вход по аккаунту


Aurophilicity as Concerted Effect Relativistic MO Calculations on Carbon-Centered Gold Clusters.

код для вставкиСкачать
Experimental Procedure
Asolutionofl(400mg, 1.18mmol)[13]andP,(150mg, 1.21 mmol)in250mL
of hexane was irradiated a t room temperature for 7 min with UV light (150-W
high-pressure mercury lamp. Quarzlampen GmbH, Hanau, FRG). After removal of the solvent under oil-pump vacuum, the residue was chromatographed
at ca. - 50 C on silanized silica gel (Merck, particle size 63-200 pm, column
100 x 3 cm). Unreacted 1 (50 mg, 12%) was eluted with petroleum ether as a
red-orange fraction. The following yellow fraction contained 2 along with small
amounts of 4 a (crude yield 69 mg. containing ca. 5% 4a); the products were
separated by recrystallization (twice) from CH,Cl,/hexane (1.1). Yields: 12 mg
( 3 % based onreacted Ijof2asyellowcrystalsand 1 m g ( 0 . 1 5 % ) o f 4 a a s d a r k
red needles [XI. Toluene as eluant afforded a pink fraction, which. at the end,
overlapped with a green fraction. A second chromatographic separation (basic
A1,O ,, activity 11. column 25 x 3 cm, watercooled) with petroleum ether!
toluene (10: 1) gave a pink fraction (crude yield: 25 mg. 4%). Recrystallization
from CH2Cl2;hexane( 2 : l ) afforded pink 3. Toluene eluted traces of a green
fraction, the exact composition of which is still unknown. Partial decomposition with formation of a brown residue occurred during both chromatographic
Received: May 18. 1989 [Z 3346 IE]
German version: Angew. Chrm. I00 (1989) 1395
CAS Registry numbers:
1,80432-28-6; 2,122647-47-6; 3,122647-48-7; 4a, 122647-49-8; 4b. 122647-501 ;C. 10544-46-4.
[I] Reviews: 0.J. Scherer. Commentr Inorg. Chem. 6 (1987) 1 ;M . Di Vaird, P.
Stoppioni, M. Peruzzini, Polyhedron 6 (1987) 351.
[2] Recent review: G. Maier, Angew. Chem. 100 (1988) 317; Angew. Chem. Int.
Ed. Engl. 27 (1988) 309; for theoretical studies on cyclo-Pa, see G. Ohanessran. P. C . Hiberty, J.-M. Lefour, J.-P. Flament, S . S. Shaik, fnorg. Chem.
27 (1988) 2219.
[31 B. A. Hess, Jr.. C. S. Ewig, L. J. Schdad, J. Org. Chem. 50 (1985) 5869.
" P / ' H ) N M R (162 MHz. 85% H,PO, ext.): 2 (333 K. CDCI,), 6 =
89.2(s):2(223K.CD,CI,):AMX2 spinsystem(A,M = P2,P4,X = Pl.P3),
&PA)= 133.3(t), '/(AX) = 313 Hz, 6(P,) = 76.8(t), 'J(MX) = 248 Hz.
ii(P,j = 53.0(dd); 3 (293 K, CDCI,), 6 = 290.0(s); 4a,b (293 K, CDCI,).
6 = 123.2(s). 126.01s). ' H N M R (200 MHz, CDCI,. 293 K. T M S int.): 2 :
h = 2.37(s); 3: b = 2.10(s); 4 a : 6 = 1.50(s); 4b: 6 = 1.49(s, 24H). 1.76(q.
4H). O.62(t. 6H), -'J(HH) = 7.4Hz. 1R (hexane): C(CO)[cm-']: 2,
1997(s). 1957(s);3: 1932(s. br).-EI-MSof2(70eV, 150 C):m/z408(M0,
15%). 3 8 0 ( M a - C 0 , 28). 352(Me-2 CO,66), 124(P?.24).62(Pf. 11).
28 (COO. 100) and other fragments. EI-MS of 3 (70 eV, 160'C): mi; 636
( M " . 3%). 608 (Me-CO. 22). 580 ( M e - 2 C 0 , 100) and other fragments. but no P, fragments.
a) 2: orthorhombic. P2,2.2; u = 8.9833(3), h = 20.7335(7), c =
8.7097(4) A; Z = 4; 1958 unique reflections (Mo,,; 1.5- < 0 < 27 ). 1836
observed with I 2 2 5(0; 188 parameters, R = 0.023, R , = 0.029 [Sc];
b) 4b: monoclinic, P2,/n; CI = 9.006(1), h = 20.442(2), c = 15.243(1)A,
1 = 94.34(1)' ; Z = 4 ; 3271 unique reflections (Mo,.; 1.5" < 0 i25"),
2140 observed with I > 2 ~ ( 0
; parameters, R = 0.064, R, = 0.064
[Sc]: c) Solution and refinement of the structures was accomplished with
the programs SHELX 76. SHELXS 86. In the crystal of 4b, the Nb2bonded Cp'-ring is oriented in such a way that the ethyl group occupies two
neighboring positions with 55% and 45% probability. Further details of
the crystal structure investigation may be obtained from the Fachinformations~entrum Karlsruhe. Gesellschaft fur wissenschaftlich-technische
Information mbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository numbcr CSD-53948, the names of the authors, and the
journal citation.
P. Binger. B. Biedenbach, R. Mynott, C. Kruger, P. Betz. M. Regitz,
A n p i . . Cliem. I00 (1988) 1219; Angeiv. Chem. In[. Ed. Engl. 27 (1988)
See for example K. Wade. Adv. Inorx. Chem. 18 (1976) 1 ; D. M. P. Mingos.
A w . Clic,m. RPS. 17(1984) 311.
Reaction of [RNb(CO),] (R = Cp* or Cp') and P, in decalin at ca. 170'C
(ca. 4 h) gives 4 a o r 4b, respectively, in ca. 2 3 % yield: 0. J. Scherer, J.
Vondung, R. Winter, unpublished.
K. Angermund, K. H. Claus, R. Goddard. C. Kruger, Angew Chem. 97
(1985) 241 ;Anxeiv. Chem. Int. Ed. EngI. 24 (1985) 237, and references cited
[lo] 0.J. Scherer. J Schwalb. H. Swarowsky, G. Wolmershiuser, W. Kaim. R.
Gross. Chem. Ber. 121 (1988) 443.
I l l ] H. G. von Schnering, T. Meyer. W. Honle, W. Schmettow, U. Hinze, W.
Bauhofer. G. Kliche, 2. Anorg. AUg. Chem. 553 (1987) 261. For extended
Huckel calculations on triple-decker complexes with cyclo-P, middle
decks. see W. Tremel, R. Hoffmann, M. Kertesz, 1 Am. Chem. Soc. I l l
(1989) 2030; E. D. Jemmis. A. C. Reddy, Organomctol/ic.s7 (1988) 1561.
For sandwich complexes, see: M. C. Kerins. N. J. Fitzpatrik. M. T.
8 (1989) 1135.
Nguyen. Pol~~hedron
[12] H. G . von Schnering, W. Honle, Chem. Rev. 88 (1988) 243.
[13] W. A. Herrmann, W. Kalcher. H. Biersack. I. Bernal, M. Creswick, Cheni.
Bcw. 114 (1981 j 1558.
Angrn . C'lirm. l n t . Ed. Engl. 28 11989)
No.I 0
Aurophilicity as Concerted Effect: Relativistic MO
Calculations on Carbon-Centered Gold Clusters **
By Notker Riisch,* Andreas Giirling, Donald E. Ellis, and
Hubert Schmidbaur *
A strong attractive interaction has been observed between
gold atoms with d" configuration and + 1 oxidation state in
numerous polynuclear gold compounds.['
I t is manifested in molecular conformations with relatively close
Au . . . Au contacts (2.9-3.0 A)['.'' o r discrete Au-Au
bonds,13,41 whose strength has been estimated from spectroscopic data to be 6-8 kcal mol-'.'31 Noteworthy is the tendency of polyaurated organogold compounds to bond further gold(]) units, [LAu]@(L = R,P), to a carbon center."."
The term aurophilicity has been coined for this phen ~ m e n o n . Particularly
striking examples of this interaction are provided by the recently synthesized carbon-cen(n =
tered gold-cluster cations [{(C,H,),PAU~,,C]("-~'@
5,6).['. 61 The X-ray structure analyses of these compounds
revealed an only slightly distorted highly symmetric arrangement of the gold atoms (trigonal-bipyramidal for n = 5,I6]
octahedral for n = 6I5l) around a central carbon atom. Accordingly, these clusters offered an ideal starting point for a
more detailed theoretical study of aurophilic interaction^,[^'
the results of which are presented here. Although this investigation focused on the analysis of the electronic structure of
the carbon-centered gold cluster [((C,H,),PAU),C]~@,our
goal was to arrive at general conclusions on the bonding in
The MO structure of the quasi-octahedral cluster is best
derived through fragment analysis, proceeding from the uncomplexed cluster [Au,]'@ via the carbon-centered cluster
[Au,C]'@ to the complete cluster [(LAu),C]'@. Any discussion of the electronic structure of a "centered" metal cluster
has to take into consideration the interplay of tangential
bonds within the metal polyhedron and of radial bonds to
both the central atom and the outer ligand~,['.~Isince this
influences the hybridization of the metal atoms. Furthermore, it is important to bear in mind that the 6s orbitals of
gold are lowered in energy owing to the relativistic increase
in mass;[93'*I sp hybridization with 6 p orbitals is thereby
made more difficult, whereas sd hybridization with 5 d orbitals is facilitated. In the following MO analysis, all three
features of the bonding in gold clusters are treated together
theoretically for the first time. Starting from the reference
configuration d", for which a (weakly) repulsive interaction
between gold(r) atom pairs is assumed,",
we used the exlent of disruption of the closed5d valence shells as a criterion
for the strength of a possible aurophilic interaction. This
approach considers only one, though important, aspect of
the Au-Au interaction; the bonding picture so obtained
must therefore be augmented by an analysis of orbital interactionsi7' (see Fig. 1 and the accompanying text).
The calculations for the systems [Au,I2@, [Au,C]'@, and
[(LAu),CI2@, as well as for [Au,]@ and [Au,C]@, were performed using the discrete variational (DV) Xu method,['21a
[*] Prof. Dr. N. Rosch, Dipl.-Chem. A. Gorling, Prof. D. E. Ellis ['I. Ph. D.
Lehrstuhl fur Theoretische Chemie der Technischen Universitiit Miinchen
Lichtenbergstrasse 4. D-8046 Garching (FRG)
Prof. Dr. H. Schmidbaur
Anorganisch-chemisches Institut der Technischen Universitiit Munchen
Lichtenbergstrasse 4, D-8046 Garching ( F R G )
[ '1 Guest from the Department of Physics and Astronomy, Northwestern
University, Evanston. IL 60201 (USA)
This work was supported by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 128 ( N . R . )and Leibniz-Programm (H.S.)).the Bund
der Freunde der Technischcn Universitit Miinchen ( N . R . ) .and the Fonds
der Chemischen Industrie.
VCH Verlugs~esellschufimhH. 0-6940 Weinheim, 1989
self-consistent LCAO-MO method within the framework of
density functional theory;" 31 both nonrelativistic and relativistic versions of the computer program are available, the
latter based on four-component Dirac spinors. Synimetryadapted molecular orbitals were constructed from atomic
orbitals, numerically determined for the atomic configurations present in the cluster by a self-consistent Mulliken population analysis.['21The DV Xci method takes into consideration all electrons, but only the valence electrons were
included in the self-consistent process. To simplify the calculations still further, we selected a model with SH, instead of
Ph,P ligands, so that the assumed symmetry of the resulting
cluster was appreciably higher (point group Th).However,
because of its nonbonding orbital perpendicular to the
molecular plane and the associated interaction, SH, is not a
fully adequate model for Ph,P.[t4]An idealized octahedral
structure was assumed in these calculations (d(Au-Au) =
3.005,r5' ~ ( A u - C =
) 2.125, ~ ( A u - S=
) 2.270, d ( S - H ) =
1.345 A, 3: (H-S-H) = 90').
We found that the use of a relativistic M O method is
essential for a complete theoretical description of the aurophilic interactions. This is shown in Table 2 by the Mulliken populations of the gold and carbon valence orbitals
and the resulting atomic charges. In all systems studied, the
Table 1. Mulliken valence orbital populations and resulting atomic chargcs Q
[\el] from nonrelativistic (nr) and relativistic (r) DV Xn MO calculations for the
clusters [Au,]'".
[Au,C]~@'.and [(LAu),CIz0 (L = SH,) as well a s for the
clnsters [Au,J@and [Au,C]@ [a].
[(LAu)*CI2" (b] nr
[Au,]" [c]
[Au,CIe [c]
+ 0.56
disruption of the Au 5 d shell of (relativistically described)
gold(r) units, [LAu]@,is likely to be small.
Comparison of the results presented above with those obtained for the systems [A@ and [Au,C]@ shows that it
should be possible to extend this analysis to other gold clusters. There is clear agreement of the charge distribution with
those of the corresponding octahedral systems, especially for
the population of the Au 5 d orbitals and for the changes
found upon relativistic treatment. Noteworthy, however, is
the higher Au 6 s population for the Au, clusters and the fact
that the charge on the central carbon atom is reduced in
nearly direct proportion to the number of ligands.
We have thus shown that the use of a relativistic MO
method yields the correct contributions ofthe Au 6s orbitals
to the disruption of the d'" configuration. In the following
discussion, we present a qualitative orbital interaction analysis of the systems [Au,]'@, [Au,C]~@,and [(LAu),C]'@
based on nonrelativistic calculations, since they offer the
advantage of symmetry classification according to the normal point groups. This analysis obviates the interpretation of
the much more complex relativistic orbitals and thus the
necessity of using double groups with their lower number of
irreducible representations. A further complication encountered in relativistic calculations is caused by appreciable
spin-orbit interaction in gold atoms. which can be neglected
in a qualitative discussion of the bonding. In the following.
only orbitals of symmetry a I g and t,, (point group 0,) are
analyzed, since the valence orbitals of the central carbon
atom only encompass these irreducible representations
(Fig. 1). A population analysis of the corresponding orbitals
of the cluster [(LAu),C]'@ is given in Table 2.
In previous discussion^^^^ 6 . 81 of the electronic structure of
Au, clusters, the closed d" shells were neglected and only
4 22
- 1.33
- 1.54
- 1.69
- 1.26
[a] Because of the largely systematic agreement between the results obtained for
the pentanuclear and the corresponding hexanuclear clusters, we did not carry
~ . Q(L) =
out the relatively involved calculation on the cluster [ ( L A U ) ~ C ][b]
0.04 (nr): + 0.04(r). [c]Values determined for the axial and equatorial Au
relativistic treatment yields the expected increase (by about
0.2) in the Au 6s population, the Au 5 d population decreasing by nearly the same amount. Compared with the inert d"
configuration, the deficit in the Au 5 d population of the Au,
cluster calculated relativistically is practically twice as large
as the deficit calculated nonrelativisticallv. The tendency toward Au-Au interaction should correspondingly increase, in
accordance with the criterion given above
of the
closed 5 d valence shell"). (Even nonrelativistic calculations
on the cluster [Au,]@, with a 5 d population of 9.80, revealed
a deficit of 0.20, so that the Au 5 d orbitals can make a
definite, though small, contribution to the Au-Au bond.)
bonds Of the gold
(to the centra1 carbon
atom as well as to the outer ligands) lead to a further reduction in the Au 5 d population, thereby improving the possibility of an aurophilic interaction, ~h~ central carbon atom
importance for the
cluster (see below), though its direct contribution to further
Fig. I . Schcmatic interaction diagram oforbitals with the irreducible representations a , , (a) and t,, (b) or 1, and t, in T, - for the systems [Au,lZe-C and
DV X a calculations,
For claritv. onlv
,, derived bv se~f-conslstent
orbitals containing dominant contributions from the carbon atom or from the
ligands L (=SH,) are represented (the latter limited to the cr interaction with
the Au, cluster). Furthermore. the diagram focuses on the 6s-5d hybridization
of the gold atoms. the numbers on the energy levels give the gold 6 s and gold
5d popiilations ['??,](in this order) The populations for the Au-6p. C, and L
orbitals are omitted (they are listed in Table 2). Unoccupied orbitals are drawn
as empty bars; the two hatched bars represent energy levels partially filled with
two electrons cach. In the bar labeled 11 18'27. the orbitals 3't," and 3t,,, arc
summarized from Table 2 : the 5d orbital population in !he 3'tlu orbital is not
given since these orbitals are largely of x character with respect t o Au-L bonding. For the selection o f the orbitals of symmetry type t,. see text [7].
Table 2 . Enei-gies and Mulliken populations [%I for those molecular orbitals of
the clustcr [(LAu),,CIza ( L = SH,) that make essential contributions to the
radial bonds (nonrelativistic calculations). See also Figure 1.
Symmetry [a]
- 19.36
- 16.44
- 12.07
-9.23 [c]
-3 7 5
Received: May 24. 1989 [Z3357 IE]
German version: Angew. Chem. 101 (1989)1410
vealed by the charge balance (Table 1 ) and the character of
the individual orbitals (Fig. 1 and Table 2).
[a] Numbering based on all valence orbitals of the cluster, irreducible representations of the point group T,; the corresponding representations for idealized
octahedral symmetry are given in parentheses with only those orbitals included
that contribute to Au-C and Au-L bonding. [b]Interaction distributed over
two orbitals. [c]HOMO.
[l] E Scherbaum, B. Huber, G. Miiller, H. Schmidbaur. A n g ~ i r .Chm7 l(J0
(1988)1600;Angrw. Cl7ern. Inr. Ed. EngI. 27(1988) 1542.
121 H. Schmidbaur, F. Scherbaum, B. Huber, G. Miiller. A n g w . Chcni. l00
(1988)441;A n ~ w Chem.
Inr. Ed. EngI. 27 (1988)419.
[3]H. Schmidbdur, W. Graf, G . Miiller, Angcir. Cliw~.100 (1988)439:Angris.
Cl7em. I n f . Ed. Ennl. 27 (1988)417: H r l v . Chim. Acru 6 9 (1986)1748: H.
Schmidbaur. A. Schier. G. Reber. G. Miiller, Inorg. Chrm. Ac,ro 147(1988)
[4]H.Schmidbaur. C. Hartmann, G. Reber. G. Miiller. Angcii.. Chw?i. Y9
(1987)1189:Angeu.. Chem. I n / . Ed. Engl. 26 (1988)1146.
[5] F. Scherbaum, A. Grohmann, B. Huber. C. Kriiger. H. Schmidbaur. Angoi'. Chem. 100 (1988)1602;Angeir. Chcjm. Inr. Ed. EngI. 27(1988)1544.
[6] F. Scherbaum. A. Grohmann. B. Huber, C. Kriiger, H. Schmidbaur.
Angew. Chem. 101 (1989)464:Angerr.. Chem. In;. Ed. EngI. /0/(1989)463.
[7] A.Gorling. N. Rosch, D. E. Ellis. G . L. Goodman, H. Schmidbaur. unpublished.
[XI D. M. P. Mingos. J. Chem. Soc. Duifon 7run.c. 1Y76. 1163.
the six (6sp) hybrid orbitals considered. The direct interaction between Au 5 d orbitals is relatively weak, but cannot be
neglected. The following values for the Au 5 d overlap integrals S can be derived from the DV Xa orbital^:^'^
S(o)= 0.039, S(x)= 0.026, S(6) = 0.002. These values are
about twice as large as those assumed in earlier calculations.[81 In the octahedron, the o(sp) hybrid orbitals span
orbitals of symmetry types a l g , t l u , and eg (in order of increasing energy). The highest occupied orbital (HOMO) of
[Au,]*@. the 2t1, o(sp) level, contains two electrons. However, the 2a,, ~ ( s p orbital
shows a significant Au 5 d population ( 3 6 % , cf. Fig. 1) and lies energetically within the
"band" of the 5 d level. Correspondingly, the 1 a l glevel, formally ascribed to the Au 5 d cluster orbitals, displays 39% sp
character. In the relativistic calculation, this energetically
lox:esl-(ving valence orbital of the cluster (1 alg) has to be
identified as the Au o(sp) level (6s, 5 7 % ; 6 p , 2 1 % ; Sd,
22 Yo).whereas the 2 a l gorbital is formally ascribed to the Au
5 d cluster orbitals."Ol The interaction with the central carbon atom leads to the expected charge transfer Au -+ C. Formally, the 2a,, and 2t,, levels of the cluster [Au,]*@ are
emptied in favor of the 2 t,, H O M O of the carbon-centered
cluster [Au,CI2@. However, the H O M O is localized to a
considerable extent on the gold atoms (6s, 27%; Sd, 34%).
In the complete cluster, [(LAu),C]*@, the character of the
H O M O changes only slightly. Nonetheless, since the reduction of the Au,-ligand interaction to a minimum number of
involved energy levels for the symmetry type t, (point group
T,,)is incomplete, the choice of the orbitals is not unambiguO U S " ~ (cf. Fig. I and Table 2).
For the orbitals formally ascribed to the Au 5 d manifold,
the radial (essentially &-like) interactions of the Au, cluster
both with the central carbon atom and with the outer six
ligands L lead to changes that can be interpreted in terms of
a classical perturbational approach" 51 (cf. Fig. 1). Examples
are the orbitals 1 a l gof [Au,]'@ and 2 a l g of [Au,C]'@; although they are largely nonbonding with respect to the AuAu interaction, energetically higher-lying orbitals of the respective starting cluster can "mix" into them through the
interaction partner C or L.I1'] Since these higher-lying orbitals display a stronger Au 6s character and a correspondingly weaker Au 5 d population, this mixing disrupts the
"closed" Au 5 d shell and establishes the orbital-dependent
prerequisite for aurophilic interaction. The effect of the outer ligands exceeds that of the central carbon atom, as re-
[Y] P. Pyykko. Chcm. Rev. XK (1988)563.
[lo] R. Arriata-Perez. G . L. Malli. Cheni. Ph,s.s. L e f t . 125 (1986)143.
[ l l ] P. K. Mehrota, R. Hoffmann. Inorg. C/7~m./7(1978)2187: Y Jiang. S.
M . Merz. Jr..R. Hoffmann.
hid. 27 (1988)2120.
[12] D.E. Ellis,G. S. Painter, P / i j s . Rer~.52(1970)2887.A.
Rosen. D.E. Ellis.
J. C/7em. Phyx 62 (1975)3039: A. Rosen. D. E. Ellis. A. Adachi. E W.
Averill. ihid. 65 (1976)3629.
[13] J. P. Dahl, J. Avery (Eds.): Local Densif?. Appruxmiurron.r in Quanfum
Chemisrry undSolidS/ule Physics, Plenum, New York 1984;S. B. Trickey
(Ed.): Ad,'. Quuntum Chem. 20 (1989).in press.
[141 Calculations are currently being performed on a cluster [ ( L A U ) ~ , C ]with
L = PH,. However, these calculations are more extensive owing to the
. will report elsewhere on the results
reduced symmetry (maximum D 3 a ) We
of this study
[15] T. A. Albright, J. K. Burdett. W. M.-H. Whangbo: Orhirol Intrrwrions in
Wiley, New York 1985.
Synthesis and Pharmacological Properties
of a Novel Cardioactive Steroid**
By Ulrich Werner. Uwe Moller, Petrn Wagner, Peter Welzel,*
Christa Zylka, Siegfiried Mechmann, Hermann Pusch,
and Helfried Giinther Glitsch *
The N a @pump of animal cells generates and maintains
the Nae and K @gradients across the cell membrane. These
ion gradients are essential for the electrical excitability of the
plasma membrane. In addition, the Na@ gradient serves as
an energy source for the transmembrane transport of specific
substances: for example, sugar and amino-acid import and
Ca2@transport out of the cell.1']
Cardioactive glycosides inhibit the Na@ pump, thereby
raising the intracellular Na@ concentration. The resulting
decrease in the Na@gradient across the sarcolemma reduces
the energy available for transport of Ca2@out of the cell by
Prof. Dr. P. Welzel. Dr. U. Werner.
Dipl.-Chem. U. Moller, DipLChem. P. Wagner
Fakultiit fur Chemie der Universitiit
Postfach 102148.D-4630 Bochum ( F R G )
Prof. Dr. H. G . Glitsch, Dr. H. Pusch.
Dr. S. Mechmann, DipLBiol. C. Zylka
Fakultiit fur Biologie der Universitlt
Postfach 102148. D-4630 Bochum ( F R G )
This work was supported by the Deutsche Forschungsgeme1nsch;ft (We
595112-3. researcher group "Konzell") and the Fonds der Chemischen
Без категории
Размер файла
430 Кб
effect, clusters, relativistic, centered, calculations, gold, aurophilicity, carbon, concerted
Пожаловаться на содержимое документа