вход по аккаунту


Empty Octahedral Hexazirconium Clusters with Only Ten Electrons [Zr6X14(PR3)4].

код для вставкиСкачать
structures of oligonucleotide-intercalator complexes.[' 51 A
similar two-ring overlap pattern has been observed in the
case of stacked acridine orange intercalators in the crystal
structure of a Pt complex attached to the acridine intercalator by a long alkyl linker.[161An infinite n-stacking interaction therefore exists throughout the crystal, as illustrated in
the stereodiagram in Figure 3. Thus, it appears that the dppz
ligand has an innate propensity for n-stacking that is no
doubt responsible for the high DNA binding affinity of 3 and
4. Observations of n-stacking interactions in the crystal
structures of more conventional organic intercalators such
as acridine orange" 61 and phenanthridinium salts["1 are
Received: December 10, 1991;
revised: February 28, 1992 [Z 5065 IE]
German version: Angew. Chem. 1992, 104, 1058
CAS Registry numbers:
3, 142260-91-1;4, 87564-74-7.
(11 J. K. Barton, Science (Washington D.C.) 1986, 233, 727; P. B. Dervan,
ibid. 1986, 232, 464.
[2] T. D. Tullius, B. A. Domhroski, Science (Washington, D.C.) 1985, 235,
679; A. M. Burkhoff, T. D. Tullius, Nalure (London) 1988, 331, 455;
A. M . Burkhoff, T. D. Tullius, Cell (Cambridge Mass.) 1987, 48, 935.
[3] S . M. Hecht, Acc. Chem. Res. 1986, 19, 83; J. Stubbe, J. W. Kozarich,
Chem. Rev. 1987, 87, 1107; K. Nagai, B. J. Carter, J. Xu, S. M. Hecht, J.
Am. Chem. Soc. 1991, l f 3 , 5099.
[4] W. A. Kalsbeck. N. Grover, H. H. Thorp, Angew. Chem. 1991,104,1525;
Angew. Chem. [tit. Ed. Engl. 1991, 30, 1517.
[5] N. Grover, H. H. Thorp, J. Am. Chem. Soc. 1991, 113, 7030.
' ! Pipes. T. J. Meyer, Inorg. Chem.
[6] K . J. Takeuchi, M. S . Thompson, D. d
1984,23, 1845.
[7] A. E. Friedman, J.-C. Chambron, J.-P. Sauvage, N. J. Turro, J. K. Barton,
J. Am. Chem. Sue. 1990, f12,4960.
[8j C,,H,,N,O,,CI,Ru:
triclinic, P i , a =15.882(11)& b =15.952(9) A. c =
16.283(9) A. u = 105.75(4)", = 94.80(5)', y =101.15(5)", ' J = 3855(4) A3,
=1.44 gem-', p(Mo,J = 8.42 cm-'. The structure was solved by
the Patterson method. Block-diagonal least-squares refinement yielded
R = 0.1074 and R, = 0.1520 for 3854 reflections with I t 2~(1)measured
on a Nicolet P3/F diffractometer up to 28 = 43" at 25 'C (Mo,,, A =
0.71073 A). Two molecules coupled via an inversion center are present in
the crystal. The high value for R is partly a result of the large number (106)
of non-hydrogen atoms refined, but primarily a result of disorder in the
CIO; counterions. Correct C,H.N analysis. Further details of the crystal
structure investigation are available on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-56384, the names of the authors, and the
journal citation.
191 N. Grover, N. Gupta, P. Singh, H. Thorp, Inorg. Chem. 1992, 31,
[lo] W. Seok, Ph.D. Thesis, University of North Carolina at Chapel Hill, 1988.
[I I] M. T. Carter, M. Rodriguez. A . J. Bard, J. Am. Chem. Soc. 1989, 1 1 1,
[I21 Equilibrium dialysis was performed according to: A. M. Pyle, J. P. Rehmann, R. Meshoyrer, C . V. Kumar, N. J. Turro, J. K. Barton, J. Am. Chem.
Soc. 1989, If I, 3051.
[13] Complex 5 was prepared by electrolysis of 3 at 0.8 V in phosphate buffer
(pH 7). [Ru0(bpy)(tpy)lzt was prepared as described in Ref. [9]. Rate
data were measured by optical spectroscopy at 1 = 406 nm, where the
kinetics of oxidation by Ru'"02+ are known to be first-order [5]. Experimental conditions for the kinetic measurements: 0.8 mM DNA, 0.08 miv
Ru''O*+, 50 mM phosphate buffer, pH 7. The change in absorption with
time can described in terms of a first order rate equation. The measurements were carried out on a Cary 14 spectrometer. The experimental conditions for electrocatalytic cleavage were identical to those described in
Ref. [5].None ofthe cleavage results is affected upon treatment with base.
[14] L. Stryer, Biochemistry, Freeman, New York, 1988, p. 76.
[IS] A. H.-J. Wang, J. Nathan% G. van der Marei, J. H. van Boom, A. Rich,
Nature (London) 1978, 276, 471 ; A.
Wang, G. J. Quigley, A. Rich.
Nucleic Acids Res. 1979, 6, 3879.
[16] B. E. Bowler, K. J. Ahmed, W. I. Sundquist, L. S . Hollis, E. E. Whang, S . J.
Am. Chem. Soc. 1989, f f f , 1299.
Lippard, .
[17] M. Cory. D. D. McKee, J. Kagan, D. W. Henry, J. A. Miller, J. Am. Chem.
Soc. 1985. 107. 2528.
0 VCH Verlagsgesellschaj! mbH,
W-6940 Wemheim, 1992
Empty Octahedral Hexazirconium Clusters
with Only Ten Electrons, [Zr,X,,(PR,),]**
By l? Albert Cotton,* Xuejun Feng, Maoyu Shang,
and William A . Wojtczak
The existence of compounds comprised of octahedral Zr,
clusters with bridging halogen atoms on all edges and one
additional bond to each zirconium atom along a four-fold
axis of the [Zr,X,,] unit was first reported many years ago.f'I
Several years later it was realized['] that these compounds,
all prepared by high-temperature reactions, contain an additional atom (e.g. Be, B, C, N, and even a transition metal
atom) in the center of the octahedron. The idea then took
hold[31that the central atom, and the electrons it could contribute to the Zr, cluster bonding, were essential to the stability of such [Zr,X,,]X, systems. However, the reportL4)in
1988 of [Zr,Cl,,(PMe,Ph),], which was made in an entirely
different way, at low temperature and in solution, showed
that an empty cluster with 12 electrons can be stable. We are
still seeking a better preparative method for such compounds, and in the course of doing so, we have found that
empty Zr, clusters with even fewer electrons (ten) can be
prepared. Herein we report on the results of the crystal structure analyses and the 31P{'H}-NMR spectra of the new clusters 1-4, as well as on SCF-Xa-SW molecular orbital calculations on the model compound [Zr,Cl,,(PH,),].
. 2CH,CN
The new compounds 1-4 were synthesized by reduction of
ZrX, (X = C1 or Br) with two equivalents of (n-C,H,),SnH[51
in benzene (CH'CI, for 1). The reduction was allowed to
proceed for a period of 36 h, during which time a dark colored precipitate collected on the bottom of the reaction vessel. The addition of one equivalent of phosphane immediately solubilized the precipitate, furnishing a deep-red solution,
which afforded very air- and moisture-sensitive crystals
upon layering. The 31P('H}-NMR spectrum of dissolved
crystals of 2 shows a singlet at S = 21.27 (Av,,, = 31.4 Hz at
20 "C, 81 MHz). The singlet shifts downfield by AS z 1 over
the temperature range -40°C to 6 0 T , which is consistent
with weak temperature-dependent paramagnetism arising
from a diamagnetic ground state having some access to a
paramagnetic excited state at higher temperature. This will
be discussed further in the context of our theoretical calculations. The direction of the peak shift is undoubtedly dependent on the particular spin transfer mechanism. The 'HNMR spectrum of 2 shows two broad peaks corresponding
to protons of the ethyl group of the bound phosphane ligand
and gives no indication of the existence of a hydridic proton
within the cluster; however, the line-broadening effect arising from the weak paramagnetism of the compound precludes any definitive statement in this regard.
The compounds 1-4 were characterized by X-ray crystallography,'61 pertinent crystallographic parameters are listed
Dr. F. A. Cotton, Dr. X. Feng, Dr. M. Shang, W A. Wojtczak
Department of Chemistry and
Laboratory for Molecular Structure and Bonding
Texas A 81 M University
College Station, TX 77843 (USA)
Ttus work was supported by the Robert A. Welch Foundation (Grant No.
A 494). We thank Mrs. Bo Hong for her assistance with the temperaturedependent "P-NMR spectra and Dr. P. Kibala for helpful suggestions
regarding the preparative scheme.
0570-0833/92/0808-i0SO$3.50+ ,2510
Angew. Chem. tnt. Ed. Engl. 1992, 31, No. 8
Table 1. Crystallographic data of the clusters 1-4
Space groupP2Jn (No. 14)
u [A]
b [A]
c [A]
a ["I
B ["i
Y ["I
V [A3]
Data with 2727
.q > 3 0 ( F 3
No. of
Pbca (No. 61)
W/mnc (No. 128)
PT (No. 2)
in Table 1, important molecular dimensions in Table 2. Figure 1 shows a molecule of 1 as viewed along its Clt-Zrax
bond. It should be noted that all hydrogen atoms of 1 were
found from a Fourier map that followed the anisotropic
refinement of the non-hydrogen atoms. The hydrogen atoms
Table 2. Selected distances [A] and angles ["I for clusters 1-4. X, = terminal
halogen atom, X, = bridging halogen atom (X = CI, Br). The terminal halogen
atoms are bound to the Zr atoms designated as Zrax.
3.301 [6] [c]
3.354 [8]
2.573 [8]
2.556 19)
2.757 [6]
2.495 (2)
81.8 [I]
80.2 [2]
2.4083 (6)
2.334 [8]
3.304 [I]
3.357 [3]
2.562 1.51
2.553 [7]
2.789 [6]
2.501 (3)
82.2 (21
80.5 [2]
2.411 (1)
2.3366 [5]
3.319 [6]
3.367 [3]
2.572 [2]
2.557 (81
2.796 [6]
2.486 (4)
82.2 [I]
80.7 [4]
2.415 [I]
2.346 [I]
3.356 (2) [d]
3.411 (1)
2.705 (1)
2.692 (81
2.777 (5)
2.677 (3)
78.55 ( 5 )
76.94 (5)
2.451 (2)
2.373 (1)
[a] Data collection conducted at -75°C. [b] Data collection conducted at
- 60 "C. [c] Square brackets denote mean deviation from the unweighted arithmetic mean; each is given for the last significant figure. [d] Parantheses denote
esd of an individual value.
Fig. 1. 1 viewed along the Zrax-Cl, bond. Hydrogen atoms have been given
arbitrary thermal parameters and heavy atoms are represented by their ellipsoids at the 50% probability level.
Angew. Chem. Int. Ed. Engl. 1992, 31, No. 8
(including the hydrogens on the CH,Cl, of crystallization
were positionally refined with fixed thermal parameters of
1.3 Beqvof the corresponding carbon atom. Compound 1
resides on a crystallographic inversion center in the monoclinic space group P2,ln. In order to determine whether adequate electron density exists at the center of the Zr, cluster
to support the hypothesis that any atom is there, we attempted to refine a hydrogen atom with fixed coordinates at
(O,O,O). The thermal parameter of the aforementioned hydrogen atom grew very large after only a few refinement cycles
by the least-square method ( B > 50 A').
The two distinct sets of Zr-Zr bond lengths (eq+q, ax-eq)
in the [Zr6X,,(PR3),]-type clusters suggest that a small but
real tetragonal distortion exists, in which the Zrax-Zreqbond
lengths are longer than the Zreq-Zreq bond lengths. This
phenomenon has been observed previously[71in solid-state
clusters of the composition [Zr,X,,Zl"+ and may be attributed to the chemical inequality of the Zraxand Zr,, , positions resulting from the disparate electron donor ability of
the terminal ligands. The bromo complex, 4, contains slightly longer Zr-Zr bonds than its chloro analogue. This trend
has also been observed in the edge-sharing bioctahedral
complexes of the elements of group IV and has been attributed to greater ligand-ligand repulsive forces of the larger
halogen atoms.181The Zr-Zr bond lengths of the compounds
1 to 3 lie in the range 3.167-3.450 8, recently reported for
centered zirconium hexanuclear clusters, with cluster based
electron counts between twelve and eighteen, that were obtained by dissolution of solid-state phases.['] Further comparison between our clusters 1-4 and those just mentioned
is unjustified, since large differences exist with respect to
ligand environments, electron counts, and the presence of
interstitial atoms.
Our ten-electron clusters can, however, be compared with
the twelve-electron cluster 5.L4I The average Zreq-Zreqbond
length of 3.319(6) A in 3 is 0.096(9) 8,longer than the Zr-Zr
distance in 5. The lengthening of the Zr-Zr-bond is not surprising, considering that removal of two electrons that are
Zr, core bonding from the t , , HOMO of 5 is required for
formation of the ten-electron cluster 3 (cf. 8 in Fig. 2). The
commensurate enlargement of the Zr, cage in 3 can be
gauged from the Zr,,,-Center radius of 2.346(1) A, compared to 2.279(2) A in 5. The degree of bond lengthening is
small, since the bond order changes only from 0.5 (5) to 0.42
(3), respectively.
Molecular orbital calculations were carried out by the
SCF-X,-SW method for the C,,-symmetric clusters 6 and 7.
The latter compound was assumed to be structurally the
same as the former except for having a hydrogen atom at its
center. For comparison, a compound of similar structure
(D3dsymmetry) but with twelve metal cluster electrons, 8b4]
was also calculated. Figure 2 shows the MO diagram for the
upper valence orbitals in these molecules. For all three molecules, the MOs in the energy range between -9 and
- 1 3 eV are mostly metal-ligand(termina1) bonding, while
the higher energy orbitals are predominantly metal-metal
Verlagsgesellschufr mbH. W-6940 Weinheim,1992
0570-0833/92/0808-l051$3.50+ ,2510
bonding and accommodate all metal cluster electrons. The
7 a , orbital in 7 provides the bonding between the metal
atoms and the centered atom and is correlated to the 18a,
orbital in 6,as indicated by the asterisks in Figure 2. Three
pairs of nearly degenerate MOs in 8 (right-hand column in
Fig. 2), each of which correlates to a level of t-symmetry of
the octahedral Zr,CIl,P6 framework, are labeled accordingly. Upon lowering the symmetry to C,,, the levels are split.
orbitals as the HOMO and LUMO, respectively. The 17a,
and 20e orbitals have the same metal-metal bonding character (Fig. 3, right). The splitting between the two is caused by
differences in metal-ligand(termina1) antibonding character
of the orbitals. In the 17a1 orbital, the antibonding is between the metal atoms and the chlorine atoms, while in the
20e orbital it is between the metal and the phosphorus atoms.
Because of this, the other possibility of a closed shell configuration by reversing the order of these two orbitals seems
E lev1
-9 ..
Fig. 3. Molecular orbital contour plots for the 18a, orbital (left) and the 17u,
orbital (right) of 6.
We are currently attempting to synthesize other hexanuclear
clusters, for example, [Zr6Cl12L6],as well as investigating
other synthetic routes for clusters of elements of Group IV.
Fig. 2. Molecular orbital diagram of the upper valence orbitals for 6-8.
According to the electronic structures shown in Figure 2,
the compound we are concerned with (Zr6ClI4(PH3),)
should be strongly paramagnetic, whether it contains a hydrogen atom at the center or not. Paramagnetism is absolutely unavoidable in the case of the hydrogen-centered model compound 7 since it contains an odd number of electrons.
However, as indicated by the 31P{
'H}-NMR spectra recorded at various temperatures, compound 2 exhibits only very
weak temperature-dependent paramagnetism, which suggests that it should have a closed-shell electronic configuration in the ground state. Thus, the possibility that the compound has a centered hydrogen atom can be eliminated. The
NMR result shows that the calculation for 6 has not correctly predicted the exact ordering of the closely-spaced MOs in
the HOMO-LUMO region (middle column of Fig. 2). This is
not surprising in view of the very similar energies of the 17a,,
20e and 18a1orbitals. The calculation may have overestimated the metal-ligand(termina1) antibonding contribution in
the 18a, orbital (see Fig. 3, left). Orbitals of the same character in other systems such as [Zr,C11,]4-,1'o~111have been
found to be much lower than the t,, level. Noticing also the
strong metal-metal bonding character with the d,, orbitals of
all metal atoms pointing towards the center of the Zr, cage,
it is then possible that the 18a1 orbital actually lies lower
than the 17a, orbital. Furthermore, if there is a larger splitting between the 17a1 and the 20e orbitals, there could be a
closed-shell electronic configuration with the 17a1 and 20e
Verlugsgeselischafi mbH. W-6940 Weinherm, 1992
All operations were carried out under an argon atmosphere using standard
vacuum-line and Schlenk techniques. The solvents were freshly distilled under
nitrogen from the appropriate drying reagent and the reactants were used as
received from the supplier.
Synthesis of 1-4: ZrX, (X = C1.0.466 g, 2.0 mmol; X = Br, 0.822 g, 2.0 mmol)
was reduced with (nC,H,),SnH (1.05mL, 4.0mmol) in 20mL of benzene
(20mL of CH,CL, for 1) for 36 h. The resulting red-brown precipitate (dark
blue for X = Br) was washed with two 10-mL portions of fresh solvent to
remove excess (nC,H,),SnH, followed by addition of 20 mL of fresh solvent.
One equivalent of PR, (R = Me; 0.20 mL, 2.0 mmol, R = Et; 0.29 mL.
2.0 mmol, R = Pr; 0.40 mL, 2.0 mmol) was added dropwise. The precipitate
was solubilized immediately, producing a deep-redibrown solution. The benzene was removed from 2 and 4 under vacuum, and CH,CI, and CH,CN were
added, respectively. The solutions were filtered through 2 cm of Celite and
layered with 25 mL of hexane (for 1 , 2 , and 3) and 25 mL of Et,O for 4. Red
crystals separated out within one to two weeks. The yields of crystalline material isolated ranged from 10-20% for 1-4.
2: "P{'H) NMR (CH,CN/(D,]benzene, 81 MHz): S = 20.97, 21.08, 21.20,
= 31.4Hz),21.83,21.95,22.08(s)(from -40 to
50 "C in 10"intervals). 'H NMR (CD,CN, 25 "C, measuring range: d = 20- 30,
0 -CH,), 2.17 (br., -CH,).
200 MHz): 6 ~ 1 . 2 (br.,
4: "P('H) NMR (CH,CN/[D,Jbenzene, 81 MHz): 6 = - 2.27 (s, Avli2 =
25.2 Hz, 21 "C).
Received: February 10, 1992 [Z5179 IE]
German version: Angew. Chem. 1992, 104. 1117.
CAS Registry numbers:
1,142438-18-4; 2,142438-19-5; 3,142457-03-2; 4,142438-21-9; 6,142438-23-1;
7, 142438-22-0; 8, 142438-24-2.
[l] J. D. Corbett, R. L. Daake, K. R. Poeppelmeier, D. H. Guthrie,
Chem. SOC.1978,100, 652.
0570-0833/92/0808-10523 3.50+ .2SjO
J. Am.
Angew. Chem. Ini. Ed. Engi. 1992, 31. No. 8
(21 R. P. Ziebdrth, J. D. Corbett, 1 Am. Chem. Soc. 1985, 107, 4571.
(31 T. Hughbanks, G. Rosenthal, J. D. Corbett, J. Am. Chem. Soc. 1988, 110,
[4] E A. Cotton, P. A. Kibala, W. J. Roth, J. Am. Chem. Soc. 1988, 110, 298.
IS] We have also found that under slightly less reducing conditions square
pyramidal pentanuclear clusters of the composition [Zr,X,,(PR,),] are
formed. These will be described in detail at a later date.
(61 Further details of the crystal structure investigations are available on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-56200, the
names of the authors, and the journal citation.
[7] R. P. Ziebarth, J. D. Corbett, 1 offsolid State Chem. 1989, 80, 56.
(81 F. A. Cotton, M. Shang, W. A. Wojtczak, Inorg. Chem. 1991, 30, 3670.
191 F. Rogel, J. D. Corbett, .
Am. Chem. Soc. 1990, 112, 8198.
[lo] J. D. Smith, J. D. Corbett. J. Am. Chem. Soc. 1985, 107, 5704.
[ l l l R. P. Ziebarth, J. D. Corbett, L Am. Chem. Soc. 1988, Iff, 3272.
sufficiently acidic to deprotonate spontaneously upon dissolution in CH,Cl, or THE Vinylidene complexes analogous
to 2a, b with organic substituents on the @-carbon are
known,15] but the unsubstituted derivatives 2a, b have not
been previously described. However, 2a has been proposed
as a reaction intermediate.I6]The complexes 2a, b have been
spectroscopically characterized, but they cannot be isolated
since upon warming to 22 “C they rapidly decompose, with
formation of the p-vinylidene complexes [(Cp(CO),M) &C=CH,)] .I6* ’I Consequently, they must be generated and
studied at low temperature.
The criss-cross cycloaddition product 3b was formed upon
addition of benzalazine to the vinylidene complex 2b [Eq.
@)I. IR monitoring indicates a clean transformation without
An Organometallic Analogue of the
“Criss-Cross” Cycloaddition Reaction **
By Colleen Kelley, Lisa A . Mercando, Michael R . Terry,
Noel Lugan, Gregory L. Geoffrey,* Zhengrian Xu,
and Arnold L. Rheingold
Azines have been known since 1917[’] to undergo consecutive [3 + 21 cycloaddition reactions with 1,3-dipolarophiles
to give bicyclic products having fused five-membered rings
[Eq. (a)], a transformation that is commonly known as the
criss-cross reaction.[’] Electron-rich azines typically require
3 b (53%)
detectable by-products, and 3b was isolated as a solid and
was spectroscopically characterized. A similar reaction occurs between the carbyne complex la and two equivalents of
benzalazine to give the analogous product 3a, with the second benzalazine equivalent necessary to deprotonate the intermediate formed between l a and the azine. The ORTEP
drawing of 3a {see Fig. 1 l8I) shows the fused five-membered
rings to be nearly planar [max. deviation = 0.17 A at C(20)]
as is the entire bridging ligand (dihedral angle [C(15)-N(I)N(2)-C(17)]-[C(20)-N(l)-N(2)-C(l8)]
= 171.5’). The Mn-
electron-deficient alkenes as partners and often need elevated temperatures and prolonged reaction times. In contrast,
azines with electron-withdrawing CF, substituents react
with a variety of substrates, including electron-rich
oIefins.“, 31 We report herein the first examples of
organometaltic analogues of this criss-cross cycloaddition
involving benzalazine and vinylidene or carbyne complexes.
I t has been found that the ethylidyne complexes 1 undergo
deprotonation to form the new vinylidene complexes 2.
This deprotonation may be accomplished by treating complexes 1 with Et,N, although the rhenium complex l b is
[*] Prof. G. L. Geoffroy, Dr. C. Kelley, L. A. Mercando, M. R. Terry
Department of Chemistry, The Pennsylvanla State University,
University Park, PA 16802 (USA)
Dr. N. Lugan
LdbOrdtOire de Chimie de Coordination du CNRS, Toulouse (France)
2. Xu, Prof. A. L. Rheingold
Department of Chemistry, University of Delaware, Newark, DE (USA)
This work was supported by the OKice of Basic Energy Sciences, U.S.
Department of Energy, and a NATO Cooperative Research Grant.
Anget<’.Chem. Int. Ed. Engl. 1992, 31, No. X
Fig. I . An ORTEP drawing of 3a. Selected bond lengths [A]; Mn(1)-CP(l),
1.791(4); Mn(2)-Cp(2), 1.782(4), Mn(I)-C(15), 1.945(3); Mn(2)-C(18),
1.936(3); N(l)-N(2), I .438(3); N(l)-C(20), 1.472(4); N(l)-C(l S), 1.312(4);
N(2)-C(17), 1.473(4); N(2)-C(lS), 1.306(4).
C(carbene) bond lengths of 1.945(3) and 1.936(3) A lie in
the typical range.[’’ The planes defined by the carbene carbon atoms and their attached carbon and nitrogen substituents do not bisect the CO-Mn-CO angle, as often found
for [Cp(CO),Mn=CRR‘] carbene cornple~es,~’~
but instead
Verlagsgesellsrhaft mbH. W-6940 Weinheim. 1992
OS70-0833/92/080X-l053 $3.50+ .2S/O
Без категории
Размер файла
482 Кб
pr3, zr6x14, clusters, electrons, octahedron, ten, empt, hexazirconium
Пожаловаться на содержимое документа