The crystal structure of Bi2W6Br18 and a new synthesis of W6Br12

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1 The crystal structure of BiWBr and a new synthesis of WBr Hans-Juergen Meyer To cite this version: Hans-Juergen Meyer. The crystal structure of BiWBr and a new synthesis of WBr. Journal of Inorganic and General Chemistry / Zeitschrift für anorganische und allgemeine Chemie, Verlag, 00, (-0), pp.. <0.00/zaac.00000>. <hal-00> HAL Id: hal-00 Submitted on Jun 0 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 The crystal structure of BiWBr and a new synthesis of WBr Journal: Zeitschrift für Anorganische und Allgemeine Chemie Manuscript ID: zaac r Wiley - Manuscript type: Article Date Submitted by the Author: 0-Mar-00 Complete List of Authors: Meyer, Hans-Juergen Keywords: tungsten cluster, bromide, synthesis

3 Page of Figure Captions Figure. Projection of the environment of pairs of bismuth atoms in the structure containing two short Bi Br distances each. Figure. Connectivity of (BiBr ) units with outer bromide cluster ligands. (W Br i ) clusters are shown as octahedra. Figure. Projection of an isolated [(W Br i )Br a ] - cluster. Figure. Unit cell of (BiBr ) [(W Br i )Br a ] (inner Br ligands are omitted).

4 Page of The crystal structure of Bi W Br and a new synthesis of W Br Markus Ströbele [a] and H.-Jürgen Meyer* [a] Dedicated to Professor Bernd Harbrecht on the Occasion of his 0th Birthday Keywords: Tungsten cluster; Bromide; Synthesis; Structure Abstract. The new tungsten bromide cluster compound Bi W Br was synthesized by reacting tungsten hexabromide with bismuth metal in a silica tube at 0 C. The structure of Bi W Br was refined by single crystal X-ray diffraction in the space group P /c with unit cell dimensions of a =.() pm, b = 0.() pm, c =.() pm and β = 0.(). The crystal structure is constructed from [(W Br i )Br a ] - anions being interconnected by outer bromine ligands with (BiBr ) units, which behave as cations in (BiBr ) [(W Br )Br ]. Short Bi Br bonding distances at.() pm and.() pm in (BiBr ) units suggest the presence of covalent interactions. Thermal decomposition of the compound leads to W Br. * Prof. Dr. H.-Jürgen Meyer juergen.meyer@uni-tuebingen.de [a] Abteilung für Festkörperchemie und Theoretische Anorganische Chemie Institut für Anorganische Chemie Ob dem Himmelreich Universität Tübingen D-0 Tübingen

5 Page of Introduction Tungsten halide cluster chemistry is represented by a remarkable widespread domain of different compounds and structures. Currently known tungsten clusters are represented by the octahedral [W X ] type cluster of W Cl [,], the octahedral [W X ] type cluster of W X with X = Cl, Br [], and the centered trigonal prismatic cluster core in W CCl []. Mixtures of such clusters were obtained in the structure of W 0 C X (X = Cl, Br) containing carbon centered trigonal prismatic and octahedral cluster moieties in one structure []. More cluster types have been discovered in the field of tungsten iodides [], just recently extended by the identification of the binary compound W I containing a square pyramidal cluster core []. Based on these tungsten halide clusters, several salt-like compounds have been synthesized in which clusters act as bulky anions []. Compounds with [W X ] type clusters have been reported with monovalent A ions in AW Cl, A W Cl [,0,], and with trivalent M ions in MW Cl M = Bi [,], Gd, Tb, Dy []. Corresponding cluster bromides were reported as NaW Br [], AW Br with A = Na, Ag [], and A W Br with A = Ag [], K [], Rb [], Cs [], Tl [], Cd [], and Cu [0]. The synthesis of W Cl has been recently established by a convenient low-temperature route based on the reduction of WCl with bismuth metal at C []. The structural characterization of the intermediate BiW Cl revealed a constitutional isomerism of this compound, which may be described by the two formulas (BiCl)[(W Cl i )Cl a ] [] and (BiCl )[(W Cl i )Cl a Cl a-a / ] []. The main differences in these structures are expressed by short Bi Cl distances at pm for (BiCl) + and at pm for (BiCl ) + with chloride ligands which remain unconnected with respect to the tungsten cluster. The similarity with the previously reported isotypic structure of (BiCl)[Mo Cl i ]Cl a [] suggests a close relationship in chemistry of these compounds. The present work proves the reactivity of tungsten hexabromide with metallic bismuth in order to develop a useful and comfortable synthesis of W Br as an alternative route to the reported reaction between tungsten metal and bromine. In course of this study, namely through reaction of WBr and metallic bismuth, we discovered the new compound Bi W Br, whose crystal structure is reported herein. Experimental Section Synthesis of Bi W Br Manipulations of the starting materials WBr and Bi (Riedel-de Haen, %) were performed in a dry box under argon atmosphere. A mixture of WBr (0. g, 0. mmol) and elementary Bi (0. g, mmol) were charged into a two chamber silica tube and sealed under vacuum. This mixture was heated in a tube furnace at 0 C for h. Afterwards, the coproduced

6 Page of BiBr was sublimed off from the bulk part (later identified as Bi W Br ) into the receiver chamber of the silica vessel, being exposed with a lower temperature (near room temperature) over the period of two days. Finally, the ampoule was cooled down to room temperature, the receiver chamber was disconnected from the product chamber, and the content of the product chamber was collected inside the dry box. Dark amber colored rhombic crystals of the new Bi W Br were selected for X-ray single crystal structure analysis. When the mixture was treated at slightly higher temperatures (at 0 C for one week) Bi W Br was decomposed into W Br and coproduced BiBr, which was subsequently sublimed off. Synthesis of (H 0) [W Br ] H O Bi W Br was dissolved in boiling concentrated HBr solution. Brownish crystals of (H O) [W Br ] H O were crystallized upon cooling the solution to room temperature. Synthesis of WBr A Schlenk tube with two gas cocks was charged with g (. mmol) W(CO) (ABCR, %) in a dry box under argon atmosphere. Afterwards, the tube inlet was connected to an argon line in order to provide an inert gas atmosphere, and the outlet was equipped with three empty washing bottles. After the vessel was cooled with liquid nitrogen,. ml of liquid Br (0. mol) were added to the solid W(CO). The reaction was initiated by allowing the vessel to warm up slowly to room temperature by removing the liquid nitrogen coolant. After resting for 0 min. at room temperature the three washing bottles were filled with alkaline sodium sulfite solution and the Schlenk tube was heated in a water bath to remove the excess of bromine from the reaction. The residual dark gray WBr powder was collected inside the dry box. X-ray Diffraction The XRD patterns of reaction products were collected with a Stadi-P (Stoe, Darmstadt) powder diffractometer using Cu-K α radiation (germanium monochromator), with Bi W Br and (H O) [W Br ] H O being obtained X-ray pure, although WBr contained some small amounts of WOBr (about %) which may be a result of an oxygen contamination of W(CO). A single crystal of Bi W Br was coated with lithelen grease and attached to the tip of a glass fibre. Single crystal diffraction data were collected with an IPDS diffractometer (STOE, Darmstadt) using monochromated Mo-K α radiation. The unit cell refinement and data reduction were carried out using the STOE IPDS software. An absorption correction was applied by using the programs X-Shape/X-Red []. The structure was refined in the space

7 Page of group P /c by full-matrix least-squares procedures using SHELX- []. All atoms were refined anisotropically. Crystallographic data and structure refinement results are summarized in Table, atom positions are listed in Table, and selected bond lengths are given in Table. A brown single crystal of (H O) [W Br ] H O was measured under analogous conditions as Bi W Br. The structure solution and refinement for (H O) [W Br ] H O was performed with the space group C/c with a =.() pm, b = 0.() pm, c = 0.0() pm, and β = 0.(), yielding R values of R = 0.0, wr = 0.0 based on all measured data. Further details on the crystal structure investigations may be obtained from the Fachinformationszentrum Karlsruhe, Eggenstein-Leopoldshafen, Germany, on quoting the depository number CSD- for Bi W Br and CSD- for (H O) [W Br ] H O. Results and Discussion The compound Bi W Br was prepared by metallothermic reduction of WBr with bismuth metal at 0 C. However, Bi W Br is thermally labile and decomposes slowly at temperatures above 0 C to yield W Br and BiBr, of which the latter can be sublimed off into the colder section (room temperature) of the reaction vessel. This procedure, as emphasized in the following reaction equations permits a comfortable access to obtain pure W Br. WBr + Bi Bi W Br + BiBr () Bi W Br W Br + BiBr () The composition Bi W Br may suggest a relationship with A [W Cl ] compounds containing [(W Cl i )Cl a ] - ions []. However, the crystal structure of Bi W Cl was refined to yield a structure which can be described as (BiBr ) [(W Br i )Br a ], reflecting a structural relation to the already known bismuth chloro-tungstenate (BiCl)[(W Cl i )Cl a ]. The structure of (BiBr ) [(W Br i )Br a ] contains two bromine atoms being involved in covalent bonding with bismuth, thus allowing a (BiBr ) moiety to act as a monovalent cation like A (+) in A [(W Br i )Br a ] compounds. The two short Bi Br distances with Br() at.() pm and Br() at.() pm are contained in a strongly distorted edge-sharing bi-octahedral Bi Br 0 moiety, displayed in Figure. All the remaining bromide atoms of this moiety, with Bi Br distances presented in Table can be referred as outer ligands of the tungsten cluster (Figure ). The [(W Br i )Br a ] - cluster (Figure ) in the structure exhibits W W distances ranging from.() to.() pm, W Br i distances ranging from 0.() to.() pm, and W Br a distances ranging from.() to.() pm. All these distances reflect typical values among bromo-tungstenate cluster units of this type. The crystal structure of (BiBr ) [(W Br i )Br a ] is displayed in Figure and shows a CsCl type

8 Page of like structural arrangement of bi-octahedral (Bi Br 0 ) units and (W Br ) cluster units. Six out of ten bromides of the bi-octahedral (Bi Br 0 ) unit are in fact outer bromide ligands of the cluster (Figure ). The given, straight forward synthesis of W Br would be challenging for the preparation of the corresponding tungsten dichloride, W Cl, too. The related bismuth chloro-tungstenate precursor having the formula BiW Cl has shown to behave thermally stable up to 0 C. Thermal treatments at higher temperatures appeared inadequate for BiW Cl because W Cl has shown to react with quartz tubing above 0 C. Therefore, a purification process via solution has been used subsequently for the synthesis of W Cl []. Following this procedure, both, the chloride and bromide compounds can be dissolved into their aqueous HCl and HBr solutions to yield (H O) [W Cl ] H O and (H O) [W Br ] H O, respectively. A structure refinement based on a single crystal measurement of (H O) [W Br ] H O (with crystal data being deposited in the ICSD) has shown that the structures of both compounds are closely related to each other (space group C/c). In addition, both compounds can be pyrolyzed to yield binary W X (X = Cl, Br) [].

9 Page of Table. Crystal data and structure refinement data of (BiBr ) [(W Br i )Br a ]. Empirical formula Bi W Br Formula weight Temperature Wavelength Crystal system. g/mol () K Space group P /c.0 pm monoclinic Unit cell dimensions a =.() pm α = 0 b = 0.() pm β = 0.() c =.() pm γ = 0 Volume.() nm Z Density (calculated). g/cm Absorption coefficient. mm - F(000) 0 Crystal size 0. x 0. x 0.0 mm Θ range for data collection. to. Index ranges - h, - k, - l Reflections collected Independent reflections (R int = 0.0) Completeness, Θ =.. % Refinement method Full-matrix least-squares on F Data / parameters / Goodness-of-fit on F 0. Final R indices [I > σ(i)] R = 0.0, wr = 0.0 R indices (all data) R = 0.0, wr = 0.0 Largest diff. peak and hole. and -. e Å -

10 Page of Table. Atomic coordinates (x 0 ) and equivalent isotropic displacement parameters (pm x 0 - ) of (BiBr ) [(W Br i )Br a ]. U eq is defined as one third of the trace of the orthogonalized U ij tensor. x y z U eq Bi() () () () () W() () () 0() () W() () () 0() 0() W() 0() () () 0() Br() () 0() 0() () Br() () () () () Br() () 0() -() () Br() () () -() () Br() () 0() () 0() Br() () () () () Br() 00() () () () Br() -() () () () Br() -() 0() () ()

11 Page of Table. Selected bond lengths (in pm) of (BiBr ) [(W Br i )Br a ]. W W:.().() W()-W().() W()-W().0() W()-W().() W()-W().() W()-W().0() W()-W().() W Br i : 0.().() W()-Br().() W()-Br() 0.() W()-Br().() W()-Br().() W()-Br().() W()-Br().() W()-Br().() W()-Br().() W()-Br().() W()-Br() 0.() W()-Br() 0.() W()-Br().() W Br a :.().() W()-Br().() W()-Br().() W()-Br().() Bi Br Bi()-Br().() Bi()-Br() 0.() Bi()-Br() 0.() Bi()-Br().(),.() Bi()-Br().()

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