Assessing Crystal Field and Magnetic Interactions in Diuranium-­‐μ-­‐ Chalcogenide Triamidoamine Complexes With UIV-­‐E-­‐UIV Cores (E = S, Se, Te): Implications for Determining the Presence or Absence of Actinide-­‐Actinide Magnetic Exchange

We report the synthesis and characterisation of a family of diuranium(IV)-­‐μ-­‐chalcogenide complexes including a detailed examination of their electronic structures and magnetic behaviours. Treatment of [U(TrenTIPS)] [1, TrenTIPS = N(CH2CH2NSiPri 3)3] with Ph3PS, selenium or tellurium affords the diuranium(IV)-­‐sulfide, selenide, and telluride complexes [{U(TrenTIPS)}2(μ-­‐E)] (E = S, 2; Se, 5; Te, 6). Complex 2 is also formed by treatment of [U(TrenTIPS){OP(NMe2)3}] (3) with Ph3PS, whereas treatment of 3 with elemental sulfur gives the diuranium(IV)-­‐persulfido complex [{U(TrenTIPS)}2(μ-­‐η2:η2-­‐S2)] (4). Complexes 2-­‐6 have been variously characterised by single crystal X-­‐ray diffraction, NMR, IR, and optical spectroscopies, room temperature Evans and variable temperature SQUID magnetometry, elemental analyses, and complete active space self consistent field spin orbit calculations. The combined characterisation data present a self-­‐consistent picture of the electronic structure and magnetism of 2, 5, and 6, leading to the conclusion that single-­‐ion crystal field effects, and not diuranium magnetic coupling, are responsible for features in their variable-­‐temperature magnetisation data. The presence of magnetic coupling is often implied and sometimes quantified by such data, and so this study highlights the importance of evaluating other factors, such as crystal field effects, that can produce similar magnetic observables, and to thus avoid misassignments of such phenomena.