Cobalt(II) complexes with pyridine and 5-[(E)-2-(aryl)-1-diazenyl]-quinolin-8-olates: synthesis, electrochemistry and X-ray structural characterization

Article abstract of DOI:10.1080/00958972.2018.1506876

Nine new cobalt(II) compounds, trans-[Co(L^PAQ)₂(Py)₂] (1), trans-[Co(L^PAQ)₂(3-MePy)₂] (2), trans-[Co(L^MeAQ)₂(Py)₂] (3), trans-[Co(L^OMeAQ)₂

Full text of DOI:10.1080/00958972.2018.1506876

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Cobalt(II) complexes with pyridine and 5-
[(E)-2-(aryl)-1-diazenyl]-quinolin-8-olates:
Synthesis, electrochemistry and X-ray structural
characterization
Tushar S. Basu Baul, Khrawborlang Nongsiej, Bruno G. M. Rocha & M. Fátima
C. Guedes da Silva
To cite this article: Tushar S. Basu Baul, Khrawborlang Nongsiej, Bruno G. M. Rocha & M. Fátima
C. Guedes da Silva (2018): Cobalt(II) complexes with pyridine and 5-[(E)-2-(aryl)-1-diazenyl]-
quinolin-8-olates: Synthesis, electrochemistry and X-ray structural characterization, Journal of
Coordination Chemistry, DOI: 10.1080/00958972.2018.1506876
To link to this article: https://doi.org/10.1080/00958972.2018.1506876
View supplementary material
Accepted author version posted online: 31
Jul 2018.
Submit your article to this journal
Article views: 4
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

Cobalt(II) complexes with pyridine and 5-[(E)-2-(aryl)-1-diazenyl]-quinolin-8-
olates: Synthesis, electrochemistry and X-ray structural characterization
TUSHAR S. BASU BAUL*†, KHRAWBORLANG NONGSIEJ†, BRUNO G. M. ROCHA‡ and
M. FÁTIMA C. GUEDES DA SILVA*‡
†Centre for Advanced Studies in Chemistry, North-Eastern Hill University, NEHU Permanent Campus,
Umshing, Shillong 793022, India
‡Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais,
1049-001 Lisboa, Portugal
Nine new cobalt(II) compounds, trans-[Co(LPAQ)2(Py)2] (1), trans-[Co(LPAQ)2(3-MePy)2] (2),
trans-[Co(LMeAQ)2(Py)2] (3), trans-[Co(LOMeAQ)2(Py)2] (4), trans-[Co(LOEtAQ)2(Py)2]·2(H2O) (5),
trans-[Co(LCAQ)2(Py)2] (6), trans-[Co(LBAQ)2(Py)2] (7), cis-[Co(LBAQ)2(3-MePy)2] (8a) and
trans-[Co(LBAQ)2(3-MePy)2]·2(3-MePy) (8b) (primary ligand: LXAQ = substituted 5-[(E)-2-
(aryl)-1-diazenyl]quinolin-8-olate; secondary ligands: Py
=
pyridine, 3-MePy
=
3-methylpyridine), have been synthesized and characterized by elemental analysis, IR and
UV-vis spectroscopy. Magnetic measurements of the cobalt compounds were performed in
1
solution by H NMR spectroscopy using the Evans’ method while their redox properties were
studied by cyclic voltammetry. Single-crystal X-ray diffraction analysis of the compounds
revealed their octahedral geometries and trans configuration, except for 8a, which has a cis
configuration. Intermolecular non-covalent interactions were detected, π···π interactions in 5,
CH··· interactions in 2 and CH··· edge-to-face (T-shaped) arrangements in 3, 4, 6 and 7.
Keywords: Substituted quinolin-8-olate; Cobalt; Secondary ligands; Magnetic moment;
Electrochemistry; Structure elucidation
1. Introduction
Quinolin-8-ol (HLQ) is a well-known complexone or sequestering reagent, which possesses two
potential protonation sites, a pyridyl nitrogen atom and a phenolate oxygen atom [1, 2]. A
structural perspective of HLQ in medicinal chemistry pertaining to biological activities,
interactions with metal ions and mechanisms of action has been described [3]. The ligand LQ
*Corresponding authors. Email: basubaul@nehu.ac.in, basubaulchem@gmail.com (T.S. Basu Baul);
fatima.guedes@tecnico.ulisboa.pt (M. Fátima C. Guedes da Silva)

chelates most of the di-valent ([M(LQ)2], M = Mn, Co, Ni, Cu and Zn) and tri-valent metal ions
([Al(LQ)3]), and consequently can be used in an arsenal for various applications in
supramolecular sensors, emitting devices or self-assembled aggregates [4-12]. Research efforts
have also focused on thin film formation of nano-sized metal quinolin-8-olates (e.g. ([M(LQ)2],
M = Co, Ni, Cu and Zn and ([Fe(LQ)3]) by application of the layer-by-layer deposition technique
[13]. [Co(LQ)2] and [Ni(LQ)2]·2H2O complexes with 1D nanobelt structures were obtained via
low-heating solid-state chemical reactions [14]. An example of a tetranuclear cluster with a
[Co4(LOQ)6Cl2] composition is also reported where the complex has four cobalt ions in two
different coordination environments, two of them with chloride ligands. Chelated LOQ (OQ =
oxyquinolin-8-olate) ligands on cobalt ions also serve as bridging ligands by connecting the
metals through μ-oxo-bridges [15]. The HLQ scaffold has been functionalized by electrophilic
aromatic substitution at the 5-position to obtain 5-[(E)-2-(aryl)-1-diazenyl]-quinolin-8-ol
(HLXAQ), which is long known as an analytical reagent for qualitative detection of metal ions
[16]. The coordinating behaviors of such reagents were then investigated towards transition
metals [17], Hg [18], U [19], RnSn [20], mixed organotin-transition metals [17], mixed ligand
organotin complexes [21] and rare earth compounds [22]. Further, considerable efforts have been
made to design and to optimize the chemical properties of transition metal HLXAQ complexes
towards new colorimetric sensors [23], porous fumed silica covalently grafted with HLXAQ to be
used as extractants for Cu(II) and Ni(II) at low concentration levels [24] and nanosized
[Co(LXAQ)2] thin films using a new exciting, static, step-by-step soft surface reaction (SS-b-SSR)
technique to achieve biological and optical properties [25].
Cobalt has become an ideal candidate to prepare metal complexes due to its diverse
coordination geometries, large magnetic anisotropy and high Curie temperature [26]. The affinity
of HLQ for cobalt(II) falls within the classical order of stability Mn2+ < Co2+ < Ni2+ < Cu2+
>
Zn2+ and the same stability sequence is also observed for other HLQ derivatives [27]. Although
cobalt complexes with HLXAQ of composition [Co(LXAQ)2] are known, to our knowledge
structurally characterized [Co(LQ)2] and [Co(LXAQ)2] complexes have not been described yet,
probably owing to their amorphous nature. The applicability of single crystals is evident in
various fields such as semiconductors, polarizers, infrared detectors, solid state lasers, non-linear
optics, piezoelectric, acoustic-optics, photosensitive materials and crystalline thin films for
microelectronics and computer industries, etc. [28]. In view of these, attention has now been

diverted to the synthesis of new Co(II) complexes based on HLXAQ, and the choice of the
complexing agent rests upon the following criteria: (i) azo compounds based on HLQ derivatives
play a central role as chelating agents and their synthetic versatility allows the generation of a
large number of derivatives; (ii) the incorporation of pyridine-based ancillary ligands in reactions
with Co(II) may enhance the solubility of the amorphous Co(LXAQ)2 compounds in addition to
their inclusion in the coordination sphere of the metal, therefore providing a basis for the
formation of stable novel mixed-ligand complexes of diverse dimensionalities and enabling their
structural determination; (iii) the resulting compounds may exhibit intense optical absorptions
over the visible region that lead to dye properties in coordination complexes; and (iv) to study
the influence of the substituents of 5-[(E)-2-(aryl)-1-diazenyl]quinolin-8-olate on the redox
properties of the compounds.
In a previous work [29], we investigated the intriguing influence of pyridine derivatives
on the synthesis of a range of Zn(II) compounds with N,O-chelating HLXAQ ligands. However,
the design and synthesis of Co(II) coordination compounds with HLXAQ ligands with predictable
aggregate and topology remains a challenging task. In this context, a series of nine new
compounds,
trans-[Co(LPAQ)2(Py)2]
(1),
trans-[Co(LPAQ)2(3-MePy)2]
(2),
trans-
[Co(LMeAQ)2(Py)2] (3), trans-[Co(LOMeAQ)2(Py)2] (4), trans-[Co(LOEtAQ)2(Py)2]·2(H2O) (5), trans-
[Co(LCAQ)2(Py)2] (6), trans-[Co(LBAQ)2(Py)2] (7), cis-[Co(LBAQ)2(3-MePy)2] (8a) and trans-
[Co(LBAQ)2(3-MePy)2]·2(3-MePy) (8b), scheme 1, were synthesized. The Co(II) compounds
were structurally characterized by IR and UV-Vis spectroscopy and by single-crystal X-ray
diffraction analysis. It is anticipated that the different pyridine ligands used in the cobalt
compounds may influence the molecular and supramolecular structures, which ultimately modify
the electronic features for future solid-state applications. The magnetic and redox properties of
1-8 were also studied.

OH
+
R
N
HCl, NaNO2, 0-5 ºC
H N
2
R
OH
N
Diazo-coupling reaction
N
(i) Co(OAc)2.4H2O
(ii) Methanol
N
HLQ
(iii) Py/3-MePy
HLXAQ
X
R
N
N
O
X
N
Co
N
O
N
N
R
Chemical structures of six coordinate complexes 1-8
where the Co atom is bonded with a secondary ligand X.
Complexa
Complex No.
1
Abbreviation
HLPAQ
R
H
X
[Co(LPAQ)2(Py)2]
Pyridine (Py)
3-Methylpyridine (3-MePy)
Pyridine (Py)
[Co(LPAQ)2(3-MePy)2]
[Co(LMeAQ)2(Py)2]
[Co(LOMeAQ)2(Py)2]
2
3
4
HLMeAQ
Me
OMe HLOMeAQ
Pyridine (Py)
OEt HLOEtAQ
[Co(LOEtAQ)2(Py)2]·S
[Co(LCAQ)2(Py)2]
Pyridine (Py)
5
6
Cl HLCAQ
Pyridine (Py)
[Co(LBAQ)2(Py)2]
Br HLBAQ
Pyridine (Py)
7
[Co(LBAQ)2(3-MePy)]
[Co(LBAQ)2(3-MePy)]·S
8a
3-Methylpyridine (3-MePy)
3-Methylpyridine (3-MePy)
8b
a S refers to solvated molecule(s): S = 2H2O for 5 and S = 2(3-MePy) for 8b
Scheme 1. Synthesis of pro-ligand HLXAQ and schematic representation of the resulting cobalt(II)
compounds 1-8.
2. Experimental
2.1. Materials
Co(OAc)24H2O (Merck), 8-hydroxyquinoline (Loba Chemie), p-ethoxyaniline, p-chloroaniline,
p-bromoaniline (Himedia), pyridine (Merck) and 3-methylpyridine (Spectrochem) were used
without further purification. p-Toluidine (Merck) and p-anisidine (CDH) were purified by
crystallization and aniline (Sd fine) was distilled prior to use. The solvents used in the reactions
were of AR grade and dried using standard procedures.

2.2. Physical measurements
Melting points were measured using a Bꢀchi melting point apparatus (M-560) and are
uncorrected. Carbon, hydrogen and nitrogen analyses were performed with a Perkin-Elmer 2400
series II instrument. IR spectra from 4000-400 cm-1 were obtained on a Perkin Elmer Spectrum
BX series FT-IR spectrophotometer in KBr discs. Absorption measurements were carried out on
a Perkin-Elmer Lambda25 spectrophotometer at ambient temperature in freshly prepared DMSO
solutions. The electrochemical experiments were performed on an EG&G PAR 273A
potentiostat/galvanostat connected to a personal computer through a GPIB interface and by using
a three-electrode cell. Cyclic voltammetry was performed in 0.2 M [NBu4][BF4] / DMSO
solutions at ambient temperature using a platinum disc-working electrode (0.5 mm diameter).
The potential was controlled vs. a Luggin capillary connected to a silver wire pseudo reference
electrode and a platinum auxiliary electrode was employed. The redox potential values of the
complexes are quoted relative to SCE; they were measured using cyclic voltammetry in the
presence of ferrocene as the internal standard (퐸1표/푥2 = 0.44 V vs. SCE in DMSO). The 퐸1표/푥2 redox
potential value for ferrocene was measured at 200 mV·s-1 in [nBu4N][BF4] / 0.1 M DMSO
solution and using the saturated calomel electrode (SCE) as reference. Magnetic measurements
1
were performed by solution H NMR using the Evans’ method [30] on a Bruker Avance 400
spectrometer operating at 400.13 MHz for 1-6 and on a Bruker Avance 300 spectrometer
operating at 300.13 MHz for 7 and 8 at room temperature in an open-air system. The
measurements were performed in a standard 5 mm NMR tube containing the paramagnetic
sample dissolved in DMSO-d6, against a co-axial reference tube filled with the same solvent. The
data treatment of NMR signals were done using the MestReNova 9.0.1 program.
2.3. Synthesis of pro-ligands and cobalt(II) complexes
The pro-ligands 5-[(E)-2-(aryl)-1-diazenyl]quinolin-8-ol (HLXAQ) viz., 5-[(E)-2-(phenyl)-1-
diazenyl]quinolin-8-ol (HLPAQ), 5-[(E)-2-(4-methylphenyl)-1-diazenyl]quinolin-8-ol (HLMeAQ),
5-[(E)-2-(4-ethoxyphenyl)-1-diazenyl]quinolin-8-ol (HLOEtAQ) and 5-[(E)-2-(4-bromophenyl)-1-
diazenyl]quinolin-8-ol (HLBAQ) [20e] and 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol
(HLOMeAQ) and 5-[(E)-2-(4-chlorophenyl)-1-diazenyl]quinolin-8-ol (HLCAQ) [20d], were
prepared starting from 8-hydroxyquinoline and the corresponding aniline using conventional
diazonium salt chemistry, in accord with literature procedures. In view of the similar preparation

methods employed for 1-8, only that for [Co(LPAQ)2(Py)2] (1) is described below, as a
representative example.
2.3.1.
Synthesis
of
trans-bis{5-[(E)-2-(phenyl)-1-diazenyl]quinolin-8-olato-k2N,O}-
bis(pyridine-kN) cobalt(II) (1). Co(OAc)2·4H2O (0.249 g, 0.999 mmol) in methanol (10 mL)
was added dropwise to a stirred solution of HLPAQ (0.5 g, 2.005 mmol) in benzene (50 mL) at
room temperature, which resulted in the immediate formation of an orange precipitate. The
reaction mixture was heated to reflux for 3 h and then filtered while hot. The residue was washed
with hot methanol (3 × 5 mL) to remove undesired materials and dried in vacuo. The dried solid
was dissolved by heating the benzene solution (5 mL) containing pyridine (0.8 mL,
10.113 mmol) and filtered while hot. Upon cooling to room temperature, the filtrate afforded
red-brown crystals of 1. Yield: 0.44 g (61%). M.p. >300 °C. Anal. Found: C, 67.93; H, 4.72; N,
15.90%. Calc. for C40H30CoN8O2: C, 67.30; H, 4.24; N, 15.71. IR (cm–1): 1596m, 1573m,
1559m, 1499s, 1464s, 1400m, 1322s, 1248s, 1188m, 1171m, 764w, 688w, 464w. Electronic
absorption data (DMSO) λmax, nm; (ε [M-1 cm-1]): 432 (sh), 490 (13171).
2.3.2. Synthesis of trans-bis{5-[(E)-2-(phenyl)-1-diazenyl]quinolin-8-olato-k2N,O}-bis(3-
methylpyridine-kN) cobalt(II) (2). Co(OAc)2·4H2O (0.249 g, 0.999 mmol) and HLPAQ (0.5 g,
2.005 mmol) were used in the reaction. The dried solid was dissolved by heating the benzene
solution (5 mL) containing 3-methylpyridine (1 mL, 10.737 mmol) and filtered while hot. The
filtrate upon slow evaporation yielded red brown crystals. Yield: 0.44 g (59%). M.p. >300 °C.
Anal. Found: C, 67.92; H, 4.75; N, 13.98%. Calc. for C42H34CoN8O2: C, 68.00; H, 4.62; N,
15.11. IR (cm–1): 1595m, 1567m, 1552m, 1497s, 1462s, 1400m, 1391m, 1325s, 1247s, 1191m,
1171m, 1135m, 1097w, 840m, 791m, 702w, 465w. Electronic absorption data (DMSO) λmax
,
nm; (ε [M-1 cm-1]): 434 (sh), 492 (11570).
2.3.3. Synthesis of trans-bis{5-[(E)-2-(4-methylphenyl)-1-diazenyl]quinolin-8-olato-k2N,O}-
bis(pyridine-kN) cobalt(II) (3). Co(OAc)2·4H2O (0.237 g, 0.951 mmol) and HLMeAQ (0.5 g,
1.899 mmol) were used in the reaction. The dried solid was dissolved in hot chloroform (15 mL)
containing pyridine (0.8 ml, 10.113 mmol) followed by dilution with benzene (1 mL) and
filtered. The filtrate upon slow evaporation yielded red-brown crystals. Yield: 0.45 g (63%).

M.p. >300 °C. Anal. Found: C, 68.32; H, 4.93; N, 15.18%. Calc. for C42H34CoN8O2: C, 68.00; H,
4.62; N, 15.11. IR (cm–1): 1596m, 1572m, 1552m, 1497s, 1461s, 1393m, 1325s, 1246s, 1188m,
1124m, 1098m, 817w, 793w, 760w, 615w, 463w. Electronic absorption data (DMSO) λmax, nm;
(ε [M-1 cm-1]): 435 (sh), 486 (11273).
2.3.4. Synthesis of trans-bis{5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-olato-
k2N,O}-bis(pyridine-kN) cobalt(II) (4). Co(OAc)2·4H2O (0.223 g, 0.895 mmol) and HLOMeAQ
(0.5 g, 1.790 mmol) were used in the reaction. The dried solid was dissolved in hot benzene
(5 mL) containing pyridine (0.8 mL, 10.113 mmol) and filtered while hot to remove any
suspended particles. The filtrate upon slow evaporation afforded red-brown crystals of 4. Yield:
0.44 g (63%). M.p. >300 °C. Anal. Found: C, 65.68; H, 4.40; N, 14.60%. Calc. for
C42H34CoN8O4: C, 65.18; H, 4.43; N, 14.49. IR (cm–1): 1596m, 1579s, 1497s, 1462s, 1402m,
1316s, 1246s, 1191m, 1104m, 1026w, 836m, 819, 760m, 603m, 515w, 470w. Electronic
absorption data (DMSO) λmax, nm; (ε [M-1 cm-1]): 433 (sh), 498 (12406).
2.3.5. Synthesis of trans-bis{5-[(E)-2-(4-ethoxyphenyl)-1-diazenyl]quinolin-8-olato-k2N,O}-
bis(pyridine-kN) cobalt(II) dihydrate (5). Co(OAc)2·4H2O (0.212 g, 0.851 mmol) and HLOEtAQ
(0.5 g, 1.704 mmol) were used in the reaction. The dried solid was dissolved in hot benzene
(5 mL) containing pyridine (0.8 ml, 10.113 mmol) and filtered while hot. The filtrate upon slow
evaporation afforded red-brown crystals. Yield: 0.46 g (67%). M.p. >300 °C. Anal. Found: C,
63.46; H, 5.18; N, 13.03%. Calc. for C44H42CoN8O6: C, 63.06; H, 5.06; N, 13.38. IR (cm–1):
1597m, 1574m, 1563m, 1497s, 1463s, 1400m, 1320s, 1239s, 1150m, 1093w, 1037w, 836w,
766w, 700w, 474w. Electronic absorption data (DMSO) λmax, nm; (ε [M-1 cm-1]): 433 (sh), 498
(12508).
2.3.6. Synthesis of trans-bis{5-[(E)-2-(4-chlorophenyl)-1-diazenyl]quinolin-8-olato-k2N,O}-
bis(pyridine-kN) cobalt(II) (6). Co(OAc)2·4H2O (0.219 g, 0.879 mmol) and HLCAQ (0.5 g,
1.762 mmol) were used in the reaction. The dried solid was dissolved in hot chloroform (15 mL)
containing pyridine (0.8 ml, 10.113 mmol) and filtered while hot. The filtrate was diluted with
benzene (1 mL) and upon slow evaporation afforded red-brown crystals. Yield: 0.45 g (65%).
M.p. >300 °C. Anal. Found: C, 61.78; H, 3.26; N, 14.04%. Calc. for C40H28Cl2CoN8O2: C, 61.38;

H, 3.61; N, 14.32. IR (cm–1): 1583s, 1561w, 1498s, 1461s, 1429w, 1395m, 1317s, 1245s,
1189m, 1136m, 1107m, 834m, 753m, 603m, 516w, 501w. Electronic absorption data (DMSO)
λmax, nm; (ε [M-1 cm-1]): 438 (sh), 503 (12343).
2.3.7. Synthesis of trans-bis{5-[(E)-2-(4-bromoophenyl)-1-diazenyl]quinolin-8-olato-k2N,O}-
bis(pyridine-kN) cobalt(II) (7). Co(OAc)2·4H2O (0.190 g, 0.762 mmol) and HLBAQ (0.5 g,
1.523 mmol) were used in the reaction. The dried solid was dissolved in hot chloroform (15 mL)
containing pyridine (0.8 mL, 10.113 mmol) and filtered to remove any suspended particles. The
filtrate was diluted with benzene (1 mL) and upon slow evaporation afforded red-brown crystals
of the desired product. Yield: 0.47 g (70%). M.p. >300 °C. Anal. Found: C, 55.35; H, 3.60; N,
12.50%. Calc. for C40H28Br2CoN8O2: C, 55.11; H, 3.24; N, 12.86. IR (cm–1): 1596m, 1571m,
1551m, 1499s, 1476m, 1462s, 1421m, 1405s, 1382m, 1323s, 1298m, 1247s, 1187m, 1130m,
829w, 792w, 735w, 702m, 656w, 603m, 466w. Electronic absorption data (DMSO) λmax, nm; (ε
[M-1 cm-1]): 444 (sh), 508 (10599).
2.3.8. Synthesis of cis-bis{5-[(E)-2-(4-bromoophenyl)-1-diazenyl]quinolin-8-olato-k2N,O}-
bis(3-methylpyridine-kN) cobalt(II) (8a) and trans-bis{5-[(E)-2-(4-bromoophenyl)-1-
diazenyl]quinolin-8-olato-k2N,O}-bis(3-methylpyridine-kN)
cobalt(II)
di-(3-
methylpyridine) solvate (8b). Co(OAc)2·4H2O (0.190 g, 0.762 mmol) and HLBAQ (0.5 g,
1.523 mmol) were used in the reaction. The dried solid was dissolved in hot benzene (5 mL)
containing 3-methylpyridine (1 ml, 10.737 mmol) and filtered while hot to remove any
suspended particles. The filtrate, upon slow evaporation, afforded red-brown, block-shaped and
red plate-type crystals as identified after visual inspection using a microscope. Crystals of both
morphologies were analyzed by single crystal X-ray crystallography and their identities were
confirmed as 8a and 8b (refer to the structural discussion). Microanalytical results of the bulk
sample containing 8a and 8b reflected variable results, which indicated the heterogeneous
distributions of the compounds in the bulk sample. The MW of the compounds is the same;
methylpyridine molecules of crystallization interfered. Yield of the bulk sample: 0.47 g (68%),
M.p. >300 °C and IR (cm–1): 1582s, 1498s, 1462s, 1429m, 1390m, 1317s, 1245s, 1187s, 1137w,
1106w, 1066w, 832w, 781w, 752w, 516w, 500w.

2.4. Single-crystal X-ray crystallography
Crystals of cobalt(II) compounds, 1 (pyridine/benzene), 2 (3-methylpyridine/benzene),
3 (pyridine/benzene/chloroform),
6 (pyridine/benzene/chloroform),
4
(pyridine/benzene),
5
(pyridine/benzene),
7
(pyridine/benzene/chloroform) and 8a and 8b
(3-methylpyridine/benzene) suitable for single-crystal X-ray structure determination were
obtained by slow evaporation of solutions of the respective compounds. The measurements were
performed on an Agilent Technologies four circle Gemini (Model No. XD-91-00-000) using
Mo K radiation ( = 0.71073 Å) from a fine-focus X-ray source. Data were collected at room
temperature using omega scans of 0.5º per frame, and a full sphere of data was obtained. The
unit cell parameters and the data reduction were obtained with the CrysAlisPro 1.171.38.41
software from Rigaku Oxford Diffraction [31]. Crystal data and refinement details are collected
in table 1, and a comparison of selected bond distances and angles is given in table 2. A
representation of all the structures is shown in figure 1 and relevant intermolecular non-covalent
interactions in figures 2 and 3. The structures were solved by direct methods using SIR-97 [32]
or SHELXS package [33] and refined with SHELXL–2014 [34]. The hydrogen atoms attached to
carbon atoms were inserted in geometrically calculated positions and included in the refinement
using the riding-model approximation, with the Uiso(H) defined as 1.2Ueq of the parent carbon
atoms for phenyl and 1.5Ueq of the parent carbon atoms for the methyl groups. The positions of
hydrogen atoms of the crystallization water molecule in 5 were calculated by means of the
CALC-OH routine of WinGX System–Version 2014.1 [35]. The structures of 1 and 3-7 contain a
disordered benzene (or pyridine) molecule with the ring sitting on an inversion center, which
could not be modeled. After running Platon/Squeeze program [36], a total of 43-49 electrons
worth of scattering were found in volumes of 143-174 Å3, which fit well for the indicated small
molecule(s). In view of the difficulty to identify the disordered molecule unambiguously, it was
excluded in the final refinement. For 2, the quality of the data is low due to very weak diffraction
of the crystal. Several attempts to get better crystals failed, but the solved structure is not in
doubt, consistent with the related compounds as well as with other characterization results. The
residual electron density in 2 is close to a phenyl ring and has no chemical meaning. In addition,
for 2 a void volume of 166 Å3 contains 12 electrons and the use of Platon/Squeeze program was
not a solution. Least-squares refinements with anisotropic thermal motion parameters for all the

non-hydrogen atoms and isotropic for the remaining atoms were employed. Figures 1-3 were
drawn with Mercury CSD (Cambridge structural database) 3.5.1 [36].
3. Results and discussion
3.1. Synthesis and spectroscopic characterization
The pro-ligands 5-[(4-(R)-phenyl)-1-diazenyl]quinolin-8-ol (HLXAQ) in benzene upon treatment
with a solution of Co(OAc)24H2O in methanol (1:2 molar ratio) afforded the respective Co(II)
compounds. In all cases, the immediate formation of a precipitate was noticed. Characterization
of the amorphous precipitates revealed compounds of composition [Co(LXAQ)2]. They were
insoluble in most common organic solvents such as methanol, ethanol, benzene, toluene,
chloroform, carbon tetrachloride and dichloromethane even after prolonged heating. These
precipitates were soluble in hot DMSO, pyridine and pyridine derivatives such as
methylpyridines. Crystallization experiments with [Co(LXAQ)2] using pure DMSO or a
combination with other common solvents invariably afforded amorphous materials. However,
when a large excess of pyridine (Py) or 3-methylpyridine (3-MePy) was added to a suspension of
the [Co(LXAQ)2] compounds in benzene or benzene/chloroform solvent mixture, the isolation of
crystalline Co(II) compounds, in which either Py (1, 3-7) or 3-MePy (2, 8a and 8b) was
coordinated to the cobalt atoms, became possible. It should be mentioned that crystallization
trials for 8 in a solvent mixture of benzene/3-methylpyridine afforded red-brown, block-shaped
(8a) and red plate-type (8b) crystals; both were characterized by single crystal X-ray
crystallography. Compounds 5 and 8b crystallized as solvates with two molecules of H2O (5) or
of 3-MePy (8b), see scheme 1. The presence of water in 5 is attributed to traces of water present
in the solvents and reagents used for the crystallization experiments. The formulations of cobalt
compounds 1-8 were ascertained from elemental analyses and subsequently by determining their
crystal structures. The characteristic IR and electronic absorption data are given in the
Experimental section.
3.2. Description of the X-ray crystal structures
The asymmetric units of 1-7, 8a and 8b comprise half of the compounds molecules, viz. a Co(II)
cation, one O,N-chelating LXAQ ligand and a N-bound pyridine (1, 3-7) or 3-methylpyridine
moiety (2, 8a and 8b), apart from a (disordered) benzene/pyridine (1, 3-7) or a 3-methylpyridine

(8b) crystallization molecules. The cobalt ions sit on inversion centers, except for 8a where it
stands on a 2-fold axis; upon symmetry expansion, octahedral type complexes with trans
geometry, excluding 8a, which has a cis configuration, are generated. The cis arrangement of the
LBAQ ligands in 8a leads to a distortion of the octahedron around the cobalt cation, as evidenced
by (see table 2) O-Co-N (metallacycle) and O-Co-NL angles of 78.85(10) and 96.21(11),
respectively, which are the smallest of all structures, as well as by the O-Co-O angle of
173.56(15) itself considerably away from the 180 measured for the other compounds. The
Co-Npyr distances [2.2047(15) – 2.171(3) Å] are larger than the Co–NL [2.097(4) – 2.1523(3) Å],
probably as a result of charge effects; in 8a the difference in those two parameters is as small as
0.019 Å (table 2). The N=N bond lengths are in the 1.243(6) – 1.264(4) Å range, typical of
double bonds between those atoms when connected to an aromatic ring (table 2) [37].
The LXAQ ligands are almost planar in 1, 3, 4, 6 and 7 as confirmed by the angles of 4.42
– 5.75 between the least-square planes of the quinolone and the phenyl rings (table 2). In 2 and
in 8b this factor assumes values of 27.98 and 23.04, in this order, probably associated with
stereochemical effects arising from the 3-methylpyridine. In 8a and in 5 the distortions of LXAQ
are intermediate, thus evidencing the effect of the geometry of the compound (in the former) and
of a bulkier substituent (OEt in the latter). The complexes with evident twisting in LXAQ ligands
(2, 5, 8a and 8b) are those with longer Co···Co intermolecular distances (table 2).
A search on the Cambridge Structural Database (CSD) [38] was performed to account for
the type and variety of metal complexes with 5-substituted (here onward referred to as X)
oxyquinolin-8-olate ligands. Forty-six entries pertain to transition metals complexes where, most
commonly, X = Cl, Br or NO2 [39], rarely with X = SO3 [40], NH2 [41], or SMe [42]. Taking the
related Co(II) complex molecules [39] for comparison, it is worth noting that the Co-O and the
Co-NL distances on the LOQ substituent (in the ranges 1.902-1.917 and 1.878-1.935 Å,
respectively), as well as the Co-Npyr bond lengths (1.926-1.982 Å) are considerably shorter than
those measured in this work (see table 2), therefore revealing the influence of the unsaturated
X-substituent in the oxyquinolin-8-olate ligands on the structural properties of the complexes. In
addition, the search also revealed that compounds where X is an unsaturated group are mainly of
lanthanides [43] or of yttrium [43a, 44], multinuclear and with the oxyquinolinolate moiety
O-bridging metal cations. Rare examples include a discrete copper complex [45] and a polymeric
zinc species [46]. Complexes of the main group metals and with 5-X-oxyquinolin-8-olate ligands

specifically with unsaturated X groups include diorganotin(IV) moieties [20b-d]. Discrete
aluminum complex molecules with X = SO2NRR' [47] and sodium dimers with X = Cl [48] are
also known.
Strong π···π interactions are found between the substituted phenyl rings of neighboring
molecules of 5 with centroid distances between the two -systems of ca. 3.82 Å (figure 2(A)).
The molecules of 3, 4, 6 and 7 are gathered by means of strong intermolecular CH··· edge-to-
face (T-shaped) arrangements [d(H···centroid)  2.8 Å; CH···centroid  177] (figure 2(B),
exemplified for 7) with the donor pyridine ligand of one molecule almost perpendicular to the
acceptor phenyl ring of an adjacent one. In 4, in addition (figure 2(C)), the pyridine moieties also
act as acceptors of one of the methoxy H-atoms of an adjacent molecule [d(H···centroid) of
2.593 Å; CH···centroid of 153].
The CH··· interactions in 2 are different and involve the quinoline moieties
(figure 3(A)) which act as acceptors from both an aromatic and a methyl H-atom from
3-methylpyridine of a vicinal molecule [d(H···centroid) of 2.73 Å, CH···centroid of 176;
d(H···centroid) of 2.96 Å, CH···centroid of 147]. In the molecules of 8a and 8b, the
relevant CH··· contacts comprise the N-containing ring of a quinoline moiety as acceptor, but
the role of donor groups is played by an aromatic H-atom from a coordinated (8a) and non-
coordinated (8b) 3-methylpyridine [in the same order: d(H···centroid) of 2.81 Å,
CH···centroid of 171; d(H···centroid) of 2.60 Å, CH···centroid of 161] (figures 3(B)
and 3(C)).
3.3. Electrochemical properties
The redox properties of cobalt compounds 1-8 (table 3) were studied by cyclic voltammetry at a
Pt electrode, in 0.2 M [nBu4N][BF4] / DMSO solutions and reveal metal and ligand based redox
processes. All the complexes exhibit (see figure 4 for 2 and figure S1 in Supplementary Material
file for the remaining compounds) two successive anodic irreversible waves, Iox and IIox, at
potential ranges of 0.44 – 0.54 and 0.73 – 0.82 V vs. SCE, respectively. The former wave can be
tentatively assigned to the Co(II)  Co(III) process and the latter to ligand based oxidation. An
intense, broad and irreversible cathodic wave (Ired) was also detected between –1.50 V and –
1.71 V vs. SCE which is believed to involve the Co(II)  Co(I) conversion. The cyclic

voltammetry of 8 did not allow us to distinguish between the cis and trans isomers in solution,
leading us to consider either an interconversion of the compounds in the electrolyte medium, or
of a negligible difference on redox potential values. The oxidation potentials of the compounds
are close to those found for tryptamine-derived salicylaldimine cobalt(II) compounds [49] and
for the di-scorpionate compound [Co{HOCH2C(pz)3}2](NO3)2 [50], but considerably lower than
those
of
the
mono-scorpionates
[Co(OSO3H)(OMe)(HOMe){HC(pz)3}]
and
[CoCl2(H2O){CH3SO2OCH2C(pz)3}] [51], the dinuclear [CoCl(-Cl)(HpzPh)3]2 or the
mononuclear [CoCl2(HpzPh)4] (HpzPh = 3-phenylpyrazole).
3.4. Magnetic studies
1
No signals were observed in the H NMR spectra of 1-8 as anticipated for the paramagnetic
character of the Co(II). The effective magnetic moment (µeff) of cobalt(II) compounds 1-8 was
estimated by NMR using Evans’ method [30]. This method relates the difference in the chemical
shift of an inert reference compound in the presence and in the absence of a paramagnetic
species. In the present work, equation A was applied where 휒푚푃 is the mass susceptibility, Δf is
the observed difference in frequency, f is the spectrometer frequency, m is the concentration of
the paramagnetic substance, 휒0 is the mass susceptibility of the solvent, and 푑0 and 푑푠 are the
densities of the solvent and of the solution, respectively.
3훥푓
휒 (푑 −푑 )
0
0
푠
휒푚푃
=
4휋푓푚 + 휒0 +
(A)
푚
With the obtained mass susceptibility, the molar susceptibility (휒푀푃 ) was calculated and then
applied in expression B (where KB is the Boltzmann constant, NA the Avogadro’s number, β the
Bohr magneton and T the absolute temperature).
3퐾
퐵
µ푒푓푓
=
2 (휒푀푃 푇)
(B)
√
푁 훽
퐴
In the present study, a co-axial double NMR tube was used, with DMSO-d6 both as solvent and
as internal standard since the resonance of this species (a quintet at  2.50 relative to TMS) was
clearly shifted by the additional magnetic field of the Co(II) paramagnetic compounds (figure 5).

The magnetic measurements for 1-8 (tables 4 and S1) led to effective magnetic moments
between 4.34 and 4.99 B.M., which are in the expected range for cobalt metal ions with
5
2
octahedral geometry and d7 high spin (t2g eg ) configuration. The exception is 6 (μeff = 3.67 μβ)
with an intermediate value between the expected ones for high and low-spin configurations [52].
4. Conclusion
A series of new Co(II) compounds 1-8 based on HLXAQ have been synthesized. They were
characterized by IR and UV-vis spectroscopies and by single-crystal X-ray diffraction analysis.
The compounds are all octahedral displaying trans geometries except for 8a, which has a cis
configuration. The compounds are redox active with Co(II)  Co(III) oxidation waves at
potentials of 0.44 – 0.54 V vs. SCE and Co(II)  Co(I) cathodic processes at –1.50 V and –
1.71 V vs. SCE. The magnetic moments of most of the compounds are in the 4.34 - 4.99 B.M.
2
range that agree with the octahedral geometry and suggest d7 high spin (t2g5 eg ) configurations.
Supplementary material
CCDC 1835529-1835537 contain the supplementary crystallographic data for 8b, 8a, 2, 1, 7, 4-6
and 3, in this order. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/getstructures. ESI file contains the cyclic voltammograms of 1, 3-8
(figure S1) and the table with the data and parameters obtained by Evans NMR method
(table S1).
Acknowledgements
The financial support of the University Grants Commission, New Delhi (Grant No. 42-396/2013
(SR) 2013, TSBB), the Council of Scientific and Industrial Research, New Delhi (Grant No. 01
(2734)/13/EMR-II, 2013, TSBB) and of the Foundation for Science and Technology (FCT),
Portugal (Project UID/QUI/00100/2013, MFCGS and BGMR). KN thanks the University Grants
Commission (UGC), New Delhi, for UGC-RGNF research fellowship. Authors (TSBB, KN)
acknowledge DST-PURSE for the diffractometer facility.

References
[1]
J. Mendham, R.C. Denny, J.D. Barnes, M.J.K. Thomas, Vogel’s Quantitative Chemical
Analysis, Prentice Hall, London (2000).
[2]
[3]
[4]
[5]
D.C. Harris, Quantitative Chemical Analysis, Freeman, New York (2010).
V. Oliveri, G. Vecchio. Eur. J. Med. Chem., 120, 252 (2016).
M. Albrecht, M. Fiege, O. Osetska. Coord. Chem. Rev., 252, 812 (2008).
F. Qian, Y. Li, S. Gradecak, D. Wang, C.J. Barrelet, C.M. Lieber. Nano Lett., 4, 1975
(2004).
[6]
[7]
[8]
Y.S. Zhao, C. Di, W. Yang, G. Yu, Y. Liu, J. Yao. Adv. Funct. Mater., 16, 1985 (2006).
C.W. Tang, S.A. Van Slyke. J. Appl. Phys., 65, 3610 (1989).
R.H. Friend, R.W. Gymer, A.B. Holmes, J.H. Burroughes, R.N. Marks, C. Taliani, D.A.
Dos Santos, J.L. Bredas, M. Logdlund, W.R. Salaneck. Nature, 397, 121 (1999).
S.C. Lyu, Y. Zhang, C.J. Lee. Chem. Mater., 15, 3294 (2003).
[9]
[10] S. Meloni, A. Palma, J. Schwartz, A. Kahn, R. Car. J. Am. Chem. Soc., 125, 7808 (2003).
[11] A. Mishra, P.K. Nayak, N. Periasamy. Tetrahedron Lett., 45, 6265 (2004).
[12] L.M. Leung, W.Y. Lo, S.K. So, K.M. Lee, W.K. Choi. J. Am. Chem. Soc., 122, 5640
(2000).
[13] M.E. Mahmoud, S.S. Haggag, T.M. Abdel-Fattah. Polyhedron, 28, 181 (2009).
[14] L. liu, L. Wang, D. Jia. J. Coord. Chem., 61, 1019 (2008).
[15] P. Khakhlary, C.E. Anson, A. Mondal, A.K. Powell, J.B. Baruah. Dalton Trans., 44,
2964 (2015).
[16] (a) J. Matheus. Ber., 21, 1644 (1888). (b) F.J. Welcher, Organic Analytical Regents,
Vol. 1, Van Nostrand, London (1947). (c) V.M. Ivanov, T.F. Rudometkina. Zh. Anal.
Khim., 33, 2426 (1978).
[17] (a) T.S. Basu Baul, T.K. Chattopadhyay, B. Majee. Ind. J. Chem., Sect. A, 23, 470
(1984). (b) I. Aiello, M. Ghedini, C. Zanchini. Inorg. Chim. Acta, 255, 133 (1997). (c) R.
Sarkar, P. Mondal, K.K. Rajak. Dalton Trans., 43, 2859 (2014). (d) S.A. Abdel-Latif, H.
Moustafa. Appl. Organomet. Chem., 31, e3876 (2017).
[18] E. El-Sawi, F.A. Moti, S. El-Messary. Bull. Soc. Chim. (Belg.), 94, 69 (1985).
[19] T.S. Basu Baul, D. Dey. Synth. React. Inorg. Met.-Org. Chem., 19, 101 (1989).

[20] (a) K.D. Ghuge, P. Umapathy, M.P. Gupta, D.N. Sen. Inorg. Nucl. Chem., 43, 653
(1981). (b) T.S. Basu Baul, T.K. Chattopadhyay, B. Majee. Polyhedron, 2, 635 (1983).
(c) B.K. Deb, A.K. Ghosh. Can. J. Chem., 65, 1241 (1987). (d) T.S. Basu Baul, A. Mizar,
X. Song, G. Eng, R. Jirásko, M. Holčapek, R. Willem, M. Biesemans, I. Verbruggen, R.
Butcher. J. Organomet. Chem., 691, 2605 (2006). (e) T.S. Basu Baul, A. Mizar, A.
Lyčka, E. Rivarola, R. Jirásko, M. Holčapek, D. de Vos, U. Englert. J. Organomet.
Chem., 691, 3416 (2006). (f) T.S. Basu Baul, A. Mizar, E. Rivarola, U. Englert.
J. Organomet. Chem., 693, 1751 (2008). (g) T.S. Basu Baul, A. Mizar, A.K. Chandra, X.
Song, G. Eng, R. Jirásko, Holčapek, D. de Vos, A. Linden. J. Inorg. Biochem., 102, 1719
(2008). (h) T.S. Basu Baul, A. Mizar, G. Ruisi, E.R.T. Tiekink. Z. Anorg. Allg. Chem.,
638, 664 (2012). (i) T.S. Basu Baul, A. Mizar, G. Eng, R. Far, A. Linden. J. Coord.
Chem., 66, 813 (2013).
[21] T.S. Basu Baul, A. Mizar, A. Paul, G. Ruisi, R. Willem, M. Biesemans, A. Linden.
J. Organomet. Chem., 694, 2142 (2009).
[22] A.Z. El-Sonbati, R.M. Issa, A.M. Abd El-Gawad. Spectrochim. Acta, Part A, 68, 134
(2007).
[23] F.-Y. Wu, X.-F. Tan, Y.-M. Wu, Y.-Q. Zhao. Spectrochim. Acta, Part A, 65, 925 (2006).
[24] (a) M. Hébrant, M. Rose-Hélène, J.-P. Joly, A. Walcarius. Colloids Surf. A, 380, 261
(2011). (b) M. Hébrant, M. Rose-Hélène, A. Walcarius. Colloids Surf. A, 417, 65 (2013).
[25] S.M. Seleim, T.A. Hamdalla, M.E. Mahmoud. Spectrochim. Acta, Part A, 184, 134
(2017).
[26] J.M.D. Coey, Magnetism and Magnetic Materials, Cambridge University Press, New
York (2010).
[27] C. Sgarlata, V. Oliveri, J. Spencer. Eur. J. Inorg. Chem., 36, 5886 (2015).
[28] S. Natarajan, G. Shanmugam, S.A. Martin. Cryst. Res. Technol., 43, 561 (2008).
[29] T.S. Basu Baul, K. Nongsiej, K. Biswas, S.R. Joshi, H. Höpfl, submitted for publication.
[30] (a) D.F. Evans. J. Chem. Soc., 2003 (1959). (b) E.M. Schubert. J. Chem. Educ., 69, 62
(1992).
[31] CrysAlisPro 1.171.38.41, Rigaku Oxford Diffraction (2015).
[32] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giacovazzo, A. Guagliardi,
A.G.G. Moliterni, G. Polidori, R. Spagna. J. Appl. Cryst., 32, 115 (1999).

[33] G.M. Sheldrick. Acta Crystallogr., Sect. A, 64, 112 (2008).
[34] L.J. Farrugia. J. Appl. Cryst., 45, 849 (2012).
[35] A.L. Spek. Acta Crystallogr., Sect. C, 71, 9 (2015).
[36] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L.
Rodriguez-Monge, R. Taylor, J. van de Streek, P.A. Wood. J. Appl. Cryst., 41, 466
(2008).
[37] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A. Guy Orpen. J. Chem. Soc., Perkin
Trans. II, S1 (1987).
[38] See the Cambridge Structural Data Base, CSD version 1.22, May 2018.
[39] Involving solely cobalt(II) complex molecules, see e.g. (a) H.-R. Zhang, T. Meng, Y.-C.
Liu, Z.-F. Chen, Y.-N. Liu, H. Liang. Appl. Organomet. Chem., 30, 740 (2016). (b) H.-R.
Zhang, K.-B. Huang, Z.-F. Chen, Y.-C. Liu, Y.-N. Liu, T. Meng, Q.-P. Qin, B.-Q. Zou,
H. Liang. MedChemComm, 7, 806 (2016).
[40] (a) F. Camerel, A. Vacher, O. Jeannin, J. Barbera, M. Fourmigue. Chem. Eur. J., 21,
19149 (2015). (b) W.-L. Zhang, Y.-Y. Liu, J.-F. Ma, H. Jiang, J. Yang, G.-J. Ping. Cryst.
Growth Des., 8, 1250 (2008).
[41] X. Chen, F.J. Femia, J.W. Babich, J. Zubieta. Inorg. Chim. Acta, 308, 80 (2000).
[42] L. Pech, Yu. Bankovsky, I. Berzina, V. Belsky, J. Ashaks. Latv. Khim. Z., No. 3, 19
(1997).
[43] See, e.g. (a) H.-L. Gao, L. Jiang, S. Liu, H.-Y. Shen, W.-M. Wang, J.-Z. Cui. Dalton
Trans., 45, 253 (2016). (b) H.-L. Gao, X.-P. Zhou, Y.-X. Bi, H.-Y. Shen, W.-M. Wang,
N.-N. Wang, Y.-X. Chang, R.-X. Zhang, J.-Z. Cui. Dalton Trans., 46, 4669 (2017).
(c) Y.-X. Zhang, M. Li, B.-Y. Liu, Z.-L. Wu, H.-Y. Wei, W.-M. Wang. RSC Adv., 7,
55523 (2017). (d) H.-L. Gao, S.-X. Huang, X.-P. Zhou, Z. Liu, J.-Z. Cui. Dalton Trans.,
47, 3503 (2018). (e) W.-M. Wang, Y.-X. Zhang, J.-C. Zhao, X.-H. Zhang, Y. Tan, Y.-Y.
Cui, Y. Shi, Z.-L. Wu. Polyhedron, 146, 161 (2018).
[44] H.-L. Gao, L. Jiang, W.-M. Wang, S.-Y. Wang, H.-X. Zhang, J.-Z. Cui. Inorg. Chem.,
55, 8898 (2016).
[45] Y.-N. Luo, X.-Z. Xu, X. Zhang, X.-Y. Yu, X.-S. Qu. Wuji Huaxue Xuebao, 29, 2655
(2013).
[46] X.-W. Wu, D. Zhang, Z.-H. Wu, J.-P. Ma. Jiegou Huaxue, 33, 1326 (2014).

[47] J.-A. Cheng, H.-P.D. Shieh. Anal. Sci.: X-Ray Struct. Anal. Online, 24, x235 (2008).
[48] A.J. Middleton, W.J. Marshall, N.S. Radu. J. Am. Chem. Soc., 125, 880 (2003).
[49] Y.-Y. Tong, M.F.C. Guedes da Silva, J.J.R. Fraústo da Silva, A.J.L. Pombeiro, P. Martin-
Zarga, G. Martin, P. Gili. Port. Electrochim. Acta, 11, 87 (1993).
[50] T.F.S. Silva, L.M.D.R.S. Martins, M.F.C. Guedes da Silva, A.R. Fernandes, A. Silva,
P.M. Borralho, S. Santos, C.M.P. Rodrigues, A.J.L. Pombeiro. Dalton Trans., 41, 12888
(2012).
[51] T.F.S. Silva, L.M.D.R.S. Martins, M.F.C. Guedes da Silva, M.L. Kuznetsov, A.R.
Fernandes, A. Silva, C.-J. Pan, J.-F. Lee, B.J. Hwang, A.J.L. Pombeiro. Chem.-Asian J.,
9, 1132 (2014).
[52] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 3rd Edn., Wiley, New York
(1972), pp. 535-542.

Figure 1. Perspective views of 1-7, 8a and 8b with the atom numbering schemes. Displacement
ellipsoids are drawn at the 30% probability level and hydrogens are omitted for clarity.
Symmetry operations “a” to generate equivalent atoms: -x, 2-y,1-z (1); 1-x,1-y,1-z (2 and 3); 1-
x,1-y,-z (4 and 8b); -x,1-y,-z (5); -x,-y,2-z (6); 2-x,2-y,1-z (7); 1-x,y,1/2-z (8a). For 5 and 8b, the
non-coordinated water or 3-methylpyridine molecules, respectively, are omitted for clarity.

(2A)
(2B)

(2C)
Figure 2. (A) π···π interactions found between the molecules of 5; (B) Intermolecular CH···
edge-to-face (T-shaped) arrangements in the structure of 7: d(H25···centroid) = 2.768 Å,
 C25H25···centroid = 178; (C) Intermolecular CH··· arrangements in the structure of 4:
d(H21B···centroid) = 2.593 Å,  C21H21B···centroid = 153; d(H18···centroid) = 2.642 Å,
 C18H18···centroid = 177.

(3A)
(3B)

(3C)
Figure 3. (A) Intermolecular CH··· arrangements in the structure of 2: d(H18···centroid) =
2.729 Å,

C18H18···centroid
=
176; d(H21A···centroid)
=
2.965 Å,
 C21H21A···centroid = 147; (B) Intermolecular CH··· arrangements in the structure
of 8a: d(H18···centroid) = 2.811 Å,  C18H18···centroid = 171; (C) Intermolecular CH···
arrangements in the structure of 8b: d(H26···centroid) = 2.603 Å,  C26H26···centroid =
161.

Figure 4. Cyclic voltammogram of 2 (3.7×10-3 M) in 0.2 M [NBu4][BF4] / DMSO at a platinum
disc working electrode (d = 0.5 mm) and at a scan rate of 0.2 V·s-1. The arrows indicate the
initial (anodic or cathodic) potential scan direction.

 (ppm)
Figure 5. 1H NMR spectrum of DMSO-d6 in the absence (top) and in the presence (bottom) of 2.

Table 1. Crystal data, data collection parameters and convergence results for 1-8.
1
2
3
4
5
6
7
8a
8b
CCDC
No.
Empiric
al
C40H30Co
N8O2
C42H34Co
N8O2
C42H34Co
N8O2
C42H34Co
N8O4
C44H42Co
N8O6
C40H28Cl2C
oN8O2
C40H28Br2C
oN8O2
C42H32Br2C
oN8O2
C54H46Br2Co
N10O2
formula
Formula
weight
713.65
741.70
741.70
773.70
837.78
782.53
871.45
899.50
1083.77
Crystal
size
0.21×0.21
×0.23
0.08×0.15
×0.10
0.02×0.22
×0.30
0.14×0.16
×0.16
0.15×0.18
×0.35
0.12×0.25×
0.29
0.15×0.23×
0.29
0.12×0.17×
0.26
0.05×0.12×0
.16
(mm)
Crystal
shape
Block
Block
Block
Block
291(2)
Triclinic
P -1
Plate
Plate
Block
Block
Plate
Tempera 291(2)
ture (K)
288(2)
Triclinic
P -1
290(2)
Triclinic
P -1
290(2)
Triclinic
P -1
292(2)
Triclinic
P -1
Crystal
system
Triclinic
Triclinic
Monoclinic
Triclinic
Space
group
P -1
P -1
C 2/c
P -1
a (Å)
b (Å)
8.6204(4)
9.5194(9)
8.3398(5)
8.3893(15) 9.3275(4)
8.3607(4)
8.3435(5)
21.8738(12) 9.5858(7)
10.4136(6) 10.4999(9) 10.9376(7) 11.1480(1
7)
10.9526(6) 10.9519(8)
11.0350(8)
10.5034(5)
17.9354(8)
90
11.3587(8)
12.5055(9)
106.055(7)
c (Å)
 (º)
10.8736(6) 11.9273(1
1)
11.3691(8) 11.2985(1
7)
13.1207(7) 11.2845(8)
11.3934(8)
99.104(6)
93.781(5)
65.975(9)
98.851(5)
100.096(1
3)
93.722(4)
98.660(6)
92.659(4)
92.575(4)
971.82(9)
70.919(9)
76.455(8)
90.973(5)
95.841(5)
93.632(14) 109.194(4) 90.993(5)
93.083(14) 111.930(5) 95.516(5)
91.195(5)
95.434(5)
104.997(5)
90
93.340(6)
 (º)
107.070(6)
1236.38(16)
 (º)
V (Å3)
1021.98(1
8)
1018.83(1
2)
1036.0(3)
1147.03(1
1)
1016.23(12) 1030.44(12) 3980.3(4)
Z
1
1
1
1
1
1
1
4
1
Dcalc
1.219
1.205
1.209
1.240
1.213
1.279
1.404
1.501
1.458
(g/cm3)
 (mm–
0.485
7662
0.463
7096
0.465
7532
0.463
8089
0.427
8330
0.597
7974
2.398
8057
2.486
8658
2.016
9143
1
)
Reflecti
ons
measure
d
Indepen
dent
4392
4181
4607
4784
5185
4587
4644
4498
5549
reflectio
ns
Reflecti
on with
I > 2σ(I)
3515
232
2450
242
3763
242
2351
251
3653
275
2608
241
3312
241
2998
250
3317
304
Number
of
paramet
ers
Rint
0.0189
0.0416
0.0505
0.1179
0.0274
0.0446
0.0775
0.0768
0.0248
0.0543
0.1115
0.0713
0.0244
0.0468
0.0263
0.0540
0.0390
0.0642
R(F) (I
 2)
wR (F2)
0.1046
0.3624
0.1141
0.2829
0.1466
0.1566
0.1181
0.1507
0.1486

(all data)
GOF
1.031
1.120
1.026
0.760
1.011
0.985
1.040
1.000
1.016
(F2)
Max.,
0.293, -
0.261
2.242, -
0.336
0.327, -
0.258
0.355, -
0.360
0.269, -
0.410
0.443, -
0.408
0.740, -
0.687
1.082, -
0.679
0.560, -
0.495
min. ρ
(e/Å3)
Table 2. Selected bond lengths (Å) and and angles (°) for compounds 1-8.
1
2
3
4
5**
6
7
8a
1.264(4)
8b
N-N
1.256(2)
1.258(9) 1.250(2)
1.243(6)
1.259(3)
1.262(4)
1.253(4)
1.258(4)
2.038(3)
2.121(3)
2.209(3)
Co-O
Co-NL
Co-Npyr
2.0517(12) 2.039(5) 2.0421(13) 2.027(4)
2.1187(16) 2.108(6) 2.0988(16) 2.097(4)
2.2047(15) 2.203(6) 2.2004(16) 2.196(4)
2.0303(16) 2.050(2)
2.1373(19) 2.103(3)
2.0560(19) 2.055(2)
2.103(2)
2.203(2)
180.00(7)
2.152(3)
2.171(3)
2.199(2)
180.0
2.200(3)
180.0
O-Co-O
180.00(7)
80.48(5)
99.52(5)
180.0
180.0
180.0
173.56(15) 180.0
O-Co-N
(metallacycle)
80.5(2)
99.5(2)
80.87(5)
99.14(5)
80.61(15) 79.96(7)
99.39(15) 100.04(7)
80.95(11) 80.69(8)
99.05(11) 99.31(8)
78.85(10)
96.21(11)
80.35(11)
O-Co-N
99.65(11)
23.04
 l.s.
quinoline-
phenyl
5.19
27.98
5.15
4.72
10.26
4.92
5.75
11.13
 l.s.
quinoline-
pyridine
86.61
8.820
85.86
9.519
85.09
8.340
87.92
8.389
79.95
9.328
86.30
8.361
86.10
8.344
87.85
9.302
86.61
9.586
Co···Co
Graphical abstract