Reductive Reactivity of the 4f75d1 Gd(II) Ion in {GdII[N(SiMe3)2]3}-: Structural Characterization of Products of Coupling, Bond Cleavage, Insertion, and Radical Reactions

Supramolecular assemblies of tetravalent terbium complex units: syntheses, structure, and materials properties

There is a growing interest in lanthanide complexes exhibiting unconventional oxidation states, primarily due to their unique electronic structures and accompanying physicochemical properties. Herein, likely the first examples of supramolecular assemblies of non-Ce(iv) tetravalent lanthanide complexes, with the general formula [Tb(OSiPh3)4Lx] n [1 (n = 2, L1 = 1,2-bis(4-pyridyl)ethane); 2 (L2 = 4,4'-bipyridine), 3 (L3 = 1,2-bis(4-pyridyl)acetylene), 4 (L4 = 1,2-bis(4-pyridyl)ethylene), and 5 (L5 = 1,4-bis(4-pyridyl)benzene)], are reported. Cyclic voltammetry studies show two successive redox events, indicating electronic interactions between the two Tb(iv) centers in the dimeric metallomacrocycle 1. Compounds 2-5 are zig-zag structured coordination polymers featuring complex units of Tb(OSiPh3)4 bridged by their respective pyridyl-based ditopic ligands. These tetravalent lanthanide species display impressive stability in air, which is believed to result from the stabilization effect of ligand Lx and the extensive multifarious interactions involving the aromatic rings of the anionic (Ph3SiO-) and bridging ligands. UV-vis absorption spectroscopic studies show that 2-5 are semiconducting, each with a narrow bandgap of ca. 1.7 eV. Magnetic property studies yielded magnetic entropy changes of ca. 8.0 J (kg K)-1 at 2.5 K and 7T, which is reasonable for a complex with high-molecular-weight ligands, suggesting the potential development of Tb(iv) complexes as molecular refrigerants due to their f7 electronic configuration.

Rare earth stibolyl and bismolyl sandwich complexes

The design of molecular rare earth complexes to achieve unique magnetic and bonding properties is a growing area of research with possible applications in advanced materials and molecular magnetics. Recent efforts focus on developing ligand frameworks that can enhance magnetic characteristics. Here we show the synthesis and characterization of a class of rare earth complexes, [(η5-C4R4Sb)Ln(η8-C8H8)] and [(η5-C4R4Bi)Ln(η8-C8H8)], featuring η5-coordinated stibolyl and bismolyl ligands. The ligand aromaticity and bonding situation within these complexes are investigated by quantum chemical calculations. Magnetic studies of the ErIII analogues reveal large barriers and intriguing properties, including waist-restricted hysteresis and slow relaxation of the magnetization, making them single-molecule magnets. Comparison between the experimental barrier and CASSCF-SO calculations indicates that relaxation in all systems occurs through high-energy excited states. These findings suggest that stibolyl and bismolyl ligands can be promising candidates for achieving high-energy barriers in Er-based SMMs, offering a pathway to molecular designs with enhanced magnetic properties.

Trigonal Planar Heteroleptic Lanthanide(III) Bis(silyl)amide Complexes Containing Aminoxyl Radicals and Anions

Modulation of the crystal field (CF) in lanthanide (Ln) complexes can enhance optical and magnetic properties, and large CF splitting can be achieved with low coordination numbers in specific geometries. We previously reported that the homoleptic near-linear Sm2+ complex [SmII{N(SiiPr3)2}2] (1-Sm) is oxidized by the 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO•) radical to give the heteroleptic, approximately trigonal planar Sm3+ complex, [SmIII{N(SiiPr3)2}2(TEMPO-)] (2-Sm). Here, we report the synthesis of homologous [LnIII{N(SiiPr3)2}2(TEMPO-)] (2-Ln; Ln = Tm, Yb) complexes by the oxidation of the parent [Ln{N(SiiPr3)2}2] (1-Ln; Ln = Tm, Yb) with TEMPO•; complexes 2-Ln all contain TEMPO- anions. The homoleptic bent Ln3+ complexes [LnIII{N(SiiPr3)2}2][B(C6F5)4] (3-Ln; Ln = Sm, Tm, Yb) were also treated with TEMPO• to yield the heteroleptic, approximately trigonal planar Ln3+ complexes [LnIII{N(SiiPr3)2}2(TEMPO•)][B(C6F5)4] (4-Ln; Ln = Sm, Tm, Yb); the cations of 4-Ln all contain TEMPO• radicals. We have compared the electronic structures of the two geometrically similar families of Ln3+ complexes with the TEMPO- anion (2-Ln) or TEMPO• radical (4-Ln) using a combination of UV-vis-NIR and EPR spectroscopy, magnetic measurements, and ab initio calculations. These studies revealed no single-molecule magnet behavior for 2-Yb despite evidence for sizable CF splitting and a high degree of purity of the ground stabilized mJ = |±7/2⟩ state, while the radical TEMPO• in 4-Yb did not significantly improve performance.

Reactivity of Strontium Hydride Supported by the Superbulky Hydrotris(pyrazolyl)borate Ligand

Hydrogenolysis of [(TpAd,iPr)Sr{CH(SiMe3)2}] (1) (TpAd,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) in hexane solution under 20 atm of H2 allowed for the isolation of strontium hydride [(TpAd,iPr)Sr(μ-H)]2 (2) in good yield. Complex 2 exhibits the dimeric nature in solid state, featuring two different bond modes between the Sr center and TpAd,iPr ligand. Treatment of complex 2 with PhC(H)═NtBu or PhCH2Bpin (Bpin = pinacolateborane) afforded the strontium amide complex [(TpAd,iPr)Sr{N(CH2Ph)(tBu)}] (4) and hydroborate complex [(TpAd,iPr)Sr{μ-HBpin(CH2Ph)}] (5), respectively. Reactions of complex 2 with 2-picoline, 2-phenylquinoline, or 2-phenylpyridine led to the formation of strontium 2-pyridylmethylene/2-picoline complex [(TpAd,iPr)Sr(2-CH2-Py)(2-picoline)] (6), reductively coupling diphenyl-biquinolide complex [{(TpAd,iPr)Sr}2(2,2'-Ph2-4,4'-dihydro-4,4'-biquinolide)] (7), and diphenyl-bipyridyl radical complex [(TpAd,iPr)Sr(6,6'-Ph2-2,2'-bipyridyl)] (8), separately. All of the complexes have been well characterized, including NMR spectrum and single-crystal X-ray analysis.

A DFT perspective on organometallic lanthanide chemistry

Computational studies of the coordination chemistry and bonding of lanthanides have grown in recent decades as the need for understanding the distinct physical, optical, and magnetic properties of these compounds increased. Density functional theory (DFT) methods offer a favorable balance of computational cost and accuracy in lanthanide chemistry and have helped to advance the discovery of novel oxidation states and electronic configurations. This Frontier article examines the scope and limitations of DFT in interpreting structural and spectroscopic data of low-valent lanthanide complexes, elucidating periodic trends, and predicting their properties and reactivity, presented through selected examples.

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.