Complexes with hafnium compounds

Formation of zirconium and hafnium complexes with polyhydroxyaromatic compounds in aqueous solution has been studied by potentiometric, spectrophotometric and ion exchange methods. Much of this work has been reviewed by Larsen. A potentiometric and lightscattering study of the zirconium(IV)-Tiron (Tiron = disodium l,2-dihydroxybenzene-3,5-disulfonate) system provides evidence for mixed hydroxo-Tiron chelates at Tiron/Zr " ratios less than 2.5, but at higher Tiron/Zr ratios the unhydrolyzed complexes [Zr2L5] and [ZrL4] (L = tetranegative anion of l,2-dihydroxybenzene-3,5-disulfonic acid) are present. ... 

Hafnium complexes with bis(cyclopentadienyl)s, 4, 731 in carbometallations, overview, 10, 255 in C-C bond formation, 10, 424 in ethylene polymerization, 4, 1139 for isotactic polypropylene, 4, 1126 metal-metal bonds, 4, 755 mixed-valence compounds, 4, 755 with pyridyl amines, for olefin polymerization, 4, 1094 in Ru-Os heterodinuclear compounds, 6, 1046 with silicon, 3, 515... 

The refractory carbides NbC and TaC and the nitride NbN, each with the sodium chloride structure, are also similar to the corresponding zirconium and hafnium compounds. Finally, it may be noted that the same group of complexing agents form complexes with Nb(V) and Ta(V) as with Zr(IV) and Hf(IV) (for example, fluoride, hydrogen peroxide, acetylacetone, and 1,2-dihydroxybenzene). 

Structures of di- and monovalent zirconium and hafnium compounds contain octahedra, chains, or layers of metal atoms with metal-metal bonds. It is this that differentiates these compounds from those of M (MX3 or molecular M2X6L4 complexes) with isolated M-M bonds. A recent reinvestigation of the ZrL structure showed two distinct Zr-Zr distances (3.507 and 3.172 A) the latter is typical for a Zr-Zr bond (see Bond Length). 

Some years ago we observed that Group IV metallocenes, i.e., the elusive monomeric units bis(i7-cyclopentadienyl)zirconium and -hafnium, readily form 1 1 complexes with conjugated dienes in their 5-trans conformation (22). To our knowledge, these complexes (3) are the first and, at the time, only known examples of mononuclear (i-/ranj-i7 -diene)metal complexes, i.e., compounds in which both double bonds of the i-irans conformer of a conjugated diene are coordinated to the same transition metal center 21). Some examples of this class of transition metal complexes are stable, isolable compounds even at room temperature 23). 

Zirconium (hafnium) can be determined with Arsenazo III directly in the extract of the thiocyanate complex with antipyrine in isoamyl alcohol [22]. The fluoride complex of zirconium (ZrFe ) has been extracted with TOA in benzene, then the extract has been shaken with Arsenazo HI solution [58]. Zirconium has also been determined after froth-flotation of the Zr compound with Arsenazo El and Zephiramine [59],... 

Tetrahydroborate complexes with third-row transition metals are much less abundant than for first or second row metals. Only complexes with lanthanum, hafnium, tungsten, rhenium and osmium have been characterised by diffraction techniques. For each metal, only a few compounds are known, making conclusions less reliable regarding the M - B distances. 

The first diarsine complex with a known coordination number of eight was prepared from o-phenylenedimethyldiarsine 110-114) and titanium tetrachloride in THE. Similarly prepared (Zr,Hf )0l4 2(diarsine) compounds are white, insoluble products. They do not melt but rather decompose (290° and 284°C for zirconium and hafnium, respectively). 

---