A cyclic hexamer of silver trifluoroacetate supported by four triphenylphosphine sulfide template molecules

Article abstract of DOI:10.1021/ic048795o

Crystallization of silver trifluoroacetate from chloroform solutions containing triphenylphosphine sulfide affords a trigonal and a monoclinic form of a 6:4 complex {[CF₃C(O)OAg]₆(Ph₃PS) ₄} of C₂ symmetry with different amounts of chloroform in the crystals. With the Ph₃PS components as template molecules, the CF₃C(O)OAg units are assembled to form a 6-membered metallacycle codetermined by metallophilic bonding and enclosed by a 24-membered ring [AgOCO]₆. A complex of the type [LAgOC(O)CF₃]₂, with L representing the isocyanide ligand ^pTolSO₂-CH ₂NC, has been shown to have a conventional bicyclic structure with three-coordinate silver atoms engaged in transannular metallophilic interactions.

Full text of DOI:10.1021/ic048795o

Inorg. Chem. 2005, 44, 673−676
A Cyclic Hexamer of Silver Trifluoroacetate Supported by Four
Triphenylphosphine Sulfide Template Molecules
Bratislav Djordjevic, Oliver Schuster, and Hubert Schmidbaur*
Department Chemie, Technische UniVersita¨t Mu¨nchen, Lichtenbergstrasse 4,
85747 Garching, Germany
Received August 30, 2004
Crystallization of silver trifluoroacetate from chloroform solutions containing triphenylphosphine sulfide affords a
trigonal and a monoclinic form of a 6:4 complex [CF3C(O)OAg]6(Ph3PS)4 of C2 symmetry with different amounts
{
}
of chloroform in the crystals. With the Ph3PS components as template molecules, the CF3C(O)OAg units are
assembled to form a 6-membered metallacycle codetermined by metallophilic bonding and enclosed by a 24-
membered ring [AgOCO]6. A complex of the type [LAgOC(O)CF3]2, with L representing the isocyanide ligand pTolSO2-
CH2NC, has been shown to have a conventional bicyclic structure with three-coordinate silver atoms engaged in
transannular metallophilic interactions.
Introduction
remain intact with the coordination number (CN) of the metal
atoms increasing to 3 or 4, preserving metallophilic bonding
as in C8,9 or losing the Ag---Ag contacts as in D (Chart 1).10
The literature is particularly rich in examples with L )
tertiary phosphines or arsines.5-17
It should be noted that the structural chemistry of the silver
carboxylates is entirely different from that of the correspond-
ing gold carboxylates, where complexes of the type [(L)-
AuOC(O)R] are generally monomers with the gold atoms
linearly two-coordinate with complementary aurophilic bond-
ing in a T-shaped geometry for small ligands L.18-23 Only
Silver(I) carboxylates [AgOC(O)R]n with no auxiliary
donor ligands have been shown to form oligomers with a
variety of structural motifs including mainly dimers with flat
eight-membered rings A1-3 or tetramers with folded 16-
membered rings B,4 the geometry of which is clearly
codetermined by metallophilic bonding between the linearly
two-coordinate metal atoms (Chart 1). Because of this low
degree of aggregation, silver carboxylates with small non-
polarizable substituents (such as perfluoroalkyl -CnF2n+1
)
are volatile in a vacuum and can be employed as sources
for the chemical vapor deposition of silver metal.5-8
With donor ligands L, the ring systems of 1:1 complexes
[(L)AgOC(O)R]n and 1:2 complexes [(L)2AgOC(O)R]n can
(9) Paramonov, S. E.; Kuz’mina, N. P.; Troyanov, S. I. Polyhedron 2003,
22, 837.
(10) Blues, E. T.; Drew, M. G. B.; Femi-Onadeko, B. Acta Crystallogr.
1977, B33, 3965.
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H. Inorg. Chim. Acta 2004, 357, 235.
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P.; Wang, R. J. Inorg. Chem. 1992, 31, 4510.
(15) Neo, S. P.; Zhou, Z. Y.; Mak, T. C. W.; Hor, T. S. A. Inorg. Chem.
1995, 34, 520.
* Author to whom correspondence should be addressed. E-mail:
H.Schmidbaur@lrz.tum.de.
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Zh. Neorg. Khim. 2000, 45, 2003.
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K.; Lang, H. J. Organomet. Chem. 2003, 669, 25.
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Chem. Mater. 2003, 13, 563. (b) Edwards, D. A.; Harker, R. M.;
Mahon, M. F.; Molloy, K. C. Inorg. Chim. Acta 2002, 328, 134.
(8) (a) Szlyk, E.; Szymanska, I.; Surdykowski, A.; Glowiak, T.; Woitczak,
A.; Golinski, A. Dalton Trans. 2003, 3404. (b) Szlyk, E.; Piszczek,
P.; Grodzicki, A.; Chaberski, M.; Golinski, A.; Szatkowski, J.;
Blaszczyk, T. Chem. Vap. Deposition 2001, 7, 111.
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10.1021/ic048795o CCC: $30.25
Published on Web 01/05/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 3, 2005 673

Djordjevic et al.
Chart 1
large ligands L may prevent the close approach necessary
for bonding Au---Au contacts.
from chloroform as pentane vapor is allowed to diffuse into
solution. With only slight variations of the experimental
conditions, which presently cannot really be specified, crops
of crystals were obtained which contained various amounts
of two crystalline phases which could be identified as
different solvates containing the same hexanuclear species
of the formula {(Ph3PS)4‚[AgOC(O)CF3]6} (2). Vacuum-
dried solvent-free samples (54% yield, mp 167 °C dec) have
been characterized by elemental analysis and NMR spec-
Results
An illustrative example for the standard behavior of the
1:1 complexes with an auxiliary ligand taken from the
isocyanide series is presented here as a reference. The
reaction between silver(I) trifluoroacetate and p-tolylsulfo-
nylmethyl isocyanide (in chloroform) affords high yields of
a colorless product {(pTolSO2CH2NC)Ag[OC(O)CF3]}2 (1).
The structure of type C shown in Figure 1 approaches C2
1
troscopy. Only one set of H and 13C resonances and a 31P
singlet (δ 46.8 ppm) were obtained for the four Ph3PS
ligands, while the equivalence of the six CF3CO2 units was
demonstrated by a 19F singlet (δ -73.4 ppm).
Crystals of compound 2 are either trigonal (with a huge
unit cell, Z ) 18) or monoclinic (Z ) 8), with space groups
R3c and C2/c, respectively. In both phases, which differ only
in their ill-defined contents of solvent molecules, complex
2 has crystallographically imposed C2 symmetry. The
geometries are very similar, and therefore, only the structure
of the molecules in the trigonal form is presented and
discussed in detail here.
The structure is best described as an extension of the series
started in formulas A and B: Following an 8- and a 16-
membered ring, a 24-membered ring assembled of six silver
atoms and six carboxylate OCO units is discernible, and in
this macrocycle the six silver atoms are connected via
metallophilic (argentophilic) bonding to give a 6-membered
metallacycle in a twisted boat conformation (Figures 2 and
3). The average Ag---Ag contact is 3.020 Å. Six corner-
sharing five-membered rings CO2Ag2 are annelated to the
metallacycle, two roughly in the best plane defined by the
silver atoms, two above, and two below.
Figure 1. Molecular structure of [pTolSO2CH2NCAgOC(O)CF3]2 (1)
(ORTEP, 50% probability ellipsoids, hydrogen atoms omitted). The structure
approaches C2 symmetry, the virtual 2-fold axis passing through the
midpoint of the lines connecting the atoms Ag1 with Ag2 and N1 with N2.
Bond distances and angles show no anomalies.
symmetry quite closely and features a metallophilic
Ag---Ag contact of 3.0213(4) Å between silver atoms which
are in a planar three-coordinate configuration.
Two pairs of triphenylphosphine sulfide molecules occupy
symmetrical positions relative to the 2-fold axis above and
below the macrocycle. Their sulfur atoms cap triangles of
silver atoms (S1 for Ag2,Ag1,Ag3* and S2 for Ag1,Ag2,
Ag3), providing each silver atom with two Ag-S contacts
in addition to its two Ag-O contacts (Figure 4). The silver
atoms thus become four-coordinate (AgO2S2) in a quasi-
By contrast, the reaction of AgOC(O)CF3 with triphen-
ylphosphine sulfide, also in a 1:1 molar ratio, gives a
colorless 3:2 adduct of the components which crystallizes
(22) Sladek, A.; Schneider, W.; Angermaier, K.; Bauer, A.; Schmidbaur,
H. Z. Naturforsch., B 1996, 51, 765.
(23) Preisenberger, M.; Schier, A.; Schmidbaur, H. Inorg. Chem. 1999,
38, 5870.
674 Inorganic Chemistry, Vol. 44, No. 3, 2005

A Cyclic Hexamer of SilWer Trifluoroacetate
Figure 5. Complete structure of complex 2 (ORTEP, 50% probability
ellipsoids except for phenyl carbon atoms and fluorine atoms, hydrogen
atoms omitted).
Figure 2. Hexanuclear subunit (CF3CO2Ag)6 of the complex [(Ph3PS)4‚
(CF3CO2Ag)6] (2) in the trigonal crystals (ORTEP, 50% probability
ellipsoids except for fluorine atoms, hydrogen atoms omitted). The projection
follows the C2 axis passing through the center of the macrocycle.
contacts (Figure 5). Phosphine sulfide coordination to silver-
(I) atoms has been observed previously,24-26 but no µ3-
coordination has been reported.
It appears that the Ph3PS molecules are templates for the
formation of the hexamer of silver trifluoroacetate. They
provide an exposed sulfur atom which can function as a
donor center for three neighboring silver centers. With the
sulfur atoms capping two different silver triples, all six silver
atoms can reach CN 4 with only four Ph3PS ligands, which
explains the 6:4 stoichiometry. This compact array is
obviously a preferred mode of organization which has the
same structure regardless of the number and distribution of
solvent molecules in the two different crystalline solvates.
Figure 3. Twisted boat form of the central metallacycle of compound 2
(point group C2 symmetry). The interatomic distances are Ag1-Ag2 )
2.9133(6) Å, Ag2-Ag3 ) 3.0464(6) Å, and Ag3-Ag1′ ) 3.1001(6) Å.
The NMR data for chloroform solutions at 20 °C indicate
that the hexanuclear aggregate enjoys great fluxionality in
solution, which renders the trifluoroacetate and the tri-
phenylphosphine sulfide ligands equivalent on the NMR time
scale. Cooling of samples to the solubility limit (ca. -50
°C) did not lead to line broadening or splitting of the 19F
and 31P signals which are to be expected for a rigid structure
with C2 symmetry. This result suggests that the Ph3PS ligands
can undergo facile intra- or intermolecular “ring hopping”,
meaning that they can move freely to other silver triangles
with concomitant flapping of the five-membered CO2Ag2
rings. Moreover, there can be flapping of the six-membered
ring of silver atoms (Figure 3). However, dissociative
mechanisms also cannot be excluded. Substitution of the Ph3-
PS units by strong donor ligands (phosphines, isocyanides)
leads to conventional complexes of other [(L)n(CF3CO2Ag]m
oligomers.
Figure 4. Subunit [(Ph3PS)4Ag6] (ORTEP, 50% probability ellipsoids,
hydrogen atoms omitted) showing the positions of the sulfur atoms above
and below the metallacycle. Each silver atom is coordinated to two sulfur
atoms and each sulfur atom to three silver atoms. The projection runs
perpendicular to the C2 axis, which passes through the midpoint of the line
connecting the atoms Ag3 and Ag3′.
(24) Bembenek, E.; Crespo, O.; Gimeno, M. C.; Jones, P. G.; Laguna, A.
Chem. Ber. 1994, 127, 835.
(25) Livingstone, S. E. In ComprehensiVe Coordination Chemistry; Wilkin-
son, G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press:
Oxford, 1987; Vol. 2, p 641.
(26) Pasechnik, M. P.; Aladzheva, I. M.; Matrosov, E. I.; Pisarevski, A.
P.; Struchkov, Y. T.; Mastryukova, T. A.; Kabachnik, M. I. IzV. Akad.
Nauk SSSR, Ser. Khim. 1994, 708; Russ. Chem. Bull. 1994, 43, 660.
tetrahedral geometry with the Ag-S and Ag-O bond lengths
in broad ranges from 2.5426 to 2.8769 Å and from 2.248 to
2.326 Å, respectively, and entertain two metallophilic
Inorganic Chemistry, Vol. 44, No. 3, 2005 675

Djordjevic et al.
Table 1. Crystal Data, Data Collection, and Structure Refinement Details for [pTolSO2CH2NCAgOC(O)CF3]2 (1), {(Ph3PS)4‚[AgOC(O)CF3]6} (2), and
{(Ph3PS)4‚[AgOC(O)CF3]6}‚(CHCl3)0.87 (2)
[pTolSO2CH2NCAg-
OC(O)CF3]2 (1)
{(Ph3PS)4‚[Ag-
OC(O)CF3]6} (2)
{(Ph3PS)4‚[AgOC(O)-
CF3]6}‚(CHCl3)0.87 (2)
empirical formula
C22H18Ag2F6N2O8S2
C84H60Ag6F18-
O12P4S4
2502.66
trigonal
R3hc
29.0992(2)
29.0992(2)
64.5822(6)
90
90
120
47359.3(6)
1.579
18
C84.87H60.87Ag6Cl2.61
F18O12 P4S4
2606.61
monoclinic
C2/c
53.1396(6)
15.1408(2)
27.3641(4)
90
120.4072(9)
90
18988.1(4)
1.824
-
fw
832.24
triclinic
P1h
cryst syst
space group
a/Å
b/Å
c/Å
10.9501(3)
11.2398(4)
13.8195(4)
104.2352(18)
96.633(2)
118.9642(12)
1386.14(7)
1.994
R/deg
â/deg
γ/deg
V/Å3
F
calcd/g cm-3
Z
2
8
F(000)
816
16.53
143
22104
13.17
143
10228
15.35
143
µ(Mo KR) (cm-1
T/K
)
no. of reflns measured
no. of unique reflns
no. of refined params/restraints
R1 [I g 2σ(I)]
39342
4763 [Rint ) 0.043]
380/0
0.0297
0.0656
354127
9649 [Rint ) 0.099]
636/0
0.0561
0.1146
274446
16477 [Rint ) 0.063]
1190/0
0.0423
0.0939
wR2a
weighting scheme
a ) 0.0079
b ) 2.0580
0.427/-0.331
a ) 0.0372
b ) 401.0217
0.610/-0.806
a ) 0.0321
b ) 94.7621
1.090/-0.638
σ
fin(max/min)/e Å-3
2
-
2
2
2
2
2
a wR2 ) {∑[w(Fo
Fc )2]/∑[w(Fo )2]}1/2; w ) 1/[σ2(Fo ) + (ap)2 + bp]; p ) (Fo + 2Fc )/3.
F06206R oil and used for intensity data collection on a Nonius
DIP 2020 diffractometer, employing graphite-monochromated Mo
KR radiation. Intensity data were corrected for absorption effects
(DELABS from PLATON). The structures were solved by a
combination of direct methods (SHELXS-97) and difference Fourier
syntheses and refined by full-matrix least-squares calculations on
F2 (SHELXL-97).27 The thermal motion of all non-hydrogen atoms
was treated anisotropically. All hydrogen atoms were calculated
and allowed to ride on their parent atoms with fixed isotropic
contributions. During the structure refinement of both crystalline
phases of the compound [(Ph3PS)4‚(CF3CO2Ag)6] (2), the atoms
of two chloroform molecules were observed. While in the trigonal
case none could be modeled satisfactorily, one of two solvent
molecules of the monoclinic form was refined but its site found to
be not fully occupied (87%). The SQUEEZE routine in PLATON
was used to modify the hkl files. Further information on crystal
data, data collection, and structure refinement is summarized in
Table 1.
Experimental Section
Preparation of Complex 1. pTolSO2CH2NC (200 mg, 1.02
mmol) and CF3CO2Ag (226 mg, 1.02 mmol) were reacted in 10
mL of CHCl3 at room temperature in the dark overnight. The
reaction mixture was evaporated to dryness in a vacuum, the residue
washed with diethyl ether, and dried in a vacuum to leave 352 mg
of a colorless solid (83% yield, mp 164 °C dec). Anal. Found: C,
30.92; H, 2.11. Calcd for C11H9AgF3NO4S (416.12): C, 31.75; H,
1
2.18. H NMR (CDCl3, 20 °C): δ 2.44, s, 3H, CH3; 4.76, s, 2H,
CH2; 7.43 and 7.88, m, 2 × 2H, C6H4. 13C{1H} NMR: δ 21.7, s,
CH3; 61.9, s, CH2; 129.2, 130.9, 132.3, and 148.1, C6H4; 163.0,
br, NC. 19F NMR: δ -74.3, s. MS (FAB): m/z 498 [L2Ag]+.
Preparation of Complex 2. A suspension of CF3CO2Ag (200
mg, 0.90 mmol) in 10 mL of dry CHCl3 was treated with a solution
of Ph3PS (266 mg, 0.90 mmol) in another 10 mL of the same solvent
at room temperature in the dark for 2 h. The solvent was
subsequently removed in a vacuum, the residue extracted with
pentane, and the colorless product crystallized from chloroform/
pentane and dried in a vacuum (204 mg, 54% yield, mp 167 °C
dec). Anal. Found: C, 41.67; H, 2.64. Calcd for C42H30Ag3F9O6P2S2
(1251.35): C, 40.31; H, 2.42. 1H NMR (CDCl3, 20 °C): δ 7.71-
7.43, m, Ph. 13C{1H} NMR: δ (for C1-C4, respectively) 128.6, d,
J ) 88.2 Hz; 129.6, d, J ) 11.9 Hz; 132.5, d, J ) 10.4; 133.6, s.
31P{1H} NMR: δ 46.8, s. 19F NMR: δ -73.4 ppm. MS (FAB):
m/z 697 [L2Ag]+. Crystals of 2‚(CHCl3)0.87 were grown from
chloroform/pentane.
Acknowledgment. This work was generously supported
by Deutsche Forschungsgemeinschaft, Fonds der Chemischen
Industrie, and Heraeus GmbH.
Supporting Information Available: X-ray file in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC048795O
Crystal Structure Determinations. Specimens of suitable
quality and size were mounted onto the ends of quartz fibers in
(27) Sheldrick, G. M. SHELXL-97, Programs for Crystal Structure
Analysis, University of Go¨ttingen, Germany, 1997.
676 Inorganic Chemistry, Vol. 44, No. 3, 2005