Wheel-like Ln₁₈ Cluster Organic Frameworks for Magnetic Refrigeration and Conversion of CO₂

Abstract

Two isostructural 2D MOFs ([Ln(CDA)(HCOO)(μ-OH)(HO)] , abbreviated as 1-Gd and 2-Dy) were successfully synthesized under solvothermal conditions. The self-assembly of lanthanide(III) nitrate and 1,1'-cyclopropane-dicarboxylic acid (HCDA) resulted in wheel-like Ln cluster second building units (SBU), which are further linked to six neighboring wheels to generate a 2D ordered honeycomb array. Both 1-Gd and 2-Dy exhibit high thermal stability and decompose above 330 °C. Moreover, they have good solvent stability in ten common solvents and pH stability with pH values from 1 to 13. Magnetic studies reveal that 1-Gd exhibits weak antiferromagnetic coupling between adjacent Gd ions and has a large magnetocaloric effect of 47.30 J kg K (Δ H = 7.0 T at 2 K), while 2-Dy shows ferromagnetic interaction between adjacent Dy ions. Interestingly, 1-Gd and 2-Dy can catalyze the cycloaddition of CO to epoxides under mild conditions and can be reused at least five rounds with negligible loss of catalytic performance.

Two Pairs of Chiral “Tower‐Like” Ln4Cr4 (Ln=Gd, Dy) Clusters: Syntheses, Structure, and Magnetocaloric Effect

“…For Dy , as we can see from Figure a, the χ M T value is 55.67 cm 3 K mol −1 at 300 K, producing a considerable difference from the theoretical value of 62.68 cm 3 K mol −1 at 300 K (on account of S =5/2, L =5, 6 H 15/2 , g J =4/3 per Dy 3+ and S =3/2, g =2 per Cr 3+ ion). Afterwards, the χ M T product rapidly decreases along with the temperature cooling, suggesting antiferromagnetic interactions between neighboring Dy 3+ ions, and reaches a minimum of 22.39 cm 3 K mol −1 at 1.8 K. We guess this gap of χ M T between the experimental and theoretical values is mainly due to thermal depopulation of the excited m J states of Dy 3+ ions and strong antiferromagnetic coupling interactions between metal ions . In a similar way, the susceptibility data can also fit the Curie–Weiss law with C =58.24 cm 3 K mol −1 and θ =−7.81 K (shown in Figure S8 in the Supporting Information).…”

“…Afterwards, the c M T product rapidly decreases along with the temperature cooling, suggesting antiferromagnetic interactions between neighboring Dy 3 + ions, and reachesaminimum of 22.39 cm 3 Kmol À1 at 1.8 K. We guess this gap of c M T between the experimental and theoretical values is mainly due to thermal depopulation of the excited m J states of Dy 3 + ions and strong antiferromagnetic coupling interactions between metal ions. [17] In as imilar way, the susceptibility data can also fit the Curie-Weiss law with C = 58.24 cm 3 Kmol À1 and q = À7.81 K (showninF igure S8 in the Supporting Information).…”

Synthesis, crystal structures and magnetic properties of two heterometallic {Ln8Cr4} (Ln = Gd3+ and Tb3+) complexes with one-dimensional wave chain structure

“…It exhibits a rapid increase at lower led and incline to keep jarless at 7 T. For compound 1, the magnetization reaches 52.06 Nb at 1.8 K and 7 T. In order to estimate the magnetocaloric effect, the Maxwell equation DS m (T) ¼ Ð [vM(T, H)/ vT] H dH can be applied to calculate DS m to the experimental value. 34 In Fig. 6, the magnetic entropy value has reached a value of about 14 J kg À1 K À1 at DH ¼ 3 T. At last, the observed maximum ÀDS m for compound 1 of 23.40 J kg À1 K À1 is obtained at 3.0 K for DH ¼ 7 T, which is less than the theoretical maximum entropy value is 44.39 (based on eight isolated Gd 3+ ions and four isolated Cr 3+ ions calculation), owing to the feeble antiferromagnetic interactions within the metal ions.…”

Rational Construction of an Exceptionally Stable MOF Catalyst with Metal‐Adeninate Vertices toward CO2 Cycloaddition under Mild and Cocatalyst‐Free Conditions

“…[14][15][16][17][18][19][20][21][22][23] MOFs have also been applied to CO 2 cycloaddition reactionb ut under high temperature and high CO 2 pressure. [24][25][26][27][28][29][30] However,c ocatalysts are required in most cases, which results in extra waste and environmental pollution. [31][32][33][34] To date, some strategies have been explored for the introduction of cocatalyst into MOFs by guest capture, postmodified skeleton and functionalization of organic ligands.…”