Cs4P2Se10: A new compound discovered with the application of solid-state and high temperature NMR

The new compound Cs₄P₂Se₁₀ was serendipitously produced in high purity during a high-temperature synthesis done in a nuclear magnetic resonance (NMR) spectrometer. ³¹P magic angle spinning (MAS) NMR of the products of the synthesis revealed that the dominant phosphorus-containing product had a chemical shift of −52.8 ppm that could not be assigned to any known compound. Deep reddish brown well-formed plate-like crystals were isolated from the NMR reaction ampoule and the structure was solved with X-ray diffraction. Cs₄P₂Se₁₀ has the triclinic space group P-1 with a=7.3587(11) Å, b=7.4546(11) Å, c=10.1420(15) Å, α=85.938(2)°, β=88.055(2)°, and γ=85.609(2)° and contains the [P₂Se₁₀]⁴⁻ anion. To our knowledge, this is the first compound containing this anion that is composed of two tetrahedral (PSe₄) units connected by a diselenide linkage. It was also possible to form a glass by quenching the melt in ice water, and Cs₄P₂Se₁₀ was recovered upon annealing. The static ³¹P NMR spectrum at 350 °C contained a single peak with a −35 ppm chemical shift and a ∼7 ppm peak width. This study highlights the potential of solid-state and high-temperature NMR for aiding discovery of new compounds and for probing the species that exist at high temperature.     

Spectroscopic and structural characterization of Na2[(VO)2(ttha)]·8H2O (ttha = triethylenetetraamine-N,N,N′,N″,N′″,N′″-hexaacetate): Interpreting the results with density functional theory

Na₂[(V^IVO)₂(ttha)]·8 H₂O (ttha = triethylenetetraamine–N,N,N′,N″,N′″,N′″–hexaacetate ion), prepared by treating [VO(H₂O)₅][(VO)₂(ttha)]·4 H₂O with Na₆(ttha), has been characterized by single crystal X-ray diffraction, infrared spectroscopy, UV–Vis absorption spectroscopy, electron spin resonance spectroscopy, and modeled by density functional theory (DFT). The X-ray structure revealed a distorted octahedral geometry around each vanadium center. The electronic absorption spectrum of [(VO)₂(ttha)]²⁻ (aq) features absorptions at ca. 200 nm (ε > 13900 L mol⁻¹ cm⁻¹), 255 nm (ε = 3480 L mol⁻¹ cm⁻¹), 586 nm (ε = 33 L mol⁻¹ cm⁻¹), and 770 nm (ε = 38 L mol⁻¹ cm⁻¹). The time-dependent density functional theory (TDDFT) calculated electronic absorption spectrum was remarkably similar to the actual spectrum, and TDDFT predicts absorption peaks at 297, 330, 458, 656, and 798 nm. TDDFT assigned the peak at 798 nm to be the α spin HOMO → LUMO transition. Hence, the peak at 770 nm in the actual spectrum is most likely the α spin HOMO → LUMO transition. Moreover, the TDDFT calculations revealed that the α spin HOMO and LUMO are partly comprised of d orbitals on both vanadium centers, and the first derivative electron spin resonance spectrum also suggests that the two unpaired electrons in [(VO)₂(ttha)]²⁻ are localized near the vanadium centers.     

Dynamics of [Zn(D2O)6] in [Zn(D2O)6][SiF6] crystal as studied by 1D, 2D spectra and spin-lattice relaxation time of H NMR

The dynamics of [Zn(D₂O)₆]²⁺ in [Zn(D₂O)₆][SiF₆] was investigated by ²H NMR one-dimensional spectra, two-dimensional exchange spectra and spin-lattice relaxation time (T₁). The lineshapes of those spectra and T₁ were dominated by the 180° flip of the water molecules and the reorientation of [Zn(D₂O)₆]²⁺ about the C₃ axis. The variation of lineshape of the one-dimensional spectrum below room temperature can be explained by only the 180° flip of the water molecules. The spectrum at room temperature showed a typical shape due to the rapid 180° flip of water molecules. The change in lineshape of the one-dimensional ²H NMR spectrum is caused by the three-site jump of [Zn(D₂O)₆]²⁺ about its C₃ axis above 333 K. Information of the reorientation of [Zn(D₂O)₆]²⁺ below 333 K could not be obtained from the one-dimensional spectrum and T₁. In this temperature range, the two-dimensional exchange spectrum was effective for analysis of molecular motion. The effects of multiple motions, the 180° flip of the water molecules and the reorientation of [Zn(D₂O)₆]²⁺ about the C₃ axis, on the lineshape of the two-dimensional exchange spectrum were studied using spectral simulation.     

Silicon/aluminum and oxygen/nitrogen ordering in lanthanum U−phase (La3Si3Al3O12N2)

High-resolution ²⁹Si, ²⁷Al, ¹⁵N, and ¹⁷O MAS NMR spectra have been obtained for both glass and crystalline samples of lanthanum U-phase, La₃Si₃Al₃O₁₂N₂. Previous X-ray single-crystal studies have shown that this phase is iso-structural with rare-earth gallogermanates of the type Ln₃Ga₅GeO₁₄, the atomic arrangement consisting of layers of [(Si,Al)(O,N)₄] tetrahedra in the x, y plane of the hexagonal unit cell, linked together in the z-direction by [AlO₆] octahedra, with rare-earth cations occupying the large holes in this network. However, previous studies obtained only a limited amount of information about cation and anion ordering, mainly deduced from bond-length data. NMR spectra have not only enabled the change in structure from glass to crystalline ceramic to be monitored, but have also given detailed ordering information about the latter, indicating partial disorder of both (Si,Al) and (O,N) on their respective sites in the tetrahedra.     

Stabilisation of heterobimetallic networks by crown ethers and hydrogen-bonding in [Ni(H2O)6][Cu3Cl8(H2O)2] · (15-crown-5)2 · 2H2O: Structure and magnetism

[Ni(H₂O)₆][Cu₃Cl₈(H₂O)₂] · (15-crown-5)₂ · 2H₂O can be conveniently prepared by the interaction of NiCl₂ · 6H₂O, CuCl₂ · 2H₂O and 15-crown-5 in water. The X-ray crystal structure reveals an ionic complex involved in a hydrogen-bonded two dimensional network with the [Ni(H₂O)₆]²⁺ and [Cu₃Cl₈(H₂O)₂]²⁻ ions sandwiched between the 15-crown-5 macrocycles. The magnetic susceptibility data (4–300 K) and magnetisation isotherms (2–5.5 K; 0–5 T) are best interpreted in terms of intra-trimer ferromagnetic coupling within the [Cu₃Cl₈(H₂O)₂]²⁻ moieties, with J ∼ 6 cm⁻¹, and antiferromagnetic coupling between the trimers, the latter mediated by H-bonding pathways. Comparisons are made to other reported quaternary ammonium salts of [Cu₃Cl₈]²⁻ and [Cu₃Cl₁₂]⁶⁻, most of which display structures that involve close stacking of such Cu(II) trimers, rather than being of the present isolated, albeit H-bonded, types.     

Structural characterization of [Fe(NO)(mnt)2] salts

The iron dithiolene compounds [Fe₂(mnt)₄]²⁻ [1]²⁻ and [Fe(NO)(mnt)₂]ⁿ (n = 1−, [2]¹⁻; n = 2−, [2]²⁻) ([mnt]²⁻ = maleonitriledithiolate = [(NC)₂C₂S₂]²⁻) have been characterized structurally by X-ray diffraction as their [Et₄N]⁺ salts at 100 K. Dianion [2]²⁻ is prepared from [2]¹⁻ by reduction with Na[Et₃BH] and is observed to have a bent Fe-NO angle at 149.9(5)° in contrast to the linear configuration of Fe-NO in [2]¹⁻ (180.0°). The change from linear to bent binding mode for NO, an increase of more than 0.1 Å in the Fe-N bond length, and the relative invariance of the Fe-S distances for [2]²⁻ versus [2]¹⁻ indicate that the NO ligand is the site of reduction. The [Et₃NH]⁺ complex of [2]¹⁻ was also identified by crystallography and found to have hydrogen bonding contacts between [Et₃NH]⁺ and the cyano nitrogen atom of an [mnt]²⁻ ligand. Furthermore, relatively close S?S contacts (3.602-3.615 Å) occur between [2]¹⁻ anions, which pack together in an offset, head-to-head fashion. These S?S contacts are absent in the structure of [Et₄N][2]. Infrared spectra show an energy decrease for, and a significant broadening of, the NO bond stretching absorption peak in [2]²⁻, which is consistent with a bent NO ligand sampling a range of conformations both by facile pivoting about the Fe-N axis and by a breathing of the Fe-NO angle.     

Novel microporous zirconium silicate (K2ZrSi3O9·2H2O) from high temperature phase transformation

A new microporous zirconosilicate K₂ZrSi₃O₉·2H₂O (AV-15) has been prepared by high-temperature phase transformation at 910 °C. Its structure has been determined ab initio from powder X-ray diffraction data. The unit cell is orthorhombic, space group C222₁ (no. 20), Z=4 with cell dimensions: a=8.105(3), b=10.684(5), c=12.030(5) Å, V=1041.76(7) Å³. The framework connection of AV-15 is essentially the same as the previously reported sodium stannosilicate AV-10 while the locations of potassium and water molecules in the former are quite different from those of the sodium and water molecules in AV-10. In AV-10 sodium and water molecules form a sinucoidal chain, while potassium and water molecules build up a linear chain in AV-15. The water molecules in AV-15 are lost on heating with a typical zeolitic behaviour. SEM shows that the particle sizes and habits of AV-15 and parent umbite material are the same. The ²⁹Si MAS NMR spectrum of AV-15 displays two resonances at ca. −89.4 and −90.1 ppm in a 1:2 intensity ratio. Thermogravimetry analysis confirms the existence of water in this material.     

Ce10[Si10O9N17]Br, Nd10[Si10O9N17]Br and Nd10[Si10O9N17]Cl oxonitridosilicate halides with a new layered structure type

The isotypic oxonitridosilicate halides Ce₁₀[Si₁₀O₉N₁₇]Br, Nd₁₀[Si₁₀O₉N₁₇]Br and Nd₁₀[Si₁₀O₉N₁₇]Cl were obtained by the reaction of the respective lanthanide metals, their oxides and halides with “Si(NH)₂” in a radiofrequency furnace at temperatures around 1800 °C, using CsBr, resp. CsCl, as a flux. The crystal structures were determined by single-crystal X-ray diffraction (Pbam, no. 55, Z=2; Ce/Br: a=10.6117(9) Å, b=11.2319(10) Å, c=11.688(8) Å, R1=0.0356; Nd/Br: a=10.523(2) Å, b=11.101(2) Å, c=11.546(2) Å, R1=0.0239; Nd/Cl: a=10.534(2) Å, b=11.109(2) Å, c=11.543(2) Å, R1=0.0253) and represent a new layered structure type. The structure refinements were performed utilizing an O/N-distribution model according to Paulings rules, i.e. nitrogen was positioned on all bridging sites and mixed O/N-occupation was assumed on the terminal sites resulting in charge neutrality of the compounds. The layers consist of condensed [SiN₂(O/N)₂] and [SiN₃(O/N)] tetrahedra of Q² and Q³ type. The chemical composition of the compounds was derived from chemical analyses for Nd₁₀[Si₁₀O₉N₁₇]Br and electron probe micro analyses (EPMA) for all three compounds. The results of IR spectroscopic investigations are reported.     

Thermochemistry of NaRb[B4O5(OH)4]·4H2O

The enthalpies of solution of NaRb[B₄O₅(OH)₄]·4H₂O in approximately 1 mol dm⁻³ aqueous hydrochloric acid and of RbCl in aqueous (hydrochloric acid + boric acid + sodium chloride) were determined. From these results and the enthalpy of solution of H₃BO₃ in approximately 1 mol dm⁻³ HCl(aq) and of sodium chloride in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(5128.02 ± 1.94) kJ mol⁻¹ for NaRb[B₄O₅(OH)₄]·4H₂O was obtained from the standard molar enthalpies of formation of NaCl(s), RbCl(s), H₃BO₃(s) and H₂O(l). The standard molar entropy of formation of NaRb[B₄O₅(OH)₄]·4H₂O was calculated from the Gibbs free energy of formation of NaRb[B₄O₅(OH)₄]·4H₂O computed from a group contribution method.     

Raman spectra and O NMR study effects of CaCl2 and MgCl2 on water structure

With various concentrations of CaCl₂ and MgCl₂ aqueous solution below 1.0 mol/l, Raman spectra of water in the OH stretch region of 2500-4000 cm⁻¹ and ¹⁷O NMR chemical shift of water are measured and the Raman spectra are deconvoluted. Both Raman spectra and ¹⁷O NMR of water show that the effect of Ca²⁺ on water structure is stronger than that of Mg²⁺. CaCl₂ and MgCl₂ destroy four hydrogen bonded water structure, but promote median water cluster size.     

Aqua bridged Cu2 dimer of a heptadentate N4O3 coordinating ligand: Synthesis,structure and magnetic properties

The N₄O₃ coordinating heptadentate imidazolidinyl phenolate ligand, H₃L (2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) forms with Cu(II) a rare aqua bridged complex [{Cu₂(μ-L)(μ-H₂O)}₂](ClO₄)₂ · 4.5H₂O (1 · 4.5H₂O). Complex 1 · 4.5H₂O contains two crystallographically different but chemically equivalent dinuclear [Cu₂(μ-L)(μ-H₂O)]⁺ cationic units in the asymmetric unit. The copper atoms of each dinuclear unit are in a distorted square-pyramidal environment and are held together by phenolate, imidazolidinyl and aqua bridges with a Cu···Cu separation of av. 3.34 Å. The compound exhibits a very weak antiferromagnetic exchange interaction (J = −0.77 cm⁻¹, ? = −2 J?₁?₂) between the two copper(II) (S = 1/2) ions. The ¹H NMR spectrum of the complex shows a total of 17 hyperfine shifted peaks, as expected from the idealized C_s symmetry of the compound, spread over a very large window of chemical shift, spanning about 250 ppm. The complex, having an appropriate intermetallic separation for catechol binding, shows catecholase like activity in MeCN at 25 °C, with the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ).     

Separation and quantification of [RhCln(H2O)6−n] (n = 0-6) complexes, including stereoisomers, by means of ion-pair HPLC-ICP-MS

A hyphenated ion-pair (tetrabutylammonium chloride—TBACl) reversed phase (C₁₈) HPLC-ICP-MS method (High Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectroscopy) for anionic Rh(III) aqua chlorido-complexes present in an HCl matrix has been developed. Under optimum chromatographic conditions it was possible to separate and quantify cationic Rh(III) complexes (eluted as a single band), [RhCl₃(H₂O)₃], cis-[RhCl₄(H₂O)₂]⁻, trans-[RhCl₄(H₂O)₂]⁻ and [RhCl_n(H₂O)_6−n]³⁻ⁿ (n = 5, 6) species. The [RhCl_n(H₂O)_6−n]³⁻ⁿ (n = 5, 6) complex anions eluted as a single band due to the relatively fast aquation of [RhCl₆]³⁻ in a 0.1 mol L⁻¹ TBACl ionic strength mobile phase matrix. Moreover, the calculated t_1/2 of 1.3 min for [RhCl₆]³⁻ aquation at 0.1 mol kg⁻¹ HCl ionic strength is significantly lower than the reported t_1/2 of 6.3 min at 4.0 mol kg⁻¹ HClO₄ ionic strength. Ionic strength or the activity of water in this context is a key parameter that determines whether [RhCl_n(H₂O)_6−n]³⁻ⁿ (n = 5, 6) species can be chromatographically separated. In addition, aquation/anation rate constants were determined for [RhCl_n(H₂O)_6−n]³⁻ⁿ (n = 3-6) complexes at low ionic strength (0.1 mol kg⁻¹ HCl) by means of spectrophotometry and independently with the developed ion-pair HPLC-ICP-MS technique for species assignment validation. The Rh(III) samples that was equilibrated in differing HCl concentrations for 2.8 years at 298 K was analyzed with the ion-pair HPLC method. This analysis yielded a partial Rh(III) aqua chlorido-complex species distribution diagram as a function of HCl concentration. For the first time the distribution of the cis- and trans-[RhCl₄(H₂O)₂]⁻ stereoisomers have been obtained. Furthermore, it was found that relatively large amounts of ‘highly’ aquated [RhCl_n(H₂O)_6−n]³⁻ⁿ (n = 0-4) species persist in up to 2.8 mol L⁻¹ HCl and in 1.0 mol L⁻¹ HCl the abundance of the [RhCl₅(H₂O)]²⁻ species is only 8-10% of the total, far from the 70-80% as previously proposed. A 95% abundance of the [RhCl₆]³⁻ complex anion occurs only when the HCl concentration is above 6 mol L⁻¹. The detection limit for a Rh(III) species eluted from the column is below 0.147 mg L⁻¹.     

Cl/Cl isotope effects in Rh NMR of [RhCln(H2O)6−n] complex anions in hydrochloric acid solution as a unique ‘NMR finger-print’ for unambiguous speciation

A detailed analysis of the ³⁵Cl/³⁷Cl isotope effects observed in the 19.11 MHz ¹⁰³Rh NMR resonances of [RhCl_n(H₂O)_6−n]³⁻ⁿ complexes (n = 3–6) in acidic solution at 292.1 K, shows that the ‘fine structure’ of each ¹⁰³Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These ³⁵Cl/³⁷Cl isotope effects in the ¹⁰³Rh NMR resonance of the [Rh^35/37Cl₆]³⁻ species manifest only as a result of the statistically expected ³⁵Cl/³⁷Cl isotopologues, whereas for the aquated species such as for example [Rh^35/37Cl₅(H₂O)]²⁻, cis-[Rh^35/37Cl₄(H₂O)₂]⁻ as well as the mer-[Rh^35/37Cl₃(H₂O)₃] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-[RhCl₄(H₂O)₂]⁻, trans-[RhCl₄(H₂O)₂]⁻, fac-[RhCl₃(H₂O)₃] and mer-[RhCl₃(H₂O)₃] based on the ¹⁰³Rh NMR line shape, other than on the basis of their very similar δ(¹⁰³Rh) chemical shift. The ¹⁰³Rh NMR resonance structure thus serves as a novel and unique ‘NMR-fingerprint’ leading to the unambiguous assignment of [RhCl_n(H₂O)_6−n]³⁻ⁿ complexes (n = 3–6), without reliance on accurate δ(¹⁰³Rh) chemical shifts.     

Phase transitions and molecular motions in [Cd(H2O)6](BF4)2 studied by DSC, H and F NMR and FT-MIR

Two solid phase transitions of [Cd(H₂O)₆](BF₄)₂ occurring on heating at T_C2=183.3 K and T_C1=325.3 K, with 2 K and 5 K hysteresis, respectively, were detected by differential scanning calorimetry (DSC). High value of entropy changes indicated large orientational disorder of the high temperature and intermediate phase. Nuclear magnetic resonance (¹H NMR and ¹⁹F NMR) relaxation measurements revealed that the phase transitions at T_C1 and T_C2 were associated with a drastic and small change, respectively, of the both spin-lattice relaxation times: T₁(¹H) and T₁(¹⁹F). These relaxation processes were connected with the “tumbling” motions of the [Cd(H₂O)₆]²⁺, reorientational motions of the H₂O ligands, and with the iso- and anisotropic reorientation of the BF₄⁻ anions. The cross-relaxation effect was observed in phase III. The line width and the second moment of the ¹H and ¹⁹F NMR line measurements revealed that the H₂O reorientate in all three phases of the title compound. On heating the onset of the reorientation of 3 H₂O in the [Cd(H₂O)₆]⁺², around the three-fold symmetry axis of these octahedron, causes the isotropic reorientation of the whole cation. The BF₄⁻ reorientate isotropically in the phases I and II, but in the phase III they perform slow reorientation only about three- or two-fold axes. A small distortion in the structure of BF₄⁻ as well as of [Cd(H₂O)₆]²⁺ is postulated. The temperature dependence of the bandwidth of the O-H stretching mode measured by Fourier transform middle infrared spectroscopy (FT-MIR) indicated that the activation energy for the reorientation of the H₂O did not change much at the T_C2 phase transition.     

Synthesis, characterization, and thermochemistry of a new form of 2MgO·3B2O3·17H2O

A new magnesium borate, β-2MgO·3B₂O₃·17H₂O, has been synthesized by the method of phase transformation of double salt and characterized by XRD, IR, and Raman spectroscopy as well as by TG. The structural formula of this compound was Mg[B₃O₃(OH)₅]·6H₂O. The enthalpy of solution of β-2MgO·3B₂O₃·17H₂O in approximately 1 mol dm⁻³ HCl was determined. With the incorporation of the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(10256.39±4.93) kJ mol⁻¹ of β-2MgO·3B₂O₃·17H₂O was obtained. Thermodynamic properties of this compound was also calculated by group contribution method.     

[P3N3F5NS(O)Cl] and [{P4N4F6(NS(Cl)N)}2], the first chloro imino- and chloro bis(imino) sulfinates

In CH₃CN solution at −30 °C, [TAS]⁺[P₃N₃F₅NS(O)F]⁻ (2) is formed from TASF and P₃N₃F₅NSO, the compound readily decomposes to give P₃N₃F₆ and [TAS]⁺[NSO]⁻. [TAS]⁺[P₃N₃F₅NS(O)Cl]⁻ (3) and [TAS⁺]₂ [{P₄N₄F₆(NS(Cl)N)}₂]²⁻ (5) were prepared from TASCl and P₃N₃F₅NSO and 1,5-P₄N₄F₆(NSO)₂, respectively, and characterised by X-ray crystallography.     

Activation of the Si-H bond of Et2SiH2 in photochemical reaction with W(CO)6: Spectroscopic characterization of intermediate W-Si compounds and the revisited crystal structure of the bis{(μ-η-hydridodiethylsilyl)tetracarbonyltungsten(I)} complex [{W(μ-η-H-SiEt2)(CO)4}2]

The photochemical reaction of W(CO)₆ with diethylsilane has been used to generate new tungsten-silicon compounds varying in stability. The initially formed η²-silane intermediate complex [W(CO)₅(η²-H-SiHEt₂)], characterized by two equal-intensity doublets with ²J_H-H = 10 Hz at δ = 5.10 (¹J_Si-H = 217 Hz) and δ = −8.05 (¹J_W-H = 38 Hz, ¹J_Si-H = 93 Hz), was detected by the ¹H NMR spectroscopy (methylcyclohexane-d₁₄, −10 °C). The η²-silane complex was converted in the dark to give more stable species. One of them was characterized by two equal-intensity proton signals observed as doublets with ²J_H-H = 5.2 Hz at δ = −8.25 and −10.39 ppm. The singlet proton resonance at δ = −9.31 flanked by ²⁹Si and ¹⁸³W satellites (¹J_Si-H = 43 Hz, ²J_Si-H = 34 Hz, ¹J_W-H = 40 Hz) was assigned to the agostic proton of the W(η²-H-SiEt₂) group in the most stable compound isolated from the photochemical reaction products in crystalline form. The molecular structure of the bis{(μ-η²-hydridodiethylsilyl)tetracarbonyltungsten(I)} complex [{W(μ-η²-H-SiEt₂)(CO)₄}₂] was established by single-crystal X-ray diffraction studies. The tungsten hydride observed in the ¹H NMR spectrum at δ = −9.31 was located in the structure at a chemically reasonable position between the W and Si atoms of the W-Si bond of the bridging silyl ligand. The reactivity of photochemically generated W-Si compounds towards norbornene, cyclopentene, diphenylacetylene, acetone, and water was studied. As was observed by IR and NMR spectroscopy, the η²-silane ligand in the complex [W(CO)₅(η²-H-SiHEt₂)] is very easily replaced by an η²-olefin or η²-alkyne ligand.     

Six-coordinate organotin(IV) complexes formed using the Kläui ligands; [CpCo{P(OR′)2O}3]SnR3 − nCln

The complexes [CpCo{P(OR′)₂O}₃]SnR_3 − nCl_n [R′ = Me, Et; R = Ph, Me] are readily prepared from the corresponding organotin chloride and the sodium salt of the Kläui ligands. The X-ray crystal structures of the full series are reported for R = Ph, n = 0-3, and these show that they are all six-coordinate, including the Ph₃Sn derivative which is the first example of a SnC₃O₃ coordination sphere. ¹H, ¹³C, ³¹P and ¹¹⁹Sn NMR spectra are reported, and interpreted in terms of significant second-order effects and fluxional processes.     

Synthesis, crystal structure and optical properties of a novel sodium lead pentaborate, NaPbB5O9

A novel sodium lead pentaborate, NaPbB₅O₉, has been successfully synthesized by standard solid-state reaction. The single-crystal X-ray structural analysis showed that NaPbB₅O₉ crystallizes in the monoclinic space group P2₁/c with a=6.5324(10) Å, b=13.0234(2) Å, c=8.5838(10) Å, β=104.971(10)°, and Z=4. The crystal structure is composed of double ring [B₅O₉]³⁻ units, [PbO₇] and [NaO₇] polyhedra. [B₅O₉]³⁻ groups connect with each other forming two-dimensional infinite _∞[B₅O₉]³⁻ layers, while [PbO₇] and [NaO₇] polyhedra are located between the layers. [PbO₇] polyhedra linked together via corner-sharing O atom forming novel infinite _∞[PbO₆] chains along the c axis. The thermal behavior, IR spectrum and the optical diffuse reflectance spectrum of NaPbB₅O₉ were reported.     

Lithium monosilicide (LiSi), a low-dimensional silicon-based material prepared by high pressure synthesis: NMR and vibrational spectroscopy and electrical properties characterization

Lithium monosilicide (LiSi) was formed at high pressures and high temperatures (1.0-2.5 GPa and 500-700°C) in a piston-cylinder apparatus. This compound was previously shown to have an unusual structure based on 3-fold coordinated silicon atoms arranged into interpenetrating sheets. In the present investigation, lowered synthesis pressures permitted recovery of large (150-200 mg) quantities of sample for structural studies via NMR spectroscopy (²⁹Si and ⁷Li), Raman spectroscopy and electrical conductivity measurements. The ²⁹Si chemical shift occurs at −106.5 ppm, intermediate between SiH₄ and Si(Si(CH₃)₃)₄, but lies off the trend established by the other alkali monosilicides (NaSi, KSi, RbSi, CsSi), that contain isolated Si₄⁴⁻ anions. Raman spectra show a strong peak at 508 cm⁻¹ due to symmetric Si-Si stretching vibrations, at lower frequency than for tetrahedrally coordinated Si frameworks, due to the longer Si-Si bonds in the 3-coordinated silicide. Higher frequency vibrations occur due to asymmetric stretching. Electrical conductivity measurements indicate LiSi is a narrow-gap semiconductor (E_b∼0.057 eV). There is a rapid increase in conductivity above T=450 K, that might be due to the onset of Li⁺ mobility.