Structural, electrochemical, and theoretical investigations of new thio- and selenoether complexes of molybdenum and tungsten

Molybdenum and tungsten complexes with tridentate bisanionic ligands ( ^-OC₂H₄XC₂H₄O ^-, X = S, Se) were synthesized and analyzed electrochemically. Crystal structures of [{MoO₂[O(CH₂)₂S(CH ₂)₂O]}₂] and [{WO₂[O(CH ₂)₂S(CH₂)₂-O]}3] were obtained. For these two complexes as well as for the virtual molybdenum trimer and the tungsten dimer, DFT calculations were performed in order to better understand the formation of two significantly different complexes for molybdenum and tungsten with the same ligand and by the same preparation method. The compound WO₂Cl₂[MeS(CH₂)₂SMe] was synthesized and characterized by crystal structure analysis. A structural and electrochemical comparison of this compound with the recently published analogous molybdenum compound and the dme analogs of molybdenum and tungsten were undertaken. All these data were used to evaluate the structural and electronic influences of replacing molybdenum by tungsten and of varying the ligand atoms (O/S/Se) from the point of view of the different coordination spheres of the molybdopterin-dependent oxygen-atom-transfer enzymes.