Aqua Ions and Simple Salts

M-O bond lengths are 2.016A (Rh) and 2.041 A (Ir), the former corresponds well to the value of 2.04 A deduced from X-ray studies on aqueous solutions of Rh(H20)6 [36]. 

Brown rhodium nitrate is reportedly formed from the reaction of Rhl3 with boiling nitric acid it forms a hexahydrate. 

In addition to the aqua ion, a range of mixed aquo-halo complexes are known [38], including all 10 isomers of Rh(H20)6 cClx Synthetic entry into the series is possible from either end, the determining factor being the labilizing effect of chloride  

This affects both the position of substitution and the rate thus RhCl(H20)5 substitutes more than an order of magnitude faster than Rh(H20)6. These substitutions are all believed to follow a dissociative (SnO reaction. Particular compounds can sometimes be obtained under specific conditions  

The rhodium(II) aqua ion is not yet completely characterized. Cr2+ reduction of Rh(H20)5Cl2+ gives a diamagnetic species believed to be Rh (aq.) [37], which may have the structure (H20)4Rh(/x-0H2)2Rh(H20)4+. 

It is believed to be metal-metal bonded (PF3)4Rh-Rh(PF3)4 and readily reacts with hydrogen 

Electrochemical reduction in MeCN of various RhCl(R3P)3 complexes give the diamagnetic Rh(R3P)4 (R3P = Ph3P, Mc2PhP), which are probably analogous to the PF3 complex. 

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We modified titration curves (Figure 2.1) assuming that a certain amount of simple metal salt containing M" ions is added to the solution containing hgand L. As this takes place, M" ions (aqua complexes) and ML" " species are formed whose total concentration is equal to c,. Some examples of simulated curves are presented in Figure 4.1 where the shift of the equihbrium potential (AEg ) versus Cj is plotted. A sharp decrease in is observed at the equivalent point, the depth of which depends on the stabihty constant K) of ML" " complex. 

Chemistry of aqueous solution of aluminum hydroxide from simple aluminum salts, such as aluminum trichloride, has been studied extensively (Cotton et al., 1999). In an aqueous solution, aqua ion, [A1(H20)6], or deprotonated ion, [Al(H20)s0H], exists stably. Th deprotonated ion forms dimer with two hydroxyl groups bridging two aluminum ions. Furthermore, the aqua ion tends to polymerize with increasing pH. Polynuclear ions, such as [Al3(OH)n], [Al6(OH)i5] +, and [Alg(OH)22] are recognized. Under extremely basic conditions, soluble aluminum tetra hydroxide ion, [Al(OH)4] , forms. Therefore, alumina sol is prepared around neutral pH. The mechanism of the polymerization leading to alumina sols, however, is not perfectly clarified. 

Unlike elements of the 3d series, 4<2 and 5d elements have the little simple aqueous cationic chemistry. The main exceptions are Y3+ and La3+ and Ag+, which forms some soluble salts (AgF, AgN03). The aqua Ag+ ion shows strong class b complexing behaviour, with an affinity for ligands such as NH3,I- and... 

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