K8[B12(BSe3)6]: A Novel Selenoborato-closo-dodecaborate with Different Anion Substitution Patterns

K8[B12(BSe3)6]: A Novel Selenoborato-closo-dodecaborate with Different AnionSubstitution Patterns

A. Hammerschmidt, A. Lindemann, M. Döch, and B. Krebs*

Münster, Institut für Anorganische und Analytische Chemie der Westfälischen Wilhelms-Universität und Sonderforschungsbereich 458

Received March 3rd, 2003.

Dedicated to Professor Heinrich Nöth on the Occasion of his 75th Birthday

Abstract. Systematic studies on selenoborates containing a B12 clus-ter entity and alkali metal cations led to the new crystalline phaseK8[B12(BSe3)6] which consists of a icosahedral B12 cluster com-pletely saturated with trigonal-planar BSe3 units and potassiumcounter-ions. For the first time three different anion substitutionpatterns are observed in one crystal structure. The new chalcog-enoborate was prepared in a solid state reaction from potassiumselenide, amorphous boron and selenium in evacuated carbon co-

K8[B12(BSe3)6]: Ein neues Selenoborato-closo-dodecaborat mit unterschiedlichenAnionen-Substitutionsmustern

Inhaltsübersicht. Gezielte Versuche zur Synthese neuer Selenobo-rato-closo-dodecaborate führten im ternären Phasengebiet K/B/Sezu der neuen Verbindung K8[B12(BSe3)6], in der ein vollständigdurch Chalkogen abgesättigter B12-Ikosaeder vorliegt. Erstmalswerden drei verschiedene Anionen-Substitutionsmuster innerhalbeiner Kristallstruktur beobachtet. Das neue Chalkogenoborat

1 Introduction

Numerous thio- and selenoborates have been synthesizedand characterized in recent years due to improved prep-aration techniques [1,2]. Binary boron sulfides and selenides[1, 3�5] as well as ternary and quaternary thio- and seleno-borates contain boron in a trigonal-planar coordination, forwhich various novel types of chalcogenoborate anions areobserved. Typical examples are the small, highly chargedanion entities [BS3]3� [6�8], [BSe3]3� [9], [B2S4]2� [10],[B2S5]2� [11], and [B3S6]3� [8,12�14], which are character-istic structural features in non-oxide chalcogenoborates ofalkali and alkaline earth metals. In contrast to a tetrahedralchalcogen coordination which is found not only in thio- butalso extensively in selenoborates [15�22], examples for bo-ron in a trigonal-planar selenium coordination are scarce.Apart from the aforementioned [BSe3]3� anion present inthe thallium compound Tl3BSe3 [9] as well as in Ba7(B-Se3)4Se [23], such a boron-selenium coordination sphere is

* Prof. Dr. B. KrebsWilhelm-Klemm-Str. 8D-48149 MünsterFax: �49 (0)251/8338366e-mail: “[email protected]“

Z. Anorg. Allg. Chem. 2003, 629, 1249�1255 DOI: 10.1002/zaac.200300052 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1249

ated silica tubes at a temperature of 850 °C. K8[B12(BSe3)6] crys-tallizes in the monoclinic space group Cm (no. 8) with a �

16.288(2) A, b � 41.617(4) A, c � 9.788(1) A, β � 109.59(1)°, andZ � 6.

Keywords: Selenoborates; Boron; Cluster compounds; Crystalstructures

wurde in einer Hochtemperatur-Feststoffreaktion aus Kaliumsele-nid, amorphem Bor und Selen in graphitierten, evakuierten Quarz-glasampullen hergestellt. K8[B12(BSe3)6] kristallisiert in der mono-klinen Raumgruppe Cm (Nr. 8) mit a � 16,288(2) A, b �

41,617(4) A, c � 9,788(1) A, β � 109,59(1)° und Z � 6.

also observed in the recently discovered cluster phases ofgeneral formulae M8[B12(BSe3)6] with M � Rb, Cs, Tl[24,25] and M4Hg2[B12(BSe3)6] [26] with M � Rb, Cs. Inthese structures [B12(BSe3)6]8� anions occur formed by B12-closo-clusters which are completely saturated with six BSe3

units. Although rather short Hg�Se distances are observedfor the latter quaternary compounds, no direct linkage be-tween the isolated anion moieties occurs in these phases.With the synthesis and structure analysis of the selenobor-ate-closo-dodecaborate Na6[B18Se17] it was possible tocharacterize the first boron selenium compound with apolymeric anionic cluster chain [27]. Recently we reportedthe first thioborato-closo-dodecaborates M8[B12(BS3)6] withM � Rb, Cs [28]. The herein presented structure ofK8[B12(BSe3)6] shows additional novel features of the struc-tural diversity in boron cluster chemistry.

2 Experimental Section

Synthesis

The synthesis of well-defined and highly pure boron chalcogencompounds is rather difficult because of the high reactivity of insitu built boron chalcogenides towards a variety of container mate-rials at elevated temperatures. The fused silica tubes usually em-

A. Hammerschmidt, A. Lindemann, M. Döch, B. Krebs

ployed for solid-state reactions are attacked by boron chalcogenidesat temperatures above 400 °C forming silicon chalcogen com-pounds by B-Si exchange at the surface of the ampoules. For thesynthesis of pure samples the reaction vessel must either be madeof boron nitride or graphite, or silica tubes coated with glassy car-bon must be used. The latter are prepared by slowly turning a silicaampoule filled with acetone vapour through the flame of an oxy-gen-hydrogen operated welding torch at about 1000 °C. In somecases, especially when longer annealing is necessary, the formertype of crucibles are employed. To protect them against oxidationthey are encapsulated in steel or tantalum ampoules under an ar-gon atmosphere, and these again are enclosed in evacuated silicatubes.

As starting materials the following products were used: potassiumselenide (prepared following a method by Thiele et al. [29]),amorphous boron (Alfa, amorphous powder, 95 %), and selenium(Strem, powder, 99.5 %).For the synthesis of K8[B12(BSe3)6] appropriate amounts of thestarting compounds were mixed up and filled into a carbon-coatedsilica tube which was thereafter sealed at a pressure of 6 Pa andinserted into a horizontal one-zone furnace. Heating and coolingprocedures for K8[B12(BSe3)6] were performed as follows:

RT ��4 h 850 °C (6h) ��4 h 700 °C ��400 h 300 °C ��4 h RT

Colourless plate-shaped crystals suitable for SXRD were obtained.The product is air and moisture sensitive and was therefore handledunder dry argon in a glove box.

Single Crystal Structure Analysis

For the data collection a single crystal was sealed into a Markcapillary under an argon atmosphere. The X-ray diffraction datafor K8[B12(BSe3)6] were collected on a BRUKER Apex dif-fractometer. The structure solution, which was possible in spacegroup Cm, was achieved by applying direct statistical methods ofphase determination using the SHELXTL PLUS program [30], andfull-matrix least-squares refinements were performed using theSHELXL-97 software programs [31]. The complete data collectionparameters and details of the structure solutions and refinementsare given in Table 1.

Thirty selenium sites were directly obtained from the electron den-sity map and subsequent refinements gave the potassium and boronpositions. Se(19), Se(20), Se(25), Se(26), Se(27), Se(30), K(1), K(2),K(4), K(5), B(19), B(20), B(25), B(26), B(27) and B(30) are foundon the special position 2a, the remaining atoms occupy the generalposition 4b in Cm. Since the structural refinement yielded a Flackparameter the data set was fitted as a partial racemic twin. Aniso-tropic refinement of the structural parameters of the potassium-and selenium atoms and isotropic refinement of the boron atomsapplying the scattering factors for neutral atoms yielded a conven-tional R-value of R1 � 0,049. Table 2 gives the coordinates of allatoms, average temperature factors and their estimated standarddeviations.

Details of the crystal structure and powder diffraction data may beobtained from the Fachinformationszentrum Karlsruhe, Gesell-schaft für wissenschaftlich-technische Zusammenarbeit, D-76344Eggenstein-Leopoldshafen, on quoting the depository numberCSD-413039, the name of the authors and this journal.

2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629, 1249�12551250

Table 1 Crystal data, details of the measurement and structuredetermination of K8[B12(BSe3)6]

Formula K8[B12(BSe3)6]Crystal dimensions 0.08 x 0.08 x 0.03 mm3

Formula weight 1928.22 g/molCrystal system monoclinicSpace group Cm (no. 8)Lattice parameter a � 16.288(2) A

b � 41.617(4) Ac � 9.788(1) Aβ � 109.59(1)°

Cell volume 6250.4(1) A3

Formula units per cell 6Calculated density 3.074 g/cm3

Measurement device BRUKER-ApexMeasurement temperature 298 KRadiation (wavelength) Mo-Kα (0.71073) A)Scan type ω-scanθ Range for data collection 0.98° < θ < 28.00°Range in h k l �21 � h � 21

�54 � k � 54�12 � l � 12

Observed reflections 31793Unique reflections 15104 [Rint. � 0.098]Unique reflections with I > 2 σ(I) 6195Data/restraints/parameters 15104 / 2 / 481Refinement program SHELXL-97 [31]Residual indices all reflections R1 � 0.142

wR2 � 0.075reflections with I > 2 σ(I) R1 � 0.049

wR2 � 0.060Absorption correction SADABS [33]Absorption coefficient 16.56 mm�1

Goodness of Fit 0.637Largest diff. peak and hole 1.08 and �1.06 e A�3

Powder Diffraction

A powder diffraction pattern of K8[B12(BSe3)6] was measured in a0.1 mm Mark capillary with a STOE STADI P powder dif-fractometer using copper radiation. The observed XRD patternwas compared to the calculated model which is computable fromsingle crystal data using the STOE powder software package [32].A comparison of observed and calculated data of K8[B12(BSe3)6] isgiven in Fig. 1, exhibiting a fairly good agreement between thetheoretical and the measured powder pattern although due to heavyabsorption by selenium for some peaks intensities are of slightlydifferent magnitude. Nevertheless, all reflections with a relativeintensity > 3 % were indicated by refinement of the lattice param-eters of K8[B12(BSe3)6].

3 Results and Discussion

The novel potassium selenoborato-closo-dodecaborateK8[B12(BSe3)6] is the first example of isolated cluster entitieswith different substitution patterns within one crystal struc-ture in selenoborate chemistry. Isolated monomeric clusterentities are known from the earlier published alkali metalselenoborato-closo-dodecaborates M8[B12(BSe3)6] and themercury containing compounds M4Hg2[B12(BSe3)6] (M �Rb, Cs) [24�26] in which the characteristic structural fea-tures are B12 icosahedra which are also observed in elemen-tary boron [34] as well as in various closo-boranes [35,36].Examples of completely substituted closo-dodecaboranesapart from halogenide or hydroxide substitued B12 clusters

K8[B12(BSe3)6]: A Novel Selenoborato-closo-dodecaborate with Different Anion Substitution Patterns

Table 2 Wyckoff positions, atom coordinates and isotropical ther-mal displacement parameters/A2 for K8[B12 (BSe3)6]

Atom WyckoffPosition x y z Ueq

a)

Se(1) 2a 0.21864 0 �0.03225 0.03038Se(2) 2a �0.21451 0 0.03782 0.03958Se(3) 2a 0.20655 0 0.30685 0.03318Se(4) 4b �0.02385 0.05194 0.29029 0.03548Se(5) 4b �0.12155 0.07546 �0.05860 0.04482Se(6) 2a �0.20743 0 �0.30138 0.05922Se(7) 4b 0.71903 0.16563 0.42143 0.04116Se(8) 4b 0.12081 0.07598 0.05733 0.03868Se(9) 4b 0.02553 0.05106 �0.29043 0.04680Se(10) 4b 0.52239 0.11028 0.20674 0.03649Se(11) 4b 0.29662 0.15744 0.22252 0.03849Se(12) 4b 0.73076 0.16661 0.77244 0.03941Se(13) 4b 0.50711 0.12165 0.82029 0.03702Se(14) 2a 0.40127 0 0.25314 0.04387Se(15) 4b 0.30781 0.16937 0.56912 0.04102Se(16) 4b 0.63561 0.24097 0.56015 0.04230Se(17) 4b 0.63905 0.08979 0.55105 0.04142Se(18) 4b 0.53852 0.21969 0.80356 0.03882Se(19) 4b 0.39472 0.08979 0.49318 0.04086Se(20) 2a �0.40046 0 �0.23267 0.06446Se(21) 4b 0.49627 0.21038 0.16522 0.04279Se(22) 4b 0.38964 0.23993 0.38311 0.04649Se(23) 4b �0.14530 0.11983 0.21335 0.06625Se(24) 4b 0.66114 0.04778 0.26989 0.05910Se(25) 4b 0.11715 0.15128 0.31713 0.05687Se(26) 4b 0.91220 0.17160 0.68794 0.06654Se(27) 4b 0.37165 0.05783 0.79365 0.06204Se(28) 4b 0.14108 0.12002 �0.21680 0.09022Se(29) 4b 0.68461 0.27977 0.88243 0.08949Se(30) 4b 0.41762 0.28574 0.11621 0.07952K(1) 2a 0.83983 0 0.39413 0.05098K(2) 2a 0.50700 0 0.02079 0.05659K(3) 4b 0.32823 0.07310 0.09745 0.06423K(4) 2a 0.39115 0 0.58054 0.07062K(5) 2a 0.59655 0 0.45744 0.12720K(6) 4b 0.99515 0.14376 0.99740 0.09636K(7) 4b 0.84713 0.09720 0.53312 0.08156K(8) 4b 0.18069 0.08335 0.51368 0.07020K(9) 4b 0.67837 0.07453 0.96036 0.08354K(10) 4b 0.32797 0.15947 0.90779 0.08990K(11) 4b 0.34734 0.25797 0.77815 0.07519K(12) 4b 0.14788 0.22515 0.19851 0.09176K(13) 4b 0.01736 0.18779 0.48930 0.13465K(14) 4b 0.72491 0.18424 0.09232 0.10542B(1) 2a �0.08751 0 �0.14863 0.0256B(2) 2a 0.09456 0 �0.02572 0.0321B(3) 2a 0.09129 0 0.14989 0.0227B(4) 4b �0.05473 0.03537 �0.03687 0.0348B(5) 2a �0.09481 0 0.02486 0.0280B(6) 4b 0.45589 0.19943 0.45143 0.0340B(7) 4b 0.60381 0.16447 0.45303 0.0268B(8) 4b 0.51323 0.14037 0.35771 0.0289B(9) 2a �0.27832 0 �0.16838 0.0396B(10) 4b 0.05695 0.03376 0.03949 0.0223B(11) 4b 0.41690 0.16219 0.35649 0.0398B(12) 4b �0.00475 0.02111 0.14692 0.0226B(13) 4b 0.61136 0.16515 0.63111 0.0239B(14) 4b 0.42242 0.16709 0.54429 0.0332B(15) 4b 0.57038 0.13055 0.53333 0.0274B(16) 4b �0.09971 0.08328 0.14841 0.0437B(17) 4b 0.45827 0.13107 0.48421 0.0255B(18) 4b 0.09971 0.08342 �0.14692 0.0422B(19) 4b 0.51479 0.14569 0.65079 0.0226B(20) 4b 0.50862 0.18354 0.33961 0.0296B(21) 4b 0.78857 0.16937 0.62361 0.0439B(22) 4b 0.51691 0.18897 0.63822 0.0350B(23) 4b 0.23755 0.15851 0.36727 0.0301B(24) 4b 0.60600 0.08175 0.34438 0.0456B(25) 2a 0.27559 0 0.17557 0.0224B(26) 4b 0.42345 0.08937 0.69907 0.0425B(27) 4b 0.43185 0.24718 0.21244 0.0404B(28) 4b 0.56717 0.19918 0.51500 0.0283B(29) 4b 0.62249 0.24832 0.75506 0.0504B(30) 4b 0.00939 0.02248 �0.14199 0.0401

a) Ueq is defined as 1/3 of the trace of the orthogonalized Uij-tensor

[37�41] are rare. Although a hydrogen-selenium exchangesucceeded in the formation of the cluster anion

Z. Anorg. Allg. Chem. 2003, 629, 1249�1255 zaac.wiley-vch.de 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1251

Fig. 1 X-Ray powder pattern of K8[B12(BSe3)6]Top: measurement (radiation: Cu Kα1); bottom: calculated pattern

Fig. 2 Three different anion substitution patterns inK8[B12(BSe3)6]

[B6(SeCN)6]2� [42] without any lower substitution sideproducts, only monosubstitution by a selenocyanate ligandis observed for a B12 cluster even under basic conditions[43]. Another example of selenium bonding to a B12 icosa-hedron is the binary boron selenide B12Se2�xBx [44]. Sinceit crystallizes in the B6P-type structure no close structuralresemblance to the herein described selenoborate is present.

The significant stability of the B12 icosahedron is basedon the ability of boron to form multicentre bonds. As wellas for boranes, Wade�s rules [45] apply also for the[B12(BSe3)6]8� anion units: with six negative charges locatedon the terminal selenium atoms, two negative charges re-main on the cluster core giving 2n�2 binding electrons perB12 moiety.

The herein presented octapotassium hexaselenoborato-closo-dodecaborate K8[B12(BSe3)6] is a novel compoundwith substituted, icosahedral boron clusters as the mainstructural feature. Besides the earlier characterized thio-and selenododecaborates M8[B12(BS(e)3)6] (M � Rb, Cs,Tl) [24�26] we report another member of the molecule-likesubstituted boron cluster family. Since we figured out thatthe above mentioned [B18S(e)18]8�-anions possess identicalsubstitution patterns of the bidentate BSe3-ligands, an ad-ditional class of substitution pattern is realized inK8[B12(BSe3)6]. For the first time the [B12(BSe3)6]8�-units


Fig. 3 Boron selenium bond relations within the anions in K8[B12(BSe3)6]

Fig. 4 Perspective view of the unit cell of K8[B12(BSe3)6] along [001].

are arranged in an asymmetric way as shown in Fig. 2.Anion B and C form an enantiomorphic couple, while foranion A we found the same arrangement of the BSe3-li-gands as in the above mentioned hexaselenoborato-closo-dodecaborates.

The average B-Se distance is determined to 2.00 A whilethe mean bond length of the endocyclic B-Se bond in thechelate-like B3Se2-ring appear as 1.98 A slightly shorter. Asexpected, the exocyclic boron-selenium bond lengths revealas the shortest with 1.89 A. Apparent uncommon lengthsare not observed for the B-B bonds within the icosahedron(1.77 A) which can be compared to those in known boroncloso-clusters [24�26,34�44]. Fig. 3 illustrates the boronselenium bond relations within the anions, while Fig. 4


shows a perspective view of the unit cell along [001]. Table3 gives a summary of all B-Se bond lengths. The chemicalenvironment of the potassium ions is mainly mirrored by asix-fold�up to an eight-fold selenium coordination wheredistances smaller than 4.15 A were taken into account (fordetails see Table 4). Strikingly, K(14) exhibits only a lowfive-fold coordination which explains the relative high meanthermal displacement parameter parallel to [100].

Theoretical Calculations

The mathematical treatment of B12 boron clusters substi-tuted with six orthothio- or selenoborate entities can be re-duced to the analysis of isomers of an icosahedron with six


Table 3 B-B and B-Se bond lengths/A with standard deviationsin K8[B12(BSe3)6]

B(1)-B(2) 1.720(18) B(5)-B(8) 1.80(2) B(19)-B(22) 1.74(2)B(1)-B(3) 1.732(18) B(5)-B(11) 1.802(19) B(20)-B(21) 1.808(17)B(1)-B(5) 1.758(18) B(6)-B(7) 1.711(19) B(20)-B(23) 1.76(2)B(1)-B(11) 1.794(18) B(6)-B(8) 1.741(19) B(21)-B(22) 1.753(18)B(1)-B(12) 1.761(18) B(7)-B(8) 1.740(19) B(21)-B(23) 1.813(19)B(2)-B(3) 1.744(19) B(7)-B(9) 1.83(2) B(21)-B(24) 1.762(18)B(2)-B(4) 1.75(2) B(7)-B(10) 1.80(2) B(22)-B(22a) 1.73(3)B(2)-B(10) 1.77(2) B(8)-B(9) 1.76(2) B(22)-B(24) 1.792(19)B(2)-B(12) 1.776(19) B(8)-B(11) 1.776(19) B(22)-B(26) 1.78(2)B(3)-B(4) 1.723(18) B(9)-B(10) 1.792(19) B(23)-B(23a) 1.76(3)B(3)-B(5) 1.793(18) B(9)-B(11) 1.758(19) B(23)-B(24) 1.759(18)B(3)-B(6) 1.756(18) B(9)-B(12) 1.744(19) B(23)-B(25) 1.75(2)B(4)-B(6) 1.780(18) B(10)-B(12) 1.824(18) B(24)-B(25) 1.754(17)B(4)-B(7) 1.756(19) B(11)-B(12) 1.739(17) B(24)-B(26) 1.772(18)B(4)-B(10) 1.761(19) B(19)-B(20) 1.78(2) B(25)-B(26) 1.79(3)B(5)-B(6) 1.776(19) B(19)-B(21) 1.734(17) B(23)-Se(23) 2.021(13)B(1)-Se(1) 2.002(13) B(14)-Se(14) 1.878(18) B(24)-Se(24) 1.998(14)B(2)-Se(2) 2.005(14) B(15)-Se(5) 1.982(17) B(25)-Se(25) 1.981(19)B(3)-Se(3) 2.017(13) B(15)-Se(6) 1.974(16) B(26)-Se(26) 2.00(2)B(4)-Se(4) 2.015(13) B(15)-Se(15) 1.912(16) B(27)-Se(19) 1.959(19)B(5)-Se(5) 1.971(14) B(16)-Se(7) 1.986(16) B(27)-Se(20) 1.98(2)B(6)-Se(6) 2.033(13) B(16)-Se(8) 2.019(17) B(27)-Se(27) 1.91(2)B(7)-Se(7) 1.998(15) B(16)-Se(16) 1.828(17) B(28)-Se(21) 1.990(16)B(8)-Se(8) 2.022(14) B(17)-Se(9) 1.963(15) B(28)-Se(22) 2.003(16)B(9)-Se(9) 2.010(15) B(17)-Se(10) 1.981(15) B(28)-Se(28) 1.865(16)B(10)-Se(10) 2.006(13) B(17)-Se(17) 1.928(16) B(29)-Se(23) 2.035(16)B(11)-Se(11) 1.991(13) B(18)-Se(11) 1.974(17) B(29)-Se(24) 1.954(16)B(12)-Se(12) 1.999(13) B(18)-Se(12) 1.950(17) B(29)-Se(29) 1.879(16)B(13)-Se(1) 1.976(16) B(18)-Se(18) 1.933(17) B(30)-Se(25) 1.97(2)B(13)-Se(2) 1.976(16) B(19)-Se(19) 2.042(19) B(30)-Se(26) 1.98(2)B(13)-Se(13) 1.868(16) B(20)-Se(20) 1.998(17) B(30)-Se(30) 1.88(2)B(14)-Se(3) 1.975(18) B(21)-Se(21) 1.984(13)B(14)-Se(4) 2.007(19) B(22)-Se(22) 2.001(14)

Symmetry operations for K8[B12(BSe3)6] in space group Cm (no. 8):

a x �y z f 1�x �y z j 1/2�x 1/2�y 1�zb 1�x y z g �1�x y z k �1/2�x 1/2�y �1�zc 1�x y 1�z h �1/2�x 1/2�y z l x �y �1�zd x y �1�z i 1�x �y 1�z m 1/2�x 1/2�y ze x y 1�z

occupied edges. At first sight this leads to an large numberof possible structures, but chemical restrictions reduce thisnumber: every boron atom of the icosahedron can formonly one additional bond, two neighbouring boron atomsare connected via the thio- or selenoborate bridge.

The above mentioned restrictions result in a small num-ber of theoretical substitution patterns. The program Dis-kreta [46] was used for the analysis together with the pro-gram biblio GAP [47]. Only eight of these isomeric patternsare possible: the one (a) observed in thio- and selenoboratechemistry, the one observed in Na6[B18Se17] (b) and threepairs of enantiomers (c � d, e � f, g � h) where b, g � h arerealized in the herein presented K8[B12(BSe3)6]. All othercombinations can be transformed by rotation in one ofthese eight patterns. Fig. 5 shows the calculated substitutionpattern of the icosahedra. Highlighted edges represent bo-ron atoms connected by the bidentate ligands. It is to beexpected that all of the theoretical cluster patterns are pos-sible. As mentioned before trigonal-planar boron entitiesare a characteristic structural feature in thioborate chemis-try but are rare in selenoborates. In B�Se chemistry struc-tures containing tetrahedrally coordinated boron are pre-vailing [2]. It would be rather interesting to coordinate suchunits to boron clusters. The facial substitution of boron ico-sahedra with four tetrahedral BQ4-entities leading to a[B12(BQ4)4]-unit (Q � S, Se) may be predicted. Starting


Table 4 K···Se bond lengths/A with standard deviations inK8[B12(BSe3)6] with d(K···Se) < 4.15 A

K(1) d K(2) d K(3) dSe(25b) 3.295(5) Se(30b) 3.271(5) Se(21) 3.260(4)Se(26c) 3.354(5) Se(27) 3.290(5) Se(17d) 3.364(5)Se(18a) 3.409(5) Se(18) 3.491(5) Se(11) 3.382(4)Se(18) 3.409(5) Se(18a) 3.491(5) Se(27) 3.434(4)Se(23b) 3.488(4) Se(17l) 3.542(4) Se(19) 3.545(4)Se(23f) 3.488(4) Se(17d) 3.542(4) Se(9) 3.722(5)Se(22c) 4.097(5) Se(8) 3.793(4)Se(22i) 4.097(5) Se(28) 4.019(5)

K(4) d K(5) d K(6) dSe(27) 3.278(5) Se(30c) 3.064(6) Se(13) 3.114(5)Se(17) 3.280(4) Se(27) 3.155(6) Se(16c) 3.143(5)Se(17a) 3.280(4) Se(18a) 3.193(5) Se(24c) 3.384(5)Se(30c) 3.294(5) Se(18) 3.193(5) Se(21c) 3.403(6)Se(20) 3.306(5) Se(26c) 3.292(6) Se(15j) 3.530(5)Se(9) 3.836(2) Se(12) 3.851(2) Se(29c) 3.666(7)Se(9a) 3.836(2) Se(12a) 3.851(2) Se(28c) 3.816(7)

K(7) d K(8) d K(9) dSe(29b) 3.327(6) Se(28e) 3.326(6) Se(24c) 3.306(5)Se(22c) 3.438(5) Se(16) 3.382(5) Se(10) 3.312(4)Se(12) 3.457(6) Se(17) 3.552(5) Se(18e) 3.332(6)Se(13) 3.471(6) Se(23) 3.573(5) Se(25c) 3.533(5)Se(1) 3.486(4) Se(9) 3.578(5) Se(30c) 3.621(6)Se(18) 3.803(6) Se(22e) 3.932(5) Se(29c) 3.655(6)Se(24c) 3.973(5) Se(7) 4.085(5) Se(12) 3.877(6)Se(23b) 4.136(5) Se(20) 4.104(5)

K(10) d K(11) d K(12) dSe(7) 3.241(4) Se(13h) 3.337(5) Se(16) 3.379(5)Se(28e) 3.303(7) Se(15e) 3.339(6) Se(14k) 3.383(6)Se(8e) 3.309(4) Se(3h) 3.391(5) Se(5h) 3.590(5)Se(14h) 3.406(6) Se(4) 3.447(4) Se(15h) 3.603(6)Se(10) 3.663(6) Se(14h) 3.518(5) Se(8) 3.691(5)Se(5e) 3.725(7) Se(2h) 3.670(5) Se(6) 3.797(6)Se(11e) 4.081(6) Se(3h) 3.866(6)

K(13) d K(14) dSe(13g) 3.070(5) Se(2d) 3.253(5)Se(16) 3.123(5) Se(15m) 3.348(9)Se(3h) 3.486(7) Se(1) 3.360(5)Se(6h) 3.583(8) Se(29b) 3.388(6)Se(15h) 3.618(9) Se(4d) 3.688(6)Se(28e) 4.090(9)

Symmetry operations see Table 3

with such an entity the formation of B10Q20-macrote-trahedra could be explained.

Acknowledgements. We thank the Deutsche Forschungsgemein-schaft and the Fonds der Chemischen Industrie for substantial sup-port of this work. We also like to thank Mrs. E. Haberberger(Mathematics Department, University of Bayreuth, Germany) forthe theoretical calculations on the icosahedral fragments.

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Fig. 5 Calculated substitution patterns of icosahedra coordinated by bidentate substituents, black edges represent boron atoms connectedvia the ligands, c) � d), e) � f) and g) � h) are mirror images (mirror plane drawn)

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Documents

K8[B12(BSe3)6]: A Novel Selenoborato-closo-dodecaborate with Different Anion Substitution Patterns