Complexes with Water

K(H0H)6 , the oxygens on the water molecules being the points of attachment. The ion is said to have a coordination number of 6, this value referring to the number of points of attachment that K" " provides to molecules or ions (ligands) which can attach. This water complex with attachments to oxygen is so very stable that displacement of the water molecules by other ligands (attaching molecules or ions) is difficult. As a result, K+... 

Figure 37 shows the structure of the water complex with the four-armed tetraaza[12]-crown-4 (10). The water molecule is located in the center of the cavity and serves as proton donor to two trans nitrogen atoms. The water molecule also accepts hydrogen bonds from OH side groups attached to the other trans nitrogen atoms. Thus a tetrahedral encapsulation of the water molecule occurs. A remarkable aspect is that the conformation of the twelve-membered ring hardly differs from that of the free ligand (10). 

The complexes formed with boron trihalides are decomposed to pyridine by boiling water. Complexes with other Lewis acids behave similarly. 

As rainwater percolates through the soil profile, fluoride-bearing minerals dissolve and release F into soil water (Figure 13.1). Fluoride is also released into soil water from mineral surfaces through desorption processes. Studies have shown that F in soil water complexes with Al and Fe, which can influence plant uptake... 

Figure 14. Variation of the MP2 BSSE-uncorrected and BSSE-corrected interaction energies of the methane-water complex with the basis set. Circles indicate results obtained using Pople basis set, while squares indicate results obtained with the aug-cc-pVxZ basis sets. The geometry is the optimum one computed at the MP2/aug-cc-pVTZ level.

The IR spectra of 4-aminopyridine revealed the large predominance of the amino form in a low-temperature argon matrix with no indication of the presence of the imino form. In the presence of water in the matrix, two 1 1 4-aminopyridine/water complexes with H-N-H---OH2 and N HO FI bonding were detected, the former being more stable by only 1.6 kcal/mol (94JST(322)113, 95JPC6387). 

AI-water complexes with more than three waters have received less attention because it is believed that such large complexes cannot be directly involved in the tautomerization. Moreover, these complexes are difficult to be spectroscopically assigned due to the complexity of their electronic [11] and vibrational [10] structures. 7AI with four waters was studied by Fohner et al. [27] using ultrafast pump-probe spectroscopy combined with theoretical calculations. Their results revealed that the proton-transfer rate increases compared to that of 7AI with two and three waters. Their deuteration studies provided proof for the occurrence of proton transfer (PT), although it was not conclusively confirmed that the proton transfer resulted in a complete tautomerization of the 7AI monomer. For even bigger clusters of 7AI with five waters, there are no experimental investigations available only a theoretical study was reported on the second hydration shell effect [45]. 

The reaction mechanism and the stereochemical diversity of the addition of water to disilene has been studied at the MP2/6-311-h+G level. Two pathways are feasible leading to syn and anti-addition. The syn addition proceeds via nucleophilic attack by water oxygen with a barrier of ca. 12 kJ mol k anti-Addition proceeds via intramolecular electrophilic attack by water hydrogen in a weakly bound disilene/water complex with antarafacial approach, in accordance with the Woodward-Hoffmann rules, and leads to an activation barrier of ca. 22 kJ mol ... 

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