Electronic structure of the transition-metal dicyanamides M[N(CN)2]2 (M=Mn,Fe,Co,Ni,Cu)

The electronic structure of M[N(CN)₂]₂ (M=Mn,Fe,Co,Ni,Cu) molecular magnets has been investigated using x-ray emission spectroscopy and x-ray photoelectron spectroscopy as well as theoretical density-functional-based methods. Both theory and experiments show that the top of the valence band is dominated by M 3d bands, while a strong hybridization between C 2p and N 2p states determines the valence-band electronic structure away from the top. The 2p contributions from nonequivalent nitrogen sites have been identified using resonant inelastic x-ray scattering spectroscopy with the excitation energy tuned near the N 1s threshold. The binding energy of the M 3d bands and the hybridization between N 2p and M 3d states both increase when going across the row from M=Mn to M=Cu. Localization of the Cu 3d states also leads to weak screening of Cu 2p and 3s states, which accounts for shifts in the core 2p and 3s spectra of the transition-metal atoms. Calculations indicate that the ground-state magnetic ordering, which varies across the series, is largely dependent on the occupation of the metal 3d shell and that structural differences in the superexchange pathways for different compounds play a secondary role.