Study of the state of uranyl orthovanadate (UO2)3(VO4)2·4H2O in aqueous solutions

The state of uranyl orthovanadate (UO₂)₃(VO₄)₂·4H₂O in aqueous solutions was studied by the methods of chemical analysis, X-ray diffraction, and IR spectroscopy. Uranyl vanadate is transformed into compounds of other composition and structure upon contact with aqueous phases of various acidity. Equilibrium constants of reactions occurring in heterogeneous systems (UO₂)₃(VO₄)₂·4H₂O-aqueous solution were calculated from the data on the solubility. Phase diagrams of bottom solid phases and of equilibrium aqueous solutions were constructed.     

Application of the Ru(bipy)2(dpp)2+ / C2O4 2− electrochemiluminescence reaction to the determination of phenol

The electrochemiluminescence (ECL) of the ruthenium di(2,2′-bipyridine)- (4,7-diphenyl-1,10-phenanthroline) complex (Ru-bipy-dpp) produced on a glassy carbon electrode was studied by cyclic voltammetry. The anodic oxidation of Ru-bipy-dpp produces ECL in the presence of oxalate in oxygen-free aqueous solutions. Threefold ECL efficiencies were obtained for Ru-bipy-dpp relative to Ru(bipy)₃ as a standard. The ECL of Ru-bipy-dpp is quenched by both oxygen and phenol. The luminescence intensity was proportional to the concentration of phenol in the range of 5–100 μM. At a phenol concentration of 100 μM, the ECL of Ru-bipy-dpp peaking at 597 nm was completely quenched. Correspondence: Dan Xiao, College of Chemistry and Chemical Engineering, Sichuan University, Chengdu 610065, P.R. China     

Vibrational spectroscopic characterization of the phosphate mineral hureaulite – (Mn,Fe)5(PO4)2(HPO4)2·4(H2O)

This research was done on hureaulite samples from the Cigana claim, a lithium bearing pegmatite with triphylite and spodumene. The mine is located in Conselheiro Pena, east of Minas Gerais. Chemical analysis was carried out by Electron Microprobe analysis and indicated a manganese rich phase with partial substitution of iron. The calculated chemical formula of the studied sample is: (Mn_3.23, Fe_1.04, Ca_0.19, Mg_0.13)(PO₄)_2.7(HPO₄)_2.6(OH)_4.78. The Raman spectrum of hureaulite is dominated by an intense sharp band at 959 cm⁻¹ assigned to PO stretching vibrations of HPO₄²⁻ units. The Raman band at 989 cm⁻¹ is assigned to the PO₄³⁻ stretching vibration. Raman bands at 1007, 1024, 1047, and 1083 cm⁻¹ are attributed to both the HOP and PO antisymmetric stretching vibrations of HPO₄²⁻ and PO₄³⁻ units. A set of Raman bands at 531, 543, 564 and 582 cm⁻¹ are assigned to the ν₄ bending modes of the HPO₄²⁻ and PO₄³⁻ units. Raman bands observed at 414, and 455 cm⁻¹ are attributed to the ν₂ HPO₄²⁻ and PO₄³⁻ units. The intense A series of Raman and infrared bands in the OH stretching region are assigned to water stretching vibrations. Based upon the position of these bands hydrogen bond distances are calculated. Hydrogen bond distances are short indicating very strong hydrogen bonding in the hureaulite structure. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral hureaulite to be understood.     

A Raman spectroscopic study of the antimonite mineral peretaite Ca(SbO)4(OH)2(SO4)2·2H2O

Raman spectra of mineral peretaite Ca(SbO)₄(OH)₂(SO₄)₂·2H₂O were studied, and related to the structure of the mineral. Raman bands observed at 978 and 980 cm^?1 and a series of overlapping bands observed at 1060, 1092, 1115, 1142 and 1152 cm^?1 are assigned to the SO₄^2? ν₁ symmetric and ν₃ antisymmetric stretching modes. Raman bands at 589 and 595 cm^?1 are attributed to the SbO symmetric stretching vibrations. The low intensity Raman bands at 650 and 710 cm^?1 may be attributed to SbO antisymmetric stretching modes. Raman bands at 610 cm^?1 and at 417, 434 and 482 cm^?1 are assigned to the SO₄^2? ν₄ and ν₂ bending modes, respectively. Raman bands at 337 and 373 cm^?1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO₄^2? and SbO stretching vibrations support the concept of the non-equivalence of these units in the peretaite structure.     

A study of zinc complexes of the metalloligand [Pt2(μ-S)2(PPh3)4] of the type [Pt2(μ-S)2(PPh3)4ZnL]+ (L = bidentate chelating ligand)

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with zinc acetate and an ancillary chelating ligand L (HL = 8-hydroxyquinoline, 8-tosylaminoquinoline or maltol) with added trimethylamine in methanol give new cationic platinum–zinc sulfide aggregates [Pt₂(μ-S)₂(PPh₃)₄ZnL]⁺, isolated as their BF₄^? salts. The complexes were characterized by NMR spectroscopy, ESI mass spectrometry, microelemental analysis, and an X-ray structure determination of the tosylamidoquinoline derivative [Pt₂(μ-S)₂(PPh₃)₄Zn(TAQ)]BF₄, which showed a distorted tetrahedral coordination geometry at zinc. Additional examples, containing picolinate, dithiocarbamate, or dithiophosphinate ligands were also synthesized and partly characterized in order to demonstrate a wider range of available derivatives.     

Identification of the cobalt(II) chloride ‘mixed’ solvate Co4Cl8(H2O)4(MeCN)6: the ionic structure trans-[Co(H2O)2(MeCN)4] trans-[Co(H2O)2(MeCN)2(CoCl4)2]

The structure of the title compound features mononuclear octahedral Co^II cations, trans-[Co(H₂O)₂(MeCN)₄]²⁺, and trinuclear anions, trans-[Co(H₂O)₂(MeCN)₂(CoCl₄)₂]^2–; the latter centrosymmetric units contain a central octahedral Co(H₂O)₂(MeCN)₂ moiety with two tetrahedral [CoCl₄]^2– ligands. These two large ions are held in a network of intra- and inter-molecular hydrogen bonding.     

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the (6)A(1) ↔ (2)T(2) Ground-State Transformation of the [FeN(4)O(2)](+) Chromophore

Several potentially tridentate pyridyl and phenolic Schiff bases (apRen and HhapRen, respectively) were derived from the condensation reactions of 2-acetylpyridine (ap) and 2'-hydroxyacetophenone (Hhap), respectively, with N-R-ethylenediamine (RNHCH(2)CH(2)NH(2), Ren; R = H, Me or Et) and complexed in situ with iron(II) or iron(III), as dictated by the nature of the ligand donor set, to generate the six-coordinate iron compounds [Fe(II)(apRen)(2)]X(2) (R = H, Me; X(-) = ClO(4)(-), BPh(4)(-), PF(6)(-)) and [Fe(III)(hapRen)(2)]X (R = Me, Et; X(-) = ClO(4)(-), BPh(4)(-)). Single-crystal X-ray analyses of [Fe(II)(apRen)(2)](ClO(4))(2) (R = H, Me) revealed a pseudo-octahedral geometry about the ferrous ion with the Fe(II)-N bond distances (1.896-2.041 ?) pointing to the (1)A(1) (d(π)(6)) ground state; the existence of this spin state was corroborated by magnetic susceptibility measurements and M?ssbauer spectroscopy. In contrast, the X-ray structure of the phenolate complex [Fe(III)(hapMen)(2)]ClO(4), determined at 100 K, demonstrated stabilization of the ferric state; the compression of the coordinate bonds at the metal center is in accord with the (2)T(2) (d(π)(5)) ground state. Magnetic susceptibility measurements along with EPR and M?ssbauer spectroscopic techniques have shown that the iron(III) complexes are spin-crossover (SCO) materials. The spin transition within the [Fe(III)N(4)O(2)](+) chromophore was modulated with alkyl substituents to afford two-step and one-step (6)A(1) ? (2)T(2) transformations in [Fe(III)(hapMen)(2)]ClO(4) and [Fe(III)(hapEen)(2)]ClO(4), respectively. Previously, none of the X-salRen- and X-sal(2)trien-based ferric spin-crossover compounds exhibited a stepwise transition. The optical spectra of the LS iron(II) and SCO iron(III) complexes display intense d(π) → p(π)* and p(π) → d(π) CT visible absorptions, respectively, which account for the spectacular color differences. All the complexes are redox-active; as expected, the one-electron oxidative process in the divalent compounds occurs at higher redox potentials than does the reverse process in the trivalent compounds. The cyclic voltammograms of the latter compounds reveal irreversible electrochemical generation of the phenoxyl radical. Finally, the H(2)salen-type quadridentate ketimine H(2)hapen complexed with an equivalent amount of iron(III) to afford the μ-oxo-monobridged dinuclear complex [{Fe(III)(hapen)}(2)(μ-O)] exhibiting a distorted square-pyramidal geometry at the metal centers and considerable antiferromagnetic coupling of spins (J ≈ -99 cm(-1)).     

Interplay between the structural and magnetic probes in the elucidation of the structure of a novel 2D layered [V4O4(OH)2(O2CC6H4CO2)4]·DMF

The title compound has been synthesized under solvothermal conditions by reacting vanadium(V) oxytriisopropoxide with terephthalic acid in N,N-dimethylformamide. A combination of synchrotron powder diffraction, infrared spectroscopy, scanning and transmission electron microscopy, and thermal and chemical analysis elucidated the chemical, structural and microstructural features of a new 2D layered inorganic-organic framework. Due to the low-crystallinity of the final material, its crystal structure has been solved from synchrotron X-ray powder diffraction data using a direct space global optimization technique and subsequent constraint Rietveld refinement. [V(4)O(4)(OH)(2)(O(2)CC(6)H(4)CO(2))(4)]·DMF crystallizes in the monoclinic system (space group P2/m (No. 10)); cell parameters: a = 20.923(4) ?, b = 5.963(4) ?, c = 20.425(1) ?, β = 123.70(6)°, V = 2120.1(9) ?(3), Z = 2. The overall structure can be described as an array of parallel 2D layers running along [-101] direction, consisting of two types of vanadium oxidation states and coordination polyhedra: face-shared trigonal prisms (V(4+)) and distorted corner-shared square pyramids (V(5+)). Both configurations form independent parallel chains oriented along the 2-fold symmetry crystallographic b-axis mutually interlinked with terephthalate ligands in a monodentate mode perpendicular to it. The morphology of the compound exhibits long nanofibers, with the growth direction along the layered [-101] axis. The magnetic susceptibility measurements show that the magnetic properties of [V(4)O(4)(OH)(2)(O(2)CC(6)H(4)CO(2))(4)]·DMF can be described by a linear antiferromagnetic chain model, with the isotropic exchange interaction of J = -75 K between the nearest V(4+) neighbours of S = 1/2.     

Preparation,crystal structure and infrared spectroscopy of the new compound Rb4Be(SeO4)2(HSeO4)2·4H2O

A new compound, Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O, crystallizes in a comparatively wide concentration range from mixed beryllium rubidium selenate solutions (from solutions containing 29.06 mass% beryllium selenate and 25.75 mass% rubidium selenate up to solutions containing 12.53 mass% beryllium selenate and 55.32 mass% rubidium selenate).Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O crystallizes in the acentric orthorhombic space group Pmn2₁ (a = 32.607(4), b = 10.676(2), c = 6.069(1) Å, V = 2112.8 ų, Z = 4, R1 = 0.047 for 4059 F_o > 4σ(F_o) and 311 variables). The crystal structure is composed of Be(H₂O)₄ tetrahedra arranged in layers at x = 0 and x = ½, alternating with broad layers built up from SeO₄ and HSeO₄ selenate tetrahedra and Rb cations. The beryllium–water layers are linked to the rest of the structure via hydrogen bonds only. The H₂O molecules as well as the OH molecules of the acid HSeO₄ groups form strong to very strong hydrogen bonds with donor–acceptor distances between 2.58 and 2.74 Å.Vibrational spectra (infrared and Raman) of Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O are presented and discussed in the region of the fundamentals of both the selenate and the beryllium tetrahedra (skeleton motions) as well as in the region of the OH vibrations at ambient and liquid nitrogen temperature (LNT). The appearance of four Raman bands corresponding to ν₁ of the selenate ions reflects the existence of four crystallographically different selenate tetrahedra in the structure. The spectroscopic experiments reveal that the ν₁ modes of the selenate ions appear at higher frequencies than some components of ν₃. Bands of an AB doublet structure (2950, 2390 cm^?1) arising from the OH stretching modes of the HSeO₄^- ions are recognized in the infrared spectra. The appearance of two infrared bands (1308, 1250 cm^?1) corresponding to δ(OH) (in-plane bending modes of the OH groups) confirms the structural data regarding the existence of two crystallographically different OH groups. The water librations are also briefly commented. The appearance of a band at a comparatively large wavenumber (1013 cm^?1) corresponding to rocking librations of the water molecules indicate that strong hydrogen bonds are formed in the title compound.     

On the Crystal Structure of [Cu(OH)_2(H_2O)_2(4-C_5H_4NCOOH)_2]

In their report of the crystal structure of the compound claimed to be [Cu(OH)2(H2O)2(4- C5H4NCOOH)2], the authors did not give any experimental details on the location and refinement of the water and hydroxyl hydrogen atoms[1]; they had assumed the presence of the carboxylic -CO2H unit on the basis of the infrared stretching frequency at 1700 cm-1 that is only of medium intensity. The cell constants for the compound are, in fact, identical, with those documented for tetraaquabis(isonicot…     

Synthesis and structure of the oxalatotetranitratouranylate complex (NH4)2[{UO2(NO3)2}2(μ4-C2O4)] · 2H2O

The reaction of diaquadinitratouranyl with ammonium nitrate in ethanol gave the single crystals of ((NH₄)₂[}UO₂(NO₃)₂}₂(μ₄-C₂O₄)] · 2H₂O (I).The structure of the complex was studied by X-ray diffraction. The crystals are monoclinic, a = 8.6497(10) Å, b = 11.7001(10) Å, c = 20.2135(10) Å, β = 93.924(10)°, space group P2₁/c, Z = 4, V = 2040.9(3) ų. The structural units of the crystal are island binuclear groups [{UO₂(NO₃)₂}₂(μ₄-C₂O₄)]^2?, ammonium cations, and crystal water molecules. The structure has a complex three-dimensional packing provided by electrostatic attraction forces of the counterions and the hydrogen bond system involving water molecules, oxalate, nitrate, and uranyl ions. The IR spectra of I confirm the X-ray diffraction data.     

Formation of mixed-metal alkoxides mediated by the reactivity of coordinated pinacol: Synthesis and molecular structures of Ce2Ti2(μ3-O)2(μ,η2-OCMe2CMe2O)4(OPri)4(PriOH)2 and of Ce2Nb2(μ3-O)2(μ,η2-OCMe2CMe2O)4(OPri)6

The addition of pinacol to mixtures of titanium and cerium isopropoxides as well as the use of insoluble titanium and cerium pinacolate synthons was investigated as a route to M-Ce (M=Ti, Nb) species. Pinacol was able to promote the formation of mixed-metal species and the first Ce-Ti and Ce-Nb species namely Ce_2Ti(pin)₂(OPrⁱ)₈ and [M₂Ce₂(μ₃-O)₂(μ,η²pin)₄(OPrⁱ)₆H_x] [M=Ti, x=2; M=Nb, x=0; pin=OCMe₂-COMe₂] were isolated and characterized by FT-IR and ¹H NMR. The latter were also characterized by X-Ray diffraction. Their structures are based on a rhombus compressed along the M⋯M direction with 6-coordinated metals. The pinacolate moieties act as bridging-chelating ligands. The metal–oxygen bond lengths vary according to M–O(pin)<M-μ₃–O<Mμ–O(pin)<Ce–OPrⁱ<Ce–μ₃O.     

Synthesis,crystal structure of Gd(H2O)(C2O4)2 · NH4 and of La(C2O4)2 · NH4. Characterization of the Ln(H2O)(C2O4)2 · NH4 with Ln=Eu…Yb

Single crystals of two lanthanide complexes, presenting similar formula Ln(H₂O)_x(C₂O₄)₂ · NH₄ with Ln=La, x=0 and Ln=Gd, x=1, have been prepared, in closed system at 200 °C. The gadolinium complex is bi-dimensional. A layer is built by the packing of the basic unit, [Gd(C₂O₄)]₄. The gadolinium atoms are related only by bischelating oxalate ligands, the ammonium ion and the water molecule (bound to the gadolinium atom) are localized into the interlayer space. The lanthanum complex is tri-dimensional. The basic building unit remains approximately the same and the packing of these units form a layer. However, within these units, the lanthanum atoms are related by either an oxalate ligand or an edge. Moreover, an oxalate ligand assumes the connection between the layers. The ammonium ion is localized into two sets of intersecting channels. Pure phase of the gadolinium complex has been prepared at 100 °C and extended to some lanthanide elements, Eu…Yb. As the size of the lanthanide ionic radius is decreasing, it is noticeable that the a unit–cell constant follows an expansion pattern while the others two follow an usual contraction one. The thermal behavior of this family shows that the anhydrous compounds are obtained and that some water molecule is sorbed during the cooling. Thus, the anhydrous compounds present a relatively open-framework with some small micropores.     

On the nature of the multiple ground states of the MMX mixed-valence chain compound, [Pt(II/III)2(n-PenCS2)4I]∞

We present a comprehensive study of the temperature dependence of the crystal structure using single-crystal X-ray diffraction and diffuse scattering, and electrical transport and magnetic properties as well as some optical properties at room temperature to elucidate the origin and the form of multiple ground states demonstrated in a previous study of the heat-capacity of the MMX chain compound, [Pt(II/III)(2)(n-PenCS(2))(4)I](∞). The present results confirm the presence of the two phase transitions, one reversible of first order at 207 K and the other nonreversible monotropic at 324 K, separating the low temperature (LT), room temperature (RT), and high temperature (HT) phases. The unit cell displays a 3-fold periodicity of -Pt-Pt-I- in the RT and HT phases because of the structural disorder which is exhibited by the dithiocarboxylato groups and the n-pentyl groups belonging to the central diplatinum unit. In addition, for the HT-phase all the dimers show this disorder. This compound undergoes a metal-semiconductor transition at T(M-S) = 235 K. The presence of diffuse streaks corresponding to 2-fold -Pt-Pt-I- periodicity in the HT and RT phases indicates dynamic valence ordering of the type -Pt(2+)-Pt(2+)-I(-)-Pt(3+)-Pt(3+)-I(-)-or-Pt(2+)-Pt(3+)-I(-)-Pt(3+)-Pt(2+)-I(-)-. For the LT-phase the diffuse scattering is condensed into clear Bragg diffraction peaks while keeping the 3-fold periodicity. This fact suggests further localization through dimerization of charges and spins confirming the diamagnetic state in the magnetic susceptibility and the low electrical conduction below 207 K. The present results are further discussed in relation to those of previous studies on the homologues, [Pt(II/III)(2)(RCS(2))(4)I](∞), R = methyl, ethyl, n-propyl, and n-butyl.     

Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe(2) (CO)(4) (κ(2) -PNP(R) )(μ-S(CH(2) )(3) S] (PNP(R) ={Ph(2) PCH(2) }(2) NR, R=Me, Ph)

The behavior of [Fe(2) (CO)(4) (κ(2) -PNP(R) )(μ-pdt)] (PNP(R) =(Ph(2) PCH(2) )(2) NR, R=Me (1), Ph (2); pdt=S(CH(2) )(3) S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP(R) appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF(3) SO(3) H or CH(3) SO(3) H; the cation with a bridging hydride ligand, 1?μH(+) (R=Me) or 2?μH(+) (R=Ph) is obtained rapidly. Only 1?μH(+) can be protonated at the nitrogen atom of the PNP chelate by HBF(4) ?Et(2) O or CF(3) SO(3) H, which results in a positive shift of the proton reduction by approximately 0.15?V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η(2) -H(2) species in the Fe(I) Fe(II) state. When R=Ph, the bridging hydride cation 2?μH(+) cannot be protonated at the amine function by HBF(4) ?Et(2) O or CF(3) SO(3) H, and protonation at the N atom of the one-electron reduced analogue is also less favored than that of a S atom of the partially de-coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2?μH(+) . The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k(obs) ≈4-7?s(-1) ) because of the slow intramolecular proton migration and H(2) release steps identified by the theoretical study.     

Dependence of the chemical properties of macrocyclic [Ni(II)(2)L(μ-O(2)CR)](+) complexes on the basicity of the carboxylato coligands (L(2-) = macrocyclic N(6)S(2) ligand)

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.     

Peculiarities of the crystal structure and packing of the host and guest molecules in the [M(4-McPy)4(NCS)2]·0.67(4-McPy)·0.33 H2O Clathrates (M = Cu(II), Mn(II); 4-MePy = 4-Methylpyridine)

The crystal structures of the two clathrates with the composition [M(4-MePy)₄(NCS)₂]·0.67(4-McPy)·0.33 H₂O (M=Cu(II), Mn(II); 4-MePy=4-methylpyridine) have been determined. These compounds are trigonal, with the [M(4-MePy)₄(NCS)₂] host molecules being centrosymmetric. The parameters of the unit cells area = 27.365(7) and 27.738(6),c = 11.303(9) and 11.250(8) Å,V = 7325(2) and 7493(2) ų, space group R , R = 0.053 and 0.109 for M = Cu(II) and Mn(II), respectively. ForZ = 9d _calcd is equal to 1.271 and 1.225 g/cm³, andd _measd is equal to 1.252(2) and 1.213(2) g/cm³ for the Cu and Mn clathrates, respectively. The coordination environment of the metal atoms in these compounds is an irregular octahedron, while in the Mn compound these distortions are rather small (Mn-N_MePy 2.30, 2.34 Å, Mn-N_NCS 2.18 Å, and Cu-N_MePy 2.06 Å, Cu-N_NCS 1.98 Å and Cu-N_MePy 2.50 Å).The molecular packing in the structures is such that the channels of variable diameter are formed along the short cell dimension (the maximum diameter is 10 Å, the minimum being 6 Å) where the guest 4-MePy and H₂O molecules are placed.     

Investigations of the thermal stability and phase transformations in the system marocco phosphorite—(NH4)3H(SO4)2.NH4HSO4

Different physical chemical methods were used to study the thermochemical processes in a system involving a natural phosphate and complex acid salts of ammonium sulphate. The products of decomposition of the double ammonium salt and the products of their interactions with the phosphate were identified. The formation of ammonium and calcium polyphosphates and the disproportionation of P₃O ₁₀ ^5? and P₂O ₇ ^4? to PO ₄ ^3? and PO ₃ ^? were found to depend on the circumstances of the thermal interactions.     

Modeling of esterification of acetic acid with n-butanol in the presence of Zr(SO4)2·4H2O coupled pervaporation

Modeling of esterification of acetic acid with n-butanol in the presence of Zr(SO₄)₂·4H₂O coupled pervaporation was studied in this paper. The influence of several process variables, such as process temperature, initial mole ratio of acetic acid over n-butanol, the ratio of the effective membrane area over the volume of reacting mixture and catalyst content, on the esterification was discussed. The calculated results for the conversion of n-butanol to water and permeation flux were consistence with the experimental data. The permselectivity and water content can be roughly estimated by the model equations.