Complexes of lanthanide nitrates with tri-isopropylphosphine oxide

Investigating Metal-Tributyl Phosphate Complexes during Supercritical Fluid Extraction of the NdFeB Magnet Using Density Functional Theory and X-ray Absorption Spectroscopy

Supercritical fluid extraction (SCFE) is gaining significant interest as a green technology for the recycling of end-of-life waste electrical and electronic equipment (WEEE). Neodymium iron boron (NdFeB) magnets, which contain large quantities of critical rare-earth elements such as neodymium, praseodymium, and dysprosium, are widely used in wind turbines and electric/hybrid vehicles. Hence, they are considered a promising secondary resource for these elements when they reach their end-of-life. Previously, the SCFE process was developed for recycling WEEE, including NdFeB; however, the process mechanism remains unexplored. Here, density functional theory, followed by extended X-ray absorption fine structure and X-ray absorption near-edge structure analyses, are utilized to determine the structural coordination and interatomic interactions of complexes formed during the SCFE of the NdFeB magnet. The results indicate that Fe(II), Fe(III), and Nd(III) form Fe(NO₃)₂(TBP)₂, Fe(NO₃)₃(TBP)₂, and Nd(NO₃)₃(TBP)₃ complexes, respectively. This theory-guided investigation elucidates the complexation chemistry and mechanism during the SCFE process by rigorously determining the structural models.

Synthesis of diphenyl-(2-thienyl)phosphine, its chalcogenide derivatives and a series of novel complexes of lanthanide nitrates and triflates

A novel synthesis of diphenyl(2-thienyl)phosphine, along with its' oxide, sulfide and selenide derivatives, is reported here. These phosphines have been characterized by NMR, IR, MS and X-Ray crystallography. The phosphine oxide derivative was reacted with a selection of lanthanide(III) nitrates and triflates, LnX₃, to give the resultant metal-ligand complexes. These complexes have also been characterized by NMR, IR, MS and X-Ray crystallography. Single crystal X-Ray diffraction data shows a difference in metal-ligand complex stoichiometry and stereochemistry depending on the counteranion (nitrate vs. triflate). The [Ln(Ar₃PO)₃(NO₃)₃] ligand-nitrate complexes are nine-coordinate to the metal in the solid state (bidentate nitrate), featuring a 1 : 3 lanthanide-ligand ratio and bear an overall octahedral arrangement of the six, coordinated ligands. Our [Ln(Ar₃PO)₃(NO₃)₃] ligand-nitrate complexes gave three examples of fac-stereochemistry, where mer-stereochemistry is almost universally observed in the literature of highly related [Ln(Ar₃PO)₃(NO₃)₃] complexes. For the Tb complexes, two different arrangements of the ligands around the metal were observed in the solid state for [Tb(Ar₃PO)₃(NO₃)₃] and [Tb(Ar₃PO)₄(OTf)₂] [OTf]. [Tb(Ar₃PO)₃(NO₃)₃] is strictly nine-coordinate, ligand mer-stereochemistry in the solid state, and [Tb(Ar₃PO)₄(OTf)₂] [OTf] is strictly octahedral, six-coordinate, with a square-planar stereochemical arrangement of the phosphine oxide ligands around the metal.

Sterically constrained tricyclic phosphine: redox behaviour, reductive and oxidative cleavage of P-C bonds, generation of a dilithium phosphaindole as a promising synthon in phosphine chemistry

The redox behaviour of sterically constrained tricyclic phosphine 3a was investigated by spectroelectrochemistry. The data suggested a highly negative reduction potential with the reversible formation of a dianionic species. Accordingly, 3a reacted with two equivalents of Li/naphthalene by reductive cleavage of a P-C bond of one of the PC4 heterocycles. The resulting dilithium compound 5 represents a phosphaindole derivative with annulated aromatic C6 and PC4 rings. It is an interesting starting material for the synthesis of new heterocyclic molecules, as was shown by treatment with Me2SiCl2 and PhPCl2. The structures of the products (6 and 7) formally reflect ring expansion by insertion of silylen or phosphinidene fragments into a P-C bond of 3a. Treatment of 3a with H2O2 did not result in the usually observed transfer of a single O atom to phosphorus, but oxidative cleavage of a strained PC4 ring afforded a bicyclic phosphinic acid, R2PO2H.

Probing a variation of the inverse-trans-influence in americium and lanthanide tribromide tris(tricyclohexylphosphine oxide) complexes

The synthesis, characterization, and theoretical analysis of meridional americium tribromide tris(tricyclohexylphosphine oxide), mer-AmBr3(OPcy3)3, has been achieved and is compared with its early lanthanide (La to Nd) analogs. The data show that homo trans ligands display significantly shorter bonds than the cis or hetero trans ligands. This is particularly pronounced in the americium compound. DFT along with multiconfigurational CASSCF calculations show that the contraction of the bonds relates qualitatively with overall covalency, i.e. americium shows the most covalent interactions compared to lanthanides. However, the involvement of the 5p and 6p shells in bonding follows a different order, namely cerium > neodymium ∼ americium. This study provides further insight into the mechanisms by which ITI operates in low-valent f-block complexes.

Field-Induced Single Molecule Magnets of Phosphine- and Arsine-Oxides

The coordination chemistry of dysprosium and terbium toward phosphine and arsine oxides was further explored. Thus, the new nitrate [M(NO₃)₃(Ph₃PO)₃] (M = Tb, 1; Dy, 2), [Dy(NO₃)₃(EtOH)(Ph₃XO)₂] (X = P, 3; As, 4), chloride [DyCl₂(Ph₃AsO)₄]Cl (5), triflate [Dy(OTf)₂(MePh₂PO)₄]OTf (6; OTf = triflate) and hexafluoroacetylacetonate [M(hfa)₃(Ph₃PO)₂] (hfa = hexafluoroacetylacetonate; M = Tb, 7; Dy, 8) complexes were isolated and fully characterized. The crystal structures of 1·CH₃CN, 2·CH₃CN, 4, 5·2.75EtOH·1.25H₂O, 6, 7, and 8 show MO₉ cores in 1, 2, and 4, with highly distorted geometry, between spherical capped square antiprism and muffin-like, hexacoordinated environments for the dysprosium ions in 5 and 6, with octahedral geometry, and octa-coordination for the lanthanoid metals in 7 and 8, with geometry closer to square antiprism. Comparison of the magnetic behavior of all the complexes allows analyzing which metal ion (Tb or Dy), phosphine or arsine oxide, or anionic ligand favor more the slow relaxation of the magnetization. Alternating current magnetic measurements show that only 2, 4, and 8 present slow relaxation of the magnetization in the presence of an external magnetic field, 8 being the complex with the highest U_eff (44.85 K) of those described herein.

Extraction and coordination studies of a carbonyl–phosphine oxide scorpionate ligand with uranyl and lanthanide(iii) nitrates: structural, spectroscopic and DFT characterization of the complexes

A scorpionate organophosphorus ligand exhibits promising extraction properties and variable denticity in f-block element complexes in the solid state and solution.