Titanium complexes oxygen-stabilized

The -titanium (TV) atom is hard, ie, not very polarizable, and can be expected to form its most stable complexes with hard ligands, eg, fluoride, chloride, oxygen, and nitrogen. Soft or relatively polarizable ligands containing second- and third-row elements or multiple bonds should give less stable complexes. The stability depends on the coordination number of titanium, on whether the ligand is mono- or polydentate, and on the mechanism of the reaction used to measure stability. 

This complex, while sensitive to oxygen and moisture, is stable for extended periods either neat or in solution. Its carbonyl stretching band (approx. 1610 cm-) in the IR spectrum in dilute solution clearly indicates a chelate structure, which endows the carbon-titanium bond of this complex with very high stability, as compared with that of simple alkyltrichlorotitaniums [25]. 

This can be achieved by using the cis molybdenum(VI)dioxo ion instead of titanium(IV). In this ion two comers of the octahedron at the molybdenum are already blocked by oxygen atoms and only two catechol units can be bound to the metal. Thus, reaction of ligand 3-H4 with MoC>2(acac)2 in the presence of potassium carbonate leads to a mononuclear macrocydic complex [3Mo0212 in which a loop-type conformation is stabilized at the peptide (Scheme 1.3.3) [23]. (Similar... 

The hydrolysis and polymerization of Al3+ under appropriate pH conditions subsequently give rise to the formation of such species as Al(OH)2+, Al2(OH)24+, Al(OH)3, and charged hydroxo cationic complexes, which can effectively remove pollutants. In this study, titanium metal is chosen as anode material mainly for its cheapness and high stability. Some materials with high oxygen evolution have also been reported. When there are some Cl- in the solution, some reactions will occur on the anode by (10.29)-(10.31). 

Zirconium metal (mp 1855°C 15°C), like titanium, is hard and corrosion resistant, resembling stainless steel in appearance. It is made by the Kroll process (Section 17-A-l). Hafnium metal (mp 2222°C 30°C) is similar. Like titanium, these metals are fairly resistant to acids, and they are best dissolved in HF where the formation of anionic fluoro complexes is important in the stabilization of the solutions. Zirconium will burn in air at high temperatures, reacting more rapidly with nitrogen than with oxygen, to give a mixture of nitride, oxide, and oxide nitride (Zr2ON2). 

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