Antimony-ligated dysprosium single-molecule magnets as catalysts for stibine dehydrocoupling

f-Element heavy pnictogen chemistry

The coordination and organometallic chemistry of the f-elements, that is group 3, lanthanide, and actinide ions, supported by nitrogen ligands, e.g. amides, imides, and nitrides, has become well developed over many decades. In contrast, the corresponding f-element chemisty with the heavier pnictogen analogues phosphorus, arsenic, antimony, and bismuth has remained significantly underdeveloped, due largely to a lack of suitable synthetic methodologies and also the inherent hard(f-element)-soft(heavier pnictogen) acid-base mismatch, but has begun to flourish in recent years. Here, we review complexes containing chemical bonds between the f-elements and heavy pnictogens from phosphorus to bismuth that spans five decades of endeavour. We focus on complexes whose identity has been unambiguously established by structural authentication by single-crystal X-ray diffraction with respect to their synthesis, characterisation, bonding, and reactivity, in order to provide a representative overview of this burgeoning area. By highlighting that much has been achieved but that there is still much to do this review aims to inspire, focus and guide future efforts in this area.

Targeted Synthesis of End-On Dinitrogen-Bridged Lanthanide Metallocenes and Their Reactivity as Divalent Synthons

High-yield syntheses of the lanthanide dinitrogen complexes [(Cp2tttM)2(μ-1,2-N2)] (1M, M = Gd, Tb, Dy; Cpttt = 1,2,4-C5tBu3H2), in which the [N2]2- ligands solely adopt the rare end-on or 1,2-bridging mode, are reported. The bulk of the tert-butyl substituents and the smaller radii of gadolinium, terbium, and dysprosium preclude formation of the side-on dinitrogen bonding mode on steric grounds. Elongation of the nitrogen-nitrogen bond relative to N2 is observed in 1M, and their Raman spectra show a major absorption consistent with N═N double bonds. Computational analysis of 1Gd identifies that the local symmetry of the metallocene units lifts the degeneracy of two 5dπ orbitals, leading to differing overlap with the π* orbitals of [N2]2-, a consequence of which is that the dinitrogen ligand occupies a singlet ground state. Magnetic measurements reveal antiferromagnetic exchange in 1M and single-molecule magnet (SMM) behavior in 1Dy. Ab initio calculations show that the magnetic easy axis in the ground doublets of 1Tb and 1Dy align with the {M-N═N-M} connectivity, in contrast to the usual scenario in dysprosium metallocene SMMs, where the axis passes through the cyclopentadienyl ligands. The [N2]2- ligands in 1M allow these compounds to be regarded as two-electron reducing agents, serving as synthons for divalent gadolinium, terbium, and dysprosium. Proof of principle for this concept is obtained in the reactions of 1M with 2,2'-bipyridyl (bipy) to give [Cp2tttM(κ2-bipy)] (2M, M = Gd, Tb, Dy), in which the lanthanide is ligated by a bipy radical anion, with strong metal-ligand direct exchange coupling.

Regulating Magnetic Relaxations of Cyano-Bridged {DyIII MoV } Systems by Tuning the N-Sites in β-Diketone Ligands

Cyano-bridged 4d-4f molecular nanomagnets have re-called increasing research interests in molecular magnetism since they offer more possibilities in achieving novel nanomagnets with versatile structures and magnetic interactions. In this work, four β-diketone ligands bearing different substitution N-sites were designed and synthesized, namely 1-(2-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL1 ), 1,3-Bis (3-pyridyl)-1,3-propanedione (HL2 ), 1-(4-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL3 ), and 1,3-Bis (4-pyridyl)-1,3-propanedione (HL4 ), to tune the magnetic relaxation behaviors of cyano-bridged {DyIII MoV } systems. By reacting with DyCl3  ⋅ 6H2 O and K4 Mo(CN)8  ⋅ 2H2 O, four cyano-bridged complexes, namely {[Dy[MoV (CN)8 ](HL1 )2 (H2 O)3 ]} ⋅ 6H2 O (1), {[Dy[MoV (CN)8 ](HL2 )(H2 O)3 (CH3 OH)]}2  ⋅ 2CH3 OH ⋅ 3H2 O (2), {[Dy[MoV (CN)8 ](HL3 )(H2 O)2 (CH3 OH)] ⋅ H2 O}n (3), and {[Dy[MoV (CN)8 ](HL4 )2 (H2 O)3 ]} ⋅ 2H2 O⋅CH3 OH (4) were obtained. Structural analyses revealed that 1 and 4 are binuclear complexes, 2 has a tetragonal structure, and 3 exhibits a stair-like polymer chain structure. The DyIII ions in all complexes have eight-coordinated configurations with the coordination spheres DyO7 N1 for 1 and 4, DyO6 N2 for 2, and DyO5 N3 for 3. Magnetic measurements indicate that 1 is a zero-field single-molecule magnet (SMM) and complexes 2-4 are field-induced SMMs, with complex 4 featuring a two-step relaxation process. The magnetic characterizations and ab initio calculations revealed that changing the N-sites in the β-diketone ligands can effectively alter the structures and magnetic properties of cyano-bridged 4d-4f nanomagnets by adjusting the coordination environments of the DyIII centers.

Structural and Magnetization Dynamics of Borohydride-Bridged Rare-Earth Metallocenium Cations

The structure and magnetic properties of the bimetallic borohydride-bridged dysprosocenium compound [{(η⁵-Cp^ttt)(η⁵-Cp^Me4t)Dy}₂(μ:κ²:κ²-BH₄)]⁺[B(C₆F₅)₄]^- ([3_Dy][B(C₆F₅)₄]) are reported along with the solution-phase dynamics of the isostructural yttrium and lutetium analogues (Cp^ttt is 1,2,4-tri(tert-butyl)cyclopentadienyl, Cp^Me4t is tetramethyl(tert-butyl)cyclopentadienyl). The synthesis of [3_M][B(C₆F₅)₄] was accomplished in the 2:1 stoichiometric reactions of [(η⁵-Cp^ttt)(η⁵-Cp^Me4t)Dy(BH₄)] (2_M) with [CPh₃][B(C₆F₅)₄], with the metallocenes 2_M obtained from reactions of the half-sandwich complexes [(η⁵-Cp^ttt)M(BH₄)₂(THF)] (1_M) (M = Y, Dy, Lu) with NaCp^Me4t. Crystallographic studies show significant lengthening of the M···B distance on moving through the series 1_M, 2_M, and 3_M, with essentially linear {M···B···M} bridges in 3_M. Multinuclear NMR spectroscopy indicates restricted rotation of the Cp^ttt ligands in 3_Y and 3_Lu in solution. The single-molecule magnet (SMM) properties of [3_M][B(C₆F₅)₄] are characterized by Raman and Orbach processes, with an effective barrier of 533(18) cm^-1 and relaxation via the second-excited Kramers doublet. Although quantum tunneling of the magnetization (QTM) was not observed for [3_M][B(C₆F₅)₄], it was, surprisingly, found in its magnetically dilute version, which has a very similar barrier of U_eff = 499(21) cm^-1. Consistent with this observation, slightly wider openings of the magnetic hysteresis loop at 2 K are found for [3_M][B(C₆F₅)₄] but not for the diluted analogue. The dynamic magnetic properties of the dysprosium SMMs and the role of exchange interactions in 3_Dy are interpreted with the aid of multireference ab initio calculations.

Magnetic hysteresis and large coercivity in bisbenzimidazole radical-bridged dilanthanide complexes

A judicious combination of radical ligands innate to diffuse spin orbitals with paramagnetic metal ions elicits strong magnetic exchange coupling which leads to properties important for future technologies. This metal-radical approach aids in effective magnetic communication of especially lanthanide ions as their 4f orbitals are contracted and not readily accessible. Notably, a high spin density on the donor atoms of the radical is required for strong coupling. Such molecules are extremely rare owing to high reactivity rendering their isolation challenging. Herein, we present two unprecedented series of bisbenzimidazole-based dilanthanide complexes [(Cp*2Ln)2(μ-Bbim)] (1-Ln = Gd, Tb, Dy, Bbim = 2,2'-bisbenzimidazole) and [K(crypt-222)][(Cp*2Ln)2(μ-Bbim˙)] -(2-Ln = Gd, Tb, Dy), where the latter contains the first Bbim3-˙ radical matched with any paramagnetic metal ion. The magnetic exchange constant for 2-Gd of J = -1.96(2) cm-1 suggests strong antiferromagnetic Gd-radical coupling, whereas the lanthanides in 1-Gd are essentially uncoupled. Ab initio calculations on 2-Tb and 2-Dy uncovered coupling strengths of -4.8 and -1.8 cm-1. 1-Dy features open hysteresis loops with a coercive field of Hc of 0.11 T where the single-molecule magnetism can be attributed to the single-ion effect due to lack of coupling. Excitingly, pairing the effective magnetic coupling with the strong magnetic anisotropy of Dy results in magnetic hysteresis with a blocking temperature TB of 5.5 K and coercive field HC of 0.54 T, ranking 2-Dy as the second best dinuclear single-molecule magnet containing an organic radical bridge. A Bbim4- species is formed electrochemically hinting at the accessibility of Bbim-based redox-active materials.

Modulation of the magnetic dynamics in two air-stable sulfur-ligated dysprosium complexes via polymerization

Two air-stable sulfur-ligated dysprosium(III) complexes [HN(Et)₃][Dy₂NaL₈] (1) and [DyNaL₄(MeOH)_x(H₂O)_2-x]_n (2) based on 2-pyridinethiol 1-oxide (HL) were synthesized and structurally characterized. Discrete 1 and polymeric 2 share the same anionic unit of [DyL₄]^- with the O₄S₄ coordination environment, but differ in the precise geometry with triangular dodecahedron geometry in 1 and biaugmented trigonal prism geometry in 2. The subtle change leads to observable temperature-independent relaxation for 2 while a faster relaxation with invisible peak for 1 at zero dc field. Under an optimal dc field, both display the typical Raman process with a smaller pre-factor and higher exponent for 2. Ab initio calculations reveal that the predicted energy barriers are 287 cm^-1 for 1 and 303 cm^-1 for 2. These results demonstrate the construction and magnetic modulation of air-stable sulfur-ligated Dy-SMM architectures.

Molecular cyclo-P3 complexes of the rare-earth elements via a one-pot reaction and selective reduction

Synthesis of new organo-lanthanide polyphosphides with an aromatic cyclo-[P₄]^2- moiety and a cyclo-[P₃]^3- moiety is presented. For this purpose, the divalent Ln^II-complexes [(NON)Ln^II(thf)₂] (Ln = Sm, Yb) ((NON)^2- = 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene) and trivalent Ln^III-complexes [(NON)Ln^IIIBH₄(thf)₂] (Ln = Y, Sm, Dy) were used as precursors in the reduction process of white phosphorus. While using [(NON)Ln^II(thf)₂] as a one-electron reducing agent the formation of organo-lanthanide polyphosphides with a cyclo-[P₄]^2- Zintl anion was observed. For comparison, we investigated a multi-electron reduction of P₄ by a one-pot reaction of [(NON)Ln^IIIBH₄(thf)₂] with elemental potassium. As products molecular polyphosphides with a cyclo-[P₃]^3- moiety were isolated. The same compound could also be obtained by reducing the cyclo-[P₄]^2- Zintl anion within the coordination sphere of Sm^III in [{(NON)Sm^III(thf)₂}₂(μ-η⁴:η⁴-P₄)]. Reduction of a polyphosphide within the coordination sphere of a lanthanide complex is unprecedented. Additionally, the magnetic properties of the dinuclear Dy^III-compound bearing a bridging cyclo-[P₃]^3- moiety were investigated.

Binuclear Triphenylantimony(V) Catecholates through N-Donor Linkers: Structural Features and Redox Properties

A series of binuclear triphenylantimony(V) bis-catecholato complexes 1–11 of the type (Cat)Ph₃Sb-linker-SbPh₃(Cat) was prepared by a reaction of the corresponding mononuclear catecholates (Cat)SbPh₃ with a neutral bidentate donor linker ligands pyrazine (Pyr), 4,4′-dipyridyl (Bipy), bis-(pyridine-4-yl)-disulfide (PySSPy), and diazobicyclo[2,2,2]octane (DABCO) in a dry toluene: Cat = 3,6-di-tert-butyl-catecholate (3,6-DBCat), linker = Pyr (1); PySSPy (2); Bipy (3); DABCO (4); Cat = 3,5-di-tert-butyl-catecholate (3,5-DBCat), linker = Bipy (5); DABCO (9); Cat = 4,5-(piperazine-1,4-diyl)-3,6-di-tert-butylcatecholate (pip-3,6-DBCat), linker = Bipy (6); DABCO (10); Cat = 4,5-dichloro-3,6-di-tert-butylcatecholate (4,5-Cl₂-3,6-DBCat), linker = Bipy (7); DABCO (11); and Cat = 4,5-dimethoxy-3,6-di-tert-butylcatecholate (4,5-(MeO)₂-3,6-DBCat), linker = Bipy (8). The same reaction of (4,5-Cl₂-3,6-DBCat)SbPh₃ with DABCO in an open atmosphere results in a formation of 1D coordination polymer {[(4,5-Cl₂-3,6-DBCat)SbPh₃·H₂O]·DABCO}_n (12). Bis-catecholate complex Ph₃Sb(Cat-Spiro-Cat)SbPh₃ reacts with Bipy as 1:1 yielding a rare macrocyclic tetranuclear compound {Ph₃Sb(Cat-Spiro-Cat)SbPh₃∙(Bipy)}₂ (13). The molecular structures of 1, 3, 4, 5, 8, 10, 12, and 13 in crystal state were established by single-crystal X-ray analysis. Complexes demonstrate different types of relative spatial positions of mononuclear moieties. The nature of chemical bonds, charges distribution, and the energy of Sb...N interaction were investigated in the example of complex 5. The electrochemical behavior of the complexes depends on the coordinated N-donor ligand. The coordination of pyrazine, Bipy, and PySSPy at the antimony atom changes their mechanism of electrooxidation: instead of two successive redox stages Cat/SQ and SQ/Cat, one multielectron stage was observed. The coordination of the DABCO ligand is accompanied by a significant shift in the oxidation potentials of the catecholate ligand to the cathodic region (by 0.4 V), compared to the initial complex.

Recent advances in heterometallic clusters with f-block metal-metal bonds: synthesis, reactivity and applications

Due to the heterometallic synergistic effects from different metals, heterometallic clusters are of great importance in small-molecule activation and catalysis. For example, both biological nitrogen fixation and photosynthetic splitting of water into oxygen are thought to involve multimetallic catalytic sites with d-block transition metals. Benefitting from the larger coordination numbers of f-block metals (rare-earth metals and actinide elements), heterometallic clusters containing f-block metal-metal bonds have long attracted the interest of both experimental and theoretical chemists. Therefore, a series of effective strategies or platforms have been developed in recent years for the construction of heterometallic clusters with f-block metal-metal bonds. More importantly, synergistic effects between f-block metals and transition metals have been observed in small-molecule activation and catalysis. This tutorial review highlights the recent advances in the construction of heterometallic molecular clusters with f-block metal-metal bonds and also their reactivities and applications. It is hoped that this tutorial review will persuade chemists to develop more efficient strategies to construct clusters with f-block metal-metal bonds and also further expand their applications with heterometallic synergistic effects.

Subcomponent self-assembly of circular helical Dy6(L)6 and bipyramid Dy12(L)8 architectures directed via second-order template effects

In situ metal-templated (hydrazone) condensation also called subcomponent self-assembly of 4,6-dihydrazino-pyrimidine, o-vanillin and dysprosium ions resulted in the formation of discrete hexa- or dodecanuclear metallosupramolecular Dy6(L)6 or Dy12(L)8 aggregates resulting from second-order template effects of the base and the lanthanide counterions used in these processes. XRD analysis revealed unique circular helical or tetragonal bipyramid architectures in which the bis(hydrazone) ligand L adopts different conformations and shows remarkable differences in its mode of metal coordination. While a molecule of trimethylamine acts as a secondary template that fills the void of the Dy6(L)6 assembly, sodium ions take on this role for the formation of heterobimetallic Dy12(L)8 by occupying vacant coordination sites, thus demonstrating that these processes can be steered in different directions upon subtle changes of reaction conditions. Furthermore, Dy6(L)6 shows an interesting spin-relaxation energy barrier of 435 K, which is amongst the largest values within multinuclear lanthanide single-molecular magnets.

Synthesis and Magnetic Properties of Antimony-Ligated Co(II) Complexes: Stibines versus Phosphines

Herein, we test the hypothesis that neutral, heavy-atom stibine donors can increase the extent of spin-orbit coupling on light, 3d transition metal. To this end, we developed a novel synthetic route toward coordinating a paramagnetic 3d metal ion─cobalt(II)─with neutral stibine ligands. Such complexes have not been reported in the literature due to the weak σ donor strength of stibines and the hard-soft mismatch between a 3d metal and a 5p ligand─which herein has been overcome using alkylated Sb donors. Magnetometry of [(SbⁱPr₂Ph)₂Co(I)₂] (1) reveals that the stibine complex 1 exhibits a higher magnitude D value (D = |24.96| cm^-1) than the spectroscopically derived value for the corresponding phosphine complex 3 (D = -13.13 cm^-1), indicative of large zero-field splitting. CASSCF/NEVPT2 calculations corroborate the experimental D values for 1 and 3, predicting D = -31.9 and -8.9 cm^-1, respectively. A re-examination of magnetic parameters across the entire series [(ER₃)₂Co(X)₂] (E = P → Sb; X = Cl → I) reveals that (i) increasingly heavy pnictogens lead to an increased X-Co-X bond angle, which is correlated with larger magnitude D values, and (ii) for a given X-Co-X bond angle, the D value is always higher in the presence of a heavy pnictogen as compared with a heavy halide. Ab initio ligand field theory calculations for 1 (stibine complex) and 3 (phosphine complex) reveal no substantial differences in spin-orbit coupling (ζ = 479.2, 480.2 cm^-1) or Racah parameter (B = 947.5, 943.9 cm^-1), an indicator of covalency. Thus, some "heavy atom effect" on the D value beyond geometric perturbation is operative, but its precise mechanism(s) of action remains obscure.

Metal–metal bond in lanthanide single-molecule magnets

This review surveys recent critical advances in lanthanide SMMs, highlighting the influences of metal–metal bonds on the magnetization dynamics.

Single-Molecule Magnets beyond a Single Lanthanide Ion: The Art of Coupling

The promising future of storing and processing quantized information at the molecular level has been attracting the study of Single-Molecule Magnets (SMMs) for almost three decades. Although some recent breakthroughs are mainly about the SMMs containing only one lanthanide ion, we believe SMMs can tell a much deeper story than the single-ion anisotropy. Here in this Perspective, we will try to draw a unified picture of SMMs as a delicately coupled spin system between multiple spin centres. The hierarchical couplings will be presented step-by-step, from the intra-atomic hyperfine coupling, to the direct and indirect intra-molecular couplings with neighbouring spin centres, and all the way to the inter-molecular and spin–phonon couplings. Along with the discussions on their distinctive impacts on the energy level structures and thus magnetic behaviours, a promising big picture for further studies is proposed, encouraging the multifaceted developments of molecular magnetism and beyond.

In this Perspective, we draw a unified picture for single-molecule magnets as delicately coupled spin systems, discuss the hierarchical couplings (from intra-atomic to inter-molecular) and their distinctive impacts on the magnetic behaviours.

Inorganometallics (Transition Metal-Metalloid Complexes) and Catalysis

While the formation and breaking of transition metal (TM)–carbon bonds plays a pivotal role in the catalysis of organic compounds, the reactivity of inorganometallic species, that is, those involving the transition metal (TM)–metalloid (E) bond, is of key importance in most conversions of metalloid derivatives catalyzed by TM complexes. This Review presents the background of inorganometallic catalysis and its development over the last 15 years. The results of mechanistic studies presented in the Review are related to the occurrence of TM–E and TM–H compounds as reactive intermediates in the catalytic transformations of selected metalloids (E = B, Si, Ge, Sn, As, Sb, or Te). The Review illustrates the significance of inorganometallics in catalysis of the following processes: addition of metalloid–hydrogen and metalloid–metalloid bonds to unsaturated compounds; activation and functionalization of C–H bonds and C–X bonds with hydrometalloids and bismetalloids; activation and functionalization of C–H bonds with vinylmetalloids, metalloid halides, and sulfonates; and dehydrocoupling of hydrometalloids. This first Review on inorganometallic catalysis sums up the developments in the catalytic methods for the synthesis of organometalloid compounds and their applications in advanced organic synthesis as a part of tandem reactions.

Imidosulfonate scorpionate ligands in lanthanide single-molecule magnet design: slow magnetic relaxation and butterfly hysteresis in [ClDy{Ph2PCH2S(NtBu)3}2]

Single-molecule magnets (SMMs) harbour vast opportunities for potential pioneering applications upon optimization like big data storage and quantum computing. Lanthanides were found to be highly suitable candidates in the design of such molecules, as they intrinsically hold a large unquenched orbital momentum and a strong spin-orbit coupling, warranting a high magnetic anisotropy. An indispensable element in successfully tailoring SMMs is the ligand design. Polyimido sulfur ligands offer a promising choice because the polar S⁺-N^--bond facilitates both electronic and geometric adaptability to various f-metals. In particular, the acute N-Ln-N bite angle generates advantageous magnetic properties. The [Ph₂PCH₂S(NtBu)₃]^- anion, introduced from [(thf)₃K{Ph₂PCH₂S(NtBu)₃}] (2) to a series of complexes [ClLn{Ph₂PCH₂S(NtBu)₃}₂] with Ln = Tb (3a), Dy (3b), Er (3c), Ho (3d), and Lu (3e), provides tripodal shielding of the metal's hemisphere as well as a side-arm donation of a soft phosphorus atom. For the Tb and Er complexes 3a and 3d, slow magnetic relaxation (U_eff = 235 and 34.5 cm^-1, respectively) was only observed under an applied dc field. The dysprosium congener 3b, however, is a true SMM with relaxation at zero field (U_eff = 66 cm^-1) and showing a butterfly hysteresis close to 3.5 K. Upon magnetic dilution with the diamagnetic and isostructural lutetium complex 3e or application of a magnetic field, the energy barrier to spin reversal is increased to 74 cm^-1.

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

Enhancing Steric Hindrance via Ligand Design in Dysprosium Complexes: From Induced Slow Relaxation to Zero-Field Single-Molecule Magnet Properties

The synthesis and magnetic characterization of three novel Dy compounds, [Dy{PPh₂S(N^tBu)₂}₂(μ-Cl₂)Li(THF)₂] (1), [Dy{PhS(N^tBu)₂}₂(μ-Cl₂)Li(THF)₂] (2), and [Dy{MeS(N^tBu)₃}₂(μ-Cl₂)Li(THF)₂] (3), based on the sulfur-nitrogen ligands RS(N^tBu)_x^- (where R = PPh₂, x = 2 for (1); R = Ph, x = 2 for (2); and R = Me, x = 3 for (3)) are reported. They represent rare examples of lanthanide-based complexes containing sulfur-nitrogen ligands, whose suitability to enhance the magnetic anisotropy in 3d metals was only recently established. Changes in the ligand field environment drastically affect the magnetic properties, with compounds 1 and 2 displaying field-induced single-molecule magnet (SMM) behavior, while compound 3 shows slow relaxation at zero field. These trends strongly suggest that ligand engineering strategies toward linear dysprosium complexes, similar to those for dysprosocenium complexes, should enhance the SMM performances of SN-based lanthanide compounds.

Stibine as a reagent in molecular chemistry - targeted synthesis of primary and secondary stibanyl-gallanes and their lighter homologues

The reactions of SbH₃ with one or two equivalents of (Dipp₂NacNac)Ga (Dipp₂NacNac = HC{C(Me)N(Dipp)}₂; Dipp = 2,6-iPr₂C₆H₃) yield the primary and secondary stibanes (Dipp₂NacNac)GaH(SbH₂) (3) and {(Dipp₂NacNac)GaH}₂(SbH) (5). Their lighter homologs were obtained from the analogous reactions with phosphine and arsine. All compounds were characterized using heteronuclear NMR-spectroscopy, IR-spectroscopy and single-crystal X-ray diffraction.

Synthesis of Unprecedented 4d/4f-Polypnictogens

A series of 4d/4f-polyarsenides, -polyarsines and -polystibines was obtained by reduction of the Mo-pnictide precursor complexes [{Cpt Mo(CO)2 }2 (μ,η2:2 -E2 )] (E=As, Sb; Cpt =tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*2 Sm] and [(CpMe4nPr )2 Sm]. For the reductive conversion of the Mo-stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo-arsenide a tetraarsacyclobutadiene and a second species with a side-on coordinated As2 2- anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.

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.

Synthesis of heteroleptic gallium-substituted antimony hydrides by stepwise β-H elimination

Heteroleptic stibanes Cp*(R)SbCl (R = Dip 1, N(SiMe₃)₂2, OB(NDipCH)₂3; Cp* = C₅Me₅; Dip = 2,6-i-Pr₂-C₆H₃) react with monovalent gallanediyl LGa (L = HC[C(Me)N(Dip)]₂) with elimination of 1,2,3,4-tetramethylfulvene, yielding heteroleptic metal-stabilized Sb hydrides [L(Cl)Ga](R)SbH (R = Dip 4, N(SiMe₃)₂5, OB(NDipCH)₂6). Compounds 1-6 were characterized by heteronuclear NMR (¹H, ¹¹B, ¹³C) and IR spectroscopy, and the solid-state structures of 4-6 were determined by single-crystal X-ray diffraction. A close correlation between the ¹H NMR chemical shift of the hydride ligand and the electronegativity of the Sb-coordinating atoms was revealed.

Hexanuclear [Cp*Dy]6 single-molecule magnet

A hexanuclear cluster [(Cp*Dy)₆K₄Cl₁₆(THF)₆], [Cp*Dy]₆, has been constructed from six {Cp*Dy^III} synthons in which the strongly coordinating Cp*^- caps determine the local anisotropy axes. Structural characterization of [Cp*Dy]₆ shows two almost parallel triangular (Cp*Dy)₃ fragments that are linked by the K⁺ and Cl^- ions. Magnetic measurements reveal slow thermal relaxation and fast quantum tunneling relaxation in the absence of an external dc field. After applying a weak dc field, the quantum tunneling relaxation is efficiently suppressed, giving a sizable energy barrier of 561 K, which represents the current record energy barrier for high nuclearity organometallic SMMs.

Slow magnetic dynamics in centrosymmetric didysprosium and equilateral triangular tridysprosium molecules

Slow magnetic dynamics were investigated in centrosymmetric didysprosium and equilateral triangular tridysprosium molecules.

Near-infrared luminescence and magnetic properties of dinuclear rare earth complexes modulated by β-diketone co-ligands

The magnetic properties of complexes based on a Schiff base ligand H₂L can be modulated by subtle changes in the coordination environment resulting from changes in the co-ligand substituents.

Coordination microenvironment perturbed single-ion magnet behavior in a β-diketone Dy(iii) complex

Employing mixed β-diketonate and bpy ligands leads to a mononuclear Dy(iii) SIM, of which the magneto-structural correlation is elucidated by the magnetic and theoretical studies, as well as a comparative study of reported analogues.

Dysprosium complexes bearing unsupported DyIII-GeII/SnII metal-metal bonds as single-ion magnets

Two dysprosium complexes bearing unsupported Dy-Ge/Sn metal-metal bonds are reported here, wherein the Dy-Ge and Dy-Sn bonds both contain relatively large covalency. The complexes exhibit slow relaxation of magnetization at zero field with energy barriers of 485 and 620 K, respectively, and the blocking temperature of 6 K.

Main Group Chemistry at the Interface with Molecular Magnetism

Innovative synthetic coordination and, increasingly, organometallic chemistry are at the heart of advances in molecular magnetism. Smart ligand design is essential for implementing controlled modifications to the electronic structure and magnetic properties of transition metal and f-element compounds, and many important recent developments use nontraditional ligands based on low-coordinate main group elements to drive the field forward. This review charts progress in molecular magnetism from the perspective of ligands in which the donor atoms range from low-coordinate 2p elements-particularly carbon but also boron and nitrogen-to the heavier p-block elements such as phosphorus, arsenic, antimony, and even bismuth. Emphasis is placed on the role played by novel main group ligands in addressing magnetic anisotropy of transition metal and f-element compounds, which underpins the development of single-molecule magnets (SMMs), a family of magnetic materials that can retain magnetization in the absence of a magnetic field below a blocking temperature. Nontraditional p-block donor atoms, with their relatively diffuse valence orbitals and more diverse bonding characteristics, also introduce scope for tuning the spin-orbit coupling properties and metal-ligand covalency in molecular magnets, which has implications in areas such as magnetic exchange coupling and spin crossover phenomena. The chemistry encompasses transition metals, lanthanides, and actinides and describes recently discovered molecular magnets that can be regarded, currently, as defining the state of the art. This review identifies that main group chemistry at the interface molecular magnetism is an area with huge potential to deliver new types of molecular magnets with previously unseen properties and applications.

A study of di(amino)stibines with terminal Sb(iii) hydrogen-ligands by X-ray- and neutron-diffraction

The bis(amidodimethyl)disiloxane ligands [O{SiMe2NR}2]2- (R = 2,6-Me2C6H3 (Ar') and 2,6-iPr2C6H3 (Ar), abbreviated [NONR]2-, are a stable support for Sb(iii) complexes of general formula Sb(NONR)X (X = Cl, H). The compounds are monomeric in the solid-state, with bidentate N,N'-coordination of the [NONR]2- and terminal chloride/hydrogen-ligands. Sb(NONAr')H was analyzed by single-crystal neutron diffraction, giving the first accurate parameters for the Sb-H bond to an antimony(iii) centre.

Mononuclear and trinuclear DyIII SMMs with Schiff-base ligands modified by nitro-groups: first triangular complex with a N–N pathway

Three Dy^III SMMs were obtained with Schiff-base ligands containing nitro-groups. The triangular complex supported by the cis–trans form of the hnc³⁻ ligand displayed the first air-stable triangular complex with a N–N pathway.

Rare-Earth Cyclobutadienyl Sandwich Complexes: Synthesis, Structure and Dynamic Magnetic Properties

The potassium cyclobutadienyl [K₂ {η⁴ -C₄ (SiMe₃ )₄ }] (1) reacts with MCl₃ (THF)_3.5 (M=Y, Dy) to give the first rare-earth cyclobutadienyl complexes, that is, the complex anions [M{η⁴ -C₄ (SiMe₃ )₄ }{η⁴ -C₄ (SiMe₃ )₃ -κ-(CH₂ SiMe₂ }]^2- , (2_M ), as their dipotassium salts. The tuck-in alkyl ligand in 2_M is thought to form through deprotonation of the "squarocene" complexes [M{η⁴ -C₄ (SiMe₃ )₄ }₂ ]^- by 1. Complex 2_Dy is a single-molecule magnet, but with prominent quantum tunneling. An anisotropy barrier of 323(22) cm^-1 was determined for 2_Dy in an applied field of 1 kOe, and magnetic hysteresis loops were observed up to 7 K.

Magnetic hysteresis up to 80 kelvin in a dysprosium metallocene single-molecule magnet

Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(Cp ^{i Pr5})Dy(Cp*)]⁺ (Cp ^{i Pr5}, penta-iso-propylcyclopentadienyl; Cp*, pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of U _eff = 1541 wave number is also measured. The magnetic blocking temperature of T _B = 80 kelvin for this cation overcomes an essential barrier toward the development of nanomagnet devices that function at practical temperatures.

Ab Initio Prediction of Tunneling Relaxation Times and Effective Demagnetization Barriers in Kramers Lanthanide Single-Molecule Magnets

Single-molecule magnets (SMMs) are promising candidates for molecule-based quantum information devices. Their main limitation is their cryogenic operative temperature. To achieve devices performing at higher temperatures, demagnetization mechanisms must be suppressed by chemical tuning. Electronic structure calculations can provide useful information to rationalize SMM behavior, but they do not provide a direct prediction for the key experimental parameters describing magnetic relaxation (i.e., tunneling relaxation time (τ_QT) and effective demagnetization barrier ( U_eff)). In this Letter, a first-principles model is proposed to predict τ_QT and U_eff for mononuclear, half-integer spin SMMs, allowing direct comparison with experiment. Model accuracy was assessed against experimental data for 18 mononuclear Ln^III complexes (15 Dy^III and 3 Er^III) and applied to 3 of the current best-performing SMMs, correctly predicting nontrivial relaxation pathways. The model shows that the combination of single-ion anisotropy and spin-spin dipolar coupling can account for the major part of tunneling demagnetization for the studied systems.

Cyclopentadienyl Ligands in Lanthanide Single-Molecule Magnets: One Ring To Rule Them All?

The discovery of materials capable of storing magnetic information at the level of single molecules and even single atoms has fueled renewed interest in the slow magnetic relaxation properties of single-molecule magnets (SMMs). The lanthanide elements, especially dysprosium, continue to play a pivotal role in the development of potential nanoscale applications of SMMs, including, for example, in molecular spintronics and quantum computing. Aside from their fundamentally fascinating physics, the realization of functional materials based on SMMs requires significant scientific and technical challenges to be overcome. In particular, extremely low temperatures are needed to observe slow magnetic relaxation, and while many SMMs possess a measurable energy barrier to reversal of the magnetization ( U_eff), very few such materials display the important properties of magnetic hysteresis with remanence and coercivity. Werner-type coordination chemistry has been the dominant method used in the synthesis of lanthanide SMMs, and most of our knowledge and understanding of these materials is built on the many important contributions based on this approach. In contrast, lanthanide organometallic chemistry and lanthanide magnetochemistry have effectively evolved along separate lines, hence our goal was to promote a new direction in single-molecule magnetism by uniting the nonclassical organometallic synthetic approach with the traditionally distinct field of molecular magnetism. Over the last several years, our work on SMMs has focused on obtaining a detailed understanding of why magnetic materials based on the dysprosium metallocene cation building block {Cp₂Dy}⁺ display slow magnetic relaxation. Specifically, we aspired to control the SMM properties using novel coordination chemistry in a way that hinges on key considerations, such as the strength and the symmetry of the crystal field. In establishing that the two cyclopentadienyl ligands combine to provide a strongly axial crystal field, we were able to propose a robust magneto-structural correlation for understanding the properties of dysprosium metallocene SMMs. In doing so, a blueprint was established that allows U_eff and the magnetic blocking temperature ( T_B) to be improved in a well-defined way. Although experimental discoveries with SMMs occur more rapidly than quantitative theory can (currently) process and explain, a clear message emanating from the literature is that a combination of the two approaches is most effective. In this Account, we summarize the main findings from our own work on dysprosium metallocene SMMs, and consider them in the light of related experimental studies and theoretical interpretations of related materials reported by other protagonists. In doing so, we aim to contribute to the nascent and healthy debate on the nature of spin dynamics in SMMs and allied molecular nanomagnets, which will be crucial for the further advancement of this vibrant research field.

Samarium Polystibides Derived from Highly Activated Nanoscale Antimony

Zintl ions in molecular compounds are of fundamental interest for basic research and application. Two reactive antimony sources are presented that allow direct access to molecular polystibide compounds. These are Sb amalgam (Sb/Hg) and ultrasmall Sb⁰ nanoparticles (d=6.6±0.8 nm), which were used independently as precursors for the synthesis of the largest f-element polystibide, [(Cp*₂ Sm)₄ Sb₈ ]. Whereas the reaction of the nanoparticles with [Cp*₂ Sm] directly led to [(Cp*₂ Sm)₄ Sb₈ ], Sm/Sb/Hg intermediates were isolated when using Sb/Hg as the precursor. These Sm/Sb/Hg intermediates [{(Cp*₂ Sm)₂ Sb}₂ (μ-Hg)] and [{(Cp*₂ Sm)₃ (μ⁴ ,η^1:2:2:2 -Sb₄ )}₂ Hg] were synthetically trapped and structurally characterized, giving insight in the formation mechanism of polystibide compounds.

Manipulating the Relaxation of Quasi- D4 d Dysprosium Compounds through Alternation of the O-Donor Ligands

Three mononuclear Dy^III complexes with the same auxiliary ligand Lz (2,4-diamino-6-pyridyl-1,3,5-triazine), [Dy(TTA)₃Lz] (1Dy) (TTA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate), [Dy(acac)₃Lz]·CH₃OH·0.5H₂O (2Dy) (acac = acetylacetonate), and [Dy(MQ)₂Lz₂]Br·CH₃OH (3Dy) (HMQ = 2-methyl-8-quinolinol), have been synthesized through alteration of the ligands containing O donors. In all three complexes, the Dy^III ions are eight-coordinate and submitted to pseudo- D_{4 d} symmetry in the first coordination sphere. It is noteworthy that the TTA ligands in 1Dy are easily substituted by other bidentate capping ligands with O donors, leading to distinct magnetic properties, which were studied experimentally and via ab initio calculations. All three complexes were found to exhibit single-molecule magnet behavior with U_eff of 22 cm^-1 (1Dy), 112 cm^-1 (2Dy), and 56 cm^-1 (3Dy) under zero applied dc field. Complex 1Dy demonstrates inferior SIM properties compared with 2Dy and 3Dy, which can be attributed to the strong electron-withdrawing effects of TTA ligands, as confirmed by theoretical calculations. However, butterfly-shaped magnetic hysteresis in 1Dy and 3Dy was observed at 1.9 K, while not in 2Dy.