An S-Shaped [Fe₄Dy₂] Complex Exhibiting Slow Relaxation of Magnetization: Synthesis, Magnetism, and Crystal Structures of a Family of [Fe₄Ln₂][Ln] Coordination Compounds (Ln = Nd, Gd, Tb, Dy, and Ho)

A series of heterobimetallic 3d−4f cluster coordination compounds has been synthesized using a Schiff-base ligand (H3L), a trinuclear iron(III) precursor complex and lanthanide nitrates as reactants. Five new isostructural complexes were prepared with the ligand in 4 different forms, i.e., neutral and 3 different levels of deprotonation, and with the general formula [FeIII4LnIII2(H2L)2(HL)2L2(CH3OH)2((CH3)3CCOO)2(NO3)2][LnIII(NO3)4(H3L)(CH3OH)]·NO3·H2O, where Ln is Nd, Gd, Tb, Dy, and Ho for compounds 1, 2, 3, 4, and 5, respectively. The single-crystal structures of two complexes were determined by X-ray diffraction, consisting of an original [FeIII4LnIII2]2+ moiety with a linear S-shaped [Ln-Fe4-Ln] core and an isolated LnIII ion coordinated by nitrate anions and the neutral Schiff-base ligand. The isostructural nature of all five coordination compounds is further illustrated both by XRPD and IR analysis. Magnetic properties of all five compounds have been studied and are discussed in light of magnetostructural considerations. Among these five compounds, the Dy (4) cluster shows frequency-dependent ac-susceptibility indicative of probable single-molecule magnet behavior.