[UF₆]²⁻: A Molecular Hexafluorido Actinide(IV) Complex with Compensating Spin and Orbital Magnetic Moments

Abstract

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Magnetism of uranium compounds probed by XMCD spectroscopy

“…(NEt 4 ) 2 [UF 6 ]•2H 2 O is the first example of a structurally well characterized octahedral fluoride (figure 9) with ionic bonds facilitating the comparison of experimental results with theoretical calculations [28]. The small susceptibility and its weak temperature dependence is typical of the ones found in other U (IV) compounds.…”

“…Additional information on the nature of the electronic ground state is provided by XANES and XMCD experiments at the U M 4,5 edges performed at the ESRF beamline ID12 at 17 T and 4 K [28]. The branching ratio B = 0.72 (1) extracted from the absorption spectra is slightly larger than expected from the theoretical prediction for the 5f 2 configuration (0.69 for the IC) scheme.…”

“…Its behaviour, assuming perfect cubic symmetry, results from the splitting of the 3 H 4 multiplet and the admixture of the excited magnetic T 1g (Γ 4 ) triplet (7). Reproduced with permission from [28].…”

“…Pioneering work on U was performed in 1995 by Collins et al who recorded XMCD at the M 4,5 edges (3d → 5f ) in uranium monosulphide (US) [10]. Since then, all ensuing XMCD studies at the M 4,5 edges of U have been carried out at the ESRF beamline ID12 [11] on a large variety of intermetallics [12][13][14][15][16][17][18][19][20][21][22][23][24][25], heterostructures [25][26][27] or molecular magnets [28].…”

Anomalous magnetism of uranium(IV)-oxo and -imido complexes reveals unusual doubly degenerate electronic ground states

“…12,13 The A 1 state is diamagnetic because it is composed of approximately 58% m J = 0, 21% m J = À4, and 21% m J = +4, 12 where the m J = 0 state is itself diamagnetic and the equal contributions of the m J = G4 states cancel out each other; this can also be mapped to spin and orbital contributions to the m J states, which can be calculated using Clebsch-Gordan coefficients 14 and can be measured experimentally. 15 On the other hand, compounds of different symmetry may not show a decrease to near-zero magnetic moment at low temperatures, signifying the presence of a degenerate paramagnetic ground state (E). For example, uranocene, [U(h 8 -C 8 H 8 ) 2 ], 16 has a magnetic moment of $2.6 m B at 300 K 17 that decreases to 1.35 m B at 4 K 18 : in this case, the D 8h symmetry of the solid-state structure splits the J = 4 spin-orbit multiplet into A 1 , E 1 , E 2 , E 3 , and B 1 + B 2 irreducible representations, for which E 3 (m J = G3) is the ground state.…”