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1.
Nat Commun ; 13(1): 201, 2022 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-35017503

RESUMO

Variations in bonding between trivalent lanthanides and actinides is critical for reprocessing spent nuclear fuel. The ability to tune bonding and the coordination environment in these trivalent systems is a key factor in identifying a solution for separating lanthanides and actinides. Coordination of 4,4'-bipyridine (4,4'-bpy) and trimethylsilylcyclopentadienide (Cp') to americium introduces unexpectedly ionic Am-N bonding character and unique spectroscopic properties. Here we report the structural characterization of (Cp'3Am)2(µ - 4,4'-bpy) and its lanthanide analogue, (Cp'3Nd)2(µ - 4,4'-bpy), by single-crystal X-ray diffraction. Spectroscopic techniques in both solid and solution phase are performed in conjunction with theoretical calculations to probe the effects the unique coordination environment has on the electronic structure.

2.
Chem Commun (Camb) ; 2022 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-35072187

RESUMO

A berkelium(III) mellitate, Bk2[C6(CO2)6](H2O)8·2H2O, was synthesized and rapidly crystallized by reacting mellitic acid, C6(CO2H)6, and BkBr3·nH2O in an aqueous medium. Single crystal X-ray diffraction shows that the compound crystallizes as a three-dimensional framework isostructural with Pu(III), Am(III), and Cm(III) mellitates. UV-vis-NIR spectroscopic studies as a function of pressure were performed using a diamond anvil cell and show that the 5f → 5f transitions of Bk3+ display enhanced hypsochromic shifting when compared to other An(III) mellitates.

3.
Nat Commun ; 12(1): 7230, 2021 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-34893651

RESUMO

Controlling the properties of heavy element complexes, such as those containing berkelium, is challenging because relativistic effects, spin-orbit and ligand-field splitting, and complex metal-ligand bonding, all dictate the final electronic states of the molecules. While the first two of these are currently beyond experimental control, covalent M‒L interactions could theoretically be boosted through the employment of chelators with large polarizabilities that substantially shift the electron density in the molecules. This theory is tested by ligating BkIII with 4'-(4-nitrophenyl)-2,2':6',2"-terpyridine (terpy*), a ligand with a large dipole. The resultant complex, Bk(terpy*)(NO3)3(H2O)·THF, is benchmarked with its closest electrochemical analog, Ce(terpy*)(NO3)3(H2O)·THF. Here, we show that enhanced Bk‒N interactions with terpy* are observed as predicted. Unexpectedly, induced polarization by terpy* also creates a plane in the molecules wherein the M‒L bonds trans to terpy* are shorter than anticipated. Moreover, these molecules are highly anisotropic and rhombic EPR spectra for the CeIII complex are reported.

4.
Nature ; 599(7885): 421-424, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34789902

RESUMO

Californium (Cf) is currently the heaviest element accessible above microgram quantities. Cf isotopes impose severe experimental challenges due to their scarcity and radiological hazards. Consequently, chemical secrets ranging from the accessibility of 5f/6d valence orbitals to engage in bonding, the role of spin-orbit coupling in electronic structure, and reactivity patterns compared to other f elements, remain locked. Organometallic molecules were foundational in elucidating periodicity and bonding trends across the periodic table1-3, with a twenty-first-century renaissance of organometallic thorium (Th) through plutonium (Pu) chemistry4-12, and to a smaller extent americium (Am)13, transforming chemical understanding. Yet, analogous curium (Cm) to Cf chemistry has lain dormant since the 1970s. Here, we revive air-/moisture-sensitive Cf chemistry through the synthesis and characterization of [Cf(C5Me4H)2Cl2K(OEt2)]n from two milligrams of 249Cf. This bent metallocene motif, not previously structurally authenticated beyond uranium (U)14,15, contains the first crystallographically characterized Cf-C bond. Analysis suggests the Cf-C bond is largely ionic with a small covalent contribution. Lowered Cf 5f orbital energy versus dysprosium (Dy) 4f in the colourless, isoelectronic and isostructural [Dy(C5Me4H)2Cl2K(OEt2)]n results in an orange Cf compound, contrasting with the light-green colour typically associated with Cf compounds16-22.

5.
Dalton Trans ; 50(41): 14537-14541, 2021 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-34635890

RESUMO

The interplay of bond strength and covalency are examined in AnO2Cl2(OPcy3)2 (An = Pu, U) complexes. The synthesis of trans-PuO2Cl2(OPcy3)2, 1-Pu, has been carried out and confirmed by single crystal X-ray diffraction along with UV-vis-NIR, and 31P NMR spectroscopies. Theoretical analysis finds that despite a higher calculated covalency for the Pu-Cl interaction, the Pu-OPcy3 interaction is stronger due to the accumulation of electron density in the interatomic region. The coordination of equatorial ligands slightly decreases the strength of the PuOyl interactions relative to the free gas phase (PuO2)2+ ion.

6.
Inorg Chem ; 60(20): 15242-15252, 2021 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-34569783

RESUMO

Using a redox-active dioxophenoxazine ligand, DOPO (DOPO = 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazine-9-olate), a family of actinide (U, Th, Np, and Pu) and Hf tris(ligand) coordination compounds was synthesized. The full characterization of these species using 1H NMR spectroscopy, electronic absorption spectroscopy, SQUID magnetometry, and X-ray crystallography showed that these compounds are analogous and exist in the form M(DOPOq)2(DOPOsq), where two ligands are of the oxidized quinone form (DOPOq) and the third is of the reduced semiquinone (DOPOsq) form. The electronic structures of these complexes were further investigated using CASSCF calculations, which revealed electronic structures consistent with metals in the +4 formal oxidation state and one unpaired electron localized on one ligand in each complex. Furthermore, f orbitals of the early actinides show a sizable bonding overlap with the ligand 2p orbitals. Notably, this is the first example of a plutonium-ligand radical species and a rare example of magnetic data being recorded for a homogeneous plutonium coordination complex.

7.
Inorg Chem ; 60(11): 7815-7826, 2021 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-33990139

RESUMO

Lanthanides such as europium with more accessible divalent states are useful for studying redox stability afforded by macrocyclic organic ligands. Substituted cryptands, such as 2.2.2B cryptand, that increase the oxidative stability of divalent europium also provide coordination environments that support synthetic alterations of Eu(II) cryptate complexes. Two single crystal structures were obtained containing nine-coordinate Eu(II) 2.2.2B cryptate complexes that differ by a single coordination site, the occupation of which is dictated by changes in reaction conditions. A crystal structure containing a [Eu(2.2.2B)Cl]+ complex is obtained from a methanol-THF solvent mixture, while a methanol-acetonitrile solvent mixture affords a [Eu(2.2.2B)(CH3OH)]2+ complex. While both crystals exhibit the typical blue emission observed in most Eu(II) containing compounds as a result of 4f65d1 to 4f7 transitions, computational results show that the substitution of a Cl- anion in the place of a methanol molecule causes mixing of the 5d excited states in the Eu(II) 2.2.2B cryptate complex. Additionally, magnetism studies reveal the identity of the capping ligand in the Eu(II) 2.2.2B cryptate complex may also lead to exchange between Eu(II) metal centers facilitated by π-stacking interactions within the structure, slightly altering the anticipated magnetic moment. The synthetic control present in these systems makes them interesting candidates for studying less stable divalent lanthanides and the effects of precise modifications of the electronic structures of low valent lanthanide elements.

8.
Inorg Chem ; 60(1): 476-483, 2021 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-33325231

RESUMO

The mellitate ion is relevant in spent nuclear fuel processing and is utilized as a surrogate for studying the interactions of f elements with humic acids. A wealth of different coordination modes gives the potential for diverse structural chemistry across the actinide series. In this study, an americium mellitate, 243Am2[(C6(COO-)6](H2O)8·2H2O (1-Am), has been synthesized and characterized using structural analysis and spectroscopy at ambient and elevated pressures. 1-Am was then compared to isomorphous neodymium (1-Nd) and samarium (1-Sm) mellitates via bond-length analysis and pressure dependence of their Laporte-forbidden f → f transitions. Results show that the pressure dependence of the f → f transitions of 1-Am is significantly greater than that observed in 1-Nd and 1-Sm, with average shifts of 21.4, 4.7, and 3.6 cm-1/GPa, respectively. This greater shift found in 1-Am shows further evidence that the 5f orbitals are more affected than the 4f orbitals when pressure is applied to isostructural compounds.

9.
Inorg Chem ; 59(24): 18035-18047, 2020 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-33238091

RESUMO

A pair of neptunium Schiff base coordination complexes, NpVIO2L(MeOH) and NpIVL2 {H2L = N,N'-bis[(4,4'-diethylamino)salicylidene]-1,2-phenylenediamine}, have been synthesized and analyzed by several characterization methods including single-crystal X-ray diffraction, electronic absorption, 1H NMR, cyclic voltammetry, and theoretical interpretation. Structural analysis reveals that NpVIO2L(MeOH) and NpIVL2 are isomorphous with the previously reported UVIO2L(MeOH) and MIVL2 (M = Pu, Ce, U, Th) complexes, respectively, allowing for a direct comparison across the series. The reduction of NpVIO2L(MeOH) in situ or direct synthesis from a (NpVO2)+ source shows evidence of a pentavalent neptunyl (NpVO2L)xn- species as determined by UV/vis/NIR and 1H NMR spectroscopy. The synthesis of (NpVO2L)xn- directly from a (NpVO2)+ starting material gives a similar spectrum. Theoretical analysis offers insight into the electronic structure for a better understanding of the bonding patterns and relative stability of the different oxidation states. Computational results show that the Np-L covalent interactions in NpIVL2 are similar to those in the NpVIO2L(MeOH) complex, indicating that neither the presence of the axial oxo ligands nor the oxidation state significantly modify the nature of the Np-L bonds.

10.
Inorg Chem ; 59(22): 16291-16300, 2020 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-33119988

RESUMO

A facile synthesis of an americium complex with a sulfur-donor ligand has been developed, allowing characterization of americium bonding from multiple perspectives via several techniques. Reaction of 243Am with S2P(OEt)2- yields the tetrakis complex [Am(S2P(OEt)2)4]- that can be crystallized as the tetraphenylarsonium salt. Structures obtained from single crystal X-ray diffraction show bond length discrepancies from the neodymium analogue consistent with the soft-donor bond enhancement common to actinides. Solid state optical spectroscopy confirms interaction of the ligand with 5f orbitals. 31P nuclear magnetic reflects the minor paramagnetism of Am(III). Computational investigations through CASSCF calculations, ligand-field density functional theory, and quantum chemical topological analysis allow a quantification of covalency or orbital interaction effects via total energy density and nephelauxetic parameters, both of which indicate greater covalency in the americium species than in the neodymium analogue or the americium aquo complex.

11.
Inorg Chem ; 59(18): 13301-13314, 2020 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-32910649

RESUMO

An approach to obtaining substantial amounts of data from a hazardous starting material that can only be obtained and handled in small quantities is demonstrated by the investigation of a single small-scale reaction of cyclooctatetraene, C8H8, with a solution obtained from the reduction of Cp'3Pu (Cp' = C5H4SiMe3) with potassium graphite. This one reaction coupled with oxidation of a product has provided single-crystal X-ray structural data on three organoplutonium compounds as well as information on redox chemistry thereby demonstrating an efficient route to new reactivity and structural information on this highly radioactive element. The crystal structures were obtained from the reduction of C8H8 by a putative Pu(II) complex, (Cp'3PuII)1-, generated in situ, to form the Pu(III) cyclooctatetraenide complex, [K(crypt)][(C8H8)2PuIII], 1-Pu, and the tetra(cyclopentadienyl) Pu(III) complex, [K(crypt)][Cp'4PuIII], 2-Pu. Oxidation of the sample of 1-Pu with Ag(I) afforded a third organoplutonium complex that has been structurally characterized for the first time, (C8H8)2PuIV, 3-Pu. Complexes 1-Pu and 3-Pu contain Pu sandwiched between parallel (C8H8)2- rings. The (Cp'4PuIII)- anion in 2-Pu features three η5-Cp' rings and one η1-Cp' ring, which is a rare example of a formal Pu-C η1-bond. In addition, this study addresses the challenge of small-scale synthesis imparted by radiological and material availability of transuranium isotopes, in particular that of pure metal samples. A route to an anhydrous Pu(III) starting material from the more readily available PuIVO2 was developed to facilitate reproducible syntheses and allow complete spectroscopic analysis of 1-Pu and 2-Pu. PuIVO2 was converted to PuIIIBr3(DME)2 (DME = CH3OCH2CH2OCH3) and subsequently PuIIIBr3(THF)x, which was used to independently synthesize 1-Pu, 2-Pu, and 3-Pu.

12.
Nature ; 583(7816): 396-399, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32669698

RESUMO

Curium is unique in the actinide series because its half-filled 5f 7 shell has lower energy than other 5f n configurations, rendering it both redox-inactive and resistant to forming chemical bonds that engage the 5f shell1-3. This is even more pronounced in gadolinium, curium's lanthanide analogue, owing to the contraction of the 4f orbitals with respect to the 5f orbitals4. However, at high pressures metallic curium undergoes a transition from localized to itinerant 5f electrons5. This transition is accompanied by a crystal structure dictated by the magnetic interactions between curium atoms5,6. Therefore, the question arises of whether the frontier metal orbitals in curium(III)-ligand interactions can also be modified by applying pressure, and thus be induced to form metal-ligand bonds with a degree of covalency. Here we report experimental and computational evidence for changes in the relative roles of the 5f/6d orbitals in curium-sulfur bonds in [Cm(pydtc)4]- (pydtc, pyrrolidinedithiocarbamate) at high pressures (up to 11 gigapascals). We compare these results to the spectra of [Nd(pydtc)4]- and of a Cm(III) mellitate that possesses only curium-oxygen bonds. Compared with the changes observed in the [Cm(pydtc)4]- spectra, we observe smaller changes in the f-f transitions in the [Nd(pydtc)4]- absorption spectrum and in the f-f emission spectrum of the Cm(III) mellitate upon pressurization, which are related to the smaller perturbation of the nature of their bonds. These results reveal that the metal orbital contributions to the curium-sulfur bonds are considerably enhanced at high pressures and that the 5f orbital involvement doubles between 0 and 11 gigapascal. Our work implies that covalency in actinides is complex even when dealing with the same ion, but it could guide the selection of ligands to study the effect of pressure on actinide compounds.

13.
Inorg Chem ; 59(15): 10794-10801, 2020 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-32648751

RESUMO

In this study, the synthesis, characterization, and pressure response of a 1D californium mellitate (mellitate = 1,2,3,4,5,6-benzenehexacarboxylate) coordination polymer, Cf2(mell)(H2O)10·4H2O (Cf-1), are reported. The Cf-O lengths within the crystal structure are compared to its gadolinium (Gd-1) and holmium (Ho-1) analogs as well. These data show that the average Cf-O bond distance is slightly longer than the average Gd-O bond, consistent with trends in effective ionic radii. UV-vis-NIR absorption spectra as a function of pressure were collected using diamond-anvil techniques for both Cf-1 and Ho-1. These experiments show that the Cf(III) f → f transitions have a stronger dependence on pressure than that of the holmium analog. In the former case, the shift is nearly linear with applied pressure and averages 6.6 cm-1/GPa, whereas in the latter, it is <3 cm-1/GPa.

14.
Inorg Chem ; 59(13): 9384-9395, 2020 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-32575992

RESUMO

The synthesis, structure, and solid-state UV-vis-NIR spectroscopy of four new f-element squarates, M2(C4O4)3(H2O)4 (M = Eu, Am, Cf) and Sm(C4O4)(C4O3OH)(H2O)2·0.5H2O, four new cationic lanthanide squarate chlorides, [M4(C4O4)5(H2O)12]Cl2·5H2O (M = Eu, Dy, Ho Er), and two new actinide squarate oxalates, M2(C4O4)2(C2O4)(H2O)4 (M = Am, Cf), are presented. All of the metal centers are trivalent. Single-crystal X-ray diffraction analysis reveals that M2(C4O4)3(H2O)4 and Sm(C4O4)(C4O3OH)(H2O)2·0.5H2O have a two-dimensional sheet structure constructed from MO7(H2O)2 monocapped square-antiprismatic (coordination number (CN) = 9) metal centers and SmO6(H2O)2 square-antiprismatic (CN = 8) metal centers, respectively, whereas M2(C4O4)2(C2O4)(H2O)4 have a three-dimensional (3D) structure constructed from MO7(H2O)2 monocapped square-antiprismatic (CN = 9) metal centers. Additionally, the cationic framework materials [M4(C4O4)5(H2O)12]Cl2·5H2O have a 3D structure constructed from two crystallographically unique MO5(H2O)3 square-antiprismatic (CN = 8) metal centers. In these structures, the squarate ligands bind to the metal centers with varying coordination modes and denticities. The results of this study provide another example of the nonparallel chemistry between the lanthanides and transplutonium elements. From the crystallographic data for the isotypic series M2(C4O4)3(H2O)4 (M = La-Nd, Sm, Eu) and the linear regression fit to a plot of the unit cell volume as a function of the cube of the ionic radius, the nine-coordinate ionic radius of Cf 3+ was determined to be 1.127 ± 0.003 Å. Finally, computational analysis of the americium and californium complexes M2(C4O4)3(H2O)4 and M2(C4O4)2(C2O4)(H2O)4 reveals three important attributes: (i) the 5f orbitals are nonbonding in all cases, with the bonding differences occurring with the empty 6d orbitals; (ii) the Cf complexes exhibit more covalent character than their Am counterparts; and (iii) there is more covalent character in the squarate-oxalate complexes than in the squarate complexes.

15.
Inorg Chem ; 59(7): 4176-4180, 2020 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-32212622

RESUMO

The structural chemistry of elements relevant to the FLiBe molten salt reactor, Th, U, Np, and Zr, including Ce and Nd (as analogues for Pu and Am, respectively), have been examined using hydrothermal synthesis at 200 °C. These reactions serve to model the reaction of molten salts under hydrolysis conditions. The results show that U and Np formed LiAnF5, while Ce formed Li4CeF8. The source of U also controlled the crystal quality, where UO2 gave small crystals, while UO3·2H2O gave very large crystals. It is likely that Be incorporation was not observed because of the high solubility of [BeF4]2- in water. Zr formed a third product, Li6BeF4ZrF8, which features isolated [BeF4]2- and [ZrF8]4- units bridged by Li+. Additionally, Li2BeF4 was regularly isolated. When little to no alkali metal was included in the reaction, M3F12(H2O) was isolated for Np, U, and Ce.

16.
Inorg Chem ; 59(5): 3085-3090, 2020 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-32037813

RESUMO

The aqueous reaction of mellitic acid (H6mell) with 242PuBr3·nH2O forms two plutonium mellitates, 242Pu2(mell)(H2O)9·H2O (Pu-1α) and 242Pu2(mell)(H2O)8·2H2O (Pu-1ß). These compounds are compared to the isomorphous lanthanide mellitates with similar ionic radii via bond length analysis. Both plutonium compounds form three-dimensional metal-organic frameworks, with Pu-1α having two unique metal centers and Pu-1ß having one. All plutonium metal centers exhibit nine-coordinate geometries. Our results show metal-oxygen bond lengths for plutonium significantly shorter than those of the previously reported lanthanum and herein reported cerium analogues, consistent with the nine-coordinate ionic radii. Clear Laporte-forbidden 5f → 5f transitions are observed in the ultraviolet-visible-near-infrared spectra and are assigned to trivalent plutonium. However, there is a distinct color difference between the two plutonium compounds.

17.
Chem Sci ; 11(10): 2770-2782, 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-34084337

RESUMO

The synthesis, characterization, and theoretical analysis of meridional americium tribromide tris(tricyclohexylphosphine oxide), mer-AmBr3(OPcy3)3, has been achieved and is compared with its early lanthanide (La to Nd) analogs. The data show that homo trans ligands display significantly shorter bonds than the cis or hetero trans ligands. This is particularly pronounced in the americium compound. DFT along with multiconfigurational CASSCF calculations show that the contraction of the bonds relates qualitatively with overall covalency, i.e. americium shows the most covalent interactions compared to lanthanides. However, the involvement of the 5p and 6p shells in bonding follows a different order, namely cerium > neodymium ∼ americium. This study provides further insight into the mechanisms by which ITI operates in low-valent f-block complexes.

18.
Inorg Chem ; 58(21): 14790-14799, 2019 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-31647651

RESUMO

The reaction of 242PuO2 with HF and LiF under hydrothermal conditions results in the formation of Li4PuF8 and LiPuF5. These compounds were structurally characterized using single-crystal X-ray diffraction, and UV-vis-near-IR absorption spectroscopy was employed to confirm the oxidation state of the plutonium in the compounds as 4+. The structure of Li4PuF8 consists of [PuF8]4- anions that adopt a bicapped trigonal-prismatic geometry with approximate C2v symmetry. These molecules are bridged by Li+ cations. In contrast, LiPuF5 forms a dense three-dimensional network constructed from [PuF9]5- units that are bridged by F- anions. The Pu4+ cations are found within tricapped trigonal prisms. Extensive theoretical analysis of the electronic and bonding interactions is included with a comparison between the results derived from complete-active-space self-consistent-field at different levels of theory, quantum theory of atoms in molecules, interacting quantum atom, natural localized molecular orbital, and Wiberg bond order analyses. Covalent interactions in these compounds are examined, and intramolecular trends in covalent and electrostatic interactions are discussed.

19.
Inorg Chem ; 58(16): 10578-10591, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31298847

RESUMO

A series of eighteen tetravalent actinide (An = Th, U, Pu) compounds were synthesized from acidic aqueous solutions containing thorium, uranium, or plutonium and a series of protonated nitrogen heterocycles. The compounds were characterized using Raman, IR, and optical absorption spectroscopies. The structures were determined using single-crystal X-ray diffraction and found to consist of [An(H2O)xCly]4-y (x = 4-7 and y = 2-4) or AnCl62- molecular units. Breaks in the structural chemistry of the early actinides were observed, with Th adopting exclusively Th-aquo-chloro species and Pu forming only PuCl62-; U crystallized as both U-aquo-chloro and UCl62-. The relationship between the solid-state structural units and the solution species was interrogated using UV-vis-near-IR absorption spectroscopy. A comparison of the solution and solid-state spectra suggested that, although prevalent in the solid state, particularly for U and Pu, AnCl62- does not exist to an appreciable extent in the reaction solution. Despite the identification of U-aquo-chloro species in solution, there are limited reports of these complexes in the solid state. Isolation of these unique actinide(IV) chlorides as reported in this work may point to the importance of nonbonding interactions in the stabilization and precipitation of AnIV structural units.

20.
Chemistry ; 25(13): 3248-3252, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30716170

RESUMO

[M(EtBTP)3 ][BPh4 ]3 ⋅3 CH3 CN (M=Nd, Am; EtBTP=2,6-bis(5,6-diethyl-1,2,4-triazin-3-yl)pyridine) have been synthesized from reactions of MCl3 ⋅n H2 O with EtBTP in acetonitrile followed by anion metathesis. Structural analysis reveals that these compounds contain M3+ cations bound by tridentate EtBTP ligands to create a tricapped trigonal prismatic geometry around the metal centers. Collection of high-resolution, single-crystal X-ray diffraction data also allowed reduction in bond lengths esd's, such that a slight contraction of Δ=0.0158(18) Šin the Am-N versus Nd-N bond lengths was observed, even though these cations ostensibly have matching ionic radii. Theoretical evaluation revealed enhanced metal-ligand bonding through back donation in the [Am(EtBTP)3 ]3+ complex that is absent in [Nd(EtBTP)3 ]3+ .

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