Spectroscopy and structures of two complete families, one mononuclear, the other binuclear, of 1:2 CuX:dptu stoichiometry (X = Cl, Br, I; 'Dptu' = N,N′-diphenylthiourea)

Article abstract of DOI:10.1039/b909167j

Crystallization of the copper(i) halides (CuX; X = Cl, Br, I) with N,N′-diphenylthiourea ('dptu' = (PhNH)₂CS) in 1:2 ratio from acetonitrile solution in ambient conditions yields a mononuclear isomorphous series of complexes of the form [XCu(dp

Full text of DOI:10.1039/b909167j

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www.rsc.org/dalton | Dalton Transactions
Spectroscopy and structures of two complete families, one mononuclear, the
other binuclear, of 1 : 2 CuX : dptu stoichiometry (X = Cl, Br, I; ‘dptu’ =
N,N¢-diphenylthiourea)†
Graham A. Bowmaker,*a Narongsak Chaichit,b John V. Hanna,c Chaveng Pakawatchai,d Brian W. Skeltone and
Allan H. Whitee
Received 8th May 2009, Accepted 14th July 2009
First published as an Advance Article on the web 13th August 2009
DOI: 10.1039/b909167j
Crystallization of the copper(I) halides (CuX; X = Cl, Br, I) with N,N¢-diphenylthiourea (‘dptu’ =
(PhNH)2CS) in 1 : 2 ratio from acetonitrile solution in ambient conditions yields a mononuclear
isomorphous series of complexes of the form [XCu(dptu)2]·H2O, an unusually complete array, with the
central copper atoms in quasi-trigonal planar environments, as shown by single crystal X-ray studies, in
turn providing a platform for comparative spectroscopic studies. Under anhydrous conditions,
anhydrous compounds may be obtained, a full series again being accessible, but now of the binuclear
form [(dptu)XCu(m-S-dptu)2CuX(dptu)], the chloride being a bis(acetonitrile) solvate, the isomorphous
bromide and iodide pair being unsolvated. A (solvated) sulfate salt is found to be of the form
[Cu(dptu)2]2(SO4), providing a novel example of a copper(I) atom being (quasi-)linearly coordinated by
◦
˚
the pair of unidentate (dptu) sulfur ligands, Cu–S 2.1770(5), 2.1811(5) A, S–Cu–S 162.18(2) . The
n(CuX) vibrational frequencies are assigned in the far-IR spectra of [XCu(dptu)2]·H2O (X = Cl, Br, I)
at 274, 207, and 190 cm-1 respectively. The broadline static 65Cu NMR spectra of [Cl2Cu2(dptu)4]·
2CH3CN and [X2Cu2(dptu)4] (X = Br, I) have been recorded at 9.4 and 7.05 T, and the spectra have
been analysed to yield the 65Cu nuclear quadrupole coupling and chemical shift parameters. The 63,65Cu
nuclear quadrupole resonance frequencies of [XCu(dptu)2]·H2O (X = Cl, Br, I) have also been
measured, and the resulting 65Cu quadrupole coupling constants are ca. 4¥ those of the dimeric
[X2Cu2(dptu)4] compounds.
Br, I) with the parent tu, of 1 : 3 stoichiometry, but that array is
Introduction
ionic [Cu(tu)3]+(•|•)X-, so that the variation in halide ion impacts
less emphatically on the form of the complex, which is a cationic
polymer, devoid of halide, which is the counterion.2) With N,N¢-
diphenylthiourea, (‘dptu’ = (PhNH)2CS), we have now obtained,
with CuX (X = Cl, Br, I), two series of complexes of 1 : 2 CuX : dptu
stoichiometry, one an isomorphous mononuclear series, of the
form [XCuL2](·H2O), defined by single crystal X-ray structure de-
terminations, which provide platforms for analytical spectroscopic
studies of these arrays; the structure of the [Cu(dptu)2]+ cation,
defined in a solvated sulfate salt, provides a useful quasi-linear
two-coordinate ‘baseline’ comparator. On preparing bulk samples
for spectroscopy, it was found that initial results were inconsistent
with expectations from the structural results, further work showing
that, working more rapidly with more concentrated solutions,
anhydrous compounds were obtained, also of similar form, across
all X = Cl, Br, I (albeit not all isomorphous), but, remarkably,
all binuclear, of the form [(dptu)XCu(m-S-dptu)2CuX(dptu)],
providing examples of a full series for that form also. We report
this work hereunder.
In a recent report1 we have summarized at some length the
fascinating array of complexes formed between simple salts of
copper(I), CuX, and (simple substituted) thiourea ligands, L (=
(x)tu), these varying from simple mononuclear complexes, of form
CuX : (x)tu (1 : n), (being [XCuLn] or [CuLn]X in form), to complex
oligonuclear arrays, some of high putative symmetry. Among the
former, despite the number and variety of systems studied, there is
a dearth of any series with a constant familial relationship across
arrays of the type [XCuLn], permitting comparison of the effect
of variation in X on bonding parameters of the array. (There is
an isomorphous (tetragonal) series for adducts of CuX (X = Cl,
aDepartment of Chemistry, University of Auckland, Private Bag 92019,
Auckland, New Zealand. E-mail: ga.bowmaker@auckland.ac.nz; Fax: +64
9 373 7422; Tel: +64 9 373 7599 ext. 88340
bPhysics Department, Thammasat University Rangsit, Pathumthani 12121,
Thailand
cDepartment of Physics, University of Warwick, Gibbet Hill Rd., Coventry,
UK CV4 7AL
dDepartment of Chemistry, Prince of Songkla University, Hat-Yai 90112,
Thailand
Experimental
eChemistry M313, School of Biomedical, Biomolecular and Chemical
Sciences, The University of Western Australia, Crawley 6009, Western
Australia, Australia
Synthesis
† CCDC reference numbers 660459–660462 and 671528–671530. For
crystallographic data in CIF or other electronic format see DOI:
10.1039/b909167j
Dichlorotetrakis(diphenylthiourea)dicopper(I) bis(acetonitrile)
solvate, [Cl2Cu2(dptu)4]·2CH3CN.
A mixture of copper(I)
8308 | Dalton Trans., 2009, 8308–8316
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chloride (0.50 g, 5 mmol) and diphenylthiourea (2.28 g, 10 mmol)
in acetonitrile (16 ml) was heated with stirring until all of the
solids dissolved, yielding a yellow solution which deposited
yellow crystals of the product upon cooling. Yield 2.64 g (89%).
Anal. calcd for C56H54Cl2Cu2N10S4: C, 56.36; H, 4.56; N, 11.74%.
Found: C, 56.2; H, 4.8; N, 11.5%.
after ‘empirical’/multiscan absorption correction (proprietary
software) (No with F > 4s(F) considered ‘observed’), which
were used in the full matrix least squares refinements on F2,
refining anisotropic displacement parameter forms for the non-
hydrogen atoms, hydrogen atoms being included following a riding
2
2
model (reflection weights: (s (Fo2) + (aP)2 (+ bP))-1, (P = (Fo
+
2
2Fc )/3)). Neutral atom complex scattering factors were employed
within the SHELXL 97 program.3 Pertinent results are given below
and in the Tables and Figures, the latter showing 20% (298 K), 50%
(153, 100 K) probability amplitude displacement ellipsoids for
the non-hydrogen atoms, hydrogen atoms having arbitrary radii
Dibromotetrakis(diphenylthiourea)dicopper(I), [Br2Cu2(dptu)4].
A mixture of copper(I) bromide (0.72 g, 5 mmol) and diphenylth-
iourea (2.28 g, 10 mmol) in acetonitrile (30 ml) was heated with
stirring to boiling, yielding a yellow solution which deposited
pale yellow crystals upon cooling. Yield 2.79 g (93%). Calcd for
C52H48Br2Cu2N8S4: C, 52.04; H, 4.03; N, 9.34%. Found: C, 52.3;
H, 4.3; N, 9.5%.
˚
of 0.1 A (where shown). See Table 1 for crystal structure and
refinement data.
Diiodotetrakis(diphenylthiourea)dicopper(I), [I2Cu2(dptu)4].
A
Infrared spectroscopy
mixture of copper(I) iodide (0.95 g, 5 mmol) and diphenylthiourea
(2.28 g, 10 mmol) in acetonitrile (40 ml) was heated with stirring
to boiling. The solution turned yellow and a microcrystalline
pale yellow solid formed. Further pale yellow solid formed upon
cooling. Yield 3.06 g (95%). Calcd for C52H48Cu2I2N8S4: C, 48.26;
H, 3.74; N, 8.66%. Found: C, 48.5; H, 4.0; N, 8.8%.
Infrared spectra were recorded at 4 cm-1 resolution as Nujol
mulls between KBr plates on a Perkin Elmer Spectrum 1000
Fourier-transform infrared spectrometer. Far-infrared spectra
were recorded using a Nicolet 8700 FTIR spectrometer on samples
suspended in Polythene disks.
Halogenobis(diphenylthiourea) copper(I) monohydrate, [XCu-
(dptu)2]·H2O (X = Cl, Br, I). Originally these were obtained
straightforwardly as nicely crystalline solids by dissolving ca.
10 mmol (ca. 2.3 g) of diphenylthiourea together with 5 mmol of
the copper(I) halide in acetonitrile (ca. 100 ml), with warming and
stirring; the yellow solutions were filtered and allowed to stand
in ambient conditions, depositing, after some time, colourless
crystals of [XCuL2]·H2O suitable for the X-ray work. (Mp X =
Cl, Br, I: 169–171, 187–190, 193–195 ◦C, respectively). Bulk
samples for spectroscopic studies were subsequently made by the
deliberate addition of water to hot solutions of [X2Cu2(dptu)4]
in acetonitrile, the water content being 10–20% by volume. The
colourless crystalline products separated upon cooling, with yields
>90%. Anal. X = Cl, calcd for C26H26CuClN4OS2: C, 54.44; H,
4.57; N, 9.77%. Found: C, 54.4; H, 4.7; N, 9.9%; X = Br, calcd for
C26H26BrCuN4OS2: C, 50.52; H, 4.24; N, 9.06%. Found: C, 50.8;
H, 4.5; N, 9.3%; X = I, calcd for C26H26CuIN4OS2: C, 46.95; H,
3.94; N, 8.42%. Found: C, 47.1; H, 4.2; N, 8.6%.
Attempts to obtain useful crystals of the 1 : 2 sulfate salt (as
an example of a species likely to yield a linearly coordinated
[Cu(dptu)2]+ array in the presence of a non- or poorly-coordinating
counterion) by commencing with an appropriate stoichiometry of
copper(II) sulfate, also in acetonitrile, were generally unsuccessful;
on one occasion a few small crystals were obtained after prolonged
standing in ambience, shown by a diffraction study to essentially
be such a material, containing cocrystallized/‘solvating’ PhNCS,
presumably arising from degradation of the ligand upon standing
in ambience. Attempts to prepare 1 : 2 or 1 : 3 sulfate or nitrate salts
by reaction of cuprous oxide and diphenylthiourea in bulk in the
appropriate molar ratios with sulfuric or nitric acid in acetonitrile
resulted in yellow solutions from which only yellow oils separated
upon evaporation of the solvent.
65Cu broadline NMR and 63/65Cu NQR spectroscopy
Static broadline 65Cu NMR data were acquired at ambient
temperatures on 7.1 T and 9.4 T systems using Varian Infinity
Plus-300 and Bruker DSX-400 spectrometers operating at 65Cu
Larmor frequencies of 85.20 MHz and 113.67 MHz, respectively.
These measurements were performed using Bruker 5/7.5 mm static
horizontal solenoid design probes. All static 65Cu data were ac-
quired with the solid echo q–t–q–t–(acquire) experiment with an
extended phase cycle to capture undistorted echoes with minimal
influence from residual echo tails.4,5 ‘Non-selective’ (solution) p/2
pulse times of 2 ms were calibrated on a solid Cu(I)Cl sample
from which a ‘selective’ (solid) q pulse of 0.6 ms was employed
in all solid echo measurements. The t delay was 20 ms and the
relaxation delay between transients was 0.5 s. Measurements at
9.4 T required one on-resonance experiment to uniformly excite
the central (-1/2↔+1/2) transition resonances. However the
broader 7.1 T resonances required recourse to the VOCS (Variable
Offset Cumulative Spectroscopy) technique to add frequency-
offset subspectra, thus ensuring the acquisition of undistorted
lineshapes.6–8 This method entails the stepping of the solid echo
experiment through a suitable number of carrier frequencies
(typically offset by 100 kHz) to uniformly excite the full width of
each central transition resonance. For these 7.1 T data, co-addition
of five subspectra (after shifting to a common spectral reference)
provided an undistorted representation of each broad lineshape.
All 65Cu isotropic chemical shifts diso are referenced directly to
Cu(I)Cl, which was assigned to d 0.0 ppm. The 65Cu signal in
Cu(I)Cl was measured at d -337.0 ppm relative to the prim◦ary
standard saturated [Cu(CH3CN)4]ClO4 in dry CH3CN at 20 C.
All 65Cu static broadline spectra were simulated with the Bruker
TOPSPIN solids package and the QUASAR solid state NMR
data simulation program 9 to deconvolute the nuclear quadrupole
and chemical shift anisotropy components contributing to these
lineshapes. This treatment facilitated an accurate measurement of
the isotropic chemical shift (diso), quadrupole coupling constant
(CQ), nuclear quadrupole asymmetry parameter (hQ), chemical
Structure determinations
Full spheres of CCD area-detector diffractometer data were
measured (w-scans; monochromatic Mo-Ka radiation, l =
˚
0.71073 A), Nt(otal) reflections merging to N unique (Rint cited)
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Table 1 Crystal/refinement data
Binuclear arrays C52H48X2Cu2N8S4,
[(dptu)XCu(m-S-dptu)2CuX(dptu)]
Mononuclear arrays C26H26XCuN4OS2, [XCu(dptu)2]·H2O
a
Cl
Br
I
SO4
Clb
Br
I
Mr/Da
573.7
618.1
665.1
611.0
1193.3
1200.2
1294.1
Crystal system
Space group
Triclinic
Triclinic
Triclinic
Orthorhombic
Pnma (#62)
17.367(1)
24.495(2)
13.292(1)
Monoclinic
P21/c (#14)
12.3405(1)
12.1787(1)
18.4154(2)
Monoclinic
P21/n (#14)
11.8704(2)
12.2178(1)
18.0909(3)
Monoclinic
P21/n (#14)
11.9993(2)
12.1609(3)
18.4265(4)
¯
¯
¯
P1 (#2)
P1 (#2)
P1 (#2)
˚
a/A
9.4076(5)
12.0075(6)
12.6204(4)
89.217(3)
73.998(3)
69.361(4)
1277
1.492
2
1.15
0.26,0.18,0.03
0.99
9.4378(5)
12.1456(6)
12.6684(4)
90.047(3)
73.966(3)
69.386(4)
1299
1.581
2
2.6
0.34,0.33,0.055
0.62
67.5
27 220
12 945 (0.039)
8308
0.034
0.095
0.045
1.00
9.5132(3)
12.4449(3)
12.7948(2)
91.807(2)
73.165(2)
69.216(2)
1340
1.648
2
2.1
0.26,0.20,0.03
0.64
75
47 834
13 635 (0.051)
8846
0.032
0.090
0.048
0.95
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
92.551(1)
106.214(1)
106.447(2)
3
˚
V/A
5655
1.435
8
1.011
0.25,0.21,0.18
0.84
2765
1.433
2
1.065
0.17,0.16,0.12
0.91
2519
1.582
2
2579
1.667
2
2.23
0.15,0.13,0.04
0.89
75
56 745
13 255 (0.045)
7367
0.048
0.123
0.052, 1.22
1.056
100
Dc/g cm-3
Z
m
Mo/mm-1
2.6
Specimen/mm
0.18,0.11,0.08
0.87
70
89 483
10 683 (0.061)
7071
0.028
0.060
0.028
0.94
Tmin/max
◦
2qmax
Nt
/
67.5
57
70
24 509
10 140 (0.049)
5615
0.039
0.090
0.039
0.84
100
65 458
7472 (0.029)
5929
0.035
0.099
0.054, 2.39
1.04
153
50 097
11 555 (0.045)
7715
0.030
0.070
0.035
0.94
N (Rint
No
R1
)
wR2
a(, b)
S
T/K
100
100
100
100
a This complex was modeled as [Cu(dptu)2](SO4)0.5·(H2O)0.5·(PhNCS)0.25 ∫ C27.75H26.25CuN4.25O2.5S2.75. Phenyl ring 41 was modeled as disordered over two
sets of sites of equal occupancy, concerted with a pair of residues modeled as water molecule oxygen atom fragments. Site occupancy of the PhNCS
residue was set at 0.5 after trial refinement; it, the water molecule components and SO2 of the anion lie in the crystallographic mirror plane. b The complex
is an acetonitrile di-solvate, C56H54Cl2Cu2N10S4.
shift anisotropy (Dd)/chemical shift span (X) and asymmetry
(hd )/skew (k), and the Euler angles a,b,g relating the nuclear
quadrupole and chemical shift tensor frames.
unit of the structure. Within each ligand, one of the NH groups
(# n2) hydrogen bonds intramolecularly to the halide atom, while
the n1 NH groups hydrogen bond to the water molecule oxygen
atom, catenating thus (Fig. 1). Although there is some variation
in the disparity in the X–Cu–S pair of angles along the series,
S–Cu–S is essentially constant, Cu–S exhibiting a slight increase
on passing from chloride to iodide (Table 2).
63Cu and 65Cu NQR frequencies (nQ,
and nQ, Cu) were
63
65
Cu
obtained at ambient temperature by solid echo pulse methods
using a Chemagnetics CMX-200 console which delivered high-
power rf pulses into a probe arrangement that was shielded from
extraneous magnetic and rf interference by a mumetal container.
Similar solid echo experiments with extended phase cycles to
those outlined above were implemented for these measurements,
utilizing power levels of ~600 Vp-p (i.e. ~212 Vrms or 940 W) and
recycle delays 0.5 s. The values of nQ(63Cu) obtained from the 63Cu
nuclei were verified by measurement of the corresponding nQ(65Cu)
from the 65Cu nuclei which are related by the ratio of the nuclear
quadrupole moments (Q):
nQ(63Cu)/nQ(65Cu) = Q(63Cu)/Q(65Cu) = 1.0806
(1)
This ensured that all reported NQR frequencies were correctly
attributed to Cu nuclei, thus eliminating the possibility of associ-
ating a measured frequency with an energy level transition from
other quadrupolar nuclei in each sample.
Results and discussion
X-Ray structures
[XCu(dptu)2]·H2O (X = Cl, Br, I) crystallize with one formula unit,
Fig. 1 Projection of a single molecule of [ClCu(dptu)2] normal to the
coordination plane.
devoid of crystallographic symmetry, comprising the asymmetric
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the present dptu complex is by far the smallest at 108.63(6)◦. These
considerations have parallels for the X = Br, I arrays, where the
body of data is more limited.
Table 2 Selected geometries [XCu(dptu)2] (X = Cl, Br, I) The three values
in each entry are for X = Cl, Br, I, respectively
Atoms
Parameter
In keeping with previous studies obtaining CuX : L (1 : n)
complexes in ionic form with uncoordinated counterion X which
were successful using X = SO4, we attempted to obtain such a
1 : 2 adduct with X = sulfate. Success here was not as clean as
could be desired, a successful crystallization on a limited scale
producing a few crystals of such an adduct but cocrystallized
with a component readily identified as the ligand degrada-
tion product phenyl isothiocyanate, additional difference map
residues being assigned as water molecule oxygen atom fragments,
thus [Cu(dptu)2](SO4)0.5(H2O)0.5(PhNCS)0.25. This comprises the
asymmetric unit of the structure: a single [Cu(dptu)2]+ cation
devoid of crystallographic symmetry, a sulfate ion with an SO2
component lying in the mirror plane of space group Pnma (the
other pair of oxygen atoms symmetry related to either side), and
phenylisothiocyanate and water molecule oxygen atom fragments
also lying in the mirror plane (Fig. 2(a)).
˚
Distances/A
Cu–X
Cu–S(1)
Cu–S(2)
2.2269(6), 2.3575(2), 2.5227(3)
2.2046(5), 2.2114(2), 2.2276(5)
2.2265(6), 2.2261(2), 2.2380(5)
Angles/◦
X–Cu–S(1)
X–Cu–S(2)
S(1)–Cu–S(2)
Cu–S(1)–C(1)
Cu–S(2)–C(2)
127.28(2), 125.575(7), 125.31(2)
124.68(2), 125.986(6), 128.05(2)
108.04(2), 108.433(7), 106.62(2)
111.18(6), 111.91(2), 112.43(7)
108.99(8), 119.94(2), 110.96(7)
˚
Out-of-plane (SCN2) copper atom deviations (dCu/A)
Plane 1
Plane 2
0.142(3), 0.173(2), 0.248(3)
0.497(3), 0.506(2), 0.511(3)
Core (XCuS2)/ligand (SCN2) interplanar dihedral angles/◦
Ligand 1
Ligand 2
16.95(5), 18.04(4), 20.89(6)
16.22(6), 16.10(4), 15.86(7)
Intraligand SCN2/C6(ar) interplanar dihedral angles/◦
Ligand 1/Ph(1)
Ligand 1/Ph(2)
Ligand 2/Ph(1)
Ligand 2/Ph(2)
63.18(7), 62.39(4), 63.16(8)
88.51(9), 88.88(4), 89.72(9)
53.81(7), 53.04(4), 51.51(7)
40.13(8), 39.01(4), 40.83(9)
˚
Hydrogen bonds: intramolecular/A
X ◊ ◊ ◊ N(12)
3.526(2), 3.5673(5), 3.684(2)
2.7, 2.7, 2.8
3.257(2), 3.510(6), 3.656(2)
2.4, 2.6, 2.8
X ◊ ◊ ◊ H(12)
X ◊ ◊ ◊ N(22)
X ◊ ◊ ◊ H(22)
˚
Hydrogen bonds: other/A
O ◊ ◊ ◊ N(11i)
O ◊ ◊ ◊ H(11i)
O ◊ ◊ ◊ N(21ii)
O ◊ ◊ ◊ H(21ii)
2.920(2), 2.9269(7), 2.930(2)
2.1, 2.1, 2.1
3.005(2), 3.0005(6), 3.010(2)
2.3, 2.3, 2.3
Transformations of the asymmetric unit: i 1 - x, 1 - y, z¯; ii x¯, 1 - y, 1 - z.
Curiously, although a number of other adducts of mononuclear
1 : 2 CuX : L composition have been structurally defined (Table 3),
all are of the form L = (substituted) etu, with, also, a pair of
ptu (SC(NHCH2)2CH2), with an angular constraint at the SC
carbon atom imposed by the five- (or six-) membered rings. All
of the pertinent NQR studies are drawn from those examples also
(the NQR studies being conducted in tandem with the structure
determinations).17–19 The coordination environment parameters
of these systems are also presented in Table 3. The scatter in
comparable parameters is large, the comparison unassisted by
data for any common ligand L across X = Cl, Br, I, except in
the present array. For the L = xetu, X = Cl adducts, Cu–Cl
distances range between 2.238(2)–2.279(2) with the mmetu ex-
ample at the lower limit, in turn just higher than the present value
Fig. 2 (a) Unit cell contents of (solvated) [Cu(dptu)2](SO4)0.5, projected
down c. (b) Projection of the [Cu(dptu)2]+ cation.
˚
of 2.2269(6) A, which is the shortest of all. By contrast the value
˚
for the ptu complex is the longest (2.317(3) A). The values of Cu–S
Viewed appropriately (Fig. 2(b)), the cation has quasi-2 sym-
˚
˚
˚
are more closely ranged, albeit between 2.205(2)–2.230(2) A with
metry. Cu–S(1,2) are 2.1811(5), 2.1770(5) A, ca. 0.05 A less than
the values observed in the [XCuL2] neutral molecular adducts
discussed above. S–Cu–S is 162.18(2)◦, with Cu–S–C 104.76(6),
106.48(6)◦. Although there are approaches to the copper atom
from the shrouding phenyl rings 2 and 3 which might account for
the above departure from S–Cu–S linearity (Cu ◊ ◊ ◊ C(21, 26, 31, 32)
the extremal values being pertinent to the one compound (L =
ipetu). The S–Cu–S angles range between 118.23(6)–121.9(1)◦, but
with that for the mmetu example outstandingly large at 134.2(1)◦,
presumably in consequence of steric hindrance between ligands,
the ptu example also slightly enlarged at 123.4(1)◦. The value for
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◦
˚
Table 3 Structurally defined [XCuL2] systems: comparative copper(I) atom environments (A,
)
Compounda
Cu–X
Cu–S
S–Cu–S
X–Cu–X
(a) X = Cl
[ClCu(metu)2]10
[ClCu(eetu)2]11
[ClCu(petu)2]12
(2 mol)
2.279(2)
2.238(2)
2.257(2)
2.2693)
2.246(2)
2.233(3)
2.2269(6)
2.317(3)
2.217(1) (¥2)
119.34(6)
118.5(1)
119.1(1)
121.9(1)
118.23(6)
134.2(1)
108.04(2)
123.4(1)
120.33(3) (¥2)
2.218(2), 2.214(2)
2.209(2), 2.223(3)
2.193(3), 2.223(2)
2.205(2), 2.230(2)
2.229(3) (¥2)
121.4(1), 120.1(1)
120.6(1), 120.4(1)
120.7(1), 117.3(1)
122.85(6), 118.92(5)
112.9(1) (¥2)
[ClCu(ipetu)2]13
[ClCu(mmetu)2]14
[ClCu(dptu)2]b
[ClCu(ptu)2]15
2.2046(5), 2.2265(6)
2.206(2) (¥2)
127.28(2), 124.68(2)
118.3(1), 110.0(2)
(b) X = Br
[BrCu(eetu)2]13
[BrCu(ipetu)2]13
[BrCu(dptu)2]b
[BrCu(ptu)2]16
2.366(2)
2.372(1)
2.3575(2)
2.405(2)
2.206(3), 2.210(2)
2.220(2), 2.220(2)
2.2114(2), 2.2261(2)
2.215(4) (¥2)
116.2(1)
120.69(8), 123.13(8)
123.34(6), 124.67(6)
125.575(7), 125.986(6)
119.6(1) (¥2)
111.98(7)
108.433(7)
120.8(2)
(c) X = I
[ICu(petu)2]13,17
[ICu(dptu)2]b
2.531(2)
2.5227(3)
2.227(4), 2.240(4)
2.2276(5), 2.2380(5)
111.4(1)
106.62(2)
122.5(1), 126.0(1)
125.31(2), 128.05(2)
a Ligand abbreviations: xetu = SCNR(CH2)2NH, R = Me (x = m), Et (e), nPr (p), Pr (ip); mmetu = SC(NMe(CH2))2; ptu = SC(NHCH2)2CH2. b This
work.
˚
2.798, 2.806, 2.867, 2.884(2) A), the explanation may be more
conveniently found to originate further afield in interactions of
the NH hydrogen atoms pairwise with nearby sulfate groups, thus:
NH(1) ◊ ◊ ◊ O(2i) 2.846(2), 1.98 (est.), NH(2) ◊ ◊ ◊ O(3i) 2.823(2), 1.95
(est.); NH(3) ◊ ◊ ◊ O(3) 2.878(2), 2.04 (est.), NH(4) ◊ ◊ ◊ O(1), 2.795(2),
1
1.99 A (est.) (i ∫ 12 - x, 1 - y, z - 12 ). S–O(1–3) are 1.480(2),
˚
˚
1.479(2), 1.475(1) (¥2) A, with O(1)–S–O(2, 3) 109.5(1), 108.8(1)
(¥2), O(2)–S–O(3) 109.14(7) (¥2), O(3)–S–O(3) 111.5(1)◦.
Examples of copper(I) linearly coordinated by a pair of uniden-
tate thio ligands are surprisingly sparse, the present seemingly
the first example of its type. Comparison may be made with the
[Cu(S·CO·Ph)2]- species,20 wherein Cu–S are 2.151(3) A, S–Cu–S
˚
◦
176.6(2) , [Cu(SAd)2]- (Ad ∫ adamantanyl) Cu–S 2.147(1) A,
˚
S–Cu–S 180◦
and, in a bi◦s(S-dithiocarbamyl) environment,
21
Cu–X 2.163(9) A, S–Cu–S 180 ,22 all essentially harmonious with
the present.
˚
Working more rapidly, with more concentrated solutions to
obviate the uptake of ambient moisture, procedures involving all
of X = Cl, Br, I readily yield the adducts of 1 : 2 stoichiometry, this
time in a new anhydrous form found to be binuclear [(dptu)XCu(m-
S-dptu)2CuX(dptu)], a novel structural type (Fig. 3) previously
only structurally defined in the 1 : 2 CuBr : etu adduct.1 In all
three complexes, the dimer is located about a crystallographic
centre of symmetry, one half comprising the asymmetric unit of
the structure; the bromide and iodide are isomorphous, but the
chloride, although crystallizing in a similar cell, is solvated with
well-defined acetonitrile, the molecular conformation being very
similar to that of the other two. Yet again, as in the previous
complexes and the parent ligand,23 it appears that hydrogen
bonding is an important contributor to the stability of the form: as
in the etu/Br adduct, the halide ion is involved in intramolecular
hydrogen bonds to each of the two ligands (Table 4). Perhaps in
consequence of these and other lattice interactions, as in the etu/Br
adduct, there are considerable distortions from mmm symmetry
among the ‘heavy atom’ (X/Cu/S) core array; in the etu/Br adduct
Cu–Sb,Sb¢ are essentially equivalent, but ‘equivalent’ angles are
Fig.
3 Projection of binuclear [(dptu)ClCu(m-S-dptu)2CuCl(dptu)]
oblique to the CuS2Cu core plane.
perhaps more disparate than in the dptu/X counterparts, where
the Cu–Sb,Sb¢ distances differ appreciably. Cu-X,St are appreciably
longer (by ca. 0.06 A) than in the [XCu(dptu)2] arrays, as befits the
increase in coordination number from three to four.
˚
IR spectroscopy
The far-IR spectra of the dptu ligand and of the complexes
[XCu(dptu)2]·H2O (X = Cl, Br, I) are shown in Fig. 4. Diphenylth-
iourea shows several bands due to internal vibrational modes,
but the region from 150 to 400 cm-1 is reasonably clear of strong
ligand bands, providing an opportunity to detect the single n(CuX)
bands expected for the simple trigonal monomer structures in
these complexes. According to previously established correlations
between the Cu–X bond length and the n(CuX) vibrational
frequencies,24 the frequencies corresponding to the Cu–X bond
8312 | Dalton Trans., 2009, 8308–8316
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Table 4 Selected geometries, [(dptu)XCu(m-S-dptu)2CuX(dptu)2] All
species in this table are (crystallographically) centro-symmetric; inversion-
generated atoms are denoted by a prime, b and t subscripts denoting
bridging and terminal sulfur atoms
X
Cl
Br
I
Bra
˚
Distances/A
Cu–X
Cu–St
2.3130(3)
2.2823(3)
2.3044(3)
2.4698(3)
2.9823(3)
3.7319(4)
2.4347(2)
2.6060(3)
2.2946(7)
2.3343(7)
2.4928(7)
3.0949(5)
3.7078(9)
2.4987(3)
2.2814(4)
2.3232(4)
2.4840(4)
3.0999(3)
3.6777(5)
2.2841(6)
2.3819(5)
2.3851(5)
2.7238(5)
3.9122(7)
Cu–Sb
Cu–Sb¢
Cu ◊ ◊ ◊ Cu¢
Sb ◊ ◊ ◊ Sb¢
Angles/◦
Cu–Sb–Cu¢
Sb–Cu–Sb¢
Sb–Cu–St
Sb–Cu–X
Sb¢–Cu–St
Sb¢–Cu–X
St–Cu–X
77.23(1)
102.77(1)
106.60(1)
115.90(1)
108.54(1)
103.60(1)
118.10(1)
80.23(1)
99.77(1)
99.23(1)
79.68(2)
100.32(2)
99.98(2)
120.89(2)
105.74(3)
103.82(2)
123.12(2)
69.69(2)
110.31(2)
106.16(2)
111.72(2)
112.75(2)
94.02(2)
121.20(1)
106.14(1)
104.62(1)
122.91(1)
121.39(2)
˚
Intramolecular hydrogen bonds/A
N(12) ◊ ◊ ◊ X
H(12) ◊ ◊ ◊ X
N(22) ◊ ◊ ◊ X
H(22) ◊ ◊ ◊ X
3.256(1)
2.39
3.198(1)
2.38
3.472(1)
2.64
3.479(1)
2.66
3.590(2)
2.78
3.607(2)
2.78
3.382(2)
2.70
3.376(2)
2.58
a Counterpart values for the etu/Br analogue (ref. 1).
lengths in Table 2 are 273, 208 and 181 cm-1 for X = Cl, Br, I
respectively. Thus the bands at 274, 207, and 190 cm-1 (Fig. 4(b–
d)) can be assigned to the n(CuX) modes in these complexes.
The n(CuS) modes in copper(I) ethylenethiourea complexes have
been assigned in the range 180–230 cm-1,25 and corresponding
vibrations involving the heavier dptu ligand are expected to occur
in a lower frequency range. Bands observed in the range 115–
160 cm-1 are in the right range to be thus assigned, but, because
these occur in the same range as vibrational modes of the ligand
(Fig. 4(a)), no definite assignments can be made.
Fig. 4 Far-IR spectra of (a) the dptu ligand, and (b–d) [XCu(dptu)2]·H2O
(X = Cl, Br, I). Bands assigned as n(CuX) are labelled with their
wavenumbers.
The far-IR spectra of [Cl2Cu2(dptu)4]·2CH3CN and of
[X2Cu2(dptu)4] (X = Br, I) are shown in Fig. 5. From the
Cu–X bond lengths in Table 4, n(CuX) bands are expected at
227, 176 and 151 cm-1 for X = Cl, Br, I respectively. In the case of
X = Cl, there is a definite band at 225 cm-1 (Fig. 5(a)) that can be
assigned as n(CuCl). For X = Br, I there are very weak bands at
175 and 146 cm-1, respectively (Fig. 5(b, c), but these are not clear
enough to allow unambiguous assignment.
strated for the tetrahedrally coordinated [Cu(t-BuNC)4]X (X =
Cl, Br, I) complexes, for example.27 For larger 65Cu quadrupole
coupling constants, the ( 1/2↔ 3/2) satellites become too broad
to detect, and the central (-1/2↔1/2) line shows a line shape due
to second-order quadrupole broadening. At lower values of the
static external field strength B0 (i.e. ≤9.4 T), if the 65Cu quadrupole
coupling constant CQ is greater than about 20 MHz, this second-
order broadening becomes too great to allow detection of this
resonance by a single solid-echo experiment, and frequency-offset
subspectral addition methods (sometimes with very large numbers
of subspectra) or NQR techniques need to be invoked. This is the
case for the compounds [XCu(dptu)2]·H2O (X = Cl, Br, I) studied
in the present work, where 65Cu coupling constants of 50 MHz or
more were determined from the NQR spectra of these compounds
(see below); these large CQ values are attributed to the distorted
trigonal copper(I) coordination environments in these compounds.
However, for the dimeric [X2Cu2(dptu)4] compounds, in which
the Cu atoms are found in distorted tetrahedral coordination
environments, at the lower B0 fields implemented in this study (i.e.
≤9.4 T), the Cu nuclear quadrupole coupling is sufficiently small to
be accommodated by a single 65Cu NMR solid-echo measurement,
or only a few solid-echo measurements in a summed frequency-
offset arrangement.
Broadline 65Cu NMR spectroscopy
Despite the high natural abundance and the relatively high
magnetic moments of the two naturally occurring isotopes of
copper, 63Cu (69.1%, I = 3/2) and 65Cu (30.9%, I = 3/2), copper
NMR spectra are usually difficult to record and interpret because
of the large nuclear quadrupole coupling that is present in most
copper compounds.26a Because of its lower nuclear quadrupole
moment, 65Cu is the preferred copper nuclide for NMR studies,
despite its lower natural abundance. In compounds where the Cu
atom lies on a site of nearly exact tetrahedral symmetry, the Cu
quadrupole coupling constant CQ is very small, and the 65Cu NMR
spectrum of a static powder sample shows a relatively sharp central
(-1/2↔1/2) line and broad ( 1/2↔ 3/2) satellites displaying
first-order quadrupole splitting. This has recently been demon-
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interaction is dominant and, since the second-order quadrupole
interaction is inversely proportional to the external magnetic field
strength B0,26b the lines are narrower at 9.4 T than at 7.05 T
(Fig. 6). The quadrupole coupling constants CQ lie in the range
15–16 MHz, and are much lower than the values observed for
the monomeric [XCu(dptu)2] compounds (50 MHz or greater; see
below). This is entirely consistent with the change from trigonal
planar to tetrahedral coordination from the monomeric to the
dimeric complexes. There is a slight trend of decreasing CQ with X
along the series Cl > Br > I (Table 5). A more pronounced trend
in the same direction is observed for the monomeric [XCu(dptu)2]
compounds (see below), and this is discussed further in the next
section.
The isotropic chemical shifts diso for [X2Cu2(dptu)4] lie in the
middle of the range -100 to 1050 ppm that has recently been
reported for a range of copper(I) coordination compopunds.28 In
this latter work it was noted that there is no simple correlation
between diso and the coordination geometry or the chemical nature
(e.g. electronegativities) of the first coordination sphere atoms.
The only noticeable trend was that complexes with phosphine
ligands showed smaller shifts (i.e. greater shielding) than those
without such ligands. The present results for [X2Cu2(dptu)4] are
consistent with both of these observations; the diso values are
higher than those for all of the phosphine ligand complexes
previously reported,28 but other trends are not consistent between
different series of compounds. Thus, there are several instances
in the phosphine ligand complexes in which change from a more
Fig. 5 Far-IR spectra of (a) [Cl2Cu2(dptu)4]·2CH3CN, and (b, c)
[X2Cu2(dptu)4] (X = Br, I).
electronegative to a less electronegative halide ligand X (e.g. from
The broadline static 65Cu NMR spectra acquired at 9.4 and
7.05 T of [Cl2Cu2(dptu)4]·2CH3CN, and [X2Cu2(dptu)4] (X =
Br, I) are shown in Fig. 6, together with simulations of the
experimental spectra obtained using the parameters given in
Table 5. The broadened lines observed in the spectra are due to the
(-1/2↔1/2) transition of the copper nucleus, and the linewidth
contains contributions from both the second-order 65Cu nuclear
quadrupole interaction and the 65Cu chemical shift anisotropy.
For the field strengths employed in this work the quadrupole
28
X = Cl to Br) results in an increase in diso
,
but the opposite
trend is observed for the present series of [X2Cu2(dptu)4] complexes
(Table 5).
63/65Cu NQR spectroscopy
The 63/65Cu NQR frequency nQ is related to the nuclear quadrupole
coupling parameters by the equation:
Fig. 6 Broadline static 65Cu NMR spectra at 9.4 and 7.05 T of (a) [Cl2Cu2(dptu)4]·2CH3CN, and (b, c) [X2Cu2(dptu)4] (X = Br, I) (exp. = experimental
spectrum; sim. = simulation using the parameters in Table 5).
8314 | Dalton Trans., 2009, 8308–8316
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Table 5 65Cu NMR data for [Cl2Cu2(dptu)4]·2CH3CN, and [X2Cu2(dptu)4] (X = Br, I)
a
b
c
d
d
e
Compound
diso (ppm)
CQ b/MHz
hQ
Xc (ppm)
k
Dd (ppm)
hd
a, b, g
[Cl2Cu2(dptu)4]·2CH3CN
[Br2Cu2(dptu)4]
[I2Cu2(dptu)4]
505
426
367
15.77
15.62
15.116
0.557
0.370
0.611
536
594
570
0.386
0.338
0.302
-454
-496
-471
0.544
0.595
0.634
-20, 174, 36
-47, 166, 7
-17, 164, 47
a Relative to Cu(I)Cl; subtract 337.0 ppm to convert to the standard [Cu(CH3CN)4]ClO4 chemical shift scale (see Experimental). b CQ = e2qQ/h is the
nuclear quadrupole coupling constant; hQ is the electric field gradient asymmetry parameter. c X = (d11 - d33), k = 3(d22 - diso)/(d11 - d33), where d11
>
d22 > d33
.
d Dd = d33 - 1/2(d11 + d22) = 3/2(d33 - diso), hd = (d22 - d11)/(d33 - diso), where |d33 - diso| ≥ |d11 - diso| ≥ |d22 - diso|. e a, b, g = Euler angles
relating the nuclear quadrupole and chemical shift tensor frames.
nQ = (1/2)CQ(1 - hQ2/3)1/2
(2)
degree of contraction of the Cu 4p orbital that is involved in
bonding with the halogen atom, in the order Cl > Br > I.30,31 The
same trend, with presumably the same cause, has been observed
in a number of other copper(I) complexes,32 and the results of the
present study provide further evidence of this. In the previously
reported studies of the [XCu(xetu)2] (X = Cl, Br, I) complexes, it
was shown that for a given X the copper NQR frequency increases
linearly with decreasing S–Cu–S angle.13 From the close similarity
of the substituted imidazolidine-2-thione and thiourea ligands, it
might be expected that the present results for the dptu complexes
would obey the same relationships, but this in not the case. The S–
Cu–S angles in the dptu complexes are considerably smaller than
those in the imidazolidine-2-thione complexes, implying that the
copper NQR frequencies for the dptu complexes would be higher,
but it is clear from the results in Table 6 that this is not the case.
Substituting the S–Cu–S angles for the dptu complexes (Table 2)
into the empirical relationships established for the imidazolidine-
2-thione complexes results in predicted copper NQR frequencies
of 35.2 and 29.5 MHz for [XCu(dptu)2]·H2O (X = Cl, Br), which
are clearly well above the observed values. This relationship is
therefore clearly not of wide applicability to [XCuL2] complexes
in which L is a general thiourea-like ligand.
where CQ is the nuclear quadrupole coupling constant and hQ
is the electric field gradient asymmetry parameter. This latter
parameter (0 ≤ hQ ≤ 1) cannot be determined from the zero-
field NQR frequency, but the assumption hQ = 0 yields the lower
limit of CQ (the minimum value of (1 - hQ2/3)1/2 in eqn (2) is 0.82;
the assumption that it is unity involves an 18% error at most).
Hence, the NQR frequencies in Table 6 imply 65Cu CQ values
in the approximate range 50–60 MHz, which are much greater
than the 15–16 MHz observed for the dimeric [X2Cu2(dptu)4]
compounds, as expected for a change from tetrahedral to trigonal
planar coordination.
The 63/65Cu NQR frequencies for [XCu(dptu)2]·H2O (X = Cl,
Br, I) are compared with those for a number of related compounds
in Table 6. The values obtained are very similar to those previously
reported for a number of trigonal [XCu(xetu)2] (X = Cl, Br, I;
xetu = N-alkylimidazolidine-2-thione (imidazolidine-2-thione ∫
ethylenethiourea, etu)) complexes (Table 6).13,17–19 Although these
studies did not include any complete families [XCu(xetu)2] with the
same xetu ligand in each member of the family, the results indicated
that in general the frequencies decrease in the order Cl > Br > I,17
and this is reflected in the selection of data for such compounds
in Table 6. The results for the homologous series of compounds
[XCu(dptu)2]·H2O confirm this trend (Table 6). A similar trend
has been observed in the copper NQR frequencies of CuX and
[CuX2]- species, and has been shown to be due to an increasing
The copper NQR frequencies for [XCu(dptu)2]·H2O are very
similar to those for [Cu(tmtu)3]X (tmtu = tetramethylthiourea;
X = BF4, ClO4; Table 6).29
Conclusion
The CuX/dptu (1 : 2) system yields two homologous series of
compounds that contain isostructural monomeric [XCu(dptu)2]
and dimeric [(dptu)XCu(m-S-dptu)2CuX(dptu)] complexes. These
provide a basis for investigating the relationship between the
structures and the spectroscopic properties of these compounds.
In particular, measurement of the 63,65Cu NQR and 65Cu NMR
spectra of the monomeric and dimeric complexes has allowed for
the first time an investigation of the change in copper nuclear
quadrupole coupling with change in coordination geometry and
change in the halide ligand. The results demonstrate the utility
of 65Cu NMR spectroscopy for the characterization of copper(I)
complexes in distorted tetrahedral coordination environments.
Table 6 Copper NQR frequencies for [XCu(dptu)2]·H2O (X = Cl, Br, I)
and related compounds
nQ/MHz
Compounda
63Cu
65Cu
[ClCu(dptu)2]·H2O b
[BrCu(dptu)2]·H2O b
[ICu(dptu)2]·H2O b
[ClCu(metu)2] c
[ClCu(eetu)2] c
28.42
27.31
25.90
26.30
25.27
23.96
29.481
28.802
28.388
30.021
27.756
28.730
26.068
27.390
27.390
[ClCu(petu)2] c
[ClCu(ipetu)2] c
[BrCu(eetu)2] c
[BrCu(ipetu)2] c
[ICu(petu)2] c
[Cu(tmtu)3]BF4
d
25.341
25.340
Acknowledgements
d
[Cu(tmtu)3]ClO4
We are grateful to AINSE (Grants No. 02190, 03011) for financial
assistance. Support from the Thailand Research Fund (Grant No.
RTA 4880008) is gratefully acknowledged.
a Ligand abbreviations: xetu as in Table 3, tmtu = tetramethylthiourea.
b This work, T ª 290 K. c Ref. 13, T = 298 K. d Ref. 29, T = 296 K.
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