The binding strengths of ligand 2,2ʹ-bipyridine-6-carboxylate (BiPCA) and 1,10-phenanthroline-2-carboxylate (PhenCA) with trivalent actinides (An) like Am(III) and Cm(III), and lanthanides (Ln) like Nd(III), Sm(III), and Eu(III) were investigated by solvent extraction, potentiometry, and crystallography. Both ligands exhibit good actinides selectivity over lanthanides and radius selectivity for intragroup Ln(III) or An(III). In comparison, PhenCA is more prominent than BiPCA in these capabilities. Single crystal structures of the Nd(III)/Eu(III) with BiPCA and PhenCA illustrate that BiPCA, as well as PhenCA, is tridentate and chelates with Nd(III)/Eu(III) by two aromatic N-donors and a carboxyl O-donor. PhenCA exhibits shorter coordination bonds to the central atom than BiPCA, in agreement with the fact that in solution PhenCA behaves stronger binding strength than BiPCA to the same lanthanide cation. However, for the lanthanide complexes with the same ligand, no regular trend of the coordination bonds has been observed between Nd(III) and Eu(III).

The extraction complexes of uranyl（Ⅵ） in HNO 3 to a hydroxyl-functionalized ionic liquid（IL） phase,HOEtmimNTf2bearing CMPO, were investigated. Three possibly successive extraction complexes, UO 2 L 2+ （L = CMPO）, UO2L 2 2+ and UO 2 L 3 2+ , were detected based on variable U/L ratios. Uranyl（Ⅵ） prefers to be extracted as complex UO 2 L 3 2+ , combining with the ions from HOEtmimNTf 2 to construct a solid material through self-assembly. The thermodynamics of complexes, UO 2 L j 2+ （j = 1-3）, were studied by spectrophotometry and microcalorimetry. All the formation reactions are principally driven by entropy, although a small part of the driving force of complexes UO 2 L 2 2+ and UO 2 L 3 2+ comes from enthalpy. Based on the thermodynamic properties for complex UO 2 L 3 2+ , we provide a possible coordination mode in HOEtmim NTf 2 : the first CMPO molecule coordinates with UO 2 2+ in a bidentate fashion while the others do in a monodentate fashion. The results offer a thermodynamic insight into the formation behaviors of the uranyl（Ⅵ）/CMPO complexes involving the special IL HOEtmimNTf 2 , which is of significance to advance the novel IL extraction strategy.

The separation of tridentate actinides from lanthanides and that between Am(III) and Cm(III) is one of the most challenging tasks in the process of partitioning-transmutation of nuclear waste. Herein, we report a novel tridentate N-N-O hybrid ligand, i.e., N-ethyl-N-tolyl-2-amide-1,10-phenanthroline (ETPhenAm), for the selective extraction toward Am(III)/Cm(III) over Eu(III) from HNO3 solutions. ETPhenAm in 3-nitrotrifluorotoluene has excellent Am(III) extraction ability and Am(III)/Eu(III) separation performance. Notably, the good selectivity of ETPhenAm toward Am(III) over Cm(III) suggests that ETPhenAm exhibits good ionic radius selectivity in the interaction with the intraseries cations such as Am(III) and Cm(III). Extractive complexes of formula M(NO3)3L and M(NO3)3L2 (M = Am, Cm, and Eu) are identified in the extraction system. HNO3 concentration in the aqueous phase heavily affects the composition of the extractive species in the organic phase because of the strong basicity of ETPhenAm. Extraction observations are validated by determining the protonation constants of the ligand and the reaction equilibrium constants for the generation of complexes M(NO3)3L and M(NO3)3L2 (M = Nd and Eu) in CH3OH/10%(v)H2O solution. The structures of complexes M(NO3)3L and M(NO3)3L2 are confirmed through X-ray diffraction of compounds [La(NO3)3(ETPhenAm)2] (I), [Nd(NO3)2(ETPhenAm)2]NO3 (II), and [Eu(NO3)2(ETPhenAm)2]NO3 center dot[Eu(NO3)3(ETPhenAm)(CH3OH)]center dot 2CH3OH (III).

Crystals of U(vi) complexes with N,N,N′,N′-tetramethyl-2,2′-bipyridine-6,6′-dicarboxamide and N,N,N′,N′-tetramethyl-1,10-phenanthroline-2,9-dicarboxamide were obtained under variable reaction conditions, and the structures were determined by single-crystal X-ray diffraction.

The thermodynamics of Th(iv) complexes with N,N,N',N'-tetramethyl-2,2'-bipyridine-6,6'-dicarboxamide (TMBiPDA) and N,N,N',N'-tetramethyl-1,10-phenanthroline-2,9-dicarboxamide (TMPhenDA) in CH3OH/10%(v)H2O (CH3OH : H2O = 9 : 1 by volume) were determined by spectrophotometry and calorimetry. The ligand TMBiPDA/TMPhenDA coordinates with the central Th atom by the tetradentate (O-N-N-O) mode, which is validated by 1H NMR in solution and crystallography in the solid. The single crystal X-ray diffraction data show that ten-coordinated thorium coordinates with two ligand molecules and two solvent molecules (water or methanol). Both ThL and ThL2 complexes (L = TMPhenDA or TMBiPDA) were detected in solution. In thermodynamics, the formation of all complexes is driven by both enthalpy and entropy. In a comparison, enthalpy is more favorable to the formation of TMBiPDA complexes, while entropy is more favorable to the formation of TMPhenDA complexes; the entropy advantages of the TMPhenDA complexes override the enthalpy advantages of the corresponding TMBiPDA complexes, giving the TMPhenDA complexes higher stability constants than the TMBiPDA complexes. In crystallography, ligand distortions occur in ThL2 complexes, and TMBiDA distorts more than TMPhenDA does; the Th-O and Th-N bonds involving TMBiPDA are slightly shorter than those involving TMPhenDA.

Complexation of U(vi) with pyridazine-3-carboxylate (PDZ) and pyrazine-2-carboxylate (PAZ) was studied by spectrophotometry, potentiometry and microcalorimetry in 1.0 mol dm−3 NaClO4.

The stability constants (log β) of 1:1 uranyl complexes with three N,O-mixed donor ligands (L = 2,2'-dipyridyl-6,6'-dicarboxylate, 3,3'-dimethyl-2,2'-bipyridine-6,6'-dicarboxylate, and 1,10-phenanthroline-2,9-dicarboxylate, denoted as BiPDA, DmBiPDA, and PhenDA, respectively) in aqueous and DMSO/20%(v)H2O solutions were determined by spectrophotometry in 0.1 M tetraethylammonium perchlorate. The effects of ligand preorganization, steric hindrance, and solvation on the binding strength of U(VI) with the three ligands were discussed. In aqueous solution, PhenDA forms stronger complexes with U(VI) than BiPDA due to its well-preorganized structure. In DMSO/20%(v)H2O solution, in contrast, the strong solvation effect of DMSO on the ligands reduces the energy gap between the trans- and cis-conformations of BiPDA, resulting in log β(UO2(BiPDA)) > log β(UO2(PhenDA)). The steric hindrance of methyl groups on DmBiPDA makes the complex UO2(DmBiPDA) of the lowest stability in both aqueous and DMSO/20%(v)H2O solutions. Single-crystal structural data of U(VI) complexes with the three ligands indicate that the ligand coordinates with UO22+ via aromatic nitrogen atoms and carboxylate oxygen atoms. There is no clear correlation between the trend of the stability constants in solutions and the U-N/O bond lengths of the three crystal complexes. Nevertheless, DmBiPDA coordinates to UO22+ in a high-strain fashion as a result of the steric hindrance of methyl groups while BiPDA in a low-strain fashion, which is in accordance with the relative complexation strength of the two respective complexes. The results from this work help us understand the effect of ligand preorganization and solvation on the binding strength of actinides with multidentate N,O-mixed ligands in solid and solutions, which is of importance in designing ligands for the partitioning of actinides from nuclear wastes.

The thermodynamics of Nd(III) and Eu(III) complexes with N, N, N', N'-tetramethyl-2,2'-bipyridine-6,6'-dicarboxamide (TMBiPDA) and N, N, N', N'-tetramethyl-1,10-phenanthroline-2,9-dicarboxamide (TMPhenDA) in CH3OH/10%(v)H2O solutions were studied. Stability constants and enthalpies of complexation were determined by absorption spectrophotometry, luminescence, and calorimetry. The stability constants of corresponding lanthanide complexes decrease in the order of TMPhenDA > TMBiPDA, while those of the corresponding ligand complexes with lanthanides decrease in the order of Nd(III) > Eu(III). The stepwise reactions for all 1:1 complexes as well as for the 1:2 Nd(III) complexes are driven by both enthalpy and entropy, while those for the 1:2 Eu(III) complexes are driven by entropy. The stronger affinity of TMPhenDA to Nd(III) and Eu(III) than that of TMBiPDA is predominantly arisen from its high preorganization. The spectra of the complexes in solutions are similar, implying that Nd(III) and Eu(III) coordinate with the two ligands in the same mode, which have been validated by 1H and 13C NMR titrations using La(III) as lanthanide tracer. The luminescence lifetimes of the Eu(III) complexes with TMBiPDA and TMPhenDA were evaluated by TRLFS. Structures of Nd(III)/TMPhenDA and Eu(III)/TMPhenDA complexes, identified by single-crystal X-ray diffractometry, show that ligand coordinates to metal in a tetradentate mode via two aromatic N-donors and two amide O-donors, and the central cation (Nd(III) or Eu(III)) is 10-coordinated by two whole TMPhenDA and two solvent (water or methanol) molecules. The M-O bond distances are almost identical, while the Nd-N bond distance is shorter than the Eu-O bond.

Pd-catalyzed Hiyama vinylation reaction of non-activated aryl chlorides and bromides under mild conditions was developed. The use of efficient vinyl donors and electron-rich sterically hindered phosphine ligands was critical for the success of the reaction. The products of this transformation can be used for Am/Cm separation, an important challenge in nuclear fuel reprocessing. The substituent effect on Am/Cm separating selectivity was also achieved, which could contribute to the development of new chromatographic materials for the separation of Am and Cm.

Complexation of a new macrocyclic compound, 2,6-dimethylformamide-calix[4]pyridine (L-1), with Eu(III) was studied by spectrophotometry. Stability constants of the Eu(III)/L-1 complex in different solvents were determined. The results reveal that L-1 forms moderately strong complexes with Eu(III) and other lanthanides in aprotic solvents and shows little binding ability with transition metals. Moreover, the binding strength of L-1 weakens significantly in protic solvents. Using 2-bromodecanoic acid as the synergistic reagent, L-1 extracts Am(III) and Eu(III) successfully with a separation factor of SFAm/Eu=1.3, and the distribution ratios of Am(III) and Eu(III) increases as the aqueous acidity is decreased. DFT computational studies were conducted to corroborate the solvent extraction data, and compare the coordination properties of Am(III)/Eu(III) complexes with L-1 and a related, 2,6-diformamidecalix[4]pyridine (L-2). The computational results suggest that L-2 could form stable complexes [ML](3+) and ML(NO3)(3) [where M represent Am(III) or Eu(III)] in aqueous phase, in sharp contrast to the case of L-1 where such complexes in aqueous phase are not stable.

Thermodynamics of the U(VI) complexation with picolinic acid (HL) was investigated under constant ionic strength (1.05 mol.kg(-1) NaClO4) with multiple techniques, including potentiometry, spectrophotometry and calorimetry. Three stepwise complexes, UO2L+, UO2L2(aq) and UO2L3-, were identified, and their formation constants were determined by potentiometric titrations at 283-313 K. The spectrophotometric work at 298 K further demonstrated the formation of these three complexes. By calorimetric titrations, stepwise enthalpies of the complexation at 298 K were determined to be Delta H-11 = -(3.43 +/- 0.24) kJ.mol(-1) , Delta H-12 = -(3.3 +/- 0.6) kJ.mol(-1), and Delta H-13 = 9.4 +/- 0.6 kJ.mol(-1). A formation of the 1:1 and 1:2 complexes is driven by both enthalpy and entropy, but the formation of the 1:3 complex by entropy only. The thermodynamic parameters also suggest that in the 1:1 and 1:2 complexes, picolinate coordinates to U (VI) through the chelation mode, i.e., one carboxylate oxygen and an aromatic nitrogen bind to the U(VI) atom. (C) 2017 Elsevier Ltd.

Extraction complexes of Eu(III), Tb(III), Tm(III), and Am(III) with three 1,10-phenanthroline-type ligands have been studied, primarily using density functional theory (DFT). The same accuracies and optimized structural geometries were obtained whether optimization of the [ML2(NO3)](2+) complexes was performed at the B3LYP/6-31G(d)/RECP or the MP2/6-31G(d)/RECP level of theory. Calculations carried out at the B3LYP/6-311G(d, p)/RECP level of theory indicated that solvation does not favor the formation of these complexes. Moreover, the ΔGg and ΔGsolv values for the reactions leading to the formation of [LnL2(NO3)](2+) complexes were seen to decrease with increasing atomic number of the lanthanide (from Eu to Tb to Tm). In addition, when a strongly hydrophobic benzo[e][1,2,4]triazine group was created in each ligand, ligand selectivity for actinides/lanthanides in acidic media improved. Even greater ligand selectivity for actinides/lanthanides in acidic media was obtained when a 5,6-diphenyl-1,2,4-triazine group was created in each ligand instead of a benzo[e][1,2,4]triazine group. Vibrational analysis and NMR spectroscopic analysis were also performed on all of the studied ligands and the metal complexes that included them. Further in-depth investigations should be undertaken in this field.

Complexation of Am(III), Nd(III), and Eu(III) with a new heterocyclic nitrogen-donor ligand, 2,9-di(quinazolin-2-yl)-1,10-phenanthroline (denoted as BQPhen in this paper), was studied by thermodynamic measurements and theoretical computations. The stability constants of two successive complexes in dimethylformamide, ML(3+) and ML2(3+) where M stands for Nd, Eu, or Am while L stands for the BQPhen ligand, were determined by absorption spectrophotometry. The enthalpy of complexation was determined by microcalorimetry. Results show that BQPhen forms ten times stronger complexes with Am(III) than Eu(III) or Nd(III) under identical conditions, suggesting that BQPhen could be used as an efficient extractant for the separations of trivalent actinides from lanthanides. The higher binding strength of BQPhen towards Am(III) than Nd(III) or Eu(III) is mainly due to the more favourable enthalpy of complexation for Am(III)/BQPhen complexes, implying a higher degree of covalence in the Am(III)/BQPhen complexes than the lanthanide(III)/BQPhen complexes. The thermodynamic trend was corroborated with computational results and validated by solvent extraction experiments that demonstrated BQPhen preferably extracted Am(III) more than Eu(III), with a separation factor of about 10. Discussions have been made to compare BQPhen with other phenanthroline derivatives such as CyMe4-BTPhen, a bis-triazine-phenanthroline derivative that was reported in the literature. Data suggest that, under identical conditions, BQPhen would form stronger complexes with Am(III), Eu(III), and Nd(III) than CyMe4-BTPhen.

Fluorescent recognition of uranyl ions was achieved using a phosphorylated cyclic peptide, which can be used as a fluorescent sensor for the detection of uranyl ions with high selectivity and sensitivity.

A novel "one-pot" reaction was developed for the synthesis of aryl or heteroaryl-substituted amidoxime compounds containing various functional groups. Fluorescence titration experiments coupled with theoretical analysis revealed that the steric hindrance and electronic effects of substituents influence the binding ability of the amidoxime compounds to uranyl ions.

A coumarin-based fluorescent probe for selective detection of hydrogen sulfide (H2S) is presented. This ‘off–on’ probe exhibited high selectivity towards H2S in aqueous solution with a detection limit of 30 nM. Notably, because of its dual nucleophilicity, the probe could avoid the interference of thiols and other sulfur containing compounds.