Synthesis, structures, adsorption behaviour and magnetic properties of a new family of polynuclear iron clusters

Abstract

Solvothermal reactions of 1,10-phenanthroline-2,9-dicarbaldehyde dioxime (H(2)phendox) with FeCl(3)·6H(2)O or FeBr(3) under solvothermal conditions yielded two trinuclear iron(III) clusters [Fe(III)(3)(mu(3)-O)(phendox)(3)]X·14H(2)O (X = Cl 1·14H(2)O, Br 2·14H(2)O) and three hexanuclear iron(III) and iron(II) clusters, [Fe(III)(6)(mu(4)-O)(2)(MeO)(6)X(4)(phendox)(2)]·MeOH (X = Cl , Br 4) and (H(3)O)[Fe(II)(6)(mu(6)-Cl)(phenda)(6)]·6H(2)O (5·6H(2)O). The phendox(2-) ligand is very useful in constructing magnetically active and stable high-nuclearity metal clusters in that the phenanthroline rings and the oxime nitrogen atoms grasp the metal ions tightly while the two oxygen atoms on the oximates can link other metal centres in the shortest pairwise magnetic exchange pathway. Adjacent Fe(3)(mu(3)-O)(phendox)(3)(+) motifs in 1 and 2 are packed by off-set pi-pi interactions of the aromatic rings on phendox(2-) to generate a 3D supramolecular architecture in the honeycomb topology and with 1D hexagonal channels in the dimension of 13 x 13 Å along the c-axis. 2 is stable upon the removal of guest molecules and the desolvated compound absorbed considerable amount of N(2), CO(2) and H(2). 3 and 4 are isostructural. Two mu(4)-O(2-) and two phendox(2-) units link four metal atoms into a coplanar butterfly-shaped unit with the mu(4)-O(2-) slightly above and below the plane (+/-0.264 Å). The other two Fe(III) ions are capped on the alternate planes via the three bridging mu(2)-methoxides and accordingly form an unprecedented hexanuclear Fe(III) cluster. Furthermore, the oximes underwent hydrolysis to yield carboxylate groups and the resulted 1,10-phenanthroline-2,9-dicarboxylate link the iron atoms to form a hexanuclear cluster of 5. Magnetic studies show that the antiferromagnetic interactions are present in the Fe(3)O core of 2 and in the (mu(6)-Cl)Fe(6)(mu-O)(12) core of 5.