Ligand substitution effects on the charge transport properties of the spin crossover complex [Fe(Htrz) (trz) (NHtrz) ](BF)y·nHO.

The complex dielectric permittivity of a series of spin crossover complexes, with variable ligand stoichiometry [Fe(Htrz) (trz) (NHtrz) ](BF) ·nHO, has been investigated as a function of temperature in a wide frequency range. In each compound, a substantial drop of the conductivity and permittivity is evidenced when going from the low spin to the high spin state, albeit with decreasing amplitude for increasing ligand substitution (i.e. for increasing x). The deconvolution of the dielectric spectra using the Havriliak-Negami equation allowed to extract the dipole and conductivity relaxation times, their distributions as well as the dielectric strengths in both spin states. Remarkably, no clear correlation appears between the conductivity changes and the lattice properties (Debye temperature) in the dilution series. We rationalize these results by considering the dimensionality of the system (1D), wherein the charge transport occurs most likely by hopping along the [Fe(Rtrz)] chains.