Iron complexes linear polynuclear

The formation of circular or linear forms seems to depend on balances between kinetic and thermodynamic control iron(II)-poly-2,2 -diimine systems with their substitutionally inert metal centers provide useful systems for disentangling thermodynamic and kinetic contributions. The mechanism of formation of circular helicates is believed to entail a kinetically favored triple helicate intermediate. Self-assembly of chiral dinuclear binaphthol-linked iron(III) porphyrin complexes into extended polynuclear species takes place through the intermediacy of fi-oxo dimers. Predetermined //-oxo-di-iron-dimers may be used in this type of synthesis. 

Metal ions in aqueous solution generally hydrolyze to form a series of mononuclear ind polynuclear hydroxy complexes. Iron(III) for example forms [FeOH] ", [Fe(OH)2], Fe(OH)3(aq), [Fe(OH)4] , [Fe2(OH)2] and probably other polynuclear species. The formation af a monohydroxy complex (equation 1) can be used as a guide to the degree of electron withdrawal by the cation. Typical pJCa values for various cations are listed in Table 2. (The pJCa values of and HjO are -1.7 and 15.7 respectively.) The tetrahedrally coordinated [Be(H20)4] ion is more acidic than expected when compared with octahedrally coordinated aqua ions of divalent metals. Each hydrogen must carry a somewhat greater portion of the positive charge than it would in an octahedral complex, and this makes removal of a proton easier. Similar considerations apply to square planar Pd (aq). Mercury(II) and tin(II) are also more acidic than would be expected. The high acidity of mercury(II) is due to the unusual stability of linear H2O—Hg—OH, while Sn (aq) has between two and three coordinated water molecules in the inner coordination sphere. ... 

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