MODELS FOR THE MOLYBDENUM(VI V) CENTERS OF THE MOLYBDENUM HYDROXYLASES AND RELATED ENZYMES - GEOMETRY, ELECTRONIC-STRUCTURE, AND EPR G-TENSOR PREDICTIONS FROM AB-INITIO AND SEMIEMPIRICAL MOLECULAR-ORBITAL STUDIES/

The geometries and electronic structures of several molybdenum(V) and molybdenum(VI) complexes with tetradentate N2S2 and N2O2 ligands (LH2 = 2-mercaptophenyl)-N,N'-dimethyl-1,2-diaminoethane, (2-hydroxyphenyl) -N,N'-dimethyl-1,2-diaminoethane) which have been proposed as models f or the molybdenum-(VI/V) centers of the molybdenum hydroxylases and re lated enzymes have been predicted using ab initio and INDO molecular o rbital methods. Ab initio and INDO geometrical predictions have been c ompared with known X-ray crystal structures for three complexes and ha ve been found to be in excellent agreement. In addition, the EPR g ten sors of the molybdenum(V) complexes have been estimated using INDO met hods. The results support previously proposed structures for both the model complexes and the enzyme molybdenum centers and are in good agre ement with EPR and EXAFS experimental data for these systems. The resu lts indicate the ligand has a profound effect on the geometry and elec tronic structures of the complexes. Insight into the electronic factor s responsible for the EPR parameters of the complexes is presented, an d application to the enzyme molybdenum centers is explored.