Cation exchange, interlayer spacing, and thermal analysis of Na/Ca-montmorillonite modified with alkaline and alkaline earth metal ions

Na-montmorillonites were exchanged with Li⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra²⁺ and Ca²⁺. Montmorillonites with interlayer cations Li⁺ or Na⁺ have remarkable swelling capacity and keep excellent stability. It is shown that metal ions represent different exchange ability as follows: Cs⁺?>?Rb⁺?>?K⁺?>?Na⁺?>?Li⁺ and Ba²⁺?>?Sr²⁺?>?Ca²⁺?>?Mg²⁺. The cation exchange capacity with single ion exchange capacity illustrates that Mg²⁺ and Ca²⁺ do not only take part in cation exchange but also produce physical adsorption on the montmorillonite. Although interlayer spacing d ₀₀₁ depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d ₀₀₁ value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36?C84?°C), the dehydration of interlayer water and the chemical-adsorption water (47?C189?°C) and dehydration of bound water of interlayer metal cation (108?C268?°C). Data show that the quantity and hydration energy of ions adsorbed on montmorillonite influence the water content in montmorillonite. Mg²⁺-modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.     

Poly(vinylamine) complexes with f‐block salts from the lanthanide series that exhibit significant glass‐transition temperature enhancement

Six f‐block salts from the lanthanide series form complexes with poly(vinyl amine) and increase the glass‐transition temperature of the polymer. Results for poly(vinylamine) complexes with EuCl₃(H₂O)₆ and TbCl₃(H₂O)₆ surpass those for d⁷ cobalt complexes that were studied previously. The glass‐transition temperature increases by 49 °C per mol % Eu³⁺ and 50 °C per mol % Tb³⁺, up to 2 mol % of the f‐block cations. At 5 mol % Eu³⁺, T_g is slightly higher than 250 °C with no visual evidence of thermal degradation of either component in the complex. This corresponds to a T_g enhancement of almost 200 °C with respect to the undiluted polymer. The increases in T_g for these lanthanide complexes with poly(vinylamine) obey the following trend: up to 2 mol % of the f‐block cation. With the exception of Gd(CH₃COO)₃, which contains different anionic ligands than all of the other trichlorides, this trend correlates inversely with the highest dehydration/dehydrochlorination temperature of each undiluted lanthanide salt, as measured via calorimetry above the melting point and verified by thermogravimetry. Waters of hydration and amino sidegroups undergo ligand substitution in the coordination sphere of the lanthanides. Since lanthanide cations are classified as hard acids, it is not unreasonable that they form complexes with the nitrogen lone pair in the amino sidegroup of the polymer, which is classified as a hard base. Micro‐clustering of several amino side groups reduces chain mobility significantly in the vicinity of each metal center, produces coordination crosslinks, and increases T_g. Complementary solution studies reveal that hydrogels form with swelling ratios between 20 and 50 at Eu³⁺ mole fractions between 0.01 and 0.05 with respect to poly(vinylamine). Infrared spectroscopic observations suggest that the amino nitrogen lone pair in poly(vinylamine) interacts with these lanthanide metal centers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1931–1938, 2000     

Hydrodebromination of bromoarenes using Grignard reagents catalyzed by metal ions

The metal salts, FeCl^·₂4H₂O, FeCl₃, NiCl₂, CoCl₂, CuBr and some iron complexes were found to be efficient catalysts for hydrodebromination of bromoarenes under mild reaction conditions with two equivalents of Grignard reagents. Among them, the iron systems showed the best behavior regarding economic and environmental considerations. All the alkyl Grignard reagents (except CH₃MgCl) and p‐tolylMgBr were promising reductive reagents with the formation of their homo‐coupling products. Copyright © 2008 John Wiley & Sons, Ltd.     

Cyanidosilicates—Synthesis and Structure

Starting from fluoridosilicate precursors in neat cyanotrimethylsilane, Me₃Si?CN, a series of different ammonium salts [R₃NMe]⁺ (R=Et, ⁿPr, ⁿBu) with the novel [SiF(CN)₅]^2? and [Si(CN)₆]^2? dianions was synthesized in facile, temperature controlled F^?/CN^? exchange reactions. Utilizing decomposable, non‐innocent cations, such as [R₃NH]⁺, it was possible to generate metal salts of the type M₂[Si(CN)₆] (M⁺=Li⁺, K⁺) via neutralization reactions with the corresponding metal hydroxides. The ionic liquid [BMIm]₂[Si(CN)₆] (m.p.=72 °C, BMIm=1‐butyl‐3‐methylimidazolium) was obtained by a salt metathesis reaction. All the synthesized salts could be isolated in good yields and were fully characterized.     

The New Cesium Praseodymium Thiophosphate Cs3Pr5[PS4]6

Transparent platelet‐shaped green single crystals of the title compound were obtained by the reaction of cesium bromide, praseodymium, sulfur, and red phosphorus in the molar ratio 1:2:8:2 with an excess of CsBr as flux in evacuated silica ampoules at 950 °C for fourteen days. Cs₃Pr₅[PS₄]₆ crystallizes monoclinically in the space group C2/c (a = 1627.78(7), b = 1315.09(6), c = 2110.45(9) pm, β = 103.276(5)°; Z = 4). Its crystal structure is different from all the other alkali‐metal containing ortho‐thiophosphates of the lanthanides, since it is not possible to formulate a layer containing the praseodymium centered sulfur polyhedra ([PrS₈]^13—, d(Pr—S) = 286 — 307 pm) and the isolated [PS₄]^3— tetrahedra (d(P—S) = 202 — 207 pm, ?(S—P—S) = 104 — 106°). All these tetrahedra are edge‐sharing with the metal polyhedra to build up a framework instead. The coordination sphere of the half occupied (Cs2)⁺ cations (CN = 10 + 2) can be described as two six‐membered sulfur rings in chair conformation containing a “cesium‐pair” in the middle. In contrast the (Cs1)⁺ cations are surrounded in the not unusual configuration of tetracapped trigonal prisms (CN = 10, better 10 + 2 as well).     

Well‐Defined Single‐Site Monohydride Silica‐Supported Zirconium from Azazirconacyclopropane

The silica‐supported azazirconacyclopropane ?SiOZr(HNMe₂)(η²‐NMeCH₂)(NMe₂) ( 1 ) leads exclusively under hydrogenolysis conditions (H₂, 150 °C) to the single‐site monopodal monohydride silica‐supported zirconium species ?SiOZr(HNMe₂)(NMe₂)₂H ( 2 ). Reactivity studies by contacting compound 2 with ethylene, hydrogen/ethylene, propene, or hydrogen/propene, at a temperature of 200 °C revealed alkene hydrogenation.     

Anionic polymerization of methyl methacrylate initiated with late transition‐metal halides/organolithium/triisobutylaluminum systems

Anionic polymerization of methyl methacrylate (MMA) initiated with late transition‐metal halides [manganese chloride (MnCl₂), iron dichloride (FeCl₂), iron trichloride (FeCl₃), cobalt chloride (CoCl₂), or nickel bromide (NiBr₂)]/organolithium [nButyllithium (nBuLi) or phenyllithium (PhLi)]/triisobutylaluminum (iBu₃Al) systems is described. Except for the system with NiBr₂, the polymerizations of MMA afforded narrow molecular weight distribution poly(methyl methacrylate)s (PMMAs) with high molecular weights in quantitative yields at 0 °C in toluene. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) analyses of the PMMAs obtained by the systems with FeCl₂, FeCl₃, and CoCl₂ revealed that the polymers had hydrogen (H) at both chain ends. Accordingly, the reaction of the transition‐metal halides with the organolithium in the presence of iBu₃Al should result in the formation of transition‐metal hydride [M‐H]^? species, which was nucleophilic enough to initiate the MMA polymerization. Because the presence of a six‐membered cyclic structure resulting from backbiting was confirmed from the MALDI‐TOF MS analyses of the PMMA obtained with the metal halide (FeCl₂, FeCl₃, or CoCl₂)/organolithium systems in the absence of iBu₃Al, the introduction of H at the ω‐chain end indicated that iBu₃Al should prevent the backbiting. However, the MnCl₂/nBuLi/iBu₃Al initiating system gave PMMAs bearing H at the α chain end and six‐membered cyclic structure at the ω chain end. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1962–1977, 2003     

The First Rare Earth Metal Thioborate: Synthesis and Crystal Structure of EuB2S4

Systematic studies on thio‐ and selenoborates containing heavier metal cations led to the new crystalline phase EuB₂S₄. The crystal structure of the europium metathioborate reveals polymeric [(B₂S₄)^2—]_n anions and divalent Eu‐cations which are connected via ionic interactions. The building blocks of the anions consist of BS₄‐tetrahedra. Condensation of these BS₄‐tetrahedra leads to corner‐ and edge‐sharing 2D‐networks running parallel to (1 0 0). Evacuated carbon coated silica tubes were used as reaction vessels since temperatures up to 990 K were applied. EuB₂S₄ crystallizes in the monoclinic space group P2₁/c (no. 14) with a = 6.4331(6)Å, b = 14.099(1)Å, c = 6.0731(6)Å, β = 110.55(8)° and Z = 4.     

Solvothermal Synthesis and Crystal Structure of a Novel Inorganic—Organic Hybrid Material,Fe2O（OH）（C5H4NCOO）SO4

IntroductionThereisatremendousactivityforthepastyearsintheareaofinorganic organichybridmaterialsinviewoftheirdi versifiedstructuresandinterestingproperties.1,2 Theeffortshavebeenmadeinsynthesizingandcharacterizingtheclassofmaterials.3Thecontrolofinorganicstructurebyanorganiccomponentrevealsaninteractivestructuralrelationinthema terials .4 Assemblyofaninorganic organichybridmaterialcanbeachievedbyselectingorganiccomponents (multidentateligands)andinorganiccomponents (transitionmetalions ,metalo…     

Separation of common monovalent and divalent cations by ion chromatography on calcined silica gel cation-exchange stationary phases, with tyramine-oxalic acid-containing crown ether mobile phases and indirect photometric detection

Summary Pure silica gels (Pia Seed 5S-60-SIL) calcined at 200, 400, 600, 800 and 1000°C for 5 h have been used as cation-exchange stationary phases in ion chromatography with indirect photometric detection for common monovalent and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺ and Ca²⁺); 0.75mm tyramine (4-(2-aminoethyl)phenol)-0.25mm oxalic acid, pH 5.0, containing crown ethers (18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) or 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)) was used as mobile phase. With increasing calcination temperature, the amounts of the crown ethers adsorbed on the calcined silica gel column increased and, consequently, the effect of the crown ethers as retention modifiers for these cations increased. Excellent simultaneous separation and highly sensitive detection of these cations at 275 nm were achieved in 17 min by use of a 150 mm×4.6 mm i.d. column packed with silica gel calcined at 1000°C and use of 0.75mm tyramine-0.25mm oxalic acid, pH 5.0, containing either 0.5mm 18-crown-6 or 5.0mm 15-crown-5 as mobile phase.     

Na2ZrS3: Ein ternäres Sulfid des Zirconiums mit aufgefüllter AlCl3‐Struktur

Na₂ZrS₃: A Ternary Zirconium Sulfide with Stuffed AlCl₃‐type Structure Dark green, plate‐like single crystals of Na₂ZrS₃ (monoclinic, C2/m; a = 664.69(6), b = 1152.5(1), c = 695.48(7) pm, β = 108.78(1)°; Z = 4) are obtained along with pale yellow platelets of NaZr₂N₂SCl (trigonal, R3m; a = 363.56(3), c = 2951.2(4) pm; Z = 3) upon oxidation of zirconium metal with sulfur and sodium azide (NaN₃) in the presence of fluxing NaCl (molar ratio 7:6:2:3) in evacuated silica tubes at 850°C within three weeks. The crystal structure is best described as stuffed AlCl₃ type with all cations (Na⁺ and Zr⁴⁺) in octahedral coordination of the S^2– anions, which build up a cubic closest packed host lattice. The internuclear metal sulfur distances range from 276 to 296 pm for all three crystallographically different Na⁺ cations, and from 258 to 260 pm for Zr⁴⁺.     

Novel Alkaline Earth Metal Chalcogenoborates: Syntheses and Crystal Structures of Sr4.2Ba2.8(BS3)4S and Ba7(BSe3)4Se

Systematic studies on quaternary thio‐ and selenoborates containing heavier alkaline earth metal cations led to the two new isotypic crystalline phases Sr_4.2Ba_2.8(BS₃)₄S and Ba₇(BSe₃)₄Se. Both compounds consist of trigonal‐planar BQ₃ (Q = S, Se) units, isolated Q^2– anions and the corresponding counter‐ions. The two new chalcogenoborates were prepared in solid state reactions from the metal sulfides (selenides), amorphous boron and sulfur (selenium). Evacuated carbon coated silica tubes were used as reaction vessels since temperatures up to 870 K were applied. Sr_4.2Ba_2.8(BS₃)₄S and Ba₇(BSe₃)₄Se crystallize in the monoclinic space group C2/c (no. 15) with a = 9.902(3) Å, b = 23.504(9) Å, c = 9.884(3) Å, β = 90.01(3)° and Z = 4 in the case of the thioborate, while for the selenoborate the lattice parameters a = 10.513(2) Å, b = 25.021(5) Å, c = 10.513(2) Å, β = 90.10(3)° were determined. X‐ray powder patterns are compared to calculated diffraction data obtained from single crystal X‐ray structure determination.     

Porphyrins Fused to N‐Heterocyclic Carbenes (NHCs): Modulation of the Electronic and Catalytic Properties of NHCs by the Central Metal of the Porphyrin

We report herein a detailed study of the use of porphyrins fused to imidazolium salts as precursors of N‐heterocyclic carbene ligands 1 M . Rhodium(I) complexes 6 M – 9 M were prepared by using 1 M ligands with different metal cations in the inner core of the porphyrin (M=Ni^II, Zn^II, Mn^III, Al^III, 2H). The electronic properties of the corresponding N‐heterocyclic carbene ligands were investigated by monitoring the spectroscopic changes occurring in the cod and CO ancillary ligands of [( 1 M )Rh(cod)Cl] and [( 1 M )Rh(CO)₂Cl] complexes (cod=1,5‐cyclooctadiene). Porphyrin–NHC ligands 1 M with a trivalent metal cation such as Mn^III and Al^III are overall poorer electron donors than porphyrin–NHC ligands with no metal cation or incorporating a divalent metal cation such as Ni^II and Zn^II. Imidazolium salts 3 M (M=Ni, Zn, Mn, 2H) have also been used as NHC precursors to catalyze the ring‐opening polymerization of L ‐lactide. The results clearly show that the inner metal of the porphyrin has an important effect on the reactivity of the outer carbene.     

Influence of H3PMo12O40/SiO2 thermal treatment on adsorbed forms of formaldehyde and formic acid

Effect of the H₃PMo₁₂O₄₀/SiO₂(P-Mo-HPA) thermal treatment on adsorbed forms of HCOOH and H₂CO has been studied by IR spectroscopy. On the sample pretreated at 150°C, HCOOH adsorbed mainly as hydrogen-bonded complexes. The HPA calcination at 350°C resulted in the formation of surface formates along with hydrogen-bonded complexes. This proves the formation of coordinatively unsaturated surface cations (Lewis acid sites) during HPA dehydration. Alteration of the surface composition due to dehydration was found to have a major influence on the H₂CO adsorbed forms.     

Homoleptic Metal Carbonyl Cations of the Electron-Rich Metals: Their Generation in Superacid Media Together with Their Spectroscopic and Structural Characterization

Homoleptic carbonyl cations of the electron-rich metals in Groups 8 through 12 are the newest members of the large family of transition metal carbonyls. They can be distinguished from typical metal carbonyl complexes in several respects. Their synthesis entails carbonylation of metal salts in such superacids as fluorosulfuric acid and “magic acid” HSO₃F? SbF₅. Thermally stable salts with [Sb₂F₁₁]^? as counterion are obtained with antimony pentafluoride as reaction medium. Both the [Sb₂F₁₁]^? anion and superacid reaction media have previously found little application in the organometallic chemistry of d-block elements. Also unprecedented in metal carbonyl chemistry are the coordination geometries with coordination numbers 4 (square-planar coordination) and 2 (linear coordination) for the cation. Formal oxidation states of the metals, and the charges of the complex cations, extend from + 1 to +3: thus CO is largely σ-bonded to the metal, and the CO bond is strongly polarized. Minimal metal → CO π-backbonding and a positive partial charge on carbon are manifested in long M? C bonds, short C? O bonds, high frequencies for C? O stretching vibrations (up to 2300 cm^?1), and small ¹³C NMR chemical shifts (up to δ_c, = 121). Prominent examples of these unusual homoleptic carbonyl cations, which were recently the subject of a Highlight in this journal, include the first carbonyl cation of a p-block metal [Hg(CO)₂]²⁺, the first trivalent carbonyl cation [Ir(CO)₆]³⁺, and the first multiply charged carbonyl cation of a 3d metal [Fe(CO)₆]²⁺. In this overview we propose to (a) outline the historical origins of cationic metal carbonyls and their methods of synthesis; (b) present a summary of the general field of carbonyl cations, which has developed over a yery short period of time; (c) discuss the structural and spectroscopic characteritics of metal–CO bonding; (d) discuss the special significance associated with reaction media and the [Sb₂F₁₁]^? anion; and (e) point to the most recent results and anticipated future developments.     

Synthesis and Characterization of 5‐Cyanotetrazolide‐Based Ionic Liquids

New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C₂N₅]^? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm^?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C₂N₅]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries.     

Catalytic properties of transition metal salts immobilized on nanoporous silica polyamine composites II: hydrogenation

The transition metal compounds Pd(OAc)₂, RhCl₃·4H₂O and RuCl₃ · nH₂O were adsorbed onto the nanoporous silica polyamine composite (SPC) particles (150–250 µm), WP‐1 [poly(ethyleneimine) on amorphous silica], BP‐1 [poly(allylamine) on amorphous silica], WP‐2 (WP‐1 modified with chloroacetic acid) and BP‐2 (BP‐1 modified with chloroacetic acid). Inductively coupled plasma‐atomic emission spectrometry analysis of the dried samples after digestion indicated metal loadings of 0.4–1.2 mmol g^?1 except for RhCl₃·4H₂O on BP‐2 which showed a metal loading of only 0.1 mmol g^?1. The metal loaded composites were then screened as hydrogenation catalysts for the reduction of 1‐octene, 1‐decene, 1‐hexene and 1, 3‐cyclohexadiene at a hydrogen pressure of 5 atm in the temperature range of 50–90 °C. All 12 combinations of SPC and transition metal compound proved active for the reduction of the terminal olefins, but isomerization to internal alkenes was competitive in all cases. Under these conditions, selective hydrogenation of 1,3‐cyclohexadiene to cyclohexene was observed with some of the catalysts. Turnover frequencies were estimated for the hydrogenation reactions based on the metal loading and were in some cases comparable to more conventional heterogeneous hydrogenation catalysts. Examination of the catalysts before and after reaction with X‐ray photoelectron spectroscopy and transmission electron microscopy revealed that, in the cases of Pd(OAc)₂ on WP‐2, BP‐1 and BP‐2, conversion of the surface‐ligand bound metal ions to metal nano‐particles occurs. This was not the case for Pd(OAc)₂ on WP‐1 or for RuCl₃ · nH₂O and RhCl₃· 4H₂O on all four composites. The overall results are discussed in terms of differences in metal ion coordination modes for the composite transition‐metal combinations. Suggested ligand interactions are supported by solid state CPMAS ¹³C NMR analyses and by analogy with previous structural investigations of metal binding modes on these composite materials. Copyright © 2011 John Wiley & Sons, Ltd.     

Studies regarding the formation from metal nitrates and diol of NiM 2 III O4 spinels, inside a silica matrix

The present study deals with preparation and characterization of spinel mixed oxide systems NiM ₂ ^III O₄, where M^III?=?Fe^III, Cr^III. In order to obtain 50% NiFe₂O₄/50% SiO₂ and 50% NiCr₂O₄/50% SiO₂ nanocomposite, we have used a versatile route based on the thermal decomposition inside the SiO₂ matrix, of some particular precursors, coordination compounds of the involved M^II and M^III cations with dicarboxylate ligands. The ligands form in the redox reaction between metal nitrates mixture and 1,3-propanediol at the heating around 140?°C of the gels (tetraethylorthosilicate?Cmetal nitrates?C1,3-propanediol?Cwater). The as-obtained precursors, embedded in silica gels, have been characterized by FT-IR spectrometry and thermal analysis. Both precursors thermally decompose up to 350?°C leading to the formation of the corresponding metal oxides inside the silica matrix. X-ray diffraction of the annealed powders have evidenced the formation of NiFe₂O₄ starting with 600?°C, and NiCr₂O₄ starting with 400?°C. This behavior can be explained by the fact that, by thermal decomposition of the Fe(III) carboxylate at 300?°C, the spinelic phase ??-Fe₂O₃ is formed, which interacts with the NiO, forming the ferrite nuclei. By thermal decomposition of chromium carboxylate, a nonstoichiometric chromium oxide (Cr₂O_3+x ) is formed. In the range 380?C400?°C, Cr₂O_3+x turns into Cr₂O₃ which immediately interacts with NiO leading to the formation of nickel chromites nuclei inside the pores of silica matrix. Both spinels have been obtained as nanocrystalites homogenously dispersed as resulted from XRD and TEM data.     

Influence of ion size on the stability of chloroplumbates containing PbCl<Stack><Subscript>5</Subscript><Superscript>−</Superscript></Stack> or PbCl<Stack><Subscript>6</Subscript><Superscript>2−</Superscript></Stack>

The enthalpies of formation of PbCl₄, PbCl₅⁻ and PbCl₆²⁻, originating from quantum mechanics, have enabled the thermodynamic behaviour of these ions with respect to Cl-detachment to be assessed. The stability of salts containing PbCl₅⁻ and PbCl₆²⁻ as a function of the dimensions of these anions and complementary cations was studied using an approach combining the Kapustinskii-Yatsimirskii equation with basic thermochemical relationships. It was found that hexachloroplumbates of monovalent metal cations will not dissociate into metal chlorides and PbCl₄, provided the complementary cations are suitably large in size. Hexachloroplumbates of divalent metal cations have not yet been synthesised since no known metal cations attain the requisite large size. Such salts will not dissociate if the divalent metal cations are able to complex suitably large electron-donating ligands. The pentachloroplumbates of both monovalent and divalent metal cations are unstable, since no known metal cations have appropriately large ionic radii. The approach adopted appears to be useful for the examination of the thermal behaviour, stability and reactivity of chloroplumbates.     

Na6[B18Se17]: The First Selenoborato‐closo‐dodecaborate with a Polymeric Chain Anion

Systematic studies on selenoborates containing a B₁₂ cluster entity and alkali metal cations led to the new crystalline phase Na₆[B₁₈Se₁₇] which consists of a icosahedral B₁₂ cluster completely saturated with trigonal‐planar BSe₃ units and sodium counter‐ions. Neighbouring cluster entities are connected in one direction via exocyclic selenium atoms forming the infinite chain anion ([B₁₈Se₁₆Se_2/2]^6–)_∞. The new chalcogenoborate was prepared in a solid state reaction from sodium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 850 °C. Na₆[B₁₈Se₁₇] crystallizes in the monoclinic space group C2/c (no. 15) with a = 18.005(4) Å, b = 16.549(3) Å, c = 11.245(2) Å, β = 91.35(3)° and Z = 4.