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Comments on the Molecular Structure and Bonding In [W4Cl(O)(OiPr)9] and [W4(O)(OiPr)10]. Analogies with Tetranuclear Carbonyl Clusters

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2.29, Li-C 2.00 A) indeed suggests that the lithium is
displaced toward the phosphorus atom. A comparison with
the structurally characterized transition-metal derivative
(PC,Me,),ZrCI, revealed no significant differences between
the bond distances o r angles of the heterocyclic anion in the
two structures.[*]
When the reduction of 2 was carried out in the absence of
TMEDA (in THF), donor-free LiPC,Me, was isolated as a
white solid.[g1In addition, 2 could be reduced with potassium; in the presence of 1.O equivalent of IS-crown-6, the salt
K( 18-crown-6)PC4Me, was isolated as colorless crystals in
Monitoring of the lithium reduction of 2 in
[ D J T H F by ' H o r "P N M R allowed the detection of an
intermediate, which could be isolated and identified as the
1,l'-biphospholyl 3.[''I This dimer was presumably formed
by a fast reaction of phospholyl anion with remaining
chlorophosphole starting material. No N M R resonances of
LiPC,Me, were observed until all of the chlorophosphole
had been consumed. In a separate experiment LiPC,Me,
was allowed to react with 2. Even at -78°C this reaction
was too fast to be followed by N M R and yielded 3 cleanly.
Protonation of the phospholyl anion (with NH,BF, or
HBF,) yielded a new compound which exhibited a fairly
complex 'H N M R spectrum. The spectroscopic data of this
material are consistent with a dimer (5 in Scheme 1)["l
formed by a Diels-Alder reaction of the 2 H-phosphole B.
which is in equilibrium with the 1 H-phosphole A. This transformation is well precedented." 31
Zirconacyclopentadienes similar to 1 are easily prepared
~ ' ~ ~transformawith a wide variety of ring s u b ~ t i t u e n t s . The
tions reported here thus represent a convenient synthetic
entry to phosphole chemistry. The isolation of pure phospholyl anions in particular should facilitate the use of these
nucleophiles in further reactions. We are currently employing 4 in the synthesis of various organometallic derivatives
and we are also investigating the extension of this chemistry
to other group 15 elements.
Experimental Procedure
NMR: Bruker WM 300 spectrometer (300 MHz for 'H, 75.47 for I3C, and
121.49 for "P). Shifts are reported relative t o T M S for ' H a n d I3C and relative
to an external PCI, reference (6 = 219) for "P. MS: Kratos MS 890. IR:
Mattson Alpha Centauri FT-IR. X-ray: Nicolet R3,,/V. M.p. uncorrected.
2 : CpJrCI,
(13.5 g, 46.2 mmol) was reduced using 46.2 m L of a 2.0 M solution
of n-butyllithium (92.4 mmol) at -78'C in T H E After addition of 2-butyne
(5.0 g, 92.4 mmol), the reaction mixture was allowed to warm to room temperature and then stirred for 16 h. The mixture was filtered, the solvent evaporated,
and the zirconium metallacycle 1 crystallized from pentane at - 30 "C (93.8 %
yield). Compound 1 ( 3 . 2 g. 9.7 mmol) was dissolved in pentane, and PCI, (1.3 g,
9.7 mmol) was added. An immediate color change from deep red to yellow was
observed. Following filtration of the reaction mixture and evaporation of the
solvent. the residue was sublimed at 0 'C and the chlorophosphole 2 was collected as an air-sensitive yellow oil (85% yield).
4: Excess lithium dispersion was added to a T H F solution of 2 (300mg.
0.17 mmol), containing an excess of TMEDA. After stirring for 1 h, the reaction mixture was filtered and thesolvent was evaporated. The phospholyl anion
was recrystallized from ether a t - 30 "C and isolated as colorless crystals (80 %
Received: May 9, 1989 [Z 3330 IE]
German version: Angew. Chem. 10f (1989) 1394
CAS Registry numbers:
1, 84101-39-3; 2, 122762-50-9; 3, 122762-51.0; 4, 122762-53-2: 5, 122762-52-1 :
Cp,ZrCI,, 1291-32-3, LiPC,Me,,
122762-55-4; 2-butyne, 503-17-3.
J = 0.9, 10.1 Hz; 3H). 1.85 (m; 1 H). 2.05(m; 1 H): "C NMR (CDJI,):
6 = 12.77(dd,J(PC) = 9.2. 15.7 Hz), 13.19(s), 14.29(s), 14.82(s). 17.02(s),
17.78 (d, J(PC) = 26.6 Hz). 21.73 (dd, J(PC) = 4.9. 31.4 Hz). 23.49 (d.
J(PC) = 33.9 Hz). 36.77 (d. J(PC) = 15.6 Hz). 50.05 (dd, J(PC) = 5.1,
9.7 Hz), 61.85 (d, J(PC) = 24.2 Hz), 68.42(s), 135.69(s). 136.35(s),
146.95(s): "PNMR(C,D,):6 = -26.90(d, J(PP) = 203 Hz),4.75(d). IR
(Nujol): C = 2712(w). 1612(m), 1304(w), 1276(w), 1202(m), 1144(m),
1123(m), 1108(w), 1086(s), 1063(s). 1025(s), 987(m), 758(m), 738(m).
698(s)cm-'. MS: 280 (Me, 1.6%). 140 (100%). M.p. = 87-90'C.
Correct eiemental analysis.
1131 C. Charrier, H. Bonnard. G. de LauLon, F. Mathey, J. Am. Chem. Suc. 105
(1983) 6871. Stable 2-alkylphospholes have been reported: F. Zurmuhlen.
M. Regitz. J. Orgunomrt. Chern. 332 (1987) C l .
(141 a) E. Negishi, T. Takahashi. Aidrichimicu Aria 18 (1985) 31; b) W. A.
Nugent, D. L. Thorn. R. L. Harlow, J. Am. Chrnz. Sac. 109 (1987) 2788.
Comments on the Molecular Structure and Bonding
in [W,CI(O)(OiPr),] and [W4(0)(OzPr)l,,].
Analogies with Tetranuclear Carbonyl Clusters
By Malcolm H. Chisholm,* Kirsten Folting,
Charles E. Hammond, John C. Huffman,
and James D.Martin
The cluster 1 was discovered as a minor product formed in
the preparation of [W4(H)2(OiPr)14]from the reactants
[W,(OtBu),] , NaOiPr/iPrOH, and Me,NHFCle.['l Com-
112549-01-6; K(1R-crown-6)PC4Me,.
[I] Review: F. Mathey, Chem. Rev. 88 (1988) 429.
[2] P. J. Fagan, W. A. Nugent. J. Am. Chem. Sac. 110 (1988) 2310.
[ 3 ] 2: ' H NMR (C,D,): 6 = 1.85 (d, J ( P H ) = 9.9 Hz; 6H). 1.42 (d,
J(PH) = 5.2Hz; 6H). "C N M R (C,D,): 6 = 11.67 (d, J(PC) =
24.2 Hz), 13.46(~). 136.04 (d, J(PC) = 19.6 Hz), 144.95 (d, J(PC) =
9.7 Hz). "P NMR (C,D,): 6 = 80.69(s). IR (neat): v ' = 2998(s), 2911(s),
2839(s), 2723(w), 1442(s), 1373(m). 1297(m), 1067(m), 782(s) cm- MS
for C,C,,CIP: calcd 174.0365. found 174.0369; ( M + 2 ) O : calcd 176.0336,
found 176.0344, The observation of a I-bromophosphole intermediate by
NMR spectroscopy has been reported: C. Charrier, H. Bonnard. F.
Mathey, D. Neibecker, J. Orgunomet. Chem. 2331 (1982) 361.
[4] a) G. Muller, H . Bonnard, F. Mathey. Phosphorus Sulfur 10 (1981) 175: b)
R. M. G . Roberts, J. Silver, A. S. Wells, Inorg. Chm. Acru IfY (1986) 1 ;c)
J.-M. AkardL. E. Deschamps. F. Mathey. Phosphorus Su//ir I 9 (1984) 45.
[5] 4: 'HNMR([D,]THF):6 = 1.86(~:6H).2.06(d,J(PH)= 10.3 Hz:6H).
2.09 (s; 12H). 2.21 (s; 4H). I3C NMR ([DJTHF). 6 = 14.03(~),16.29(d.
J(PCI = 29.4 Hz), 45.15(s). 56.12(s). 125.17(s). 135.09(d. J(PC)
= 33.2 Hz): 3 ' P N M R ([DJTHF): 6 = 64.66(s). 1R (Nujol): i= 2720(w),
1289(s), 1249(w). 1184(w), 1161(m). 1130(m). 1102(w), 1067(w), 1038(s),
1018(m). 946(m). 892(w). 789(m) cm-'. M.p. 101 -104 'C. Correct elemental andlysis.
[6] Colorless crystals from penlane, monoclinic, P2,in. II = 8.927(2). h =
15.857(3), c = 12.704(2)
= 108.870(14) , Z = 4, R = 0.072. Further
details of the crystal structure investigation may be obtained from the
Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlichtechnische Information mbH, D-7514 Eggenstein-Leopoldshafen 2
(FRG), on quoting the depository number CSD-53940. the names of the
authors, and the journal citation.
[7] a) G. Kaufmann. F. Mathey, Phasphurus 4 (1974) 231: b) C . Guimon, G.
Pfister-Guillouzo. F. Mathey. Nouv. J. Chim. 3 (1979) 725; c) N M. Kostic.
R. F. Fenske. 0rgunomerallic.s 2 (1983) 1008.
[8] F. Nief, F. Mathey. L. Ricard. F. Robert. 0rgunonzeiullic.r 7 (1988) 921.
[9] LiPC,Me,: ' H NMR ((DJTHF): 6 = 1.87 (s: 6H). 2.07 (d, J ( P H ) =
10.2 HL; 6H). "P NMR (ID,]-THF): 6 = 62.94(s). This compound was
previously prepared in situ: C. Charrier, F. Mathey. Tetruhedron Lei/. 28
(1987) 5025 (see also Ref. (81).
[lo] K(18-crown-6)PC,Me4: ' H NMR (C,D,): 6 = 2.50 (s; b H ) , 2.87 (d,
J ( P H ) = 10.6 HI: 6H). 3.13 (s; 24 H); "P NMR (C,D,): d = 74.16(s),
M.p. 210-212 C.
[ I l l 3: ' H NMR ([DJTHF): 6 = 1.74(t, J(PH) = 5 Hz; 12H). 1.82 (s; 12H);
"CNMR([D,]THF):S = 13.20(t,J(PC) = 1 1 . 3 H ~ )13.78(s).
J ( P C ) = 3.3 Hz). 142.63 (t. J ( P C ) = 5.6 Hz). "P NMR ([DJTHF):
6 = -9.40(s), IR (Nujol): B = 2717(w), 1598(m), 1316(m). 1260(m),
1143(s), 1067(s), 1020(s), 958(m), 904(m), 786(m) cm-I. Correct eiernental
[12] 5 : 'H NMR (CD,CI,): 6 = 0.83 (dd, J = 7.0, 15.4 Hz: 3H). 1.10 (dd.
J = 7.4, 19.7 Hz: 3H). 1.19 (s; 3H). 1.43 (t, J = 0.9 Hz; 3H). 1.45 (d,
VCH I/i.rlugsge.sell.~rhafr
mhH. 0-6940 Weinhein?, t989
[*] Prof. M. H . Chisholm, Dr. K. Folting. C. E. Hammond, Dr. J. Huffman,
J. D. Martin
Department of Chemistry and Molecular Structure Center,
Indiana University
Bloomington, IN 47405 (USA)
[**I This work was supported by the Department of Energy, Office of Basic
Sciences. Chemistry Division.
Angrw. Chem. Inr. Ed. EngI. 28 11989) N o . 10
pound 1 is very soluble in hexane and is readily obtained as
orange crystals from Et,O. This allows it to be isolated in
analytically pure form and easily separated from
and [W,(OiPr),,], which are present in the
reaction mixture. The reaction pathway leading to 1 is not
The cluster 2 is observed as a minor product in the thermal
decomposition of [W,(OiPr),,] in hydrocarbon solvents and
is also formed upon addition ofH,O (0.5 equiv.) to solutions
of [W,(OtBu),] in hexane/iPrOH. Compound 2 forms analytically pure, dark red-brown crystals from Et,O and reacts
with Me,NHFCle (I equiv.) to generate 1.
The ' H N M R spectra of 1 and 2 suggest that they are
structurally related, having five types of OiPr ligands. In 2
these form five pairs with one having nondiastereotopic
methyl groups, whereas in 1 they are in the integral ratio
2:2:2:2:1 with the methyl groups of the unique isopropyl
ligand being nondiastereotopic. Evidently both molecules
have one plane of symmetry.
The molecular structure of 1, deduced from an X-ray
study,"] is shown in Figure 1. A WCl(0iPr) unit caps a W,
@ alkoxide
Q 0x0
The bonding in 1 is best understood from a fragment
molecular orbital analysis.[31We consider the cluster to be
formed from the fragments WCI(0R) and W,(O)(OR), and
have investigated the bonding by using the method of Fenske
for the model compound [W,Cl(O)(OH),] . An
OH bond distance of 0.96 A was used; otherwise, bond distances and bond angles for the model compound were taken
from the solid-state molecular structure of 1 and idealized to
C, symmetry. The important interactions are shown in Figure 2.
0 tungsten
Fig. 1 . Two views of the central W,CI(O),, skeleton of [W,Cl(O)(OiPr),]. Pertinent distances [A1 and angles ("]: W1-W2 2.847(2), WI-W3 2.958(2), W1-W4
2.48411); W2-W3 2.965(2), W2-W4 2.47011) W3-W4 2.547(1), W4-Cl5
2.462(4). W - 0 (terminal) 1.88(2) (averaged), W - 0 (0x0) 1.92(1), W - 0 (p-OR)
2.01 -2.07; C15-W4-039 85.8(4).
triangle that is supported by two bridging OiPr ligands and
one bridging 0x0 group. The geometry about each tungsten
atom in the basal plane corresponds to a square plane
formed by two terminal OiPr ligands and two oxygen atoms
from either two bridging alkoxide ligands or one bridging
alkoxide and one 0x0 ligand. Of particular note are the short
W-W distances of ca. 2.50 A from the tungsten atoms of the
W, unit to the capping WCl(0iPr) unit and the longer W-W
distances in the basal plane (2.85-2.96A). In a localized
valence bond (V.B.) description, these are suggestive of a
significant contribution of resonance form B relative to the
fully delocalized form A for a 12-electron M, unit.
The ' H NMR spectrum of 1 is entirely consistent with the
structure observed in the solid state and the structure of 2 can
most reasonably be formulated as being related to that of 1
by the formal replacement of Cl by OiPr. In solution, however, there must be facile rotation of the W(OiPr), unit of 2
above the W, fragment.
Angew,. Chein. In,. Ed. Engl. 28 (1989) No. 10
Fig. 2. Frontier orbital interactions showing the formation of [WCl(O)(OH),]
Ordinate: €Lev].
from the fragments WCI(0H) and W,(p-O)(p-OH),(OH),.
The molecular orbitals of the W,(O)(OH), fragment are
similar to those seen in the W,(OR), fragmentr5] of
[W,(OR),(p,-CMe)],'61 though the presence of the bridging
0x0 group results in a reduction of symmetry from C,, to C,
and a loss of one electron from the M, cluster fragment. The
orbitals of the WCI(0H) fragment are reminiscent of those
expected for an ML, fragment except for the notable mixing
of the la" and 2a" orbitals so as to minimize the n antibonding between the tungsten d, and oxygen p, electrons.
On combining the fragments, the filled la' and la" orbitals
of WCI(0H) find their match with unoccupied 4a' and 2a"
nonbonding orbitals of the tritungsten fragment. Similarly,
the la', 2a', and la" W-W bonding orbitals and the 3a' occupied nonbonding orbital of the W, fragment, made up of the
in-phase combinations of tungsten z2 orbitals, interact
strongly with the respective 2a', 2a", 3a'. and 4a' unoccupied
orbitals of the ML, cap. Placing electrons into M, nonbonding (or weakly antibonding) orbitals and withdrawing electrons from the M, bonding orbitals causes the Mulliken
atomic charges to be - 0.631 for the capping tungsten atom
and 1.407, 1.407, and 1.343 for the tungsten atoms in the
:c) VCH Verla~.~~:esellschqfi
mhH, 0.6940 Wcinheim, 1989
Complexation of a Novel Organoytterbium(r1)
Ligand with Dimethylplatinum(ii): Crystal Structure
of the Resulting Heterobimetallic Complex **
basal plane. This results in a severe weakening of the M-M
bonding in the basal plane and leads to M-M multiple bonding to the capping tungsten atom."] The importance of the
V.B. description depicted by resonance structure B, relative
to that of A, is apparent. A slightly weaker interaction would
be obtained were the WCl(0) fragment rotated by 18O'such
that the CI was directed toward the bridging 0x0 group owing to an increased population of the W-0 n* orbitals.
We have previously discussed''] the relationships between
d3-W(OR), and d9-Co(CO), and their respective clusters of
formula M,X,(p,-Y)
( M = W, X = OR, Y = CRr6] or
Pral). Aspects of the bonding in 1 are reminiscent of the
hypothetical cluster 3 discussed by Hoffjl?unn,['l where the
By Glen B. Deacon,* Andreas Dietrich, Crnig M . Forsyth,
and Herbert Schumann *
Dedicared fo Prqfissor Friedo Huber on [he occasion
of his 60th hirthdny
Heterobimetallic complexes (see, e.g. Ref. [I]) have attracted attention because of the possibility of unusual catalytic activity, including redox catalysis due to cooperative
reactivity involving both metal centers. We now report a new
organoytterbiuni(i1) ligand 1, as well as the preparation and
crystal structure of a derived heterobimetallic complex 4
with Yb" and Pt" centers. The present example is novel
among organolanthanoid d-block-element bimetallic comp l e x e ~ [ ~in- ~having
the laiithanoid in the donor rather than
the acceptor part of the molecule.
Metalation of diphenylphosphinocyclopentadiene'51with
bis(pentafluorophenyl)ytterbiuniL6I gives the phosphinoytterbocene I as a green air-sensitive solid171(Scheme 1). Dissolution of 1 in THF gives a wine-red solution from which
orange-red 2 is isolated. The distinctive identities of 1 and 2
are evident from solid-state visible spectra.r71The chemical
shift of the single 3 1 P N M R resonance of 1 in THF['] is
indicative('] of equivalent uncoordinated phosphane groups.
This result, together with the similarity of the visible spectra
of 1 in T H F and solid 2, suggests no P -+ Yb coordination in
the latter, but such bonding cannot be ruled out for solid 1.
Thus, 2 probably has pseudo-tetrahedral eight coordination
for ytterbium as observed in 4 (see below).
Reaction of a suspension of 1 in toluene with PtMe,(cod)
(cod = cis,&-cycloocta-I ,5-diene) results in displacement of
cyclooctadiene and formation of the air-sensitive heterobimetallic complex 31a1(Scheme 1). Coordination of the
hydrides of4[''' are treated as protons. We suggest here that
the Os,(CO);' fragment is related to the Co,(CO), fragment
in a similar fashion as W,(O)(OR), is to W,(OR),. Furthermore, we suggest an internal isolobal analogy relates the yz
and zz orbitals of the d4-WCI(OH) fragment to the xz and sp
hybrid orbitals of the d'O-PtL, fragment. From this simple
analysis. we conclude that the orientation of the respective
ML, fragments to the M, plane should be rotated by 90" for
the early and late cluster elements, W versus Os, as indeed is
observed by X-ray crystallography. Nonetheless. the orthogonal sets of orbitals in both ML, and M,X, fragments allow
facile rotation of the capping ML, groups, as seen here from
the 'H N M R spectrum of 2 in [DJtoluene at 22 "C.
Received: May 16. 1989 [Z 3339 IE]
German version: Angew. Chem. 101 (1989) 1399
[l] M. H.Chisholm. J. C. Huffman.C. A. Smith,J. A m . Chem. Sor. lOci(1986)
222; M. Akiyama, M. H. Chisholm, D. A. Haitko. D. Little, F. A. Cotton,
M. W. Extine. J! Am. Chem. Sac. 101 (1979) 2504.
[2] Crystal data for [Wd(Cl)(0)(OiPr)J 1 !2 ( E t 2 0 ) at - 146 C: ( I =
41.172(18). h = 9.185(2). c = 22.718(8) A. fi = 97.15(2)'. 2 = 8, Q ~ , , =, ~
2.113 g ~ m - space
~ . group C2jc. Of 6513 reflections collected (Mo,,),
6 i
2 0 < 45 ), 5594 were unique and the 4851 reflections having F >
3 a(F) were used in the full least-squares refinement. The asymmetric iinit
contains one W, complex and one half molecule of ether (solvent) located
at a twofold axis. All the hydrogen atoms. except those on the solvent were
introduced in fixed calculated positions. The full-matrix least-squares refinement was completed using anisotropic thermal parameters on the
atoms in the W, complex and isotropic thermal parameters on the solvent
atoms (O(43) through C(45)) and fixed hydrogen atoms. The final residuals
are R = 0.051 and R , ( I . ) = 0.050. Further details of the crystal structure
investigations may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH.
D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository
number CSD-53966. the names of the authors. and the journal
[3] R. Hoffmann, Angeic. Chem. 94 (1982) 725; Angeii. Chrm. Inr. Ed. EngI.
21 (1982) 711; T. A. Albright, J. K . Burdett. M. H. Whangbo: Orhiruf
bitrrucrions in Chemistrj, Wiley, New York 1985.
[4] M. B. Hall, R. F. Fenske, /norK. C h m . 11 (1972) 768.
[5] M. H. Chisholm, D. L. Clark, M. J. Hampden-Smith. D. M. Hoffman.
Angrir. Chcm. 101 (1989) 446; Angric. Chem. Int. Ed. Engl. 28 (1989)432:
M. H. Chisholm, B. K. Conroy, J. D. Martin, unpublished.
[6] M. H. Chisholm, K . Folting, J. A. Heppert. D. M. Hoffman, J. C. Huffman. J! Am. Chem. Sac. 107 (1985) 1234.
[7J For comparison: W-W = 2.732(2) A in [W,(p,-CMe)(OiPr),] from [ 6 ] )
and 2 757(1) A in [W3(p3-P)(OiPr)9] from [XI).
181 M. H. Chisholm, K . Folting, J. W. Pasterczyk, Inorg. Chem. 27 (1988)
[9] B. E. R. Shilling, R. Hoffmann, J. Am. Chcm. Sac. 10t (1979) 3456.
[lo] L. J. Farrugia. J. A. K . Howard, P. Mitrprachachon, J. L. Spenser.
F. G. A. Stone. P. Woodward. J. Chem. Soc. Chc,m. Commun. 1978.
(0 YCH Vcrlag.~ge.reN~cl7uft
mhH. D-6940 Wrinheim, 1989
Scheme 1. Reagents and conditions: a) 2 C,H,PPh,, THFIOEt,, 20 C. 40 h.
evaporation to dryness. then 80 -C.
vacuum for 2 h. followed by toluene, 20 C.
24 h; b) THF. 20 C, 10 min; c) PtMe,(cod). toluene. 20 C. 22 h: d ) slow cooling of a saturated solution in hot T H E
phosphane groups is evident from the single 31PN M R
resonancets1, which shows the expected1'] downfield shift
from that of the free ligand 1 , and from the P-Pt coupling,[*]
which is similar in magnitude to that (1856 Hz) of
cis-PtMe,(PEt,), .I9] Crystallization of 3 from T H F yielded
single crystals of 4 (Scheme 1). An X-ray crystal structure
[*] Dr. G . B. Deacon, C. M. Forsyth
Chemistry Department, Monash University
Clayton, Victoria 3168 (Australia)
Prof. Dr. H. Schumann. DipLChem. A. Dietrich
Institut fur Anorgankche iind Analytische Chemie
der Technischen Universitat
Strasse des 17. Juni 135, D-I000 Berlin 12
Orgdnolanthanoids, Part 16, and Organometdllic Lanthanoid Compounds, Part 51. This work was supported by the Australian Research
Council, the Fonds der Chemrschen Industrie, and the Deutsche
Forschungsgemeinschaft. Part 15: G. B. Deacon, D. L. Wilkinson, Aust. J.
Chcw. 4 2 (1989) 845. Part 50: H. Schumann, P. R. Lee, J. Loebel, Chrm.
Ber., in press.
0570-0833/89~10/0-137/JB (J2.50iO
Angris. Chrm. Int. Ed. Ennl. 28 (1989) N o . I0
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bonding, structure, carbonyl, clusters, molecular, w4cl, oipr, tetranuclear, comments, analogies
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