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CsPr9NbBr15N6 A New Type of Interstitially Stabilized Cluster Compound.

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[ I ] Revie\+s: a j S. E . Egan, R. A. Weinberg, " V t r w 1993. 365. 7x1: h) M. S.
Boguski. F. McCormick. ;hid. 1993. 366, 643. c ) J. L. Bos, Muror. RK\. 1988.
19.i. 255.
[2] Revica : A. 1,evitsky. E m . J B i o d i r w 1994. 2736. 1.
f31 For applications of S-farnesyliited pepttdes. see. for instiiiice: 'I) M . D.
Schaber. M. B. O'Hara. V. M. Garsky, S. D. Mosscr. J. D. Bergstrom, S. L
Mooi-es. M . S. Marshall. P. A. Fricdinan. R. A. F. Dixon. J. B. Gihhs. J. B i d
C / t ~ i t .1990, 265. 14701; h) S. L . Moores. M . D. Schaber. S D. Mosser. E.
Rands. M. B. O'Hara, V. M. Garsky. M. S . Marshall. D. L Pompliano. J. B.
Gihhs. i/iid. 1991. 266, 14603: c) D. L. Poinpliano. E Rands. M. D. Schaber.
S. D. Mosser. N. 1.Anthony. J. B. Gihbs, Biochc~niiirr:1~
1992.31. 3800; d j D. L
Poinplinno. R. P. Goinrz. N . J. Anthony. J. A i i i . C/irw. .SO(..
1992, 114, 7945
[4] W. A Maltese, FASEB J. 1990. 4, 3319, and references thet-ein.
[5] H. Waldtnann. P. StAber. M Schelhaiis. unpublished.
[6] Reviews: a) Ff. Waldmann. D. Sehastian. C'/irwi. R I Y 1994. 94. 91 1 hj ti.
Waldin;inn in Eiiz,~.i?ie
C'uruInt.5 in Orgntric S,~~iir/ir,sii
-- A ( ' o ~ i i p r i ~ / i c ~ t i .Homlsi~r~
h ~ r ~ lRJ/.
i . I / (Eds : K.Drauz. H . Wc~ldm;inn),VCH. Wcinhcini, 1995. p. 851
[7] a ) H. Waldmann, Eiruiiedroti L(,/r.1988, 2Y. 1131; h) Lichi~.,A t i n ('/wii. 1988.
a) C Smnhale. M.-R. Kula, .4pp/. B I O ~ ~ / I1987.
W I . Y. 251 : hi J. B i ~ ~ d i i i1988.
7. 49: c ) E . Matsun1ur:i. T. Shin, S . Muran, M . Sakagucln. T. K;i\cano. A p w .
Btld. C ' / t < ~ l i f .19x5. 49. 3643.
[9] This priiiciple has successfull) been used to develop :I prodrug concept. L. N .
.lungheiin. 7. A. Shepherd, C'hcm. R r v 1Y94. 94. 1553.
1101 Thc AcOZ group was u,ed in pcptide cheinistrq heforc (G. Le Corre. E. GuiheJampel. M. Wakselman. 7i,rua/ir&oii 1978, 34. 3105). It can be removed noneniymatically by trcatiiicnt with hydr:trinc. N a 2 C 0 , . o r H,O,:NH ,, that is.
coiiditions that cannot he applied for the conbtruction o f sensitive peptide
coiijugtites ltkc the N-/<o\ pcptide I .
0. R. Bolin. I.-l. Sytwii. F. Humiec. .I. Meienliofer, / / I / . .I Pryr. Re.\. 1989. 3.7.
353. and references thercin.
H. Waldinann, A. Heuser, Bioorg. Mcd. C~/i[wi. 1994. 3. 477. and reference\
a ) H W;ildm;inn. H. Kunr. Lidiijp A t i i i . ( ~ ' / i < w i1983.
1712: h) S FriedrichBochnitschek. H. Waldniann. H. Kunr. J. OF,^. C/io?i. 19x9, 54. 751
M . Liakopoulou~Kyrr~ikides.
P / i ~ , r [ J ~ / j [ , ~ i i1985,
; . \ ~ i ~24.
~ ' 1593.
CsPr,NbBr,,N,: A New Type of Interstitially
Stabilized Cluster Compound**
Michael LuIei and John D. Corbett"
Synthetic research conducted with some knowledge of electronic and structural principles has led to the discovery of a large
variety of interstitially stabilized rare earth metal cluster halides.". 21 A characteristic structural feature of the vast majority
of these compounds is rare earth element octahedra M, which
occur either isolated (e.g. in Pr,Br,,Co[31) or condensed through
common metal edges to oligomers (e.g. in Yl,IZoR~,'41)or infinite chains (e.g. in Pr,I,Ru[']). A smaller number of halides
contain tetrahedra M, which may also be isolated from each
other (e.g. in Yb,0C1,[6') or formed into either edge-sharing
dimers (e.g. in Gd,CI,N[71) or infinite chains (e.g. in
Na2Pr,Br,N0[81). Except for the Gd,CI, structure type,['] the
foregoing octahedral and tetrahedral cluster units exist only
with a centered (interstitial) heteroatom. While octahedra may
be centered by either transition metals (e.g. Mn, Ru, Ir) or main
group elements (e.g. B, C. N). the tetrahedra known so far only
form with N or 0 as interstitial atoms, probably because of the
size of the void. In all cases, the centered atoms provide not only
central bonding to the cluster, but in the reduced examples,
[*] Prnf. J. D. Corhctc, Dr. M . Lulei
Department of Chemistry
Iowa State Univeraity, .4mes. 1A 5001 1 (USA)
Telefax: Int. code + (515) 294-5718
Thiu I-esearcli was supported by tlic National Science Foundation -Solid State
Chemistry- under DMR-9207361 and was carried out in the f~iciliticsof Ames
Laboratory, U . S. Department of Energy M . L. thanks the Alexnnder-\onHumboldt Foundation for :i Fcodor-Lyncn Fellowship.
valence electrons as well that aid in fulfilling cervnin
minimal electron counts necessary for metal -metal bonding
of the electron-poor rare earth metals. As the recent
examples of Na2Pr,C1,0211"1 versus Na2Pr,Br,N0 nicely
illustrate, it appears possible to change the chemical and
physical properties (e.g. conductivity, magnetic susceptibility.
and color of the compound) by varying the interstitial
atoms. Crystals of Na,Pr,CI,O,
with the formulation
(Na '),(Pr3+)J(CI-)9(02-)Z(e-)are black because of the surplus electron. and the compound can therefore be viewed as
"reduced", while Na,Pr,Br,NO with the precise electron count
(Na+),(Pr3 +),(Br-),(N3-)(OZ -) crystallizes as green, transparent crystals and is an insulator or "simple" salt. However. the two
compounds are isostructural with similar metal-metal distances
within chains formed by edge-sharing tetrahedra centered by
either 0 o r disordered 0 and N. respectively. Instead of changing the interstitial atom, we have found that it is also possible to
introduce heterometal atoms in the rare earth metal cluster
framework to modify the structure and physical properties.
We report here the first example of a rare earth metal halide in
which one rare earth metal atom has been substituted by a transition metal atom. leading to a new structure and cluster type.
CsPr,NbBr, sNbcrystallizes as large, green, transparent crystals.'"' As shown in Figure 1,["] the core of the new structure
[Pr,NbN,] consists of a niobium atom centering a tricapped trigonal prism of praseodymium atoms (six Prl as trigonal prism,
three Pr2 as caps; distances: P r l - N b 3.405, P r 2 - N b 3.380,
Prl -Prl 3.917, Prl -Pr2 3.921 A). Nitrogen atoms center the
six tetrahedral Pr,Nb cavities in this metal array (distances:
Prl - N 2.32, Pr2-N 2.25, N b - N 2.13 A). The [Pr,NbN,] unit
can therefore also be regarded as the condensation product of
six Pr,Nb(N) tetrahedra that share three edges and the niobium
atom with each other to form a trigonal prism of tetrahedra.
Evidently, niobium substitution is responsible for this arrangement since M,N tetrahedra usually form
chains. as mentioned
earlier. The reason
might be the high formal ionic charge o r oxidation state of niobium
relative to the praseodymium atoms. According to Coulomb's
Law. the gain for the
Madelung part of the
lattice energy["J
maximized when each
of the (formally) highly
charged anions N 3 are
bonded to N b s t but also have 3Pr3 as nearest
neighbors. This is efficiently achieved in the
new cluster arrangement; of course, the
real charges are doubtlessly lower but somewhat proportional.
All 18 Pr-Pr edges
on the surface of this
Fig. I Crystal structure of CsPr,NbBr,,N,:
V i e w of thc [Pr,NbN,,] unit approximately
cluster are bridged by
along [I101 (a) and along [OOl] (hi (6(S,) syinone of three crystallotnetry. ellipsoids at 99 'YO probability: the lines
graphically distinct brobetween the metal atoms represent only gcomine atoms (Fig. 2).
metric relationships)
A i i g i w C % c r i i . Inr. Ed. Eiipl. 1995, 34. No. -70
Fig. 2 ('ry\tal w u c t u r c ofCsPr,NbBr,,N,: [OOl] view or the cluater unit with its
Fig. 4. Cryaral structure ofCsPr,NhBr,,N; View of the unit ccll 'ilong [OOl] uith
one layer about := 1,'4 to show the connectivity of Br3 and Br7 around Cs (atoms
coded a s in Figure 3 , Cs: large bl'ick circles (6(S,) syminctryl
h r o n i i n c c i i \ ~ i r t t i ~ r (99%
n ~ n ~ ellipsoids. the Brl atoms that bridge the Prl - P r l edges
normal to
havc been omitted for clarity)
which also serve to connect the clusters into a three-dimensional
network. Brl bridges both the Prl -Prl edges that lie p a r d k l to
[I 101 and half of the Prl -Pr2 edges and serves to link the clusters
as Brl'
only along the c axis (Fig. 3). Br2 bridges the remain-
Fig 3. Crystal structure nf
CsPr,NbBr,,N,: View of
the unit cell approxirnnte1) along [11O] showing
the Brl"
(N: black: metal iilomb:
gray; B r l : white: Br2.
B r ? ; Cs atom> are omitted)
ing Prl Pr2 edges. while Br3 is located over the Prl -Prl edge
parallel to (. and is also 0.4 A more distant to Pr2 (Fig. 2). Both
Br2 and Br3 connect the clusters through the cesium atom to form
layers about (0. 0, 11'4) (Fig. 4) and (0. 0, 3/4) in the unit cell.
The tvm layers are rotated 180. relative to each other around
[001]. The result is a Pr,NbN,(Brl'-i),2,2(Br2i)6(Br3i)3
complex unit (Fig. 2) complemented by only
one Cs ion which centers a tricapped trigonal prism of bromine
atoms (six Br:! in the trigonal prism, three Brl as caps).
The assunicd oxidation state formulation (Cs+)(Pr"),(Nb' t ) ( B r - ) i T ( N 3 - ) 6shows that there are no electrons left for
metal metal bonding, and CsPr,NbBr,,N, can be regarded as a
"non-reduced" closed-shell cluster compound or "simple" salt.
However. thr structure exhibits many features common to the
traditional "reduced" cluster compounds: The PI--Pr distances
in the [Pr,NbN,] unit (3.92A) are very similar to those in
(a= 3.94 A) and in Pr,13Ru('71( J = 3.93 A) with
isolated Pr,Ru octahedra and infinite chains of the same type of
octahedra, respectively. The short Nb-Pr separations within
the cluster are evidently caused by a matrix effect"*] from nitrogen and are therefore mainly determined by the N b - Nand Pr-N
distances. This effect can also be observed in the bhared edges of
the /rcrr,s-edge-sharing Pr, tetrahedra chain in Na,Pr,Br,NO and
the isotypic but slightly reduced Na,Pr,CI,O,. Furthermore.
the connectivity of the bromines in CsPr,NbBr, iN,, is reminiscent of that in many other rare earth metal cluster compounds.
The discovery of this surprising cluster may therefore forecast
still more novel chemistry and structures. The introduction of
other high-valent heteroatoms like zirconium or molybdenum
instead of niobium into the rare earth element network, or a
change of all o r some of the interstitial nitrogen atoms to oxygen
(or other) atoms should be considered as a route to new (and
perhaps "reduced") variants with different chcmical and physical properties.
E.vpcrit?I P M I ~ I /Proc,cdio.c
The synthetic and sublimation techniques for PrBr, m d thc rciictioii procedurch
utilizing welded N h tuhiiig h,i\c been described before [19.20]. C'\Br (Baker. 99.9 I % )
was dried by slow heating under dynamic vacuuiii and then wbliined. while N a N ,
(Aldrich. 99.9%) was used iis received as ;I source of nitrogcii m d a s the o u i d i h g
iigent for the N h container. Reaction mixtures with the o\'er:iII \tachtometry
CsNaPr,Br,,,N, were heated a t 750 C for ZX days. Accol-ding to Gutniei powdcr
diffraction. the products were crystals ofCsPr,NbBr,5N,, ( 7 0 " , , )a n d NaBr (lo'!/,)
besides iin unknown phase ( z20'%).After the formula and \tructure were deterinined by single cryatal diffrxtion. 1v.0 cry7t;ils wcre a n a l ~ r e i lby cncrgy-dispersive
X-ra) spectroscopy to confirm the niobium content and the \toichiometry.
Received: M:i! 33. 1995 [Z8021 IE]
German version: Aiigiw. C ' l i w i . 1995. 107, 2463 2465
Keywords: halides lanthanide compounds
pounds . nitrides - solid-state structures
. niobium
[ I ] J. D. Corbett i i i Modwii i'twspiwji,l,\ in / i w i ~ , ~ ~ i<'ri
~ i / C 7 r c ,n i i i i r i . (Ed. E.
Parthe). Kluwer. Dordrecht. 1992. p 27.
[2] A. Simon. H. Mattuusch. G . J. Miller. W. Bauliot'er. I i K Kremsr in Iluiiii/wok oii Ill? P/zrsii.\ und'i
of KLIW Eor.ili.\. lid I 5 ( b d s . K . A.
Gschneidcr Jr., L. E y i n g ) , Elsevier. Amsterdam. 1991. p. IYI.
[3] R. Llusar. J. D. Corhett. /itorX. C X i w i . 1994. 33. 84Y.
[4]M . W Payiie. M. Ebihara. J. D. Corbett. .4irgciv. C h m . 1991. 103. 842: Angcn.
Chm?.Int. GI.EngI. 1991, 3(J, 856.
[5] M. W. Paync. P. K. Dorhout. J. D. Corbett. Iiiorg. Chiw. 1991. 30, 1467.
[6] T. Schleid. G . Meyer, %. Anorg. A / / g . Cheni. 1987. 554, 118.
(71 A. Simon. T. Koehler, J. P I .1986. 116. 219.
[HI M . Lulei, S. J. Steinwand. J. D. Corbctt. Inorg. Chern. 1995, 34. 2671
[9] J. E. Mee. J. D. Corbett. Inorx. Cheni. 1965. 4, 88: D. A . Lokken. J. D. Corbett.
J. Ain. C h m . Soc. 1970. 92. 1799: A. Simon, N. Holrer. H. Mattausch. Z.
Anorx. Allg. Chenr. 1979. 456. 207
[lo] H. Mattfeld, G. Meyer. 2. Aiiorg. AUK. Chcm. 1994. 620, X5.
[I I ] Crystal structure analysis of CsPr,NbBr, ? N h :lattice conrtants for the hexagonal cell (space group P6,:ni). [t =12.070 ( 2 ) . c =13.%01 (4)& were obtained
from Guinicr powder patterns (d = 1.540562 A ) ~V = 1741.2 (8) A'. Z = 2 ,
p = 5.31 g c m - I . 13042 data ( + / I , - k . + l ; 20< 65 ) were collected with the
aid of a CAD4 diffractometer (23 "C, Mo,, radiation. / r = 307.6 cin '. crystal
dimensions 0.2 x 0.1 x 0.3 mm, min.;max. transmission: 0 865:1.091), The
structure was solved by direct methods (SHELXS) [I>]. Programs utilized were
those in the instrument package TEXSAN [13]. The residuals for the anisotropic refinement were R ( F ) = 0.029, R, = 0.030 with 2020 independent
reflections ( I , < MG > 3 o ( I 0 ) .empirical absorption correction by 4 Y scans
followed by DIFABS [14]) and 54 variables. Further details of the crystal
structure investigation and results may be obtained from the authors (J.D.C)
o r from the Fachinformations7entrum Karlsruhe. D-76344. Eggenstein-Leopoldshafen (Germany), on quoting the depository number CSD-59021
[12] G. M. Sheldrick. SHELXS-86. Universitit Gottingen. Germany. 1986.
(131 TEXSAN, version 6.0. Molecular Structure Corp.. The Woodlanda. Texas.
[I41 N. Walker. D. Stuart. Acto C r j ~ ~ t o h gScwt.
r . A, 1983, 3Y. 159.
[15] All drawings were produced with ATOMS, Shape Software. Kingsport. Tennessee.
[I61 R. Hoppe. Angen.. Chmi. 1966, 78.52: Angcw. Chiw. Inl. Ed. Eiigl. 1966.5.95.
ihid. 1970. 82, 7 and 1970. Y. 20.
1171 M. W. Paync, P. K . Dorhoat. S. J. Kim. T. R. Hughhanks, J. D. Corbcrt, firorx.
Chenr. 1992. 31, 1389.
[18] J. D . Corbett. J. So/;(/ Store Chem. 1981, 37. 335.
[I91 M . W. Paynr. J. D. Corbett, Inurg. CYicni. 1990, 29. 2246.
[20] J. D. Corbett. Inorg. S w i h 1983. 22. 15. 31
In the attempt to prepare a titanaazacyclobutane complex by
C- H o-bond metathesis. the toluene solution obtained from the
reaction of [TiCl,(thf),] with an excess of [(Me,Si),NLi] was
thermolyzed (Scheme 1) .I8]The initially intense blue color of
[Ti(N(SiMe,),J,] rapidly changed to green. After evaporation
* THF:
An Unusual and Highly Fluxional Titanium
Organometallic Compound**
Pietro Berno, Hilary Jenkins, Sandro Gambarotta,*
Johan Blixt, Glenn A. Facey, and Christian Detellier
The ability of transition and main group metal amides to
function as precursors in the preparation of metal nitrides"]
with useful physical properties is one of the key points in the
current revival of interest in the synthesis and characterization
of these species. Our interest in the utilization of organic amides
to support low-valent early transition metal complexes['] has
been prompted by the observation that these ligands may be
directly involved in a variety of transformations, which include
C-H o-bond metathesis,[31 hydrogenoly~is,[~~
dehydrogenat i ~ n , [ hydrogen
transfer reactionsJ6] and the stabilization of
methylidene functions.['] In view of the relevance of this type of
reactivity in the Ziegler-Natta process, we became interested in
studying the chemical behavior of medium-valent titanium
amides. In this paper we describe the unexpected formation of
a rare example of an alkyl(alky1idene) titanium species from a
homoleptic titanium(m) amide starting material.
Prof. S. Gambarotta, P. Berno. H. Jenkins. J. Blixt, G . A. Faccy, C . Detellier
Department of Chemistry. University of Ottawa
Ottawa. Ont K I N 6N5 (Canada)
TelePax: Int. code +(613) 562-5170
This work was supported by the Natural Sciences and Engineering Research
Council of Canada (operating and strategic grants). tmeda = N . N . N ' . N ' tetramcthylethylenediamine.
of solvent, the residual waxy solid was treated with a mixture of
CH,CI, and TMEDA and subsequently recrystallized from hexane to yield well-formed, extremely air-sensitive, colorless
needles of a new compound (1). Surprisingly, the IR spectrum
did not display the characteristic absorptions of the silazanide
group. The complex tested negatively for chlorine and positively
for lithium and combustion analysis data were in good agreement with the formulation [(Ti(p-CH,),(p-CH,)] { tmeda)Li) ,] T H F . Chemical degradation experiments with gaseous
HCI carried out with a Toepler pump yielded about 77% of the
expected amount of gas which was identified by gas chromatography as CH, (99.5 % with small amounts of ethane. traces of
propane. and no ethylene). Magnetic measurements in both the
solid state and solution showed the complex to be diamagnetic
and therefore either oxidation to the tetravalent state or reduction to the divalent state had to have occurred (see below).
Compound 1 is stable at room temperature in both the solid
state and solution but does react violently with moisture and air.
The molecular structure of 1 was elucidated by X-ray analysisrY1and consists of a monomeric [Ti(p-CH,),(p-CH,)] unit in
which the titanium atom resides in an octahedral environment
surrounded by six carbon atoms. the position of only one having
been determined, while the positions of the others were generated by the symmetry operators of the R3c space group (Fig. 1).
Fig. 1. Crystal structure of I . Selected bond lengths
and angles [ I : Til-C4
2.615(4). C4-Lil 2.19518). Li1-Nl 2.137(9). Til-Lil 3.027(9). Til-H4c 2.229. C4H4c 1 072. Til-H4c-C4 98.7, H4c-C4-H4b 110.8, H4a-C4-H4c 109.9. H4c-C4-Lil
108.7. Only two the hydrogen atoms not participating in hydrogen bonds are
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clusters, stabilizer, cspr9nbbr15n6, compounds, interstitial, typed, new
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