Synthesis and characterization of nickel complex of 4-amino-3- pyridinethiolate

Article abstract of DOI:10.3987/COM-13-S(S)2

A Ni(Hapt)2 complex, apt = 4-amino-3-pyridinethiolate, is isolated and characterized by X-ray crystallography, cyclic voltammetry, and UV-Vis spectroscopy.

Full text of DOI:10.3987/COM-13-S(S)2

HETEROCYCLES, Vol. 88, No. 1, 2014, pp. -. © 2014 The Japan Institute of Heterocyclic Chemistry
Received, 5th March, 2013, Accepted, 26th March, 2013, Published online, 3rd April, 2013
DOI: 10.3987/COM-13-S(S)2
SYNTHESIS AND CHARACTERIZATION OF NICKEL COMPLEX OF
4-AMINO-3-PYRIDINETHIOLATE
Kouzou Matsumoto,* Maho Nishizawa, Yasukazu Hirao, Hiroyuki Kurata,
and Takashi Kubo*
Department of Chemistry, Graduate School of Science, Osaka University, 1-1
Machikaneyama, Toyonaka, Osaka 560-0043, Japan
E-mail: matsumoto@isc.senshu-u.ac.jp, kubo@chem.sci.osaka-u.ac.jp
Abstract – A Ni(Hapt)2 complex, apt = 4-amino-3-pyridinethiolate, is isolated and
characterized by X-ray crystallography, cyclic voltammetry, and UV-Vis
spectroscopy.
The metal complex system M(XYC6H4)2 (X, Y = NH, O, S) shows high redox activity 1 and therefore have
attracted intense interest as a molecular component of electro-conductive and magnetic materials.2 The
electron transfer reaction of the complexes is a ligand-centered process, which has been judged by ESR
studies and quantum chemical calculations.1 Recent sophisticated DFT calculations applied with the
broken-symmetry method demonstrate that the M(XYC6H4)2 system possess radical character on the
ligands and unpaired electrons are coupled anti-ferromagnetically through the metal center to afford singlet
diradical ground state.3 This peculiar electronic structure may provide third-order non-linear optical
properties such as two-photon absorptions to the M(XYC6H4)2 system, according to the theoretical work by
us.4 In this way, the ligands in the M(XYC6H4)2 system play an important role in their physical properties
and new combination of metals and ligands expands the possibility of the M(XYC6H4)2 system for
functional materials. Herein we report the synthesis and characterization of a new Ni complex (1) with
ligands of 4-amino-3-pyridinethiolate (apt).
Figure 1. Metal complex system M(XYC6H4)2 and a new Ni complex (1)
_____________________________________________________________________________________
Dedicated to Professor Victor Snieckus on the occasion of his 77th birthday.

Scheme 1. Synthetic route for 1. In parentheses, the literature yields5 are given. TETD = tetraethylthiuram
disulfide.
The ligand (2) of Ni(Hapt)2 1 was prepared according to the reported procedure.5 We found that most of the
steps gave much better yields than the reported ones. The ligand 2 was obtained as a colorless solid
quantitatively, which gradually changed to oil in air. The reaction of 2 with NiCl2•6H2O in water in a sealed
degassed tube at room temperature afforded yellow crystals of 1 suitable for X-ray crystallographic
analysis.6 As will be mentioned below, 1 is subjected to oxidation in a solution state, and therefore, the
degassed condition was required for obtaining 1.
Figure 2 shows the X-ray structure of 1.7 There are two crystallographically independent molecules in the
unit cell. 1 forms N–H···O hydrogen bonds (N1···O1, 2.955Å; N3···O2, 2.980Å) with water molecules
(Figure 2a). Strong bond length alternation is observed in the ligands (Figure 2b), indicating the ground
state of 1 can be best described by the chemical structure depicted in Figure 1.
Figure 2. (a) ORTEP drawing of 1. Disordered water molecules with small occupancy are omitted for
clarity. (b) Molecular geometries of 1.

Cyclic voltammogram (Figure 3a) of 1 gave reversible and irreversible redox waves at –0.40 V (E1/2) and
+0.12 V (Epa), respectively. The first oxidation potential of –0.40 V is lower than that of tetrathiafulvalene
(TTF, E1/2 = –0.09 V vs. Fc/Fc+), indicating that 1 has very high electron donor ability. The irreversibility of
the second oxidation wave might come from deprotonation at the N-atom of the pyridine ring during the
oxidation process. Because the HOMO of 1 is distributed mostly on the ligands, the oxidation is a
ligand-centered process. UV-Vis spectrum (Figure 3b) of 1 gave absorption peaks at 407 nm and 272 nm
shortly after dissolving in methanol, while after one day the spectrum totally changed to give new peaks at
398 nm and 322 nm, probably due to the oxidation of 1 by air. Unfortunately, the decomposed species could
not be identified.
Figure 3. (a) Cyclic voltammogram (solid line, V vs. Fc/Fc+) of 1. Dashed line is the voltammogram with
the scan range of –0.67 to –0.07 V. Measurement conditions; in 0.1M nBu4NClO4/DMF, scan rate = 100
mV/s, WE = glassy carbon, CE = Pt, RE = Ag/Ag+, rt. HOMO of 1 is also shown.8 (b) UV-Vis spectra of 1
(solid line) shortly after dissolving in methanol and (dashed line) after one day.
In summary, we isolated a new Ni complex with ligands of 4-amino-3-pyridinethiolate (apt). The complex,
Ni(Hapt)2, was found to possess a high electron donating ability by cyclic voltammetry. Investigation on
functional properties of Ni(Hapt)2 such as electro-conductivity and two-photon absorption are now in
progress in our group.
ACKNOWLEDGEMENTS
This work was in part by the Grant-in-Aid for Scientific Research on Innovative Areas “Reaction
Integration” (No. 2105) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

REFERENCES AND NOTES
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6. 1: yellow prisms; mp 100.0 ˚C (dec); HRMS (ESI): calcd for C10H8N2NiS4: 370.9700. Found:
370.9730; Anal. calcd for C10H8N2NiS4•2H2O: C, 34.81; H, 4.09; N, 16.24. Found: C, 35.14; H, 3.89;
N, 16.31; IR (KBr) cm–1: 3332, 3244, 1509.
7. Crystal data for Ni(Hapt)2•2H2O: C10H10N4NiO2S2, Mw = 341.05, triclinic, P-1 (#2), a = 7.1342(13), b
= 8.4502(15), c = 12.257(2) Å,  = 76.766(3), = 73.110(3),  = 76.561(4)°, V = 677.2(2) Å3, T = 200
K, Z = 2, (calcd) = 1.672 g cm–3, (MoK) = 1.74 mm–1, reflections collected = 6674, unique
reflections = 3069, Rint = 0.083, param. refined = 193, R1 = 0.044 (I > 2(I)), wR2 = 0.141 (all data),
GOF = 1.05. CCDC-927361.
8. Quantum chemical calculation of 1 was performed at the B3LYP level of theory using Firefly version
7.1.G software package.9 The double-zeta valence basis set with SBKJC10 effective-core potential (for
Ni atom) as well as the 6-31G basis set (for C, H, N, S atoms) were employed in the calculations.
9. A. A. Granovsky, Firefly version 7.1.G, http://classic.chem.msu.su/gran/firefly/index.html.
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