Pentanuclear Heterometallic {Mn^III₂Ln₃} (Ln = Gd, Dy, Tb, Ho) Assemblies in an Open-Book Type Structural Topology: Appearance of Slow Relaxation of Magnetization in the Dy(III) and Ho(III) Analogues

The reaction of Ln­(III) nitrate and Mn­(ClO₄)₂·6H₂O salts in the presence of a multidentate sterically unencumbered ligand, (<i>E</i>)-2,2′-(2-hydroxy-3-((2-hydroxyphenylimino)­methyl)-5-methylbenzylazanediyl)­diethanol (<b>LH</b>_<b>4</b>) leads to the isolation of four isostructural pentanuclear hetereometallic complexes [Mn^III₂Gd₃(LH)₄(NO₃)­(HOCH₃)]­ClO₄·NO₃ (<b>1</b>), [Mn^III₂Dy₃(LH)₄(NO₃)­(HOCH₃)]­ClO₄·NO₃ (<b>2</b>), [Mn^III₂Tb₃(LH)₄(NO₃)­(HOCH₃)]­ClO₄·NO₃ (<b>3</b>), and [Mn^III₂Ho₃(LH)₄(NO₃)­(HOCH₃)]­ClO₄·NO₃ (<b>4</b>) with an open-book type structural topology. <b>1</b>–<b>4</b> are dicationic and crystallize in the achiral space group, <i>P</i>2₁/<i>n</i>. A total of four triply deprotonated ligands, [LH]^3–, are involved in holding the pentameric metal framework, {Mn^III₂Ln₃}. In these complexes both the lanthanide and the manganese­(III) ions are doubly bridged, involving phenolate or ethoxide oxygen atoms. The magnetochemical analysis reveals the presence of global antiferromagnetic interactions among the spin centers at low temperatures in all the four compounds. AC susceptibility measurements show the presence of temperature dependent out-of-phase <i>ac</i> signal for compounds <b>2</b> and <b>4</b> indicating an SMM behavior