Further considerations on the structure and bonding in edge-sharing bioctahedral complexes

From WCl6 to WCl2: Properties of Intermediate Fe-W-Cl Phases

Phenomenological studies of WCl6 reduction with transition metal powders M = Mn, Fe, and Co have been recently reported. These reactions involve a series of reductive intercalation steps of M atoms into layered tungsten chloride arrangements, followed by exsolution of MCl2. In the series M = Fe, the presence of divalent iron is evidenced for Fe(x)WCl6, FeW2Cl10, Fe2W2Cl10, and (Fe,W)Cl2 by Mössbauer spectroscopy. Magnetic properties are reported. Bonding characteristics between tungsten atoms in edge-sharing [W2Cl10](n-) bioctahedra reveal that a double bond can be addressed to FeW2Cl10. A similar situation appears for Fe2W2Cl10, due to the localized and thus nonbonding character of the two electrons in the δ orbitals of this compound.

Through-ring bonding in edge sharing dimers of octahedral complexes

A study of the preferred structures for the M2X2 rings in the binuclear complexes of types [M2(mu-XR2)2L8] and [M2(mu-XR3)2L8] is presented, based on qualitative orbital arguments supported by extended Hückel calculations on Cr compounds. The main conclusions are confirmed by DFT calculations on key compounds of Cr and Mn and agree well with the results of a structural database analysis. With the simplified electron counting scheme deduced, complexes with six or four electrons available for bonding of the M2X2 framework are predicted to have two possible minimum energy structures, with either a short M-M or X-X distance, whereas compounds with eight framework electrons are expected to present no short through-ring distance. Such a behavior is consistent with the framework electron rules reported earlier for compounds with different coordination spheres and provides a general description of the structure and bonding in a variety of compounds with M2X2 diamonds. Metal-metal bonding across the ring can be equally predicted taking into account only the bonding characteristics of the t2g-like orbitals for the XR2- but not for the XR3-bridged complexes. In addition, the framework electron counting scheme has the advantage of being independent of the formal oxidation state assigned to the metal atom.