Theoretical study on the electronic structure and properties of synthetic MoFe3S3 compounds

We examine the electronic structure of a series of MoFe3S3 compounds whose spectroscopic and structural parameters have been recently published (J. Han, K. Beck, N. Ockwig, D. Coucouvanis, J Am Chem Soc 1999, 121, 10448). The synthetic Mo/Fe/S compounds under examination are close structural and functional analogs of essential parts of the FeMo‐cofactor in the enzyme nitrogenase. Using the ZINDO program and the projected unrestricted Hartree–Fock (PUHF) method, we have demonstrated that these compounds exhibit antiferromagnetic coupling between the metal atoms, with calculated triplet and singlet ground states. The metal atoms are found in reduced oxidation states, namely Mo(III), Fe(II), and Fe(I), in agreement with the experimental isomer shifts and the Mössbauer data previously reported. The addition of carbonyl groups to the MoFe3S3 clusters leads to a withdrawal of electron density from the Mo/Fe/S core and thus affects the strength of the metal–metal and metal–sulfur bonds in the compounds. We also show that the removal of pyridine from the coordination of the Mo atom has a notable effect on the electron delocalization in the Mo/Fe/S core and may lead to preferential localization of the electron density on the iron atoms. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001