文摘
The nature of chemical bonding in the complex carbides Sc3[Fe(C2)2] (1) and Sc3[Co(C2)2] (2)has been explored by combined experimental and theoretical charge density studies. The structures ofthese organometallic carbides contain one-dimensional infinite TC4 (T = Fe, Co) ribbons embedded in ascandium matrix. Bonding in 1 and 2 was studied experimentally by multipolar refinements based on high-resolution X-ray data and compared to scalar-relativistic electronic structure calculations using the augmentedspherical wave method. Besides substantial covalent T-C bonding within the TC4 ribbons, one also observesdiscrete Sc-C bonds of noticeable covalent character. Furthermore, our study highlights that even tinydifferences in the electronic band structure of solids might be faithfully recovered in the properties of theLaplacian of the experimental electron density. In our case, the increase of the Fermi level in theorganometallic Co(d9) carbide 2 relative to its isotypic Fe(d8) species 1 is reflected in the charge densitypicture by a significant change in the polarization pattern displayed by valence shell charge concentrationsof the transition metal centers in the TC4 units. Hence, precise high-resolution X-ray diffraction data providea reliable tool to discriminate and analyze the local electronic structures of isotypic solids, even in thepresence of a severe coloring problem (Z(Fe)/Z(Co) = 26/27).
