Water distance

Although X-ray and neutron diffraction and scattering methods give only approximate estimates of hydration numbers they can provide precise measures of ion-water distances in solution. In calcium chloride and bromide solutions of various concentrations, Ca-0 distances of between 2.40 and 2.44 A have been reported (167,168,171,172) Ca-0 — 2.26A was claimed in an early X-ray investigation of molar calcium nitrate solution (167,186). EXAFS and LAXS studies showed a broad and asymmetric distribution of Ca-0 distances centered on a mean value of 2.46 A (174). 

From the data in Table I it is clear that the potential with the 3-body corrections yields lower values for the interaction energies, and (not reported) larger ion-water distances. In addition, for n=5 and n=6 we find, respectively, one and two water molecules in the second solvation shell, whereas the 2-body potential gives one water molecule in the second shell... 

Inset a) refers to the starting configuration, t=0 fs, with the 5 water molecules in the first hydration shell. Inset b) refers to t=70 fs some rearrangement starts to occur, especially for the left most water molecule. At t=l 10 fs (inset c)) one ion-water distance is above the threshold value, the water starts to leave the first hydration shell. Finally, at t=210 fs, one water molecule is in the second hydration shell and the remaining four... 

Another important topic of interest has been the interpretation of the observed ion-water distances d(i...w) [4-6] in terms of the ionic radii in solutions and the radii of water molecules. The present author made the surprising observation recently [7] that d(i...w) increases linearly with the covalent radius d(A) of the atom [9], for mary ions according to the eqrration. 

The synthetic compounds of para. VII contain multiple groups which form five-membered chelate rings. Although the metal-oxygen distances, Tables 4 and 5, vary by amounts large compared with the standard deviations, it is clear that sodium-water distances are shorter than sodium-ether oxygen distances, even for the most flexible ligand, (XVIII). 

Tables 21 and 22 provide structural parameters for neutral aqua-triorganyltin adducts. The longest tin-water distance of 2.500 A is found for the 3-pyridylacrylato derivative (Table 21, entry 9). The coordinate bond of 2.253 A in SnPh3(SCN) (entry 10) is the shortest. The strengthening of the O — Sn bond in compounds with the same SnR3 groups is accompanied by an increase in the tin pyramidalization. This is reflected in the corresponding decrease in the deviation of the tin atom from the equatorial plane (ASn) of the neighboring carbon atoms.

From water Distance from sea bottom From roiled bottom sediments with 10 ms/1 concentration... 

Table 11.1 Actinide aqua ions - numbers of bound water molecules and metal-water distances"...

Metal Hydration energy (kj mol ) Metal- -water distance (A)... 

Ph iron-water distance (2.0 A) and movement of the iron into the heme... 

X-ray structure with Fe-Water distance of 2.00 A and iron moved into the porphyrin plane... 

Ion Counter- ion Concentration (molality) Ion-water distances (A) Hydration number ( MO Tilt angle 0 (deg) Method / reference... 

---