Reactions in the M(HCOO)2-CS(NH2)2-H 2O (M = Mg, Mn, Cd) systems at 25°C

Article abstract of DOI:10.1134/S0036023606050226

Complex formation in the M(HCOO)₂-CS(NH₂) ₂-H₂O (M = Mg, Mn, Cd) systems at 25°C is studied using the isothermal solubility method. In the Cd(HCOO)₂-CS(NH ₂)₂-H₂O system, a congruently dissolving compound Cd(HCOO)₂ ? 2CS(NH₂)₂ is found and characterized by X-ray powder diffraction and IR spectroscopy. The Mg(HCOO)₂-CS(NH₂)₂-H₂O and Mn(HCOO)₂-CS(NH₂)₂-H₂O systems are eutonics at this temperature. Data on carbamide and thiocarbamide complexes of divalent metal formates are systematized. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S0036023606050226

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2006, Vol. 51, No. 5, pp. 814–818. © Pleiades Publishing, Inc., 2006.
Original Russian Text © V.Z. Vasileva, P.P. Petrova, 2006, published in Zhurnal Neorganicheskoi Khimii, 2006, Vol. 51, No. 5, pp. 880–884.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Reactions in the M(HCOO) –CS(NH ) –H O
2
2 2
2
(
M = Mg, Mn, Cd) Systems at 25°C
a
b
V. Z. Vasileva and P. P. Petrova
a
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria
b
South Western University “Neofit Rilski,” Blagoevgrad, Bulgaria
Received September 10, 2005
Abstract—Complex formation in the M(HCOO) –CS(NH ) –H O (M = Mg, Mn, Cd) systems at 25°C is stud-
2
2 2
2
ied using the isothermal solubility method. In the Cd(HCOO) –CS(NH ) –H O system, a congruently dissolv-
2
2 2
2
ing compound Cd(HCOO) · 2CS(NH ) is found and characterized by X-ray powder diffraction and IR spec-
2
2 2
troscopy. The Mg(HCOO) –CS(NH ) –H O and Mn(HCOO) –CS(NH ) –H O systems are eutonics at this
2
2 2
2
2
2 2
2
temperature. Data on carbamide and thiocarbamide complexes of divalent metal formates are systematized.
DOI: 10.1134/S0036023606050226
Thiocarbamide complexes of inorganic salts are analysis and X-ray powder diffraction. Analytical grade
well studied [1–10]. These compounds are attractive for thiocarbamide was used.
their nonlinear-optical properties [5–8]. They are also
Solubility in the Mg(HCOO) –CS(NH ) –H O and
2
2 2
2
promising precursors for sulfide preparation [9, 10].
Thiocarbamide compounds of metal formates are
poorly studied. Compound Cd(HCOO) · 2CS(NH )
Mn(HCOO) –CS(NH ) –H O systems was studied
2
2 2
2
using the Khlopin supersaturation release method [22].
Aqueous solutions of two components of a system
taken in various proportions were prepared at
2
2 2
(
1
1 : 2) was synthesized by a preparative technique [11,
2]. Compound Zn(HCOO) · CS(NH ) (1 : 1) was
2
2 2
(
80−90)°C; then, the solution was cooled in a thermo-
reported to crystallize at 40°C [13]. We studied solubil-
ity in the Zn(HCOO) –CS(NH ) –H O system at 25°C
stat to the working temperature (25°C) and vigorously
stirred until achieving a constant concentration of the
saturated solution, i.e., until equilibration. The equili-
bration time was 15–20 h. The Cd(HCOO)2–
CS(NH ) –H O system at 25°C was studied using the
2
2 2
2
and found compound Zn(HCOO) · 2CS(NH ) in [14].
2
2 2
The Co(HCOO) –CS(NH ) –H O system at 25°C does
2
2 2
2
not form compounds [15].
2
2
2
isothermal solubility method, because cadmium sulfide
is evolved when cadmium formate is heated in the pres-
ence of thiocarbamide. The equilibration time in this
system was about 3–4 days. Temperature maintenance
accuracy was within ±0.1 K. Then, the suspension was
filtered, and the resulting liquid phase and wet solid
phase (residue) were analyzed. A 2% excess of formic
acid was in the solution to preclude hydrolysis. The
Mg , Mn , and Cd concentrations in the liquid
phases and wet residues were determined complexo-
metrically at pH 10 (ammonia buffer) in the presence of
Eriochrome Black T [23]. Thiocarbamide was deter-
mined gravimetrically as sulfate ions after oxidizing it
with hydrogen peroxide [24]. The composition of the
solid phase was determined using the Schreinemakers
method of wet residues [25].
In this work, we study the Mg(HCOO) –CS(NH ) –
2
2 2
H O and Mn(HCOO) –CS(NH ) –H O systems at
2
2
2 2
2
2
5°C. Our goals were to determine the mutual solubili-
ties of the components and to elucidate whether new
compounds are formed. We also study the Cd(HCOO)2–
CS(NH ) –H O system in order to determine crystalli-
2
2
2
zation conditions for Cd(HCOO) · 2CS(NH ) . These
2
2 2
systems have not yet been studied. Solubility data for
magnesium, manganese, and cadmium formates and
thiocarbamide solubilities were borrowed from [16–18].
2+
2+
2+
EXPERIMENTAL
The starting formates were prepared by reacting
cadmium carbonate or basic magnesium and manga-
nese carbonates (all of analytical grade) with dilute
Solid phases were identified using X-ray powder
aqueous formic acid. The formates were recrystallized. diffraction and IR spectroscopy. The X-ray powder dif-
The compositions of the recrystallized formates were fraction experiment was carried out on a DRON-3 dif-
Mg(HCOO) · 2H O [19], Mn(HCOO) · 2H O [20], fractometer (CuK radiation, Ni filter). IR spectra were
2
2
2
2
α
and Cd(HCOO) · 2H O [21] as derived from chemical recorded as KBr pellets on a Bruker IFS 25 FTIR
2
2
8
14

REACTIONS IN THE M(HCOO) –CS(NH ) –H O (M = Mg, Mn, Cd) SYSTEMS
815
2
2 2
2
Table 1. Solubilities in the Mg(HCOO) –CS(NH ) –H O system at 25°C
2
2 2
2
In liquid phase, wt %
Mg(HCOO)2 CS(NH2)2
In wet residue, wt %
Solid phase
Mg(HCOO) · 2H O
Mg(HCOO)2
CS(NH2)2
11.99
10.92
10.10
10.63
10.57
10.51
–
–
–
2
2
4.03
51.02
53.92
57.21
39.60
18.14
2.89
2.13
–
2.17
3.25
4.01
29.13
58.94
72.67
67.88
–
The same
7.15
"
"
10.54
10.80
10.87
11.25
12.15
13.39
Mg(HCOO) · 2H O + CS(NH )
2
2
2 2
The same
CS(NH2)2
The same
"
8
4
.53
.78
–
Table 2. Solubilities in the Mn(HCOO) –CS(NH ) –H O system at 25°C
2
2 2
2
In liquid phase, wt %
Mn(HCOO)2 CS(NH2)2
In wet residue, wt %
Solid phase
Mn(HCOO)2
CS(NH2)2
6.28
5.33
5.25
5.42
5.23
5.20
5.16
2.19
–
–
–
–
Mn(HCOO) · 2H O
2 2
3.78
53.52
65.12
50.07
43.59
20.69
2.10
1.16
–
1.51
2.03
4.46
30.08
51.14
72.06
67.78
–
The same
8.49
"
"
10.14
11.74
11.55
11.60
12.75
13.39
Mn(HCOO) · 2H O + CS(NH )
2 2
2
2
The same
CS(NH2)2
The same
"
Table 3. Solubilities in the Cd(HCOO) –CS(NH ) –H O system at 25°C
2
2 2
2
In liquid phase, wt %
Cd(HCOO)2 CS(NH2)2
In wet residue, wt %
Solid phase
Cd(HCOO) · 2H O
Cd(HCOO)2
CS(NH2)2
12.45
16.60
16.57
–
–
–
2
2
1.03
67.31
50.20
43.25
36.10
49.76
38.51
42.06
35.81
44.25
30.17
9.35
9.20
Cd(HCOO) · 2H O + CS(NH )
2 2 2 2
1.08
22.45
31.52
25.93
38.05
30.03
34.11
31.20
37.12
57.18
77.38
76.13
The same
Cd(HCOO) · 2CS(NH )
9
6
3
2
3
3
4
5
5
3
.41
.63
.44
.72
.09
.71
.62
.55
.60
.07
1.23
2
2 2
2.03
The same
4.60
"
"
"
"
"
5.56
12.00
13.90
17.85
24.53
24.77
20.11
13.39
Cd(HCOO) · 2CS(NH ) + CS(NH )
2 2
2
2 2
The same
CS(NH2)2
The same
1.22
–
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 5 2006

8
16
VASILEVA, PETROVA
Cd(HCOO)2
solution is 10.51 wt % magnesium formate and
0.87 wt % thiocarbamide. Each component slightly
1
decreases its solubility when the other is added,
because of salting out.
Cd(HCOO) · 2H O
2
2
7
5
System Mn(HCOO) –CS(NH ) –H O. Experi-
2
2 2
2
mental solubility data at 25°C, compiled in Table 2,
likewise do not show compound formation in this sys-
tem. The solubility isotherm of the system has two
Cd(HCOO) · 2CS(NH )
2
2 2
5
0
branches: the longer branch is due to Mn(HCOO) ·
2
2
H O [20] (the least soluble component), and the short
2
2
5
branch is due to thiocarbamide; the branches meet at a
eutonic point, whose coordinates are 5.20 wt %
Mn(HCOO) and 11.55 wt % CS(NH ) . Each compo-
2
2 2
H O
CS(NH2)2
nent slightly decreases its solubility when the other is
added, because of salting out. The manganese formate
solubility drops from 6.28 to 5.20 wt %; the thiourea
solubility drops from 13.39 to 11.55 wt %.
2
0
25
50
75
100
Fig. 1. Solubility diagram for the Cd(HCOO) –CS(NH ) –
H O system at 25°C.
2
2 2
2
System Cd(HCOO) –CS(NH ) –H O at 25°C.
2
2 2
2
The solubility data for this system are compiled in
Table 3. The solubility diagram is shown in Fig. 1. The
following three phases crystallize in the system:
Cd(HCOO) · 2H O [21], CS(NH ) [26], and a congru-
instrument. A reaction with potassium bromide was not
observed.
2
2
2 2
ently dissolving compound Cd(HCOO) · 2CS(NH ) .
Cadmium formate dihydrate has a very narrow crystal-
lization field. Most of the diagram is occupied by the
RESULTS AND DISCUSSION
2
2 2
System Mg(HCOO) –CS(NH ) –H O. The results
2
2 2
2
of our investigation of the system at 25°C (Table 1) crystallization field of the compound whose composi-
show that chemical compounds are not formed at this tion was found graphically using the Schreinemakers
temperature; i.e., the system is a simple eutonic. The method. The concentration bounds of formation were
solubility isotherm consists of two branches due to the
crystallization of two phases: Mg(HCOO) · 2H O [19]
determined for the compound from 16.60 to 5.60 wt %
cadmium formate and from 1.03 to 24.77 wt % thiocarb-
and CS(NH ) [26]. The composition of the eutonic amide in the liquid phase.
2
2
2
2
Absorbance
1
1
1
0
0
0
0
.4
.2
.0
.8
.6
.4
.2
0
4
000
3500
3000
2500
2000
1500
1000
500
ν, cm–1
–
1
Fig. 2. IR spectrum of Cd(HCOO) · 2CS(NH ) in the region 4000–400 cm .
2
2 2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 5 2006

REACTIONS IN THE M(HCOO) –CS(NH ) –H O (M = Mg, Mn, Cd) SYSTEMS
817
2
2 2
2
Table 4. Assignment of IR bands for Cd(HCOO)2
2CS(NH2)2
·
Calcd., wt %: Cd(HCOO) , 57.08; CS(NH ) ,
2 2 2
42.92. Found, wt %: Cd(HCOO) , 56.70; CS(NH ) ,
2 2 2
4
3.61.
The structure of Cd(HCOO) · 2CS(NH ) was stud-
ν, cm–1
Assignment
2
2 2
3
3
3
3
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
377 s
νas (N–H)
ied comprehensively in [11, 12]. The crystals are
orthorhombic, space group P2 2 2 , with the unit cell
parameters a = 8.00(0) Å, b = 17.87(8) Å, c =
295 m
183 sh
058 s
1
1 1
3
.93(3) Å, Z = 2. Each Cd atom is coordinated octahe-
νs (N–H)
drally by four S atoms lying in one plane, and two O
atoms belonging to the formate groups in the trans
position to the plane of the sulfur atoms. Our X-ray
powder diffraction analysis showed that the compound
isolated differs structurally from its precursors
927 sh
830 m
754 w
697 w
665 w
657 v s
637 v s
630 s
ν1 (C–H)
–
2ν HCOO
5
(Cd(HCOO) · 2H O [21] and Cs(NH ) [26]). Interpla-
2 2 2 2
nar distances and intensity ratios for Cd(HCOO) ·
2
2
δ (NH2)
CS(NH ) coincide with the data in [12].
2 2
The IR absorption spectra of thiocarbamide com-
ν4as (COO)
pounds of inorganic salts were studied in [27–29].
However, we failed to find data on the IR spectra of
Cd(HCOO) · 2CS(NH ) in the literature. Our IR-spec-
607 m
569 w
510 m
425 m
375 m
340 v s
135 w
110 w
098 w
νas (C–N)
νas (C–S)
2
2 2
–
1
troscopic investigation in the region 4000–400 cm
Fig. 2) showed bands due to the vibrations in thiocarb-
(
amide molecules and formate groups. Band assignment
was with reference to [27–29] for thiocarbamide and
[30–32] for formate groups. The results of the IR inves-
ν5 (C–H)
ν2s (COO)
tigation correlate with crystal data for Cd(HCOO) ·
νs (C–N)
ν6 (C–H)
2
2
CS(NH ) [12].
2 2
A comparative analysis of carbamide and thiocarb-
amide compounds with formates of several divalent
metals was carried out. Table 5 summarizes data on
carbamide and thiocarbamide complexes of Mg, Mn,
Fe, Co, Ni, Zn, and Cd formates.
781 m
720 w
690 w
634 m
589 m
502 m
ν3s (O–C–O)
νs (C–S)
δ (NH2)
Both families of compounds have 1 : 2 formulas:
δas (N–C–N)
M(HCOO)2
·
2CO(NH2)2 and M(HCOO)2
·
2
CS(NH ) . Carbamide or thiocarbamide molecules
δs (S–C–N)
2 2
substitute for the two water molecules in formate dihy-
drates [19–21]. Carbamide forms compounds with all
of the aforementioned formates [33–36]; thiocarbam-
ide, with zinc and cadmium formates only [12, 14].
Note: Band notation: v s, very strong; s, strong; m, medium inten-
sity; w, weak; sh, shoulder.
Crystals of the compound isolated from the system This holds for the reactions of carbamide and thiocarb-
were dried in air and characterized by chemical analy- amide with other inorganic salts [1]. It is known from
sis, X-ray powder diffraction, and IR spectroscopy. the literature that carbamide has a stronger tendency
Chemical analysis showed the following:
toward complex formation than thiocarbamide. The
Table 5. Formation of carbamide and thiocarbamide complexes of Mg, Mn, Fe, Co, Ni, Zn, and Cd formates
M(HCOO) · 2H O
M(HCOO) · 2CO(NH )
M(HCOO) · 2CS(NH )
2 2 2
2
2
2
2 2
Mg(HCOO) · 2H O [19]
Mg(HCOO) · 2CO(NH ) [33]
Not formed [this work]
2
2
2
2 2
Mn(HCOO) · 2H O [20]
Mn(HCOO) · 2CO(NH ) [33–35]
The same
2
2
2
2 2
Fe(HCOO) · 2H O [20]
Fe(HCOO) · 2CO(NH ) [33]
–
2
2
2
2 2
Co(HCOO) · 2H O [20]
Co(HCOO) · 2CO(NH ) [33]
Not formed [15]
2
2
2
2 2
Ni(HCOO) · 2H O [20]
Ni(HCOO) · 2CO(NH ) [33]
–
2
2
2
2 2
Zn(HCOO) · 2H O [21]
Zn(HCOO) · 2CO(NH ) [33]
Zn(HCOO) · 2CS(NH ) [14]
2
2
2
2 2
2
2 2
Cd(HCOO) · 2H O [21]
Cd(HCOO) · 2CO(NH ) [34–36]
Cd(HCOO) · 2CS(NH ) [11, 12, this work]
2 2 2
2
2
2
2 2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 5 2006

8
18
VASILEVA, PETROVA
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1
9. G. de With, S. Harkema, and P. G. J. van Hummel, Acta
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 51 No. 5 2006