Influence of a N-Heterocyclic Core on the Binding Capability of N,O-Hybrid Diamide Ligands toward Trivalent Lanthanides and Actinides

N,O-hybrid diamide ligands with N-heterocyclic skeletons are one of the promising extractants for the selective separation of actinides over lanthanides in a highly acidic HNO₃ solution. In this work, three hard-soft donor mixed diamide ligands, pyridine-2,6-diylbis(pyrrolidin-1-ylmethanone) (Pyr-PyDA), 2,2'-bipyridine-6,6'-diylbis(pyr-rolidine-1-ylmethanone) (Pyr-BPyDA), and (1,10-phenanthroline-2,9-diyl)bis(pyrrolidin-1-ylmethanone) (Pyr-DAPhen), were synthesized and used to probe the influence of N-heterocyclic cores on the complexation and extraction behaviors with trivalent lanthanides and actinides. ¹H NMR titration experiments demonstrated that 1:1 metal-to-ligand complexes were mainly formed between the three ligands and lanthanides, but 1:2 type complexes were also formed between tridentate Pyr-PyDA and Lu(III). The stability constants (log β) of these three ligands with two typical lanthanides, Nd(III) and Eu(III), were determined through spectrophotometric titration. It is found that Pyr-DAPhen formed the most stable complexes, while Pyr-PyDA formed the most unstable complexes with lanthanides, which coincided well with the following solvent extraction results. The solid-state structures of 1:1 type complexes of these three ligands with La(III), Nd(III), and Er(III) in nitrate media were identified by a single-crystal X-ray diffraction technique. Nd(III) and Er(III) were 10-coordinated with Pyr-PyDA, Pyr-BPyDA, and Pyr-DAPhen via one ligand molecule and three nitrate ions. La(III), because of its larger ionic radius, was 11-coordinated with Pyr-DAPhen through one ligand molecule, three nitrate ions, and one methanol molecule. Solvent extraction experiments showed that the preorganized phenanthroline-derived Pyr-DAPhen had the best extraction performance for trivalent actinide among the three ligands tested. This work provides some experimental insights into the design of more efficient ligands for trivalent actinide separation by adjusting the N-heterocyclic cores.

Recent achievements in copper catalysis for C–N bond formation

A mini-review describes the development of the catalysis by Cu(I) complexes aimed at the formation of C–N bond at the Lomonosov MSU during 2010s. The main approach employs the amination of aryl and heteroaryl halides with the amines and polyamines, in this direction a great versatility of starting compounds was achieved: adamantane-containing amines, linear diamines, oxadiamines and polyamines, various aryl iodides and bromides, derivatives of pyridine, and quinoline were used for this purpose. In more peculiar cases, the copper catalysis was used for steroids transformations, including vinylation of azoles, wide-spread “click” reactions for the conjugate syntheses, and successful heterogenezation of the copper catalysts were also undertaken.

Crystal structure of di-μ-hydroxido-bis-{aqua-[ethyl (1,10-phenanthrolin-3-yl)phospho-nato-κ2 N,N']copper(II)} hepta-hydrate

In the title compound, [Cu2(OH)2{C12H7N2(PO3C2H5)}2(H2O)2]·7H2O, two Cu2+ cations are bridged by two hydroxide groups, forming a centrosymmetric binuclear complex. Each Cu2+cation is further coordinated by the N atoms of a bidentate ethyl (1,10-phenanthrolin-3-yl)phospho-nate anion and a water mol-ecule in a square-pyramidal geometry. In the crystal, a network of O-H⋯O hydrogen bonds involving the P(O)(O-)(OEt) groups, bridging hydroxyl groups, coordinated and uncoordinated water mol-ecules generates a three-dimensional supra-molecular structure. The ethyl group exhibits disorder and was modelled over three sites with occupancies of 0.455, 0.384 and 0.161.

Spectrally-resolved third-harmonic generation and the fundamental role of O-HCl hydrogen bonding in Oh, Td-cobalt(ii) tetraphenylmethane-based coordination polymers

The reaction of a phosphonate-diester tetraphenylmethane-based tecton, tetrakis[4-(diethoxyphosphoryl)phenyl]methane, (L) with cobalt(ii) chloride afforded a centrosymmetric coordination polymer (CP), [L·2Co(H₂O)₄²⁺·2CoCl₄^2-]_n, 2-Cl, possessing simultaneously octahedral (O_h) and tetrahedral (T_d) metal centers. This material served as a model compound for the demonstration of factors influencing the spectral dependence of one of the nonlinear optical (NLO) phenomena, the third-harmonic generation (THG). The spectrally-resolved THG (SR-THG) measurements in the range from 1125 to 1750 nm revealed that a maximum of THG response is obtained when the fundamental beam is around 1300 nm. The SR-THG study was combined with an analysis of the self-absorption effects of pumping and of third-harmonic radiation; based on these results, we put forward a hypothesis that the THG action spectrum is influenced more by the ability of the material to self-absorb the third harmonic rather than by the extent of self-absorption of the pumping radiation. Apart from investigations of NLO properties, we have explored coordination and particularly the supramolecular interactions that build up the 2-Cl CP. Despite the tetrahedral, spatial shape of the ligand L, CP 2-Cl has a two-dimensional net. The structure was found to be strongly supported by O-HCl hydrogen bonds, since each CoCl₄^2- complex anion is an acceptor of eight of such interactions within a distorted square grid layer of cobalt(ii) ions. While coordination and hydrogen-bonded nets are both featuring the sql topology when treated separately, the consideration of both of them as topological paths yields a trinodal 4,4,6-connected net, described by the point symbol (4²·8⁴)(4⁵·6)₂(4⁶·6⁶·8³)₂. SR-THG and structural studies of 2-Cl have been also supported by far- and mid-infrared spectroscopy, UV-Vis-NIR solid state absorption analysis, thermogravimetry and preliminary magnetic characterization.