Kinetics and equilibria of alkaline-earth-metal complex formation with cryptands in methanol

Cox, Brian G.; Truong, Ng. van; Garcia-Rosas, J.; Schneider, Hermann

doi:10.1021/j150649a030

Cited by 26 publications

(7 citation statements)

References 5 publications

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“…Yb II 2 exhibits a lengthening of both M−O bonds on the benzo-bearing arm of the cryptand that is also observed with Eu II 2 due to the decreased Lewis basicity imparted by the electron-withdrawing aromatic ring. 11,15 A feature of Yb II 2 that is not observed with Eu II 2 is that one of the M−O bonds on the benzo-bearing arm is considerably longer than the other. We hypothesize that this lengthening is a result of the rigidity imposed by the benzo ring on cryptand 2 preventing the benzo-bearing arm of the cryptand from contorting to accommodate ideal bond lengths from the coordinating atoms to the smaller Yb II ion.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Spectroscopic and Electrochemical Trends in Divalent Lanthanides through Modulation of Coordination Environment

et al. 2020

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Due to the importance of both visible-light luminescence and lanthanides in modern society, the influence of the ligand environment on complexes of YbII were studied and compared with analogous complexes of EuII. Four ligands with systematically varied electronic and steric characteristics were used to probe the coordination environment and electronic and redox properties of the corresponding YbII-containing complexes. Strong-field nitrogenous donors gave rise to bathochromic shifts, leading to visible-light absorption by YbII. Trends in properties across the series of YbII-containing complexes were compared to trends reported for the analogous EuII-containing complexes, revealing the translatability of coordination environment effects across the divalent lanthanide series. These studies provide valuable information regarding the behavior of small and medium-sized divalent lanthanides outside of the solid state.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Spectroscopic and Electrochemical Trends in Divalent Lanthanides through Modulation of Coordination Environment

et al. 2020

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“…Organic macrocycles are excellent metal ion chelators and have been extensively studied for their efficacy in solution-phase separations. − Cryptands such as 2.2.2 and 2.2.2B (5,6-benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacos-5-ene) depicted in Figure are well-known for their high affinity for low valent metals due to the high number of coordination sites for metal ions and large cavity size. ,− Additionally, the steric encumbrance of the cryptand prevents interaction between redox active species from the environment surrounding the cryptand with the metal ion the cryptand encapsulates . This property is especially advantageous for stabilizing low valent metal ions that are susceptible to oxidation such as divalent lanthanides.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Stabilization and Tunability of Divalent Europium 2.2.2B Cryptates

et al. 2021

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Lanthanides such as europium with more accessible divalent states are useful for studying redox stability afforded by macrocyclic organic ligands. Substituted cryptands, such as 2.2.2B cryptand, that increase the oxidative stability of divalent europium also provide coordination environments that support synthetic alterations of Eu(II) cryptate complexes. Two single crystal structures were obtained containing nine-coordinate Eu(II) 2.2.2B cryptate complexes that differ by a single coordination site, the occupation of which is dictated by changes in reaction conditions. A crystal structure containing a [Eu(2.2.2B)Cl] + complex is obtained from a methanol−THF solvent mixture, while a methanol−acetonitrile solvent mixture affords a [Eu-(2.2.2B)(CH 3 OH)] 2+ complex. While both crystals exhibit the typical blue emission observed in most Eu(II) containing compounds as a result of 4f 6 5d 1 to 4f 7 transitions, computational results show that the substitution of a Cl − anion in the place of a methanol molecule causes mixing of the 5d excited states in the Eu(II) 2.2.2B cryptate complex. Additionally, magnetism studies reveal the identity of the capping ligand in the Eu(II) 2.2.2B cryptate complex may also lead to exchange between Eu(II) metal centers facilitated by π-stacking interactions within the structure, slightly altering the anticipated magnetic moment. The synthetic control present in these systems makes them interesting candidates for studying less stable divalent lanthanides and the effects of precise modifications of the electronic structures of low valent lanthanide elements.

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“…[8] Furthermore, to examine the influence of Lewis basicity on oxidative stability, phenyl rings were introduced to decrease the electron-donating ability of the adjacent oxygen atoms of ligands 3 – 5 by a resonance withdrawing effect. [12] The extent of electron withdrawal was modulated by varying the electron density of the phenyl ring through the addition of a fluorine atom ( 4 ) or by increasing the number of rings ( 5 ). Phenyl-ring-containing cryptands 3 – 5 also have an influence on cavity size because each phenyl ring decreases the cavity size of the cryptand.…”

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confidence: 99%

Oxidatively Stable, Aqueous Europium(II) Complexes through Steric and Electronic Manipulation of Cryptand Coordination Chemistry

et al. 2010

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A series of cryptands have been prepared and they demonstrate the relationship between oxidative stability of aqueous EuII and ligand properties (see figure). One of these EuII complexes is more stable than FeII in hemoglobin and appears to be the most oxidatively-stable aqueous EuII species known. The high stability of EuII is expected to enable the use of the unique magnetic and optical properties of this ion in vivo.

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Kinetics and equilibria of alkaline-earth-metal complex formation with cryptands in methanol

Cited by 26 publications

References 5 publications

Spectroscopic and Electrochemical Trends in Divalent Lanthanides through Modulation of Coordination Environment

Spectroscopic and Electrochemical Trends in Divalent Lanthanides through Modulation of Coordination Environment

Understanding the Stabilization and Tunability of Divalent Europium 2.2.2B Cryptates

Oxidatively Stable, Aqueous Europium(II) Complexes through Steric and Electronic Manipulation of Cryptand Coordination Chemistry

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