Homometallic Fe4III and Heterometallic {Fe4IIILn2III} ( Ln = Dy, Tb) Complexes - Syntheses, Structures, and Magnetic Properties

The sequential reaction of the multisite coordination ligand 2-methoxy-6-{[2-(2-hydroxyethylamino)ethylimino]methyl}phenol (LH2) with Fe(ClO4)(2)4H(2)O or a combination of Fe(ClO4)(2)4H(2)O and Ln(NO3)(3)5H(2)O [Dy-III and Tb-III] in the presence of tetramethylammonium hydroxide and pivalic acid (pivH) under ambient conditions afforded a homometallic tetranuclear Fe-III complex and heterometallic hexanuclear Fe-III/Ln(III) complexes, namely, [Fe-4((3)-O)(2)(L)(4)]3CH(3)CN2CH(3)OH (1), [Fe4Dy2((3)-O)(2)(L)(2)(O2CCMe3)(10)(MeOH)]2CH(3)CN (2), and [Fe4Tb2((3)-O)(2)(L)(2)(O2CCMe3)(10)(HO2CCMe3)]H2O (3). Compounds 1-3 crystallize in the monoclinic system in space group P2(1)/n (Z = 4). The homometallic tetranuclear derivative 1 possesses three contiguous four-membered Fe2O2 rings in a ladderlike configuration. Each of the iron centers is hexacoordinate (2N, 4O) in a distorted octahedral geometry. On the other hand, 2 and 3 contain two symmetrically related Fe(2)Ln units that are joined to each other through oxygen atoms from the ethoxide side arms of the ligand L2-; the two lanthanide ions are located at the opposite ends of the hexanuclear core. In 2 and 3, the lanthanide centers are eight- (distorted trigonal dodecahedron) and nine-coordinate (distorted monocapped square antiprism), respectively, and the iron centers are hexacoordinate (distorted octahedral). Magnetic studies on 2 and 3 reveal the presence of weak antiferromagnetic coupling between the Fe-III and Ln(III) ions.