Acido ligands

LMCTegrc0 tj(x is placed at a higher energy than the lowest lying acido ligand to Co (III) excited states and photoredox reactions are, respectively, initiated in each of these excited states, a nonradiative conversion of one into the other electronic state must be sluggish or not available. The experimental observations clearly demonstrate that the photophysics of LMCT states in complexes Com(NH2R)sX2 + with R = alky is different from that with R = H and exemplifies how the properties of the excited state have control over the photochemical properties. 

The ammonia and amine complexes are the most numerous chromium derivatives and the most extensively studied. They include the pure ammine [CrAm6]3+, the mixed ammine-aqua types, that is, [CrAm4 (H20) ]3+ (n = 0-4, 6), the mixed ammine-acido types, that is, [CrAm6 X ](3" )+ (n = 1-4, 6), and mixed ammine-aqua-acido types, for example, [CrAm6 m(H20) Xm](3 m7+ (here Am represents the monodentate ligand NH3 or half of a polydentate amine such as ethylenediamine, and X an acido ligand such as halide, nitrite, or sulfate ion). These complexes provide examples of virtually all kinds of isomerism possible in octahedral complexes. 

TABLE 3 Reaction yields of amine and acido ligand aquation in aqueous solutions of Cr(III) complexes at ambient temperatures... 

The formation constant, /3, for Ga -bipy complex is almost independent of [H ], but for the analogous phen species, /3i, and 2 increase at lower [H ], probably owing to the formation of mixed hydroxoamine complexes." Mixed complexes of Ga" with bipy or phen have been detected for a variety of acido-ligands (anions of oxalic, tartaric, or malonic acids etc.). ... 

The syntheses of the diacido complexes where both of the acido ligands are the same were accomplished by the reaction of the dichloro complex with an excess of NaX at an elevated temperature. The salts were often isolated as the perchlorates by the addition of HCIO4 to the cold reaction mixture and overall yields of about 70% were obtained. The method of preparation of rran5-[Ir(en)2Br2]C104 described here was the procedure generally used for the syntheses of salts of other cis and trans-diacido complexes. 

Titanocene Dihalides and Pseudohalides. When both acido ligands X in the titanocene system (CsH5)2TiX2 were represented either by the halide ligands F, Cl, Br, or by pseudohalide ligands, e.g. NCS or pronounced antitumor activity was found... 

A further extension of the modification of the titanocene system is the total replacement of one cyclopentadienyl ring in (C5H5)2TiX2 by an additional acido ligand Y which may be identical with the other two addo ligands X or different from them With XXXVIII-XL, weak antiproliferative activity was retained. 

Numerous titanocene derivatives ( 5115)271X2 were tested which had been modified at the position of the acido ligands X. Investigating the antitumor activity of titanocene dihalides and bis(pseudohalides) VII-XI revealed compounds which were equally potent as I, the optimum cure rate amounting to 100%. In the case of VIII with X = Br, the therapeutic range was enlarged leading to an increase of the therapeutic index (T.I.) to 4.5 (Fig. 9), compared with 3.3 after application of I. 

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