Low-dimensional compounds containing cyano groups: VIII. A spectral and thermal study of dicyanoargentates containing aliphatic diamine ligands

Article abstract of DOI:10.1016/j.tca.2004.02.003

The synthesis, spectral and thermal properties of dicyanoargentates, namely Cu(tn)₂Ag₂(CN)₄ (I) (tn = 1,3-diaminopropane), Cu_8-xAg_x(tn)₃(CN)₁₀ x=0.25 (II), Cu(pn)₂Ag₂(CN)₄ (III) (pn = 1,2-diaminopropane) and Cu₂(dabn)₂(NH₃)Ag₄(CN) ₈·2H₂O (IV) (dabn = 1,4-diaminobutane) are reported. All complexes were isolated from reaction mixtures containing K[Ag(CN)₂], CuSO₄ and N-donor ligands (tn, pn and dabn, respectively). Infrared spectra confirm the presence of characteristic functional groups and are consistent with the known structures of complexes (I), (III) and (IV). Thermal decompositions of complexes (I)-(IV) begin by endothermic liberation of ligand molecules followed by strong exothermic redox decomposition of the cyano groups. Comparison of the initial decomposition temperatures of complexes (I)-(IV) yields the following order of the thermal stability (IV)<(I)<(III)<(II).

Full text of DOI:10.1016/j.tca.2004.02.003

Thermochimica Acta 419 (2004) 231–237
Low-dimensional compounds containing cyano groups
VIII. A spectral and thermal study of dicyanoargentates
containing aliphatic diamine ligands
L’ubica Triš cˇ ´ı ková , Ivan Poto cˇ nˇ ák , Jozef Chomi cˇ , Thomas Müllerc
a
b,∗
b
a
Department of Physical Sciences, Faculty of Science, University of Žilina, Hurbanova 15, SK-010 26 Žilina, Slovak Republic
b
Department of Inorganic Chemistry, Institute of Chemistry, P.J. Šafárik University, Moyzesova 11, SK-041 54 Košice, Slovak Republic
c
Institute of Inorganic Chemistry, Martin Luther University, Halle-Wittenberg, Kurt-Mothes-Strasse 2, D-06120 Halle, Germany
Received 7 November 2003; received in revised form 4 February 2004; accepted 13 February 2004
Available online 21 April 2004
Abstract
The synthesis, spectral and thermal properties of dicyanoargentates, namely Cu(tn)
CN)10 x = 0.25 (II), Cu(pn) Ag (CN) (III) (pn = 1,2-diaminopropane) and Cu (dabn)
butane) are reported. All complexes were isolated from reaction mixtures containing K[Ag(CN)
2
Ag
2
(CN)
4
(I) (tn = 1,3-diaminopropane), Cu
)Ag (CN) O (IV) (dabn = 1,4-diamino-
·2H
], CuSO and N-donor ligands (tn, pn and
8
-
x
Ag
x
(tn)
3
(
2
2
4
2
2
(NH
3
4
8
2
2
4
dabn, respectively). Infrared spectra confirm the presence of characteristic functional groups and are consistent with the known structures of
complexes (I), (III) and (IV). Thermal decompositions of complexes (I)–(IV) begin by endothermic liberation of ligand molecules followed
by strong exothermic redox decomposition of the cyano groups. Comparison of the initial decomposition temperatures of complexes (I)–(IV)
yields the following order of the thermal stability (IV) < (I) < (III) < (II).
©
2004 Elsevier B.V. All rights reserved.
Keywords: Copper(II) dicyanoargentates; Structure-IR-spectroscopy relationships; Thermal decomposition
1
. Introduction
also produce polymeric structures via Ag–Ag interactions
2,5,7,10–12]. The varieties of dicyanoargentates with dia-
[
The chemistry of cyano-bridged coordination polymers is
magnetic cadmium atom have recently attracted attention of
Iwamoto’s research group [5,7,11,13], but the thermal sta-
bility and stoichiometry associated with thermal decomposi-
tion of dicyanoargentates have been studied only to a lesser
extent [14–16].
Here we present the results of spectral and thermal study
of four dicyanoargentates with aliphatic diamine ligands
1,3-diaminopropane (tn), 1,2-diaminopropane (pn) and
1,4-diaminobutane (dabn) namely, Cu(tn)2Ag2(CN)4 (I),
Cu8-xAgx(tn)3(CN)10 x = 0.25 (II), Cu(pn)2Ag2(CN)4 (III)
and Cu2(dabn)2(NH3)Ag4(CN)8·2H2O (IV), respectively.
of current interest due to the remarkable diversity of struc-
tural types that may be obtained from these systems. The
interest of our research group in low-dimensional solids con-
taining cyano bridges has been outlined in the previous pa-
pers [1–3] and in a recent review [4]. We are particularly
−
interested in the use of dicyanoargentate anion [Ag(CN)2]
−
as building blocks. The [Ag(CN)2] anion can behave as:
(
i) a rod ligand building up multi-dimensional structures by
bridging between two coordination centres [5,6], (ii) as an
unidentate ligand, blocking some coordination sites of the
central atom [1,7], or (iii) as a discrete anion playing the role
of space filler [8,9], but compounds, in which dicyanoar-
gentate anions exhibit simultaneously two different struc-
tural functions, are quite common. Moreover, this anion can
2. Experimental
2.1. Synthesis of the complexes
∗
Corresponding author. Tel.: +421-55-6228114;
All chemicals required for syntheses, i.e. copper(II) sul-
phate pentahydrate (CuSO4·5H2O), silver nitrate (AgNO3),
fax: +421-55-6222124.
E-mail address: potocnak@kosice.upjs.sk (I. Poto cˇ nˇ a´ k).
0
040-6031/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2004.02.003

2
32
L’. Triš cˇ ´ı kov a´ et al. / Thermochimica Acta 419 (2004) 231–237
potassium cyanide (KCN), 1,2-diaminopropane (C3H10N2),
,3-diaminopropane (C3H10N2) and 1,4-diaminobutane
C4H12N2) were purchased in analytical grade and used
44.78; Cu 13.55%. Calculated for C H31N13Ag4Cu2O2
16
1
(
(Mr = 996.10): C 19.29; H 3.14; N 18.28; Ag 43.32; Cu
12.76%.
without further purification. Potassium dicyanoargentate
K[Ag(CN)2] was prepared from silver nitrate and potassium
cyanide.
2.2. Apparatus
Blue-violet crystals of (I) were prepared according to
the literature [1] by successive addition of 2 M aqueous tn
The carbon, hydrogen and nitrogen microanalyses were
performed using a CHNS-O Carlo Erba EA 1108 Elemental
Analyzer. The silver and copper contents were determined
using a SpectrAA-30 Varian spectrometer after mineraliza-
tion of the samples with diluted HNO3.
3
3
(
2 cm , 4 mmol) and 0.2 M aqueous K[Ag(CN)2] (10 cm ,
3
2
1
mmol) to 0.1 M aqueous solution of CuSO4 (10 cm ,
mmol). The solution thus formed was filtered to avoid
any presence of solid impurities and left aside for crys-
tallization. Blue-violet crystals appeared within a week.
The crystals were filtered off followed by washing with
a small portion of cold water and then dried in air. The
compound is air stable and insoluble in water, alcohols and
acetone. Elemental analysis of (I): experimentally found: C
The IR spectra of the compounds were recorded
on a MATTSON 5000 FT–IR Spectrometer in the
4000–300 cm range using KBr pellets.
−
1
The TG, DTA, DTG measurements were carried out using
NETZSCH STA 409 C instrument under dynamic conditions
◦
−1
in air atmosphere with heating rate 10 C min and sample
weights were approximately 20 mg.
2
3.00; H 3.75; N 20.75; Cu 11.95; Ag 41.25%. Calculated
for C10H20N8Ag2Cu (Mr = 531.61): C 22.59; H 3.79; N
The solid thermal decomposition products were identi-
fied using powder X-ray diffraction patterns recorded on a
2
1.08; Cu 11.94; Ag 40.58%.
Crystals of (II) were prepared in a similar way but the
Mikrometa 2 diffractomer equipped with Cr K radiation
␣
amount of tn was decreased (K[Ag(CN)2], CuSO4 and tn
were in the molar ratio of 1:2:1) and red-violet crystals of (II)
appeared within a week days. The crystals were filtered off
followed by washing with a small portion of cold water and
then dried in air. The compound is air stable and insoluble
in water, alcohols and acetone. Elemental analysis of (II):
experimentally found: C 22.99; H 2.89; N 21.97; Ag 2.76;
Cu 49.18%. Calculated for C19H30N AgxCu8−x, x = 0.25
(λ = 2.29092 Å) monochromatized with vanadium foil.
3. Results and discussion
The same general procedure is often used for the prepa-
ration of solid cyanocomplexes exhibiting polymeric struc-
tures with various degrees of dimensionality. This method
is based on a combination of suitable building blocks and
is so-called “brick and mortar” method [19]. The building
blocks in solution are formed by complex cations with
at least two coordination sites occupied by weak ligands
(brick) and bridging cyanocomplex anions (mortar), which
can replace the weak ligands, and thus inducing polymer-
ization of the structure in solid. Such method was also used
in the preparation of our studied compounds. In this way
we have prepared following dicyanoargentates by using var-
1
6
(
Mr = 1001.96): C 22.78; H 3.02; N 22.37; Ag 2.69; Cu
4
9.15%.
The complex (III) was prepared according to the litera-
3
ture [17] by successive addition of 2 M aqueous pn (1 cm ,
3
2
mmol) and 0.2 M aqueous K[Ag(CN)2] (10 cm , 2 mmol)
3
to 0.1 M aqueous solution of CuSO4 (10 cm , 1 mmol). The
dark-violet solution thus formed was filtered to avoid any
presence of solid impurities and left aside for crystallization.
Dark violet needles appeared within 1 h. The crystals were
filtered off followed by washing with a small portion of cold
water and then dried in air. The compound is air stable and
insoluble in water, alcohols and acetone. Elemental analysis
of (III): experimentally found: C 22.68; H 3.64; N 20.91; Cu
ious “bricks” as [Cu(tn)2]2 , [Cu(pn) ] , [Cu(dabn)2]
+
2+
2+
2
−
and the same “mortar” [Ag(CN) ] : blue-violet crys-
2
tals of Cu(tn) Ag (CN) (I) [1], red–violet crystals of
2
2
4
Cu8 Ag (tn) (CN) x = 0.25 (II), dark-violet crys-
-x
x
3
10
1
5
1.29; Ag 43.60%. Calculated for C10H20N8Ag2Cu (Mr =
31.61): C 22.59; H 3.79; N 21.08; Cu 11.95; Ag 40.58%.
The preparation of (IV) was carried out as follows [18]: a
2 2 4
tals of Cu(pn) Ag (CN) (III) [17] and blue crystals of
Cu (dabn) (NH )Ag (CN) ·2H O (IV) [18]. All com-
2
2
3
4
8
2
pounds are air stable and insoluble in water, alcohols
and acetone. Other dicyanoargentates with a general for-
mula of Cu(L) Ag (CN) ·nH O (where L: N-donor lig-
blue precipitate containing [Cu(dabn)2]2 cations, formed
by mixing of 0.1 M copper sulphate solution (10 cm ,
1
2
ammonia solution (1.5 cm ). The blue solution thus formed
was mixed with 0.2 M solution of K[Ag(CN)2] (10 cm ,
+
3
2
2
4
2
3
2+
mmol) and 2 M aqueous 1,4-diaminobutane (1 cm ,
and) with [Cu(4-Mepy) ] (4-Mepy = 4-methylpyridine),
2
2
+
2+
2+
2+
mmol), was dissolved by addition of concentrated (26%)
n = 0 [10], [Cu(NH ) ] , n = 0 [14], [Cu(en) ]
3
2
2
3
(en = 1,2-diaminoethane), n = 0 [15], [Cu(phen) ]
2
2
3
(phen = 1,10-phenanthroline), n = 1 [16], [Cu(bpy) ]
ꢀ
2+
2
mmol). The resulting blue solution was left to crystallize.
(bpy = 2,2 -bipyridine), n = 1 [20], [Cu(py) ]
(py
2
Blue crystals of (IV) were obtained after 2 days. The crystals
were filtered off followed by washing with a small portion
of cold water and then dried in air. Elemental analysis of
= pyridine), n = 0 [21] “bricks” have been previously pre-
pared in the same way. The formation of the mixed-valence
complex (II) is an expression of the Cu(II)/Cu(I) redox
equilibrium in the presence of cyano and tn ligands in
(IV): experimentally found: C 19.21; H 3.08; N 17.88; Ag

L’. Triš cˇ ´ı kov a´ et al. / Thermochimica Acta 419 (2004) 231–237
233
air. Similar processes led to the formation of Cu(II)/Cu(I)
cyanoargentates containing ammonia and pyridine, namely
Table 2
The vibration wave numbers (cm 1) of cyanide group for K[Ag(CN)2]
27], (I), (II), (III) [17] and (IV)
−
[
Cu(NH3)pyAg3−xCux(CN) ·py, x = 1.243 and 0.39 [3], or
5
Assignment K[Ag(CN)2] (I)
ꢀ
(II)
(III)
(IV)
4
-methylpyridine, namely Cu(4-Mepy)3Ag2−xCux(CN)4,
x = 0.07, respectively [22].
+
ν3 ν(CN),
2179w
2164vs
2136s
u
2160m
2140vs
2148s
3
.1. Spectral study
2
132s
2108vs 2133s
362m 390s
ꢀ
+
ν4 ν(AgC),
390s
412w
388w
u
The measured IR spectra confirm the presence of all char-
402w
acteristic functional groups in the prepared complexes. The
vibration wave numbers of the bands confirming the pres-
ence of tn, pn and dabn in the spectra of (I)–(IV) are sum-
marized in Table 1, together with some relevant spectral data
for comparison. The vibrations observed in the spectrum of
free tn, pn [23] and dabn [24] were found in the spectra of
_
+
N
C
N
Cu
N
N
(I)–(IV), but the bands were shifted as a consequence of the
N
C
Ag
C
N
Ag
N
ligand coordination. The presence of dicyanoargentates in
the prepared complexes is proved by strong ν(CN) stretching
bands. The position of the stretching ν(CN) vibration is an
important tool in distinguishing between terminal and bridg-
ing character of the cyano group. This band is observed at
C
N
Scheme 1. Structural diagram for (I).
−1
2
080 cm in ionic KCN [25]. As a consequence of a cyano
group coordination, ν(CN) band is shifted towards higher
frequencies. In the solid K[Ag(CN)2] with terminal cyano
groups only, the ν(CN) position is at 2140 cm , while in
from the bridging cyano groups. The relative intensities of
the absorption bands correspond to the number of the respec-
tive types of cyano groups in the structure of (I) (Scheme 1).
According to the known crystal structure of (III) [17]
(Scheme 2) we have expected several ν(CN) vibrations for
cyano groups. However, the spectrum contains only one
ν(CN) absorption band at 2133 cm despite the presence
of both terminal and bridging cyano groups in the structure
of (III). This may be caused by the interplay of two effects:
(1) the slight increase of the terminal group absorption band
position due to its involvement in hydrogen bonds system,
−
1
AgCN containing bridging cyano groups, this band is shifted
−
1
to 2164 cm [26,27]. The use of different N-donor ligand
tn, pn and dabn) led to a various types of structures and to
(
a different function of the cyano groups (terminal or bridg-
ing, respectively), which is reflected by the ν(CN) stretching
vibration position in IR spectra of (I)–(IV) (Table 2).
−
1
−
1
In (I), the strong bands observed at 2132 and 2148 cm
can be attributed to the stretching vibration of terminal cyano
−
1
groups, whereas the medium band at 2160 cm may arise
Table 1
The vibration wave numbers (cm 1) of tn [23], pn [23], dabn [24], (I), (II), (III) [17] and (IV)
−
Assignment
tn
(I)
(II)
pn
(III)
dabn
(IV)
ν(NH2)
ν(NH2)
ν(CH2)
ν(CH2)
ν(CH2)
ν(CH2)
δ(NH2)
δ(NH2)
ρw(CH2)
ρw(CH2)
ρt(CH2)
δt(NH2)
ν(CN)
3360s
3282s
3332s
3256s
2968m
2944s
2892m
2840w
1612vs
1472m
1406m
3301s
3245s
2941m
3369s
3284s
3329s
3264s
3346s
3280s
3327w
3269w
2978m
2945m
2887m
2868w
1582s
1469m
1380m
1364m
1250m
1149s
2983w
2954m
2923m
2879w
1599s
1455m
1384w
1375m
1301w
1195w
1070m
1052s
2925vs
2855s
2835vs
1601s
1471m
1434m
1369m
1319w
1096m
1069m
2958vs
2922s
2861s
2926vs
2890m
2853vs
1606s
1497s
1390w
1353vw
1309vw
1145vw
1070m
1585s
1470w
1401m
1603s
1455m
1375m
1349m
1299m
1186w
1061m
1313m
1095w
1056w
1027s
1096w
1060w
1043m
ν(CN)
ρw(NH2)
ρw(NH2)
ρr(CH2) +
ρw(NH2)
ρr(CH2)
ρr(CH2)
1009s
1019m
954w
970s
904s
888m
901s
884m
931w
878m, br
863m, br
738w
864m, br
861m, br

2
34
L’. Triš cˇ ´ı kov a´ et al. / Thermochimica Acta 419 (2004) 231–237
Me
473
Exo
N
N
N
N
C
Ag
C
N
Cu
N
C
Ag
C
N
DTA
DTG
N
∆T
2
98
1
78
Me
Scheme 2. Structural diagram for (III).
Endo
and (2) the slight decrease of the bridging group absorption
band position due to the weaker coordination of the bridging
cyano group to the copper atom, resulting in overlapping of
both ν(CN) absorption bands. Similar situation was found
in the Cu(en)2Ag2(CN)4 (en = ethylendiamine) compound
for which the single ν(CN) absorption band was observed
TG
0
-
-
-
10
20
30
2tn
−
1
at 2136 cm [2].
The spectrum of (II) contains one ν(CN) absorption band
2(CN)2
600
−
1
at rather low value of 2108 cm . As the position of ν(CN)
stretching vibration in KCu(CN)2 is at lower wave num-
ber than in KAg(CN)2 [26,27] we suppose that the lower
ν(CN) wave number in (II) could be caused by partial sub-
stitution of silver cation by cupric ion. Because there is
only one ν(CN) absorption band in (II), we can expect ei-
ther polymeric structure with only bridging cyano groups, or
the structure may contain both terminal and bridging cyano
groups involved in hydrogen bonds and in a weak coordi-
nation to the copper atom respectively, as observed in (III)
and Cu(en)2Ag2(CN)4 [2].
-40
50
-
0
200
400
Temperature / ˚C
Fig. 1. Thermal curves for (I).
step. Thermal decompositions of the compounds (I)–(IV)
are multi-stage processes.
The TG, DTA and DTG curves for (I) are shown in Fig. 1.
The thermal decomposition of (I) consists of two distin-
guished stages corresponding to the separated release of tn
molecules and cyano groups decomposing. Complex (I) is
stable up to 150 C. In the 150–368 C temperature range,
a weight loss of 26.8% corresponding to the release of two
tn molecules (calc 27.8%) is observed during endothermic
multi-stage process (these stages are overlapped). The sec-
Taking into consideration the known structure of (IV) [18]
−
1
(
Scheme 3), the strong band at 2136 cm can be attributed
to the stretching vibration of terminal cyano group, while
◦
◦
−
1
those at 2179 and 2164 cm can arise from the bridging
cyano groups.
3
.2. Thermal study
◦
ond step in the 368–514 C temperature range, with ob-
served weight loss of 16.6%, involves the decomposition of
cyanides (calc 16.6%). Their decomposition includes oxida-
tion of four CN groups to form two cyanogen molecules
The usual way of thermal decomposition of cyano com-
plexes is characterized by liberation of N-donor ligands fol-
lowed by separated decomposition of all cyano groups in one
−
during reduction of two silver cations and one half of oxy-
gen molecule from the air ambient. This process is accom-
panied by a strong exothermic effect as a consequence of the
cyanogen molecules pyrolysis. The final thermal decompo-
sition product is a mixture of CuO (tenorite, 45-0937) and
metallic Ag (4-0783) detected by X-ray powder diffractom-
etry (solid residue 56.6%; calc 55.6%). The most probable
thermal decomposition scheme for (I) is:
NH3
N
Cu
Cu
N
N
N
C
Ag
C
C
N
Ag
C
.
2 H O
2
Cu
◦
◦
1
50–368 C
368–514 C
N
Cu(tn)2Ag (CN)4 −−−−−→ CuAg (CN)4 −−−−−→ CuO
N
Cu
2
2
2
tn
2(CN)2
Cu
N
+
2Ag
N
N
C
C
The TG, DTA and DTG curves for (II) are shown in Fig. 2
The thermal decomposition of this complex consists of the
three tn molecules release in two steps followed by decom-
posing of all cyano groups in one step. Complex (II) is sta-
Ag
Ag
C
C
N
N
◦ ◦
ble up to 225 C. In the 225–282 C temperature range a
Scheme 3. Structural diagram for (IV).

L’. Triš cˇ ´ı kov a´ et al. / Thermochimica Acta 419 (2004) 231–237
235
Exo
534
490
Exo
DTA
DTG
240
270
25
DTA
∆
T
∆
T
2
DTG
Endo
Endo
TG
TG
0
0
tn
-
-
-
-
-
10
20
30
40
50
2
pn
-
-
-
-
-
10
20
30
40
50
2
tn
5
(CN)2
2(CN)2
0
200
400
600
0
200
400
600
Temperature / ˚C
Temperature / ˚C
Fig. 3. Thermal curves for (III).
Fig. 2. Thermal curves for (II).
◦
◦
(
maximum at 270 C in DTA). In the 420–540 C temper-
weight loss of 7.4% corresponding to the release of one tn
molecule (calc 7.4%) is observed during endothermic pro-
ature range an observed weight loss of 17.5% involves the
decomposition of cyanides (calc 16.6%). The decomposi-
tion includes oxidation of four CN groups to form two
−
cess. It is overlapped by another endothermic process in the
◦
2
82–436 C temperature range, with observed weight loss
cyanogen molecules during reduction of two silver cations
and one half of oxygen molecule from the air ambient. This
process is accompanied by a strong exothermic effect (max-
of 12.2%, corresponding to the release of two tn molecules
◦
(
calc 14.8%). The third step in the 436–577 C tempera-
◦
ture range, with observed weight loss of 16.7%, involves
the decomposition of cyanides. This process is accompanied
by a strong exothermic effect as a consequence of pyroly-
sis of cyanogen molecules. These are formed by oxidation
imum at 490 C in DTA) as a consequence of the pyrolysis
of cyanogen molecules. The final thermal decomposition
product is a mixture of CuO (tenorite, 45-0937) and metal-
lic Ag (4-0783) detected by X-ray powder diffractometry
(solid residue 55.5%; calc 55.6%). The most probable
thermal decomposition scheme for (III) is:
−
of CN groups during reduction of silver cations and oxy-
gen molecules from the present air, and simultaneously, the
copper(I) is oxidized by atmospheric oxygen (calc 13.6%).
The final thermal decomposition product is a mixture of
CuO (tenorite, 45-0937) and metallic Ag (4-0783) detected
by X-ray powder diffractometry (solid residue 63.7%; calc
◦
◦
2
15–420 C
420–540 C
Cu(pn) Ag (CN) −−−−−→ CuAg (CN) −−−−−→ CuO
2
4
4
2
2
2
pn
2(CN)2
+2Ag
6
4.2%). The most probable thermal decomposition scheme
The thermal decomposition of (IV) consists of the H2O,
NH3 and tn molecules release, followed by cyano groups
decomposing. The TG, DTA and DTG curves for (IV) are
for (II) is:
◦
2
25–282 C
Cu7.75Ag0.25(tn)3(CN)10 −−−−−→ Cu7.75Ag0.25(tn)2
◦
shown in Fig. 4. Complex (IV) is stable up to 80 C. In
1tn
◦
◦
the 80–110 C temperature range a weight loss of 5.5%
2
82–436 C
×
×
(CN)10 −−−−−→ Cu7.75Ag0.25
corresponding to the release of two H2O and one NH3
molecules (calc 5.3%) is observed during endothermic pro-
2tn
◦
4
36–577 C
(CN)10 −−−−−→ 7.75CuO + 0.25Ag
◦
cess. In the 110–310 C temperature range, observed weight
5
(CN)2
loss of 17.9% involves the endothermic release of two dabn
The TG, DTA and DTG curves for (III) are shown
molecules (calc 17.7%). The decomposition of cyanides with
a weight loss of 18.2% is observed in the 310–370 C tem-
◦
◦
in Fig. 3. Complex (III) is stable up to 215 C. In the
◦
2
15–420 C temperature range a weight loss of 27.0%
perature range (calc 17.7%). This process is accompanied
by a strong exothermic effect as a consequence of the py-
rolysis of four cyanogen molecules, which are formed by
corresponding to the release of two pn molecules (calc
2
7.8%) is observed during endothermic process (maximum
◦
−
at 225 C in DTA) followed by small exothermic effect
oxidation of eight CN groups during reduction of four

2
36
L’. Triš cˇ ´ı kov a´ et al. / Thermochimica Acta 419 (2004) 231–237
Exo
spectra confirm the presence of all function groups. More-
3
64
over, the number and intensity of ν(CN) stretching vibrations
observed in the spectra of the complexes (I), (III) and (IV),
respectively, are in consistence with the presence of bridging
and terminal cyano groups in the structures of corresponding
complexes. We assume, on the base of the IR-spectrum of
complex (II) that this complex is either of polymeric struc-
ture with only bridging cyano groups, or the structure may
contain both terminal and bridging cyano groups involved
in hydrogen bonds and in a weak coordination to the copper
atom, respectively.
Thermal decompositions of the complexes (I)–(IV) are
multi-stage processes, which begin by diamine or water
molecules liberation followed by decomposition of all cyano
groups. Comparison of the initial decomposition tempera-
tures yields the following order of thermal stability (IV) <
∆
T
DTA
9
0
DTG
Endo
TG
0
2
H O+NH3
2
-
-
-
-
-
10
20
30
40
50
2dabn
4(CN)2
(
I) < (III) < (II). Similar thermal decompositions of di-
cyanoargentates with separated decomposition of organic
ligands and cyano groups were previously observed in other
dicyanoargentates with N-donor ligands and are usual for
this type of compounds [14–16,20–22]. Complexes contain-
ing chelate ligands are more thermally stable than the com-
plexes with monodentate ligands.
0
200
400
600
Temperature / ˚C
Fig. 4. Thermal curves for (IV).
silver cations and one oxygen molecule from the air ambi-
ent. The final thermal decomposition product is a mixture of
CuO (tenorite, 45-0937) and metallic Ag (4-0783) detected
by X-ray powder diffractometry (solid residue 58.4%; calc
Acknowledgements
This work was supported by the Grant Agency VEGA
5
9.3%). The most probable thermal decomposition scheme
(grant no. 1/0447/03) and grant APVT-20-009902.
of (IV) is:
◦
8
0–110 C
Cu2(dabn)2(NH3)Ag (CN)8 · 2H2O −−−−−−→
4
2
H2O, 1NH3
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◦
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10–310 C
Cu2Ag (dabn)2(CN)8 −−−−−→
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dabn
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◦
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