Water hexamer anion

A possible isomerization pathway for the = 6 cluster has been proposed on the basis of the quantum chemical calculations of Conbariza et al. [59] and Kim et al. [33]. In the predicted most stable structure for the ground state [59], the 1 ion lies on the surface of a V-shaped solvent network. It has been assumed that the initially excited state has a similar geometry, in which the excess electron is weakly bound by the net dipole moment of the solvent network. The supposed form after isomerization resembles the stable half-cage structure for the water hexamer anion [33], in which the excess electron is confined by dangling hydrogens of waters. 

Figure 10.34 Crystal structure of the Sr2+ salt of the metallo-hemicarcerand 10.38, assembled from two hemispherical octa-anionic ligands, 10.37, and four Fe(II) ions. The cavity contains a discrete water hexamer.34...

N. Mikami, Infrared spectroscopic evidence for protonated water clusters forming nanoscale cages, Science 304, 1134-1137 (2004). (e) S. B. Suh, H. M. Lee, J. Kim, J. Y. Lee, and K. S. Kim, Vibrational spectra and electron detachment energy of the anionic water hexamer,... 

Various polyphosphates are effective sequestering agents under appropriate conditions. The best known of these is sodium hexametaphosphate (10.14), the cyclic hexamer of sodium orthophosphate. Further examples are the cyclic trimer sodium trimetaphosphate (10.15), as well as the dimeric pyrophosphate (10.16), the trimeric tripolyphosphate (10.17) and other linear polyphosphates (10.18). All of these polyanions function by withdrawing the troublesome metal cation into an innocuous and water-soluble complex anion by a process of ion exchange as shown in Scheme 10.7 for sodium hexametaphosphate. Hence these compounds are sometimes referred to as ion-exchange agents. 

The enzyme is a hexamer, actually a dimer of trimers made up of 291-residue polypeptide chains.28 Aceto-acetyl-CoA is a competitive inhibitor which binds into the active site and locates it. From the X-ray structure of the enzyme-inhibitor complex it can be deduced that the carboxylate group of E144 abstracts a proton from a water molecule to provide the hydroxyl ion that binds to the P position (Eq. 13-6, step a) and that the E164 carboxyl group donates a proton to the intermediate enolate anion in step b.28 The hydroxyl group... 

C the product is Rli6(CO)i6. This is consistent with an endothermic equilibrium from the tetramer to the hexamer (equation 22). A two-step synthesis of Rli4(CO)i2 at room temperature and atmospheric pressure involves the reduction of the [RhCh] anion to [RhCl2(CO)2] with copper, followed by reduction with water and CO in the presence of a sodium citrate buffer. The yields are nearly quantitative. 

The thorium ion, Th4+, is more resistant to hydrolysis than other 4+ ions but undergoes extensive hydrolysis in aqueous solution at pH higher than 3 the species formed are complex and dependent on the conditions of pH, nature of anions, concentration, etc. In perchlorate solutions the main ions appear to be Th(OH)3 +, Th(OH)2+, Th2(OH) +, Th4(OH) +, while the final product is the hexamer Th6(OH)95 of course, all these species carry additional water.19 Hexameric ions exist also for Nbv and for Ce1 v and Ulv [M604(0H)J12 + ions are found in crystals of the sulfates. The metal atoms are linked by hydroxo or oxo bridges. In crystals of the hydroxide, Th(OH)4, or the compound Th(0H)2Cr04 HzO, chain-like structures have been identified, the repeating unit being Th(OH)2+ in solution, the polymers may have similar form (28-1) or may additionally be cross-linked. 

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