18130-74-0Relevant articles and documents
Enhancing the anion affinity of urea-based receptors with a Ru(terpy) 22+ chromophore
Baggi, Giorgio,Boiocchi, Massimo,Ciarrocchi, Carlo,Fabbrizzi, Luigi
, p. 5273 - 5283 (2013/06/26)
Covalent linking of a Ru(terpy)22+ substituent improves recognition and sensing properties of the urea subunit toward anions. Urea's anion affinity is enhanced by the electrostatic attraction exerted by the RuII cation and by the electron-withdrawing effect exerted by the entire polypyridine-metal complex. Such an enhancement of the anion affinity, which results from the combination of a through-space and a through-bond effect, is greater than that exerted by the classical neutral electron-withdrawing substituent nitrophenyl. Small yet significant modifications of π-π* and MLCT bands of the Ru(terpy)22+ chromophore, detected through UV-vis spectrophotometric titrations, allowed the determination of the constants for the formation of receptor-anion H-bond complexes in diluted MeCN solution. On 1H NMR titration experiments, carried out under more concentrated conditions, the interaction of a second Cl- ion was observed, taking place through an outer-sphere mechanism. The Ru(terpy) 22+ substituent favors the deprotonation of a urea N-H fragment on addition of a second equivalent of fluoride, with formation of HF2-.
Tetrafluorophosphite, PF4-, anion
Christe, Karl O.,Dixon, David A.,Mercier, Hélène P. A.,Sanders, Jeremy C. P.,Schrobilgen, Gary J.,Wilson, William W.
, p. 2850 - 2858 (2007/10/02)
N(CH3)4+PF4-, the first example of a PF4- salt, has been prepared from N(CH3)4F and PF3 using either CH3CN, CHF3, or excess PF3 as a solvent. The salt is a white, crystalline solid which is thermally stable up to 150 °C where it decomposes to N(CH3)3, CH3F, and PF3. The structure of the PF4- anion was studied by variable temperature 31P and 19F NMR spectroscopy, infrared and Raman spectroscopy, SCF, MP2, local and nonlocal density functional calculations, a normal coordinate analysis, and single-crystal X-ray diffraction. The anion possesses a pseudo trigonal bipyramidal structure with two longer axial bonds and an equatorial plane containing two shorter equatorial bonds and a sterically active free valence electron pair. In solution, it undergoes an intramolecular exchange process by the way of a Berry pseudorotation mechanism. The vibrational frequencies observed for PF4- in solid N(CH3)4PF4 are in excellent agreement with those calculated for free gaseous PF4-. The X-ray diffraction study tetragonal, space group P4?21m, a = 8.465(3) A?, c = 5.674(2) A?, Z = 2, R = 0.0723 for 268 observed [F ≥ σ(F)] reflections suffers from a 3-fold disorder with unequal occupancy factors for the equatorial fluorine atoms of PF4- but confirms its pseudo trigonal bipyramidal structure and the axial P-F bond length calculated for the free ion.
