Low-temperature template synthesis of [4,6,6-trimethyl-2,6-dithioxo-3,7-diazanon-4-enebis(imidothioato)]copper(II) in gelatin-immobilized Cu2[Fe(CN)6] matrix materials

Article abstract of DOI:10.1023/A:1013965618797

Complexation in gelatin-immobilized copper(II) hexacyanoferrate(II) matrices on contact with alkaline (pH l O) aqueous solutions containing dithiooxamide and acetone was studied. Under these conditions, template synthesis occurs to give the chelate CuL [L

Full text of DOI:10.1023/A:1013965618797

Russian Journal of General Chemistry, Vol. 71, No. 11, 2001, pp. 1676 1681. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 11, 2001,
pp. 1768 1774.
Original Russian Text Copyright
2001 by Mikhailov.
Low-Temperature Template Synthesis of [4,6,6-Trimethyl-
2,6-dithioxo-3,7-diazanon-4-enebis(imidothioato)]copper(II)
in Gelatin-Immobilized Cu2[Fe(CN)6] Matrix Materials
O. V. Mikhailov
Kazan State Technological University, Kazan, Tatarstan, Russia
Received January 10, 2000
Abstract Complexation in gelatin-immobilized copper(II) hexacyanoferrate(II) matrices on contact with
alkaline (pH 10) aqueous solutions containing dithiooxamide and acetone was studied. Under these conditions,
template synthesis occurs to give the chelate CuL [L is 4,6,6-trimethyl-2,6-dithioxo-3,7-diazanon-4-enebis-
(imidothioato) ligand], with dithiooxamide and acetone acting as ligand synthons. The reaction pattern was
suggested. Attempted reaction of dithiooxamide and acetone in solution in the absence of Cu(II) does not
yield this ligand.
Previously [1 4] we have studied complexation
reactions occurring on contact of gelatin-immobilized
O 33.2. (H2CuO2)n . Calculated, %: H 2.04; Cu 65.31;
O 33.61. Computer treatment of the kinetic curves
copper(II) hexacyanoferrate(II) matrix materials with D = f(CF, C0L, t) showed that in the examined con-
aqueous solutions of dithiooxamide. The latter, in
principle, can act as a so-called ligand synthon (lig-
son) in template synthesis [5, 6]. We believe [7] that
immobilization of metal compounds can facilitate
template synthesis under mild conditions, which was
confirmed, in particular, in our previous papers [8, 9]
by the examples of the reaction systems dithioox-
amide + formaldehyde and dithiooxamide + glyoxal.
In this work we examined the possibility of a similar
synthesis in the system dithiooxamide + acetone.
centration and time range (CF, C0L, t) dithiooxamide
or acetone molecules are not added, but two hydrox-
ide anions are taken up per copper(II) ion. Thus, it is
evident that in this system the complexation proper is
preceded by transformation of copper(II) hexacyano-
ferrate(II) into polymeric copper(II) hydroxide, which
is the initial form for subsequent transformations.
nCu2[Fe(CN)6] + 4nOH
2[Cu(OH)2]n + n[Fe(CN)6]4 .
A similar phenomenon was already noted in
[1 4, 10, 11] for the systems Cu(II) dithiooxamide,
Cu(II) quinoxaline-2,3-dithiol, and Cu(II) 8-quino-
linethiols.
When the gelatin-immobilized Cu2[Fe(CN)6] mat-
rix material reacts with an alkaline solution con-
taining dithiooxamide H2NC(=S)C(=S)NH2 and ace-
tone H3CC(=O)CH3, at concentrations of dithiooxamide
C0L < 10 M, any concentrations of Cu2[Fe(CN)6] in
At CF = 0.1 1.0, C0L > 5.0 10 mol dm ,
t = 2 10 min, and molar ratio dithiooxamide : ace-
tone >2.0, compound II is formed, imparting a dark
green color to the gelatin layer. The spectral character-
istics of this layer coincide with those of the com-
plex [Cu(HL)2]n (H2L is dithiooxamide) described in
[1 4]. On breakdown of the gelatin matrix containing
II, a black-green compound is isolated with the empir-
ical formula C4H6CuN4S4, consistent with the compo-
sition [Cu(HL)2]n. Found, %: C 15.8; H 2.1; Cu 21.0;
N 18.8; S 42.2. C4H6CuN4S4. Calculated, %: C 15.89;
H 1.98; Cu 21.19; N 18.55; S 42.39. However, at
5
2
3
the matrix CF, dithiooxamide : acetone molar ratios
of 0.5 2.0, and sufficiently long (t > 6 min) contact
of the matrix with the solution, the initial red-brown
color of the matrix changes to the grayish blue color,
which is due to formation of compound I. The elec-
tronic spectrum of gelatin-immobilized matrices con-
taining this substance exhibits a broad band with
680 700 nm and coincides with the spectrum of
max
gelatin-immobilized polymeric copper hydroxide
[Cu(OH)2]n [1]. The breakdown of the matrix material
allows isolation of a gray-blue substance which can
be identified by chemical analysis as polymeric
copper(II) hydroxide. Found, %: H 2.1; Cu 64.7;
CF = 0.1 2.0, C0L = 3.0 10 2.0 10 mol dm ,
t = 2 10 min, and molar ratio dithiooxamide : ace-
3
1
3
1070-3632/01/7111-1676$25.00 2001 MAIK Nauka/Interperiodica

LOW-TEMPERATURE TEMPLATE SYNTHESIS
1677
0
0
Fig. 1. Curves D = (C , C , t) in the system Cu(II) dithiooxamide acetone in the cordinate section [C = const, varied C ,
F
L
F
L
0
variable t] at the dithiooxamide : acetone ratio of (a) 0.50 and (b) 1.00. Dithiooxamide concentration C , M: (1, 1 ) 3.0
10 , (2, 2 ) 6.5 10 , and (3, 3 ) 1.2 10 ; C , mol dm : (dashed line) 0.70 and (solid line) 1.00. The optical densities D
L
3
3
2
3
F
were measured with a light filter with
450 nm.
max
0
0
Fig. 2. Curves D = (C , C , t) in the system Cu(II) dithiooxamide acetone in the coordinate section [C = const, varied t,
F
L
L
0
3
3
variable C ] at the dithiooxamide : acetone ratio of (a) 0.50 and (b) 1.00. C , M: (I) 3 10 , (II) 6.5 10 , and (III) 1.2
10 ; t, min: (1) 1, (2) 2, (3) 4, (4) 6, and (5) 10. The optical densities D were measured with a light filter with
F
L
3
450 nm.
max
tone = 0.5 1.0, compound III is formed, imparting to
the gelatin matrix a greenish brown color (Figs. 1 3).
It is significant that this compound is formed only on
contact of the gelatin-immobilized copper(II) hexa-
tion, the brown coloration of the polymeric matrix
layer may be due either to the reduction Cu(II)
Cu(I) [it is well known that under appropriate condi-
tions Cu(II) oxidizes organic compounds containing
cyanoferrate matrix with aqueous alkaline solutions carbonyl and thiocarbamoyl groups], to formation of
containing dithiooxamide and acetone simultaneously.
It should be particularly emphasized in this connec-
tion that in the absence of acetone no compounds of
such a color are formed in the system at any concen-
trations of dithiooxamide in solution and copper(II)
hexacyanoferrate(II) in the gelatin matrix (Fig. 3).
This means that dithiooxamide and acetone simultane-
ously participate in the complexation. In this connec-
heteroligand coordination compounds of copper(II)
with dithiooxamide and acetone in the inner sphere,
or, finally, to inner-sphere transformations of dithio-
oxamide and acetone yielding Cu(II) complexes with
certain new ligands constructed from the above
molecules. The correct alternative can be chosen by
comparing the experimental data with the theoretical
expectations.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 11 2001

1678
MIKHAILOV
suggest that in our system a certain new ligand is
formed, involving both dithiooxamide and acetone.
It is significant that this combined ligand is not
formed on simple mixing of aqueous solutions of di-
thiooxamide and acetone containing no copper: The
absorption spectra of aqueous-alkaline (pH > 9.0)
solutions of dithiooxamide do not change on adding
acetone. Hence, the new ligand can form only in the
presence of a metal ion, in particular, Cu(II), i.e., we
apparently deal with a template synthesis in the sys-
tem Cu(II) dithiooxamide acetone in the gelatin-im-
mobilized Cu2[Fe(CN)6] matrix.
Dithiooxamide is an ambidentate ligand; it can, in
principle, form five-membered rings with (S,S), (N,S),
or (N,N) coordination:
Fig. 3. Electronic absorption spectra of gelatin-immobilized
coordination compounds formed (1 3) in the system
3
Cu(II) dithiooxamide acetone at C = 0.60 mol dm
,
F
0
3
C
= 3.0 10 M, t = 2 min, and ratio of the initial
L
ligsons of (1) 0.50, (2) 1.00, and (3) 2.00, and (4) in
3
the system Cu(II) dithiooxamide at C = 0.60 mol dm
,
F
0
2
C
= 1.0 10 M, and t = 4 min. Thickness of the mat-
L
rix polymer layer 20 m.
Based on the whole set of the experimental data
and on theoretical considerations, we can suggest
the following alternatives of the template synthesis in
the ternary system under consideration:
When the gelatin matrices containing III are broken
down, brown substances with the empirical formula
C10H14CuN4S4 are isolated. These compounds are
paramagnetic (
= 1.94 1.96 B) and at 295 300 K
give an ESR siegfnf al with g| | = 2.24 2.26 and g =
2.07 2.09, which unambiguously indicates the copper
oxidation state +2 and rules out the redox process
(a) Formation of a Cu(II) coordination compound
with two (S,S)-donor chelating ligands, each being
formed by condensation of one dithiooxamide mole-
cule with two acetone molecules [scheme (1)]:
Cu(II)
Cu(I). All these substances contain no oxy-
gen and have the same empirical formula (see above),
irrespective of the dithiooxamide : acetone molar ratio
in the contacting solution (varied in the range 0.5
1.0). Found, %: C 31.8; H 3.6; Cu 16.4; N 15.0;
S 33.0. C10H14CuN4S4. Calculated, %: C 31.45;
H 3.67; Cu 16.63; N 14.67; S 33.58. The absence of
oxygen rules out formation of heteroligand complexes
of Cu(II) incorporating acetone.
There are no published data on complexation of
Cu(II) with acetone; the spectral characteristics of
the gelatin-immobilized Cu2[Fe(CN)6] matrix do not
change on contact with alkaline solutions of acetone,
which indicates that no acetone complexes are formed
under these conditions. This fact is quite natural, as
acetone, according to the Pearson’s concept, is a hard
base, whereas Cu(II) is a soft acid {the orbital electro-
negativity of Cu(II) in aqueous solutions is 0.55
[12]}. In special experiments we detected no reaction
of aqueous-alkaline acetone solution with any of the
known [1 4] immobilized Cu(II) chelates with dithio-
oxamide formed by complexation in the gelatin-im-
mobilized Cu2[Fe(CN)6] matrix, irrespective of pH
and acetone concentration in solution. These facts
(1)
(b) Formation of a copper(II) coordination com-
pound with the (N,N,S,S)-donor chelating ligand
constructed from two dithiooxamide and two acetone
molecules [scheme (2)]:
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 11 2001

LOW-TEMPERATURE TEMPLATE SYNTHESIS
1679
Although the content of the enol form is insignifi-
cant (the molar ratio of the enol and keto forms in
water at 25 C is 1 : 106) [13], it can participate in
reactions as intermediate species, and three theoreti-
cally possible reaction pathways involving the enol
form should be considered.
(d) Formation of a Cu(II) complex with two (S,S)-
donor chelating ligands. This case is similar to that
described by scheme (1) in that each ligand is con-
structred from one dithiooxamide molecule and two
acetone molecules, but intramolecular dehydration
results in removal of four, and not two, water mole-
cules [scheme (5)]:
(2)
(c) Formation of a Cu(II) complex with the
(N,N,N,N)-donor ligand constructed from two dithio-
oxamide and four acetone molecules [scheme (3)]:
(5)
(e) Formation of a Cu(II) complex with the
(N,N,S,S)-donor ligand formed by scheme (6), which
resembles scheme (2) but involves removal of a
double amount of water.
(3)
It is well known that acetone is characterized by
the keto enol tautomerism [scheme (4)]:
(6)
(4)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 11 2001

1680
MIKHAILOV
1
(f) Formation of a Cu(II) complex with the
range <1000 cm in which, according to [14], the
(Cu N) and (Cu S) bands should be expected, the
observed bands cannot be assigned unambiguously.
(N,N,N,N)-donor ligand formed from two dithioox-
amide and four acetone molecules by scheme (7),
which resembles scheme (3) but involves removal of
four water molecules.
1
The spectra contain bands at 2850 and 2930 cm ,
which, according to [14], can be assigned to (CH2).
All these facts are consistent with the structure of
the product formed by scheme (6). The results of
the mathematical analysis of the kinetic curves D =
f(CF, C0L, t), performed according to [15] for the
range (CF, C0L, t) in which the brown complex is
formed, show that the template synthesis involves ad-
dition of two dithiooxamide and two acetone mole-
cules per Cu(II) ion. The stoichiometric ratio of the
ligand and Cu(II) in the elementary reaction event, cal-
culated from the experimental data, is 1.0 : 1.2, which
is close to the theoretical ratio of 1.0 : 1.0. It can be
readily seen that only scheme (6) is consistent with
the whole set of the experimental data, including the
empirical formula of the product, C4H6CuN4S4 (III).
Thus, we can conclude that in the system Cu(II)
dithiooxamide acetone under specific conditions of
complexation in the gelatin-immobilized Cu2[Fe(CN)6]
matrix a template synthesis occurs yielding [4,6,6-tri-
methyl-2,8-dithioxo-3,7-diazanon-4-enebis(imidothio-
ato)]copper(II) according to Eq. (8):
(7)
The product formed by any of schemes (1) (3)
should contain oxygen, which is inconsistent with the
actual empirical formula, C4H6CuN4S4. Hence, if in
our ternary system the template synthesis takes place,
it can occur only by schemes (5) (7). The isolated
product is practically insoluble in such organic sol-
vents as ethanol, acetone, chloroform, benzene, and
tetrachloromethane and slightly soluble in dimethyl-
formamide, dimethyl sulfoxide, and hexamethylphos-
phoramide. The electronic spectra of dimethylform-
amide and dimethyl sulfoxide solutions of this com-
pound practically coincide with the spectra of the
gelatin layers from which the compound was isolated.
The DTA data show that the compound is very stable
to heating and does not undergo thermolysis even at
600 C. The IR spectrum of the complex contains
(8)
It is interesting that the structure of the template
synthesis product formed in the system Cu(II) dithio-
oxamide acetone differs significantly from that for
coordination compounds detected previously in the
systems M(II) dithiooxamide formaldehyde (M = Co,
Ni, Cu) [8, 16, 17]. However, a similar difference was
observed previously [5, 6] between the systems M(II)
1,2-ethylenediamine formaldehyde and M(II) 1,2-
ethylenediamine acetone (M = Ni, Cu).
1
a broad (NH) band at 3400 3500 cm , characteristic
of noncoordinarted NH or NH2 groups; hence, at least
a part of nitrogen atoms remains noncoordinated. The
EXPERIMENTAL
1
spectra contain also the bands (C=S) at 680 cm
1
(commonly observed in the range 570 705 cm ) and
The optical densities of gelatin-immobilized metal
chelate matrices were measured in the transmission
mode with a Macbeth TD-504 photometer (working
1
(C=N) at 1645 cm (commonly observed at 1625
1
1690 cm [14]). Unfortunately, in the wave number
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 11 2001

LOW-TEMPERATURE TEMPLATE SYNTHESIS
1681
range of optical density 0.1 5.0, accuracy 2 rel.%).
The electronic absorption spectra were taken with
a Specord UV Vis spectrophotometer in the range
400 800 nm with an accuracy of 2 rel.%. The IR
spectra were taken with a UR-20 spectrometer. The
pH values were measured on a pH-340 pH meter with
an accuracy of 0.05. The ESR spectra were recorded
with a Bruker ESR-200D spectrometer at 298 K.
99-03-99212) and Centrum of Basic Natural Science,
Ministry of Education of the Russian Federation
(project no. 97-0-9.2-13) for financial support.
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were treated with aqueous-alkaline solutions contain-
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2.0) : 1. The dithiooxamide concentration in solution
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and temperature (20.0 0.1 C). The contact time of
the gelatin-immobilized Ce2[Fe(CN)6] matrix materi-
als with the ligson solutions was 1 10 min. After
complexation completion, the gelatin matrix was
washed in running water for 15 min and dried for
2 3 h at room temperature. The complexation kinetics
were described by the dependences D = f(CF, C0L, t),
where D is the optical density of the gelatin-immobi-
lized metal chelate matrix material corresponding to
the intitial concentration of Cu2[Fe(CN)6] in the mat-
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matrix with solutions of proteolytic enzymes [18].
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fact suggests that, similar to the other known systems
metal ion (N,O,S)-donor chelating ligand [7], gelatin
does not participate in complexation as ligand. All
chemicals used for preparing gelatin-immobilized
Cu2[Fe(CN)6] matrices and performing complexation
were of analytically pure or chemically pure grade and
were used without additional purification.
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ACKNOWLEDGMENTS
The author is grateful to the Russian Foundation
for Basic Research (project nos. 96-03-32112 and
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