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Hf3Te2 A New and Remarkable Layered Compound.

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the susceptibility of the complex. Due to the lower zero-point
energy of Cr -D bonds, they are expected to be slightly shorter
than Cr-H bonds. H / D substitution in 1 may therefore lead to
small changes in the H(D) positions, and possibly even to contraction of the Cr-Cr distances. Such structural changes should
affect the coupling constant J of the antiferromagnetic interaction (i.e. IJ~Do,-,
I < IJD+,
I), leading to a shift in the relative
population of the various spin states and hence the average
susceptibility. Some support for this proposal is provided by the
observation that the direction of the isotope shifts induced by
deuteriation in all cases parallels the effects of a decrease in
temperature. While x, of solid 1 decreases upon cooling. the
13C N M R resonances of the ring carbons and the methyl group
of the ethyl substituent move upfield, and those of the methylene
carbon and the ring-bound methyl groups shift downfield.
Examination of Table 1 reveals shifts in the same directions
brought about by progressive deuterium incorporation. According to our proposal, both cooling and deuteriation are expected to shift the spin equilibrium toward lower average spin
multiplicity, and the parallel effects on the chemical shifts are
consistent with this notion.
Whatever the mechanisms responsible for PIECS, they seem
to occur with some regularity. and they can be very large. The
following demonstrates how this phenomenon can be put to
good use. Note. that the mixed isotopomers [DJ-1. [DJ-l. and
[D,]-l each feature two sets of chemically inequivalent Cp" ligands. Thus, one might have expected a total of eight resonances
in Figure 1 for each kind of carbon atom. One possible explana-
ers for fluxional processes involving hydride migration in metal
clusters range from 3 to 19 kcalmol
and encompass the
value found for 1 . This straightforward detection and kinetic
characterization of the hydride migration in I would have been
impossible for a diamagnetic analogue, in other words in the
absence of PIECS.
A number of examples suggest that NMR spectra of paramagnetic compounds frequently exhibit unusually large isotope
effects on chemical shifts. Under favorable circumstances. these
isotope shifts may facilitate experiments on paramagnetic complexes (e.g. labeling studies. dynamic N M R studies, etc.), which
cannot be done with diamagnetic molecules.
Experinierital Procedure
1. To a stirred suspension of 1.004 g (8.17 mmol) of CrCI, in 60 rnL of T H F was
added 1.271 g (8 14 mmol) of EtMe,C,Li. The reaction was allowed to stir for 2 h
at room temperature. To this solution was slowly added 8.1 mL (8.1 mmol) of
LiHBEt, (1.0 M in T H F ) by syringe. The mixture was stirred for another 30 min.
and then the T H F was removed under vacuum. The resultingsticky brown solid was
extracted with pentane and the extract filtered. The pentane solution was concentrated and cooled to -30 C to yield 0.991 g (1.22 mmol. 60%) of 1. ' H N M R
(C,D,): 6 =7.Y (s, 6 H ) . 7.3 (s. 6 H ) , 3.4 (5, 2 H ) . 1.1 (s. 3H): I3C N M R (C,D,):
(s), 2714 (w). 1448 (s). 1365 (s), 1303 (w). 1018 (m). 945 (w). 551 (5)cm-I. Analysis calculated f o r C,,H,,Cr,:
C 65.65; H X.97. Found: C 65 55: H 8.88.
{I,,, (299 K)= 3.50 p,, (1.75 pB:Vr).
[D,]-1. The procedure was the same as described above, except LiDBEt, ( 9 5 % D)
was used. A mixture of[Cp,Cr,(ji,-D),] ([DJl, ca. 80%) and [Cp:Cr4(p3-D)3(p3H)] ([D3]-l,ca. 20%) was obtained. ' H N M R (C,D,): [DJ-1: 6 = 6.8 (s), 6.2 (s).
3.1 ( S ) . 1.1 (S);[D,]-l:i)=7.0(s),6.4(S),3.1 (s), 1.1 (sj;'3CNMR(C,D,):[D,]-l:
93.0. 86.8, 34.8 ppm.
Received: June 10, 1994 [ Z 7025 IE]
German version. Angeiv. C h m . 1994, 106. 2389
[ I ] 1. Bertini. C. Luchinat, M M R o/ Purun~ugnericMolecules iri Bio/i~gicolSwfems.
Benjamin,'Cummings. Menlo Park, CA. USA, 1986.
[2] a) R. R. Horn. G. W Everett. Jr..J. Am. Chrin. Sor. 1971,93,7173; b) B. Evans.
K . M. Smith, G N. La Mar. D. B. Viscio, ihril. 1977, 99. 7070: c ) K . H.
Theopold. J. Silvestre, E. K . Byrne. D. S. Richeson. 0rgunornerullrr.c 1989, 8.
2001 : d ) N. Hebendanr F H. Kohler, F. Scherbaum, B. Schlesinger. Mugn.
Rrson. Chcrii. 1989,27.798; e) C. J. Medforth, F.-Y. Shiau. G. N. La Mar, K. M.
Smith, J. Cheni. SOC. Cheni. Comniun. 1991, 590.
(31 K. H. Theopold. A r c . Chefn. RFS.1990. 23. 263.
[4] R . A. Heintr. B. S. Haggerty. H. Wan. A. L. Rheingold, K. H. Theopold,
Aiigm.. Chcni. 1992. f04. 1100: Angcw. Cheni. In!. Ed. Engl. 1992, 31. 1077
Mug". Rcson. Spec'rrosr. 1988, 20. 207.
[5] P. E. Hansen. P ~ o g Nucl.
[h] a) L. R. Nevinger, J. B. Keister. O,.gurronzrrrr/lrr. 1YYO. 9. 2312; b) E. Band, E. L.
Muetterties, Chern. Rci,. 1978. 78.639; c) J. Evans. A d i . Orgunnme!. Chi,rn. 1977,
16. 319.
298 K
273 K
248 K
223 K
Fig 1. Temperature dependence of the I3C NMR resonances attributed to thc
methyl groups of the ethyl suhstituents of [Cp:Cr,(jr.~-H),~,,({i~-D)"]
(I? = 0-4).
tion for the observation of one resonance only for each isotopomer is the occurrence of a fluxional process. Such a process
might be frozen out at lower temperature. Accordingly. Figure 2
shows the temperature dependence of one set of I3C N M R resonances. Upon cooling. the three intermediate resonances
broaden. collapse, and eventually reemerge to give a total of at
least seven peaks. The estimated rate constant for the exchange
process at the coalescence temperature is k,,, li = 120 s - ', and
substitution of this value into the Eyring equation yields
AG * = 12 kcal mol- '. Previously determined activation barri-
Hf,Te,: A New and Remarkable Layered
Compound **
Robert L. Abdon and Timothy Hughbanks*
Binary, early-transition-metal chalcogenides of surprisingly
simple composition continue to be found. Recent attention to
this chemistry and advances in synthetic methodology have produced Ta,S, ,[l.'] Ta,Te, ,[31 Ta,Te,,[41 and Ta,Se.['] Investigations of tantalum- and niobium-rich chalcogenides have yielded
novel layered materials with structures related to the body-cen[*I Prof. T Hughbanks. R. L. Abdon
Department of Chemistry
Texas A & M University. College Station. TX 77843 (USA)
Telefax: Int. code +(409)847-8860
[**I This work was generously supported by the National Science Foundation
(Grant DMR-9215890) and by the Robert A. Welch Foundation (Grant A1132).
tered cubic (bcc) metals. Ta,Se can be regarded as an insertion
phase containing four layers of bcc-like tantalum sandwiched
between layers of selenium. An isostructural sulfide exists in the
ternary compound Ta, 6oNb,,,S.[h. 'I At the composition
(M,S,) five layers of bcc metal are found between
the sulfide layers.[81 Mixed tantalum/niobium sulfides having
higher niobium content have been prepared,['.
but their
structures are similar to the niobium-rich sulfides Nb, ,S, and
Nb,,S, , which are less closely related to the bcc-metal structure.
Preparative investigations of hafnium-rich tellurides incorporating later 3 d transition metals have produced Hf,MnTe, and
Hf,FeTe, .I' These materials are structurally related to the
condensed cluster Ta compounds Ta,,M,Se,, Ta,MSe,, and
Ta,MZS,.["In our attempts to prepare related, ternary
compounds of hafnium and tellurium, the binary phase Hf,Te,
was discovered. This remarkable material is the only reduced,
binary hafnium telluride, and like Ta,Se, it has a simple structure a n d composition.
We prepared Hf,Te, by direct reaction of stoichiometric
amounts of the elements (Hf 96.9%, including 2.9% Zr, and Te
99.99%: Johnson Matthey) in sealed N b capsules, which were
in turn sealed in evacuated and flame-baked silica tubes. The
temperature of the reaction vessel was increased uniformly to
1000 'C over 5 days, and the product was isolated in quantitative yield after 10 more days at this temperature. Attempts to
grow single crystals by vapor phase transport with TeCI, repeatedly produced only microcrystalline powders. However, by employing KC1 as a flux (molar ratio, 2 KCI: 1 Hf,Te,) and cycling
the reaction temperature between 950 "C and 1000 "C repeatedly
over a two-week period, black, square crystals suitable for
single-crystal X-ray studies were obtained (Table l)." 51 No contamination by niobium was detected in elemental analysis of the
Fig. I . The Hf,Te, structure viewed approximately along the (110) direction. Hf
atoms are shown as dotted circles and Teas open circles. Only interatomic distances
less than 3.6 are shown as bonds.
The electronic band structure of Hf,Te, was calculated with
the extended Hiickel method.[16' The Fermi level lies just below
a pronounced minimum in the total density of states (DOS)
diagram (Fig. 2 a). Projected DOS diagrams show that the ener-
Table I . Structui-'11parameters for Hf,Te,: space group I4,mrnni (no. 139). Z
( I = 3.68.77(3)A. ( ' = 1 7 . 9 0 1 ( 2 ) ~ .
-1 1
U (equiv)
Te 1
x 1031
7 (1)
7 (1)
7 (1)
As in Ta,Se and the mixed Ta/Nb sulfides, Hf,Te, is formally
an insertion phase related to that of bulk body-centered
cubic metal. After every three layers of hafnium, two layers of
tellurium are inserted. The result is a layered structure in which
slabs are made up from three square nets of hafnium sandwiched between two layers of tellurium (Fig. 1). These Te-Hf,Te sandwiches are stacked, with only weak interlayer interactions, to form the full three-dimensional structure. Within the
slabs, thc more oxidized metal centers (Hf2) are those bound to
four tellurium atoms at the exterior of the layer. Each of these
metal atoms forms four bonds to the hafnium atoms ( H f l ) in
the central net (3.1229(4) A) and one longer bond through the
slab (3.4454(12) A) to a symmetry-equivalent atom. Each tellurium is five-coordinate with respect to hafnium atoms in the
same slab (Tel - H f 2 , 4 x 2.9120(5); T e l - H f l , 1 x 3.0245(9) A).
Guinier powder films show two very weak lines, suggesting the
possibility of a ( b b a x P b ) superlattice. The existence of this
superlattice could not be detected in the single crystal study, and
currently is under investigation.
Fig. 2 a) Total density of states (DOS) diagram for Hf,Te,. The energy range
includes the Te 5p bands and the Hf d and s bands. b) Tellurium contribution to the
DOS. c) Hafnium contribution to the DOS. Filled levels are shaded.
gy levels between - 15.0 and - 10.5 eV are primarily localized
on Te (Fig. 2b), while the higher levels have mainly H f d and s
character (Fig. 2c). The mixing of Hf-based orbitals into the
Te-based manifold gives evidence for significant Hf- Te covalency. Crystal orbital overlap populations (COOPS)['71 yielded
a valence electron concentration (VEC) that indicates that all
levels with strongly Hf-Hf bonding character are filled (Fig. 3).
At the same time, these levels have only moderately antibonding
Hf-Te character. Isoelectronic Zr,Te, adopts a defect-WC
structure, as d o the other known Group IV chalcogenides of the
same composition."'
Although these calculations rationalize the structure of Hf,Te,, the underlying factors controlling
the choice between structural types for isoelectronic compounds
remain unclear.
The title compound belongs to a broader class of chalcogenides having a structure based on the stacking of 44 nets of
atoms. The transition from three-dimensional to two-dimensional structures in these materials is determined by the lattice
Synthesis and Characterization of the First
Compounds Containing a Stable Phosphirenyl
Cation: Crystal and Molecular Structure of
Anthony G. Avent, F. Geoffrey N. Cloke,
Kevin R. Flower, Peter B. Hitchcock,
John F. Nixon,* and David M. Vickers
Phosphirenium salts 1" 31 do not exhibit aromatic behaviorC4]presumably because the 3dn-2pn interaction between the
phosphorus atom and the C=C double bond is weak as in the
isoelectronic ~ilirene.[~]
On the other hand it has been proposed[61that a strong 3pn-2pn interaction might be expected
between the electron-deficient phosphorus atom and the double
bond in the phosphirenyl cation 2 which represents the simplest
Fig. 3. Crystal orbital overlap population (COOP) curves showing averaged Hf Hf
interactions in Hf,Te,. Levels above the energy axis are bonding while those below
are antibonding. Filled levels are shaded.
constant a and the size of the chalcogenide. In ZrGeTe (PbFCI
type), the stacking sequence of the nets is Te-Zr-Ge,-Zr-Te. The
larger a dimension of 3.866 A reduces steric crowding in the Te
nets and permits much shorter Zr-Te contacts between adjacent
layers. On the other hand, isostructural ZrSiTe has a significantly shorter a axis (3.692 A) that precludes such interlayer Zr-Te
In Hf,Te, the a dimension is only 3.6837(3) A,
slightly shorter than that of ZrSiTe. The Hf-Te contacts between adjacent layers in Hf,Te, are 4.195 A, too long for significant Hf-Te bonding. The Te-Te distances between adjacent
layers of 3.785 A suggest that the structure is highly two-dimensional, with van der Waals interactions between the slabs.
Received: May 19, 1994 [Z 6950163
German version: Angew. Chem. 1994. 106, 2414
[l] S:J. Kim, K. S. Nanjundaswamy. T Hughbanks, Inorg. Clien?. 1991. 30, 159164.
[2] H. Wada. M. Onoda, Mu/er. Res. Bull. 1989, 24, 191-196.
[3] M. Conrad. B. Harbrecht in l V t h Eur. Conj. Solrd S m e Chrm., Gesellschaft
Deutscher Chemiker, Dresden, 1992, p 324.
[4] M. Conrad, B. Harbrecht. J. alloy^ Coinp. 1992. 187. 181- 192.
[5] B. Harbrecht, Angrn. Cliem. 1989. / O f . 1696-1698; Angeiv. C'heni. h t . Ed.
Engl. 1989, 28, 1660-1662.
[6] K . S. Nanjundaswamy. T. Hughbanks. J. SolrdSrure Cliem. 1992. YK. 27X-290.
[7] X. Yao. G . J. Miller. H. F. Franzen, J. Alloys Coinp. 1992. 183. 7-17.
[8] X. Yao. H. F. Franzen. J An?. Chem. Soc. 1991, 113. 1426-1427.
[9] X. Yao. H. F. Franzen. J. Solid Stute Chem. 1990. 86. 88-93.
[lo] X. Yao. H . F. Franzen. J Alloys Comp. 1992, 182. 299-312.
[ l l ] R. L. Abdon. T. Hughbanks, Chon. Mureu. 1994, 6. 424-428.
[12] B. Harbrecht. J. Le.s.s Comn?on M e / . 1988, 141, 59 71.
[13] M. Conrad. B. Harbrecht. J. Alloi,, Conip. 1993. 197. 57 64.
[I41 B. Harbrecht. H. F. Franzen. J Less Commoii Met. 1985, 113, 349-360
[15] Single-crystal X-ray analysis: intensity data were collected on a Siemens R3
diffractometer with Mo,, radiation ( p =75.518 mm-I); crystal size
0.2 x 0.2 x 0.001 mm; 0-20 scan. 2fI,,, =70'; 1014 reflections ( * / I . + k , I),
laminar empirical absorption correction based on psi-scans, 188 independent
reflection$ I > 2 4 1 ) . R(F,).'R,,(F2)= 0.0197:0.0512. Further details of the
crystal structure investigation are available on request from the Director of the
Cambridge Crystallographic Data Centre. 12 Union Road. GB-Cambridge
CB2 IEZ. on quoting the full journal citation.
[16] R. Hoffmann. J. Clwm. Phi.s. 1963, 39, 1397-1398, M. Whangbo. R. Hoffmann. 1 Am. Chem. Soc. 1978. 100. 6093-6098. Parameters for Hf were obtained from a charge-iterative calculation on Hf,S. Parameters for Te were
taken from ref. [ I I ]
[17] T. Hughbanks. R. Hoffmann. J A m . Cllein. Soc. 1983, /US, 3528-3537
[IS] H. Hahn. B. Harder. U. Mutschke. P. Ness, Monutsh Clicm. 1957,292, X2-96.
[I91 H. Hahn, P. Ness. Z. Anorg. A/%. C'heni. 1959. 302. 39-49.
[20] H . Sodeck. H. Mikler, K. Komarek. Munutsli. Cheni. 1979. f f f j , 1-8.
[21] H. Onken. K. Vierheilig, H. Hahn. Z . Anoi-X. A / / , .C/irm. 1964. 233, 267-279
[22] W. Bensch. P. Durichen, Acru CrJ,srullugr.Sect. C 1994, 50. 346-348.
2n-aromatic species containing phosphorus. To date, however,
all attempts to synthesize this type of compound have been
for example treatment of the chlorophosphirene ring ClPC(Ph)=kPh with metal salts containing the
[BFJ or [BPhJ ions led only to the fluoro- or phenyl-sub7
stituted phosphirenes XPC(Ph)=CPh (X = F. Ph), respectively.
Theoretical calculations on silirenyl cations['] suggest that, if
synthesized, they would not be aromatic; on the other hand it
has been proposed that phosphirenyl cations would receive
some extra stabilization by cyclic delocalization if the destabilizing e-TC
interaction were suppressed by P c o m p l e ~ a t i o n . [O1~ ~
We describe herein the first synthesis of the phosphirenyl
cation 2, (R=tBu) as a ligand in the red-orange nickel complex
3, whose structure has been elucidated by mass spectrometric
and multinuclear NMR studies and confirmed by a singlecrystal X-ray structural study on its [W(CO),] adduct 4.
VCH ~ ~ r / u , ~ ~ ~ e ~mhH,
e l / ,D-6Y45f
s ~ / i ~ Weinhein?,
Recently" we described the first direct application of metal
vapor synthesis using phosphaalkynes; cocondensation of
Prof. Dr. J. F. Nixon. Dr. A G . Avent. Prof. Dr. F. G . N. Cloke,
Dr. K. R. Flower, Dr. P. B. Hitchcock, D. M Vickers
School of Chemistry and Molecular Sciences
University of Sussex
GB-Brighton, BNl 9QJ. Sussex (UK)
Telefax' Int. code +(273)677196
We thank the Engineering and Physcial Sciences Research Council for their
continuing support of our work
0570-0833:94:2222-233fjS 10 00 + .25;0
A n g e w C/imi. I f i r . Ed. Ens/. 1994, 33, Yo. 22
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