The coordination chemistry of copper(I) in liquid ammonia, trialkyl and triphenyl phosphite, and tri-n-butylphosphine solution

Article abstract of DOI:10.1039/b400888j

The coordination chemistry of the solvate complexes of the relatively soft electron-pair acceptor copper(I) has been studied in solution and solid state in seven solvents with strong electron-pair donor properties, liquid ammonia, trimethyl, triethyl, triisopropyl, tri-n-butyl and triphenyl phosphite, and tri-n-butylphosphine. The solvate complexes have been characterised by means of EXAFS and ⁶³Cu NMR spectroscopy, and in some cases also by ⁶⁵Cu NMR spectroscopy. The copper(I) ion is three-coordinated, most probably in a coplanar trigonal fashion, in liquid ammonia with a mean Cu-N bond distance of 2.00(1) A. No ⁶³Cu NMR signal has been detected from the ammonia solvated copper(I) ion in liquid ammonia, which supports a three-coordination. The phosphite and phosphine solvated copper(I) ions are tetrahedral with Cu-P bond distances in the range 2.24-2.28 A in both solution and solid state as determined by EXAFS spectroscopy. The tetrahedral configuration of these complexes has been confirmed by ⁶³Cu and ⁶⁵Cu NMR spectroscopy through the J(⁶³Cu-³¹P) and J(⁶⁵Cu-³¹P) couplings. The fact that two of the investigated complexes, [Cu(P(OC₆H₅₎₃₎₄]^- and [Cu(P(C₄H₉₎₃₎₄]⁺, are ⁶³Cu and ⁶⁵Cu NMR silent is probably caused by a significantly angular distorted tetrahedral configuration.

Full text of DOI:10.1039/b400888j

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The coordination chemistry of copper(I) in liquid ammonia,
trialkyl and triphenyl phosphite, and tri-n-butylphosphine solution†
Kersti B. Nilsson and Ingmar Persson*
Department of Chemistry, Swedish University of Agricultural Sciences, P.O. Box 7015,
SE-750 07 Uppsala, Sweden
Received 19th January 2004, Accepted 5th March 2004
First published as an Advance Article on the web 24th March 2004
The coordination chemistry of the solvate complexes of the relatively soft electron-pair acceptor copper() has been
studied in solution and solid state in seven solvents with strong electron-pair donor properties, liquid ammonia,
trimethyl, triethyl, triisopropyl, tri-n-butyl and triphenyl phosphite, and tri-n-butylphosphine. The solvate complexes
have been characterised by means of EXAFS and 63Cu NMR spectroscopy, and in some cases also by 65Cu NMR
spectroscopy. The copper() ion is three-coordinated, most probably in a coplanar trigonal fashion, in liquid
ammonia with a mean Cu–N bond distance of 2.00(1) Å. No 63Cu NMR signal has been detected from the ammonia
solvated copper() ion in liquid ammonia, which supports a three-coordination. The phosphite and phosphine
solvated copper() ions are tetrahedral with Cu–P bond distances in the range 2.24–2.28 Å in both solution and solid
state as determined by EXAFS spectroscopy. The tetrahedral configuration of these complexes has been confirmed
by 63Cu and 65Cu NMR spectroscopy through the J(63Cu–31P) and J(65Cu–31P) couplings. The fact that two of the
investigated complexes, [Cu(P(OC6H5)3)4]ϩ and [Cu(P(C4H9)3)4]ϩ, are 63Cu and 65Cu NMR silent is probably caused
by a significantly angular distorted tetrahedral configuration.
normal due to the triple bond, while the electron density
around the pyridine nitrogen has a similar expansion as in
the amines and ammonia. This results in significantly shorter
Cu–N bond distances to nitriles than to amines and pyridines,
Introduction
Already more than hundred years ago Bodländer showed that
the dominating copper() species in aqueous ammonia solution
is the diamminecopper() complex, [Cu(NH3)2]ϩ, logβ2 = 8.74.1
even though the Cu–N bond is stronger to pyridine than to
Three decades later Bjerrum showed that the stepwise stability
constants are logK1 = 5.93 and logK2 = 4.93. Thus, the first
complex is somewhat stronger than the second one, and that the
acetonitrile as seen in the heats of solvation of the copper()
ion, ∆svHo = Ϫ734 and Ϫ679 kJ molϪ1, respectively,11 and by the
fact that copper() forms fairly strong complexes with pyridine
diamminecopper() complex is dominating (>98%) in solutions
in acetonitrile solution, logβ1 = 1.85, logβ2 = 2.52 and logβ3 =
with a free ammonia concentration of 1.0 mmol dmϪ3 or more.2
3.26.12 A study of the preferential solvation of copper() in the
The same order of magnitude of the logβ2 value given by
acetonitrile–pyridine system has been made by 63Cu NMR
Bjerrum has later been confirmed by several authors.3 Much
spectroscopy.13 The changes in chemical shift, line width
later Bjerrum showed the presence of a very weak trisammine-
and integrated signal intensities are most pronounced at low
copper() complex, [Cu(NH3)3]ϩ, logK3 = Ϫ1.42.4 Stevenson
concentrations of pyridine, indicating a strong preferential
and coworkers have also reported spectrophotometric studies
solvation by pyridine in this region. The most stable and
on the copper()–ammonia system indicating the formation of
common configuration of the copper() ion is the tetrahedron.
a weak third complex with a logK3 value of less than Ϫ2.7,5
The reported three-coordinated solvate complexes are usually
later revised to Ϫ1.3,5 which is very close to the value reported
considered to exist because of the bulkiness of the ligands.14
by Bjerrum. The very small stability constant reveals that this
A limited number of studies on the standard electrode poten-
complex is present, but never dominating (ca. 3.5 and 27% at
tials of metal couples in liquid ammonia have been reported.
log[NH3] = 0.0 and 1.0, respectively, using Bjerrum’s values of
K1–K3), in highly concentrated aqueous ammonia solution, see
Fig S1 (ESI†). An EXAFS study of the diamminecopper() ion
in 6.5 mol dmϪ3 aqueous ammonia solution showed a linear
structure with a Cu–N bond length of 1.88(2) Å.6 The structure
of the copper() ion in liquid ammonia has not been reported so
far, but as a weak third complex is formed in aqueous systems
and a trigonal complex is assumed to be formed in solid state,7
it is reasonable to believe that the coordination number of the
ammonia solvated copper() ion in liquid ammonia is at least
three.
The solvated copper() ion is tetrahedral in the N-donor
solvents acetonitrile and pyridine, with mean Cu–N bond
distances of 1.99 and 2.06 Å in solution,8 and 1.99 and 2.046 Å
in the solid state, respectively.9,10 The reason for the shorter
Cu–N bond distance in acetonitrile is that the electron density
around the nitrogen atom in acetonitrile is less expanded than
The standard electrode potentials of the couples Cu2ϩ/Cu(s),
Cu2ϩ/Cuϩ and Cuϩ/Cu(s) vs. the hydrogen electrode, Hϩ/H2(g),
in liquid ammonia, are reported to be ϩ0.40, ϩ0.44 and ϩ0.36
V, respectively.15 This gives a disproportionation constant, KD,
of the copper() ion in liquid ammonia of 0.044 molϪ1 dm3.
2 Cuϩ(liq. NH3)
Cu(s) ϩ Cu2ϩ(liq. NH3):
KD = 0.044 molϪ1 dm3
The disproportionation constant shows that copper() is
completely dominating (>99%) at copper() concentrations
below 0.1 mol dmϪ3, while an increasing copper() concen-
tration shifts the equilibrium somewhat to the right with 91%
present as copper() when the total copper concentration is 1.0
mol dmϪ3. This shows that the copper() ion is sufficiently stable
in liquid ammonia to be studied by EXAFS spectroscopy,
without any significant interference from copper(). However,
when 63Cu NMR spectroscopy is applied, the presence of
copper() is of greater importance. The line broadening effects
are 2% when 1% of the copper is present as copper(), while
an increase in the copper() content to 9% results in a line
broadening effect of 870%.16
† Electronic supplementary information (ESI) available: Fig. S1: The
complex distribution function for the copper()–ammonia system in
water. Figs. S2–S11: Fits of the experimental EXAFS data and the
individual contributions from the different scattering paths. See http://
www.rsc.org/suppdata/dt/b4/b400888j/
D a l t o n T r a n s . , 2 0 0 4 , 1 3 1 2 – 1 3 1 9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
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A single crystal X-ray determination of [Ag(NH3)3]NO3,
crystallised from liquid ammonia, reveals a three-coordination
around silver with a Ag–N bond distance of 2.281(7) Å.7
A single crystal X-ray determination of the corresponding
copper() complex precipitated from liquid ammonia was not
possible to perform, but the authors stated that Guinier data
reveal that the nitrate salts of the ammonia solvated copper()
and silver() complexes are isostructural (same space group and
similar unit cell parameters). This strongly indicates that the
ammonia solvated copper() ion is three-coordinated in the
solid state.7 The only tetrahedral copper() ammine complex
reported, [Cu(NH3)3(CO)][Co(CO)4] has Cu–N bond distances
in the range 2.067–2.092 Å.17
The structure of the tetrakis(trimethylphosphine)copper()
complex in the solid state shows a mean Cu–P bond distance of
2.270 Å with a small variation in the individual bond distances
as well as in the mean distance between different salts.18–20
The mean Cu–P bond distance in the only reported tetra-
kis(trimethyl phosphite)copper() complex in the solid state is
shorter, 2.242 Å.21 This difference in Cu–P bond distances is
certainly dependent on a less expanded electron density around
the phosphorus atom in the phosphite compared with a
phosphine. The difference is due to the markedly higher elec-
tronegativity on the oxygen atoms bound to phosphorus in
phosphites than on the corresponding carbon atoms in the
phosphines, in a similar way as discussed for the nitrogen donor
solvents above. No crystal structure of a triphenyl phosphite
solvated copper() ion has been reported. The two solid state
structures for tetrakis(triphenylphosphine)copper() complexes
reveal that the Cu–P bond distances are markedly longer, and
also different. There are three equally distant longer (mean
2.586 Å) and one shorter Cu–P bond (mean 2.495 Å).19,22 The
three-coordinated tris(triphenylphosphine)copper() complex
in the hexafluorophosphate salt shows a distorted trigonal
planar environment around copper with Cu–P bond distances
in the range 2.277–2.301 Å and P–Cu–P angles in the range
113.28–125.20Њ. Two other three-coordinated complexes show
mean Cu–P bond distances of 2.295 Å.23
The structure around silver() in the tetrakis(triphenyl-
phosphine)silver() complexes is similar to the corresponding
copper() complexes. The Ag–P bond distances in these
complexes are also very long, but only slightly longer than in
the copper() complexes.24 The cone angle of the ligand is the
steric parameter, θ, for symmetric ligands (all three substituents
are the same), which is the apex angle of a cylindrical cone
centred 2.28 Å from the centre of the phosphorus atom. This
angle just touches the van der Waals radii of the outermost
atoms of a physical model of the different phosphite and
phosphine ligands. It is possible that the long bond distances
are due to the very large cone angle (145Њ) of the triphenyl-
phosphine ligand.25 This may cause the metal–P bond distance
in the tetrakis(triphenylphosphine)metal complexes to be
controlled by the shortest distance the triphenylphosphine
ligands can have in a tetrahedral configuration due to the size
of the phosphorus atom and the cone angle of the PC3 entity.
Such sterical restrictions are not expected for the triphenyl
phosphite ligand with a cone angle of 128Њ.25
Changes in the coordination chemistry have been observed
when the soft or relatively soft d10 metal ions are transferred
from oxygen donor solvents to the sulfur donor solvent
N,N-dimethylthioformamide, (CH3)2NCHS (DMTF)26,27 and
to liquid ammonia,28 both being strong electron-pair donors
with DS values of 52 and 69, respectively.29 In relatively weak
electron-pair donor solvents such as water, dimethyl sulfoxide
and acetonitrile, the mono- and divalent d10 metal ions are
tetrahedral and octahedral, respectively.8,30 The copper() and
silver() ions remain tetrahedral in DMTF solution, while the
solid silver() solvate of the perchlorate salt is basically three-
coordinated in a dimer. The ammonia solvated silver() ion is
three-coordinated in both liquid ammonia and in the solid
state.7,31 The DMTF and ammonia solvated gold() ions are
linear in both solution and the solid state.27,31 The solvated
zinc() and mercury() ions are tetrahedral in DMTF solution
and in liquid ammonia, while the cadmium() ion maintains its
octahedral configuration in these solvents,26,28 as well as the
thallium() ion, which is octahedral in all solvents studied so
far; water, dimethyl sulfoxide and liquid ammonia.28
The values of the Gibbs energies of transfer, ∆tGo, of the soft
monovalent d10 metal ions from water to the soft solvents
triethyl phosphite and pyridine are strongly negative, i.e. for
silver() Ϫ70.8 and Ϫ58.8 kJ molϪ1, respectively.32 The solvents
used in this study are regarded to have soft bonding character
with DS values of 69, 56 and 76 for liquid ammonia, tri-n-butyl
phosphite and tri-n-butylphosphine, respectively.29 These prop-
erties imply that the solvation of the relatively soft copper()
electron-pair acceptor in liquid ammonia, and phosphite and
phosphine solvents is very strong.
The aims of the study were to reveal any changes in the
coordination of copper() when transferred from aqueous to
liquid ammonia or from weaker electron-pair N-donor solvents
to stronger ones such as liquid ammonia, and to determine any
differences in coordination between the strong electron-pair
donor solvents coordinating through nitrogen and phosphorus.
Experimental
Chemicals
The solvents of reagent grade, purchased from Sigma-Aldrich,
were used without further purification except for dioxane,
which was distilled and kept under nitrogen atmosphere prior
to use. Tetrakis(acetonitrile)copper() perchlorate, [Cu(CH3-
CN)4]ClO4, 1, was prepared as described elsewhere.33 Liquid
ammonia was distilled from 25% aqueous ammonia (Analytical
grade, Merck) and used within a few hours. Attempts have been
made to use liquid ammonia from gas cylinders, but the purity
of the solvent produced this way was not satisfactory. The
distillation was performed by careful heating of the aqueous
ammonia, and then trapping the ammonia onto a “cold
finger” filled with ethanol and solid carbon dioxide. The liquid
ammonia was then kept in a flask at a temperature of about 220
K. In order to avoid the presence of water, bottles and flasks
containing gaseous and/or liquid ammonia were connected to
tubes filled with solid sodium hydroxide pastilles before contact
with air.
Synthesis and preparation of solutions
Solid 1 was used as starting material for the preparations of
the liquid ammonia, trialkyl and triphenyl phosphite and tri-
n-butylphosphine solutions of copper(), from which also solid
phases were precipitated. In the EXAFS experiment, the liquid
ammonia solution of copper() was prepared by dissolving 1 in
liquid ammonia at about 200 K and it was kept in dry nitrogen
atmosphere. Hydrazine, N2H4 (Aldrich, 1.25% by volume), was
added in order to reduce any copper() formed through air-
oxidation back to copper() by oxidation of hydrazine to N2.6
Hydrazine does not compete with the solvent as ligand to
copper() since it is a much weaker Lewis base than ammonia.34
All liquid ammonia solutions studied by 63Cu NMR and
EXAFS spectroscopy were prepared immediately before the
measurements, and the solutions were stable for 2–4 h, the time
required for these experiments. If the solutions are stored for
a longer time, or if the hydrazine concentration is too high,
copper() oxide will precipitate.
The solid compounds tetrakis(trimethyl phosphite)copper()
perchlorate,
phosphite)copper() perchlorate [Cu(P(OC2H5)3)4]ClO4 (3),
tetrakis(triisopropyl phosphite)copper() perchlorate,
[Cu(P(OCH3)3)4]ClO4
(2),
tetrakis(triethyl
[Cu(P(OCH(CH3)2)3)4]ClO4 (4) and tetrakis(triphenyl phos-
phite)copper() perchlorate, [Cu(P(OC6H5)3)4]ClO4 (5) were
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Table 1 Concentrations (mol dmϪ3) of complexes analysed by 63Cu
NMR and/or 65Cu NMR (N), and EXAFS Spectroscopy (E) in this
work.
moment effects, solvent and anion dependent, and also depend-
ent on the presence of water and copper(), both of them
broadening the line width.16 Furthermore, the line widths have
been found to increase with temperature and linearly with the
viscosity.37
Sample
[Cuϩ]
Method
The 63Cu and 65Cu NMR spectra were recorded at 106.05 and
113.63 MHz, respectively, on a Bruker 400 DRX spectrometer
equipped with a multinuclear BBO probe. The chemical
shifts are given relative to a 0.15 mol dmϪ3 solution of
[Cu(P(OC2H5)3)4]ClO4 in chloroform, used as external reference
as suggested by Kroneck et al.; [Cu(CH3CN)4]BF4 or 1 in
acetonitrile have often been used as reference, but the Larmor
frequency and the line width of the copper() signal in these
solvates are temperature sensitive.35 The number of data points
in each data acquisition was 64 k. A pulse width of 6 µs was
used, with a recycle delay of 3 s, and the number of scans was
usually 256. The samples were kept in rotating cylindrical tubes
with an outer diameter of 5 mm at 300 or 260 K. The ammonia
solvated copper() ion in liquid ammonia was prepared at 220
K, and then transferred into cooled air-tight 5 mm NMR tubes
(Wilmad®). The NMR tubes were filled with argon and then
closed. The temperature was allowed to rise to 300 K, causing a
significant pressure of ammonia in the NMR tube. 5% CD3CN
was used as a lock signal.
[Cu(NCCH3)4]ClO4 (1) in NH3(l)
0.15
0.30
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.70
0.15
0.40
0.70
0.15
0.15
0.20
0.15
0.15
0.15
N
E
N
N
N
E
N
N
N
E
N
E
[Cu(NCCH3)4]ClO4 (1) in NH3(l)
[Cu(P(OCH3)3)4]ClO4 (2) in CHCl3
[Cu(P(OCH3)3)4]ClO4 (2) in P(OCH3)3
[Cu(P(OCH3)3)4]ClO4 (2) in C4H8O2
[Cu(P(OCH3)3)4]ClO4 (2) in P(OCH3)3 ϩ C4H8O2
[Cu(P(OC2H5)3)4]ClO4 (3) in CHCl3
[Cu(P(OC2H5)3)4]ClO4 (3) in P(OC2H5)3
[Cu(P(OC2H5)3)4]ClO4 (3) in C4H8O2
[Cu(P(OC2H5)3)4]ClO4 (3) in P(OC2H5)3
[Cu(P(OCH3(CH3)2)3)4]ClO4 (4) in CHCl3
[Cu(P(OCH3(CH3)2)3)4]ClO4 (4) in C4H8O2
[Cu(NCCH3)4[ClO4 (1) in P(OC4H9)3
[Cu(NCCH3)4]ClO4 (1) in P(OC6H5)3
[Cu(NCCH3)4]ClO4 (1) in P(C4H9)3
[Cu(NCCH3)4]ClO4 (1) in P(C4H9)3
[Cu(NCCH3)4]ClO4 in CH3CN
E
N
N
E
N
N
N
[Cu(NC5H5)4]ClO4 in NC5H5
[Cu((SCHN(CH3)2)4]ClO4 in (CH3)2NCHS
prepared by dissolving 1 to saturation in the respective solvent
at 325 K, and when the solutions were slowly cooled down to
room temperature, white crystals could be isolated by filtration.
The trimethyl, triethyl and triphenyl phosphite solutions of
copper() were prepared by dissolving 2, 3 and 5 in the respect-
ive solvent. However, the solubility of 4 in triisopropyl
phosphite is very low, but by dissolving it in dioxane or chloro-
form it was possible to reach sufficiently high concentrations of
the solvate complex for EXAFS, and 63Cu and 65Cu NMR
measurements, respectively. The tri-n-butyl and triphenyl
phosphite and tri-n-butylphosphine solutions of copper()
were prepared by dissolving 1 in the respective solvent. Tetra-
kis(N,N-dimethylthioformamide)- and tetrakis(pyridine)-
copper() perchlorate were prepared as described elsewhere.10,27
The solutions of tetrakis(trimethyl phosphite)- and tetra-
kis(triethyl phosphite)copper() perchlorate in chloroform (the
latter used as a reference in the 63Cu and 65Cu NMR measure-
ments) were found to be very sensitive to oxidation. These
solutions were therefore prepared in a glove box under nitrogen
atmosphere, and then transferred into NMR tubes, which were
filled with argon before sealing to avoid oxidation. No pre-
cautions concerning the atmosphere were taken when handling
the other samples, and no colour changes of these solutions
were observed, which should have implied oxidation of
copper().
EXAFS. Data collection. Copper K-edge X-ray absorption
spectra were recorded at the wiggler beam line 4–1 at the
Stanford Synchrotron Radiation Laboratory (SSRL) on two
occasions. The EXAFS station was equipped with a Si[220]
double crystal monochromator. SSRL was operated at 3.0 GeV
and a maximum current of 100 mA. The data collection was
performed in transmission mode, and for the phosphite and
phosphine solutions at ambient room-temperature. When
measuring copper() in liquid ammonia solution the temper-
ature of the sample was kept at about 200 K. Higher order
harmonics were reduced by detuning the second mono-
chromator to 50% of maximum intensity at the end of the
scans.
The solid compounds were diluted in boron nitride to give
an edge step of about one unit in the logarithmic intensity
ratio, and kept in 1 mm brass frames with Mylar tape
windows. The phosphite and phosphine solutions of copper()
were measured in sample cells with 1.5–2 mm Vitone spacers
and 35–55 µm glass windows. The copper() ammonia solution
was kept in a 2 mm titanium spacer with 35–55 µm glass
windows equipped with a copper rod dipped into a methanol–
liquid nitrogen cooling mixture maintaining a temperature of
ca. 175 K.38 The temperature, however, slowly increased during
the experiment due to evaporation of the liquid nitrogen. This
sample cell was placed into a Perspex® box (50 × 50 × 50 mm)
with Mylar tape windows. The box was filled with nitrogen
gas in order to avoid ice formation on the cell windows, and
it was equipped with a 8 mm gasket sealed aperture for the
cooling rod.
The concentrations of the solutions used in the 63Cu and 65Cu
NMR measurements were the same as in previous studies to
make comparisons straightforward. The concentrations used in
the EXAFS experiments were chosen to match the expected
optimal signal-to-noise ratio, and a higher concentration may
cause a significant disproportionation reaction, see Intro-
duction. The concentrations of the studied solvates are
summarised in Table 1.
The energy scale of the X-ray absorption spectra was
calibrated by assigning the first inflection point of the K edge
of a copper foil to 8980.3 eV.39 For each sample 3–6 scans were
averaged, giving satisfactory data (k3-weighted) up to k = 14
Methods
Å
Ϫ1. For the liquid ammonia solution of copper() the first of
63Cu and 65Cu NMR. The copper isotopes 63Cu and 65Cu have
natural abundances of 69.1 and 30.9%, respectively, nuclear
spins of 3/2 and quadrupole moments of Q = Ϫ0.211 × 10Ϫ28
and Ϫ0.195 × 10Ϫ28 m2, respectively. Thereby they couple
strongly to local electric field gradients. The quadrupole
moments cause significant line broadening when the charge
is unevenly distributed.35 Consequently only complexes with
regular tetrahedral or cubic symmetry are NMR active.36 We
have chosen to use mainly 63Cu NMR spectroscopy to be able
to make comparisons with previous studies. The line widths of
the 63Cu NMR signals are, in addition to the quadrupole
the collected scans and a smoothed average of the first two
scans were used in separate data treatments. The results were
similar and the data from the first scan is reported here. The
EXAFSPAK program package was used for all of the data
treatment.40
Data analysis. The EXAFS oscillations were obtained after
performing standard procedures for pre-edge subtraction,
normalisation and spline removal. The k3-weighted model
functions were calculated using ab initio calculated phase and
amplitude parameters obtained by the FEFF7 program
package (version 7.02).41 Input to the FEFF7 program was
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prepared by assuming appropriate angles and distances for
the structure around copper() and appropriate cone angles
for the phosphites and tri-n-butylphosphine.25
Results and discussion
Copper(I) in liquid ammonia
The EXAFS spectrum of copper() in liquid ammonia is
strongly dominated by the contributions from the first shell of
nitrogen atoms, and the three-leg scattering path Cu–N–N was
included in the refinements in order to improve the fit, see Figs. 1
and S2 (ESI†). The Cu–N bond distance 2.00(1) Å (Table 2)
strongly indicates a trigonal coplanar configuration around
copper(), upon comparison with Cu–N bond distances in
previously analysed two-, three- and four-coordinated copper()
complexes.24
Fig. 2 Normalised XANES spectra of the analysed complexes:
[Cu(NH3)3]ϩ in liquid NH3 (offset 4.5); [Cu(P(OCH3)3)4]ClO4 (2) (offset
4.0); [Cu(P(OCH3)3)4]ϩ in a mixture of P(OCH3)3 and C4H8O2 (offset
3.5); [Cu(P(OC2H5)3)4]ClO4 (3) (offset 3.0); [Cu(P(OC2H5)3)4]ϩ in
P(OC2H5)3 (offset 2.5); [Cu(P(OCH(CH3)2)3)4]ClO4 (4) (offset 2.0);
[Cu(P(OCH(CH3)2)3)4]ϩ in C4H8O2 (offset 1.5); [Cu(P(OC4H9)3)4]ϩ in
P(OC4H9)3 (offset 1.0); [Cu(P(OC6H5)3)4]ClO4 (5) (offset 0.5) and
[Cu(P(C4H9)3)4]ϩ in P(C4H9)3 (no offset).
substrate complex of galactose oxidase.43 When the analysis of
the trisamminecopper() complex with 63Cu NMR spectroscopy
failed because of a large line broadening, a highly symmetrical
T d symmetry must be discarded.
An adsorption microcalorimetry study reports the room
temperature adsorption of ammonia on copper() and silver()
when dispersed in a zeolite, ZSM-5.44 A tetraamminecopper()
complex was assumed to be formed, as tetrahedral is the most
common configuration of copper(), although totally five
ammonia molecules per copper() atom were adsorbed. Three
of these ammonia molecules were found to be bound more
strongly to each copper() ion than the other two.44
Fig.
1
k3-Weighted EXAFS data of experimental (solid) and
theoretical (dashed) data of the analysed complexes: [Cu(NH3)3]ϩ in
liquid NH3 (no offset); [Cu(P(OCH3)3)4]ClO4 (2) (offset Ϫ10);
[Cu(P(OCH3)3)4]ϩ in a mixture of P(OCH3)3 and C4H8O2 (offset Ϫ15);
[Cu(P(OC2H5)3)4]ClO4 (3) (offset Ϫ20); [Cu(P(OC2H5)3)4]ϩ in
P(OC2H5)3 (offset Ϫ25); [Cu(P(OCH(CH3)2)3)4]ClO4 (4) (offset Ϫ30);
[Cu(P(OCH(CH3)2)3)4]ϩ in C4H8O2 (offset Ϫ35); [Cu(P(OC4H9)3)4]ϩ in
P(OC4H9)3 (offset Ϫ40); [Cu(P(OC6H5)3)4]ClO4 (5) (offset Ϫ45) and
[Cu(P(C4H9)3)4]ϩ in P(C4H9)3 (offset Ϫ50).
The assumption of a three-coordinated complex is also
consistent with the well-known pre-edge features that copper()
complexes exhibit at ca. 8984 eV, which is connected to the
configuration around copper(), as the splitting of the 4p
orbitals is correlated to the geometry of the copper site
(Fig. 2).42 For a linear complex the transition of an electron
from the 1s to the 4px,y states would result in an intense pre-edge
peak at lower energy than the 1s to 4pz transition. Three- and
four-coordinated complexes exhibit decreasingly strong pre-
edge features. The pre-edge features of the ammonia solvated
copper() ion show a similar normalised amplitude (0.69; cf.
Other examples of trigonal copper() complexes are
[Cu(CN)3]2Ϫ present as planar monomeric entities in
Na2Cu(CN)3ؒ3H2O,45 and [Cu(NC5H4CH3)3]ϩ in solid [Cu(2-
picoline)3]ClO4 with Cu–N bond distances and N–Cu–N angles
in the ranges 1.97–2.02 Å and 113–139Њ, respectively.46 The
reason for three-coordination of copper() in liquid ammonia is
obviously not steric hindrance, instead electronic reasons are
most probably causing the strong covalent Cu–N interactions
and a coordination number lower than sterically allowed.
Theoretical calculations performed on [Cu(NH3)n]ϩ (n = 1–4)
have revealed decreasing binding energies for the third and
fourth ligands, and the authors relate the results to increased
ligand–ligand repulsion,47 which is in agreement with our
experimental results.
0.63
0.05) and energy (8984 eV) as previously found for
a three-coordinated complex,42 and are in good agreement
with the XANES spectrum of the assumed three-coordinated
D a l t o n T r a n s . , 2 0 0 4 , 1 3 1 2 – 1 3 1 9
1315

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Table 2 Results of Cu K-edge EXAFS data analysis using k3-weighting. The parameters are frequency (N ), mean bond distances (d/Å), Debye–
Waller parameter (σ2/Å2), threshold energy (Eo/eV) and amplitude reduction factor (So )
2
σ2
Eo
So
2
Sample
Scattering path
N
d
[Cu(NH3)3]ϩ in NH3(l)
Cu–N
Cu–N–N
3
6
2.004(6)
3.69(6)
0.0097(8)
0.01(1)
8984(1)
0.77
[Cu(P(OCH3)3)4]ClO4 (2) (s)
Cu–P
4
12
24
12
2.245(2)
3.17(3)
3.53(3)
4.13(2)
0.0050(2)
0.020(2)
0.009(2)
0.007(3)
8986.2(4)
8985.7(5)
8986.2(4)
8987.7(5)
8985.8(4)
8984.8(9)
8986.2(4)
8983.8(4)
8984.1(6)
0.65
0.86
0.78
0.86
0.86
0.88
0.47
0.93
0.70
Cu ؒ ؒ ؒ O
Cu–P–O
Cu–P–P
[Cu(P(OCH3)3)4]ϩ (2) in P(OCH3)3
[Cu(P(OC2H5)3)4]ClO4 (3) (s)
Cu–P
4
12
24
12
2.245(2)
3.17(2)
3.52(2)
4.17(3)
0.0044(2)
0.023(3)
0.013(3)
0.009(3)
Cu ؒ ؒ ؒ O
Cu–P–O
Cu–P–P
Cu–P
4
12
24
12
2.245(2)
3.18(3)
3.54(2)
4.12(3)
0.0059(2)
0.021(2)
0.010(3)
0.007(3)
Cu ؒ ؒ ؒ O
Cu–P–O
Cu–P–P
[Cu(P(OC2H5)3)4]ϩ (3) in P(OC2H5)3
[Cu(P(OCH(CH3)2)3)4]ClO4 (4) (s)
[Cu(P(OCH(CH3)2)3)4]ϩ (4) in C4H8O2
[Cu(P(OC4H9)3)4]ϩ in P(OC4H9)3
[Cu(P(OC6H5)3)4]ClO4 (5) (s)
Cu–P
4
12
24
12
2.258(2)
3.17(2)
3.54(2)
4.16(3)
0.0046(2)
0.019(2)
0.007(2)
0.009(4)
Cu ؒ ؒ ؒ O
Cu–P–O
Cu–P–P
Cu–P
4
12
24
12
2.279(2)
3.18(1)
3.57(1)
4.16(2)
0.0059(2)
0.018(1)
0.019(1)
0.008(1)
Cu ؒ ؒ ؒ O
Cu–P–O
Cu–P–P
Cu–P
4
12
24
12
2.258(5)
3.16(3)
3.54(3)
4.20(4)
0.0061(2)
0.021(3)
0.011(4)
0.008(5)
Cu ؒ ؒ ؒ O
Cu–P–O
Cu–P–P
Cu–P
4
12
24
12
2.249(2)
3.14(3)
3.52(3)
4.18(4)
0.0034(2)
0.027(1)
0.013(4)
0.006(5)
Cu ؒ ؒ ؒ O
Cu–P–O
Cu–P–P
Cu–P
4
12
24
12
2.255(3)
3.22(2)
3.57(2)
4.20(3)
0.0088(3)
0.020(2)
0.012(2)
0.013(4)
Cu ؒ ؒ ؒ O
Cu–P–O
Cu–P–P
[Cu(P(C4H9)3)4]ϩ in P(C4H9)3
Cu–P
4
12
24
12
2.278(2)
3.39(1)
3.79(1)
4.30(3)
0.0059(3)
0.03(1)
0.02(2)
Cu ؒ ؒ ؒ C
Cu–P–C
Cu–P–P
0.007(4)
could be observed from the complexes of copper() in triphenyl
phosphite and tri-n-butylphosphine in spite of cooling.
Copper(I) in trialkyl and triphenyl phosphite and tri-n-butyl-
phosphine
The absence of NMR signals for some of the copper()
phosphite species have earlier been explained by equilibria with
two- or three-coordinated species,36 and large ligand cone
angles25 have been considered to cause steric hindrance within
regular T d symmetry. The absence of NMR signals strongly
indicates that the configuration around copper() deviates
significantly from a regular tetrahedron. However, the results
from EXAFS data (Table 2) show that the Cu–P bond distances
(2.245–2.279 Å) are in accordance with a four-coordinated
tetrahedral structure, in spite of undetectable NMR signals.
Furthermore, the Debye–Waller factor coefficients of the Cu–P
bond distances are small and similar for all complexes studied,
which strongly indicates that any distortion is angular, while the
Cu–P bond distances seem to be within a narrow range (Table
2). The features of the XANES region in the EXAFS spectrum
of the tetrakis(triphenyl phosphite)copper() complex (Fig. 2)
at 8995–9005 eV show a transition which is absent or weaker
in the other tetrahedral complexes. The fits of the EXAFS
functions and the Fourier transforms are given in Figs. 1 and 3,
and the fits including the contributions from the individual
scattering paths are given in Figs. S2–S11 (ESI†).
The majority of the copper() phosphite complexes analysed
exhibit NMR spectra with nicely appearing quintets due to
spin–spin coupling between 63Cu or 65Cu and 31P, showing a
symmetric tetrahedral configuration of the CuP4 entity of the
studied complexes. The 63Cu NMR results of the investigated
complexes are compared with results reported previously, with
reference to the chemical shift δ, the line width ∆ν and the
coupling constants J(63Cu–31P) and J(65Cu–31P) as summarised
in Table 3. 63Cu NMR signals of the tetrakis(triisopropyl
phosphite)copper() complex dissolved in chloroform could
only be detected when the sample was cooled to 260 K (Fig. 4).
In addition to 63Cu NMR, the tetrakis(trimethyl phosphite)-,
tetrakis(triisopropyl phosphite)-, tetrakis(triphenyl phosphite)-
and tetrakis(tri-n-butylphosphine)copper() complexes were
analysed using 65Cu NMR, as the quadrupole moment of this
nucleus is somewhat lower. The resolution of the J(65Cu–31P)
coupling is better, and using this nucleus it is possible to
distinguish
a quintet for the tetrakis(triisopropyl phos-
phite)copper() complex at 260 K (Fig. 4). The line width
is essentially the same. Neither 63Cu nor 65Cu NMR signals
D a l t o n T r a n s . , 2 0 0 4 , 1 3 1 2 – 1 3 1 9
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Table 3 63Cu and 65Cu NMR parameters (the parameters in italic refer to 65Cu data); chemical shift (δ/ppm), line width (∆ν/Hz), coupling constant,
J(63Cu–31P) or J(65Cu–31P)/Hz, and temperature (T /K) of copper() complexes coordinated with liquid ammonia, trialkyl- and triphenyl phosphites,
tri-n-butylphosphine, acetonitrile, pyridine and DMTF at 260 or 300 K. [Cu(P(OC2H5)3)4]ϩ in CHCl3 has been used as reference (marked bold)a
Sample
δ
∆ν
J(63/65Cu–31P)
T
Ref.
a
b
b
[Cu(NH3)3]ϩ in NH3(l)
–
300/260
300
[Cu(P(OCH3)3)4]ϩ in CHCl3
[Cu(P(OCH3)3)4]ϩ in CDCl3
[Cu(P(OCH3)3)4]ϩ in P(OCH3)3
[Cu(P(OCH3)3)4]ϩ in P(OCH3)3
[Cu(P(OCH3)3)4]ϩ in P(OCH3)3
[Cu(P(OCH3)3)4]ϩ in P(OCH3)3
[Cu(P(OCH3)3)4]ϩ in C4H8O2
[Cu(P(OC2H5)3)4]؉ in CHCl3
[Cu(P(OC2H5)3)4]ϩ in CHCl3
[Cu(P(OC2H5)3)4]ϩ in P(OC2H5)3
[Cu(P(OC2H5)3)4]ϩ in P(OC2H5)3
[Cu(P(OC2H5)3)4]ϩ in C4H8O2
[Cu(P(OCH(CH3)2)3)4]ϩ in CHCl3
[Cu(P(OCH(CH3)2)3)4]ϩ in CHCl3
[Cu(P(OC4H9)3)4]ϩ in CHCl3
[Cu(NCCH3)4]ϩ in CH3CN
Ϫ8
174
166
134
98
1220
1223
1208
1294
1214
Ϫ6 1c
36
b
Ϫ9
300
300
b
Ϫ9
Ϫ9.2 0.5c
115
100
292
149
137
195
210
516
3400
3200
430
520
1520
4400
48
Ϫ9
Ϫ8
0
300
300
300
35
b
1214
1209
1209
1201
1224 30
1203
b
0
1c
36
b
0
300
0
0.4c
48
b
0
300
260
260
b
b
Ϫ15
Ϫ15
3
Ϫ91
19
1210 40
1312
36
b
300
300
300
b
b
[Cu(NC5H5)4]ϩ in C5H5N
[Cu((SCHN(CH3)2)4]ClO4 in DMTF
33
a No signal was detected for the following complexes: [Cu(NH3)3]ϩ in liquid NH3 at 260 K, [Cu(P(OCH(CH3)2)3)4]ϩ in C4H8O2 at 300 K,
[Cu(P(OC6H5)3)4]ϩ in P(OC6H5)3 at 260 K, and [Cu(P(C4H9)3)4]ϩ in P(C4H9)3 at 260 K. b This work. c Recalculated when authors are using 0.1 mol
(kg solvent)Ϫ1 [Cu(NCCH3)4]BF4 in CH3CN as a reference.
Fig. 4 65Cu (top) and 63Cu NMR spectra (bottom) of [Cu(P(OCH3-
(CH3)2)3)4]ϩ in CH3Cl at 260 K.
Neither 63Cu nor 65Cu NMR spectra show any signal from
the copper() complexes with the ligands displaying the largest
ligand cone angles; θ = 128Њ for P(OC6H5)3 and θ = 132Њ
for P(C4H9)3.25 According to the lengths of the multiple
Cu–P–P scattering pathways (Cu–P–P = 4.12–4.30 Å; Table 2),
the complexes with large line broadening in the copper NMR
spectra deviate more from a regular tetrahedron (Cu–P–P =
4.07–4.14 Å) than complexes where 63Cu and 65Cu NMR
signals are detected. Complexes in solution seem to deviate
slightly more from a regular tetrahedron than corresponding
complexes in solid state. However, Szlyk and Szymanska49
have reported a 63Cu NMR resonance signal from the
[Cu(P(OC6H5)3)n]ϩ complex in acetonitrile–triphenyl phosphite
mixtures with a shift of 46 ppm with respect to the [Cu(CH3-
CN)4]ClO4 reference in acetonitrile, but a lower symmetry than
T d was assumed (C3v or C2v). The shift of the analysed com-
pound is Ϫ45 ppm after recalculation to the tetrakis(triethyl
Fig. 3 Fourier transforms of experimental (solid) and theoretical
(dashed) data of the analysed complexes: [Cu(NH3)3]ϩ in liquid NH3
(×3) (no offset); [Cu(P(OCH3)3)4]ClO4 (2) (offset Ϫ2.0); [Cu(P-
(OCH3)3)4]ϩ in a mixture of P(OCH3)3 and C4H8O2 (offset Ϫ3.5);
[Cu(P(OC2H5)3)4]ClO4 (3) (offset Ϫ5.0); [Cu(P(OC2H5)3)4]ϩ in
P(OC2H5)3 (offset Ϫ6.5); [Cu(P(OCH(CH3)2)3)4]ClO4 (4) (offset Ϫ8.0);
[Cu(P(OCH(CH3)2)3)4]ϩ in C4H8O2 (offset Ϫ9.5), [Cu(P(OC4H9)3)4]ϩ in
P(OC4H9)3 (offset Ϫ11.0); [Cu(P(OC6H5)3)4]ClO4 (5) (offset Ϫ12.5) and
[Cu(P(C4H9)3)4]ϩ in P(C4H9)3 (offset Ϫ14.0).
D a l t o n T r a n s . , 2 0 0 4 , 1 3 1 2 – 1 3 1 9
1317

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phosphite)copper() reference. This is far away from the region
where the shifts of the tetrakis(trialkyl phosphite)copper()
complexes are observed, cf. Table 3, and it is doubtful which
kind of complex the reported signal is coming from.
Program is supported by the Department of Energy, Office of
Biological and Environmental Research, and by the National
Institutes of Health, National Center for Research Resources,
Biomedical Technology Program.
Spectra of the copper() phosphite complexes in dioxane
show a broader line width than in chloroform or trialkyl
phosphites, possibly due to a slight distortion of the symmetry
(Table 3). This may be due to different solvation of the
complexes in the solvents used. The chemical shifts are rather
constant in the different solvents, as expected (Table 3).16 The
tetrakis(trialkyl phosphite)copper() complex showing a 63Cu
NMR signal with the highest density of electrons around the
copper() nucleus (δ = Ϫ15) is [Cu(P(OCH(CH3)2)3)4]ϩ and the
one with the lowest electron density (δ = 3) is [Cu((OC4H9)3)4]ϩ.
The tetrakis(triisopropyl phosphite)copper() complex does
show a slightly longer Cu–P bond distance, while the other
complexes have essentially the same Cu–P bond lengths (Table
2). The chemical shift of this complex is probably also affected
by the shielding from the triisopropyl “umbrella”. The differ-
ences in shielding of the copper() nucleus of the other com-
plexes can be explained by the lengths of the alkyl chains of
the trialkyl phosphites, and of these the tetrakis(trimethyl
phosphite)copper() complex exhibits the highest electron
density around copper.
The calculated Cu–P–O angles are in the range 108.5(1.7)Њ
(tetrakis(tri-n-butyl phosphite)copper() perchlorate) to
112.6(1.3)Њ (tetrakis(triphenyl phosphite)copper() perchlorate),
and the Cu–P–C angle in tetrakis(tri-n-butylphosphine) is
111.1(6)Њ. The fairly small Debye–Waller parameters of the
analysed complexes imply that only one species is present in all
samples (Table 2).
In contrast to the theoretical calculations performed on
[Cu(NH3)n]ϩ (n = 1–4), calculations on [Cu(PH3)4]ϩ have
revealed greater stability for the third and fourth phosphine
ligands,50 which is also in agreement with our experimental
results.
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D a l t o n T r a n s . , 2 0 0 4 , 1 3 1 2 – 1 3 1 9
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