Z Kartal

Ş Şentürk

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FT-IR Spectroscopic Study of M(Benzoic Acid)2Ni(CN)4 Complexes
(M = Ni, Cd, Co and Mn)
Z. Kartal and Ş. Şentürk
Physics Department, Faculty of Arts and Sciences, Dumlupınar University, Kütahya, Turkey
Reprint requests to Dr. Z. K; E-mail: zkartal@dumlupinar.edu.tr
Z. Naturforsch. 60a, 285 – 288 (2005); received January 14, 2005
Complexes of M(benzoic acid)2Ni(CN)4 (M = Ni, Cd, Co and Mn) are obtained for the first time.
The observed spectra indicate that the obtained complexes are new examples of Hofmann-type com-
plexes. — PACS NO: 33.20.Ea, 33.20.Tp
Key words: Benzoic Acid; Infrared Spectroscopy; Tetracyanonickelate;
Hofmann-type Compounds.
1. Introduction
Many Hofmann-type complexes with the gen-
eral formula ML2Ni(CN)4 were produced by using
N-donor ligand molecules such as ammonia [1],
pyridine [2], and products of pyridine [3, 4]; O-donor
ligand molecules such as water [5], dioxane [6],
dimethylsulfoxide [7], urea [8], pyridine-1-oxide
[9], and dimethylformamide [10]; S-donor ligand
molecules such as 1,3-thiazolidin-2-thion [11] and
dimethylthioformamide [12]. In the above formula,
M is a transition metal atom having the valence
+2, and L is either a bidentate or two monodentate
molecules. In the present study we used for the first
time benzoic acid (BA) as a ligand to produce new
Hofmann-type complexes with the general formula
M(BA)2Ni(CN)4 (M = Ni, Cd, Co and Mn). These
Fig. 1. The molecular structure of
the benzoic acid monomer.
0932–0784 / 05 / 0400–0285 $ 06.00 c© 2005 Verlag der Zeitschrift für Naturforschung, Tübingen · http://znaturforsch.com
complexes were investigated in the infrared range of
4000 – 400 cm−1.
The BA molecule contains carboxyl groups, namely
carbonyl and hydroxyl [13]. Each group (carbonyl and
hydroxyl) contains an oxygen atom, which can donate
electrons. BA has monomer and dimmer shapes [14].
The molecular structure of the monomer is shown in
Figure 1.
The electron density of the BA monomer was cal-
culated at the restricted Hartree-Fock level using the
PM3 method in the MOPAC 97 program package. The
calculations indicate that the oxygen atom 9 has a
higher electron density than the oxygen atom 8 and
the hydrogen atom 15. Hence we expect that the bind-
ing happens with the oxygen atom 9. There are vari-
ous infrared spectroscopy studies reported for the BA
molecule [14 – 19].
286 Z. Kartal and Ş. Şentürk · FT-IR Spectroscopic Study of M(Benzoic Acid)2Ni(CN)4 Complexes
Fig. 2. The infrared spectrum of Ni(BA)2Ni(CN)4.
2. Experimental
In this study all chemicals, namely BA (C7H6O2;
Fluka, ≥ 99.5%), NiCl2 ·6H2O, (Fluka, 98%), CdCl2 ·
2H2O, (Fluka, 96%), CoCl2 · 6H2O, (Fluka, 99%),
MnCl2 · 4H2O, (Fluka, 99%), and KCN (Fluka, 98%),
were used without further purification. First, 1 mmol
K2Ni(CN)4 was solved in distillated water, and then
2 mmol BA were solved in distillated water. After that,
the second solution was added to the first under stir-
ring. Then 1 mmol of MCl2 (M = Ni, Cd, Co and
Mn), solved in distillated water, was added to the mix-
ture, which was stirred for 5 d. The compounds ob-
tained were filtered, washed with pure water, ethanol
and ether, and kept in a desiccator containing P2O5.
Infrared spectra of these compounds were recorded
at room temperature with a Perkin-Elmer BX FT-IR
Spectrometer having a resolution of 4 cm−1.
The freshly prepared samples were analyzed
(CHNS-932, LECO) to determine the amount of C,
H, and N with the following results (found% / calcu-
lated %):
• Ni(BA)2Ni(CN)4: C = 46.40/46.42, H =
02.59/02.60, N = 12.02/12.03,
• Cd(BA)2Ni(CN)4: C = 41.63/41.62, H =
02.31/02.33, N = 10.78/10.79,
• Co(BA)2Ni(CN)4: C = 46.37/46.40, H =
02.59/02.60, N = 12.01/12.02,
• Mn(BA)2Ni(CN)4: C = 46.77/46.80, H = 02.61/
02.62, N = 12.12/12.13.
3. Results and Discussion
The IR spectrum of the Ni(BA)2Ni(CN)4 complex
is shown in Fig. 2 as an example. The assignments
were made by treating the ligand BA molecules and
the [Ni(CN)4]2− ion as isolated units to determine the
shifts for each one. The results obtained from the IR
spectral data can be analyzed for a) vibrating ligand
molecules, b) [Ni(CN)4]2− ion units.
3.1. Ligand Vibrations
The BA monomer have a planar structure and be-
longs to the Cs point group. It has 39 normal vi-
Z. Kartal and Ş. Şentürk · FT-IR Spectroscopic Study of M(Benzoic Acid)2Ni(CN)4 Complexes 287
Assignment [14] BA Ni-(BA)-Ni Cd-(BA)-Ni Co-(BA)-Ni Mn-(BA)-Ni
OH str (100) 3341 s 3260 m 3298 s 3268 s 3288 m
C4H str (96) 2975 s 2970 sh 2968 sh 2972 sh 2965 sh
C3H str (49), C5H str (49) 2930 w 2920 w 2926 w 2925 w 2925 w
C3H str (48), C5H str (48) 2888 m 2856 s 2856 s 2856 s 2856 s
C=O str (68) 1700 s 1630 m 1633 s 1630 s 1621 s
Ring str (71) 1605 w 1600 w 1600 w
Ring str (77) 1585 w 1580 w 1582 w 1586 w 1583 w
C4H bend (35), ring str (27) 1453 m 1461 s 1461 m 1460 m 1461 m
CH bend (25), C-COOH str (20) 1381 m 1377 m 1377 m 1377 w 1379 w
Ring str (88) 1273 m 1220 w 1217 w 1218 w
CH bend (67), OH bend (19) 1177 w 1156 w 1164 w 1170 w 1180 vw
C-O str (29), ring bend (15), 1091 s 1086 w 1092 w 1094 w 1090 w
OH bend (13)
CH oop (74), ring oop (22) 1050 s 1054 w 1060 w 1042 w 1046 w
CH oop (54), ring oop (35) 882 s 864 m 874 w 859 m 870 sh
CH oop (92) 715 m 725 m 720 m 723 m 724 m
Ring bend (49),C-O bend (27) 655 w 620 w 609 w 686 w 660 sh
C=O oop (59), ring oop (30), 434 m 488 w 475 w 485 m 474 w
Ring bend (30)
Table 1. IR vibrational wave-
numbers (cm−1) of the solid
BA and BA in the M-(BA)-Ni
complexes.
str, stretching; bend, bending; oop,
out-of-plane; s, strong; m, medium;
w, weak; vw, very weak; sh, shoul-
der. Potential energy distributions
(%) are given in brackets.
brations, namely 27 A′ (planar) and 12 A′′ (out-of-
plane). These vibrations are IR active [14]. The as-
signments and the wavenumbers of the IR bands of
the BA molecule observed in the IR spectra of the
M(BA)2Ni(CN)4 complexes are given in Table 1, to-
gether with the wavenumbers of solid phase BA.
The observed small frequency shifts are due to
changes of the environment of the BA molecule and
the pairing of the internal vibration of the BA molecule
with the vibrations of the M-O band. Small frequency
shifts were reported in other studies [2, 20]. Notice-
able frequency shifts were observed as stretched fre-
quencies of C=O and OH. For the solid BA molecule
the frequencies of C=O at 1700 cm−1 are shifted to
lower frequencies by around 67 – 79 cm−1. This shift
shows that the BA molecule is directly connected to
the metal through the oxygen of the carbonyl group.
The frequencies of OH at 3341 cm−1 for the solid BA
molecule are shifted to lower frequencies by around
43 – 81 cm−1 for the obtained complexes. This shift
indicates that the C=O bond becomes weak due to the
interaction of the oxygen atom in the carbonyl group
with the metal atom of [M-Ni(CN)4]. As a result, the
carbon atom extracts the electrons of the OH group.
Frequency shifts to higher frequencies were also ob-
served for the complexes. For example, the C=O (out-
of-plane) frequencies shifted by around 40 – 54 cm−1.
This is because the bonding of the (CO-M) makes dif-
ficult the out-of-plane bending motion for the C=O.
Similar shifts were observed in Şenyel’s study [10]. We
think that the observed peaks at 3613 and 3502 cm−1
result from water molecules in the complexes.
3.2. [Ni(CN)4]−2 Vibrations
If a unit cell has the symmetry D4h, then seven nor-
mal modes are expected to be in a vibration spec-
trum. Four of them must be active in the IR spec-
trum, and the remaining in the Raman spectrum. The
IR active vibrational modes are Euδ (CN), Euυ(Ni-
CN), A2uπ(Ni-CN) and Euδ (Ni-CN). Since we ob-
served these four bands in the infrared spectrum, our
complexes have a square planar environment. The fre-
quencies of the [Ni(CN4]2− group vibrations in com-
plexes are assigned on the basis of the work of Mc-
Cullough [21], who presented vibrational data for the
ion [Ni(CN)4]2− in Na2Ni(CN)4. The vibrational wave
numbers of [Ni(CN)4]2− in our complexes are given in
Table 2, together with McCullough’s data and the data
for complexes of Co(1-PT)-Ni-Bz [22] for comparison.
As the stretched vibrations of the CN group of
K2Ni(CN)4 were observed in the 2122 cm−1 region,
the band υ(CN) for the complex of M-(BA)-Ni shifted
to the high frequency range by around 33 – 44 cm −1.
The same shift also appeared in the plane bending
δ (Ni-CN) for the complexes around 2 – 13 cm−1. The
shifts show that both bands are connected to the
metal.
The stretch of υ(Ni-CN) was observed at 560 cm−1
for the Ni-(BA)-Ni complex, at 558 cm−1 for the Cd-
(BA)-Ni complex and at 561 cm−1 for the Mn-(BA)-Ni
complex.
The characteristic υ(CN) and δ (Ni-CN) frequen-
cies observed are similar to the Hofmann-type com-
plexes, indicating that the |M-Ni(CN)4|∞ layers were
288 Z. Kartal and Ş. Şentürk · FT-IR Spectroscopic Study of M(Benzoic Acid)2Ni(CN)4 Complexes
Table 2. IR vibrational wavenumbers (cm−1) of the [Ni(CN)4]2− group in the M-(BA)-Ni complexes.
Assignment [21] Na2Ni(CN)4 [21] Co-(1-PT)-Ni [22] Ni-(BA)-Ni Cd-(BA)-Ni Co-(BA)-Ni Mn-(BA)-Ni
υ(CN) 2132 2136 2166 s 2157 s 2161 s 2155 s
Hot band 2128 2127 sh 2115 sh 2120 w 2116 sh
υ(Ni-CN) 543 554 w 560 w 558 w 561 m
π (Ni-CN) 448 477 m 488 w 475 w 485 w 479 vw
δ (Ni-CN) 433 433 w 446 m 431 s 442 s 438 s
s, strong; m, medium; w, weak; vw, very weak; sh, shoulder; ν , stretching; π, out-of-plane bending; δ , in-plane-bending.
preserved [23]. These polymeric layers are hold in par-
allel by Van der Waals interactions between the BA.
The α type cavity occurs in these complexes. The cav-
ities have a volume depending on the type of the tran-
sition metal. The BA molecules are located below and
above the plane. The nickel atoms are surrounded by
four carbon atoms of the cyanide groups, and the metal
atoms M are also surrounded by four nitrogen atoms of
the cyanide groups, and at the same time two oxygen
atoms of the carbonyl groups of the BA molecules are
bonded to the metal atoms in the regular square plane.
As a conclusion, the compounds M(benzoic acid) 2
Ni(CN)4 (M = Ni, Cd, Co and Mn) are new examples
of Hofmann-type complexes.
Acknowledgements
The authors thank Dr. Halil Berber from the Chem-
istry Department of Anadolu University, Eskişehir,
Turkey for performing the theoretical calculations and
Prof. Dr. Cemil Öğretir from the Chemistry Depart-
ment of Osmangazi University, Eskişehir, Turkey for
the MOPAC 97 program.
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FT-IR Spectroscopic Study of M(Benzoic Acid) 2 Ni(CN) 4 Complexes (M = Ni, Cd, Co and Mn)

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FT-IR Spectroscopic Study of M(Benzoic Acid) 2 Ni(CN) 4 Complexes (M = Ni, Cd, Co and Mn)

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