Anisotropic Change in the Magnetic Susceptibility of a Dynamic Single Crystal of a Cobalt(II) Complex

Abstract

Atypically anisotropic and large changes in magnetic susceptibility, along with a change in crystalline shape, were observed in a Co II complex at near room temperature. This was achieved by combining oxalate molecules, acting as rotor, and a Co II ion with unquenched orbital angular momentum. A thermally controlled 908 rotation of the oxalate counter anion triggered a symmetry-breaking ferroelastic phase transition, accompanied by contraction-expansion behavior (ca. 4.5 %) along the long axis of a rod-like single crystal. The molecular rotation induced a minute variation in the coordination geometry around the Co II ion, resulting in an abrupt decrease and a remarkable increase in magnetic susceptibility along the direction perpendicular and parallel to the long axis of the crystal, respectively. Theoretical calculations suggested that such an unusual anisotropic change in magnetic susceptibility was due to a substantial reorientation of magnetic anisotropy induced by slight disruption in the ideal D 3 coordination environment of the complex cation.

Influence of a Counteranion on the Zero-Field Splitting of Tetrahedral Cobalt(II) Thiourea Complexes

“…The study related to the secondary effect due to the cations and/or anions in the crystal lattice, which, in turn, can be correlated to ZFS parameter, is rare in the literature. 31,44,45 Here we aim at investigating the influence of anions present in the crystal lattice and how they alter the coordination environment around cobalt(II) centers/ZFS. We report a family of complexes with various counteranions, which are structurally characterized by single-crystal X-ray diffraction (XRD).…”

A Molecular Crystal Shows Multiple Correlated Magnetic and Ferroelectric Switchings

“…Because the principal z-axis of the g tensor (g zz ) coincides with the molecular C 3 axis parallel to the crystal long axis, the lower value of χ M T para indicates an easy-plane magnetic anisotropy of the complex cations. 35 At the phase-transition points, two stepwise magnetic anomalies are observed in the χ M T para curve. As shown in Figure 3, the χ M T para , which shows an abrupt decrease at ca.…”

“…Because the orbital angular momentum of high-spin Co(II) coordinated in a distorted trigonal antiprismatic coordination geometry is sensitive to this structural variation, the magnetic property of the single crystal is potentially switched by the minute structural change in the complex cations upon the ferroelectric structural change of the single crystal. 35,[48][49][50] Magnetic susceptibility was measured on both the single crystal and powder samples of 1 to examine the potential magnetic switching during phase transitions. As shown in Figure 3 and Supporting Information Figure S10, the magnetic susceptibility of 1 is highly anisotropic, where the χ M T value of single-crystal perpendicular to the crystal long axis (χ M T perp ) is much larger than that parallel to the single-crystal long axis (χ M T para ).…”

“…[28][29][30][31][32][33][34] Our previous study on single-crystal [Co II (en) 3 ](ox) (en = ethylenediamine; ox 2− = oxalate dianions) revealed that the unquenched orbital angular momentum of [Co II (en) 3 ] 2+ cations is highly susceptible to minor changes in coordination configuration. 35 In this compound, the order-disorder phase transition of ox 2− dianions in cavities encapsulated by five complex cations is reminiscent of the perovskite compounds that exhibit ferroelectric properties, which are derived from the polarization of dynamic molecular cations in their frameworks. 36,37 For example, several ferroelectric metal-free perovskite materials that feature ordered-disordered motion of organic cations in cavities constructed by NH 4 + and halogen anions have been synthesized.…”

Humidity Sensitive Structural Dynamics and Solvatomagnetic Effects in a 3D Co(II)-Based Coordination Polymer

“…16 The symmetrybreaking coordination environment around Co(II) ions induced by thermally activated rotation of oxalate (ox 2− ) counteranions leads to the change of anisotropic magnetic susceptibility for [Co(en) 3 ](ox). 18 Moreover, humidity-induced switching of the magnetic ordering was reported in a (Co x Mn 1−x )[Cr(CN) 6 ] 2/3 •zH 2 O network with 1/3 vacant [Cr(CN) 6 ] 3− , owing to the reversal of sublattice magnetization of Co(II) in different humidity. 20 Herein, we present a reversible two-step single-crystal-tosingle-crystal (SCSC) structural transformation of a chiral Co(II)-based framework, [Co 3 (pimda) 2 (H 2 O) 5 ] (1), triggered by the two-step release of coordinated water molecules.…”