The cyclic "silver-diphos" motif [Ag2(μ- diphosphine)2]2+ as a synthon for building up larger structures

Article abstract of DOI:10.1021/ic800664f

The dinuclear, cyclic structural motif [Ag₂(diphosphine) ₂]²⁺, here termed the "silver-diphos" motif, previously observed in many diphosphine-silver complexes, has been investigated as a synthon for building up larger structures such as coordination cages and polymers. A series of ligands containing one to four meta-substituted diphosphine groups, attached via a central core, has been synthesized from the corresponding fluoroarenes by reaction with KPPh₂. Upon reaction with silver salts, the target synthon is adopted by meta-substituted diphosphines 1,3-bis(diphenylphosphino)benzene (L1), 2,6-bis(diphenylphosphino)benzonitrile (L2), and 3,5-bis(diphenylphosphino)benzamide (L3), each of which gives a single species in solution consistent with the expected dimeric complexes [Ag ₂L₂(anion)₂]. X-ray crystal structures of [Ag₂(L1)₂(OTf)₂] and [Ag₂(L2) ₂(SbF₆)₂] confirm the adoption of the silver-diphos motif in the solid state. Amide-functionalized diphosphine L3 forms a hydrogen-bonded chain structure in the solid state via the amide group. A discrete boxlike cage [Ag₄(L4)₂][SbF₆] ₄ based on two silver-diphos synthons is formed when the tetraphosphine Ph₂Sn{3,5-bis(diphenylphosphino)benzene}₂ (L4) reacts with silver(I). Its single-crystal X-ray structure reveals a central cavity of minimum diameter, ca. 5.0 A, which contains a single SbF ₆^- counterion disordered over two sites. In contrast to the highly selective behavior of the di- and tetra-phosphines L1-L4, the heptaphosphine P{3,5-bis(diphenylphosphino)benzene}₃ L5 and the hexaphosphine PhSn{3,5-bis(diphenylphosphino)benzene}₃ L6 give dynamic mixtures upon reaction with silver salts in solution. This nonspecific behavior is rationalized by the fact that their diphosphine groups are not appropriately disposed to form stable discrete structures based on the silver-diphos synthon. By contrast, the octaphosphine Sn{3,5- bis(diphenylphosphino)benzene}₄ L7 does selectively form a single, discrete, highly symmetrical product in solution, [Ag₄(L7)(OTf) ₄]. In this case, the ligand unexpectedly adopts an interarm tetra-chelating coordination mode, resulting in a continuous 24-membered ring around the periphery of the molecule. To understand the adoption of this unusual coordination mode, the alternative diphosphine Ph₂Sn(3- diphenylphosphinobenzene)₂ L8, which models a single interarm chelating site of L7, was also investigated. By contrast to L7, its coordination was nonspecific, giving mixtures of silver complexes upon reaction with AgOTf. The selective interarm chelation by L7 may therefore be stabilized by the continuous coordination ring in [Ag₄(L7)(OTf)₄]; that is, the four chelating sites can be thought of as acting in a cooperative manner. Alternatively, interarm steric repulsions between phenyl groups may favor interarm chelation. Overall, we conclude that, if the diphosphine groups are appropriately articulated to act independently (i. e., they are adequately separated and oriented), the silver-diphos synthon can be a useful tool for the coordination-based self-assembly of larger structures.

Full text of DOI:10.1021/ic800664f

Inorg. Chem. 2008, 47, 8367-8379
The Cyclic “Silver-Diphos” Motif [Ag2(µ-diphosphine)2]2+ as a Synthon
for Building up Larger Structures
Philip W. Miller,† Mark Nieuwenhuyzen,† Jonathan P. H. Charmant,‡ and Stuart L. James*,†
Centre for the Theory and Application of Catalysis (CenTACat), School of Chemistry and
Chemical Engineering, Queen’s UniVersity Belfast, DaVid Keir Building, Stranmillis Road, Belfast,
Northern Ireland, United Kingdom BT9 5AG, and School of Chemistry, The UniVersity of Bristol,
Cantocks Close, Bristol United Kingdom BS8 1TS
Received April 17, 2008
The dinuclear, cyclic structural motif [Ag2(diphosphine)2]2+, here termed the “silver-diphos” motif, previously observed in
many diphosphine-silver complexes, has been investigated as a synthon for building up larger structures such as
coordination cages and polymers. A series of ligands containing one to four meta-substituted diphosphine groups, attached
via a central core, has been synthesized from the corresponding fluoroarenes by reaction with KPPh2. Upon reaction
with silver salts, the target synthon is adopted by meta-substituted diphosphines 1,3-bis(diphenylphosphino)benzene (L1),
2,6-bis(diphenylphosphino)benzonitrile (L2), and 3,5-bis(diphenylphosphino)benzamide (L3), each of which gives a single
species in solution consistent with the expected dimeric complexes [Ag2L2(anion)2]. X-ray crystal structures of [Ag2(L1)2(OTf)2]
and [Ag2(L2)2(SbF6)2] confirm the adoption of the silver-diphos motif in the solid state. Amide-functionalized diphosphine
L3 forms a hydrogen-bonded chain structure in the solid state via the amide group. A discrete boxlike cage [Ag4(L4)2][SbF6]4
based on two silver-diphos synthons is formed when the tetraphosphine Ph2Sn{3,5-bis(diphenylphosphino)benzene}2
(L4) reacts with silver(I). Its single-crystal X-ray structure reveals a central cavity of minimum diameter, ca. 5.0 Å, which
contains a single SbF6- counterion disordered over two sites. In contrast to the highly selective behavior of the di- and
tetra-phosphines L1-L4, the heptaphosphine P{3,5-bis(diphenylphosphino)benzene}3 L5 and the hexaphosphine PhSn{3,5-
bis(diphenylphosphino)benzene}3 L6 give dynamic mixtures upon reaction with silver salts in solution. This nonspecific
behavior is rationalized by the fact that their diphosphine groups are not appropriately disposed to form stable discrete
structures based on the silver-diphos synthon. By contrast, the octaphosphine Sn{3,5-bis(diphenylphosphino)benzene}4
L7 does selectively form a single, discrete, highly symmetrical product in solution, [Ag4(L7)(OTf)4]. In this case, the ligand
unexpectedly adopts an interarm tetra-chelating coordination mode, resulting in a continuous 24-membered ring around
the periphery of the molecule. To understand the adoption of this unusual coordination mode, the alternative diphosphine
Ph2Sn(3-diphenylphosphinobenzene)2 L8, which models a single interarm chelating site of L7, was also investigated. By
contrast to L7, its coordination was nonspecific, giving mixtures of silver complexes upon reaction with AgOTf. The
selective interarm chelation by L7 may therefore be stabilized by the continuous coordination ring in [Ag4(L7)(OTf)4]; that
is, the four chelating sites can be thought of as acting in a cooperative manner. Alternatively, interarm steric repulsions
between phenyl groups may favor interarm chelation. Overall, we conclude that, if the diphosphine groups are appropriately
articulated to act independently (i. e., they are adequately separated and oriented), the silver-diphos synthon can be a
useful tool for the coordination-based self-assembly of larger structures.
Introduction
understanding of coordination-based self-assembly. It is
valuable to identify examples of unusual self-assembly, as
well as synthons which may reliably be employed for the
design of new discrete or polymeric coordination structures.1–3
While N- and O-donor ligands have been extensively
studied in coordination self-assembly,1,2 tertiary phosphines
have been less explored.3 Despite this, several unique
Studying the coordination behaviors of multidentate
ligands is important for expanding our knowledge and
* Author to whom correspondence should be addressed. E-mail. s.james@
qub.ac.uk.
†
Queen’s University Belfast.
The University of Bristol.
‡
10.1021/ic800664f CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 18, 2008 8367
Published on Web 08/12/2008

Miller et al.
structures and insights have resulted from the study of these
ligands in this context. These include the selective assembly
of unsaturated partial polyhedral structures,3a polar mixed-
ligand cages,3a,b cages with external calixarene-like binding
sites,3c exohedral anion templation,3d nanoporous phases,3e
and the identification ring-opening polymerization relation-
ships between discrete and polymeric structures.3f This rich
diversity of behavior results in part from the relatively bulky
and irregular shapes of these building blocks, as well as their
flexibilities in adopting both divergent and convergent
bridging conformations. In addition, their amenability to 31
P
NMR spectroscopy aids greatly in gaining insight into
behavior in solution.
Here, we describe an investigation into the utility of the
cyclic [Ag2(diphosphine)2]2+ (here termed “silver-diphos”)
structural motif for building up larger structures in a rational
way. This structural motif (Figure 1a) has previously been
found to be adopted by silver complexes of a wide range of
flexible diphosphines with oligomethylene backbones4 but
has not, to our knowledge, been probed as a usable “synthon”
for building up larger structures. It is topologically closely
related to the widespread classical carboxylic acid dimer
(Figure 1b)5 as well as the silver carboxylate synthon recently
described by Brammer et al.6 (Figure 1c). Larger structures
could be built up by making further connections on dia-
metrically opposite points on the backbones of the two
diphosphines. A promising backbone type in this regard
would be 1,3,5-trisubstituted aryl rings, with the two phos-
phino groups in mutually meta positions, as well as being
Figure 1. Cyclic silver-diphosphine structures (a), topologically related
synthons based on carboxylic acids (b) and silver carboxylates (c), and
proposed use of meta-substituted diphosphines to build up larger structures
investigated in this paper (d).
meta to the backbone functionality (X in Figure 1d). We
describe here an investigation into a series of ligands which
contain from one to four such diphosphine groups (specif-
ically 3,5-bis(diphenylphosphino)benzenetri-yl) attached to
a central core via this position, as shown in Figure 2.
(1) (a) For an overview of discrete coordination cages, see: Fujita, M.;
Tominaga, M.; Hori, A.; Therrien, B. Coord. Chem. ReV. 2005, 38,
369–378. (b) Sweigers, G. F.; Malafetse, T. J. Coord. Chem. ReV.
2002, 225, 91. (c) Caulder, D. L.; Raymond, K. N. Acc. Chem. Res.
1999, 32, 975. (d) Stang, P. J. Chem.sEur. J. 1998, 4, 19. (e) Fujita,
M. Chem. Soc. ReV. 1998, 27, 417. (f) Leninger, S.; Olenyuk, B.;
Stang, P. J. Chem. ReV. 2000, 100, 853. (g) Argent, S. P.; Adams, H.;
Riis-Johannessen, T.; Jefferey, J. C.; Harding, L. P.; Ward, M. D.
J. Am. Chem. Soc. 2006, 128, 72. (h) Seidel, S. R.; Stang, P. J. Acc.
Chem. Res. 2002, 35, 972–983. (i) Maurizot, V.; Kawano, M.; Fujita,
M. Dalton Trans. 2006, 2750–2756. (j) Sumby, C. J.; Hardie, M. L.
Angew. Chem., Int. Ed. 2005, 44, 6395–6399. (k) Lutzen, A. Angew.
Chem., Int. Ed. 2005, 44, 1000–1002. (l) Hiraoka, S.; Harano, K.;
Shiro, M.; Shionoya, M. Angew. Chem., Int. Ed. 2005, 44, 2727–
2731. (m) Hiraoka, S.; Shiro, M.; Shionoya, M. J. Am. Chem. Soc.
2004, 126, 1214–1218. (n) Hiraoka, S.; Hirata, K.; Shionoya, M.
Angew. Chem., Int. Ed. 2004, 43, 3814–3818.
Results and Discussion
Synthesis and Characterization of Ligands Contain-
ing meta-Diphosphine Groups. All phosphines were syn-
thesized from their corresponding fluoroarenes by reaction
(4) (a) Kitagawa, S.; Kondo, M.; Kawata, S.; Wada, S.; Maekawa, M.;
Munakata, M. Inorg. Chem. 1995, 34, 1455. (b) Tiekink, E. R. T.
Acta. Crystallogr., Sect. C 1990, 46, 1933. (c) Ho, D. M.; Bau, R.
Inorg. Chem. 1983, 21, 4073. (d) Neo, S. P.; Zhou, Z.-Y.; Mak,
T. C. W.; Hor, T. S. A. Inorg. Chem. 1995, 34, 520. (e) van der Ploeg,
A. F. M. J.; van Koten, G.; Spek, A. L. Inorg. Chem. 1979, 18, 1052.
(f) van der Ploeg, A. F. M. J.; van Koten, G. Inorg. Chim. Acta 1981,
51, 225. (g) Ruina, Y.; Hou, Y. M.; Xue, B. Y.; Wang, D. M.; Jin,
D. M. Transition Met. Chem. (Dordrecht, Neth.) 1996, 21, 28. (h)
Ruina, Y.; Hou, Y. M.; Xue, B. Y.; Wang, D. M.; Jin, D. M. Acta
Crystallogr., Sect. B 1976, 32, 2521. (i) Caruso, F.; Camalli, M.;
Rimml, H.; Venanzi, L. M. Inorg. Chem. 1995, 34, 673. (j) Caruso,
F.; Camalli, M.; Rimml, H.; Venanzi, L. M. J. Org. Chem. 1980, 45,
2995. (k) Caruso, F.; Camalli, M.; Rimml, H.; Venanzi, L. M. Inorg.
Chim. Acta 1997, 69, 262. (l) Brown, J. M.; Lucy, A. R. J. Organomet.
Chem. 1986, 314, 2411. (m) Wood, F. E.; Hvoslef, J.; Balch, A. L.
J. Am. Chem. Soc. 1983, 105, 6986.
(2) (a) For overviews of polymer and framework coordination structures,
see: Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004,
43, 2334. (b) Rowsell, J. L. C.; Yaghi, O. M. Microporous Mesoporous
Mater. 2004, 73, 3. (c) Rosseinsky, M. J. Microporous Mesoporous
Mater. 2004, 73, 15. (d) Janiak, C. Dalton Trans. 2003, 2781. (e)
James, S. L. Chem. Soc. ReV. 2003, 32, 276.
(3) For examples of phosphine-based assembly, see:(a) Zhang, J. Y.;
Miller, P. W.; Nieuwenhuyzen, M.; James, S. L. Chem.sEur. J. 2006,
12, 2448–2453. (b) Miller, P.; Nieuwenhuyzen, M.; Charmant, J. P. H.;
James, S. L. CrystEngComm 2004, 6, 408–412. (c) Zhang, J. Y.;
Nieuwenhuyzen, M.; Charmant, J. P. H.; James, S. L. Chem. Commun.
2004, 2808–2809. (d) Miller, P. W.; Nieuwenhuyzen, M.; Xu, X. L.;
James, S. L. Chem. Commun. 2002, 2008. (e) James, S. L.; Mingos,
D. M. P.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 2323.
(f) Xu, X.; Nieuwenhuyzen, M.; Chambers, M.; MacLean, E.; Teat,
S. J.; James, S. L. Chem. Commun. 2002, 78. (g) Xu, X. L.;
Nieuwenhuyzen, M.; James, S. L. Angew. Chem., Int. Ed. 2002, 41,
764. (h) Lozano, E.; Nieuwenhuyzen, M.; James, S. L. Chem.sEur.
J. 2001, 7, 2644–2651. (i) Brandys, M.; Puddephatt, R. J. J. Am. Chem.
Soc. 2002, 124, 3946. (j) Wheaton, C. A.; Jennings, M. C.; Puddephatt,
R. J. J. Am. Chem. Soc. 2006, 128, 15370. (k) James, S. L. Macromol.
Symp. 2003, 196, 187. (l) Zhang, J.; Xu, X.; James, S. L. Chem.
Commun. 2006, 4218.
(5) (a) Sharma, C. V. K.; Desiraju, G. R. In PerspectiVes in Supramo-
lecular Chemistry; Desiraju, G. R., Ed.; Wiley: New York, 1996; Vol.
II. (b) Braga, D.; Grepioni, F.; Sabatino, P.; Desiraju, G. R.
Organometallics 1994, 13, 3532. (c) Brammer, L.; Mareque Rivas,
J. C.; Atencio, R.; Fang, S.; Pigge, F. C. J. Chem. Soc., Dalton Trans.
2000, 3855.
(6) Brammer, L.; Burgard, M. D.; Eddleston, M. D.; Rodger, C. S.; Rath,
N. P.; Adams, H. CrystEngComm 2002, 4, 239.
8368 Inorganic Chemistry, Vol. 47, No. 18, 2008

The Cyclic “SilWer-Diphos” Motif [Ag2(µ-diphosphine)2]2+
Figure 3. X-ray crystal structure of L3 showing the H-bonded chain formed
by the amide groups.
Figure 4. Formal representations of the possible orientations of the lone
pairs for meta-diphosphine groups.
been recognized as a recurring packing motif for amides.9
Rotation about the bond between phosphorus and the central
aryl ring can lead to a variety of lone pair orientations, which
in their extreme manifestations can be termed divergent,
alternate, or convergent, as illustrated in Figure 4. The
convergent conformation is necessary to form the silver-
diphos motif, but it is interesting that the divergent confor-
mation is also possible for noncoordinated meta-substituted
diphosphines, as seen in this crystal structure. The packing
mode adopted is likely to be a tradeoff between the amide
H bonding and the packing of the phenyl rings. It is possible
that both the conformation (divergent lone pairs) and the
extended packing (linear versus dimeric H-bonding motif)
will have been influenced by the preferred packing modes
of the bulky aryl substituents in the lattice.
The tetraphosphine bis-3,5{bis(diphenylphosphino)ben-
zenetri-yl}diphenylstannane L4 was prepared by reaction of
the corresponding tetrafluoride with four equivalents of
potassium diphenylphosphide, to yield an analytically pure
white solid in 69% yield. The 31P NMR spectrum showed a
single resonance at -4.8 ppm. The new heptaphosphine with
one central and six peripheral phosphine groups, tris{3,5-
bis(diphenylphosphino)benzenetri-yl}phenyl phosphine L5,
was prepared by reaction of the corresponding hexafluoride
precursor, tris(3,5-difluorophenyl)phosphine, with six equiva-
lents of potassium diphenylphosphide and was obtained as
a white powder in 84% yield following workup from
methanol. The fast atom bombardment mass spectrometry
(FAB-MS) spectrum of the product showed a signal at 1367
Figure 2. Multidentate ligands L1-L7 bearing meta-diphosphine units
and diphosphine L8 which models a single interarm chelate coordination
site of L7.
with potassium diphenylphosphide in THF. For 1,3-bis-
(diphenylphosphino)benzene ligand L1, this is different from
the previously reported method.7 L1 was isolated in 90%
yield as a viscous liquid, similar to its description in the
previous report. 2,6-Bis(diphenylphosphino)benzonitrile L2
was prepared according to the literature procedure,8 starting
from the corresponding difluoride. 3,5-Bis(diphenylphosphi-
no)benzamide L3 was obtained as a white crystalline solid
in 82% yield following recrystallization from methanol.
Single crystals suitable for X-ray diffraction were obtained
by the slow cooling of a methanolic solution of L3. The
X-ray crystal structure (Figure 3) displays H-bonding
between amide groups on adjacent molecules to give a chain
with one NH · · · O hydrogen bond per molecule (with a
N · · · O distance of 2.879(12) Å and a N-H · · · O angle
166.2(7)°). The most common amide packing mode, the
cyclic H-bonded dimer (analogous to the carboxylic acid
dimer), is not adopted; however, this type of chain has also
(7) McFarlane, H. C. E. Polyhedron 1988, 7, 1875–1879.
(8) Hingst, M.; Tepper, M.; Stelzer, O. Eur. J. Inorg. Chem. 1998, 73–
82.
(9) Leiserowitz, L.; Hagler, A. T. Proc. R. Soc. London 1983, A388, 133.
Inorganic Chemistry, Vol. 47, No. 18, 2008 8369

Miller et al.
Figure 5. View of one of the independent octaphosphine molecules in the
crystal structure of L7. H atoms have been omitted for clarity.
m/z, indicating the molecular ion. The 31P NMR spectrum
showed a signal at -2.3 ppm for the central phosphorus atom
and a more intense signal at -3.6 ppm for the six equivalent
peripheral phosphine groups. The 1H NMR spectrum showed
complex overlapping multiplets of 69 aromatic hydrogen
atoms from 7.23 to 7.06 ppm. The 13C NMR spectrum
showed a number of unresolved peaks from 139.3 to 138.9
ppm due to overlapped multiplets, which account for the
carbon atoms in the three phenyl rings attached to the central
phosphorus atom. The carbon signals of the exterior phenyl
groups are assignable from their multiplicities and the
magnitudes of their 31P,13C coupling constants.
The hexaphosphine tris{3,5-bis(diphenylphosphino)ben-
zenetri-yl}phenyl stannane L6 was prepared from tris{3,5-
bis(difluorophenyl)phenylstannane. A workup with methanol
and column chromatography yielded L6 as a cream-colored
solid in 71% yield. The octaphosphine tetrakis{3,5-
bis(diphenylphosphino}benzetriyl)stannane L7 was prepared
by the phosphination of tetrakis(3,5-difluorophenyl)stannane
and obtained as a white powder in 81% yield following a
workup from methanol. The FAB-MS spectrum showed a
peak at 1900 m/z, which corresponds to the molecular ion.
The 31P NMR spectrum showed a single resonance at -5.2
ppm. Single crystals of L7 suitable for X-ray diffraction were
obtained by slow diffusion from an acetone solution.
Two independent molecules were found in the crystal, one
of which is shown in Figure 5. The ligand displays the
expected tetrahedral geometry at the central tin atom, albeit
distored, with with C · · · Sn · · · C bond angles ranging from
102.32(15)° to 114.35(15)°. There are eight independent
meta-diphosphine units in the crystal, four of which adopt
divergent conformations, three of which adopt alternate
conformations, and one adopting a convergent conformation.
Coordination to Silver(I). Dimeric Complexes with
Diphosphines L1, L2, and L3. 1,3-Bis(diphenylphosphi-
no)benzene L1 has previously been demonstrated to form
dimeric dimetallic rings with platinum(II) and palladium(II)
via the M2(diphos)2 bridging coordination mode. These
Figure 6. (a) 31P NMR spectrum of [Ag2(L1)2(O3SCF3)2] in CDCl3/
CH3NO2 (4:1). (b) X-ray crystal structure of [Ag2(L1)2(O3SCF3)2]. (c) View
to emphasize the stepped conformation of the central rings.
structures are clearly analogous to the silver-diphos motif.10
A CDCl3/CH3NO2 (4:1) solution containing equimolar
amounts of L1 and AgO3SCF3 gave a 31P NMR spectrum
with characteristic one-bond couplings to the spin 1/2 silver
isotopes 107Ag and 109Ag (Figure 6).
The complex exhibited a distinctive downfield chemical
shift (14.5 ppm), relative to that of the free ligand. The
magnitude of the coupling constant 1J(109Ag,31P) ) 587 Hz
indicates that two phosphorus atoms coordinate at each silver
(10) Alcock, N. W.; Judd, L.; Pringle, P. G. Inorg. Chim. Acta 1986, 113,
L13-L15.
8370 Inorganic Chemistry, Vol. 47, No. 18, 2008

The Cyclic “SilWer-Diphos” Motif [Ag2(µ-diphosphine)2]2+
center.11 L1 reacted also with other silver(I) salts in a mixture
of CDCl3/CH3NO2 (4:1), again to give characteristic one-
bond coupling to 107Ag and 109Ag in 31P NMR spectra at
room temperature. However, use of the more strongly
coordinating solvent mixture CDCl3/CH3CN (4:1) gave 31P
NMR spectra which were broader, in which 107/109Ag,31P
coupling was unresolved at room temperature. This suggests
that acetonitrile in excess can compete with the phosphine
for coordination at the silver(I) centers causing some Ag-P
dissociation. Chemical shift and coupling constant data are
summarized in the experimental section. Crystals suitable
for X-ray diffraction studies were grown by the slow
diffusion of diethyl ether into a 0.044 M solution of
[Ag2(L1)2(O3SCF3)2] in CDCl3/CH3NO2.
The X-ray crystal structure (Figure 6) confirms the
expected cyclic dimeric structure. Two diphosphine ligands
bridge the two silver ions, with an inversion center at the
center of the molecule. The H · · ·H distance between the two
central rings of the ligands is 3.85(2) Å, and the Ag · · · Ag
distance is 4.99(3) Å, both of which are too large for any
significant interaction.12 However, there is a short O · · · H
contact of 2.38(2) Å between each of these H atoms and O
atoms of the triflate anions, which may help to stabilize the
structure. The central phenyl rings do not point directly
toward each other, but adopt a “stepped” conformation
(Figure 6c). This is similar to that seen in the platinum
complex [(PtCl2)(L1)2]10 and the nanoporous silver polymer
based on 1,3,5-tris(diphenylphosphino)benzene.3e The co-
ordination at silver is not linear, but slightly bent with a
P-Ag-P angle of 155.80(5)°. The two triflate anions each
coordinate to different silver centers, in terminal monodentate
fashion, with Ag-O distances of 2.586(4) Å.
Although the nitrile-diphosphine L2 has been previously
reported,6 its coordination chemistry has not been investi-
gated, to our knowledge. It provides an interesting test of
the silver-diphos synthon since the nitrile group could
potentially interfere sterically or via coordination to silver.
When L2 was reacted with AgO3SCF3, in a 1:1 ratio in
CDCl3/CH3NO2 (4:1), characteristic one-bond coupling to
107Ag and 109Ag is seen in the 31P NMR spectrum. Relative
to the free ligand, the complex exhibited a downfield
chemical shift of 9.7 ppm with 1J(109Ag,31P) ) 587 Hz, again,
indicating the coordination of two phosphorus atoms to each
silver center. The FT-IR spectrum of the complex showed
two absorptions due to nitrile groups, one at 2211 cm-1 due
to the ligand itself and another at 2267 cm-1 most likely
due to residual acetonitrile used in the crystallization
coordinated to the Ag centers (see below).
diphosphine ligands. The main difference between the dimers
relates to additional coordination of acetonitrile. Two of the
dimers contain centers of symmetry with one molecule of
acetonitrile coordinated at each silver(I) center. In one of
the dimers, the coordination is approximately linear; that is,
the Ct N-Ag angle is 178(3)°. In the other, the acetonitrile
coordination is angled; that is, the Ct N-Ag angle is
132(3)°. The third dimer is noncentrosymmetric, with two
acetonitrile molecules coordinated to one silver(I) center and
none to the other. Despite the asymmetry of the acetonitrile
coordination in this dimer, the ring structure is not greatly
distorted, with P-Ag distances of 2.408(7) and 2.399(7) Å
for the two-coordinate AgP2 center, being similar than the
2.446(7) and 2.439(7) Å P-Ag distances at the AgP2N2
center. The P-Ag-P angles differ more notably, however,
at 165.3(3) Å for the AgP2 center and 145.3(3) Å for the
AgP2N2 center. Each dimer adopts the same type of stepped
conformation as observed for [Ag2(L1)2(O3SCF3)2]. This
conformation is in fact imposed by the need to accommodate
the two nitrile groups (Figure 7b). The interligand N· · ·C
distances of the nitrile groups are 3.28(10), 3.26(10) and
3.04(10) Å for each of the three dimers which are similar to
the combined van der Waals radii (1.70 for C, 1.55 for N
gives 3.25 Å).13
The three dimers differ only slightly in their P-Ag bond
lengths, which range from 2.399(7) to 2.448(7) Å and are
comparable to those in [Ag2(L1)2(O3SCF3)2]. The P-Ag-P
angles in the three dimers range from 141.7(2) to 165.3(3)°.
These angles are also comparable to those of [Ag2(L1)2-
(O3SCF3)2]. The Ag · · ·Ag distances within the three dimers,
however, are 5.88(15), 6.12(15), and 5.57(15) Å, which are
on average almost 1 Å larger than that in [Ag2(L1)2(O3-
SCF3)2] (Ag · · · Ag ) 4.99(3) Å). This may be attributed to
the steric bulk of the nitrile groups at the center of these
dimers or the coordination of acetonitrile at the silver centers.
Ligand L3 is of interest since it can potentially exhibit
crystal packing which is directed both by the silver-diphos
synthon and by hydrogen bonding via the amide group.
[Ag2(L3)2(O3SCF3)2] was prepared by reaction of L3 with
one equivalent of silver triflate in pure acetonitrile. The use
of this coordinating solvent was necessary because of the
lower solubility of L3. The 31P NMR spectrum showed two
broad signals at room temperature without resolved phos-
phorus-silver coupling, indicating P-Ag dissociation on the
NMR time scale. This is expected due to the large excess of
coordinating solvent present. However, on cooling to -30
°C, a single phosphorus environment with characteristic,
sharp one-bond coupling to 107Ag and 109Ag was observed,
with 1J(109Ag,31P) ) 496 Hz, which indicates the coordination
of two phosphorus atoms to each of the silver centers. It is
likely therefore that the silver-diphos motif is adopted by
this complex in solution, in common with L1 and L2. The
complex was isolated as a white powder by the addition of
excess diethyl ether to an acetonitrile solution. The FAB-
MS spectra showed peaks at 1343 and 596 m/z, which
correspond to [Ag2(L3)2(O3SCF3)]+ and [Ag2(L3)2]2+, re-
Crystals suitable for X-ray diffration were obtained by the
slow diffusion of diethyl ether into a solution of
[Ag2(L2)2][SbF6]2 in CHCl3/CH3CN. The X-ray crystal
structure showed three independent dimeric structures (Figure
7a). The silver-diphos motif is present in all three individual
dimeric molecules, with two silver ions bridged by two
(11) Verkade J. G.; Quin, L. D. Phosphorus-31 NMR Spectroscopy in
Stereochemical Analysis Organic Compounds and Metal Complexes;
VCH Publishers: New York, 1987.
(12) Pyykko, P. Chem. ReV. 1997, 97, 597–636.
(13) Bondi, A. J. Phys. Chem. 1964, 68, 411–451.
Inorganic Chemistry, Vol. 47, No. 18, 2008 8371

Miller et al.
Figure 7. (a) The molecular structures of the three independent dimers found in the crystal of [Ag2(L2)2(SbF6)2]. (b) View to emphasize the stepped
conformation enforced by the presence of the nitrile functions. Hydrogen atoms, SbF6 counterions, and solvent molecules have been omitted for clarity.
spectively. Unfortunately, crystals of the complex suitable
for X-ray diffraction could not be obtained.
“arched” rather than “stepped”, in order to form a discrete
rather than polymeric structure, which indicates a significant
aspect of the flexibility of the silver-diphos motif. The interior
C-Sn-C angle of 110.2(2)° is, within error, the same as
the exterior C-Sn-C angle of 109.8(3)° between the phenyl
groups, suggesting very little strain about the tin centers. The
silver centers are almost linear, with P-Ag-P bond angles
of 169.72(6)° and 166.21(6)°. One of the coordinating SbF6
anions was located inside the cage, disordered over two sites,
and weakly bridging between two silver centers with Ag · · ·F
distances of 2.975(16) and 3.192(17) Å. A pair of weakly
coordinating SbF6 anions, related by crystallographic sym-
metry and disordered over two sites, are located outside the
cage with a Ag · · · F distance of 2.949(16) Å, and the fourth
anion was found to be noncoordinating. The exterior dimen-
sions of the cage are approximately 18 × 20 × 14 Å between
the furthest H atoms of the phenyl rings. The interior of the
cage is an open cavity with a Sn · · · Sn distance of ca. 10.4
Å, two long Ag · · · Ag distances (ca. 8.7 Å), and two shorter
Ag · · · Ag distances (ca. 5.9 Å). Taking into account the van
der Waals radii of the framework atoms, the cavity can
accommodate a sphere of diameter 5.0 Å. The cavity has
two large access windows which could permit anions and
solvent to diffuse in and out of the cage. The 19F NMR
spectrum of the cage prepared from AgBF4, [Ag4(L4)(BF4)4]
showed only one chemical environment for the BF4 anions,
Cage Complex Based on Tetraphosphine L4. The
tetraphosphine L4 has two meta-diphosphine arms connected
through a diphenyl tin group. The arrangement of the
diphosphine groups should allow for the bridging coordina-
tion mode as seen for L1, L2, and L3, between two or more
L4 ligands. This could lead to either discrete or polymeric
structures, as shown in Figure 8a.
The reaction of L4 with two equivalents of silver triflate
in CDCl3/CH3NO2 (4:1) gave a solution exhibiting a sharp
31P NMR spectrum, indicating a single phosphorus environ-
ment, with well-resolved 107Ag,31P and 109Ag,31P coupling.
The 109Ag,31P coupling constant of 574 Hz indicates that two
phosphorus atoms bond to each silver center. The FAB-MS
spectrum for the silver hexafluoroantimonate complex showed
a peak at 1615 m/z which corresponds to the [Ag4(L4)2-
(SbF6)2]2+ dication. Crystals suitable for X-ray diffraction
studies were obtained by the slow diffusion of diethyl ether
into a CHCl3/CH3NO2 (4:1) solution of L4 and AgSbF6. A
crystal structure determination revealed the discrete boxlike
cage structure shown in Figure 8b, consistent with the
solution state 31P NMR and FAB-MS spectra. The bridging
coordination mode of each diphosphine arm is analogous to
that seen in the disphosphine complexes described above.
However, the conformation of these motifs is necessarily
8372 Inorganic Chemistry, Vol. 47, No. 18, 2008

The Cyclic “SilWer-Diphos” Motif [Ag2(µ-diphosphine)2]2+
Figure 9. Diamandoid network (a) and linear chain of cages (b), both based
on silver-diphos motifs which could be expected to form using octaphos-
phine L7.
-
There was no apparent difference between the included SbF6
and BF4- counterions with regard to templation of the cage,
that is, the stability of the cage or its rate of formation (in
all of our NMR studies of silver-phosphine assemblies to
date, NMR spectra show that equilibrium is already achieved
by the time the NMR spectrum is run).
Dynamic Mixtures Formed by L5 and L6. Heptaphos-
phine L5 and hexaphosphine ligand L6 might be expected
to form either extended coordination polymers or discrete
structures. However, construction of simple models reveals
that, in contrast to L4, the disposition of the three diphos-
phine arms of each of these ligands is not appropriate for
the formation of stable discrete cages. Solutions of mixtures
of L5 or L6 with three equivalents of silver(I) salts gave
31P NMR spectra which were broad with no resolved
107/109Ag,31P coupling. This suggests dynamic exchange at
the silver centers on the NMR time scale, consistent with
the formation of dynamic mixtures of oligomers. At -60
°C, 31P spectra were sharp and showed evidence of coupling
to silver; however, a large number of P environments was
present in each case, confirming the nonselective coordination
of these ligands. Repeated attempts to obtain single crystals
resulted only in the formation of amorphous powders.
Chelate Coordination of Four Metal Ions by
Octaphosphine L7. L7 has four diphosphine arms emanating
from a central tetrahedral Sn center. If it were to adopt the
silver-diphos motif upon reaction with silver(I), a three-
dimensional diamondoid network polymer could be expected
(Figure 9a). Alternatively, a one-dimensional polymer could
be expected on the basis of catenated cages analogous to
Figure 8. (a) Schematic representations of a discrete Ag4(L4)2 cage versus
a linear polymer, both based on the silver-diphos motif, that can be expected
on the reaction of L4 with silver(I). (b) Side-on and end-on views of the
X-ray crystal structure of the discrete cage [Ag4(L4)2(SbF6)2]2+ showing
the boxlike structure and the included SbF6 anion, which is disordered over
two sites. H atoms are omitted for clarity. The necessarily arched
conformation of the silver-diphos connections can be seen in the side-on
view.
suggesting that they are able to diffuse freely in and out of
the structure at room temperature on the NMR time scale.
Inorganic Chemistry, Vol. 47, No. 18, 2008 8373

Miller et al.
that formed by the tetraphosphine L4 (Figure 9b). Simple
models show that it is not possible to form a stable discrete
structure based on the silver-diphos motif. When a solution
of L7 in CDCl3 was added to a solution of silver(I) salts in
CH3CN at a ligand-to-metal ratio of 1:4, sharp signals
showing well-resolved 107Ag,31P and 109Ag,31P coupling were
observed, suggesting that a stable discrete structure had in
fact formed (Figure 10). The sharp spectrum obtained for
these complexes and the magnitude of the 109Ag,31P coupling
(in the range 546-545 Hz) indicate the formation of a single
highly symmetrical species in solution with AgP2 coordina-
tion centers. This was surprising because of the expected
formation of oligomeric or polymeric species, as described
above. The spectrum could however be explained if there
was chelation of silver ions between the diphos arms.
Crystals of [Ag4(L7)(O3SCF3)4] were obtained by the slow
diffusion of diethyl ether into a CHCl3/CH3NO2 solution of
the complex. An X-ray structure determination confirmed
the formation of this tetra-chelate structure (Figure 10).
Four 10-membered chelate rings are formed by the
coordination of silver ions between the diphenylphosphino
arms of L7. This results in a continuous 24-membered
coordination ring around the periphery of the molecule. The
meta-diphosphine arms necessarily adopt the divergent
conformation indicated in Figure 4. Ag-P bond distances
range from 2.4211(17) to 2.4680(18) Å. The silver centers
are nonlinear, with P-Ag-P angles ranging from 145.42(6)
to 151.22(6)°. Three of the silver centers have monodentate
triflate anions coordinated with Ag · · · O distances ranging
from 2.452(8) to 2.733(7) Å. The fourth has a bidentate
triflate anion with Ag · · ·O distances of 2.616(5) and 2.705(5)
Å and an expectedly acute O-Ag-O angle of 53.70(16)°.
This chelate coordination mode was not observed for
L4-L6, and therefore it appears to be uniquely stabilized
in the case of L7. It is possible that it becomes favored for
L7 due to the formation of the continuous large ring. This
behavior can alternatively be described in terms of cooper-
ativity between the four interarm sites. In particular, since
coordination of silver between the arms reduces the rotational
freedom about the Sn-C bonds, decoordination of a single
silver ion from the saturated complex [Ag4(L7)(OTf)4] leaves
a free coordination site which remains preorganized for chelation
due to silver chelation of the sites to either side. In other words,
neighboring coordination sites may act in a mutually cooperative
manner to favor the chelate coordination mode. Cooperative
binding of metal ions by oligodentate ligands has previously
been described in terms of positive homotropic allosteric
effects.14 However, this has previously referred to the strength
of binding rather than the mode of binding.
Figure 10. 31P NMR spectrum of [Ag4(L7)(O3SCF3)4] in CDCl3/CH3CN
(4:1) and X-ray crystal structure of [Ag4(L7)(O3SCF3)4] showing the
interarm tetra-chelate coordination mode adopted.
its four sites.
When a solution of L8 in CDCl3 was added to solution of
AgO3SCF3 in CH3CN in a 1:1 molar ratio, the 31P NMR
spectrum revealed a broad signal at 12.6 ppm (Figure 11),
in contrast to the sharp signals with 107/109Ag,31P coupling
observed for [Ag4(L7)(O3SCF3)4] (Figure 10), and indicative
of dynamic behavior. On cooling to -30 °C, the 31P NMR
spectrum displayed two main sets of 107Ag,31P and 109Ag,31P
1
doublets. The J(109Ag,31P) coupling constants for these
species were 533 and 500 Hz, indicating that both were based
on AgP2 coordination centers. Of the two complexes formed,
one could potentially be the chelate complex, but at least
one of them must be based on bridging coordination, for
example, the dimer formed through a silver-diphos motif,
[Ag2(L8)2(OTf)2] (Figure 11). Therefore, diphosphine L8,
unlike octaphosphine L7, does not selectively form a chelate
complex with silver(I). This supports the idea that the
selective chelation at the four sites of L7 arises from
cooperative behavior. However, since L7 and L8 are not
isosteric, it remains possible that the selective chelation by
L7 is a result of steric repulsions between the phenyl groups
on adjacent arms, which would be expected to favor
divergent conformations and so interarm chelation.
Conclusions
Diphosphines based on meta-substitution at an aryl ring
adopt the target dimeric silver-diphos synthon upon reaction
with silver salts. In extending this principle to ligands
containing up to four such diphosphine groups attached to a
central core, it is clear that, if the diphosphine groups are
appropriately articulated, as in L4, larger stuctures, such as
cages, based on the silver-diphos synthon can form selec-
tively. Where the ligand structure does not permit simulta-
neous adoption of the silver-diphos synthon at all diphosphine
sites to form a discrete structure, a mixture of oligomeric
The diphosphine bis(3-diphenylphosphinophenyl)diphe-
nylstannane L8 was prepared as a model compound to test
this aspect. Diphosphine L8 has two diphenylphosphine
groups in the meta positions of two independent phenyl
groups and therefore has the potential to form a single chelate
ring in an analogous fashion to a single coordination site of
[Ag4(L7)(O3SCF3)4]. Since L8 has only one chelating site
available, it would be less predisposed to chelation than L7
if the latter does exhibit cooperative chelate binding between
8374 Inorganic Chemistry, Vol. 47, No. 18, 2008

The Cyclic “SilWer-Diphos” Motif [Ag2(µ-diphosphine)2]2+
Experimental Section
General. All chemicals purchased from commercial sources were
of reagent grade and used without further purification. All reactions
involving air-sensitive reagents were carried out under an inert
atmosphere of nitrogen using predried solvents. 2,6-Bis(diphe-
nylphosphino)benzonitrile (L3) was prepared according to the
literature procedure.8 NMR spectra were recorded on Bruker AM
300 MHz or AM 500 MHz spectrometers. 31P and 13C NMR spectra
are proton-decoupled. 1H NMR spectra were referenced to the protio
residue in the solvent, 31P NMR spectra to external 85% H3PO4
(aq), and 19F NMR spectra to CFCl3. Melting points were
determined using an Electrothermal 9100 melting point apparatus.
Infrared spectra were recorded on a Perkin-Elmer 983G spectro-
photometer equipped with a Perkin-Elmer 3700 data station. Solid
samples were recorded as KBr pressed discs. Mass spectra were
recorded on a VG Autospec.
Synthesis of Fluoroaryl Precursors. Tris(3,5-difluorophenyl)-
phosphine (Precursor to L4). The following method differs from
that reported in the literature.15 To magnesium turnings (0.5 g, 20
mmol) was added a crystal of iodine and a solution of bromo-3,5-
difluorobenzene (1.00 g, 5.2 mmol) in diethyl ether (15 mL). The
reaction was left to stand for approximately 15 min, after which
time it proceeded with no external heating. A further solution of
bromo-3,5-difluorobenzene (2.35 g, 12.2 mmol) in diethyl ether
(35 mL) was added dropwise to bring the reaction to a steady reflux.
Upon complete addition of the bromo-3,5-difluorobenzene solution,
the reaction was brought back to reflux for 1 h, forming a light
brown/orange solution. The reaction was then allowed to cool to
room temperature and phosphorus trichloride (0.58 g, 4.3 mmol)
added gradually. A precipitate forms almost instantaneously, and
the reaction was slightly exothermic. After addition of the
phosphorus trichloride was complete, the reaction was brought to
reflux for a further 2 h. The reaction was then placed in an ice
bath, the excess Grignard reagent hydrolyzed using HCl (10%, 50
mL), and the resulting aqueous phase extracted with diethyl ether
(4 × 50 mL). The combined fractions were dried over anhydrous
magnesium sulfate. The magnesium sulfate was removed by
filtration and the solvent removed in vacuo to yield a viscous brown
oil that was sublimed under reduced pressure (0.01 mmHg, 100
°C) to give an analytically pure white crystalline solid (0.88 g, 56%).
Elem anal. calcd (%): C, 58.39; H, 2.45. Found: C, 58.32; H, 2.37.
1H NMR (300 MHz, CDCl3): δ 6.86 (tt, 3 H), 3J(19F,1H) ) 8.7 Hz,
4J(1H,1H) ) 2.1 Hz, 6.82-6.74 (m, 6 H).13C NMR (75 MHz,
1
3
CDCl3): δ 163.2 (ddd, CFar), J(19F,13C) ) 253.5 Hz, J(19F,13C)
) 11.2 Hz, J(31P,13C) ) 11.2 Hz, 139.2 (dt, CP), J(31P,13C) )
3
1
Figure 11. (a) Variable-temperature 31P NMR spectra of diphosphine L8
and AgO3SCF3 (1:1) in CDCl3/CH3CN (4:1) showing the nonselective
coordinating behavior and a proposed equilibrium based on AgP2 centers,
which would explain the two main species observed.
16.2 Hz, J(19F,13C) ) 6.6 Hz, 116.1 (m, CHar), 105.6 (t, CHar),
3
2J(19F,13C) ) 25.1 Hz).19F-{1H} NMR (282 MHz, CDCl3): δ
-108.2 (s). 31P-{1H} NMR (121 MHz, CDCl3): δ -0.5 (s). EI-
MS m/z (%): 370 (100) [M+].
Bis(3,5-difluorophenyl)diphenylstannane (Precursor to L5).
3,5-Difluorophenyl-magnesium-bromide (0.54 M, 54 mmol) was
prepared analogously to that of tris(3,5-difluorophenyl)phosphine
structures was observed in solution (L5 and L6). An
interesting exception to this was the discrete complex formed
by octaphosphine L7, which is based on the alternative
coordination mode of interarm chelation. This complex
provides an interesting case in which cooperativity between
the coordination sites and the build up of interarm steric
congestion leads to selective interarm chelation. Extending
this work further, by ensuring that the diphosphine groups
in an oligo(diphosphine) ligand are sufficiently well-separated
to act independently, it should be possible to generate further
polymeric and cage structures in a rational way based on
the silver-diphos synthon.
(14) (a) Takeuchi, M.; Ikeda, M.; Sugasaki, A.; Shinkai, S. Acc. Chem.
Res. 2001, 34, 865–873. (b) Shinkai, S.; Ikeda, M.; Sugasaki, A.;
Takeuchi, M. Acc. Chem. Res. 2001, 34, 494–503. (c) Rebek, J. J.
Acc. Chem. Res. 1984, 17, 258–264. (d) Rebek, J., Jr.; Costello, T.;
Marshall, L.; Wattely, R.; Gadwood, R. C.; Onan, K. J. Am. Chem.
Soc. 1985, 107, 7481–7487. (e) Traylor, T. G.; Mitchell, M. J.;
Ciconen, J. P.; Nelson, S. J. Am. Chem. Soc. 1982, 104. (f) Tabushi,
I.; Sasaki, T. J. Am. Chem. Soc. 1983, 105, 2901–2902. (g) Tabushi,
I. Pure Appl. Chem. 1998, 60, 581–586. (h) Takeuchi, M.; Imada, T.;
Shinkai, S. Angew. Chem., Int. Ed. 1998, 37, 2096–2099. (i) Glass,
T. E. J. Am. Chem. Soc. 2000, 122, 4522–4523.
(15) Davies, S. G.; Derome, A. E.; McNally, J. P. J. Am. Chem. Soc. 1991,
113, 2854–2861.
Inorganic Chemistry, Vol. 47, No. 18, 2008 8375

Miller et al.
(1). To this was added a solution of diphenyl-tin-dichloride (7.37
g, 21.4 mmol) dissolved in diethyl ether (30 mL). The reaction
was brought to reflux for 2 h, after which the excess Grignard
reagent was hydrolyzed using HCl (10%, 50 mL). The resulting
aqueous phase was extracted with diethyl ether (4 × 50 mL). The
combined fractions were dried over anhydrous magnesium sulfate.
The magnesium sulfate was filtered off and the solvent removed
in Vacuo to yield a crude yellow solid (9.2 g) that was recrystallized
from ethanol to give an off-white crystalline solid (6.4 g, 62%).
Elem anal. calcd (%): C, 57.76; H, 3.23. Found: C, 57.76; H, 3.10.
M.p.: 135-136 °C. 1H NMR (300 MHz, CDCl3): δ 7.58-7.51 (m,
4 Har), 7.47-7.40 (m 6 Har), 7.10-7.04 (m, 4 Har), 6.84 (tt, 2 Har),
2J(19F,1H) ) 9.2 Hz, 4J(1H,1H) ) 2.3 Hz.13C NMR (75 MHz,
CDCl3): δ 163.2 (dd, CFar), 1J(19F, 13C) ) 255.0 Hz, 3J(19F,13C) )
10.0 Hz, 141.2 (s, CSnar), 137.0 (s, CHar), 135.4 (s, CHar), 129.2
brought to reflux for 2 h. The reaction was allowed to cool, and a
solution of diphenyl-tin-dichloride (2.5 g, 7.3 mmol) in diethyl ether
(10 mL) was added dropwise. A white precipitate formed almost
immediately. The reaction was heated to reflux for a further 4 h,
after which it was allowed to cool, and HCl (10%, 100 mL) added.
The aqueous layer was extracted with diethyl ether (5 × 50 mL)
and dried over anhydrous magnesium sulfate. The magnesium
sulfate was removed by filtration and the solvent removed in Vacuo.
A white crystalline solid was obtained upon recrystallization from
diethyl ether (2.30 g, 68%). Elem anal. calcd (%): C, 62.24; H,
3.92. Found: C, 62.12; H, 3.84. M.p.: 180-181 °C. 1H NMR (300
MHz, CDCl3): δ 7.66-7.02 (m, 24 Har). 13C NMR (75 MHz,
CDCl3): δ 163.0 (d, CFar), 1J(19F,13C) ) 251.3 Hz, 140.1 (s, CSnar),
4
137.1 (s, CHmeta), 136.7 (s, CSnar), 132.7 (d, CHortho), J(19F,13C)
) 3.2 Hz, 130.2 (d, CHmeta), 3J(19F,13C) ) 6.6 Hz, 129.6 (s, CHpara),
2
2
(s, CHar), 119.0 (m, CHar), 105.1 (t, CHar), J(19F,13C) ) 24.9 Hz.
128.9 (s, CHortho), 123.4 (d, CHpara), J(19F,13C) ) 18.5 Hz, 116.4
19F-{1H} NMR (282 MHz, CDCl3): δ -109.7 (s). EI-MS m/z (%):
(d, CHortho), 2J(19F,13C) ) 20.9 Hz. DEPT 45 13C NMR (75 MHz,
500 (100) [M+].
CDCl3): δ 137.1 (s, CHmeta), 132.7 (d, CHortho), J(19F,13C) ) 3.2
4
Tris(3,5-difluorophenyl)phenylstannane (Precursor to L6).
3,5-Difluorophenyl-magnesium-bromide (0.64 M, 32 mmol) was
prepared analogously to tris(3,5-difluorophenyl)phosphine (1). To
this was added trichloro phenyltin (1.5 mL, 2.76 g, 9.1 mmol)
dropwise at 0 °C with stirring. A white precipitate formed almost
immediately. The reaction was brought to reflux for 2 h, after which
the excess Grignard reagent was hydrolyzed using HCl (10%, 50
mL). The resulting aqueous phase was extracted with diethyl ether
(4 × 50 mL). The combined fractions were dried over anhydrous
magnesium sulfate. The magnesium sulfate was removed by
filtration and the solvent removed in Vacuo to yield a crude yellow
solid that was recrystallized from diethyl ether to give a white
crystalline solid (3.20 g, 65%). Elem anal. calcd (%): C, 53.87; H,
2.64. Found: C, 54.34; H, 2.55. M.p.: 161-162 °C. 1H NMR (300
MHz, CDCl3): δ 7.30-7.15 (m, 14 Har). 13C NMR (75 MHz,
Hz, 130.2 (d, CHmeta), 3J(19F,13C) ) 6.6 Hz, 129.6 (s, CHpara), 128.9
2
(s, CHortho), 123.4 (d, CHpara), J(19F,13C) ) 18.5 Hz, 116.4 (d,
CHortho), 2J(19F,13C) ) 20.9 Hz. 19F-{1H} NMR (121 MHz, CDCl3):
δ -112.7. EI-MS m/z (%): 405 (100), 464 (65) [M+].
SynthesisofPhosphineLigands. 1,3-Bis(diphenylphosphino)-
Benzene (L1). This procedure differs from that reported in the
literature.8 To potassium diphenylphosphide (20 mL, 0.5 M THF,
11.2 mmol) was added 1,3-difluorobenzene (0.44 mL, 4.5 mmol),
dropwise. The mixture was allowed to stir for 1 h and then was
brought to reflux overnight. THF was removed under reduced
pressure, and methanol (100 mL) was added. The mixture was
then heated to reflux for 4 h, after which the methanol was
decanted off, yielding a white sticky product that was dried in
Vacuo (1.79 g, 89%). Elem anal. calcd (%): C, 80.71; H, 5.42.
Found: C, 80.01; H, 5.49. 1H NMR (300 MHz, CDCl3): δ
7.20-7.49 (m, 24 H). 31P-{1H} NMR (121 MHz, CDCl3): δ -4.9
(s); -39.9 (s) (HPPh2, contaminant). EI-MS m/z (%): 108 (100),
446 (5) [M+].
1
CDCl3): δ 173.0 (s, CHar), 162.7 (dd, CFar), J(19F,13C) ) 246.2
Hz, 3J(19F,13C) ) 15.3 Hz, 152.9 (t, CSnar), 3J(19F,13C) ) 14.6 Hz,
2
106.72-106.3 (m, CHar), 102.5 (t, CHar), J(19F,13C) ) 26.3 Hz.
19F-{1H} NMR (282 MHz, CDCl3): δ -109.0 (s). EI-MS m/z (%):
3,5-Bis(diphenylphosphino)benzamide (L3). To 3,5-difluoro-
benzamide (1.50 g, 9.55 mmol) was added potassium diphe-
nylphosphide (40 mL, 0.5 M THF, 20 mmol), and the mixture was
refluxed overnight. THF was removed under reduced pressure.
Methanol (100 mL) was then added, which resulted in the formation
of a white crystalline solid. The crystalline solid was filtered off
and washed with methanol (3 × 50 mL) and dried in the air (3.82
g, 82%). Elem anal. calcd (%): C, 76.07; H, 5.15; N, 2.86. Found:
536 (15) [M+], 459 (100).
Tetrakis(3,5-difluorophenyl)stannane (Precursor to L7). 3,5-
Difluorophenyl-magnesium-bromide (0.7 M, 104 mmol) was pre-
pared analogously to tris(3,5-difluorophenyl)phosphine (1), and to
this was added tin tetrachloride (2.43 mL, 5.42 g, 21 mmol)
dropwise at 0 °C with stirring. A white precipitate formed almost
immediately. The reaction was brought to reflux for 2 h, after which
the excess Grignard reagent was hydrolyzed using HCl (10%, 50
mL). The resulting aqueous phase was extracted with diethyl ether
(4 × 50 mL). The combined fractions were dried over anhydrous
magnesium sulfate. The magnesium sulfate was removed by
filtration and the solvent removed in Vacuo to yield a crude yellow/
brown solid (10.02 g) that was recrystallized from dichloromethane
to give a white crystalline solid (3.32 g, 28%). Elem anal. calcd
(%): C, 50.48; H, 2.12. Found: C, 50.08; H, 1.92. M.p.: 208-209
°C. 1H NMR (300 MHz, CDCl3): δ 7.17-6.89 (m). 13C NMR (75
MHz, CDCl3): δ 163.4 (dd, CFar), 1J(19F,13C) ) 256.3 Hz,
3J(19F,13C) ) 10.2 Hz, 138.3 (t, CSnar), 3J(19F,13C) ) 4.5 Hz,
119.39-118.55 (m, CHar), 106.4 (t, CHar), 2J(19F,13C) ) 24.7
Hz. 19F-{1H} NMR (282 MHz, CDCl3): δ -108.2 (s). EI-MS m/z
(%): 572 (50) [M+].
1
C, 75.93; H, 5.02; N, 2.54. H NMR (300 MHz, CDCl3): δ 7.74
1
(d, 2 CH), J(31P,1H) ) 5.0 Hz, 7.30-7.18 (m, 21 CH), 6.00 (s,
-NH2). 13C NMR (75 MHz, CDCl3): δ 168.8 (s, Ccarbonyl), 141.5
2
1
(t, CHar), J(31P,13C) ) 13.8 Hz, 139.0 (dd, CPar), J(31P,13C) )
19.0 Hz, J(31P,13C) ) 4.0 Hz, 136.1 (d, CPar), J(31P,13C) ) 11.0
Hz, 133.6 (d, CHortho), 2J(31P,13C) ) 20.0 Hz, 133.6 (s, Car), 132.7
(d, CHar), 2J(31P,13C) ) 25.0 Hz, 129.0 (s, CHpara), 128.6 (d, CHmeta),
3J(31P,13C) ) 7.5 Hz. 31P-{1H} NMR (121 MHz, CDCl3): δ -4.7
(s). EI-MS m/z (%): 491 (100), 488 (55) [M+].
3
1
Bis{bis-3,5(diphenylphosphino)benzenetriyl}diphenyl Stan-
nane (L4). To bis(3,5-difluorophenyl)diphenylstannane (2.0 g, 4.0
mmol) was added potassium diphenylphosphide (36 mL, 0.5 M in
THF, 18.0 mmol). The reaction was slightly exothermic and was left
to stir at ambient temperature for 1 h and then brought to reflux
overnight. The workup procedure was analogous to that of (L4) and
yielded a white powder (3.20 g, 69%). Elem anal. calcd (%): C, 74.30;
Bis(3-fluoro-phenyl)diphenyl-stannane (Precursor to L8). The
Grignard reagent 3-fluorobenzene magnesium bromide was prepared
by a method similar to that of tris(3,5-difluoro-phenyl)phosphine
(1). 1-Bromo-3-fluorobenzene (2.0 mL, 18.2 mmol) was added to
magnesium turnings (0.5 g, 21 mmol) in diethyl ether (50 mL) and
1
H, 4.85. Found: C, 74.12; H, 4.97. H NMR (300 MHz, CDCl3): δ
7.49-7.14 (m, 56 Har). 13C NMR (75 MHz, CDCl3): δ 142.7 (d, CHar),
2J(31P, 13C) ) 22.4 Hz, 139.7 (t, CHar), 2J(31P, 13C) ) 15.8 Hz, 138.8
8376 Inorganic Chemistry, Vol. 47, No. 18, 2008

The Cyclic “SilWer-Diphos” Motif [Ag2(µ-diphosphine)2]2+
(t, CPar), 3J(31P, 13C) ) 5.9 Hz, 138.3 (dd, CPar), 1J(31P, 13C) ) 15.2
Hz, 3J(31P,13C) ) 4.2 Hz, 137.5 (s, CPar), 137.3 (s, CHortho), 137.2 (d,
CPar), 1J(31P,13C) ) 9.8 Hz, 134.0 (d, CHortho), 2J(31P,13C) ) 19.7 Hz,
129.43 (s, CHpara), 129.1 (s, CHpara), 129.0 (s, CHmeta), 128.8 (d,
CHmeta), 3J(31P,13C) ) 11.5 Hz. 31P-{1H} NMR (121 MHz, CDCl3):
δ -4.8 (s). FAB-MS m/z(%): 1164 (100) [M+].
C, 53.14; H, 3.46. M.p.: 285 °C (dec.). 31P-{1H} NMR (121 MHz,
1
CDCl3\CH3NO2): δ 14.5 (d,d), J(109Ag,31P) ) 587 Hz. FAB-MS
m/z (%): 154 (100), 1259 (20) [Ag2(L1)2(O3SCF3)]+.
[Ag2(L2)2(SbF6)2]. Needlelike crystals were obtained by slow
diffusion of diethyl ether into a 0.044 M complex solution in CDCl3/
CH3CN over a period of 1 week. Yield: 45%. Elem anal. calcd
(%): C, 45.68; H, 2.84; N, 1.72. Found: C, 45.53; H, 2.91; N, 1.92.
M.p.: >300 °C (dec.). 31P-{1H} NMR (121 MHz, CDCl3/CH3CN):
δ 12.5 and 9.1 (b), 1J(109Ag,31P) ) unresolved. FT-IR (cm-1): 471.2,
493.8, 505.6, 557.6, 597.8, 659.1, 695.1, 747.6, 796.2, 849.8, 926.0,
998.6, 1026.5, 1072.9, 1097.9, 1162.1, 1187.1, 1215.3, 1269.7,
1312.0, 1331.3, 1398.0, 1437.4, 1481.0, 1560.4, 1585.8, 16.17.1,
2210.8, 2267.2, 3056.2. FAB-MS m/z (%): 1392 (100), 1394 (95)
[Ag2(L2)2(SbF6)]+.
Tris{3,5-bis(diphenylphosphino)benzenetriyl}phosphine
(L5). To tris(3,5-difluorophenyl)phosphine (1.5 g, 4.05 mmol) was
added potassium diphenylphosphide (53 mL, 0.5 M in THF, 27.0
mmol). The reaction was slightly exothermic and was left to stir at
ambient temperature for 1 h and then brought to reflux overnight.
The solvent was removed under reduced pressure to yield a thick,
red oil. The excess phosphide was hydrolyzed using methanol (3
× 40 mL), which resulted in a sticky white substance. The product
was then refluxed for 4 h in methanol, and upon cooling, an off-
white solid formed (4.55 g, 82%). Elem anal. calcd (%): C, 79.06;
H, 5.09. Found: C, 78.82; H, 5.14. 1H NMR (300 MHz, CDCl3): δ
7.23-7.06 (m, 69 Har). 13C NMR (75 MHz, CDCl3): δ 139.0-138.4
(m), 138.2 (dt, CPar), 1J(31P,13C) ) 10.9 Hz, 3J(31P,13C) ) 4.8 Hz,
136.6 (d, CPar), 1J(31P,13C) ) 11.5 Hz, 133.4 (d, CHortho) 2J(31P,13C)
[Ag2(L2)2(O3SCF3)2]. 31P-{H} NMR (121 MHz, CDCl3\CH3CN):
1
δ 9.7 (d,d), J(109Ag,31P) ) 587 Hz.
[Ag2(L3)2(O3SCF3)2]. A solution of 3,5-bis(diphenylphosphino)
benzamide (L3; 100 mg, 0.21 mmol) in acetonitrile (5 mL) was
added to a solution of silver triflate (54 mg, 0.21 mmol) in
acetonitrile (2 mL). A white precipitate was obtained by the addition
of diethyl ether to the solution in 90% yield. Elem anal. calcd (%):
C, 51.49; H, 3.38; N, 1.88. Found: C, 50.96; H, 3.30; N, 1.85. M.p.:
>300 °C (dec.). (300 K) 31P-{1H} NMR (121 MHz, CD3CN): δ
broad signals at 12.1 and 8.4, coupling unresolved. (273 K) 31P-
{1H} NMR (202 MHz, CD3CN): δ broad signals at 11.7 and 9.5,
coupling unresolved. (243 K) 31P-{1H} NMR (202 MHz, CD3CN):
3
) 19.8 Hz, 128.5 (s, CHpara), 128.4 (d, CHmeta), J(31P,13C) ) 7.0
Hz. 31P-{1H} NMR (121 MHz, CDCl3): δ -2.3 (s, 1 P), -3.6 (s,
6 P). FAB-MS m/z (%): 1367 (100) [M+].
Tris(3,5-bis(diphenylphosphino)benzenetriyl)phenyl-stanna-
ne (L6). L6 was prepared analogously to L5 from tris(3,5-
difluorophenyl)phenylstannane. A sticky cream-colored product was
obtain, which was further purified by silica gel column chroma-
tography using dichloromethane as the mobile phase. Yield: 71%.
Elem anal. calcd (%): C, 75.25; H, 4.87. Found: C, 73.14; H, 5.08.
1H NMR (300 MHz, CDCl3): δ 7.48-7.03 (m, 74 Har). 13C NMR
(75 MHz, CDCl3): δ 142.9 (d, CHar), 2J(31P, 13C) ) 25.6 Hz, 139.8
(t, CHar), 2J(31P, 13C) ) 12.4 Hz, 138.3 (t, CPar), 3J(31P, 13C) ) 6.7
Hz, 138.4 (dd, CPar), 1J(31P, 13C) ) 15.5 Hz, 3J(31P,13C) ) 3.4 Hz,
137.3 (d, CPar), 1J(31P,13C) ) 11.4 Hz, 137.0 (s, CHortho), 137.0 (s,
CSnar), 133.9 (d, CHortho), 2J(31P,13C) ) 19.5 Hz, 129.4 (s, CHpara),
1
δ 10.1 (d), J(109Ag,31P) ) 496 Hz. FT-IR (cm-1): 469.4, 515.9,
557.8, 573.8, 636.8, 693.0, 743.7, 800.5, 850.5, 895.3, 998.8,
1026.8, 1096.5, 1168.7, 1234.9, 1289.2, 1376.8, 1436.5, 1457.0,
1481.1, 1540.3, 1560.0, 1605.0, 1664.6, 3056.3, 3345.1, 3430.4.
FAB-MS m/z (%): 596 (100) [Ag2(L3)2]2+
[Ag2(L3)2(O3SCF3)]+.
, 1343 (34)
Complexation with Tetraphosphine L4. In a typical prepara-
tion, a solution of tetraphos (L4) (100 mg, 0.086 mmol) in
chloroform (4 mL) was added to a solution of silver(I) salt (0.172
mmol) AgX (X ) NO3, O3SCF3, ClO4, SbF6, BF4, or PF6) in
nitromethane (1 mL). 31P NMR spectra were run in a mixture of
CDCl3\CH3NO2 (4:1). NMR data for complexes with various anions
are available in the Supporting Information.
3
129.2 (s, CHmeta), 129.1 (s, CHpara), 128.9 (d, CHmeta), J(31P,13C)
) 7.0 Hz. 31P-{1H} NMR (121 MHz, CDCl3): δ -5.2 (s) and -39.8
(HPPh2). FAB-MS m/z (%): 1531 (100) [M+].
Tetrakis{bis(3,5-diphenylphosphino)benzenetriyl} Stannane
(L7). L7 was prepared analogously to L5 from tetrakis(3,5-
difluorophenyl)stannane. An analytically pure sample was obtained
by recrystallization from acetone. Yield: 84%. Elem anal. calcd
(%): C, 75.84; H, 4.88. Found: C, 75.89; H, 5.02. M.p.: 142-143
°C (acetone). 1H NMR (300 MHz, CDCl3): δ ) 7.59-7.05 (m, 92
[Ag4(L4)2(SbF6)4]. Needlelike crystals suitable for X-ray dif-
fraction were obtained by the slow diffusion of diethyl ether into
a solution of [Ag4(L4)2(SbF6)4] in CHCl3/CH3NO2 (4:1; 0.0172 M)
over a period of 1 week. Yield: 53%. Elem anal. calcd (%): C,
46.72; H, 3.05. Found: C, 46.44; H, 2.80. 31P-{1H} NMR (121
1
MHz): δ 14.9 (d,d), J(109Ag,31P) ) 595 Hz. FAB-MS m/z (%):
2
Har). 13C NMR (75 MHz, CDCl3): δ 142.1 (d, CHar), J(31P, 13C)
1615 (100) [Ag4(L4)2(SbF6)2]2+
.
) 28.6 Hz, 140.0 (t, CHar), 2J(31P, 13C) ) 10.3 Hz, 138.4 (dd, CPar),
1J(31P, 13C) ) 15.9 Hz, 3J(31P,13C) ) 2.8 Hz, 137.9 (t, CPar), 3J(31P,
Complexation with Octaphosphine L7. In a typical preparation,
a solution of L7 (152 mg, 0.08 mmol) in chloroform (4 mL) was
added to a solution of silver(I) salt (0.32 mmol) AgX (X ) NO3,
O3SCF3, ClO4, SbF6, BF4, or PF6) in acetonitrile (1 mL).31P NMR
spectra were run in a mixture of CDCl3\CH3CN (4:1). NMR data
for complexes with various anions are available in the Supporting
Information.
1
13C) ) 7.5 Hz, 137.4 (d, CPar), J(31P,13C) ) 11.6 Hz, 133.9 (d,
CHortho), 2J(31P,13C) ) 19.4 Hz, 129.0 (s, CHpara), 128.9 (d, CHmeta),
3J(31P,13C) ) 6.9 Hz. 31P-{1H} NMR (121 MHz, CDCl3): δ -5.2
(s). FAB-MS m/z (%): 1900 (100) [M+].
Complexation with Silver. Complexes with Diphosphines
L1, L2, and L3. In a typical preparation, a solution of ligand (L1,
L2, or L3; 100 mg, 0.224 mmol) in chloroform (4 mL) was added
to a solution of silver(I) salt AgX (X ) NO3, O3SCF3, ClO4, SbF6,
BF4, or PF6; 0.224 mmol) in acetonitrile (1 mL) or nitromethane
(1 mL). NMR data for complexes with various anions are available
in the Supporting Information.
[Ag2(L1)2(O3SCF3)2]. Needlelike crystals were obtained by slow
diffusion of diethyl ether into a 0.044 M complex solution in CDCl3/
CH3NO2 over a period of 1 week. Yield: 53%. Elem anal. calcd
(%): [Ag2(L1)2(O3SCF3)2]·0.25(CHCl3): C, 52.93; H, 3.44. Found:
[Ag4(L7)(O3SCF3)4]. Crystals suitable for X-ray diffraction
studies were obtained by the slow diffusion of diethyl ether into a
solution of [Ag4(L7)(O3SCF3)4] in CHCl3/CH3CN (4:1; 0.016 M)
over a period of 1 week. Yield: 85%. Elem anal. calcd (%): C,
50.86; H, 3.17. Found: C, 47.41; H, 3.08. M.p.: 280 °C (dec.). 31P-
{1H} NMR (121 MHz): δ 12.9 (d,d), 1J(109Ag,31P) ) 542 Hz. FAB-
MS m/z (%): 2780 (100) [Ag4(L7)(O3SCF3)3]+, 1316 (10)
[Ag4(L7)(O3SCF3)2]2+
.
X-Ray Crystallographic Section. Crystal data for each structure
are given in Table 1. A crystal was mounted onto the diffractometer
Inorganic Chemistry, Vol. 47, No. 18, 2008 8377

Miller et al.
Table 2. Comparison of Key Bond Lengths and Angles in Crystal
Structures of [Ag2(L1)2(OTf)2] and [Ag2(L2)2(SbF6)2]
[Ag2(L2)2(SbF6)2]
[Ag2(L1)2(OTf)2]
1
2
3
Ag· · ·Ag (Å)
Ag-P (Å)
4.99(3)
2.4225(15)
2.4027(15)
5.88(15) 6.12(15) 5.57(15)
2.433(7) 2.422(7) 2.439(7)
2.448(7) 2.445(7) 2.446(7)
2.399(7)
2.408(7)
Ag-O (Å)
Ag-N
2.586(4)
2.32(3)
2.52(3)
2.38(4)
2.53(6)
P-Ag-P (deg)
Ag-N-C (deg)
155.80 (5)
141.7(2) 156.4(3) 165.3(3)
145.3(3)
178(3)
132(3)
160(4)
158(6)
at room temperature for 3,5-bis(diphenylphosphino)benzamide, L3,
and tetrakis{3,5-bis(diphenylphosphino}benzenetriyl)stannane, L7,
and at low temperature under nitrogen at 153 K for [Ag2(L1)2-
(O3SCF3)2] and 213 K for [Ag2(L2)2(SbF6)2]. The structures were
solved using direct methods and refined with the SHELXTL version
5 software, and the non-hydrogen atoms were refined with
anisotropic thermal parameters, except for disordered atoms, which
are isotropic. Hydrogen-atom positions were added at idealized
positions with a riding model and fixed thermal parameters (Uij )
1.2Ueq for the atom to which they are bonded). The function
minimized was ∑[w(|Fo|2 - |Fc|2)] with reflection weights w-1
)
[σ2|Fo|2 + (g1P)2 + (g2P)] where P ) [max|Fo|2 + 2|Fc|2]/3.
Additional material available from the Cambridge Crystallographic
Data Centre comprises relevant tables of atomic coordinates, bond
lengths and angles, and thermal parameters.
For tetrakis{3,5-bis(diphenylphosphino}benzetriyl)stannane, L7,
the atomic displacement parameters of the ring C97a-C102 shows
evidence of probable disorder; however, this could not be modeled.
In [Ag2(L2)2(SbF6)2], the anions are severely disordered, and it was
not possible to model all of the orientations separately. We have
attempted to account for this by modeling two main positions and
distributing the electron density uniformly over the fluorine atoms
for both orientations of all of the anions. The atomic displacement
parameters of some atoms in some phenyl rings and the solvent
moieties show evidence of possible disorder; however, this could
not be modeled.
For [Ag4(L4)2][SbF6] · 2CHCl3 · 4CH3NO2 and [Ag4(L7)(O3-
SCF3)4], single crystals were coated in perfluoropolyether oil and
mounted on glass fibers. X-ray measurements were made using a
Bruker Proteum CCD area-detector diffractometer with Cu KR
radiation (λ ) 1.5418 Å).16 Intensities were integrated17 from
several series of exposures, each exposure covering 0.3° in ω, and
the total data set being almost a sphere. Absorption corrections were
applied, on the basis of multiple and symmetry-equivalent measure-
ments.18 The structures were solved by direct methods and refined
by least-squares on weighted F2 values for all reflections.19 All
non-hydrogen atoms were assigned anisotropic displacement pa-
rameters and refined without positional constraints. The positions
of the methyl hydrogen atoms were assigned by a rotating group
refinement with fixed, idealized C-H distances. All other hydrogen
atoms were constrained to ideal geometries. All hydrogen atoms
(16) SMART diffractometer control software, version 5.625; Bruker AXS
Inc.: Madison, WI, 1997-2002.
(17) SAINT integration software, version 7.06A; Bruker AXS Inc.: Mad-
ison,WI, 1997-2003.
(18) Sheldrick G. M. SADABS, version 2.05; University of Go¨ttingen:
Go¨ttingen, Germany, 2003.
(19) SHELXTL program system, version 6.14; Bruker-AXS Inc.: Madison,
WI, 2000-2003.
8378 Inorganic Chemistry, Vol. 47, No. 18, 2008

The Cyclic “SilWer-Diphos” Motif [Ag2(µ-diphosphine)2]2+
were assigned isotropic displacement parameters equal to 1.5 times
(methyl hydrogen atoms) or 1.2 times (all other hydrogen atoms)
that of their parent atom.
An area of residual electron density was found in the final
electron density difference map of [Ag4(L7)(O3SCF3)4]. All attempts
to model the two disordered molecules of chloroform thought to
be present in this space using discrete atoms failed. This area of
the structure has been modeled by applying a diffuse solvent model
correction to the X-ray intensity data using the Squeeze program
of the Platon software suite.20
The tetracation in [Ag4(L4)2][SbF6]·2CHCl3 ·4CH3NO2 sits on
a crystallographic inversion center. Stoichiometry thus demands
that the asymmetric unit contain two counterions. One of these
shows disorder in the position of four of its fluorine atoms, and
distance restraints between the fluorine atoms of the second
component of this disorder have been used in order to produce
sensible geometry. The second anion is disordered over two sites.
One of these sites is close to the inversion center at the center of
the cation cage, thus dictating the disorder over the nonsymmetry
related sites to be exactly 50:50. The asymmetric unit also contains
one molecule of chloroform that is disordered over two sites in an
80:20 ratio. This situation is again complicated by these sites being
close to an inversion center. Two molecules of nitromethane
complete the contents of the asymmetric unit.
Refinement proceeded smoothly to give the residuals shown in
Table 2. Complex neutral-atom scattering factors were used.21
Supporting Information Available: Additional figures and a
CIF crystallographic file. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC800664F
(20) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
(21) International Tables for Crystallography; Kluwer, Dordrecht, The
Netherlands, 1992; Vol. C.
Inorganic Chemistry, Vol. 47, No. 18, 2008 8379