Lifetime of water molecule

The average lifetime of water molecules in the second coordination shell can be obtained from the MD simulation and was found to be in the range of 20-25 ps for the poly(amino-carboxylate) complexes and 56 ps for the polyamino-phosphonate based [Gd(DOTP)]5- [97]. These residence times are long if compared to those of second sphere water around the aqua ions of lan-... 

Swift, T. /., and R. E. Connick NMR-Relaxation Mechanism of O17 in Aqueous Solutions of Paramagnetic Cations and the Lifetime of Water Molecules in the First Coordination Sphere. J. chem. Phys. 37, 307 (1962). Erratum J. chem. Phys. 41, 2553 (1964). 

A. Theories of Fast and Slow Exchange. In 1957i Zimmerman and Britten published a theoretical treatment of the relaxation of water protons absorbed on silica gel (l6). In this system, both uni- and multiphasic relaxation decays were observed. The authors were able to account for the change in the number of observed phases by taking into account the relaxation times of the water protons in bound (absorbed) or free (non-absorbed) states, and the lifetimes of water molecules in each state. Two asymptotic expressions were derived, which have frequently been used in subsequent studies of water relaxation. 

FIG. 3 Rates of exchange (s" ) and characteristic lifetimes of water molecules in the inner co-ordination spheres of the metals. (From Ref 15.)... 

Supkowsky, R. M. Horrocks, de W. On the determination of the number of water molecules, q, coordinated to europium(IH) ions in solution from luminescence decay lifetimes. Inorg. Chim. Acta 2002, 340, 44-48. 

Excitation spectra have been of considerable use recently in studying both hydration numbers (by lifetime measurements) and inner-sphere complexation by anions (by observing appearance of the characteristic frequencies for e.g. the Eu3+ 5D0-+ 7F0 transition for the different possible species). Thus using a pulsed dye laser source, it was possible to demonstrate the occurrence of inner sphere complexes of Eu3+ with SCN, CI or NO3 in aqueous solution, the K values being 5.96 2, 0.13 0.01 and 1.41 0.2 respectively. The CIO4 ion did not coordinate. Excited state lifetimes suggest the nitrate species is [Eu(N03)(HzO)6,s o.4]2+ the technique here is to compare the lifetimes of the HzO and the corresponding D20 species, where the vibrational deactivation pathway is virtually inoperative.219 The reduction in lifetime is proportional to the number of water molecules complexed.217 218... 

Parker and co-workers have reported a novel method for the selective detection of carboxy anions by time-delayed luminescence using the Eu(III) and Tb(III) complexes of 85 [59]. Luminescence measurements on the coordina-tively unsaturated complexes in aqueous solution showed significant increases in lifetime and emission intensity in the presence of anions. This behaviour is consistent with the anions displacing water from the non-ligated coordination sites at the metal centre. Studies allowed the number of water molecules (q) remaining coordinated in the presence of added anions to be estimated. For the triflate salt of the Eu(III) receptor q=2.14, whereas with hydrogencarbonate... 

It is well known [54,270] that the macroscopic dielectric relaxation time of bulk water (8.27 ps at 25°C) is about 10 times greater than the microscopic relaxation time of a single water molecule, which is about one hydrogen bond lifetime [206,272-274] (about 0.7 ps). This fact follows from the associative structure of bulk water where the macroscopic relaxation time reflects the cooperative relaxation process in a cluster of water molecules. 

Europium(III) exchanged zeolites have been studied by a number of research groups. Arakawa and coworkers (20, 21 ) report the luminescence properties of europium(III)-exchanged zeolite Y. Emission spectra were measured under a variety of conditions and bands for europium(II) were observed after thermal treatment of the europium(III) Y zeolites. A mechanism was proposed for the thermal splitting of water which involved the cycling of europium between the two different oxidation states. Europium MSssbauer experiments (22 ) also show that on thermal treatment of europium-(III) zeolites that europium(II) is formed. Stucky and coworkers (23, 24) studied the phosphorescence lifetime of these europium-(lll) zeolites and showed that the inverse of the lifetime (the decay constant) was linearly related to the number of water molecules surrounding the europium(III) ion in the zeolite supercages. These studies involved zeolites A, X, Y and ZSM-5. 

Another matter concerns the time of reaction between a set of water molecules after an ion has just pushed its way into the middle of them. Thus, if the lifetime of molecules in the primary solvation shell is sufficiently short, there must be somejumps in which the ion is bare or at least only minimally clothed. How is the hydration number affected by the time needed for the solvent molecules buried in the solvent layer to break out of that attachment and rotate so that their dipoles are oriented toward the ion to maximize the energy of interaction (cos 0 = 1) ... 

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