Solid-state 31P NMR characterisation of phosphinine-stabilised gold nanoparticles and a phosphinine-gold complex

Article abstract of DOI:10.1039/c000695e

Solid-State ³¹P NMR studies reveal that phosphinine ligands employed for the stabilisation of gold nanoparticles react in part during the synthesis, and that the particles are stabilised by a mixture of intact phosphinine units together with several other surface-bound species. The spectral data of these species are characteristic for phosphine-type donors although unambiguous structure assignment was as yet unfeasible. The spectral data of surface-bound phosphinines were verified by comparison with the spectrum of an authentic complex [(1)AuCl]. The metal-bound phosphinines in both the complex and the nanoparticles prefer η¹(P)-coordination to a single metal atom, and the observation of splittings arising from coupling with ¹⁹⁷Au (I = 3/2) nuclei indicates that these ligands are not mobile. The fraction of intact phosphinines on the nanoparticles drops with decreasing steric protection although the observed product distribution shows no simple relation with substituent patterns.

Full text of DOI:10.1039/c000695e

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Solid-state 31P NMR characterisation of phosphinine-stabilised gold
nanoparticles and a phosphinine-gold complex
Samith Komath Mallissery and Dietrich Gudat*
Received 12th January 2010, Accepted 3rd March 2010
First published as an Advance Article on the web 24th March 2010
DOI: 10.1039/c000695e
Solid-State 31P NMR studies reveal that phosphinine ligands employed for the stabilisation of gold
nanoparticles react in part during the synthesis, and that the particles are stabilised by a mixture of
intact phosphinine units together with several other surface-bound species. The spectral data of these
species are characteristic for phosphine-type donors although unambiguous structure assignment was
as yet unfeasible. The spectral data of surface-bound phosphinines were verified by comparison with
the spectrum of an authentic complex [(1)AuCl]. The metal-bound phosphinines in both the complex
1
and the nanoparticles prefer h (P)-coordination to a single metal atom, and the observation of
splittings arising from coupling with 197Au (I = 3/2) nuclei indicates that these ligands are not mobile.
The fraction of intact phosphinines on the nanoparticles drops with decreasing steric protection
although the observed product distribution shows no simple relation with substituent patterns.
modes in metal complexes of aromatic phosphorus heterocycles
Introduction
and is also receptive to dynamic effects, we set out to perform a
31P NMR study of phosphinine stabilised gold nanoparticles to
characterise the ligand binding in these particles, and report on
the results of these investigations here.
Colloidal nanoparticles consisting of noble metals have great po-
tential for applications like electronics,1 catalysis,2,3 or non-linear
optics.4 A common synthesis of such particles involves reduction
of a suitable metal salt in the presence of a stabilising ligand.
Whereas normally thiols, amines, or tertiary phosphines are used
for this purpose,5 some time ago the first gold nanoparticles
stabilised by phosphinines (phosphabenzenes) A were prepared.6,7
These species deviate from classical phosphines by exhibiting a
formally sp2-hybridised phosphorus atom as part of an aromatic
p-electron system,8 and were regarded as interesting ligands for
metal particles since their nature as strong p-acceptor ligands
was considered to deprive the metal core of some of its electron
density.6
Phosphinines have been extensively employed as ligands in
transition metal complexes and are known to support a variety
of coordination modes. Binding in mononuclear complexes may
Scheme 1 Molecular structure (A) and metal coordination modes (B–F)
of phosphinines.
1
occur through the phosphorus lone-pair (h -coordination, B)
6
or the p-system (h -coordination, C).8,9 In addition, a single
phosphinine can also act as a bridging ligand to two or even
three metal centres as in D–F and behaves then as a mixed s,p-
donor with variable electron donating abilities.8 Since any of these
binding modes is in principle also feasible for phosphinines on a
gold nanoparticle, it is clear that an account of the interaction
between ligands and surface—and thus of the net electron density
on the metal cluster—is quite intricate, and that further structural
insight into the ligand binding mode is highly desirable in order
to deepen the understanding of the electronic structure of these
materials. In addition, knowing that phosphine ligands on gold
nanoparticles may be fluxional and move between different metal
atoms,10 the dynamics of surface bound ligands also requires
attention. As 31P NMR spectroscopy is a sensitive probe of binding
Results and discussion
For our studies we prepared gold nanoparticles 1-NP-0.2, 1-NP-
0.5, 2-NP-0.5, and 3-NP-0.5 via the published procedure6 by
sodium naphthalenide reduction of [(thp)AuCl] (thp = tetrahy-
drothiophene) in the presence of 0.2 or 0.5 equivalents of
phosphinines 1 (structure A with R1 = R2 = Ph, R3 = H), 2
(structure A with R1 = R3 = H, R2 = Ph), or 3 (structure A with
R1 = R3 = Ph, R2 = H), respectively. The different substitution
pattern was expected to have some influence on the behaviour of
the ligands during particle synthesis. Thus, the 2,6-unsubstituted
phosphinine 2 (A; R1 = R3 = H, R2 = Ph) is reported to provide
superior stabilisation of nanoparticles as the absence of bulky a-
substituents facilitates binding of the ligand to the particle,6 and
we reckoned that the increased steric bulk should render ligands
1 and 3 more robust against decomposition during the reduction
process.
Institut fu¨r Anorganische Chemie, Universita¨t Stuttgart, Pfaffenwaldring 55,
70550, Stuttgart, Germany. E-mail: gudat@iac.uni-stuttgart.de; Fax: (+49)
711 685 64241
4280 | Dalton Trans., 2010, 39, 4280–4284
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Table 1 31P NMR data of phosphinines 1 and 3, phosphinine-stabilised
Au-nanoparticles, and complex [(1)AuCl] (Letters in parentheses behind
isotropic chemical shifts denote tentative assignment to one of the
coordination modes depicted in Schemes 1, 2)
Entry
#1
1-NP-0.5 a
1-NP-0.2a
2-NP-0.5b
3-NP-0.5c
diso
176.5 (B)
-218
0.00
72%
64.4 (G)
17%
38.2
8%
18.2
3%
178.4 (B)
-220
0.00
51%
64.7 (G)
20%
34.7
6%
18.9
20%
165.7 (B)
d
Dd
e
h
Int.f
diso
4%
67.2 (G)
7%
38.5
38%
#2
#3
#4
75.0 (G)
7%
Int.f
diso
38.9
19%
24.7
27%
46.1
8%
Int.f
diso
Int.f
diso
123.7 (E)
18%
88.2
Int.f
diso
8.9
39%
Int.f
33%
a Ligand structure A with R1 = R2 = Ph, R3 = H; b Ligand structure A
with R1 = R3 = H, R2 = Ph; c Ligand structure A with R1 = R3 = Ph,
R2 = H; d Dd = d33 - (d11 + d22)/2; e h = (d22 - d11)/(d33 - diso); f Relative
intensities of deconvoluted spinning sideband manifolds
Fig. 1 161.9 MHz 31P CP-MAS NMR spectra of a) 1-NP-0.5 (nrot 6.5 kHz,
256 transients), b) 1-NP-0.2 (nrot 10.0 kHz, 256 transients) c) 2-NP-0.5
(nrot 12.0 kHz, 4096 transients) d) 3-NP-0.5 (nrot 14.5 kHz, 2048 transients)
c) [(1)AuCl] (nrot6.0 kHz, 256 transients). The upper traces in each pair
show experimental spectra and the lower traces the deconvolution results
obtained with the data given in Table 1; isotropic lines are marked with
asterisks.
Table 2 31P NMR data of phosphinines 1 and 3, and complex [(1)AuCl]
1a
3b
[(1)AuCl]a
diso
211
-473
0.09
189.7
-478
0.48
180.4
-223
0.02
c
Dd
d
h
a Ligand structure A with R1 = R2 = Ph, R3 = H; b Ligand structure A with
R1 = R3 = Ph, R2 = H; c Dd = d33 (d11 + d22)/2; d h = (d22 - d11)/(-d33
-
Analytical characterisation of the purple solid materials ob-
tained after removal of all volatiles and washing of the residue
with hexane revealed that the carbon content is close to the
one expected for samples with phosphinine : Au ratios of 1 : 2
and 1 : 5 (e.g., 1-NP-0.2 found 24.2, calcd 25.1%; 1-NP-0.5 found
46.8, calcd 43.9%), in agreement with previous findings based on
thermoanalytical studies.6
d
iso).
the complex (see Fig. 2) features a single spinning sideband series
whose lines show a fine structure that is attributable to scalar and
residual dipolar interactions between 31P and 197Au nuclei (I =
3/2, nat. abundance 100%) and will be discussed further below.
Similar splittings had previously been observed for gold complexes
of tertiary phosphines.11 Deconvolution of each sideband into two
mixed Gaussian/Lorentzian lines and analysis of the intensity
distribution in each subset allowed us to determine two effective
shielding tensors with closely similar principal values which were
combined to an average tensor (Table 2). We are aware that this
method neglects effects arising from dipolar and quadrupolar
interactions and should introduce systematic errors; however, we
think that the approach is tolerable as these errors are small
compared with the total tensor anisotropy.
The pure solid samples were transferred in a glove box into
standard 4 mm zirconia rotors, and 31P NMR spectra were
recorded using magic angle spinning (MAS) for resolution and
cross polarisation (CP) for sensitivity enhancement. Measurement
of spectra at different spin rates allowed clear identification of
isotropic lines and deconvolution of each spectrum into between
four or five spinning sideband manifolds (Fig. 1). The experiments
gave no evidence for unusually short relaxation times or chemical
shifts outside the normal range which are characteristic for
paramagnetic species, and led us to conclude that all samples
studied are not significantly paramagnetic. All isotropic chemical
shifts and the anisotropy and asymmetry of the magnetic shielding
tensor of the signal denoted as #1 are listed in Table 1; tensor data
for the remaining species were computed in the deconvolution but
are not discussed further as the number of observed sidebands
was too small to give reliable results. Even without a quantitative
evaluation being possible, the spectra allow us to estimate that the
tensor anisotropies of these species are generally small and do not
exceed a range of some 50–100 ppm which is typical for many
tertiary phosphine derivatives.
Fig. 2 161.9 MHz 31P CP-MAS NMR spectrum of [(1)AuCl] (nrot 6.0 kHz,
256 transients). The isotropic line is marked with an asterisk.
As references, we recorded also the 31P CP-MAS spectra of the
free ligands 1, 3 and the model complex [(1)AuCl] which was easily
prepared from 1 and [(thp)AuCl] (see Table 2). The spectrum of
The isotropic chemical shift in solid [(1)AuCl] (diso = 180.3)
matches the solution value of 177.3 ppm. The moderate negative
coordination shift (Dd = -31) is a typical feature of complexes
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 4280–4284 | 4281
©

View Article Online
1
containing h (P)-bound phosphaarenes.12 The metal coordination
decreasing ligand-to-metal ratio decimated at the expense of the
species with the lowest isotropic chemical shift (#4) whereas
the amounts of other products remain essentially unchanged. The
change in product distribution indicates that the phosphaarene
exhibits a stronger tendency to undergo side reactions (e.g.
reduction or nucleophilic attack at phosphorus to form species
such as G or H, respectively) when the relative excess of the other
reactants increases.
further results in a pronounced reduction of the tensor anisotropy.
The deconvolution results of the spectra of nanoparticles 1-NP-
0.2 and 1-NP-0.5 derived from phosphinine 1 reveals that both
samples contain the same surface-bound species. The apparent
deviations between both spectra owe to differences in the relative
abundance of individual components and an increased linewidth
in the spectrum of 1-NP-0.2 which is presumably caused by a
larger inhomogeneity of the chemical environment; this is in
accord with previous findings6 that the nanoparticles become
more polydisperse and polymorphic with a decreasing number
of stabilising phosphinine ligands.
The 2-NP-0.5 spectrum contains three signals (#1–#3, Table 1)
with chemical shifts that match those of appropriate components
in 1-NP-0.5, thus suggesting the presence of species with sim-
ilar structures in both samples. In addition, 2-NP-0.5 contains
two further components whose chemical shifts are intermediate
between those of a coordinated phosphinine (species #1) and the
other, “phosphine-type” species. The chemical shift of one of these
specimens (d = 123.7) is clearly outside the range for phosphine-
type derivatives but is compatible with observed shifts in com-
plexes with m2-bridging phosphinine17 or zwitterionic phosphonio-
benzophospholide ligands,18 and is therefore tentatively assigned
to a phosphinine unit which binds in a m2-bridging mode to
two surface atoms (E, Scheme 1). A coexistence of terminal
and m2-coordinated phosphinines is in accord with the lower
steric hindrance around the phosphorus atom in 2. Evaluation
of signal intensities reveals, however, that the better accessibility is
apparently paid for by a higher reactivity of the p-electron system
of the ligand, so that the relative abundance of intact phosphinines
is on the whole lower than in nanoparticles derived from the
sterically more protected ligand 1.
The isotropic and anisotropic shielding data of the species
denoted as #1 match those of the model complex [(1)AuCl], and
31
the isotropic chemical shift compares further to d P values found
in the solution spectra of gold(I) complexes13 and solid-state NMR
spectra of copper(I) complexes of h (P)-bound phosphinines.14
1
1
These findings led us to assign this species to an intact h (P)-
coordinated phosphinine which binds via its lone-pair to a single
gold atom on the nanoparticle surface (B, Scheme 1). This
assignment is also supported by the finding that the individual
spinning sidebands display a similar fine structure due to 31P,197Au
coupling as has been observed for [(1)AuCl] (cf. Fig. 1, 2; the failure
to resolve a similar fine structure in the spectrum of 1-NP-0.2 is
due to the substantially increased linewidth).
Less stringent structural assignments are feasible for the re-
maining species #2–#4. As phosphinines react in specific cases
with noble metal halides to yield oxidative addition products
G (Scheme 2) rather than simple complexes,15 and with sodium
naphthalenide to give diphosphine dianions H,16 it is conceivable
that similar products are also formed on the surface of the
nanoparticles. Based on a comparison with known chemical shifts
for the metal-bound phosphorus atom in type G compounds (e.g.
The lines of all the species detected in the spectrum of 2-
NP-0.5 are of similar or even larger width than the signals in
the spectrum of 1-NP-0.2, suggesting that the extensive chemical
transformations induce likewise a marked inhomogeneity of the
chemical environment.
d P 65.5 for M = Pt, X = Cl15) we identify surface-species #2
The chemical shifts of the five components detected in the
31P spectrum of 3-NP-0.5 exclude the presence of any intact
phosphinine units. On the other hand, three of these species
(#2–#4) have again comparable chemical shifts as components
observed in the other nanoparticle samples, thus suggesting that
again reaction products with similar structures have been formed.
The chemical shifts of the other two components (d = 46.1,
8.9) are again too unspecific for a detailed structural assignment.
Considering that the sterical protection of the phosphorus atom in
ligand 3 should be similar to that in 1, the different distribution of
surface products in 1-NP-0.5 and 3-NP-0.5 suggests strongly that
the behaviour of the phosphinine ligands during the nanoparticle
synthesis is no simple function of the substituent pattern, and
that the protection of the whole aromatic ring (and not just the
phosphorus coordination site) is important.
31
(diso = 65) as the most likely candidate for this structural type.
Further support for this assignment comes from the finding that
EDX analysis of the nanoparticles gave evidence for the presence
of an appreciable amount of chlorine on the surface.
Scheme 2
Identification of the remaining species is less straightforward
although the observed chemical shifts and large linewidths seem
compatible with the presence of gold complexes of phosphine-type
donors such as a P-bound diphosphine H (arguing that the free
ligands resonate at higher field and complex formation is usually
accompanied by deshielding). It must be admitted, however, that
the chemical shifts of these signals are diagnostically not very
significant and we cannot rule out that products arising from other
side reactions of phosphinine 1 are actually present.
Coordination of a P-donor ligand to a gold atom as observed in
[(1)AuCl] and the surface species 1-NP-0.5#1 introduces coupling
with the quadrupolar 197Au nucleus that may induce broadening
or even splitting of the lines in solid-state 31P NMR spectra.11
Theoretically, the lineshape in a MAS spectrum of a spin -1/2
nucleus I coupled to a quadrupolar nucleus S can be described
as a complicated function of the scalar (JIS) and dipolar (DIS)
couplings, the nuclear quadrupole coupling constant cs, resonance
frequency ns and asymmetry of the electric field gradient (efg)
tensor h of S, and the relative orientation of efg and coupling
tensors.19 Simple splittings whose size is independent of the
Analysis of the relative intensities of individual sideband
manifolds reveals that the intact phosphinine (species #1) is with
4282 | Dalton Trans., 2010, 39, 4280–4284
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
magnetic field are expected if J ꢀ D and c is small, or if the
ratio c/ns becomes large; the spectrum appears in the first case
as a symmetrical quartet (for S = 3/2) and in the second case as
a doublet,19 and both patterns were in fact observed for gold(I)
complexes of tertiary phosphines.11 The obvious deviation of the
lineshapes in the spectra of [(1)AuCl] and AuNP-0.5 from the
simple patterns suggests that c lies in an intermediate range, which
is also in accord with the observed magnetic field dependence of the
line profile (Fig. 3).19 Attempts to simulate20 the coupling pattern
allowed us to produce lineshapes that were qualitatively similar to
the experimental ones and supported the assignment of the fine
structure arising from coupling in a 31P, 197Au spin pair; however,
finding that quite similar simulation results could be produced
with several different sets of parameters, we conclude that further
interpretation of observed lineshapes is not meaningful.
Experimental
General remarks
All manipulations were carried out under a dry argon atmosphere
and solvents were dried by standard procedures. Phosphinines 1–
3 and phosphinine stabilised gold nanoparticles 1-NP-0.5, 1-NP-
0.2, 2-NP-0.5 were prepared as reported earlier.6,21 Nanoparticles
3-NP-0.5 were prepared according to the same route. EI-MS:
Varian MAT 711, 70eV. Elemental analysis: Perkin-Elmer 24000
CHN/O Analyser. Melting points were determined in sealed
capillaries. EDX-analysis of 1-NP-0.5 was performed with a
CAMECA SX100 electron beam microprobe.
NMR experiments
Solution NMR spectra were recorded on a Bruker Avance 250
spectrometer (1H: 250.1 MHz, 13C: 62.8 MHz, 31P: 101.2 MHz)
at 303 K. Solid-state CP-MAS NMR spectra were recorded on a
Bruker Avance 400 spectrometer (31P: 161.9 MHz) equipped with a
4 mm MAS probe. Solid samples were prepared in standard ZrO2
rotors. MAS experiments were carried out using spinning speeds
between 6 and 15 kHz. Cross polarisation was applied using a
ramp-shaped contact pulse and mixing time between 3 and 5 ms.
Chemical shifts are referenced to ext. TMS (1H, 13C) or 85% H3PO4
(N = 40.480747 MHz, 31P). Anisotropic shielding parameters listed
in Table 1 were determined by evaluation of sideband intensities
using routines provided by the spectrometer software. The splitting
of individual sidebands in the spectra of [(1)AuCl] and 1-NP-0.5
was handled by deconvoluting each sideband into two ([(1)AuCl])
or four (1-NP-0.5) lines with mixed Gaussian/Lorentzian shapes
and analysing the intensity distribution in each subset separately.
This approach yielded effective shielding tensors with closely
similar principal values which were combined to an average tensor
whose data are listed in Table 1.
Fig. 3 Expansions of the isotropic line in the spectrum of 1-NP-0.5 at
resonance frequencies of 161.9 MHz (upper trace) and 121.5 MHz (lower
trace).
[(1)AuCl]: Phosphinine
1 (150 mg, 0.36 mmol) and
[AuCl(SC4H8)] (110 mg, 0.36 mmol) were weighed inside a glove
box. Freshly distilled CH2Cl2 (5 ml) was then added and the
mixture allowed to stir at RT for about 15 min. Completion of
the reaction was checked by 31P NMR spectroscopy. The solution
was then concentrated under reduced pressure. Addition of hexane
gave a pale yellow precipitate which was collected by filtration.
Conclusions
We have demonstrated the application of solid-state NMR to
characterise gold nanoparticles produced by reduction of soluble
gold salts in the presence of phosphinines. The spectra allowed
us to detect, in addition to metal-bound intact phosphinine units,
several surface-bound species that are obviously formed by chemi-
cal transformation of the originally supplied ligands. The observed
spectral data of these species are characteristic for phosphine-type
donors but no complete and unambiguous structure assignment is
◦
1
Yield: 210 mg (95%); m.p. 177 C. 31P{ H} NMR (CD2Cl2): d =
1
177.30. H NMR (CD2Cl2): d = 7.20–7.31(m, 2 ¥ C6H5, 10 H),
4
7.34 (br s, 2 ¥ C6H5, 10 H), 7.72 (d, JHP = 7.11 Hz, 1 H, H-4).
1
13C{ H} NMR (CD2Cl2): d = 128.31 (2 C), 128.57 (4 C), 128.77
(d, 4JCP = 1.4 Hz, 4 C), 128.83 (2 C), 129.88 (d, 4JCP = 1.3 Hz, 4
C), 130.89 (d, 3JCP = 11.5 Hz, 4 C), 135.79 (d, 3JCP = 26.3 Hz, 1
C, C-4), 136.99 (d, 2JCP = 12.2 Hz, 2 C), 140.38 (d, 3JCP = 8.9 Hz,
1
as yet feasible. The intact phosphinines prefer h (P)-coordination
to a single metal atom, and the observation of explicit splittings
arising from coupling interaction with quadrupolar 197Au nuclei
indicates that these ligands are not mobile. The fraction of
intact phosphinines decreases when the steric protection of the
ligands becomes less efficient although the observed product
distribution shows no simple relation with substituent patterns.
The findings reported here suggest that the previously noted6
superior stabilisation of nanoparticles by phosphinines having no
bulky a-substituents is due not only to a tighter binding of these
ligands to the particle but to the fact that these species give higher
yields of more strongly donating phosphine-type products which
may also play a role.
2
1
2 C), 150.39 (d, JCP = 8.2 Hz, 2 C, C-3/5), 156.27 (d, JCP
=
34.2 Hz, 2 C, C-26). MS (EI = 70eV): m/z (%) = 632.1 (100) [M+],
400.2 (75) [M+-AuCl]. C29H21PClAu (632.88): calcd. C 55.04, H
3.34; found. C 54.52, H 3.46.
Acknowledgements
Financial support by the Deutsche Forschungsgemeinschaft
(Graduate College 448 “Modern NMR Methods in Material
Science; scholarship for S.K.M.) is gratefully acknowledged. We
thank Prof. Dr K. Mu¨ller (Institut fu¨r Physikalische Chemie,
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 4280–4284 | 4283
©

View Article Online
University of Stuttgart) for recording the 121.5 MHz 31P NMR
spectrum of 1-NP-0.5, Dr J. Opitz, J. Trinkner and K. Wohlbold
(Institut fu¨r Organische Chemie, University of Stuttgart) for
measuring the mass spectrum of [(1)AuCl], and Dr C. Lipp
(Institut fu¨r Anorganische Chemie) for performing the EDX-
analysis of 1-NP-0.5.
Soc., Dalton Trans., 1999, 881; E. N. de Silva, G. A. Bowmaker and
P. C. Healy, J. Mol. Struct., 2000, 516, 263; P. C. Healy, B. T. Loughrey,
G. A. Bowmaker and J. V. Hanna, Dalton Trans., 2008, 3723.
12 D. Gudat, M. Nieger, K. Schmitz and L. Szarvas, Chem. Commun.,
2002, 1820.
13 N. Me´zailles, L. Ricard, F. Mathey and P. Le Floch, Eur. J. Inorg.
Chem., 1999, 2233.
14 M. Shiotsuka, T. Tanamachi, T. Urakawa, M. Munakata and Y.
Matsuda, J. Supramol. Chem., 2002, 2, 211.
15 M. Doux, C. Bouet, N. Me´zailles, L. Ricard and P. Le Floch,
Organometallics, 2002, 21, 2785; M. Doux, C. Bouet, N. Me´zailles,
L. Ricard and P. Le Floch, Eur. J. Inorg. Chem., 2003, 3878.
16 L. Cataldo, S. Choua, T. Berclaz, M. Geoffroy, N. Me´zailles, L. Ricard,
F. Mathey and P. Le Floch, J. Am. Chem. Soc., 2001, 123, 6654.
17 B. Schmid, L. M. Venanzi, T. Gerfin, V. Gramlich and F. Mathey, Inorg.
Chem., 1992, 31, 5117; P. Le Floch, N. Maigrot, L. Ricard, C. Charrier
and F. Mathey, Inorg. Chem., 1995, 34, 5070; M. T. Reetz, E. Bohres,
R. Goddard, M. C. Holthausen and W. Thiel, Chem.–Eur. J., 1999, 5,
2101.
18 D. Gudat, M. Schrott, V. Bajorat, M. Nieger, S. Kotila, R. Fleischer
and D. Stalke, Chem. Ber., 1996, 129, 337; D. Gudat, M. Schrott and M.
Nieger, J. Chem. Soc., Chem. Commun., 1995, 1541; D. Gudat, A. W.
Holderberg, N. Korber, M. Nieger and M. Schrott, Z. Naturforsch.,
1999, 54b, 1244.
Notes and references
1 R. Shenhar and V. M. Rotello, Acc. Chem. Res., 2003, 36, 549.
2 A. Roucoux, J. Schulz and H. Patin, Chem. Rev., 2002, 102, 3757.
3 S. Jansat, M. Gomez, K. Philippot, G. Muller, E. Guiu, C. Claver, S.
Castillon and B. Chaudret, J. Am. Chem. Soc., 2004, 126, 1592.
4 H. Inouye, K. Tanaka, I. Tanahashi and K. Hirao, Phys. Rev. B:
Condens. Matter Mater. Phys., 1998, 57, 11334.
5 M. C. Daniel and D. Astruc, Chem. Rev., 2004, 104, 293.
6 A. Moores, F. Goettmann, C. Sanchez and P. Le Floch, Chem.
Commun., 2004, 2842.
7 C. Vilain, F. Goettmann, A. Moores, P. Le Floch and C. Sanchez,
J. Mater. Chem., 2007, 17, 3509.
8 P. Le Floch, Coord. Chem. Rev., 2006, 250, 627.
9 P. Le Floch and F. Mathey, Coord. Chem. Rev., 1998, 178–180, 771.
10 F. A. Vollenbroek, P. C. Bouten, J. M. Trooster, J. P. Van Der Berg and
J. J. Bour, Inorg. Chem., 1980, 19, 2685.
11 S. J. Berners-Price, L. A. Colquhoun, P. C. Healy, K. A. Byriel and J. V.
Hanna, J. Chem. Soc., Dalton Trans., 1992, 3357; L. Baker, R. C. Bott,
G. A. Bowmaker, P. C. Healy, B. W. Skelton, P. Schwerdtfeger and A. H.
White, J. Chem. Soc., Dalton Trans., 1995, 1341; K. Angermair, G. A.
Bowmaker, E. N. de Silva, P. C. Healy, B. E. Jones and H. Schmidbaur,
J. Chem. Soc., Dalton Trans., 1996, 3121; G. A. Bowmaker, C. L. Brown,
R. D. Hart, P. C. Healy, C. E. F. Rickard and A. H. White, J. Chem.
19 E. M. Menger and W. S. Veeman, J. Magn. Reson., 1982, 46, 257; A. J.
Olivieri, J. Magn. Reson., 1989, 81, 201; A. J. Olivieri, J. Am. Chem.
Soc., 1992, 114, 5758; A. J. Olivieri, Solid State Nucl. Magn. Reson.,
1993, 1, 345; R. K. Harris and A. J. Olivieri, Prog. Nucl. Magn. Reson.
Spectrosc., 1992, 24, 435; A. J. Olivieri, J. Magn. Reson., Ser. A, 1993,
101, 313.
20 Program WSolids1, K. Eichele and R. E. Wasylishen, Dalhousie Univ.,
Halifax, Canada.
21 G. Ma¨rkl and H. Olbrich, Angew. Chem., Int. Ed. Engl., 1966, 5, 588;
G. Ma¨rkl, Angew. Chem. Int. Ed., 1966, 5, 846.
4284 | Dalton Trans., 2010, 39, 4280–4284
This journal is
The Royal Society of Chemistry 2010
©