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The binary zirconium and hafnium polyazides [PPh4]2[M(N3)6] (M=Zr, Hf) were obtained in near quantitative yields from the corresponding metal fluorides MF4 by fluoride–azide exchange reactions with Me3SiN3 in the presence of two equivalents of [PPh4][N3]. The novel polyazido compounds were characterized by their vibrational spectra and their X-ray crystal structures. Both anion structures provide experimental evidence for near-linear M-N-N coordination of metal azides. The species [M(N3)4], [M(N3)5]− and [M(N3)6]2− (M=Ti, Zr, Hf) were studied by quantum chemical calculations at the electronic structure density functional theory and MP2 levels.

The structure of triclinic disodium hafnium disilicate, Na2HfSi2O7, has been determined by laboratory powder X-ray diffraction and refined by the Rietveld refinement. The structure is a framework made of alternate layers of HfO6 octa­hedra and SiO4 tetra­hedra linked by common O atoms. Sodium atoms are located in the voids of the framework, aligned into tunnels along the [010] direction. Na2HfSi2O7 is isostructural with the parakeldyshite Na2ZrSi2O7 phase.

A highly efficient one-pot method for the synthesis of a variety of α-aminophosphonates via the one-pot three-component reaction of aldehyde, amine, and phosphite has been developed using only 2 mol % HfCl 4 as the catalyst. The NMR evidence strongly indicated the catalytic roles of Hf(IV) on the activation of aldehyde, phosphite, and imine intermediate.

The fabrication of polynary fluoride nanocrystals (NCs) at ambient temperature is a well-known challenge, since heating is generally required to produce crystallized nanomaterials. Herein we report a convenient solution-phase strategy, namely, a complex chemical route, for producing pure and doped heptafluo-zirconate/hafnate NCs under ambient conditions. The production of nanocrystals is highly dependent on the chelating agent, the feed ratio of oleic acid to Zr4+, and the feed ratio of F− to Zr4+. The functionalization of these NCs by means of doping strategy was also achieved at ambient temperature. Down-shifting and up-converting fluorescence was realized in these zirconium/hafnium-based matrices. The proposed method for preparing Zr4+/Hf4+-containing fluorides is simple, efficient, cheap and easy to mass produce, which might open up a new way for the synthesis of polynary fluorides.

This microreview summarizes examples of Hf(OTf)4-mediated or -catalyzed organic reactions. Hafnium triflate possesses four strongly electron-withdrawing OTf groups, together with an ionic radius of intermediate range (Al < Ti < Hf, Zr < Sc < Ln), and has an oxophilic hard character typical of group IV metals. This Lewis acid shows outstanding performance in catalytic Friedel–Crafts acylation reactions and Mannich-type reactions of imines, hydrazones, and N,O-acetals. Several natural products have also been synthesized by use of Hf(OTf)4-mediated or -catalyzed reactions. Moreover, Hf(OTf)4 has a number of potent features in carbohydrate syntheses. Hf(OTf)4 possesses many unique characteristics that distinguish it from other Lewis acids. The unique characteristics of Hf(OTf)4 should make this compound a major candidate for selection as a Lewis acid in the future.

The first protocol for the direct synthesis of macrodiolides from equimolar mixtures of diols and dicarboxylic acids catalyzed by Hf(OTf)4 is developed giving products in 58-96% yield.

Crystalline precipitates resulting from the hydrolysis and subsequent condensation of HfIV aqueous acidic solutions are characterized by single crystal XRD and Raman spectroscopy.

Amorphous SiHfBCN ceramics are prepared from a commercial polysilazane (HTT 1800), which is modified by reactions with Hf(NEt2)4 and BH3·SMe2 (toluene, -50 °C for 2 h and 25 °C for 24 h), and subsequently cross-linked (200 °C, 3 h) and pyrolyzed (1100 °C).

A simple, efficient, and environmentally benign method for the N-formylation of primary and secondary amines under mild reaction conditions is presented.

The alkali hafnium fluorides Li2HfF6 (I), Na5Hf2F13 (II), K2Hf3OF12 (III), K3HfOF5 (IV), and (NH4)3HfOF5 (V) are hydrothermally prepared from aqueous solutions of HfF4, LiF, NaF, KF, KHF2, RbF, or CsF (sealed Ag ampule, autoclave, 400—600 °C, several days).

This chapter reviews the literature reported during 2010 on titanium, zirconium and hafnium.

The process tolerates some sensitive functional groups and is applied to the reaction of substituted chromene hemiacetals with indoles, furans and sterically hindered anilines.

Hafnium (IV) bis(perfluorooctanesulfonyl)imide complex is found to be an efficient catalyst for the multicomponent condensation of β-naphthol, aromatic aldehydes and urea or amides in perfluorodecalin to afford the corresponding substituted amidomethyl naphthols in good yields. The remarkable features of this new procedure are high yields, shorter reaction times, reusability of catalyst and simple work-up procedures.

The hafnium compound HFC effectively promotes the intramolecular hydroamination of unactivated alkenes yielding pyrrolidine and piperidine derivatives.

The hafnium catalytic system bearing a chiral bishydroxamic acid ligand in general exhibits better results in terms of reactivity and enantioselectivity than the analogous zirconium catalyst.

The electrochemical reduction of hafnium tetrachloride has been studied in molten equimolar NaCl-hCl from 700 to 900 o C. Using voltammetry on a tungsten electrode, only the +IV and 0 oxidation states of Hf have been shown to exist in the electrolyte. Convolution analysis has permitted calculation of the diffusion coefficients, and shown that the exchange was quasi-reversible at 700 and 800 o C, but reversible at 900 o C. Fluoride additions led to a more stable fluoro-complex HfF 6 2- , which was reduced in a single step to metallic hafnium. The exchange was shown to be reversible, and the diffusion coefficients were determined, in the 700 to 900 o C temperature range

Spherical colloidal particles of amorphous hafnium hydroxysulphate of narrow size distribution have been prepared by ageing at room temperature acidic solutions of hafnium oxychloride in the presence of metal sulphates. On calcination the powders crystallized into monoclinic hafnia, yet retained their spherical shape. The effects of several parameters (concentration of reagents, nature of the acid and the sulphate salt) on the characteristics of the precipitated particles were studied in detail. A mechanism for the formation of such particles is suggested.

The synthesis of the new ternary hafnium tellurides Hf[sub 8]Te[sub 6]M (M = Mn, Fe) is reported. The single-crystal structure of the Mn-containing compound has been determined. Hf[sub 8]Te[sub 6]Mn crystallizes in the orthorhombic space group Pmmn (No. 59) with lattice parameters a = 25.816 [angstrom], b = 3.7614 [angstrom], c = 7.605 [angstrom] (Z = 2); the lattice parameters for the Fe analog show a slight shortening of the b axis: a = 25.815 [angstrom], b = 3.7309 [angstrom], c = 7.598 [angstrom]. The Hf[sub 8]Te[sub 6]M structure possesses tricapped trigonal-prismatic Hf clusters centered by M. The trigonal prism dimensions are such that Hf-Hf contacts between triangular faces are long (3.761 [angstrom]) and the triangular faces themselves are isosceles (d(Hf-Hf): 2 [times] 3.160 [angstrom], 3.565 [angstrom]). The Te atoms are 4-, 5-, and 6-coordinate with respect to Hf and serve to sheath the metal framework to produce large Te-lined cavities within the structure. Resistivity measurements between 77 and 250 K show Hf[sub 8]Te[sub 6]Mn to be metallic as predicted by band-structure calculations. The same calculations also indicate that Hf-M bonding is of overriding importance in stabilizing these metal-metal bonded structures. There is no significant Te-Te bonding. 44 refs., 8more » figs., 5 tabs.« less

Many Hf-HfCl{sub 4}-Z systems have been explored to establish the stability and structures of Hf{sub 6}(Z)Cl{sub 12}Cl{sub n} cluster phases relative to the large variety known for zirconium. The slowness of Hf-HfCl{sub 4} reactions and the limited number of new phases required special care in synthesis to avoid excessive HfCl{sub 4} pressures. Only B and C interstitials (Z) gave cluster phases, namely (1) AHf{sub 6}Cl{sub 14}Z with A = Li, Na, K, or nothing and Z = B or C, in stuffed versions of the orthorhombic Nb{sub 6}Cl{sub 14} structure; (2) orthorhombic AHf{sub 6}Cl{sub 15}C with A = K or Cs separately occupying one of the two different cation lattice sites in the CsKZr{sub 6}Cl{sub 15}B structure type; (3) cubic Na{sub {approximately}0.8}Hf{sub 6-}Cl{sub 15}B (stuffed Ta{sub 6}Cl{sub 15}) plus Na{sub 0.8}Hf{sub 6}Cl{sub 15}B in a tetragonal subgroup when prepared with more sodium. The Na{sub 1.0}Zr{sub 6}Cl{sub 15}B analogue of the last was also prepared and structurally refined [Na{sub 0.8(2)}Hf{sub 6}Cl{sub 15}B, Ia{bar 3}d, Z = 16, a = 21.428(2){angstrom}, R/R{sub w} = 5.3/4.3%; Na{sub 0.76(6)}Hf{sub 6}Cl{sub 15}B, Na{sub 1.04(5)}Zr{sub 6}Cl{sub 15}B, I4{sub 1}/acd, Z = 16, a = 21.540(2), 21.622(2) {angstrom}, c = 21.387(3), 21.793(3) {angstrom}, R/R{sub w} = 5.5/5.4%,more » respectively]. The tetragonal distortions in the last are in the opposite sense (c/a = 0.9929 for Hf, 1.0079 for Zr). Both distortions from cubic seem to give smaller clusters, slightly longer M-Cl{sup a{minus}a} distances, and an additional secondary chlorine neighbor about one of the split, fractional sodium positions. Volumes of hafnium cluster phases are 1.6-2.9% smaller than those of the analogous zirconium compounds and, in one comparable case, d(M-B) is {approximately}0.03 {angstrom} less for Hf than for Zr.« less

The title compounds have been prepared from the elemental components by arc-melting and subsequent annealing. Single crystals of U₃TiSb₅ and U₃MnSb₅ were obtained from a tin flux and their structures were determined from single-crystal X-ray data: P6₃/mcm, Z = 2; a = 913.9(2), c = 611.2(1) pm, R = 0.011 (233 structure factors, 14 variables) for U₃TiSb₅ and a = 916.8(2), c = 613.2(1) pm, R = 0.015 (427 structure factors, 14 variables) for U₃MnSb₅. The lattice constants of the isotypic compounds are: a = 908.2(2), c = 608.3(2) pm for U₃VSb₅ and a = 911.0(1), c = 611.5(1) pm for U₃CrSb₅. The structure of these antimonides may be regarded as an “anti”-type structure of Hf₅Sn₃Cu with the antimony atoms on the hafnium sites, while the positions of the uranium and transition metal atoms correspond to the positions of the tin and copper atoms. A comparison of the interatomic distances of U₃TiSb₅ with those of U₃Sb₄, USb₂, and a-antimony suggests oxidation numbers according to (U⁺ᴵᴵᴵ)₃Ti⁺ᴵⱽ(Sb1⁻ᴵᴵᴵ)₃(Sb2⁻ᴵᴵ)₂, where the Sb2 atoms form weakly bonded chains

The purity of tantalum, hafnium and scandium metals obtained by electrolysis in molten salts is compared with literature data on the purity of these metals produced by other methods. The advantage of electrorefining in high temperature electrolytes for high purity rare metal production is shown.

Hafnium(IV) trifluoromethanesulfonate (hafnium(IV) triflate, Hf(OTf)4) was synthesized from hafnium tetrachloride and trifluoromethanesulfonic acid. The triflate thus prepared was found to be effec...

The early transition metals, especially Zr, Hf, Hb and Ta, exhibit a metal-rich chemistry that is often surprising in its structural and physical aspects. Unfamiliarity with this chemistry is illustrated by the discovery of several new binary compounds in the Ta-S, Ta-Se, Ta-Te, and Hf-Te systems within the past few years. Some striking differences observed between the metal-rich chalcogenides of Zr and Hf or between Nb and Ta challenge basic presumptions about the similarity of these congeneric pairs. The factors controlling the structural anisotropy of a new class of tetragonal layered compounds that includes Ta 2 Se, Ta 2− x Nb x S, Hf 3 Te 2 , and ZrZTe (Z  Si, Ge, Sn) are discussed. Strongly early-late transition intermetallic bonding leads to the formation of an expanding class of compounds that includes Ta 9 M 2 S 6 (M  Fe, Co, Ni), Ta 11 M 2 Se 8 (M  Fe, Co, Ni), Ta 8 NiSe 8 and the newly discovered hafnium tellurides, Hf 8 MTe 6 (M  Mn, Fe, Co, Ni, Ru) and Hf 5 MTe 3 (M  Fe, Co). Our efforts to dismantle solid-state Zr-halide cluster compounds is described. Ambient temperature molten salts help us achieve the controlled excision of [(Zr 6 Z)CL 18 ] n− from solid state precursors; we describe the applications of electronic and NMR spectroscopies in characterizing clusters in solution. Finally, we discuss bonding in metal-rich systems, with particular emphasis on localized bonding descriptions for metalmetal bonds in extended metal-linked networks. Such localized descriptions increase our understanding of otherwise anomalous properties and illuminate the artificiality of separate “metallic” and “covalent” bonding concepts.

The solid state reactions of tellurium oxide with zirconium and hafnium oxides were investigated employing thermogravimetry (TG), differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. The only compounds reported in these two pseudo-binary systems are ZrTe3O8 and HfTe3O8, respectively. From the results obtained in these studies it is concluded that these compounds can be synthesized in the solid state in the pure form from their binary component oxides by heating the stoichiometric mixtures to temperatures as low as 900 to 950K where the vaporization of the more volatile component TeO2, is insignificant.

Microstructures, hydrogen storage properties and electrode properties of vanadium-based alloys of V 3 TiNi 0.56 M 1 (M = Al, Si, Mn, Fe, Co, Cu, Ge, Zr, Nb, Mo, Pd, Hf and Ta; x = 0.046 and 0.24 were investigated in order to clarify the influences of additives. All additives, except for zirconium and hafnium, did not change the phase structure composed of a vanadium-based solid solution main phase and a TiNi-based secondary phase. A little addition of an element M with x = 0.046 to V 3 TiNi 0.56 did not significantly change the storage capacity, preserving a higher discharge capacity than 290 A h kg 1 . Further addition of Group IVB–VIIB elements (Zr, Hf, Nb, Ta, Mo and Mn) scarcely changed the hydrogen storage properties with x = 0.24, while the addition of Group VIII–IVA elements (Fe, Co, Cu, Al, Ge and Si), except for Pd, brought about a decrease in the hydrogen storage capacity obtained between 3.3 and 0.01 MPa. The alloys V 3 TiNi 0.56 M 0.24 (M = Hf, Nb, Ta and Pd) showed a higher discharge capacity than 330 A h kg 1 .

The four-component condensation of dimedone (I), aldehydes (II), active methylene compounds (III), and ammonium acetate is conducted in the presence of the title catalyst in perfluorodecalin to produce the polyhydroquinoline derivatives (IV) in good to very good yields.

The nonstoichiometric ternary barium hafnium arsenide Ba0.8Hf12As17.7 has been synthesized through reaction of the elements at 950 °C in a tin flux, and its structure has been determined by single-...

A new copper hafnium sulfide Cu2HfS3 has been prepared from solid state reaction at 600–1300°C. The compound of Cu2HfS3 crystallizes in the trigonal system, space group P 3 1c(No. 163) with a=6.4588(4) A and c=12.1943(5)A. The measured density is 6.10 gcm−3, which is consistent with Z=4 for the formula unit. The crystal structure of Cu2HfS3 was determined from four-circle X-ray diffractometer data, and refined to a reliability factor R=5.9% for 541 independent reflections. Hf and Cu atoms are coordinated by six, four and three S atoms to form HfS6 octahedra, CuS4 tetrahedra and CuS3 triangles, respectively. The structural feature of Cu2HfS3 is the alternative packing of layers of HfS6 octahedra and the composite layers of CuS3 and CuS4 tetrahedra along the c direction.

In the continuously expanding panorama of Group 4 metallocene complexes and the extensive research devoted to their use as olefin polymerization catalysts, fluorenyl complexes of zirconium and hafnium play a very special role. This singularity can be explained in terms of a particularly versatile bonding potential of the fluorenyl ligand causing a facile change from η5 → η3 → η1 (ring slippage) and thus providing new coordination sites in catalytic cycles. The substitution of fluorenyl ligands in unbridged or bridged (ansa) metallocene complexes allows the variation of steric requirements and symmetry of these complexes. Both parameters have a strong influence on the catalytic activity and stereospecifity as soon as these catalyst precursors are activated with cocatalysts like methylalumoxane (MAO). Synthetic methods, X-ray structures and catalyst activities are discussed for several compounds together with updated literature.