Subsolidus phase relations in the systems CeO2RE2O3 (RE2O3 = C-type rare earth sesquioxide)

The systems CeO₂RE₂O₃ (RE₂O₃ = C-type rare earth sesquioxide) were studied to: (1) investigate the claims of several workers for the existence of a complete solid solution series between CeO₂ and RE₂O₃ and (2) to characterize the weak C-type X-ray diffraction peaks reported by others from samples in the single-phase fluorite solid solution region. It is shown that a complete solid solution series does not exist, and an explanation for the observations of others reporting such is tendered. It is also shown that the observation of C-type reflections in the supposed single-phase fluorite field can be attributed to the partial reduction of Ce⁴⁺ to Ce³⁺ at the firing temperature, resulting in the movement of the bulk composition into a two-phase field of the CeO₂RE₂O₃Ce₂O₃ phase diagram, rather than the formation of a domain structure due to ordering.     

35Cl NQR in N3P3Cl4Ph2 and N3P3Cl4(NMe2)2

³⁵Cl NQR has been investigated in two cyclotriphosphazene derivatives N₃P₃Cl₄Ph₂ and N₃P₃Cl₄(NMe₂)₂. The observed frequencies are assigned to the various chlorines and the temperature variation of the NQR frequencies studied in the range from 77 K to 300 K. The results are analysed using the Bayer-Kushida-Brown approach. Torsional (librational) frequencies are found to fall in the range 10–25 cm^?1 and are found to be only slightly temperature dependent.     

The crystal structure of Lu3S4: A new population wave structure

The monosulfide of lutetium loses lutetium preferentially upon vaporization in vacuo at 1750°C, and the quenched samples exhibit a new structure which is formed by an ordering of metal vacancies on the rock-salt type lattice.     

Bromine NQR study of structure and molecular torsional motion in N4P4Br8 and N3P3Br6

The bromine NQR spectrum of tetrameric bromocyclophosphazene, N₄P₄Br₈, has been studied in the temperature range from 77 to 300 K. The negative temperature coefficients of the resonance frequencies have been analysed using Bayer-Kushida-Brown equations. Torsional modes in the frequency range 10–15 cm^?1 are shown to characterise the observed motional averaging and are only slightly temperature dependent. The multiplicity and relative intensities of resonances in the trimer, N₃P₃Br₆, have been correlated with the known electron density distribution. The results for the bromo-derivatives are compared with those reported for the corresponding chloro-derivatives.     

Pressure dependence of 35Cl NQR in hexachloro- (N3P3Cl6) and octachloro- (N4P4Cl8) cyclophosphazenes

High pressure studies of ³⁵Cl NQR in the hexachlorocyclophosphazene N₃P₃Cl₆ and in the K- and T-forms of octachlorocyclophospha     

The reported ion Fe3S2(NO)5: A re-investigation

Salts reported to contain the iron-sulphur cluster nitrosyl anion Fe₃S₂(NO)₅⁻ are shown to be identical with those containing the well-known anion Fe₄S₃(NO)₇⁻.     

Fragmentierung des schwefeldiimidsystems in tBu2PN=S=NPtBu2 an dreikernigen osmiumclustern. Synthese,feströrperstruktur und dynamische eigenschaften von Os3(CO)11[PtBu2(NH2)] und HOs3(CO)9PtBu2N(H)S]

The phosphino-substituted sulphur diimide, S(NP^tBu₂)₂, reacts with the trinuclear osmium clusters Os₃(CO)₁₁(NCMe) and H₂Os₃(CO)₁₀ with cleavage of one of the NS bonds to give the cluster compounds Os₃(CO)₁₁[P^tBu₂(NH₂)] (I) and HOs₃(CO)₉[P^tBu₂N(H)S] (II), respectively. In the solid state, I contains a closed Os₃ triangle with the phosphine ligand bonded equatorially to an osmium atom through the phosphorus. In solution intramolecular dynamic processes are observed which are explained by carbonyl migration and pseudoration mechanisms. The osmium cluster II, in the solid state, forms an irregular Os₃ triangle which is bridged by a [P^tBu₂N(H)S] system, and the longest edge of which is bridged by a μ₂-hydride. In contrast to I, molecule II is relatively rigid in solution; only pseudorotations are observed as dynamic phenomena.     

Phases in the Ba3Fe1+xS5 series: The structure of β-Ba9Fe4S15 and its low-temperature α polymorph

The crystal structure of β-Ba₉Fe₄S₁₅ shows that it is a phase in the infinitely adaptive series of compounds Ba₃Fe_1+xS₅, 0 ? x ? 1. The material is synthesized by reacting a slightly sulfur-rich mixture at 900°C in a sealed quartz ampoule. Lattice constants are a = 25.212(3), Å, b = 9.594(1), Å, c = 12.575(1), Å, Pnma, z = 4. Three thousand thirty-three structure amplitudes were refined to R = 0.049. BaS₆ trigonal prisms share triangular faces to form infinite columns; the columns in turn share edges and create nearly hexagonal enclosures. Within these rings are additional Ba and S and tetrahedral interstices are created which can be occupied by Fe. The variation of the Fe occupancy from ring to ring gives rise to phases in which one dimension is an integral multiple of the 8.5-Å repeat observed in one end member of the series, Ba₃FeS₅. The other end member is Ba₃Fe₂S₅. At temperatures below 900°C a polymorphic phase is formed. Its lattice constants are a = b = 9.634(1), Å, c = 34.311(3)Å, $\text{I4}{}_1\text{a}\text{, z = 4}$. One thousand five hundred eighty-three structure amplitudes were refined to R = 0.0483. Trigonal prisms and bisdisphenoids articulate to form a complex three-dimensional structure. Two of the S atoms in the structure have statistical site occupancies.     

The crystal structure of Ca3Cu3(PO4)4

Single crystals of Ca₃Cu₃(PO₄)₄ synthesized hydrothermally at 420°C and 55 kpsi (3.8 kbar) were found to occur in the space group $\text{P2}{}_1\text{a}$ (No. 14) with a = = 17.619(2), b = 4.8995(4), c = 8.917(1)Å, β = 124.08(1)°, and Z = 2. Full-matrix least-squares refinement of the structure using diffractometer data converged to a final anisotropic R = 0.037 (R_w = 0.046). The two calcium atoms are in six- and nine-coordination and the two copper-containing polyhedra (four- and five-coordinated) are similar to those previously found in Cu₃(PO₄)₂.     

The crystal and molecular structure of Rh2(CH3CO2)4[HCON(CH3)]2—effect of ligands on metalmetal bonding

The structure of Rh₂(CH₃CO₂)₄(DMF)₂ {DMF = HCON(CH₃)₂} has been determined by single crystal X-ray methods. The compound crystallizes with eight formula units in a cell of dimensions: a = 29.438(7) Å, b = 7.978(2) Å, c = 20.279(5) Å, β = 113.20(4)°, V = 4377.5 ų, space group C2/c. The structure has been refined by full-matrix least-squares method to a final R = 0.030 for the 4156 observed data. Two Rh(II) atoms are linked by four acetate groups forming a dimeric unit, where the RhRh distance is 2.383(1) Å. The coordination sphere about each Rh atom is completed by a DMF molecule; the average RhO(DMF) distance is 2.296(3) Å.     

Infrared study of some specificities of the dπpπ interaction in organogermanium compounds

The analysis is presented for the frequencies of stretching modes ν(GeH) in the IR spectra of organogermanium compounds R₂XGeH, RX₂GeH, RXYGeH, X₂YGeH and XYGeH₂ (where R is a substituent which does not make a d_πp_π bond with germanium, and X and Y are groups capable of d_πp_π interaction with germanium). It is shown that ν(GeH) in these compounds is dependent on both the I effect of R, X and Y, and the d_πp_π interaction in GeX and GeY bonds. If only one substituent capable of d_πp_π interaction with germanium is present, the value of such an effect is determined by itsσo_Rconstant. However, when germanium is bound to several substituents capable of d_πp_π interaction its magnitude depends on the effective charge at germanium which is determined by the inductive and mesomeric effects of X and Y. The data obtained are compared to the dependences observed in the IR spectra of similar organosilicon compounds.     

Ca7Au3 and Ca5Au4, two structures closely related to the Th7Fe3 and Pu5Rh4 types

Two new intermetallic compounds have been synthetized and structurally studied by single crystal diffractometric data: Ca₇Au₃ (oP80, space groupPbca,a = 20.742(8), b = 18.036(8), c = 6.665(2) A?,Z = 8, R = 0.051) and Ca₅Au₄ (mP18, space groupP2₁/c, a = 8.028(3), b = 8.019(6), c = 7.727(3) A?, β = 109.16(6)°,Z = 2, R = 0.104). Both atomic arrangements, which represent new structural types, are based on Au-centered Ca trigonal prisms and are geometrically related to the Th₇Fe₃ and Pu₅Rh₄ structures.     

Vibrational and luminescence spectra of a new binuclear uranyl complex [(C2H5)4N]2[UO2F(NO3)2]2

The preparation, vibrational and luminescence spectra of the title compound are described. The complex has bidentate nitrate groups and bridging fluoride ions. The spectra are assigned in detail and interpreted as showing couplings between the uranyl antisymmetric stretching modes and between the nitrate modes within the dimer, the coupling energy being 17 cm^? in the former case. There is no clear evidence for electronic coupling involving the uranyl groups.     

Further studies of phosphine adducts of niobium(IV) and tantalum(IV) chlorides: New seven- and eight-coordinate compounds with trimethylphosphine: NbCl4(PMe3)3 and Ta2Cl8(PMe3)4

The reaction of NbCl₄(THF)₂ with an excess of PMe₃ in toluene solution afforded a 70% isolated yield of green NbCl₄(PMe₃)₃. When a slurry of TaCl₅ in toluene containing a slight excess of PMe₃ was reduced with sodium amalgam overnight, a 60% yield of orange to red (depending on crystal size) Ta₂Cl₈(PMe₃)₄ was obtained. Both compounds have been fully characterized by X-ray crystallography. NbCl₄(PMe₃)₃ forms monoclinic crystals (P2₁/c) with unit cell dimensions a = 15.061(3) Å, b = 11.677(4) Å, c = 11.583(4) Å, β = 91.71(3)°, V = 2036(2) ų, and Z = 4. It is isomorphous with its TaCl₄(PMe₃)₃ homolog, and the bond lengths and angles are very similar. Ta₂Cl₈(PMe₃)₄ forms cubic crystals (Im3) with a = 16.377(2), V = 4392(2) ų and Z = 6. It is thus isomorphous with its niobium homolog, and the internal dimensions are quite comparable. The Ta-Ta distance is 2.830(1) Å, consistent with the existence of a single bond.     

Synthesis and molecular structure of [Au3Ru4(μ3-H)(CO)12(PPh3)3]

The title compound can be prepared in good yield by heating either [Ru₄(μ-H)₄(CO)₁₂] or [Au₂Ru₄(μ₃-H)₂(CO)₁₂(PPh₃)₂] with [AuMe(PPh₃)] in toluene. The related compound [Au₃Ru₄(μ₃-H)(μ-dppm)(CO)₁₂(PPh₃)] has also been prepared. Both trigoldtetraruthenium clusters undergo dynamic behaviour in solution, involving intramolecular rearrangement of the metal core, as revealed by variable temperature NMR studies. The crystal structure of [Au₃Ru₄(μ₃-H)(CO)₁₂(PPh₃)₃] has been established by an X-ray diffraction study. The metal atom core comprises a trigonal bipyramidal AuRu₄ unit with two AuRu₂ faces capped by gold atoms.     

Crystal structure of Fe2P2O7

Fe₂P₂O₇ crystallizes in the $\text{C}\text{1}$ space group with lattice parameters a = 6.649(2)Å, b = 8.484(2)Å, c = 4.488(1)Å, α = 90.04°, β = 103.89(3)°, γ = 92.82(3)°, and ?_cal = 3.86 g/cc. It is essentially isostructural with β-Zn₂P₂O₇. As in the Zn compound, the bridging oxygen atom in the P₂O₇ group shows a high anisotropic thermal motion. It appears that the P-O-P bond angle is linear as a result of extensive π bonding with the p orbitals on the bridging oxygen atom. The high thermal motion is vibration of the atom into cavities in the structure.     

The preparation and X-ray structure of (disulphurdinitrido)bis(triphenylphosphine) platinum(II)—tetrachloroform solvate,Pt(S2N2)(PPh3)2·4CHCl3

Reaction of Pt(PPh₃)₃ with S₄N₄H₄ gives cis-Pt(S₂N₂)(PPh₃)₂ (1) in 45% yield. 1 was characterised be IR     

Chemistry in fuming nitric acids—I. NMR spectroscopic study of PF5, HPO2F2 and P4O10 in the solvent system 44 wt.% N2O4 in 100% HNO3

³¹P and ¹⁹F NMR spectroscopy has been used to elucidate the nature of the interaction of PF₅, HPO₂F₂ and P₄O₁₀ with the solvent system 44 wt.% N₂O₄ in 100% HNO₃ (“High Density Acid”, HDA). PF₅ generates the species PF₆^?, HPO₂F₂ and HF (with some H₂PO₃F present as a minor product). HPO₂F₂ gives rise to H₂PO₃F and HF (with smaller amounts of PF₆ also present). The ³¹P NMR spectrum of P₄O₁₀ in HDA exhibits four resonances assigned to P(OH)₄⁺, H₄P₂O₇, (HPO₃)₄ and a mixture of cyclic and branched phosphoric acids, respectively.     

Closest packing in dense oxides: The structure of a polymorph of Co3(AsO4)2

Crystals of Co₃(AsO₄)₂ were grown from the melt of a mixture of Co₂As₂O₇ and As₂O₅. The crystals are isostructural with Mg₃(AsO₄)₂ and are tetragonal with a = 6.858(2), c = 18.872(5) Å, Z = 6, and space group $\text{I}\text{4}\text{2d}$. A total of 1048 independent reflections were measured by diffractometer and used in the full-matrix refinement to a final R value of 0.069. The structure contains two distinct AsO₄ groups. Two of the cobalt ions are octahedrally coordinated and a third occupies a $\text{4}$ site with four short and four long CoO distances. The crystal structure of Co₃ (AsO₄)₂ is not based on the continuous three-dimensional closest packing of oxygen atoms. Nevertheless the number of oxygen atoms per cubic centimeter is 5.4 × 10²², which falls in the range of values for hexagonal and cubic closest packed structures. A better measure of the degree to which closest packing is achieved by a structure is suggested. It is based on an analysis of the polyhedra of oxygen atoms which surround each of the oxygen atoms in a structure and their relation to the polyhedra in ideally closest packed structures. In order to facilitate the analysis, polytopes of 11- and 12-vertex polyhedra were studied. A new decahexahedral 11-vertex polyhedron was found.     

Formation and transformation of Pb2SiO4

A new modification of Pb₂SiO₄ was formed by the simultaneous hydrolysis of lead and silicon alkoxides, followed by washing and drying. It has a