Mat. Res. Bull. Vol. 3, pp. 437-444, 1968. Pergamon Press, Inc. Printed in the United States. METAL-METAL BONDING IN La4Re6019 and RUTILE- RELATED DIOXIDES T. P. Sleight and C. R. Hare Department of Chemistry State University of New York at Buffalo Buffalo, New York 14214 and A. W. Sleight Central Research Department* E. I. du Pont de Nemours and Company Wilmington, Delaware 19898 (Received March 22, 1968; Communicated by J. B. Goodenough) ABSTRACT Extended Huckel calculations have been used to rationalize the existence of a Re-Re double bond across the edge-shared octahedra in La4Re6019. By analogy, double bonds are prob- ably also present in the distorted rutiles: MoO 2, NO 2, and a-ReO 2. Quantitative energy diagrams are not given, but it is shown qualitatively that the molecular levels of primar- ily metal-metal bonding character are very sensitive to the separation of the bridging oxygens, as well as to the metal-metal distance. Introduction The structure of La4Re6019 can be depicted as a network of dimerlc units, Re2010 -3 1/J,'A which are essentially two octahedra sharing an edge (1,2). The Re-Re distance is 2.42 ~ which, accord- ing to Cotton (3), corresponds to a bond order of two. A valence bond approach with d2sp 3 metal hybridization used for metal-ligand bonding allows the remaining three d orbitals to point toward the *Contribution No. 1416 437