Synthesis and spectral, thermal and structural characterization of a vitamin B13 complex of nickel(II) with 2-aminothiazole, mer-[Ni(HOr)(H 2O)2(ata)2]

Article abstract of DOI:10.1515/znb-2007-0610

Themer-bis(2-aminothiazole)diaqua-orotato-nickel(II) complex, mer-[Ni(HOr)(H₂O)₂(ata)₂] (1), was synthesized and characterized by spectral (IR and UV/vis) and thermal studies. In addition, the crystal structure of the complex was determined by single crystal X-ray diffraction. The complex crystallizes in the triclinic system, space group Pl. The orotate ligand is coordinated to the nickel(II) atom through a nitrogen atom of the pyrimidine ring and an oxygen atom of the carboxylate group as a bidentate dianion. The coordination of the Ni(II) ion is extended to six by the two 2-aminothiazoles (ata) and two water molecules. The thermal decomposition has been studied in a static air atmosphere.

Full text of DOI:10.1515/znb-2007-0610

Synthesis and Spectral, Thermal and Structural Characterization of a
Vitamin B13 Complex of Nickel(II) with 2-Aminothiazole,
mer-[Ni(HOr)(H2O)2(ata)2]
Okan Zafer Yes¸ilela, Kamber Akdag˘b, Hu¨meyra Pas¸aog˘lub, and Orhan Bu¨yu¨kgu¨ngo¨rb
a Department of Chemistry, Faculty of Arts and Sciences, Eskis¸ehir Osmangazi University,
26480 Eskis¸ehir, Turkey
b Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University,
55139, Kurupelit-Samsun, Turkey
Reprint requests to Dr. O. Z. Yes¸ilel. Fax: +90 222 2393578. E-mail: yesilel@ogu.edu.tr
Z. Naturforsch. 2007, 62b, 818 – 822; received January 2, 2007
The mer-bis(2-aminothiazole)diaqua-orotato-nickel(II) complex, mer-[Ni(HOr)(H2O)2(ata)2] (1),
was synthesized and characterized by spectral (IR and UV/vis) and thermal studies. In addition, the
crystal structure of the complex was determined by single crystal X-ray diffraction. The complex
¯
crystallizes in the triclinic system, space group P1. The orotate ligand is coordinated to the nickel(II)
atom through a nitrogen atom of the pyrimidine ring and an oxygen atom of the carboxylate group as
a bidentate dianion. The coordination of the Ni(II) ion is extended to six by the two 2-aminothiazoles
(ata) and two water molecules. The thermal decomposition has been studied in a static air atmosphere.
Key words: Orotato Complex, Vitamin B13 Complex, 2-Aminothiazole
Introduction
O
C
OH
Aminothiazoles are a group of biologically impor-
tant compounds having a wide range of activities
such as anti-tumor, anti-anoxic and anti-oxidant prop-
erties [1, 2]. Previous reports have shown that amino-
thiazoles possess anti-oxidant activity and inhibit lipid
peroxidation [2, 3]. 2-Aminothiazoles [Scheme 1. (a)]
are known mainly as biologically active compounds
with a broad range of activities and as intermediates
in the synthesis of antibiotics, well known sulfa drugs,
and some dyes [4]. Metal complexes of vitamin B13
[orotic acid, uracil-4-carboxylic acid, 1,2,3,6-tetra-
hydro-2,6-dioxo-4-pyrimidine carboxylic acid, H3Or,
Scheme 1. (b)] and its derivatives continue to attract at-
tention because of their multidentate functionality and
their pivotal role in bioinorganic chemistry [5]. Orotic
acid is a precursor in the biosynthesis of pyrimidine
bases and nucleic acids in living organisms [6] and
has been widely exploited in medicine. Besides its
biological importance, vitamin B13 is also an inter-
esting potentially multidentate ligand. It can be co-
ordinated to metal ions through the nitrogen atoms,
the two carbonyl oxygen and the carboxylate oxy-
gen atoms as a monodentate, bidentate and polyden-
tate donor. The most common coordination mode of
(4)
(3)
H
(5)
(6)
NH2
N
(2)
S
N
O
N(1)
H
O
(a)
(b)
Scheme 1. (a) Orotic acid, H3Or, (b) 2-aminothiazole, ata.
HOr2− is ligation through the deprotonated nitrogen
atom of the pyrimidine and one carboxylate oxygen
atom so forming a five-membered chelate ring. Crys-
tal structures were described for mononuclear Ni(II)-
orotate complexes with triethanolamine [7], 4-meth-
ylimidazole [8], imidazole [9], nicotine amide [10],
water [11, 12], 2,2ꢀ-bipyridylamine, 1,10-phenanthrol-
ine, and 2,9-dimethyl-1-1,10-phenanthroline[13], with
the orotate ligands acting as bidentate donors. In poly-
meric [Ni(HOr)(H2O)3]n [13, 14] and [Ni(HOr)(NH3)-
(H2O)2]n [15] complexes, orotate acts as a bridging
ligand [orotato-N(3), Oacid, O(6) or O(2)]. In some of
the complexes, orotate acts as a counter ion [15 – 18].
Orotic acid exhibits a double or triple hydrogen-
bonding functionality, depending on the metal coor-
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O. Z. Yes¸ilel et al. · Vitamin B13 Complex of Nickel(II) with 2-Aminothiazole, mer-[Ni(HOr)(H2O)2(ata)2]
819
Table 1. IR spectral data of 1 (cm−1) and of orotic acid.
dination mode. The potential for molecular recogni-
tion of organic molecules may have interesting impli-
cations in both pharmaceutical and materials chem-
istry, where the orotate or hydrogenorotate anions
can be used as versatile synthons for the assembly
of metal-organic supramolecular architectures [19]. In
this study, we describe the synthesis, spectroscopic (IR
and UV/vis), thermal and structural characterization of
mer-[Ni(HOr)(H2O)2(ata)2] (1).
Assignment
ν(OH)
Orotic acid [22]
3241 sh
–
1a
3453 s
3350, 3292 s
3139 s
ν(NH2)
ν(N(3)H)
3154 m
3137 m
3099 s
ν(N(1)H)
ν(CH)
–
2937 w
1650 vs
1625 vs
1592 vs
1492, 1535 m
1209 m
ν(C=Oacid + C(2)=O)
ν(C(6)=O) + νring
ν(C=C) + νring
ν(C=N)
1729, 1719 vs
1700 vs
1653 vs
1435 s
ν(C=S)
–
a Abbreviations: w – weak; m – medium; s – strong; vs – very strong;
b – broad.
Results and Discussion
Magnetic susceptibility and UV/vis spectrum
the orotate ligand. The strong exothermic stage is as-
sociated with the burning of the organic residue. The fi-
nal decomposition product is NiO. The total mass loss
is 82.80% (calcd. 83.37%) for the 30 – 525 ◦C temper-
ature range.
The Ni(II) complex exhibits a magnetic moment
of 2.92 BM, which corresponds to two unpaired elec-
trons. The UV/vis spectrum of a solution in H2O ex-
hibits absorption bands at 394 (ε = 18 L mol−1 cm−1),
638 (ε = 5) and 895 nm (ε = 4), assigned to the 3A2g
→
3
3
3
3
3T1g (P), A2g → T1g and A2g → T2g d-d transi-
tions, respectively. The ∆o value for Ni(II) has been
calculated as 11170 cm−1 [21].
IR Spectrum
The most significant frequencies in the IR spec-
trum of 1 are given in Table 1. The spectrum shows
a strong band at 3453 cm−1 due to aqua ligands. The
bands at 3350 and 3292 cm−1 are attributed to the
NH2 stretching vibration of the ata ligands. The weak
band at 2937 cm−1 is due to νCH vibrations. The
carbonyl stretching bands of the free orotic acid ob-
Fig. 1. The AD:DA pairs present in the crystal structure of 1,
showing the intra- and some of the intermolecular hydrogen
bonding.
served at 1729 and 1719 cm−1 (νC=O(acid) + νC(2)=O
)
Crystal structure of 1
and 1700 cm−1 [νC(6)=O + νring] [22] are shifted
The details of the crystal structure are given in Ta-
ble 2. The molecular structure is shown in Fig. 1.
Selected bond distances and angles are given in
Table 3. The crystal structure consists of discrete
[Ni(HOr)(H2O)2(ata)2] molecules. The Ni(II) ion has
a distorted octahedral configuration with a bidentate
HOr2− ligand, two water and two ata ligands (Fig. 1).
The N and O atoms of the orotate anion are bonded to
the metal cation to form a five-membered chelate ring
to 1650 and 1625 cm−1 in the spectrum of 1. This shift
indicates that the orotate ligand is coordinated as a di-
anion through the nitrogen atom of the pyrimidine ring
and an oxygen atom of the carboxylate group. The in-
tense band at 1592 cm−1 corresponds to νCC vibrations
of the pyrimidine ring, while the ν(C=N) and ν(C−N) vi-
brations are observed at 1534 and 1280 cm−1, respec-
tively.
˚
[Ni(1)–N(1) = 2.055 (2) and Ni(1)–O(1) = 2.049(2) A].
All N–Ni–N, N–Ni–O and O–Ni–O bond angles devi-
Thermal analysis
The thermal decomposition of 1 was followed by ate significantly from 90 or 180◦, which is presumably
DTG up to 1000 ◦C◦in a static air atmosphere. The first a result of the steric constraints arising from the shape
stage at 147 – 200 C is related to the release of two of the ligands. The C–O distances are almost equal in
wate◦r ligands with an endothermic effect (DTGmax
=
the uncoordinated HOr2− anion and its Ni(II) and Li(I)
197 C, mass loss found 9.12 %, calcd. 8.03 %). The complexes [23]. In 1, the C–O bond lengths are in the
following stages at 201– 448 ◦C are related to the de- range 1.254(3)– 1.244(3) A, which is comparable with
˚
composition of the ata ligand and decarboxylation of those in similar Ni(II) complexes [8, 17].
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O. Z. Yes¸ilel et al. · Vitamin B13 Complex of Nickel(II) with 2-Aminothiazole, mer-[Ni(HOr)(H2O)2(ata)2]
◦
˚
Table 2. Crystal data and structure refinement parameters Table 3. Selected bond lengths (A) and angles ( ) in 1.
for 1.
Ni1–O2
Ni1–O3
N5–C11
N3–C8
N6–C11
N4–C8
S1–C11
S2–C8
2.107(2)
2.049(2)
1.307(4)
1.313(4)
1.339(4)
1.346(4)
1.735(3)
1.728(3)
Ni1–N1
Ni1–N5
S1–C10
S2–C7
C9–C10
C7–C6
N5–C9
N3–C6
2.055(2)
2.080(3)
1.719(4)
1.714(5)
1.332(5)
1.343(5)
1.385(4)
1.374(4)
Empirical formula
Formula weight [g mol−1
Crystal size [mm3]
Temperature [K]
Wavelength (MoKα ) [A]
Crystal system
Space group
C11H14N6O6S2Ni
449.11
]
0.220×0.157×0.070
293(2)
˚
0.71073
triclinic
¯
P1
Unit cell dimensions:
O3–Ni1–N3
N1–Ni1–N3
N5–Ni1–N3
O2–Ni1–N3
C11–N5–C9
C8–N3–C6
N3–C8–N4
N5–C11–N6
N4–C8–S2
92.03(9)
90.10(10)
87.57(10)
95.00(10)
110.4(3)
110.9(3)
125.1(3)
124.4(3)
121.2(2)
121.7(3)
89.45(17)
O3–Ni1–O1
N1–Ni1–O1
N5–Ni1–O1
O1–Ni1–O2
C9–C10–S1
C6–C7–S2
N3–C8–S2
N5–C11–S1
C10–C9–N5
C7–C6–N3
C7–S2–C8
83.89(9)
93.65(9)
88.67(10)
89.61(10)
110.0(3)
110.2(3)
113.7(2)
113.9(2)
116.3(3)
115.7(3)
89.54(17)
˚
a,b,c [A]
8.294(1), 8.710(1),12.060(1)
97.42(7), 99.00(1), 95.78(7)
846.8(1)
2
1.436
1.761
2.51–28.01
13465
3990
integration
R1 = 0.0469; wR2 = 0.1826
R1 (all data) = 0.9600
0.974
α,β,γ [◦]
3
˚
V [A ]
Z
Absorption coefficient [mm−1
]
Dcalc. [Mg m−3
]
θ range for data collection [deg]
Measured reflections
Independent reflections
N6–C11–S1
C10–S1–C11
Absorption correction
Final R indices [F2 ≥ 2σ(F2)]
Goodness-of-fit on F2
Table 5. Hydrogen bonding interactions in 1.
Larges−t d3ifference peak and hole
0.725 / −0.962
D–H···A
d(D–H)
(A)
0.86
0.86
0.86
0.86
0.92(2)
0.93(2)
0.93(2)
0.86
d(H···A)
d(D···A)
<(DHA)
(◦)
˚
[e A
]
˚
˚
˚
(A)
(A)
N2–H2···O6i
1.98
2.80
2.03
2.54
1.90(5)
1.79(2)
2.20(6)
2.18
2.55
2.58
2.826(3)
3.292(3)
2.861(3)
3.320(4)
2.682(3)
2.714(3)
2.953(4)
2.867(3)
3.090(4)
3.246(4)
2.633(3)
170.1
118.1
162.8
151.0
141(6)
173(6)
137(7)
136.1
121.3
135.6
153(5)
N4–H4A···S1ii
N4–H4B···O4iii
N6–H6B···N4ii
O1–H1A···O5iv
O1–H1B···O4v
O2–H2B···O5iv
N4–H4A···O3
N6–H6A···O1
N6–H6A···O3
O2–H2A···O6
0.86
0.86
0.93(2)
1.77(3)
Symmetry operations: i 2−x, 1−y, 1−z; ii 1−x, −y, 2−z; iii 2−x,
−y, 2−z; iv x−1, y, z; v 2−x, 1−y, 2−z.
ing HOr2− ligand of another Ni(II) complex. These
DA:AD type hydrogen bonds involve the pyrimidine
carbonyl and the amide N–H groups [N(2)···O(6)i
i
i
◦
˚
˚
2.826(3) A, H···O(6) 1.98 A, N(2)–H···O(6) 170.1 ;
i: 2−x, 1−y, 1−z]. Double hydrogen bonds are found
in nature in guanine tetrads (or G quartets) [24] which
are stabilized by a central sodium ion. Some of these
interactions are illustrated in Fig. 2. There are also hy-
drogen bonds between ata and aqua ligands.
Fig. 2. The hydrogen bonding interactions and the unit cell
packing of 1.
The orotato ligand is almost planar (the r.m.s de-
˚
viations are 0.0593 A). A comparison of the Ni–O1,
Ni–N3, M–Nata distances, and the O1–Ni–N3 and
Nata–M–Nata angles for the orotate and ata metal com-
plexes is given in Table 4.
The crystal is stabilized by strong intermolecular
H bonds N–H···O, O–H···O etc. The details of this
hydrogen bonding are given in Table 5. The orotate
ligand is involved in hydrogen bonds with neighbor-
ing orotate ligands and aqua ligands through its N
and O atoms. As shown in Figs. 1 and 2, each of the
Experimental Section
All chemicals were purchased as analytical grade. The
IR spectrum was obtained with a Bruker Tensor 27 FT-IR
spectrometer using KBr pellets in the 4000 – 400 cm−1
range. Elemental analyses for C, H and N were performed
using a Carlo Erba 1106 microanalyzer. The magnetic sus-
HOr2− ligands is doubly H-bonded to a correspond- ceptibility measurement was performed at r. t. using a Sher-
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O. Z. Yes¸ilel et al. · Vitamin B13 Complex of Nickel(II) with 2-Aminothiazole, mer-[Ni(HOr)(H2O)2(ata)2]
821
Table 4. Comparison of the bond lengths and angles of selected Ni-HOr complexes and [ZnCl2(ata)2].
˚
˚
˚
Complexes
Ni–O1 (A)
Ni–N3 (A)
O1–Ni–N3 (◦)
80.0(1)
M–Nata (A)/Nata–M–Nata (◦)
–
–
–
–
–
–
–
[Ni(HOr)(H2O)4]·H2O [20]
2.023(3)
2.064(2)
2.073(1)
2.078(2)/2.061(2)
2.064(1)
2.053(3)
2.08(1)
2.049(3)
2.056(2)
2.048(2)
2.084(2)/2.118(2)
2.072(2)
2.067(3)
2.08(1)
[Ni(HOr)(H2O)3]n [14]
79.41(7)
80.21(6)
79.66(6)/79.92(6)
80.12(5)
79.47(11)
78.7(5)
80.08(6)
–
83.89(9)
[Ni(HOr)(H2O)3(na)]·2H2O [10]
[Ni(HOr)(H2O)(4-mim)3]2 ·5H2O [8]
[Ni(HOr)(H2O)2(im)2] [9]
[Ni(HOr)(bipy)(H2O)2]·2H2O [11]
[Ni(HOr)(NH3)(H2O)2]n [19]
[Ni(HOr)(H2O)(tea)]·H2O [7]
[ZnCl2(ata)2] [29]
2.029(1)
–
2.100(2)
2.085(2)
–
2.108(2)
–
2.024(2), 2.011(2)/109.59(2)
2.080 (3), 2.108(3)/87.6(1)
[NiHOr(H2O)2(ata)2] (this work)
wood Scientific MXI model Gouy magnetic balance. The Crystallographic analysis
UV/vis spectrum was obtained for an aqueous solution of
Diffraction experiments were carried out at 296 K on a
Stoe IPDS diffractometer. The structure was solved by Di-
rect Methods using the program SHELXS-97 [25]. All non-
hydrogen atoms were refined anisotropically by full-matrix
least-squares methods with SHELXL-97 [25]. All hydro-
gen atoms except H1A, H1B, H2A and H2B were located.
Data collection: X-Area; cell refinement: X-Area; data re-
duction: X-RED [26]; molecular graphics: ORTEP-3 for Win-
dows [27]; software used to prepare material for publication:
WinGX [28].
the complex (10−3 M) with a Unicam UV2 spectrometer in
the range 900 – 190 nm. A Perkin Elmer Diamond TG/DTA
thermal analyzer was used to record simultaneous TG, DTG
and DTA curves in static air atmosphere at a hea◦ting rate
of 10 ◦C min−1 in the temperature range 20 – 1000 C using
platinum crucibles.
mer-[Ni(HOr)(H2O)2(ata)2] (1)
A solution of 2-aminothiazole (0.51 g, 5 mmol) in ethanol
(10 mL) was added dropwise and with stirring to a solu-
tion of [Ni(HOr)(H2O)4]·H2O [20] (0.76 g, 2.5 mmol) in
CCDC 632158 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data request/cif.
◦
distilled water (30 mL). The solution was heated to 60 C
in a temperature-controlled bath and stirred for 5 h. The
reaction mixture was then cooled to r. t. The blue crystals
formed were filtered, washed with ethanol and dried in air.
C11H14N6O6S2Ni (449.11): calcd. C 29.42, H 3.16, N 18.71;
found C 29.34, H 3.16, N 18.73.
Acknowledgement
This work was supported by the Eskisehir Osmangazi Uni-
versity (project No 200619013).
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