Abstract
The syntheses, structures, magnetic and thermodynamic properties of three related triethanolamine-based GdIII complexes are described. The smallest, a dimer ([Gd2]), can be viewed as the subunit from which the two larger complexes, a linear tetramer ([Gd2]2) and a cyclic hexamer ([Gd2]3), are composed by further deprotonation of the triethanolamine ligand. In all cases, nearest neighbour magnetic ions are weakly correlated by antiferromagnetic isotropic exchange, whose strength does not change significantly from one complex to another; J ranging from -0.10 to -0.13 cm-1. Therefore, rather than the strength of the coupling, it is the spin topology that is the dominant factor in determining the differences between the physical properties - specifically, the nuclearity and the transition from open (dimer and tetramer) to cyclic (hexamer) boundary conditions. Indeed the hexanuclear wheel reaches the continuum limit of classical Heisenberg spin chains. In terms of the magnetocaloric properties, the smaller the nuclearity, the larger the magnetic entropy and adiabatic temperature changes.
Highlights
Molecule-based materials consist of molecular building blocks that can be linked together in various ways to create larger, more complex 0–3D species
Chemical synthesis is a powerful tool because it can lead to a bottom-up approach to examining magnetic interactions in a controlled fashion and, as such, to materials with designer properties.[2]
The GdIII ions are bridged by two μ-O-atoms (O1 and symmetry equivalent (s.e.)) derived from the sole deprotonated arm of two triethanolamine ligands to form a planar [Gd2O2]4+ motif
Summary
Molecule-based materials consist of molecular building blocks that can be linked together in various ways to create larger, more complex 0–3D species. The reaction of Gd(NO3)3·6H2O with H3tea in the presence of 1 equivalent of base (acetate) in methanol results in the formation of the alkoxide bridged gadolinium dimer [Gd(H2tea) (NO3)2]2·2MeOH (1·2MeOH, Fig. 1; see the Experimental section for full details).
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