Synthesis, characterization and structural comparisons of phosphonium and arsenic dithiocarbamates with alkyl and phenyl substituents

Article abstract of DOI:10.1016/j.poly.2014.03.003

The synthesis and characterization of the new arsenic dithiocarbamate complex As[S₂CNPh₂]₃ and three new phosphonium dithiocarbamates [PPh₄][S₂CNR₂], where R ₂ = Et₂, (CH₂)₅ and Ph₂, are reported. As[S₂CNPh₂]₃ was prepared by treating AsI₃ with three equivalents of NaS₂CNPh ₂ in a 2:1 mixture of H₂O and EtOH. The precipitate that formed was recrystallized from hot toluene to yield yellow prisms of As[S ₂CNPh₂]₃ suitable for single-crystal X-ray diffraction (XRD). Attempts to prepare the known compound As[S ₂CN(CH₂)₅]₃ using a similar route resulted in a mixture of As[S₂CN(CH₂)₅] ₃ and the mixed iodide species As[S₂CN(CH ₂)₅]₂I. Single-crystals of both compounds were isolated from concentrated Et₂O/CHCl₃ solutions and their structures are described here for the first time. [PPh₄][S ₂CNR₂] salts were prepared for comparison to arsenic dithiocarbamates by metathesis reactions with PPh₄Br and NaS ₂CNR₂ in acetonitrile. All three salts could be obtained in high-purity from MeCN/Et₂O solutions and crystal structures of [PPh₄][S₂CNEt₂] and [PPh₄][S ₂CN(CH₂)₅] reveal charge-separated phosphonium cations and dithiocarbamate anions. The five new crystal structures are used to compare dithiocarbamate bond distances and angles in the presence and absence of arsenic. Nuclear magnetic resonance (NMR) spectra, infrared (IR) spectra, microanalyses, and melting points of the compounds are reported.

Full text of DOI:10.1016/j.poly.2014.03.003

Polyhedron 75 (2014) 110–117
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and structural comparisons of phosphonium
and arsenic dithiocarbamates with alkyl and phenyl substituents
Courtney M. Donahue a, Isabella K. Black a, Samantha L. Pecnik a, Thomas R. Savage a, Brian L. Scott b,
Scott R. Daly a,
⇑
a The George Washington University, Department of Chemistry, 725 21st St., NW Washington, DC 20052, USA
b Los Alamos National Laboratory, Los Alamos, NM 87545, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and characterization of the new arsenic dithiocarbamate complex As[S2CNPh2]3 and three
new phosphonium dithiocarbamates [PPh4][S2CNR2], where R2 = Et2, (CH2)5 and Ph2, are reported.
As[S2CNPh2]3 was prepared by treating AsI3 with three equivalents of NaS2CNPh2 in a 2:1 mixture of
H2O and EtOH. The precipitate that formed was recrystallized from hot toluene to yield yellow prisms
of As[S2CNPh2]3 suitable for single-crystal X-ray diffraction (XRD). Attempts to prepare the known com-
pound As[S2CN(CH2)5]3 using a similar route resulted in a mixture of As[S2CN(CH2)5]3 and the mixed
iodide species As[S2CN(CH2)5]2I. Single-crystals of both compounds were isolated from concentrated
Et2O/CHCl3 solutions and their structures are described here for the first time. [PPh4][S2CNR2] salts were
prepared for comparison to arsenic dithiocarbamates by metathesis reactions with PPh4Br and NaS2CNR2
in acetonitrile. All three salts could be obtained in high-purity from MeCN/Et2O solutions and crystal
structures of [PPh4][S2CNEt2] and [PPh4][S2CN(CH2)5] reveal charge-separated phosphonium cations
and dithiocarbamate anions. The five new crystal structures are used to compare dithiocarbamate bond
distances and angles in the presence and absence of arsenic. Nuclear magnetic resonance (NMR) spectra,
infrared (IR) spectra, microanalyses, and melting points of the compounds are reported.
Received 25 November 2013
Accepted 6 March 2014
Available online 19 March 2014
Keywords:
Dithiocarbamates
Arsenic
Phosphonium
Crystal structure
X-ray diffraction
Sulfur ligand
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
comparisons of several new phosphonium and arsenic dithiocarba-
mate complexes to be used in these efforts [8].
The chemistry of arsenic dithiocarbamates has been investi-
gated since the first half of the 20th century [1–4]. While it is gen-
erally understood that dithiocarbamate ligands form robust
complexes with arsenic and other ‘‘soft’’ p-block elements (as is of-
ten rationalized in terms of Pearson’s hard–soft acid–base theory)
[5], it is less clear how varying the dithiocarbamate substituents af-
fects As–S bonding and electronic structure. From a broad perspec-
tive, As–S bonding is of interest because of its role in arsenic
toxicity mechanisms [6], and dithiocarbamate substituents appear
to play a significant role in related arsenic binding and distribution
in liquid–liquid extraction studies [7]. Our aim is to evaluate the
role of dithiocarbamate substituents in As[S2CNR2]3 electronic
structure using S K-edge X-ray absorption spectroscopy (XAS),
which requires a series of dithiocarbamate salts and arsenic
complexes with high-purity and well-defined bond metrics.
Here we describe the synthesis, characterization and structural
2. Results and discussion
2.1. Synthesis of [PPh4][S2CNR2] and As[S2CNR2]3
In preparation for XAS studies, a systematically modified series
of As[S2CNR2]3 and [PPh4][S2CNR2] complexes were prepared
(Scheme 1). These compounds were selected to determine how
(1) the orientation of alkyl substituents and (2) the type of substi-
tuent (alkyl versus aryl) would affect dithiocarbamate bonding and
electronic structure. As reported previously and shown below [9],
the ethyl substituents in S2CNEtÀ2 are typically found in a trans con-
formation while the alkyl-substituents in S2CN(CH2)À5 adopt a cis
conformation that is enforced by the six-membered piperidyl
heterocycle.
The salts [PPh4][S2CNR2], where R2 = Et2 (1a), (CH2)5 (1b), and
Ph2 (1c), were first prepared so that the bonding and structures
of each anion could be evaluated in the absence of arsenic. The
non-coordinating tetraphenylphosphonium cation (PPh+4) was
⇑
Corresponding author. Tel.: +1 202 994 6934.
E-mail address: srdaly@gwu.edu (S.R. Daly).
http://dx.doi.org/10.1016/j.poly.2014.03.003
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

C.M. Donahue et al. / Polyhedron 75 (2014) 110–117
111
chosen in preference to more traditional alkali metal cations in an
effort to minimize intermolecular cationÁ Á Ásulfur interactions that
could otherwise interfere with spectroscopic transitions associated
with sulfur. In general, the synthesis of [PPh4][S2CNR2] salts are rel-
atively unexplored; only the structure of [PPh4][S2CNMe2] has
been reported from crystals obtained adventitiously from a failed
reaction [10]. The salts 1a–1c were prepared by metathesis reac-
tions of NaS2CNR2 with PPh4Br in acetonitrile (MeCN). After re-
moval of the solvent and extraction with MeCN, analytically pure
1a–1c could be obtained in high yield by vapor diffusion of diethyl
ether (Et2O) into the MeCN solutions. Large yellow prisms of 1a
and 1b suitable for single-crystal X-ray diffraction (XRD) were
collected and 1c formed as a yellow microcrystalline solid.
Scheme 1. Numbering system used for phosphonium and arsenic
dithiocarbamates.
Fig. 1. Molecular structure of [PPh4][S2CNEt2], 1a. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms have been omitted from the figure.
Table 1
Crystallographic data for [PPh4][S2CNEt2] (1a), [PPh4][S2CN(CH2)5] (1b), As[S2CN(CH2)5]3 (2b), As[S2CNPh2]3ÁC7H8 (2cÁC7H8), and As[S2CN(CH2)5]2I (3).
1a
1b
2b
2cÁC7H8
3
Formula
C
29H30NPS2
C30H30NPS2
499.64
C18H30N3S6As
555.73
C46H38N3S6As
849.97
C12H20N2S4IAs
522.36
FW (g molÀ1
)
487.63
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
13.4423(18)
14.0324(18)
14.3843(19)
90.00
111.482(2)
90.00
2524.8(6)
4
monoclinic
P21/c
8.916(5)
28.434(15)
10.252(5)
90.00
99.040(6)
90.00
2567(2)
4
monoclinic
P21/c
17.2691(19)
11.8716(13)
12.1686(14)
90.00
107.589(2)
90.00
2378.1(5)
4
triclinic
P1
orthorhombic
P212121
6.0207(7)
15.3440(18)
19.444(2)
90.00
90.00
90.00
1796.3(4)
4
1.932
ꢀ
10.437(4)
13.306(4)
16.024(5)
84.200(5)
89.661(5)
72.601(5)
2112.0(12)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc (g cmÀ3
)
1.283
0.292
1.293
0.289
1.552
1.967
1.337
1.134
l
(mmÀ1
)
4.068
h Range (°)
R(int)
1.63/30.21
0.0497
2.14/27.80
0.0443
1.24/30.12
0.0414
1.613/27.704
0.0564
1.69/28.36
0.0669
Data/restraints/parameters
7015/0/298
1.038
0.0349
5952/0/307
1.024
0.0350
6520/0/278
1.072
0.0283
9589/95/505
0.985
0.0434
4462/0/181
0.914
0.0298
Goodness-of-fit (GOF) on F2
R1 [I > 2
r
(I)]a
wR2 (all data)b
Largest peak and hole (e ÅÀ3
T (K)
0.0940
0.0845
0.0611
0.1040
0.0527
)
0.0452/À0.338
0.362/À0.282
0.405/À0.508
0.388/À0.378
0.523/À0.450
293(2)
120(1)
293(2)
293(2)
293(2)
P
P
a
R1
=
|Fo| À |Fc||/| |Fo| for reflections with Fo2 > 2
r
(F2o).
P
P
b
2
wR2 = [ w(Fo À Fc2)2/ (Fo2)2]1/2 for all reflections.

112
C.M. Donahue et al. / Polyhedron 75 (2014) 110–117
Table 2
Selected bond distances and angles of phosphonium dithiocarbamates 1a and 1b.
Compound
Bond distances (Å)
S–C
Bond angles (°)
S–C–S
C–N
N–R
C–N–R
R–N–R
[PPh4][S2CNEt2]
(1a)
[PPh4][S2CN(CH2)5]
(1b)
1.712(1)
1.722(1)
1.712(2)
1.720(2)
1.359(2)
1.468(2)
1.466(2)
1.470(2)
1.462(2)
121.69(7)
122.2(1)
123.0(1)
124.0(1)
123.8(1)
114.8(1)
1.357(2)
121.34(9)
111.5(1)
It should be clearly noted that 2a and 2b have been reported
previously [2,11,12], and are only included here to describe a
slightly modified version of their synthesis and report the structure
of 2b. Despite the long history of arsenic dithiocarbamate chemis-
try, phenyl-substituted 2c has never been described.
2.2. Crystal structures
The structures of the phosphonium salts 1a and 1b were deter-
mined by single-crystal XRD (Table 1). The structures reveal
charge-separated phosphonium cations and dithiocarbamate an-
ions that are free of significant intermolecular cation–anion inter-
actions, as expected given the use of the non-coordinating PPh4+
cation (Fig. 1). The closest intermolecular sulfur contacts in 1a
and 1b involve a phenyl hydrogen atom on PPh+4 at 2.79 and
2.83 Å, respectively, which are just within the sum of the van der
Waals radii for H and S at 2.89 Å [13,14]. The C–S bond distances
in both anions are roughly equivalent at 1.71–1.72 Å, as would
be expected for even charge delocalization over both C–S bonds
(Table 2). The largest difference between the structures is the
aforementioned trans versus cis orientation of the alkyl substitu-
ents (Fig. 2). The enforced six-membered piperidyl ring also causes
a decrease in the R–N–R bond angle from 114.8° in S2CNEtÀ2 (1a) to
111.5° in S2CN(CH2)À5 (1b). The remaining bond angles and dis-
tances for 1a and 1b are all approximately identical within error.
The molecular structures of As[S2CN(CH2)5]3 (2b) and
As[S2CNPh2]3 (2c) are provided in Figs. 3 and 4. As is typical for
Fig. 2. Comparison of the dithiocarbamate anions S2CNEtÀ2 (left) and S2CN(CH2)À5
(right) from the XRD data of 1a and 1b. Ellipsoids are drawn at the 50% probability
level. Hydrogen atoms and the tetraphenylphosphonium cations have been omitted
from the figure.
The As[S2CNR2]3 complexes, where R2 = Et2 (2a), (CH2)5 (2b),
and Ph2 (2c), were prepared by treating As2O3 or AsI3 with three
equivalents of NaS2CNR2. As2O3 and AsI3 can both be used to pre-
pare alkyl-substituted 2a and 2b as long as the appropriate solvent
is used (aqueous HCl and MeCN, respectively). Attempts to prepare
the piperidyl derivative 2b using AsI3 and a different solvent (H2O/
EtOH) resulted in a mixture containing a small amount of 2b and
the heteroleptic species As[S2CN(CH2)5]2I (3) (see below). In
contrast, a similar reaction with AsI3 and three equivalents of
NaS2CNPh2 in H2O/EtOH yielded As[S2CNPh2]3 (2c).
Fig. 3. Molecular structure of As[S2CN(CH2)5]3, 2b. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms and the disordered component of the piperidyl ring
bonded to C18 have been omitted from the figure.

C.M. Donahue et al. / Polyhedron 75 (2014) 110–117
113
Fig. 4. Comparison of the sulfur bond distances in the structures of [PPh4][S2CNR2]
(left) and As[S2CNR2]3 (right).
homoleptic arsenic dithiocarbamate complexes, the coordination
geometry around each arsenic atom can be described as distorted
octahedral with three short As–S bonds (2.32–2.38 Å) forming
one triangular face and three long AsÁ Á ÁS contacts (2.76–2.96 Å)
that form the opposite face (Table 3). The longer AsÁ Á ÁS distances
are attributed to steric interactions with the stereoactive lone pair
on arsenic [4]. To facilitate the remaining discussion, we will dis-
tinguish the two sulfur environments as As–S (bonding) and AsÁ Á ÁS
(close-contact). The S–C bond distances in each dithiocarbamate li-
gand reflect the different sulfur environments; the sulfur atoms
bound to arsenic (As–S) have S–C bond distances of ca. 1.76 Å
whereas the AsÁ Á ÁS sulfur atoms have shorter S–C bond distances
that range between 1.67 and 1.69 Å (Fig. 5). The three R–N–R
angles in phenyl substituted 2c are larger than those in 2b
(116–119° versus 112–113°), which reflects the increased steric
bulk of the phenyl substituents.
Fig. 5. Extended molecular structure of As[S2CN(CH2)]2I, 3. Ellipsoids are drawn at
the 50% probability level. Hydrogen atoms have been omitted from the figure.
of blocks (2b) and a large number of brown needles with the com-
position As[S2CN(CH2)5]2I (3). Single crystal XRD of the needles re-
veal a coordination polymer with As[S2CN(CH2)5]+2 fragments that
are loosely bridged together by the iodide (Fig. 6). The As–I dis-
tances of 3.48 and 3.59 Å are well outside those expected for
authenticated terminal As–I single bonds (2.6–2.8 Å) but they fall
within the calculated van der Waals distances for As and I
(3.83 Å) [13,15,16]. Bridging As–I bonds have precedence for being
exceptionally long compared terminal As–I bonds; for example, the
dimers [AsI2(MeS(CH2)2SMe)]2(l-I)2 and [AsI2{o-C6H4(AsMe2)2}]2
(l-I)2 have bridging As–I distances of 3.34 and 3.43 Å [16,17].
Iodide aside, the coordination environment around each As atom
is best described as a distorted see-saw geometry based on the
arrangement of the four sulfur atoms. The As–S and S–C bond
Attempts to prepare 2b using AsI3, followed by recrystallization
of the reaction precipitate by vapor diffusion of diethyl ether into
chloroform solutions, resulted in the formation of a small number
Table 3
Selected bond distances and angles for the arsenic dithiocarbamates 2b, 2c, and 3.
Bond distances (Å)
Bond angles (°)
As[S2CN(CH2)5]3 (2b)
As1–S2
As1–S4
As1–S6
As1–S1
As1–S3
As1–S5
N1–C6
N2–C12
N3A–C18
N3B–C18
N1–C1
2.3411(5)
2.3314(5)
2.3253(5)
2.8907(5)
2.8633(5)
2.9384(6)
1.334(2)
1.329(2)
1.361(3)
1.369(6)
1.475(2)
1.473(2)
S2–C6
S4–C12
S6–C18
S1–C6
S3–C12
S5–C18
N2–C7
N2–C11
N3A–C13A
N3B–C13B
N3A–C17A
N3B–C17B
1.764(2)
1.763(2)
1.760(2)
1.686(2)
1.691(2)
1.689(2)
1.472(2)
1.472(2)
1.478(3)
1.467(8)
1.478(4)
1.476(8)
S1–As1–S2
S1–As1–S3
S1–As1–S4
S1–As1–S5
S1–As1–S6
S2–As1–S3
S2–As1–S4
S2–As1–S5
S2–As1–S6
C1–N1–C5
C7–N2–C11
68.39(2)
99.79(2)
159.14(2)
111.28(1)
98.34(2)
87.82(2)
93.23(2)
153.89(2)
86.43(2)
111.9(1)
112.9(1)
S3–As1–S4
S3–As1–S5
S3–As1–S6
S4–As1–S5
S4–As1–S6
S5–As1–S6
S1–C6–S2
S3–C12–S4
S5–C18–S6
C13–N3B–C17
C13–N3A–C17
68.60(2)
117.20(1)
157.41(2)
89.58(2)
89.93(2)
67.60(2)
119.1(1)
117.9(1)
119.0(1)
112.6(5)
112.6(2)
N1–C5
As[S2CNPh2]3 (2c)
As1–S1
As1–S3
As1–S5
As1–S2
As1–S4
As1–S6
C11–N1
C21–N1
C31–N2
C41–N2
C51–N3
C61–N3
2.334(1)
2.333(1)
2.383(1)
2.763(1)
2.95(1)
2.958(1)
1.452(3)
1.457(4)
1.449(4)
1.448(3)
1.450(4)
1.453(4)
S1–C1
S3–C2
S5–C3
S2–C1
S4–C2
S6–C3
C1–N1
C2–N2
C3–N3
1.751(3)
1.755(3)
1.748(3)
1.680(3)
1.678(3)
1.669(3)
1.345(4)
1.347(3)
1.355(3)
S1–As1–S2
S1–As1–S3
S1–As1–S4
S1–As1–S5
S1–As1–S6
S2–As1–S3
S2–As1–S4
S2–As1–S5
S2–As1–S6
S3–As1–S4
S3–As1–S5
S3–As1–S6
70.23(3)
93.38(3)
149.17(3)
87.70(3)
96.74(3)
89.48(3)
84.75(3)
157.70(3)
117.25(3)
67.95(3)
88.66(3)
153.24(3)
S4–As1–S5
S4–As1–S6
S5–As1–S6
S1–C1–S2
S3–C2–S4
S5–C3–S6
C11–N1–C21
C31–N2–C41
C51–N3–C61
114.94(3)
110.94(3)
67.15(3)
118.7(2)
121.9(2)
121.9(2)
119.0(2)
116.2(2)
115.7(2)
As[S2CN(CH2)5]2I (3)
As1–S1
As1–S4
As1–S2
As1–S3
As1–I1
As1–I1aa
N1–C6
2.302(1)
2.303(1)
2.496(1)
2.512(1)
3.5906(8)
3.479(1)
1.314(4)
1.329(5)
S1–C6
S4–C12
S2–C6
S3–C12
N1–C3
N1–C4
N2–C9
N2–C11
1.749(4)
1.744(4)
1.715(4)
1.707(4)
1.478(5)
1.470(5)
1.473(5)
1.470(5)
S1–As1–S2
S3–As1–S1
S1–As1–S4
S3–As1–S2
S4–As1–S2
S3–As1–S4
C3–N1–C4
C9–N2–C11
74.45(4)
88.00(4)
97.27(4)
151.93(4)
86.37(4)
74.08(3)
113.2(4)
113.8(4)
S1–As1–I1
S2–As1–I1
S3–As1–I1
S4–As1–I1
S2–C6–S1
S3–C12–S4
80.80(4)
126.34(4)
70.18(3)
144.25(4)
114.1(2)
114.7(2)
N2–C12
a
Symmetry transformation used to generate equivalent atoms: a = x + 1,y,z.

114
C.M. Donahue et al. / Polyhedron 75 (2014) 110–117
Fig. 6. Molecular structure of As[S2CNPh2]3ÁC7H8, 2cÁC7H8. Ellipsoids are drawn at
the 35% probability level. The toluene solvate and the hydrogen atoms have been
omitted from the figure.
distances in each ligand do not deviate as much as those in 2b.
There is a 0.2 Å difference between the As–S bonds in each ligand
(versus >0.4 Å in 2b) and all four S–C bonds fall within the range of
1.71–1.75 Å. Overall the structure of heteroleptic As[S2CNR2]2I
complexes are relatively rare. While the synthesis of 3 and other
As[S2CNR2]2I complexes have been reported [18], only one other
structure is known [19].
Given that the reaction of AsI3 with three equivalents of
NaS2CN(CH2)5 yielded crystals of 3 and 2b, we analyzed the crude
reaction precipitate by powder XRD to evaluate the relative pro-
portion of each compound in the mixture. The powder XRD data
is presented in Fig. 7 with the calculated powder XRD pattern of
2b (top) and 3 (bottom) from the single crystal diffraction data
for comparison. The data indicates that the major product in the
reaction precipitate is the mixed iodide complex 2b. The incom-
plete metathesis in H2O/EtOH solutions contrasts the reaction
behavior reported for AsI3 and sodium dialkyldithiocarbamates in
MeCN. For example, it was reported that the reaction of AsI3 with
three equivalents of NaS2CNEt2 in MeCN yielded As[S2CNEt2]3 in
79% yield [9]. The difference in the AsI3 metathesis chemistry be-
tween EtOH/H2O and MeCN reaction solvents appears to result
from differences in solubility: As[S2CN(CH2)5]2I precipitates from
EtOH/H2O before the metathesis is complete whereas all arsenic-
containing species remain soluble in MeCN.
Fig. 7. Experimental powder XRD pattern of the precipitate obtained from the
reaction of AsI3 and three equivalents of NaS2CN(CH2)5 (black). Top – comparison
with the calculated powder XRD pattern from the single crystal diffraction data for
3 (red). Bottom – comparison with the calculated powder XRD pattern from the
single crystal diffraction data for 2b (blue). (Color online.)
NMR spectra at d = 24.4. The arsenic dithiocarbamates exhibit sim-
ilar 1H NMR shifts as their phosphonium analogs and the NMR
shifts for 2a and 2b closely match those reported previously in
units of
s [12,21]. The spectrum of 2a reveals a triplet at d = 1.29
and a quartet at d = 3.88 for the methyl and methylene protons,
and the lack of additional peaks is consistent with retention of
the C3 symmetry in solution. The proton NMR spectrum of 2b also
yields two peaks despite having three unique proton environments
in the piperidyl substituents. The peaks appear as broadened sing-
lets at d = 1.69 and 4.05 (6:4 ratio) compared to the three reso-
nances at d = 1.49, 1.60, and 4.38 (4:2:4 ratio) in the proton NMR
spectrum of 1b. The peak broadening and coalescence of three
peaks to two in the spectrum of 2b can likely be attributed to dif-
ferent conformations of the six-membered piperidyl ring within
each ligand. As observed for As[S2CN(CH2)5]3, the proton NMR
spectrum of As[S2CN(CH2)5]2I (3) also exhibits two broad singlets
but with slightly different shifts than 2b at d = 1.75 and 3.93. The
presence of only two peaks indicates that the two unique dithio-
carbamate environments observed in the solid-state are equivalent
in solution on the NMR timescale.
2.3. Spectroscopic analysis
IR data were collected on the phosphonium salts 1a–1c and on
the complimentary arsenic complexes 2a – 2c. It is generally
agreed that the C–NR2 stretches and C–S stretches for dithiocarba-
All seven compounds were characterized by NMR spectroscopy.
The 1H and 31P NMR spectra of the phosphonium salts 1a–1c
were collected in CD3CN and the 1H NMR spectra of the arsenic
dithiocarbamates 2a–2c and 3 were collected in CDCl3. In general,
the proton spectra of the phosphonium salts are unexceptional and
exhibit peak splittings and integrations that reflect each of the
dithiocarbamate anions. Similar to data obtained on tetraphenyl-
phosphonium dithiophosphinates [20], the proton NMR spectra
of 1a–1c reveal multiplets for the PPh+4 cation between d = 7.65
and 7.94 and a complimentary singlet is observed in the 31P{1H}
mates typically fall in the range of 1400–1500 and 930–1030 cmÀ1
,
respectively [4,22]. Overall, the spectra of 1a–1c are strikingly sim-
ilar, which can be attributed in part to the tetraphenylphospho-
nium cation that is common to all three salts. Identical peaks,
however, are also observed in the C–NR2 and C–S stretching re-
gions for all three compounds at 1434, 1458 and 1480 cmÀ1 and
at 948, 970, and 994 cmÀ1, respectivly. Despite the localization of

C.M. Donahue et al. / Polyhedron 75 (2014) 110–117
115
prepared according to literature methods [7,23]. AsI3 (Alfa Aesar),
As2O3 (Mallinckrodt), PPh4Br (Acros), NaS2CNEt2Á3H2O (Mallinck-
rodt), and conc. HCl (Fisher) were used as received. Solvents were
purchased from commercial vendors and used as received. H2O
was purified to 18.2 MW-cm resistivity using a Siemens LoboStar
UV2 ultra-pure water purification system.
Elemental analyses were carried out by Midwest MicroLab, LLC
(Indianapolis, IN). The infrared spectra were recorded on a Perkin-
Elmer Frontier FTIR Spectrometer using an attenuated total reflec-
tance (ATR) sampling accessory. The 1H and 31P NMR data were ob-
tained using an Agilent NMR spectrometer at 400 and 121 MHz,
respectively. Chemical shifts are reported in d units (positive shifts
to high frequency) relative to TMS (1H) and H3PO4 31P). Melting
(
points were determined in open capillaries on a Thomas-Hoover
Unimelt apparatus.
4.2. [PPh4][S2CNEt2], (1a)
To a mixture of NaS2CNEt2Á3H2O (0.215 g, 0.954 mmol) and
PPh4Br (0.403 g, 0.961 mmol) was added MeCN (5 mL). The mix-
ture was stirred for 30 min, which yielded a yellow solution and
a white precipitate. The mixture was evaporated to dryness under
vacuum. MeCN (3 mL) was added to the solid residue and the mix-
ture was filtered into a 20 mL scintillation vial. Yellow crystals of
1a were grown over the course of a week by vapor diffusion with
diethyl ether (20 mL). Yield: 0.374 g (80.4%). Mp: 176–177 °C Anal.
Calc.: C, 71.43; H, 6.2; N, 2.87; S, 13.15. Found: C, 71.20; H, 6.14; N,
2.82; S, 12.70%. 1H NMR (CD3CN, 25 °C): d 1.16 (t, CH3, 6H), 4.10 (q,
NCH2, 4H), 7.65–7.77 (m, PPh4, 16H), 7.90–7.94 (m, PPh4, 4 H).
31P{1H} NMR (CD3CN, 25 °C): d 24.4 (s, PPh4). IR (cmÀ1): 606 w,
616 w, 648 w, 686 vs 720 vs 750 m, 758 m, 810 w, 840 w, 850
w, 882 m, 900 w, 916 w, 936 w, 948 w, 970 m, 994 m, 1024 w,
1044 w, 1068 w, 1104 vs 1108 m, 1158 w, 1200 m, 1208 m,
1242 m, 1276 w, 1318 w, 1340 w, 1360 w, 1390 m, 1434 s, 1458
w, 1480 m, 1584 w, 2846 w, 2938 w, 2988 w, 3036 w.
Fig. 8. Comparison of the IR spectra for As[S2CNEt2]3 (bottom; blue),
As[S2CN(CH2)5]3 (middle; black), and As[S2CNPh2]3 (top; red). The assigned C–S
and C–NR2 stretching regions and peaks are emphasized with the dashed boxes.
(Color online.)
C–S bonds in the structures of the arsenic dithiocarbamates, the IR
peaks in the spectra of 2a–2c do not change much except for those
assigned to C–S stretching bands in As[S2CNPh2]3. The alkyl-substi-
tuted 2a and 2b exhibit strong peaks between 970 and 1002 cmÀ1
that compare well to m(CS) peaks previously reported [12,21], but
these appear to shift to higher energy in the spectrum of 2c at
1002, 1022 and 1034 cmÀ1 (Fig. 8). Given the change in substitu-
ents from alkyl to aryl, the unique shift in the C–S stretching fre-
quencies for 2c is likely attributed to the addition of
p-
conjugation between the phenyl substituents and the -orbitals
p
delocalized over carbon, nitrogen and sulfur. The higher energy
shift indicates an increase in C–S double-bond character, which is
consistent with increased p-mixing with phenyl.
4.3. [PPh4][S2CN(CH2)5], (1b)
3. Conclusion
Prepared as described for 1a with PPh4Br (0.410 g, 0.978 mmol)
and NaS2CN(CH2)5 (0.229 g, 0.965 mmol). Yield: 0.313 g (64.9%).
Mp: 174–175 °C. Anal. Calc.: C, 72.11; H, 6.20; N, 2.80; S, 12.83.
Found: C, 71.97; H, 6.00; N, 2.86; S, 13.21%. 1H NMR (CD3CN,
25 °C): d 1.49 (m, 4H), 1.60 (m, 2H), 4.38 (vt, NCH2, 4H), 7.65–
7.77 (m, PPh4, 16H), 7.89–7.94 (m, PPh4, 4H). 31P{1H} NMR (CD3CN,
25 °C): d 24.4 (s, PPh4). IR (cmÀ1): 606 w, 6116 w, 686 vs 720 vs 752
m, 758 vm, 810 w, 850 w, 882 m, 934 w, 948 m, 970 s, 994 m, 1022
w, 1068 w, 1106 s, 1118 m, 1158 w, 1200 m, 1208 m, 1240 m, 1276
w, 1318 w, 1340 w, 1358 w, 1390 m, 1434 s, 1458 w, 1480 m, 1584
w, 2846 w, 2936 w, 2988 w, 3036 w.
In summary, we have reported the synthesis and characteriza-
tion of As[S2CNPh2]3 and several new tetraphenylphosphonium
dithiocarbamates. The [PPh4][S2CNR2] salts have the qualities de-
sired for spectroscopic analysis; they can be prepared in high pur-
ity and the structures of [PPh4][S2CNEt2] and [PPh4][S2CN(CH2)5]
reveal a lack of appreciable intermolecular cation–sulfur interac-
tions. In total, five new crystal structures have been reported,
and these have provided important structural metrics needed to
support spectroscopic comparisons of dithiocarbamates in the
presence and absence of arsenic. Varying the substituents attached
to nitrogen does not appear to impart significant changes in
As[S2CNR2]3 bond distances and angles, but a clear difference is ob-
served in the C–S stretching region when alkyl substituents in 2a
and 2b are changed to phenyl in 2c. The IR results suggested that
the dithiocarbamate substituents do affect sulfur bonding when
bound to arsenic, and future reports will describe S K-edge X-ray
absorption spectroscopy (XAS) efforts aimed at quantifying these
contributions as they pertain to As[S2CNR2]3 electronic structure
and As–S bonding.
4.4. [PPh4][S2CNPh2], (1c)
Prepared as described for 1a with PPh4Br (0.31 g, 0.75 mmol)
and NaS2CNPh2 (0.20 g, 0.75 mmol). Mp: 130–131 °C. Anal. Calc.:
C, 76.13; H, 5.18; N, 2.40; S, 10.99. Found: C, 75.71; H, 5.15; N,
2.40; S, 10.87%. 1H NMR (CD3CN, 25 °C): d 7.05–7.09 (m, Ph2, 2H),
7.20–7.25 (m, Ph2, 4H), 7.30–7.33 (m, Ph2, 4H), 7.65–7.77 (m,
PPh4, 16H), 7.89–7.94 (m, PPh4, 4H). 31P NMR (CD3CN, 25 °C): d
24.4 (s, PPh4). IR (cmÀ1): 604 w, 616 w, 686 w, 718 vs 750 m
758 m, 810 w, 850 w, 882 m, 900 w, 934 w, 948 m, 970 m, 994
m, 1024 w, 1044 w, 1068 w, 1106 s, 1118 m, 1158 w, 1200 m,
1208 m, 1242 m, 1276 w, 1316 w, 1340 w, 1358 w, 1390 m,
1434 s, 1458 w, 1482 w, 1584 w, 1480 m, 1584 w, 2846 w, 2938
w, 2988 w, 3038 w.
4. Experimental
4.1. General considerations
Unless specified otherwise, all reactions were performed in air.
The dithiocarbamate salts NaS2CN(CH2)5 and NaS2CNPh2 were

116
C.M. Donahue et al. / Polyhedron 75 (2014) 110–117
4.5. As[S2CNEt2]3, (2a)
4.9. Crystallographic details
Prepared with slight modification of a known procedure [24]. To
a solution of NaS2CNEt2 (1.371 g, 6.06 mmol) in water (10 mL) was
added a solution of As2O3 (0.201 g, 1.02 mmol) in concentrated
hydrochloric acid (5 mL). A thick yellow precipitate formed and
the mixture was stirred for 1 h. The solid was collected by filtration
and light green crystals were obtained after recrystallization
from chloroform. Yield: 0.65 g (61%). Mp: 139–140 °C. Anal. Calc.:
C, 34.66; H, 5.82; N, 8.08; S, 37.02. Found: C, 34.68; H, 6.03; N,
8.06; S, 36.66%. 1H NMR (CDCl3, 25 °C): d 1.29 (t, CH3, 18H), 3.88
(q, CH2, 12H). IR (cmÀ1): 600 w, 776 m, 834 s, 912 m, 982 m,
1002 w, 1066 m, 1076 m, 1086 m, 1094 m, 1142 s, 1200 s, 1270
vs 1298 w, 1354 m, 1372 m, 1422 vs 1450 m, 1458 m, 1486 vs
2868 w, 2932 w, 2972 w.
Single crystals of 1a and 1b were obtained by vapor diffusion of
diethyl ether into acetonitrile solutions and were mounted in a ny-
lon cryoloop or MiTeGen mount with Paratone-N oil in air. The
data were collected on a Bruker diffractometer with an APEX II
charge-coupled-device (CCD) detector. Data for 1b were collected
at 120 K using a Cryo industries of America G2 low temperature
device. All other data were collected at room temperature. Single
crystals of 2b and 3, obtained by vapor diffusion of diethyl ether
into chloroform solutions, were treated identically, as were
single crystals of 2c obtained from toluene. The instrument was
equipped with graphite monochromatized Mo K
a X-ray source
(k = 0.71073 Å) with monocapillary optics. Data collection and ini-
tial indexing and cell refinement were handled using APEX II soft-
ware [25]. Frame integration, including Lorentz-polarization
corrections, and final cell parameter calculations were carried out
using SAINT+ software [26]. The data were corrected for absorption
using redundant reflections and the SADABS program [27]. The
structure was solved using direct methods and difference
Fourier techniques. All hydrogen atom positions were idealized,
and were allowed to ride on the attached carbon atoms. The final
refinement included anisotropic temperature factors on all non-
hydrogen atoms. Data collection and refinement details are listed
in Table 1.
4.6. As[S2CN(CH2)5]3, (2b)
Prepared as described for 2a using NaS2CN2(CH2)5 and As2O3.
Mp: 228–229 °C. Anal. Calc.: C, 38.90; H, 5.44; N, 7.56; S, 34.62.
Found: C, 38.87; H, 5.75; N, 7.48; S, 34.19. 1H NMR (CDCl3,
25 °C): d 1.69 (br s, 18H), 4.05 (br s, 12H). IR (cmÀ1): 602 m, 616
w, 646 w, 688 m, 720 m, 758 w, 808 w, 848 m, 858 m, 886 m,
948 s, 970 s, 996 s, 1018 w, 1044 w, 1072 w, 1106 vs 1134 m,
1162 w, 1228 vs 1256 w, 1262 w, 1280 m, 1320 w, 1352 w,
1428 s, 1434 s, 1453 w, 1474 sh, 1480 s, 1584 w, 2850 m, 2938
m, 2982 w, 3038 w.
Powder XRD of the bulk precipitate obtained from the reaction
of AsI3 with three equivalents of Na[S2CN(CH2)5] were collected on
Rigaku Miniflex II equipped with a Cu Ka X-ray source. Scans were
collected from 2h = 3–60° at a scan speed of 2° per minute and a
sampling width of 0.020°. The power was set to 15 kV and 30 mA.
4.7. As[S2CNPh2]3, (2c)
To a suspension of AsI3 (0.142 g, 0.312 mmol) in a 1:1 solution
of ethanol and deionized water (20 mL) was added a solution of
NaS2CNPh2 (0.302 g, 0.927 mmol) in deionized water (10 mL). A
thick off-white precipitate formed and the mixture was heated to
50 °C for 2 h. The mixture was cooled to room temperature and fil-
tered. The solid was allowed to dry in air overnight. To the solid
was added to 120 mL of toluene and the mixture was heated to re-
flux to completely dissolve the solid. The yellow solution was
slowly cooled to RT and then stored at 4 °C. Yellow prisms formed
overnight. The collected crystals were exposed to dynamic vacuum
for 30 min to remove the toluene solvate in the crystal lattice.
Yield: 0.070 g (28%). Mp: > 250 °C. Anal. Calc.: C, 57.97; H, 3.74; N
5.20; S, 23.81. Found: C, 58.28; H, 3.76; N, 4.99; S, 22.83%. 1H
NMR (CDCl3, 25 °C): d 7.31–7.49 (m). IR (cmÀ1): 624 m, 630 w,
646 m, 668 w, 688 m, 698 s, 746 m, 752 m, 776 w, 818 w, 834
w, 884 w, 912 w, 982 w, 1002 m, 1022 m, 1034 s, 1074 m, 1096
w, 1142 w, 1154 w, 1202 w, 1268 m, 1290 m, 1306 m, 1332 sh,
1347 vs 1450 w, 1488 s, 1588 w, 2870 w, 2972 w, 3050 w.
Acknowledgements
Funding for this work was provided by the George Washington
University. Los Alamos National Laboratory is operated by Los Ala-
mos National Security, LLC, for the National Nuclear Security
Administration of U.S. Department of Energy under Contract
DEAC52-06NA25396. We would like to thank the Cahill Group at
GW, especially Gian Surbella and Andrew Kerr, for their assistance
collecting portions of the XRD data.
Appendix A. Supplementary data
CCDC 973372, 973373, 973374, 973375, 973376 contain the
supplementary crystallographic data for compounds 1a, 1b, 2b,
2c, and 3, respectively. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
4.8. As[S2CN(CH2)5]2I, (3)
References
To a suspension of AsI3 (0.252 g, 0.553 mmol) in a 1:1 solution
of ethanol and deionized water (20 mL) was added a solution of
NaS2CN(CH2)5 (0.339 g, 1.85 mmol) in deionized water (10 mL),
as described for the preparation of 2c. A white precipitate immedi-
ately formed and the mixture was stirred for 15 min. The mixture
was filtered and the solid was dissolved in chloroform. Vapor dif-
fusion of diethyl ether into the chloroform solution over several
days resulted in the formation of brown needles (3; major product)
and blocks (2b; minor product). The crystallized yield of 3 was low
(ꢀ30 mg), but was sufficient to obtain the following data: Anal.
Calc.: C, 27.59; H, 3.86; N5.36; I, 24.29. Found: C, 26.98; H, 3.70;
N, 5.11; I, 23.91%. 1H NMR (CDCl3, 25 °C): d 1.75 (br s, 12H), 3.93
(br s, 8H). Powder XRD of the precipitate from an identical syn-
thetic prep indicated that the major product was 3.
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