Synthesis, structure and magnetic properties of a novel octairon(III) citrate complex

A novel octairon(III) citrate complex, (Him)(9)[Fe-8(mu (3)-O)(2)(mu (2)- O H)(2)(cit)(6)(CH3CO2)(2)(im)(2)](ClO4). 13H(2)O has been obtained from DMF solution, by reacting ferric perchlorate, citric acid and imidazole in a 1: 1:5 ratio. This compound crystallizes in the monoclinic space group P2(1)/n with a=15.271(1), b=19.940(1), c=44.197(1) Angstrom, beta =91.965(1)degree s, V=13450.2(9) Angstrom (3) and Z=4. The complex consists of two equivalen t tetranuclear units, which are not symmetrically related and are linked to gether by two of the six tetraionized citrate ligands. The iron(iii) ions a re antiferromagnetically coupled. Assumption of a four S=5/2 spin system ba sed on H=-2 Sigma (i <j) J(ij)S(i)S(j) leads to satisfactory agreement with the experimental magnetic behavior, with g=2.0 and J(13)=J(23)=-32.1 cm(-1 ), J(12)=J(14)=-14.5 cm(-1), J(24)=J(34)=-11.1 cm(-1).