A novel paramagnetic coordination polymer, fabricated from Co(NCS)2 and 2-pyridinecarbaldehyde isonicotinoylhydrazone

Article abstract of DOI:10.1016/j.ica.2021.120335

We report on a mixed cobalt(II)/cobalt(III) heteroleptic coordination polymer of the salt-like structure {[(Co^IIIL₂)₂Co^II(NCS)₂][Co^II(NCS)₄]}_n?a(solvent) (1?a(solvent)), obtained by a reaction of Co(NCS)₂ with 2-pyridinecarbaldehyde isonicotinoylhydrazone (HL). Complex 1?a(solvent) contains 15.52% of solvent molecules, which fits to six molecules of EtOH per one [(Co^IIIL₂)₂Co^II(NCS)₂][Co^II(NCS)₄] species, and the structure of the crystals can be assigned to the {[(Co^IIIL₂)₂Co^II(NCS)₂][Co^II(NCS)₄]}_n?6EtOH composition. 1?a(solvent) was found to be stable after drying at 80 °C for several days, yielding a solvent-free complex 1. The FTIR data of both structures supports the complete loss of solvents after drying, while the general framework remains intact. As evident from the comparison of the experimental X-ray powder diffraction data of 1 with the calculated powder pattern generated from the single crystal X-ray data of 1?a(solvent), the former complex partially loses its crystallinity; however, the experimental powder pattern resembles the calculated one. Thus, the overall structure of 1 is similar to that of 1?a(solvent). The crystal structure of 1?a(solvent) is constructed from the V-shaped (Co^IIIL₂)⁺ cations, where the metal ion is N₄S₂-coordinated by two L. These (Co^IIIL₂)⁺ cations are interlinked through Co^II(NCS)₂ molecules by coordination via free 4-pyridyl nitrogen atoms, yielding a 1D polymeric cationic chain {[(Co^IIIL₂)₂Co^II(NCS)₂]²⁺}_n, which are interlinked into a 3D framework through a bunch of bifurcated (N)C–S?π(2-Py) and linear (NN)C–H?O non-covalent interactions. Due to such 3D aggregation, a half of rhombohedral cells are filled by the interlayered [Co^II(NCS)₄]^2– anions, while the other half of cells is free from non-volatile species and filled with volatile solvent molecules, yielding 1D tubular voids, which occupy about 17% of unit cell volume. Direct current variable-temperature magnetic susceptibility measurements on a polycrystalline sample of 1?a(solvent) were carried out in the temperature range 1.8–300 K. The magnetic behaviour of 1?a(solvent) indicates the presence of magnetic anisotropy of the Co^II ions and/or very weak intermolecular exchange interactions. The surface and pore properties of 1 and HL were calculated by N₂ adsorption at 77 K. In addition, CO₂ adsorption properties of 1 and HL at different temperatures were determined. It was found that 1 increased both textural and CO₂ adsorption properties.

Full text of DOI:10.1016/j.ica.2021.120335

Inorganica Chimica Acta 522 (2021) 120335
Contents lists available at ScienceDirect
Inorganica Chimica Acta
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Research paper
A novel paramagnetic coordination polymer, fabricated from Co(NCS)2 and
2-pyridinecarbaldehyde isonicotinoylhydrazone
Burak Aya, Ghodrat Mahmoudib *, Ali Akbar Khandarc, Farhad Akbari Afkhamic,
,
,
i,
j,
*
Atakan Toprakd, Fedor I. Zubkove, Jonathan Whitef, Julia Kłakg, Damir A. Safinh
a Çukurova University, Arts and Science Faculty, Department of Chemistry, 01330 Adana, Turkey
b Department of Chemistry, Faculty of Science, University of Maragheh, P.O. Box 55181-83111, Maragheh, Iran
c Department of Inorganic Chemistry, Faculty of Chemistry, University of Tabriz, 51666-16471 Tabriz, Iran
d Department of Chemistry and Chemical Process Technology, Bülent Ecevit University, 67800 Zonguldak, Turkey
e Organic Chemistry Department, Faculty of Science, Peoples’ Friendship University of Russia (RUDN University), Miklukho-Maklaya Str. 6, Moscow 117198, Russian
Federation
f BIO-21 Molecular Science and Biotechnology, University of Melbourne, Parkville, Victoria 3052, Australia
g Faculty of Chemistry, University of Wroclaw, 14, F. Joliot-Curie Str.50-383 Wroclaw, Poland
h University of Tyumen, Volodarskogo Str. 6, 625003 Tyumen, Russian Federation
i Kurgan State University, Sovetskaya Str. 63/4, 640020, Russian Federation
j Innovation Center for Chemical and Pharmaceutical Technologies, Ural Federal University named after the First President of Russia B.N. Eltsin, Mira Str. 19,
Ekaterinburg 620002, Russian Federation
A R T I C L E I N F O
A B S T R A C T
Keywords:
We report on a mixed cobalt(II)/cobalt(III) heteroleptic coordination polymer of the salt-like structure
{[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙a(solvent) (1∙a(solvent)), obtained by a reaction of Co(NCS)2 with 2-pyr-
idinecarbaldehyde isonicotinoylhydrazone (HL). Complex 1∙a(solvent) contains 15.52% of solvent molecules,
which fits to six molecules of EtOH per one [(CoIIIL2)2CoII(NCS)2][CoII(NCS)4] species, and the structure of the
crystals can be assigned to the {[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙6EtOH composition. 1∙a(solvent) was
found to be stable after drying at 80 ◦C for several days, yielding a solvent-free complex 1. The FTIR data of both
structures supports the complete loss of solvents after drying, while the general framework remains intact. As
evident from the comparison of the experimental X-ray powder diffraction data of 1 with the calculated powder
pattern generated from the single crystal X-ray data of 1∙a(solvent), the former complex partially loses its
crystallinity; however, the experimental powder pattern resembles the calculated one. Thus, the overall structure
of 1 is similar to that of 1∙a(solvent). The crystal structure of 1∙a(solvent) is constructed from the V-shaped
(CoIIIL2)+ cations, where the metal ion is N4S2-coordinated by two L. These (CoIIIL2)+ cations are interlinked
through CoII(NCS)2 molecules by coordination via free 4-pyridyl nitrogen atoms, yielding a 1D polymeric
cationic chain {[(CoIIIL2)2CoII(NCS)2]2+}n, which are interlinked into a 3D framework through a bunch of
Cobalt
Coordination polymer
Crystal structure
X-ray crystallography
Magnetic properties
Adsorption properties
bifurcated (N)C–S⋯π(2-Py) and linear (NN)C–H⋯O non-covalent interactions. Due to such 3D aggregation, a
half of rhombohedral cells are filled by the interlayered [CoII(NCS)4]2– anions, while the other half of cells is free
from non-volatile species and filled with volatile solvent molecules, yielding 1D tubular voids, which occupy
about 17% of unit cell volume. Direct current variable-temperature magnetic susceptibility measurements on a
polycrystalline sample of 1∙a(solvent) were carried out in the temperature range 1.8–300 K. The magnetic
behaviour of 1∙a(solvent) indicates the presence of magnetic anisotropy of the CoII ions and/or very weak
intermolecular exchange interactions. The surface and pore properties of 1 and HL were calculated by N2
adsorption at 77 K. In addition, CO2 adsorption properties of 1 and HL at different temperatures were deter-
mined. It was found that 1 increased both textural and CO2 adsorption properties.
* Corresponding authors at: University of Tyumen, Volodarskogo Str. 6, 625003 Tyumen, Russian Federation (D.A. Safin).
E-mail addresses: ghodratmahmoudi@gmail.com (G. Mahmoudi), damir.a.safin@gmail.com (D.A. Safin).
https://doi.org/10.1016/j.ica.2021.120335
Received 29 January 2021; Received in revised form 2 March 2021; Accepted 2 March 2021
Available online 9 March 2021
0020-1693/© 2021 Elsevier B.V. All rights reserved.

B. Ay et al.
Inorganica Chimica Acta 522 (2021) 120335
1. Introduction
generally interact with each other by hydrogen bonds (involving the
amide groups), which are important for constructing supramolecular
arrays [23–33]. Thus, using this type of ligands is of particular interest
for the formation of supramolecular architectures and especially CPs and
MOFs. Furthermore, we have recently directed our attention to
intriguing coordination chemistry of poly-N-donor ligands, viz. tris(4-
pyridyl)-1,3,5-triazine (TPT) [34–37] and 2,4,6-tris(2-pyrimidyl)-
1,3,5-triazine (TPymT) [38–45]. Notably, we have also shed light on the
barely unstable porous MOF of TPT with Co(NCS)2 [34,35].
Coordination polymers (CPs) [1–3] are crystalline materials and a
family of coordination compounds that are made by the spontaneous
self-assembly of two building blocks including metal ions (nodes) and
bridging ligands (linkers) in which the coordination bonds lead to the
formation of an infinite array of metal-ligand units that extends into one,
two or three dimensions [4–9]. CPs have become of great importance in
different fields and many practical applications such as catalysis, mag-
netic and optical materials, etc. [10,11]
In this work we continue our comprehensive studies on the coordi-
nation chemistry of the pyridine-hydrazine based chelating-bridging
ligands. Herein we describe the design, construction and deep struc-
tural investigations on new mixed cobalt(II)/cobalt(III) heteroleptic
coordination polymer of the salt-like structure, obtained from the re-
Of CPs, the so-called metal-organic frameworks, abbreviated as
MOFs [1–3], is an outstanding class of compounds. Since MOFs were
first discovered and reported by Omar Yaghi in the middle of 90s of past
century [12], they have become an ever-growing area of both funda-
mental and applied chemistry and were in the limelight of many studies.
It is worth mentioning a number of themed collections of articles about
MOFs [13–18].
action
of
Co(NCS)2
with
2-pyridinecarbaldehyde
iso-
nicotinoylhydrazone, HL (Scheme 1). We also report on magnetic
properties of the obtained complex as well as adsorption properties to-
wards N2 and CO2 of both HL and complex.
MOFs are usually constructed from metal ions or their clusters,
linked by organic ligands, yielding porous structures. As such, both
coordination and non-covalent bonds are of importance as a driving
force for the design of structures of interest. Porousity of MOFs dictates
one of their most outstanding, but not limited, practical applications for
gas storage and separation [10,19–22]. Thus, crystal engineering ap-
proaches are a powerful tool in the synthesis of MOFs with fine tuned
porous shape and volume. However, the ability to predict and control
the supramolecular assembly of molecules still remains a challenge, and
much more work is required to understand the inter- and intramolecular
forces that determine the patterns of molecular structure and crystal
packing.
2. Experimental and theoretical methods
2.1. Physical measurements
Infrared spectra (KBr pellets) were recorded with a Perkin-Elmer RX-
1 spectrometer in the range 400–4000 cmꢀ 1. Thermogravimetric (TG)
analyses were performed by a Perkin Elmer Pyris Diamond TG/DTA
instrument in a dynamic air atmosphere (100 mL∙minꢀ 1) from 25 ◦C to
950 ◦C with a 10 ◦C minꢀ 1 heating rate. Microanalyses were performed
using a Thermo Flash 2000 CHNS analyzer. The magnetization of a
powdered sample of 1∙a(solvent) was measured over the temperature
range 1.8–300 K using a Quantum Design SQUID-based MPMSXL–5-type
magnetometer. The superconducting magnet was generally operated at
On the other hand, pyridine-hydrazine based chelating-bridging li-
gands could potentially coordinate to the metal centers through their
pyridyl nitrogen atoms and especially those are containing amide groups
N
H
N
N
O
N
HL
Co(NCS)2
S
C
S
C
S
C
N
CoII
N
CoII
N
CoII
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
C
C
C
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
S
S
S
O
O
N
N
O
O
N
N
O
O
N
N
N
N
O
O
N
N
O
O
N
N
O
O
solvent
solvent
solvent
S
C
S
C
molecules
molecules
molecules
S
S
S
N
CoII
N
CoII
C
N
CoII
C
N
CoII
C
N
N
N
N
N
N
N
N
N
N
N
N
N
N
C
N
N
N
N
C
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
C
C
C
C
C
C
C
C
C
C
C
C
S
S
S
S
S
S
S
S
S
S
S
S
N
N
Co
N
N
N
S
S
S
S
S
S
C
C
C
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
S
S
S
O
O
N
N
O
O
N
N
O
O
N
N
N
N
O
O
N
N
O
O
N
N
O
O
solvent
solvent
solvent
S
C
S
C
molecules
molecules
molecules
S
S
S
N
CoII
N
CoII
C
N
CoII
C
N
CoII
C
N
CoII
N
N
N
N
N
N
N
N
N
N
N
N
N
C
N
C
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
C
C
C
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
N
CoIII
N
S
S
S
O
O
N
N
O
O
N
N
O
O
N
N
N
N
O
O
N
N
O
O
N
N
O
O
solvent
solvent
solvent
S
C
S
C
molecules
molecules
molecules
S
S
S
N
CoII
N
CoII
C
N
CoII
C
C
N
CoII
N
N
N
N
N
N
N
C
N
C
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
CoII
N
N
N
C
C
C
S
S
S
1 a(solvent)
Scheme 1. Synthesis of 1∙a(solvent).
2

B. Ay et al.
Inorganica Chimica Acta 522 (2021) 120335
a field strength ranging from 0 to 5 T. Measurements were performed at
magnetic field 0.5 T. The SQUID magnetometer was calibrated with the
palladium rod sample. Corrections are based on subtracting the sample –
holder signal and contribution χD estimated from the Pascal’s constants
[46]. The surface and pore characteristics of 1 and HL were determined
by volumetric method using a Quantachrome Instruments Autosorb-1C
device with N2 adsorption–desorption at 77 K. The CO2 adsorp-
tion–desorption by the samples of 1 and HL were measured using the
same method and device at different temperatures (0, 25, 50 and 75 ◦C).
Prior to N2 and CO2 adsorption–desorption measurements, degas pro-
cess under vacuum was carried out at 75 ◦C for 5 h.
lose solvent molecules at room temperature up to about 100 ◦C (Fig. 1).
The experimental weight loss due to solvent elimination is 15.52%,
which nicely fits to the calculated value of 15.69%. This weigh loss
nicely corresponds to six molecules of EtOH, which was used as a
crystallization medium, per one [(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]
species. Thus, the structure of the freshly obtained crystals can tenta-
tively be assigned to the {[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙6EtOH
composition. However, one should note that 96% EtOH was used as a
crystallization medim, which might mean that water molecules can also
be trapped as a lattice solvent.
After solvent elimination, compound 1∙a(solvent) decomposes in
two main steps, each of which is, most likely, a superposition of two or
even more barely observed decomposition steps (Fig. 1).
2.2. Synthesis
The bulk sample of 1∙a(solvent) was dried at 80 ◦C for several days
to probe the solvent loss as well as thermal stability of the framework.
According to the TG analysis the dried sample does not contain solvent
molecules and the general shape of the TG curve nicely resembles that of
1∙a(solvent) after about 100 ◦C, though a clear difference is visible after
about 600 ◦C (Fig. 1).
To a solution of CoSO4⋅7H2O (0.337 g, 1.2 mmol) in MeOH (20 mL)
was added KNCS (0.233 g, 2.4 mmol). The resulting mixture was stirred
for 0.5 h at room temperature. The white precipitate was filtered off. The
ligand HL (0.091 g, 0.4 mmol) was then added to a hot solution of the
filtrate. The resulting solution was stirred for 3 h under reflux followed
by cooling to room temperature. The final solution was left for slow
evaporation. After few days, green precipitate was formed, which was
isolated by filtaration and recrystallized from 96% EtOH. After about
one week, X-ray suitable green plate-like single crystals of 1∙a(solvent)
were formed, which were isolated by filtration and few of them were
used for single crystal X-ray diffraction. The remaining bulk sample was
dried at 80 ◦C for several days. Yield of the dried sample: 0.125 g (84%).
1. Anal. Calc. for C54H36Co4N22O4S6 (1485.12): C 43.67, H 2.44 and
N 20.75; found: C 43.55, H 2.33 and N 20.62%.
The FTIR spectrum of 1∙a(solvent) contains an intense band at
2070 cmꢀ 1, accompanied with a shoulder at 2120 cmꢀ 1 (Fig. 2), which
can be assigned to the stretching vibration of the C=N bonds of the
isothiocyanate ligands. These bands are in the region, characteristic of
the N-coordinated therminal isothiocyanate ions [49]. The band at
455 cmꢀ 1 (Fig. 2), assigned to the bending vibration of the NCS ligands,
further supports the binding of isothiocyanate anions to metal centers
via its N-terminal. The FTIR spectrum of 1∙a(solvent) also exhibits an
intense band at 1610 cmꢀ 1, accompanied with a less intense shoulder at
1635 cmꢀ 1 (Fig. 2). This band corresponds to the carbonyl fragment and
partially overlapped with the bands for the C=N, C=C and N–N bonds
from the organic ligands L. In addition, the IR spectrum contains an
intense and broad band with several maxima from about 2950 cmꢀ 1 to
3670 cmꢀ 1 (Fig. 2), corresponding for the OH groups and overlapped
with the bands of the aliphatic CH functions.
2.3. X-ray powder diffraction
X-ray powder diffraction for a bulk sample was carried out using a
Rigaku Miniflex X-ray powder diffractometer (λ = 1.54059 Å).
The FTIR spectrum of the dried sample 1 is very similar to that of 1∙a
(solvent); however, a number of remarkable changes can be highlighted.
Particularly, bands for the stretching vibration of the C=N bonds of the
isothiocyanate ligands are now more resolved. While the main band is
shown at the same wavenumber of about 2070 cmꢀ 1, the other band is
remarkably shifted to high frequencies and is shown at about 2150 cmꢀ 1
(Fig. 2). This can tentatively be explained by shortening of the C–N
bonds of some of the isothiocyanate ligands, which were initially
involved in hydrogen bonding with the lattice solvent molecules.
Notably, the IR spectrum of 1 does not exhibit a characteristic band for
the OH group in the range 3000–3600 cmꢀ 1 (Fig. 2). This testifies to the
2.4. Single-crystal X-ray diffraction
Diffraction data of the freshly obtained crystals were collected on an
Oxford Diffraction SuperNova CCD diffractometer with Cu-Kα radiation
(λ = 1.54184 Å). The crystals were solved by direct methods using
SHELXS-2013 [47] and refined by full-matrix least-squares methods on
F2 using SHELXL-2013 [48]. All non-hydrogen atoms were refined with
anisotropic parameters. The OH hydrogen atom of 1 were located in a
difference map refined freely. Disordered solvent was removed using
Squeeze [48].
Crystal data for 1∙a(solvent). C50H36Co3N18O4S2, C4CoN4S4, sol-
vent; Mr = 1485.13 g molꢀ 1, T = 220(2) K, monoclinic, space group Cm,
a = 12.6297(12), b = 23.369(2), c = 12.037(2) Å, β = 91.691(13)◦,
V = 3551.1(7) Å3, Z = 2,
ρ
= 1.389 g cmꢀ 3
,
μ
(Cu-K
α
) = 9.311 mmꢀ 1, re-
flections: 24,638 collected, 6541 unique, Rint = 0.043, R1(all) = 0.0616,
wR2(all) = 0.1400, S = 1.046.
CCDC 2002739 contains the supplementary crystallographic data.
These data can be obtained free of charge via 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) 1223–336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
3. Results and discussion
A reaction of Co(NCS)2, prepared in-situ from CoSO4 and KNCS, with
HL in MeOH leads to a mixed cobalt(II)/cobalt(III) heteroleptic coor-
dination polymer of the salt-like structure {[(CoIIIL2)2CoII(NCS)2]
[CoII(NCS)4]}n∙a(solvent) (1∙a(solvent)) (Scheme 1). Complex was
isolated through recrystallization from EtOH as air-stable green plate-
like X-ray suitable single crystals with a good yield, testifying the for-
mation of the reported composition as a main final product.
Fig. 1. TG analyses of 1∙a(solvent) (black) and 1 (red) performed in a dynamic
According to the TG analysis data, complex 1∙a(solvent) starts to
air atmosphere.
3

B. Ay et al.
Inorganica Chimica Acta 522 (2021) 120335
Table 1
Selected bond lengths (Å) and angles (◦) for 1∙a(solvent).
Bond lengths
Co1–NPy
Co1–N(N)
Co1–O
1.916(7), 1.941(7)
1.845(7), 1.846(7)
1.901(5), 1.904(5)
Co2–NPy
Co2–N(CS)
Co3–N(CS)
CH–N(N)
N–N
2.184(7), 2.185(7)
2.041(9), 2.070(8)
1.934(12), 1.957(9), 1.972(11)
1.291(11), 1.298(10)
1.364(10), 1.374(10)
1.290(9), 1.312(9)
C–O
(Co2)N–C(S)
(Co2N)C–S
(Co3)N–C(S)
(Co3N)C–S
1.099(14), 1.135(15)
1.629(13), 1.640(12)
1.155(14), 1.164(19), 1.300(18)
1.513(16), 1.571(12), 1.607(15)
Bond angles
N
N
N
Py–Co1–NPy
Py–Co1–N(N)
Py–Co1–O
91.9(3)
82.4(3), 83.2(3), 99.4(3), 101.7(3)
92.5(3), 91.4(3), 165.0(3), 165.5(3)
175.1(3)
Fig. 2. FTIR spectra of 1∙a(solvent) (black) and 1 (red).
N(N)–Co1–N(N)
N(N)–Co1–O
O–Co1–O
82.4(3), 82.7(3), 93.3(3), 94.8(3)
88.0(2)
absence of solvent molecules in the structure of 1.
N
Py–Co2–NPy
84.8(2), 95.6(3), 179.4(2)
89.6(3), 89.7(2), 91.0(3)
179.0(4)
Thus, the FTIR spectrum of 1∙a(solvent) supports the presence of
solvent, most likely EtOH, molecules in the structure of this complex,
while the dried complex 1 is completely free from lattice solvents.
Compound 1∙a(solvent) crystallizes in monoclinic space group Cm
and its asymmetric unit consists of one binuclear heteroleptic [(CoIIIL2)
CoII(NCS)2]+ cation and one [CoII(NCS)3]– anion. The structural analysis
shows the CoIII cation, namely Co1, is coordinated by two deprotonated
ligands L through two 2-pyridyl nitrogen atoms, two diaza nitrogen
atoms and two carbonyl oxygen atoms, yielding a monomuclear cationic
(CoIIIL2)+ building unit with a CoN4O2 chromophore (Fig. 3). The co-
ordination polyhedron is best described as a distorted octahedron with
the Co1–NPy/O bond lengths ranging from 1.901(5) to 1.941(7) Å
(Table 1). The Co1–N(N) bonds are clearly shorter and of 1.845(7) Å.
The bond angles, formed by the cis-situated coordination atoms, vary
from 82.4(3)◦ to 101.7(3)◦, while the same angles, formed by the trans-
oriented donors are more than 165◦ (Table 1). The pyridyl rings within
the same organic ligand are rotated relative to each other to about 20◦.
In general, two ligands L are coordinated to Co1 almost orthogonal as
evidenced from the dihedral angles of about 81◦ and 88◦ between the
least square planes, formed by the whole ligands or by their chelate
fragments, respectively (Table 1).
N
Py–Co2–N(CS)
N(CS)–Co2–N(CS)
N(CS)–Co3–N(CS)
Co2–N–C(S)
105.9(3), 109.4(3), 111.7(4), 114.4(5)
154.8(9), 162.2(10)
Co3–N–C(S)
170.8(11), 172.9(9), 172.6(12)
177.3(13), 179.7(11)
(Co2)N–C–S
(Co3)N–C–S
174.1(13), 177.8(14), 178.2(9)
Dihedral angles
2-Py⋯4-Py
19.8(4), 20.4(4)
88.39
2-PyC(H)NNCO⋯2-PyC(H)NNCO
L⋯L
80.62
coordination polyhedron is best described as a slightly distorted octa-
hedron with the Co2–NPy and Co2–N(CS) bond lengths being about 2.18
and 2.05 Å, respectively, with the two N-bound isothiocyanate ligands
occupying apical positions (Table 1). The bond angles, formed by the cis-
situated coordination atoms, vary from 84.8(2)◦ to 95.6(3)◦, while the
same angles, formed by the trans-oriented donors are almost linear
(Table 1). As a result of this aggregation, a 1D polymeric cationic chain
{[(CoIIIL2)2CoII(NCS)2]2+
} is formed in the crystal structure of 1∙a
n
The general V-shaped structure of the (CoIIIL2)+ cation together with
the presence of non-coordinated 4-pyridyl fragments dictate further self-
assembling in the structure of 1∙a(solvent). Particularly, the (CoIIIL2)+
cations are interlinked trough CoII(NCS)2 species, which metal ion is
named as Co2, yielding a CoN6 chromophore (Fig. 3). The resulting
(solvent) (Fig. 4). This chain consists of rhombohedral cells with the
CoII–CoIII distances of about 8.94 Å, while the CoII⋯CoII and CoIII⋯CoIII
separations are about 12.04 and 13.22 Å, respectively. The
CoII⋯CoIII⋯CoII and CoIII⋯CoII⋯CoIII angles are about 84.62◦ and
95.41◦, respectively.
1D polymeric cationic chains {[(CoIIIL2)2CoII(NCS)2]2+
} are side-
n
by-side interlinked into a 2D layer (Fig. 5) through bifurcated (N)
C–S⋯π(2-Py) non-covalent interactions (Table 2), formed by one of the
2-pyridyl rings of adjacent (CoIIIL2)+ cations and the sulfur atom of one
of the [CoII(NCS)4]2– anions, which is penetrated orthogonal in the
middle of the cavity formed by four 2-pyridyl fragments (Fig. 5). The
resulting supramolecular 2D layers are further interlinked through a
banch of (NN)C–H⋯O non-covalent interactions (Table 2), formed be-
tween the imine CH hydroge atoms and carbonyl oxygen atom from an
adjacent 2D layer. As a result, supramolecular 3D framework is formed
(Fig. 6). Due to such 3D aggregation, a half of the rhombohedral cells of
1D polymeric cationic chains is filled by the sulfur atoms of the second
[CoII(NCS)4]2– isothiocyanate anions, which is opposite to that situated
in the cavity formed by four 2-pyridyl fragments from two adjacent
(CoIIIL2)+ cations (Fig. 6). Remaining two [CoII(NCS)4]2– isothiocyanate
anions are situated in the plane orthogonal to the plane formed by the
first two anions, and placed between the 2D layers (Fig. 6).
Notably, the other half of the rhombohedral cells is free from non-
volatile species and filled with volatile solvent molecules (Scheme 1,
Fig. 3. Crystal structure of 1∙a(solvent) (50% atomic displacement ellipsoids
are shown). Color code: H = black, C = gold, N = blue, O = red, S = yel-
low, Co = magenta.
4

B. Ay et al.
Inorganica Chimica Acta 522 (2021) 120335
Fig. 4. A 1D polymeric cationic chain {[(CoIIIL2)2CoII(NCS)2]2+
S = yellow, Co = magenta.
}
in the crystal structure of 1∙a(solvent). Color code: H = black, C = gold, N = blue, O = red,
n
see discussion above). As a result, 1D tubular voids are formed, which
occupy about 17% of unit cell volume. Thus, the obtained compound
1∙a(solvent) is a mixed cobalt(II)/cobalt(III) porous metal-organic
framework.
indicates some similarities as well as highlights its uniqueness, of which
the most remarkable ones are, in our opinion, the formation of porous
structure, and the crucial influence of the ancillary isothiocyanate li-
gands in the global structure formation and stabilization.
It should be also added, that the discrete mononuclear non-
coordinated [CoII(NCS)4]2– anions counterbalance 1D polymeric
cationic chains {[(CoIIIL2)2CoII(NCS)2]2+}n. These anions adopt a
tetrahedral configuration with a CoN4 chromophore, formed by four N-
bound isothiocyanate anions (Fig. 3). The Co3–N(CS) bond lengths are
about 1.95 Å, while the (Co3)N–C(S) and (Co3N)C–S bonds are in the
ranges 1.155(14)–1.300(18) and 1.513(16)–1.607(15) Å, respectively
(Table 1). The Co3–N–C(S) and (Co3)N–C–S bond angles are almost
linear and vary from 170.8(11)◦ to 178.2(9)◦ (Table 1).
The bulk sample 1 was studied by X-ray powder diffraction and the
experimental powder pattern was compared with the calculated powder
pattern generated from the single crystal X-ray data of 1∙a(solvent). As
evident from the obtained results, significant lost of crystallinity can be
highlighted for 1, though some peaks resemble those in the calculated X-
ray powder pattern of 1∙a(solvent) (Fig. 7). Thus, the crystal structure of
1 is a challenge due to partial amorphization.
The magnetic properties of 1∙a(solvent) were determined over the
temperature range of 1.8–300 K. Plots of reciprocal magnetic suscepti-
bility, 1/χm and χmT product versus T (χm is the molar magnetic sus-
Notably, to the best of our knowledge, only three crystal structures of
cobalt(II/III) complexes with HL are known, namely [CoIII(HL)L]
(NO3)2∙0.5MeOH⋅H2O (2) and [CoIIIL2CoIICl3]∙2H2O (3) [50] and
[CoII(HL)2](NO3)2 (4) [51]. From the structures of these complexes a
number of general and specific features can be highlighted: i) all the
reported complexes exhibit a non-porous discrete structure; ii) the cobalt
(II) ion tends to be oxidized to cobalt(III) upon complexation; iii) the HL
ligands in the structures of complexes 2 and 4 are protonated at its
isonicotinoyl nitrogen atom; i.e., the protonated ligand is present in a
zwitterionic pyridinium/amidate form; iv) complexes 2 and 4 exhibit a
salt-like structure; v) complex 3 is a mixed cobalt(II)/cobalt(III) com-
pound, where organic ligands are N2O-coordinated to CoIII, while the
CoII is in a tetrahedral NCl3 coordination environment formed by one of
the 4-pyridyl nitrogen atoms and three chloride anions. Comparison of
these listed features of the reported complexes 2–4 with the structural
findings of the reported in this work complex 1∙a(solvent) clearly
ceptibility per a CoII2CoIII unit) are given in Fig. 8. The value χmT at
2
300 K is 5.89 cm3 molꢀ 1 K (6.87 B.M.) and remains constant down to
about 100 K. This magnetic moment is higher than the theoretical value
of 3.74 cm3 molꢀ 1 K (5.47 B.M.) for the spin-only value of two
magnetically isolated CoII ions with S = 3/2 and g = 2.0 and lies within
the range observed in other high-spin CoII compounds [52–55], indi-
cating spin-orbit contributions to the spin-only value. The two hex-
acoordinate CoIII shows diamagnetic low-spin states of a d6 electron
configuration. Upon cooling, χmT continuously decreases to reach a
value of 3.15 cm3 molꢀ 1 K (5.03 B.M) at 1.8 K. The decrease of χmT at
low temperatures can be basically caused by depopulation of the higher-
energy spin-orbit levels of the cobalt(II) centers and/or very weak
intermolecular exchange interactions. Additionally, there are no
maximum of the molar susceptibility at low temperature for 1∙a(sol-
vent). Thus, significant antiferromagnetic interactions in the solid state
5

B. Ay et al.
Inorganica Chimica Acta 522 (2021) 120335
Fig. 5. A 2D layer, constructed from the 1D polymeric cationic chains {[(CoIIIL2)2CoII(NCS)2]2+}n and discreted [CoII(NCS)4]2– anions, in the crystal structure of 1∙a
(solvent). Color code: H = black, C = gold, N = blue, O = red, S = yellow, Co = magenta.
can be excluded. No alternating current (AC) magnetic susceptibility
Table 2
signals were observed both in the absence and in the presence of applied
Weak non-covalent interactions lengths (Å) and angles (◦) for 1∙a(solvent).
static fields.
D–X⋯A
d(D–X)
d(X⋯A)
d(X⋯A)
∠(DXA)
The values of Curie and Weiss constants for 1∙a(solvent) were
determined from the 1/χm = f(T) relation. The obtained Curie constant is
5.92 cm3 molꢀ 1 K, while the Weiss temperature is negative and rela-
tively small (θ = –4.2 K). The obtained non-zero value of the Curie-Weiss
temperature very probable just reproduces the decrease of the product
χmT with lowering temperature due to the spin-orbit coupling rather
(NN)C–H⋯O
(NN)C–H⋯O
(Co3N)C–S⋯
0.93
2.60
3.446(10)
3.382(9)
3.747(11)
152
0.93
2.54
150
π(2-Py)
1.607(15)
3.869(5)
73.6(4)
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Inorganica Chimica Acta 522 (2021) 120335
Fig. 6. A 3D crystal packing of 1∙a(solvent). Hydrogen atoms were omitted for clarity. Color code: 1D polymeric cationic chain {[(CoIIIL2)2CoII(NCS)2]2+}n = red and
blue, [CoII(NCS)4]2– anion = green.
than the weak antiferromagnetic interaction [55].
splitting effect for the cobalt(II) ions and/or weak intermolecular anti-
ferromagnetic interaction.
To confirm the nature of the ground state of 1∙a(solvent), we
investigated the variation of the magnetization, M, with respect to the
The crystal structure of 1∙a(solvent) reveals that (CoIIIL2)+ cations
are interlinked through CoII(NCS)2 spaces, yielding a 1D polymeric
cationic chain {[(CoIIIL2)2CoII(NCS)2]2+}n. Additionally, the discrete
mononuclear non-coordinated [CoII(NCS)4]2– anions counterbalance 1D
polymeric cationic chains. Since the hexacoordinate CoIII cations are
diamagnetic, the magnetization in this sample results only from one
octahedral and one tetrahedral CoII ions. Taking into account the large
field at 2 K. The molar magnetization M per the CoII2CoIII entity is
2
expressed in μB units. The compound does not reach the saturation in the
applied field range and the magnetization at 5 T is about 5 μB (Fig. 9).
The shape of the curve does not follow the Brillouin function for two
uncoupled CoII ions of the S = 3/2 ground state with g = 2 in the absence
of zero-field splitting and demonstrate the role played by zero-field
7

B. Ay et al.
Inorganica Chimica Acta 522 (2021) 120335
Fig. 10. N2 adsorption-desorption isotherms of 1 and HL at 77 K.
Fig. 7. Calculated (black) and experimental (red) X-ray powder diffraction
patterns of 1∙a(solvent) and 1.
Table 3
Textural properties of 1 and HL.
BET (m2/
g)
Vmicro
Vmeso
Vtotal
Average pore size
(Å)
(cm3/g)
(cm3/g)
(cm3/g)
1
30.3
1.1
0.012
0.036
0.048
0.001
63.2
41.5
HL
0.0004
0.0006
distance (>12 Å) between the paramagnetic CoII ions in the chain, we
can assume almost total magnetic isolation of the CoII(NCS)2 blocks.
However, the nearest CoII⋯CoII distance between the CoII(NCS)2 units
and [CoII(NCS)4]2– anions is 5.78 Å and the exchange by the crystal
lattice is possible. Even in the case of several cobalt(II) interacting
centers, there is no easy way to calculate their magnetic coupling due to
the intense value of the spin-orbit coupling that these ions exhibit under
two different coordination scheme. It is known that the main factors
determining decreasing of magnetic moment in the low temperature
range can be attributed to the zero-field splitting (ZFS) of the CoII ions
and/or very weak intermolecular exchange interactions. A similar
compound is known in the literature and its structure is made up of two
CoIII-based [Co(bpcam)2]+ cations and CoII-based [Co(NCS)4]2–anions
(Hbpcam = bis(2-pyrimidylcarbonyl)amide) [56]. Its magnetic behav-
iour is directly defined by the zero-field splitting effects (DCo) of the
pseudotetrahedral [Co(NCS)4]2– anion. In the structure of 1∙a(solvent),
there is an additional hexacoordinate CoII ion. In this case, any trials to
fit magnetic data to determine the magnetic anisotropy parameters as
well as magnetic interaction result in overparametrization since both
CoII ions with different symmetry have to be considered. Thus, a quan-
titative analysis of 1∙a(solvent) is not possible and it is difficult to decide
which of these factors is dominant in magnetic behaviour.
Fig. 8. Temperature dependence of experimental 1/χm (the solid line is the fit
to the Curie-Weiss law) and χmT (χm is the molar magnetic susceptibility per a
CoII2CoIII2 unit) for 1∙a(solvent).
We have also studied adsorption properties of 1 towards N2 and CO2
in comparison to HL. It was found that HL has a Brunauer-Emmett-Teller
surface area of 1.1 m2/g, while 1 has a surface area of 30.3 m2/g
(Fig. 10, Table 3). This increase in the surface area relative to the ligand
is caused by the voids formed upon amorphization of 1. It was also
established, that the N2 isotherms of 1 (Fig. 10) conform to the type II
isotherm according to the classification of IUPAC and a H3 type hys-
teresis occurs in desorption [57]. Type II isotherms and H3 hysteresis
loop of 1 show that it has non-porous or macroporous adsorbent. Ac-
cording to the non-local density functional theory (NLDFT) pore distri-
bution, a very low volume of mesopores are formed (Fig. 11), which is
due the stacking of crystalline structures and small voids formed by
amorphization [58].
Fig. 9. Field dependence of the magnetization (M per a CoII2CoIII entity) for
2
1∙a(solvent). The solid line is the Brillouin function curve for the system of two
uncoupled CoII spins with S = 3/2 and g = 2.0 in the absence of zero-
field splitting.
The CO2 adsorption-desorption measurements of 1 and HL were
performed at different temperatures (0, 25, 50 and 75 ◦C). Although HL
exhibits a very low CO2 adsorption at 25 ◦C, complex 1 adsorption is
about 10 times higher at the same temperature (Fig. 12). For 1, as the
8

B. Ay et al.
Inorganica Chimica Acta 522 (2021) 120335
the experimental powder pattern resembles the calculated one. Thus,
the overall structure of 1 is similar to that of 1∙a(solvent).
The crystal structure of 1∙a(solvent) is constructed from the V-sha-
ped (CoIIIL2)+ cations, where the metal ion is coordinated by two
deprotonated ligands L through the 2-pyridyl and diaza nitrogen atoms
as well as the carbonyl oxygen atom. These (CoIIIL2)+ cations are further
interlinked through CoII(NCS)2 molecules by coordination via free 4-
pyridyl nitrogen atoms, yielding a 1D polymeric cationic chain
{[(CoIIIL2)2CoII(NCS)2]2+}n. This chain consists of rhombohedral cells
with the CoII–CoIII distances of about 8.94 Å, while the CoII⋯CoII and
CoIII⋯CoIII separations are about 12.04 and 13.22 Å, respectively. 1D
polymeric cationic chains are interlinked into a 3D framework through a
bunch of bifurcated (N)C–S⋯π(2-Py) and linear (NN)C–H⋯O non-co-
valent interactions. Due to such 3D aggregation, a half of rhombohedral
cells are filled by the [CoII(NCS)4]2– isothiocyanate anions, while the
other half of cells is free from non-volatile species and filled with volatile
solvent molecules, yielding 1D tubular voids, which occupy about 17%
of unit cell volume.
Fig. 11. The pore size distribution curve of 1.
Magnetic results for 1∙a(solvent) suggest that the effect of zero-field
splitting of CoII ions and/or very weak antiferromagnetic exchange in-
teractions between the CoII ions in the crystal lattice are totally
responsible for the decrease of the magnetic moment at low
temperatures.
Finally, complex 1∙a(solvent), as well as its solvent-free derivative 1,
are of potential interest as new porous coordination polymer for specific
binding and storage guest molecules as evidenced from the reported
herein adsorption properties towards N2 and CO2. The obtained com-
pounds extend a family of functional cobalt coordination polymers
[64,65].
5. Author statement
All persons who have made substantial contributions to the work
reported in the manuscript (e.g., technical help, writing and editing
assistance, general support).
Fig. 12. CO2 adsorption-desorption isotherms of 1 and HL at different
temperatures.
Declaration of Competing Interest
temperature increases, the CO2 adsorption decreases steadily. However,
1 exhibits efficient CO2 adsorption even at high temperatures such as
50 ◦C and 75 ◦C (Fig. 12). Furthermore, 1 does not reach equilibrium for
the CO2 adsorption at all temperatures. Based on these results, we can
claim that 1 can reach a higher CO2 adsorption capacity at higher
pressure values. We believe that, in accordance with the literature
[59–63], 1 is an efficient adsorbent for CO2 thanks to its N-functional
sites and Co metal in its structure.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgements
We are grateful to the University of Maragheh and Iran Science Elites
Federation for the financial support of this research. This paper has been
supported by the RUDN University Strategic Academic Leadership Pro-
gram (recipient F. I. Zubkov).
4. Conclusions
In summary, we have synthesized and fully characterized a mixed
cobalt(II)/cobalt(III) heteroleptic coordination polymer of the salt-like
structure {[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙a(solvent) (1∙a(sol-
vent)), which was obtained by a reaction of Co(NCS)2, prepared in-situ
from CoSO4 and KNCS, with 2-pyridinecarbaldehyde iso-
nicotinoylhydrazone (HL) in MeOH. X-ray suitable crystals of complex
were isolated by recrystallization from EtOH. As evidenced from the TG
analysis data, 1∙a(solvent) contains 15.52% of solvent molecules, which
nicely fits to six molecules of EtOH per one [(CoIIIL2)2CoII(NCS)2]
[CoII(NCS)4] species, and the structure of the freshly obtained crystals
can be assigned to the {[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙6EtOH
composition. After drying 1∙a(solvent) at 80 ◦C for several days, a
solvent-free complex 1 is formed. The FTIR data of both structures
support the complete loss of solvents after drying, while the general
framework remains intact. As evident from the comparison of the
experimental X-ray powder diffraction data of 1 with the calculated
powder pattern generated from the single crystal X-ray data of 1∙a
(solvent), the former complex partially loses its crystallinity; however,
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.ica.2021.120335.
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