Single-Ion Behavior in New 2-D and 3-D Gadolinium 4f7 Materials: CsGd(SO4)2 and Cs[Gd(H2O)3(SO4)2]·H2O

The recent creation of 4f7 gadolinium materials has enabled vital studies of the free-ion properties of the Gd(III) cations. While the 8S ground state in a trivalent Gd compound is, in principle, isotropic, it has been demonstrated that there is a residual orbital angular momentum affected by the crystal field and structural distortion in certain systems. By exploiting the atomistic control innate to material growth, we address a fundamental question of how the isotropic nature of Gd(III) is preserved in different dimensionalities of crystal structures. To achieve this, we designed two new trivalent Gd materials possessing two structurally distinct features, a 2-D CsGd(SO4)2 and a 3-D Cs[Gd(H2O)3(SO4)2]·H2O. The tunability of the structural dimension is facilitated by O–H---O hydrogen bonds. The structural divergence between the two compounds allows us to investigate each material individually and make a comparison between them regarding their physical properties as a function of lattice dimension. Our results demonstrate that structural dimensions have a negligible effect on the single-ion behavior of the materials. Magnetization measurements for the Gd(III) complexes yielded paramagnetic states with the isotropic spin-only nature. Specific heat data suggest that there is a lack of magnetic phase transition down to T = 1.8 K, and coupled lattice vibrations in the materials are attributable to strong covalent bonding characters of the (SO4)2– and H2O ligands. This work offers a pathway for retaining the single-ion property of Gd(III) while constructing the large spin magnetic moment S = 7/2 in large-scale extended frameworks.