Hydrothermal Synthesis, Single-Crystal Structure Analysis, and Solid-State NMR Characterization of Zn2(OH)0.14(3)F0.86(3)(PO4)

The zinc fluoro phosphate Zn₂F(PO₄) has been produced by hydrothermal synthesis employing hydrofluoric acid as a mineralizer in a H₂O or D₂O medium. A single-crystal X-ray synchrotron diffraction analysis of Zn₂F(PO₄) shows that the zinc fluoro phosphate is monoclinic, a=9.690(1), b=12.793(1), and c=11.972(1) Å, β=108.265(1)°, space group P2₁/c, No. 14, Z=16. Reflections hkl with k=2n+1 are weak but significant and the structure shows pseudosymmetry. Zn₂F(PO₄) has the wagnerite-type M₂F(XO₄) structure with four Zn atoms each coordinated to four O atoms and one F atom while four other Zn atoms are coordinated to four O atoms and two F atoms. A difference Fourier map, calculated from the single-crystal X-ray data, shows additional electron density close to the four fluorine atoms, indicating a possible partial substitution of F⁻ by OH⁻ ions. This is unambiguously confirmed by ³¹P-{¹H} cross-polarization magic-angle spinning (MAS) and by ¹H/²H MAS NMR spectroscopy. The narrow line width observed for the ¹H resonance and the unique set of ²H quadrupole coupling parameters (obtained for the Zn₂F(PO₄) sample using D₂O as medium) show that ¹H/²H is present as OH(D) groups rather than as water of crystallization in the structure. Quantitative ¹H MAS NMR analysis shows that the composition of the sample is Zn₂(OH)_0.14(3)F_0.86(3)(PO₄). The high-speed ¹⁹F MAS NMR spectrum exhibits two resolved resonances with equal intensity, which are ascribed to an overlap of resonances from the four distinct fluorine sites in Zn₂(OH)_0.14(3)F_0.86(3)(PO₄).     

One‐Dimensional Holodirected Lead(II) Coordination Polymer, [Pb(μ2‐TPPZ)(NO3)(ClO4)]n (TPPZ = 2, 3, 5, 6–tetra(2‐pyridyl)pyrazine)

A lead(II) complex with 2,3,5,6‐tetra(2‐pyridyl)pyrazine (TPPZ), nitrate, and perchlorate ligands has been synthesized and characterized by CHN elemental analysis and IR and ²⁰⁷Pb NMR spectroscopy. The single crystal X‐ray data of the [Pb₂(μ‐TPPZ)₂(NO₃)₂(ClO₄)₂] compound show that the complex is a one‐dimensional coordination polymer and that the Lead atom has a less‐common, ten‐coordinate holodirected geometry.     

Synthesis and Characterization of trans‐PdII Trimethylsilylchalcogenolates

The trans‐bis(trimethylsilyl)chalcogenolate palladium complexes, trans‐[Pd(ESiMe₃)₂(PnBu₃)₂] [E = S ( 1 ) and Se ( 2 )] were synthesized in good yields and high purity by reacting trans‐[PdCl₂(PBu₃)₂] with LiESiMe₃ (E = S, Se), respectively. These complexes were characterized by ¹H, ¹³C{¹H}, ³¹P{¹H} (and ⁷⁷Se{¹H}) NMR spectroscopy and single‐crystal X‐ray analysis. The reaction of 2 with propionyl chloride led to the formation of trans‐[Pd(SeC(O)CH₂CH₃)₂(PnBu₃)₂] ( 3 ), a trans‐bis(selenocarboxylato) palladium complex and thus established a new method for the formation of this type of complex. Complex 3 was characterized by ¹H, ¹³C{¹H}, ³¹P{¹H} and ⁷⁷Se{¹H} NMR spectroscopy and a single‐crystal X‐ray structure analysis.     

Subtle Interplay of Weak Intermolecular Interactions. Crystal Structures of Lead(II) Complexes with 4,4′‐Dimethyl‐2,2′‐bipyridine

Three adducts of the N,N′‐bidentate aromatic base 4,4′‐dimethyl‐2,2′‐bipyridine (dmbpy) of lead(II) salts, [Pb(dmbpy)₂(NO₃)₂] ( 1 ), [Pb(dmbpy)₂(ClO₄)₂] ( 2 ) and [Pb(dmbpy)(NCS)₂]_n ( 3 ) have been synthesized and characterized by elemental analysis, IR, ¹H‐NMR and ¹³C‐NMR spectroscopy and studied by thermal analysis as well as X‐ray crystallography. The single‐crystal structures of these complexes show that the 6s electrons of lead(II) constitute a stereochemically active lone pair (SALP). The coordination numbers of the Pb^II ions are eight and seven, respectively. The supramolecular features in these complexes are guided/controlled by weak directional intermolecular interactions.     

Synthesis,Characterization, and X‐ray Structures of Ru3(CO)9(dotpm)(L) Complexes [L = PPh3, P(C6H4Cl‐p)3, and PPh2(C6H4Br‐p)]

The reaction of Ru₃(CO)₁₀(dotpm) ( 1 ) [dotpm = (bis(di‐ortho‐tolylphosphanyl)methane)] and one equivalent of L [L = PPh₃, P(C₆H₄Cl‐p)₃ and PPh₂(C₆H₄Br‐p)] in refluxing n‐hexane afforded a series of derivatives [Ru₃(CO)₉(dotpm)L] ( 2 – 4 ), respectively, in ca. 67–70 % yield. Complexes 2 – 4 were characterized by elemental analysis (CHN), IR, ¹H NMR, ¹³C{¹H} NMR and ³¹P{¹H} NMR spectroscopy. The molecular structures of 2 , 3 , and 4 were established by single‐crystal X‐ray diffraction. The bidentate dotpm and monodentate phosphine ligands occupy equatorial positions with respect to the Ru triangle. The effect of substitution resulted in significant differences in the Ru–Ru and Ru–P bond lengths.     

Three‐dimensional Hemidirected Mixed‐ligand Lead(II) Coordination Polymer, [Pb2(bpa)2(SCN)3(NO3)]n (bpa = 1,2‐di(4‐pyridyl)ethane)

A new 3D hemidirected mixed‐ligand lead(II) coordination polymer with the ligand 1,2‐di(4‐pyridyl)ethane bpa) and the two metal coordinated anions nitrate and thiocyanate, [Pb₂(bpa)₂(SCN)₃(NO₃)]_n ( 1 ), has been synthesized and characterized by CHN elemental analysis, IR‐, ¹H‐ and ¹³C NMR spectroscopy. The single crystal X‐ray data of compound 1 show that the complex is a three‐dimensional coordination polymer with two different Pb atoms with stereoactive electron lone pairs and six‐ and five‐coordinate hemidirected geometries, respectively.     

Heteropolynuclear Sodium(I) Lead(II) Complex: Crystal and Molecular Structure of a Novel 3‐D Polymer, [(en)Pb(μ3‐ONO)2Na(μ3‐ONO)2Na(μ‐O2ClO2)Na]n

A novel 3D polymeric heteropolynuclear sodium(I) lead(II) complex containing different ligands, [NaPb(ClO₄)(en)(NO₂)₂] was synthesized and characterized by elemental analysis and IR, and ¹H‐, ¹³C‐, and ²⁰⁷Pb‐NMR spectroscopy. The single‐crystal X‐ray data of [NaPb(ClO₄)(en)(NO₂)₂]_n established that the complex is a three‐dimensional polymer, [(en)Pb(μ₃‐ONO)₂Na(μ₃‐ONO)₂Na(μ‐O₂ClO₂)Na]_n. The Pb and Na atoms have four‐ and eight‐coordinate geometry, respectively. The lone pair of electrons at the Pb^II atom is ‘stereochemically active’.     

Coordination Mode of the Nickel(II) Cation with N‐Diisopropoxyphosphinyl‐p‐bromothiobenzamide

Reaction of the potassium salt of N‐diisopropoxyphosphinyl‐p‐bromothiobenzamide p‐BrC₆H₄C(S)NHP(O)(OiPr)₂ ( HL ) with Ni(NO₃)₂ in aqueous EtOH leads to complex of formula [Ni(HL‐O)₂(L‐O,S)₂] ( 1 ). The structure of 1 was investigated by single crystal X‐ray diffraction analysis, IR, ¹H and ³¹P{¹H} NMR spectroscopy, MALDI and microanalysis. The nickel(II) ion in 1 has a tetragonal‐bipyramidal environment, (O^ax)₂(O^eq)₂(S^eq)₂, with two neutral ligand molecules coordinated in axial positions through the oxygen atoms of the P=O groups. The equatorial plane of bipyramide is formed by two anionic ligands involving 1,5‐O,S‐coordination mode. The chelating ligands are bound in trans configuration.     

Low‐temperature sol–gel transformation of methyl silicon precursors to silica‐based hybrid materials

Six new methyl silicon (IV) precursors of the type [MeSi{ON?C(R)Ar}₃] [when R = Me, Ar = 2‐C₅H₄N ( 1 ), 2‐C₄H₃O ( 2 ) or 2‐C₄H₃S ( 3 ); and when R = H, Ar = 2‐C₅H₄N ( 4 ), 2‐C₄H₃O ( 5 ) or 2‐C₄H₃S ( 6 )] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. ¹H and ¹³C{¹H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by ²⁹Si{¹H} NMR signals in the region expected for tetra‐coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds ( 2 and 4 ) were studied as single source molecular precursor for low‐temperature transformation to silica‐based hybrid materials using sol–gel technique. Formation of homogenous methyl‐bonded silica materials (MeSiO_3/2) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon‐methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPrⁱ)₃ in equimolar ratio in anhydrous toluene yielded a brown‐colored viscous liquid of the composition [MeSi{ON?C(CH₃)C₄H₃O}₃.Al(OPrⁱ)₃]. Spectroscopic techniques ¹H, ¹³C{¹H}, ²⁷Al{¹H} and ²⁹Si{¹H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m²/g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range. Copyright © 2008 John Wiley & Sons, Ltd.     

1H,89Y HMQC and Further NMR Spectroscopic and X‐ray Diffraction Investigations on Yttrium‐Containing Complexes Exhibiting Various Nuclearities

2D ¹H,⁸⁹Y heteronuclear shift correlation through scalar coupling has been applied to the chemical‐shift determination of a set of yttrium complexes with various nuclearities. This method allowed the determination of ⁸⁹Y NMR data in a short period of time. Multinuclear NMR spectroscopy as function of temperature, PGSE NMR‐diffusion experiments, heteronuclear NOE measurements, and X‐ray crystallography were applied to determine the structures of [Y₅(OH)₅(L ‐Val)₄(Ph₂acac)₆] ( 1 ) (Ph₂acac=dibenzoylmethanide, L ‐Val=L ‐valine), [Y( 2 )(OTf)₃] ( 3 ), and [Y₂( 4 )(OTf)₅] ( 5 ) ( 2 : [(S)P{N(Me)N?C(H)Py}₃], 4 : [B{N(Me)N?C(H)Py}₄]^?) in solution and in the solid state. The structures found in the solid state are retained in solution, where averaged structures were observed. NMR diffusion measurements helped us to understand the nuclearity of compounds 3 and 5 in solution. ¹H,¹⁹F HOESY and ¹⁹F,¹⁹F EXSY data revealed that the anions are specifically located in particular regions of space, which nicely correlated with the geometries found in the X‐ray structures.     

A Raman spectroscopic study of the phosphate mineral pyromorphite Pb5(PO4)3Cl

A series of selected pyromorphite minerals Pb₅(PO₄)₃Cl from different Australian localities has been studied by Raman spectroscopy complemented with selected infrared spectroscopy. The Raman spectrum of unsubstituted pyromorphite shows a single band at around 920 cm⁻¹ but for the natural minerals two bands at 919 and ∼932 cm⁻¹ attributed to the ν₁ (PO₄)³⁻ stretching vibration. The observation of multiple bands is attributed to the non-equivalence of phosphate units in the pyromorphite structure and the reduction in symmetry of the (PO₄)³⁻ units. This symmetry reduction is confirmed by the observation of multiple bands in both the ν₄ bending region (500–595 cm⁻¹) and the ν₂ bending region (350–500 cm⁻¹). The presence of isomorphic substitution of (PO₄)³⁻ by (AsO₄)³⁻ units is identified by the ν₁ symmetric stretching bands at around 824 and 851 cm⁻¹ and the ν₂ bending region around 331 and 354 cm⁻¹. Contrary to expectation Raman bands in the 3320–3700 cm⁻¹ region are observed and assigned to OH stretching bands of OH units resulting from the substitution of chloride anions in the pyromorphite structure. This study brings in to question the actual formula of natural pyromorphite as it is better represented as Pb₅(PO₄,AsO₄)₃(Cl,OH) · xH₂O.     

The structure and solubility of carbonated hydroxyl and chloro lead apatites

The properties of carbonated hydroxyl and chloro lead apatites, Pb₁₀(PO₄)₆(OH)₂ and Pb₁₀(PO₄)₆Cl₂, serve as models for the incorporation of carbonate into their medically important calcium analogs, and there is likely incorporation of carbonate in an insoluble lead phosphate phase during lead remediation. We have synthesized a series of carbonated lead hydroxyl- and lead chloro-apatites at 60–80 °C. The incorporation of carbonate into the apatite structure was documented by X-ray powder diffraction, IR and Raman spectroscopy, ²⁰⁷Pb solid state NMR spectroscopy, and elemental analysis. The carbonate content was determined by combustion analysis and confirmed by Raman spectroscopic analysis. As carbonate content increases in hydroxyl lead apatite, Raman spectra show changes in the phosphate stretching modes at 925 and 950 cm⁻¹, an increase in intensity and downshift of a new peak at 1050 cm⁻¹, and changes in the spectral features of the O–H stretch at about 3560 cm⁻¹. The variation in unit cell parameters for the chloro lead apatite as a function of carbonate content is similar to that documented for B-type substitution in calcium apatites. The ²⁰⁷Pb NMR spectra corroborate B-type substitution. For the hydroxyl lead apatite, the changes in cell parameters suggest a combination of A- and B-type substitution. Solubilities of the carbonated lead apatites, determined by ICP-MS, increase slightly at low to moderate carbonate content, but more strongly at ca. 5.0 wt.% carbonate content. K_sp values extrapolated to zero carbonate content reveal that the chloro lead apatite is indeed less soluble than the hydroxyl analog.     

Two‐Dimensional Holo‐ and Hemidirected Lead(II) Coordination Polymers: Synthetic,Spectroscopic, Thermal,and Structural Studies of [Pb(μ‐SCN)2(μ‐ebp)1.5]n and {[Pb(μ‐OAc)(μ‐ebp)](ClO4)}n (ebp=4,4′‐[(1E)‐Ethane‐1,2‐diyl]bis[pyridine]; OAc=Acetato)

Two new coordination polymers of Pb^II complexes with bridging 4,4′‐[(1E)‐ethane‐1,2‐diyl]bis[pyridine] (ebp), thiocyanato, and acetato ligands, [Pb(μ‐SCN)₂(μ‐ebp)_1.5]_n ( 1 ) and {[Pb(μ‐OAc)(μ‐ebp)](ClO₄)}_n ( 2 ), were synthesized and characterized by elemental analysis, FT‐IR, ¹H‐ and ¹³C‐NMR, thermal analysis, and single‐crystal X‐ray diffraction. In 1 , the Pb²⁺ ions are doubly bridged by both the ebp and the SCN⁻ ligands into a two‐dimensional polymeric network. The seven‐coordinate geometry around the Pb²⁺ ion in 1 is a distorted monocapped trigonal prism, in which the Pb²⁺ ions have a less‐common holodirected geometry. In 2 , the Pb²⁺ ions are bridged by AcO⁻ ligands forming linear chains, which are also further bridged by the neutral ebp ligands into a two‐dimensional polymeric framework. The Pb²⁺ ions have a five‐coordinate geometry with two N‐atoms from two ebp ligands and three O‐atoms of AcO⁻. Although ClO acts as a counter‐ion, it also makes weak interactions with the Pb²⁺ center. The arrangement of the ligands in 2 exhibits hemidirected geometry, and the coordination gap around the Pb²⁺ ion is possibly occupied by a configurationally active lone pair of electrons.     

Kristallstrukturelle,Festkörper‐31P‐CP/MAS‐NMR,TOSS, 31P‐COSY‐NMR und mechanistische Beiträge zur Koordinationschemie des Octacarbonyldicobalts mit den Liganden Bis(diphenylphosphanyl)amin,Bis(diphenylphosphanyl)methan und 1,1,1‐Tris(diphenylphosphanyl)ethan

Chemistry of Polyfunctional Molecules. 133. X‐Ray Crystal Structural, Solid‐state ³¹P CP/MAS NMR, TOSS, ³¹P COSY NMR, and Mechanistic Contributions to the Co‐ordination Chemistry of Octacarbonyldicobalt with the Ligands Bis(diphenylphosphanyl)amine, Bis(diphenylphosphanyl)methane, and 1,1,1‐Tris(diphenylphosphanyl)ethane Co₂(CO)₈ reacts with bis(diphenylphosphanyl)amine, HN(PPh₂)₂ (Hdppa, 1 ), in two steps to afford the known compound [Co(CO)(Hdppa‐κ²P)₂][Co(CO)₄] · 2 THF ( 6 a · 2 THF). The intermediate [Co(CO)₂(Hdppa‐κ²P) · (Hdppa‐κP)][Co(CO)₄] · dioxane · n‐pentane ( 5 · dioxane · n‐pentane) was isolated for the first time and was characterized by X‐ray analysis. The cation 5 ⁺ exhibits a slightly distorted trigonal‐bipyramidal geometry. Detailed ³¹P‐NMR investigations (solid‐state CP/MAS NMR, TOSS, ³¹P‐COSY, ³¹P‐EXSY) showed that the additional tautomer [Co(CO)₂(Hdppa‐κ²P)(Ph₂P–N=P(H)Ph₂‐κP)]⁺ ( 5 ′⁺) is present in solution. The tautomer equilibrium is slow in the NMR time scale. In contrast to the solid state only tetragonal pyramidal species of 5 are found in solution. At –90 °C there is slow exchange between the three diastereomeric species 5 a ⁺– 5 c ⁺. Compound 5 forms [Co(CO) · (Hdppa‐κ²P)₂]BPh₄ · THF ( 6 b · THF) in THF with NaBPh₄ under CO‐Elimination. A X‐ray diffraction investigation shows that the cation 6 ⁺ consists of a slightly distorted trigonal‐bipyramidal co‐ordination polyeder. However, a distorted tetragonal‐pyramidal structure has been found for the cation 7 ⁺ of the related compound [Co(CO)(dppm)₂][Co(CO)₄] · 2 THF ( 7 · 2 THF; dppm = bis(diphenylphosphanyl)methane, Ph₂PCH₂PPh₂). A comparison with the known [8] trigonal‐bipyramidal stereoisomer, ascertained for 7 ⁺ of the solvent‐free 7 , is described. In solutions of 6 a · 2 THF and 7 · 2 THF ¹³C{¹H}‐ and ³¹P{¹H}‐NMR spectra indicate an exchange of all CO and organophosphane molecules between cobalt(I) cation and cobalt(–I) anion. A concerted mechanism for the exchange process is discussed. CO elimination leads to discontinuance of the cyclic mechanism by forming binuclear substitution products such as the isolated Co₂(CO)₂ · (μ‐CO)₂(μ‐dppm)₂ · 0.83 THF ( 8 · 0.83 THF), which was characterized by spectroscopy and X‐ray analysis. For the dissolved [Co(CO)₂CH₃C(CH₂PPh₂)₃][Co(CO)₄] · 0.83 n‐pentane ( 9 a · 0.83 n‐pentane) no CO and triphos exchange processes between the cation and the anion are observed. Metathesis of 9 a · 0.83 n‐pentane with NaBPh₄ yields [Co(CO)₂CH₃C(CH₂PPh₂)₃]BPh₄ ( 9 b ) which has been characterized by single‐crystal X‐ray analysis. The cation shows a small distorted tetragonal‐pyramidal structure.     

X‐ray Diffraction and Solid‐State NMR Studies of a Germanium Binuclear Complex

A compound formulated as (C₄H₁₂N₂)[Ge₂(pmida)₂(OH)₂] ? 4 H₂O (where pmida^4?=N‐(phosphonomethyl)iminodiacetate and C₄H₁₂N₂²⁺=piperazinedium cation), containing the anionic [Ge₂(pmida)₂(OH)₂]^2? complex, has been synthesised by the hydrothermal approach and its structure determined by single‐crystal X‐ray diffraction analysis. Several high‐resolution solid‐state magic‐angle spinning (MAS) NMR techniques, in particular two‐dimensional ¹H–X(¹³C,³¹P) heteronuclear correlation (HETCOR) and ¹H–¹H homonuclear correlation (HOMCOR) experiments incorporating a frequency‐switched Lee–Goldburg (FS‐LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic–organic hybrids. We assigned the NMR resonances with the help of C ??? H and P ??? H internuclear distances obtained through systematic statistical analyses of the crystallographic data. The compound was further characterised by powder X‐ray diffraction techniques, IR and Raman spectroscopy, and by elemental and thermal analyses (thermogravimetric analysis and differential scanning calorimetry).     

Heteronuclear NMR Spectroscopy as a Surface‐Selective Technique: A Unique Look at the Hydroxyl Groups of γ‐Alumina.

The surface hydroxyl groups of γ‐alumina dehydroxylated at 500 °C were studied by a combination of one‐ and two‐dimensional homo‐ and heteronuclear ¹H and ²⁷Al NMR spectroscopy at high magnetic field. In particular, by harnessing ¹H–²⁷Al dipolar interactions, a high selectivity was achieved in unveiling the topology of the alumina surface. The terminal versus bridging character of the hydroxyl groups observed in the ¹H magic‐angle spinning (MAS) NMR spectrum was demonstrated thanks to ¹H–²⁷Al RESPDOR (resonance‐echo saturation‐pulse double‐resonance). In a further step the hydroxyl groups were assigned to their aluminium neighbours thanks to a {¹H}‐²⁷Al dipolar heteronuclear multiple quantum correlation (D‐HMQC), which was used to establish a first coordination map. Then, in combination with ¹H–¹H double quantum (DQ) MAS, these elements helped to reveal intimate structural features of the surface hydroxyls. Finally, the nature of a peculiar reactive hydroxyl group was demonstrated following this methodology in the case of CO₂ reactivity with alumina.     

Über Bleisilberphosphate mit Apatitstruktur

On Lead Silver Phosphates with the Apatite Structure The hitherto unknown leas silver phosphate (Pb₈Ag₂PO₄)₆ has been prepared. It has an apatite structure with unoccupied halide positions like the analogous lead alkali compounds and forms solid solutions with Pb₁₀(PO₄)₆O, Pb₁₀(PO₄)₆(OH)₂, and Pb₁₀(PO₄)₆Cl₂. At 800°C, Pb₈Ag₂(PO₄)₆ decomposes to solid Pb₃(PO₄)₂ and PbAgPO₄. (Pb, Ag) apatites have been precipitated from aqueous solutions. On the side being richer in Ag they can approximately be formulated as solid solutions between Pb₈Ag₂(PO₄)₆ and Pb₁₀(PO₄)₆(OH)₂. However, the i.r. spectrum reveals clear differences compared with thermal and hydrothermal preparations. The distribution of cations shows nonideal behaviour with reduced tendency for fixation of Ag⁺, if the content of Ag in the precipitate is high. The compound PbAgPO₄ decomposes below 520°C to Pb₈Ag₂(PO₄)₆ and Ag₃PO₄. The arsenate apatite Pb₈Ag₂(AsO₄)₆ decomposes below 530°C to Pb₃(AsO₄)₂ and Ag₃AsO₄.     

The structure of mimetite,arsenian pyromorphite and hedyphane – A Raman spectroscopic study

The minerals mimetite Pb₅(AsO₄)₃Cl, arsenian pyromorphite Pb₅(PO₄,AsO₄)₃Cl and hedyphane Pb₃Ca₂(AsO₄)₃Cl have been studied by Raman spectroscopy complimented with infrared spectroscopy. Mimetite is characterised by a band at 812–3 cm⁻¹ attributed to the A_g mode. For the arsenian pyromorphite this band is observed at 818 cm⁻¹ and for hedyphane at 819 cm⁻¹. For mimetite and hedyphane bands at 788 and 765 cm⁻¹ are attributed to A_u and E_1u vibrational modes and are both Raman and infrared active. For the arsenian pyromorphite, Raman bands at 917–1014 cm⁻¹ are attributed to phosphate stretching vibrations. Raman spectroscopy clearly identifies bands attributable to isomorphous substitution of arsenate by phosphate. The observation of low intensity bands in the 3200–3550 cm⁻¹ region are assigned to adsorbed water and OH units, thus indicating some replacement of chloride ions with hydroxyl ions.     

Characterization, conductivity and photocatalytic studies of AHfM(PO4)3 (A = Na and Ag; M = Ti and Zr) powders synthesized by sol–gel method

Materials belonging to NASICON family of compositions NaHfM(PO₄)₃ and AgHfM(PO₄)₃ (M = Ti and Zr) are prepared by sol–gel and ion exchange methods, respectively. Ethylene glycol is used as a gelating agent. All the compositions are characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, ³¹P MAS NMR, UV–Vis DRS, XPS and energy dispersive spectral methods. All these phosphates are crystallized in rhombohedral lattice with space group $R\overline{3} c$ R 3 ¯ c . These compounds exhibit characteristic PO₄ vibrational modes in their FT-IR spectra. The ³¹P MAS NMR gave broad signals indicating distribution of chemical environments around P ion. The dc and ac conductivity of AgHfM(PO₄)₃ (M = Ti and Zr) are higher compared to their sodium containing compounds. The Cole–Cole plots of impedance show semicircles between 373 and 623 K. The variation of dc conductivity with temperature follows the Arrhenius equation. The photocatalytic activity of all the samples was studied against methylene blue decomposition using sun light. AgHfM(PO₄)₃ (M = Ti and Zr) have shown higher photoactivity than the sodium containing Nasicons.     

Hydrogen phosphate and dihydrogen phosphate salts of 4‐amino­azobenzene

4‐Amino‐trans‐azobenzene {or 4‐[(E)‐phenyl­diazen­yl]aniline} can form isomeric salts depending on the site of protonation. Both orange bis{4‐[(E)‐phenyl­diazen­yl]anilinium} hydrogen phos­phate, 2C₁₂H₁₂N₃⁺·HPO₄²⁻, and purple 4‐[(E)‐phenyl­diazen­yl]­anilinium dihydrogen phosphate phosphoric acid solvate, C₁₂H₁₂N₃⁺·H₂PO₄⁻·H₃PO₄, (II), have layered structures formed through O—H⋯O and N—H⋯O hydrogen bonds. Additionally, azobenzene fragments in (I) are assembled through C—H⋯π inter­actions and in (II) through π–π inter­actions. Arguments for the colour difference are tentatively proposed.