Vibrational spectroscopic study on some Hofmann type clathrates: M(1-Phenylpiperazine)2Ni(CN)4·2G (M = Ni, Co and Cd; G = aniline)

Article abstract of DOI:10.1016/j.molstruc.2008.08.005

New Hofmann type aniline clathrates in the form of M(pp)₂Ni(CN)₄.2G (where pp = 1-phenylpiperazine, G = aniline and M = Ni, Co and Cd) have been prepared in powder form and FT-IR and Raman spectra have been reported. The thermal beha

Full text of DOI:10.1016/j.molstruc.2008.08.005

Journal of Molecular Structure 919 (2009) 41–46
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Journal of Molecular Structure
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Vibrational spectroscopic study on some Hofmann type clathrates:
M(1-Phenylpiperazine)2Ni(CN)4ꢀ2G (M = Ni, Co and Cd; G = aniline)
a
Cemal Parlak a,b, Özgür Alver a,b, , Mustafa Sßenyel
*
a Department of Physics, Science Faculty, Anadolu University, 26470, Eskißsehir, Turkey
b Plant, Drug and Scientific Research Centre, Anadolu University, 26470, Eskißsehir, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 May 2008
Received in revised form 8 August 2008
Accepted 8 August 2008
Available online 19 August 2008
New Hofmann type aniline clathrates in the form of M(pp)2Ni(CN)4.2G (where pp = 1-phenylpiperazine,
G = aniline and M = Ni, Co and Cd) have been prepared in powder form and FT-IR and Raman spectra have
been reported. The thermal behaviour of these clathrates has been investigated by thermo-gravimetric
analysis (TGA) and differential thermal analysis (DTA). The results suggest that these compounds are sim-
ilar in structure to the Hofmann type clathrates and their structures consist of corrugated polymeric lay-
ers of | M–Ni(CN)4
|
with the pp spanned between two metal (M) atoms, of the consecutive two layers.
1
Keywords:
Ó 2008 Elsevier B.V. All rights reserved.
Hofmann type clathrates
Inclusion compounds
1-Phenylpiperazine
Aniline
IR and Raman spectra
1. Introduction
are limited when compared to the Hofmann type benzene clath-
rates [8–14]. In the present work, we have synthesised three new
The Hofmann type clathrates are two component inclusion
M(pp)2Ni(CN)4ꢀ2An clathrates (abbreviated hereafter as M–pp–
Ni–An) using aniline molecule as a guest molecule, where M = Ni,
Co and Cd and An = aniline, for the first time and investigated their
FT-IR and Raman spectra. We have also reported the Raman spec-
tra of M–pp–Ni host structures for comparison. Additionally, we
have studied the thermal behaviour of these clathrates with TGA
and DTA techniques.
compounds. They are composed of a host lattice and a guest mol-
ecule which are linked without ordinary chemical union, but
throughout complete enclosure of one set of molecules in a suit-
able structure formed by another [1–2]. Their general formula is
M(II)L2M0(II)(CN)4ꢀnG where, M is octahedrally coordinated metal:
Mn, Fe, Co, Ni, Cu, Zn or Cd; M0 is square-planar coordinated metal:
Ni, Pd or Pt; L is a unidentate ligand molecule and n is the number
of G (guest) molecules depending on the bulkiness of the ligand
and the guest molecule [1–6]. The host framework consists of
two-dimensional polymeric layers composed of ML2 cations and
M0(CN)4 anions. The M0 atoms are coordinated to four C atoms of
the CN groups in a square planar environment. M atoms are octa-
hedrally surrounded by six N atoms, four of them from the CN
groups and the other two from two ligand molecules. The ligand
molecules lie between the layers. The empty spaces of varying
shapes and dimensions, in which guest molecules may be encapsu-
lated are provided by the layers and the ligands as blocking units.
In our previous study, we reported the infrared spectroscopic
study of M(pp)2Ni(CN)4 (M = Ni, Co, Cd, Pd or Mn) Hofmann type
complexes [7]. Studies on the Hofmann type aniline clathrates
2. Experimental
All the chemicals were purchased from Aldrich and used with-
out further purification. The M–pp–Ni–An (M = Ni, Co and Cd)
compounds were prepared as follows: 1 mmol of K2Ni(CN)4 was
dissolved in the distilled water and left for stirring with a magnetic
stirrer. After a short time slightly more than 2 mmol of the liquid
pp was added to the solution dropwise and then 3 mmol of aniline
was added to the prepared solution. Finally, 1 mmol of MCl2 dis-
solved in the distilled water was added to the mixture prepared
drop wise, again under stirring. The final mixture was stirred for
a week at room temperature. The obtained products were filtered
and washed with distilled water, ethanol and ether successively
and stored in a desiccator containing guest vapour.
The compounds were analyzed for metals via Perkin-Elmer
4300 ICP-OES and for C, H and N via Fisons EA-1108 elemental ana-
lyser. Ni, Co and Cd metals were investigated at 231.604, 228.616
and 228.802 nm, respectively. The results of elemental analyses
* Corresponding author. Address: Department of Physics, Science Faculty, Anad-
olu University, 26470, Eskißsehir, Turkey. Tel.: +90 222 335 05 80x3668; fax: +90 222
320 49 10.
E-mail address: ozguralver@anadolu.edu.tr (Ö. Alver).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.08.005

42
C. Parlak et al. / Journal of Molecular Structure 919 (2009) 41–46
Table 1
Elemental analysis of the M–pp–Ni–An (M = Ni, Co and Cd) clathrates
Empirical formula of samples and Mr(g)
Elemental analysis, found/(calculated) (%)
C
H
N
Ni
15.81
(16.03)
7.88
Co
Cd
Ni(C10H14N2)2Ni(CN)4.2C6H5NH2
Mr = 732.17
58.92
(59.06)
58.93
5.66
(5.78)
5.65
18.88
(19.13)
18.86
–
–
7.89
–
–
–
Co(C10H14N2)2Ni(CN)4.2C6H5NH2
Mr = 732.41
Cd(C10H14N2)2Ni(CN)4.2C6H5NH2
Mr = 785.89
(59.04)
54.86
(55.02)
(5.78)
5.26
(5.39)
(19.12)
17.66
(17.82)
(8.01)
7.34
(7.47)
(8.05)
–
–
–
14.06
(14.30)
are given in Table 1. Infrared spectra of the clathrates were re-
corded in the region of (4000–400) cmꢁ1 via Perkin-Elmer FT-IR
2000 spectrometer at a resolution of 4 cmꢁ1. In order to provide
better identifications for the vibrational bands of the clathrates
prepared in this study two different mulls (nujol and hexachloro-
1,3-butadiene) were used. In the MIR region of spectrum, bands
of nujol and hexachloro-1,3-butadiene were reported at 1377,
1461, 2858, 2925 and 655, 793, 852, 941, 981, 1170, 1564,
1610 cmꢁ1, respectively. The Raman spectra of the clathrates were
recorded in the region of (2800–1650) cmꢁ1 via Bruker Senterra
Dispersive Raman Microscope using the 532 nm line of a 3B diode
laser. TGA and DTA curves of the clathrates were recorded using a
Setaram Labsys TG/DTA with ca. 6.0 mg of sample and a scaning
rate of 5 minꢁ1 under argon, temperatures between about 20–
200 °C. All the analyses of these clathrates were carried out imme-
diately to avoid any declathration.
These shifts in frequencies have been explained in terms of cou-
pling of the internal vibration of pp molecule with MAN vibrations
[3–14,20]. Another strong CN stretching frequency attributed to
phenyl attached to one of the nitrogens of piperazine has not
shifted in the compounds. Regarding the phenyl ring within the
pp ligand, the vibrational bands of the molecule experiences small
shifts due to coordination of pp molecule.
From the comparison of the spectral data presented in Table 2,
we have concluded that the pp molecules in investigated com-
pounds have been coordinated as a unidentate ligand coordinating
only through the NH nitrogen. Unidentate coordination of the pp
ligand has been also supported by the shifts in the position of
the NH deformation mode from the free ligand value of 1670–
1600 cmꢁ1 and no shift in the position of the CN stretching (Table
2, Fig. 1) [7,15].
3.2. Ni(CN)4 group vibrations
3. Results and discussions
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-
tional data of the Ni(CN)4 ion in Na2Ni(CN)4 reported by McCul-
lough et al. [21]. Since the ion is not coordinated to cations, it
can be treated as an isolated unit. Therefore, we have used it as a
reference for finding out whether coordination to the M is taking
place. The vibrational data for the Ni(CN)4 groups in our clathrates
are given in Table 3 along with McCullough et al’s. data. The wave-
numbers of the infrared [7] and Raman spectra of the Ni(CN)4
group in the related host structures are also listed in Table 3.
The assigned IR and Raman wavenumbers for the Ni(CN)4 group
in the compounds studied appear to be much higher than those for
isolated Ni(CN)4 units (Table 3, Figs. 1 and 2). Such frequency shifts
have been observed for other Hofmann type [3–6] and Hofmann
type aniline [8–13] clathrates and are attributed to the mechanical
coupling of the internal modes of Ni(CN)4 with the M–NC vibra-
tions. The characteristic frequencies of the Ni(CN)4 group are found
to be similar to those of the Hofmann type clathrates suggesting
that coordination around the Ni atom is square planar, and that |
The infrared and Raman spectra of the M–pp–Ni–An (M = Ni, Co
and Cd) clathrates are compatible with each other which implies
that the compounds have similar spectral features. The infrared
spectra of the Ni–pp–Ni complex and Ni–pp–Ni–An clathrate are
given in Fig. 1. The Raman spectra of the Cd–pp–Ni complex and
Cd–pp–Ni–An clathrate are given in Fig. 2 as an example. The spec-
tral analysis of each compound has been performed by taking into
account the pp ligand molecule, Ni(CN)4 ions and guest molecule
individually.
3.1. 1-Phenylpiperazine vibrations
The pp molecule has been used as a ligand in various complexes
[7,15–17]. Due to steric hinderance present in the boat form, the
free pp exists in chair conformation [15]. However, this molecule
can also coordinate in the boat [16] and chair form as a bidentate
ligand [17] or as a unidentate ligand coordinating only through the
nitrogen of NH [7,15]. In our previous study, we reported the vibra-
tional assignments and the frequencies of the free pp molecule
both theoretically and experimentally in the region of (4000–
400) cmꢁ1 [18]. The assignments and the frequencies of the funda-
mental bands observed in the infrared spectra of the clathrates un-
der study are given in Table 2, together with our previous data, for
comparison.
The spectral data for pp in the clathrates exhibit characteristics
of a coordinated ligand (Table 2, Fig. 1). On coordination, the NH
and CH2 stretching frequencies attributed to piperazine ring within
the pp ligand should decrease and increase due to the consecutive
inductive effects, respectively (on coordination, NH and CN bonds
should become weaker and CH bonds should become stronger)
[19]. It is clearly observed in Table 2 and Fig. 1 that these require-
ments are fulfilled for pp in our compounds. The observed shifts of
the vibrational frequencies are consistent with previously reported
Hofmann-Td-type complexes and clathrates of piperazine [20].
M–Ni(CN)4
|
1
layers have been preserved.
3.3. Aniline vibrations
The assignments and the frequencies of the vibrational bands
for aniline of the clathrates are given in Table 4 along with the fre-
quencies of aniline in the liquid and gaseous phase [22]. Although
some vibrational bands of aniline have been obscured by some
vibrational bands of pp, comparison with the various vibrational
modes of liquid aniline has revealed the presence of characteristic
bands of aniline in these clathrates. According to chemical results,
the number of guest molecules in the present compounds is two
(n = 2). This result has been observed for other Hofmann type ani-
line clathrates [8–10]. The ma(NH2) and ms(NH2) modes of aniline in
Hofmann type aniline clathrates shift to lower frequencies than in
vapour aniline (3500 and 3418 cmꢁ1), and to slightly higher fre-
quencies than in liquid aniline (3440 and 3360 cmꢁ1) [9–10]. In

C. Parlak et al. / Journal of Molecular Structure 919 (2009) 41–46
43
Fig. 1. The IR spectra of the Ni–pp–Ni complex in nujol (a), the Ni–pp–Ni–An clathrate in nujol (b) and hexachloro-1,3-butadiene (c). N: Bands of nujol, Indicated
wavenumbers: Bands of pp and aniline molecules in hexachloro-1,3-butadiene.
the Hofmann type aniline clathrates studied here,
m
a and
m
s modes
clathrates, the out of plane deformation mode, c(CH), of aniline
occur in the regions of (3467–3471) cmꢁ1 and (3362–3372) cmꢁ1
,
shows an upward shift of about 14 cmꢁ1 when compared to the li-
quid aniline (751 cmꢁ1) [9]. This case is attributed to the formation
respectively (Table 4, Fig. 1). These values are in compliance with
the previously observed shifts [9–10]. In Hofmann type aniline
of weak hydrogen bonding between the p-cloud of the aniline ring

44
C. Parlak et al. / Journal of Molecular Structure 919 (2009) 41–46
Fig. 2. The Raman spectra of the Cd–pp–Ni complex (a) and the Cd–pp–Ni–An clathrate (b).
Table 2
The vibrational frequencies (cmꢁ1) of pp in the M–pp–Ni–An (M = Ni, Co and Cd) clathrates
Moda
Assignmenta
ppa
Ni–pp–Ni–An
Co–pp–Ni–An
Cd–pp–Ni–An
m1
m5
m8
m9
m
m
m
m
m
m
m
(NH)
(CH)
(CH)
(CH)
(CH2)
(CH2)
(CH2)
3278 sb
3091 m
3036 m
3023 m
2944 s
2881 w
2824 vs
1670 w
1600 vs
1498 vs
1452 s
1380 s
1325 s
1235 vs
1190 m
1146 s
1081 m
1059 s
1032 s
992 s
3256 s
3091 w
3037 s
3016 w
2951 sb
2894 mb
2828 vsb
1642 w
1603 vs
1499 vs
1453 sb
1380 sb
1336 s
1254 vs
1177 vs
1156 m
1112 s
1045 s
1026 m
1007 m 990 s
923 vs
882 s
3255 s
3092 w
3035 m
3016 w
2951 vsb
2894 mb
2827 sb
1640 w
1603 vs
1500 vs
1453 sb
1380 sb
1339 s
1254 vs
1176 s
1156 s
1111 s
1040 vs
–
3256 s
3093 w
3031 wb
3013 wb
2950 sb
2893 wb
2826 sb
1640 w
1601 vs
1501 vs
1452 sb
1380 sb
1340 s
1254 vs
1182 s
1152 m
1111 s
1039 s
–
989 vs
923 vs
881 s
803 sh
757 vs
690 vs
646 m
519 m
ꢂ
m11
m13
m14
m15
m17
m21
m22
m26
m29
m32
m33
m36
m38
m39
m41
m43
m46
m50
m53
m54
m57
m59
m60
m64
(NH)def.
m
mring
ds(CH2)
m
m
d(CH) + t(CH2)
d(CH)
d(CH) +
d(CH)+
mring
mring
ring breathing
w(CH2)
c
(CC)
(CN)
ring + t(CH2)
m
16(au)
qr(CH2)
1001 s 990 s
922 vs
882 s
937 s
881 s
(CH) + mring
–
800 mb
758 vs
693 vs
625 s
517 vs
437 m
806 s
806 s
(CH)def.
cring
dring + ring band
dring
dring
755 vs
691 vs
651 m
521 s
ꢂ
756 vs
690 vs
650 m
520 s
ꢂ
ꢂ, Obscured by Ni(CN)4 band; vs, very strong; s, strong; m, medium; w, weak; b, broad.
a
Taken from reference [18].
In hexachloro-1,3-butadiene.
b

C. Parlak et al. / Journal of Molecular Structure 919 (2009) 41–46
45
Table 3
The vibrational frequencies (cmꢁ1) of the Ni(CN)4 group in the M–pp–Ni–An (M = Ni, Co and Cd) clathrates
Assignmenta
Na2Ni(CN)4
M–pp–Ni
Ni
M–pp–Ni–An
Ni
a
Co
Cd
Co
Cd
m
m
m
m
1(CN), A1g
4(CN), B1g
8(CN), Eu
9(NiC), Eu
(2149)
(2141)
2132
543
(2184) vs
(2174) vs
2166 vsb
562 mb
(2176) vs
(2164) vs
2159 vsb
558 mb
(2162) vs
(2151) vs
2147 vsb
557 mb
(2184) vs
(2173) vs
2165 vs
562 m
(2175) vs
(2164) vs
2154 vs
561 s
(2161) vs
(2150) vs
2143 vs
557 m
d (NiCN), Eu
433
440 vsb
436 vsb
424 vsb
441 vs
433 vs
426 vs
a,b
Taken from reference [21] and [7], respectively. The bands observed in the Raman spectra are given in parentheses. vs, very strong; s, strong; m, medium.
Table 4
The vibrational frequencies (cmꢁ1) of aniline in the M–pp–Ni–An (M = Ni, Co and Cd) clathrates
Assignmenta
Liquid anilinea
Gas anilinea
Ni–pp–Ni–An
Co–pp–Ni–An
Cd–pp–Ni–An
NH2 stretch A00
NH2 stretch A0
2 ꢃ 1620 A0
3440 s
3360 vs
3212 w
3072 w
1926 w
1837 w
1618 vs
1600 s
1500 s
1468 vs
1312 w
1278 s
1175 s
1154 s
880 m
826 vw
751 vs
691 s
3500
3418
3230
–
1922
1830
1619
–
3471 m
3367 vs
3213 w
3072 w
1928 m
1837 m
1620 vs
ꢂ
3469 m
3362 vs
3210 w
3070 w
1929 m
1837 w
1619 vs
ꢂ
3467 m
3372 s
3205 sh
3071 w
1930 m
1838 w
1619 vs
CH stretch A0
2 ꢃ 968 A0
874 + 968 A0
NH2 bend A0
Ring stretch A0
Ring stretch A0
Ring stretch A00
CH bend ip A00
X-sensitive A0
CH bend ip A00
CH bend ip A00
CH bend op A0
CH bend op A0
CH bend op A00
Ring def.op A0
NH2 wagging
Ring def. Ip A00
X-sensitive ip A0
X-sensitive op A0
ꢂ
1503
–
–
ꢂ
ꢂ
ꢂ
1467 sb
1312 w
1275 s
ꢂ
1461 sb
–
1460 sb
–
1279
1173
–
874
825
750
690
664
–
1274 s
ꢂ
1274 s
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
821 vw
ꢂ
825 vw
ꢂ
–
ꢂ
ꢂ
ꢂ
ꢂ
670 w
618 m
527 m
501 s
671 w
618 w
540 w
504 vs
671 w
618 w
541 m
503 s
–
619 w
–
502 vs
–
500
ꢂ: Obscured by pp bands. vs, very strong; s, strong; m, medium; w, weak; sh, shoulder; ip, in-plane; op, out-of-plane; def, deformation.
a
Taken from reference [22].
In hexachloro-1,3-butadiene.
b
Table 5
The decomposition temperatures (°C) of the M–pp–Ni–An (M = Ni, Co and Cd)
clathrates
Sample
Decomposition
I
II
III
Ni(C10H14N2)2Ni(CN)4ꢀ2C6H5NH2
Co(C10H14N2)2Ni(CN)4ꢀ2C6H5NH2
Cd(C10H14N2)2Ni(CN)4ꢀ2C6H5NH2
88.68
88.33
88.75
131.46
131.88
134.79
208.17
208.22
210.26
due to interactions between NH2 of aniline and
p-cloud of phenyl
ring of pp. Another type of possible interaction of NH2 of aniline
with -cloud of the CN of the host lattice is not evident. Because,
p
CN vibrations of the host structure and clathrates are very close
to each other which means that aniline and CN of the host struc-
ture have no interaction.
Fig. 3. The TGA and DTA curves of the Ni–pp–Ni–An clathrate.
and the ligand molecule of the host [9–10]. However, identification
of interaction of aniline with host structure is difficult for this
3.4. Thermal behaviour
study. Because the
c
(CH) bands of aniline in the investigated clath-
In this work, we have discussed vibrational spectroscopic prop-
erties of the prepared clathrates up till now. In order to support the
conclusion obtained in the infrared and Raman studies, we have
also examined the thermal behaviour of these clathrates with
TGA and DTA techniques.
rates have been obscured by CH deformation band (m54) of pp. This
band of the pp in hosts occurs at 762 cmꢁ1 for Ni, 763 cmꢁ1 for Co
and 760 cmꢁ1 for Cd [7] while the same mode of pp in clathrates
appears at 755, 756 and 757 cmꢁ1, respectively (Table 2, Fig. 1).
However, when compared to its liquid and gaseous phase,
vibrations of aniline shows convincing alterations for the clath-
rates prepared in this study (Table 4) which is most probably
m
(NH2)
The TGA and DTA curves of the Ni–pp–Ni–An compound are gi-
ven in Fig. 3 as an example. The TGA results indicate that samples
are stable at room temperature. By heating, however, all of them

46
C. Parlak et al. / Journal of Molecular Structure 919 (2009) 41–46
gradually lose guest and ligand molecules between about 40–
140 °C. DTA curves show three endothermic transitions for present
compounds. The first and second decomposition stages about 88
and 132 °C indicate that the two aniline guest and pp ligand mol-
ecules leave the host structure, respectively. The final decomposi-
tion stage about 209 °C is the decomposition of cyanide to yield the
respective metals. After this temperature, the structures of the
compounds decompose. The results manifest the formation of the
clathrating. The decomposition temperatures of M–pp–Ni–An
(M = Ni, Co and Cd) clathrates are given in Table 5. Similar decom-
position stages have been observed for other Hofmann type com-
plexes [7,23] and clathrates [24–25].
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4. Conclusion
The vibrational spectroscopic study of three new Hofmann type
aniline clathrates has shown that they have similar structures con-
sisting of infinite two-dimensional polymeric layers formed with
Ni(CN)4 ions bridged by M(pp)2 (M = Ni, Co and Cd) cations and
pp molecules in clathrates have been coordinated as a unidentate
ligand coordinating only through the NH nitrogen. Furthermore,
weak hydrogen bonding between NH2 of aniline and
p-cloud of
pp of the host lattice has been observed. In conclusion, the com-
pounds presented in this study are further examples of the
Hofmann type aniline clathrates.
[25] A. Sopkova, J. Bubanec, J. Thermal Anal. 12 (1977) 97.