Synthesis and electronic properties of transition metal complexes containing sulfonamidoquinoline ligands

Article abstract of DOI:10.1016/j.poly.2021.115269

The coordination chemistry of 4-nitro-N-(quinolin-8-yl)benzenesulfonamide has been expanded. Crystal structures of bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ²N,N′]cobalt(II) (2), diaqua-bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ²N,N′]nickel(II) (3), and bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ²N,N′]zinc(II) (4) containing this ligand in ML₂ stoichiometry were obtained. The nickel complex is isolated as a dihydrate. The degree of tetrahedrality for the four coordinate copper, cobalt, and zinc complexes was quantitatively compared by calculating the τ₄ geometric parameters. Zinc complex 4 was found to be the most tetrahedral, while copper complex 1-NO₂ deviated most from tetrahedral geometry. The magnetic moment calculated for 1-NO₂ showed inconsistencies when measured in solution and in the solid state. Only a Cu⁺² center exists in solution, while a possible mixed spin state of Cu⁺² and Cu⁺³ is proposed in the solid state. With a more electron releasing substituent on the ligand of the copper complex as seen in complex 1-Me, this behavior is not observed and Cu⁺² exists in solution and solid state. A reversible reduction at the same potential (?1.5 V vs. ferrocene) for both the ligand and the complex suggests possible redox activity of this class of ligand.

Full text of DOI:10.1016/j.poly.2021.115269

Journal Pre-proofs
Synthesis and Electronic Properties of Transition Metal Complexes Contain‐
ing Sulfonamidoquinoline Ligands
Matthew T. Gole, Patrick Pauls, Sage F. Hartlaub, Chip Nataro, Lauren M.
Rossiter, Abby R. O'Connor, Benny C. Chan
PII:
S0277-5387(21)00251-5
DOI:
Reference:
https://doi.org/10.1016/j.poly.2021.115269
POLY 115269
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Polyhedron
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Revised Date:
Accepted Date:
26 February 2021
5 May 2021
12 May 2021
Please cite this article as: M.T. Gole, P. Pauls, S.F. Hartlaub, C. Nataro, L.M. Rossiter, A.R. O'Connor, B.C.
Chan, Synthesis and Electronic Properties of Transition Metal Complexes Containing Sulfonamidoquinoline
Ligands, Polyhedron (2021), doi: https://doi.org/10.1016/j.poly.2021.115269
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Synthesis and Electronic Properties of Transition Metal
Complexes Containing Sulfonamidoquinoline Ligands
Matthew T. Golea, Patrick Paulsa, Sage F. Hartlaubb, Chip Natarob, Lauren M. Rossitera*, Abby R.
O’Connora*, Benny C. Chana*
aDepartment of Chemistry, The College of New Jersey, 2000 Pennington Rd. Ewing, NJ, 08628,
USA
bDepartment of Chemistry, Lafayette College, Easton, PA 18042, USA
* rossitel@tcnj.edu, oconnora@tcnj.edu, chan@tcnj.edu
Abstract
The coordination chemistry of 4-nitro-N-(quinolin-8-yl)benzenesulfonamide has been expanded.
Crystal structures of bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]cobalt(II) (2),
diaqua-bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]nickel(II) (3), and bis[4-nitro-N-
(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]zinc(II) (4) containing this ligand in ML2 stoichiometry
were obtained. The nickel complex is isolated as a dihydrate. The degree of tetrahedrality for the
four coordinate copper, cobalt, and zinc complexes was quantitatively compared by calculating
the τ4 geometric parameters. Zinc complex 4 was found to be the most tetrahedral, while copper
complex 1-NO2 deviated most from tetrahedral geometry. The magnetic moment calculated for 1-
NO2 showed inconsistencies when measured in solution and in the solid state. Only a Cu+2 center
exists in solution, while a possible mixed spin state of Cu+2 and Cu+3 is proposed in the solid state.
With a more electron releasing substituent on the ligand of the copper complex as seen in complex
1-Me, this behavior is not observed and Cu+2 exists in solution and solid state. A reversible
reduction at the same potential (-1.5 V vs. ferrocene) for both the ligand and the complex suggests
possible redox activity of this class of ligand.
Keywords: Coordination complexes, Copper, magnetic moment, Quinoline sulfonamides,
X-ray crystal structures
1.
Introduction
8-Aminoquinoline (Figure 1) and its derivatives are versatile bidentate ligands in
coordination chemistry. The luminescence of quinoline has been a subject of study.[1] This
property extends to quinoline derivatives and their metal complexes, with zinc, cadmium, and
mercury, exhibiting photoluminescence at room temperature.[2] Complexes of 8-aminoquinoline
have also been prepared containing the lanthanides.[3] Additionally, complexation of this family
of ligands with ruthenium forms an electroactive polymer.[4] In the preceding complexes, the
amino group remains neutral upon coordination. 8-Aminoquinoline can serve as a building block
for the synthesis of more complex ligands with increased functionality.
1

Figure 1. Structures of quinoline, 8-aminoquinoline, and aryl sulfonamide quinoline.
The addition of aryl sulfonyl moieties to 8-aminoquinoline (Figure 1) results in a class of
monoanionic bidentate ligands with diverse properties. Complexes containing these ligands are
of interest for their antifungal properties,[5],fluorescent properties, and role as sensors in
biological systems.[6] Moreover, studies demonstrate the ability of these ligands to inhibit zinc(II)
dependent metalloproteinases[7] and HIV-1 replication.[8] The ability of these complexes to form
uniquely colored chelate precipitates based on the identity of the metal cation makes them useful
for qualitative analysis of metals in solution.[9] Structurally similar ethylene linked
pyridinesulfonamide ligands chelate to transition metals in a conformation comparable to the
quinoline based ligands [10,11] and iridium complexes that possess this ligand catalyze the
transfer hydrogenation of ketones and aldehydes.[12–14] Numerous coordination complexes
containing sulfonamidoquinoline ligands have been reported in literature, along with their crystal
structures. For example, copper[15,16] and manganese[17] complexes with tolyl, phenyl, and
naphthyl substituted sulfonamidoquinoline ligands with L2M formulas serve as DNA nuclease
agents, that cleaveDNA by radical processes.[16,18] DNA cleavage is also observed in a
copper(II) complex containing one sulfonamidoquinoline and one bipyridine ligand.[19] Nickel
complexes containing the same derivatives of the sulfonamidoquinoline are also known.[20]
Studies of the antiprotozoal effects of zinc and copper complexes with a wide range of
sulfonamide derivatives were performed.[21,22] Additionally, crystal structures of copper and zinc
complexes containing 4-nitro-N-(quinolin-8-yl)benzenesulfonamide are reported and these
species exhibit chemical nuclease activity.[23–25] The reported copper complex has a distorted
square planar geometry and was identified as a copper(II) complex by cyclic voltammetry and
electron paramagnetic resonance.[25] Coordination complexes with these ligands are also
applied in catalysis. For example, a palladium complex containing 3-nitro-N-(quinolin-8-
yl)benzenesulfonamide catalyzes stereospecific allyl-aryl coupling reactions[26] and a ruthenium
complex catalyzes transfer hydrogenation of acetophenone derivatives.[27]
As of yet, the redox activity of sulfonamidoquinoline ligands in transition metal complexes
is not reported. There is increased interest in redox-active ligands for their use in catalysis.
Additionally, improvements in X-ray crystallography and spectroscopic techniques have allowed
for better electronic structural determinations of coordination complexes.[28] These aid in the
identification of the presence of a radical-based ligand. Non-innocent ligands have been of
interest in bioinorganic chemistry in reference to the single electron reactions that occur within
enzymes.[29]Ligand-based redox activity is also observed in complexes that exhibit π-stacking in
the solid state.[30] Non-innocent ligands play an important role as electron reservoirs in the
catalytic cycle in certain organocatalysts.[31] Identification of these properties in
sulfonamidoquinoline ligands would open up a new area of research including metal-catalyzed
transformations.
We are interested in reevaluating the physical properties and solid-state structures of
copper, zinc, and nickel complexes containing the 4-nitro-N-(quinolin-8-yl)benzenesulfonamide
2

ligand. Here, we report X-ray structures for several coordination complexes containing the 4-nitro-
N-(quinolin-8-yl)benzenesulfonamide ligand. The degree of tetrahedrality for the four coordinate
copper (1-NO2), cobalt (2), and zinc (4) complexes was quantitatively compared by calculating
the τ4 geometric parameters. Zinc complex 4 is the most tetrahedral, while copper complex 1-NO2
was the most square planar. Based on magnetic susceptibility measurements performed on an
Evans balance in the solid state, the copper complex possesses Cu+2 oxidation state. The Evans
NMR method for the determination of magnetic moment in solution has confirmed the metal
centers are in the +2 oxidation state. The structural evaluation of these complexes herein serves
to aid in the continued investigation of the potential applications of these complexes.
2. Materials and Methods
2.1 General Methods
Unless otherwise noted, all reactions were performed under atmospheric conditions with solvents
that were not dried or degassed. Microwave synthesis was performed on a Biotage+ Initiator
1
Microwave Reactor set to high absorbance. All H NMR spectra were obtained with a Bruker
Biospin UltraShield 400 MHz nuclear magnetic resonance spectrometer. Chemical shifts are
reported in reference to residual CHCl3 (δ 7.24 for 1H) unless noted otherwise. X-ray diffraction
was performed on a Bruker APEX II Single Crystal X-Ray Diffractometer with CCD detector at
100 K. Infrared spectra were obtained on a Perkin-Elmer Spectrum Two Fourier Transform
Infrared Spectrometer. Mass susceptibility measurements were carried out on a Johnson Matthey
Mark I Magnetic Susceptibility Balance. Cyclic voltammetry was performed with ferrocene as a
reference. Elemental analyses were performed by Intertek Pharmaceutical Services of
Whitehouse, NJ.
2.2 Materials
8-Aminoquinoline was obtained from TCI. 4-Toluenesulfonyl chloride, cobalt(II) acetate, and
zinc(II) chloride were purchased from Acros Organics. 4-Nitrobenzenesulfonyl chloride and
benzenesulfonyl chloride were purchased from Alfa Aesar. Copper(II) acetate, anhydrous
nickel(II) chloride, nickel(II) chloride hexahydrate, methanol, and methylene chloride were
purchased from Sigma Aldrich. Chloroform-d was purchased from Cambridge Isotope
Laboratories and dried over molecular sieves. All other reagents were used as purchased.
2.3 Synthesis of Sulfonamidoquinoline ligands
4-Methyl-N-(quinolin-8-yl)benzenesulfonamide, N-(quinolin-8-yl)benzenesulfonamide, and 4-
nitro-N-(quinolin-8-yl)benzenesulfonamide were synthesized using a literature procedure.[7] The
1
p-nitro substituted compound required recrystallization from methanol. The H NMR and IR
spectra obtained for each ligand were consistent with reported values.
2.4 Synthesis of bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]copper(II) (1-
NO2), bis[4-methyl-N-(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]copper(II) (1-Me), and
bis[N-(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]copper(II) (1-H)
All copper complexes were prepared by an adapted literature procedure.[15] In a 250 mL beaker,
the sulfonamidoquinoline ligand was dissolved in boiling methanol (150 mL). Copper(II) acetate
monohydrate was dissolved in methanol (30 mL) and added dropwise to the hot solution
containing the ligand while stirring. The solution turned brown and was homogeneous. After
several minutes, a brown precipitate formed. The solution was cooled and continued to stir for 3
h at 22 °C. The solution was filtered and the solid washed three times with methanol (5 mL). For
complex 1-NO2, 4-nitro-N-(quinolin-8-yl)benzenesulfonamide (281 mg, 0.853 mmol) reacted with
copper(II) acetate monohydrate (86 mg, 0.430 mmol) to yield a brown powder (281 mg, 0.390
mmol, 92%). Dark green X-ray quality crystals of 1-NO2 were obtained by vapor diffusion of a
3

dichloromethane saturated solution of 1-NO2 with hexanes. Anal. Calcd for C30H20N6CuO8S2: C,
50.03; H, 2.80; N,11.67. Found: C, 49.74; H, 2.79; N,11.74.
For complex 1-Me, 4-methyl-N-(quinolin-8-yl)benzenesulfonamide (302 mg, 1.01 mmol) reacted
with copper(II) acetate monohydrate (102 mg, 0.509 mmol) to yield a brown powder (279 mg,
0.424 mmol, 83%). For complex 1-H, N-(quinolin-8-yl)benzenesulfonamide (302 mg, 1.06 mmol)
reacted with copper(II) acetate monohydrate (102 mg, 0.509 mmol) to yield a brown powder (310
mg, 0.492 mmol, 92%).
2.5 Synthesis of bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]cobalt(II) (2)
This complex was prepared by an adapted literature procedure.[15] 4-Nitro-N-(quinolin-8-
yl)benzenesulfonamide (149 mg, 0.455 mmol) was dissolved in boiling methanol (40 mL).
Cobalt(II) acetate tetrahydrate (57 mg, 0.229 mmol) was dissolved in methanol (5 mL) and added
dropwise to the hot ligand solution while stirring. A homogeneous red solution resulted and after
several minutes, a red precipitate formed. The solution was heated to reduce the volume by half
causing the product to precipitate. The solution was filtered and the precipitate was washed three
times with methanol (5 mL). The complex was isolated as a red powder (118 mg, 0.165 mmol,
73%). Dark red X-ray quality crystals were obtained by vapor diffusion of a dichloromethane
saturated solution of 2 with hexanes. Anal. Calcd for C31H22N6CoCl2O8S2: C, 46.51; H, 2.77; N,
10.50. Found: C, 47.00; H, 2.85; N, 10.43. The elemental analysis is consistent with one molecule
of dichloromethane per complex which is consistent with the XRD determined unit cell of the
sample submitted for elemental analysis.
2.6
Synthesis
of
diaqua-bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]
nickel(II) (3)
This complex was prepared by an adapted literature procedure.[20] 4-Nitro-N-(quinolin-8-
yl)benzenesulfonamide (102 mg, 0.322 mmol) was dissolved of CH2Cl2 (50 mL). Triethylamine
(89 μL, 0.644 mmol) was added to the solution while stirring. Nickel(II) chloride hexahydrate (37.2
mg, 0.156 mmol) was dissolved in methanol (5 mL) and added dropwise to the solution of the
ligand while stirring. Crystals formed upon slow evaporation of the solution over several days.
Redissolving the crystals in minimal dichloromethane and cooling in an ice bath for 5 min resulted
in precipitation of the product. The powder form of the product was washed three times with
methanol (5 mL) and collected via vacuum filtration. The complex was isolated as a pale green
powder (74.2 mg, 0.0989 mmol, 64%). Anal. Calcd for C30H24N6NiO10S2: C, 47.96; H, 3.22;
N,11.19. Found: C, 47.93; H, 2.96; N,10.43.
2.7 Synthesis of bis[4-nitro-N-(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]zinc(II) (4)
This complex was prepared by an adapted literature procedure.[32] 4-Nitro-N-(quinolin-8-
yl)benzenesulfonamide (101 mg, 0.308 mmol) was dissolved in methanol (15 mL). 2 M NH4OH
(461 μL, 0.922 mmol) was added to the ligand solution. Zinc(II) chloride (22.3 mg, 0.164 mmol)
was dissolved in methanol (1 mL) and added dropwise to the ligand solution while stirring resulting
in a yellow solution. A yellow precipitate formed and was washed three times with methanol (5
mL) and then dissolved in a minimal amount of CH2Cl2 and crystallized via vapor diffusion with
hexanes. (60.6 mg, 0.0839 mmol, 54.6%) Small pale yellow and colorless crystals formed and
were characterized by single crystal X-ray diffraction. Colorless crystals were determined to be
the uncoordinated ligand. Suitable elemental analysis could not be obtained after several sample
submissions. 1H NMR (400 MHz, CDCl3) δ 8.67 (dd, J = 4.68, 1.47 Hz, 1H), 8.46 (dd, J = 8.32,
1.49 Hz, 1H), 8.38 (dd, J = 6.96, 1.81 Hz, 2H), 8.20 (dd, J = 6.96, 1.83 Hz, 2H),7.63 (quartet, J =
4.33 Hz, 1H), 7.50 (d, J = 4.49 Hz, 2H), 7.45 (quartet, J = 4.40 Hz, 1H).
4

2.9 Evans Balance Magnetic Susceptibility Measurements
Magnetic susceptibility measurements were repeated in triplicate for each sample. Equations to
determine the effective magnetic moment (µeff) were obtained from literature.[33] Diamagnetic
susceptibility of the sulfonamidoquinoline ligands and metal ions were estimated using the method
described in the literature.[34]
2.10 Evans Method
An adapted literature procedure was performed.[35] The complex (7 mg) and tetramethylsilane
(30 μL) were added to a 1 mL volumetric flask and diluted to volume with CDCl3. 500 μL of this
solution was pipetted into a coaxial tube which was then inserted into an NMR tube.
Tetramethylsilane (30 μL) was added to a 1 mL volumetric flask and diluted to volume with CDCl3.
500 μL of this solution was added to the NMR tube. Magnetic moments were determined by the
degree the TMS peak shifted (Δν).
2.11 X-ray Crystallography
Single crystals were selected for analysis on a Bruker-AXS SMART Apex II X-ray diffractometer
using Mo Kα radiation with a graphite monochromator. All samples were mounted using a
MiTeGen MicroMount and NVH oil. Data were collected at 100°C. Unit cells were determined by
taking 12 data frames, 0.5° ϕ, in three sections of the Ewald sphere. Full hemispheres were
collected on each crystal and integrated using SAINT Plus. Data were corrected for absorption
correction using SADABS. Structures were solved by the use of direct methods. Least squares
refinement on F2 was used for all reflections. Straightforward structure solution, refinement, and
the calculations of measurements were accomplished with the SHELXTL package. Non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were placed in idealized, theoretical
positions. Hydrogens on the coordinated water on complex 3 were found from the electron density
maps and refined using a free riding model.
2.12. Electrochemistry
For the electrochemical experiments conducted on 1-NO2, a CH Instruments Model CHI260D
potentiostat was used. The experiment was performed at room temperature (22 + 1 °C) under an
argon atmosphere at a scan rate of 100 mV/s using a glassy carbon working electrode (1.0 mm).
This electrode was polished with 1.0 mm and 0.25 mm diamond paste and rinsed with methylene
chloride before use. A non-aqueous Ag/AgCl electrode separated from the solution by a glass frit
served as the reference electrode and the counter electrode was a platinum wire. Experiments
were performed in dried DMF (10 mL)[36] with 0.1 M tetrabutylammonium hexafluorophosphate
as the supporting electrolyte. Analyte concentrations were 1.0 mM. Ferrocene (FcH) was added
as an internal standard giving a solution that was 0.1 mM in FcH after the initial electrochemical
measurement. All reported data was background subtracted.
3. Results and Discussion
3.1 Synthesis of sulfonamidoquinoline ligands
All sulfonamidoquinoline ligands were prepared by reaction of 8-aminoquinoline with
substituted aryl sulfonamides, using a microwave procedure.[7] The nitro-substituted ligand was
1
recrystallized from methanol. H NMR and IR spectral characterization of the ligands was
consistent with previous reports.
3.2 Synthesis and characterization of coordination complexes
5

Scheme 1. Synthesis of coordination complexes 1 - 4.
The copper complexes 1 and cobalt complex 2 were synthesized from the metal acetates
and the desired N-(quinolin-8-yl)benzenesulfonamide ligand in a methanol solution (Scheme 1).
The copper complexes are known in the literature and the synthesized compounds are consistent
with what has been reported.[16,25] Nickel complex 3 was synthesized from nickel chloride
hydrate and two equivalents of the 4-nitro-N-(quinolin-8-yl)benzenesulfonamide ligand in CH2Cl2
in the presence of triethylamine. Complex 4 was synthesized from zinc chloride hydrate and two
equivalents of the 4-nitro-N-(quinolin-8-yl)benzenesulfonamide ligand in methanol using NH3OH
as a base. Complexes 3 and 4 required base to deprotonate the ligand. The acetate anion served
as the base for deprotonation to yield complexes 1 and 2. All of the coordination complexes were
synthesized in moderate to good yields (55-92%). Complexation of the ligand to the metal center
was readily confirmed by the disappearance of the NH peak at ~3300 cm-1 for the free ligand in
the infrared spectrum of the product.
X-ray quality crystals of 1-NO2 and 2 were obtained from slow evaporation of the
methanolic solution. X-ray crystal structures for complexes 1-NO2 and 2 were collected at 100K,
differing from the reported temperature of 299 K for the known species in the literature.[23] The
6

structure of 1-NO2 contained pseudo symmetry and a the literature solution was attempted in the
monoclinic space groups, C2/c and CC. In our low temperature analysis, the higher symmetry
models diverged with multiple atoms becoming non-positive definite during anisotropic
refinements, lower r-values (0.047, 0.050) and a poor goodness of fit (~0.7, ~0.6), respectively.
The final space group for 1-NO2 was assigned as triclinic, P-1 as the anisotropic refinement did
not diverge, the goodness of fit was much closer to 1, but a slightly higher r-value (0.0526) was
observed when compared to the literature report. Crystals of nickel complex 3 and zinc complex
4 were obtained by dissolving the complex in minimal dichloromethane followed by vapor diffusion
in hexanes. Selected bond lengths (Å) and bond angles (°) for complexes 1-NO2 and 2-4 are
found in Table 1. X-ray diffraction parameters for complexes 1-NO2 and 2-4 are found in Table 2.
Crystal structures for complexes 1-NO2 and 2-4 are shown in Figure 2.
Figure 2. X-ray crystal structures of complexes 1-NO2 – 4. For complexes 3 and 4
dichloromethane solvent omitted for clarity.
Table 1. Selected bond lengths (Å) and bond angles (°).
7

Complex 1-NO2
Complex 2
Complex 3
Complex 4
Bond Lengths
Cu – N1
1.997(3)
1.953(3)
1.996(3)
1.955(3)
Co – N1
Co – N2
Co – N4
Co – N5
2.043(3)
1.981(3)
2.032(3)
1.982(3)
Ni – N1
2.052(3)
2.103(3)
2.071(3)
2.133(3)
Zn – N1
2.049(3)
1.970(3)
2.032(3)
1.969(3)
Cu – N2
Cu – N4
Cu – N5
Ni – N2
Ni – N4
Ni – N5
Zn – N2
Zn – N4
Zn – N5
Bond angles
N1-Cu-N4
N2-Cu-N5
138.41(12)
162.57(12)
N1-Co-N4
121.95(11) N1-Ni-N4
92.90(12)
N1-Zn-N4
111.69(11)
129.15(12)
(α)
N2-Co-N5
130.10(12) N2-Ni-N5 169.37(12) N2-Zn-N5
(β)
Table 2. Crystallography parameters for complexes 1-NO2, 2, 3, and 4.
Complex
1-NO2
2
3
4
Chemical
formula
C30H20N6O8S2Cu C30H20N6O8S2C
o
C31H26Cl2N6O10S2Ni C31H22Cl2N6O8S2Z
n
Formula
weight
720.18
715.58
836.30
806.93
Crystal
system
Triclinic
Orthorhombic
Orthorhombic
Monoclinic
Space group P-1
Pbca
P212121
10.2413(13)
14.7107(18)
22.500(3)
90
90
90
3389.8(7)
P21/n
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Color
habit
Size
10.886(7)
15.5950(10)
17.3877(11)
22.1119(14)
90
90
90
16.996(2)
8.7489(10)
22.838(3)
90
105.239(2)
90
10.900(7)
13.177(8)
97.685(7)
97.766(9)
98.998(7)
1510.9(16)
5995.9(7)
3276.5(7)
and Clear dark green Red plate
block
Clear pale green Clear pale yellow
needle block
0.511x0.046x0.035 0.420x0.173x0.074
0.420x0.112x0.0 0.114x0.069x0.
70
029
Z
2
8
4
4
T (K)
100(2)
MoKα
100(2)
MoKα
100(2)
MoKα
296(2)
MoKα
Radiation
type
Dcalc g cm-3
1.583
1.585
1.639
1.636
8

μ (mm-1)
0.924
0.775
0.921
1.102
Final
R
R1 = 0.0526
R1 = 0.0393
R1 = 0.0398
R1 = 0.0410
indices [I >
2σ(I)]
wR2 = 0.1010
wR2 = 0.0742
wR2 = 0.0660
wR2 = 0.1094
R indices (all R1 = 0.1060
R1 = 0.0833
wR2 = 0.0906
1.005
R1 = 0.0624
wR2 = 0.0723
1.038
R1 = 0.0495
wR2 = 0.1148
1.073
data)
wR2 = 0.1208
Goodness-
of-fit (GOF)
0.973
The coordination environment of the metal centers (Figure 3) varies with the identity of the
metal center. Complexes 1-NO2, 2 and 4 are four coordinate complexes, whereas nickel complex
3 is octahedral. Complex 3 exhibits octahedral geometry due to the coordination of two water
molecules at the nickel center. The zinc complex 4 reported here differs from a previously reported
zinc complex which contains a coordinated water molecule. The structural parameters for the two
molecules are similar.[24]
The steric influences around the octahedral nickel center in complex 3 increase the bond
distance between the sulfonamido nitrogen and the metal center. For example, the Ni – N5 bond
is approximately 0.15 Å longer than the equivalent Co – N11 bond (Table 1). This shows that the
sulfonamido portion of the ligand is closer to the metal center in the 4-coordinate complexes. To
examine the structural differences between the different coordination complexes, including
complex 1-NO2, τ4 parameters were calculated.[6] These parameters quantitatively characterize
the geometry of four coordinate complexes on a spectrum ranging from perfectly square planar
(τ = 0) to perfectly tetrahedral (τ = 1). Ligand-metal-ligand bond angles designated α and β
(defined in Table 1) were used to calculate τ, and the results are found in Table 3. The angle
between the cyclic nitrogens was designated α, and the angle between the sulfonamido nitrogens
was designated β. The coordination chemistry at each metal center is evident from the polyhedral
rendition for each complex, as depicted in Figure 3. Zn complex 4 possesses the most tetrahedral
geometry while Cu complex 1-NO2 is nearly square planar, whereas Ni complex 3 exhibits
octahedral geometry.
Figure 3. Coordination environment for Co, Ni, Cu and Zn analogues.
Table 3. τ4 values for copper, cobalt and zinc complexes containing 4-nitro-N-(quinolin-8-
yl)benzenesulfonamide ligands.
α
β
Complex
τ
1-NO2
138.47°
162.66°
0.418
2
4
121.954° 130.08° 0.766
113.039° 128.310° 0.841
The τ4 values show copper complex 1-NO2 deviates the most from tetrahedrality with a τ
value of 0.418. This is consistent with the observed distorted square planar geometry and is in
line with reports for other copper complexes that possess substituted sulfonamidoquinoline
ligands.[15] Zinc complex 4 exhibits nearly perfect tetrahedral geometry. Cobalt complex 2 lies
9

between complexes 1-NO2 and 4 in terms of tetrahedrality. A τ4 value was not determined for
nickel complex 3 due to its octahedral geometry; the nickel hydrate complex 3 is octahedral with
two coordinated water molecules in cis configuration at the nickel center.
3.3 Magnetic susceptibility and cyclic voltammetry
The room temperature solid state magnetic moment of complexes 1-NO2, 1-Me, 1-H, and
4 were obtained using an Evans balance (Table 4). The values for copper complexes 1-Me and
1-H and cobalt species 2 correspond to the spin only magnetic moment for Cu2+ and Co2+,
respectively,[33] as expected for a complex containing two anionic ligands. A slightly higher value
for the effective magnetic moment, when compared to the spin only magnetic moment expected
for a Cu+2 metal center, was seen in copper complex 1-NO2 containing the electron withdrawing
p-nitro substituted sulfononamidoquinoline ligand. The effective magnetic moment of 2.37 BM for
1-NO2 is in between one and two unpaired spins, which suggests potentially a mixture of two
copper electronic states - Cu+2 and Cu+3. This is not observed for 1-Me, bearing an electron
releasing substituent, in which the effective magnetic moment of 1.87 BM aligns with the spin only
magnetic moment for on unpaired spin. The value for 1-H is in between at 2.01 BM. To evaluate
this further, the magnetic properties of the three copper complexes was also evaluated in the
solution phase.
Table 4. µeff values obtained at 295 K.
Complex
1-NO2
µeff (BM)
2.37
1-Me
1-H
2
1.87
2.01
3.04
Due to the higher than predicted µeff values, in the solid state, for the copper complex 1-
NO2, the solution phase effective magnetic moment values were determined for all three copper
derivatives for comparison. The Evans NMR method was employed to determine the solution
phase effective magnetic moment for each of the copper complexes 1-NO2, 1-Me, and 1-H (Table
5). The oxidation state for copper in each complex, 1-NO2, 1-Me, and 1H, is consistent with Cu+2.
The calculated effective magnetic moment of all of the copper complexes now aligns quite well
with the predicted spin-only µs values when in solution. A possible explanation for the variation of
the µeff values in the solid state for complex 1-NO2 is that the sulfonamidoquinoline ligands are
non-innocent.
Table 5. µeff Values obtained at 300 K using the Evans NMR method for copper derivatives 1-
NO2, 1-Me, and 1H.
Complex
1-NO2
µeff (BM)
1.82
1-Me
1-H
1.76
1.81
The electrochemical properties of 1-NO2 were then probed due to the variation in the
effective magnetic moments observed in the solid state versus solution state. The redox potentials
of complex 1-NO2 and the 4-nitro-N-(quinolin-8-yl)benzenesulfonamide ligand were determined
10

using cyclic voltammetry. Cyclic voltammetry data of complex 1-NO2 has been previously reported
in the literature.[25] However, the reduction potentials were collected using a limited sweep range.
Upon expanding the sweep range, new interesting electrochemical features were found for the
complex.
Figure 4. Overlay CV of 4-nitro-N-(quinolin-8-yl)benzenesulfonamide ligand (black line) and
complex 1-NO2 (blue line) in DMF versus ferrocene. Scan rate is 100 mV/s, with 0.1 M [NBu4][PF6]
as the supporting electrolyte, data is not background subtracted.
Complex 1-NO2 has two reversible reduction waves, one at -0.64 V and the other at -1.52
V. The additional reversible wave at -1.52 V versus FcH observed for 1-NO2 (Figure 4) was not
reported previously. This wave aligns with the reversible wave at -1.55 V observed in the CV of
the 4-nitro-N-(quinolin-8-yl)benzenesulfonamide ligand. This supports the hypothesis that this
ligand could be reversibly reduced allowing it to sustain an additional electron to become a
radical, and thus be redox active.
Further examination of the packing of 1-NO2 in the solid state also sheds some light on
the possibility for redox activity for the 4-nitro-N-(quinolin-8-yl)benzenesulfonamide ligand. The 1-
NO2 complex exhibits π-stacking in the solid state (Figure 5), and this was also previously
reported for 1-Me.[23] Similar stacking has been seen before in complexes containing non-
innocent ligands.[30] This interaction could allow stabilization of a radical on this type of ligand.
Although the π-stacking is observed in the solid state for 1-NO2 and 1-Me only 1-NO2 exhibits
non-innocent behavior in the solid state. This is likely attributed to the presence of the electron
withdrawing nitro group capable of aiding in stabilization of an additional electron at the ligand. In
the case of 1-Me, the electron releasing substituent would destabilize the ligand from supporting
an additional electron.
11

Figure 5. Pi-stacking observed in the solid state structure of 1-NO2.
4. Conclusion
4-Nitro-N-(quinolin-8-yl)benzenesulfonamide was synthesized by microwave reaction,
and five coordination complexes containing this ligand were synthesized in good yields.
Complexes 2-4 were characterized by IR spectroscopy, elemental analysis, and X-ray
crystallography. The cobalt (2) and zinc (4) complexes were four coordinate, while the nickel
hydrate complex 3 was octahedral with two coordinated water molecules in cis configuration. In
the solid-state structure of the iron complex 7, methanol and the sulfonyl oxygens on the ligand
were coordinated to the metal center forming an octahedral bridged dimer. Upon extended
exposure to air, the dimer converted to an extended chain structure. Magnetic susceptibility data
confirms a +2 oxidation state for complexes 2-4. A qualitative study of the structure of four
coordinate complexes 1-NO2, 2, and 4 (Cu, Co, Zn, respectively) was conducted by calculating
the τ4 parameters to assess the degree of tetrahedrality. The zinc complex 4 is nearly tetrahedral,
while the copper complex 1-NO2 has a distorted square planar structure. The magnetic moment
of the copper complex 1-NO2 was used to determine that the metal center is Cu+2 in solution. In
the solid state, the effective magnetic moment of 1-NO2 is in between the predicted values for one
or two unpaired spins, suggesting a mixture of Cu+2 and Cu+3. This suggests probable redox
activity behavior of the 4-nitro-N-(quinolin-8-yl)benzenesulfonamide ligand. In addition, expansion
of the sweep width used for the cyclic voltammetry measurements of complex 1-NO2 showed the
ligand could be reduced reversibly, providing support for non-innocent behavior. The highly
electron withdrawing character of the nitro substituent on the ligand aids in stabilizing additional
electrons at the ligand. Further studies to investigate the potential redox activity of the 4-nitro-N-
(quinolin-8-yl)benzenesulfonamide ligand and its application in redox activity are future avenues
to explore.
Declaration of interests
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.
Appendix A. Supplementary data
12

CCDC <2064459> contains the supplementary crystallographic data for <bis[4-nitro-N-(quinolin-
8-yl)benzenesulfonamidato-κ2N,N’]copper(II) (1-NO2)>.
CCDC <2064457> contains the supplementary crystallographic data for <bis[4-nitro-N-(quinolin-
8-yl)benzenesulfonamidato-κ2N,N’]cobalt(II) (2)>.
CCDC <2064458> contains the supplementary crystallographic data for <diaqua-bis[4-nitro-N-
(quinolin-8-yl)benzenesulfonamidato-κ2N,N’]nickel(II) (3)>.
CCDC <2064455> contains the supplementary crystallographic data for <bis[4-nitro-N-(quinolin-
8-yl)benzenesulfonamidato-κ2N,N’]zinc(II) (4)>.
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.
Acknowledgements
This work was supported by the Donors of the American Chemical Society Petroleum Research
Fund (ACS PRF UNI#3 53605 to A. R. O’C). X-ray crystallography (#0922931) and NMR data
(#1125993) were collected on instruments purchased through MRI grants from the National
Science Foundation. Dr. Chan thanks the University of Pennsylvania, Department of Chemistry
and Dr. Eric Schelter for hosting his sabbatical leave and the fruitful discussions with his research
group on this work.
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Graphical Abstract:
Transition metal complexes with 4-nitro-N-(quinolin-8-yl)benzenesulfonamide ligands were
prepared and characterized by X-ray crystallography. Magnetic studies of 1-NO2 were
reevaluated and show the complex to possess a Cu+2 metal center in solution and mixed Cu+2
and Cu+3 in the solid state. The electrochemistry of 1-NO2 supports redox activity for this ligand.
15

Table 1. Selected bond lengths (Å) and bond angles (°).
Complex 1-NO2
Complex 2
Complex 3
Complex 4
Bond Lengths
Cu – N1
1.997(3)
1.953(3)
1.996(3)
1.955(3)
Co – N1
Co – N2
Co – N4
Co – N5
2.043(3)
1.981(3)
2.032(3)
1.982(3)
Ni – N1
2.052(3)
2.103(3)
2.071(3)
2.133(3)
Zn – N1
2.049(3)
1.970(3)
2.032(3)
1.969(3)
Cu – N2
Cu – N4
Cu – N5
Ni – N2
Ni – N4
Ni – N5
Zn – N2
Zn – N4
Zn – N5
Bond angles
N1-Cu-N4
N2-Cu-N5
138.41(12)
162.57(12)
N1-Co-N4
121.95(11) N1-Ni-N4
92.90(12)
N1-Zn-N4
111.69(11)
129.15(12)
(α)
N2-Co-N5
130.10(12) N2-Ni-N5 169.37(12) N2-Zn-N5
(β)
Table 2. Crystallography parameters for complexes 1-NO2, 2, 3, and 4.
Complex
1-NO2
2
3
4
Chemical
formula
C30H20N6O8S2Cu C30H20N6O8S2C
o
C31H26Cl2N6O10S2Ni C31H22Cl2N6O8S2Z
n
Formula
weight
720.18
715.58
836.30
806.93
Crystal
system
Triclinic
Orthorhombic
Orthorhombic
Monoclinic
Space group P-1
Pbca
P212121
10.2413(13)
14.7107(18)
22.500(3)
90
90
90
3389.8(7)
P21/n
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
10.886(7)
15.5950(10)
17.3877(11)
22.1119(14)
90
90
90
16.996(2)
8.7489(10)
22.838(3)
90
105.239(2)
90
10.900(7)
13.177(8)
97.685(7)
97.766(9)
98.998(7)
1510.9(16)
V (Å3)
5995.9(7)
3276.5(7)
16

Color
habit
Size
and Clear dark green Red plate
block
Clear pale green Clear pale yellow
needle block
0.511x0.046x0.035 0.420x0.173x0.074
0.420x0.112x0.0 0.114x0.069x0.
70
029
Z
2
8
4
4
T (K)
100(2)
MoKα
100(2)
MoKα
100(2)
MoKα
296(2)
MoKα
Radiation
type
Dcalc g cm-3
1.583
1.585
1.639
1.636
μ (mm-1)
0.924
0.775
0.921
1.102
Final
R
R1 = 0.0526
R1 = 0.0393
R1 = 0.0398
R1 = 0.0410
indices [I >
2σ(I)]
wR2 = 0.1010
wR2 = 0.0742
wR2 = 0.0660
wR2 = 0.1094
R indices (all R1 = 0.1060
R1 = 0.0833
wR2 = 0.0906
1.005
R1 = 0.0624
wR2 = 0.0723
1.038
R1 = 0.0495
wR2 = 0.1148
1.073
data)
wR2 = 0.1208
Goodness-
of-fit (GOF)
0.973
Table 3. τ4 values for copper, cobalt and zinc complexes containing 4-nitro-N-(quinolin-8-
yl)benzenesulfonamide ligands.
α
β
Complex
τ
1-NO2
138.47°
162.66°
0.418
2
4
121.954° 130.08° 0.766
113.039° 128.310° 0.841
Table 4. µeff values obtained at 295 K.
Complex
1-NO2
µeff (BM)
2.37
1-Me
1-H
2
1.87
2.01
3.04
Table 5. µeff Values obtained at 300 K using the Evans NMR method for copper derivatives 1-
NO2, 1-Me, and 1H.
Complex
1-NO2
µeff (BM)
1.82
1-Me
1-H
1.76
1.81
17