Magnetic Properties of Organic Molecular Crystals via an Algebraic Heisenberg Hamiltonian. Applications to WILVIW, TOLKEK, and KAXHAS Nitronyl Nitroxide Crystals

Abstract

A computational approach to the study of magnetism in molecular crystals is outlined, and applications are presented for three purely organic nitronyl nitroxide (NN) crystals: WILVIW (p-N-methylpyridiniumNN + ‚ I -), TOLKEK (R-2-hydroNN), and KAXHAS (β-p-nitrophenylNN). Data from ab initio electronic structure computations are used to parametrize an algebraic Heisenberg Hamiltonian. The magnetic susceptibility as a function of temperature χ(T) is, in turn, obtained directly from the computed energy levels of the algebraic Heisenberg Hamiltonian. The parametrization of the two site interaction parameters J AB requires the identification of the (one-, two-, or three-dimensional) magnetic motifs (e.g., spin ladders, etc.) from a study of the magnetic structure of the crystal. The energy levels of the magnetic motif are then computed as a function of the extension of the constituent magnetic building blocks along the crystallographic axes until convergence on χ(T) can be demonstrated. Rapid convergence has been demonstrated, showing that a simple model (the minimal magnetic model space) can be used as a realistic model of the magnetic motif for an infinite crystal lattice. Applications to the three organic NN crystals have demonstrated the efficacy of this theoretical approach for the simulation of the experimental magnetic susceptibility and heat capacity data.

A First-Principles Analysis of the Magnetism of CuII Polynuclear Coordination Complexes: the Case of [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4•2.5H2O

“…However, none of these computed curves fully match the experimental data, not even when applying a linear scaling factor to the energy to improve the agreement. Notably the use of similar scaling factors was previously found to induce full reproducibility of the experimental magnetic susceptibility curve in purely organic molecular magnets [4,5]. Cu4 (1) Cu4 (2) exp.…”

“…The structure of the [Cu 4 (bpy) 4 4+ cations along the bc-axes, which then stack along the a axis ( Figure 3). Figure 1 Table 1) is through-space and thus it is expected to be smaller than through-bond d 1 -d 3 pair interactions.…”

“…Our aim is to complete an initial report on this crystal [3], which was mainly addressed to defining its magnetic structure in order to adequately fit the experimental magnetic susceptibility curve. Here, we will apply our recently proposed first principles bottom-up approach [4] to the study of this crystal, thus allowing a full understanding of its magnetic properties. This is the first time we apply such methodology to crystals of polynuclear coordination complexes whose magnetic interactions are of a through-bond nature, although it has been previously shown to give appropriate descriptions of the magnetism in purely organic molecular crystals [5] and in metal containing crystals where the magnetic interaction is through-space [5].…”

“…This is the first time we apply such methodology to crystals of polynuclear coordination complexes whose magnetic interactions are of a through-bond nature, although it has been previously shown to give appropriate descriptions of the magnetism in purely organic molecular crystals [5] and in metal containing crystals where the magnetic interaction is through-space [5]. The [Cu 4 (bpy) 4 Table 1.…”

Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals

“…Cluster Heisenberg models comprising all the interactions within this limit are proposed and the corresponding Hamiltonian is then solved with the calculated exchange coupling parameters. Once the thermodynamic properties are obtained, they can be compared with the experimental values to check the validity of the model [8]. Although this approach can account for the magnetic properties of several NN-based solids, it fails to give the synthetic chemist some guidelines for the design of ferromagnetic compounds.…”