Mechanochemical and solution synthesis, X-ray structure and IR and 31P solid state NMR spectroscopic studies of copper(i) thiocyanate adducts with bulky monodentate tertiary phosphine ligands

Article abstract of DOI:10.1039/c2dt30579h

A number of adducts of copper(i) thiocyanate with bulky tertiary phosphine ligands, and some nitrogen-base solvates, were synthesized and structurally and spectroscopically characterised. CuSCN:PCy₃ (1:2), as crystallized from pyridine, is shown by a single crystal X-ray study to be a one-dimensional polymer.(Cy₃P)₂CuSCN(Cy₃P)₂CuSCN. (1) with the four-coordinate copper atoms linked end-on by S-SCN-N bridging thiocyanate groups. A second form (2), obtained from acetonitrile, was also identified and shown by IR and ³¹P CPMAS NMR spectroscopy to be mononuclear, with the magnitude of the dν_Cu parameter measured from the ³¹P CPMAS and the ν(CN) value from the IR clearly establishing this compound as three-coordinate [(Cy₃P) ₂CuNCS]. Two further CuSCN/PCy₃ compounds CuSCN:PCy ₃ (1:1) (3), and CuSCN:PCy₃:py (1:1:1) (4) were also characterized spectroscopically, with the dν_Cu parameters indicating three- and four-coordinate copper sites, respectively. Attempts to obtain a 1:2 adduct with tri-t-butylphosphine have yielded, from pyridine, the 1:1 adduct as a dimer [(But3P)(SCNNCS)Cu(PBut3)] (5), while similar attempts with tri-o-tolylphosphine (from acetonitrile and pyridine (= L)) resulted in solvated 1:1:1 CuSCN:P(o-tol)₃:L forms as dimeric [{(o-tol) ₃P}LCu(SCNNCS)CuL{P(o-tol)₃}] (6 and 8). The solvent-free 1:1 CuSCN:P(o-tol)₃ adduct (7), obtained by desolvation of 6, was characterized spectroscopically and dν_Cu measurements from the ³¹P CPMAS NMR data are consistent with the decrease in coordination number of the copper atom from four (for 6) (P,N(MeCN)Cu,S,N) to three (for 7) (PCuS,N) upon loss of the acetonitrile of solvation. These results are compared with those previously reported for mononuclear and binuclear PPh₃ adducts which demonstrate a clear tendency for the copper centre to remain four-coordinate. The IR spectroscopic measurements on these compounds show that bands in the far-IR spectra provide a much more definitive criterion for distinguishing between bridging and terminal bonding than does an often-used empirical rule based on ν(CN) in the mid-IR, which leads to the wrong conclusion in some cases.

Full text of DOI:10.1039/c2dt30579h

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PAPER
Mechanochemical and solution synthesis, X-ray structure and IR and
31P solid state NMR spectroscopic studies of copper(I) thiocyanate adducts
with bulky monodentate tertiary phosphine ligands†
Graham A. Bowmaker,*a John V. Hanna,*b Robert D. Hart,c Peter C. Healy,d Scott P. King,b Fabio Marchetti,e
Claudio Pettinari,*f Brian W. Skelton,c,g Aurel Tabacaruf and Allan H. Whitec
Received 13th March 2012, Accepted 17th April 2012
DOI: 10.1039/c2dt30579h
A number of adducts of copper(I) thiocyanate with bulky tertiary phosphine ligands, and some
nitrogen-base solvates, were synthesized and structurally and spectroscopically characterised.
CuSCN : PCy3 (1 : 2), as crystallized from pyridine, is shown by a single crystal X-ray study to be a one-
dimensional polymer ...(Cy3P)2CuSCN(Cy3P)2CuSCN... (1) with the four-coordinate copper atoms linked
end-on by S-SCN-N bridging thiocyanate groups. A second form (2), obtained from acetonitrile, was also
identified and shown by IR and 31P CPMAS NMR spectroscopy to be mononuclear, with the magnitude
of the dνCu parameter measured from the 31P CPMAS and the ν(CN) value from the IR clearly
establishing this compound as three-coordinate [(Cy3P)2CuNCS]. Two further CuSCN/PCy3 compounds
CuSCN : PCy3 (1 : 1) (3), and CuSCN : PCy3 : py (1 : 1 : 1) (4) were also characterized spectroscopically,
with the dνCu parameters indicating three- and four-coordinate copper sites, respectively. Attempts to
obtain a 1 : 2 adduct with tri-t-butylphosphine have yielded, from pyridine, the 1 : 1 adduct as a dimer
SCN
NCS
[(But3P)( )Cu(PBut3)] (5), while similar attempts with tri-o-tolylphosphine (from acetonitrile and
SCN
NCS
pyridine (= L)) resulted in solvated 1 : 1 : 1 CuSCN : P(o-tol)3 : L forms as dimeric [{(o-tol)3P}LCu(
)
CuL{P(o-tol)3}] (6 and 8). The solvent-free 1 : 1 CuSCN : P(o-tol)3 adduct (7), obtained by desolvation
of 6, was characterized spectroscopically and dνCu measurements from the 31P CPMAS NMR data are
consistent with the decrease in coordination number of the copper atom from four (for 6) (P,N(MeCN)Cu,
S,N) to three (for 7) (PCuS,N) upon loss of the acetonitrile of solvation. These results are compared with
those previously reported for mononuclear and binuclear PPh3 adducts which demonstrate a clear
tendency for the copper centre to remain four-coordinate. The IR spectroscopic measurements on these
compounds show that bands in the far-IR spectra provide a much more definitive criterion for
distinguishing between bridging and terminal bonding than does an often-used empirical rule based on
ν(CN) in the mid-IR, which leads to the wrong conclusion in some cases.
structures of the parent copper(I) thiocyanate1 and its complex
Introduction
anions2 has been little exploited among complexes of group 15
donor ligands beyond those of nitrogen. With copper(I) poten-
tially four-coordinate and the thiocyanate group potentially
ambidentate SCN, there is a considerable capacity for the for-
mation of complexes of the form CuSCN : L (1 : 2) with mono-
dentate ligands L. With simple monodentate N-donor systems
such as pyridine (‘py’) bases, there has been a dominant ten-
dency for those to form single-stranded 1 : 2 polymers ...CuL2.
NCS.CuL2.NCS... or double-stranded 1 : 1 arrays, the ‘extended
stair polymer’, derivative of the ‘stair’ polymer common among
Despite their relative ease of synthesis, the promise of formation
of interesting extended lattice architectures inherent in the
aSchool of Chemical Sciences, University of Auckland, Auckland 1142,
New Zealand
bDepartment of Physics, University of Warwick, Coventry CV47AL, UK
cSchool of Chemistry and Biochemistry M310, The University of Western
Australia, Crawley, WA 6009, Australia
dSchool of Science, Griffith University, Nathan 4111, Queensland,
Australia
eSchool of Science and Technology, University of Camerino, S Agostino
1, 62032 Camerino, MC, Italy
copper(I) halide (CuX; X = Cl, Br, I) complexes, comprising
SCN
NCS
fSchool of Pharmacy, University of Camerino, S Agostino 1, 62032
Camerino, MC, Italy
alternate four- (CuS2Cu) and eight-membered Cu( )Cu rings,
the copper environments being L2CuNS and LCuS2N respect-
ively.3 Adducts with monodentate P, As, Sb (, Bi) donors are less
well studied: whereas 1 : 2 adducts of copper(I) halides, CuX,
with trialkyl/arylphosphine ligands PR3 may be of mononuclear
[(R3P)2CuX] or binuclear [(R3P)2CuX2Cu(PR3)2] forms:4 that of
gCentre for Microscopy, Characterisation and Analysis, The University
of Western Australia, Crawley, WA 6009, Australia
†Electronic supplementary information (ESI) available: CCDC 781134
(1), 780720 (5), 796280 (6), 805233 (8). For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c2dt30579h
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 7513–7525 | 7513

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the pseudohalide thiocyanate salt with triphenylphosphine has
(1.120 g, 4.00 mmol), in anhydrous MeCN (20 mL). The sus-
pension was stirred at room temperature for 5 h, and the colour-
less solid product was filtered off and dried under vacuum. Yield
65% (0.44 g, 0.95 mmol). Recrystallisation from pyridine (py)
yielded colourless crystals identified as polymeric CuSCN : PCy3
(1 : 2)(∞|∞), 1. Anal. Calcd for C37H66CuNP2S, C, 65.12; H,
9.75; N, 2.05; S, 4.70; Found: C, 65.12; H, 9.63; N, 2.12%. IR
ν(CN) = 2071 cm−1. Method 2. β-CuSCN (0.061 g, 0.5 mmol)
and PCy3 (0.280 g, 1.0 mmol) were ground together with a
mortar and pestle, first dry and then after addition of MeCN
(0.35 mL). As the grinding progressed the mixture formed a
white paste, which was allowed to dry in the air before sampling
for IR spectroscopy. Yield 95.9% (0.327 g, 0.48 mmol). The IR
spectrum showed a very strong ν(CN) band at 2071 cm−1 and a
much weaker band at 2121 cm−1. This mechanochemical treat-
ment was repeated once with addition of further MeCN
(0.35 mL). The IR spectrum of the final product showed the
ν(CN) band at 2071 cm−1, with no trace of the 2121 cm−1 band;
the latter is probably due to the 1 : 1 complex (see below).
SCN
been shown to be binuclear [(Ph3P)2Cu( )Cu(PPh3)2] in both
NCS
of the phases identified.5 There is also limited structural data for
mixed nitrogen/phosphorus ligand adducts of the form CuSCN :
monodentate P-base : monodentate N-base: (1 : 1 : 1).6,7 The
present report describes extension of this work via the attempted
synthesis and characterization of further 1 : 2 CuSCN : PR3
(tertiary phosphine) adducts with bulky substituents, R, describ-
ing the unusual structures and spectroscopy of the complexes
obtained with tricyclohexylphosphine (PCy3) (1 : 2), and tri-
t-butylphosphine (PBut3) (1 : 1), and the formation of 1 : 1 : 1
CuSCN : PR3 : N-donor adducts with tri-o-tolylphosphine,
P(o-tol)3, and acetonitrile and pyridine. The ready accessibility
of a number of novel species and/or forms by way of mechano-
chemical synthesis8,9 has led us to explore several of the
CuSCN/PR3 systems in this manner, resulting in high-yield
syntheses of bulk spectroscopic samples of a number of the com-
plexes, as well as providing a greater insight into the range of
such complexes that can be formed in these systems.
CuSCN : PCy3 (1 : 2), 2. CuSCN (0.123 g, 1.00 mmol)
was reacted with tricyclohexylphosphine, PCy3, (0.841 g,
3.00 mmol), in anhydrous MeCN (20 mL). The suspension was
stirred at room temperature for 5 h, and the colourless solid
product was filtered off and dried under vacuum. Yield 95%
(0.64 g, 0.95 mmol). 2 is soluble in chloroform, insoluble in
methanol, acetonitrile, acetone and dimethylsulfoxide. Mp
170–172 °C. Anal. Calcd for C37H66CuNP2S, C, 65.12; H, 9.75;
N, 2.05; S, 4.70; Found: C, 65.22; H, 10.06; N, 1.72; S, 4.21%.
Experimental
General materials and experimental procedures
All chemicals were purchased from Aldrich (Milwaukee, WI)
and used as received, except in the case of the CuSCN used in
the mechanochemical experiments, where the pure β-polymorph,
prepared as previously described,10 was used. All the reactions
and manipulations were performed in the air, except in the case
of reactions involving PBut3, which were carried out under nitro-
gen. Acetonitrile was dried over aluminium oxide. Solvent evap-
orations were always carried out under vacuum using a rotary
evaporator. The samples for microanalysis were dried in vacuo
to constant weight (20 °C, ca. 0.1 Torr). Elemental analyses
(C, H, N, S) were performed in-house with a Fison Instrument
1108 CHNS-O Elemental analyzer. IR spectra were recorded
from 4000 to 650 cm−1 with a Perkin-Elmer System 2000 FT-IR
instrument, or from 4000 to 380 cm−1 at 4 cm−1 resolution on
dry powders using a Perkin Elmer Spectrum 400 FT-IR spec-
trometer equipped with a Universal ATR sampling accessory.
Far-infrared spectra were recorded from 700 to 30 cm−1 at
4 cm−1 resolution using a Perkin Elmer Spectrum 400 FT-IR
spectrometer on samples suspended in Polythene disks. Solution
1H and 31P NMR spectra were recorded on a 400 Mercury Plus
Varian instrument operating at room temperature (400 MHz for
1
IR ν(CN) = 2059 cm−1. H NMR (CDCl3, 293K): δ, 1.27, 1.84
(m br, 66H, PCy3). 31P NMR (CDCl3, 293K): δ, 34.7s, 24.1s br,
13.6s, 12.3s br. ESI-MS (MeCN) (+) (m/z, relative intensity %):
281.2(100) [Cy3PH]+, 623.5(30) [Cu(PCy3)2]+, 746.3(5)
[Cu2(NCS)(PCy3)2]+.
CuSCN : PCy3 (1 : 1), 3. Method 1. CuSCN (0.123 g,
1.00 mmol) was reacted with tricyclohexylphosphine, PCy3,
(0.560 g, 2.00 mmol), in MeCN (20 mL). The suspension was
stirred at 70 °C for 4 h, and the colourless solid product was
filtered off and dried under vacuum. Yield 80% (0.32 g,
0.80 mmol). 3 is insoluble in chloroform, methanol, acetonitrile,
acetone and dimethylsulfoxide. Mp 242 °C (dec.). Anal. Calcd
for C19H33CuNPS, C, 56.76; H, 8.27; N, 3.48; S, 7.97; Found:
C, 56.66; H, 8.43; N, 3.34; S, 7.62%. IR ν(CN) = 2116 cm−1
.
1H and 162.1 MHz for 31P). H chemical shifts (δ) are reported
1
Method 2. β-CuSCN (0.097 g, 0.8 mmol) and PCy3 (0.224 g,
0.8 mmol) were ground together with a mortar and pestle, first
dry and then after addition of MeCN (0.35 mL). As the grinding
progressed the mixture formed a white paste, which was allowed
to dry in the air before sampling for IR spectroscopy. The IR
spectrum showed a very strong ν(CN) band at 2118 cm−1 and a
much weaker band at 2174 cm−1. This mechanochemical treat-
ment was repeated once with addition of further MeCN
(0.35 mL). Yield 94.7% (0.305 g, 0.76 mmol). The IR spectrum
of the final product showed the ν(CN) band at 2119 cm−1, with
the 2174 cm−1 band now exceedingly weak. This latter band is
due to a very small amount of unreacted β-CuSCN. A further
cycle of mechanochemical treatment with MeCN (0.3 mL) pro-
duced no further change in the spectrum.
in parts per million (ppm) from SiMe4 while 31P shifts (δ) are
reported in ppm vs. 85% H3PO4. Peak multiplicities are abbre-
viated: singlet, s; doublet, d; triplet, t; quartet, q; and multiplet,
m. The positive electrospray mass spectra (ESI MS) were
obtained using a Series 1100 MSI detector HP spectrometer,
using an acetonitrile mobile phase. The melting points are uncor-
rected and were determined using an STMP3 Stuart scientific
instrument and on a capillary apparatus.
Synthesis
CuSCN : PCy3 (1 : 2), 1. Method 1. CuSCN (0.123 g,
1.00 mmol) was reacted with tricyclohexylphosphine, PCy3,
7514 | Dalton Trans., 2012, 41, 7513–7525
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CuSCN : PCy3 : py (1 : 1 : 1), 4. Method 1. CuNCS (0.122 g,
1.0 mmol) was added to a solution of PCy3 (0.280 g, 1.0 mmol)
in pyridine (10 mL). The solution was reacted for 6 h at room
temperature. Upon slow evaporation of py, a colourless precipi-
tate formed which was filtered off and washed with 1 mL of the
pyridine. Yield 85% (0.408 g, 0.85 mmol). It is soluble in
chloroform and dimethylsulfoxide. Anal. Calcd for
C24H38CuN2PS: C, 59.90; H, 7.97; N, 5.82; S, 6.65%. Found:
C, 60.32; H, 8.34; N, 5.94; S, 6.34%. IR ν(CN) = 2109,
the product showed that it was a mixture of 6 and unreacted
P(o-tol)3.
CuSCN : P(o-tol)3 : py (1 : 1 : 1), 8. This compound was
obtained by reacting CuSCN (0.122 g, 1.0 mmol) and P(o-tol)3
(0.307 g, 1.0 mmol) in 10 mol of pyridine. The solution was
reacted for 24 h at room temperature. Upon slow evaporation of
the py, a colourless crystalline deposit formed which was filtered
off and washed with 1 mL of py. Yield 55% (0.278 g,
0.55 mmol). It is slightly soluble in dimethylsulfoxide. Mp
248–252 °C (dec.). Anal. Calcd for C27H26CuN2PS, C, 64.20;
H, 5.19; N, 5.55; S, 6.35%. Found: C, 64.10; H, 5.18; N, 5.52;
2093 cm−1 1H-NMR (CDCl3, 293 K): δ 1.25mbr, 1.84mbr
.
(66H, PC18H33) 7.66t (2H, CHmeta-Py), 8.10t (1H, CHpara-Py),
8,75m (2H, CHortho-Py). 31P NMR (CDCl3, 293K): δ, 24.89s,
21.50br, 13.24sbr. Method 2. β-CuSCN (0.085 g, 0.7 mmol) and
PCy3 (0.196 g, 0.7 mmol) were ground together with a mortar
and pestle, first dry and then after addition of pyridine (0.128 g,
1.62 mmol). As the grinding progressed the mixture formed a
pale green paste, which changed to a pale yellow powder when
the mixture was allowed to dry in the air before sampling for IR
spectroscopy. Yield 97.9% (0.33 g, 0.69 mmol). The IR spec-
trum (ν(CN) = 2108, 2094 cm−1) is identical to that of the
product obtained by Method 1.
S, 6.43%. IR ν(CN) = 2104 cm−1
.
CuSCN : PPh3 (1 : 2), triclinic polymorph, 9. A solution of
KSCN (1.458 g, 15.0 mmol) in water (15 mL) was added to a
solution of Cu(NO3)2·2.5H2O (0.700 g, 3.00 mmol) in water
(10 mL), resulting in the formation of a black precipitate. The
resulting mixture was added with rapid stirring to a warm sol-
ution of PPh3 (1.97 g, 7.5 mmol) in EtOH (25 mL). The mixture
changed colour to yield a pale pink solution and a flocculent
white precipitate. This mixture was stirred with heating for about
15 min and the product was collected and washed with water,
followed by EtOH and then MeCN. The white powder product
was dried at 75 °C for ca. 3 h, yield 91.2% (1.77 g, 2.74 mmol).
The product was identified by its IR spectrum, ν(CN) =
CuSCN : PBut3 (1 : 1), 5. This colourless, crystalline com-
pound was obtained by reacting CuSCN (0.124 g, 1.0 mmol)
and tri-t-butylphosphine, PBut3, (0.808 g, 4 mmol), in pyridine
under a nitrogen atmosphere. Yield 65% (0.21 g, 0.65 mmol). 5
is soluble in chloroform and dimethylsulfoxide. Mp 230 °C
(dec.). Anal. Calcd for C13H27CuNPS, C, 48.20; H, 8.40; N,
4.32; S, 9.90; Found: C, 47.85; H, 8.31; N, 4.58; S, 10.25%. IR
2095 cm−1 5b
.
CuSCN : PPh3 (1 : 2), monoclinic polymorph, 10. A sample of
the triclinic polymorph 9 (1.38 g, 2.14 mmol) was dissolved in
hot pyridine (3 mL) to yield a pale yellow solution. No product
separated upon cooling to ambient temperature so the solution
was allowed to lose solvent by slow evaporation from an open
conical flask in the fume cupboard. Pale yellow crystals of
product formed after 2 d and were collected and washed with a
small quantity of ice-cold pyridine, yield 89.7% (1.23 g,
1.90 mmol). The product was identified by its IR spectrum,
1
ν(CN) = 2111 cm−1. H NMR (CDCl3, 293K): δ, 1.4s br (21H,
PBut3), 1.73s, 1.75s (6H, PBut3). 31P NMR (CDCl3, 293K): δ,
−28.4sbr. 31P NMR (CDCl3, 223K): δ, 27.5, 45.5, 59.82, 67.5,
69.0, 69.5, −28.51s.
CuSCN : P(o-tol)3 : MeCN (1 : 1 : 1), 6. Method 1. This com-
pound was obtained by reacting CuSCN (0.062 g, 0.5 mmol)
and tri-o-tolylphosphine, P(o-tol)3, (0.600 g, 2.0 mmol), in
methanol for 4 h. A colourless compound slowly formed, that
upon recrystallisation from MeCN gives colourless 6. Yield 80%
(0.125 g, 0.40 mmol). 6 is moderately soluble in chloroform
and dimethylsulfoxide. Mp 242 °C (dec.). Anal. Calcd
for C24H24CuN2PS, C, 61.72; H, 5.18; N, 6.00; S, 6.87; Found:
ν(CN) = 2104, 2082 cm−1 5b
.
CuSCN : PPh3 : py (1 : 1 : 2), 11. CuSCN (0.484 g, 4.0 mmol)
and PPh3 (1.048 g, 4.0 mmol) were dissolved in hot pyridine
(10 mL) to produce a yellow solution from which pale yellow
crystals of the product separated upon cooling in an ice bath.
Yield 85.9% (1.86 g, 3.43 mmol). The product was identified by
C, 62.08; H, 5.37; N, 5.65; S, 6.64%. IR ν(CN) = 2101 cm−1
.
its IR spectrum, ν(CN) = 2065 cm−1 5b
.
1H NMR (CDCl3, 293K): δ, 2.0s (3H, CH3CN), 2.49s (9H,
CH3P(o-tol)3), 6.76t, 7.09m, 7.27m, 7.32m (12H, C6H4P(o-tol)3).
Method 2. β-CuSCN (0.061 g, 0.5 mmol) and P(o-tol)3 (0.152 g,
0.5 mmol) were ground together with a mortar and pestle, first
dry and then after addition of MeCN (0.30 mL). As the grinding
progressed the mixture formed a white paste, which was allowed
to dry in the air before sampling for IR spectroscopy. Yield
98.1% (0.229 g, 0.49 mmol). The IR spectrum showed a very
strong ν(CN) band at 2102 cm−1 (SCN) and a very weak ν(CN)
band at 2264 cm−1 (MeCN). Heating the product for 3 d at
50 °C resulted in loss of the 2264 cm−1 band and a shift of the
2102 cm−1 band to 2105 cm−1. This indicates the formation of
the solvent-free 1 : 1 adduct CuSCN : P(o-tol)3 (1 : 1), 7. The
same result was obtained by mechanochemical treatment of 6
with EtOH. The mechanochemical reaction of CuSCN : P(o-tol)3
(1 : 2) with MeCN was also carried out, but the IR spectrum of
CuSCN : PPh3 : py (1 : 1 : 1), 12. [CuSCN(PPh3)(py)2], 11
(0.271 g, 0.5 mmol) was ground in a mortar and pestle with
acetonitrile (0.4 mL) and grinding was continued until the
mixture was dry. This process was repeated, monitoring the pro-
gress of the reaction gravimetrically and by IR spectroscopy,
which showed that the reaction was complete after four cycles of
mechanochemical treatment. Yield 99.6% (0.231 g, 0.50 mmol).
The product was identified by its IR spectrum, ν(CN) = 2102,
2092 cm−1 5b
.
Structure determinations
Full spheres of CCD/area-detector diffractometer data were
measured (monochromatic Mo Kα radiation (λ = 0.71073 Å),
ω-scans; T ca. 100 K) yielding Nt(otal) reflections, these merging
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 7513–7525 | 7515

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to N unique (Rint cited), after ‘analytical’/face-indexed absorp-
tion corrections, which were used in the full matrix least squares
refinements on F2, refining anisotropic displacement parameter
forms for the non-hydrogen atoms, hydrogen atom treatment
following a riding model (reflection weights: (σ2(F02) + (aP)2)−1
(P = (F20+ 2F2c)/3)); No reflections with I > 2σ(I) were considered
‘observed’. Neutral atom complex scattering factors were
employed within the SHELXL 97 program.11 Pertinent results
are given below and in the tables and figures, the latter showing
the non-hydrogen atoms with 50% probability amplitude
displacement ellipsoids, hydrogen atoms (where shown) having
arbitrary radii of 0.1 Å.
(during acquisition) were used in all 31P CPMAS measurements.
The reported 31P chemical shifts were externally referenced to
the IUPAC standard of 85% H3PO4 via a secondary solid refer-
ence of ammonium dihydrogen phosphate (NH4 [H2PO4]) which
exhibits a 31P shift at δ 1.0 ppm; this secondary reference
material was also used to set the Hartmann–Hahn condition. The
2D 31P CPCOSY experiment was implemented with the TPPI
(time proportional phase incrementation) method15–17 for acqui-
sition of phase-sensitive data in both the F1 and F2 dimensions.
The application of this technique has been discussed in detail
elsewhere,19–21 with the recycle delay, contact period, 1H π/2
pulse width and MAS rate being the same as those implemented
in the above 1D 31P CPMAS experiments. A total of 256 F1
increments were acquired into 256 word blocks, with both
dimensions zero-filled to 1 K words and weighted with Gaussian
multiplication prior to Fourier transformation.
Crystal/refinement data
CuSCN : PCy3 (1 : 2)(∞|∞), 1 ≡ C37H66CuNP2S, Mr = 682.5.
Monoclinic, space group P21/n (C2h5, No. 14 (variant)), a =
13.3546(3), b = 11.6352(6), c = 23.1007(14) Å, β = 92.171(3)°,
Results and discussion
V = 3586.9(3) Å3. Dc (Z = 4 dimers) = 1.264 g cm−3. μMo
=
Synthesis
0.78 mm; specimen: 0.52 × 0.48 × 0.30 mm; ‘T’min/max = 0.93.
2θmax = 70°; Nt = 56128, N = 14 818 (Rint = 0.045), No
10 096; R1 = 0.035, wR2 = 0.085 (a = 0.044); S = 0.92. |Δρmax| =
1.14 e Å−3
=
From the interaction of copper(I) thiocyanate and tricyclohexyl-
phosphine in 1 : 4 metal salt to phosphine ligand ratio, in pyri-
dine at room temperature, we obtained the unsolvated derivative
1, CuSCN : PCy3 (1 : 2)(∞|∞), a colourless, air and moisture
stable compound, showing a sharp melting point, poorly soluble
in chlorinated solvents, and insoluble in MeOH, MeCN and
dimethylsulfoxide. This product was shown by X-ray crystallo-
graphy to have an infinite single-stranded polymeric structure ...
(Cy3P)2CuSCN(Cy3P)2CuSCN..., and is characterized by ν(CN)
= 2071 cm−1 in the IR. Less reproducibly, (on two occasions) a
1 : 2 product with ν(CN) = 2059 cm−1 was obtained, which was
shown by IR and 31P CPMAS NMR spectroscopy to be a mono-
meric form [(Cy3P)2CuNCS], 2 (see below). Two further
CuSCN : PCy3 compounds, both of 1 : 1 composition, were pre-
pared: CuSCN : PCy3 (1 : 1), 3, and CuSCN : PCy3 : py
(1 : 1 : 1), 4, but did not yield crystals suitable for an X-ray struc-
ture determination. The solution NMR data of 2 are consistent
with dissociation–decomposition of the complex in CDCl3
solution, accompanied by the formation of OPCy3.
.
CuSCN : PBut3 (1 : 1)2, 5 ≡ C26H54Cu2N2P2S2, Mr = 647.9.
Monoclinic, space group P21/n, a = 11.0989(3), b = 12.2641(4),
c = 12.1268(4) Å, β = 96.516(3)°, V = 1640.01(9) Å3. Dc (Z = 2
dimers) = 1.312 g cm−3. μMo = 1.54 mm; specimen: 0.27 × 0.09
× 0.04 mm; ‘T’min/max = 0.76. 2θmax = 65°; Nt = 17653, N =
5437 (Rint = 0.036), No = 3890; R1 = 0.034, wR2 = 0.085 (a =
0.034); S = 1.09. |Δρmax| = 0.57 e Å−3
.
CuSCN : P(o-tol)3 : MeCN (1 : 1 : 1)2, 6 ≡ C48H48Cu2N4P2S2,
Mr = 934.0. Monoclinic, space group P21/c (C2h5, No. 14), a =
9.3118(2), b = 17.5977(4), c = 13.3941(4) Å, β = 101.068(3)°,
V = 2154.02(9) Å3. Dc (Z = 2 dimers) = 1.440 g cm−3. μMo
=
1.20 mm; specimen: 0.26 × 0.13 × 0.11 mm; ‘T’min/max = 0.90.
2θmax = 67°; Nt = 27484, N = 7971 (Rint = 0.043), No = 5502;
R1 = 0.032, wR2 = 0.070 (a = 0.035); S = 0.91. |Δρmax| =
0.56 e Å−3
.
CuSCN : P(o-tol)3 : (py) (1 : 1 : 1)2, 8 ≡ C54H52Cu2N4P2S2,
Mr = 1010.1. Monoclinic, space group P21/c, a = 16.107(5), b =
9.505(5), c = 16.249(5) Å, β = 104.168(5)°, V = 2412(2) Å3. Dc
(Z = 2 dimers) = 1.391 g cm−3. μMo = 1.08 mm−1; specimen: =
0.37 × 0.21 × 0.13 mm; ‘T’min/max = 0.77. 2θmax = 75°; Nt =
93483, N = 12 473 (Rint = 0.038), No = 9359; R1 = 0.028, wR2 =
The corresponding reaction between CuSCN and PBut3
always produced the complex CuSCN : PBut3 (1 : 1)2, 5, with a
1 : 1 CuSCN : PBut3 ratio, even when the reaction was carried
out using a large excess of PBut3. The dimeric structure of this
complex was determined by X-ray crystallography to be [(But3P)
Cu(SNCCNS)Cu(PBut3). The solution NMR data are consistent with
dissociation–decomposition of the complex in CDCl3 solution,
accompanied by the formation of OPBut3. The dimer 6 was
obtained when the reaction between CuSCN and P(o-tol)3 was
carried out in MeOH, and the product was recrystallised from
MeCN, but the solvent in this case acts as a coordinating ligand,
accommodated by a four-coordinate copper centre. A similar
pyridine-solvated dimeric product 8 was obtained from pyridine
solution.
0.074 (a = 0.042); S = 0.99. |Δρmax| = 0.67 e Å−3
.
31P CPMAS NMR spectroscopy
Conventional solid-state 31P cross-polarisation,12 magic-angle-
spinning13 (CPMAS) NMR data were obtained at ambient temp-
erature using a Bruker DSX-400 (9.40 T) spectrometer operating
at a 31P Larmor frequency of 161.92 MHz. Spin temperature
alternation techniques14 were also implemented to eliminate
spectral artefacts. These measurements were undertaken using a
Bruker 3.2 mm double-air-bearing probe in which MAS frequen-
cies of ∼10–12 kHz were achieved. An initial 1H π/2 pulse
width of 3 μs, recycle delay of 15–30 s, Hartmann–Hahn contact
period of 2–5 ms and a 1H decoupling field of 80–85 kHz
For comparison purposes, the corresponding CuSCN : PPh3
systems were investigated. The 1 : 2 complexes CuSCN : PPh3
(1 : 2)2, triclinic polymorph, 9,5a and monoclinic polymorph,
10,5b were prepared, but the preparation of the previously
described CuSCN : PPh3 (1 : 1)2,6 could not be reproduced.
7516 | Dalton Trans., 2012, 41, 7513–7525
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Structure determinations
The tendency of some of the above systems to form solvates
or polymorphs initially led to problems in identifying some of
the different phases involved. Also, our expectation that all of
the systems studied should form both 1 : 1 and 1 : 2 adducts was
not realized in the products of the solution syntheses. In order to
provide greater clarity in these matters, some of the CuSCN/PR3
reactions were investigated by the method of solvent-assisted
mechanochemical synthesis, which has recently been shown to
be applicable to the synthesis of a range of different types of
coordination compound.8,9 The reactions generally proceeded
very easily in one or two cycles of such treatments using aceto-
nitrile as the assisting solvent (see Experimental). The CuSCN/
PCy3 reactions yielded the polymeric 1 : 2 complex 1 from a
1 : 2 mixture of the reactants, and the 1 : 1 complex 3 from a
1 : 1 mixture. Mechanochemical synthesis did not yield the
mononuclear 1 : 2 complex 2, even if a reactant ratio of 1 : 2.5
was used, or if ethanol was used instead of acetonitrile in the
solvent-assisted process. The 1 : 1 CuSCN/P(o-tol)3 reaction
yielded the acetonitrile adduct CuSCN : P(o-tol)3 : MeCN
(1 : 1 : 1)2, 6, the increase in mass of the product being consistent
with the addition of one MeCN molecule per CuSCN in the
structure and confirmed by the presence of a ν(CN) band at
2264 cm−1 due to the coordinated MeCN. IR spectroscopy
showed that this could be removed to yield 7 by heating the
compound at 50 °C or by mechanochemical treatment with
ethanol. The IR spectrum of the 1 : 2 CuSCN/P(o-tol)3 reaction
showed that this produced a mixture of 6 and unreacted
P(o-tol)3. This was also the case if ethanol was used instead of
MeCN in the solvent-assisted reaction, showing that the lack of
formation of a 1 : 2 complex is not due to competition for the
copper(I) site by MeCN, but, rather, appears to be due to
the steric bulk of the P(o-tol)3 ligand. In contrast to this, the
CuSCN/PPh3 system yielded only the 1 : 2 complex CuSCN :
PPh3 (1 : 2)2 (triclinic polymorph), 9; the IR spectrum of the
product of the 1 : 1 reaction showed that it consisted of a mixture
of 9 and unreacted CuSCN. This was also the case for several
attempted solution-based reactions aimed at producing a 1 : 1
Among the structurally characterized 1 : 1 and 1 : 2 complexes of
monodentate group 15 donors with copper(I) thiocyanate, three
important motifs may be identified:
(i) The single-stranded polymer, wherein one or two ligands
may be pendant from the copper atoms of an ...MSCNMSCNM...
array. In some measure the stoichiometry of this form may be
determined by ligand bulk, e.g., the adduct formed by crystalliz-
ing CuSCN from 2,6-dimethylpyridine solution is of 1 : 1 stoi-
chiometry with trigonal planar coordination about the copper
atom. By contrast, the adducts with a similar spine obtained
from 2-methylpyridine or quinoline are of 1 : 2 CuSCN : L stoi-
chiometry, although a 1 : 1 adduct of the former may be obtained
if the ligand is diluted with acetonitrile, this being of the
‘expanded stair’ form, (ii).3a
(ii) With copper(I) and silver(I) halides, MX, crystallized from
pyridine bases, the ‘stair’ or ‘ladder’ polymer form is frequently
obtained, an extension of the tetrameric ‘chair’ form which is
usually obtained with phosphine ligands:4
With the pseudohalogen, thiocyanate, this may become an
‘expanded stair’ form:
comprising alternating four- and eight-membered rings, with
quinoline as the ligand.3b The stoichiometry of these forms is
necessarily MX : L (1 : 1) in the context of four-coordinate metal
atoms. The extent to which steric factors dictate the adoption of
the latter form is unclear.
complex, and the previously reported synthesis of the 1 : 1
(iii) With tertiary phosphine ligands PR3 (no derivatives have
6
complex CuSCN : PPh3 (1 : 1)2
could not be reproduced.
yet been recorded with arsine or stibine counterpart donors), the
SCN
NCS
Thermal decomposition of [CuSCN(PPh3)(py)2] 11 yielded a
mixture of 9 and β-CuSCN.
only form yet defined is the CuSCN : L (1 : 2) dimer [L2M(
)
ML2], with an eight-membered central ring, for PR3 = PPh3,5 an
expansion of the binuclear form recorded for numerous
other halide complexes.22 For the only example reported
for N- and P-bases in combination, the adduct CuSCN : PPh3 :
2-mpy (2-methylpyridine) (1 : 1 : 1), the array found is of the
binuclear form.6
A further advantage of the mechanochemical synthesis
method relates to the fact that the solution reactions often
involved very long reaction times, due to the low solubility of
CuSCN in the reaction medium. If care was not taken to exclude
moisture or air, this resulted in oxidation of the phosphine to the
corresponding phosphine oxide, e.g., in the case of PCy3, result-
ing in impure products or products of unintended composition.
These problems were completely avoided in the mechanochem-
ical syntheses, which were complete within a few minutes.
The above results reveal a clear trend in the preferred compo-
sition of CuSCN : PR3 (1 : n) complexes with increasing steric
bulk of the substituent R. For R = Ph only the 1 : 2 complex can
be reproducibly obtained. For R = Cy, both 1 : 1 and 1 : 2 com-
plexes are readily accessible. For R = o-tol, only the 1 : 1
complex can be prepared, although an additional smaller ligand
(e.g., MeCN or py) can be accommodated in the structure. For
R = But, only the 1 : 1 complex is formed, even when a large
excess of PBut3 is used.
The results of the single crystal X-ray study of CuSCN : PCy3
(1 : 2) show it to be of the single-stranded polymer form (i):
–Cu(P2)–SCN–Cu(P2)–SCN–, one formula unit, devoid of crys-
tallographic symmetry comprising the asymmetric unit of the
structure (Fig. 1, Table 1). The structure is the first of this type to
be recorded for a 1 : 2 Cu,AgSCN : P(,As,Sb)R3 adduct. Bond
lengths and angles presented in Table 1 (footnote) are compared
with those of the range of (pyridine-) N-base counterparts found
in ref. 3a and are rendered somewhat uninformative by the great
divergence in the latter. However, we note that Cu–S,N(NCS) are
longer in the present adduct, with P–Cu–P considerably larger
than N–Cu–N, these changes probably due to a combination of
steric and electronic effects.
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Fig. 1 Projection of a single strand of the polymer of CuSCN : PCy3
(1 : 2)(∞|∞), 1 (b horizontal in the page).
Table 1 Selected non-hydrogen geometry, CuSCN : PCy3 (1 : 2)(∞|∞)
1
Atoms
Parameter
Atoms
Parameter
Distances (Å)
Cu–P(1)
Cu–P(2)
Cu⋯Cu
2.2962(3)
2.2989(4)
6.4736(3)
Cu–S
Cu–N′
2.4282(4)
2.0637(11)
Angles (°)
P(1)–Cu–P(2)
P(1)–Cu–S
P(1)–Cu–N
P(2)–Cu–S
P(2)–Cu–N
125.184(13)
111.046(13)
107.77(3)
108.857(13)
106.65(3)
S–Cu–N′
Cu–S–C
Cu–N′–C′
S–C–N
92.15(3)
112.44(4)
150.61(10)
175.06(12)
Primed atoms are symmetry related (2-axis). In the N-base counterparts
of ref. 3a (compounds 3–7 therein), ranges for Cu–S,N(CS), N(py-base)
are: 2.290(4)–2.380(4); 1.944(9)–2.00(1), 2.074(3)–2.113(5) Å, and for
N(py)–Cu–N, N(py)–Cu–N(py), N(py)–Cu–S, N(py)–Cu–N(CS),
S–Cu–N(CS), Cu–S–C 101.6(3)–117.4(3), 102.9(3)–123.3(2), 98.8(4)–
122.3(4), 105.7(3)–113.1(4), 100.3(5), 105.9(4)°.
The other complexes defined herein are centrosymmetric
SCN
NCS
dimers, of the form [L1,2Cu( )CuL1,2] (Fig. 2), one half of
each dimer comprising the asymmetric unit of each structure;
core geometries are presented in Table 2.
SCN
Fig. 2 Projections of centrosymmetric binuclear (a) [(But3P)Cu( )-
NCS
Cu(PBut3)], 5, normal to the central ring plane (see text); (b) [(o-tol3P)-
(L)Cu(SNCCNS)Cu(L)(P(o-tol)3)], (i) L = MeCN, 6, (ii) L = py, 8, through
the central Cu(SNCCNS)Cu ring.
The results of the single crystal X-ray study on CuSCN : PBut3
(1 : 1) confirm that stoichiometry and show it to be centrosym-
SCN
NCS
metric binuclear [But3PCu]( )CuPBut3], with the copper atom
in a trigonal, closely planar coordination environment (Table 2);
the totality of the PCu(NSCCNS)CuP array is closely planar (χ2 167;
maximum defining atom deviation 0.016(2) Å), again the first
structure so defined for this core. The form of the complex con-
trasts with that of the 1 : 1 halide analogues which are all (X =
Cl, Br, I) of the tetrameric cubanoid form.23 However, a series of
counterpart binuclear halide complexes has been recorded for
the P(o-tol)3 ligand.24,25 For that series there is a strong sugges-
tion that the Cu–P distances increase on passing from X = Cl
(2.19) to X = Br (2.20) to X = I (2.24 Å), straddling the present
value of 2.2122(5) Å.24
atom, raising the coordination number to four, and increasing the
counterpart Cu–P, S(CN)/N(CS) distances accordingly. The aceto-
nitrile molecule is less tightly bound than the N(CS) component,
with the Cu–N–C angle well removed from linearity (156.6(1)°).
The Cu(SNCCNS)Cu array is quasi-planar (χ2 4.7 × 104; maximum
defining atom deviation 0.152(1) Å), albeit less closely so than
in the previous structure. There are parallel examples23 with brid-
ging halogen atoms for the bromide (two forms) and iodide; in
these centrosymmetric dimers Cu–P are 2.242(9), 2.252(2) (Br),
2.269(2) (I), (cf. the present 2.2690(4)) with Cu–N 2.10(3),
2.151(8) (Br), 2.041(4) (I), cf. 2.045(1) Å; the X–Cu–X′ angles
within the dimers are 98.7(1), 97.52(3) (Br), 98.22(4)° (I), some-
what smaller than the present (102.00(3)°). (see also the
The 1 : 1 adduct of CuSCN with P(o-tol)3, although a similar
centrosymmetric dimer, crystallizes with a coordinated molecule
of solvent acetonitrile or pyridine associated with the copper
7518 | Dalton Trans., 2012, 41, 7513–7525
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SCN
NCS
Table 2 Selected non-hydrogen geometries, [((o-tol)3P)(L)Cu( )Cu-
NCS
[(Ph3P)(2-mpy)Cu( )Cu(2-mpy)(PPh3)]
Table 3 Wavenumbers (cm−1) of selected bands in the IR spectra of
CuSCN and some of its complexes with tertiary phosphines PR3
(L)(P(o-tol)3)] (L = MeCN, py) 6, 8, [(But3P)Cu( )Cu(PBu3t )] 5,
SCN
SCN
NCS
Compound
ν(CN)
ν(CuN) ν(CuS)
Atomsa
Parameterb
Atomsa
Parameterb
α-CuSCNa
2150
2172
2071
2059
2116
2109,
2093
2111
2101
250
242
204
—
265
236
210
203
168
242
228
215
Distances (Å)
Cu–P
β-CuSCNa
2.2690(4), 2.2304(6), Cu–S
2.2122(5), 2.2149(5)
2.0447(12), 2.0892
(11), —, 2.106(2)
2.3997(4), 2.4488(8),
2.3171(6), 2.4170(5)
2.0156(12),
2.0000(9), 1.940(2),
2.009(2)
CuSCN : PCy3 (1 : 2) (∞|∞)
CuSCN : PCy3 (1 : 2) 2
CuSCN : PCy3 (1 : 1) 3
1
Cu–N
(CMe, py)
Cu–N
CuSCN : PCy3 : py (1 : 1 : 1) 4
Cu⋯Cu
5.2808(2), 5.1623
(14), 5.1291(4),
5.2626(4)
[(But3P)Cu( )Cu(PBut3), 5
SCN
[(o-tol3P)(MeCN)Cu( )Cu(MeCN)-
(P(o-tol)3)] 6
242
218
216
188
NCS
SCN
NCS
CuSCN:P(o-tol)3 (1 : 1) 7 (= 6 after loss 2105
231
216
219
181
Angles (°)
P–Cu–S
of MeCN)
SCN
NCS
118.18(2), 107.33(2), S–Cu–N′ 102.00(3), 106.08(3),
120.50(2), 114.83(2) 105.37(5), 101.21(5)
111.46(4), 115.09(5), ΣP–Cu– 331.6, 328.5, 360.0,
134.13(5), 117.71(5) S,N 333.8
110.35(4), 126.65(3), S–Cu–N 106.94(4), 99.45(4),
[(o-tol3P)(py)Cu( )Cu(py)(P(o-tol)3)] 2104
8
P–Cu–N′
a Data from ref. 10.
P–Cu–N
(CMe, py)
Cu–S–C
—, 116.61(5)
—, 103.34(5)
107.11(5), 99.82(3),
—, 100.75(7)
97.10(5), 93.78(3),
97.02(7), 97.18(7)
179.0(1), 178.46(9),
178.7(2), 179.0(2)
166.8(1), —, —, —
N′–Cu–
N
S–C–N
Cu–N′–
C(S)
156.6(1), 160.54(7),
158.8(2), 154.0(2)
to the 2100 cm−1 boundary that distinguishes bridging from
terminal bonding in the case of the 1 : 1 CuSCN : PR3 com-
plexes, those of known structures (5, 6 and 8) all having double
Cu–N–C
(Me)
SCN bridged dimeric structures and having ν(CN) > 2100 cm−1
.
a Primed atoms are inversion related. b Listed in order for the four
compounds in the heading. Data for the CuSCN : PPh3 : 2-mpy complex
from ref. 6.
However, exceptions to this rule are found in the case of com-
plexes with CuSCN : PR3 = 1 : 2, for example compound 1,
which has a single-strand SCN bridged polymeric structure, with
ν(CN) well below 2100 cm−1, at 2071 cm−1. The corresponding
PPh3 complexes 9 and 10 have double SCN bridged dimeric
structures with ν(CN) = 2095 cm−1 and 2104, 2082 cm−1 respec-
tively,5b which are closer to the expected >2100 cm−1 range of
the empirical rule stated above. Evidently the rule fails in the
case of infinite polymeric chain structures, as has been noted
elsewhere.29 It will be shown below that bands in the far-IR
spectrum provide a much more definitive criterion for dis-
tinguishing between bridging and terminal bonding.
The far-IR spectra of the series of CuSCN/PCy3 complexes
studied in this work are shown in Fig. 3. The PCy3 complexes
are particularly suitable for this investigation, because the
uncomplexed PCy3 molecule shows no bands of significant
intensity below 370 cm−1, and in previous studies of the halide
complexes MX : PCy3 (1 : n) (M = Cu, Ag; X = Cl, Br, I; n = 1,
2) this has allowed unambiguous assignment of the ν(MX)
modes involving the coordinated halide.30–32 The far-IR spectra
of the present CuSCN complexes show bands below 300 cm−1
that are clearly sensitive to the composition and structure of the
compounds. In a previous study we have assigned bands in
this region to the ν(CuN) and ν(CuS) modes of the coordinated
thiocyanate,10 and the wavenumbers for the α- and β-CuSCN
polymorphs are given in Table 3. The ν(CuN) and ν(CuS) wave-
numbers are quite similar, but the assignment ν(CuN) > ν(CuS)
was based on arguments relating to the structures of the two
polymorphs, and is consistent with the corresponding assign-
ments in AgSCN,33 and in a range of terminally bound thiocya-
nate and isothiocyanate complexes.34,35 For complexes 1, 5, 6, 8
that contain bridging SCN, a pair of closely spaced bands in
each have been assigned to ν(CuN) and ν(CuS) bands, with
ν(CuN) > ν(CuS) as in CuSCN itself (Table 3). The variation in
the wavenumbers of these bands from one compound to another
comments above regarding the unsolvated halide forms). Values
for CuSCN : PPh3 : 2-mpy (1 : 1 : 1)2,6 are also presented for
comparison with the present ones in Table 2. In the acetonitrile
solvate, the acetonitrile ligand is clearly more strongly bound
than the pyridine ligands in their complexes, at the expense of
the strength of the Cu–P bonds, which are stronger in the latter.
In the unsolvated PBut3 complex, the diminution in the Cu–P dis-
tance is rather minor as compared to the changes in the Cu–S,N
(thiocyanate) distances; surprisingly, the angle between the latter
two bonds is diminished, while P–Cu–N(SCN) is greatly
enlarged.
IR spectroscopy
Selected bands in the IR and far-IR spectra of a selection of the
compounds studied in this work are listed in Table 3. The ν(CN)
band of the thiocyanate group, which occurs at about 2170 cm−1
in CuSCN,10 shows a decrease in frequency upon complexation
with the phosphine ligands. In both the α- and β-CuSCN poly-
morphs, the SCN group is bridging26,27 and ν(CN) occurs above
2100 cm−1 (Table 3).10 The complexes studied in the present
work whose structures are known contain either bridging
or S-bonded terminal SCN groups. An empirical correlation
between the thiocyanate bonding mode and the ν(CN) wavenum-
ber states that ‘ν(CN) is generally lower in N-bonded complexes
(near and below 2050 cm−1) than in S-bonded complexes (near
2100 cm−1)’ and that ‘bridging complexes exhibit ν(CN) well
above 2100 cm−1’.28 The results for the present set of complexes
are in broad agreement with these rules, particularly in relation
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Fig. 4 Plot of ν(CuX) vs. d(CuX) for X = S (●), N (ο); data points for
β-CuSCN and compounds 1, 5, 6, 8. The continuous lines are best fits to
eqn (1), with b = 5546, 1306 and m = 3.87, 2.57 for X = S, N
respectively.
SCN. For complex 2, only a single band is observed in the
far-IR in the ν(CuN)–ν(CuS) region, at 242 cm−1 (Fig. 3(b)). On
this basis we conclude that this compound contains terminally
bound SCN. According to the empirical rules mentioned above,
the ν(CN) value of 2059 cm−1 is indicative of N-bound SCN, so
we propose that 2 is a mononuclear species with trigonal P2CuN
bonding, which is very different to the structure of the corres-
ponding AgSCN complex in which, although also mononuclear
three-coordinate, the SCN is S-bound.31
Fig. 3 Far-IR spectra of (a) CuSCN : PCy3 (1 : 2)(∞|∞), 1, (b) CuSCN :
PCy3 (1 : 2), 2, (c) CuSCN : PCy3 (1 : 1), 3, (d) CuSCN : PCy3:py
(1 : 1 : 1), 4; bands assigned to ν(CuN) and ν(CuS) are labelled with
their wavenumbers.
Solid state 31P MAS NMR spectroscopy
The 31P CPMAS NMR data of complexes 1–10 are shown in
Fig. 5–7, and the derived NMR parameters are listed in Table 4.
Characteristic 31P CPMAS NMR spectra of copper(I)–phosphine
systems consist of quartets due to the 2I + 1 = 4 splitting arising
can be correlated with changes in the CuN and CuS bond
lengths, as follows. Correlations of the type
ν ¼ brꢀm
ð1Þ
1
from J(63,65Cu,31P) coupling between 63,65Cu (I = 3/2) and 31P
(I = 3/2) nuclei. The multiplet resonances arising from 31P coup-
ling to 65Cu are observed just outside of those arising from coup-
ling to 63Cu, due to the slightly larger magnetic moment of the
former. Furthermore, the resonances associated with a 1J
(63Cu,31P) multiplet are more than double the intensity of those
attributed to its 1J(65Cu,31P) counterpart; this arises from the
different natural abundances of the 63Cu and 65Cu isotopes (69.1
and 30.9%, respectively). The measured separations between the
quartet resonances increase from high to low frequency due to
the presence of residual dipolar coupling from incomplete MAS
averaging between the (I = 1/2) 31P and the quadrupolar (I = 3/2)
63,65Cu nuclei.18,42–46 Theoretical calculations of this scenario
have been reported using exact42 and first-order perturbation43,44
approaches. For the 31P–63,65Cu case a first-order analysis pre-
dicts a four-line 31P spectrum in which the outer two resonances
(δ1, δ4) are shifted upfield while the inner two resonances
(δ2, δ3) shift downfield by an amount d such that:
have previously been recorded for the M–X bonds in coinage
metal halide (M = Cu, Ag, Au; X = Cl, Br, I) complexes, and in
coinage metal tu, etu compounds (M = Cu, Ag; X = S), where ν
is the ν(MX) vibrational wavenumber/cm−1 and r is the d(MX)
bond length Å−1 36–41
Applying this to the ν(CuN) and ν(CuS)
.
bands for β-CuSCN and the complexes 1, 5, 6, 8 (ν(CuX) wave-
numbers from Table 3; Cu–X bond lengths from ref. 26 and
Tables 1 and 2) yields the fits shown in Fig. 4, with b = 5546,
1306 and m = 3.87, 2.57 for X = S, N respectively. This shows
that these vibrations have a similar dependence on bond length
to those of the other M–X bonds studied previously,36–41 and
supports the assignments made here. It can also be noted that
observation of both ν(CuN) and ν(CuS) bands in a particular
complex provides an unambiguous proof of the presence of brid-
ging SCN, in contrast to the empirical rule based on ν(CN),
which leads to the wrong conclusion in the case of 1 (see
above). Based on the presence of ν(CuN) and ν(CuS) bands in
the far-IR, it can be concluded that complexes 3, 4 and 7, for
which crystal structures are not available, all contain bridging
1JðCu; PÞ ¼ J ¼ ðΔ12 þ 2Δ23 þ Δ34Þ=4
ð2Þ
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Fig. 5 31P CPMAS NMR spectra (9.4 T, νr = 12 kHz) of (a) CuSCN :
PCy3 (1 : 2)(∞|∞), 1, (b) CuSCN : PCy3) (1 : 2), 2, (c) CuSCN : PCy3
(1 : 1), 3 and (d) CuSCN : PCy3 : py (1 : 1 : 1), 4.
Fig. 6 31P CPMAS NMR spectra (9.4 T, νr = 12 kHz) of (a)
and
SCN
NCS
[(o-tol3P)(MeCN)Cu( )Cu(MeCN)(P(o-tol)3)], 6, (b) CuSCN : P(o-tol
SCN
NCS
(1 : 1), 7, (c) [(o-tol3P)(py)Cu( )Cu(py)(P(o-tol)3)], 8, (d), (e)
d ¼ ðΔ23 ꢀ Δ12Þ=2 ¼ ðΔ34 ꢀ Δ23Þ=2 ¼ ðΔ34 ꢀ Δ12Þ=4 ð3Þ
SCN
NCS
[(Ph3P)2Cu( )Cu(PPh3)2], 9 (symmetrical), 10 (unsymmetrical), (f)
[CuSCN(PPh3)(py2)], 11 and (g) CuSCN : PPh3 : py (1 : 1 : 1) 12.
where Δ12, Δ23, Δ34 are the three line separations characterising
each quartet. To a first order approximation, d is linearly depen-
dent on field strength, and multiplication of d by the 63Cu
Zeeman frequency νCu yields a field independent parameter dνCu
that is suitable for comparison of results from spectra recorded at
different field strengths. This first order treatment yields
expression (4) below which relates the magnitude of dνCu and
appropriate spin-Hamiltonian parameters:
dνCu ¼ 0:15ðD ꢀ ΔJ=3Þð3cos2βD ꢀ 1
þ ηsin2βDcos2αDÞCQ;Cu
ð4Þ
where CQ,Cu = e2qQ/h is the 63Cu quadrupole coupling constant,
η is the electric field gradient tensor (EFG) asymmetry para-
meter, Deff = (D − ΔJ/3) which incorporates the Cu–P dipolar
coupling constant, D, the anisotropy in the J tensor, ΔJ, and the
polar angles defining the orientation of the Cu–P internuclear
vector with respect to the principal axis system of the EFG
tensor, αD and βD.43b,47 The dνCu parameter obtained from the
31P spectrum is a valuable tool for the comparison and qualitat-
ive analysis of the structure and coordination of the 63,65Cu
metal centre when X-ray structural data are unavailable.
Fig. 7 31P CPMAS NMR study (9.4 T, νr = 12 kHz) of the time pro-
SCN
NCS
gression from (a) as synthesized [(o-tol3P)(MeCN)Cu( )Cu(MeCN)-
SCN
NCS
(P(o-tol)3)], 6, to (b) a partial mixture of [(o-tol3P)-(MeCN)Cu( )-
Cu(MeCN)- (P(o-tol)3)], 6, and CuSCN : P(o-tol)3) (1 : 1), 7, after ca.
6 months, and (c) a final product of CuSCN : P(o-tol)3) (1 : 1), 7, after
further heating and desolvation at 50° C for 24 h.
The features described above are readily apparent in the 31P
CPMAS NMR data of complexes 1–10 shown in Fig. 5–7, and
selected systems from this suite have been studied with the 2D
31P CPCOSY technique as shown in Fig. 8. The spectrum of the
polymer CuSCN : PCy3 (1 : 2)∞|∞ 1 shown in Fig. 5(a) exhibits
additional complexities to the above description arising from the
two independent P atoms in the asymmetric unit. Apart from the
confirming the unambiguous assignment of each multiplet and
2
the occurrence of J(31P, 31P) coupling. From Table 4 the dνCu
values for 1 of 3.9 and 4.5 (× 109 Hz2; i.e. mid-range CQ values
of <20 MHz) are highly characteristic of a four-coordinate 63Cu
environment with soft P, N, S-donor ligands in the immediate
coordination sphere.18,48 The 31P CPMAS NMR data for com-
plexes CuSCN : PCy3 (1 : 2) 2, CuSCN : PCy3 (1 : 1) 3 and
CuSCN : PCy3 : py (1 : 1 : 1) 4 (see Fig. 5(b)–(d)) are far broader
1
appearance of two J(63,65Cu,31P) quartets in the 31P CPMAS
spectrum, further splitting is observed to influence each reson-
ance emanating from the 2J(31P, 31P) between the inequivalent
P sites in the CuP2 unit. A corresponding 31P 2D CPCOSY spec-
1
and exhibit only J(63,65Cu,31P) structure. Although viable crys-
tals and reliable X-ray structural analyses are not available for
these systems, some useful structural aspects can be elucidated
from these 31P CPMAS NMR data. The much larger dνCu values
1
trum of 1 in Fig. 8(a) clearly shows each J(63,65Cu,31P) quartet
symmetrically disposed about the main diagonal, thus
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of 13.9 and 15.4 (× 109 Hz2) for 2 and 3, respectively, (i.e. large
CQ values of >30 MHz) indicate that a planar, three-coordinate
Cu environment is fundamental to these structures; the large
downfield movement of the 31P isotropic chemical shift (δ(31P))
from δ ∼ 0 ppm (for 1) to δ > 13 ppm (for 2 and 3) further sup-
ports this conclusion. This contrasts markedly with the dνCu and
δ(31P) data for the pyridine coordinated complex CuSCN : PCy3 :
py (1 : 1 : 1) 4 which suggests that it is four-coordinate (in
similar fashion to 1), and is nominally dimeric or polymeric.
are clearly resolved from the dominant 63Cu quartet. Inspection
of the dνCu values from Table 4 (3.1 and 4.1 (× 109 Hz2),
respectively) shows that these values clearly reside within the
four-coordinate range discussed above, consistent with the X-ray
crystal structure analyses reported above. However, complex 7,
derived from the partial thermal decomposition of 6 (involving
the loss of one CH3CN molecule), exhibits a much increased
dνCu value of 12.8 (× 109 Hz2) suggesting that this product
is characterised by a three-coordinate Cu position, with the
possibility that such a component could be contained within an
SCN-bridged dimeric structure. The decomposition process is
demonstrated in Fig. 7, where initially under unforced conditions
of normal aging 6 is observed to transform to an apparent
mixture of 6 and the newly formed 7 after a period of ca.
6 months (see Fig. 7(a) and (b)). This decomposition is
From Fig. 6(a)–(c) the 31P CPMAS NMR data for the P(o-
SCN
NCS
tol)3 systems [(o-tol3P)(MeCN)Cu( )Cu(NCMe)(P(o-tol)3)] 6,
the thermally derived CuSCN : P(o-tol)3) (1 : 1) 7 and [(o-tol3P)-
(py)Cu(SNCCNS)Cu(py)(P(o-tol)3)] 8, respectively, can be observed.
The spectra for the dimeric systems 6 and 8 yield multiplet struc-
tures with narrow individual linewdiths, and the 65Cu satellites
Fig. 8 Two dimensional 31P CPCOSY MAS NMR spectra (9.4 T, νr = 12 kHz) of (a) CuSCN : PCy3 (1 : 2)(∞|∞), 1, (b)[(Ph3P)2Cu( )Cu(PPh3)2],
SCN
NCS
SCN
NCS
9 (symmetrical), (c), (d) [(Ph3P)2Cu( )Cu(PPh3)2], 10 (disordered, unsymmetrical) at small and large vertical expansion, respectively.
7522 | Dalton Trans., 2012, 41, 7513–7525
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accelerated to completion by further heating at 50° C for 24 h,
thus yielding the fully transformed complex 7.
throughout this process as indicated by the low dνCu values for 9
and 10 reported in Table 4. The 2D 31P CPCOSY data of Fig. 8
(b)–(d) are crucial in the study of these systems. Complex 9 has
two inequivalent P atom positions within the CuP2 component,
It is interesting to note that, although a large change in dνCu is
reported with this transformation to a lower Cu coordination
number for the P(o-tol)3 systems, the corresponding change in
δ(31P) is not pronounced. An upfield shift of only ∼4 ppm is
measured between the four-coordinate complex 6 (δ −14.4 ppm)
and the three-coordinate complex 7 (δ −18.6 ppm); this contrasts
markedly with shift differences exhibited by the PCy3 systems
where downfield shifts of up to ∼20 ppm are detailed between
the four-coordinate complex 1 and three-coordinate complexes 2
and 3 (see Table 4). A possible explanation may be that, for 1 vs.
2, 3, the change in coordination number entails the loss of a
strongly coordinated ligand (SCN in 2, PCy3 in 3), resulting in a
large change in chemical shift. By contrast, for 6 vs. 7, the
change is associated with loss of a weakly coordinated ligand
(MeCN), hence the small change in chemical shift. Furthermore,
the 31P chemical shift values for the P(o-tol)3 systems, typically
centred at δ ca. −16 ppm, are representative of shielded P
environments, relative to those in the PCy3 systems located at δ
ca. 0 ppm, thus reflecting the greater electron withdrawing
capacity of the Cy moiety.
1
so that the two J(63,65Cu,31P) quartets display the influence of
2
additional J(31P, 31P) coupling (see Fig. 8(b)); this result is very
similar to that shown for 1 in Fig. 8(a). In contrast, 10 possesses
some intrinsic positional disorder in one of the bridging SCN
elements which essentially produces two dimeric motifs within
the one structure. The 1D 31P CPMAS spectrum of 10 (see
Fig. 6(e)) presents intractable data which lack the necessary reso-
lution to support any meaningful measurements. However, the
corresponding 2D 31P CPCOSY data of Fig. 8(c) and (d) clearly
resolve the four P positions and accurate measurements of all
parameters are facilitated. It is clear from the low dνCu values
measured from 10 (see Table 4) that both dimeric arrangements
emanating from this disorder remain unambiguously four-coordi-
nate, consistent with the reported X-ray crystal structure.5b Simi-
larly, mechanochemical transformations on other PPh3 adducts
such as [CuSCN(PPh3)(py2)], 115b,6 efficiently yield the pyri-
dine-deficient structure CuSCN : PPh3 : py) (1 : 1 : 1), 12, which
nominally possesses a four-coordinate Cu environment (in a
dimeric or polymeric framework) as evidenced by the low dνCu
values of 1.8 and 3.2 (× 109 Hz2), respectively. This behaviour
may be compared with the PCy3 and P(o-tol)3 systems discussed
above, where a clear propensity for change to a three-coordinate
Cu environment upon thermal transformation exists, as demon-
strated by the large changes in the measured dνCu values.
Additional 31P CPMAS NMR measurements on previously
reported PPh3 systems such as CuSCN : PPh3 (1 : 2) (symmetri-
cal and unsymmetrical dimer, 9,5a 10,5b) and pyridine
coordinated variants such as [CuSCN(PPh3)(py2)]5b,6 and
CuSCN : PPh3 : py (1 : 1 : 1)5b are also given in Table 4. These
reveal a shift range centred around δ ca. −5 ppm which is in
between these characteristic P(o-tol)3 and PCy3 shift ranges. Of
particular note is the stability that PPh3 affords the CuSCN
system in maintaining a four-coordinate arrangement. A recrys-
tallisation of symmetrical dimeric CuSCN : PPh3 (1 : 2) 9 in the
presence of pyridine produces the disordered unsymmetrical
dimer 10; a subsequent mechanochemical treatment in the pres-
ence of acetonitrile facilitates the reformation of the original
dimer 9. The Cu atom remains distinctly four-coordinate
Conclusion
A number of adducts of copper(I) thiocyanate with bulky tertiary
phosphine ligands PR3, and some nitrogen-base solvates,
have been synthesized and structurally and spectroscopically
characterised. The results reveal a clear trend in the preferred
Table 4 31P CPMAS NMR parameters measured at 9.4 T; where 63Cu and 65Cu multiplet splitting is observed only data for the 63Cu component is
reported
Compound
δ(31P)/ppma Δ12/Hz Δ23/Hz Δ34/Hz 1J(CuP)/Hzb d/Hzc dνCu/109 Hz2 Refs.
CuSCN : PCy3 (1 : 2)(∞|∞) 1d
2.8
1065
1066
786
1209
1187
1480
1800
1564
1448
1765
1544
1062
1206
1094
1231
1214
1310
1834
1584
1565
1917
1674
1085
1223
1152
1179
1164
1264
1672
1539
1477
1720
1571
1054
1195
1099
42
37
131
145
35
29
121
39
20
13
4.5
3.9
13.9
15.4
3.7
3.1
12.8
4.1
2.1
1.4
This work
−2.1
13.7
22.6
5.8
−14.4
−18.6
−16.4
−2.9
−6.5
1.4
CuSCN : PCy3 (1 : 2) 2
CuSCN : PCy3 (1 : 1) 3
This work
This work
This work
This work
This work
This work
5a
1253
1443
1448
1434
1520
1005
1143
1054
CuSCN : PCy3 : py (1 : 1 : 1) 4
SCN
NCS
[(o-tol3P)(MeCN)Cu( )Cu(MeCN)(P(o-tol)3)] 6
CuSCN : P(o-tol)3 (1 : 1) 7 (= 6 after loss of MeCN)
SCN
NCS
[(o-tol3P)(py)Cu( )Cu(py)(P(o-tol)3)] 8
NCS
[(Ph3P)2Cu( )Cu(PPh3)2] 9 (centrosymmetric)d
SCN
SCN
NCS
[(Ph3P)2Cu( )Cu(PPh3)2] 10 (disordered,
25
2.7
5b
unsymmetrical dimer)e segment 1
−7.1
−1.3
−5.7
−6.8
−9.7
1113
1016
1152
1516
1392
1211
996
1231
1588
1489
1230
1133
1230
1582
1510
1191
1035
1211
1569
1470
29
29
20
17
30
3.1
3.1
2.1
1.8
3.2
segment 2
5b
[CuSCN(PPh3)(py)2] 11
CuSCN : PPh3 : py (1 : 1 : 1) 12
5b, 6
5b
a δ(31P) = (δ1 + δ2 + δ3 + δ4)/4; referenced against 85% H3PO4. b J = (Δ12 + 2Δ23 + Δ34)/4. c d = (Δ34 − Δ12)/4. d Two P sites in the asymmetric unit.
e Four P sites in the asymmetric unit.
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8 (a) G. A. Bowmaker, N. Chaichit, C. Pakawatchai, B. W. Skelton and
A. H. White, Dalton Trans., 2008, 2926; (b) G. A. Bowmaker,
N. Chaichit, C. Pakawatchai, B. W. Skelton and A. H. White,
Can. J. Chem., 2009, 87, 161; (c) G. A. Bowmaker, B. W. Skelton and
A. H. White, Inorg. Chem., 2009, 48, 3185; (d) G. A. Bowmaker,
C. Pakawatchai, S. Saithong, B. W. Skelton and A. H. White, Dalton
Trans., 2009, 2588; (e) G. A. Bowmaker, C. Pakawatchai, S. Saithong,
B. W. Skelton and A. H. White, Dalton Trans., 2010, 4391;
(f) G. A. Bowmaker, J. V. Hanna, B. W. Skelton and A. H. White, Dalton
Trans., 2009, 5447; (g) G. A. Bowmaker, J. V. Hanna, B. W. Skelton and
A. H. White, Chem. Commun., 2009, 2168; (h) G. A. Bowmaker,
C. Di Nicola, C. Pettinari, B. W. Skelton, N. Somers and A. H. White,
Dalton Trans., 2011, 40, 5102; (i) G. A. Bowmaker, Effendy,
J. V. Hanna, P. C. Healy, S. P. King, C. Pettinari, B. W. Skelton and
A. H. White, Dalton. Trans., 2011, 40, 7210; ( j) G. A. Bowmaker,
J. V. Hanna, B. W. Skelton and A. H. White, Dalton Trans., 2012, 41,
5409.
composition of CuSCN : PR3 (1 : n) complexes with increasing
steric bulk of the substituent R. For R = Ph only the 1 : 2
complex can be reproducibly obtained. For R = Cy, both 1 : 1
and 1 : 2 complexes are readily accessible. For R = o-tol, only
the 1 : 1 complex can be prepared, although an additional
smaller ligand (e.g. MeCN or py) can be accommodated in the
structure. For R = But, only the 1 : 1 complex is formed, even
when a large excess of PBut3 is used. Solvent-assisted mechano-
chemical synthesis helped unravel some unexpected complexities
in these systems, and is a more rapid and high-yielding method
than conventional solution synthesis for the preparation of bulk
pure samples of the compounds concerned.
9 (a) T. Friscic and W. Jones, Cryst. Growth Des., 2009, 9, 1621;
(b) T. Friscic, A. V. Trask, W. Jones and W. D. S. Motherwell, Angew.
Chem., Int. Ed., 2006, 45, 7546; (c) A. N. Swinburne and J. W. Steed,
CrystEngComm, 2009, 11, 433; (d) T. Friscic and L. Fabian, CrystEng-
Comm, 2009, 11, 743; (e) E. H. H. Chow, F. C. Strobridge and T. Friscic,
Chem. Commun., 2010, 46, 6368; (f) F. C. Strobridge, N. Judas and
T. Friscic, CrystEngComm, 2010, 12, 2409; (g) T. Friscic, J. Mater.
Chem., 2010, 20, 7599; (h) C. J. Adams, H. M. Colquhoun,
P. C. Crawford, M. Lusi and A. G. Orpen, Angew. Chem., Int. Ed., 2007,
46, 1124; (i) D. Braga, S. L. Giaffreda, F. Grepioni, A. Pettersen,
L. Maini, M. Curzi and M. Polito, Dalton Trans., 2006, 1249;
( j) D. Braga, M. Curzi, A. Johansson, M. Polito, K. Rubini and
F. Grepioni, Angew. Chem., Int. Ed., 2006, 45, 142; (k) L.-F. Yang,
M.-L. Cao, Y. Cui, J.-J. Wu and B.-H. Ye, Cryst. Growth Des., 2010, 10,
1263; (l) V. Strukil, L. Fabian, D. G. Reid, M. J. Duer, G. J. Jackson,
M. Eckert-Maksic and T. Friscic, Chem. Commun., 2010, 46, 9191;
(m) C. E. Willans, S. French, K. M. Anderson, L. J. Barbour,
J.-A. Gertenbach, G. O. Lloyd, R. J. Dyer, P. C. Junk and J. W. Steed,
Dalton Trans., 2011, 40, 573; (n) Y.-H. Tan, L.-F. Yang, M.-L. Cao,
J.-J. Wu and B.-H. Ye, CrystEngComm, 2011, 13, 4512; (o) D. Cincic,
M. Juribasic, D. Babic, K. Molcanov, P. Sket, J. Plavec and M. Curic,
Chem. Commun., 2011, 47, 11543; (p) C. Jobbagy, T. Tunyogi,
G. Palinkas and A. Deak, Inorg. Chem., 2011, 50, 7301; (q) S. L. James,
C. J. Adams, C. Bolm, D. Braga, P. Collier, T. Friscic, F. Grepioni,
K. D. M. Harris, G. Hyett, W. Jones, A. Krebs, J. Mack, L. Maini,
A. G. Orpen, I. P. Parkin, W. C. Shearouse, J. W. Steed and
D. C. Waddell, Chem. Soc. Rev., 2012, 41, 413.
Acknowledgements
We thank Dr Zoran D. Zujovic for the measurement of some
exploratory 31P CP MAS NMR spectra at 7.0 T. J.V.H. thanks
EPSRC and the University of Warwick for partial funding of the
solid state NMR infrastructure at Warwick, and acknowledges
additional support for this infrastructure obtained through
Birmingham Science City: Innovative Uses for Advanced
Materials in the Modern World (West Midlands Centre for
Advanced Materials Project 2), with support from Advantage
West Midlands (AWM) and partial funding by the European
Regional Development Fund (ERDF). J.V.H. acknowledges
the facilities of HECToR, the UK’s national high-performance
computing service, which is provided by UoE HPCx Ltd at the
University of Edinburgh, Cray Inc. and NAG Ltd, and funded by
the Office of Science and Technology through EPSRC’s High
End Computing Programme.
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Dalton Trans., 2012, 41, 7513–7525 | 7525