“…As expected, our DFT calculations for [UO 2 Cl 4 ] 2– show strong mixing in a D 4 h ligand field with the axial oxo ligands. Consistent with previous reports, the U–O interaction is characterized by six antibonding orbitals of 2 e u (5f π ), 1 a 2 u (5f σ ), 1 a 1 g (6d σ ), and 1 e g (6d π ) symmetry, Figure . − ,− In comparison to the highly covalent U–O bonds, the equatorial Cl ligands are calculated to form U–Cl interactions that have far less Cl 3p-character. The Cl 3p σ-type symmetry-adapted linear combinations (SALCs) of atomic orbitals span e u + a 1 g + b 1 g symmetries and can mix with U 5f and 6d orbitals to form U–Cl σ-bonding interactions of 2 e u (U–Cl 5f σ , U–O 5f π ), 1 a 1 g (U–Cl 6d σ , U–O 6d σ ), and 1 b 1 g (U–Cl 6d σ , U–O 6d δ ) symmetries (Figure and Table ).…”
Section: Resultssupporting
confidence: 84%
“…Theoretical and experimental studies on the uranyl ion, [UO 2 ] 2+ , have provided foundational models for understanding electronic structure and bonding in molecular actinide science. − Of particular interest are their relevance to understanding the environmental speciation of [UO 2 ] 2+ , its role in nuclear fuel reprocessing schemes, and its potential as a photocatalyst for solar fuel formation. − In the course of studying [UO 2 ] 2+ , the series of dianionic uranyl(VI) tetrahalides[UO 2 X 4 ] 2– (X = Cl, Br, I)have emerged as popular analytes for spectroscopic and computational studies. − ,− These highly symmetric D 4 h compounds are attractive because they can be prepared in high yields, can be isolated as large single crystals, and are air and moisture stable. Of equal importance, the tetrahalide derivatives can be used as convenient aqueous and nonaqueous starting materials in uranium(VI) synthetic schemes. − …”
Synthetic routes to salts containing uranium bis-imido tetrahalide anions [U(NR)(2)X(4)](2-) (X = Cl(-), Br(-)) and non-coordinating NEt(4)(+) and PPh(4)(+) countercations are reported. In general, these compounds can be prepared from U(NR)(2)I(2)(THF)(x) (x = 2 and R = (t)Bu, Ph; x = 3 and R = Me) upon addition of excess halide. In addition to providing stable coordination complexes with Cl(-), the [U(NMe)(2)](2+) cation also reacts with Br(-) to form stable [NEt(4)](2)[U(NMe)(2)Br(4)] complexes. These materials were used as a platform to compare electronic structure and bonding in [U(NR)(2)](2+) with [UO(2)](2+). Specifically, Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state and time-dependent hybrid density functional theory (DFT and TDDFT) were used to probe U-Cl bonding interactions in [PPh(4)](2)[U(N(t)Bu)(2)Cl(4)] and [PPh(4)](2)[UO(2)Cl(4)]. The DFT and XAS results show the total amount of Cl 3p character mixed with the U 5f orbitals was roughly 7-10% per U-Cl bond for both compounds, which shows that moving from oxo to imido has little effect on orbital mixing between the U 5f and equatorial Cl 3p orbitals. The results are presented in the context of recent Cl K-edge XAS and DFT studies on other hexavalent uranium chloride systems with fewer oxo or imido ligands.
“…As expected, our DFT calculations for [UO 2 Cl 4 ] 2– show strong mixing in a D 4 h ligand field with the axial oxo ligands. Consistent with previous reports, the U–O interaction is characterized by six antibonding orbitals of 2 e u (5f π ), 1 a 2 u (5f σ ), 1 a 1 g (6d σ ), and 1 e g (6d π ) symmetry, Figure . − ,− In comparison to the highly covalent U–O bonds, the equatorial Cl ligands are calculated to form U–Cl interactions that have far less Cl 3p-character. The Cl 3p σ-type symmetry-adapted linear combinations (SALCs) of atomic orbitals span e u + a 1 g + b 1 g symmetries and can mix with U 5f and 6d orbitals to form U–Cl σ-bonding interactions of 2 e u (U–Cl 5f σ , U–O 5f π ), 1 a 1 g (U–Cl 6d σ , U–O 6d σ ), and 1 b 1 g (U–Cl 6d σ , U–O 6d δ ) symmetries (Figure and Table ).…”
Section: Resultssupporting
confidence: 84%
“…Theoretical and experimental studies on the uranyl ion, [UO 2 ] 2+ , have provided foundational models for understanding electronic structure and bonding in molecular actinide science. − Of particular interest are their relevance to understanding the environmental speciation of [UO 2 ] 2+ , its role in nuclear fuel reprocessing schemes, and its potential as a photocatalyst for solar fuel formation. − In the course of studying [UO 2 ] 2+ , the series of dianionic uranyl(VI) tetrahalides[UO 2 X 4 ] 2– (X = Cl, Br, I)have emerged as popular analytes for spectroscopic and computational studies. − ,− These highly symmetric D 4 h compounds are attractive because they can be prepared in high yields, can be isolated as large single crystals, and are air and moisture stable. Of equal importance, the tetrahalide derivatives can be used as convenient aqueous and nonaqueous starting materials in uranium(VI) synthetic schemes. − …”
Synthetic routes to salts containing uranium bis-imido tetrahalide anions [U(NR)(2)X(4)](2-) (X = Cl(-), Br(-)) and non-coordinating NEt(4)(+) and PPh(4)(+) countercations are reported. In general, these compounds can be prepared from U(NR)(2)I(2)(THF)(x) (x = 2 and R = (t)Bu, Ph; x = 3 and R = Me) upon addition of excess halide. In addition to providing stable coordination complexes with Cl(-), the [U(NMe)(2)](2+) cation also reacts with Br(-) to form stable [NEt(4)](2)[U(NMe)(2)Br(4)] complexes. These materials were used as a platform to compare electronic structure and bonding in [U(NR)(2)](2+) with [UO(2)](2+). Specifically, Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state and time-dependent hybrid density functional theory (DFT and TDDFT) were used to probe U-Cl bonding interactions in [PPh(4)](2)[U(N(t)Bu)(2)Cl(4)] and [PPh(4)](2)[UO(2)Cl(4)]. The DFT and XAS results show the total amount of Cl 3p character mixed with the U 5f orbitals was roughly 7-10% per U-Cl bond for both compounds, which shows that moving from oxo to imido has little effect on orbital mixing between the U 5f and equatorial Cl 3p orbitals. The results are presented in the context of recent Cl K-edge XAS and DFT studies on other hexavalent uranium chloride systems with fewer oxo or imido ligands.
“…The uranyl oxygen atoms remain singly coordinated to the central U atom only, although it is possible that they accept hydrogen bonds. Bond lengths within each U 6+ polyhedron average 1.79 Å for U−O and 2.31 Å for U−F and are consistent with those in other structures containing this building unit. ,,, Bond valence summations , for the U(1) and U(2) sites are 5.6 and 5.8 vu, respectively. 1 Top: ORTEP diagram (probability ellipsoids 50%) of the U1 and U2 local environments.…”
Section: Resultssupporting
confidence: 76%
“…Bond lengths within each U 6+ polyhedron average 1.79 Å for U-O and 2.31 Å for U-F and are consistent with those in other structures containing this building unit. 10,17,28,29 Bond valence summations 30,31 for the U(1) and U(2) sites are 5.6 and 5.8 vu, respectively.…”
Compounds NDUF-1 ([C(6)H(14)N(2)](UO(2))(2)F(6); P2(1)/c, a = 6.9797(15) A, b = 8.3767(15) A, c = 23.760(5) A, beta = 91.068(4) degrees, V = 1388.9(5) A(3), Z = 4), NDUF-2 ([C(6)H(14)N(2)](2)(UO(2))(2)F(5)UF(7).H(2)O), NDUF-3 ((NH(4))(7)U(6)F(31); R3, a = 15.4106(8) A, c = 10.8142(8) A, V = 2224.1(2) A(3), Z = 3), and NDUF-4 ([NH(4)]U(3)F(13)) have been synthesized hydrothermally from fixed composition reactant mixtures over variable time periods [DABCO (C(6)H(12)N(2)), UO(2)(NO(3))(2).6H(2)O, HF, and H(2)O; 2-14 days]. Observed is a systematic evolution of the structural building units within these materials from the UO(2)F(5) pentagonal bipyramid in NDUF-1 and -2 to the UF(8) trigonal prism in NDUF-2 and finally to the UF(9) polyhedron in NDUF-3 and -4 as a function of reaction time. Coupled to this coordination change is a reduction of U(VI) to U(IV) as well as a breakdown of the organic structure-directing agent from DABCO to NH(4)(+). These processes contribute to a structural transition from layered topologies (NDUF-1) to chain (NDUF-2), back to layered (NDUF-3), and ultimately to framework (NDUF-4) connectivities. The synthesis conditions, crystal structures, and possible transformation mechanisms within this system are presented.
“…Upon simulations of 1 ns at 200 K or 300 K, 2 PF 6 - ( n = 6) or 8 PF 6 - ( n = 12) anions dissociated, leading to an equatorial coordination of four anions only (two monodentate and two bidentate). The resulting CN is 6, which is larger than the CN of 5 in the UO 2 F 4 (OH 2 ) 2- complex. , The first-shell anions are quasi-static in the gas phase, which contrasts with the rapid spinning motions observed in IL solutions, “catalyzed” by neighboring imidazolium + ions.…”
Using molecular dynamics simulations, we compare the solvation of uranyl and strontium nitrates and uranyl chlorides in two room-temperature ionic liquids (ILs): [BMI][PF(6)] based on 1-butyl-3-methylimidazolium(+),PF(6)(-) and [EMI][TCA] based on 1-ethyl-3-methylimidazolium(+),AlCl(4)(-). Both dissociated M(2+),2NO(3)(-) and associated M(NO(3))(2) states of the salts are considered for the two cations, as well as the UO(2)Cl(2) and UO(2)Cl(4)(2)(-) uranyl complexes. In a [BMI][PF(6)] solution, the "naked" UO(2)(2+) and Sr(2+) ions are surrounded by 5.8 and 10.1 F atoms, respectively. The first-shell PF(6)(-) anions rotate markedly during the dynamics and are coordinated, on the average, monodentate to UO(2)(2+) and bidentate to Sr(2+). In an [EMI][TCA] solution, UO(2)(2+) and Sr(2+) coordinate 5.0 and 7.4 Cl atoms of AlCl(4)(-), respectively, which display more restricted motions. Four Cl atoms sit on a least motion pathway of transfer to uranyl, to form the UO(2)Cl(4)(2)(-) complex. The free NO(3)(-) anions and the UO(2)Cl(4)(2)(-) complex are surrounded by imidazolium(+) cations ( approximately 4 and 6-9, respectively). The first shell of the M(NO(3))(2) and UO(2)Cl(2) neutral complexes is mostly completed by the anionic components of the IL, with different contributions depending on the solvent, the M(2+) cation, and its counterions. Insights into energy components of solvation are given for the different systems.
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