Direct Reactions of Iodine‐Activated Rare‐Earth Metals with Phenols of Varying Steric Bulk

Heterometallic 3d-4f Alkoxide Precursors for the Synthesis of Binary Oxide Nanomaterials

In this study, a new method for the synthesis of heterometallic 3d-4f alkoxides by the direct reaction of metallic lanthanides (La, Pr, Nd, Gd) with MCl₂ (M = Mn, Ni, Co) in 2-methoxyethanol was developed. The method was applied to the synthesis of the heterometallic oxo-alkoxide clusters [Ln₄Mn₂(μ₆-O)(μ₃-OR)₈(HOR)_xCl₆] (Ln = La (1), Nd (2), Gd (3); x = 0, 2, 4); [Pr₄M₂(μ₆-O)(μ₃-OR)₈(HOR)_xCl₆] (M = Co (4), Ni (5); x = 2, 4); and [Ln₄Mn₂(μ₃-OH)₂(μ₃-OR)₄(μ-OR)₄(μ-Cl)₂(HOR)₄Cl₆] (Ln = La (11) and Pr (12)). Mechanistic investigation led to the isolation of the homo- and heterometallic intermediates [Pr(μ-OR)(μ-Cl)(HOR)Cl]_n (6), [Co₄(μ₃-OR)₄(HOR)₄Cl₄] (7), [Ni₄(μ₃-OR)₄(HOEt)₄Cl₄] (8), [Mn₄(μ₃-OR)₄(HOR)₂(HOEt)₂Cl₄] (9), and [Nd(HOR)₄Cl][CoCl₄] (10). In the presence of an external M(II) source at 1100 °C, 1-4 and 12 were selectively converted into binary metal oxide nanomaterials with trigonal or orthorhombic perovskite structures, i.e., LaMnO₃, GdMnO₃, NdMnO₃, Pr_0.9MnO₃, and PrCoO₃. Compound 5 decomposed into a mixture of homo- and heterometallic oxides. The method presented provides a valuable platform for the preparation of advanced heterometallic oxide materials with promising magnetic, luminescence, and/or catalytic applications.

Rare Earth Starting Materials and Methodologies for Synthetic Chemistry

The number of rare earth (RE) starting materials used in synthesis is staggering, ranging from simple binary metal-halide salts to borohydrides and "designer reagents" such as alkyl and organoaluminate complexes. This review collates the most important starting materials used in RE synthetic chemistry, including essential information on their preparations and uses in modern synthetic methodologies. The review is divided by starting material category and supporting ligands (i.e., metals as synthetic precursors, halides, borohydrides, nitrogen donors, oxygen donors, triflates, and organometallic reagents), and in each section relevant synthetic methodologies and applications are discussed.

Six-coordinated dinuclear lanthanide(III) amide complexes: investigation of magnetization relaxation dynamics and their electronic structures

A series of rare six-coordinated dinuclear Ln(III) complexes [Ln₂(μ-Cl)₂Cl₄Li₂(L)₂(THF)₆] were structurally characterized using a bulky amide ligand (L; Ln = Gd(1), Dy(2) and Y(3)). Detailed magnetic studies disclose that a weak antiferromagnetic coupling exists within 1 (-0.09 cm^-1) and 2 (-0.07 cm^-1; -2J Hamiltonian). Additionally, this study unveils the importance of the amide ligand at the coordination site of Dy(III), which manifests a slow relaxation of magnetization in the absence of an external magnetic field. This has been rationalized by detailed ab initio calculations as well as the electronic structure determination of 1 and 2.

A simple one-pot route to stable formamidinatoiodidolanthanoid(III) complexes from lanthanoid metals

A number of formamidinatoiodidolanthanoid(III) complexes, [Ln(DFForm)₂I(thf)₂] and [Ln(DFForm)I₂(thf)₃] (DFFormH = N,N'-bis(2,6-difluorophenyl)formamidine) and [Ln(DippForm)I₂(thf)₃] (DippFormH = N,N'-bis(2,6-diisopropylphenyl)formamidine) have been synthesized in good yields by one-pot direct reactions of the corresponding free metals with iodine and DFFormH or DippFormH in suitable ratios and are stable to rearrangement.

Low-coordinate Sm(ii) and Yb(ii) complexes derived from sterically-hindered 1,2-bis(imino)acenaphthene (ArBIG-bian)

Reduction of Ar^BIG-bian with metallic Sm or Yb affords monomeric Ln(ii) complexes. In (Ar^BIG-bian)Sm, the metal reveals a low coordination number. The stabilization of the Sm center is provided by interaction with three Ph rings.

Emergence of the structure-directing role of f-orbital overlap-driven covalency

FEUDAL (f’s essentially unaffected, d’s accommodate ligands) is a longstanding bonding model in actinide chemistry, in which metal-ligand binding uses 6d-orbitals, with the 5f remaining non-bonding. The inverse-trans-influence (ITI) is a case where the model may break down, and it has been suggested that ionic and covalent effects work synergistically in the ITI. Here, we report an experimentally grounded computational study that quantitatively explores the ITI, and in particular the structure-directing role of f-orbital covalency. Strong donor ligands generate a cis-ligand-directing electrostatic potential (ESP) at the metal centre. When f-orbital participation, via overlap-driven covalency, becomes dominant via short actinide-element distances, this ionic ESP effect is overcome, favouring a trans-ligand-directed geometry. This study contradicts the accepted ITI paradigm in that here ionic and covalent effects work against each other, and suggests a clearly non-FEUDAL, structure-directing role for the f-orbitals.

In actinide chemistry, a longstanding bonding model describes metal-ligand binding using 6d-orbitals, with the 5f-orbitals remaining non-bonding. Here the authors explore the inverse-trans-influence — a case where the model breaks down — finding that the f-orbitals play a crucial role in dictating a trans-ligand-directed geometry.

Packing polymorphism in the structure of trans-aqua-[N,N'-bis-(salicyl-idene)ethane-1,2-di-amine-κ4 O,N,N',O']chlorido-manganese(III) monohydrate

The crystal structure of the title complex (systematic name: trans-aqua-chlorido-{2,2'[ethane-1,2-diylbis(nitrilo-methyl-idyne)]diphenolato-κ4 O,N,N',O'}manganese(III) monohydrate), [Mn(C16H14N2O2)Cl(H2O)]·H2O has been reported previously in the space group P21/n [Panja et al. (2003 ▸). Polyhedron, 22, 1191-1198]. We obtained the same hydrated complex through an alternative synthesis, and crystallized a new polymorph, in the space group P21. The mol-ecular conformation of the complex is virtually unmodified, but the absence of the glide plane in the new polymorph halves the unit-cell parameter c, affording a non-centrosymmetric crystal structure with Z = 2, while the previously reported crystal is centrosymmetric with Z = 4. Both phases represent a case of packing polymorphism, similar to other dimorphic crystal structures retrieved from the Cambridge Structural Database.

The inverse-trans-influence in tetravalent lanthanide and actinide bis(carbene) complexes

Across the periodic table the trans-influence operates, whereby tightly bonded ligands selectively lengthen mutually trans metal-ligand bonds. Conversely, in high oxidation state actinide complexes the inverse-trans-influence operates, where normally cis strongly donating ligands instead reside trans and actually reinforce each other. However, because the inverse-trans-influence is restricted to high-valent actinyls and a few uranium(V/VI) complexes, it has had limited scope in an area with few unifying rules. Here we report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data suggest the presence of an inverse-trans-influence. Studies of hypothetical praseodymium(IV) and terbium(IV) analogues suggest the inverse-trans-influence may extend to these ions but it also diminishes significantly as the 4f orbitals are populated. This work suggests that the inverse-trans-influence may occur beyond high oxidation state 5f metals and hence could encompass mid-range oxidation state actinides and lanthanides. Thus, the inverse-trans-influence might be a more general f-block principle.