Oximato-Based Ligands in 3 d/4 f-Metal Cluster Chemistry: A Family of {Cu3Ln} Complexes with a "Propeller"-like Topology and Single-Molecule Magnetic Behavior

A new family of heterometallic [Cu6M4] (M = Gd, Tb, Dy and Y) clusters derived from the combined use of selected pyridyl poly-alcohol ligands

The combined use of 2-(2-pyridyl)-1,3-propane-diol (pypdH2) and 2-hydroxymethyl-2-(2-pyridyl)-1,3-propane-diol (pyptH3) in Cu2+/4f chemistry has afforded a new family of isostructural [Cu6M4(pypt)4(pypdH)4(NO3)8] [M = Gd (1), Tb (2), Dy (3), and Y (4)] complexes. These compounds are based on an unprecedented three-layered symmetric [Cu6M4(μ-OR)16]8+ structural core, formed from the connection of the metal ions by bridging alkoxide arms of the organic ligands. Direct current magnetic susceptibility studies for complexes 1-3 revealed the presence of dominant ferromagnetic exchange interactions, suggesting the existence of large spin ground state values. Alternating current magnetic studies indicate the presence of slow-magnetic relaxation in 1-3.

Photoluminescence and magnetic properties of isostructural europium(III), gadolinium(III) and terbium(III) oxamate-based coordination polymers

Developing and investigating advanced multifunctional materials with magnetic properties as candidates for assembling spin qubits for quantum computing is imperative. A new polytopic ligand based on oxamate and aniline was used to promote the synthesis of three neutral homometallic lanthanide-coordinated polymers. New complexes with the formula {Ln(phox)3(DMSO)2(H2O)}n, where Ln = Eu3+ (1), Gd3+ (2), and Tb3+ (3) [phox = N-(phenyl)oxamate and DMSO = dimethylsulfoxide], were synthesized and well characterized by spectroscopic methods as well as X-ray crystallographic analysis. All crystalline structures comprise neutral zigzag chains. The lanthanide ions are linked by three phox ligands, in which two oxygen atoms from two different ligands are responsible for connecting the trivalent lanthanide ions, and one phox ligand completes the coordination sphere in a bis-bidentate mode, together with two DMSO molecules and one water coordination molecule. The coordination sphere of lanthanide ions consisted of spherical capped square antiprism (CSAPR-9) symmetry. The magnetic properties of 1-3 were investigated in the 2-300 K temperature range. The dynamic (ac) magnetic properties of 2 reveal a frequency dependence involving the phonon bottleneck mechanism below 33 K under nonzero applied dc magnetic fields, resulting in an example of a field-induced single-molecule magnet. Solid-state photophysical measurements for Eu3+ (1) and Tb3+ (3) complexes indicate that the N-(phenyl)oxamate ligands are very efficient in sensitizing the lanthanide(III) ions in the visible region of the electromagnetic spectrum. Compounds 1 and 3 exhibited an emission in the red and green regions, respectively. Experimental results and theoretical calculations using the Sparkle/RM1 method support a quantum efficiency of ∼72% for 1, suggesting its potential as a candidate for light conversion molecular devices (LCMDs).

Theoretical exploration of single-molecule magnetic and single-molecule toroic behaviors in peroxide-bridged double-triangular {MII3LnIII3} (M = Ni, Cu and Zn; Ln = Gd, Tb and Dy) complexes

Detailed state-of-the-art ab initio and density functional theory (DFT) calculations have been undertaken to understand both Single-Molecule Magnetic (SMM) and Single-Molecule Toroic (SMT) behaviors of fascinating 3d-4f {M3Ln3} triangular complexes having the molecular formula [MII3LnIII3(O2)L3(PyCO2)3](OH)2(ClO4)2·8H2O (with M = Zn; Ln = Dy (1), Tb (2) & Gd (3) and M = Cu; Ln = Dy (4), Tb (5) & Gd (6)) and [Ni3Ln3(H2O)3(mpko)9(O2)(NO3)3](ClO4)·3CH3OH·3CH3CN (Ln = Dy (7), Tb (8), and Gd (9)) [mpkoH = 1-(pyrazin-2-yl)ethanone oxime]. All these complexes possess a peroxide ligand that bridges the {LnIII3} triangle in a μ3-η3:η3 fashion and the oxygen atoms/oxime of co-ligands that connect each MII ion to the {LnIII3} triangle. Through our computational studies, we tried to find the key role of the peroxide bridge and how it affects the SMM and SMT behavior of these complexes. Primarily, ab initio Complete Active Space Self-Consistent Field (CASSCF) SINGLE_ANISO + RASSI-SO + POLY_ANISO calculations were performed on 1, 2, 4, 5, 7, and 8 to study the anisotropic behavior of each Ln(III) ion, to derive the magnetic relaxation mechanism and to calculate the LnIII-LnIII and CuII/NiII-LnIII magnetic coupling constants. DFT calculations were also performed to validate these exchange interactions (J) by computing the GdIII-GdIII and CuII/NiII-GdIII interactions in 3, 6, and 9. Our calculations explained the experimental magnetic relaxation processes and the magnetic exchange interactions for all the complexes, which also strongly imply that the peroxide bridge plays a role in the SMM behavior observed in these systems. On the other hand, this peroxide bridge does not support the SMT behavior. To investigate the effect of bridging ions in {M3Ln3} systems, we modeled a {ZnII3DyIII3} complex (1a) with a hydroxide ion replacing the bridged peroxide ion in complex 1 and considered a hydroxide-bridged {CoIII3DyIII3} complex (10) having the formula [Co3Dy3(OH)4(OOCCMe3)6(teaH)3(H2O)3](NO3)2·H2O. We discovered that as compared to the LoProp charges of the peroxide ion, the greater negative charges on the bridging hydroxide ion reduce quantum tunneling of magnetization (QTM) effects, enabling more desirable SMM characteristics and also leading to good SMT behavior.

Synthesis and characterization of two self-assembled [Cu6Gd3] and [Cu5Dy2] complexes exhibiting the magnetocaloric effect, slow relaxation of magnetization, and anticancer activity

Two new paths for coordination driven self-assembly reactions under the binding support of 2-((1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol (H₂L) have been discovered from the reactions of Cu(ClO₄)₂·6H₂O, NEt₃ and GdCl₃/DyCl₃·6H₂O in MeOH/CHCl₃ (2 : 1) medium. A similar synthetic protocol is useful to provide two different types of self-aggregated molecular clusters [Cu₆Gd₃(L)₃(HL)₃(μ₃-Cl)₃(μ₃-OH)₆(OH)₂]ClO₄·4H₂O (1) and [Cu₅Dy₂(L)₂(HL)₂(μ-Cl)₂(μ₃-OH)₄(ClO₄)₂(H₂O)₆](ClO₄)₂·2NHEt₃Cl·21H₂O (2). The adopted reaction procedure established the importance of the HO^- and Cl^- ions in the mineral-like growth of the complexes, derived from solvents and metal ion salts. In the case of complex 1, one Gd^III center has been trapped at the central position of the core upheld by six μ₃-OH and three μ₃-Cl groups, whereas for complex 2 one Cu^II center was trapped using four μ₃-hydroxo and two μ-chlorido groups. The magnetothermal behavior of 1 has been examined for a magnetocaloric effect of -ΔS_m = 11.3 J kg^-1 K^-1 at 2 K for ΔH = 7 T, whereas the magnetic susceptibility measurements of 2 showed slow magnetic relaxation with U_eff = 15.8 K and τ₀ = 9.8 × 10^-7 s in zero external dc field. Cancer cell growth inhibition studies proved the potential of both the complexes with interestingly high activity for the Cu₆Gd₃ complex against human lung cancer cells. Both complexes 1 and 2 also exhibited DNA and human serum albumin (HSA) binding abilities in relation to the involved binding sites and thermodynamics.

Magnetic and optical studies of a new family of multidimensional and multiproperty PO-lanthanide(III) derived systems

A new family of lanthanide compounds has been synthesized using 1,2-bis(diphenylphosphino)ethane dioxide (dppeO₂) as an O-donor ligand through the phosphoryl group to lanthanide(III) cations and structurally, magnetically and optically studied. Depending on the lanthanide, two different topologies appear: the two-dimensional structure [Ln^III(dppeO₂)_1.5(NO₃)₃(H₂O)_0.5]_n (Ln = Ce (1), Sm (2) and Dy (6)) and the one-dimensional structure [Ln(dppeO₂)(NO₃)₃DMF]_n (Ln = Eu (3), Gd (4) and Tb (5)). Some of the Ln-derived complexes have been used as structural probes, while others have been synthesized to use the specific characteristics of each cation to take advantage of their magnetic/luminescence properties. Complex 6 presents slow relaxation of the magnetization while 2, 3 and 5 present emitting properties in the visible range.

Tetranuclear [Cu3Ln] complexes derived from a tetraketone-type ligand

A series of tetranuclear [Cu₃Ln] complexes, [Cu₃Gd(L)₃(NO₃)₂(H₂O)₃](NO₃)·H₂O (1), [Cu₃Tb(L)₃(NO₃)₂(H₂O)₃](NO₃) (2) and [Cu₃Dy(L)₃(NO₃)₃(H₂O)₂]·1.5(H₂O) (3), were synthesized by a one-pot reaction using a simple tetraketone-type ligand (H₂L = (3Z,5Z)-4,5-dihydroxy-3,5-octadiene-2,7-dione). X-ray structural analyses revealed that each complex has a planar tetranuclear core of [Cu₃Ln] (Ln = Gd, Tb, and Dy), in which the Ln ion is accommodated in the centre of a Cu₃O₆ metallocycle. A cryomagnetic study revealed that all complexes show intramolecular ferromagnetic interactions between Cu(II) and Ln(III) ions. The [Cu₃Gd] complex (1) has an S_T = 5 spin ground state and shows a magneto-caloric effect with a maximum magnetic entropy change (-ΔS_m) of 16.4 J kg^-1 K^-1 (5 T, 2.4 K). On the other hand, the [Cu₃Tb] complex (2) shows a slow magnetic relaxation behavior under a zero magnetic field. The analysis of an Arrhenius plot reveals that the effective energy barrier of spin reversal is 13.1 K. The [Cu₃Dy] complex (3) also shows a slow magnetic relaxation under 1300 Oe dc magnetic field with an effective energy barrier of 6.82 K.

Metallocyclic CuII-LnIII Single-Molecule Magnets from the Self-Assembly of 1,4-Diformylnaphthalene-2,3-diol

We report the synthesis and characterization of seven new tetranuclear 3d-4f complexes derived from the 3:3:1 reaction of 1,4-diformylnaphthalene-2,3-diol (H₂ L) with copper(II) nitrate and a lanthanide salt, Ln = Tb [L ₃Cu₃TbCl₂(NO₃)₂(H₂O)₂] (C1), Ho [L ₃Cu₃HoCl₃(H₂O)₃(MeOH)](H₂O) (C2), Er [L ₃Cu₃ErCl₃(H₂O)_3.5(MeOH)_0.5](H₂O) (C3), Gd [L ₃Cu₃Gd(NO₃)₂(H₂O)₂(MeOH)](NO₃) (C4), Dy [L ₃Cu₃Dy(NO₃)₂(H₂O)₂(MeOH)](NO₃) (C5), Yb [L ₃Cu₃Yb(NO₃)₂(H₂O)₂(MeOH)](NO₃) (C6), and La [L ₃Cu₃La(NO₃)₂(H₂O)₂(MeOH)](NO₃) (C7). Structural elucidation showed that the self-assembly using the acyclic ligand system was successful for all seven complexes, which exhibit the same near-planar Cu₃LnO₁₂ core. Five complexes (C1, C2, and C4-C6) were magnetically characterized at 300 K and 1.8 K. Complexes C1, C4, and C5 were observed to have ferromagnetic ground states and showed appreciable frequency dependence in their AC magnetic measurements, which yielded effective barriers between 7.82(4) and 13.2(3) K, confirming the presence of single-molecule magnet properties.

TBN-triggered, manipulable annulations of o-hydroxyarylenaminones for divergent syntheses of oximinochromanones and oximinocoumaranones

Divergent synthesis provides an indispensable route to rapid acquisition of structurally diverse chemical scaffolds from identical starting materials. Herein, we describe unprecedented divergent annulations of o-hydroxyarylenaminones promoted by tert-butyl nitrite (TBN) under mild conditions. Two different types of benzo-oxa-heterocycle, including oximinochromanones and oximinocoumaranones, were smoothly assembled with a broad substrate scope and good functional group compatibility.

Tuning the coordination behavior of an unexplored asymmetric multidentate ligand for developing diverse heterometallic architectures with luminescent and magnetic properties

Three types of heterometallic species including metal clusters and a metal macrocycle have been developed by tuning the coordination behavior of a new asymmetric ligand with metal cations and anions.

Coordination control of a semicarbazide Schiff base ligand for spontaneous aggregation of a Ni2Ln2 cubane family: influence of ligand arms and carboxylate bridges on the organization of the magnetic core

A new family of tetranuclear [Ni₂Ln₂O₄] cubane complexes has been assembled from carbazido ligand by altering the 4f ions without changing the core topology, which provided weak ferromagnetic and antiferromagnetic interactions.

Modulating the structural topologies and magnetic relaxation behaviour of the Mn–Dy compounds by using different auxiliary organic ligands

A MnIII4Dy^III complex and a one-dimensional chain containing MnIII2Dy^III units have been obtained by using different combinations of organic ligands, and a slow magnetic relaxation behavior was observed for both complexes.

Self-assembled octanuclear [Ni5Ln3] (Ln = Dy, Tb and Ho) complexes: synthesis, coordination induced ligand hydrolysis, structure and magnetism

Octanuclear NiII5LnIII3 complexes obtained with ligand H₂L show ferromagnetic interactions for Ni₅Dy₃ and Ni₅Tb₃ while antiferromagnetic interactions for Ni₅Ho₃.