Binding forms of gold(III) from solutions by cadmium diethyl dithiocarbamate: Thermal behavior and role of secondary interactions in the supramolecular self-assembly of polymeric Complexes ([Au{S2CN(C 2H5)2}2][AuCl4]) n and [Au{S2CN(C2H5) 2}Cl2] n

Article abstract of DOI:10.1134/S1070328414020080

The chemisorption interaction between the binuclear cadmium diethyl dithiocarbamate (EDtc), [Cd₂{S₂CN(C₂H ₅)₂}₄], (chemisorbent I) and AuCl₃ solutions in 2 M HCl results in the formation of polymeric gold(III) complexes: ([Au{S₂CN(C₂H₅)₂} ₂][AuCl₄]) _n (II) and [Au{S ₂CN(C₂H₅)₂}Cl₂] _n (III) with the same Au: EDtc: Cl ratio (1: 1: 2). The alternating centrosymmetric cations and anions of complex II are structurally self-assembled to form linear polymeric chains: the gold atom in [Au{S₂CN(C ₂H₅)₂}₂]⁺ forms secondary Au(1)...Cl(1) bonds (3.7784 A) with two neighboring [AuCl ₄]^- anions. This binding is additionally strengthened by secondary S(1)...Cl(1) interactions (3.4993 A). The mixed-ligand complex III comprises two structurally non-equivalent molecules [Au{S ₂CN(C₂H₅)₂}Cl₂]: A - Au(1) and B - Au(2), each being in contact with two nearest neighbors through pairs of unsymmetrical secondary bonds: Au(1)...S(1)^a/b 3.4361/3.6329; and Au(2)...S(4)^c/d 3.4340/3.6398 A. At the supramolecular level, this gives rise to independent zigzag-like polymeric chains, (...A...A...A...) _n and (...B...B...B...) _n along which antiparallel isomeric molecules of III alternate. The chemisorption capacity of cadmium diethyl dithiocarbamate calculated from the gold(III) binding reaction is 963.2 mg of gold per 1 g of the sorbent. The recovery conditions for the bound gold were elucidated by simultaneous thermal analysis of II and III. The DSC curves reflect different sets of heat effects, because thermolysis occurs for complex molecules (III) or for cations and anions (II). Nevertheless, the patterns of experimental TG curves are similar despite different structures of the complexes. The final product of thermal transformations is reduced gold.

Full text of DOI:10.1134/S1070328414020080

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2014, Vol. 40, No. 2, pp. 100–108. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © T.A. Rodina, A.V. Ivanov, A.V. Gerasimenko, 2014, published in Koordinatsionnaya Khimiya, 2014, Vol. 40, No. 2, pp. 99–107.
Binding Forms of Gold(III) from Solutions by Cadmium Diethyl
Dithiocarbamate: Thermal Behavior and Role of Secondary
Interactions in the Supramolecular SelfꢀAssembly of Polymeric
Complexes ([Au{S2CN(C2H5)2}2][AuCl4])n and
[Au{S2CN(C2H5)2}Cl2]n
T. A. Rodinaa, b, A. V. Ivanova, *, and A. V. Gerasimenkoc
a Institute of Geology and Nature Management, Far Eastern Branch, Russian Academy of Sciences,
Blagoveshchensk, Amur Region, 675000 Russia
b Amur State University, Blagoveshchensk, Amur Region, 675027 Russia
c Institute of Chemistry, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, 690022 Russia
*eꢀmail: alexander.v.ivanov@chemist.com
Received July 3, 2013
Abstract—The chemisorption interaction between the binuclear cadmium diethyl dithiocarbamate (EDtc),
[
Cd2{S2CN(C2H5)2}4], (chemisorbent
I
) and AuCl3 solutions in 2 M HCl results in the formation of polyꢀ
meric gold(III) complexes: ([Au{S2CN(C2H5)2}2][AuCl4])n
(
II) and [Au{S2CN(C2H5)2}Cl2]n III) with the
(
same Au : EDtc : Cl ratio (1 : 1 : 2). The alternating centrosymmetric cations and anions of complex II are
structurally selfꢀassembled to form linear polymeric chains: the gold atom in [Au{S2CN(C2H5)2}2]+ forms
secondary Au(1)⋅⋅⋅Cl(1) bonds (3.7784 Å) with two neighboring [AuCl4]– anions. This binding is additionally
strengthened by secondary S(1)⋅⋅⋅Cl(1) interactions (3.4993 Å). The mixedꢀligand complex III comprises two
structurally nonꢀequivalent molecules [Au{S2CN(C2H5)2}Cl2]: A—Au(1) and B—Au(2), each being in conꢀ
tact with two nearest neighbors through pairs of unsymmetrical secondary bonds: Au(1)⋅⋅⋅S(1)a/b
3.4361/3.6329; and Au(2)⋅⋅⋅S(4)c/d 3.4340/3.6398 Å. At the supramolecular level, this gives rise to indepenꢀ
dent zigzagꢀlike polymeric chains, (⋅⋅⋅A⋅⋅⋅A⋅⋅⋅A⋅⋅⋅) and (⋅⋅⋅B⋅⋅⋅B⋅⋅⋅B⋅⋅⋅) along which antiparallel isomeric
n
molecules of III alternate. The chemisorption capancity of cadmium diethyl dithiocarbamate calculated from
the gold(III) binding reaction is 963.2 mg of gold per 1 g of the sorbent. The recovery conditions for the bound
gold were elucidated by simultaneous thermal analysis of II and III. The DSC curves reflect different sets of
heat effects, because thermolysis occurs for complex molecules (III) or for cations and anions (II). Neverꢀ
theless, the patterns of experimental TG curves are similar despite different structures of the complexes. The
final product of thermal transformations is reduced gold.
DOI: 10.1134/S1070328414020080
INTRODUCTION
were preparatively isolated. Gold complexes with
dithio ligands, both dithiocarbamates and dithiophosꢀ
phates, can behave as highly efficient anticancer
agents [18], sensors for volatile chemicals [19] or
luminophores [20–22].
Dithiocarbamate cadmium(II) complexes [1–4]
and adducts they form with organic Nꢀdonor bases
[5–9] are of interest as precursors of film and nanoꢀ
crystalline cadmium sulfides. When searching for antiꢀ
dotes against cadmium intoxication, the ability of
dialkyl dithiocarbamates to bind cadmium into stable
Here we considered the reaction of freshly precipiꢀ
tated cadmium diethyl dithiocarbamate (EDtc)
1
[
Cd2{S2CN(C2H5)2}4] (chemisorbent I) with a soluꢀ
compounds appears an important feature [10–12].
tion of AuCl3 in 2 M HCl and elucidated the sorption
capacity of this material. The heterogeneous
gold(III)ꢀbinding reaction includes chemisorption
and ion exchange. Two individual gold species with the
same Au : EDtc : Cl ratio (1 : 1 : 2) were preparatively
isolated, namely, (i) a polymeric gold(III) complex of
One more important aspect of the possible practical
application of cadmium dithiocarbamates is due to
their ability to efficiently collect gold from acidic soluꢀ
tions [4, 14–17]. As individual goldꢀbinding species, a
variety of polynuclear and heteropolynuclear comꢀ
plexes with highly intricate supramolecular structures
ionic structure ([Au{S2CN(C2H5)2}2][AuCl4])n
and (ii) polymeric mixedꢀligand complex
[Au{S2CN(C2H5)2}Cl2]n III . The molecular and
supramolecular structures of II and III were estabꢀ
(II)
a
1
Despite high toxicity of cadmium, a metalloenzyme in which
cadmium linked to two (or more) thiolate groups of amino acids
acts as the active site was isolated from a marine diatom [13].
(
)
100

BINDING FORMS OF GOLD(III) FROM SOLUTIONS
101
lished from Xꢀray diffraction data. At the supramolecꢀ orange precipitate was filtered off, washed with water,
ular level, the obtained compounds selfꢀassemble into and dried on the filter. Transparent yellow prismatic
polymeric chains through Au⋅⋅⋅S, Au⋅⋅⋅Cl, and Cl⋅⋅⋅
S
(II) and needle (III) crystals of the complexes for
secondary bonds. The recovery conditions of the Xꢀray diffraction were obtained simultaneously from
bound gold and the thermal behavior of complexes II methanol. 13C MAS NMR (
δ
, ppm): II
,
⎯
188.8
CH3);
and III were studied by simultaneous thermal analysis
(STA).
(
⎯
S2CN=); 50.6 (–CH2–); 17.7, 14.8 (1 : 1,
III, 195.4 (32),* 195.0 (1 : 1, –S2CN=); 52.5, 52.2
(3 : 1, ⎯CH2–); 16.8, 15.9 (1 : 1, –CH3). * Asymmetꢀ
ric 13C–14N doublet [25, 26], in Hz.
EXPERIMENTAL
The 13C MAS NMR spectra were recorded on a
Commercial sodium diethyl dithiocarbamate triꢀ CMXꢀ360 spectrometer (Agilent/Varian/Chemagnetꢀ
hydrate (SigmaꢀAldrich) was used as received. The ics InfinityPlus) operating at 90.52 MHz with a superꢀ
initial binuclear complex, chemisorbent
pared according to reported data [23, 24]. The initial formation. The spectra were recorded with proton
sodium salt and complex
were characterized using crossꢀpolarization and 13C–1H decoupling by radioꢀ
the 13C MAS NMR data (
, ppm): Na{S2CN(C2H5)2}
frequency field at the proton resonance frequency
3H2O (1 : 2 : 2): 206.5 (–S2CN=); 48.6 (–CH2–); 13.2 [30]. Samples weighing ~80 mg were placed in a
(–CH3). [Cd2{S2CN(C2H5)2}4]: 203.3(28)*, 4.0 mm ZrO2 ceramic rotor. The magic angle spinning
199.2(26)* (1 : 1, –S2CN=); 53.1, 52.4, 51.4 (1 : 1 : 2, was at 6100–6700(1) Hz; the number of acquisitions
I, was preꢀ conducting magnet (В0 = 8.46 T) and Fourier transꢀ
I
δ
⋅
–CH2–); 13.6, 12.9, 12.7, 12.4 (1 : 1 : 1 : 1, –CH3). was 1000–1120; the duration of proton
π
/2 pulses was
s; 1H–13C contact time was 2.5 ms; and pulse
spacing was 3.0 s. The isotropic 13C chemical shifts
, ppm) are referred to one of components of external
crystalline adamantane [31] (
tetramethylsilane [32]).
* Asymmetric 13C–14N doublets [25, 26], in Hz.
3.3–4.9 μ
The sorption of gold(III) was conducted in the
static mode. 10 mL portions of a solution of H[AuCl4]
containing 108.40 mg of gold were added to 100ꢀmg
(
δ
δ = 38.48 ppm relative to
portions of sorbent I and the mixtures were magnetiꢀ
Single crystal Xꢀray diffraction analysis of II and III
was performed on a Bruker Kappa APEX II diffractoꢀ
cally stirred for 1–90 min. After certain periods of
time, 0.1 mL samples were taken from the solutions to
determine the residual concentration of gold. The
meter (MoKα radiation,
λ = 0.71073 Å, graphite
monochromator) at 170(2) K. The absorption correcꢀ
tions were applied by single crystal face indexes. The
structure of II was determined by the direct method
and refined by the least squares method (on F2) in the
fullꢀmatrix anisotropic approximation for nonꢀhydroꢀ
gen atoms. The gold atom coordinates in III were
determined from analysis of the function of interꢀ
atomic vectors; the other nonꢀhydrogen atoms were
located from a series of difference electron density
maps. A preliminary refinement of the resulting model
degree of sorption (
tion
S, %) was calculated by the relaꢀ
S
= [(
с – сr)/с] × 100,
where
с is the initial and сr is the residual contents of
gold in the solution. The amount of adsorbed gold(III)
is determined by this difference. The gold content in
the solutions was found on a 1st class Hitachi atomic
absorption spectrometer (design type 180–50).
2
Synthesis of II and III. Polymeric bis(
thyldithiocarbamatoꢀ ')gold(III) tetrachloroauꢀ
rate(III) (II) and dichloro( ꢀdiethyldithiocarbamꢀ
atoꢀ ')gold(III) (III) were synthesized by the reacꢀ
N,Nꢀdieꢀ
of structure III gave a high
R
ꢀfactor of 0.13. Considerꢀ
S,S
ing the similarity of periods
а
and and based on analꢀ
с
N,N
ysis of Fo and Fc values, microꢀtwinning of the crystals
of III was suggested. The introduction of the twin
law for the second component with respect to the first
one 0 0 1/0 –1 0/1 0 0 resulted in a sharp decrease in
S,S
tion of freshly precipitated cadmium diethyl
dithiocarbamate with solutions of AuCl3 in 2 M HCl.
The heterogeneous reaction can be represented as folꢀ
lows:
the
Rꢀfactor (down to 0.0140). The corrected mass
coefficients of the twin components are 0.6270(3) and
0.3730(3). In both structures, the positions of hydroꢀ
gen atoms were calculated geometrically and included
in the refinement according to the “riding” model.
Cd {S CN(C H ) } + 4H AuCl =
]
[
]
[
2
2
2
5
2
4
4
= Au{S CN(C H ) } AuCl
2][
+
]
[
2
2
5
2
4
The data collection and editing and the refinement
of the unit cell parameters were performed by the
APEX2 [33] and SAINT [34] programs; the structure
solution and refinement calculations were carried out
by the SHELXTL/PC programs [35]. The atom coorꢀ
dinates, bond lengths, and bond angles are deposited
with the Cambridge Crystallographic Data Centre
(no. 942469 (II) and 942470 (III); deposit@
ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Selected crystallographic and structure refinement
+ 2[Au{S2CN(C2H5)2}Cl2] + 2CdCl2 + 4HCl.
A solution of AuCl3 in 2 M HCl (20 mL) containꢀ
ing 216.8 mL of gold was added to 200 mg of freshly
precipitated cadmium diethyl dithiocarbamate and
the mixture was stirred for 1.5 h. The resulting yellowꢀ
2
The preparation of complexes of this type reported in the literaꢀ
3+
+
ture [27–29] includes Au to Au reduction, synthesis of
gold(I) dibutyl dithiocarbamate followed by its halogenation
with bromine or chlorine.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
No. 2
2014

102
RODINA et al.
Table 1. Crystallographic data, experimental details, and refinement parameters for the structures II and III
Value
Parameter
II
III
Empirical formula
M
C10H20N2S4Cl4Au2
832.25
C5H10NS2Cl2Au
416.13
Crystal system
Space group
Monoclinic
Monoclinic
P
21/n
P21/n
a
, Å
, Å
7.85410(10)
12.3999(2)
10.9665(2)
99.7470(10)
1052.61(3)
2
17.2247(2)
7.05300(10)
17.2298(2)
97.6270(10)
2074.66(5)
8
b
c
, Å
β
V
Z
, deg
, Å3
ρcalcd, g cm3
, mm–1
(000)
2.626
2.665
μ
14.822
15.040
F
768
1536
Crystal size, mm
0.42
×
0.29
×
0.24
0.40
× 0.07 × 0.05
Data collection range of θ, deg
2.50–30.65
1.19–32.32
Ranges of reflection indices
–11
–17
–15
≤
≤
≤
h
k
l
≤
≤
≤
11,
17,
15
–25
–10
–25 ≤ l
≤
≤
h
k
≤
≤
≤
25,
10,
25
The number of measured reflections
26993
67860
The number of independent reflections (Rint
)
3251 (0.0194)
2939
7090 (0.0254)
6815
The number of reflections with I > 2σ(I)
The number of refined parameters
106
204
GOOF
1.094
1.062
R
R
ꢀFactors on F2 > 2
σ(
F2
)
R
1 = 0.0107
wR2 = 0.0266
R
1 = 0.0140
wR2 = 0.0335
ꢀFactors for all reflections
R
1 = 0.0127
R1 = 0.0158
wR2 = 0.0275
wR2 = 0.0327
Extinction coefficient
0.00434(6)
Not refined
Residual electron density (min/max),
e
/Å3
–0.550/0.591
–1.302/2.012
data for II and III are summarized in Table 1 and bond and temperature and sensitivity calibrations for the
lengths and bond angles are in Table 2.
specified temperature program and heating rate were
used. The melting points of the complexes were indeꢀ
pendently determined on a PTP(M) setup (OSJC
Khimlaborpribor).
The thermal behavior of II and III was studied by
STA with simultaneous recording of thermogravimeꢀ
try (TG) and differential scanning calorimetry (DSC)
curves. The measurements were performed on an STA
449C Jupiter (NETZSCH) instrument in corundum
crucibles with a lid having an opening that ensured a
vapor pressure of 1 atm during substance decomposiꢀ
RESULTS AND DISCUSSION
Table 3 shows the kinetic data on gold(III) binding
tion. The samples were heated to 1100°C at a 5°C/min by chemisorbent I reflecting the variation of the degree
rate in an argon atmosphere. For clearer manifestation of gold sorption on the time of contact of the sorbent
of the heat effects, additional measurement in alumiꢀ with the AuCl3–2 M HCl solution in the static mode.
num crucibles were carried out in the initial stage. The A working solution (10 mL) with gold content of
sample weight was 3.437 to 4.871 mg. The temperature 10.84 mg/mL was used. Even in the first minute of the
was measured to an accuracy of 0.7
was determined to an accuracy of
measurement of TG and DSC curves, a correction file 10th minute) to light yellow; and the precipitates
°
C
and the weight contact, the color of the sorbent precipitates changed
1
×
10–4 mg. In the from white to yellowꢀorange and later (by the
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
No. 2
2014

BINDING FORMS OF GOLD(III) FROM SOLUTIONS
103
Table 2. Selected bond lengths (
d
) and bond (
ω
) and torsion (ϕ) angles in II* and III**
Compound II
Bond
d
, Å
Bond
N(1)–C(2)
N(1)–C(4)
Au(2)–Cl(1)
Au(2)–Cl(2)
Cl(1)···S(1)
d, Å
Au(1)–S(1)
Au(1)–S(2)
Au(1)···Cl(1)
S(1)–C(1)
S(2)–C(1)
N(1)–C(1)
2.3306(2)
2.3310(2)
3.7784(3)
1.7333(10)
1.7242(10)
1.2976(13)
1.4776(13)
1.4787(13)
2.2760(3)
2.2714(3)
3.4993(4)
Angle
ω
, deg
Angle
ω, deg
S(1)Au(1)S(2)
S(1)Au(1)S(2)a
Au(1)S(1)C(1)
Au(1)S(2)C(1)
S(1)C(1)S(2)
S(1)C(1)N(1)
75.511(8)
104.489(8)
86.41(3)
86.60(3)
111.28(6)
S(2)C(1)N(1)
C(1)N(1)C(2)
C(1)N(1)C(4)
C(2)N(1)C(4)
Cl(1)Au(2)Cl(2)
Cl(1)Au(2)Cl(2)b
124.37(8)
120.14(9)
120.84(9)
118.98(8)
90.227(11)
89.773(11)
124.34(8)
Angle
ϕ, deg
Angle
ϕ, deg
Au(1)S(1)S(2)C(1)
S(1)Au(1)C(1)S(2)
S(1)C(1)N(1)C(2)
174.90(6)
175.44(5)
179.83(8)
S(1)C(1)N(1)C(4)
S(2)C(1)N(1)C(2)
S(2)C(1)N(1)C(4)
–2.59(14)
–0.11(14)
177.47(8)
Compound III
Molecule A
Molecule B
Bond
d
, Å
Bond
Au(2)–S(3)
d, Å
Au(1)–S(1)
Au(1)–S(2)
2.3057(5)
2.2904(5)
3.4361(5)
3.6329(5)
2.3224(5)
2.3173(6)
1.735(2)
1.727(2)
1.296(3)
1.481(3)
1.480(3)
2.2919(6)
2.3042(6)
3.4340(7)
3.6398(7)
2.3227(6)
2.3233(6)
1.733(2)
1.729(2)
1.296(3)
1.472(3)
1.485(3)
Au(2)–S(4)
Au(2)···S(4)c
Au(2)···S(4)d
Au(2)–Cl(3)
Au(2)–Cl(4)
S(3)–C(6)
Au(1)···S(1)a
Au(1)···S(1)b
Au(1)–Cl(1)
Au(1)–Cl(2)
S(1)–C(1)
S(2)–C(1)
S(4)–C(6)
N(1)–C(1)
N(1)–C(2)
N(1)–C(4)
N(2)–C(6)
N(2)–C(7)
N(2)–C(9)
Angle
ω
, deg
Angle
ω, deg
S(1)Au(1)S(2)
S(1)Au(1)Cl(1)
S(1)Au(1)Cl(2)
S(2)Au(1)Cl(1)
S(2)Au(1)Cl(2)
Cl(1)Au(1)Cl(2)
Au(1)S(1)C(1)
Au(1)S(2)C(1)
S(1)C(1)S(2)
S(1)C(1)N(1)
S(2)C(1)N(1)
C(1)N(1)C(2)
C(1)N(1)C(4)
C(2)N(1)C(4)
75.73(2)
96.74(2)
169.03(2)
172.34(2)
93.30(2)
94.23(2)
87.17(7)
87.85(7)
109.11(11)
125.5(2)
125.4(2)
121.6(2)
120.4(2)
117.7(2)
S(3)Au(2)S(4)
S(3)Au(2)Cl(3)
S(3)Au(2)Cl(4)
S(4)Au(2)Cl(3)
S(4)Au(2)Cl(4)
Cl(3)Au(2)Cl(4)
Au(2)S(3)C(6)
Au(2)S(4)C(6)
S(3)C(6)S(4)
S(3)C(6)N(2)
S(4)C(6)N(2)
C(6)N(2)C(7)
C(6)N(2)C(9)
C(7)N(2)C(9)
75.57(2)
93.62(2)
171.93(2)
169.16(2)
96.75(2)
94.09(2)
87.84(7)
87.55(8)
108.87(12)
124.8(2)
126.3(2)
121.4(2)
120.7(2)
117.6(2)
Angle
ϕ
, deg
Angle
ϕ, deg
Au(1)S(1)S(2)C(1)
S(1)Au(1)C(1)S(2)
S(1)C(1)N(1)C(2)
S(1)C(1)N(1)C(4)
S(2)C(1)N(1)C(2)
S(2)C(1)N(1)C(4)
175.83(12)
176.18(11)
–1.5(3)
–175.6(2)
176.1(2)
Au(2)S(3)S(4)C(6)
S(3)Au(2)C(6)S(4)
S(3)C(6)N(2)C(7)
S(3)C(3)N(2)C(9)
S(4)C(6)N(2)C(7)
S(4)C(6)N(2)C(9)
–175.45(12)
–175.82(11)
2.7(3)
179.5(2)
–174.9(2)
–1.5(3)
1.9(3)
a
b
* Symmetry codes:
–x
, –
y
+ 1, –
z
;
x
–
x
, –
y
y
+ 1, –
+ 1/2, –
z
+ 1.
+ 1/2;
a
b
c
d
**
–x
+ 3/2,
y
– 1/2, –
z
+ 1/2;
–
+ 3/2,
z
–
x
+ 1/2,
y
+ 1/2, –
z
+ 1/2;
2014
–x + 1/2, y – 1/2, –z + 1/2.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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RODINA et al.
Sorption degree,
Table 3. Binding kinetics of gold(III) by sorbent
I
S
(%) at contact duration, min
Au3+ concentration, mg/mL
(total content, mg)
1
10
20
30
60
90
10.84 (108.4)
75.65
86.39
87.57
86.42
89.51
90.00
became much more bulky. Simultaneously, working obtained simultaneously, namely, thin needles and
larger prisms of complexes III and II, respectively.
solutions were bleached. From the data of sorption
experiments, the sorption capacity of was estimated
as 975.6 mg of gold per 1 g of sorbent. When calculated
from the formation of complexes II and III, it was
somewhat lower, being 963.2 mg. The changes
I
A 13C MAS NMR study of selected crystals of difꢀ
ferent shapes demonstrated that they are spectrally
nonꢀidentical (Fig. 1). In both cases, the 13C MAS
NMR spectra exhibit resonance signals for the
=NC(S)S–, –CH2–, and –CH3 groups (see the Synꢀ
thesis of II and III). The dithiocarbamate groups,
which are most sensitive, to the structural state of the
EDtc ligands, are responsible for two (1 : 1) or one 13C
resonance signals (Fig. 1). This implies that III has two
groups of nonꢀequivalent EDtc ligands, whereas all
ligands of compound II are structurally equivalent.
The much lower 13C chemical shifts of the =NC(S)S–
observed during the interaction of sorbent
I with a
solution of AuCl3 reflect the successive formation of
new compounds. (Earlier, it was found that the initial
stage of sorption is accompanied by formation of the
ionic complex ([Au{S2CN(C2H5)2}2]2[Cd2Cl6])n [16].)
In order to verify these conclusions, a sample of sorꢀ
bent
I saturated with gold(III) to a limited degree was
dissolved in methanol with moderate heating. From
the prepared solution, two types of yellow crystals were groups in the compounds in question compared with
a
b
200
180 60
50
40
, ppm
30
20
10
δ
13
Fig. 1. C CP/MAS NMR spectra of (
a) needle crystals of III and (b) prismatic crystals of II. The number of acquisitions/sample
spinning frequency are 1040/6.7 and 1120/6.1 kHz, respectively.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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BINDING FORMS OF GOLD(III) FROM SOLUTIONS
(а) (b)
105
x
z
0
x
z
0
y
y
Fig. 2. Projection of structures (a) II and (b) III on the plane yz. The polymeric chains are arranged along
z
and
y, respectively.
the initial binuclear complex [Cd2{S2CN(C2H5)2}4] are fourꢀmembered metal rings [AuS2C]. The Au⋅⋅⋅
C
disꢀ
attributable to redistribution of the EDtc ligands into tances (2.817, 2.821, and 2.8160 Å) that are much
the inner sphere of gold(III). The electron system of shorter than the sums of the van der Waals radii of
gold may be involved more efficiently in the additional these atoms (3.36 Å) [36] point to the existence of
shielding of the carbon nuclei of dithiocarbamate transꢀannular interaction between the gold and carbon
groups. Thus, 13C MAS NMR data attest to the formaꢀ atoms. The atoms in the metal rings show a tetrahedral
tion in the [Cd2{S2CN(C2H5)2}4]–[AuCl4]––2 M HCl deviation from the planar configuration: the AuSSC
sorption system of two new compounds as individual and SAuCS torsion angles somewhat (by
4°–5°) deviꢀ
binding forms of gold from aqueous solutions. This ate from 180° (Table 2). The diagonal angles SAuCl
conclusion was verified by solving the structures of II
and III by Xꢀray diffraction.
(169.03°–172.34°) in III are also indicative of the disꢀ
tortion of planes of the [AuS2Cl2 cisꢀchromophores.
]
The unit cells of II and III comprise 2 and 8 forꢀ
Owing to mesomeric effect, the C2NC(S)S groups
are almost planar: the deviation of the SCNC torsion
mula units
[
[
Au{S2CN(C2H5)2}2][AuCl4
]
and
Au{S2CN(C2H5)2}Cl2], respectively (Fig. 2). In ionic
compound II, one gold atom coordinates two strucꢀ
turally equivalent EDtc ligands in the 'ꢀbidentate
angles from 180° or 0° does not exceed 5° (Table 2).
The N C(S)S bond length (1.2976 and 1.296 Å),
⎯
S,S
which is intermediate between the typical double
C=N (1.27 Å) and single C–N (1.46 Å) bond lengths,
reflects a considerable contribution of double bonding
and admixing of the sp2 to sp3 hybrid state of nitrogen
and carbon atoms.
mode, thus forming the centrosymmetric
[Au{S2CN(C2H5)2}2]+ cation. The second Au atom in
the centrosymmetric [AuCl4]– anion is surrounded by
four. pairwise nonꢀequivalent, chlorine atoms (Au–
Cl, 2.2714 and 2.2760 Å). In both coordination
spheres, gold forms planar tetragonal chromophores:
In the structural ordering of complexes II and III at
the supramolecular level, the crucial role is played by
[
AuS4] and [AuCl4] (lowꢀspin intraorbital dsp2ꢀhybrid
3
state of the central gold atom). Complex III has a
mixed coordination sphere containing two chlorine
atoms along with EDtc. The structure of III comprises
two nonꢀequivalent [Au{S2CN(C2H5)2}Cl2] moleꢀ
cules, which are related as conformational isomers in
view of the observed differences. In both isomeric
molecules, the cisꢀ[AuS2Cl2] chromophores have a
nearly planar structure; all chlorine atoms are strucꢀ
turally nonꢀequivalent (Au–Cl, 2.3173–2.3233 Å).
In both compounds, the coordination of EDtc is
secondary bonds of three types: Au⋅⋅⋅S, Au⋅⋅⋅Cl, and
S
⋅⋅⋅Cl
[Au{S2CN(C2H5)2}2]+ cation forms secondary bonds
Au(1)⋅⋅⋅Cl(1) 3.7784 Å) with two nearest [AuCl4]–
.
In II
,
the gold atom of each
(
anions (Fig. 3a). Likewise, each [AuCl4]– anion interꢀ
acts with two neighboring cations. This cation–anion
binding is additionally enhanced by S(1)⋅⋅⋅Cl(1) secꢀ
ondary bonds (3.4993 Å) [38]. The described contacts
give rise to linear polymeric chains arranged along the
z
axis (the Au(2)Au(1)Au(2) and Au(1)Au(2)Au(1)
close to
the narrow range from 2.2904 to 2.3310 Å), the bindꢀ
ing strength being somewhat higher in complex III
This coordination is accompanied by the formation of
S,S'ꢀisobidentate (the Au⎯S bond length is in
3
The concept of secondary bonds was firstly proposed in [37] to
describe interactions between atoms at distances comparable
with the sums of their van der Waals radii.
.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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106
RODINA et al.
(a)
(b)
S(1)a
Cl(1)b
Cl(2)
Au(2)
Cl(2)b
C(3)
C(5)
S(1)
Cl(1)
Cl(2)
Cl(1)
N(1)
C(1)
Au(1)
C(2)
C(4)
C(3)
S(2)
C(5)
S(1)a
S(2)
C(2)
Au(1)
C(1)
S(2)a
N(1)
C(4)
S(1)
S(1)b
S(4)c
C(10)
C(9)
S(4)
Cl(4)
Cl(3)
Au(2)
C(6)
N(2)
C(8)
S(3)
C(7)
S(4)d
Fig. 3. Pattern of construction of polymeric chains in complexes (a) II and (b) III. The double dashed lines indicate the secondary
bonds (a) Au⋅⋅⋅Cl and (b) Au⋅⋅⋅ ; the dotted line corresponds to (a) ⋅⋅⋅Cl secondary bonds.
S
S
angles are 180.00°; the Au(1)⋅⋅⋅Au(2) distance is parison, the sum of the van der Waals radii of sulfur
5.4832 Å) with the complex cations and anions alterꢀ and gold is 3.46 Å [36].) This gives rise to independent
nating along the chains (Fig. 2a). The mutual spatial
orientation of the neighboring polymeric chains is
determined by the secondary bonds, S(1)⋅⋅⋅Cl(2)d and
Cl(2)⋅⋅⋅S(1)e of 3.4734 Å (shown by the dotted lines in
Fig. 2a), which are even somewhat shorter than the
corresponding bonds within the chains (for compariꢀ
son, the sum of the van der Waals radii of sulfur and
chlorine is 3.55 Å [36]).
zigzagꢀlike polymeric chains of two types
(⋅⋅⋅A⋅⋅⋅A⋅⋅⋅A⋅⋅⋅) and (⋅⋅⋅B⋅⋅⋅B⋅⋅⋅B⋅⋅⋅) with antiparallel
n
isomeric molecules of III alternatinng along the chains.
In these chains, the Au(1)–Au(1) and Au(2)–Au(2)
distances are 4.27905 and 4.27744 Å, respectively; the
Au(1)Au(1)Au(1) and Au(2)Au(2)Au(2) angles are
111.00° and 111.06°, respectively.
To establish the conditions of recovery of the bound
gold, thermal behavior of II and III was studied by
STA under argon, TG and DSC curves being recorded
simultaneously. Generally, the course of TG curves for
II and III is roughly the same. We will consider it in
more detail in relation to the TG curve for complex III
The supramolecular structure of the mixedꢀligand
complex III is also characterized by 1D polymeric
structure (Fig. 2b). However, the polymeric chain is
built according to a different principle than that
described above for II. Since III comprises two isoꢀ
meric [Au{S2CN(C2H5)2}Cl2] molecules, A—Au(1)
and B—Au(2), each of them being in contact with two
nearest neighbors through pairs of unsymmetrical secꢀ
(Fig. 4
the compound is thermally stable up to ~170
intensive thermolysis occurs in the narrow range of
, which is reflected in the TG curve as a
Au(2)⋅⋅⋅S(4)c/d, 3.4340/3.6398 Å (Fig. 3b). (For comꢀ steeply descending part. The next slightly sloping part
a
). The early region of the curve indicates that
°С. The
ondary bonds: Au(1)⋅⋅⋅S(1)a/b, 3.4361/3.6329, and 170–310
°С
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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2014

BINDING FORMS OF GOLD(III) FROM SOLUTIONS
DSC, mW/mg
107
TG, %
a
d
10
100
90
80
70
60
50
1060.8°C
272.0°C
8
143.8°C
290.4°C
277.3°C
6
276.9°C
278.6°C
271.0
279.0
°C
4
°C
1062.6°C
b
c
291.6°C
2
150
200
250
300
47.82%
0
200
400
600
800
1000 T, °C
Fig. 4. (a) TG and (b, c) DSC curves for complexes (b) II and (a, c) III. (d) Enlarged view of the lowꢀtemperature part of DSC
curves.
up to 660
products. For II, these parts are somewhat shifted: the reduced gold: the extrapolated m.p. is 1060.8
major weight loss occurs in the range of 125–290
°С is due to desorption of the thermolysis curves show an endotherm reflecting melting of
°C.
°С,
indicating simultaneous thermolysis of both the cation
and the anion; the subsequent desorption occurs up to
ACKNOWLEDGMENTS
The authors are grateful to Prof. O.N. Antzutkin
(Luleå University of Technology, Luleå, Sweden) for
providing the opportunity to record 13C MAS NMR
spectra.
This work was supported by the Fundamental
Research Program of the Presidium of the RAS
“Development of Methods for Preparation of Chemiꢀ
cals and Design of New Materials” and Presidium of
the FarꢀEast Branch of the RAS (projects nos. 12ꢀIꢀ
P8ꢀ01 and 12ꢀIIIꢀAꢀ04ꢀ040).
~700
°С. The weight of the residue at 1100°C was
47.26 or 47.82% of the initial weight for II and III
,
respectively, which does not differ significantly from
the calculated value (47.33%) for the reduced gold.
After opening of the crucible, small pinkꢀorange gold
beads 0.005 to 0.05 mm in diameter without visible
signs of slag were detected on the bottom.
Despite the similar course of TG curves for II and
III, the DSC curves of these complexes are substanꢀ
tially different (Fig. 4
292°C, the DSC curves (Fig. 4
three (III) endotherms (with peaks at 277.3, 278.6 and
271.0, 279.0, 291.6 , respectively), which reflects
b–4
d
). In the range from 270 to
d) show two (II) or
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Translated by Z. Svitanko
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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2014