skip to main content
Explore Scholarly Publications and Datasets in the NSF-PAR

  • NSF Public Access
  • Search Results
  • Accepted Manuscript: Peculiarities of crystal structures and photophysical properties of Ga III /Ln III metallacrowns with a non-planar [12-MC-4] core
Title: Peculiarities of crystal structures and photophysical properties of Ga III /Ln III metallacrowns with a non-planar [12-MC-4] core
A new series of gallium( iii )/lanthanide( iii ) metallacrown (MC) complexes ( Ln-1 ) was synthesized by the direct reaction of salicylhydroxamic acid (H 3 shi) with Ga III and Ln III nitrates in a CH 3 OH/pyridine mixture. X-ray single crystal analysis revealed two types of structures depending on whether the nitrate counterion coordinate or not to the Ln III : [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 4 (NO 3 )](py) 2 (Ln = Gd III , Tb III , Dy III , Ho III ) and [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 5 ](NO 3 )(py) (Ln = Er III , Tm III , Yb III ). The representative Tb-1 and Yb-1 MCs consist of a Tb/YbGa 4 core with four [Ga III –N–O] repeating units forming a non-planar ring that coordinates the central Ln III through the oxygen atoms of the four shi 3− groups. Two H 2 shi − groups bridge the Ln III to the Ga III ring ions. The Yb III in Yb-1 is eight-coordinated while the ligation of the nine-coordinated Tb III in Tb-1 is completed by one chelating nitrate ion. Ln-1 complexes in the solid more » state showed characteristic sharp f–f transitions in the visible (Tb, Dy) and near-infrared (Dy, Ho, Er, Yb) spectral ranges upon excitation into the ligand-centered electronic levels at 350 nm. Observed luminescence lifetimes and absolute quantum yields were collected and discussed. For Yb-1 , luminescence data were also acquired in CH 3 OH and CD 3 OD solutions and a more extensive analysis of photophysical properties was performed. This work demonstrates that while obtaining highly luminescent lanthanide( iii ) MCs via a direct synthesis is feasible, many factors such as molar absorptivities, triplet state energies, non-radiative deactivations through vibronic coupling with overtones of O–H, N–H, and C–H oscillators and crystal packing will strongly contribute to the luminescent properties and should be carefully considered. « less
Authors:
; ; ; ; ;
Award ID(s):
1664964
Publication Date:
NSF-PAR ID:
10174914
Journal Name:
Inorganic Chemistry Frontiers
Volume:
7
Issue:
7
Page Range or eLocation-ID:
1553 to 1563
ISSN:
2052-1553
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ( , Dalton Transactions)
    The reduction potentials (reported vs. Fc + /Fc) for a series of Cp′ 3 Ln complexes (Cp′ = C 5 H 4 SiMe 3 , Ln = lanthanide) were determined via electrochemistry in THF with [ n Bu 4 N][BPh 4 ] as the supporting electrolyte. The Ln( iii )/Ln( ii ) reduction potentials for Ln = Eu, Yb, Sm, and Tm (−1.07 to −2.83 V) follow the expected trend for stability of 4f 7 , 4f 14 , 4f 6 , and 4f 13 Ln( ii ) ions, respectively. The reduction potentials for Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, that form 4f n 5d 1 Ln( ii ) ions ( n = 2–14), fall in a narrow range of −2.95 V to −3.14 V. Only cathodic events were observed for La and Ce at −3.36 V and −3.43 V, respectively. The reduction potentials of the Ln( ii ) compounds [K(2.2.2-cryptand)][Cp′ 3 Ln] (Ln = Pr, Sm, Eu) match those of the Cp′ 3 Ln complexes. The reduction potentials of nine (C 5 Me 4 H) 3 Ln complexes were also studied and found to be 0.05–0.24 V more negative than those of the Cp′more »3 Ln compounds.« less
  2. ; ; ; ; ; ( , Chemical Science)
    A family of Zn 16 Ln(HA) 16 metallacrowns (MCs; Ln = Yb III , Er III , and Nd III ; HA = picoline- (picHA 2− ), pyrazine- (pyzHA 2− ), and quinaldine- (quinHA 2− ) 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 Zn 16 Ln(HA) 16 family by synthesizing MCs with two new ligands, naphthyridine- (napHA 2− ) and quinoxaline- (quinoHA 2− ) hydroximates. Zn 16 Ln(napHA) 16 and Zn 16 Ln(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 (S 1 ), triplet (T 1 ) and intra-ligand charge transfer (ILCT) states have been determined. Ln III -centered total ( Q LLn) and intrinsic ( Q LnLn) quantum yields, sensitization efficiencies ( η sens ), observed ( τ obs ) and radiative ( τ rad ) luminescence lifetimes havemore »been recorded and analyzed in the solid state and in CH 3 OH and CD 3 OD solutions for all Zn 16 Ln(HA) 16 . We found that, within the Zn 16 Ln(HA) 16 family, τ rad values are not constant for a particular Ln III . The close in energy positions of T 1 and ILCT states in Zn 16 Ln(picHA) 16 and Zn 16 Ln(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 LLn are observed for Zn 16 Ln(quinHA) 16 in the solid state or in CD 3 OD solutions. With these data at hand, we are now capable of creating MCs with desired properties suitable for NIR optical imaging.« less
  3. ; ; ; ; ; ; ; ; ( , Chemical Science)
    The synthesis of a novel family of homoleptic COT-based heterotrimetallic self-assemblies bearing the formula [LnKCa(COT) 3 (THF) 3 ] (Ln( iii ) = Gd, Tb, Dy, Ho, Er, Tm, and Yb) is reported followed by their X-ray crystallographic and magnetic characterization. All crystals conform to the monoclinic P 2 1 / c space group with a slight compression of the unit cell from 3396.4(2) Å 3 to 3373.2(4) Å 3 along the series. All complexes exhibit a triple-decker structure having the Ln( iii ) and K( i ) ions sandwiched by three COT 2− ligands with an end-bound {Ca 2+ (THF) 3 } moiety to form a non-linear (153.5°) arrangement of three different metals. The COT 2− ligands act in a η 8 -mode with respect to all metal centers. A detailed structural comparison of this unique set of heterotrimetallic complexes has revealed consistent trends along the series. From Gd to Yb, the Ln to ring-centroid distance decreases from 1.961(3) Å to 1.827(2) Å. In contrast, the separation of K( i ) and Ca( ii ) ions from the COT-centroid (2.443(3) and 1.914(3) Å, respectively) is not affected by the change of Ln( iii ) ions. The magnetic property investigationmore »of the [LnKCa(COT) 3 (THF) 3 ] series (Ln( iii ) = Gd, Tb, Dy, Ho, Er, and Tm) reveals that the Dy, Er, and Tm complexes display slow relaxation of their magnetization, in other words, single-molecule magnet (SMM) properties. This behaviour is dominated by thermally activated (Orbach-like) and quantum tunneling processes for [DyKCa(COT) 3 (THF) 3 ] in contrast to [ErKCa(COT) 3 (THF) 3 ], in which the thermally activated and Raman processes appear to be relevant. Details of the electronic structures and magnetic properties of these complexes are further clarified with the help of DFT and ab initio theoretical calculations.« less
  4. ; ; ; ; ; ( , Chemical Science)
    Lanthanide metallocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to transition metal ions. Herein, we present a systematic study of the structural and magnetic properties of the ferrocenophanes, [LnFc 3 (THF) 2 Li 2 ] − , of the late trivalent lanthanide ions (Ln = Gd ( 1 ), Ho ( 2 ), Er ( 3 ), Tm ( 4 ), Yb ( 5 ), Lu ( 6 )). One major structural trend within this class of complexes is the increasing diferrocenyl (Fc 2− ) average twist angle with decreasing ionic radius ( r ion ) of the central Ln ion, resulting in the largest average Fc 2− twist angles for the Lu 3+ compound 6 . Such high sensitivity of the twist angle to changes in r ion is unique to the here presented ferrocenophane complexes and likely due to the large trigonal plane separation enforced by the ligand (>3.2 Å). This geometry also allows the non-Kramers ion Ho 3+ to exhibit slow magnetic relaxation in the absence of applied dc fields, rendering compound 2 a rare example of a Ho-based single-molecule magnet (SMM)more »with barriers to magnetization reversal ( U ) of 110–131 cm −1 . In contrast, compounds featuring Ln ions with prolate electron density ( 3–5 ) don't show slow magnetization dynamics under the same conditions. The observed trends in magnetic properties of 2–5 are supported by state-of-the-art ab initio calculations. Finally, the magneto-structural relationship of the trigonal prismatic Ho-[1]ferrocenophane motif was further investigated by axial ligand (THF in 2 ) exchange to yield [HoFc 3 (THF*) 2 Li 2 ] − ( 2-THF* ) and [HoFc 3 (py) 2 Li 2 ] − ( 2-py ) motifs. We find that larger average Fc 2− twist angles (in 2-THF* and 2-py as compared to in 2 ) result in faster magnetic relaxation times at a given temperature.« less
  5. ; ; ( , Metallomics)
    G-quadruplexes (GQs), spatial assemblies of guanine-rich DNA strands, play an important role in the regulation of gene expression and chromosome stabilization. These structures are recognized to be useful in cancer therapies as the presence of multiple G-quadruplexes in a telomeric strand stops cancer cell proliferation. Metallacrowns of the type 12-MC-4 form planar structures that have remarkable similarity to G-tetrads in terms of dimension, shape and the ability to bind alkali metal and lanthanide cations in a central cavity. The interaction between the Sm( iii )[12-MC Ga(III)shi -4] (SmMC) metallacrown (MC) and human telomeric G-quadruplex structures was examined using several methods including CD titrations, CD melting temperatures, fluorescence titration of SmMC with GQ/Na + , fluorescence intercalator displacement (FID) assays and methods measuring the MC quenching effect on the Tb 3+ /GQ luminescence. It was proven that the studied metallacrown acted as a sensing probe and interacted with quadruplex DNA. The Stern–Volmer quenching constant ( K as ) of Tb 3+ /GQ luminescence was calculated to be 3.9 × 10 5 M −1 . The binding constant using the indirect FID method gave the result of 1.3 × 10 5 M −1 . CD melting temperature experiments reveal the following patternmore »– the higher the concentration of the complex the lower the registered T m for quadruplex DNA, which indicates a destabilizing effect of SmMC at higher GQ : MC ratios. These data implicate a shape and size selective interaction between MCs and GQs that may be exploited for telomere detection.« less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email