Faculté des sciences

DFT studies on the magnetic exchange across the cyanide bridge

Atanasov, Mihail ; Comba, Peter ; Daul, Claude A.

In: The Journal of Physical Chemistry A, 2006, vol. 110, no. 49, p. 13332 -13340

Exchange coupling across the cyanide bridge in a series of novel cyanometalate complexes with CuII-NC-MIII (M = Cr and low-spin Mn,Fe) fragments has been studied using the broken-symmetry DFT approach and an empirical model, which allows us to relate the exchange coupling constant with σ-, π-, and π*-type spin densities of the CN⁻ bridging ligand. Ferromagnetic... Plus

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    Summary
    Exchange coupling across the cyanide bridge in a series of novel cyanometalate complexes with CuII-NC-MIII (M = Cr and low-spin Mn,Fe) fragments has been studied using the broken-symmetry DFT approach and an empirical model, which allows us to relate the exchange coupling constant with σ-, π-, and π*-type spin densities of the CN⁻ bridging ligand. Ferromagnetic exchange is found to be dominated by π-delocalization via the CN⁻π pathway, whereas spin polarization with participation of σ orbitals (in examples, where the dz ² orbital of MIII is empty) and π* orbitals of CN⁻ yields negative spin occupations in these orbitals, and reduces the CuII- MIII exchange coupling constant. When the dz ² orbital of MIII is singly occupied, an additional positive spin density appears in the σ(CN) orbital and leads to an increase of the ferromagnetic Cu- NC-M exchange constant. For low-spin [MIII(CN)₆]³⁻ complexes, the dz² orbital occupancy results in high-spin metastable excited states, and this offers interesting aspects for applications in the area of molecular photomagnetism. The DFT values of the exchange coupling parameters resulting from different occupations of the t2g orbitals of low-spin (t2g⁵) FeIII are used to discuss the effect of spin-orbit coupling on the isotropic and anisotropic exchange coupling in linear Cu-NC-Fe pairs.