High1H Relaxivity Gadolinium-Grafted Mesoporous Silica Materials

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.

Comparisons of lanthanide/actinide +2 ions in a tris(aryloxide)arene coordination environment

Nd, like U, prefers a f⁴ configuration with the tris(aryloxide)arene ligand rather than the 4f³5d¹ configuration found in tris(cyclopentadienyl) complexes.

A new series of Ln³⁺ and Ln²⁺ complexes has been synthesized using the tris(aryloxide)arene ligand system, ((^Ad,MeArO)₃mes)^3–, recently used to isolate a complex of U²⁺. The triphenol precursor, (^Ad,MeArOH)₃mes, reacts with the Ln³⁺ amides, Ln(NR₂)₃ (R = SiMe₃), to form a series of [((^Ad,MeArO)₃mes)Ln] complexes, 1-Ln. Crystallographic characterization was achieved for Ln = Nd, Gd, Dy, and Er. The complexes 1-Ln can be reduced with potassium graphite in the presence of 2.2.2-cryptand (crypt) to form highly absorbing solutions with properties consistent with Ln²⁺ complexes, [K(crypt)][((^Ad,MeArO)₃mes)Ln], 2-Ln. The synthesis of the Nd²⁺ complex [K(crypt)][((^Ad,MeArO)₃mes)Nd], 2-Nd, was unambiguously confirmed by X-ray crystallography. In the case of the other lanthanides, crystals were found to contain mixtures of 2-Ln co-crystallized with either a Ln³⁺ hydride complex, [K(crypt)][((^Ad,MeArO)₃mes)LnH], 3-Ln, for Ln = Gd, Dy, and Er, or a hydroxide complex, [K(crypt)][((^Ad,MeArO)₃mes)Ln(OH)], 4-Ln, for Ln = Dy. A Dy²⁺ complex with 18-crown-6 as the potassium chelator, [K(18-crown-6)(THF)₂][((^Ad,MeArO)₃mes)Dy], 5-Dy, was isolated as a co-crystallized mixture with the Dy³⁺ hydride complex, [K(18-crown-6)(THF)₂][((^Ad,MeArO)₃mes)DyH], 6-Dy. Structural comparisons of 1-Ln and 2-Ln are presented with respect to their uranium analogs and correlated with density functional theory calculations on their electronic structures.

A simple approach to a new T8-POSS based MRI contrast agent

A simple synthesis of a new nanoglobular T₈-silsesquioxane based contrast agent for the application in MRI is reported.