FT-IR spectroscopic investigation of some Hofmann type complexes: M(1-phenylpiperazine)2Ni(CN)4 (M = Ni, Co, Cd, Pd or Mn)

Article abstract of DOI:10.1016/j.saa.2007.10.024

New Hofmann type complexes in the form of M(pp)₂Ni(CN)₄ (where pp = 1-phenylpiperazine and M = Ni, Co, Cd, Pd or Mn) 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.saa.2007.10.024

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Spectrochimica Acta Part A 70 (2008) 367–375
FT-IR spectroscopic investigation of some Hofmann type complexes:
M(1-phenylpiperazine)2Ni(CN)4 (M = Ni, Co, Cd, Pd or Mn)
a,b
Mustafa S¸enyela, Cemal Parlaka,b,∗, Ozgur Alver
¨
¨
a Department of Physics, Science Faculty, Anadolu University, 26470 Eskis¸ehir, Turkey
b Plant, Drug and Scientific Research Centre, Anadolu University, 26470 Eskis¸ehir, Turkey
Received 2 February 2007; received in revised form 19 October 2007; accepted 21 October 2007
Abstract
New Hofmann type complexes in the form of M(pp)2Ni(CN)4 (where pp = 1-phenylpiperazine and M = Ni, Co, Cd, Pd or Mn) have been prepared
in powder form and their infrared spectra have been reported in the range of (4000–400) cm−1. The thermal behaviours of these complexes have
been investigated by differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA). Ni(pp)2Ni(CN)4 complex has been examined via
transmission electron microscope (TEM). 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|∞ with the pp molecule bounded to the metal atom (M).
© 2007 Elsevier B.V. All rights reserved.
PACS: 33.20.Ea; 33.20.Tp; 82.75−z
Keywords: Hofmann type complexes; 1-Phenylpiperazine; IR spectra; TGA; DTA; TEM
1. Introduction
Cd, Pd or Mn, for the first time and spectral properties of
these compounds have been investigated in the IR region of
(4000–400) cm−1. We have studied the thermal behaviour of
these complexes with DTA and TGA techniques. In addition to
that we have taken TEM image of M Ni complex.
Hofmann type host structures are defined with the general
formula of M(L)2Ni(CN)4 [1,2]. In this host structure, the L cor-
responds to a bidentate or a pair of unidentate ligand molecules
and the M is for a divalent transition metal. Based on this
structure, metal(II) tetracyanonickelate complexes have been
developed using N-donor ligands such as ammonia [3], pyri-
dine [4]; O-donor ligands such as water [5], dimethylformamide
[6], dioxane [7] and S-donor ligands as dimethylthioformamide
[8]. The Hofmann type host framework is formed from infi-
nite |M–Ni(CN)4|∞ layers with four planar coordination around
Ni atom. This structure provides ␣-type cavity similar to rect-
angular box for the guest molecules [9,10]. The model of the
Hofmann type host structure is schematically illustrated in Fig. 1
[11,12].
2. Experimental
All the chemicals used were reagent grade (Aldrich) and they
were used without further purification. The complexes M–pp–Ni
(M = Ni, Co, Cd, Pd or Mn) were prepared as following: at
first step 1 mmol of MCl2 was dissolved in the distilled water,
then to this solution 1 mmol of K2Ni(CN)4 dissolved in the dis-
tilled water was added under stirring. After a short time slightly
more than 2 mmol of the liquid pp were added to the mix-
ture prepared drop wise, again under stirring. The final mixture
was left for stirring around a week at room temperature. The
obtained product was filtered and washed with water, ethanol
and ether successively and dried in a desiccator which included
P2O5.
In this work, we have prepared M(pp)2Ni(CN)4 com-
plexes (abbreviated hereafter as M–pp–Ni), where M = Ni, Co,
Infrared spectra of the complexes as nujol and hexachloro-
1,3-butadiene were recorded in the region of (4000–400) cm−1
via Perkin-Elmer FT-IR 2000 spectrometer at a resolution
of 4 cm−1. In the MIR region of spectrum, bands of nujol
∗
Corresponding author at: Plant, Drug and Scientific Research Centre,
Anadolu University, 26470 Eskis¸ehir, Turkey. Tel.: +90 222 335 0580;
fax: +90 222 320 4910.
E-mail address: cparlak@anadolu.edu.tr (C. Parlak).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.10.024

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M. S¸enyel et al. / Spectrochimica Acta Part A 70 (2008) 367–375
and hexachloro-1,3-butadiene were reported at 1377 cm−1
,
,
,
1461 cm−1, 2858 cm−1, 2925 cm−1 and 655 cm−1, 793 cm−1
852 cm−1, 941 cm−1, 981 cm−1, 1170 cm−1, 1564 cm−1
1610 cm−1, 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 analyser. Ni, Co, Cd, Pd
and Mn metals were investigated at 231.604 nm, 228.616 nm,
228.802 nm, 340.458 nm and 257.61 nm, respectively. TGA and
DTA curves of the complexes were recorded using a Setaram
Labsys TG/DTA with ca. 6.0 mg of sample and a scanning rate
of 5 ◦ min−1 under argon between about 20–200 ◦C. TEM image
of M Ni complex was taken with a G2 Spirit BioTwin (FEI
Company Tecnai) transmission electron microscope by using
an accelerating voltage of 120 kV and 11 Mega pixel Morada
Camera.
Fig. 1. The model for the Hofmann type host structure (open circle: 6-coordinate
M, solid circle: square planar Ni, open column: an ambident ligand, thick line:
CN bridge and thin line: edge of cavity).
Fig. 2. Infrared spectra of the Ni(pp)2Ni(CN)4 complex in nujol (a) and hexachloro-1,3-butadiene (b).

M. S¸enyel et al. / Spectrochimica Acta Part A 70 (2008) 367–375
369
3. Results and discussions
(C4H10N2). This molecule has been used as a ligand in various
complexes [13–16]. The free pp exists in a chair conformation
because of the steric crowding present in the boat form [14].
However, this molecule can also coordinate in the boat form as
a bidentate ligand [15], in the chair form as a bidentate ligand
[16] or as a unidentate ligand coordinating only through the NH
nitrogen [14]. In our previous study, we reported the vibrational
assignmentsandthefrequenciesofthefreeppmoleculeboththe-
oretically and experimentally in the region of (4000–400) cm−1
[17]. The assignments and the frequencies of the fundamental
bands observed in the infrared spectra of the compounds under
study have been given in Table 1, together with our previous
data, for comparison.
The infrared spectra obtained for the M–pp–Ni (M = Ni, Co,
Cd, Pd or Mn) complexes are compatible with each other. This
indicates that the compounds have similar spectral features. The
spectra of the M–pp–Ni (M = Ni, Co, Cd, Pd or Mn) compound
are given in Figs. 2–6. The spectral analysis of each compound
have been performed by taking into account the pp molecule
and Ni(CN)4 ions individually. The spectral interpretations have
been started with pp vibrations.
3.1. pp vibrations
The spectral data for pp in the complexes exhibit character-
istics of a coordinated ligand (Table 1). On coordination, the
The free pp consists of high basic strength and a bulky phenyl
group ( C6H5) attached to one of the nitrogen of piperazine
Fig. 3. Infrared spectra of the Co(pp)2Ni(CN)4 complex in nujol (a) and hexachloro-1,3-butadiene (b).

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M. S¸enyel et al. / Spectrochimica Acta Part A 70 (2008) 367–375
Fig. 4. Infrared spectra of the Cd(pp)2Ni(CN)4 complex in nujol (a) and hexachloro-1,3-butadiene (b).
NH and CH2 stretching frequencies attributed to piperazine
molecule within the pp ligand should decrease and increase
due to the consecutive inductive effects, respectively (on coor-
dination, NH and NC bonds should become weaker and CH
bonds should become stronger) [18]. It is clearly observed
in Table 1 that these requirements are fulfilled for pp in our
compounds. The observed shifts of the vibrational frequen-
cies are consistent with the Hofmann-Td-type complexes and
clathrates of piperazine molecule reported [19]. These shifts
in frequencies have been explained in terms of coupling of
the internal vibration of pp molecule with M–N vibrations
[6,8,11,12,20–25]. It is noted that the general shifting in fre-
quency of the pp modes with different metals in the complexes
or clathrates studied is in the order: Pd > Ni > Co > Cd > Mn,
which is in agreement with the increasing order of the sec-
ond ionization potential of these metals [26]. Another strong
CN stretching frequency attributed to phenyl attached to one
of the nitrogen of piperazine has not shifted in the compounds.
Regarding the phenyl molecule within the pp ligand, the vibra-
tional bands of the molecule possess small shifts. This presents
that the molecule causes environmental changes on the com-
plexion.
From the comparison of the spectral data presented in Table 1,
we have concluded that the pp molecules in our compounds have
been coordinated in the chair form as a unidentate ligand coor-
dinating only through the NH nitrogen. Unidentate coordination
of the pp ligand has been also supported by the shifts in the posi-
tion of the NH deformation mode from the free ligand value of

M. S¸enyel et al. / Spectrochimica Acta Part A 70 (2008) 367–375
371
Fig. 5. Infrared spectra of the Pd(pp)2Ni(CN)4 complex in nujol (a) and hexachloro-1,3-butadiene (b).
1670–1600 cm−1 andnoshiftinthepositionoftheCNstretching
[14].
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 Hof-
mann type complexes [6,8,20–23] or clathrates [11–12,24–25]
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, Cd, Pd or Mn) in the host compounds investigated.
In this work, we have discussed infrared spectroscopic prop-
erties of the prepared complexes up till now. Furthermore, in
order to support the conclusions obtained in the infrared stud-
ies, we have conducted the elemental and TGA–DTA analyses
of these complexes. We have also presented the TEM image of
M Ni complex to see the host structure and the cavities.
3.2. Ni(CN)4 group vibrations
Assignments of the bands for the Ni(CN)4 ion in the spec-
tra of the present compounds have been carried out by means
of vibrational data of the Ni(CN)4 ion in Na2Ni(CN)4 reported
by McCullough et al. [27]. Since the ion is not coordinated to
cations [27], it can be treated as an isolated unit. Therefore, we
have used it as a reference for finding out whether coordina-
tion to the metals M is taking place. The spectral data for the
Ni(CN)4 groups in our complexes are given in Table 2 along
with McCullough et al’s data.

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M. S¸enyel et al. / Spectrochimica Acta Part A 70 (2008) 367–375
Fig. 6. Infrared spectra of the Mn(pp)2Ni(CN)4 complex in nujol (a) and hexachloro-1,3-butadiene (b).
We have calculated the percentage amount of C, H, N, Ni
all of them gradually lose two ligand molecules in a single
step between about 40 ◦C and 140 ◦C. DTA curves show two
endothermictransitionsforpresentcompounds. Thefirstdecom-
position stage about 100 ◦C indicates that the pp ligand molecule
leaves the host structure. The second decomposition stage about
160 ◦C is decomposition of cyanide to yield the respective met-
als. The decomposition temperatures of M–pp–Ni (M = Ni, Co,
Cd, Pd and Mn) complexes are given in Table 4. Such decom-
position stages have been observed for other Hofmann type
complexes [28] and clathrates [29].
and M in our complexes with the help of molecular weight
of those compounds. The calculated values have been com-
pared with the experimental data and the results have been
given in Table 3. According to these results, the calculated val-
ues are in compliance with the experimental findings. In order
to compare the experimental values, the correlation graphic
based on the calculations has been presented in Fig. 7. The
correlation values for C, H, N, Ni and M results are found to
be 0.99974, 0.99877, 0.99882, 0.99998 and 0.99992, respec-
tively.
TEM image of Ni(pp)2Ni(CN)4 complex is given in Fig. 9. In
the apparent figure, the 10 ␮m of the captured image is enlarged
by a factor of 220,000. While dark regions in Fig. 9 correspond to
the host structure, the gray ones are the base of 300 mesh formuar
The TGA and DTA curves of the Cd–pp–Ni compound are
given in Fig. 8 as an example. The TGA results indicate that
samples are stable at room temperature. By heating, however,

M. S¸enyel et al. / Spectrochimica Acta Part A 70 (2008) 367–375
373
Table 1
The vibrational frequencies (cm−1) of pp in the M–pp–Ni (M = Ni, Co, Cd, Pd or Mn) compounds
Moda
Assignmenta
ppa
Ni–pp–Ni
Co–pp–Ni
Cd–pp–Ni
Pd–pp–Ni
Mn–pp–Ni
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯
␯(NH)
␯(CH)
␯(CH)
␯(CH)
␯(CH)
␯(CH2)
␯(CH2)
␯(CH2)
(NH)def.
␯(CC)
3278 sb
3091 m
3059 m
3036 m
3023 m
2944 s
2881 w
2824 vs
1670 w
1600 vs
1579 m
1498 vs
1452 s
1407 sh
1380 s
1325 s
1235 vs
1190 m
1146 s
1081 m
1059 s
1032 s
992 s
3256 s
3255 s
3254 s
3257 s
3251 s
1
3092 m
3069 wb
3033 wb
3019 mb
2957 sb
2894 w b
2827 sb
1640 w
1603 vs
1574 m
1502 vs
1453 sb
1423 wb
1380 sb
1337 s
3092 m
3068 wb
3032 shb
3018 mb
2956 sb
2897 w b
2825 sb
1638 vw
1603 vs
1573 m
1502 vs
1452 sb
1422 wb
1380 sb
1337 m
1254 vs
1178 m
1158 m
1111 s
3093 mb
3067 wb
3031 wb
3013 mb
2953 s
3091 m
3069 wb
–
3092 mb
3066 shb
3032 mb
3019 mb
2952 sb
2894 mb
2825 sb
1645 w
1601 vs
1574 m
1501 vs
1452 vsb
1423 wb
1380 sb
1336 m
1253 vs
1178 m
1153 m
1110 m
1040 m
1023 m
1005 s, 989 m
922 vs
5
7
8
3021 mb
2957 vsb
2894 wb
2829 vsb
1640 w
1602 vs
1577 m
1499 vs
1453 vsb
1421 shb
1380 sb
1337 s
9
11
13
14
15
17
18
21
22
24
26
29
32
33
36
38
39
41
43
46
50
53
54
55
57
59
60
63
64
2896 wb
2827 sb
1641 w
1601 vs
1573 m
1502 vs
1452 sb
1424 mb
1380 sb
1336 m
1254 vs
1182 m
1153 m
1111 s
␯
␯
ring
ring
␦s(CH2)
w(CH2)
␯(CN)
␯
ring + t(CH2)
␦(CH) + t(CH2)
␦(CH)
␦(CH) + ␯16(au)
␦(CH) + ␳r(CH2)
1255 vs
1180 m
1159 m
1112 s
1255 vs
1178 m
1159 m
1112 s
1044 s
1025 s
1005 s, 990 s
923 vs
863 m
804 w
763 vs
732 w
692 vs
652 m
523 vs
487 m
Obs.c
␯
␯
1046 s
1043 s
1040 s
ring
ring
1024 m
1006 s, 990 m
923 vs
866 m
811 sh
762 vs
728 w
689 vs
652 m
1024 m
1001 s, 989 s
921 vs
865 m
808 vw
763 vs
727 w
690 s
650 m
521 s
1023 m
1000 m, 987 s
923 vs
868 m
805 vw
760 vs
726 w
688 s
647 m
517 s
Ring breathing
w(CH2)
␥(CH) + ␯
937 s
881 s
865 m
805 vw
760 vs
725 w
689 s
639 m
520 s
486 m
Obs.c
ring
–
800 mb
758 vs
735 sh
693 vs
625 s
517 vs
485 w
437 m
(CH)def.
␥(CH)
␥
ring
␦
␦
ring + ring band
521 s
487 m
Obs.c
ring
␳r(NH)
487 m
Obs.c
484 m
Obs.c
␦
ring
The initials are for vs: very strong, s: strong, m: medium, w: weak, vw: very weak, b: broad, sh: shoulder.
a
Taken from reference [17].
In hexachloro-1,3-butadiene.
Obs., obscure.
b
c
Table 2
The vibrational frequencies (cm−1) of the Ni(CN)4 group in the M–pp–Ni (M = Ni, Co, Cd, Pd or Mn) compounds
Assignmenta
Na2Ni(CN)4
Ni–pp–Ni
Co–pp–Ni
Cd–pp–Ni
Pd–pp–Ni
Mn–pp–Ni
a
␯8(CN), Eu
␯9(NiC), Eu
␲(NiC), A2u
␦(NiCN), Eu
2132
543
448
433
2166 vs
562 m
–
2159 vs
558 m
–
2147 vs
557 w
–
2169 vs
563 w
–
2144 vs
557 w
–
440 vs
436 vs
424 vs
441 vs
436 vs
a
Taken from Ref. [26]. vs: very strong, m: medium, w: weak.
Table 3
Elemental analysis and colours of the M–pp–Ni (M = Ni, Co, Cd, Pd or Mn) compounds
Empirical formula of sample (formula weight)
Colour
Elemental analysis, found/(calculated) (%)
C
H
N
Ni
M
Ni(C10H14N2)2Ni(CN)4 (545,91984)
Co(C10H14N2)2Ni(CN)4 (546,15964)
Cd(C10H14N2)2Ni(CN)4 (599,63744)
Pd(C10H14N2)2Ni(CN)4 (593,64644)
Mn(C10H14N2)2Ni(CN)4 (542,16449)
Violet
Pink
White
Violet
Brown
52.39 (52.80)
52.29 (52.78)
47.74 (48.07)
48.18 (48.56)
52.65 (53.17)
5.02 (5.17)
5.01 (5.17)
4.59 (4.71)
4.64 (4.75)
5.03 (5.20)
19.98 (20.53)
19.91 (20.51)
18.33 (18.69)
18.48 (18.87)
20.02 (20.67)
21.16 (21.50)
10.54 (10.75)
9.55 (9.79)
9.71 (9.89)
10.62 (10.83)
–
10.58 (10.79)
18.51 (18.74)
17.61 (17.93)
9.93 (10.13)

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M. S¸enyel et al. / Spectrochimica Acta Part A 70 (2008) 367–375
Fig. 8. TGA and DSC curves of the Cd(pp)2Ni(CN)4 complex.
Table 4
The decomposition temperatures (◦C) of M–pp–Ni (M = Ni, Co, Cd, Pd and Mn)
compounds
Sample
Decomposition
First
Second
Ni(C10H14N2)2Ni(CN)4
Co(C10H14N2)2Ni(CN)4
Cd(C10H14N2)2Ni(CN)4
Pd(C10H14N2)2Ni(CN)4
Mn(C10H14N2)2Ni(CN)4
102.81
101.54
103.19
102.23
100.72
160.41
160.33
163.72
159.11
159.27
Fig. 9. TEM image of Ni(pp)2Ni(CN)4 complex.
coated grids which represent the formation of the cavities for the
guest molecules in the host structure.
4. Conclusion
The IR spectroscopic studies of five new complexes have
shown that they have similar structures consisting of infinite
two-dimensional polymeric layers formed with Ni(CN)4 ions
Fig. 7. Plot of the calculated vs. the experimental C (a), H (b), N (c), Ni (d) and
M (e) percentage amounts in the complexes.

M. S¸enyel et al. / Spectrochimica Acta Part A 70 (2008) 367–375
375
bridged by M(pp)2 (M = Ni, Co, Cd, Pd and Mn) cations and
pp molecules in compounds have been coordinated in the chair
form as a unidentate ligand coordinating only through the NH
nitrogen. In conclusion, the compounds presented in this study
are further examples of the Hofmann type complexes.
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