X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the V $L_{2,3}$ and C and N $K$ edges reveal bonding and backbonding interactions in films of the 400 K magnetic semiconductor $\mathrm{V}[\mathrm{TCNE}{]}_{x\sim 2}$. In V spectra, $d_{xy}$-like orbitals are modeled assuming ${\mathrm{V}}^{2+}$ in an octahedral ligand field, while $d_{z^2}$ and $d_{x^2-y^2}$ orbitals involved in strong covalent $\sigma$ bonding cannot be modeled by atomic calculations. C and N MCD, and differences in XAS from neutral TCNE molecules, reveal spin-polarized molecular orbitals in $\mathrm{V}[\mathrm{TCNE}{]}_{x\sim 2}$ associated with weaker $\pi$ bonding interactions that yield its novel properties.

• Received 20 February 2008

DOI:https://doi.org/10.1103/PhysRevLett.100.257204