4-Oxo-7-fluoro-1,10-phenanthroline-2,9-diamides: Synthesis, Structural Features, Lanthanide Complexes, and Am(III)/Ln(III) Solvent Extraction

A highly efficient synthetic approach was developed for the synthesis of unsymmetrical 1,10-phenanthroline-2,9-diamides with two different substituents in the fourth and seventh positions of the phenanthroline core. The structures of these ligands were confirmed using various spectral methods including 2D-NMR and X-ray analysis. Quantum chemical calculations supported the presence of tautomeric forms of these ligands. Furthermore, it was discovered that these compounds exhibit polydentate ligand behavior toward lanthanide nitrates. The structural characteristics of the complexes formed between these ligands and lanthanide nitrates were investigated both in the solid state and in solution. To further understand the binding properties of these novel unsymmetrical ligands, the binding constants for potential complexes were quantitatively measured by using UV-vis spectrophotometric titration. This allowed for a comprehensive analysis of the binding affinity and stability of these complexes. Extraction experiments of f-elements were performed for symmetrical and unsymmetrical diamides. Overall, this study presents significant advancement in the synthesis and characterization of unsymmetrical 1,10-phenanthroline-2,9-diamides and provides valuable insights into their potential applications as polydentate ligands for lanthanide nitrates.

First 24-Membered Macrocyclic 1,10-Phenanthroline-2,9-Diamides-An Efficient Switch from Acidic to Alkaline Extraction of f-Elements

A reaction of acyl chlorides derived from 1,10-phenanthroline-2,9-dicarboxylic acids with piperazine allows the preparation of the corresponding 24-membered macrocycles in good yield. The structural and spectral properties of these new macrocyclic ligands were thoroughly investigated, revealing promising coordination properties towards f-elements (Am, Eu). It was shown that the prepared ligands can be used for selective extraction of Am(III) from alkaline-carbonate media in presence of Eu(III) with an SF_Am/Eu up to 40. Their extraction efficiency is higher than calixarene-type extraction of the Am(III) and Eu(III) pair. Composition of macrocycle-metal complex with Eu(III) was investigated by luminescence and UV-vis spectroscopy. The possibility of such ligands to form complexes of L:Eu = 1:2 stoichiometry is revealed.

Pyrrolidine-Derived Phenanthroline Diamides: An Influence of Fluorine Atoms on the Coordination of Lu(III) and Some Other f-Elements and Their Solvent Extraction

Three pyrrolidine-derived phenanthroline diamides were studied as ligands for lutetium trinitrate. The structural features of the complexes have been studied using various spectral methods and X-ray. The presence of halogen atoms in the structure of phenanthroline ligands has a significant impact on both the coordination number of lutetium and the number of solvate water molecules in the internal coordination sphere. The stability constants of complexes with La(NO3)3, Nd(NO3)3, Eu(NO3)3, and Lu(NO3)3 were measured to demonstrate higher efficiency of fluorinated ligands. NMR titration was performed for this ligand, and it was found that complexation with lutetium leads to an approximately 13 ppm shift of the corresponding signal in the 19F NMR spectrum. The possibility of formation of a polymeric oxo-complex of this ligand with lutetium nitrate was demonstrated. Experiments on the liquid–liquid extraction of Am(III) and Ln(III) nitrates were carried out to demonstrate advantageous features of chlorinated and fluorinated pyrrolidine diamides.

A Promising 1,3,5-Triazine-Based Anion Exchanger for Perrhenate Binding: Crystal Structures of Its Chloride, Nitrate and Perrhenate Salts

The reaction of pyridine with cyanuric chloride was studied under microwave activation as well as in the presence of silver nitrate. The product of hydrolysis containing two pyridinium rings and chloride anion was isolated. The structures of these anion exchanger salts with chloride, nitrate and perrhenate anions are discussed.

Solvation-Anionic Exchange Mechanism of Solvent Extraction: Enhanced U(VI) Uptake by Tetradentate Phenanthroline Ligands

Phenanthroline diamides (L) demonstrated a unique ability to extract uranium from nitric acid solutions into a polar organic solvent forming complexes of 1:2 stoichiometry as tight ion pairs {[UO₂LNO₃]⁺[UO₂(NO₃)₃]^-} by a novel extraction mechanism, which is a combination of two already well-known mechanisms: solvation and ion-pair anion exchange. A UV-vis study was used to confirm the formation of such complexes directly in the organic phase. Moreover, chemical synthesis and single crystal growth were performed to confirm unambiguously the structure of the complexes in the solid state.

Competing Routes in the Extraction of Lanthanide Nitrates by 1,10-Phenanthroline-2,9-diamides: An Impact of Structure of Complexes on the Extraction

The fact of the fracture of the extraction curve of lanthanides by 1,10-phenanthroline-2,9-diamides is explained in terms of the structure of complexes, solvent extraction data and quantum chemical calculations. The solvent extraction proceeds in two competing directions: in the form of neutral complexes LLn(NO₃)₃ and in the form of tight ion pairs {[LLn(NO₃)₂ H₂O]⁺ (NO₃^-).

Predictive Models for HOMO and LUMO Energies of N-Donor Heterocycles as Ligands for Lanthanides Separation

Quantum chemical calculations combined with QSPR methodology reveal challenging perspectives for the solution of a number of fundamental and applied problems. In this work, we performed the PM7 and DFT calculations and QSPR modeling of HOMO and LUMO energies for polydentate N-heterocyclic ligands promising for the extraction separation of lanthanides because these values are related to the ligands selectivity in the respect to the target cations. Data for QSPR modeling comprised the PM7 calculated HOMO and LUMO energies of N-donor heterocycles, including several types of both known and virtual undescribed polydentate ligands. Ensemble modeling included various molecular fragments as descriptors and different variable selection techniques to build consensus models (CMs) on a training set of 388 ligands using external cross-validation. CMs were then verified to make predictions for two external test sets: 45 ligands (T1) that were similar to the ligands of the training set, and 1546 structures (T2), which were substantially different from the ligands of the training set. The consensus models predict well in 5-fold cross-validation (RMSE_HOMO =0.097 eV, RMSE_LUMO =0.064 eV), and on the external test sets (T1: RMSE_HOMO =0.26 eV, RMSE_LUMO =0.24 eV; T2: RMSE_HOMO =0.26 eV, RMSE_LUMO =0.17 eV). An analysis of the results reveals that substituents in heteroaromatic rings of the ligands and at the amide nitrogens can deeply influence their metal binding properties.

Synthetic Model of the Phosphate Binding Protein: Solid-State Structure and Solution-Phase Anion Binding Properties of a Large Oligopyrrolic Macrocycle

The macrocyclic receptors 4-6 were synthesized via the anion-templated condensation of appropriately chosen dialdehyde and diamine building blocks. Whereas all three products could be obtained directly via the appropriate choice of reaction conditions, the larger [3+3] product, 6, which incorporates three of each precursor subunit, could also be obtained conveniently via an indirect procedure involving ring expansion of the smaller [2+2] macrocycle 4. As detailed earlier (Sessler, J. L.; Katayev, E. A.; Pantos, G. D.; Reshetova, M. D.; Khrustalev, V. N.; Lynch, V. M.; Ustynyuk, Y. A. Angew. Chem. 2005, 117, 7552-7556; Angew. Chem., Int. Ed. 2005, 44, 7386-7390), this ring expansion occurs under thermodynamic control in the presence of HSO4- and H2PO4- anions in acetonitrile solution and serves to effect the conversion of 4 to 6. An analysis of the X-ray crystal structure of complex 6H22+.HPO42- revealed a strong resemblance to the active site of the phosphate binding protein (PBP) with similar structural analogies being drawn between the active site of the sulfate binding protein (SBP) and the corresponding hydrogensulfate anion complex. In both cases, the anions are bound in a 1:1 fashion in the solid state through a complementary hydrogen bond network involving both the receptor 6 and the anions. UV-vis spectroscopic titrations provide support for the conclusion that macrocycle 6 binds the hydrogensulfate and dihydrogenphosphate anion (studied as the corresponding tetrabutylammonium salts) with high selectivity and affinity in acetonitrile (log Ka for the first binding interaction approaching 7), albeit with different receptor-to-anion binding stoichiometries (1:1 vs 1:3 for HSO4- and H2PO4-, respectively).

Dioxygen activation by diiminodipyrromethane complexes of Ni, Pd, and Pt

Diiminodipyrromethane complexes of Ni, Pd, and Pt are able to activate O2, resulting in a metal-dependent autoxidation of the ligand.

Bipyrrole- and Dipyrromethane-Based Amido-imine Hybrid Macrocycles. New Receptors for Oxoanions

Three new amido-imine-type hybrid macrocycles based on substituted pyrrole units have been synthesized and shown to act as effective receptors for oxoanions in the solid state and in acetonitrile solution. One of the macrocycles in question, compound 15, was characterized by X-ray diffraction analysis as the free macrocycle and as a complex with sulfuric acid. A comparison of the resulting structures reveals that this receptor is capable of undergoing a conformational change and, as a consequence, varying the number of donor sites that can interact with a bound substrate. This system and the other two new receptors described in this work (macrocycles 14 and 16, respectively) display a high affinity toward oxoanions (studied as their tetrabutylammonium (TBA) salts), with association constants on the order of 10(7) M-1 being determined in acetonitrile solution using standard UV-vis spectroscopic titration methods. A competitive titration method was used to determine affinity constants in excess of ca. 10(6) M-1. Two of the receptors (14 and 15) were found to bind acetate, hydrogen sulfate, and dihydrogen phosphate anion well, and the bipyrrole-based receptor (14) was also found to bind the perrhenate anion. In contrast, the bis-dipyrromethane-derived receptor (16) was found to bind chloride anion preferentially. The unusual selectivity displayed by 16 for this spherical anion was rationalized on the basis of single-crystal X-ray diffraction data and DFT modeling calculations, which revealed a rigid structure appropriately suited for chloride anion recognition.

Magnetic Isotope Effect in the Photolysis of Organotin Compounds

Photolysis of organotin molecules RSnMe3 is shown to be a spin selective radical reaction accompanied by fractionation of magnetic, (117,119)Sn, and nonmagnetic, (118,120)Sn, isotopes between starting reagents and products. A primary photolysis process is a homolytic cleavage of the C-Sn bond and generation of a triplet radical pair as a spin-selective nanoreactor. Nuclear spin dependent triplet-singlet conversion of the pair results in the tin isotope fractionation. Experimentally detected isotope distribution unambiguously demonstrates that the classical, mass-dependent isotope effect is negligible in comparison with magnetic, spin-dependent isotope effect.

Catalytic homogeneous hydrogenation of compounds containing X ? O semipolar bonds (X = N, S, P) with para-hydrogen as a promising route for preparation of para-water

The quantum-chemical simulation (DFT, PBE, TZ2p basis set) of the mechanism of catalytic hydrogenation of compounds containing R(n)X --> O semipolar bonds (R(n)X = N(2), Me(2)S, C(5)H(5)N, Ph(3)P) on the Wilkinson catalyst (Ph(3)P)(3)RhCl with para-hydrogen showed that this process proceeds with retention of proton nuclear spin correlation, which enables a principal possibility to synthesize para-H(2)O, i.e. the nuclear spin isomer of water with antiparallel proton spins, using this route.

Synthesis and Anion Binding Properties of 2,5-Diamidothiophene Polypyrrole Schiff Base Macrocycles

[reaction: see text] Two easy-to-synthesize polypyrrolic 2,5-diamidothiophene Schiff base macrocycles are reported, along with their anion binding properties as determined via UV-vis spectroscopic titrations carried out in dichloroethane. There is a striking difference between the interactions with anions of the two macrocycles, a finding ascribed to differences in their rigidity. For example, the more flexible dipyrromethane-derived macrocycle displays a 1.2:1 hydrogen sulfate versus nitrate selectivity, while its more rigid bipyrrole-derived congener shows a 7.4:1 selectivity in favor to hydrogen sulfate.

Fine Tuning the Anion Binding Properties of 2,6-Diamidopyridine Dipyrromethane Hybrid Macrocycles

The synthesis, characterization, and anion-binding properties of a series of 2,6-diamidopyridine dipyrromethane hybrid macrocycles is presented. As part of this work, a new method for effecting the oxidation of dipyrromethane-based macrocycles in organic solvents has been developed. The macrocyclic frameworks presented here stand out because of their ease of synthesis and tunable anion-binding properties. Evidence for anion binding was obtained from UV-vis spectroscopic titrations carried out in acetonitrile. The results clearly indicate that by changing the flexibility, cavity size, and directionality of anion-binding moieties in the macrocyclic framework the anion selectivity may be changed dramatically. These results are in accord with density functional theory molecular modeling calculations performed on one member of the series.

Synthesis and study of a new diamidodipyrromethane macrocycle. An anion receptor with a high sulfate-to-nitrate binding selectivityElectronic supplementary information (ESI) available: detailed experimental data and UV-vis spectrophotometric titration data. See http://www.rsc.org/suppdata/cc/b4/b403665d/

A new 2,6-diamidopyridinedipyrromethane hybrid macrocycle () has been synthesized that shows a high selectivity for dihydrogen phosphate and hydrogen sulfate relative to nitrate in acetonitrile solution as judged from UV-vis spectrophotometric titrations; this leads to the suggestion that this or related systems might find use in nuclear waste remediation applications requiring the selective removal of hydrogensulfate from nitrate-rich waste mixtures.