Low-valent f-block metals have intrinsic luminescence, electrochemical, and magnetic properties that are modulated with ligands, causing the coordination chemistry of these metals to be imperative to generating critical insights needed to impact modern applications. To this end, we synthesized and characterized a series of twenty-seven complexes of f-metal ions including EuII, YbII, SmII, and UIII and hexanuclear clusters of LaIII and CeIII to study the impact of tris[2-(2-methoxyethoxy)ethyl]amine, a flexible acyclic analogue of the extensively studied 2.2.2-cryptand, on the coordination chemistry and photophysical properties of low-valent f-block metals. We demonstrate that the flexibility of the ligand enables luminescence tunability over a greater range than analogous cryptates of EuII in solution. Furthermore, the ligand also displays a variety of binding modes to f-block metals in the solid state that are inaccessible to cryptates of low-valent f-block metals. In addition to serving as a ligand for f-block metals of various sizes and oxidation states, tris[2-(2-methoxyethoxy)ethyl]amine also deprotonates water molecules coordinated to trivalent triflate salts of f-block metal ions, enabling the isolation of hexanuclear clusters containing either LaIII or CeIII. The ligand was also found to bind more tightly to YbII and UIII in the solid state compared to 2.2.2-cryptand, suggesting that it can play a role in the isolation of other low-valent f-block metals such CfII, NpIII, and PuIII. We expect that our findings will inspire applications of tris[2-(2-methoxyethoxy)ethyl]amine in the design of light-emitting diodes and the synthesis of extremely reducing divalent f-block metal complexes that are of interest for a wide range of applications.

Radiographic mapping of hypoxia is needed to study a wide range of diseases. Complexes of Eu(II) are a promising class of molecules to fit this need, but they are generally limited by their rapid oxidation rates in vivo. Here, a perfluorocarbon-nanoemulsion perfused with N2 , forms an interface with aqueous layers to hinder oxidation of a new perfluorocarbon-soluble complex of Eu(II). Conversion of the perfluorocarbon solution of Eu(II) into nanoemulsions results in observable differences between reduced and oxidized forms by magnetic resonance imaging both in vitro and in vivo. Oxidation in vivo occurrs over a period of ≈30 min compared to <5 min for a comparable Eu(II)-containing complex without nanoparticle interfaces. These results represent a critical step toward delivery of Eu(II)-containing complexes in vivo for the study of hypoxia.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The title molecule, C17H15FO2, was synthesized by a Claisen–Schmidt condensation with 4-fluorobenzaldehyde and 4′-ethoxyacetophenone. The torsion angles between the 4-fluorophenyl ring and the alkene and the 4′-ethoxyphenyl ring and the 2-propen-1-one are −1.2 (4) and 1.2 (3)°, respectively; however, there is a larger torsion between the bonds comprising the 2-propen-1-one unit of 12.0 (4)°. The crystal packing is stabilized by intermolecular C—H...O/F hydrogen bonding, π–π stacking, and H–π interactions.

The effect of ligands' energy levels on thermal dependence of lanthanide emission was examined to create new molecular nanothermometers. A series of Ln2Ga8L8'L8″ metallacrowns (shorthand Ln2L8'), where Ln = Gd3+, Tb3+, or Sm3+ (H3L' = salicylhydroxamic acid (H3shi), 5-methylsalicylhydroxamic acid (H3mshi), 5-methoxysalicylhydroxamic acid (H3moshi), and 3-hydroxy-2-naphthohydroxamic acid (H3nha)) and H2L″ = isophthalic acid (H2iph), was synthesized and characterized. Within the series, ligand-centered singlet state (S1) energy levels ranged from 23,300 to 27,800 cm-1, while triplet (T1) energy levels ranged from 18,150 to 21,980 cm-1. We demonstrated that the difference between T1 levels and relevant energies of the excited 4G5/2 level of Sm3+ (17,800 cm-1) and 5D4 level of Tb3+ (20,400 cm-1) is the major parameter controlling thermal dependence of the emission intensity via the back energy transfer mechanism. However, when the energy difference between S1 and T1 levels is small (below 3760 cm-1), the S1 → T1 intersystem crossing (and its reverse, S1 ← T1) mechanism contributes to the thermal behavior of metallacrowns. Both mechanisms affect Ln3+-centered room-temperature quantum yields with values ranging from 2.07(6)% to 31.2(2)% for Tb2L8' and from 0.0267(7)% to 2.27(5)% for Sm2L8'. The maximal thermal dependence varies over a wide thermal range (ca. 150-350 K) based on energy gaps between relevant ligand-based and lanthanide-based electronic states. By mixing Tb2moshi8' with Sm2moshi8' in a 1:1 ratio, an optical thermometer with a relative thermal sensitivity larger than 3%/K at 225 K was created. Other temperature ranges are also accessible with this approach.

A set of (Ln[14-MCZn(II)N(quinHA)-5])2Ln2Zn2(quinHA)2(ph)2(Hph)4(OH)8(H2O)4 metallacrowns (Ln-1, Ln = Tb, Gd, or Yb; H2quinHA = quinaldic hydroxamic acid, H2ph = phthalic acid) have been synthesized via solution-state self-assembly. The metallacrowns possess an uncommon topology within the metallacrown family where two rarely seen 14-metallacrown-5 moieties are fused by a Yb2Zn2(quinHA)2 bridge. Moreover, Yb-1 analyzed in the solid state exhibits a characteristic near-infrared luminescence signal arising from Yb3+2F5/2→2F7/2 transition despite the proximity of high energy O-H oscillators.

We describe a study of the influence of amine-containing ligands on the photoredox-relevant properties of EuII toward the rational design of EuII-containing catalysts for visible-light-promoted photoredox reactions. We report our observations of the effects of the degree of functionalization of amines, denticity, and macrocylic ligands on the absorbance of EuII. Ligands that contain secondary amines bathochromically shift the absorbance of EuCl2 relative to ligands that contain primary or tertiary amines. Similarly, ligands of larger denticity have a larger bathochromic shift of the absorbance than ligands of smaller denticity. We observed that macrocyclic ligands have a larger effect on the absorbance of EuCl2 than nonmacrocyclic ligands. Also, we report the photoredox reactivity of four new EuII-containing complexes. These observations are potentially influential in understanding the ligand properties that promote the use of EuII in visible-light-promoted photoredox catalysis.

A series of cationic and neutral p-Br and p-NO2 pyridine substituted Eu(III) and Gd(III) coordination complexes serve as versatile synthetic intermediates. Nucleophilic aromatic substitution occurs readily at the para position under mild conditions, allowing C-N and C-C bond forming reactions to take place, permitting the introduction of azide, amino and alkynyl substituents. For Eu(III) complexes, this approach allows late stage tuning of absorption and emission spectral properties, exemplified by the lowering of the energy of an LMCT transition accompanied by a reduction in the Eu-Npy bond length. Additionally, these complexes provide direct access to the corresponding Eu(II) analogues. With the Gd(III) series, the nature of the p-substituent does not significantly change the EPR properties (linewidth, relaxation times), as required for their development as EPR spin probes that can be readily conjugated to biomolecules under mild conditions.

Two types of 3d-4f compounds are presented, [Dy-4(III) Mn-4(III) (OH)(2)(O2C2H3)(3)(shi)(4)(H(2)shi)(4)(Hsal)(3)(DMF)(4)](-)3DMF (Dy-1) and [Ln(6)(III) Mn-2(III) Mn-2(IV) (shi)(6)(Hshi)(4)(H(2)shi)(2)(Hsal)(4)(DMF)(8)]center dot 4H(2)O (Ln-2) (Ln = Dy or Gd, H(3)shi = salicylhydroxamic acid, H(2)sal = salicylic acid). While neither Dy-1 and Dy-2 demonstrated a significant barrier to magnetization relaxation, out-of-phase ac magnetic susceptibility was observed in both cases. Gd-2 showed potential as a magnetocoolent with gravimetric entropy changes reaching a maximum of 18.89 J.kg(-1).K-1 at 3 K and Delta H = 7 T. This value represents approximately 53% of the theoretical maximum. (C) 2021 Elsevier Ltd. All rights reserved.

The title compounds, [Fe 4 (C 2 H 3 O 2 ) 6 (C 7 H 4 O 3 )FO(C 5 H 5 N) 3 ]·C 5 H 5 N·0.24H 2 O ( 1-F ) and [Fe 4 (C 2 H 3 O 2 ) 6 (C 7 H 4 O 3 )ClO(C 5 H 5 N) 3 ]·H 2 O ( 1-Cl ) were synthesized using a self-assembly reaction in methanol and pyridine with stoichiometric addition of salicylhydroxamic acid (H 3 shi), acetic acid (HOAc), and the appropriate ferric halide salt. The compounds crystallize as solvates, where 1-F has one pyridine molecule that is disordered about a twofold axis and one water molecule with an occupancy of 0.24 (2); and 1-Cl has one water molecule that is disordered over two sites with occupancies of 0.71 (1) and 0.29 (1). The space groups for each analog differ as 1-F crystallizes in Fdd 2 while 1-Cl crystallizes in P 2 1 . The difference in packing is due to changes in the intermolecular interactions involving the different halides. The two molecules are mostly isostructural, differing only by the torsion of the pyrine ligands and slight orientation changes in the acetate ligands. All of the iron(III) ions are in six-coordinate octahedral ligand field geometries but each one exhibits a unique coordination environment with various numbers of O (four to six) and N (nought to two) atom donors. Bond-valence sums confirm each iron is trivalent. The hydroximate ligand is bound to three iron(III) ions using a fused chelate motif similar to those in metallacrown compounds.

The title compounds, [Fe-4(C2H3O2)(6)(C7H4O3)FO(C5H5N)(3)]center dot C5H5N center dot 0.24H(2)O (1-F) and [Fe-4(C2H3O2)(6)(CH4O3)CIO(C5H5N)(3)]center dot H2O (1-Cl) were synthesized using a self-assembly reaction in methanol and pyridine with stoichiometric addition of salicylhydroxamic acid (H 3 shi), acetic acid (HOAc), and the appropriate ferric halide salt. The compounds crystallize as solvates, where 1-F has one pyridine molecule that is disordered about a twofold axis and one water molecule with an occupancy of 0.24 (2); and 1-Cl has one water molecule that is disordered over two sites with occupancies of 0.71 (1) and 0.29 (1). The space groups for each analog differ as 1-F crystallizes in Fdd2 while 1-Cl crystallizes in P2(1). The difference in packing is due to changes in the intermolecular interactions involving the different halides. The two molecules are mostly isostructural, differing only by the torsion of the pyrine ligands and slight orientation changes in the acetate ligands. All of the iron(III) ions are in sixcoordinate octahedral ligand field geometries but each one exhibits a unique coordination environment with various numbers of O (four to six) and N (nought to two) atom donors. Bond-valence sums confirm each iron is trivalent. The hydroximate ligand is bound to three iron(III) ions using a fused chelate motif similar to those in metallacrown compounds.

The title metallacrown (MC) complexes LnIII[15-MCFeIIIN(shi)-5](OAc)2Cl(C5H5N)6 (Ln1), where OAc– is acetate, shi3− is salicylhydroximate, and Ln = Gd and Dy, were synthesized via a self-assembly reaction in methanol and pyridine. Single crystals were grown using slow evaporation and characterized using X-ray diffraction. Seven-coordinate capped octahedron geometries were observed for the lanthanide ion in both complexes, which is uncommon for trivalent lanthanide species. The 15-MC-5 is a ruffled metallacrown archetype similar to previously reported mixed-valent manganese metallacrowns. The title metallacrown (MC) complexes LnIII[15-MCFeIIIN(shi)-5](OAc)2Cl(C5H5N)6 (Ln1), where OAc– is acetate, shi3− is salicylhydroximate, and Ln = Gd and Dy, contains seven-coordinate capped octahedron geometries for the lanthanide ion in both complexes, which is uncommon for trivalent lanthanide species.

Multimodal probes capable of combining imaging modalities within a single molecule are in high demand today as they can provide information at both molecular and anatomical levels. Herein, we investigated a series of gallium(III)/lanthanide(III) bis(12-MC-4) metallacrowns (MCs) with the general composition {Ln[12-MCGaIIIN(shi)-4]}2(iph)4 (Ln-Ix, x = 0, 4, 8, 12), where shi and iph are salicylhydroximate and isophthalate ligands, respectively, or their iodinated derivatives. We demonstrate that for Yb-Ix the attenuation in X-ray computed tomography (XCT) imaging and near-infrared (NIR) luminescence properties can be finely tuned by controlled structural modifications based on iodo groups. Solutions of Yb-Ix appear to be 22-40 times more efficient as XCT agents in comparison to the commercially available iobitridol, while providing an intense emission signal in the NIR range with total quantum yields up to 8.6 %, which are among the highest values reported so far. Therefore, these molecules are promising potential bimodal agents for combined NIR luminescence and XCT imaging.