in the relevant chemical reactions.As one of the most widely explored sulfur oxide molecules,the chemical properties of sulfur dioxide?SO₂?have been the subject of numerous studies.However,the coordination chemistry of sulfur dioxide is mainly limited to a few noble metals and lanthanides while that of other transition metal-SO₂ complexes is far less understood.In addition to sulfur dioxide,sulfur monoxide?SO?is also a kind of sulfur oxide molecules of interest.However,its unstable character under ambient condition due to rapid disproportionation to S₂O and SO₂ makes it highly challenging to make transition metal-sulfur monoxide complexes using general synthetic procedures.In this thesis,a series of actinide,lanthanide and transition metal-sulfur dioxide and monoxide complexes were prepared through the reactions of laser-ablated metal atoms with sulfonyl fluoride?SO₂F₂?and thionyl fluoride?SOF₂?in argon or neon matrixes at 4 K.The product structures were identified by their characteristic infrared absorptions,isotopic frequency ratios upon ¹⁸O and ³⁴S substitutions and theoretical calculations.The major results are listed below:?1?Actinide,lanthanide and transition metal-sulfur dioxide complexes:Group 3 and 4metal atoms reacted with SO₂F₂ to form MF₂??²-O₂S?complexes in which the sulfur dioxide ligand is bonded to the metal center through two oxygen atoms.The SO₂ ligand in group 3complexes can be considered as SO₂^-based on the S-O bond lengths and O-S-O stretching vibrational frequencies,which is also supported by the similarity in natural charge distribution between SO₂ and SO₂^-.In contrast,group 4 metal-sulfur dioxide complexes are better described as SO₂^2-with longer S-O bonds and lower O-S-O stretching vibrational frequencies.For other 3d metals from Fe to Zn and 4d,5d metal atoms such as Ru,Rh and Au,sulfur dioxide complexes in the form of MF₂??¹-OSO?containing?¹-OSO ligand were identified.These molecules were formed via F atom transfer reactions under UV-vis irradiation.The S-O bond lengths and O-S-O stretching vibrational frequencies of SO₂ are close to those of triatomic SO₂ molecule,indicating the SO₂ ligand should be considered as?SO₂?⁰ in these 3d,4d and 5d metal complexes,and the bonding between MF₂ and SO₂ is mainly electrostatic resulting from the interaction between positively charged metal center and negatively charged oxygen atom of SO₂.The lanthanide and SO₂F₂ reaction products were characterized to have bidentate SO₂^-ligands,similar with the cases of group 3 metals.The antisymmetric and symmetric O-S-O stretches of the complexes are almost independent on lanthanide centers while the F-Ln-F stretches exhibit red shifts from Ce to Lu as a result of lanthanide contraction.A ThF₂??³-O₂S?complex is formed when Th reacted with SO₂F₂.The calculated Th-O and Th-S bond lengths are 2.251 and 2.681?respectively,shorter than the standard Th-O and Th-S single bond lengths,indicating that the SO₂ ligand is coordinated to the thorium center through all the three atoms in a?³ fashion.Such bonding motif is further supported by bonding analysis,and a new coordination mode of sulfur dioxide is established for the first time.?2?Actinide,lanthanide and transition metal-sulfur monoxide complexes:The reactions of group 5 and 6 metal atoms with SO₂F₂ resulted in the formation of the OMF₂??²-OS?complexes,in which the sulfur monoxide ligand is in a side-on bonded fashion.The S-O bond lengths of OMF₂??²-SO??M=V,Nb,Ta?were computed to be about 0.134?shorter than those of group 6 metal-SO complexes.Consistent with the variation in bond length,the S-O stretching frequencies of OMF₂??²-SO??M=Mo,W?are red-shifted by about 150 cm^-1compared with those of group 5 OMF₂??²-SO?.On the basis of the bond length,vibrational frequency and natural charge,the SO ligand in the OMF₂??²-SO??M=V,Nb,Ta?complexes can be considered as a superoxo-like ligand?SO^-?,and the OMF₂??²-SO??M=Mo,W?complexes contain a SO^2-ligand that is analogous to the peroxo ligand.Different from group 5 and 6 metal-sulfur monoxide complexes,the OTiF₂??¹-OS?complex was produced under UV-vis irradiation that induces the isomerization of TiF₂?O₂S?and S-O bond cleavage.The titanium center in the OTiF₂??¹-OS?complex is coordinated by oxygen of SO forming an end-on oxygen-bound geometry,which completely differs from the geometry of SO in OMF₂??²-SO??M=V,Nb,Ta,Mo,W?.Besides the coordination mode,the SO ligand in this end-on oxygen-bound complex can better described as a neutral ligand?SO?⁰.The Th and SOF₂ reaction product,ThF₂??²-SO?,features a side-on bound SO ligand that is close in nature to the peroxo-like SO^2-ligand of OMF₂??²-SO??M=Mo,W?.For unraium,a sulfur substituted uranyl fluoride[S=U=O]F₂ instead of the SO complex was obtained via the reaction of uranium atoms and SOF₂ upon UV-vis irradiation.Bonding analysis reveal triple bond characters for the U-O and U-S bonds,and the U-O bond is more covalent than the U-S bond.This demonstrates the first example where sulfur substituted uranyl?VI?can be stabilized by electron-withdrawing ligands such as fluorine.