Identification of seven-coordinate LnIII ions in a LnIII[15-MCFe III N(shi)-5](OAc)2Cl species crystallized from methanol and pyridine

The title metallacrown (MC) complexes Ln^III[15-MC_Fe^IIIN(shi)-5](OAc)₂CI(C₅H₅N)₆ (Ln1), where OAc^- is acetate, shi^3- 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.

Visible and near-infrared emitting heterotrimetallic lanthanide-aluminum-sodium 12-metallacrown-4 compounds: discrete monomers and dimers

The luminescence properties of two types of heterotrimetallic aluminum-lanthanide-sodium 12-metallacrown-4 compounds are presented here, LnNa(ben)₄[12-MC_{Al(III)N(shi)}-4] (LnAl4Na) and {LnNa[12-MC_{Al(III)N(shi)}-4]}₂(iph)₄ (Ln2Al8Na2), where Ln = Gd^III, Tb^III, Er^III, and Yb^III, MC is metallacrown, ben^- is benzoate, shi^3- is salicylhydroximate, and iph^2- is isophthalate. The aluminum-lanthanide-sodium metallacrowns formed with benzoate are discrete monomers while, upon replacement of the benzoate with the dicarboxylate isophthalate, two individual metallacrowns can be joined to form a dimer. In the solid state, the terbium version of each structure type displays emission in the visible region, and the erbium and ytterbium complexes emit in the near-infrared. The luminescence lifetimes (τ_obs) and quantum yields have been collected under ligand excitation (QLLn) for both LnAl4Na monomers and Ln2Al8Na2 dimers. Several of these values tend to be shorter (luminescence lifetimes) and smaller (quantum yields) than the corresponding values recorded for the structurally similar gallium-lanthanide monomer and dimer 12-MC-4 molecules. However, the quantum yield value recorded for the visible emitting Tb2Al8Na2 dimer, 43.9%, is the highest value observed in the solid state to date for a Tb^III based metallacrown.

Near-Infrared Lanthanide-Based Emission from Fused Bis[Ln(III)/Zn(II) 14-metallacrown-5] Coordination Compounds

A set of (Ln[14-MC_{Zn(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 Yb^{3+ 2}F_5/2→²F_7/2 transition despite the proximity of high energy O-H oscillators.

Tuning the photophysical properties of lanthanide(iii)/zinc(ii) ‘encapsulated sandwich’ metallacrowns emitting in the near-infrared range

A family of Zn₁₆Ln(HA)₁₆ metallacrowns (MCs; Ln = Yb^III, Er^III, and Nd^III; HA = picoline- (picHA²⁻), pyrazine- (pyzHA²⁻), and quinaldine- (quinHA²⁻) hydroximates) with an ‘encapsulated sandwich’ structure possesses outstanding luminescence properties in the near-infrared (NIR) and suitability for cell imaging. Here, to decipher which parameters affect their functional and photophysical properties and how the nature of the hydroximate ligands can allow their fine tuning, we have completed this Zn₁₆Ln(HA)₁₆ family by synthesizing MCs with two new ligands, naphthyridine- (napHA²⁻) and quinoxaline- (quinoHA²⁻) hydroximates. Zn₁₆Ln(napHA)₁₆ and Zn₁₆Ln(quinoHA)₁₆ exhibit absorption bands extended into the visible range and efficiently sensitize the NIR emissions of Yb^III, Er^III, and Nd^III upon excitation up to 630 nm. The energies of the lowest singlet (S₁), triplet (T₁) and intra-ligand charge transfer (ILCT) states have been determined. Ln^III-centered total (Q^L_Ln) and intrinsic (Q^Ln_Ln) quantum yields, sensitization efficiencies (η_sens), observed (τ_obs) and radiative (τ_rad) luminescence lifetimes have been recorded and analyzed in the solid state and in CH₃OH and CD₃OD solutions for all Zn₁₆Ln(HA)₁₆. We found that, within the Zn₁₆Ln(HA)₁₆ family, τ_rad values are not constant for a particular Ln^III. The close in energy positions of T₁ and ILCT states in Zn₁₆Ln(picHA)₁₆ and Zn₁₆Ln(quinHA)₁₆ are preferred for the sensitization of Ln^III NIR emission and η_sens values reach 100% for Nd^III. Finally, the highest values of Q^L_Ln are observed for Zn₁₆Ln(quinHA)₁₆ in the solid state or in CD₃OD solutions. With these data at hand, we are now capable of creating MCs with desired properties suitable for NIR optical imaging.

We have created a family of ‘encapsulated sandwich’ Zn₁₆Ln(HA)₁₆ metallacrowns and by detailed quantitative analysis demonstrated how the nature of the hydroximate ligand impacts photophysical properties of these complexes.

Crystal structures of three anionic lanthanide-aluminium [3.3.1] metallacryptate complexes

The three isomorphous [3.3.1] metallacryptate complexes bis-(pyridinium) di-aqua-dipyridine-hexa-kis-[μ3-salicyl-hydroximato(3-)]bis-[μ2-salicyl-hydroxim-ato(1-)]hexa-aluminiumgadolinium-pyridine-water (1/7.396/1), (C5H6N)2[GdAl6(C7H6NO3)2(C7H4NO3)7(C5H5N)1.855(H2O)2]·7.396C5H5N·H2O or [Hpy]2[GdAl6(H2shi)2(shi)7(py)1.855(H2O)2]·7.396py·H2O, 1, bis-(pyridinium) di-aqua-dipyridine-hexa-kis-[μ3-salicyl-hydroximato(3-)]bis-[μ2-salicyl-hydroxim-ato(1-)]hexa-aluminiumdysprosium-pyridine-water (1/7.429/1), (C5H6N)2[DyAl6(C7H6NO3)2(C7H4NO3)7(C5H5N)1.855(H2O)2]·7.429C5H5N·H2O or [Hpy]2[DyAl6(H2shi)2(shi)7(py)1.891(H2O)2]·7.429py·H2O, 2, and bis-(pyrid-in-ium) di-aqua-dipyridine-hexa-kis-[μ3-salicyl-hydroximato(3-)]bis-[μ2-salicyl-hydrox-imato(1-)]hexa-aluminiumytterbium-pyridine-water (1/7.386/1), (C5H6N)2[YbAl6(C7H6NO3)2(C7H4NO3)7(C5H5N)1.855(H2O)2]·7.429C5H5N·H2O or [Hpy]2[YbAl6(H2shi)2(shi)7(py)1.818(H2O)2]·7.386py·H2O, 3, where Hpy+ is pyridinium, shi3- is salicyl-hydroximate, and py is pyridine, consist of an aluminium-based metallacryptand that captures an Ln III ion in the central cavity. The metallacryptand portions are comprised of an Al-N-O repeat unit; thus, they can be considered three-dimensional metallacrowns. The encapsulated Ln III ions are nine-coordinate with a spherical capped-square-anti-prism geometry, while the six AlIII ions are all octa-hedral. Four of the AlIII ions are chiral centers with 2 Δ and 2 Λ stereoconfigurations. The remaining two AlIII ions have trans chelate rings from two different shi3- ligands. For 1-3, a section of the main mol-ecule is disordered induced by the presence or absence of a pyridine ligand coordinated to one of the AlIII ions. In the absence of the pyridine moiety, an H2shi- ligand moves into the space otherwise occupied by the pyridine and the phenol oxygen atom coordinates to the AlIII ion. The movement of the H2shi- ligand induces movement for the Ln III ion, for another AlIII ion that also binds the same H2shi- ligand, and for one of the shi3- ligands coordinated to the latter AlIII ion. For 1-3 the occupancy ratio of the metallacryptand portions refined to 0.8550 (13):0.1450 (13), to 0.8909 (13):0.1091 (13), and to 0.8181 (14):0.1819 (14), respectively.

Crystal structures of two dysprosium-aluminium-sodium [3.3.1] metallacryptates that form two-dimensional sheets

The two [3.3.1] metallacryptate complexes, namely, poly[[μ3-acetato-hexa-kis-(μ-N,N-di-methyl-formamide)-bis-(N,N-di-methyl-formamide)bis-[salicyl-hydroxi-mato(2-)]hepta-kis-[salicyl-hydrox-im-ato(3-)]hexa-aluminium(III)dysprosium(III)penta-sodium(I)] N,N-di-methyl-formamide tetra-solvate monohydrate], [DyAl6Na5(OAc)(Hshi)2(shi)7(DMF)8]·4DMF·H2O or {[DyAl6Na5(C7H5NO3)2(C7H4NO3)7(C2H3O2)(C3H7NO)8]·4C3H7NO·H2O} n , 1, and poly[[di-μ4-acetato-nona-kis-(μ-N,N-di-methyl-form-amide)-octa-kis-(N,N-di-methyl-formamide)tetra-kis-[sali-cyl-hydroximato(2-)]tetra-deca-kis-[salicyl-hydroximato(3-)]dodeca-aluminium(III)didysprosium(III)deca-sodium(I)] N,N-di-methyl-form-amide 6.335-solvate], [DyAl6Na5(OAc)(Hshi)2(shi)7(DMF)8.5]2·6.335DMF or {[Dy2Al12Na10(C7H5NO3)4(C7H4NO3)14(C2H3O2)2(C3H7NO)17]·6.335C3H7NO} n , 2, where shi3- is salicyl-hydroximate and DMF is N,N-di-methyl-formamide, both consist of an aluminium-based metallacryptand. In 1 and 2, the metallacryptand encapsulates a dysprosium(III) ion in the central cavity, and the resulting metallacryptates are connected to each other via sodium-DMF linkages to generate a two-dimensional sheet. The metallacryptates of 1 and 2 are the three-dimensional analogues of metallacrowns as the metallacryptates contain a metal-nitro-gen-oxygen cyclic repeat unit throughout the complexes. For 1 the building block of the two-dimensional sheet is comprised of only one type of metallacryptate, which is connected to four neighboring metallacryptates via four sodium-DMF linkages. In 2, the building block is a dimeric unit of two metallacryptates. Each dimeric metallacryptate unit is connected to four other dimeric units via six sodium-DMF linkages. The two metallacryptates of each dimeric unit can be considered enanti-omers of each other. In both 1 and 2, chirality is imparted to the metallacryptate due to the Λ and Δ propeller configurations of the four octa-hedral aluminium ions of the metallacryptand shell.

Wheel-like 6 luminescent lanthanide complexes covering the visible and near-infrared domains

Luminescence properties of wheel-like lanthanide complexes.

Peculiarities of crystal structures and photophysical properties of GaIII/LnIII metallacrowns with a non-planar [12-MC-4] core

The direct synthetic approach can be used to create a series of visible and near-infrared emitting Ga^III/Ln^III metallacrowns with a non-planar [12-MC-4] core.

A new family of {Co4Ln8} metallacrowns with a butterfly-shaped structure

A series of cobalt–lanthanide metallacrowns (MCs) {CoIII4Ln₈} (Ln = Dy³⁺1, Ho³⁺2 and Tm³⁺3) based on pyrazinehydroxamic acid (H₂pyzha) and pyrazinic acid (Hpyzic) ligands have been synthesized.