Aquation Other Complexes

The di- -sulphido-bis[oxotriaquamolybdenum(v)] ion [structure (17) with oxo-bridges replaced by sulphido-bridges] is reported to be very stable even in strong acid solutions, unlike (17) which dissociates into paramagnetic monomeric species.  

Titanium(iv).—The kinetics of the autocatalytic hydrolysis of hexafluoro-titanate(iv) have been examined titrimetrically, at 0 and at 25 °C in aqueous solution. The results were discussed in terms of the establishment of the following equilibria  

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When acido groups, halides, thiocyanate, azide, acetate, and nitrate are present in the coordination sphere of cobalt(III), they appear to be oxidized in preference to coordinated ammonia. Many of the radicals thus produced are capable of oxidizing ammonia released from the complex or of interfering in other ways with the reduction process, and these systems have proved very difficult to understand even in general terms. Quantum yield and other data for a number of acidopentammine and certain other complexes are given in Table IV the data on the aquation reactions of some of the complexes are considered in Section I1I-D. 

The aquation reactions of the other complexes do not proceed to completion, even in the absence of added X . Under these conditions two alternative methods may be used to evaluate k. In the first method k is obtained from a study of the initial rate of aquation in the time viterval when the anation reaction may be neglected. In the second method the aquation is studied in alkaline solution where the formation of CoCCN OH-3 tends to drive the reaction to completion. 

Figure 8.12 Schematic representation of trace metal interactions in a system containing an inorganic surface, micro-organisms and micro-organism exopolymers (adapted from Lion eta/., 1988). In a natural aquatic system other complexing substances will be present, namely fulvic-type compounds, which will interact with the metals, the solid surface and the biopolymers (Buffi eetal., 1998).

Comparison of data in Tables II and III for the cobalt triad indicates that aquation proceeds, on average, about the same for Rh(III) as for Co(III) and substantially slower for iridium(III). As has been observed earlier, however, lability of CF3SO3" complexes is actually enhanced relative to other complexes (such as Cl" complexes) for iridium(III), and for second- and third-row metal ions generally. The property of CF3SO3" as a good leaving group is essentially constant, but the rate of displacement is clearly mediated by the metal ion aquation of the iridium(III) complex is over 100 times slower than for cobalt(III) whereas loss from the exceptionally inert platinum(IV) is slower still (84). 

Equation (3.6) has the same form as equation (3.5) with A = 1.0 and B = log k., (which relates to the back anation reaction). The aquation of Cr(III) and other complexes has been treated similarly. 

Other Complexes. Following an earlier study which showed that chloride and bromide ions (X ) catalyse the aquation of the [Co(NH3)5(ONO)] + ion, a similar behaviour has now been established for the analogous [Cr(NH3)6(ONO)] + ion ... 

Markham, K. R., R. Mues, and H. D. Zinsmeister Luteolin 7-glucuronide-3 -mono(frfl 5)ferulylglucoside and Other Unusual Flavonoids in the Aquatic Liverwort Complex, Riccia fluitans. Phytochem. 17, 1601 (1978). 

Other complexes for whose aquation in mixed aqueous solvents kinetic parameters have been obtained include [Co(RNH2)6Cl] + in aqueous dioxan, and of c -[Co(NH2CH2CH20H)(en)2Cl] + (ref. 19) and several dioximato-complexes [Co(LLH)2(S03H)Cl] (refs. 35—37) in several aqueous organic mixed solvents. Activation parameters are collected together in Table 5. As an extension of the dioximato-complex aquation work, one might add that the kinetics of thermal decomposition of some of these complexes have been studied in the solid state. ... 

Whereas considerations of transition enthalpies and of activation volumes have led to evidence useful in confirming the mechanism of aquation in cobalt(m)-ammin6-ligand complexes, an attempt to derive similarly useful information from a comparison of kinetic and solubility parameters proved unsuccessful. No correlation was found between enthalpies of activation for aquation of complexes [Co(NH3)5X] +, with X = F, Cl, Br, I, NCS, N3, or NO2, and the respective enthalpies of solution of their perchlorate salts. In fact it seems impossible to correlate these activation enthalpies with any other apparently reasonable parameter, though it does seem that there is a correlation between activation entropies and the entropies of solvation of the leaving anions. ... 

Other materials based on EDA have also been suggested as fungicides. The most important of the imida2oline type (162) is 2-heptadecyl-2-imida2oline (163), prepared from EDA and stearic acid [57-11-4]. It is used as the acetate salt for control of apple scab and cherry leaf spot. A 2 1 EDA—copper sulfate complex has been suggested for control of aquatic fungi (164). 

The pentammine aqua ion [Ru(NH3)j(H20)]2+, best made by zinc amalgam reduction and aquation of [Ru(NH3)5C1]2+, undergoes extensively studied substitution reactions first order in both the ruthenium complex and the incoming ligand (e.g. NH3, py) and is a convenient source of other... 

Contemporary forest declines were initiated about 1950-1960, virtually simultaneously throughout the industrial world at the same time as damage to aquatic systems and structures became apparent. A broad array of natural and anthropogenic stresses have been identified as components of a complex web of primary causal factors that vary in time and space, interact among each other, affect various plant growth and development systems and may result in the death of trees in mountainous ecosystems. As these ecosystems decline, the alterations in forest ecology, independent of the initial causal complex, become themselves additional stress factor complexes leading to further alterations. 

Al(III) is an example of an aquatic ion that forms a series of hydrated and protonated species. These include AlOrf Al(OH)J, Al(OH)3, and other forms in addition to AP. (For simplicity, we omit the H2O molecules that complete the structures of these complexes.) Most of these species are amphoteric (able to act as an acid or a base). Thus the speciation of Al(III) and many other aquatic ions is sensitive to pH. In this case, an aggregate variable springs from the conservation of mass condition. In the case of dissolved aluminum, the total dissolved aluminum is given by... 

Transport in solution or aqueous suspension is the major mechanism for metal movement from the land to the oceans and ultimately to burial in ocean sediments. In solution, the hydrated metal ion and inorganic and organic complexes can all account for major portions of the total metal load. Relatively pure metal ores exist in many places, and metals from these ores may enter an aquatic system as a result of weathering. For most metals a more common sequence is for a small amount of the ore to dissolve, for the metal ions to adsorb onto other particulate matter suspended in flowing water, and for the metal to be carried as part of the particulate load of a stream in this fashion. The very insoluble oxides of Fe, Si, and A1 (including clays), and particulate organic matter, are the most important solid adsorbents on which metals are "carried."... 

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