133
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
DOI: 10.17344/acsi.2024.9095
Scientific paper
Manganese, Cobalt, Nickel and Zinc Complexes with 
Pyrazine-2-carboxylic Acid
Saša Petriček
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, 1000 Ljubljana
* Corresponding author: E-mail: sasa.petricek@fkkt.uni-lj.si
Received: 12-02-2024
Abstract
New complexes of zinc (1), manganese(II) (2 and 2a), cobalt(II) (3) and nickel(II) chloride (4), with pyzaH (pyra-
zine-2-carboxylic acid) were synthesized. The pyzaH molecules are coordinated as monodentate ligands only through 
heterocyclic nitrogen in 1, 2 and 3, as shown by single crystal X-ray diffraction analysis. The chloride ions are coordinated 
as terminal ligands in 1, [ZnCl
2
(pyzaH)
2
]∙2H
2
O, but act as bridging ligands in the 1D complexes [MCl
2
(pyzaH)
2
]
n
∙2nH
2
O 
(M = Mn, 2, Co, 3). The supramolecular architectures of the complexes differ due to the coordination of the chlorides, 
the hydrogen bonds and the parallel stacking arrangements of the pyzaH molecules. In contrast to the isolated crystals 
of 1, 2 and 3, the manganese(II) (2a) and nickel(II) (4), compounds do not contain water. According to the IR spectra 
and the results of thermal analyzes, the proposed formula is [MCl
2
(pyzaH)
2
]. Powder X-ray and thermal analysis results 
demonstrate the isostructural nature of complexes 2a and 4. The low thermal stability of 1 is due to the monodentate 
coordination of pyzaH in 1. Thermal decomposition of 1, 2a and 4 in air produces oxides MO (M = Mn, Ni, Zn).
Keywords: Complex, zinc, manganese(II), pyrazine-2-carboxylic acid, structure, thermal stability.
1. Introduction
Pyrazine-2-carboxylic acid (pyzaH) plays an impor-
tant role in medicine with its antimycobacterial activity. It 
is formed inside the mycobacterial cells by enzymatic con-
version of the prodrug pyrazinamide, which has been used 
in combination with other antituberculotics for over sixty 
years.
1,2 
The interest and demand of the pharmaceutical 
industry in tuning the physical and chemical properties of 
active pharmaceutical ingredients stimulates studies on 
cocrystals.
3
 The possibility of extensive hydrogen bonding 
makes pyzaH a perfect candidate for the isolation of co-
crystals. Two nitrogen and one oxygen atom in the pyzaH 
molecule act as acceptors of hydrogen bonds and the hy-
droxyl group acts as a donor of hydrogen bond. Cocrystals 
of pyzaH with gallic acid
4
 or even ternary cocrystals with 
pyridine-4-carboxamide and pentanedioic acid
3
 have been 
described in the literature.
The ability to ligate and deprotonate the pyzaH mol-
ecule is favorable for catalysis. A combination of vanadium 
compounds and pyzaH, a promoter acid with the advantage 
of several coordination modes, can provide efficient and ver-
satile catalytic systems for the mild oxidation of alkanes.
5,6
The proton in the hydroxyl group of pyzaH can be 
transferred to the nitrogen atom in the zwitterion or easi-
ly removed by forming the anion pyza
−
. The observation of 
coordinated pyzaH as a zwitterion has been documented in 
complexes of copper(I), [Cu
2
I
2
(pyzaH)
2
]
n
.
3nH
2
O, and bis-
muth(III), [Bi(Ph)(pyza)
2
(pyzaH)]∙H
2
O.
7,8
 The anion pyza
−
 
enables the crystallization of various salts with organic 
cations, for example piperazin-1,4-diium, cytosin-3-ium,
4
 
4-methyl-1,3-benzothiazol-2(3H)-iminium,
9
 phenylmeth-
anaminium,
10
 2-methylpropan-2-aminium
11 
or 4-(dimeth-
ylamino)pyridin-1-ium.
12
 Numerous coordination modes 
of pyza
−
 have been discovered in hundreds of complex 
compounds and in many homo- or heterometallic organic 
frameworks in the Cambridge structural database.
13
Despite a smaller variety of coordination modes for 
the molecule than for the anion pyza
−
, four types of pyzaH 
ligation were found in the complexes (Scheme 1).
Scheme 1. Coordination modes of pyzaH with Harris notation.
14

134
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
The chelate coordination of pyzaH (Scheme 1a), b)) 
to a single metal ion was found in one cadmium and two 
copper(II) complexes.
15−17
 These complexes are either di-
nuclear or polymeric with bridging halide or dicyanamide 
ions. Two bridging chloride ions connect two copper ions in 
a dinuclear complex [CuCl
2
(pyzaH)
2
]
2
.
16
 The coordinated 
O-donor atoms originate from either the carbonyl (Scheme 
1a)) or the hydroxyl group (Scheme 1b)) of pyzaH.
16
 In the 
polymeric [Cu(C
2
N
3
)
2
(pyzaH)
2
]
n
,
 
bridging dicyanamide 
ions link copper ions to form a 2D structure, while bridging 
iodide ions link cadmium ions in [CdI
2
(pyzaH)
2
]
n
 to form 
1D chains.
15,17
 The chelate coordination mode of pyzaH in 
both polymeric complexes is presented by Scheme 1a).
A combination of chelating and bridging coordina-
tion (Scheme 1c)) of a single pyzaH molecule is present 
in homometallic and heterometallic polymeric complex-
es. This coordination mode has been demonstrated in the 
one-dimensional coordination polymers [CoBr
2
(H
2
O)
(pyzaH)]
n
·nH
2
O
18
 and [Zn
2
(H
2
O)
4
(pyzaH)
2
)(SO
4
)
2
]
n
.
19
 
Pyrazine-2-carboxylic acid has appeared as an alternative 
to pyrazine-2,3-dicarboxylic acid in the preparation of 
metal organic frameworks, which have been the focus of 
many studies in recent decades. Of particular interest are 
heterometallic complexes of silver(I) and rhenium(VII) or 
silver(I) and iron(II) with pyzaH and pyza
−
 as bridging li-
gands.
20,21
 In the search for materials that are efficient in 
the conversion of solar energy due to their special optical 
properties and small band gap, oxide-organic hybrid solids 
of pyzaH, silver(I) and rhenium(VII) have been prepared. 
The silver ions in [Ag(pyzaH)(ReO
4
)]
n
 are connected by 
chelate and bridging ligation of pyzaH (Scheme 1c)) and 
ReO
4
− 
bridges.
20
 In the three-dimensional metal-organic 
framework {[Ag
2
Fe
2
(MeOH)
2
(pyza)
4
(pyzaH)](ClO
4
)
2
}
n
∙ 
3nMeOH with interesting catalytic and magnetic proper-
ties, pairs of silver(I) ions are connected by molecules of 
pyzaH (Scheme 1c)), while pyza
−
 links silver(I) to iron(II) 
and iron(II) to iron(II) ions.
21
As a monodentate ligand is pyzaH always bond-
ed via a nitrogen atom (Scheme 1d)). This type of coor-
dination is characteristic of complexes with metal ions, 
which act as soft acids.
7,22−25 
Copper(I) complexes with 
monodentate coordination of pyzaH and bridging iodide 
or chloride ions are 1D polymers.
7,22
 In the mononuclear 
[HgBr
2
(pyzaH)
2
]
25
 two molecules of pyzaH are coordinat-
ed to mercury(II) as N-donor ligand and in the anions of 
[ReX
5
(pyzaH)]
−
 only one molecule of pyzaH fulfills the 
coordination sphere of rhenium(IV).
23,24
 Salts containing 
[ReX
5
(pyzaH)]
− 
have been
 
used as starting compounds for 
the syntheses of heterometallic compounds with rheni-
um(IV) and silver(I), which exhibit interesting magnetic 
properties.
In previous studies, the coordination modes of 
neutral 3-hydroxypyridin-2-one (dhpH
2
) and pyridin-2-
one (Hhp) with the ions of the first-row transition met-
als were compared with the binding of the corresponding 
anions, dhpH
−
 and hp
−
.
26−28
 The number of complexes 
with dhpH
−
 and hp
−
 far exceeds the number of complex-
es with coordinated molecules. Similarly, complexes with 
pyza
−
 predominate in the literature, so we decided to fo-
cus on the coordination compounds of pyzaH and some 
transition metals in the fourth period. In contrast to the 
numerous complexes of pyza
−
 and the first-row transition 
metal(II) ions
13 
only one cobalt(II),
18 
one zinc
19 
and two 
copper(II)
16,17 
complexes with coordinated pyzaH were 
characterized by single crystal X-ray diffraction.
 
Chelate 
coordination of pyzaH (Scheme 1a), b)) was observed in 
copper(II) complexes and a combination of chelate and 
bridging ligation (Scheme 1c)) in cobalt(II) and zinc com-
plexes.
16−19 
The ability of pyzaH to coordinate to some 3d 
transition metal chlorides was investigated. New complex-
es of manganese(II), cobalt(II), nickel(II) and zinc were 
synthesized. We were interested in the coordination mode 
of pyzaH in the new complexes and in supramolecular ag-
gregations due to hydrogen bonding. The thermal decom-
position of the complexes was evaluated and correlated 
with the structural parameters.
2. Materials and Methods
2. 1. General
Cobalt(II) chloride hexahydrate (Carlo Erba, 98.0%), 
manganese(II) chloride tetrahydrate (Merck, 99 %), man-
ganese(II) sulfate monohydrate (Sigma Aldrich, 99.0%), 
nickel chloride (Sigma Aldrich, 97.0%), zinc chloride 
(Merck, 98%), zinc acetate dihydrate (Johnson Matthey 
GmbH, 99.5%), pyrazine-2-carboxylic acid (Fluka, 98%) 
and solvents, methanol, ethanol or acetonitrile, were used 
as purchased without further purification.
IR spectra (4000–600 cm
−1
) were acquired using a 
PerkinElmer Spectrum 100 equipped with a Specac Gold-
en Gate Diamond ATR as a solid sample support.
Elemental analyzes (C, H and N) were performed 
with a PerkinElmer 2400 Series II CHNS/O microanalyz-
er at the University of Ljubljana (Department of Organic 
Chemistry).
Thermal analyzes were performed using a Mettler 
Toledo TG/DSC 1 instrument (Mettler Toledo, Schwer-
zenbach, Switzerland) in air at a gas flow of 100 mL/min. 
The mass of the samples ranged from 7.6 mg to 9.9 mg. The 
samples in the platinum crucibles were heated from room 
temperature to 650 °C at a heating rate of 5 °C /min. In 
each case, the baseline was subtracted.
2. 2. Preparation Procedures
2. 2. 1. Synthesis of [ZnCl
2
(pyzaH)
2
]∙2H
2
O (1)
Method A
The solvent (acetonitrile, 25 mL) was added to pyzaH 
(0.414 g, 3.34 mmol) and ZnCl
2
 (0.228 g, 1.67 mmol). The 
white suspension was stirred in a Schlenk flask with an 
open side arm at 60 °C for one hour. Crystals 1 grew from 

135
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
the filtrate during slow evaporation of the solvent in six 
days.
Method B
The solvent (acetonitrile, 25 mL) and the solution of 
HCl (2.0 mL, 2.0 M) were added to pyzaH (0.414 g, 3.34 
mmol) and Zn(CH
3
COO)
2
∙2H
2
O (0.367 g, 1.67 mmol). 
The white suspension was stirred in a Schlenk flask with 
an open side arm at 60 °C for one hour. Crystals 1 grew 
from the filtrate during slow evaporation of the solvent in 
four days.
Anal. Calc. Mass fractions of the elements in crys-
tals 1, w/%, for C
10
H
12
Cl
2
N
4
O
6
Zn (M
r
 = 420.5 g/mol): C, 
28.56; H, 2.88; N, 13.32. Found: C, 28.48; H, 2.78; N, 13.02. 
IR (ATR cm
−1
) 3456 m, 3346 m, 3082 w, 2429 w, 1895 w, 
1698 vs, 1634 w, 1609 m, 1530 w, 1480 w, 1410 m, 1306 vs, 
1175 s, 1157 s, 1066 s, 1028 s, 997 m, 983 m, 875 m, 836 m, 
777 m, 721 w, 707 m.
2. 2. 2.  Synthesis of [MnCl
2
(pyzaH)
2
]
n
∙2nH
2
O (2) 
and [MnCl
2
(pyzaH)
2
] (2a)
The solvent (methanol, 25 mL) and a solution of 
concentrated HCl (2.0 mL) were added to pyzaH (0.414 
g, 3.34 mmol) and MnSO
4
∙H
2
O (0.282 g, 1.67 mmol). The 
solution was obtained after four days of stirring at room 
temperature and then stored in an open beaker. Crystals 
2 grew in the solution during evaporation of the solvent. 
The crystals were unstable outside the solution, only X-ray 
diffraction analysis was performed.
The solvent (methanol, 25 mL) was added to pyzaH 
(0.414 g, 3.34 mmol) and MnCl
2
∙4H
2
O, (0.331 g, 1.67 
mmol). The solution obtained after stirring at room tem-
perature for four days was dried in vacuo and the non-aq-
uas complex 2a, [MnCl
2
(pyzaH)
2
],
 
was gained.
Anal. Calc. Mass fractions of the elements in 2a, 
w/%, for C
10
H
8
Cl
2
MnN
4
O
4
 (M
r
 = 374.0 g/mol): C, 32.11; 
H, 2.16; N, 14.98. Found: C, 32.13; H, 2.20; N, 14.89. IR 
(ATR cm
−1
) 3515 bw, 3088 w, 2487 bw, 2156 w, 1720 vs, 
1592 w, 1435 m, 1408 m, 1321 vs, 1199 w, 1171 m, 1143 s, 
1056 s, 1021 s, 953 w, 869 m, 843 m, 771 s, 734 m.
2. 2. 3. Synthesis of [CoCl
2
(pyzaH)
2
]
n
∙2nH
2
O (3)
The solvent (acetonitrile, 25 mL) and the solution 
of HCl (2.0 mL, 2.0 M) were added to pyzaH (0.248 g, 
2.00 mmol) and CoCl
2
∙6H
2
O (0.256 g, 1.08 mmol). The 
suspension was stirred in a beaker at 70 °C for one hour. 
Violet crystals 3 grew in the filtrate during evaporation of 
the solvent in air.
Anal. Calc. Mass fractions of the elements in the crys-
tals 3, w/%, for C
10
H
12
Cl
2
CoN
4
O
6
 (M
r
 = 414.1 g/mol): C, 
29.01; H, 2.92; N, 13.53. Found: C, 28.83; H, 2.78; N, 13.12. 
IR (ATR cm
−1
) 3511 m, 3366 s, 3086 m, 2500 bw, 1980 bm, 
1691 vs, 1596 s, 1525 w, 1479 w, 1455 w, 1401 m, 1308 s, 
1175 s, 1156 s, 1060 s, 1028 s, 871 m, 831 m, 776 s, 703 m.
2. 2. 4. Synthesis of [NiCl
2
(pyzaH)
2
] (4)
The solvent (acetonitrile, 25 mL) and a solution of 
concentrated HCl (2.0 mL) were added to pyzaH (0.372 g, 
3.00 mmol) and NiCl
2
 (0.194 g, 1.50 mmol). The suspen-
sion was stirred in a Schlenk flask at room temperature 
for five days and then filtered. The non-aquas compound 
4, [NiCl
2
(pyzaH)
2
],
 
was obtained in the precipitate. When 
the reaction was repeated at elevated temperature (60 °C, 2 
hours), a mixture of [NiCl
2
(pyzaH)
2
] and [Ni(pyza)
2
] was 
found in the precipitate. No crystals were isolated from the 
solution of 4 in methanol; when the solvent evaporated a 
mixture of 4 and [Ni(pyza)
2
] was obtained according to 
the IR spectrum.
Anal. Calc. Mass fractions of the elements in 4, w/%, 
for C
10
H
8
Cl
2
N
4
NiO
4
 (M
r
 = 377.8 g/mol): C, 31.79; H, 
2.13; N, 14.83. Found: C, 32.07; H, 2.12; N, 14.35. IR (ATR 
cm
−1
) 3102 w, 2051 bw, 1721 vs, 1592 w, 1435 m, 1409 m, 
1323 vs, 1200 w, 1177 m, 1146 s, 1062 s, 1024 s, 955 w, 866 
m, 845 m, 768 s, 735 w.
2. 3. X-ray Structure Determinations
Single crystal X-ray diffraction data were collect-
ed on an Agilent SuperNova Dual Source diffractometer 
with an Atlas detector, using graphite-monochromatized 
Mo-Kα radiation at 150 K. Data reduction and integra-
tion were performed using the CrysAlis PRO software 
package.
29
 Corrections for absorption (multi-scan) were 
applied in all cases. All structures were solved by direct 
methods implemented in SIR−2014 or SHELXT and 
refined by a full−matrix least squares procedure based 
on F
2
 with SHELXL.
30,31
 The positions of the hydrogen 
atoms in pyzaH were unambiguously located from the 
residual electron density maps for all compounds and 
the hydrogen atoms in water only in compounds 1 and 
2. Only the positions of the hydrogen atoms in water 
were refined using O−H distance restraints with U
iso
(H) 
= 1.5U
eq
(O). All other hydrogen atoms were placed at 
geometrically calculated positions and refined using a 
riding model. The details of the crystal data collections 
and the refinement parameters of the complexes 1−3 are 
summarized in Table 1.
The figures depicting the structures were prepared 
by ORTEP3 and Mercury.
32,33
X-ray powder diffraction data were collected using a 
PANalytical X´Pert PRO MPD diffractometer with reflec-
tion geometry using Cu-K
α1
 (λ = 1.5406Å) in the 2θ range 
from 5° to 70° with a step of 0.034° and an integration time 
of 100 s.
3. Results and Discussion
3. 1. Synthetic Aspects
The syntheses and reaction conditions are shown in 
Scheme 2.

136
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
Scheme 2. Syntheses of compounds 1−4 and 2a.
Complex 1 was crystallized after the reaction of 
ZnCl
2
 and pyzaH in acetonitrile or ethanol at elevated tem-
perature. The reaction of Zn(CH
3
COO)
2
·2H
2
O and pyzaH 
in acetonitrile at 60 °C also resulted in complex 1, when 
HCl solution was added. When water was added to the sol-
vent, methanol or ethanol, a deprotonated form of pyzaH 
and water molecules are coordinated to central zinc ions in 
the crystals of the known compound [Zn(H
2
O)
2
(pyza)
2
].
34
All reactions of the manganese(II) salts with pyzaH 
took place at room temperature. A solution obtained af-
ter the reaction of manganese chloride tetrahydrate with 
pyzaH in methanol was dried in vacuo. The powder gained 
contains [MnCl
2
(pyzaH)
2
, 2a, according to IR spectrum, 
X-ray powder diffraction, CHN and thermal analysis. The 
reaction of MnSO
4
·4H
2
O and pyzaH in methanol and HCl 
solution resulted in crystals of 2. The crystals grew in the 
solution during evaporation of the solvent from the open 
beaker.
The addition of HCl solution to a suspension of  
CoCl
2
·6H
2
O and pyzaH in acetonitrile at elevated temper-
Table 1. Crystallographic data, data collection and structure refinement data for the compounds 1−3.
 1 2 3
Molecular formula C
10
H
12
Cl
2
N
4
O
6
Zn C
10
H
12
Cl
2
MnN
4
O
6 
C
10
H
12
Cl
2
CoN
4
O
6
Color colorless colorless violet
For. mass (g/mol) 420.5 410.07 414.07
Cryst. syst. monoclinic monoclinic monoclinic 
Radiation type Mo Kα Mo Kα Mo Kα
Space gr. C2/c (no. 15) P2
1
/n (no. 14) P2
1
/n (no. 14)
a (Å) 13.2469(6) 6.4539(3) 6.443(2)
b (Å) 5.4354(2) 3.6104(2) 3.5352(5)
c (Å) 21.8060(11)  31.8942(15) 31.379(4)
β (
o
) 102.365(5) 94.649(4)  95.014(19)
V (Å
3
) 1533.66(12) 740.73(3) 712.0(1)
Z (form.) 4 2 2
D
cal.
 (g cm
−3
) 1.82 1.84 1.93
µ (mm
−1
) 1.985 1.288 1.619
Crystal size (mm) 0.3 × 0.2 × 0.2 0.02 × 0.05 × 0.05 0.1 × 0.05 × 0.02
θ Range (
o
) 3.15−27.5 2.6−30.4 2.61−27.5
Collected refl. 7366 13711 4499
Unique refl. 1756 2074 1650
R
int 
0.023 0.035 0.084
Observed refl. 1678 1704 1228
No. param. 117 115 107
R
a
 (I > 2.0 σ(I)) 0.0187 0.032 0.0914
wR
2
b 
0.0509 0.043 0.198
S 1.07 1.13 1.22
Max/min res. elec. d. (e Å
−3
) –0.26, 0.41 –0.35, 0.47 –0.60, 1.15
a 
R = Σ(|F
o
| - |F
c
|)/Σ|F
o
|, 
b
 wR
2
 = (Σ[w(F
o
2
 - F
c
2
)
2
]/Σ(wF
o
2
)
2
)
1/2.
CCDC - 2406449 (1), 2406448 (2), contain the supplementary crystallographic data for this paper. These data can be 
obtained free of charge at http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic 
Data Centre, 12 Union Road, Cambridge CB2 1EZ,UK; Fax: +44-1223-336033; or e-mail: deposit@ccdc.cam.ac.uk.

137
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
ature was necessary to isolate complex 3. In the reactions 
of CoCl
2
·6H
2
O and pyzaH in a solvent that was a 1:1 mix-
ture of ethanol or acetonitrile and water, a deprotonated 
form of pyzaH and water molecules are coordinated to 
central cobalt ions in yellow crystals of the known com-
pound [Co(H
2
O)
2
(pyza)
2
].
34
In contrast to zinc and manganese chlorides, reac-
tions of cobalt or nickel chlorides and pyzaH only resulted 
in complexes with ligated pyzaH in the presence of HCl. 
While the cobalt complex 3 was only isolated after the 
reaction at elevated temperature, the nickel compound 4 
was obtained at room temperature. The reaction of nick-
el chloride and pyzaH in the presence of HCl at elevat-
ed temperature gave a mixture of 4, [Ni(H
2
O)(pyza)
2
]
n
,
 
and
 
[Ni(H
2
O)
2
(pyza)
2
].
34, 35
 The dimeric copper complex  
[CuCl
2
(pyzaH)]
2
 was also prepared only in the presence 
of HCl at room temperature, similar to nickel complex 4.
16
3. 2. IR Spectra
The presence of hydrogen bonded water molecules 
in the spectra of 1 and 3 was detected by broad bands at 
3511 cm
−1 
and 3456 cm
−1
, whereas these bands are not vis-
ible in the spectra of 2a and 4 (Figures S1−S4).
The typical band for carboxylic acid ν(C=O) appears 
in pure pyzaH at 1709 cm
−1
. This band is only slightly 
shifted in the new complexes 1−4. In aqua zinc and co-
balt complexes, 1 and 3, the band ν(C=O) was observed at 
1698 cm
−1 
and 1691 cm
−1
 respectively. The crystal struc-
tures of these two compounds confirm a monodentate co-
ordination of pyzaH via an N-donor atom. The frequen-
cy change is similar to that of the copper(I) compound  
[CuCl(pyzaH)
2
]
n
∙2nH
2
O (1690 cm
−1
) with the same coor-
dination mode of pyzaH. The shift is attributed to different 
hydrogen bonding in pure and coordinated pyzaH.
22
 Ox-
ygen atoms in carbonyl groups are involved as acceptors 
of hydrogen bonds in 1, 3 and [CuCl(pyzaH)
2
]
n
∙2nH
2
O, 
but do not participate in hydrogen bonds connecting pure 
pyzaH. In contrast, a shift of ν(C=O) to higher wavenum-
bers was observed in the spectra of non-aquas complexes 
2a (1720 cm
−1
) and 4 (1721 cm
−1
). A similar shift to higher 
wavenumbers was also observed in two ionic rhenium(IV) 
complexes, [ReX
5
(pyzaH)]
−
 (X = Cl, 1718 cm
−1
; X = Br, 
1730 cm
−1
) where pyzaH acts as the terminal N-donor 
ligand.
23,24 
The wavenumber indicating ν(C=O) in the 
spectrum of cocrystals [MnCl
2
(H
2
O)
2
]
n
∙2nHhp (Hhp = 
pyridin-2-one, 1699 cm
−1
) is also higher than in pure Hhp 
(1681 cm
−1
).
28
Asymmetric vibrations of carboxylate at much 
lower frequencies were observed in the complexes with 
coordinated ion pyza
−
 instead of the ν(C=O) band at 
1710 cm
−1
.
34
 Strong bands for carboxylate vibrations in 
[M(H
2
O)
2
(pyza)
2
] were observed at 1647 cm
−1 
(M = Zn), 
1629 cm
−1 
(M = Mn), 1633 cm
−1 
(M = Co) and 1624 cm
−1 
(M = Ni).
34
 The absence of bands for carboxylate vibra-
tions in the new complexes 1−4 unambiguously proves 
coordination of the molecule pyzaH to a central ion in all 
new compounds.
3. 3. Description of the Structures
3. 3. 1.  Crystal structure of [ZnCl
2
(pyzaH)
2
]∙2H
2
O 
(1)
Two pyzaH molecules and two chloride ions fulfill 
coordination sphere of zinc in 1 in a distorted tetrahedral 
mode (Figure 1a). The asymmetric unit comprises one wa-
ter molecule and one half of the complex molecule, with 
the zinc ion lying on a twofold rotation axis. In 1, pyzaH 
acts as a monodentate N-donor ligand in contrast to the 
chelate coordination of pyzaH in [Zn
2
(H
2
O)
4
(pyzaH)
2
)
(SO
4
)
2
]
n
 and in the other complexes of the first row tran-
sition metal(II) ions, Co(II) and Cu(II).
16−19
 The mono-
dentate coordination via the N-donor atom was also 
calculated for the isostructural mercury(II) complex  
[HgBr
2
(pyzaH)
2
]∙2H
2
O (Figure 1b).
25
Figure 1. a) ORTEP drawing of [ZnCl
2
(pyzaH)
2
] (1). The atoms are 
represented by displacement ellipsoids at the 25% probability level. 
The hydrogen atoms are shown as spheres of arbitrary radius. b) 
Structure overlay of 1 (red) and [HgBr
2
(pyzaH)
2
] (blue).
The Zn−N and Zn−Cl bond lengths in 1 are in the 
same range (Table 1) as in many zinc chloride complex-
es displaying tetrahedral geometry with monodentate 
aromatic ligands coordinated via an N-donor atom. The 
ligands in the compared complexes are pyrazine-2-car-

138
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
boxamide, 2-methylpyrazine, 2-aminopyrazine or 
2,6-dichloropyrazine.
36−39
 Significantly longer bonds 
were found in a six numbered coordination environ-
ment of zinc in [ZnCl
2
(pyza)
2
]
2− 
(Zn−Cl 2.574(3) Å,  
Zn−N 2.109(7) Å) or in the homoleptic complex ion 
[Zn(pyza)
3
]
−
 (Zn−N from 2.153(2) Å to 2.174(2) Å) 
with chelate coordination of pyrazine-2-carboxy-
late.
40,41
Figure 2. Molecules of 1. a) Each complex molecule is a donor of two and an acceptor of four hydrogen bonds. b) Complex molecules are connected 
to water molecules by hydrogen bonds and form wavy layers parallel to the ac plane. c) The wavy layers are linked by hydrogen bonds into a 3D 
structure.

139
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
Table 2. Selected geometric parameters (Å, °) in [ZnCl
2
(pyzaH)
2
] 
(1). 
Zn1−Cl1 2.1963(3) N1−Zn1−N1
i
 99.09(6)
Zn1−N1 2.0677(11) Cl1−Zn1−Cl1
i
 126.74(2)
O1−C5 1.2133(17) Cl1−Zn1−N1 106.01(3)
O2−C5 1.3048(17) Cl1−Zn1−N1
i
 107.81(3)  
Symmetry code: (i) 1 − x, y, ½ − z.
A distortion of the tetrahedral angles in 1 is evident 
in a sharper N1−Zn1−N1
i
 and a larger Cl1−Zn1−Cl1
i
 an-
gle (Table 2). A similar deviation was also observed for 
the angles in tetrahedral zinc chloride complexes with 
pyrazine-2-carboxamide and 2,6-dichloropyrazine.
36,39
 
An even stronger distortion of the tetrahedra was detect-
ed in the complex of [HgBr
2
(pyzaH)
2
] due to the steric 
requirements of the bulkier bromide ions (N1−Hg1−N1
i
 
86.9(6)°, Br1−Hg1−Br1
i
 153.72(12)°).
25
 Consequently, the 
dihedral angle between the planes through organic lig-
ands is larger in 1 (84.27(11)°) than in [HgBr
2
(pyzaH)
2
] 
(78.4(9)°). On the other hand, a less pronounced distor-
tion of the tetrahedra was observed in some [ZnCl
2
L
2
] (L 
= 2-aminopyrazine, apyz, or 2-methylpyrazine, mpyz). 
In [ZnCl
2
(apyz)
2
], the Cl−Zn−Cl (114.58(2)°) angle is 
sharper and the N−Zn−N (106.52(7)°) angle is wider than 
in 1.
38
 In [ZnCl
2
(mpyz)
2
], only a wider Cl−Zn−Cl angle 
(125.41(4)°or 128.26(4)°) differs significantly from the tet-
rahedral angle.
37
All good hydrogen bond donors, OH in water and 
the hydroxyl group of pyzaH are engaged in hydrogen 
bonding in 1, the acceptors are uncoordinated nitrogen at-
oms and carbonyl oxygen atoms in the molecules of pyzaH 
(Table 3) and oxygen atoms in water.
Table 3. Hydrogen bonds (Å, °) for [ZnCl
2
(pyzaH)
2
] (1).  
D−H
….
A D−H H
….
A D
….
A D−H
….
A
O2−H11
….
O3
ii 
0.83(2) 1.71(3) 2.523(2) 169(3)
O3−H31
….
O1
iii 
0.76(2) 2.07(2) 2.7992(2) 161(2)
O3−H32
….
N2
iv 
0.81(3) 2.07(3) 2.864(2) 166(2)  
Symmetry code: (ii) 1 − x, −y, 1 − z; (iii) ½ + x, 3/2 + y, z, (iv) x, 2 + 
y, z.
Each complex molecule forms altogether six hydro-
gen bonds with six water molecules (Figure 2 a). Solvate 
molecules of water are involved as donors (O3−H31∙∙∙∙O1
iii
,
 
O3−H32∙∙∙∙N2
iv
) and acceptors (O2−H11∙∙∙∙O3
ii
) of hydro-
gen bonds creating R
4
4
(12) and R
4
4
(14) bonding motifs 
(Figure 2 b). Many donor and acceptor groups involved in 
intermolecular hydrogen bonding enable construction of a 
3D structure (Figure 2 b), c)).
3. 3. 2.  Crystal structure of 2, [MnCl
2
(pyzaH)
2
]
n
∙ 
2nH
2
O and 3, [CoCl
2
(pyzaH)
2
]
n
∙2nH
2
O
Complexes 2 and 3 are isostructural (Figure 3 a)); the 
manganese(II) chloride complex with pyzaH is depicted in 
Figure 3 b). The crystal structure was perfectly refined only 
for 2, while the poor quality of crystals 3 resulted in a less 
accurate refinement of the crystal structure.
Figure 3. a) Structure overlay of [MnCl
2
(pyzaH)
2
]
 n
∙2nH
2
O (2 blue) and [CoCl
2
(pyzaH)
2
]
 n
∙2nH
2
O (3 red). b) ORTEP drawing of [MnCl
2
(pyzaH)
2
]
 n
∙ 
2nH
2
O (2). The atoms are represented by displacement ellipsoids at the 25% probability level. The hydrogen atoms are shown as spheres of arbitrary 
radius.

140
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
Four chloride ions and two nitrogen atoms of pyzaH 
in trans positions are coordinated to each metal(II) ion in 
2 and 3 in an octahedral mode. An edge sharing of octa-
hedra results in linear chains with double chloride bridges 
connecting the metal(II) ions in a 1D coordination poly-
mer. The chains are parallel to the b axis. All M
2
Cl
2
 rings in 
the chains of 2 and 3 are coplanar due to the monodentate 
N-donor ligands in trans positions (Figure 4). Similar neu-
tral manganese(II) polymer chains with coplanar Mn
2
Cl
2
 
rings are found in only a few structures, for example, in 
cocrystals of [MnCl
2
(H
2
O)
2
]
n
 and pyridin-2-one (Hhp) 
or 4-aminopyridinium chloride (apyCl).
28,42
 N-donor li-
gands are usually coordinated in cis positions to manga-
nese(II) in [MnCl
2
]
n
 chains, leading to the formation of 
zigzag chains as in [MnCl
2
(maepy)]
n
 (maepy = (meth-
ylamino)ethylpyridine).
43
 The adjacent Mn
2
Cl
2
 rings in  
[MnCl
2
(maepy)]
n
 are almost perpendicular with a dihe-
dral angle of 84.58°. Planar Mn
2
Cl
2
 rings were also found 
in a complex of pyza
−
, [MnCl(H
2
O)(pyza)]
n
. In this com-
plex, linear chains of manganese(II) ions linked by bridg-
ing pyza
−
 are connected in a 2D structure by double chlo-
ride bridges forming isolated Mn
2
Cl
2
 rings.
44
The close proximity of the pyrazine rings within the 
same chain enables an off-center parallel stacking arrange-
ment of the coordinated pyzaH molecules in 2 (Figure 4).
45
 
The relevant parameters of this interaction in 2 are: centroid−
centroid distance 3.610(1) Å, interplanar distance 3.414(1) Å, 
dihedral angle 0° and offset angle 19.0°. As a consequence of 
the interactions between parallel coordinated pyzaH mole-
cules the bond lengths Mn−Cl and Mn∙∙∙∙Mn distances in 2 
(Table 4) are shorter than in compounds with similar chains 
of coplanar Mn
2
Cl
2
 rings. In cocrystals of [MnCl
2
(H
2
O)
2
]
n
 
or in the complex [MnCl
2
(maepy)]
n
, Mn−Cl bonds are ap-
proximately 0.10 Å longer and Mn∙∙∙∙Mn distances from 0.15 
Å to 0.33 Å longer.
28, 42, 43
 Mn∙∙∙∙Mn distances in 2 are also 
shorter than in [MnCl(H
2
O)(pyza)]
n
 (3.664(4) Å).
44
 Mn−N 
bond lengths in 2 and in [MnCl
2
(maepy)]
n
 (2.303(1) Å) are 
in the same range.
43
Figure 4. Coplanar Mn
2
Cl
2
 rings and an off-center parallel stacking 
arrangement of the coordinated pyzaH molecules in 2.
As far as we know 1D polymers of cobalt ions con-
nected solely by double chloride bridges have only been de-
scribed in cocrystals of [CoCl
2
(H
2
O)
2
]
n
 and Me
3
NHCl.
46
 
Chains of cobalt ions are also characteristic of [Co
2
Cl
4
(di-
glyme)]
n
 (diglyme = di(2-methoxyethyl) ether) with oc-
tahedrally and tetrahedrally coordinated cobalt ions con-
nected by single and double chloride bridges.
47
 Similar to 
2, the interactions between pyrazine rings in 3 result in 
shorter Co∙∙∙∙Co distances (Table 4) than in [CoCl
2
(H
2
O)
2
]
n
 
(3.637(3) Å), while in [Co
2
Cl
4
(diglyme)]
n
 a shorter and a 
longer Co∙∙∙∙Co distance corresponding to one (4.306(1) Å) 
or two (3.124(1) Å, 3.436(1) Å) bridging chloride ions 
connecting adjacent cobalt(II) ions were calculated.
46,47
Table 4. Selected geometric parameters (Å, °) in [MnCl
2
(pyzaH)
2
]
n
∙ 
2nH
2
O (2) and [CoCl
2
(pyzaH)
2
]
n
∙2nH
2
O (3).
Mn1−Cl1 2.4990(5) Co1−Cl1 2.416(2)
Mn1−Cl1
i
 2.5134(5) Co1−Cl1
i
 2.454(2)
Mn1−N1 2.3021(13) Co1−N1 2.165(6)
O1−C5 1.216(2) O1−C5 1.215(10)
O2−C5 1.298(2) O2−C5 1.298(8)
Mn1…Mn1
i
 3.6104(2) Co1…Co1
i
 3.535(1)
Cl1−Mn1−N1 88.52(4) Cl1−Co1−N1 88.57(18)
Cl1
i
−Mn1−N1 88.12(4) Cl1
i
−Co1−N1 89.40(18)
Cl1−Mn1−Cl1
i
 92.16(1) Cl1−Co1−Cl1
i
 
 
93.07(7)
Cl1−Mn1−Cl1
ii
 87.85(1) Cl1−Co1−Cl1
ii
 86.93(7)
Symmetry code: (i) x, 1 + y, z; (ii) (ii) −x, −1 − y, −z.
All good hydrogen bond donors and acceptors are 
involved in hydrogen bonding. Each coordinated pyzaH 
is a donor of one (O2−H2∙∙∙∙O3) and an acceptor of two 
(O3−H31∙∙∙∙N2
iii
, O3−H32
….
O1
iv
)
 
hydrogen bonds involv-
ing three water molecules (Figure 5 a), Table 5). Infinite 
[MnCl
2
(pyzaH)
2
]
n 
chains are connected to the 3D struc-
ture by hydrogen bonds engaging water molecules (Figure 
5 b)).
Table 5. Hydrogen bonds (Å, °) in [MnCl
2
(pyzaH)
2
]
n
∙2nH
2
O (2). 
D−H
….
A D−H H
….
A D
….
A D−H
….
A
O2−H2
….
O3 0.840 1.690 2.523(2) 174.0
O3−H31
….
N2
iii 
0.83(3) 2.07(3) 2.895(2) 171(3)
O3−H32
….
O1
iv 
 0.82(3) 2.19(3) 2.971(2) 159(3) 
Symmetry code: (iii) ½ − x, −½ + y, ½ − z; (iv) −½ − x, ½ + y, ½ − z.
3. 3. 3. X-ray Powder Diffraction Analysis
The results of the X-ray powder diffraction analysis 
confirm the isostructural nature of complexes 2a and 4 
(Figure 6). Minor differences in the unit cell dimensions 
are expected due to a larger Mn
2+
 (83 pm) and a small-
er Ni
2+
 (69 pm) ion in complexes 2a and 4. Due to the 
larger unit cell of complex 2a, the diffraction peaks of this 
complex are at lower 2θ values than the peaks for com-
plex 4. The shift of the diffraction peaks of the compared 

141
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
complexes is negligible at lower 2θ values, but increases at 
higher angles.
As expected, the calculated X-ray diffraction powder 
pattern of 2 differs from the one measured for 2a (Figure 
S5).
3. 4. Thermal Analysis
The result of the thermal analysis of complex 1 is de-
picted in Figure 7. Water molecules that are not coordinat-
ed to zinc ions evaporate between 110 °C and 160 °C in the 
first decomposition step. The mass loss in this step (8.6%) 
corresponds to exactly two moles of water per one mole of 
compound 1 (8.6%). The decomposition continues in sev-
eral poorly resolved steps up to a temperature of 585 °C. 
The reactions are endothermic, with the exception of the 
last reaction, the formation of zinc oxide in air, which is 
exothermic. The total mass loss observed during the anal-
ysis is higher (86 %) than expected for the conversion of 
[ZnCl
2
(pyzaH)
2
]∙2H
2
O to ZnO (80.6%), probably due to 
the evaporation of some zinc prior to oxidation.
Complex 1 is thermally less stable than pure pyra-
zine-2-carboxylic acid, which decomposes completely 
in air in the temperature range between 170 °C and 220 
°C.
34
 In contrast to pyzaH, the decomposition of 1 is com-
pleted at a higher temperature (585 °C). A comparison 
of the thermal analysis of 1 and the zinc complex with 
pyrazine-2-carboxylate, [Zn(H
2
O)
2
(pyza)
2
] in air, shows 
some important differences.
34
 The loss of water occurs in 
[Zn(H
2
O)
2
(pyza)
2
] at a higher temperature (170 °C) in a 
Figure 5. a) Each coordinated pyzaH molecule in complex 2 is a donor of one and an acceptor of two hydrogen bonds. b) The chains of [Mn-
Cl
2
(pyzaH)
2
]
n
 are connected to water molecules by hydrogen bonds and form the 3D structure.

142
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
well-defined first step, which is due to the coordination of 
water to the zinc ion in the complex. While the decompo-
sition of 1 immediately follows dehydration at 170 °C, the 
second decomposition step of [Zn(H
2
O)
2
(pyza)
2
] does not 
begin until 280 °C. The lower thermal stability of 1 com-
pared to [Zn(H
2
O)
2
(pyza)
2
] is explained by the monoden-
tate coordination of pyzaH in 1 and the chelate ligation of 
pyza
−
 in [Zn(H
2
O)
2
(pyza)
2
]. The thermal decomposition 
of both 1 and [Zn(H
2
O)
2
(pyza)
2
] is completed at 585 °C 
with the formation of ZnO.
The results of the thermal analysis confirm the iso-
structural nature of complexes 2a and 4 (Figure 8). Both 
compounds decompose in air in two steps, with the first 
step starting at temperatures above 170 °C and the second 
one above 300 °C. Thermal stability up to 170 °C indicates 
anhydrous complexes of manganese(II), 2a, and nickel, 4. 
The thermal decomposition of complex 4 is completed at 
510 °C and of complex 2a at 530 °C with the formation of 
metal(II) oxides. The total mass loss observed for 2a (81.1 
%) and 4 (83 %) at 520 °C agrees well with the calculat-
ed mass loss for the conversion of [MCl
2
(pyzaH)
2
] to MO  
(M = Mn, 81 %; Ni, 80.2 %). The last step of the decompo-
sition is strongly exothermic, which indicates the forma-
tion of metal(II) oxides in air. The oxidation of MnO takes 
place above 590 °C as shown by the mass gain (Figure 8).
The thermal decomposition of the complexes with 
pyrazine-2-carboxylate, [M(H
2
O)
2
(pyza)
2
] (M = Mn, Ni), 
is also a two-step process.
34
 In the first step, in the tem-
perature range between 150 °C and 170 °C, a minor mass 
loss (≈10 %) due to coordinated water is observed. The 
rest of the mass loss occurs in the second step above 360 
°C giving MO. The decomposition of [M(H
2
O)
2
(pyza)
2
]  
(M = Mn, Ni) is completed at a lower temperature (420 °C) 
than the decomposition of 2a and 4 (530 °C and 510 °C).
4. Conclusions
The new manganese(II), cobalt(II), nickel(II) and 
zinc complexes with pyzaH were prepared from the cor-
responding chlorides and pyzaH under mild conditions 
at room temperature or in moderately heated solutions 
in open Schlenk flasks. The isolation of the cobalt (3) 
and nickel (4) complexes required the addition of hydro-
chloric acid. The manganese(II) (2) and zinc (1) chloride 
complexes with pyzaH were also prepared from the corre-
sponding sulfate or acetate in the presence of HCl.
Figure 6. Measured X-ray powder diffractograms for 2a (in blue) and 4 (in red).
Figure 7. Thermal analysis of [ZnCl
2
(pyzaH)
2
]∙2H
2
O (1).

143
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
The results of X-ray diffraction analysis revealed the 
mononuclear nature of complex 1 and polymeric chains 
in complexes 2 and 3. This confirms that tetrahedral com-
plexes are more readily formed with Zn
2+
 than with cati-
ons of other d-block elements. The preference of Zn
2+
 ions 
to form tetrahedral complexes resulted in mononuclear 
Zn
2+
 complex in contrast to 1D polymers in 2 and 3 with 
octahedral coordination of Mn
2+
 and Co
2+
. The coordina-
tion of pyzaH as a terminal N-donor ligand was previously 
found only in compounds with metal ions characterized as 
soft acids. In our study, the same monodentate coordina-
tion of pyzaH was found in all three complexes, including 
complex 2 with Mn(II), which is considered a hard acid. 
The M
2
Cl
2
 rings forming chains in 2 and 3 are coplanar 
due to the trans coordinated pyzaH molecules. The prox-
imity of the pyrazine rings within the same chain allows 
an off-center parallel stacking arrangement of the coordi-
nated pyzaH molecules in 2 and 3. The hydrogen bonds 
between the water molecules and the coordinated pyzaH 
molecules in 1, 2 and 3 lead to 3D structures.
The thermal stability of the complex 1 with mono-
dentate coordination of pyzaH is lower than the thermal 
stability of [Zn(H
2
O)
2
(pyza)
2
] with chelate ligation of 
pyza
−
. During the thermal decomposition of 1, 2a and 4 in 
air, oxides MO (M = Mn, Ni, Zn) are formed.
Acknowledgments and founding
The author would like to thank the students Tina 
Boh, Klara Derganc, Natlija Papež and Žiga Počervina for 
their help with the syntheses and the colleagues Romana 
Cerc Korošec and Damjan Erčulj for the thermogravimet-
ric measurements.
The author acknowledges the support of the Center 
for Research Infrastructure at the University of Ljubljana, 
Faculty of Chemistry and Chemical Technology, which is 
part of the Network of Research and Infrastructural Cen-
tres UL (MRIC UL) and is financially supported by the 
Slovenian Research Agency (Infrastructure program No. 
I0-0022).
This research was funded by the Slovenian Research 
Agency (Grant no. P1-0230-0175).
5. References
  1.  P. Singh, A. K. Mishra, S. K. Malonia, D. S. Chauhan, V. 
D. Sharma, K. Venkatesan, V. M. Katoch, J. Commun. 
Dis. 2006, 38, 288–298.   DOI:10.1016/j.dld.2006.01.026
  2.  M. Stehr, A. A. Elamin, M. Singh, Curr. Top. Med. Chem. 
2014, 14, 110–129. 
 DOI:10.2174/1568026613666131113152908
  3.  H. Kulla, A. A. L.Michalchuk, F. Emmerling, Chem. Com-
mun. 2019, 55, 9793–9796.   DOI:10.1039/C9CC03034D
  4.  K. D. Prasad, S. Cherukuvada, R. Ganduri, L. D. Stephen, S. 
Perumalla, T. N. G. Row, Cryst. Growth Des. 2015, 15, 858–
866.   DOI:10.1021/cg501642m
  5.  A. M. Kirillova, G. B. Shul’pinb, Coordin. Chem. Rev. 2013, 
257, 732–754.   DOI:10.1016/j.ccr.2012.09.012
  6.  M. Sutradhar, L. M. Martins, M. F. C. G. da Silvaa, A. J. L. 
Pombeiroa, Coordin. Chem. Rev. 2015, 301–302, 200−239.
 DOI:10.1016/j.ccr.2015.01.020
  7.  M. A. S. Goher, T. C. W. Mak, Polyhedron 1995, 14, 2587–
2594.   DOI:10.1016/0277-5387(94)00489-2
  8.   O. Anjaneyulu, D. Maddileti, K. C. K. Swamy, Dalton Trans. 
2012, 41,1004–1012.   DOI:10.1039/C1DT11207D
  9.  S. Li, K. Hu, X. Gao, S. Jin, B. Chen, Z. Chen, L. He, D. Wang, 
J. Mol. Struct. 2022, 1261, 132770.
 DOI:10.1016/j.molstruc.2022.132770
10.   W . Xu, K. Hu, Y. Lu, H. Ye, S. Jin, M. Li, M. Guo, D. Wang, J. 
Mol. Struct. 2020, 1219, 128554.
 DOI:10.1016/j.molstruc.2020.128554
11.  X. Y ang, Y . Zhu, X. Chen, X. Gao, S. Jin, B. Liu, L. He, B. Chen, 
D. Wang, J. Mol. Struct. 2021, 1251
 DOI:10.1016/j.molstruc.2021.131917
12.  W . Fang, B. Chen, D. Chen, S. Wang, Y. Yan, S. Jin, W . Xu, D. 
Wang, J. Mol. Struct. 2020, 1203, 127353.
 DOI:10.1016/j.molstruc.2019.127353
13.  See the Cambridge Structural Database (CSD, version June 
2024): C. R. Groom, I. J. Bruno, M. P. Lightfoot and S. C. 
Ward, Acta Cryst. 2016, B72, 171−179.
 DOI:10.1107/S2052520616003954
14.  R. A. Coxall, S. G. Harris, D. K. Henderson, S. Parsons, P . A. 
Tasker, R. E. P . Winpenny, J. Chem. Soc., Dalton Trans. 2000, 
2349–2356.   DOI:10.1039/b001404o
15.  D. M. Ciurtin, M. D. Smith, H. C. zur Loye, Polyhedron 2003, 
22, 3043–3049.   DOI:10.1016/S0277-5387(03)00430-3
16.  C. L. Klein, L. M. Trefonas, C. J. O'Connor, R. J. Majeste, 
Cryst. Struct. Commun. 1981, 10, 891–894.
17.  S. Konar, U. Saha, M. Dolai, S. Chatterjee, J. Mol. Struct. 2014, 
1075, 286–291.   DOI:10.1016/j.molstruc.2014.06.080
18.  C. Dares, R. Fournier, A. B. P . Lever, Acta Crystallogr. E 2011, 
67, m1798–m1799.   DOI:10.1107/S1600536811048628
19.  X. H. Zhao, Russ. J. Coord. Chem. 2011, 37, 585–588.
Figure 8. Thermal analysis of 2a (black lines) and 4 (green lines).

144
Acta Chim. Slov. 2025, 72, 133–144
Petriček:   Manganese, Cobalt, Nickel and Zinc Complexes with   ...
 DOI:10.1134/S1070328411080124
20.   H. Lin, X. Wu, P . A. Maggard, Inorg. Chem. 2009, 48, 11265–
11276.   DOI:10.1021/ic901749r
21.  S. Nayak, K. Harms, S. Dehnen, Inorg. Chem. 2011, 50, 2714–
2716.   DOI:10.1021/ic1019636
22.  M. A. S. Goher, F . A. Mautner, R. Vicente, J. Mol. Struct. 2007, 
846, 28–33.   DOI:10.1016/j.molstruc.2007.01.016
23.  L. Arizaga, R. Gonzalez, D. Armentano, G. De Munno, M. A. 
Novak, F . Lloret, M. Julve, C. Kremer, R. Chiozzone, Eur. J. In-
org. Chem. 2016, 1835–1845.   DOI:10.1002/ejic.201501487
24.  A. Cuevas, C. Kremer, M. Hummert, H. Schumann, F . Lloret, 
M. Julve, J. Faus, Dalton Trans. 2007, 342–350.
 DOI:10.1039/B611888G
25.  G. W . Wang, W . Y. Wu, L. H. Zhuang, J. T. Wang, Acta Crys-
tallogr., Sect.E: Struct. Rep. Online 2008, 64, m13.
 DOI:10.1107/S1600536807061491
26.  S. P et r iče k, Polyhedron 2019, 167, 11−25.
 DOI:10.1016/j.poly.2019.03.050
27.  S. P et r iče k, Molecules 2020, 25, 846−869.
 DOI:10.3390/molecules25040846
28.  S. P et r iče k, J. Mol. Struct. 2022, 1260, 132790.
 DOI:10.1016/j.molstruc.2022.132790
29.   CrysAlisPro, version 1.171.43.121a; Rigaku Oxford Diffrac-
tion: Y arnton, UK, 2024.
30.   M. C. Burla, R. Caliandro, B. Carrozzini, G. L. Cascarano, 
C. Cuocci, C. Giacovazzo, M. Mallamo, A. Mazzone, G. Po-
lidori, J. Appl. Cryst. 2015, 48, 306−309.
 DOI:10.1107/S1600576715001132
31.   G. M. Sheldrick, Acta Crystallogr. 2015, C71, 3–8.
 DOI:10.1107/S2053229614024218
32.   J. J. Farrugia, J. Appl. Cryst. 1997, 30, 565.
 DOI:10.1107/S0021889897003117
33.   C. F. Macrae, I. Sovago, S. J. Cottrell, P. T. A. Galek, P. Mc-
Cabe, E. Pidcock, M. Platings, G. P . Shields, J. S. Stevens, M. 
Towler and P . A. Wood, J. Appl. Cryst. 2020, 53, 226−235.
 DOI:10.1107/S1600576719014092
34.  G. Świderski, S. Wojtulewski, M. Kalinowska, R. . Świsłoc-
ka, A. Z. Wilczewska, A. Pietryczuk, A. Cudowski, W. Le-
wandowski, Polyhedron 2020, 175, 114173.
 DOI:10.1016/j.poly.2019.114173
35.  M. Shahwaz Ahmad, M. Khalid, M. Shahnawaz Khan, M. 
Shahid, M. Ahmad, Cryst. Eng. Comm. 2021, 23, 6253–6266.
 DOI:10.1039/D1CE00815C
36.  S. A. Shirvan, S. H. Dezfuli, Acta Crystallogr., Sect.E: Struct. 
Rep. Online 2012, 68, m546. 
 DOI:10.1107/S1600536812013888
37.  C. Nather, I. Jess, S. Mangelsen, Z. Naturforsch., B. Chem. Sci. 
2023, 78, 113−120.   DOI:10.1515/znb-2022-0306
38.  S. Gao, S. W . Ng, Acta Crystallogr., Sect.E: Struct. Rep.Online 
2011, 67, m1049−m1050.   DOI:10.1107/S1600536811026031
39.  C. Hu, U. Englert, Acta Cryst. 2001, C57, 1251−1252.
 DOI:10.1107/S0108270101012136
40.  H. R. Khavasi, A. Gholami, M. Hosseini, L. Nikpoor, K. Es-
kandari, Cryst. Growth Des. 2020, 20, 2266−2274.
 DOI:10.1021/acs.cgd.9b01385
41.  N. Podjed, B. Modec, J. Mol. Struct. 2023, 1284, 135457.
 DOI:10.1016/j.molstruc.2023.135457
42.  D. Zaouali Zgolli, H. Boughzala, A. Driss, Acta Crystallogr. 
2009, E65, m921.   DOI:10.1107/S1600536809026804
43.  D. Domide, O. Hübner, S. Behrens, O. Walter, H. Wadepohl, 
E. Kaifer, H. J. Himmel, Eur. J. Inorg. Chem. 2011, 1387–1394. 
 DOI:10.1002/ejic.201100019
44.  D. Huang, X. Zhang, C. Chen, F. Chen, Q. Liu, D. Liao, L. Li, 
L. Sun, Inorg. Chim. Acta 2003, 353, 284−291.
 DOI:10.1016/S0020-1693(03)00325-6
45.  C. J a ni a k, J. Chem. Soc. Dalton Trans. 2000, 3885–3896.
 DOI:10.1039/b003010o
46.  D. B. Losee, J. N. McElearney, G. E. Shankle, R. L. Carlin, 
Phys. Rev. B 1973, 8, 2185–2196.
 DOI:10.1103/PhysRevB.8.2185
47.  S. Petriček, Croat. Chem. Acta 2011, 84, 515–520.
 DOI:10.5562/cca1747
Except when otherwise noted, articles in this journal are published under the terms and conditions of the  
Creative Commons Attribution 4.0 International License
Povzetek
Sintetizirali smo nove koordinacijske spojine cinkovega (1), manganovega(II) (2 in 2a), kobaltovega(II) (3) in niklje-
vega(II) klorida (4) s pyzaH (pirazin-2-karboksilna kislina). Rezultati rentgenske strukturne analize potrjujejo, da se 
molekule pyzaH koordinirajo v spojinah 1, 2 in 3 kot enovezni ligandi prek obročnega dušikovega atoma. Kloridni 
ioni so vezani kot terminalni ligandi v enojedrni spojini 1, [ZnCl
2
(pyzaH)
2
]∙2H
2
O, oziroma kot mostovni ligandi v 1D 
kompleksih [MCl
2
(pyzaH)
2
]
n
∙2nH
2
O (M = Mn, 2, Co, 3). Razlike v vezavi kloridnih ionov, interakcijah med vezanimi 
molekulami pyzaH in vodikovih vezeh v izoliranih spojinah omogočajo različno povezavo gradnikov v snovi. V naspro-
tju s kristali izoliranimi za spojine 1, 2 in 3 v spojinah mangana(II) (2a) in niklja(II) (4) ni vezana voda. Za spojini 2a in 
4 lahko glede na IR spektre in rezultate termične analize predpostavimo formulo [MCl
2
(pyzaH)
2
]. Rezultati rentgenske 
praškovne analize in termične analize potrjujejo, da sta spojini 2a in 4 izostrukturni. Monodentatna vezava molekul 
pyzaH v 1 je vzrok za nizko termično stabilnost kompleksa 1. Po termičnem razpadu spojin 1, 2a in 4 v zraku nastanejo 
MO (M = Mn, Ni, Zn).