Cobalt, hexaammine

DR. DAVID McMILLIN (Purdue University) In view of all of this, would you comment on the differences between the selfexchange rate constants for the cobalt hexaammine, trisethyl-... 

Gessner RV, Quigley GJ, Wang AH-J, van der Marel GA, van Boom JH, Rich A (1985) Structural basis for stabilization of Z-DNA by cobalt hexaammine and magnesium cations. Biochemistry 24 237 - 240... 

This chapter has been concerned with the effect of structural properties of cobalt(III) hexaamines on their other properties. Included in this review have been complexes ranging from cobalt hexaammine, to complexes composed of three secondary and three tertiary amine donors... 

Linkage isomerization reactions, 465 Linked redox centres, 493 Liquid-liquid extraction, 538-549 Lowry, Thomas Martin, 16 Luteocobalt—see Cobalt, hexaammine-Luteocobaltic chloride —see Cobalt, hexaammine-, chloride... 

Metal-complex adsorption can directly lead to surface reaction, as has been observed recently for cobalt ammine complexes adsorbing over carbon substrates [41, 42]. The uptake of cobalt hexaammine (CoHA), [(NH3)6Co]+3... 

Figure 3.8 Cobalt hexaammine adsorption cobait species on siiica, and (d) 200°C over silica and carbon with simiiar PZCs (4) caicined 5.15 wt% Co particies on carbon, (a) uptake versus pH, and (b) pH shifts, (From [41] with permission from Eisevier.) STEM images of (c) 450°C caicined 1.8 wt%...

In the preparation of a)balt(III) hexaammine salts by ihe aerial oxidation of cobalt(II) in aqueous ammonia it is possible, in the absence... 

LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

A series of 12 complexes of Co(III) with both ionic and covalent azide groups was prepared and most were easily detonable as dry salts, especially at elevated temperatures [1]. Polarography is an accurate and safe method of analysis for azides [2], Hexaammine-cobalt, -chromium and -rhodium hexaazidocobaltates are explosive, particularly in the dry state [3],... 

DR. SUTIN Various values for the cobalt-nitrogen distances in the hexaammines have been reported. Part of this variation is almost certainly due to lattice (counter-ion) effects. Recent literature values for the Co-N distances in... 

In their first publication on this subject,59 Werner and Miolati showed that the molecular conductances (fx) of coordination compounds decreased as successive molecules of ammonia were replaced by acid residues (negative groups or anions). For cobalt(III) salts, they found that fi for luteo salts (hexaammines) > fi for purpureo salts (acidopentaammines) > /t for praseo salts (di-acidotetraammines). The conductance fell almost to zero for the triacidotriammine Co(N02)3-(NH3)3 and then rose again for tetracidodiammines, in which the complex behaved as an anion. By such measurements, Werner and Miolati determined the number of ions in complexes of cobalt(III), platinum(II) and platinum(IV). They not only found support for the coordination theory, but they also elucidated the process of dissociation of salts in aqueous solution and followed the progress of aquations. 

The proposed mechanism for dye formation is shown in Scheme 2. The initial step is the reaction of phthalaldehyde and ammonia to form the intermediate (102), which can either dehydrate and polymerize to form the oligomeric dye mixture (103 n = 2—6) or reduce cobalt(IH) hexaammine, thereby releasing more ammonia and amplifying the response.206 208... 

Cobalt(III) hexaammine trifluoroacetate is coated together with iodoform (photolytic acid generator) and 4-phenylcatechol (reductant). An imagewise exposure is made, and the exposed film is then placed face-to-face with a base-activatable diazo recording layer. Upon heating, ammonia is liberated in the unexposed areas and a positive image is formed in the diazo layer. 

A multicomponent positive-imaging process using ammonia release has been described by Ricoh.211 The components of the system are (1) a cobalt(III) hexaammine complex, (2) a quinone photoreductant, (3) a chelating agent such as dimethylglyoxime, (4) a leuco dye (triarylmethane type), (5) a photooxidant (biimidazole) and (6) an organic acid (toluenesulfonic acid). 

Cobalt(III) hexaammine is quite inert to hydrolysis. In strongly basic media ([OH ] = 0.1 to 2.1 M) the reaction rate increases and [OH ] apparently reaches a limiting value around 1 M, where the reaction becomes independent of [OH ], 3 x 10 s at 61.8°, (i = 2.0 (157). The mechanism of the reaction involves the SnI(CB) pathway. The limiting rate observed at high pH is thought to refiect a pre-equilibrium ion pair formation between the complex ion and OH , rather than the first-order reaction of the fuly deprotonated complex ion. The rate of... 

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