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Understanding how structural changes of the ligand scaffold influence the coordination chemistry of early actinides is indispensable for the development of selective ligands for e.g. decontamination purposes. To obtain a profound insight into the electronic und bonding properties of early actinides, Schiff base ligands based on the salen type, have been extensively used in our group and others.[1–4] Schiff bases have shown to be excellent model ligands due to their accessible synthesis and easy functionalization and their ability to coordinate to the 5f-elements. In this respect, we have been exploring the coordination chemistry of the early actinides (Th – Pu) with pyrophen, a pure nitrogen donor ligand formed by a condensation reaction of 2-formylpyrrole with o-phenylendiamine.[5,6] A series of homoleptic 2:1 complexes has been synthesized, allowing the comparison of the hard oxygen donor of the phenolate group in the salophen system versus the soft nitrogen donor of the pyrrolide group in pyrophen. Quantum chemical calculations along with spectroscopic studies by nuclear magnetic resonance (NMR) and single crystal x-ray diffraction (SC-XRD) have been performed to elucidate the influence of hard and soft donors on the bonding strength. In solution, as confirmed by NMR, we encountered just one set of signals corresponding to a 2:1 homoleptic complex in the pyrophen system compared to two sets of signals corresponding to 2:1 homoleptic isomers present in the salophen case. In the solid state, crystallographic analysis shows that the salophen ligand adopts a sandwich like structure whereas in the pyrophen system a pincer like arrangement is preferred (see figure below). Figure 1 Uranium(IV) complexes of salophen (left) and pyrophen (right) References [1] T. Radoske et al., Dalton Transactions 2020, 49, 17559–17570. [2] R. Kloditz et al., Inorg. Chem. 2021, 60, 2514–2525. [3] L. Köhler et al., Chemistry – A European Journal 2021, 27, 18058–18065. [4] B. E. Klamm et al

The 5f electrons of particularly the early actinides are found to participate in bonding, e.g. to organic ligands, in contrast to the strongly shielded 4f electrons of the lanthanides. Reactivity and complexation strength of such bonds are affected by donor properties of the ligand and the electronic situation of the actinide metal center. Furthermore, coinciding properties of ligand and actinide ion regarding Pearson’s principle of hard and soft acids and bases (HSAB) can even drive the development of selective ligands, e.g. for extraction processes. Here, soft N-donor ligands were found to interact stronger with trivalent actinides in comparison to their harder lanthanide analogues.1 To evaluate how these electronic properties can be extended to a series of tetravalent actinides and their interactions with N-donor ligands, we have studied the complexation of tetravalent Th, Pa, U, Np, and Pu with the amidinate (S,S)-N,N’-bis-(1-phenylethyl)-benzamidine (PEBA), and the Schiff base N,N’-ethylene-bis((pyrrole-2-yl)methan¬imine (pyren).2-4 Complex syntheses using one equivalent of AnCl4(dme)x (An = Th, U, Np, Pu; x = 0 for U, x = 2 for Th, Np, Pu) and three equivalents of PEBA, or two equivalents of pyren led to isostructural heteroleptic 3:1 complexes [AnCl(PEBA)3] or homoleptic 2:1 complexes [An(pyren)2]. Both series were analyzed in the solid state by SC-XRD and IR, as well as in solution by NMR spectroscopy. SC-XRD results and quantum chemical calculations (QCC) revealed differences in AnIV–ligand bond length and strength between the different nitrogen donors (Namidinate, Nimine, Npyrrolide). In addition, with the help of QCC, trends regarding the covalency of the metal-ligand bonds could be derived and assigned to the involved orbitals. Delocalization indices for N–PaIV showed a strong preference of the highly polarizable 5f 1 configuration of PaIV to pyren in its homoleptic complex. This effect disappears in the heteroleptic amidinate complex. Calculated quadrup

Reaction of the N-heterocylic carbene ligand iPrIm (L1) and lithium bis(trimethylsilyl)amide (TMSA) as a base with UCl4 resulted in U(IV) and U(V) complexes. Uranium’s +V oxidation state in (HL1)2[U(V)(TMSI)Cl5] (TMSI = trimethylsilylimido) (2) was confirmed by HERFD-XANES measurements. Solid state characterization by SC-XRD and geometry optimisation of [U(IV)(L1)2(TMSA)Cl3] (1) indicated a silylamido ligand mediated inverse trans influence (ITI). The ITI was examined regarding different metal oxidation states and was compared to transition metal analogues by theoretical calculations.

Actinide coordination chemistry has attracted chemists´ interest for decades in terms of nuclear safety, catalysis, or radiopharmaceutical research. Especially the early actinides exhibit an unusually large range of oxidation states, which originates in the near degeneracy of the 5f, 6d and 7s energy levels. This offers unique chemical and physical properties, not yet fully understood. Schiff bases like the mixed N, O donor ligands of the salen (Bis(salicyliden)ethylendiamine) family are frequently chosen systems for complexation studies, because of their advantageous ability to stabilize a large number of metals including actinides, as well as their tuneable electronical and sterical properties. Based on pyrrole structural relatives of salen can be constructed, which only exhibit N-donor functionalities. This provides the possibility to investigate and compare the binding situation between early actinides and N atoms in different environments. In this study a complex series with Th and U as well as the transuranic elements Np and Pu with the pyrrole-based ligand 1,2-ethylenediamine-N,N’-bis(1H-pyrrol-2-yl)methylene (H2pyren) H2L1 was synthesized. Characterization in solid state (via SC-XRD) shows an 8-fold coordination at the metal centre, where all N donors participate. Moreover, the An−Npyrrolide bond distance is in all cases shorter, compared to the An−Nimine bond. Quantum chemical calculations, including Pa(IV) prove not only the bond shortening, but also an increased bond strength for An−Npyrrolide over An−Nimine. Comparison to the salen system shows preference of the mixed N,O donor ligand over its pure N,N donor relative for Th as well as U-Pu. For Pa, however, the pyren ligand is preferred over salen, pointing to a special role of the f 1 electron configuration in actinide(IV) coordination chemistry. Synthesis of a mixed pyren salen complex shows a significant expansion of the 1H NMR shift range and altered signal position compared to the bis complexes. Thi

In contrast to the strongly shielded 4f electrons of the lanthanides, 5f electrons of particularly the early actinides are found to participate in bonding, e.g. to organic ligands. Reactivity and complexation strength of such bonds are the most influenced by donor properties of the ligand and the electronic situation of the actinide metal center. Furthermore, coinciding properties of ligand and actinide ion regarding Pearson’s principle of hard and soft acids and bases (HSAB) can even drive the development of selective ligands, e.g. for extraction processes. Here, soft N-donor ligands were found to interact stronger with trivalent actinides in comparison to their harder lanthanide analogues.1 To evaluate how these HSAB properties can be extended to a series of tetravalent actinides and their interactions with N-donor ligands, we have studied the complexation of tetravalent Th, Pa, U, Np, and Pu with N,N’-ethylene-bis((pyrrole-2-yl)methanimine (pyren) in comparison to its structural N,O-analogue, the salen ligand.2 Complex syntheses using one equivalent of AnCl4(dme)x (An = Th, U, Np, Pu; x = 0 for U, x = 2 for Th, Np, Pu) and two equivalents of pyren led to isostructural 2:1 complexes, which were analyzed in the solid state by SC-XRD and IR, as well as in solution via NMR spectroscopy. SC-XRD results and quantum chemical calculations revealed differences in AnIV–ligand bond length and strength within pyren (Nimine vs. Npyrrolide donors) or salen (Nimine vs. Ophenolate). Interestingly, the overall bond strength of the N-donor vs. N,O-donor to An(IV), however, is almost equal for both, [An(pyren)2] and [An(salen)2] (An = Th-Pu). Delocalization indices even confirmed slightly more covalent interactions between the N,O-donor salen and Th, U, Np, and Pu in comparison with pyren. For Pa, on the other hand, this trend is reversed. QTAIM analysis could prove particularly strong interactions with the pure N-donor ligand pyren. This extraordinarily good electron sharing betwe

This set includes single-crystal X-ray diffraction, IR, HERFD XANES and quantumchemical calculation data for the characterization of the synthesized U(IV) amido and U(V) imido complexes. Furthermore with this the inverse trans influence can be evaluated.

Schiff bases like the mixed N, O donor ligands of the salen (Bis(salicyliden)ethylendiamin) family are frequently chosen systems for complexation studies. Advantageous is their ability to stabilize a large number of metals including actinides, as well as their tuneable electronical and sterical properties.1–4 Pyrrol-based ligands are salen’s structural relatives, but only exhibit N-donor functionalities. This provides the possibility to investigate and compare the binding situation between early actinides and N atoms in different environments. In this study a complex series from Th to Pu with the pyrrol-based ligands 1,2-ethylenediamine-N,N’-bis(1H-pyrrol-2-yl)methylene (pyrenH2) L¹ H₂ and 1,2-benzenediamine-N,N’-bis(1H-pyrrol-2-yl)methylene (pyrophenH2) L² H₂ was synthesized. Characterization in solution (NMR) and solid state (SC-XRD) in combination with quantum chemical calculations reveal the different binding situations to the different N donors at the electronic level, which leads to unique paramagnetic behavior in solution. 1 B. E. Klamm et al., Chem. Commun., 2018, 54, 8634–8636. 2 A. N. Dame et al., Eur. J. Inorg. Chem., 2015, 2015, 2996–3005. 3 B. E. Klamm et al., Inorg. Chem., 2018, 57, 15389–15398. 4 T. Radoske et al., Chem. – Eur. J., 2020, 26, 16853–16859.

We report a series of isostructural tetravalent actinide (Th, U-Pu) complexes with the N-donor ligand N,N'-ethylene-bis((pyrrole-2-yl)methanimine) (H₂ L, H₂ pyren). Structural data from SC-XRD analysis reveal [An(pyren)₂ ] complexes with different An–N(imine) vs. An–N(pyrrolide) bond lengths, respectively. Quantum chemical calculations elucidate the bonding situation, including differences in covalent character of the coordinative bonds. A comparison to the intensely studied analogous N,N′‐ethylene‐bis(salicylideneimine) (H₂ salen) based complexes [An(salen)₂ ] displays on average almost equal electron sharing of pyren or salen with the An(IV), pointing to a potential ligand-cage-driven complex stabilization. This is shown in the fixed ligand arrangement of pyren and salen in the respective An(IV) complexes. The overall bond strength of the pure N-donor ligand pyren to An(IV) (An=Th, U, Np, Pu) is slightly weaker compared to salen, with the exception of the Pa(IV) complex, which exhibits extraordinarily high electron sharing of pyren with Pa(IV). Such an altered ligand preference within the early An(IV) series points to a specificity of the 5f¹ configuration, which can be explained by polarization effects of the 5f electrons, allowing strongest f electron backbonding from Pa(IV) (5f¹ ) to the N-donors of pyren.

Removing f-elements from anthropogenically contaminated sites is a challenging, but ecologically important task. Some of these elements are not only radioactive, but also chemically toxic and can spread through various pathways in the environment. The present work investigates f-element sorption on biogenic silica, which may be a promising “green” material for remediation. Commercially available diatomaceous earth (DE) and the cleaned cell walls of the diatom species Stephanopyxis turris (S.t.) and Thalassiosira pseudonana (T.p.) are compared with artificial mesocellular foam (MCF) as porous silica reference material. Trivalent europium was chosen as model sorptive for chemically similar trivalent actinides. Accordingly, Eu(III) in concentrations of 10-3 M and 10-5 M was sorbed on the four silica materials at varying pH values. The zeta potentials of the implemented sorbents under the same conditions were determined. In addition, the sorption reaction and the aqueous speciation of Eu(III) in the (bio)silica suspensions were modeled using the Diffuse Double Layer (DDL) model. With time-resolved laser-induced fluorescence spectroscopy (TRLFS), two different uptake mechanisms can be discerned, surface adsorption and incorporation/precipitation.

Diese Daten beinhalten die Synthese und Charakterisierung neuartiger Actinid (Th, U, Np, Pu) Komplexe mit pyrrolbasierten Liganden, sowie ebenfalls die Ligandsynthese. Darunter fallen SC-XRD, NMR, IR, UV-VIS und EA Daten. Des weiteren quantenchemische Berechnungen zu den Systemen, sowie der Vergleich zum bereits bekannten Salen System.