Magnetic susceptibility measurements on a frozen solution of FeClminus;4anions in isopropanol in the 0.07ndash;4.2 K temperature range

摘要

Magnetic susceptibility measurements in the range 0.07ndash;4.2 K have been performed on a 0.32 M solution of lsqb;FeCl4rsqb;minus;anions in isopropanol. At 0.1 K the experimental susceptibility is more than an order of magnitude smaller than that corresponding to a single lsqb;FeCl4rsqb;minus;monomer, a fact which clearly suggests the formation of dimers of lsqb;FeCl4rsqb;minus;with antiferromagnetic coupling. A careful analysis of the susceptibility curve has been performed allowing the existence of dimers as well as of monomers in the solution. Moreover, zerohyphen;field splitting terms of the formDlsqb;s2zminus;1/3s(s+1)rsqb; have also been introduced in the theoretical description of both monomers and dimers. The experimental susceptibility can be satisfactorily explained along these lines and is consistent with the following conclusions: (1) Around 90percnt; of the lsqb;FeCl4rsqb;minus;units present in the solution are in dimer form while the remainder are present as monomers; (2) The effective exchange interaction between the two ferric ions involved in a dimer isJ=(0.15plusmn;0.02) cmminus;1. This value is consistent with a Fendash;Clndash;Sndash;Clndash;Fe superexchange path whereScould be a solvent molecule; and (3) The lsqb;FeCl4rsqb;minus;units do not display a rightTdsymmetry but they are distorted by the interaction with the solvent giving rise to a valueD=minus;(0.60plusmn;0.10) cmminus;1. The present results point out that magnetic susceptibility measurements in that range of temperature can provide us with useful and detailed information on the solutendash;solute and solutendash;solvent interactions in liquid solutions involving a paramagnetic complex.