Molecular and electronic structure of terminal and alkali metal-capped uranium(V) nitride complexes

Abstract

Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin–orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin–orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin–orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field.

Molecular single-ion magnets based on lanthanides and actinides: Design considerations and new advances in the context of quantum technologies

“…Indeed, some examples of 5f-SIM systems based on U 3+ (5f 3 , J = 9/2) [24,27,28,30,[118][119][120][121][122][123], and U 5+ (5f 1 , J = 5/2) [25,26] ions have been reported in the last few years. Both are Kramers ions (S = half integer) with large values of angular momentum, J, which are guaranteed to possess a doubly-degenerate mJ ground state-an important requirement in SIM research.…”

“…In a subsequent study, a series of uranium(V) nitrides assembled from the same ligand, (79), (M = Li, Na, K, Rb, and Cs) ( Fig. 15b and c) demonstrated improved SIM behaviour (Ueff = 20 -40 K) [26], due to an enhanced ligand field splitting at uranium(V). The study enabled an increased understanding of crystal field effects in U V -SIMs by replacing O 2-with N 3-in such isostructural and isoelectronic compounds.…”

“…Single-ion magnets (SIMs) are simply a subclass of SMMs wherein the electronic spin term originates from a single magnetic centre [7,8]. In SIMs, the ion bearing the spin is most commonly a transition metal [9][10][11][12][13], lanthanoid [14][15][16][17][18][19][20][21][22], or actinoid [23][24][25][26][27][28][29][30]. The term SIM is somewhat of a misnomer: all SIMs are molecular in nature since the ligand field is a vital prerequisite for their slow relaxation.…”

Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

“…Recently,a spart of our work on actinide-ligand multiple bonds, [11] we reported uranium and thorium phosphinidene complexes using the parent phosphinidene (HP) 2À , [12] despite the large triplet-singlet energy gap of approximately 22 kcal mol À1 for free PH, [4g] which had previously only been seldom observed as af leeting spectroscopic intermediate or probed theoretically.…”

“…[1,2] However, although such complexes were first reported three decades ago, [3] they remain ar elatively rare class of metal-ligand multiple bond. This relative paucity reflects the inherent nature of the phosphinidene functional group,which as af ree moiety is very reactive due to the P-triplet ground state and unsaturated valence shell.[4] Stabilization of aphosphinidene by metal-coordination is an attractive strategy, [1] but normally also demands as terically bulky group at phosphorus to kinetically stabilize the M=PR linkage.Indeed, it is notable that under ambient conditions all isolable transition-metal phosphinidene complexes exhibit sterically demanding Rg roups to kinetically protect these vulnerable M=PR bonds; [3,[5][6][7][8][9] in abroader sense the only exceptions are where fundamental, elegant species such as H 2 M = PH (M = Ti,Z r, and Hf) have been prepared and spectroscopically observed under cryogenic conditions.[10] Early transitionmetal phosphinidene complexes are perhaps the most developed of all metal-phosphinidenes,s oi ti ss urprising that an early transition-metal parent phosphinidene has not yet been realized under ambient conditions.Recently,a spart of our work on actinide-ligand multiple bonds, [11] we reported uranium and thorium phosphinidene complexes using the parent phosphinidene (HP) 2À , [12] despite the large triplet-singlet energy gap of approximately 22 kcal mol À1 for free PH, [4g] which had previously only been seldom observed as af leeting spectroscopic intermediate or probed theoretically.[4] Those two actinide complexes are the only two M = PH complexes yet isolated outside cryogenic spectroscopic experiments,a nd were supported by the very sterically demanding triamidoamine ligand N(CH 2 CH 2 NSiPr …”