Single-Ion Magnetism of the [DyIII(hfac)4]- Anions in the Crystalline Semiconductor {TSeT1.5}●+[DyIII(hfac)4]- Containing Weakly Dimerized Stacks of Tetraselenatetracene

The oxidation of tetraselenatetracene (TSeT) by tetracyanoquinodimethane in the presence of dysprosium(III) tris(hexafluoroacetylacetonate), DyIII(hfac)3, produces black crystals of {TSeT1.5}●+[DyIII(hfac)4]- (1) salt, which combines conducting and magnetic sublattices. It contains one-dimensional stacks composed of partially oxidized TSeT molecules (formal averaged charge is +2/3). Dimers and monomers can be outlined within these stacks with charge and spin density redistribution. The spin triplet state of the dimers is populated above 128 K with an estimated singlet-triplet energy gap of 542 K, whereas spins localized on the monomers show paramagnetic behavior. A semiconducting behavior is observed for 1 with the activation energy of 91 meV (measured by the four-probe technique for an oriented single crystal). The DyIII ions coordinate four hfac- anions in [DyIII(hfac)4]-, providing D2d symmetry. Slow magnetic relaxation is observed for DyIII under an applied static magnetic field of 1000 Oe, and 1 is a single-ion magnet (SIM) with spin reversal barrier Ueff = 40.2 K and magnetic hysteresis at 2 K. Contributions from DyIII and TSeT●+ paramagnetic species are seen in EPR. The DyIII ion rarely manifests EPR signals, but such signal is observed in 1. It appears due to narrowing below 30 K and has g4 = 6.1871 and g5 = 2.1778 at 5.4 K.

Heteroatom-Modulated Assembly of Hexalanthanoid-Containing Polyoxometalate-Based Coordination Networks

Two series of lanthanoid (Ln)-containing polyoxometalates (POMs) {[Ln₆(ampH)₄(H₂O)_24-n(ampH₂)_n(PW₁₁O₃₉)₂]·21H₂O (Ln = Tb, n = 0 (1), Ln = Er, n = 1 (2)) and K₂[Ln₆(ampH)₄(H₂O)₂₂(SiW₁₁O₃₉)₂]·23H₂O (Ln = Tb (3), Er (4)) (ampH₂ = (aminomethyl) phosphonic acid)} have been synthesized with tri-lacunary Keggin-type POMs containing different types of heteroatoms. Compounds 1 and 2 display neutral organic-inorganic hybrid POM molecules containing {Ln₆(ampH)₄} ({Ln₆}) cores sandwiched by two {PW₁₁O₃₉} units. By changing the heteroatoms from P^V to Si^IV, the extended 2D networks of 3 and 4 were successfully isolated where the adjacent {Ln₆} clusters were connected by {SiW₁₁O₃₉} moieties. Luminescence performances and magnetic properties of 1-4 have been systematically surveyed. The solid-state fluorescence spectra of 1-4 display characteristic emissions of Ln components resulting from the 4f-4f transitions, and energy transfer from the POM segments to Ln³⁺ centers in 1 and 3 has been observed based on the lifetime decay behaviors. Furthermore, all compounds can be utilized as electrocatalysts toward reduction of nitrite with high stability.

Synthesis of Isomeric Tb3+ -Phthalocyanine Double-Decker Complexes Depending on the Difference in the Direction of Coordination Plane and Their Magnetic Properties

A C_4h symmetrically substituted phthalocyanine, 1,8,15,22-tertrakis(2,4-dimethylpent-3-oxy)phthalocyanine (H₂ TdMPPc), was used to synthesize Tb³⁺ -phthalocyanine double-decker complexes ([Tb(TdMPPc)₂ ]s). Because H₂ TdMPPc has C_4h symmetry, S,S, R,R, and meso isomers of [Tb(TdMPPc)₂ ] were obtained depending on the difference in the direction of the coordination plane of two C_4h -type phthalocyanines with respect to a central Tb³⁺ ion. We investigated the physical properties of these [Tb(TdMPPc)₂ ] isomers, including their single-ion magnetic properties, and found that the spin-reversal energy barrier (U_eff ) of the meso isomer was apparently higher than that of the enantiomers. Detailed crystal structural analyses indicated that the meso isomer has a more symmetrical structure than do the enantiomers, thereby suggesting that the higher U_eff of the meso isomer originated from the more highly symmetrical structure.

Rare-earth based tetrapyrrolic sandwiches: chemistry, materials and applications

This review summarises advances in chemistry of tetrapyrrole sandwiches with rare earth elements and highlights the current state of their use in single-molecule magnetism, organic field-effect transistors, conducting materials and nonlinear optics.

A sextuple-decker heteroleptic phthalocyanine heterometallic samarium-cadmium complex with crystal structure and nonlinear optical properties in solution and gel glass

A sextuple-decker heteroleptic phthalocyanine heterometallic compound (1) with a subunit arrangement of {(Pc)Sm(Pc)Cd(Pc*)Cd(Pc*)Cd(Pc)Sm(Pc)} has been prepared and analyzed using various spectroscopic instruments, in which four unsubstituted phthalocyanine anions (Pc) and two substituted analogues (Pc*) with n-pentoxyl substituents at eight peripheral positions are connected through the complexation of two Sm(III) and three Cd(II) ions. In particular, its sextuple-decker structure has been disclosed by the single-crystal X-ray diffraction technique. The solution and gel glass forms of this compound display third-order nonlinear optical properties due to the intrinsic conjugated nature over the sextuple-decker sandwich complex.

cis-Silicon phthalocyanine conformation endows J-aggregated nanosphere with unique near-infrared absorbance and fluorescence enhancement: a tumor sensitive phototheranostic agent with deep tissue penetrating ability

Organic phototheranostic nanomedicines with an optimized near-infrared (NIR) biological transparent window (700-900 nm) are highly desirable for the diagnosis and treatment of deep-seated tumors in clinic. As excellent organic photosensitizers for photodynamic therapy (PDT) with outstanding photo- and thermo-stability, phthalocyanines (Pcs) have been used as the building blocks of single-component nanomedicines. However, to the best of our knowledge, all the Pc-based single-component self-assemblies reported to date are of an H-aggregate nature. This results in the simultaneous self-quenching of fluorescence emission and photodynamic activity as well as greatly reduced tissue penetration due to blue-shifted absorption. In the present work, intramolecular hydrogen bonding was formed between the two long and flexible axial NH2-terminated diethylene glycol ligands of the amphiphilic SiPc molecule (SiPc-NH2) in solution, leading to the employment of a cis-conformation of this molecule according to the 1H-NMR spectroscopy result, which as a building block then further self-assembled into monodisperse nanospheres (SiPcNano) with a J-aggregation nature on the basis of electronic absorption spectroscopic results. As a result, SiPcNano exhibited significantly enhanced red-shifted absorption in the NIR range of 750-850 nm and fluorescence emission. This in combination with the increased photodynamic effect for SiPcNano triggered by the protonation of amine groups due to the acidic nature of tumors endowed effective synergistic NIR photodynamic and photothermal effects in different cancer cells and thus effective inhibition of tumor growth in A549 tumor-bearing mice on the basis of a series of in vitro and in vivo evaluations. The present result provides a new approach for constructing novel single-component NIR organic nanomedicines for multifunctional cancer therapy.

Mononuclear Dysprosium Alkoxide and Aryloxide Single-Molecule Magnets

Recent studies have shown that mononuclear lanthanide (Ln) complexes can be high‐performing single‐molecule magnets (SMMs). Recently, there has been an influx of mononuclear Ln alkoxide and aryloxide SMMs, which have provided the necessary geometrical control to improve SMM properties and to allow the intricate relaxation dynamics of Ln SMMs to be studied in detail. Here non‐aqueous Ln alkoxide and aryloxide chemistry applied to the synthesis of low‐coordinate mononuclear Ln SMMs are reviewed. The focus is on mononuclear Dy^III alkoxide and aryloxide SMMs with coordination numbers up to eight, covering synthesis, solid‐state structures and magnetic attributes. Brief overviews are also provided of mononuclear Tb^III, Ho^III, Er^III and Yb^III alkoxide and aryloxide SMMs.

Lanthanoid Complexes as Molecular Materials: The Redox Approach

The development of molecular materials with novel functionality offers promise for technological innovation. Switchable molecules that incorporate redox-active components are enticing candidate compounds due to their potential for electronic manipulation. Lanthanoid metals are most prevalent in their trivalent state and usually redox-activity in lanthanoid complexes is restricted to the ligand. The unique electronic and physical properties of lanthanoid ions have been exploited for various applications, including in magnetic and luminescent materials as well as in catalysis. Lanthanoid complexes are also promising for applications reliant on switchability, where the physical properties can be modulated by varying the oxidation state of a coordinated ligand. Lanthanoid-based redox activity is also possible, encompassing both divalent and tetravalent metal oxidation states. Thus, utilization of redox-active lanthanoid metals offers an attractive opportunity to further expand the capabilities of molecular materials. This review surveys both ligand and lanthanoid centered redox-activity in pre-existing molecular systems, including tuning of lanthanoid magnetic and photophysical properties by modulating the redox states of coordinated ligands. Ultimately the combination of redox-activity at both ligands and metal centers in the same molecule can afford novel electronic structures and physical properties, including multiconfigurational electronic states and valence tautomerism. Further targeted exploration of these features is clearly warranted, both to enhance understanding of the underlying fundamental chemistry, and for the generation of a potentially important new class of molecular material.

The construction of dynamic dysprosium-carboxylate ribbons by utilizing the hybrid-ligand conception

By utilizing the hybrid-ligand conception, three novel dysprosium complexes Dy(2-py-4-pmc)(L)(H2O) (H2-py-4-pmc = 2-(2-pyridyl)pyrimidine-4-carboxylic acid; L = fumarate (fum, 1), succinate (suc, 2), or pimelate (pim, 3)) have been successfully synthesized. Structural analysis reveals that the dicarboxylate ligands connect 2-py-4-pmc--protected Dy3+ to form one-dimensional molecular ribbons. Magnetic measurements indicate that the three complexes exhibit typical slow magnetic relaxation under a zero dc field with effective reversal barriers Ueff of 180 K, 145 K and 137 K for 1-3, respectively, which is mainly attributed to the strong Ising anisotropy of dysprosium ions induced by the appropriate arrangement of carboxylate groups. Ab initio calculations demonstrate that the charge distribution around dysprosium ions and the magnetic interactions between them are key contributions to their different dynamic behaviour.

Blocking like it's hot: a synthetic chemists' path to high-temperature lanthanide single molecule magnets

Progress in the synthesis, design, and characterisation of single-molecule magnets (SMMs) has expanded dramatically from curiosity driven beginnings to molecules that retain magnetization above the boiling point of liquid nitrogen. This is in no small part due to the increasingly collaborative nature of this research where synthetic targets are guided by theoretical design criteria. This article aims to summarize these efforts and progress from the perspective of a synthetic chemist with a focus on how chemistry can modulate physical properties. A simple overview is presented of lanthanide electronic structure in order to contextualize the synthetic advances that have led to drastic improvements in the performance of lanthanide-based SMMs from the early 2000s to the late 2010s.

Phthalocyanine-polyoxotungstate lanthanide double deckers

Two archetypal tetradentate ligands with square donor patterns, namely phthalocyanate and monolacunary Keggin-type polyoxotungstate, coordinate to rare earth ions to yield C_s-symmetric heteroleptic double-decker complexes.

Supramolecular structures of terbium(iii) porphyrin double-decker complexes on a single-walled carbon nanotube surface

This work mainly reports the observation of novel supramolecular structures of Tb^III-5,15-bisdodecylporphyrin (BDP, C12P) double-decker complexes on the surfaces of single-walled carbon nanotubes (SWNTs) performed by scanning tunneling microscopy under an ultra-high vacuum and low temperature, atomic force microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, and ultraviolet-visible spectroscopy. The molecules formed a well-ordered self-assembled helix-shaped array with regular periodicity on the tube surface. Additionally, some magnetic properties of the BDP-molecule as well as the resulting BDP-SWNT composites were investigated by superconducting quantum interference measurements. The molecule exhibits single-molecule magnetic (SMM) properties and the composite's magnetization increases almost linearly with decreasing temperature which is possibly due to the coupling between porphyrin molecules and SWNTs. Consequently, this may enable the development of more advanced spintronic devices based on porphyrin-nanocarbon composites.

For the first time, using scanning probe microscopy, the supramolecular structures of terbium porphyrin double-decker complexes were observed on single-walled carbon nanotubes surfaces, where the molecules formed a well-ordered self-assembled array.

Bis[1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninato]terbium Double-Decker Single-Ion Magnets

For the purpose of further exploring the effect of nonperipherally attached substituents on single-ion magnet (SIMs) performance, tetrasubstituted bis[1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninato]terbium double-deckers, in both the reduced form TbH[Pc(α-OC₅H₁₁)₄]₂ (1) and the neutral form Tb[Pc(α-OC₅H₁₁)₄]₂ (2), were prepared. Single-crystal X-ray diffraction analysis for 2 unambiguously demonstrates the pinwheellike molecular structure with C₄ symmetry. Magnetic investigations of the two bis(phthalocyaninato)terbium double-deckers reveal their characteristic SIM nature. 2 exhibits SIM performance superior to that of 1, as revealed by the larger energy barrier of 466 K for the former species and 431 K for the latter species due to the presence of organic radical-f (radical-Tb) interactions. The enhanced SIM performance of 2 in comparison to 1 actually stems from the presence of radical-f interactions and an enhanced ligand field strength. The latter positive factor is indicated by the electrostatic potential around the terbium ion on the basis of density functional theory (DFT) calculations.

Solvent-tuned magnetic exchange interactions in Dy2 systems ligated by a μ-phenolato heptadentate Schiff base

A series of binuclear dysprosium compounds, namely, [Dy(api)]₂ (1), [Dy(api)]₂·2CH₂Cl₂ (2), [Dy(Clapi)]₂·2C₄H₈O (3), and [Dy(Clapi)]₂·2C₃H₆O (4) (H₃api = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazoline; H₃Clapi = 2-(2′-hydroxy-5′-chlorophenyl)-1,3-bis[3′-aza-4′-(2′′-hydroxy-5′′-chlorophenyl)prop-4′-en-1′-yl]-1,3-imidazolidine), have been isolated by the reactions of salen-type ligands H₃api/H₃Clapi with DyCl₃·6H₂O in different solvent systems. Structural analysis reveals that each salen-type ligand provides a heptadentate coordination pocket (N₄O₃) to encapsulate a Dy^III ion and all of the Dy^III centers in 1–4 adopt a distorted square antiprism geometry with D_4d symmetry. Magnetic studies showed that compound 1 did not exhibit single-molecule magnetic (SMMs) behavior. With the introduction of different lattice solvents, compounds 2–4 showed filed-induced slow magnetic relaxation with barriers U_eff of 18.2 K (2), 28.0 K (3) and 16.4 K (4), respectively. Ab initio calculations were employed to interpret the magnetization behavior of 1–4. The combination of experimental and theoretical data reveal the importance of the weak exchange interaction between the Dy^III ions in the observation of slow magnetic relaxation, and a relaxation mechanism has been developed to rationalize the observed difference in the U_eff values. The different lattice solvents influence Dy–O–Dy bond angles and thus alter the torsion of the square antiprism geometry, consequently resulting in distinct magnetic interactions and the magnetic behavior.

Solvent-tuning changes the magnetic exchange interaction and results in different magnetic relaxation dynamics in Dy₂ systems ligated by a μ-phenolato heptadentate Schiff base.

Hemiporphyrazine-Involved Sandwich Dysprosium Double-Decker Single-Ion Magnets

Both heteroleptic (phthalocyaninato)(hemiporphyrazinato) and homoleptic bis(hemiporphyrazinato) dysprosium double-decker complexes, Dy[H(Hp)₂] (1) and Dy[H(Pc)(Hp)] (2) (H₂Pc = metal-free phthalocyanine; H₂Hp = metal-free hemiporphyrazine), were designed, synthesized, and structurally characterized. The dysprosium center in both double-deckers are octa-coordinated with a nearly ideal square-antiprismatic coordination geometry, which provides an increased molecular anisotropy for the dysprosium ion and ensures the strengthened magnetic properties of both single-ion magnets (SIMs) in terms of coordination geometry. Magnetic studies reveal that both double-deckers exhibit typical SIM behavior with a spin reversal energy barrier of 80.1 ± 6.3 K for 1 and 57.3 ± 3.8 K for 2 as well as the hysteresis loops emerging at 3 K. In particular, introduction of two Hp ligands with four pyridine nitrogen atoms coordinated with the dysprosium spin center endows Dy[H(Hp)₂] (1) with the thus far highest energy barrier among the sandwich-type dysprosium SIMs with N₄-macrocyclic ligands, revealing the potential applications of sandwich-type lanthanide complexes with Hp ligands in molecular-based information storage.

Fabricating Bis(phthalocyaninato) Terbium SIM into Tetrakis(phthalocyaninato) Terbium SMM with Enhanced Performance through Sodium Coordination

The non-peripherally substituted 1,4,8,11,15,18,22,25-octa(butoxy)-phthalocyanine-involved unsymmetrical heteroleptic bis(phthalocyaninato) terbium double-decker, Tb(Pc){H[Pc(α-OC₄ H₉ )₈ ]} (Pc=unsubstituted phthalocyanine) (1), was revealed to exhibit typical single ion magnet (SIM) behavior with effective energy barrier, 180 K (125 cm^-1 ), and blocking temperature, 2 K, due to the severe deviation of the terbium coordination polyhedron from square-antiprismatic geometry. Fabrication of this double-decker compound into the novel tetrakis(phthalocyaninato) terbium pseudo-quadruple-decker Na₂ {Tb(Pc)[Pc(α-OC₄ H₉ )₈ ]}₂ (2) single molecule magnet (SMM) not only optimizes the coordination polyhedron of terbium ion towards the square-antiprismatic geometry and intensifies the coordination field strength, but more importantly significantly enhances the molecular magnetic anisotropy in the unsymmetrical bis(phthalocyaninato) double-decker unit, along with the change of the counter cation from H⁺ of 1 to Na⁺ of 2, leading to an significantly enhanced magnetic behavior with spin-reversal energy barrier, 528 K (367 cm^-1 ), and blocking temperature, 25 K. The present result is surely helpful towards developing novel tetrapyrrole lanthanide SMMs through rational design and self-assembly from bis(tetrapyrrole) lanthanide single ion magnet (SIM) building block.

Distribution of the unpaired electron in neutral bis(phthalocyaninato) yttrium double-deckers: An experimental and theoretical combinative investigation

The location of the unpaired electron in neutral bis(phthalocyaninato) yttrium double-decker complexes, with different substituents, has been studied on the basis of both experimental methods and density functional theory (DFT) calculations over the molecular structures, atomic charges, electronic absorption, infrared spectra, and electron paramagnetic resonance. The results reveal the location of the unpaired electron mainly on the carbon atoms of both tetrapyrrole chromophores with the population distribution obviously affected by the peripheral substituents.

Single Ion Magnets from 3d to 5f: Developments and Strategies

Single-ion magnets (SIMs), exhibiting slow magnetization relaxation in the absence of the magnetic field, originate from their single spin-carrier centre. In pursuit of high-performance magnetic properties, such as high spin-reversal barrier and high blocking temperature, various metal centres were investigated to establish SIMs, including 3d and 5d transition metal ions, 4f lanthanide ions, and 5f actinide ions, which possess unique zero-field splitting and magnetic properties. Therefore, proper ligand field is of great importance to different types of metals. In the given great breakthroughs since the first SIM, [Pc₂ Tb]^- (Pc=dianion of phthalocyanine), was reported, strategies of ligand field design have emerged. In this review, the developments of SIMs with different metal centres are summarized, as well as the possible strategies.

Modulating the Magnetic Interaction in New Triple-Decker Dysprosium(III) Single-Molecule Magnets

A new type of dinuclear dysprosium(III) complex based on phthalocyanine and salicylaldehyde derivatives (HL-R), [Dy₂(Pc)₂(L-R)₂(H₂O)]·2THF (R = OCH₃ (1), OC₂H₅ (2); H₂Pc = phthalocyanine; HL-OCH₃ = 2-hydroxy-3-methoxybenzaldehyde; HL-OC₂H₅ = 3-ethoxy-2-hydroxybenzaldehyde), was successfully synthesized and structurally characterized. Complex 1 features a sandwich-type triple-decker structure, where two coplanar L-OCH₃ ligands lie in the middle layer shared by two eight-coordinated Dy^III ions and two Pc ligands are located in the outer layer. In 2, the introduction of an ethoxy group generates a noncoordination mode for the O_alkoxy atom. Magnetic studies indicate that complex 1 behaves as a zero-field single-molecule magnet with a higher energy barrier, while 2 exhibits a fast tunneling relaxation process. Theoretical calculations revealed that changes in the ligand field environment around Dy^III ions can significantly affect the arrangement of the main magnetic axes and further result in distinct magnetic interactions as well as different relaxation behaviors.

Single-ion magnets with D4d symmetry based on electron-donating β-diketonate Dy(iii) complexes

Four single-ion magnets based on electron-donating β-diketonate Dy(iii) complexes have been designed and isolated to explore the magnetism–structure relationship.

Heteroleptic chiral bis(phthalocyaninato) terbium double-decker single-ion magnets

Chiral binaphthyl and dibutylamino were incorporated onto the periphery of the bis(phthalocyaninato) terbium SIM, confirming the effectiveness of tuning the double-decker SIM peroperties thorugh tuning the molecular magnetic anisotropy.

Elucidation of the two-step relaxation processes of a tetranuclear dysprosium molecular nanomagnet through magnetic dilution

A new centrosymmetric tetranuclear aggregate [Dy₄(L)₂(OAc)₈(CH₃OH)₂] (1) was assembled using a unique symmetrical Schiff base ligand 1,5-bis(salicylidene)-carbohydrazide (H₂L).

Chiral bis(phthalocyaninato) terbium double-decker compounds with enhanced single-ion magnetic behavior

Introducing chirality into bis(phthalocyaninato) terbium single-ion magnets was revealed to be an alternative method towards enhancing magnetic behavior.

A New Bis(phthalocyaninato) Terbium Single-Ion Magnet with an Overall Excellent Magnetic Performance

Bulky and strong electron-donating dibutylamino groups were incorporated onto the peripheral positions of one of the two phthalocyanine ligands in the bis(phthalocyaninato) terbium complex, resulting in the isolation of heteroleptic double-decker (Pc)Tb{Pc[N(C₄H₉)₂]₈} {Pc = phthalocyaninate; Pc[N(C₄H₉)₂]₈ = 2,3,9,10,16,17,23,24-octakis(dibutylamino)phthalocyaninate} with the nature of an unsymmetrical molecular structure, a square-antiprismatic coordination geometry, an intensified coordination field strength, and the presence of organic radical-f interaction. As a total result of all these factors, this sandwich-type tetrapyrrole lanthanide single-ion magnet (SIM) exhibits an overall enhanced magnetic performance including a high blocking temperature (T_B) of 30 K and large effective spin-reversal energy barrier of U_eff = 939 K, rendering it the best sandwich-type tetrapyrrole lanthanide SIM reported thus far.

Marriage of phthalocyanine chemistry with lanthanides: a single-ion magnet with a blocking temperature up to 25 K

A combination of rich phthalocyanine chemistry such as peripheral substitution and the unique properties of lanthanides to enhance organic radical-f interaction is expected to afford new SIMs with a higher working temperature.