Zirconium tetrahalides

A few zirconium tetrahalide adducts with urea and its derivatives have been reported. Known compounds include [ZrF4 (Me2N)2CO ],130 [ZrCI4 (H2N)2CO 2]131 and... 

Zirconium monochloride and zirconium monobromide [31483-18-8] are prepared in better purity by equilibration of mixed lower halides with zirconium foil at 625°C (184—185) or by slowly heating zirconium tetrahalide with zirconium turnings at 400—800°C over a period of two weeks and hoi ding at 800—850°C for a few additional days (186). Similar attempts to produce zirconium monoiodide [14728-76-8] were unsuccessfiil it was, however, obtained from the reaction of hydrogen iodide with metallic zirconium above 2000 K (187). 

Turnbull (1 ) measured the enthalpies of reaction for the dissolution of the zirconium tetrahalides in caustic and in... 

This way, the tracer would locally take the place of the modifier through a sort of exchange reaction. The energetic effects of such reactions can be estimated from the regularities in energies of the appropriate chemical bonds. The required thermochemical data for zirconium tetrahalides can be found in Ref. [100], for other halides in Refs. [101,102], The following relations between the bond energies can be noted ... 

The free energies of formation of corresponding hafnium and zirconium compounds are also nearly equal, so that separation by preferential reaction of one species is difficult, too. Table 7.9 compares the free energies of formation of hafnium and zirconium tetrahalides at 1000 K. 

The zirconium tetrahalides react with esters to form ZrX4 2 ester adducts (302, 303, 330, 407-410, 412) in which, coordination number six is attained. On the basis of dipole moments (Table XIII), it is concluded that the adducts have the cis structure. This has been supported, at least in the case of ZrCl4 2011300 0 02115, by the infrared spectrum (330). Oryoscopic studies in benzene solution of the 2 1 adducts of zirconium tetrachloride and ethyl formate, ethyl acetate, and ethyl butryrate show that these complexes tend to decompose to the 1 1 species, the extent of dissociation increasing with the number of carbon atoms in the acid radical. The estimated dissociation constant is about 5 x 10", whereas for the ethyl acetate adduct of zirconium tetrabromide it is only 2 X 10". The approximate dissociation constant of the complex zirconium tetraiodide 2 ethyl acetate is 3.5 x 10". The 1 1 species were synthesized by direct reaction in benzene with strictly stoichiometric ratios of the reactants. Oryoscopic determination of molecular weights of the 1 1 complexes indicate that these complexes generally... 

Reaction with hydrogen occurs at temperatures of 300 to 1,000°C forming a brittle dihydride, ZrH2. Zirconium combines with halogens at high temperatures forming tetrahalides. Reactions occur in the range 200 to 400°C. Sohd tetrahalides sublime above 300°C. 

Zirconium(IV) and hafnium(IV) chlorides and bromides form 1 2 adducts of the type [ZrX4(RCN)2] (R = Me, Et, Pr or Ph X = Cl or Br) and [HfX4(MeCN)2] (X = Cl or Br).11SM24 These complexes may be prepared by (i) direct reaction of the metal tetrahalide with an excess of the nitrile120 123 or (ii) electrochemical oxidation of zirconium or hafnium metal in the presence of a solution of chlorine or bromine in acetonitrile.118 The adducts are moisture-sensitive, white solids, insoluble in nonpolar solvents, but soluble in acetonitrile. In the later solvent, [ZrBr4(MeCN)2 behaves as a nonelectrolyte.122... 

Zirconium and hafnium tetrahalides form six-, seven- and eight-coordinate adducts with polydentate phosphine and arsine ligands. The 1 1 adducts [MXt(dppe)] and [MX dpae)] (M = Zr, X = C1 or Br M = Hf, X = C1 dppe = Ph2PCH2CH2PPh2, dpae = Ph2AsCH2CH2AsPh2) have been prepared in benzene media. IR spectra of the [MCLt(dppe)] complexes exhibit four v(M—Cl) modes in the 353-278 cm-1 region, consistent with a six-coordinate octahedral structure.45... 

In the gas phase, the tetrahalides exist as monomeric regular tetrahedral molecules. This has been established by electron diffraction and vibrational spectroscopy. Bond lengths and vibrational frequencies are listed in Table 16. Force constants for M—X bond stretching are slightly larger for the hafnium tetrahalides than for the zirconium analogues the force constants decrease appreciably as X varies in the order Cl > Br > I.506... 

The anhydrous zirconium (IV) halidesf are freshly sublimed in vacuo at 250-300°C. 2,4-pentanedione (Matheson Coleman and Bell b.p. 136-140°C.) is freshly distilled through a small fractionating column before use. The anhydrous tetrahalides and the products are readily hydrolyzed and must be handled in a dry-box or in a plastic bag filled with dry nitrogen. J All glassware is dried at 180°C. and is cooled, whenever possible,... 

Zirconium and hafnium tetrahalides react with hydrogen peroxide in alkali solution to yield M(0H)300H. The maximum content of peroxo units per metal atom has been observed in K4Zr(02)4 6H2O, which is a derivative of the unknown orthoperzirconic acid Zr(OOH)4. 

Zirconium and hafnium tetrahalides form a variety of double halides with metal halides. The most widespread composition is Q2MX6 (Q = monovalent cation) but the QMX5 complexes and fluoride complexes Q3MF7 and Q4MF8 are also documented. Q2MX6 chlorides and bromides consist of [MXe] octahedra. The complex chloride anions [MCls]" and [MCle]" have been detected in molten MCI4 (equation 15) ... 

The tetrahalides of titanium and zirconium generally afford six-coordinate adducts with bipyridyl and phenanthroline (157, 158, 266),... 

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