FT-IR spectroscopic investigation of some Hofmann type complexes: M(2-(1-Cyclohexenyl)ethylamine)2Ni(CN)4 (M = Ni, Co)

Article abstract of DOI:10.1016/j.molstruc.2008.05.041

New Hofmann type complexes in the form of M(CyHEA)₂Ni(CN)₄ (where CyHEA = 2-(1-cyclohexenyl)ethylamine; M = Ni or Co) have been prepared in powder form and their infrared spectra have been reported in the range of 4000-400 cm^-1<

Full text of DOI:10.1016/j.molstruc.2008.05.041

Journal of Molecular Structure 892 (2008) 311–315
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
FT-IR spectroscopic investigation of some Hofmann type complexes:
M(2-(1-Cyclohexenyl)ethylamine)2Ni(CN)4 (M = Ni, Co)
a,
Tekin Izgi , Cemal Parlak b,c, Türkay Aytekin c, Mustafa Sßenyel c
_
*
a Department of Physics, Science Faculty, Inonu University, Malatya 44069, Turkey
b Plant, Drug and Scientific Research Centre, Anadolu University, Eskißsehir 26470, Turkey
c Department of Physics, Science Faculty, Anadolu University, Eskißsehir 26470, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
New Hofmann type complexes in the form of M(CyHEA)2Ni(CN)4 (where CyHEA = 2-(1-cyclohexenyl)eth-
ylamine; M = Ni or Co) have been prepared in powder form and their infrared spectra have been reported
in the range of 4000–400 cmꢀ1. The thermal behaviour of these complexes has been investigated by dif-
ferential thermal analysis (DTA) and thermo-gravimetric analysis (TGA). The results suggest that these
compounds are similar in structure to Hofmann type complexes and their structures consist of polymeric
layers |M–Ni(CN)4|1 with the CyHEA molecule bound to the metal atom (M).
Received 10 December 2007
Received in revised form 8 May 2008
Accepted 28 May 2008
Available online 6 June 2008
Keywords:
Hofmann type complexes
Ó 2008 Published by Elsevier B.V.
2-(1-Cyclohexenyl)ethylamine
Infrared spectra
DTA
TGA
1. Introduction
HEA–Ni (M = Ni and Co) were prepared as following: at first step
1 mmol of MCl2 was dissolved in the distilled water, then to this
Hofmann type host structures are defined with the general for-
mula of M(L)2Ni(CN)4 [1,2]. In this host structure, the L corre-
sponds a bidentate or a pair of unidentate ligand molecules and
the M corresponds a divalent transition metal. Based on this struc-
ture, metal (II) tetracyanonickelate complexes have been devel-
oped using N-donor ligands such as ammonia [3], pyridine [4],
O-donor ligands such as water [5], dimethylformamide [6], diox-
ane [7] and S-donor ligands as dimethylthioformamide [8]. The
Hofmann type host frame work is formed from infinite |M–
Ni(CN)4|1 layers with four planar coordination around Ni atom.
solution 1 mmol of K2Ni(CN)4 dissolved in the distilled water was
added under stirring. After a short time slightly more than 2 mmol
of the liquid CyHEA were added to the mixture prepared drop wise,
again under stirring. The reaction mixture was stirred for 2 days at
room temperature. The obtained product was filtered and washed
with water, ethanol, ether successively and dried in a desiccator
which included P2O5.
Infrared spectra of the complexes as nujol and hexachloro-1,3-
butadiene were recorded in the region of 4000–400 cmꢀ1 via Per-
kin–Elmer FT-IR 2000 spectrometer at a resolution of 4 cmꢀ1. In
the MIR region of spectrum, bands of nujol and hexachloro-1,3-
butadiene were reported at 1377, 1461, 2858, 2925 cmꢀ1 and
655, 793, 852, 941, 981, 1170, 1564, 1610 cmꢀ1, respectively. The
compounds were analyzed for metals via a Perkin–Elmer 4300
ICP-OES and for C, H and N via a Fisons EA-1108 elemental ana-
lyser. Ni and Co metals were investigated at 231.604 and
228.616 nm, respectively. The results of elemental analysis have
been as follows (found %/calculated %):
This structure provides
a-type cavity similar to rectangular box
for the guest molecules [9,10]. The model of the Hofmann type host
structure is schematically illustrated in Fig. 1 [11,12].
In this work, we have prepared M(CyHEA)2Ni(CN)4 complexes
(abbreviated here after as M–CyHEA–Ni), where M = Ni or Co, for
the first time and spectral properties of them have been investigated
in the IR region of 4000–400 cmꢀ1. We have also studied the thermal
behaviour of these complexes with DTA and TGA techniques.
TGAand DTAcurvesof the complexeswere recordedusinga Seta-
ram Labsys TG/DTA with ca. 6.1 mg of sample and a scanning rate of
5° minꢀ1 under argon between about 0 and 220 °C temperatures.
2. Experimental
All the chemicals used were reagent grade (Aldrich) and they
were used without further purification. The complexes M–Cy-
3. Results and discussion
The infrared spectra obtained for the M–CyHEA–Ni (M = Ni or
Co) complexes are compatible with each other. This indicates that
* Corresponding author. Tel.: +90 422 341 0010; fax: +90 422 341 0037.
E-mail address: tizgi@inonu.edu.tr (T. Izgi).
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0022-2860/$ - see front matter Ó 2008 Published by Elsevier B.V.
doi:10.1016/j.molstruc.2008.05.041

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T. Izgi et al. / Journal of Molecular Structure 892 (2008) 311–315
the compounds have similar spectral features. The spectra of the
M–CyHEA–Ni (M = Ni or Co) compounds are given in Figs. 2 and
3. The spectral analysis of each compound have been performed
by taking into account the CyHEA molecule and Ni(CN)4 ions indi-
vidually. The spectral interpretations start with CyHEA vibrations.
3.1. 2-(1-Cyclohexenyl)ethylamine vibrations
We have studied the vibrational assignments and frequencies
both experimental and theoretical study of CyHEA [13]. The calcu-
lated and experimental IR data for the CyHEA in the complexes, to-
gether with the spectral data for the CyHEA molecule are given in
Table 1. The vibrational frequencies of the CyHEA molecule usually
increase on the complexes compounds [13]. It is clearly observed
in Table 1 that the N–H asymmetric and symmetric stretching
bands which appear as a strong at 3366 and 3288 cmꢀ1 attribute
Fig. 1. The model for the Hofmann type host structure (open circle, 6-coordinate M;
solid circle, square planar Ni; open column, an ambient ligand; thick line, CN
bridge; thin line, edge of cavity).
Fig. 2. Infrared spectra of Ni–CyHEA–Ni complex in nujol (a) and hexachloro-1,3-butadiene (b).

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T. Izgi et al. / Journal of Molecular Structure 892 (2008) 311–315
313
Fig. 3. Infrared spectra of Co–CyHEA–Ni complex in nujol (a) and hexachloro-1,3-butadiene (b).
to ethylamine, respectively. The strong band at 3366 cmꢀ1 is
shifted to 3354 cmꢀ1 as a medium band. Another strong band at
3288 cmꢀ1 shifts to 3286 cmꢀ1 for Ni–CyHEA–Ni, and to
3287 cmꢀ1 for the Co–CyHEA–Ni compounds. The medium brought
band at 1600 cmꢀ1 is shifted 1590 cmꢀ1 as a medium band. Fur-
thermore, some increase shifts are observed for the vibrational
band of the CyHEA molecule in the frequency range from 448 to
857 cmꢀ1. The downward shifts in frequencies were explained in
terms of coupling of the internal vibration of the CyHEA molecule
M–N vibrations. The medium m1 and weak m23 bands at between
3000 and 3100 cmꢀ1 result from cyclohexene while the medium
C–H stretching band at 2995 cmꢀ1 arises from ethylamine. The
very strong bands attributed to ethylamine attached to cyclohex-
ene appear at between 2830 and 2920 cmꢀ1. Most of bands in be-
low the 1300 cmꢀ1 arise from cyclohexene. Similar studies [14–16]
obvious that similar spectral features of coordinations are fre-
quency shifts of ligand molecules in the complexes comparison
with free ligand molecules by virtue of the ligand molecule com-
plexed to the metal atom and also small shifts occured owing to
changes in the environment.
3.2. Ni(CN)4 group vibrations
Assignments of the bands for the Ni(CN)4 ion in the spectra of
the present compounds have been carried out by means of vibra-
2ꢀ
tional data of the NiðCNÞ4 ion in Na2Ni(CN)4 reported by McCul-
lough et al. [17]. Since the ion is not coordinated to cations [17], it
can be treated as an isolated unit. Therefore, we have used it as a
reference for finding out whether coordination to the metals M is
taking place. The spectral data for the Ni(CN)4 groups in our com-
plexes are given in Table 2 along with McCullough et al.’s data.
The vibrational frequencies of the Ni(CN)4 group in the com-
plexes appear to be much higher than those for isolated Ni(CN)4
ion. Such frequency shifts have been observed for other Hofmann

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T. Izgi et al. / Journal of Molecular Structure 892 (2008) 311–315
Table 1
The vibrational frequencies (cmꢀ1) of the CyHEA ligand molecule in the M–CyHEA–Ni (M = Ni or Co) compounds
Assignmenta
CyHEAa (experimental)
CyHEAa B3LYP (6-31G(d) (calculated)
Ni–CyHEA–Ni
Co–CyHEA–Ni
N–H a-str
N–H s-str
m23
3366 s
3288 s
3374
3273
3080
3008
2993
2934
2901
2899
2848
2838
1662
1633
1505
1492
1475
1401
1373
1363
1346
1329
1313
1269
1254
1239
1133
1084
1068
1057
1024
964
3354 m
3286 m
–
3354 m
3287 m
–
3097 w
3043 m
2995 m
2926 vs
2894 vw
2877 vw
2857 vs
2836 vs
1666 m
1600 mb
1505 vw
1473 vw
1448 vw
1438 s
1384 w
1370 vw
1344 m
1334 w
1307 w
1269 m
1242 w
1215 w
1136 m
1086 w
1066 w
1049 w
1022 w
966 w
m1
3043 vw
2994 w*
2928 vs*
2911 w*
2885 sh*
2855 m*
2834 vs
1665 w
1590 m
1505 vw
1460 w*
–
3046 vw
2995 vw*
2928 vs*
2911 w*
2888 sh*
2854 m*
2834 vs
1665 vw
1590 m
1505 vw
1460 w*
–
C–H str (CH3)
m
m
2 + C–H str (CH3)
25 + C–H str (CH2)
m26
m
m
27 + C–H str (CH3)
5 + C–H str (CH2)
m6
NH2 sciss
CH2 sciss
C–H bend (CH3)
m
28 + C–H bend (CH3)
m8
1437 m
–
1437 m
–
CH2 wag
m
9 + C–H bend (CH3)
1361 sh*
1343 vw
–
1365 sh*
1346 vw
–
m10
m30
NH2 twist
m32
1307 w
1270 w
1242 vw
1217 w
1138 m
1093 m
1062 m
1038 m
–
985 m
919 vw
900 vw
868 vw
819 w
1307 vw
1270 w
1242 vw
1217 vw
1138 m
1092 m
1061 m
1036 m
–
981 m
919 vw
900 vw
868 vw
820 w
m
11 + CH2 twist
m12
m34
(C–C,C–N) a-str
m15
m35
m
36 + CH3 rock
m16
m37
m17
m38
919 m
906 vw
857 w
953
942
836
830
m
18 + CH2 rock
829 m
m
19 + NH2 wag
800 m
720 sh
647 w
497 vw
448 w
781
733
671
499
801 m
723 vw
653 vw
499 vw
472 vw
801 m
723 vw
649 vw
492 vw
473 vw
m39
m40
m20
m41
436
a
Taken from Ref. [13]; v, very; s, strong; m, medium; w, weak; sh, shoulder; b, broad; str, stretching; bend, bending; sciss, scissoring; twist, twisting; wag, wagging; rock,
rocking.
*
In hexachloro-1,3-butadiene.
served. If the unit cell has D4h symmetry, only four fundamental
vibrations are expected in the spectrum above 400 cmꢀ1 [21–23].
In this work, we have discussed infrared spectroscopic proper-
ties of the prepared complexes up till now. Furthermore, in order
to support the conclusions obtained in the infrared studies, we
have conducted the elemental and TGA–DTA analyses of these
complexes.
We have calculated the percentage amount of C, H, N, Ni and M
in our complexes with the help of molecular weight of those com-
pounds. The calculated values have been compared with the exper-
imental data and the results have been given in Table 3. According
to these results, the calculated values are in compliance with the
experimental findings.
Table 2
The vibrational frequencies (cmꢀ1) of the Ni(CN)4 group in the M–CyHEA–Ni (M = Ni
or Co) compounds
Assignmenta
Na2Ni(CN)4
Ni–CyHEA–Ni
Co–CyHEA–Ni
a
m
m
8(CN), Eu
9(NiC), Eu
2132 vs
543 w
448 w
433 vs
2171 vs
554 w
457 sh
441 vs
2165 vs
543 w
456 sh
437 vs
p
(NiC), A2u
d(NiCN), Eu
a
Taken from Ref. [18]; v, very; s, strong; sh, shoulder; w, weak.
type complexes [6,8,15,16,18,19] or clathrates [11,12,20,21] and
are attributed to the mechanical coupling of the internal modes
of Ni(CN)4 with the M–NC vibrations. It follows that the N-termini
of the Ni(CN)4 group are bound to a M metal atom (M = Ni, Co) in
the host compounds investigated.
3.3. Thermal behaviour
The studies regarding the Hofmann type complexes explain that
shifts arise from the mechanical coupling of the internal modes of
Ni(CN)4 with metal as both ends of the CN group are bounded to
the transition metals [6,8,15,16,19]. According to the shifts in the
present complexes can be attributed to the mechanical coupling
of the internal modes of Ni(CN)4 with metal.
The characteristic m(CN) and d(NiCN) frequencies are found to
be similar to those known for the Hofmann type complexes
[2,14], indicating that the |M–Ni(CN)4|1 layers have been pre-
The TGA and DTA curves of the compounds are given in Fig. 4.
The TGA and DTA results indicate that samples are stable at room
temperature. By heating, however, both of them gradually lose two
ligand molecules in a single step between about 40 and 140 °C.
DTA curves show two endothermic transitions for present com-
pounds. The first decomposition stage about 90 °C indicates that
the CyHEA ligand molecule leaves host structure. The second
decomposition stage about 150 °C is decomposition of cyanide to
yield the respective metals. The decomposition temperatures of

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T. Izgi et al. / Journal of Molecular Structure 892 (2008) 311–315
315
Table 3
Elemental analysis and colours of the M–CyHEA–Ni (M = Ni or Co) compounds
Empirical formula of sample (formula weight)
Colour
Elemental analysis, found/calculated (%)
C
H
N
Ni
Ni(C8H15N)2Ni(CN)4 (471,87,944)
Co(C8H15N)2Ni(CN)4 (472,11,924)
Violet
Pink
50.94 (50.91)
48.94 (50.87)
6.32 (6.40)
5.95 (6.40)
17.55 (17.80)
16.85 (17.80)
24.50 (24.87)
12.24 (12.43)
As a result, the similarities of the spectral features found for the
present compounds with the Hofmann type complexes let us con-
clude that the compounds presented in this study are further
examples of Hofmann type complexes.
4. Conclusion
The IR spectroscopic study of two new complexes has shown
that they have similar structures consisting of infinite two-dimen-
sional polymeric layers formed with Ni(CN)4 ions bridged by M(Cy-
HEA)2 (M = Ni and Co) cations and CyHEA molecules in compounds
have been coordinated in the chair form as a unidentate ligand
coordinating only through the NH nitrogen. In conclusion, the com-
pounds presented in this study are further examples of the Hof-
mann type complexes.
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Fig. 4. TGA and DTA curves of the Ni–CyHEA–Ni (a) and Co–CyHEA–Ni (b)
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_
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Table 4
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The decomposition temperatures (°C) of M–CyHEA–Ni (M = Ni or Co) compounds
Sample
Decomposition
First
Second
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Ni(C8H15N)2Ni(CN)4
Co(C8H15N)2Ni(CN)4
93.21
92.81
153.82
151.32
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M–CyHEA–Ni (M = Ni, Co) complexes are given in Table 4. Such
decomposition stages have been observed for other Hofmann type
complexes [24] and clathrates [25].