As a consequence of increasing global energy demand and depleting fossil fuels, artificial photosynthesis, i.e., subsequent photocatalytic water oxidation and CO2 reduction, has become significant for providing renewable energy. To...

Three complexes bearing the molecular formula [Fe(X‐OMe‐SalEen)2]NCY⋅nH2O; X=6, Y=S, n=0 (1); X=5, Y=S, n=1.5 H2O (2) and X=4, Y=Se, n=0 (3), where 6‐OMe‐SalEen=2‐((E)‐(2‐(ethylamino)ethylimino)methyl)‐6‐methoxyphenol, 5‐OMe‐SalEen=2‐((E)‐(2‐(ethylamino)ethylimino)methyl)‐5‐methoxyphenol, and 4‐OMe‐SalEen=2‐((E)‐(2‐(ethylamino)ethylimino)methyl)‐4‐methoxyphenol, have been synthesized, characterized and their spin crossover behavior has been studied. The ligands differ in the position of the methoxy group (ortho, meta, and para) of the phenoxide ring directly bonded to the Fe center. Complex 1 and 3 comprise FeIII centers, whereas rare crystallographically independent high‐spin and low‐spin FeIII centers are present in complex 2. Complex 1 shows a sharp and hysteric spin crossover behavior with a hysteresis loop having 4 K width. Complex 2 shows spin crossover for the FeIIILS in solvated form which after desolvation becomes stable at the high spin. Complex 3 shows abrupt and incomplete spin crossover above room temperature. Magneto‐structural correlation and UV‐Vis spectroscopy have been done to study spin‐crossover behavior and the spin transition temperature of the complexes.

Three heterometallic hexanuclear 3d–4f complexes bearing the formula [Cu2(L)2Ln4(L)4(o‐van)2] [L=2‐((E)‐((2‐hydroxyphenyl)imino]methyl)phenol; o‐van=ortho‐vanillin] (LnIII=GdIII (1), DyIII (2), and TbIII (3)) have been synthesized and characterized. DC magnetic susceptibility measurements reveal overall antiferromagnetic interactions in 1 and 3, whereas co‐existence of ferro‐ as well as antiferromagnetic interactions were observed in 2. The magnetocaloric effect has been observed for 1 with an entropy change (−ΔSm) of 22.3 J kg−1 K−1 at 3 K and 7 T. Zero‐field single molecule magnet (SMM) behaviour has been observed for 2, where Raman relaxation and quantum tunneling of magnetization (QTM) played a role in magnetization relaxation. The Cu−O−Ln angle well explains the magnetic exchange coupling occurring in the complexes. BS‐DFT calculation for the complexes provides an estimate of the exchange interactions between the paramagnetic centres. Ab initio calculations performed for complex 2 established a good correlation to the experimental relaxation dynamics.

Herein, two polyoxometalate (POM)-ligated tetranuclear rare-earth metal complexes having the molecular formula [Cs x K 24−x {Ln 4 (H 2 O) 8 (α-AsW 9 O 33 ) 4 }]•yH 2 O {x = 5, y = 20, and Ln = Tb(III) (1); and x = 6, y = 28, and Ln = Dy(III) (2)} were synthesized by a one-pot reaction with LnCl 3 •6H 2 O using di-lacunary [As 2 W 19 O 67 (H 2 O)] 14− precursor and characterized. The structural analysis shows that the building units [α-AsW 9 O 33 ] 9− are bridged by four rare-earth ions, where one [α-AsW 9 O 33 ] 9− bridged two Ln(III) centers asymmetrically by μ 2 -O and terminal oxygen atoms. The [α-AsW 9 O 33 ] 9− units are orthogonal to each other, resembling as vanes of a windmill. The magnetic studies disclosed the presence of large magnetic anisotropy and slow relaxation of magnetization behavior [U eff = 15.2 K (1) and 26 K (2)] in the absence of an external magnetic field. Detailed analysis of relaxation dynamics confirmed that the QTM process in 2 (τ QTM = 2.50 × 10 −4 s) is slower as compared to complex 1 (τ QTM = 2.38 × 10 −4 s), and the relaxation process mainly follows the shortcut pathways (such as QTM, optical, and acoustic phonon process) rather than the thermally activated Orbach process. Further, the ab initio calculations show high axial ground states with minimum transverse anisotropy and provide a good agreement between calculated and experimental magnetic data for both complexes. It has also been observed that the local symmetry (D 4d subgroup) around the metal centers in 1 provides higher axiality and stabilizes m J = ±6 of Tb(III) more as compared to m J = ±15/2 of Dy (III) in 2, resulting in higher energy splitting of the ground state in the former complex. The combined experimental and theoretical observations suggest that the high axial nature of the ground state with minimum transverse anisotropy resulting from local ligand field symmetry is responsible for the observed zero-field single-molecule magnet (SMM) behavior in the studied complexes. Notably, complex 1 is the first example of a POM-based terbium complex that shows SMM behavior in the absence of an external field.

Polyoxometalates (POM), as an inorganic polydentate oxygen donor, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with interesting structures and attractive properties. Herein, we...