Field‐Induced Single‐Ion‐Magnetic Behavior of Octahedral Co^II in a Two‐Dimensional Coordination Polymer

Abstract

Two 2D coordination polymers have been synthesized by employing V-shaped flexible terpyridine-based ligand L [L = 4′-(4-methoxyphenyl)-4,2′:6′,4′′-terpyridine] as linker and M II (M = Co II , Fe II ) as nodes. Structural analysis of both complexes revealed the formation of a rare [4+4] metallocyclic unit. The extension of these cyclic units into two dimensions gives rise to an interdigitated 2D sheet structure in which the methoxy group of the ligand is oriented above and below the sheet IntroductionOver the past few decades, coordination polymers (CPs) have attracted extensive research interest owing to the variety of their architectures and intriguing topologies [1] as well as potential applications. [2] Apart from their structural role in supporting solid-state architectures, the metal ions in CPs are the source of some useful physical properties, for example, the blocking of magnetization, and molecules having such properties are known as single-molecule magnets (SMMs). [3,4] SMMs are known for their potential applications in high-density data storage, quantum computing, and molecular spintronics. [3] Recently, there has been particular interest in molecular systems with only one spin carrier, large magnetic anisotropy, no intermetallic interactions, and properties similar to SMMs called single-ion magnets (SIMs). The most interesting feature of SIMs [5] is the possibility of tuning their magnetic anisotropy through the regulation of the coordination number and ligand field. In parallel with the extensive study of lanthanide-based SIMs, [5] significant effort has also been devoted to the research of transition-metal-based SIMs. [6][7][8] A common feature of all the reported transition-metal-based SIMs is the low coordination number of the metal centers, for which the single-ion anisotropy is enhanced due to unrestricted orbital angular momentum by limiting the coordination number of the metal ion. [9] Among 3d SIMs, Co II -based complexes are the most interesting because of their non-integer spin ground state, [10] which reduces the probability of quantum tunneling of magnetization (QTM). [11] Recently, a few octahedral Co II complexes have been [a] for their helpful scientific discussions.

Field-Induced Single-Ion Magnet Behaviour in Two New Cobalt(II) Coordination Polymers with 2,4,6-Tris(4-pyridyl)-1,3,5-triazine

“…At 300 K, the χ M T values for 1 and 2 are 2.826 and 3.103 cm 3 ·mol −1 ·K, respectively, which are significantly higher than the spin-only value for a high-spin Co II ion with g = 2 (1.875 cm 3 ·mol −1 ·K). These high values can be attributed to the orbit contribution and significant spin-orbit coupling (SOC) and are comparable to the reported values (2.1-3.8 cm 3 ·mol −1 ·K) for high-spin Co II centres in the distorted octahedral geometry [11][12][13][14][15][16][17][18]. Upon cooling, the χ M T curves decrease very slowly down to the vicinity of 50 K and then abruptly decrease to 2 K, which is typical of anisotropic mononuclear Co II complexes [4].…”

“…In addition, to gain a clear scope on reported non-isolated Co II SIMs, the magnetic properties of these systems, including magnetic anisotropy parameters and energy barriers, are compiled in Table S3. From this table, we noticed that the single-ion magnetism in 1D, 2D, and 3D Co II coordination polymers with local Oh symmetry only exhibit an easy-plane type of magnetic anisotropy [11][12][13][14][15][16][17][18]. The situation in the present compounds further support this phenomenon.…”

“…For 1, the linear variation of the logarithm of relaxation times at the whole temperature region indicates a dominating Orbach relaxation. It is worth noting that such phenomena have also been observed in some other 2D Co II based SIMs with octahedral local geometry [9][10][11][12][13][14][15][16]. However, multiple relaxation pathways are strongly suggested by the curvature of the Arrhenius plot of 2.…”

“…Intense efforts have been devoted to the design and synthesis of isolated 3d SIMs with coordination numbers ranging from two to eight in various geometries [6]. Furthermore, the field-induced SIM behaviour has also been explored in some one-dimensional (1D) [7,8], two-dimensional (2D) [9][10][11][12][13][14][15][16], and even three-dimensional (3D) Co II coordination frameworks [17,18], as long as the magnetic coupling between the spin centres can be ignored. The magnetic anisotropic spin centres in the frameworks can be well isolated by organic linkers or diamagnetic cyanometallates, and thus can be regarded as isolated single-ion magnetic centres.…”

Modulating the Slow Relaxation Dynamics of Binuclear Dysprosium(III) Complexes through Coordination Geometry

“…The fit of the χ M " vs. χ M data using the generalized Debye model [31,32] produced the values of α within the ranges 0.05-0.27 (1) and 0.08-0.32 (2), signifying the narrow distribution of the relaxation time. Effective energy barrier (U eff ) and relaxation time (τ 0 ) were calculated from the Arrhenius Equation (1) [33][34][35]:…”