Thermal and structural characterization of a series of homoleptic Cu(II) dialkyldithiocarbamate complexes: Bigger is only marginally better for potential MOCVD performance

Article abstract of DOI:10.1016/S0277-5387(03)00264-X

A series of Cu(II) dialkyldithiocarbamate complexes, Cu(S₂CNRR′)₂, with R = R′ = n-Bu (1); i-Bu (2); c-Hex (3); CH₂Ph (4); R = n-Bu, R′ = Et (5); R = n-Pr, R′ = c-PrCH₂ (6); R = R′ = n-Pr (7); i-Pr (8); allyl (9), were prepared. The thermal properties of the complexes were investigated to determine if their potential performance in chemical vapor deposition processes was affected by the nature of the peripheral substituents of the ancillary ligands. Modest gains in volatility were noted for 2 and 7 over the most often utilized complex with R = R′ = Et, while 1 and 8 had thermal parameters and stability comparable to this standard. Unsymmetrical substitution, such as in 5, also improved volatility, with some loss of stability for this particular compound. X-ray diffraction studies of complexes 1-6 suggested that long range Cu?S interactions in the solid-state have little bearing on the thermal properties of this class of Cu(II) complexes.

Full text of DOI:10.1016/S0277-5387(03)00264-X

Polyhedron 22 (2003) 1575ꢁ1583
/
www.elsevier.com/locate/poly
Thermal and structural characterization of a series of homoleptic
Cu(II) dialkyldithiocarbamate complexes: bigger is only marginally
better for potential MOCVD performance
Silvana C. Ngo, Kulbinder K. Banger, Mark J. DelaRosa, Paul J. Toscano *,
John T. Welch *
Department of Chemistry, The University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY 12222, USA
Received 12 November 2002; accepted 24 March 2003
Abstract
A series of Cu(II) dialkyldithiocarbamate complexes, Cu(S2CNRR?)2, with Rꢀ
/
R?ꢀ/n-Bu (1); i-Bu (2); c-Hex (3); CH2Ph (4);
Rꢀn-Bu, R?ꢀEt (5); Rꢀn-Pr, R?ꢀc-PrCH2 (6); RꢀR?ꢀn-Pr (7); i-Pr (8); allyl (9), were prepared. The thermal properties of
/
/
/
/
/
/
the complexes were investigated to determine if their potential performance in chemical vapor deposition processes was affected by
the nature of the peripheral substituents of the ancillary ligands. Modest gains in volatility were noted for 2 and 7 over the most
often utilized complex with Rꢀ
Unsymmetrical substitution, such as in 5, also improved volatility, with some loss of stability for this particular compound. X-ray
diffraction studies of complexes 1ꢁ6 suggested that long range Cu S interactions in the solid-state have little bearing on the
/
R?ꢀ/Et, while 1 and 8 had thermal parameters and stability comparable to this standard.
/
/
ꢀ ꢀ ꢀ
/
thermal properties of this class of Cu(II) complexes.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Copper(II) complexes; Dialkyldithiocarbamate ligands; Chemical vapor deposition; Volatility; Crystal structures; Thermal studies
1. Introduction
For another familiar class of MOCVD precursors, the
metal b-diketonates, it is well-known that the steric size
of the peripheral substituents of the ancillary ligands can
have a profound effect on the performance of the
Metal-organic chemical vapor deposition (MOCVD)
is an attractive method for preparing thin films having
well-defined composition and morphology for electronic
precursor under MOCVD conditions [1,3ꢁ5]. While a
/
applications [1ꢁ
among others [10ꢁ
/
7]. For example, Nomura et al. [8,9],
couple of the previous studies on Cu(S2CNRR?)2 com-
plexes have investigated the effect of increasing the
chain length of R and R? in symmetrically substituted
ligands on thermal decomposition properties [9,19],
/14], have studied the use of copper(II)
dialkyldithiocarbamates, Cu(S2CNRR?)2, as single-
source precursors for the growth of semiconducting
copper sulfide thin films. In addition, these complexes
have been investigated for use as an MOCVD precursor
or as a reactant useful for the preparation of single
source MOCVD precursors for mixed metal sulfide
most have concentrated on the complex with Rꢀ
/
R?ꢀ
/
Et [8,11,12]. We felt that a more thorough examination
of the effect of branched and unsaturated substituents,
as well as unsymmetrical substitution of the ancillary
ligands, on MOCVD properties was in order, since
recent accounts have demonstrated that beneficial
changes of physical properties for dialkyldithiocarba-
mate complexes of copper [14,18] and other metals
phases, such as copperꢁ
copper-doped cadmium sulfide [19].
/
indium sulfide [15ꢁ18] or
/
[10,20ꢁ22] can arise from such modifications. Herein,
we report on the synthesis and X-ray structural char-
acterization of Cu(S2CNRR?)2, comprising the symme-
/
* Corresponding author. Tel.: ꢂ
3462.
/
1-518-442-3127; fax: ꢂ1-518-442-
/
E-mail addresses: ptoscano@csc.albany.edu (P.J. Toscano),
jwelch@uamail.albany.edu (J.T. Welch).
trically substituted complexes with Rꢀ
/
R?ꢀn-Bu (1), i-
/
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00264-X

1576
S.C. Ngo et al. / Polyhedron 22 (2003) 1575ꢁ1583
/
Bu (2), c-Hex (3), or CH2Ph (4), and the unsymme-
trically substituted complexes with Rꢀn-Bu, R?ꢀEt
(5) and Rꢀn-Pr, R?ꢀc-PrCH2 (6). The thermal
properties of these six complexes, along with those of
the symmetrically substituted complexes RꢀR?ꢀn-Pr
(7), i-Pr (8), or allyl (9), were studied by thermogravi-
metric analysis (TGA) and differential scanning calori-
metry (DSC) in order to assess the effect of the
peripheral substituents thereon and whether the packing
mode of the molecules can be correlated to bulk
volatility.
diethyl ether (100 ml) and filtered. Evaporation of the
solvent gave crystalline black solids, which were dried in
vacuo. Yields and elemental analyses for each complex
follow:
/
/
/
/
/
/
Cu[S2CN(n-Bu)2]2 (1): yield, 64%; Anal. Calc. for
C18H36CuN2S4: C, 45.78; H, 7.68. Found: C, 45.85;
H, 7.50%.
Cu[S2CN(i-Bu)2]2 (2): yield, 91%; Anal. Calc. for
C18H36CuN2S4: C, 45.78; H, 7.68. Found: C, 46.00;
H, 7.87%.
Cu[S2CN(c-Hex)2]2 (3): yield, 75%; Anal. Calc. for
C26H44CuN2S4: C, 54.18; H, 7.69. Found: C, 54.21;
H, 7.79%.
2. Experimental
Cu[S2CN(CH2Ph)2]2 (4): yield, 85%; Anal. Calc. for
C30H28CuN2S4: C, 59.23; H, 4.64. Found: C, 59.50;
H, 4.80%.
2.1. Materials and physical measurements
Cu[S2CN(n-Bu)(Et)]2 (5): yield, 69%; Anal. Calc. for
C14H28CuN2S4: C, 40.41; H, 6.78. Found: C, 40.47;
H, 6.89%.
Cu[S2CN(n-Pr)(c-PrCH2)]2 (6): yield, 70%; Anal.
Calc. for C16H28CuN2S4: C, 43.66; H, 6.41. Found:
C, 43.78; H, 6.60%.
Cu[S2CN(n-Pr)2]2 (7): yield, 74%; Anal. Calc. for
C14H28CuN2S4: C, 40.41; H, 6.78. Found: C, 40.64;
H, 6.90%.
Cu[S2CN(i-Pr)2]2 (8): yield, 58%; Anal. Calc. for
C14H28CuN2S4: C, 40.41; H, 6.78. Found: C, 40.49;
H, 6.69%.
Reagents and solvents obtained commercially were of
reagent grade and used as received unless otherwise
noted. TGA data were recorded on a TA Instruments
TGA 2050 thermogravimetric analyzer under dynamic
dry dinitrogen (total flow rate 100 cm3 minꢃ1), using
platinum pans containing a sample size of 1ꢁ3 mg, with
/
a ramp rate of 5.0 8C minꢃ1. DSC measurements were
obtained using a TA Instruments DSC 2920 differential
scanning calorimeter on 1.0ꢁ/3.0 mg of sample in
hermetically sealed aluminum pans (dry N2 flow
rateꢀ
20 cm3 minꢃ1, 1 atm pressure) at a heating rate
/
of 10.0 8C minꢃ1 up to 500 8C and referenced relative to
indium. Elemental analyses were performed by MHW
Laboratories (Phoenix, AZ).
Cu[S2CN(allyl)2]2 (9): yield, 86%; Anal. Calc. for
C14H20CuN2S4: C, 41.20; H, 4.94. Found: C, 41.05;
H, 5.10%.
2.2. General preparation of Li(S2CNRR?)×
/3H2O
2.4. X-ray crystallography
The procedure follows a modification of the literature
method [23]. The appropriate amine (RR?NH; 40 mmol)
Crystals of 1ꢁ3, 5 and 6 suitable for X-ray diffraction
/
was added to a stirring slurry of LiOH×
/
H2O (2.0 g, 48
studies were obtained by slow evaporation of saturated
diethyl ether/pentane solutions at ambient temperature,
while crystals of 4 were similarly obtained from satu-
rated THF/pentane solution. X-ray data were collected
at ambient temperature using a Bruker R3m diffract-
mmol) in water (3 ml) and CS2 (3.6 g, 48 mmol) in
benzene (10 ml). An exothermic reaction ensued,
followed by formation of yellow to orange precipitates.
After 1 h, petroleum ether was added and the reaction
mixture was filtered. The solids were washed well with
petroleum ether and dried in vacuo to give
ometer in the v/2u mode with variable scan speed (3ꢁ
/
20 8C minꢃ1, except for 2: u/2u mode, 4ꢁ20 8C minꢃ1
/
)
Li(S2CNRR?)×
which were used in the next procedure without further
purification. Typical yields ranged from 70 to 90%.
/
3H2O as white to pale yellow solids,
and graphite monochromated Mo Ka radiation (lꢀ
/
˚
0.71073 A). Check reflections were measured every 200
reflections during data collection and gave no indication
of crystal decay. Data were corrected for background,
attenuators, Lorentz and polarization effects in the
usual fashion [24]. A semi-empirical absorption correc-
tion was applied to 1, 4, 5, and 6 using the c-scan
method.
Structures were solved by direct methods and refined
by full-matrix least-squares procedures on jF2j with
SHELXTL-97, version 6.12 [25]. All non-hydrogen atoms
were refined anisotropically except for 3. For 3, only the
heteroatoms and the carbon atom of the chelate ring of
2.3. General preparation of Cu(S2CNRR?)2 (1ꢁ9)
/
A solution of Li(S2CNRR?)×
water (40 ml) was added to a stirred solution of
CuCl2×2H2O (0.28 g, 1.6 mmol) in water (40 ml). The
/
3H2O (3.2 mmol) in
/
immediate formation of a brown precipitate was ob-
served. The solid product was filtered, washed with
copious amounts of water, and then finally with a small
amount of pentane. The crude product was dissolved in

S.C. Ngo et al. / Polyhedron 22 (2003) 1575ꢁ
/1583
1577
the ligand were refined anisotropically, due to a paucity
of data. The peripheral side chains attached to N(1) of
the crystallographically full, independent molecule of 6
were disordered; that is, the n-Pr and c-PrCH2 groups
appeared to be superimposed on one another at each
site. The disorder was modelled with the n-Pr substi-
tuent having 55% occupancy on the side involving the
C(2) atom and 45% occupancy on the side involving the
C(5) atom. The c-PrCH2 substituent had the corre-
spondingly opposite occupancies. Hydrogen atom posi-
Table 1
Crystallographic data and parameters for 1ꢁ
/
6
1
2
Formula
Formula weight
C18H36CuN2S4
472.3
C18H36CuN2S4
472.3
Crystal color, habit Dark redꢁ
/brown,
Dark brown, parallele-
piped
plate
Crystal dimensions 0.10ꢄ/0.30ꢄ/0.50
0.80ꢄ
/
0.80ꢄ0.90
/
(mm)
Crystal system
Space group
triclinic
¯
1 (No. 2)
monoclinic
P
/
P21/n (No. 14)
9.707(3)
11.241(2)
12.057(4)
90
tions were calculated geometrically and fixed at a CÃ
/
H
˚
a (A)
9.212(4)
9.950(3)
15.252(6)
71.71(3)
82.77(3)
68.03(3)
1230.9(8)
2
˚
distance of 0.96 A and were not refined, with the
exception of the hydrogen atoms of the disordered
substituents in 6, the positions of which were neither
located nor set. Crystal data and further data collection
parameters are summarized in Table 1.
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
101.82(2)
90
3
˚
V (A )
Z
1287.7(6)
2
1.218
Dcalc (g cmꢃ3
)
1.274
12.31
m (Mo Ka) (cmꢃ1
F(0 0 0)
)
11.77
502
3. Results and discussion
502
50.0
2u max (8)
Reflections
collected
55.0
3052
3.1. Synthesis
4495
The homoleptic Cu(II) complexes, Cu(S2CNRR?)2
Independent
eflections
4317 (Rint
ꢀ
/
3.63%)
2926 (Rint
ꢀ
/
5.26%)
(Rꢀ
Rꢀn-Bu, R?ꢀ
R?ꢀn-Pr (7), i-Pr (8), allyl (9)) were prepared straight-
/
R?ꢀ/n-Bu (1), i-Bu (2), c-Hex (3), CH2Ph (4);
Observed
reflections
Tmin/Tmax
3026 (Iꢀ
/
2.0s(I))
2211 (I ꢀ
/
2.0s(I))
/
/
Et (5); Rꢀn-Pr, R?ꢀc-PrCH2 (6); Rꢀ
/
/
/
/
0.755/0.930
226
N/A
115
forwardly in high yield via the metathesis of copper(II)
chloride with the lithium salt of the dialkyldithiocarba-
mate ligand. The complexes were purified easily by
recrystallization for the X-ray diffraction and thermal
studies.
Number of
parameters
a
R1
0.0480
0.103
0.0574
0.162
1.06
b
wR2
Goodness-of-fit on 1.02
F2 c
3
4
3.2. Thermal studies
Formula
Formula weight
C26H44CuN2S4
576.4
C30H28CuN2S4
608.3
TGA data for copper complexes 1ꢁ9 are collected in
/
Crystal color, habit Dark brown, paralle- Dark brown, parallele-
lepiped piped
Crystal dimensions 0.10ꢄ0.20ꢄ 0.25ꢄ
Table 2. Experiments were conducted at atmospheric
pressure under a nitrogen purge. The temperature of the
maximum rate of weight loss (TMWL) was used as a
measure of the relative volatilities of the complexes;
however, care much be exercised in these cases, since
weight loss could be associated with the decomposition,
as well as the vaporization of the complexes. For the
symmetrically substituted complexes Cu(S2CNR2)2
/
/0.20
/
0.30ꢄ0.30
/
(mm)
Crystal system
Space group
monoclinic
triclinic
¯
P1 (No. 2)
C2/c (No. 15)
18.156(11)
10.259(7)
16.206(9)
90
/
˚
a (A)
13.855(4)
14.429(3)
16.353(3)
64.94(2)
73.24(2)
84.05(2)
2835.0(11)
4
˚
b (A)
˚
c (A)
a (8)
b (8)
(Rꢀn-Bu, 1; i-Bu, 2; n-Pr, 7; i-Pr, 8), the TGA traces
/
101.40(5)
90
exhibited single weight loss peaks, with minimal residue,
in accord with volatilization being the main thermal
event [26]. Surprisingly, the steric size of R has only a
small effect on TMWL, though 2 is arguably the best of
the four complexes, having the lowest TMWL and leaving
essentially no residue. The observed TMWL values for 2
g (8)
3
V (A )
˚
2959(3)
4
1.294
Z
Dcalc (g cmꢃ3
)
1.425
10.88
m (Mo Ka) (cmꢃ1
F(0 0 0)
)
10.37
1228
1260
45.0
2u max (8)
Reflections
collected
40.0
1455
7732
and 7 are ca. 15ꢁ
[27,28]. Unsymmetrically substituted Cu(S2CNRR?)2
(Rꢀn-Bu, R?ꢀEt (5) and Rꢀn-Pr, R?ꢀc-PrCH2
/
20 8C lower than that found for Rꢀ
/
Et
Independent
reflections
Observed
1370 (Rint
675 (Iꢀ 2.0s(I))
N/A
ꢀ
/
2.96%)
7413 (Rint
4054 (Iꢀ
0.886/0.946
ꢀ
/
6.66%)
/
/
/
/
(6)) evaporated somewhat less efficiently, leaving larger
residues. Although 5 left a relatively large residue likely
indicating that volatilization was accompanied by de-
/
/
2.0s(I))
reflections
Tmin/Tmax

1578
S.C. Ngo et al. / Polyhedron 22 (2003) 1575ꢁ1583
/
Table 1 (Continued)
DSC data (vide infra). In these latter two cases, the
observed amount of residue is very close to that
predicted for CuS based on the composition of the
complexes [9,27].
For the DSC studies, the samples were heated under a
dinitrogen atmosphere, using hermetically sealed alumi-
num pans, to eliminate weight loss associated with
sublimation. All complexes, except for 3, showed two
endotherms (Table 2). The first, sharp endotherm is
attributed to melting. The melting points that we
obtained for compounds that have been previously
reported were in good agreement with literature values
[9,26,27,29].
3
4
Number of
parameters
91
667
a
R1
0.0800
0.170
0.0745
0.135
1.07
b
wR2
Goodness-of-fit on 1.03
F2 c
5
6
Formula
Formula weight
C
416.2
14H28CuN2S4
C16H28CuN2S4
440.2
Crystal color, habit Dark red, hexagonal
prism
Brown-red, rectangular
prism
Crystal dimensions 0.20ꢄ
/
0.45ꢄ
/
0.50
0.20ꢄ
/
0.50ꢄ
/
0.70
The second, broader endotherm in the DSC traces of
these compounds is more controversial and has been
alternatively assigned to volatilization or decomposition
(mm)
Crystal system
Space group
monoclinic
triclinic
¯
P1 (No. 2)
P21/n (No. 14)
8.540(1)
8.637(1)
13.694(2)
90
/
[26ꢁ29]. We argue that it likely can be assigned to either
/
˚
a (A)
8.833(3)
11.741(4)
15.555(4)
90.17(3)
96.91(2)
92.29(3)
1600.1(9)
3
˚
of these processes or a combination of both, depending
upon the complex. For 1, 2, 8, and 9, the temperature of
the second endotherm in the DSC trace for these
complexes is close to the TMWL in the TGA experiments,
even taking into account uncertainty introduced by the
broadness of the DSC absorption. Given this corre-
spondence, and since little residue remains in the TGA
studies for these complexes, the second endotherm is
likely associated with volatilization. For 3, 5, and 6,
there is also fair to excellent agreement between the
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Z
Dcalc (g cmꢃ3
93.78(1)
90
3
˚
1007.9(2)
2
1.371
)
1.370
14.15
m (Mo Ka) (cmꢃ1
F(0 0 0)
)
14.93
438
693
50.0
2u max (8)
Reflections
collected
50.0
1842
5861
temperature of the second DSC endotherm and TMWL
;
Independent
reflections
Observed
1765 (Rint
1311 (Iꢀ
ꢀ
/
1.25%)
5636 (Rint
ꢀ
/
2.50%)
however, the larger residues suggest that significant
decomposition is occurring along with volatilization.
The data for 4 and 9 indicate that decomposition
happens with little volatilization. In fact, large
exotherms were observed in the DSC trace of 9 at
temperatures near TMWL, showing that this complex
decomposes readily and is probably too unstable for use
in MOCVD applications.
/
2.0s(I))
4186 (I ꢀ
/
2.0s(I))
reflections
Tmin/Tmax
0.536/0.941
97
0.647/0.994
341
Number of
parameters
a
R1
0.0450
0.113
0.0538
0.144
1.04
b
wR2
Goodness-of-fit on 1.06
F2 c
3.3. X-ray diffraction studies
a
R1ꢀ
/
ajjFojꢃ
wR2ꢀ
[aw(Fo2ꢃ
GOFꢀ
[aw(Fo2ꢃ
/
jFcjj/ajFoj.
Fc2)2/aw(Fo2)2]1/2
Fc2)2/(Nobs Nparams)]1/2, based on F2 for all
b
c
/
/
.
White and coworkers have previously noted that the
solid-state structures of homoleptic Cu(II) dialkyldithio-
carbamate complexes can roughly be broken down into
two classes as a function of the dominant packing forces
that are present [30]. In the first, the molecules of
/
/
ꢃ/
data.
composition, this complex demonstrates that the TMWL
can be significantly lowered by unsymmetrical substitu-
tion of the ligand periphery, a factor which has been
complex pack as centrosymmetric dimers with long Cu/
ꢀ ꢀ ꢀ
/
S contacts involving a fifth apical coordination site on
recently exploited with Rꢀ
/
n-Hex, R?ꢀMe [14].
/
one molecule and a sulfur atom from the other molecule
of the pair and vice versa. In the second type of packing,
the molecules pack as monomers with intermolecular H/
The TGA behavior for 3, 4, and 9 was considerably
more complex. In each case the TGA was bimodal,
having two temperatures of maximum weight loss. For
3, the c-Hex substituents likely add too much to the
molecular weight of the complex so that significant
decomposition occurs simultaneously with volatiliza-
tion. On the other hand, the reactive peripheral sub-
stituents in 4 and 9 seem to lead to easier decomposition
pathways, with little or no volatilization as suggested by
ꢀ ꢀ ꢀ
/
S contacts as the dominant solid-state interaction.
These workers concluded that the intermolecular inter-
actions in both cases must be comparable in energy [30].
In the present study, we have found examples of both
types of solid-state packing motif, as well as one
example that includes both dimeric and monomeric
structural types simultaneously and one example that

S.C. Ngo et al. / Polyhedron 22 (2003) 1575ꢁ
/1583
1579
Table 2
TGA and DSC data for Cu(S2CNRR?)2, (1ꢁ
/9)
Cu(II)
Substituents
TGA
TMWLa(8C)
DSC
Complex
R, R?
Weight loss (%)
Residue (%)
Endotherms (8C)
1
2
3
4
5
6
7
8
9
n-Bu, n-Bu
i-Bu, i-Bu
286
273
98.4
99.9
1.6
0.1
57; 273
148; 283
278
c-Hex, c-Hex
CH2Ph, CH2Ph
n-Bu, Et
216; 285
286; 323
245
16.2; 63.7
79.6; 6.1
86.0
20.1
14.3
14.0
8.6
204; 237
66; 244
103; 267
102; 272
177; 303
82; 100 b
n-Pr, c-PrCH2
n-Pr, n-Pr
i-Pr, i-Pr
294
279
91.4
97.2
2.8
5.0
298
231; 254
95.0
73.7
allyl, allyl
26.3
a
Temperature of maximum weight loss.
Exotherms were also observed at 210 and 263 8C.
b
does not truly fit into either category. Throughout the
following discussion, symmetry-related atoms are desig-
nated with an ‘a’ attached to the label, while similar
atoms in crystallographically independent molecules of
the asymmetric unit of the unit cell are designated with
‘primes’.
Cu[S2CN(n-Bu)2]2 (1) is emblematic of the first type
of packing pattern, namely the dimeric form (Fig. 1), in
which the asymmetric unit of the unit cell contains an
entire molecule that is half of the centrosymmetric
dimer. The crystal studied here corresponds to the ‘a-
phase’ for this compound, reported previously by White
between the two copper atoms of the dimer, is slightly,
but significantly longer than the remaining three CuÃ
distances in the basal plane. The coordination is
completed by a long Cu(1) S(1a) interaction (2.902(1)
ꢀ ꢀ ꢀ
A; symmetry transformation: ꢃx, 1.0ꢃy, ꢃz) at the
/
S
/
/
˚
/
/
/
apical position of the pyramid. This distance is sig-
˚
nificantly longer than for Cu(S2CNEt)2 (2.844(1) A)
˚
[31,32] and Cu[S2CN(n-Pr)2]2 (2.740(1) A) [32ꢁ
/34],
significantly shorter than for Cu[S2CN(2-pyridyl)2]2
˚
(3.230(3) A) [35], but is similar to that for Cu[S2CN(al-
˚
lyl)2]2 (2.888(2) A) [36]; thus, the apical bridging distance
between molecules in the dimers seems to be governed at
least in part by the steric size of the peripheral
substituents of the ligands. For 1, there is one long H/
and coworkers [30]. Our results (2umax
precise than in the prior structure determination
(2umax 408) and thus, are included here.
ꢀ
/
508) are more
˚
S interaction of 3.09(1) A between H(2b) and S(3a)
ꢀ ꢀ ꢀ
/
ꢀ
/
Each copper atom of the centrosymmetric dimer of 1
can be considered to have approximately square pyr-
amidal geometry. With the more precise data, we now
atoms within the dimer. The copper atoms in 1 are
˚
3.783(1) A distant, somewhat longer than in other,
˚
similar dimers (range: 3.42ꢁ
/
3.59 A) [31ꢁ
/
36].
Even so, the bond lengths (Table 3) in the basal plane
of the coordination sphere are not significantly per-
turbed from those found for the monomeric, square
planar complexes (vide infra) and are similar to those
can say with better confidence that the Cu(1)Ã
/
S(1)
bond, which involves the sulfur atom that bridges
found for other dimeric Cu(II) dialkyldithiocarbamates
˚
[31ꢁ36]. The copper atom is 0.27 A above the approx-
/
imate, ‘ruffled’ basal plane defined by the four sulfur
atoms towards the side on which the apical Cu S
/
ꢀ ꢀ ꢀ
/
interaction occurs. The dihedral angle between the
planes defined by the dialkyldithiocarbamate chelates
is 156.3(3)8.
Table 3
˚
Selected bond lengths (A) and angles (8) for Cu[S2CN(n-Bu)2]2 (1)
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)
ꢀ ꢀ ꢀ
/
S(1)
S(2)
S(3)
S(4)
2.323(1)
2.307(1)
2.302(1)
2.301(1)
2.902(1)
S(1)Ã
S(1)Ã
S(1)Ã
S(2)Ã
S(2)Ã
S(3)Ã
/
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
/
S(2)
S(3)
S(4)
S(3)
S(4)
S(4)
76.7(1)
169.0(1)
102.1(1)
101.2(1)
164.0(1)
76.9(1)
/
/
/
/
/
/
/
/
/
a
Fig. 1. Molecular structure and atom numbering scheme for dimeric
Cu[S2CN(n-Bu)2]2 (1). Atoms related by the symmetry transformation
/
/
S(1a)
/
/
/
/
(ꢃ
/
x, 1.0ꢃ
/
y, ꢃz) are designated by ‘a’. Hydrogen atoms are omitted
/
a
Symmetry transformation (ꢃ
/
x, 1.0ꢃ
/
y, ꢃz).
/
for clarity.

1580
S.C. Ngo et al. / Polyhedron 22 (2003) 1575ꢁ1583
/
Cu[S2CN(CH2)5]2 [40,41], and Cu[S2CN(CH2)4]2 [42]
and are slightly, but probably not significantly, shorter
on average than for the five-coordinate dimeric Cu(II)
complexes (vide supra).
Cu[S2CN(n-Pr)(c-PrCH2)]2 (6) presents the first in-
stance in which both five-coordinate, centrosymmetric
dimers and square planar monomers co-crystallize.
Here, the asymmetric unit of the unit cell contains an
entire, crystallographically independent molecule, which
is half of a centrosymmetric dimer, as well as a crystal-
lographically independent half of a four-coordinate
monomer. The dimer portion (Fig. 3) has quite typical
bonding parameters, including a bridging Cu(1)
/
ꢀ ꢀ ꢀ
Cu(1a) separation
S bond lengths in the coordina-
tion sphere are virtually uniform (Table 5) with the
/
S(4a)
Fig. 2. Molecular structure and atom numbering scheme for Cu[S2C-
˚
N(i-Bu)2]2 (2). Atoms related by the symmetry transformation (ꢃ
/
x,
distance of 2.761(2) A and a Cu(1)
/
ꢀ ꢀ ꢀ
/
ꢃ
/
y, ꢃz) are designated by ‘a’. Hydrogen atoms are omitted for
/
˚
of 3.596(1) A. The CuÃ
/
clarity. The atom numbering schemes for the coordination spheres of
Cu[S2CN(c-Hex)2]2 (3) and Cu[S2CN(n-Bu)(Et)]2 (5) are identical
˚
copper atom 0.29 A above the, once again, ‘ruffled’
(symmetry transformations: (0.5ꢃ
/
x, 0.5ꢃ
/
y, ꢃ
/
z) for 3; (ꢃ
/
x, 1.0ꢃy,
/
1.0ꢃz) for 5).
/
basal plane defined by the four sulfur atoms. The
chelates make a dihedral angle of 152.8(3)8. The n-Pr
and c-PrCH2 substituents of the dialkyldithiocarbamate
ligand containing S(1) and S(2) are disordered with
nearly equal site occupancies for the two orientations.
Thus, there are almost equal populations of the trans-
and cis-geometries, with the former just slightly pre-
ferred (see Section 2).
The copper atom of the monomer entity of 6 is
situated on a center of symmetry (Fig. 4); the coordina-
tion sphere is planar and the peripheral substituents of
the ligands adopt the trans-geometry according to this
crystallographic constraint. Bonding parameters are
unremarkable and quite typical for the four-coordinate
On the other hand, Cu[S2CN(i-Bu)2]2 (2) (Fig. 2),
Cu[S2CN(c-Hex)2]2 (3), and unsymmetrically substi-
tuted Cu[S2CN(n-Bu)(Et)]2 (5) adhere to the second
packing motif and are square planar monomers. In each
case, the copper atom is situated on a center of
symmetry and the asymmetric unit consists of one half
of a molecule; as a consequence, the peripheral sub-
stituents of 5 adopt the trans-geometry. The coordina-
tion spheres are perfectly planar as dictated by the
crystallographic position of the copper atom. In each
case, there are weak, intermolecular H
/
ꢀ ꢀ ꢀ
3.15(1) A; we find no correlation
S bond lengths and these interactions,
/
S interactions
˚
in the range 2.91(1)ꢁ
between the CuÃ
/
bonding motif (vide supra). A number of H
/
ꢀ ꢀ ꢀ
/
S inter-
/
˚
3.15(1) A occur between the
actions in the range 2.98(1)ꢁ
/
as speculated for the centrosymmetric b-phase of
Cu[S2CN(n-Bu)2]2 [30]. Bond distances and angles
(Table 4) in the coordination spheres of 2, 3, and 5 are
analogous to those in related monomeric complexes,
such as Cu[S2CN(i-Pr)2]2 [32,37,38], the ‘b-phase’ of
Cu[S2CN(n-Bu)2]2 [30], Cu[S2CN(Me)(Ph)]2 [39],
dimer and monomer molecules.
Finally, Cu[S2CN(CH2Ph)2]2 (4) appears to be ex-
emplar of a packing design not previously observed. The
molecules aggregate as weak dimers (Fig. 5), but not in
Table 4
˚
Selected bond lengths (A) and angles (8) for Cu[S2CN(i-Bu)2]2 (2),
Cu[S2CN(c-Hex)2]2 (3), and Cu[S2CN(n-Bu)(Et)]2 (5)
2
3
5
Bond lengths
Cu(1)Ã
Cu(1)Ã
/
S(1)
2.268(1)
2.302(1)
2.281(5)
2.304(4)
2.301(1)
2.292(1)
/S(2)
Bond angles
S(1)ÃCu(1)Ã
S(1)ÃCu(1)Ã
S(1)ÃCu(1)Ã
S(2)ÃCu(1)Ã
/
/
S(2)
77.6(1)
102.4(1)
180.0 a,d
180.0 a,d
76.8(2)
103.2(2) b
180.0 b,d
180.0 b,d
77.3(1)
102.8(1) c
180.0 c,d
180.0 c,d
a
/
/
S(2a)
S(1a)
S(2a)
/
/
/
/
Fig. 3. Molecular structure and atom numbering scheme for the more
predominant configuration of the dimeric moiety of Cu[S2CN(n-Pr)(c-
a
b
c
Symmetry transformation (ꢃ
Symmetry transformation (0.5ꢃ
Symmetry transformation (ꢃx, 1.0ꢃ
/
x, ꢃ
x, 0.5ꢃ
y, 1.0ꢃ
/
y, ꢃ
/
z).
/
/
y, ꢃ
/
z).
PrCH2)]2 (6). Atoms related by the symmetry transformation (ꢃ
1.0ꢃy, 1.0ꢃz) are designated by ‘a’. Hydrogen atoms are omitted for
clarity.
/x,
/
/
/
z).
/
/
d
Symmetry enforced.

S.C. Ngo et al. / Polyhedron 22 (2003) 1575ꢁ
/1583
1581
Table 5
the manner of the centrosymmetric dimer units de-
scribed above for 1 and the crystallographically inde-
pendent dimer molecule of 6. For 4, the plane of the
coordination sphere of the first, crystallographically
independent molecule of the dimer (Fig. 5; primed
labels) is approximately perpendicular to the plane of
the coordination sphere of the second independent
molecule (Fig. 5; unprimed labels), with a dihedral angle
between these planes of 88.8(3)8. There is only one weak
˚
Selected bond lengths (A) and angles (8) for the dimeric (molecule 1)
and monomeric (molecule 2) moieties of Cu[S2CN(n-Pr)(c-PrCH2)]2
(6)
Molecule 1
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)
/
S(1)
S(2)
S(3)
S(4)
2.309(1)
2.322(2)
2.323(1)
2.322(1)
2.761(2)
S(1)Ã
S(1)Ã
S(1)Ã
S(2)Ã
S(2)Ã
/
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
/
S(2)
S(3)
S(4)
S(3)
S(4)
76.5(1)
162.9(1)
100.0(1)
103.4(1)
167.8(1)
/
/
/
/
/
/
/
/
/
/
ꢀ ꢀ ꢀ
/
S(4a) a
/
/
Cu
/
ꢀ ꢀ ꢀ
/
S interaction between Cu(1?) and S(3) at a distance
Molecule 2
˚
Cu(2)Ã
Cu(2)Ã
/
S(5)
2.276(2)
2.291(2)
S(5)Ã
S(5)Ã
S(5)Ã
S(6)Ã
/
Cu(2)Ã
Cu(2)Ã
Cu(2)Ã
Cu(2)Ã
/
S(6)
77.0(1)
103.0(1)
180.0 c
180.0 c
of 3.468(3) A. The four sulfur donor atoms for the
molecule with the fifth coordination interaction (primed
labels) form a relatively unruffled, planar coordination
/S(6)
/
/
S(6a) b
S(5a) b
S(6a) b
/
/
/
/
˚
sphere (Table 6), with the copper atom 0.086 A out of
a
b
c
Symmetry transformation (ꢃ
Symmetry transformation (1.0ꢃ
Symmetry enforced.
/x, 1.0ꢃ
/y, 1.0ꢃ
/z).
this plane towards S(3); the dihedral angle between the
planes defined by the chelate ligands (168.3(3)8) indi-
cates some puckering. The four-coordinate moiety of the
dimer (unprimed labels) has close to expected values for
a square plane (Table 6), with the copper atom
essentially in the plane of the four sulfur donors; the
two planes defined by the ligands are nearly coincident
(dihedral angle 174.5(3)8). Bond lengths and angles in
the coordination spheres of both crystallographically
independent molecules are unexceptional. There are
/x, ꢃy, ꢃ
/
/z).
several intermolecular
˚
H
/
ꢀ ꢀ ꢀ
/
S
interactions in the
3.02(1)ꢁ3.18(1) A range.
/
At this point, we can make some observations on
packing and solid-state aggregation tendencies for
Cu(II) dialkyldithiocarbamate complexes. If the copper
atom occupies a general position in the unit cell, one
generally observes a centrosymmetric, dimeric associa-
Fig. 4. Molecular structure and atom numbering scheme for the
monomeric moiety of Cu[S2CN(n-Pr)(c-PrCH2)]2 (6). Atoms related
tion, which contains mutual Cu
/
ꢀ ꢀ ꢀ
/
S interactions between
the two metal centers. In this solid-state motif, the
coordination planes of the two molecules of the dimer
are approximately parallel to each other and necessarily
are oriented such that the axes containing the nitrogen
atoms of the ligands are also parallel. This packing
pattern has been seen for Cu(S2CNRR?)2 in the present
by the symmetry transformation (1.0ꢃ
/
x, ꢃ
/
y, ꢃz) are designated by
/
‘a’. Hydrogen atoms are omitted for clarity.
Table 6
˚
Selected bond lengths (A) and angles (8) for the two crystallographi-
cally independent molecules of Cu[S2CN(CH2Ph)2]2 (4)
Molecule 1
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
/
S(1)
S(2)
S(3)
S(4)
2.301(3)
2.279(3)
2.291(3)
2.286(3)
S(1)Ã
S(1)Ã
S(1)Ã
S(2)Ã
S(2)Ã
S(3)Ã
/
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
Cu(1)Ã
/
S(2)
S(3)
S(4)
S(3)
S(4)
S(4)
77.9(1)
179.5(1)
102.9(1)
101.7(1)
178.8(1)
77.6(1)
/
/
/
/
/
/
/
/
/
/
/
/
/
Molecule 2
Cu(1?)Ã
Cu(1?)Ã
Cu(1?)Ã
Cu(1?)Ã
Cu(1?)
/
S(1?)
S(2?)
S(3?)
S(4?)
2.264(3)
2.304(3)
2.286(3)
2.317(3)
3.468(3)
S(1?)Ã
S(1?)Ã
S(1?)Ã
S(2?)Ã
S(2?)Ã
S(3?)Ã
/
Cu(1?)Ã
Cu(1?)Ã
Cu(1?)Ã
Cu(1?)Ã
Cu(1?)Ã
Cu(1?)Ã
/
S(2?)
77.7(1)
178.1(1)
102.1(1)
103.0(1)
170.0(1)
77.5(1)
/
/
/
S(3?)
S(4?)
S(3?)
S(4?)
S(4?)
/
/
/
/
/
/
Fig. 5. Molecular structures and atom numbering scheme for the
coordination spheres of the two crystallographically independent
molecules of Cu[S2CN(CH2Ph)2]2 (4). Hydrogen atoms are omitted
for clarity.
/
ꢀ ꢀ ꢀ
/
S(3)
/
/
/
/

1582
S.C. Ngo et al. / Polyhedron 22 (2003) 1575ꢁ1583
/
study with Rꢀ
and previously for Rꢀ
allyl [36], and 2-pyridyl [35]. The only exception that
occurs is for 4 with RꢀR?ꢀCH2Ph; here, as discussed
above, we observed a dimer consisting of two crystal-
lographically independent molecules with both copper
atoms sited on general positions and with only one weak
/
R?ꢀ
/
n-Bu 1 (the so-called ‘a-phase’ [30])
4. Conclusions
/
R?ꢀEt [31,32], n-Pr [32ꢁ34],
/
/
We have investigated a series of Cu(II) dialkyldithio-
carbamate complexes, in the hopes of identifying trends
in volatility based on the nature of the peripheral
substituents of the ancillary ligands. In particular, we
were interested in whether increased steric bulk of these
/
/
substituents might mitigate Cu/
ꢀ ꢀ ꢀ
/
S interactions in the
Cu/
ꢀ ꢀ ꢀ
/
S interaction. The planes of the coordination
spheres are approximately orthogonal to each other in
this case.
solid-state, thereby increasing the volatility of the
complex. We determined the structures of six complexes,
including those for which the molecules crystallized as
centrosymmetric dimers, as four-coordinate, square
planar monomers, as a mixture of these two structural
types, and as a newly discovered ‘side-on’ dimer, in
order to assess the importance of such solid-state
intermolecular contacts.
Alternatively, the copper atom of Cu(S2CNRR?)2
might be situated on a center of symmetry, which
generally results in a square planar monomeric complex
with no long-range Cu
observed by us for 2 (Rꢀ
Hex), and 5 (Rꢀn-Bu, R?ꢀ
for RꢀR?ꢀi-Pr [32,37,38], n-Bu (‘b-phase’) [30], Rꢀ
Me, R?ꢀPh [39] and the piperidine [40,41] and pyrro-
lidine [42] analogues. The only exception here is for Rꢀ
R?ꢀMe, where the copper atom is sited on a center of
/
ꢀ ꢀ ꢀ
/
S interactions. This motif was
R?ꢀi-Bu), 3 (RꢀR?ꢀc-
Et), as well as previously
/
/
/
/
/
/
The Cu(S2CNRR?)2 complexes with the best charac-
teristics for potential MOCVD application, namely
good volatility accompanied by minimal decomposition,
/
/
/
/
/
were 1, 2, 7, and 8, which have the substituents Rꢀ
R?ꢀn-Bu, i-Bu, n-Pr, and i-Pr, respectively. Both 2 and
7 had TMWL values that were lower than that reported
for the more studied derivative with RꢀR?ꢀEt [27,28],
/
/
/
symmetry and an infinite chain structure was deter-
mined in which each copper atom has two long-range
/
/
Cu/ꢀ ꢀ ꢀ
/S interactions with two symmetry-equivalent mo-
while 1 and 8 were comparable to this compound.
Complexes 5 and 6 performed somewhat less efficiently
in volatilization experiments, but demonstrated that
unsymmetrical substitution of the peripheral ligand
positions could lead to even higher volatilities (that is,
lower TMWL). Complexes with ligand substituents that
lecules on either side of its coordination sphere along the
c direction [43]. The coordination spheres of the
molecules in the chain are approximately parallel;
however, the orientation is such that the axes containing
the nitrogen atoms of the ligands are approximately
orthogonal to each other for each pair of molecules in
the infinite chain [43]. This may be a unique case, given
the small size of the peripheral Me substituents.
were too large (3; Rꢀ
groups (4; RꢀR?ꢀCH2Ph), or were too reactive (9;
RꢀR?ꢀallyl), were not suitable for MOCVD applica-
/
R?ꢀ
/
c-Hex), contained phenyl
/
/
/
/
Thus, there are two main packing motifs observed for
Cu(S2CNRR?)2. To a degree, larger steric size for the
peripheral substituents of the ligands tends to favor
packing of the complex molecules as monomers, while
smaller groups tend to encourage packing of the metal
complexes as dimers. However, other factors are clearly
at work as well, such as the solvent of crystallization.
tions due to either decreased volatility and/or facile
decomposition.
The volatility of the complexes showed little depen-
dence on whether Cu
/
ꢀ ꢀ ꢀ
/
S interactions were present in the
solid-state. Of the four best complexes, 1 and 7 crystal-
lized in the centrosymmetric dimer motif, while 2 and 8
crystallized as four-coordinate monomers, with no long-
For Rꢀ
/
R?ꢀn-Bu, a hydrocarbyl group that is inter-
/
range Cu
previously suggested that the Cu
/
ꢀ ꢀ ꢀ
/
S contacts. White and coworkers have
mediate in steric bulk, two different crystalline morphol-
ogies have been prepared, namely the ‘a-phase’, which
contains centrosymmetric dimers, and the ‘b-phase’,
which contains well-separated monomers [30]. The
former was obtained from the relatively nonpolar
solvent mixture of chloroform-light petroleum, while
/
ꢀ ꢀ ꢀ
/S interactions in the
dimers are weak and comparable in energy to other
intermolecular interactions in the solid-state, based on
their ability to crystallize Cu[S2CN(n-Bu)2]2 in each of
the two packing modes [30]. Mass spectroscopic studies
for Cu(S2CNRR?)2 (Rꢀ
/
R?ꢀEt, n-Pr, n-Bu, i-Bu) [44]
/
the latter crystals grew from ethanolꢁchloroform. We
also gained the formation of the ‘a-phase’ from diethyl
ether-n-pentane mixture. We note that our present study
/
and gas-phase electron diffraction studies of
Cu(S2CNMe)2 [45] clearly demonstrate that these com-
plexes are all monomers in the gas phase, no matter the
nature of the original solid-state packing pattern. This
also includes 6 (Rꢀ
/
n-Pr, R?ꢀc-PrCH2), in which both
/
monomer (copper atom on center of symmetry) and
centrosymmetric dimer moieties were observed simulta-
neously in the same crystal. Apparently the unsymme-
underscores the general weakness of the Cu/
ꢀ ꢀ ꢀ
/
S interac-
tions and the relative ease of overcoming and breaking
them; apparently, they have a relative lack of import in
determining volatility. Based on our results, it appears
that improvements in the volatility of Cu(II) dialkyl-
dithiocarbamate complexes likely will come with the
trically substituted ligand of
6
has peripheral
substituents of intermediate size, allowing both solid-
state aggregation types to coexist.

S.C. Ngo et al. / Polyhedron 22 (2003) 1575ꢁ
/1583
1583
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145.
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[16] R. Nomura, Y. Seki, K. Konishi, H. Matsuda, Appl. Organomet.
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5. Supplementary material
[19] S.M. Zemskova, S.V. Sysoev, L.A. Glinskaya, R.F. Klevtsova,
S.A. Gromilov, S.V. Larionov, Electrochem. Soc. Proc. 97 (1997)
1429.
Full lists of crystallographic data for 1 (CCDC-
196807), 2 (CCDC-196808), 3 (CCDC-196809), 4
(CCDC-196810), 5 (CCDC-196811), and 6 (CCDC-
196812), including atomic coordinates, bond lengths
and angles, and anisotropic thermal parameters have
been deposited with the Cambridge Crystallographic
Data Centre. Copies of this information may be
obtained from The Director, CCDC, 12 Union Road,
[20] P. O’Brien, J.R. Walsh, I.M. Watson, L. Hart, S.R.P. Silva, J.
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