Stabilizing large easy-axis type magnetic anisotropy in molecular complexes is a challenging task, yet it is crucial for the development of information storage devices and applications in molecular spintronics. Achieving this requires a deep understanding of electronic structure and the relationships between structure and properties to develop magneto-structural correlations that are currently unexplored in the literature. Herein, a series of five-coordinate distorted square pyramidal CoII complexes [Co(L)(X2)].CHCl3 (where X = Cl (1), Br (2), or I (3)) is reported, all exhibiting easy-axis magnetic anicotropy. The size of the zero field splitting axial parameter (D) is quantitatively determined (1 = -72; 2 = -67 and 3 = -25 cm-1) using a cantilever torque magnetometry which is further firmly supported by magnetic susceptibility, and EPR measurements. The study of the magnetization relaxation dynamics reveals field-induced slow relaxation of magnetization due to the predominant Raman relaxation process. Theoretical calculations on 1-3 and optimized model complexes of 1 reveal insights into the electronic structure and highlight the impact of steric and electronic effects on modulating the D values. Overall, the studies reported pave the way for designing a new generation of CoII complexes with enhanced axiality and a lower rhombicity.

Single-molecule toroids (SMTs), with vortex-like magnetic anisotropy axes, hold promise for quantum technologies, but controlling their toroidal states on the surface remains challenging. To address this, the SMT behavior of [Dy3(µ3-OH)2L3Cl(H2O)5]Cl3 (where L = ortho-vanillin) grafted onto Au(111), MgO has been studied, and graphene surfaces in pristine form (1) and with pyrene (2) and (CH2)8S (3) linkers, using periodic density functional theory and ab initio CASSCF/RASSI-SO methods. Both pristine and chemically functionalized molecules are stable on Au(111) and graphene surfaces; however, functionalization provides higher binding energies and, in some cases, enhances the SMT properties. The MgO surface, however, is found to be unsuitable as it abstracts an H atom from the molecule, leading to the loss of its SMT characteristics. The energy gap (ΔE) between the toroidal (nonmagnetic) and spin-flip (magnetic) states in complex 1 on Au(111) and graphene surfaces are 6.9 and 6.6 cm-1, respectively. Complexes 2 on Au(111) and 3 on graphene exhibit ΔE and toroidal blocking fields of 9.8 cm-1/1.2 T and 6.8 cm-1/0.83 T, respectively, representing the highest recorded values for this class of SMTs. These findings demonstrate the potential of surface stabilization to improve the functionality and applicability of SMTs in advanced quantum technologies.

Synthesis of nonameric cationic clusters [Dy-9(acac)(16)(mu(3)-OH)(8)(mu(4)-OH)(2)]OH6H(2)O (1), [Dy8Tb (acac)(16)(mu(3)-OH)(8)(mu(4)-OH)(2)]OH2H(2)O (2), and [Gd-9(acac)(16)(mu(3)-OH)(8)(mu(4)-OH)(2)]OH6H(2)O (3) (acac = acetylacetonate) is reported. The emission spectrum of 1 shows Dy(III) ion characteristic bands assignable to the F-4(9/2) -> H-6(J) (J = 15/2 to 9/2) transitions. Emission due to both Dy(III) and Tb(III) ions is observed for 2 in the visible range, with Tb(III) specific bands appearing due to the D-5(4) -> F-7(J) (J = 6, 4, and 3) transitions. Cluster 3 exhibits a significant magnetocaloric effect (MCE), with -Delta S-m values increasing with decrease in temperature and increase in field, reaching -Delta S-m(max) = 20.98 J kg(-1) K-1 at 2 K and 9 T. Isotropic magnetic coupling constants (J(s)) in 3 derived from density functional theory (DFT) calculations reveal that the exchange interactions are antiferromagnetic and weak. Compound 3 possesses S = 7/2 ground state arising from the central Gd(III) ion along with several nested excited states due to competing antiferromagnetic interactions that yield reasonably large MCE values. Utilizing computed exchange coupling interactions, we have performed ab initio CASSCF/RASSI-SO/POL_ANISO calculations on antiferromagnetic 1 and 2 to estimate the exchange interactions using the Lines model. For 2, Dy(III)Tb(III) exchange interactions were extracted for the first time and were found to be weakly antiferromagnetically coupled.

Tetranuclear [2 x 2] square-grid-like Ln(III) clusters have been synthesized by reacting LnCl(3)6H(2)O salts with bis[alpha-hydroxy(p-bromophenyl)methyl]phosphinic acid [R2PO2H, where R = CH(OH)PhBr] and pivalic acid. Single-crystal X-ray diffraction studies show the formation of [Me4N](2)[Ln(4)(mu(2)-eta(1):eta(1)-PO2R2)(8)(eta(2)-CO2But)(4)(mu(4)-CO3)] [Ln = Er (1), Dy (2), and Tb (3)]. Direct-current studies reveal significant ferromagnetic interactions between Dy-III in 2 and Tb-III in 3 and an antiferromagnetic interaction between Er-III in 1. Dynamic magnetic susceptibility measurements confirm a single-molecule magnet (SMM) behavior in both 0 and 1200 Oe applied magnetic fields for 2. Complexes 2 and 3 show single molecular toroic (SMT) behavior with a mixed magnetic moment.

Revealing single-phase multiferroic (MF) materials in conventional bulk oxides is an exceptionally daunting task. However, achieving strong magnetoelectric (ME) coupling at room temperature (RT) in these materials is even more formidable despite their envisioned applications in multi-state memory storage devices, spintronics, magnetic field sensors, etc. The weak ME coupling in single-phase MF materials is primarily due to the ferro/antiferromagnetic ordering observed at very low temperatures, contrasting with ferroelectric ordering typically discerned at RT. These challenges can be effectively addressed by leveraging discrete molecular-based MF materials. Nonetheless, molecular-based ferroelectric materials remain in their infancy due to challenges in achieving polar point groups in these complexes. By overcoming these hurdles through meticulous molecular engineering, we have unveiled a discrete molecular complex, [CoIII3DyIII(L)6].4MeOH (Co3Dy), which exhibits an unprecedentedly strong ME coupling constant (α) value of 250 mVcm⁻¹Oe⁻¹ at RT. This robust ME coupling at or above RT presumably originates from the coupling between magnetostriction and ferroelectric phenomena observed in the paramagnetic Co3Dy complex. To demonstrate the ME coupling and harness the large α value, we have developed an ME nanogenerator device using Co3Dy to convert weak stray magnetic fields into electrical energy. This device produces an output voltage of ~ 430 mV and an output current of 0.3 µA under a small AC magnetic field amplitude of 24.2 Oe.

Metal complexes containing organic photoswitches are capable of modulating the steric and electronic environment around the metal center through photoisomerization, enabling their use in photoswitchable catalysis. Herein, we design a new class of photoswitchable tripodal tetradentate ligands L1-L3 that can readily form air-stable Cu(i) complexes (C1-PF6, C1-BF4, C2, C3). The design strategy integrates flexible spacers and phenylazopyrazole units in the same ligand framework that ensures efficient photoisomerization and sustained stability of the photoswitched state. The complexes were screened for catalyzing the CuAAC reaction between alkynes and azides and C1-PF6 was identified as a catalyst capable of exerting temporal control over the reaction through photoisomerization. Based on the optimized conditions and the substrate scope, the ZZZ (photoswitched) form of complex C1-PF6 exhibits substantially improved catalytic performance compared to its EEE (native) form. In this article, we describe detailed experimental and computational investigations aimed at understanding how photoisomerization regulates the catalytic activity of Cu(i) complexes of arylazopyrazole-based tripodal tetradentate ligands.

Molecular toroidal states have come to the forefront as candidates for next-generation quantum information devices owing to their bistability and protection from weak, short-range magnetic interactions. The protection offered by these non-magnetic vortex spin states proves to be a double-edged sword as inferring their existence in a molecular system has yet to be achieved through experimental means alone. Here, we investigate the anomalous, sickle-shaped, single-crystal magnetisation profile arising in mu-SQUID measurements of a novel CrDy3 molecule. Theoretical modelling supported by ab initio calculations demonstrates that the weak field CrDy3 spin dynamics is resultant from quantum superposition of the CrIII spin states determined by three competing interactions: (i) the alignment of the CrIII magnetic moment to the external magnetic field, (ii) the zero-field splitting of the CrIII ground quartet, and (iii) coupling to the remnant magnetisation of the toroidal ground state in the Dy3 triangle. If zero-field splitting of the central transition metal ion is quenched, it operates as a quantum spin sensor, which can be exploited to experimentally discriminate between ferrotoroidic and antiferrotoroidic ground states in MDy6 double triangle complexes through electron paramagnetic resonance experiments and single-crystal magnetisation measurements with a restricted field sweeping domain.

The reaction of bulky trimethylsilylanilide (N-TMSA) ligand with various lanthanide salts led us to isolate unusual and unique four-coordinate monomeric Ln(III) complexes which are challenging to isolate and not surprisingly rare in the literature. The single crystal X-ray diffraction unveils that all the complexes are monomeric and isostructural with the general molecular formula of [Ln(N-TMSA)3(THF)] where Ln = Dy (1) or Yb (2). Both complexes are found to possess distorted tetrahedral geometry. For all the complexes, detailed dc and ac susceptibility measurements were performed and both 1 and 2 show frequency-dependent out-of-phase susceptibility signals only in the presence of an optimum external magnetic field. The experimental observations are well supported by theoretical calculations and developed magneto-structural correlation using the various model complexes.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The {3d-4f} pentanuclear complexes with the formula [Cr(2)(III)Ln(3)(III)(PhCO2)(7)(OH)(6) ((PrO)-Pr-i)(NO3)(H2O)(3)] ((PrO)-Pr-i = isopropoxide) (where Ln = Dy (1), Gd (2)) have been synthesized and characterized using magnetic and theoretical studies. The metal core of complexes 1 and 2 has a trigonal bipyramidal arrangement with three Ln(III) ions in the triangular plane and two Cr-III ions occupying the axial positions. These ions are held together by six mu(3)-OH bridges and seven carboxylate bridges. The dc magnetic susceptibility data reveal ferromagnetic interactions presiding between Cr-III and Ln(III) ions in 1 and 2. The fitting of the susceptibility curve employing the DFT calculated J (vide infra), yield J(Gd)(-Gd)(III)(III) = +0.008 cm(-1), J(Cr)(-Gd)(III)(III) = +0.27 cm(-1), and J(Cr)(-Cr)(III)(III) = -0.007 cm(-1) for 2. The dynamic (ac) magnetic susceptibility studies on 1 indicate slow relaxation of magnetization with a U-eff value of 30.9 K (21.4 cm(-1)) and Tau(0) = 4.09 x 10(-10) s. These extracted parameters are among the highest for any reported {(CrDyIII)-Dy-III} complexes. DFT and ab initio CASSCF/RASSI-SO/SINGLE_ANISO/POLY_ANISO calculations were carried out to estimate the exchange interactions and their role in quenching the quantum tunneling of magnetization (QTM) behavior. Ab initio calculations on the Dy-III ions reveal three asymmetric Dy-III centers with the estimated single ion barrier in the range of 78-184 cm(-1), however, with a large QTM probability. Despite a triangular {Dy-3} motif, the g(zz) axes do not align in the triangular plane as observed in the {(CrDy6III)-Dy-III} single-molecule toroids (SMT) reported earlier by us. This is essentially due to the presence/absence of the (PrO-)-Pr-i/carboxylate group that alters the charge distribution around the Dy-III ion and hence the orientation of the corresponding g(zz) axis. The combination of DFT and ab initio CASSCF calculations yield J(Dy)(-Dy)(III)(III) = +0.012 cm(-1), J(Cr)(-Dy)(III)(III) = +1.20 cm(-1), and J(Cr)(-Cr)(III)(III) = -0.95 cm(-1) for 1. The mechanism of magnetization relaxation developed for the {(Cr2Dy3III)-Dy-III} cluster reveals that the relatively strong ferromagnetic Cr-III-Dy-III exchange interaction reduces the ground state QTM significantly yielding a U-eff of 38.6 cm(-1), which agrees with the experimental value. Thus, our study iterates the importance of Cr-III ion to enhance the exchange coupling in the {3d-4f} family of clusters.

A new class of photoactive and chelating ligands L1–3 and their transition metal complexes incorporated with phenylazo-3,5-dimethylpyrazole photoswitches.