Holmium (Ho) is a lanthanide element with a high magnetic moment. Here, we create an amorphous metalorganic framework (MOF) that has no long-range periodic order but retains the basic components of MOF by using isophthalic acid as an organic linker and Ho as a metal species. The resulting spherical Ho-MOF particles disperse well in a solvent and exhibit excellent magnetic properties in response to magnets. Since Ho has almost no coloring, Ho-MOF particles are a colorless magnetic material, unlike conventional iron oxide particles. Taking advantage of the colorless property, the selective adsorption of dyes on Ho-MOF particles can be easily visually confirmed by magnetically separating the particles. In addition, present versatile processes that enable adaptation of lanthanide elements other than Ho enable the development of colorless multifunctional MOF particles.

The seven-coordinate Ho(III) aqua-tris-(dibenzoylmethane)(DBM) complex, referred to as Ho-(DBM) 3 • H 2 O, was first reported in the late 1960s. It has a threefold symmetric structure, with Ho at the center of three dibenzoylmethane ligands and hydrogen-bonded water to ligands. It is considered that the hydrogen bonds between the water molecule and the ligands surrounding Ho play an important role in the formation of its symmetrical structure. In this work, we developed new force-field parameters for classical molecular dynamics (CMD) simulations to theoretically elucidate the structure and dynamics of Ho-(DBM) 3 •H 2 O. To develop the force field, structural optimization and molecular dynamics were performed on the basis of ab initio calculations using the plane-wave pseudopotential method. The force-field parameters for CMD were then optimized to reproduce the data obtained from ab initio calculations. Validation of the developed force field showed good agreement with the experimental crystalline structure and ab initio data. The vibrational properties of water in Ho-(DBM) 3 •H 2 O were investigated by comparison with bulk liquid water. The vibrational motion of water was found to have a characteristic mode originating from stationary rotational motion along the c-axis of Ho(III) aqua-tris(dibenzoylmethane). Contrary to expectations, the hydrogen-bond dynamics of water in Ho-(DBM) 3 •H 2 O were found to be almost equivalent to those of bulk liquid water except for librational motion. This development route for force-field parameters for CMD and the establishment of water dynamics can advance the understanding of water-coordinated metal complexes with high coordination numbers such as Ho-(DBM) 3 •H 2 O.

The seven-coordinate Ho(III) aqua-tris(dibenzoylmethane) complex, referred to as Ho-(DBM)3.H2O, was first reported in the late 1960s. It has a three-fold symmetric structure, with Ho at the center of three {\ligand} ligands and hydrogen bonded to a water molecule. It is considered that the hydrogen bonds between the water molecule and the ligands surrounding Ho play an important role in the formation of its symmetrical structure. In this work, we developed new force-field parameters for classical molecular dynamics (CMD) simulations to theoretically elucidate the structure and dynamics of Ho-(DBM)3.H2O. To develop the force field, structural optimization and molecular dynamics were performed on the basis of ab initio calculations using the plane-wave pseudopotential method. The force-field parameters for CMD were then optimized to reproduce the data obtained from the ab initio calculations. Validation of the developed force field showed good agreement with the experimental crystalline structure and the ab initio data. The vibrational properties of water in Ho-(DBM)3.H2O were investigated by comparison with bulk liquid water. The vibrational motion of water was found to have a characteristic mode originating from stationary rotational motion along the c axis of Ho(III) aqua-tris(dibenzoylmethane). Contrary to expectations, the hydrogen-bond dynamics of water in Ho-(DBM)3.H2O were found to be almost equivalent to those of bulk liquid water except for librational motion. This development route for force-field parameters for CMD and the establishment of water dynamics can advance the understanding of water-coordinated metal complexes with high coordination numbers such as Ho-(DBM)3.H2O.

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