Methylamine Separations Enabled by Cooperative Ligand Insertion in Copper–Carboxylate Metal–Organic Frameworks

Monomethylamine (NH2CH3), dimethylamine (NH(CH3)2), and trimethylamine (N(CH3)3) are important chemical feedstocks that are produced industrially as an azeotropic mixture and must be separated using an energy-intensive thermal distillation. While solid adsorbents have been proposed as alternatives to distillation for separating various industrial gas mixtures, methylamine separations remain largely unexplored in this context. Here, we investigate two isoreticular frameworks Cu(cyhdc) (cyhdc2- = trans-1,4-cyclohexanedicarboxylate) and Cu(bdc) (bdc2- = 1,4-benzenedicarboxylate) as prospective candidates for this challenging separation, motivated by the recent discovery that Cu(cyhdc) reversibly captures ammonia through a unique framework-to-coordination polymer phase change. Through a combination of gas adsorption and powder X-ray diffraction analyses, we find that Cu(cyhdc) and Cu(bdc) reversibly bind large quantities of mono- and dimethylamine through framework-to-coordination polymer phase change mechanisms, although both frameworks adsorb only moderate amounts of trimethylamine via physisorption. Single-crystal X-ray diffraction analysis of select mono- and dimethylamine containing phases suggests that the number of hydrogen bond donors available and the linker donor strength are key factors influencing amine uptake. Finally, investigation of the tricomponent adsorption behavior of both materials reveals that Cu(cyhdc) is selective for the capture of monomethylamine from a range of mono-, di-, and trimethylamine mixtures

[UF6](2-): A molecular hexafluorido actinide(IV) complex with compensating spin and orbital magnetic moments

The first structurally characterized hexafluorido complex of a tetravalent actinide ion, the [UF6]2- anion, is reported in the (NEt4)2[UF6]2H2O salt (1). The weak magnetic response of 1 results from both U(IV) spin and orbital contributions, as established by combining X-ray magnetic circular dichroism (XMCD) spectroscopy and bulk magnetization measurements. The spin and orbital moments are virtually identical in magnitude, but opposite in sign, resulting in an almost perfect cancellation, which is corroborated by ab initio calculations. This work constitutes the first experimental demonstration of a seemingly non-magnetic molecular actinide complex carrying sizable spin and orbital magnetic moments

Magnetic Blocking at 10 K and a Dipolar-Mediated Avalanche in Salts of the Bis(η⁸‑cyclooctatetraenide) Complex [Er(COT)₂]⁻

The structures and magnetic properties of [K­(18-crown-6)]⁺ (<b>1</b>) and [K­(18-crown-6)­(THF)₂]⁺ (<b>2</b>) salts of the η⁸-cyclooctatetraenide sandwich complex [Er­(COT)₂]⁻ (COT^2– = cyclooctatetraene dianion) are reported. Despite slight differences in symmetry, both compounds exhibit slow magnetic relaxation under zero applied dc field with relaxation barriers of ∼150 cm^–1 and waist-restricted magnetic hysteresis. Dc relaxation and dilution studies suggest that the drop in the magnetic hysteresis near zero field is influenced by a bulk magnetic avalanche effect coupled with tunneling of the magnetization. Through dilution with [K­(18-crown-6)­(THF)₂]­[Y­(COT)₂] (<b>3</b>), these phenomena are substantially quenched, resulting in an open hysteresis loop to 10 K. Importantly, this represents the highest blocking temperature yet observed for a mononuclear complex and the second highest for any single-molecule magnet. A comprehensive comparative analysis of the magnetism of [K­(18-crown-6)]­[Ln­(COT)₂] (Ln = Sm, Tb, Dy, Ho, Yb) reveals slow relaxation only for [K­(18-crown-6)]­[Dy­(COT)₂] (<b>4</b>) with weak temperature dependence. Collectively, these results highlight the utility of an equatorial ligand field for facilitating slow magnetic relaxation in the prolate Er^III ion

Magnetic Blocking at 10 K and a Dipolar-Mediated Avalanche in Salts of the Bis(η⁸‑cyclooctatetraenide) Complex [Er(COT)₂]⁻

The structures and magnetic properties of [K­(18-crown-6)]⁺ (<b>1</b>) and [K­(18-crown-6)­(THF)₂]⁺ (<b>2</b>) salts of the η⁸-cyclooctatetraenide sandwich complex [Er­(COT)₂]⁻ (COT^2– = cyclooctatetraene dianion) are reported. Despite slight differences in symmetry, both compounds exhibit slow magnetic relaxation under zero applied dc field with relaxation barriers of ∼150 cm^–1 and waist-restricted magnetic hysteresis. Dc relaxation and dilution studies suggest that the drop in the magnetic hysteresis near zero field is influenced by a bulk magnetic avalanche effect coupled with tunneling of the magnetization. Through dilution with [K­(18-crown-6)­(THF)₂]­[Y­(COT)₂] (<b>3</b>), these phenomena are substantially quenched, resulting in an open hysteresis loop to 10 K. Importantly, this represents the highest blocking temperature yet observed for a mononuclear complex and the second highest for any single-molecule magnet. A comprehensive comparative analysis of the magnetism of [K­(18-crown-6)]­[Ln­(COT)₂] (Ln = Sm, Tb, Dy, Ho, Yb) reveals slow relaxation only for [K­(18-crown-6)]­[Dy­(COT)₂] (<b>4</b>) with weak temperature dependence. Collectively, these results highlight the utility of an equatorial ligand field for facilitating slow magnetic relaxation in the prolate Er^III ion

Magnetic Blocking at 10 K and a Dipolar-Mediated Avalanche in Salts of the Bis(η⁸‑cyclooctatetraenide) Complex [Er(COT)₂]⁻

The structures and magnetic properties of [K­(18-crown-6)]⁺ (<b>1</b>) and [K­(18-crown-6)­(THF)₂]⁺ (<b>2</b>) salts of the η⁸-cyclooctatetraenide sandwich complex [Er­(COT)₂]⁻ (COT^2– = cyclooctatetraene dianion) are reported. Despite slight differences in symmetry, both compounds exhibit slow magnetic relaxation under zero applied dc field with relaxation barriers of ∼150 cm^–1 and waist-restricted magnetic hysteresis. Dc relaxation and dilution studies suggest that the drop in the magnetic hysteresis near zero field is influenced by a bulk magnetic avalanche effect coupled with tunneling of the magnetization. Through dilution with [K­(18-crown-6)­(THF)₂]­[Y­(COT)₂] (<b>3</b>), these phenomena are substantially quenched, resulting in an open hysteresis loop to 10 K. Importantly, this represents the highest blocking temperature yet observed for a mononuclear complex and the second highest for any single-molecule magnet. A comprehensive comparative analysis of the magnetism of [K­(18-crown-6)]­[Ln­(COT)₂] (Ln = Sm, Tb, Dy, Ho, Yb) reveals slow relaxation only for [K­(18-crown-6)]­[Dy­(COT)₂] (<b>4</b>) with weak temperature dependence. Collectively, these results highlight the utility of an equatorial ligand field for facilitating slow magnetic relaxation in the prolate Er^III ion

Magnetic Blocking at 10 K and a Dipolar-Mediated Avalanche in Salts of the Bis(η⁸‑cyclooctatetraenide) Complex [Er(COT)₂]⁻

The structures and magnetic properties of [K­(18-crown-6)]⁺ (<b>1</b>) and [K­(18-crown-6)­(THF)₂]⁺ (<b>2</b>) salts of the η⁸-cyclooctatetraenide sandwich complex [Er­(COT)₂]⁻ (COT^2– = cyclooctatetraene dianion) are reported. Despite slight differences in symmetry, both compounds exhibit slow magnetic relaxation under zero applied dc field with relaxation barriers of ∼150 cm^–1 and waist-restricted magnetic hysteresis. Dc relaxation and dilution studies suggest that the drop in the magnetic hysteresis near zero field is influenced by a bulk magnetic avalanche effect coupled with tunneling of the magnetization. Through dilution with [K­(18-crown-6)­(THF)₂]­[Y­(COT)₂] (<b>3</b>), these phenomena are substantially quenched, resulting in an open hysteresis loop to 10 K. Importantly, this represents the highest blocking temperature yet observed for a mononuclear complex and the second highest for any single-molecule magnet. A comprehensive comparative analysis of the magnetism of [K­(18-crown-6)]­[Ln­(COT)₂] (Ln = Sm, Tb, Dy, Ho, Yb) reveals slow relaxation only for [K­(18-crown-6)]­[Dy­(COT)₂] (<b>4</b>) with weak temperature dependence. Collectively, these results highlight the utility of an equatorial ligand field for facilitating slow magnetic relaxation in the prolate Er^III ion

Magnetic Blocking at 10 K and a Dipolar-Mediated Avalanche in Salts of the Bis(η⁸‑cyclooctatetraenide) Complex [Er(COT)₂]⁻

The structures and magnetic properties of [K­(18-crown-6)]⁺ (<b>1</b>) and [K­(18-crown-6)­(THF)₂]⁺ (<b>2</b>) salts of the η⁸-cyclooctatetraenide sandwich complex [Er­(COT)₂]⁻ (COT^2– = cyclooctatetraene dianion) are reported. Despite slight differences in symmetry, both compounds exhibit slow magnetic relaxation under zero applied dc field with relaxation barriers of ∼150 cm^–1 and waist-restricted magnetic hysteresis. Dc relaxation and dilution studies suggest that the drop in the magnetic hysteresis near zero field is influenced by a bulk magnetic avalanche effect coupled with tunneling of the magnetization. Through dilution with [K­(18-crown-6)­(THF)₂]­[Y­(COT)₂] (<b>3</b>), these phenomena are substantially quenched, resulting in an open hysteresis loop to 10 K. Importantly, this represents the highest blocking temperature yet observed for a mononuclear complex and the second highest for any single-molecule magnet. A comprehensive comparative analysis of the magnetism of [K­(18-crown-6)]­[Ln­(COT)₂] (Ln = Sm, Tb, Dy, Ho, Yb) reveals slow relaxation only for [K­(18-crown-6)]­[Dy­(COT)₂] (<b>4</b>) with weak temperature dependence. Collectively, these results highlight the utility of an equatorial ligand field for facilitating slow magnetic relaxation in the prolate Er^III ion

Magnetic Blocking at 10 K and a Dipolar-Mediated Avalanche in Salts of the Bis(η⁸‑cyclooctatetraenide) Complex [Er(COT)₂]⁻

The structures and magnetic properties of [K­(18-crown-6)]⁺ (<b>1</b>) and [K­(18-crown-6)­(THF)₂]⁺ (<b>2</b>) salts of the η⁸-cyclooctatetraenide sandwich complex [Er­(COT)₂]⁻ (COT^2– = cyclooctatetraene dianion) are reported. Despite slight differences in symmetry, both compounds exhibit slow magnetic relaxation under zero applied dc field with relaxation barriers of ∼150 cm^–1 and waist-restricted magnetic hysteresis. Dc relaxation and dilution studies suggest that the drop in the magnetic hysteresis near zero field is influenced by a bulk magnetic avalanche effect coupled with tunneling of the magnetization. Through dilution with [K­(18-crown-6)­(THF)₂]­[Y­(COT)₂] (<b>3</b>), these phenomena are substantially quenched, resulting in an open hysteresis loop to 10 K. Importantly, this represents the highest blocking temperature yet observed for a mononuclear complex and the second highest for any single-molecule magnet. A comprehensive comparative analysis of the magnetism of [K­(18-crown-6)]­[Ln­(COT)₂] (Ln = Sm, Tb, Dy, Ho, Yb) reveals slow relaxation only for [K­(18-crown-6)]­[Dy­(COT)₂] (<b>4</b>) with weak temperature dependence. Collectively, these results highlight the utility of an equatorial ligand field for facilitating slow magnetic relaxation in the prolate Er^III ion

Record High Single-Ion Magnetic Moments Through 4f(n)5d(1) Electron Configurations in the Divalent Lanthanide Complexes [(C5H4SiMe3)3Ln]⁻.

The recently reported series of divalent lanthanide complex salts, namely [K(2.2.2-cryptand)][Cp'3Ln] (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm; Cp' = C5H4SiMe3) and the analogous trivalent complexes, Cp'3Ln, have been characterized via dc and ac magnetic susceptibility measurements. The salts of the complexes [Cp'3Dy](-) and [Cp'3Ho](-) exhibit magnetic moments of 11.3 and 11.4 μB, respectively, which are the highest moments reported to date for any monometallic molecular species. The magnetic moments measured at room temperature support the assignments of a 4f(n+1) configuration for Ln = Sm, Eu, Tm and a 4f(n)5d(1) configuration for Ln = Y, La, Gd, Tb, Dy, Ho, Er. In the cases of Ln = Ce, Pr, Nd, simple models do not accurately predict the experimental room temperature magnetic moments. Although an LS coupling scheme is a useful starting point, it is not sufficient to describe the complex magnetic behavior and electronic structure of these intriguing molecules. While no slow magnetic relaxation was observed for any member of the series under zero applied dc field, the large moments accessible with such mixed configurations present important case studies in the pursuit of magnetic materials with inherently larger magnetic moments. This is essential for the design of new bulk magnetic materials and for diminishing processes such as quantum tunneling of the magnetization in single-molecule magnets