Trihydroxo-bridged complexes

Bridge cleavage of di- and trihydroxo-bridged complexes in acidic or basic solution provides a convenient method for the synthesis of the corresponding monohydroxo-bridged (32-36, 133, 214-218) and dihydroxo-bridged (50, 76, 100, 132, 174, 185, 186, 188) species, as exemplified by reaction Eqs. (18)-(20). 

In the dinuclear complexes two octahedrally coordinated metal ions are bound together by one, two, or three hydroxide ions by sharing a corner, an edge, or a face, as shown in structures 1-3. These mono-, di-, and trihydroxo-bridged binuclear structures are known for... 

Only a few trihydroxo-bridged chromium(III) complexes have been studied. The cation (metacn)Cr(OH)3Cr(metacn)3+ has J = 128 cm-1 (137, 138), and the corresponding tacd complex has J = 96 cm-1 (98). 

Cobalt(III) complexes made by reaction Eq. (2) have been reported for L3 = (NH3)3, dien, (py)3, tacn, and tach (99,132,174,185,186,188). For L3 = dpt and metacn, trihydroxo-bridged cobalt(III) complexes have been prepared by oxidation (02 or H202) of aqueous cobalt(III) solutions in the presence of the amine (95,97). The dpt complex has also been made by hydrolysis of Co(dpt)23 + in aqueous solution (95). 

Oxidation of cobalt(II) with 02 or H202 may also yield di- or trihydroxo-bridged dinuclear complexes, some of which have already been mentioned in Section IV,A. Other examples may be found in the literature (248- 250). 

Several trihydroxo-bridged rhodium(III) complexes are known, but their hydrolysis reactions have been studied only briefly. The tacn complex undergoes a rapid two-stage reaction in acidic solution to give [Pg.149]

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