Synthesis, Structural Characterization, and Magnetic Properties of Lanthanide Arsolyl Sandwich Complexes

Abstract

A series of trivalent lanthanide sandwich complexes [(η 5 -C 4 R 4 As)Ln(η 8 -C 8 H 8 )] using three different arsolyl ligands are reported. The complexes were obtained via salt elimination reactions between potassium arsolyl salts and lanthanide precursors [LnI(COT)(THF) 2 ] (Ln = Sm, Dy, Er; COT = η 8 -C 8 H 8 ). The resulting compounds exhibit classical sandwich complex structures with one notable exception. Characterization was conducted in both the solid state using single-crystal X-ray diffraction and in solution for the Sm compounds using NMR spectroscopy. Furthermore, the magnetic properties of an Er complex were investigated, revealing distinctive single-molecule-magnet behavior characterized by an energy barrier of U eff = 323.3 K. Theoretical calculations were employed to support and interpret the experimental findings, with a comparative analysis performed against previously reported complexes.

Heteroleptic Rare Earth Tetraalkylphospholide Cyclooctatetraenide Sandwich Complexes

“…The three 5M complexes along with 6 feature η 8 -COT rings along with an η 5 -TEP ring, while 6 presents an additional bond between the TEP P-atom lone pair on one {La(COT)(TEP)} unit to a second La metal centre (La-P = 3.1781(3) Å). This interaction is similar to the dimeric arsolide COT complex [Sm(COT)(μ-TMAs)]2 (TMAs = {AsC4Me4}) [67] , and also the silole complex [La{(μ-COT)K(THF)2}(μ-SiC4-2,5-TMS-3,4-Ph)]2 [80] , [Nd(COT)(DSP)(THF)] which are monomeric [51,54,67,81] . In 5Sc, two of the ethyl groups lie in the plane of the TEP ring, somewhat sterically shielding the P-atom, and the other two point away from the metal, whereas in 5Lu and 5Y three point away from the metal and one lies in the plane of the ring.…”

“…[61] Crystallisation of 1M complexes from THF gave large yellow blocks suitable for single crystal XRD in fair to excellent yields (49-81%). After drying under The 1 H NMR spectra for 2-6 are characteristic of complexes with these ligand sets [51,67] The CH2 groups for the remaining TEP complexes (5Sc, 5Y, 6) show more complex coupling patterns or broadened features which may arise due to aggregation processes in solution or unresolved long-range coupling to the metal centre (see Supporting Information). In complex 3, the COT 1 H resonance appears as a doublet (δH = 6.14; 2 JHY = 1.0 Hz) due to the presence of 89 Y (I = 1 /2, 100% natural abundance), while in all other complexes, including 5Y, the COT group appears as a singlet over a small range (δH = 6.24-6.31).…”

“…do not show coupling to the metal centre), and span a reasonably narrow range (δP = 81.36-95. 67) with no clear trend between the chemical shift or structural parameters in the solid state (see Supporting Information). The 45 Sc NMR spectra of 2Sc and 5Sc each reveal a single broad resonance at 13.04 ppm and −18.15 ppm respectively, and the 89 Y-1 H HSQC spectra of 3 and 5Y reveal 89 Y chemical shifts of −155.43 and −91.39 ppm respectively, both arise from coupling to the COT ring protons.…”

Phospholyl and Arsolyl Triple-Decker Sandwich Complexes of Europium(II) and Strontium(II)

“…All deuterated solvents were degassed by freeze–pump–thaw cycles. The starting materials [EuI 2 (thf) 2 ], 36 K 2 COT, 37 K(Dtp), 17 K(Dtas), 38 and [{(Cp*)(thf) 2 Eu} 2 {μ-C 8 H 8 }] 12 were prepared according to literature known procedures. SrI 2 was obtained from commercial sources and used without further purification.…”

Ligand–Metal Complementarity in Rare-Earth and Actinide Chemistry

“…Roesky and co-workers have explored the influence of arsolyl ligands, {η 5 -AsC 4 R 4 }, on the coordination environment and magnetic properties of several Ln III ions (Sm, Dy, and Er), finding that the nuclearity of [RE­(η 8 -COT)­(η 5 :μ n -AsC 4 R 4 )] n (Ln = Sm, Dy, Er; n = 1, 2; COT = {C 8 H 8 }) complexes depends on the steric protection at the 2,5 positions of the {AsC 4 R 4 } ring with large Sm III ions, but with small Dy III and Er III ions, monomeric complexes are obtained even with small R groups such as in {AsC 4 Me 4 }. The softer {AsC 4 R 4 } ligand gives magnetic properties at Er III that are similar to those of the phosphorus analog, but slightly worse than those of the corresponding Cp R (Cp R = substituted Cp ligand) congeners . Complexes of Er III using the COT ligand, and 1,4-(trialkyl)­silylated variants thereof, have been known for some time, and many have SMM properties.…”