Characterization of quasi-one-dimensional S=1/2 Heisenberg antiferromagnets Sr2Cu(PO4)2 and Ba2Cu(PO4)2 with magnetic susceptibility, specific heat, and thermal analysis

Properties of Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ having [Cu(PO₄)₂]_∞ linear chains in their structures with Cu-O-P-O-Cu linkages were studied by magnetic susceptibility (T=2-400 K, H=100 Oe) and specific heat measurements (T=0.45-21 K). Magnetic susceptibility versus temperature curves, χ(T), showed broad maxima at T_M=92 K for Sr₂Cu(PO₄)₂ and T_M=82 K for Ba₂Cu(PO₄)₂ characteristic of quasi-one-dimensional systems. The χ(T) data were excellently fitted by the spin susceptibility curve for the uniform S=1/2 chain (plus temperature-independent and Curie-Weiss terms) with g=2.153(4) and J/k_B=143.6(2) K for Sr₂Cu(PO₄)₂ and g=2.073(4) and J/k_B=132.16(9) K for Ba₂Cu(PO₄)₂ (Hamiltonian H=JΣS_iS_i+1). The similar J/k_B values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, T_N, were below 0.45 K. Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ are an excellent physical realization of the S=1/2 linear chain Heisenberg antiferromagnet with k_BT_N/J<0.34% together with Sr₂CuO₃ (k_BT_N/J≈0.25%) and γ-LiV₂O₅ (k_BT_N/J<0.16%). Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ were stable in air up to 1280 and 1150 K, respectively.     

Effect of hydration on conductivity of Ba4La x Ca2 − x Nb2O11 + 0.5x (x = 0.5, 1, 1.5, 2) phases

Substitution of Ca by La in initial cubic double perovskite Ba₄(Ca₂Nb₂)O₁₁[VO]₁ allowed obtaining phases with a similar structure with a lower content of structural oxygen vacancies, Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} [VO]_{1 ? 0.5x} (x = 0.5, 1, 1.5, 2). The impedance technique was used to measure the temperature dependences of conductivity in the atmosphere of dry and humid air. Transport numbers determined using the EMF method in an oxygen-air and water steam concentration cells point to the predominantly hole nature of conductivity in the high-temperature region (T > 600°C) and to predominance of proton conductivity in the low-temperature region. Activation energies of hole and proton conductivity were calculated. Thermogravimetric measurements were carried out under heating from 25 to 1000°C with simultaneous mass-spectrometric determination of evolved H₂O and CO₂. The properties of the studied Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} (x = 0.5, 1, 1.5, 2) phases were compared with the earlier studied Ba_{4 ? x} La _x (Ca₂Nb₂)O_{11 + 0.5x} phases with similar lanthanum content.     

Ternary rare-earth alumo-silicides—single-crystal growth from Al flux, structural and physical properties

A number of rare-earth alumo-silicides (R-Al-Si) have been synthesized from the corresponding elements by high-temperature reactions, carried out in excess of aluminum to serve as a flux. Under these experimental conditions, large single crystals of all R-Al-Si ternary phases were readily produced. The crystal structures these ternaries adopt were studied by means of powder and single-crystal X-ray diffraction and were classified as follows: (1) the early rare-earths (R=La, Ce, Pr, Nd, Sm, Gd) yield RAl_xSi_2−x, x∼1, non-stoichiometric ternary derivatives of the body-centered α-ThSi₂-type; (2) the late rare-earths (R=Tb, Dy, Ho, Er, Tm) form stoichiometric R₂Al₃Si₂ compounds that crystallize in the C-centered monoclinic Y₂Al₃Si₂-type; (3) the divalent Eu and Yb produce EuAl₂Si₂ and YbAl₂Si₂ with the trigonal CaAl₂Si₂-type, whereas the last lanthanide element, Lu, forms LuAlSi with C-centered orthorhombic YAlGe-type. These structural trends are reviewed, and the evolution of the basic physical properties such as magnetism, heat capacity and electrical resistivity when moving across the series is described in detail.     

Excess molar volumes of (ethyl formate or ethyl acetate + an isomer of hexanol) at 298.15 K

Excess molar volumes V_m^E were determined over the entire composition range at 298.15 K for ethyl formate or ethyl acetate + hexan-1-ol, +2-methylpentan-1-ol, +3-methylpentan-2-ol, +2-methylpentan-3-ol, +3-methylpentan-3-ol, +2-methylpentan-2-ol, +4-methyl-pentan-2-ol, and +hexan-2-ol. Excess volumes were determined from density measurements made with a vibrating-tube densimeter. The V_m^E values were all positive, decreasing with the n value of the ester: C_n?1H_2n?1CO₂C₂H₅.     

Poly(3-dodecylthiophene) membranes for gas separations

Solution cast membranes of poly(3-dodecylthiophene) (PDDT) were studied for the room temperature separation of N₂, O₂, and CO₂. A procedure for fabricating reproducible, smooth, uniformly thick (∼35 μm), defect-free membranes is described. Permeability values were measured for as-cast PDDT membranes (P_N2=9.4, P_O2=20.2, P_CO2=88.2 Barrers) and selectivity values were calculated (α_O2/N2=2.2, α_CO2/N2=9.4). Chemically induced oxidation (∼23%) with SbCl₅ resulted in a decrease in permeability (P_N2=3.5, P_O2=10.5, P_CO2=48.5 Barrers) and a corresponding increase in permselectivity (α_O2/N2=3.0, α_CO2/N2=14.0). Reduction of the oxidized membrane with hydrazine partially reversed these trends (P_N2=5.4, P_O2=15.1, P_CO2=62.9 Barrers, α_O2/N2=2.8, α_CO2/N2=11.6). The chemical compositions of as-cast, oxidized, and hydrazine-treated PDDT membranes were determined using elemental analysis and energy dispersive X-ray spectrometry. Membrane microstructure was investigated by optical microscopy, TappingMode™ atomic force microscopy and scanning electron microscopy. The composition and microscopy results were correlated with changes in gas-transport properties.     

Glycolate Ti1 − x Fe x (OCH2CH2O)2 − x/2 as a precursor for the preparation of quasi-one-dimensional (1D) solid solutions Ti1 − x Fe x O2 − 2x/2 (0 ≤ x ≤ 0.1)

Quasi-one-dimensional (1D) solid solutions Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti₃Fe₂(OCH₂CH₂O)₉ were described. It was found that the synthesized Ti_{1 ? x} Fe _x O_{2 ? 2x/2} solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti_{1 ? x} Fe _x O_{(2 ? x/2) ? yCy)} and also composites on its basis, which contain an excess amount of carbon, was proposed.     

Group ib organometallic chemistry : XXXIV. Thermal behaviour and chemical reactivity of tetranuclear Me2N-substituted diarypropenylcopper-copper anion (Vi2Cu4X2) and mixed diarylpropenyl/organocopper (Vi2Cu4R2) compounds

Thermal decomposition of configurationally pure 1,2-diarylpropenylcopper compounds Z-Vi₂CU₄Br₂ and Z-Vi₂Cu₄R₂ [Vi  (2-Me₂NC₆H₄)CC(Me)-(C₆H₄Me-4), R  2-Me₂NC₆H₄ or 4-MeC₆H₄CC] predominantly results in the formation of ViH. In contrast, only dimers (ViVi) were formed on thermolysis of (Z-ViCu₂OTf)_η which is a further illustration of the influence of the counter anion on the reactivity of organocopper cluster compounds. However, in both cases partial inversion of configuration, giving mixtures of isomers, was observed. The thermolysis of (Z-ViCu₂OTf)_η is discussed in terms of OTf-enhanced intraaggregate electron-transfer processes. The formation of incipient vinyl cations which are η²-coordinated to the copper cluster can explain the observed isomerization.Also in the hydrolysis reaction of Z-Vi₂Cu₄Br₂ mixtures of isomeric ViH compounds were obtained, the E/Z ratio being dependent on the type of reagent used. Mixtures of isomeric ViX compounds (X  Br, Cl, I) were formed in the reaction of Z-Vi₂Cu₄Br₂ with I₂ and CuCl₂. An explanation for the occurrence of isomerization is presented.Dimers (ViVi) were almost absent in the product mixture resulting from the reaction of Z-Vi₂Cu₄Br₂ with CuCl₂. In contrast, ViVi is obtained in about 50% yield from the reaction of ViLi with CuCl₂ which is in accord with earlier observations for the reaction of aryllithium compounds with cupric halides.Highly selective E-ViBr formation was observed in the reaction of E-ViLi with AgBr. This reaction probably proceeds via a thermally unstable Z-ViAg₂Br intermediate.     

Construction of metal-organic frameworks through coordination and hydrogen bonding interactions: Syntheses, structures and photoluminescent properties of metal complexes with macrocyclic ligand

A macrocyclic ligand L with two diethylenetriamine units linked by two rigid biphenylene spacers was used as building block for construction of metal-organic frameworks. A silver(I) complex with macrocyclic and open-chain mix-type ligands [Ag₂(L)(L′)](ClO₄)₂ (1) [L′=1,6-bis(4-imidazol-1′-ylmethylphenyl)-2,5-diazahexane] was obtained by reaction of L and L′ together with AgClO₄·H₂O. It is interesting that the open-chain tetradentate ligand L′ only served as a bidentate ligand to bridge the Ag₂L units into an infinite one-dimensional (1D) cationic chain. Neutral 1D chain coordination polymer [Cu₂(L)(μ-SO₄)₂]·3H₂O·3MeOH (2) is formed by sulfate bridges between the neighboring Cu₂L units. When L reacted with nickel(II) sulfate instead of copper(II) sulfate, a monomacrocycle molecular complex [Ni₂(L)(H₂O)₄(SO₄)₂] (3) was obtained in which the sulfate anion acts as monodentate ligands rather than as bridges. When Cd(II) salts were used for the reactions with L, another two neutral 1D coordination polymers, [Cd₂(L)(μ-Cl)₂Cl₂]·2H₂O (4) and [Cd₂(L)(μ-Br)₂Br₂] (5), with the same structure were isolated. All the synthesized complexes exhibit three-dimensional framework structures linked by various hydrogen bonds. The photoluminescent properties of the synthesized complexes were studied in the solid state at room temperature, and the Ag(I) and Cd(II) complexes were found to show strong blue luminescence.     

Substituted salen–Ru(II) complexes as catalysts in the asymmetric cyclopropanation of styrene by ethyl diazoacetate: the influence of substituents and achiral additives on activity and enantioselectivity

A series of alkyl-, halogen- and nitro-substituted salen ligands, 1, have been employed in the asymmetric cyclopropanation of styrene with ethyl diazoacetate by its ruthenium(II) complex with [RuCl₂(p-cymene)]₂ or RuCl₂(PPh₃)₃ as precursors. The introduction of appropriate electron withdrawing groups in the salen ligands benefited the enantioselectivity of the reaction. Some additives, including O-donor, N-donor and P-donor ligands, were added to the reaction to improve the enantioselectivity and activity, and e.e.s of up to 80% were achieved. In the salen/[RuCl₂(p-cymene)]₂ system, the (1R,2S)-isomer was obtained in 80.2% e.e. by using the salen ligand 1f derived from 3,5-dibrominated salicylaldehyde with Et₃N as additive. E.e.s of up to 81.3% for (1S,2R)-isomers were achieved by using the complex 2 synthesized from the nitro-substituted ligand 1m and RuCl₂(PPh₃)₃. A possible mechanism was also discussed.     

From simple rings to one-dimensional channels with calix[8]arenes, water clusters, and alkali metal ions

The macrocycle 4-tert-butylcalix[8]arene (L) was reacted with alkali metal carbonates (Li₂CO₃, Na₂CO₃, K₂CO₃, Rb₂CO₃, and Cs₂CO₃) at the interface of a biphasic THF/water system. Needle-like crystals with a general formula [A_x(4-tert-butylcalix[8]arene-xH)(THF)_y(H₂O)_z] (with A=Li, Na, K, Rb, Cs, x=1, 2, y=4, 5, 8, and z=6, 7) were thereby obtained. The solid state structures were investigated by X-ray diffraction of single crystals and by TGA measurements. They do not appear to be maintained in solution.     

Optically active rhodium complexes with indenyl-linked phosphane ligands

The optically active indenyl-linked phosphane ligands (S)-[2-(3H-inden-1-yl)-1-phenylethyl]diphenylphosphane (L₁) and (S)-[2-(4,7-dimethyl-3H-inden-1-yl)-1-phenyl-ethyl]diphenylphosphane (L₂) were synthesized in three steps from (R)-1-phenylethane-1,2-diol in excellent yields. Their lithium salts reacted with [Rh(μ-Cl)(η²-CH₂CH₂)₂]₂ at −78 °C in THF affording the planar chiral complexes (S,R_pl + S_pl)-[Rh(η⁵-indenyl-CH₂CH(Ph)PPh₂-kP)(η²-CH₂CH₂)] and (S,R_pl + S_pl)-[Rh(η⁵-4,7-dimethylindenyl-CH₂CH(Ph)PPh₂-kP)(η²-CH₂CH₂)] as 61:39 and 15:85 mixtures of diastereomers. The complexes were isolated in optically pure form by column chromatography. The stereochemical configuration of one of the diastereomers was determined by X-ray crystallography. The complexation of L₂ was studied in different solvents and with several Rh precursors and diastereomeric excesses up to 76% were achieved. The ability of the chiral ligands to control the stereochemistry at the metal center was tested by oxidative addition of methyl iodide. Diastereomeric excesses greater than 98% were observed.     

Stereoisomeric Pt(IV) complexes with threonine

Stereoisomeric Pt(IV) complexes with threonine (ThrH = HOCH(CH₃)CH(NH₂)COOH, ??-amino-??-hydroxybutyric acid) were obtained. In the complexes trans-[Pt(S-ThrH)₂Cl₄] and trans-[Pt(R-ThrH)(S-ThrH)Cl₄], the ThrH molecules act as monodentate ligands coordinated through the NH₂ group. In the complexes cis- and trans-[Pt(S-Thr)₂Cl₂] and trans-[Pt(R-Thr)(S-Thr)Cl₂], the deprotonated ligands are coordinated in a bidentate fashion through the NH₂ and COO^?-groups (R,S is the absolute configuration of the asymmetric carbon atom). All the complexes were identified using elemental analysis, IR spectroscopy, and ¹⁹⁵Pt, ¹³C, and ¹H NMR spectroscopy. The complexes trans-[Pt(S-ThrH)₂Cl₄] · 3H₂O and cis-[Pt(S-Thr)₂Cl₂] · 2H₂O were additionally characterized by X-ray diffraction.     

The ferromagnetic and paramagnetic properties of heusler alloys (Ni1−xCox)2MnSn

Mixed Heusler alloys with composition (Ni_1?xCo_x)₂MnSn (x = 0–1). were prepared. They were single phase with L2₁ structure. Magnetic measurements were undertaken in the ferromagnetic and paramagnetic regions. Magnetic parameters, such as Curie temperature, paramagnetic Curie temperature, and spontaneous moment μ₀₀ depend linearly on the composition. The linear variation of μ₀₀ is phenomenologically interpreted by a linear variation of the magnetic moment of manganese between 4.0 μ_B for Ni₂MnSn to 3.6 μ_B for Co₂MnSn, cobalt having a constant moment of 0.75 μ_B over the whole concentration range.     

Synthesis and properties of BF2- & PO2-complexes of mono meso-heterocycle substituted 25-oxasmaragdyrins and derivatives

BF₂- and PO₂-smaragdyrins containing one five membered heterocycle such as pyrrole, thiophene and furan at one of the meso-position of corresponding 25-oxasmaragdyrins were synthesized by treating the appropriate mono meso-heterocycle substituted 25-oxasmaragdyrin with BF₃.OEt₂ and POCl₃ respectively in CH₂Cl₂ under mild reaction conditions. All macrocycles were thoroughly characterized by HR-MS and 1D and 2D NMR spectroscopy. The presence of a five membered heterocycle in place of a six membered aryl group significantly alters the electronic properties of the smaragdyrin macrocycle as reflected in their spectral and electrochemical properties. The meso-pyrrole BF₂-smaragdyrin was subjected to a Vilsmeier-Haack reaction to prepare meso-(α-formyl pyrrolyl) BF₂-smaragdyrin which was subsequently used to prepare meso-(α-dipyrromethanyl pyrrolyl) BF₂-smaragdyrin. The further use of meso-heterocycle substituted BF₂- and PO₂-oxasmaragdyrins was demonstrated by treating meso-pyrrolyl BF₂-smaragdyrin with pentafluorobenzaldehyde in CHCl₃ under mild acid catalysed conditions to afford an unusual dipyrromethanyl bridged BF₂-smaragdyrin dyad which exhibits excellent photophysical properties.     

Nickel deficiency in RENi2-xP2 (RE=La, Ce, Pr). Combined crystallographic and physical property studies

Large single crystals from RENi_2-xP₂ (RE=La, Ce, Pr) were synthesized from the pure elements using Sn as a metal flux, and their structures were established by X-ray crystallography. The title compounds were confirmed to crystallize in the body-centered tetragonal ThCr₂Si₂ structure type (space group I4/mmm (No. 139); Pearson's symbol tI10), but with a significant homogeneity range with respect to the transition metal. Systematic synthetic work, coupled with accurate structure refinements indicated strong correlation between the degree of Ni-deficiency and the reaction conditions. According to the temperature dependent dc magnetization measurements, LaNi_2-xP₂ (x=0.30(1)), as expected, is Pauli-like paramagnetic in the studied temperature regime, while the Ce-analog CeNi_2-xP₂ (x=0.28(1)) shows the characteristics of a mixed valent Ce³⁺/Ce⁴⁺ system with a possible Kondo temperature scale on the order of 1000 K. For three different PrNi_2-xP₂ (x?0.5) samples, the temperature and field dependence of the magnetization indicated typical local moment 4f-magnetism and a stable Pr³⁺ ground state, with subtle variations of T_C as a function of the concentration of Ni defects. Field-dependent heat capacity data for CeNi_2-xP₂ (x=0.28(1)) and PrNi_2-xP₂ (x=0.53(1)) are discussed as well.     

Spectroscopic properties of meso-thienylporphyrins with different porphyrin cores

The absorption and fluorescence properties of a series of meso-thienylporphyrins with different porphyrin cores (N₄, N₃O, N₃S and N₂S₂ cores) were studied and compared with the corresponding meso-tetraarylporphyrins. The replacement of six-membered phenyl groups with five-membered thienyl groups at meso-positions resulted in red shifts and broadening of absorption and emission bands, low quantum yields and decreased S₁ state lifetimes and the maximum effects were observed for meso-tetrathienylporphyrin with N₂S₂ porphyrin core. Similar observations were noted for the dications of meso-thienylporphyrins compared to the dications of the corresponding meso-tetraarylporphyrins. These results suggest that the replacement of six-membered aryl group with five-membered thienyl groups at meso-positions, the electronic properties of the porphyrin were altered significantly.     

Synthesis,optical properties,and photocatalytic activity of lanthanide-doped anatase

Quasi-one-dimensional (1D) Ti_{1 ? x} Ln _x O_{2 ? x/2} anatase solid solutions were prepared by heating Ti_{1 ? x} Ln _x (OCH₂CH₂O)_{2 ? x/2} precursors, where Ln = Nd, Eu, Tb, Er (x = 0.025), or Sm (0.005 ≤ x ≤ 0.025), in air. These solid solution were found to have a photocatalytic activity in hydroquinone oxidation in aqueous solution under exposure to UV radiation. UV-Vis absorption spectra were recorded for Ti_{1 ? x} Ln _x O_{2 ? x/2} (Nd, Sm, Eu, Tb, or Er). The electronic structure and optical absorption spectra were calculated for anatase doped with neodymium, samarium, or terbium.     

Mono and dinuclear palladium complexes of o-alkyl substituted arylphosphane ligands: Solvent-dependent syntheses, NMR-spectroscopic characterization and X-ray crystallographic studies

Palladium(II) chloride complexes of o-alkyl substituted phosphanes were prepared in various solvents with the phosphane ligands o-methylphenyldiphenylphosphane, o-ethylphenyldiphenylphosphane, o-isopropylphenyldiphenylphosphane, o-cyclohexylphenyldiphenylphosphane and o-phenylphenyldiphenylphosphane. The structures of the complexes were characterized by ¹H NMR and ³¹P NMR spectroscopy and elemental analysis. The X-ray structures of PdCl₂(o-methylphenyldiphenylphosphane)₂, PdCl₂(o-isopropylphenyldiphenylphosphane)₂, PdCl₂(o-cyclohexylphenyldiphenylphosphane)₂, PdCl₂(o-phenylphenyldiphenylphosphane)₂, [PdCl₂(o-methylphenyldiphenylphosphane)]₂, [PdCl₂(o-ethylphenyldiphenylphosphane)]₂ and [PdCl₂(o-cyclohexylphenyldiphenylphosphane)]₂ were also determined. We report a systematic, solvent-dependent method to prepare palladium(II) complexes of the aryl phosphines o-methylphenyldiphenylphosphane, o-cyclohexylphenyldiphenylphosphane and o-phenylphenyldiphenylphosphane with a desired nuclearity. We demonstrated that chlorinated solvents promote the formation of dinuclear chlorine-bridged palladium complexes for all five ligands. The ligands preferentially form mononuclear palladium complexes in other solvents where the starting materials are only weakly soluble in the solvent.     

Highly enhanced in-field critical current density of MgB2 superconductor by combined addition of burned rice husk and nano Ho2O3

With the aim of improving flux pinning and in-field critical current density [J_C(H)], two physically and chemically different additives – burned rice husk (BRH) and nano Ho₂O₃ were introduced into in situ MgB₂ superconductor. The effects of the above two additives were studied individually and combinedly. Ho₂O₃ decomposed and reacted with B to form HoB₄, without any substitution. BRH caused considerable amount of C substitution at B site and formed Mg₂Si and Mg₂C₃ secondary phases. Addition of Ho₂O₃ improved the J_C(H) only marginally, but BRH improved the J_C(H) strongly. Combined addition of Ho₂O₃ with BRH was found to be much more effective than their solo addition for the enhancement of J_C(H) of MgB₂.     

Structures and synthesis of framework Rb and Cs uranyl arsenates and their relationships with their phosphate analogues

Two hydrated uranyl arsenates, Cs₂(UO₂)[(UO₂)(AsO₄)]₄(H₂O)₂ (CsUAs) and Rb₂(UO₂)[(UO₂)(AsO₄)]₄(H₂O)_4.5 (RbUAs), were synthesized by hydrothermal methods. Intensity data were collected at room temperature using MoKα radiation and a CCD-based area detector. The crystal structure of RbUAs was solved by direct methods, whereas the structure model of the phosphate Cs₂(UO₂)[(UO₂)(PO₄)]₄(H₂O)₂ was used for CsUAs; both were refined by full-matrix least-squares techniques on the basis of F² to agreement indices (CsUAs, RbUAs) wR₂=0.061,0.041, for all data, and R₁=0.032,0.021, calculated for 5098, 4991 unique observed reflections (|F_o|>4σ_F), respectively. The compound CsUAs is orthorhombic, space group Cmc2₁, Z=4, a=15.157(2), b=14.079(2), c=13.439(2) Å, V=2867.9(1) Å³. RbUAs is monoclinic, space group C2/m, Z=4, a=13.4619(4), b=15.8463(5), c=14.0068(4) Å, β=92.311(1)°, V=2985.52(2) Å³. The structures consist of sheets of arsenate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO₂)(AsO₄)]⁻, that are topologically identical to the uranyl silicate sheets in uranophane-beta. These sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with two arsenate tetrahedra on each of two adjacent sheets and whose fifth equatorial vertex is an H₂O group, resulting in an open framework with alkali metal cations in the larger cavities of the structures. CsUAs is isostructural with its phosphate analogue, and has two Cs atoms and a H₂O group in its structural cavities. RbUAs is not isostructural with its phosphate analogue, although it has a homeotypic framework. Its structural cavities are occupied by three Rb atoms and four H₂O groups; one Rb position and three of the interstitial H₂O groups are half-occupied. The partial occupancies of these positions probably result from the accommodation of the larger As atoms (relative to P) in the framework and resultant larger cavities.