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1.
J Am Chem Soc ; 146(5): 3279-3292, 2024 Feb 07.
Artículo en Inglés | MEDLINE | ID: mdl-38264991

RESUMEN

The synthesis of previously unknown bis(cyclopentadienyl) complexes of the first transition metal, i.e., Sc(II) scandocene complexes, has been investigated using C5H2(tBu)3 (Cpttt), C5Me5 (Cp*), and C5H3(SiMe3)2 (Cp″) ligands. Cpttt2ScI, 1, formed from ScI3 and KCpttt, can be reduced with potassium graphite (KC8) in hexanes to generate dark-red crystals of the first crystallographically characterizable bis(cyclopentadienyl) scandium(II) complex, Cpttt2Sc, 2. Complex 2 has a 170.6° (ring centroid)-Sc-(ring centroid) angle and exhibits an eight-line EPR spectrum characteristic of Sc(II) with Aiso = 82.6 MHz (29.6 G). It sublimes at 200 °C at 10-4 Torr and has a melting point of 268-271 °C. Reductions of Cp*2ScI and Cp″2ScI under analogous conditions in hexanes did not provide new Sc(II) complexes, and reduction of Cp*2ScI in benzene formed the Sc(III) phenyl complex, Cp*2Sc(C6H5), 3, by C-H bond activation. However, in Et2O and toluene, reduction of Cp*2ScI at -78 °C gives a dark-red solution, 4, which displays an eight-line EPR pattern like that of 1, but it did not provide thermally stable crystals. Reduction of Cp″2ScI, in THF or Et2O at -35 °C in the presence of 2.2.2-cryptand, yields the green Sc(II) metallocene iodide complex, [K(crypt)][Cp″2ScI], 5, which was identified by X-ray crystallography and EPR spectroscopy and is thermally unstable. The analogous reaction of Cp*2ScI with KC8 and 18-crown-6 in Et2O gave the ligand redistribution product, [Cp*2Sc(18-crown-6-κ2O,O')][Cp*2ScI2], 6, as the only crystalline product. Density functional theory calculations on the electronic structure of these compounds are reported in addition to a steric analysis using the Guzei method.

2.
Inorg Chem ; 63(14): 6217-6230, 2024 Apr 08.
Artículo en Inglés | MEDLINE | ID: mdl-38502000

RESUMEN

The factors affecting the formation and crystal structures of unusual 6d1 Th(III) square planar aryloxide complexes, as exemplified by [Th(OArMe)4]1- (OArMe = OC6H2tBu2-2,6-Me-4), were explored by synthetic and reduction studies of a series of related Th(IV) tetrakis(aryloxide) complexes, Th(OArR)4 (OArR = OC6H2tBu2-2,6-R-4). Specifically, electronic, steric, and countercation effects were explored by varying the aryloxide ligand, the alkali metal reducing agent, and the alkali metal chelating agent. Salt metathesis reactions between ThBr4(DME)2 (DME = 1,2-dimethoxyethane) and 4 equiv of the appropriate potassium aryloxide salt were used to prepare a series of Th(IV) aryloxide complexes in high yields: Th(OArH)4 (OArH = OC6H3tBu2-2,6), Th(OArtBu)4 (OArtBu = OC6H2tBu3-2,4,6), Th(OArOMe)4 (OArOMe = OC6H2tBu2-2,6-OMe-4), and Th(OArPh)4 (OArPh = OC6H2tBu2-2,6-Ph-4). Th(OArH)4 can be reduced by KC8, Na, or Li in the absence or presence of 2.2.2-cryptand (crypt) or 18-crown-6 (crown) to form dark purple solutions that have EPR and UV-visible spectra similar to those of the square planar Th(III) complex, [Th(OArMe)4]1-. Hence, the para position of the aryloxide ligand does not have to be alkylated to obtain the Th(III) complexes. Furthermore, reduction of Th(OArOMe)4, Th(OArtBu)4, and Th(OArPh)4 with KC8 in THF generated purple solutions with EPR and UV-visible spectra that are similar to those of the previously reported Th(III) anion, [Th(OArMe)4]1-. Although many of these reduction reactions did not produce single crystals suitable for study by X-ray diffraction, reduction of Th(OArH)4, Th(OArtBu)4, and Th(OArOMe)4 with Li provided X-ray quality crystals whose structures had square planar coordination geometries. Reduction of Th(OArPh)4 with Li also gave a product with EPR and UV-visible spectra that matched those of [Th(OArMe)4]1-, but X-ray quality crystals of the reduction product were too unstable to provide data. Neither Th(Odipp)4(THF)2 (Odipp = OC6H3iPr2-2,6) nor Th(Odmp)4(THF)2 (Odmp = OC6H3Me2-2,6) could be reduced to Th(III) products under similar conditions. Reduction of U(OArH)3(THF) with KC8 in the presence of 2.2.2-cryptand (crypt) was examined for comparison and formed [K(crypt)][U(OArH)4], which has a tetrahedral arrangement of the aryloxide ligands. Moreover, no further reduction was observed when either [K(crypt)][U(OArH)4] or [K(crown)(THF)2][U(OArH)4] were treated with KC8 or Li.

3.
J Phys Chem A ; 2024 Jul 16.
Artículo en Inglés | MEDLINE | ID: mdl-39012067

RESUMEN

Singlet-triplet (ST) gaps are key descriptors of carbenes, because their properties and reactivity are strongly spin-dependent. However, the theoretical prediction of ST gaps is challenging and generally thought to require elaborate correlated wave function methods or double-hybrid density functionals. By evaluating two recent test sets of arylcarbenes (AC12 and AC18), we show that local hybrid functionals based on the "common t" local mixing function (LMF) model achieve mean absolute errors below 1 kcal/mol at a computational cost only slightly higher than that of global hybrid functionals. An analysis of correlation contributions to the ST gaps suggests that the accuracy of the common t-LMF model is mainly due to an improved description of nondynamical correlation which, unlike exchange, is not additive in each spin-channel. Although spin-nonadditivity can be achieved using the local spin polarization alone, using the "common", i.e., spin-unresolved, iso-orbital indicator t for constructing the LMF is found to be critical for consistent accuracy in ST gaps of arylcarbenes. The results support the view of LHs as vehicles to improve the description of nondynamical correlation rather than sophisticated exchange mixing approaches.

4.
J Chem Phys ; 160(4)2024 Jan 28.
Artículo en Inglés | MEDLINE | ID: mdl-38252940

RESUMEN

The natural determinant reference (NDR) or principal natural determinant is the Slater determinant comprised of the N most strongly occupied natural orbitals of an N-electron state of interest. Unlike the Kohn-Sham (KS) determinant, which yields the exact ground-state density, the NDR only yields the best idempotent approximation to the interacting one-particle reduced density matrix, but it is well-defined in common atom-centered basis sets and is representation-invariant. We show that the under-determination problem of prior attempts to define a ground-state energy functional of the NDR is overcome in a grand-canonical ensemble framework at the zero-temperature limit. The resulting grand potential functional of the NDR ensemble affords the variational determination of the ground state energy, its NDR (ensemble), and select ionization potentials and electron affinities. The NDR functional theory can be viewed as an "exactification" of orbital optimization and empirical generalized KS methods. NDR functionals depending on the noninteracting Hamiltonian do not require troublesome KS-inversion or optimized effective potentials.

5.
J Comput Chem ; 44(11): 1105-1118, 2023 Apr 30.
Artículo en Inglés | MEDLINE | ID: mdl-36636945

RESUMEN

We present the design and implementation of libkrylov, an open-source library for solving matrix-free eigenvalue, linear, and shifted linear equations using Krylov subspace methods. The primary objectives of libkrylov are flexible API design and modular structure, which enables integration with specialized matrix-vector evaluation "engines." Libkrylov features pluggable preconditioning, orthonormalization, and tunable convergence control. Diagonal (conjugate gradient, CG), Davidson, and Jacobi-Davidson preconditioners are available, along with orthonormal and nonorthonormal (nKs) schemes. All functionality of libkrylov is exposed via Fortran and C application programming interfaces (APIs). We illustrate the performance of libkrylov for eigenvalue calculations arising in time-dependent density functional theory (TDDFT) in the Tamm-Dancoff approximation (TDA) and discuss the convergence behavior as a function of preconditioning and orthonormalization methods.

6.
Inorg Chem ; 62(2): 706-714, 2023 Jan 16.
Artículo en Inglés | MEDLINE | ID: mdl-36595714

RESUMEN

The sterically bulky aryloxide ligand OAr* (OAr* = -OC6H2-Ad2-2,6tBu-4; Ad = 1-adamantyl) has been used to generate Ln(II) complexes across the lanthanide series that are more thermally stable than complexes of any other ligand system reported to date for 4fnd1 Ln(II) ions. The Ln(III) precursors Ln(OAr*)3 (1-Ln) were synthesized by reacting 1.2 equiv of Ln(NR2)3 (R = SiMe3) with 3 equiv of HOAr* for Ln = La, Ce, Nd, Gd, Dy, Yb, and Lu. 1-Ce, 1-Nd, 1-Gd, 1-Dy, and 1-Lu were identified by single-crystal X-ray diffraction studies. Reductions of 1-Ln with potassium graphite (KC8) in tetrahydrofuran in the presence of 2.2.2-cryptand (crypt) yielded the Ln(II) complexes [K(crypt)][Ln(OAr*)3] (2-Ln). The 2-Ln complexes for Ln = Nd, Gd, Dy, and Lu were characterized by X-ray crystallography and found to have Ln-O bond distances 0.038-0.087 Å longer than those of their 1-Ln analogues; this is consistent with 4fn5d1 electron configurations. The structure of 2-Yb has Yb-O distances 0.167 Å longer than those predicted for 1-Yb, which is consistent with a 4f14 electron configuration. Although 2-La and 2-Ce proved to be challenging to isolate, with 18-crown-6 (18-c-6) as the potassium chelator, La(II) and Ce(II) complexes with OAr* could be isolated and crystallographically characterized: [K(18-c-6)][Ln(OAr*)3] (3-Ln). The Ln(II) complexes decompose at room temperature more slowly than other previously reported 4fn5d1 Ln(II) complexes. For example, only 30% decomposition of 2-Dy was observed after 30 h at room temperature compared to complete decomposition of [Dy(OAr')3]- and [DyCp'3]- under similar conditions (OAr' = OC6H2-2,6-tBu2-4-Me; Cp' = C5H4SiMe3).

7.
J Am Chem Soc ; 144(37): 17064-17074, 2022 09 21.
Artículo en Inglés | MEDLINE | ID: mdl-36074041

RESUMEN

Examination of the reduction chemistry of Nd(NR2)3 (R = SiMe3) under N2 has provided connections between the in situ Ln(III)-based LnIII(NR2)3/K reductions of N2 that form side-on bound neutral (N=N)2- complexes, [(R2N)2(THF)Ln]2[µ-η2:η2-N2], and the Ln(II)-based [LnII(NR2)3]1- reductions by Sc, Gd, and Tb that form end-on bound (N=N)2- complexes, {[(R2N)3Ln]2[µ-η1:η1-N2]}2-, which are dianions. The reduction of Nd(NR2)3 by KC8 under dinitrogen in Et2O in the presence of 18-crown-6 (18-c-6) forms dark yellow solutions of [K2(18-c-6)3]{[(R2N)3Nd]2N2} at low temperatures that become green as they warm up to -35 °C in a glovebox freezer. Green crystals obtained from the solution turn yellow-brown when cooled below -100 °C, and the yellow-brown compound has an end-on Nd2(µ-η1:η1-N2) structure. The yellow-brown crystals isomerize in the solid state on the diffractometer upon warming, and at -25 °C, the crystals are green and have a side-on Nd2(µ-η2:η2-N2) structure. Collection of X-ray diffraction data at 10 °C intervals from -50 to -90 °C revealed that the isomerization occurs at temperatures below -100 °C. In the presence of tetrahydrofuran (THF), the dianionic {[(R2N)3Nd]2N2}2- system can lose an amide ligand to provide the monoanionic [(R2N)3NdIII(µ-η2:η2-N2)NdIII(NR2)2(THF)]1-, characterized by X-ray crystallography. These data suggest a connection between the in situ Ln(III)/K reductions and Ln(II) reductions that depends on solvent, temperature, the presence of a chelate, and the specific rare-earth metal.


Asunto(s)
Amidas , Furanos , Isomerismo , Ligandos , Modelos Moleculares , Solventes
8.
Inorg Chem ; 61(19): 7365-7376, 2022 May 16.
Artículo en Inglés | MEDLINE | ID: mdl-35504019

RESUMEN

Heteroleptic U(III) complexes supported by bis(cyclopentadienyl) frameworks have been synthesized to examine their suitability as precursors to U(II) complexes. The newly synthesized (C5Me5)2U(OC6H2tBu2-2,6-Me-4), (C5Me5)2U(OC6H2Ad2-2,6-tBu-4) (Ad = 1-adamantyl), (C5Me5)2U(C5H5), and (C5Me5)2U(C5Me4H) are compared with (C5Me5)2U[N(SiMe3)2], (C5Me5)2U[CH(SiMe3)2], and (C5Me5)U[N(SiMe3)2]2. An improved synthesis of (C5Me5)2U(µ-Ph)2BPh2 was developed, which was used to synthesize (C5Me5)2U(C5Me4H). Since the X-ray crystal structure of (C5Me5)2U(OC6H2tBu2-2,6-Me-4) contained two very different molecules in the asymmetric unit with 115.7(5)° and 166.0(5)° U-O-Cipso angles, the (C5Me4H)2U(OC6H2tBu2-2,6-Me-4) and (C5Me5)2Ce(OC6H2tBu2-2,6-Me-4) analogues were synthesized and characterized by X-ray diffraction for comparison. Electrochemical studies in THF with a 100 mM [nBu4N][BPh4] supporting electrolyte showed U(IV)/U(III) and U(III)/U(II) redox couples for all the heteroleptic complexes except (C5Me5)2U(C5H5). Chemical reduction of all heteroleptic compounds formed dark blue solutions characteristic of U(II) when reacted with KC8 at -78 °C, but none formed isolable U(II) complexes. The targeted U(II) complexes, [(C5Me5)2U(OC6H2tBu2-2,6-Me-4)]1-, {(C5Me5)2U[CH(SiMe3)2]}1-, [(C5Me5)2U(C5H5)]1-, and [(C5Me5)2U(C5Me4H)]1-, were analyzed by density functional theory, and a 5f36d1 electron configuration was found to be the ground state in each case.

9.
Inorg Chem ; 61(44): 17713-17718, 2022 Nov 07.
Artículo en Inglés | MEDLINE | ID: mdl-36282945

RESUMEN

The utility of γ irradiation for generating unstable, low oxidation state molecular species containing rare-earth metal ions in frozen solution has been examined. The method was evaluated by irradiating Ln(III) precursors (Ln = Sc, Y, and La) in a solid matrix of 2-methyltetrahydrofuran at 77 K with a 700 keV 137Cs source to generate free electrons capable of reducing the Ln(III) species. These experiments yielded EPR and UV-visible spectroscopic data that matched those of the known Ln(II) species [(C5H4SiMe3)3YII]1-, [(C5H4SiMe3)3LaII]1-, and {ScII[N(SiMe3)2]3}1-. Irradiation of the La(III) complex LaIII[N(SiMe3)2]3 by this method gave EPR and UV-visible absorption spectra consistent with {LaII[N(SiMe3)2]3}1-, a species that had previously eluded preparation by chemical reduction. Specifically, the irradiation product exhibited an axial EPR spectrum split into eight lines by the I = 7/2 139La nucleus (g⊥ = 1.98, g|| = 2.06, Aave = 519.1 G). The UV-visible absorption spectrum contains broad bands centered at 390 and 670 nm that are consistent with a La(II) ion in a trigonal ligand environment based on time-dependent density functional theory which qualitatively reproduces the observed spectrum. Additionally, the rate of formation of the [(C5H4SiMe3)3YII]1- species during the irradiation of (C5H4SiMe3)3YIII was monitored by measuring the concentration via UV-visible spectroscopy over time to provide data on the rate at which a molecular species is reduced in a glass via γ irradiation.


Asunto(s)
Complejos de Coordinación , Metales de Tierras Raras , Modelos Moleculares , Ligandos , Iones/química
10.
J Chem Phys ; 157(16): 164107, 2022 Oct 28.
Artículo en Inglés | MEDLINE | ID: mdl-36319432

RESUMEN

An analytical implementation of static dipole polarizabilities within the generalized Kohn-Sham semicanonical projected random phase approximation (GKS-spRPA) method for spin-restricted closed-shell and spin-unrestricted open-shell references is presented. General second-order analytical derivatives of the GKS-spRPA energy functional are derived using a Lagrangian approach. By resolution-of-the-identity and complex frequency integration methods, an asymptotic O(N4⁡log(N)) scaling of operation count and O(N3) scaling of storage is realized, i.e., the computational requirements are comparable to those for GKS-spRPA ground state energies. GKS-spRPA polarizabilities are assessed for small molecules, conjugated long-chain hydrocarbons, metallocenes, and metal clusters, by comparison against Hartree-Fock (HF), semilocal density functional approximations (DFAs), second-order Møller-Plesset perturbation theory, range-separated hybrids, and experimental data. For conjugated polydiacetylene and polybutatriene oligomers, GKS-spRPA effectively addresses the "overpolarization" problem of semilocal DFAs and the somewhat erratic behavior of post-PBE RPA polarizabilities without empirical adjustments. The ensemble averaged GKS-spRPA polarizabilities of sodium clusters (Nan for n = 2, 3, …, 10) exhibit a mean absolute deviation comparable to PBE with significantly fewer outliers than HF. In conclusion, analytical second-order derivatives of GKS-spRPA energies provide a computationally viable and consistent approach to molecular polarizabilities, including systems prohibitive for other methods due to their size and/or electronic structure.

11.
J Chem Phys ; 157(11): 111102, 2022 Sep 21.
Artículo en Inglés | MEDLINE | ID: mdl-36137777

RESUMEN

It has been known for more than a decade that the gauge variance of the kinetic energy density τ leads to additional terms in the magnetic orbital rotation Hessian used in linear-response time-dependent density functional theory (TDDFT), affecting excitation energies obtained with τ-dependent exchange-correlation functionals. While previous investigations found that a correction scheme based on the paramagnetic current density has a small effect on benchmark results, we report more pronounced effects here, in particular, for the popular M06-2X functional and for some other meta-generalized gradient approximations (mGGAs). In the first part of this communication, this is shown by a reassessment of a set of five Ni(II) complexes for which a previous benchmark study that did not impose gauge invariance has found surprisingly large errors for excitation energies obtained with M06-2X. These errors are more than halved by restoring gauge invariance. The variable importance of imposing gauge invariance for different mGGA-based functionals can be rationalized by the derivative of the mGGA exchange energy integrand with respect to τ. In the second part, a large set of valence excitations in small main-group molecules is analyzed. For M06-2X, several selected n → π* and π→π⊥ * excitations are heavily gauge-dependent with average changes of -0.17 and -0.28 eV, respectively, while π→π‖ * excitations are marginally affected (-0.04 eV). Similar patterns, but of the opposite signs, are found for SCAN0. The results suggest that reevaluation of previous gauge variant TDDFT results based on M06-2X and other mGGA functionals is warranted.

12.
J Am Chem Soc ; 143(40): 16610-16620, 2021 10 13.
Artículo en Inglés | MEDLINE | ID: mdl-34586787

RESUMEN

The capacity of X-ray photoelectron spectroscopy (XPS) to provide information on the electronic structure of molecular organometallic complexes of Ln(II) ions (Ln = lanthanide) has been examined for the first time. XPS spectra were obtained on the air-sensitive molecular trivalent 4fn Cp'3LnIII complexes (Ln = Sm, Eu, Gd, Tb; Cp' = C5H4SiMe3) and compared to those of the highly reactive divalent complexes, [K(crypt)][Cp'3LnII] (crypt = 2.2.2-cryptand), which have either 4fn+1 (Sm, Eu) or 4fn5d1 electron configurations (Gd, Tb). The Ln 4d, Si 2p, and C 1s regions of the Ln(III) and Ln(II) complexes were identified and compared. The metal 4d peaks of these molecular lanthanide complexes were used diagnostically to compare oxidation states. The valence region of the Gd(III) and Gd(II) complexes was also examined with XPS and density function theory/random phase approximation (DFT/RPA) calculations, and this led to the tentative assignment of a signal from the 5d1 electron consistent with a 4f75d1 electron configuration for Gd(II).

13.
J Am Chem Soc ; 143(22): 8465-8475, 2021 Jun 09.
Artículo en Inglés | MEDLINE | ID: mdl-34029482

RESUMEN

We report the synthesis and characterization of the trinuclear 4d-4f compounds [Co(C5Me5)2][(C5Me5)2Ln(µ-S)2Mo(µ-S)2Ln(C5Me5)2], 1-Ln (Ln = Y, Gd, Tb, Dy), containing the highly polarizable MoS43- bridging unit. UV-Vis-NIR diffuse reflectance spectra and DFT calculations of 1-Ln reveal a low-energy metal-to-metal charge transfer transition assigned to charge transfer from the singly occupied 4dz2 orbital of MoV to the empty 5d orbitals of the lanthanides (4d in the case of 1-Y), mediated by sulfur-based 3p orbitals. Electron paramagnetic resonance spectra collected for 1-Y in a tetrahydrofuran solution show large 89Y hyperfine coupling constants of A⊥ = 23 MHz and A|| = 26 MHz, indicating the presence of significant yttrium-localized unpaired electron density. Magnetic susceptibility data support similar electron delocalization and ferromagnetic Ln-Mo exchange for 1-Gd, 1-Tb, and 1-Dy. This ferromagnetic exchange gives rise to an S = 15/2 ground state for 1-Gd and one of the largest magnetic exchange constants involving GdIII observed to date, with JGd-Mo = +16.1(2) cm-1. Additional characterization of 1-Tb and 1-Dy by ac magnetic susceptibility measurements reveals that both compounds exhibit slow magnetic relaxation. Although a Raman magnetic relaxation process is dominant for both 1-Tb and 1-Dy, an extracted thermal relaxation barrier of Ueff = 68 cm-1 for 1-Dy is the largest yet reported for a complex containing a paramagnetic 4d metal center. Together, these results provide a potentially generalizable route to enhanced nd-4f magnetic exchange, revealing opportunities for the design of new nd-4f single-molecule magnets and bulk magnetic materials.

14.
Inorg Chem ; 60(21): 16316-16325, 2021 Nov 01.
Artículo en Inglés | MEDLINE | ID: mdl-34644069

RESUMEN

Density functional theory (DFT) calculations on four known and seven hypothetical U(II) complexes indicate the importance of coordination geometry in favoring 5f36d1 versus 5f4 electronic ground states. The known [Cp″3U]-, [Cptet3U]-, and [U(NR2)3]- [Cp″ = C5H3(SiMe3)2, Cptet = C5Me4H, and R = SiMe3] anions were found to have 5f36d1 ground states, while a 5f4 ground state was found for the known compound (NHAriPr6)2U. The UV-visible spectra of the known 5f36d1 compounds were simulated via time-dependent DFT and are in qualitative agreement with the experimental spectra. For the hypothetical U(II) compounds, the 5f36d1 configuration is predicted for [U(CHR2)3]-, [U(H3BH)3]-, [U(OAr')4]2-, and [(C8H8)U]2- (OAr' = O-C6H2tBu2-2,6-Me-4). In the case of [U(bnz')4]2- (bnz' = CH2-C6H4tBu-4), a 5f3 configuration with a ligand-based radical was found as the ground state.

15.
J Chem Phys ; 155(4): 040902, 2021 Jul 28.
Artículo en Inglés | MEDLINE | ID: mdl-34340391

RESUMEN

This Perspective reviews recent efforts toward selfconsistent calculations of ground-state energies within the random phase approximation (RPA) in the (generalized) Kohn-Sham (KS) density functional theory context. Since the RPA correlation energy explicitly depends on the non-interacting KS potential, an additional condition to determine the energy as a functional of the density is necessary. This observation leads to the concept of functional selfconsistency (FSC), which requires that the KS density equals the interacting density defined as the functional derivative of the ground-state energy with respect to the external potential. While all existing selfconsistent RPA schemes violate FSC, the recent generalized KS semicanonical projected RPA (GKS-spRPA) method takes a step toward satisfying it. This leads to systematic improvements in densities, binding energy curves, reference state stability, and molecular properties compared to non-selfconsistent RPA as well as optimized effective potential RPA. GKS-spRPA orbital energies accurately approximate valence and core ionization potentials, and even electron affinities of non-valence bound anions. The computational cost and performance of GKS-spRPA are compared to those of related selfconsistent schemes, including GW and orbital optimization methods, and limitations are discussed. Large differences between KS and interacting densities observed in the absence of FSC and the well-rounded performance of GKS-spRPA suggest that the KS potential as a density functional should be defined via the FSC condition for explicitly potential-dependent density functionals.

16.
J Am Chem Soc ; 142(20): 9302-9313, 2020 05 20.
Artículo en Inglés | MEDLINE | ID: mdl-32223162

RESUMEN

Lanthanide-based dinitrogen reduction chemistry has been expanded by the discovery of the first end-on Ln2(µ-η1:η1-N2) complexes, whose synthesis and reactivity help explain the reduction of N2 by the combination of trivalent Ln(NR2)3 complexes (R = SiMe3) and potassium. The formation of end-on versus the more common side-on Ln2(µ-η2:η2-N2) complexes is possible by using recently discovered Ln(II) complexes ligated by three NR2 amide ligands (R = SiMe3). The isolated Ln(II) tris(amide) complex [K(crypt)][Tb(NR2)3] (crypt = 2.2.2-cryptand), 1-Tb, reacts with dinitrogen in Et2O at -35 °C to form the end-on bridging dinitrogen complex [K(crypt)]2{[(R2N)3Tb]2[µ-η1:η1-N2]}, 2-Tb. The 18-crown-6 (18-c-6) Tb(II) analogue, [K(18-c-6)2][Tb(NR2)3], 3-Tb, also reacts with N2 to form an end-on product, [K2(18-c-6)3]{[(R2N)3Tb]2[µ-η1:η1-N2]}, 4-Tb. The reaction of 1-Gd with dinitrogen forms a complex with the same composition as 2-Tb but with both side-on and end-on bonding of the N2 unit in the same crystal, [K(crypt)]2{[(R2N)3Gd]2[µ-ηx:ηx-N2]} (x = 1 and 2), 5-Gd. Similarly, the 18-c-6 Gd(II) complex, 3-Gd, generates a product with both binding modes: [K2(18-c-6)3]{[(R2N)3Gd]2[µ-ηx:ηx-N2]} (x = 1, 2), 6-Gd. All of these new reduced dinitrogen complexes, 2-Tb, 4-Tb, 5-Gd, and 6-Gd, have three ancillary amide ligands per metal. In contrast, the side-on bound complexes, [(THF)(R2N)2Ln]2[µ-η2:η2-N2], 7-Ln, observed previously in Ln(NR2)3/K/N2 reactions, have only two amides per metal. A connection between these systems related to their formation was observed in the structure of the bimetallic penta-amide complex, [K(THF)6]{[(THF)(R2N)2Gd][µ-η2:η2-N2][Gd(NR2)3]}, 8-Gd, synthesized at -196 °C. Reaction conditions are crucial in this dinitrogen reaction system. When 5-Gd and 6-Gd are warmed above -15 °C, they reform Gd(II) complexes. If 1-Gd is dissolved in THF instead of Et2O under N2, the irreversible formation of an (N2)3- complex [K(crypt)][(THF)(R2N)2Gd]2[µ-η2:η2-N2], 9-Gd, is observed.

17.
Nat Chem Biol ; 14(3): 276-283, 2018 03.
Artículo en Inglés | MEDLINE | ID: mdl-29334380

RESUMEN

The discovery of functional RNAs that are critical for normal and disease physiology continues to expand at a breakneck pace. Many RNA functions are controlled by the formation of specific structures, and an understanding of each structural component is necessary to elucidate its function. Measuring solvent accessibility intracellularly with experimental ease is an unmet need in the field. Here, we present a novel method for probing nucleobase solvent accessibility, Light Activated Structural Examination of RNA (LASER). LASER depends on light activation of a small molecule, nicotinoyl azide (NAz), to measure solvent accessibility of purine nucleobases. In vitro, this technique accurately monitors solvent accessibility and identifies rapid structural changes resulting from ligand binding in a metabolite-responsive RNA. LASER probing can further identify cellular RNA-protein interactions and unique intracellular RNA structures. Our photoactivation technique provides an adaptable framework to structurally characterize solvent accessibility of RNA in many environments.


Asunto(s)
Azidas/química , Conformación de Ácido Nucleico , ARN/química , Solventes/química , Cristalografía por Rayos X , Guanosina/química , Células HeLa , Humanos , Enlace de Hidrógeno , Ligandos , Luz , Biología Molecular , Unión Proteica , Pliegue de Proteína , Mapeo de Interacción de Proteínas , Purinas/química , ARN Ribosómico 18S/química , Ribonucleoproteína Nuclear Pequeña U1/química , Thermoanaerobacter
18.
19.
J Chem Phys ; 152(18): 184107, 2020 May 14.
Artículo en Inglés | MEDLINE | ID: mdl-32414256

RESUMEN

TURBOMOLE is a collaborative, multi-national software development project aiming to provide highly efficient and stable computational tools for quantum chemical simulations of molecules, clusters, periodic systems, and solutions. The TURBOMOLE software suite is optimized for widely available, inexpensive, and resource-efficient hardware such as multi-core workstations and small computer clusters. TURBOMOLE specializes in electronic structure methods with outstanding accuracy-cost ratio, such as density functional theory including local hybrids and the random phase approximation (RPA), GW-Bethe-Salpeter methods, second-order Møller-Plesset theory, and explicitly correlated coupled-cluster methods. TURBOMOLE is based on Gaussian basis sets and has been pivotal for the development of many fast and low-scaling algorithms in the past three decades, such as integral-direct methods, fast multipole methods, the resolution-of-the-identity approximation, imaginary frequency integration, Laplace transform, and pair natural orbital methods. This review focuses on recent additions to TURBOMOLE's functionality, including excited-state methods, RPA and Green's function methods, relativistic approaches, high-order molecular properties, solvation effects, and periodic systems. A variety of illustrative applications along with accuracy and timing data are discussed. Moreover, available interfaces to users as well as other software are summarized. TURBOMOLE's current licensing, distribution, and support model are discussed, and an overview of TURBOMOLE's development workflow is provided. Challenges such as communication and outreach, software infrastructure, and funding are highlighted.

20.
Angew Chem Int Ed Engl ; 59(37): 16141-16146, 2020 Sep 07.
Artículo en Inglés | MEDLINE | ID: mdl-32441487

RESUMEN

Lanthanide triflates have been used to incorporate NdIII and SmIII ions into the 2.2.2-cryptand ligand (crypt) to explore their reductive chemistry. The Ln(OTf)3 complexes (Ln=Nd, Sm; OTf=SO3 CF3 ) react with crypt in THF to form the THF-soluble complexes [LnIII (crypt)(OTf)2 ][OTf] with two triflates bound to the metal encapsulated in the crypt. Reduction of these LnIII -in-crypt complexes using KC8 in THF forms the neutral LnII -in-crypt triflate complexes [LnII (crypt)(OTf)2 ]. DFT calculations on [NdII (crypt)]2+ ], the first NdII cryptand complex, assign a 4f4 electron configuration to this ion.

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