The Year-Long Development of Microorganisms in Uncompacted Bavarian Bentonite Slurries at 30 and 60 °C.

In the multibarrier concept for the deep geological disposal of high-level radioactive waste (HLW), bentonite is proposed as a potential barrier and buffer material for sealing the space between the steel canister containing the HLW and the surrounding host rock. In order to broaden the spectra of appropriate bentonites, we investigated the metabolic activity and diversity of naturally occurring microorganisms as well as their time-dependent evolution within the industrial B25 Bavarian bentonite under repository-relevant conditions. We conducted anaerobic microcosm experiments containing the B25 bentonite and a synthetic Opalinus Clay pore water solution, which were incubated for one year at 30 and 60 °C. Metabolic activity was only stimulated by the addition of lactate, acetate, or H2. The majority of lactate- and H2-containing microcosms at 30 °C were dominated by strictly anaerobic, sulfate-reducing, and spore-forming microorganisms. The subsequent generation of hydrogen sulfide led to the formation of iron-sulfur precipitations. Independent from the availability of substrates, thermophilic bacteria dominated microcosms that were incubated at 60 °C. However, in the respective microcosms, no significant metabolic activity occurred, and there was no change in the analyzed biogeochemical parameters. Our findings show that indigenous microorganisms of B25 bentonite evolve in a temperature- and substrate-dependent manner.

Interaction of Uranium(VI) with α-Amylase and Its Implication for Enzyme Activity.

Because of its chemo- and radiotoxicity, the incorporation of uranium into human body via ingestion potentially poses a serious health risk. When ingested, the gastrointestinal fluids are the primary media to interact with uranium, eventually influencing and even determining its biochemical behavior in the gastrointestinal tract and thereafter. The chemical interactions between uranium and the components of gastrointestinal fluids are, however, poorly understood to date. In this study, the complexation of uranium(VI) (as the uranyl ion, UO22+) with the protein α-amylase, one of the major enzymes in saliva and pancreatic juices, was investigated over a wide range of pH or uranium/α-amylase concentrations covering physiological conditions. Macroscopic sorption experiments suggested a strong and fast complexation of UO22+ to α-amylase between pH 5 and 7. Potentiometric titration was employed to determine the complex stability constants for the relevant UO22+ α-amylase complexes, which is crucial for reliable thermochemical modeling to assess the potential health risk of uranium. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that α-amylase is interacting with UO22+ primarily via its carboxylate groups presumably from the aspartic acid and glutamic acid side chains. The effect of UO22+ on the enzyme activity was also investigated to understand the potential implication of uranium for the in vivo functions of the digestive fluids, indicating that the presence of uranium inhibits the enzyme activity. This inhibitory effect can be, however, suppressed by an excess of calcium.

Synthesis and Characterization of Heterometallic Iron-Uranium Complexes with a Bidentate N-Donor Ligand (2,2'-Bipyridine or 1,10-Phenanthroline).

The coordination chemistry of the diimine ligands, 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen), with d- and f-block metals has been extensively explored during the last century to yield many technological and industrial applications. Despite this long history, the chemistry of these diimine ligands in heterometallic systems containing multiple metals is poorly understood even to date. This study reports, for the first time, a systematic investigation into the coordination behavior bipy/phen in the heterometallic iron-uranium system covering all the combinations of the possible redox couples (i.e., Fe2+/Fe3+ and U4+/U6+) that are potentially relevant to the actual engineered or environmental systems. In total, 11 new compounds of pure uranium and heterometallic Fe-U complexes were successfully synthesized and structurally characterized. The synthesized compounds show an intriguing structural variety in terms of the nuclearity of the metal center (mono- and dinuclear arrangements for both Fe and U) and the manner of crystal packing based on different intra- and intermolecular interactions (e.g., π···π interactions, hydrogen bonding, etc.). The results also highlight the similarity of the fundamental coordination properties of bipy and phen toward Fe and U, regardless of the oxidation states of the metals, as well as the striking dissimilarity in their chemical behavior upon crystal packing.

Impact of Haloarchaea on Speciation of Uranium-A Multispectroscopic Approach.

Haloarchaea represent a predominant part of the microbial community in rock salt, which can serve as host rock for the disposal of high level radioactive waste. However, knowledge is missing about how Haloarchaea interact with radionuclides. Here, we used a combination of spectroscopic and microscopic methods to study the interactions of an extremely halophilic archaeon with uranium, one of the major radionuclides in high level radioactive waste, on a molecular level. The obtained results show that Halobacterium noricense DSM 15987T influences uranium speciation as a function of uranium concentration and incubation time. X-ray absorption spectroscopy reveals the formation of U(VI) phosphate minerals, such as meta-autunite, as the major species at a lower uranium concentration of 30 µM, while U(VI) is mostly associated with carboxylate groups of the cell wall and extracellular polymeric substances at a higher uranium concentration of 85 µM. For the first time, we identified uranium biomineralization in the presence of Halobacterium noricense DSM 15987T cells. These findings highlight the potential importance of Archaea in geochemical cycling of uranium and their role in biomineralization in hypersaline environments, offering new insights into the microbe-actinide interactions in highly saline conditions relevant to the disposal of high-level radioactive waste as well as bioremediation.

[UO2 Cl2 (phen)2 ], a Simple Uranium(VI) Compound with a Significantly Bent Uranyl Unit (phen=1,10-phenanthroline).

A simple synthesis based on UO2 Cl2 ⋅n H2 O and 1,10-phenanthroline (phen) resulted in the formation of a new uranyl(VI) complex [UO2 Cl2 (phen)2 ] (1), revealing a unique dodecadeltahedron coordination geometry around the uranium center with significant bending of the robust linear arrangement of the uranyl (O-U-O) unit. Quantum chemical calculations on complex 1 indicated that the weak but distinct interactions between the uranyl oxygens and the adjacent hydrogens of phen molecules play an important role in forming the dodecadeltahedron geometry that fits to the crystal structure of 1, resulting in the bending the uranyl unit. The uranyl oxygens in 1 are anticipated to be activated as compared with those in other linear uranyl(VI) compounds.

Synthesis of Coordination Polymers of Tetravalent Actinides (Uranium and Neptunium) with a Phthalate or Mellitate Ligand in an Aqueous Medium.

Four metal-organic coordination polymers bearing uranium or neptunium have been hydrothermally synthesized from a tetravalent actinide chloride (AnCl4) and phthalic (1,2-H2bdc) or mellitic (H6mel) acid in aqueous media at 130 °C. With the phthalate ligand, two analogous assemblies ([AnO(H2O)(1,2-bdc)]2·H2O; An = U4+ (1) or Np4+ (2)) have been isolated, in which the square-antiprismatic polyhedra of AnO8 are linked to each other via µ3-oxo groups with an edge-sharing mode to materialize infinite zigzag ribbons. The phthalate molecules play a role in connecting the adjacent zigzag chains to build a two-dimensional (2D) network. Water molecules are bonded to the actinide center or found intercalated between the layers. With the mellitate ligand, two distinct structures have been identified. The uranium-based compound [U2(OH)2(H2O)2(mel)] (3) exhibits a three-dimensional (3D) structure composed of the dinuclear units of UO8 polyhedra (square antiprism), which are further linked via the µ2-hydroxo groups. The mellitate linkers use their carboxylate groups to connect the dinuclear units, eventually building a 3D framework. The compound obtained for the neptunium mellitate ([(NpO2)10(H2O)14(Hmel)2]·12H2O (4)) reveals oxidation of the initial NpIV to NpV under the applied hydrothermal synthetic conditions, yielding the neptunyl(V) (NpO2+) unit with a pentagonal-bipyramidal NpO7 environment. This further leads to the formation of a layered assembly of the square-frame NpO7 sheets via the bridging oxygen atoms from the neptunyl oxo groups, which further coordinate to the pentagonal equatorial coordination plane of the adjacent neptunium unit (i.e., cation-cation interactions). In compound 4, the mellitate molecules act as bridging linkers between the NpO7 sheets by using four of their carboxylage groups, eventually building up a 3D structure.

Fate of Plutonium at a Former Nuclear Testing Site in Australia.

A series of the British nuclear tests conducted on mainland Australia between 1953 and 1963 dispersed long-lived radioactivity and nuclear weapons debris including plutonium (Pu), the legacy of which is a long-lasting source of radioactive contamination to the surrounding biosphere. A reliable assessment of the environmental impact of Pu contaminants and their implications for human health requires an understanding of their physical/chemical characteristics at the molecular scale. In this study, we identify the chemical form of the Pu remaining in the local soils at the Taranaki site, one of the former nuclear testing sites at Maralinga, South Australia. We herein reveal direct spectroscopic evidence that the Pu legacy remaining at the site exists as particulates of Pu(IV) oxyhydroxide compounds, a very concentrated and low-soluble form of Pu, which will serve as ongoing radioactive sources far into the future. Gamma-ray spectrometry and X-ray fluorescence analysis on a collected Pu particle indicate that the Pu in the particle originated in the so-called "Minor trials" that involved the dispersal of weapon components by highly explosive chemicals, not in the nuclear explosion tests called "Major trials". A comprehensive analysis of the data acquired from X-ray fluorescence mapping (XFM), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) suggests that the collected Pu particle forms a "core-shell" structure with the Pu(IV) oxyhydroxide core surrounded by an external layer containing Ca, Fe, and U, which further helps us to deduce a possible scenario of the physical/chemical transformation of the original Pu materials dispersed in the semiarid environment at Maralinga more than 50 years ago. These findings also highlight the importance of the comprehensive physical/chemical characterization of Pu contaminants for reliable environmental- and radiotoxicological assessment.

Formation of neptunium(IV)-silica colloids at near-neutral and slightly alkaline pH.

The reducing conditions in a nuclear waste repository render neptunium tetravalent. Thus, Np is often assumed to be immobile in the subsurface. However, tetravalent actinides can also become mobile if they occur as colloids. We show that Np(IV) is able to form silica-rich colloids in solutions containing silicic acid at concentrations of both the regions above and below the "mononuclear wall" of silicic acid at 2 × 10(-3) M (where silicic acid is expected to start polymerization). These Np(IV)-silica colloids have a size of only very few nanometers and can reach significantly higher concentrations than Np(IV) oxyhydroxide colloids. They can be stable in the waterborne form over longer spans of time. In the Np(IV)-silica colloids, the actinide--oxygen--actinide bonds are increasingly replaced by actinide--oxygen--silicon bonds due to structural incorporation of Si. Possible implications of the formation of such colloids for environmental scenarios are discussed.

Optimizing the design and synthesis of supported silver nanoparticles for low cost water disinfection.

Silver nanoparticles (AgNPs) were successfully synthesized and impregnated on silica using chemical reduction methods. XPS and Ag K-edge XANES analysis revealed that the impregnation of AgNPs onto silica using a chitosan + sodium borohydride (NaBH4) method results in higher silver loading and Ag(0)/Ag(I) ratio compared to that obtained using NH3 + NaBH4/glucose methods. The effects of the dosage of chitosan on silver loading, Ag(I) release, and bactericidal activities of AgNP-impregnated silica were investigated, with results showing that, at high dosages of chitosan, Ag(I) released from AgNP-impregnated silica plays an important role in disinfection, while AgNP-mediated bactericidal action dominates at low dosages of chitosan. To further decrease the manufacturing cost, partially oxidized "black rice husk ash" containing substantial residual carbon was applied as AgNP support and found to lead to a greater degree of silver impregnation and to exhibit a longer disinfection lifetime than that of lower carbon content silica supports. On the basis of these findings, it is clear that considerable scope exists for careful optimization in the design and production of AgNP-based bactericidal materials for water treatment purposes.

Solution speciation of plutonium and Americium at an Australian legacy radioactive waste disposal site.

During the 1960s, radioactive waste containing small amounts of plutonium (Pu) and americium (Am) was disposed in shallow trenches at the Little Forest Burial Ground (LFBG), located near the southern suburbs of Sydney, Australia. Because of periodic saturation and overflowing of the former disposal trenches, Pu and Am have been transferred from the buried wastes into the surrounding surface soils. The presence of readily detected amounts of Pu and Am in the trench waters provides a unique opportunity to study their aqueous speciation under environmentally relevant conditions. This study aims to comprehensively investigate the chemical speciation of Pu and Am in the trench water by combining fluoride coprecipitation, solvent extraction, particle size fractionation, and thermochemical modeling. The predominant oxidation states of dissolved Pu and Am species were found to be Pu(IV) and Am(III), and large proportions of both actinides (Pu, 97.7%; Am, 86.8%) were associated with mobile colloids in the submicron size range. On the basis of this information, possible management options are assessed.

Investigation of continuous changes in the electric-field-induced electronic state in Bi(1-x)Ca(x)FeO(3-δ).

Amongst the most interesting phenomena in correlated oxide systems are the doping-driven competitions between energetically similar ground states found in, e.g., high-Tc superconductors and colossal magnetoresistance manganites. It has recently been reported that doped multiferroics also exhibit this generic concept of phase competition. Here, we employ photoelectron emission microscopy (PEEM) to demonstrate evidence of systematic changes in the electronic structure of Bi(1-x)Ca(x)FeO(3-δ) treated by electrically controlled hole carrier doping, the outcome of which clearly correlates with the local modulation of electronic conductivity observed in the same material.

Globular pattern formation of hierarchical ceria nanoarchitectures.

Dissipative structures often appear as an unstable counterpart of ordered structures owing to fluctuations that do not form a homogeneous phase. Even a multiphase mixture may simultaneously undergo one chemical reaction near equilibrium and another one that is far from equilibrium. Here, we observed in real time crystal seed formation and simultaneous nanocrystal aggregation proceeding from CeIV complexes to CeO2 nanoparticles in an acidic aqueous solution, and investigated the resultant hierarchical nanoarchitecture. The formed particles exhibited two very different size ranges, resulting in further pattern formation with opalescence. The hierarchically assembled structures in solutions were CeO2 colloids, viz. primary core clusters (1-3 nm) of crystalline ceria and secondary clusters (20-30 nm) assembled through surface ions. Such self-assembly is widespread in multi-component complex fluids, paradoxically moderating hierarchical reactions. Stability and instability are not only critical but also complementary for co-optimisation around the nearby free energy landscape prior to bifurcation.

Hydrolysis of tetravalent cerium for a simple route to nanocrystalline cerium dioxide: an in situ spectroscopic study of nanocrystal evolution.

Despite the rapid developments in recent nanocrystal research and their expanding applications, the evolution mechanism of nanocrystals remains veiled for the most part due to the lack of appropriate analytical techniques. Here we demonstrate one promising multi-spectroscopic approach for the in situ investigation of nanocrystal evolution. That is, the formation of nanocrystalline cerium dioxide (NC-CeO2) has been probed by dynamic light scattering (DLS), X-ray absorption spectroscopy (XAS) and high-energy X-ray scattering (HEXS). The obtained results indicate that the fine colloidal particles of NC-CeO2 are formed in an acidic aqueous solution simply through the hydrolysis of the initial precursor of small oligomer Ce(IV) species. This information on how NC-CeO2 evolves is fundamental to simplifying and alleviating the synthetic strategy for NC-CeO2 production.

Crystal structure and solution species of Ce(III) and Ce(IV) formates: from mononuclear to hexanuclear complexes.

Cerium(III) and cerium(IV) both form formate complexes. However, their species in aqueous solution and the solid-state structures are surprisingly different. The species in aqueous solutions were investigated with Ce K-edge EXAFS spectroscopy. Ce(III) formate shows only mononuclear complexes, which is in agreement with the predicted mononuclear species of Ce(HCOO)(2+) and Ce(HCOO)2(+). In contrast, Ce(IV) formate forms in aqueous solution a stable hexanuclear complex of [Ce6(µ3-O)4(µ3-OH)4(HCOO)x(NO3)y](12-x-y). The structural differences reflect the different influence of hydrolysis, which is weak for Ce(III) and strong for Ce(IV). Hydrolysis of Ce(IV) ions causes initial polymerization while complexation through HCOO(-) results in 12 chelate rings stabilizing the hexanuclear Ce(IV) complex. Crystals were grown from the above-mentioned solutions. Two crystal structures of Ce(IV) formate were determined. Both form a hexanuclear complex with a [Ce6(µ3-O)4(µ3-OH)4](12+) core in aqueous HNO3/HCOOH solution. The pH titration with NaOH resulted in a structure with the composition [Ce6(µ3-O)4(µ3-OH)4(HCOO)10(NO3)2(H2O)3]·(H2O)9.5, while the pH adjustment with NH3 resulted in [Ce6(µ3-O)4(µ3-OH)4(HCOO)10(NO3)4]·(NO3)3(NH4)5(H2O)5. Furthermore, the crystal structure of Ce(III) formate, Ce(HCOO)3, was determined. The coordination polyhedron is a tricapped trigonal prism which is formed exclusively by nine HCOO(-) ligands. The hexanuclear Ce(IV) formate species from aqueous solution is widely preserved in the crystal structure, whereas the mononuclear solution species of Ce(III) formate undergoes a polymerization during the crystallization process.

Synthesis and characterization of antibacterial silver nanoparticle-impregnated rice husks and rice husk ash.

Silver nanoparticle (AgNP)-impregnated rice husks/rice hush ash (RHs/RHA) were successfully synthesized, and their potential application as antibacterial materials in water disinfection was investigated with particular attention given to the use of both white rice husk ash (WRHA) and black rice husk ash (BRHA) produced by the combustion of RHs as AgNP supports. AgNPs, with diameter of ∼20 nm, were anchored tightly onto RHA, with the emplacement of the AgNPs on these supports increasing the antibacterial activity of the AgNPs through diminution in the extent of nanoparticle aggregation. Ag K-edge XANES analysis revealed that AgNP-impregnated RHs/RHA are composed of both Ag(0) and Ag(I) species with the Ag(I)/Ag(0) ratio following the order WRHA (65:35) > RHs (59:41) > BRHA (7:93). Sodium thioglycolate, a strong Ag(I) ligand, significantly affected the bactericidal activities of AgNP-impregnated RHs/RHA, suggesting that Ag(I) released from AgNP-impregnated RHs/RHA plays an important role in disinfection. The rate constants of oxidative and dissociative dissolution of Ag(0) and Ag(I) species associated with BRHA are 5.0 × 10(-4) M(-1)s(-1) and 1.0 × 10(-5) s(-1), respectively, while those associated with WRHA are 7.0 × 10(-2) M(-1)s(-1) and 2.0 × 10(-4) s(-1) respectively, demonstrating that the rate of dissolution of silver associated with BRHA is particularly slow. As such, the bactericidal "lifetime" of this material is long and exhibits a lower health risk as a result of release of Ag(I) to consumers than does AgNP-impregnated WRHA.

Specific cooperative effect of a macrocyclic receptor for metal ion transfer into an ionic liquid.

An intramolecular cooperative extraction system for the removal of strontium cations (Sr(2+)) from water by use of a novel macrocyclic receptor (H(2)ßDA18C6) composed of diaza-18-crown-6 and two ß-diketone fragments in ionic liquid (IL) is reported, together with X-ray spectroscopic characterization of the resulting extracted complexes in the IL and chloroform phases. The covalent attachment of two ß-diketone fragments to a diazacrown ether resulted in a cooperative interaction within the receptor for Sr(2+) transfer, which remarkably enhanced the efficiency of Sr(2+) transfer relative to a mixed ß-diketone and diazacrown system. The intramolecular cooperative effect was observed only in the IL extraction system, providing a 500-fold increase in extraction performance for Sr(2+) over chloroform. Slope analysis and potentiometric titration confirmed that identical extraction mechanisms operated in both the IL and chloroform systems. Extended X-ray absorption fine structure spectroscopy revealed that the average distance between Sr(2+) and O atoms in the Sr(2+) complex was shorter in IL than in chloroform. Consequently, Sr(2+) was held by H(2)ßDA18C6 more rigidly in IL than in chloroform, representing an important factor dominating the magnitude of the intramolecular cooperative effect of H(2)ßDA18C6 for Sr(2+). Furthermore, competitive extraction studies with alkaline earth metal ions revealed that the magnitude of the intramolecular cooperative effect depended on the suitability between metal ion size and the cavity size of H(2)ßDA18C6. Sr(2+) was successfully recovered from IL by controlling the pH in the receiving phase, and the extraction performance of H(2)ßDA18C6 in IL was maintained after five repeated uses.

Structure of the {U13} polyoxo cluster U13O8Cl x (MeO)38-x (x = 2.3, MeO = methoxide).

The structure of a new type of polyoxo cluster complex that contains thirteen uranium atoms, {U13}, is reported. The complex crystallized from methanol containing tetra-valent uranium (UIV) with a basic organic ligand, and was characterized as di-chloridoocta-cosa-µ2-methano-lato-octa-kis-(methano-lato)octa-µ4-oxido-trideca-uranium, [U13(CH3O)35.7Cl2.3O8] or [U13(µ4-Ooxo)8Cl x (MeO)38-x ] (x = 2.3, MeO = methoxide) (I), by single-crystal X-ray diffraction. The characterized {U13} polyoxo cluster complex (I) possesses a single cubic uranium polyhedron at the centre of the cluster core. To the best of our knowledge, this is the very first example of a polyoxo actinide complex that bears a single cubic polyhedron in its structure. The cubic polyhedron in I is well comparable in shape with those in bulk UO2. The U-O bonds in the cubic polyhedron of I are, however, significantly shorter than those not only in bulk UO2 but also in another analogue in the {U38} cluster. This shortening of U-O bonds, together with BVS calculations and the overall negative charge (2-) of I, suggests that the central uranium atom in I, which forms the single cubic coordination polyhedron, is presumably oxidized to the penta-valent state (UV) from the original tetra-valent state (UIV). Complex I is, hence, the first example of a polyoxo cluster possessing a single cubic coordination polyhedron of UV.

Local coordination about La(3+) in molten LaCl3 and its mixtures with alkali chlorides.

The local structure around the La(3+) ions in molten LaCl(3) and its mixtures with alkali and alkaline earth chlorides has been investigated by using extended X-ray absorption fine structure (XAFS) and molecular dynamics (MD) techniques. Such mixtures, which are of current technological interest, are known to be thermodynamically nonideal, and there has been a good deal of work to understand the structural effects factors that contribute to the nonideality. New experimental methods allow observations at the La K-absorption edge at the high temperatures of interest, and the ability of the technique to obtain reliable information even at very low La(3+) concentrations in multicomponent mixtures is demonstrated. Both the mean La(3+)-Cl(-) interionic separation and the mean La(3+) coordination number are found to decrease as the concentration of La(3+) in the mixture decreases. The rate of decrease depends on the identity of the alkali and alkaline earth cations present in the mixtures in a way that parallels the degree of nonideality of the different systems; it is greatest for those alkali cations that coordinate Cl(-) weakly. In dilute mixtures with such cations La(3+) is able to adopt a very stable octahedral coordination geometry but this is inhibited by the presence of more strongly coordinating cations like Li(+) and Mg(2+).

Solvent Extraction of Technetium(VII) and Rhenium(VII) Using a Hexaoctylnitrilotriacetamide Extractant.

Liquid-liquid extraction for the removal of pertechnetate (99TcO4-) and perrhenate (ReO4-) is reported based on using the tripodal extractant N,N,N',N',N″,N″-hexa-n-octylnitrilotriacetamide (HONTA) composed of three amide groups and a tertiary amine. The extraction behaviors were compared with those using alkyldiamideamines (ADAAM(Oct) and ADAAM(EH)), and the commercial amine-type extractant, trioctylamine (TOA). HONTA quantitatively extracted 99TcO4- and ReO4- in the pH range from 1.0 to 2.5 by the co-extraction of protons. The extraction performance of the extractants was improved in the order of HONTA > ADAAM(Oct) > ADAAM(EH) > TOA. 99TcO4- and ReO4- in the extracting phase were successfully stripped using neutral aqueous solutions as the receiving phase, and the extraction ability of HONTA was maintained after five repeated uses.

Systematic comparison of the structure of homoleptic tetradentate N2O2-type Schiff base complexes of tetravalent f-elements (M(IV) = Ce, Th, U, Np, and Pu) in solid state and in solution.

A series of tetradentate N2O2-type Schiff base complexes with tetravalent 4f- and 5f-block metals, [M(salpn)2] (H2salpn = N,N'-disalicylidene-1,3-diaminopropane; M = Ce, Th, U, Np, and Pu), were prepared to systematically investigate their solid state structure, and their complexation behaviour in solution with the goal to investigate the subtle differences between 4f- and 5f-elements. X-ray diffraction revealed that all investigated metal cations form [M(salpn)2] complexes. All the complexes show the same ligand arrangement with meridional conformation, amongst which only Ce(iv) exhibits unique behaviour upon crystallisation. [Ce(salpn)2] crystallises in two less symmetric systems (P1[combining macron] or P21/n), whilst all the other [M(salpn)2] crystallise in a more symmetric orthorhombic system (Pban). Quantum chemical calculations suggest that the observed structural peculiarity of Ce(iv) stems from the geometrical flexibility due to the more "ionic" nature of bonds to the 4f element. 1H NMR measurements revealed that [M(salpn)2] forms two different species in solution with and without an additional solvent molecule, where the relative distribution of the two species depends mainly on the ionic radius of the metal centre. Again, Ce(iv) behaves differently from the tetravalent actinides with a higher ratio of the solvent-molecule-coordinated species than the ratio expected from its ionic radius. Hence, this study is successful in observing subtle differences between 4f- (i.e. Ce) and 5f-elements (actinides; Th, U, Np, and Pu) both in the solid state and in solution on an analytically distinguishable level, and in relating the observed subtle differences to their electronic structure.