Zirconium compounds complexing

Table V-32 Values for the enthalpy of formation of Zr(HP04)2 H20(cr) at 298.15 K. The data have been corrected in this review using the selected enthalpies for zirconium compounds/complexes and auxiliary data (Chapter IV). The uncertainties have been calculated as 95% confidence limits.

Zirconium [7440-67-7] is classified ia subgroup IVB of the periodic table with its sister metallic elements titanium and hafnium. Zirconium forms a very stable oxide. The principal valence state of zirconium is +4, its only stable valence in aqueous solutions. The naturally occurring isotopes are given in Table 1. Zirconium compounds commonly exhibit coordinations of 6, 7, and 8. The aqueous chemistry of zirconium is characterized by the high degree of hydrolysis, the formation of polymeric species, and the multitude of complex ions that can be formed. 

Hydroxyl Compounds. The aqueous chemistry of zirconium is complex, and in the past its understanding was compHcated by differing interpretations. In a study of zirconium oxide chloride and zirconium oxide bromide, the polymeric cation [Zr4(OH)g (H20)jg was identified (189) the earlier postulated moiety [Zr=0] was discarded. In the tetramer, the zirconium atoms are coimected by double hydroxyl bridges (shown without the coordinating water molecules) ... 

Various zirconium compounds are used as delayed crosslinkers, (see Table 17-12). The initially formed complexes with low-molecular-weight compounds are exchanged with intermolecular polysaccharide complexes, which cause delayed crosslinking. 

A particulate gel breaker for acid fracturing for gels crosslinked with titanium or zirconium compounds is composed of complexing materials such as fluoride, phosphate, sulfate anions, and multicarboxylated compounds. The particles are coated with a water-insoluble resin coating, which reduces the rate of release of the breaker materials of the particles so that the viscosity of the gel is reduced at a retarded rate [205]. 

Many of the most important achievements in organic chemistry in the last 20—25 years have been associated in some way with the use of transition metal complexes. Among these complexes, an increasingly important place is occupied by zirconium compounds, which have a number of unique properties enabling them to be used as highly reactive reagents in organic synthesis [1—9]. 

Dicarbonyl coupling (8,483). This Ti-catalyzed coupling offers a useful route to cyclic sesquiterpenes such as humulene (4). The precursor is obtained by coupling a vinylic zirconium compound (1) with the u-allylpalladium complex (2) to give, after deprotection, the keto aldehyde 3 in 84% yield. This product couples to humulene as a single isomer in 60% yield. 

Cycloreversion of four-membered metallacycles is the most common method for the preparation of high-valent titanium [26,27,31,407,599-606] and zirconium [599,601] carbene complexes. These are usually very reactive, nucleophilic carbene complexes, with a strong tendency to undergo C-H insertion reactions or [2 -F 2] cycloadditions to alkenes or carbonyl compounds (see Section 3.2.3). Figure 3.31 shows examples of the generation of titanium and zirconium carbene complexes by [2 + 2] cycloreversion. 

The electronic spectra of niobium(IV) and -(V) and zirconium(IV) complexes 126,127) have been reported but not interpreted. The spectrum of Nb(ethyl-dtp)4 is of particular interest since the compound is probably 8-co-ordinate. Discussion of the spectrum of binuclear molybdenum complexes 130,131) employed the molecular orbital model of Blake, Cotton and Wood for MO2O3LX complexes s). 

Only a small number of zirconium(III) and hafnium(III) complexes are known. Nearly all of these are metal trihalide adducts with simple Lewis bases, and few are well characterized. Just one zirconium(III) complex has been characterized structurally by X-ray diffraction, the chlorine-bridged dimer [ ZrCl PBu,) ]- Although a number of reduced halides and organometallic compounds are known in which zirconium or hafnium exhibits an oxidation state less than III, coordination compounds of these metals in the II, I or 0 oxidation states are unknown, except for a few rather poorly characterized Zr° and Hf° compounds, viz. [M(bipy)3], [M(phen)3] and M Zr(CN)5 (M = Zr or Hf M = K or Rb). 

CF2)2C2(AsMe2)2 (tfars), in acetonitrile (sealed tube, eight days at 100 °C, six months at room temperature) yields [ZrCl3(tfars)] -MeCN as a brown solid. A weak IR band at 2255 cm-1 indicates that the acetonitrile is not coordinated to the metal. This compound is a nonelectrolyte in acetonitrile and exhibits a magnetic moment at room temperature of 1.73 BM. It appears to be the first magnetically dilute zirconium(III) complex to have been reported.20... 

Fig. 14. Structures of a ethylene-bridged zirconium compound (above) and of a metal-stabilized cationic 1,3-propanediyl-bridged iron complex (below) including an ORTEP representation of the latter (223).

Evidence for this is rather sparse, but recent XPS work on the interaction of zirconium compounds with polymer particles [5] and corona discharge-treated polypropylene [6] supports the view that zirconium will react with the surface carboxyl functionality. Interestingly, titanium complexes are believed [6] to prefer to bond to surface hydroxyl groups. 

Rochon, A.M., Nowak, Z., Zagorski, Z.P. 1976. On compounds complexing zirconium in irradiated (TBP-dodecane) 0.5 M HN03 systems. Radiochem. Radioanal. Lett. 27(1) 1-8. 

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