Counterion Effect on the Spin-Transition Properties of the Cation [Fe(btzx)(3)](2+) (btzx = m-Xylylenebis(tetrazole))

The influence of the counter-anion on the structure and the spin-transition properties of original ID bis(tetrazole) Fe-II systems, namely [Fe(btzx)(3)]X-2 (X=PF6- (1), CF3SO3- (2) and ClO4- (3); btzx-m-xylylene-bis(tetrazole)) is studied. The X-ray crystal structures of compounds 1 and 2 are described in detail. These structures present a solvent molecule encapsulated within pockets formed by btzx ligands along the ID coordination chains. Compound 2 is shown to be the first structurally characterised alternating HS-LS 1D spin-transition system (HS high spin, LS-low spin). The magnetic susceptibility measurements of all three compounds are compared. The degree of completion and the transition temperature are both drastically influenced by the counterion used, while surprisingly, the cooperative nature of the transition is not affected by the choice of counterion. Compounds 1 and 2 are further studied by Mossbauer spectroscopy and their distinct LIESST properties are compared.