Structural and spectroscopic studies on three- and two-co-ordinate copper(I) halide tribenzylphosphine complexes

Article abstract of DOI:10.1039/b007698h

Three-co-ordinate, monomeric 1:2 complexes of tribenzylphosphine (PBz₃) with copper(I) halides, [Cu(PBz₃)₂X] (X = Cl, Br or I), have been synthesized and characterized by single crystal structure determinations, solid state ³¹P CPMAS NMR spectroscopy and low frequency vibrational spectroscopy. The two PBz₃ ligands show different conformational structures and this is reflected in a distorted 'P₂CuX' geometry for each complex. Solid state ³¹P CPMAS spectra show asymmetric quartets with ¹J(³¹P-⁶³Cu) ranging from 1.23 to 1.46 kHz and asymmetry parameters, dν_Cu, ranging from 8 × 10⁹ to 13 × 10⁹ Hz². Reported also are the synthesis, structure, solid state ³¹P NMR and far-IR spectra of the two-co-ordinate complex [Cu(PBz₃)₂][CuCl₂] and the crystal structure of the dimeric 1:1 chloride complex, [Cu₂(PBz₃)₂Cl₂]·3C₆ H₆, this latter structure being the first of this type reported for the PBz₃ ligand. Attempts to synthesize a 1:1 chloro complex using acetonitrile, rather than chloroform, as solvent led to the formation of tribenzylphosphine oxide. The conversion of [Cu₂(PBz₃)₂Cl₂]·3C₆ H₆ into [Cu(PBz₃)₂][CuCl₂] upon removal of benzene of solvation was followed by far-IR spectroscopy. The vibrational spectra of the bulk 1:1 and 1:2 complexes are consistent with the crystal structures. Bands due to the ν(CuX) modes of the neutral complexes and those due to the [CuX₂]^- ions in the ionic complexes have been assigned, and the relationship between the spectra and the structures of the compounds is discussed.

Full text of DOI:10.1039/b007698h

View Article Online / Journal Homepage / Table of Contents for this issue
Structural and spectroscopic studies on three- and two-co-ordinate
copper(I) halide tribenzylphosphine complexes
Eric W. Ainscough,*a Andrew M. Brodie,*a Anthony K. Burrell,a Graham H. Freeman,a
Geoffrey B. Jameson,a Graham A. Bowmaker,b John V. Hannac and Peter C. Healyd
a Chemistry – Institute of Fundamental Sciences, Massey University, Private Bag 11 222,
Palmerston North, New Zealand
b Department of Chemistry, University of Auckland, Auckland, New Zealand
c ANSTO NMR Facility, C/- Materials Division, Private Mail Bag 1, Menai,
NSW 2234, Australia
d School of Science, Griffith University, Brisbane, Queensland 4111, Australia
Received 22nd September 2000, Accepted 2nd November 2000
First published as an Advance Article on the web 22nd December 2000
Three-co-ordinate, monomeric 1:2 complexes of tribenzylphosphine (PBz3) with copper() halides, [Cu(PBz3)2X]
(X = Cl, Br or I), have been synthesized and characterized by single crystal structure determinations, solid state
31P CPMAS NMR spectroscopy and low frequency vibrational spectroscopy. The two PBz3 ligands show different
conformational structures and this is reflected in a distorted ‘P2CuX’ geometry for each complex. Solid state 31
CPMAS spectra show asymmetric quartets with 1J(31P–63Cu) ranging from 1.23 to 1.46 kHz and asymmetry
parameters, dνCu, ranging from 8 × 109 to 13 × 109 Hz2. Reported also are the synthesis, structure, solid state 31
P
P
NMR and far-IR spectra of the two-co-ordinate complex [Cu(PBz3)2][CuCl2] and the crystal structure of the dimeric
1:1 chloride complex, [Cu2(PBz3)2Cl2]ؒ3C6H6, this latter structure being the first of this type reported for the PBz3
ligand. Attempts to synthesize a 1:1 chloro complex using acetonitrile, rather than chloroform, as solvent led to
the formation of tribenzylphosphine oxide. The conversion of [Cu2(PBz3)2Cl2]ؒ3C6H6 into [Cu(PBz3)2][CuCl2] upon
removal of benzene of solvation was followed by far-IR spectroscopy. The vibrational spectra of the bulk 1:1 and
1:2 complexes are consistent with the crystal structures. Bands due to the ν(CuX) modes of the neutral complexes
and those due to the [CuX2]Ϫ ions in the ionic complexes have been assigned, and the relationship between the
spectra and the structures of the compounds is discussed.
Introduction
Experimental
Interest in two- and three-co-ordinate copper() complexes
arises from their relative rarity, especially when compared with
the extensive chemistry for four-co-ordinate copper().1
Recently, it has been shown that the reaction of 1:1 stoichio-
metric ratios of copper() bromide and tribenzylphosphine
(PBz3) yields the salt [Cu(PBz3)2][CuBr2]2 rather than the
expected dimeric or tetrameric complex [Cu(PBz3)Br]n (n = 2 or
4). With hexafluorophosphate as anion, and a 1:2 Cu:PBz3
stoichiometric ratio, we were able to isolate the two-co-ordinate
salt [Cu(PBz3)2]PF6.3 Crystal structure determinations on both
these compounds show the [Cu(PBz3)2]ϩ cation to be linear
with the P–Cu–P angle equal to 180Њ. This was a somewhat
unexpected result since similar two-co-ordinate copper phos-
phine complexes have been obtained previously only for very
bulky phosphine ligands such as trimesitylphosphine.4 This
structural outcome been ascribed3 to non-covalent bonding
interactions between the phenyl groups on the two ligands
which sweep back over the copper to generate an intra-
molecular form of the sixfold phenyl embrace (6PE).5 In our
current investigations of the reactions of copper() halides with
tribenzylphosphine in 1:1 and 1:2 stoichiometric ratios we
have isolated crystalline samples of the three-co-ordinate 1:2
complexes [Cu(PBz3)2X], for X = Cl, Br and I, the two-co-
ordinate 1:1 complex [Cu(PBz3)2][CuCl2] and the three-co-
ordinate dinuclear complex [Cu2(PBz3)Cl2]ؒ3C6H6. These have
been characterized by single crystal X-ray diffraction studies,
solid state 31P CPMAS NMR spectroscopy and by low
frequency vibrational spectroscopy with the outcomes reported
here.
All chemicals were reagent grade or better and solvents were
dried by the usual methods. Solvents were distilled before use
and all reactions were carried out under a dinitrogen atmo-
sphere. Tribenzylphosphine was obtained from the Aldrich
Chemical Co. Copper() halides6 and [Cu(PBz3)2][CuBr2]2 were
prepared according to literature preparations. Microanalyses
were performed by the Campbell Microanalytical Laboratory,
University of Otago. Mass spectra were obtained using a Varian
VG70-250S double-focussing magnetic sector spectrometer by
the method of liquid secondary ion mass spectroscopy
(LSIMS) using m-nitrobenzyl alcohol as the matrix. Isotope
abundance calculations were performed to identify the ions.
Preparation of the complexes
[Cu(PBz3)2Cl]. CuCl (0.038 g, 0.383 mmol) and PBz3 (0.34 g,
1.125 mmol) were refluxed in 10 mL of chloroform for 15
min and the resulting solution was cooled then filtered. The
chloroform was removed using a rotary evaporator and the
white solid recrystallised from 20:1 ethanol–acetone (ca. 10
mL) to give 0.21 g (77%) of colourless crystals, mp 147–155 ЊC
(Found: C, 71.49; H, 5.97. Calc. for C42H42ClCuP2: C, 71.28; H,
5.96%).
[Cu(PBz3)2Br]. CuBr (0.108 g, 0.75 mmol) and PBz3 (0.685 g,
2.25 mmol) were refluxed in 15 mL acetonitrile for 3 h and the
resulting solution was cooled then filtered. The filtrate was
allowed to stand overnight to produce 0.324 g (57%) of colour-
less crystals of the product, which were filtered off and dried
144
J. Chem. Soc., Dalton Trans., 2001, 144–151
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b007698h

View Article Online
in vacuo, mp 140–143 ЊC (Found: C, 67.33; H, 5.75; Br, 10.52.
Calc. for C42H42BrCuP2: C, 67.07; H, 5.63; Br, 10.62%).
α = 94.710(5), β = 97.485(4), γ = 95.759(5)Њ, U = 1453.1(8) Å3,
T = 163 K, Z = 2, µ(Mo-Kα) = 0.918 mmϪ1, 17080 reflections
measured, 5107 unique (Rint = 0.0646) which were used in
all calculations. The final wR2 = 0.1187, R1 = 0.0933,
R1[I > 2σ(I)] = 0.0502.
[Cu(PBz3)2I]. CuI (0.143 g, 0.75 mmol) and PBz3 (0.685 g,
2.25 mmol) were refluxed in 15 mL of acetonitrile for 3 h and
on cooling crystals of the product formed, which were filtered
off and dried in vacuo. The yield was 0.37 g (62%), mp 171–
173 ЊC (Found: C, 62.85; H, 5.04. Calc. for C42H42ICuP2: C,
63.12; H, 5.30%). The above product was formed even if a 1:1
ratio of CuI to PBz3 was used.
X-Ray analysis. Data collection, reduction, solution and
refinement were performed as previously described.8,9 However,
refinement of [Cu(PBz3)2][CuCl2] presented several challenges.
¯
Refinement in rhombohedral space groups (R3, R3, for which
¯
data merged poorly) and in triclinic space groups (P1 and P1)
[Cu(PBz3)2][CuCl2]. To a stirred suspension of CuCl (0.143 g,
1.5 mmol) in 10 mL of chloroform was added PBz3 (0.463 g,
1.52 mmol) in 10 mL of the same solvent, and the mixture
refluxed until the CuCl had dissolved (ca. 10 min). The solution
was cooled, filtered and the volume reduced by half using a
rotary evaporator. Hexane (45 mL) was added and the solution
left to stand overnight. The resulting white powder was filtered
off and recrystallized from 2:1 acetone–ethanol (about 50 mL)
to yield 0.5 g (83%) of colourless crystals of the product, mp
199–202 ЊC (Found: C, 62.29; H, 5.20. Calc. for C21H21ClCuP:
C, 62.53; H, 5.25%).
If the above reaction was carried out in refluxing acetonitrile
(30 mL) for 3 h using the same reagents, colourless crystals of
tribenzylphosphine oxide (0.3 g, 63% yield), mp 219–222 ЊC
(lit.7 217 ЊC), were obtained on cooling (Found: C, 78.34; H,
6.40. Calc. for C21H21OP: C, 78.73; H, 6.61%). m/z 321 (MHϩ,
100) and 641 (M2Hϩ, 7%).
died with R1 ≈ 0.28. Refinements assuming three-fold twinning
(trilling) lead to improved values for R1. The penultimate
model, with twin matrix 0 -1 0 0 0 1 1 0 0, led to values for wR2
and R1 (data for which F > 4σ( F )) of 0.328 and 0.107. At this
stage, (i) seven reflections for which F(calc.) Ӷ F(obs.) were
omitted, (ii) restraints on eccentricity of atomic displacement
parameters were introduced, and (iii) two peaks 2.15 Å from
each copper atom were assigned as alternative orientations of
the [Cu(PBz3)2]ϩ and [CuCl2]Ϫ moieties with a fixed thermal
parameter (U = 0.04 Å, similar to Uequiv of the major P and Cl
atoms) and occupancy set to the complement of the occupancy
of the major component, which was refined as a free variable.
Final values for wR2 and R1 were 0.2428 and 0.0924. The
occupancy of the major component is 0.945(7). No attempt was
made to model the alternative orientation of the benzyl
moieties of the tribenzylphosphine. Unit cell contents given are
corrected to whole numbers for C and H atoms. Although
modelled successfully as an alternative orientation, at least from
the perspective of least-squares refinement and absence of
residual electron density above the noise level of the final
difference Fourier map, the peaks are probably artifacts arising
from the alternative trigonal twin law.
[Cu2(PBz3)2Cl2]ؒ3C6H6. [Cu(PBz3)2][CuCl2] (0.457 g, 0.565
mmol) was dissolved in 20 mL of boiling benzene and left to
stand overnight. The resulting crystals of the product were
filtered off and quickly air-dried, since they readily lost benzene
over a short time (3–4 h), reverting to the ionic form [Cu-
(PBz3)2][CuCl2]. The pure dimeric product melted at 45–48 ЊC,
solidified at ca. 75 ЊC and then melted again at 173–175 ЊC as
the solvated benzene was removed. It was not possible to obtain
analytical data corresponding to the trisolvate (e.g. Found: C
66.15; H 5.75% corresponds to ca. 0.75 mol of benzene per
dimeric unit. Calc. 66.16; H 5.51%).
CCDC reference number 186/2263.
See http://www.rsc.org/suppdata/dt/b0/b007698h/ for crystal-
lographic files in .cif format.
Spectroscopy
Far-infrared spectra were recorded at 4 cmϪ1 resolution at room
temperature as Polythene discs on a Digilab FTS-60 Fourier
transform infrared spectrometer employing an FTS-60V
vacuum optical bench with a 5 line mmϪ1 wire mesh beam
splitter, a mercury lamp source and a pyroelectric triglycine
sulfate detector. Raman spectra were recorded at 4.5 cmϪ1
resolution using a Jobin–Yvon V1000 spectrometer equipped
with a cooled photomultipler (RCA C31034A) detector. The
514.5 nm exciting line from a Spectra physics Model 2016
argon–ion laser was used.
Crystallography
Crystal data. [Cu(PBz3)2Cl]. C42H42ClCuP2, M = 707.69,
monoclinic, space group C2/c, a = 25.4813(3), b = 12.2113(1),
c = 25.1532(3) Å, β = 109.571(1)Њ, U = 7374.5(1) Å3, T = 291 K,
Z = 8, µ(Mo-Kα) = 0.780 mmϪ1, 21077 reflections measured,
7955 unique (Rint = 0.0153) which were used in all calculations.
The final wR2 = 0.0906, R1 = 0.0410, R1[I > 2σ(I)] = 0.0328.
[Cu(PBz3)2Br]. C42H42BrCuP2, M = 752.15, monoclinic,
space group P21/n, a = 22.7747(4), b = 14.4082(2), c = 23.4308(5)
Å, β = 100.986(1)Њ, U = 7547.7(2) Å3, T = 291 K, Z = 8, µ(Mo-
Kα) = 1.750 mmϪ1, 43932 reflections measured, 16605 unique
(Rint = 0.0205) which were used in all calculations. The final
wR2 = 0.0938, R1 = 0.0668, R1[I > 2σ(I)] = 0.0388.
[Cu(PBz3)2I]. C42H42ICuP2, M = 799.14, monoclinic, space
group P21/n, a = 10.001(2), b = 14.529(3), c = 26.330(5) Å,
β = 94.68(3)Њ, U = 3813(1) Å3, T = 291 K, Z = 4, µ(Mo-
Kα) = 1.494 mmϪ1, 13921 reflections measured, 6717 unique
(Rint = 0.0377) which were used in all calculations. The final
wR2 = 0.1202, R1 = 0.0860, R1[I > 2σ(I)] = 0.0409.
31P CPMAS solid state NMR spectra were acquired at room
temperature operating at a field strength of B0 = 9.40 T and a
31P Zeeman frequency (νP) of 162.92 MHz. Conventional cross
polarisation10 and magic angle spinning techniques,11 coupled
with spin temperature alternation to eliminate spectral
artifacts,12 were implemented using a Bruker 4 mm double air
bearing probe in which MAS frequencies ≥ 10 kHz were
achieved. A recycle delay of 20 s, a 1H–31P contact period of 10
1
ms and a H π/2 pulse length of 3 µs were common to all
spectra. No spectral smoothing was invoked prior to Fourier
transformation. Two-dimensional correlation spectroscopy
(COSY) experiments were implemented with the time-
proportional phase incrementation (TPPI) method13 for
acquisition of phase-sensitive data in both F1 and F2 dimen-
sions. The application of this technique has been discussed in
detail elsewhere.14 The recycle delay, contact period, 1H π/2
pulse length and MAS spinning rate were the same as those
implemented for the one-dimensional experiments. A total
of 256 F1 increments were acquired into 256 word F2 blocks,
with both dimensions zero filled to 1 K words and weighted
with sine bell apodization prior to Fourier transformation. The
[Cu(PBz3)2][CuCl2]. C42H42Cl2Cu2P2, M = 806.68, triclinic,
¯
space group P1, a = 9.7619(3), b = 9.7619(3), c = 9.7619(3) Å,
α = 90.02(3), β = 90.02(3), γ = 90.02(3)Њ, U = 930.26(5) Å3,
T = 203 K, Z = 1, µ(Mo-Kα) = 1.402 mmϪ1, 3522 reflections
measured, 2429 unique (Rint = 0.0146) which were used in
all calculations. The final wR2 = 0.2428, R1 = 0.0924,
R1[I > 2σ(I)] = 0.0894.
[Cu2Cl2(PBz3)2]ؒ3C6H6. C33H33ClCuP, M = 559.55, triclinic,
¯
space group P1, a = 9.902(3), b = 10.432(4), c = 14.326(5) Å,
J. Chem. Soc., Dalton Trans., 2001, 144–151
145

View Article Online
31P chemical shifts for all experiments were externally referenced
to external solid triphenylphosphine which exhibits a chemical
shift of Ϫ9.9 ppm with respect to 85% H3PO4.
Results and discussion
Synthesis
The reaction of CuX with PBz3 in a 1:2 mole ratio in chloro-
form (X = Cl) or acetonitrile (X = Br or I) yielded the 1:2 com-
plexes [Cu(PBz3)2X], which have been shown by single crystal
X-ray crystallography to contain three-co-ordinate copper()
(see below). In the case of CuCl, if the reaction was carried out
in a 1:1 mole ratio the ionic two-co-ordinate complex, [Cu-
(PBz3)2][CuCl2], was isolated. Attempts to prepare this complex
in acetonitrile following the literature method2 for the bromo
analogue, [Cu(PBz3)2][CuBr2], gave tribenzylphosphine oxide in
good yield. Presumably the oxygen arise from traces in the
solvent implying that CuCl acts as a reagent/catalyst in this
solvent for the oxidation of PBz3. In contrast, under similar
conditions in the presence of CuBr or CuI, this reaction does
not occur to any significant extent. Attempts to prepare a 1:1
iodo complex failed regardless of the CuI:PBz3 molar ratio
used.
When [Cu(PBz3)2][CuCl2] was recrystallized from hot
benzene a product with a low melting point was obtained and
this was shown by X-ray crystallography (see below) to be the
benzene-solvated dimer [Cu2(PBz3)2Cl2]ؒ3C6H6. This product
rapidly loses its solvated benzene and reverts to the ionic form,
suggesting the latter complex is obtained as a dissociation
product of the initially formed dimeric isomer according to
eqn. (1). Dimer species are also observed under the conditions
2CuCl ϩ 2PBz3 → [Cu2(PBz3)2Cl2] →
[Cu(PBz3)2][CuCl2] (1)
used to record the positive ion liquid secondary ionization
mass spectra, although the most prominent peaks† for all the
complexes reported in this study are assigned to the mono-
meric [Cu(PBz3)2]ϩ ion at m/z 671 (100%) and its derivatives,
[Cu(PBz3)]ϩ (367, 60–95%) and [Cu(PBz)]ϩ (185, ≈20%). For
the ionic 1:1 complexes, [Cu(PBz3)2][CuX2] (X = Cl or Br), the
dicopper ions, [Cu2(PBz3)2X]ϩ, are seen with moderate intensity
(X = Cl m/z 771; X = Br 815, ≈20%) as well as weak peaks
assignable to [Cu2(PBz3)2X2]ϩ (X = Cl 806; X = Br 896, ≈3%)
and [Cu3(PBz3)2Cl2]ϩ (869, ≈3%). In contrast, in the mass
spectra of the [Cu(PBz3)2X] 1:2 complexes, the dicopper
[Cu2(PBz3)2X]ϩ peaks, although still observed, are much weaker
(X = Cl m/z 771, 8%; X = Br 815, 3%; X = I 861, 3%). The mass
spectrum of [Cu2(PBz3)2Cl2]ؒ3C6H6 is similar to that seen for
the ionic isomer.
Fig. 1 ORTEP15 diagrams of (a) [Cu(PBz3)2Cl], (b) [Cu(PBz3)2Br]
(Molecule A), (c) [Cu(PBz3)2I]. Ellipsoids are drawn at the 40%
probability level in all figures.
Structural determinations
139.86(3)Њ. The Cu–P distances in the three-co-ordinate mole-
cules vary, with Cu–P(1) being longer in each case [2.2399(5)–
2.2509(7) Å] and Cu–P(2) shorter [2.2127(8)–2.2396(7) Å]. As
well, significant changes in the conformational structure of the
PBz3 ligands occur with co-ordination of the halides. The P(2)
ligand adopts approximately C3 symmetry, similar to that
observed for the two-co-ordinate complexes with the three
phenyl groups oriented towards the copper site (torsion angles
Cu–P(2)–C(2n)–C(2n1) < 90Њ, Table 2). However, in the P(1)
ligand, one phenyl ring is rotated away from the copper atom
such that the torsion angle Cu–P(1)–C(12)–C(121) > 90Њ. For
the chloride complex this ring is trans to the Cu–Cl bond, while
for the iodide complex and both molecules in the bromide
complex it is cis to the Cu–X bond. The P(2)–Cu–X angle is
consistently larger than the P(1)–Cu–X angle, reflecting a
movement of the halide towards the less sterically hindered P(1)
ligand.
The structure determinations of the 1:2 complexes of copper()
halides for X = Cl, Br and I with PBz3 are consistent with their
formulation as monomeric three-co-ordinate [Cu(PBz3)2X]
species. One, two and one molecules constitute the asymmetric
units of the cells for X = Cl, Br and I, respectively. Represent-
ative views of the molecular structures are shown in Fig. 1 with
relevant geometric parameters listed in Table 1. Comparison of
these data with those of the two-co-ordinate [Cu(PBz3)2]X
(X = PF6 or CuBr2) complexes2,3 and [Cu(PBz3)2][CuCl2] (see
below) show that co-ordination of the halide anion to the
copper results in a lengthening of the Cu–P (see footnote e
in Table 1) bond lengths from 2.19–2.20 to 2.21–2.25 Å and a
decrease in the P–Cu–P angles from 180 to 136.53(2)–
† Peaks quoted are for the most abundant isotopomer. Percentages are
relative intensities.
146
J. Chem. Soc., Dalton Trans., 2001, 144–151

View Article Online
Table 1 Geometric parameters (bond lengths in Å and angles in Њ) for two-co-ordinate, [Cu(PBz3)2]X (X = PF6, CuCl2 or CuBr2), and three-co-
ordinate, [Cu(PBz3)2X] (X = Cl, Br or I), complexes
X
Cu–P(1)
Cu–P(2)
Cu–X
P(1)–Cu–P(2)
P(1)–Cu–X
P(2)–Cu–X
Two-co-ordinate
2.191(1)b
2.205(3)b
2.196(1)b
180.0(Ϫ)c
180.0(Ϫ)c
180.0(Ϫ)c
a
PF6
2.191(1)
2.205(3)
2.196(1)
CuCl2 d
2.079(4)
2.2076(8)
2.2077(8)
CuBr2
Three-co-ordinate
Cl 2.2399(5)
2.2275(5)
2.2127(8)
2.2396(7)
2.234(1)
2.2521(6)
2.4034(4)
2.3995(4)
2.5865(8)
136.53(2)
138.92(3)
139.86(3)
139.78(5)
105.34(2)
100.76(2)
106.92(2)
105.11(4)
117.76(2)
119.83(2)
113.09(2)
115.07(4)
e
BrAe
BrB
I
2.2436(7)
2.2509(7)
2.239(1)
a Ref. 3. b Identical due to crystallographically imposed symmetry. c Precisely 180Њ because Cu sits at a centre of symmetry. d Ref. 2. e BrA and BrB refer
to the two different molecules in the asymmetric unit. Hence for Molecule A, to facilitate comparison with the other compounds, the atoms labelled
as Cu(1), P(11) and P(12) in Fig. 1 are referred to as Cu, P(1) and P(2) respectively.
Table 2 Torsion angles (Њ) for two-co-ordinate, [Cu(PBz3)2][CuCl2], and three-co-ordinate, [Cu(PBz3)2X] (X = Cl, Br or I), complexes
a
a
CuCl2
Cl
BrA
BrB
I
Cu–P(1)–C(11)–C(111)
Cu–P(1)–C(12)–C(121)
Cu–P(1)–C(13)–C(131)
Cu–P(2)–C(21)–C(211)
Cu–P(2)–C(22)–C(221)
Cu–P(2)–C(23)–C(231)
Ϫ50(1)
Ϫ53(1)
Ϫ49(1)
50(1)
53(1)
49(1)
49.8(1)
Ϫ58.1(2)
Ϫ142.7(2)
Ϫ56.2(2)
84.9(3)
50.7(3)
162.6(2)
55.1(2)
Ϫ69.2(2)
Ϫ54.7(2)
Ϫ60.3(2)
Ϫ54.8(5)
Ϫ152.9(4)
Ϫ51.2(4)
75.3(4)
174.3(1)
Ϫ49.79(1)
70.1(1)
59.2(1)
55.5(2)
46.0(2)
53.7(3)
52.5(4)
61.9(4)
a See footnote e in Table 1.
Fig. 2 ORTEP diagram of [Cu(PBz3)2][CuCl2].
The single crystal structure of [Cu(PBz3)2][CuCl2] (Fig. 2 and
Tables 1 and 2) confirms that the complex contains discrete
[Cu(PBz3)2]ϩ cations with a linear P–Cu–P co-ordination, as
also observed when the anion is [PF6]Ϫ or [CuBr2]Ϫ.2,3 As in the
other two structures, the phenyl groups of the PBz3 swing back
over the copper atom to generate a sixfold phenyl embrace
(6PE)5 as the hydrogen atoms of each phenyl group are directed
towards the plane of the phenyl group on the opposite ligand.
The structure of the benzene-solvated dimeric complex,
[Cu2(PBz3)2Cl2]ؒ3C6H6, consists of discrete centrosymmetric
dimers separated by co-crystallized benzene molecules (Fig. 3).
However, there are several close contacts between these benzene
molecules and the complex. This is most evident with the
benzene that effectively caps the tribenzylphosphine ligands
(see Fig. 3). Several of the H atoms on the phosphine have close
(3.0–3.5 Å) contacts with the benzene which clearly stabilize
the dimeric nature of the complex. The ‘PCuCl2CuP’ unit is
essentially planar, closely approximating D2h symmetry with
insignificant differences in the Cu–Cl distances or P–Cu–Cl
angles (Table 3). The Cu–P bond length of 2.185(1) Å is similar
Fig. 3 ORTEP diagram of [Cu2(PBz3)2Cl2]ؒ3C6H6. One C6H6 molecule
of solvation is included.
to those observed for other 1:1 dimeric complexes (Table 3) and
slightly shorter than the distances of 2.19–2.20 Å observed for
the two-co-ordinate 1:2 complexes and of 2.21–2.25 Å for the
three-co-ordinate 1:2 complexes. The PBz3 ligand adopts the C3
conformation observed for the two-co-ordinate complexes, with
the phenyl groups oriented towards the ‘CuCl2Cu’ core [torsion
angles Cu–P–C(n)–C(n1): 57.9(3), 64.4(3), 70.2(3)Њ], although
the two ligands are not close enough to interact.
Solid state 31P CPMAS NMR spectroscopy
The 1-D 31P CPMAS NMR spectra for the complexes studied
in this work are shown in Fig. 4 with the 2-D spectra for the
chloride and bromide 1:2 complexes in Fig. 5. The NMR
parameters derived from these spectra are listed in Table 4. The
results obtained are similar to those reported for other
copper() phosphine complexes under high magnetic field
J. Chem. Soc., Dalton Trans., 2001, 144–151
147

View Article Online
Table 3 Geometric parameters (bond lengths in Å and angles in Њ) for dimeric [Cu2(PR3)2Cl2] complexes
PR3
Cu–P
Cu–Cl
Cl ؒ ؒ ؒ Cl
Cu ؒ ؒ ؒ Cu
Cu–Cl–Cu
P–Cu–Cl
Cl–Cu–Cl
PBz3
2.185(1)
2.191(1)
2.183(2)
2.305(1)
2.302(1)
2.289(2)
2.316(2)
2.285(2)
2.322(2)
3.439(1)
3.402(2)
3.439(3)
3.065(1)
3.103(1)
3.066(1)
83.41(4)
84.74(6)
83.44(7)
131.14(4)
132.07(4)
132.47(6)
131.98(6)
127.40(7)
136.05(7)
96.59(4)
95.26(5)
95.56(7)
a
P(o-Tol)3
b
PCy3
a Ref. 16, P(o-Tol)3 = tris(2-methylphenyl)phosphine. b Ref. 17, PCy3 = tris(cyclohexyl)phosphine.
Table 4 31P CP-MAS NMR data for two-co-ordinate, [Cu(PBz3)2]X, and three-co-ordinate, [Cu(PBz3)2X], complexes at B0 = 9.40 T
a
δiso
∆21/kHz
∆32/kHz
∆43/kHz
1J/kHz
d/kHz
d1/kHz
dνCu/109 Hz2
Two-co-ordinate
[Cu(PBz3)2][CuCl2]
29.6
30.9
29.9
1.00
1.03
0.98
1.63
1.58
1.66
1.92
1.91
1.93
1.54
1.52
1.56
0.23
0.22
0.24
0.05
0.03
0.05
24.3
23.3
25.4
[Cu(PBz3)2][CuBr2]b
b
[Cu(PBz3)2]PF6
Three-co-ordinate
[Cu(PBz3)2Cl]
6.8
Ϫ3.5
6.3
1.8
4.2
1.15
1.00
1.30
1.03
1.09
1.09
1.41
1.23
1.46
1.26
1.39
1.37
1.64
1.37
1.60
1.50
1.58
1.56
1.41
1.23
1.46
1.26
1.36
1.34
0.12
0.09
0.08
0.12
0.12
0.12
0.01
0.02
0.00
0.00
0.02
0.02
13
10
8
12
13
12
[Cu(PBz3)2Br] (A)c
[Cu(PBz3)2Br] (B)c
[Cu(PBz3)2I]
6.0
a The average chemical shift, with respect to free PPh3, of the centre points of the four lines of the quartet (δ1 ϩ δ2 ϩ δ3 ϩ δ4)/4. The values can be
transformed to chemical shifts with respect to 85% H3PO4 by subtraction of 9.9 ppm. b Ref. 3. c See footnote e in Table 1.
Fig. 4 1-D Solid state 31P CPMAS NMR spectra of (a) [Cu(PBz3)2Cl],
(b) [Cu(PBz3)2Br], (c) [Cu(PBz3)2I], (d) [Cu(PBz3)2][CuCl2].
(B0 > ≈7 T) and slow 63,65Cu relaxation conditions14,18–20 in that
they consist of asymmetric quartets arising from quadrupolar
perturbed scalar (J) and dipolar coupling between the spin 1/2
31P and spin 3/2 63,65Cu nuclei. The linewidths are too broad
to resolve the J-coupled multiplets attributed to each copper
isotope and the spectra are dominated by 31P resonances
associated with the more abundant 63Cu nuclei. The linewidth
2
is too broad also to resolve geminal J(31P–31P) coupling. The
Fig. 5 2-D Solid state 31P CPMAS COSY NMR spectra of (a) [Cu-
(PBz3)2Cl], (b) [Cu(PBz3)2Br].
overlap of the peaks in each quartet precludes accurate
148
J. Chem. Soc., Dalton Trans., 2001, 144–151

View Article Online
measurement of the chemical shift and line spacing data from
the 1-D spectra, but reasonable values of these parameters have
been estimated from the two-dimensional 31P CPMAS COSY
spectra which separate the two 1J(P–Cu) coupled quartets
above and below the main diagonal (Fig. 5). For the three-co-
ordinate [Cu(PBz3)2X] (X = Cl, Br or I) complexes, the average
chemical shifts of δ 2–7 represent a significant upfield shift from
the value of δ ca. 30 observed for the ionic two-co-ordinate
[Cu(PBz3)2]X (X = PF6, CuCl2 or CuBr2) complexes. For [Cu-
(PBz3)2Cl], the quartets centred at δ 6.8 and Ϫ3.5 [Fig. 5(a)]
are assigned to P(2) and P(1) respectively on the basis of correl-
1
ation of the J(31P–63Cu) coupling constants of 1.41 and 1.23
kHz with the shorter and longer Cu–P bond lengths. For [Cu-
(PBz3)2Br], two distinct AB patterns are expected for each of
the two crystallographically independent molecules in the
crystal lattice. However, only three quartets can be identified in
the spectra of the complex (Fig. 4). The 2-D spectra show two
multiplets (at δ 6.3 and 1.8) to be 2J(31P–31P) coupled with
1J(31P–63Cu) values of 1.46 and 1.26 kHz which are assigned to
P(2) and P(1) of molecule A on the basis of the significant
differences in the Cu–P(1,2) bond lengths. The third, more
intense quartet at δ 4.2, is assigned as an unresolved but
strongly AB-coupled pair of quartets from the two P atoms of
molecule B, the similar chemical shifts values being consistent
with the small differences in the Cu–P bond lengths found
for this molecule. For [Cu(PBz3)2I], one quartet only is observed
and, as for molecule B of the bromide complex, is assigned
as an unresolved but strongly AB coupled pair of quartets,
consistent with the similar Cu–P distances in this complex.
Fig. 6 Far-IR spectra of the 1:1 complexes: (a) [Cu2(PBz3)2Cl2]ؒ
3C6H6; (b) [Cu2(PBz3)2Cl2]ؒ3C6H6 during its conversion into [Cu-
(PBz3)2][CuCl2]; (c) [Cu(PBz3)2][CuCl2] formed from [Cu2Cl2(PBz3)2]ؒ
3C6H6 by complete removal of C6H6; (d) [Cu(PBz3)2][CuBr2]. The
ν(CuCl) bands in (a) and the bands due to [CuX2]Ϫ in (c) and (d) are
labeled with their wavenumbers.
1
The values of J(31P–63Cu) of 1.2–1.4 kHz for these three-co-
ordinate complexes are significantly smaller than the 1.52–1.56
kHz recorded for the two-co-ordinate complexes,3,18 reflecting
transfer of electron density away from the Cu–P bonds with co-
ordination of the halide.
The spacings between the lines of each quartet are not
symmetric but show a significant increase in the upfield
direction. This phenomenon arises from perturbation of
the simple J spectrum by dipolar interactions between the
phosphorus and the quadrupolar copper nuclei. First order
analysis21 predicts a field dependent shift of the outer two lines
upfield and the inner two lines (δ2, δ3) downfield by a magnitude
d such that (∆32 Ϫ ∆21) = (∆43 Ϫ ∆32) = 2d, from which d =
(∆43 Ϫ ∆21)/4. Multiplication of
d
by the 63Cu Zeeman
frequency yields a field-independent parameter dνCu that is
suitable for comparison of results obtained from spectra
recorded at different field strengths.
The first-order analysis also generates eqn. (2) for dνCu where
χCu = e2qQ/h is the 63Cu quadrupolar coupling constant,
dνCu = (3χCuDeff/20)(3cos2βD Ϫ 1 ϩ ηsin2βDcos 2αD) (2)
Fig. 7 Far-IR spectra of the 1:2 complexes: (a) [Cu(PBz3)2Cl], (b)
[Cu(PBz3)2Br], (c) [Cu(PBz3)2I], (d) [Cu(PBz3)2]PF6. The ν(CuX) bands
are labeled with their wavenumbers.
Deff = (D Ϫ ∆J/3) (D = (µ0/4π)γPγCuh/4π2r3 is the Cu–P dipolar
coupling constant and ∆J is the anisotropy in the J tensor),
η is the asymmetry parameter of the electric field gradient
(EFG) tensor, and αD and βD are the polar angles defining the
direction of the Cu–P internuclear vector with respect to the
principal axial system (PAS) of the EFG tensor. In practice,
higher order quadrupole effects22,23 result in the line spacings
deviating from this first order model with (∆32 Ϫ ∆21) >
2d > (∆43 Ϫ ∆32). These effects are generally small and are
recorded for the present compounds as upfield shifts of peaks
1 and 3 and a downfield shift of peaks 2 and 4 by a correction
term of magnitude d1 such that ∆21 = J Ϫ 2d Ϫ 2d1, ∆32
J ϩ 2d1 and ∆43 = J ϩ 2d Ϫ 2d1; from which d = (∆43 Ϫ ∆21)/4 as
before, d1 = (∆32 Ϫ J)/2 while J = (∆21 ϩ 2∆32 ϩ ∆43)/4.
For the present three-co-ordinate complexes, dνCu values
range from 8 × 10Ϫ9 to 13 × 109 Hz2 and are very similar to
the values of (10–11) × 109 Hz2 found for [Cu(PPh3)2X]
complexes24 and (6–10) × 109 Hz2 found for [Cu{PPh2(o-
Tol)})2X] complexes.25 These results suggest that for these
structurally related complexes the 63Cu NQR frequencies are
likely to be comparable to the values of 33.17 and 33.93 MHz
recorded for [Cu(PPh3)2Cl] and [Cu(PPh3)2Br].26
Vibrational spectroscopy
The far-IR spectra of the 1:1 and 1:2 complexes are shown in
Figs. 6 and 7 respectively. The spectra contain a number of
bands due to the co-ordinated PBz3, but comparison with the
spectrum of uncomplexed PBz3 allows assignments of the
bands due to the ν(CuX) modes of the neutral complexes and
those of the [CuX2]Ϫ ions in the ionic complexes. These assign-
ments are compared with those for some related compounds in
Table 5.
=
The spectra in Fig. 6(a)–6(c) show the conversion from
[Cu2(PBz3)2Cl2]ؒ3C6H6 into [Cu(PBz3)2][CuCl2] that occurs with
loss of benzene of solvation during recording of the spectrum
J. Chem. Soc., Dalton Trans., 2001, 144–151
149

View Article Online
Table 5 Bond lengths d(CuX) and vibrational frequencies ν(CuX) for
two-co-ordinate [Cu(PBz3)2]X, three-co-ordinate [Cu(PBz3)2X] and
related complexes
bond lengths by the previously reported empirical relationship
between these quantities.30 The ionic complex [Cu(PBz3)2]PF6
shows a partially split band at 555 and 557 cmϪ1 due to the
Ϫ 31
ν4(T1u) mode of PF6
,
together with bands due to the co-
Compound
d(CuX)/Å
ν(CuX)/cmϪ1
ordinated PBz3 (Fig. 7). These latter bands show essentially the
same frequencies and relative intensities as those of the 1:1
complexes [Cu(PBz3)2][CuX2] (Fig. 6), confirming the ionic
nature of these complexes.
[Cu2(PBz3)2Cl2]
2.302(1), 2.305(1)
2.289(2), 2.316(2)
2.079(4)
230, 208
237, 207
409 (IR)
404 (IR), 304 (Raman)
[Cu2{P(o-Tol)3}2Cl2]a
[Cu(PBz3)2][CuCl2]
[NBun ][CuCl2]b
2.107(1)
In addition to the ν(CuX) and anion bands, these complexes
should in principle show bands due to the ν(CuP) vibrations,
but these are more difficult to assign. Previous ν(MP) assign-
ments for Group 11 metal phosphine complexes (132 cmϪ1 in
[Ag(PPh3)2Br]; 160 cmϪ1 in [Au(PPh3)2Br]; 107, 121 cmϪ1 in
[Cu(PPh3)3Cl]; 174 cmϪ1 in [Cu4(PMe3)3Cl4])32–34 suggest that
these occur in the range 100–180 cmϪ1. The only evidence of a
possible ν(CuP) band in this region for the present complexes is
the band at 170 cmϪ1 in the far-IR spectrum of [Cu(PBz3)2Br]
(Fig. 7). The ν(MP) modes are normally only observed in the
Raman spectra,32–34 but they can also occur in the IR when the
frequencies of the ν(MP) and ν(MX) are similar, so that mixing
of these two vibrations can occur. This possibly occurs in
[Cu(PBz3)2Br], in a situation similar to that previously observed
for [Au(PMe3)Br].35
4
[Cu(PBz3)2][CuBr2]
2.2076(8), 2.2027(8) 326 (IR), 196 (Raman)
[NBun ][CuBr2]b
2.226(1)
2.2521(6)
2.208(2)
321 (IR), 191 (Raman)
262
298
4
[Cu(PBz3)2Cl]
[Cu(PPh3)2Cl]c
[Cu(PBz3)2Br]
[Cu(PPh3)2Br]c
[Cu(PBz3)2I]
2.3995(4), 2.4034(4) 183
2.346(2)
2.5865(8)
2.524(2)
218
153
184
[Cu(PPh3)2I]d
a Ref. 16. b Refs. 27 and 28. c Refs. 24 and 29. d Ref. 24.
of the former compound. This series of spectra allows the
unambiguous assignment of the two bands at 230 and 208 cmϪ1
in the spectrum of [Cu2(PBz3)2Cl2]ؒ3C6H6 to the ν(CuCl) modes
of the ‘Cu2Cl2’ moiety in this complex. These are very similar
to the values 237 and 207 cmϪ1 reported previously16 for the
structurally related complex, [Cu2{P(o-Tol)3}2Cl2] (see Table 5).
The ideal point group symmetry of the isolated dimer
[Cu2L2X2] is D2h. The symmetry types and activities of the
fundamentals due to vibrations of the D2h Cu2X2 core (x paral-
lel to the Cu ؒ ؒ ؒ Cu diagonal, y parallel to the X ؒ ؒ ؒ X diagonal)
are 2Ag(R) ϩ B1g(R) ϩ B1u(IR) ϩ B2u(IR) ϩ B3u(IR). These
involve contributions from CuX bond stretching ν(CuX)
(Ag ϩ B1g ϩ B2u ϩ B3u) and in-plane (Ag) and out-of-plane
(B1u) deformation. Thus two IR-active ν(CuX) modes of B2u
and B3u symmetry are predicted for this structure. For a
perfectly square ‘Cu2X2’ unit the two IR-active normal modes
involve displacement of X and Cu along the positive and
negative x directions respectively (B3u) or a similar vibration in
the y direction (B2u). For an isolated square ‘Cu2X2’ unit these
two modes would have the same frequency. A distortion in
which two angles on opposite corners of the square are
decreased and the other two are increased results in no change
of symmetry, but leads to a separation in frequency of the two
ν(CuX) IR modes. This is possibly part of the reason for the
splitting of the two ν(CuCl) bands in [Cu2L2Cl2] for which the
Cu–Cl–Cu and Cl–Cu–Cl angles are 83.41(4), 96.59(4)Њ
(L = PBz3) and 84.74(6), 95.26(5)Њ [L = P(o-Tol)3].16 Another
possible cause of the splitting is the inequality of the strengths
of the two inequivalent Cu–Cl bonds in the ‘Cu2Cl2’ units,
which is reflected in the different Cu–Cl bond lengths (Table 5).
This inequivalence is less for the L = PBz3 than for the L = P-
(o-Tol)3 complex, which is consistent with the greater difference
in the two ν(CuCl) frequencies observed for the latter (Table 5).
For the ionic complexes [Cu(PBz3)2][CuX2] (X = Cl or Br)
three vibrational bands are expected for the [CuX2]Ϫ ion: two
ν(CuX) modes [ν1(R); ν3(IR)] and one δ(XCuX) mode [ν2(IR)].
All three of these are observed for the X = Br case, but the ν1
mode is obscured by ligand bands in the Raman spectrum of
the X = Cl compound. The ν(CuX) values are about 5 cmϪ1
Conclusion
The present study shows that the reaction of copper() halides
with tribenzylphosphine in a 1:2 stoichiometric ratio results in
the formation of crystalline three-co-ordinate [Cu(PBz3)2X]
complexes with co-ordination of the halide disrupting the
intramolecular sixfold phenyl embrace observed between the
two ligands for ionic [Cu(PBz3)2]ϩ with non-co-ordinating
anions. It has also provided good evidence that the formation
of [Cu(PBz3)2][CuX2] salts for X = Cl or Br is likely to proceed
through a dimeric intermediate, [Cu2(PBz3)2X2], but that for
X = I only the 1:2 complex is formed under all stoichiometric
ratios.
Acknowledgements
We acknowledge support of this work by grants from the New
Zealand Lottery Grants Board, Massey University, the
University of Auckland Research Committee, the Australian
Research Council and the Australian Institute of Nuclear
Science and Engineering (AINSE) for funding of AINSE
Project No. 00/064.
References
1 B. J. Hathaway, in Comprehensive Coordination Chemistry, eds.
G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon Press,
Oxford, 1987, vol. 5, p. 533 and references therein.
2 P. D. Akrivos, P. P. Karagiannidis, C. P. Raptopoulou, A. Terzis and
S. Stoyanov, Inorg. Chem., 1996, 35, 4082.
3 E. W. Ainscough, A. M. Brodie, A. K. Burrell, J. V. Hanna, P. C.
Healy and J. M. Waters, Inorg. Chem., 1999, 38, 201.
4 A. Bayler, A. Schier, G. A. Bowmaker and H. Schmidbaur, J. Am.
Chem. Soc., 1996, 118, 7006.
5 M. Scudder and I. Dance, J. Chem. Soc., Dalton Trans., 1998, 3155;
M. Scudder and I. Dance, J. Chem. Soc., Dalton Trans., 1998, 3167.
6 R. N. Keller and H. D. Wycoff, Inorg. Synth., 1946, 2, 1; G. B.
Kauffman and R. P. Pinnell, Inorg. Synth., 1960, 6, 3.
7 V. Ettel and J. Horak, Collect. Czech. Chem. Commun., 1961, 26,
1949.
higher than those previously reported for [NBun ][CuX2], which
4
is consistent with the slightly shorter Cu–X bond lengths in the
former complexes (Table 5). The δ(XCuX) frequencies (107 and
79 cmϪ1 for X = Cl and Br respectively) are slightly lower than
those in [NBun ][CuX2] (111 and 81 cmϪ1).28
4
The 1:2 complexes [Cu(PBz3)2X] (X = Cl, Br or I) show
halogen-sensitive bands at 262, 183 and 153 cmϪ1 respectively,
which are readily assigned as the ν(CuX) modes (Fig. 7). The
frequencies of these modes are significantly lower than those of
the corresponding PPh3 complexes,24,29 which is consistent with
the trend in the Cu–X bond lengths (Table 5). The observed
frequencies agree reasonably well with those predicted from the
8 M. R. Waterland, T. J. Simpson, K. C. Gordon and A. K. Burrell,
J. Chem. Soc., Dalton Trans., 1998, 185.
9 G. M. Sheldrick, SHELXL 97, Universität Göttingen, 1997.
10 A. Pines, M. G. Gibby and J. S. Waugh, J. Chem. Phys., 1973, 59,
569.
11 E. R. Andrew, A. Bradbury and R. Eades, Nature (London), 1958,
182, 1659.
12 E. O. Stejskal and J. Schaefer, J. Magn. Reson., 1975, 18, 560.
150
J. Chem. Soc., Dalton Trans., 2001, 144–151

View Article Online
25 G. A. Bowmaker, L. M. Engelhardt, P. C. Healy, J. D. Kildea, R. I.
Papasergio and A. H. White, Inorg. Chem., 1987, 26, 3533.
26 T. Okuda, M. Hiura and H. Negita, Bull. Chem. Soc. Jpn., 1981, 54,
1920; T. Okuda, M. Hiura, K. Yamada and H. Negita, Chem. Lett.,
1977, 367.
13 G. Bodenhausen, R. L. Vold and R. R. Vold, J. Magn. Reson., 1980,
37, 93; D. Marion and K. Wuethrich, Biochem. Biophys. Res.
Commun., 1983, 113, 967; T. Allman, J. Magn. Reson., 1989, 83, 637.
14 J. V. Hanna, M. E. Smith, S. N. Stuart and P. C. Healy, J. Phys.
Chem., 1992, 96, 7560.
15 C. K. Johnson, ORTEPII, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
16 G. A. Bowmaker, J. V. Hanna, R. D. Hart, P. C. Healy and A. H.
White, Aust. J. Chem., 1994, 47, 25.
27 M. Asplund, S. Jagner and M. Nilsson, Acta Chem. Scand., Ser. A,
1983, 37, 57.
28 G. A. Bowmaker, L. D. Brockliss and R. Whiting, Aust. J. Chem.,
1973, 26, 29.
17 M. R. Churchill and F. J. Rotella, Inorg. Chem., 1979, 18, 166.
18 S. Kroeker, J. V. Hanna, R. E. Wasylichen, E. W. Ainscough and
A. M. Brodie, J. Magn. Reson., 1998, 135, 308.
19 J. V. Hanna, R. D. Hart, P. C. Healy, B. W. Skelton and A. H. White,
J. Chem. Soc., Dalton Trans., 1996, 2321.
20 G. A. Bowmaker, Effendy, J. V. Hanna, P. C. Healy, J. C. Reid,
C. E. F. Rickard and A. H. White, J. Chem. Soc., Dalton Trans.,
2000, 753.
21 A. Olivieri, J. Am. Chem. Soc., 1992, 114, 5788.
22 E. M. Menger and W. S. Veeman, J. Magn. Reson., 1982, 46, 257.
23 S. H. Alarcon, A. C. Olivieri and R. K. Harris, Solid State Nucl.
Magn. Reson., 1993, 2, 325.
29 G. A. Bowmaker and D. A. Rogers, J. Chem. Soc., Dalton Trans.,
1984, 1249.
30 G. A. Bowmaker, P. C. Healy, J. D. Kildea and A. H. White,
Spectrochim. Acta, Part A, 1988, 44, 1219.
31 K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, Wiley, New York, 5th edn., 1997, Part A,
p. 216.
32 G. A. Bowmaker, Effendy, J. V. Hanna, P. C. Healy, B. W. Skelton
and A. H. White, J. Chem. Soc., Dalton Trans., 1993, 1387.
33 G. A. Bowmaker, R. D. Hart, E. N. de Silva, B. W. Skelton and
A. H. White, Aust. J. Chem., 1997, 50, 553.
34 G. A. Bowmaker, R. D. Hart, B. E. Jones, B. W. Skelton and A. H.
White, J. Chem. Soc., Dalton Trans., 1995, 3063.
35 K. Angermaier, G. A. Bowmaker, E. N. de Silva, P. C. Healy, B. E.
Jones and H. Schmidbaur, J. Chem. Soc., Dalton Trans., 1996, 3121.
24 G. A. Bowmaker, J. C. Dyason, P. C. Healy, L. M. Engelhardt,
C. Pakawatchai and A. H. White, J. Chem. Soc., Dalton Trans.,
1987, 1089.
J. Chem. Soc., Dalton Trans., 2001, 144–151
151