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Molecular Shell-Like Dilithium (Silyl)phosphanediide and Dilithium (Silyl)arsanediide Aggregates with an [Li6O]4+ Core.

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Rb,P,. Cs,Pf,, and Rb,As, are the only stable phases in the
corresponding binary systems in which homonuclear polyanions form multiple bonds (the P-P bond length in the three
hexaphosphides is 215 pin as opposed to 221 pm for a P-P
single bond"'). This stabilization effect can also be seen in the
formation of Ba,Li,Si, and Ba,,Ge,O, even under very unfavorable conditions: the former in the synthesis of BaSi, from
LiCl fluxes,[31and the latter as a byproduct in the reactions of
oxygen-contaminated starting rnaterial~.~'~
In this context, the
existence of the radical anion P:- (analogous to the ozonide
anion) is even more remarkable. This anion occurs in the thermally unstable phase K4P3,[',I and can be obtained formally by
cleaving a P:- ring with four additional electrons. Thus. it appears that for the heavier group 14 and 15 elements 10 x electron
Hiickel arenes such as Xz- are an alternative to the formation
of discrete double bonds.
Thus, it would be worthwhile to reinvestigate thoroughly all
of those phases containing graphite or heterographite nets. in
which the atoms of the anionic 63-net show VEC # 4.[l5I Evidently. the formation of metallic phases can be avoided in a
simple manner by variation of the stoichiometric ratio of these
atoms o r by formation of vacancies: [Li,Si,]'instead of
[Li,Si,]*-; [o2Pbl4-instead of [PJ4-. Al,n,B, instead of AIB,,
for instance, would be a variant containing benzene-analogous
anions B i 2 - (6 x-electron Huckel arenes).
Received- December 21. 1995 [Z8686IE]
German version: An,!yti,. Cheni. 1996, 108, 1062- 1064
Keywords: electron localization . germanium compounds * silicon compounds Zintl phases
111 M. Worle, R. Nesper, G. Mair. M. Schwarr. H. G von Schnering. 2. Anorg.
A&. Cliivn. 1995, 621. 1 153.
[2] H. Axel. K. H. Janzon. H. Schifer. A. Weiss, Z.Nu/c~rfnrsc/i.
B 1968. 23. 108.
[3] E.1. Gladishevskij, Dopni'idt Akud Nuuk. Ukr. RSR 1959. 3. 294.
[4] P. Villars. L. D. Calvert. fwi-son:s Hundhook of Ci:i-stu//oKrciphicDuru forIntcrnic~rollicPhuscv. 2nd ed.. 1991. ASM International.
IS] Ba,Li,Si, and Ba,Li,Ge, were synthesired quantitatively by rcacfion of the
elements in a stoichiometric ratio of 4.2 1 . 6 (excess Li to avoid loss at high
temperatures) in arc-welded N b ampoules under reduced Ar pressure at
1000 C. Single crystals for X-ray structure determination were obtained by
slow cooling to 400 C and subsequent annealing at this temperature.
[6] Crystal structurc of Ba,Li2Si,,: M , =731.7 g mol-I: ii = 872.6(2). h =
1517.4(3), c =1932.2(4) pm: space group Fd&/-D;f (No. 70): Z = 8;
V=192.58cm3 mol-'.p,,,,, = 3.799gcm--'; N ( h k l ) = 677;575ofthem with
F 2 2 a ( F ) , R,", = 0.049 (range of data collection - 1 < h 511, - 1 s k < 19.
- 1 I I < 2 5 ) ; R,,,,,, = 0.034. Crystal structure of Ba,Li,Ge,:
M, =
998.78gmol-I. u=890.1(1). h=1546.9(2). c = 1 9 4 3 0 ( 2 ) p m ; spacegroup
Fi/dd-D$! (No. 70); Z = 8: V = 201.38 cm'mol-I, pSdlcd
= 4.960 g ~ m - ~ :
N ( h k / ) = 773; 586 of them with F 2 2 a ( F ) . R,,,, = 0.037 (range of data collection - 1 < h 5 1I. - 1 < k < 20. - 1 5 I < 25); R,,,,, = 0.038: Siemens-P4
four-circle diffractometer (graphite monochromator, scintillation counter,
Mo,, radiation. o scan. 3.5' < 2 0 < 5 5 ' . 293 K): empirical absorption correction by $ scan; program package SHELXTL. Further details of the crystal
structure investigations are available on request from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen. on quoting the depository numbers CSD-404707 (Bd,Li,Si,) and CSD-404705 (Ba,Li,Ge,).
[7] H.-P. Abicht, W. Honle, H. G. von Schnering, 2. Anorg. A&. Chcwi. 1984,
519. 7.
[8] W. Honle, Dissertation, Universitiit Miinster 1975; W. Honle, J. Wolf. D. Weher. H . G. von Schnering. Colli,cted Ahsrracrs lWd Europ. Con{. .So/id Srure
Cheni. 1986, Vol. 1, p. 45.
[9] Single crystals of Bdi,,Ge,03 were obtained upon thermal decomposition (2 h.
450 .C. ultra high vacuum) of an oxygen-contaminated alloy of nominal composition Na,BaGe. Polycrystalline Ba,,GelO, is available from a reaction of
BaO. Ba. and NaCe under similar decoinposition conditions and subsequent
[lo] Crystal structure of Ba,,,Ge-0,: M , =1929.53 g m o l - ' ; u =1170.1 (2).
c = 509.5(1)pm: space group f 6 , n 1 i i n i 1 - 0 ~ ~(No 191). Z = 1 :
363.79cm3 inol-'.
= 5 304 gem--': N ( h k / ) = 320: 246 of them with
F z 3 o(l.'). R,,,, = 0.070 (range of data collection 0 5 h 5 13. 0 < k 5 13.
< I < 6); R,,,,, = 0.045: Siemens-P4 four-circle diffractometer (graphite
monochromator, scintillation counter, Mo,, radiation. i o scan. 4 5 2 0 5 55 ,
293 K): empirical absorption corrcction via $ scan: program package
SHELXTL. Further details of the crystal mucture investigation are available
on request from the Fachinformationszentrum Karlsruhe. D-76344 Eggenstein-Leopoldshafen, on quoting the depository number CSD-404706.
[ l l ] A D. Becke. K. E. Edgecombe. J C%eni.f/ij.s. 1990. Y2. 5397.
1121 A. Savin. A. D. Becke. J. Flad, R Nesper. H. W. Preuss. H G. von Schnering,
Atigc'ii'. Chiw. 1991. 103. 421 : Angeit. Clieni. I n / G I . E I I ~ 1991,
30. 409.
[13] A Savin. B. Silvi. F. Colonna. Cun. J Cheni., in press.
[I41 H G von Schnering, M. Hartweg. U. Hartweg, Angcdit.. C%em. 1989. 101. 98:
A u y m Chcnl.I n ! . E d &g/. 1989. 28. 56.
[15] Sincc the suhmission of this communication Sr,Li,Si, has been prepared. The
compound also forms orthorhomhiccrystals(u = 852.5(1), h = 1481.2(2). c =
IX16(2) pm. spice group Frlrld)[l6]. We areconvinced that it isident~caltothe
phase described by Miiller ct al. [17], Sr,Li,Si,, 2 SrA,Liz& :
which wiis assumed to adopt the AIB, structure type with a statistical distribution of Li and Si.
[I61 U . Bolle. K . Peters. W. Carrillo-Cabrera. H. Cr von Schnering. unpublished.
[I71 W. Muller. A. Schifer, A. Weiss. Z. Natuif~ir,sch.B. 1969. 24, 650.
Molecular, Shell-Like
Dilithium (Sily1)phosphanediide and
Dilithium (Sily1)arsanediide Aggregates
with an [Li,0l4+ Core**
Matthias Driess,* Hans Pritzkow, Stefan Martin,
Stefan Rell, Dieter Fenske, and Gerhard Baum
Drdimietl to Professor Kurt Delinick(.
on the occasion of' his 65th h i r t h d q
Dilithium derivatives of primary amines, phosphanes, and
arsanes of the type [RELi,], (R = alkyl, aryl, silyl; E = N, P,
As), which are useful nucleophilic building blocks in the element
organic chemistry of nitrogen, phosphorus, and arsenic, are
molecular aggregates and structurally represent an intermediate
between the molecular compounds R,E and the typical saltlike
solid-state compounds Li,E (lithium pnictides) . Their structures, however, have not been well established o r are not known,
since these compounds have only been obtained as insoluble,
X-ray amorphous solids.['' Recently the decameric dilithium
(2-naphthyl) azanediide 1 and the dimeric dilithium phosphanediide-fluorosilane adduct 2,13]which are soluble in ether
and aromatic solvents, were structurally characterized.
RPLi, . 2RF
1, R = x-CioH,
2. R
We have been investigating the synthesis and structure of the
dilithium (sily1)phosphanediides and arsanediides 3 which form
a spherical cluster framework and are soluble as a result of their
easily variable lipophilic shell.[31Since the degree of aggregation
3, E
P, As; R
alkyl, aryl
[*] Priv.-Doz. Dr. M. Dricss, Dr. H. Pritzkow, S. Martin, S. Rell
Anorganisch-chemisches lnstitut der Universitit
Im Neuenheimer Feld 270, D-69120 Heidelberg (Germany)
Fax: Int. code +(6221) 54 41 97
e-mail: dpO!!i ix urz.uni-heidelberg de
Prof. Dr. D. Fenske. G . Baum
lnstitut fur Anorganische Chemie der Technischen Universitit
Engesserstresse. D-76128 Karlsruhe (Germany)
This work wiis supported by the Deutsche Forschungsgemeinschaft (Schwerpunktprogranim "Polyedermolekule") a n d the Fonds der Chemischen Industric.
is largely determined by the steric bulk of the triorganosilyl
group. we were interested in the reactivity of 3 as a function of
cluster size. We have now observed that the double lithiation of
the primary silylphosphane 4 and silylarsane 6 in the presence of
LizO results i n the octaineric and dodecameric aggregates 5 and
7. respectively. Surprisingly the cavities of these compounds are
filled with an octahedral [Li,O]"+ cluster framework. The compositions of the aggregates have been confirmed by correct elemental an.L' I,\ses.
Compound 5 is formed by the lithiation of 4 with two equivalents o f tiBuLi in the presence of Li,O in toluene o r Et,O and
can be isolated in 69 % yield as light yellow crystals. The origin
of the incorporated LizO has not yet been explained. Since 5 can
also be pi-oduccd in toluene. the hydrolysis product in commercial tiBuLi solutions, LiOH. could be the potential source for
0 2 - .We ha\e evidence that other Li,O-free aggregates are
formed upon rigorous exclusion of LiOH/Li,O.
R = Me,(iPrMc,C')Si
A crystal structure analysis of 5["]revealed the presence of an
aggregate with approximately 422 symmetry (Fig. 1); only the
fourfold axis is required crystallographically. The twofold axes
Fill 1 Keprcsciitation 0 1 the ahell-like form of 5 in the crystal For clarity the ailyl
groitpa ha\? hccii omitted. OLi,, shell = green. red. P, shell = qellov.. L i , ,
.;hell = hluc Sclccfcd distmces [A]. SI P 2 IYS(2). Li P 2.39 2.46( I)for outer Lr
i i t o i i i ~2 . 5 N l ) . 2 % ( I )
[or inner cquatorial LI atoms. 2 . 9 l ( l ) . 2.93(1) for inner
;Ipic:ll L.1 :Ito!ll,. 1-1 0 I x1 190(2)
run parallel to u and h and provide pseudo symmetry. The
cluster has eight formal units of dilithium phosphanediide and
a Li,O molecule. The cationic (Li centers) and anionic (P and 0
centel-s) building blocks show close packing. The structure is
topologically best described as an ionogenic cluster formed by
three closed shells and covered by the lipophilic silyl groups
(Fig. 1 ) . The eight P atoms comprise a strongly distorted cube,
which is surrounded by a Li,, cuboctahedral shell and surrounds ii Li,,O octahedron.
The Li centers of the Li,, shell each sit over an edge of the P,
cube, whercas the Li centers of the Li,O cluster are each located
over B Lice. This P,partial structure is evidently preferred to the
anti-prismatic or the bisdisphenoid ordering which are possible
alternatives. An important aspect of this ~ I L I S I ;1. loi-m:ition is
that only twelve of the total sixteen Li centers ai :placed on the
exterior, that is on the edges, of the P8 framcnoi-k: thus. the
remaining Li ions must be placed in the cavitq These four Li
ions are electronically stabilized by binding to the formal 02ion of Li,O, thus resulting in a [Li,0l4+ cluster. Sixfold coordination of 0'- by metal cations in n z o k c d a v coinpounds is very
unusual and has as yet only been observed in a dilithiomethaneLi,O aggregater51 and in a mixed lithium barium-(fcvfbutoxide)-oxide aggregate.[']
The Li-P distances to the external ,Li centers are very similar
and lie in the range of 2.39-2.46(1) A ; the Li - P distances for
the internal Li centers are 2.56 and 2.58(1), as well as 2.91 and
2.93(1) A; that is, they correspond with the values observed for
lithium phosphanide~.[~]
Thf Li- Li distances i n the Li,? cuboctahedron are longer than 3 A, and thosein the Li,O framework
are significantly shorter (2.63-2.67(2) A ) . It has not yet been
clarified if these relatively short distances implq bonding7 interactions. whereas the P-P distances (>4!1) clexly show that
there are no P-P bonds present. The L i - 0 distances in the
[Li,O]'+ aggregate (1.81 - 1.90(2)A ) are significantly shorter
than in solid Li,O (1.98 A). In addition. the Li centers of the
[Li,O]"+ aggregate are each coordinated by four P atoms.
The filled cluster shows a slight tendency 10 dissociate in
solution. Cryoscopic investigations provided a degree of aggregation of I T z 7.7. Crystals dissolved in benzene show three
broad signals (r, =70&85 Hz) in the 31PN M R spectrum at
(j = - 336.9. -340.1, and -355.9 in an intensity ratio of
15: 15: I . The main signals were assigned to the two different P
atoms on the intact cluster. while the remaining weak signal is
presumably due to an unknown dissociate. The -Li N M R spectrum only shows one broad signal at 6 = 0.9 ( v i = 1 1 5 Hz) that
indicates either a fast Li exchange or only minor differences in
the 6 values for the various 7Li centers. Because of the limited
solubility in toluene no measurements below 0 C were possible.
A cluster comprising three shells of platonic units is present in
7 which is topologically closely related to 5. The As centers form
a slightly distorted AS,^ icosahedron. in which all of the twenty
triangular Faces are each capped by a Li center (Fig. 2 left). The
twenty Li centers thereby form ii pentagondodecahedron as dual polyhedral framework with approximately I , point symmetry. The remaining four Li cations are found in the cavity of the
approximately spherical [AsiZLiZO]'.- framework (diameter ca.
8 A). As in 5. these Li ions bind to an encapsuliited Li,O molecule leading to formation of a [Li,O]'+ octahedral core. The
formation of the approximately 0,-symmetrical cluster in the
cavity of the /,-symmetrical [As, ,Liz,]'- aygregate is very
unusual and reflects a "symmetry frustration" which is caused
by the stoichiometry. The [Li,O]'+ octahedron is. therefore,
tilted with respect to the orientation of the A b I Zicosahedron;
a C , axis of the octahedron coincides with ;I C , axis of the
Li,, shell.
The Li-As distances in the As,,Li2, framework he between
2.559(9)-2.76( 1) A. and are thus in the range ofvalues obtained
for lithium arsanide.I8]The Li-Li distances in the Li,, dodecahedron are 2.89(1) and 3.09(1) A, whereas. like in 5, the Li-Li
distances in the Li,O framework are significantly shorter
(2.52(1)-2.81(1) A ) . The large As-As distances ( > 4 A) indicate that there are no As- As bonds; the Li - 0 distances are
similar to those in 5. The Li centers of the Li,O framework are,
as expected. still coordinated to nearby As centers (Fig. 2 right);
four Li centers have relatively short distances to three As atoms
each, and two Li centers are only close to two As atoms. These
distances correspond to those in the As,,Liz,, framework. 'Li
N M R spectra measured at various temperature intervals from
[3] M. Driess, S. Rell, H Pritzkow.
R. Janoschek, C/iiw~. C ~ n i i ~ i i f i i .
1996. 305.
[4]5 C,,,H,,,Li,,OP,SiX.2C.H,.
tetragonal. P4.11. CI = 22.565(11). L =
16.393(8) A. v = 8347 h3, z = 2.
The crystals are twinned (twin axis
[ I 101). Three crystals were investigated from which two showed a 1 : 1
ratio of the two components. the
third showed a ratio of 1 . 1 2 The
iesulrs of the three refinements corresponded well with one another
There are disordered solvent molecules (toluene) in the space between
the clusters. Intensity ineasureinents: Siemens-STOE AED2 fourcycle diffractometer. Mo,, i-adiation. ('1 scan. T = - 70 C.measurement range 20m4x= 47 . 6187 independent reflections (4000 observed
with I > 2n(/)). empirical absorption correction. Structure solution
with direct methods [9a]. relinement with all reflections against f'
(9 b] (383 parametei-s. non-hydrogen atoms anisotropic. hydrogen
Fig 2. Left: Representation of the shell-like form of 7 in thc crystal. For clarity the orgnnic groups ha\e been oinitted
atoms in calculated positions with
SI = Ira). A > , >zhell = yellou. Li,,, ahell = blue. OLi, shell = green. red. Selected distance\ [A]: Si As 2.394 - 2 309(2). Li As
the same tcmperaturc Sactors.
2.559(9) 2.76(l) for w t c r LI atoms. 2.55 2.63(1) for inncr Li atoms coordinated to two As atoms. 7.60- 2.YY( I ) for inner Li
toluene inoleculez as rigid sixatoms coordinated to three As atoms. 110 1.85 l.90(1). Right connection of the Li,,O octahedron (red. green) with the As
inembered rinzs isotroDic1. Rl =
centers (yellow)
0.0717. ii.R2 = 0 2334 (all dai'i) 7:
C,,H,,,As,Li,,O,, Ji,. iiionoclinic. P?, i i (NO 14). = 19.480(2).
-40 to 25 - C show that the structure is maintained in solution.
h = 19 130(2). 1 = 19.540(2) A. /i= 91 92 . V =7353 A'. 2 = 4. Intensity measurements: Siemens-STOE IPDS diffractometer. Mo,, radiation. T = - 100 -C.
The spectra show two sorts of Li in the Li,O framework and one
measurement range 20,,,, = 52 . 14136 independent reflections (10481 observed
more sort of Li in the As,,Li,, framework ( 6 = -1.65 and
with I > 2 n ( / ) ) .Structure solution with direct methods [Ya]. refinement with all
-0.66, and 2.05, respectiveiy, in a ratio of 1:2: 10). Cryoscopic
reflections against F' [9 h] (664 parameters, hydrogen and non-hydrogen atoms
measurements gave a degree of aggregation of n z 11 3.
anisotropic). RI = 0.0607. ivR2 = 0.1288 (all data) Further details of the crysti11 structure in\estigations can be obtained from the Fachinformationszentrum
The question of whether other hyperlithiated cluster cations
Karlzruhe. D-76344 Eggenstein-Leopoldshafen. on quoting the depository
of main group elements such as [Li,SI4' and [Li,CI4+ can be
numbers CSD-404962 (5) and 404961 (7).
internally stabilized is currently under investigation.
[ 5 ] H.-J. Gdis. J Vollhardt. H. Gunther, D. Moskau, H. J. Linder, S. Braun. 1 An7.
Cliiwi. Siii. 1988. 110. 978.
161 H. Bock. T. H a w k . C . Nither, N. Rosch, M. Staufer, 0. D. Hiberlen. A i ~ g ~ i i ' .
E.vperinwntul Procedurr
Cliiwi. 1995. 107. 1438. Angeii'. Clien?. In/. Ed. Engl. 1995, 34, 1353.
5: Coinpound 4 (1.3 g. 4.89 mniol) in toluene (20 m L ) waz allowed t o i-cact with
[7] G. Rccker. B. Eschbach. D. Kishammer, 0. Mundt. 2.Anor-g A//g. Clieiii. 1994.
Li,O-containing nBuLi (0.63 g, 9.78 mniol. 2 . 5 in
~ hexane) at -50 C The yellow
620. 29. and references therein: M. Driess, G . Huttner. N . Knopf, H. Pritzkow.
solution was slowly warmed to 25 C and then concentrated in vacuum (10.' Torr)
L Zsolnai. A i i p i i . C/iiw7. 1995, 107. 354; Angrit.. C/iem. Inr. Ed. B i g / . 1995. 34.
to half its volume. After a few days at 25 C, light yellow. air-sensitive crystals had
formed Yield- 0.90 g (0 39 mmol. 6 5 % ) . ' H N M R (300 MHz. C,D,). 6 = 1 20[ X I A. M At-if. R. A Jones. K . B. Kidd, J Ciirni Snr. Chem Conimui7. 1986. 1440:
P.B Hitchchock. M . F. Lappert. S. J. Smith. J. Orgunor?i~r.C%em. 1987, 320.
+Me). 6.72 (s. 16 H. arom. H)
C27: L Zsoliiai. G.Huttner. M. Driess, A n g m . Cl~en7.1993, 105. 1549: Angeii..
C/ic,i7i, / i f / . Ed EiigI. 1993, 32,1439.
7: Compound 6(6 0 g. 27.24 inmol) was dissolved in EtzO (90 m L ) 'itid treated with
[9] a ) G M Shrldrick. SHELXS86, Universitat Gottingen, 1986. b) G. M
Li,O-containing i7BuLi (23.83 g. 54.48 niniol: 1 . 6 ~ solutioii
in hexane) a t 20 C
Sheldrick. SHELXLY3. Universitit Gottingen. 1993.
The color o f t h e solution changed upon slow warming to 25 C Si-om light yellow, t o
orange. An ormge-browm solid w i b obtained upon conccntratiiig thc d u l i o i i in
\'iciium (10
Torr). Thc solid was taken up in toluene ( 3 0 m L ) and gi-aducill!
dissolved a t 80 C. Fi-actional crystallization provided orange-qellow. iiir-seiisiti\e
cryst'ils. Yield: 4.XO g ( I 71 mmol: 75"iO) ' H NMR (300 MH7. C,D,): d = 0.68 is.
(scpt . 12 H. CHMe,. J(H.H)
= 6.X
Rcceivcd- Deccmbcr 18. 1995 (286581E]
German version. Ai~gi'ii. Ciiivn. 1996. 108. 1064 1066
Keywords: arsenic compounds * clusters * lithium compounds *
phosphorus compounds
[ I ] K. Issleib. A. Tzzchach. C / i ~ i ~Ber.
i . 1959. Y2. 1118. G. W. Parshall, R. V. Lindsey. Ji-.. J A ~ J Ciiiw
Sol. 1959. X I . 6273: G.Fritz. H. Schifer, W HBlderich.
Z Aiioi,? Ally. CIiiw7 1974. 407. 266. R . Appcl. K . Geisler. J Orgmioi7ic1 CIiiwi
1976. 112. 61: G Becker. 0. Mundt. M. Rossler. E Schneider. Z . Aiior~y.A / / c .
Cl7mii. 1978. 433. 42
(11 D. R. Armstrong. D. Bai-r. W. Clegg. S R. Drake. R. J Singer. R. Snmtli. D.
Stalke. D S Wright. Aii~qeii C h 7 i . 1991. 103. 1702; Ai7geii.. Cliivi. h i / . E d
Dig/. 1991. 30. 1707.
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like, corel, molecular, aggregates, shell, sily, arsanediide, li6o, dilithium, phosphanediide
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