Nickel(II) complex of 4-amino-N-(2-pyrimidinyl)benzenesulfonamide: Synthesis, spectroscopic characterization, antimicrobial activity, crystal structure, and hirshfeld surface analysis

Article abstract of DOI:10.1080/15533174.2016.1158186

A nickel complex of 4-amino-N-(2-pyrimidinyl)benzenesulfonamide (sulfadiazine) has been synthesized and characterized by elemental analysis, infrared, UV-Vis, and 1H NMR spectroscopy. The title compound, [Ni(C₁₀H₉N₄O₂S)2(C₅H₅N)₂](C₅H₅N)(H₂O)₂ crystallizes in monoclinic system with space group P21 and ZD2. X-ray analysis revealed that Ni(II) ion exhibits a distorted octahedral geometry. The Hirshfeld surfaces are performed to study the nature of interactions and their quantitative contributions toward crystal packing. The results of spectral and thermal data suggest that the binding of nickel atom to the sulfonamidic nitrogen is in agreement with the crystal structure determination. Nickel sulfadiazine presents different antibacterial behavior against Escherichia coli and Staphylococcus aureus strains.

Full text of DOI:10.1080/15533174.2016.1158186

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Nickel(II) complex of 4-Amino-N-(2-
pyrimidinyl)benzenesulfonamide: Synthesis,
spectroscopic characterization, antimicrobial
activity, crystal structure and Hirshfeld surface
analysis
Sanjay M. Tailor & Urmila H. Patel
To cite this article: Sanjay M. Tailor & Urmila H. Patel (2016): Nickel(II) complex of 4-Amino-N-
(2-pyrimidinyl)benzenesulfonamide: Synthesis, spectroscopic characterization, antimicrobial
activity, crystal structure and Hirshfeld surface analysis, Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry, DOI: 10.1080/15533174.2016.1158186
To link to this article: http://dx.doi.org/10.1080/15533174.2016.1158186
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Published online: 15 Jun 2016.
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Nickel(II) complex of 4-Amino-N-(2-pyrimidinyl)benzenesulfonamide: Synthesis, spectroscopic
characterization, antimicrobial activity, crystal structure and Hirshfeld surface analysis
Sanjay M. Tailor* and Urmila H. Patel
Department of Physics, Sardar Patel University, Vallabh Vidyanagar - 388 120, Gujarat, India
*Corresponding author:E-mail: sanjay_tailor10@yahoo.com
Abstract
Nickel complex of 4-Amino-N-(2-pyrimidinyl)benzenesulfonamide (sulfadiazine) has been
synthesized and characterized by elemental analysis, infrared, UV-Vis and 1H NMR
spectroscopy. The title compound, [Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2 crystallizes in
monoclinic system with space group P21 and Z=2. X-ray analysis revealed that Ni(II) ion
exhibits a distorted octahedral geometry. The Hirshfeld surfaces are performed to study the
nature of interactions and their quantitative contributions towards crystal packing. The results of
spectral and thermal data suggest that binding of nickel atom to the sulfonamidic nitrogen are in
agreement with the crystal structure determination. Nickel sulfadiazine presents different
antibacterial behavior against Escherichia coli and Staphylococcus aureus strains.
Keywords
Ni complex; Spectroscopic analysis; Crystal structure; Hirshfeld surface; Thermogravimetric
study; Antimicrobial activity
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1. Introduction
Among the many different families of organic–inorganic chemicals being currently investigated
due to their wide scale applications, sulfonamides and their N-derivatives are one of the
outstanding groups [1]. Sulfadiazine is considered as a Sulfa-drug derived from the parent
compound, sulfanilamide, which consider important class of drugs with several types of
pharmacological agents possessing antibacterial [2], antithyroid [3], diuretic [4,5],
hypoglycaemic [6], and anti-carbonic anhydrase [7,8]. The pharmacological activity of these
types of molecules is often enhanced by complexation with metal ions [9,10]. Thus, rapid
healing of skin disorders has been promoted by silver sulfadiazine complex [11,12] in human
topical burn therapy, and zinc sulfadiazine complex [13,14] in the prevention of bacterial
infection in burned animals, where the effectiveness of burn treatment seems to depend not only
on the presence of a metal ion [slow release of the Ag(I) or Zn(II)], but also crucially on the
nature of the material to which the metal ion is bound [13]. Sulfadiazine (sdz), a well-known
antibiotic sulfonamide, widely used for their bactericidial action and X-ray structures of them
have been reported [15,16]. Our interest is in the synthesis and characterization of metallic
complexes bearing sulfonamide ligands. Since several sulfonamide metal complexes showed
more activity than free ligand [17–19]. Sulfadiazine can act as a monodentate or a bidentate
ligand containing several groups with donor atoms those are able to interact with metal ions: Ar–
NH2, NH sulfonamide, SO2–R and N heterocyclic atoms (Figure 1).
Recently, the prediction and computation of molecular crystal structures through the aspect of
intermolecular interactions, structural elucidation, crystal design and crystal engineering, also
have aroused much attention [20–22]. The main approach is through Hirshfeld surfaces, which
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serves as a powerful tool for elucidating molecular crystal structures [23]. Hirshfeld surfaces are
space partitioning construct that summarizes the crystal packing into a single 3-D surface, and
the surface can be reduced to a 2-D fingerprint plot, which summarizes the complex information
on intermolecular interactions present in molecular crystals [22].
The crystal structures of [Cu(sdz)2(NH3)2] and [Hg(sdz)2(DMSO)2] are reported by Brown et al.
[24] and Garcia-Raso et al. [25], respectively. Additionally, Menabue et al. [26] reported the
cadmium complex of sulfadiazine [Cd(sdz)2].2H20 having distorted tetrahedral geometry. Along
with this, single crystal X-ray structure of [Ni(C10H9N4O2S)2(C5H5N)2]·0.5H2O is reported by
Wang et al. [27].
In the present study, synthesis, spectroscopic characterization and antibacterial assays over gram
positive and gram negative pathogenic bacterial strains of Ni(II) complex with sulfadiazine are
described. A new crystal structure for the nickel sulfadiazine complex along with the influence
of nickel metal on the ligand in terms of intermolecular interactions by using Hirshfeld surfaces
and fingerprint plots are also reported here.
2. Experimental
2.1. Materials and methods
Sodium sulfadiazine (Sigma, >99%), nickel acetate and all other reagents are of the highest grade
commercially available and used without further purification.
2.2. Physical measurements
Elemental analysis (C, H, N) is carried out using a Perkin Elmer 2400-II CHN elemental
analyzer. IR spectra are recorded on a Perkin Elmer Spectrum GX FT-IR Spectrometer using
KBr pellet. UV-Vis spectra (200-800 nm) are recorded on a Shimadzu UV-3600 spectrometer in
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DMSO. 1H NMR spectra are recorded on a Bruker Avance DPX-200 spectrometer in d6-DMSO.
Electrical conductivity is measured using EQ-660A conductivity meter. Thermogravimetric
analysis is carried out at heating rate of 5°C min–1 in the temperature range of 25–967°C under
nitrogen flow of 100 mL min–1 by a simultaneous TGA/DTA analyzer using Seiko SII-EXSTAR
TG/DTA-7200.
2.3. Synthesis of the complex
Sodium salt of sulfadiazine (0.545 g, 2 mmol) is dissolved in hot methanol and to this, an
aqueous solution of nickel acetate (0.176 g, 1 mmol) is added with constant stirring and the
mixture is refluxed for 3 hours. A light blue precipitate is formed, filtered and washed with hot
distilled water and methanol successively and dried in a desiccator over anhydrous CaCl2. The
yield at the end of reaction for the complex is around 35%. The results for [C20H22N8Ni1O6S2]
are: Anal. Calcd. (%): C, 40.49; H, 3.73; N, 18.88. Found (%): C, 40.16; H, 3.47; N, 17.54.
The complex is insoluble in water and in most of the common solvents but soluble in Dimethyl
sulfoxide (DMSO), Dimethylformamide (DMF) and pyridine. A very few numbers of tiny light
blue single crystals are grown from pyridine solvent adequate for X-ray structure analysis.
2.4. X-ray crystallography
Crystallographic data are collected on a Bruker Kappa APEX-II CCD diffractometer with
graphite monochromated MoK radiation (λ= 0.71703 Ǻ) at T = 296.15 K. The X-ray diffraction
data are corrected for Lorentz-polarization factor and scaled for absorption effects by evaluation
of multi-scans. The structure is solved by direct methods with SHELXS-2013 [28] and
anisotropic thermal parameters for all non hydrogen atoms are refined by full-matrix least
squares procedure against F2 with SHELXL-2013 [29]. The H atoms are positioned
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geometrically with N–H=0.90Ǻ for NH2 and C–H=0.93Ǻ for aromatic H atoms respectively. In
addition they are constrained to ride on their parent atoms with Uiso(H)=1.2 Ueq (carrier atoms of
CH, NH). The calculations concerning the molecular geometry, the choice and verification of the
space group, the analysis of hydrogen bonds and C–H∙∙∙π interactions are performed by
PLATON [30]. The molecular graphics are done with ORTEP-3 [31] and WinGX [32].
2.5. Hirshfeld surface calculations
Molecular Hirshfeld surfaces [33] in the crystal structure have been constructed based on the
electron distribution calculated as the sum of spherical atom electron densities [34]. For a given
crystal structure and set of spherical atomic electron densities, the Hirshfeld surface is unique
[35] suggesting the possibility of gaining additional imminent into the intermolecular interaction
of molecular crystals. Hirshfeld surfaces and the associated 2-D fingerprint plots are generated
using the Crystal Explorer 3.1 [36]. When the CIF file is read into the Crystal Explorer program
for analysis, all bond lengths to hydrogen are automatically modified to typical standard neutron
values (C–H = 1.083 Å and N–H = 1.009 Å). The 2-D fingerprint plots displayed by using the
standard 0.6–2.8 Å view with the de and di distance scales displayed on the graph axes. The
normalized contact distance (dnorm) based on both de, di and the vdw radii of the atom, given by
Eq. (1) enables identification of the regions of particular importance to intermolecular
interactions [33]. Because of the symmetry between de and di in the expression for dnorm , where
two Hirshfeld surfaces touch, both will display a red spot identical in color intensity as well as
size and shape.
dnorm  d rvdw / rvdw  d r vdw / r vdw (1)




i
i
i
e
e
e
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2.6. Microbiological assays
Micro broth dilution method is used to determine the minimal inhibitory concentration (MIC) of
the antimicrobial agent against gram negative (Escherichia coli) and gram positive
(Staphylococcus aureus). The steps for performing the Micro broth dilution method are based on
recommendations from the National Committee for Clinical Laboratory Standards [37].
The standard strains used are Escherichia coli MTCC 422 and Staphylococcus aureus MTCC 96.
Mueller Hinton Broth is used as Nutrient medium at 37˚C to grow and dilute the drug suspension
for the test bacteria. The solvent DMSO is used as diluent to get desired concentration of drugs
to test upon standard bacterial strains. Serial dilutions are prepared in primary and secondary
screening. Each synthesized compound and standard drugs are diluted obtaining 2000 μg/mL
concentration, as a stock solution. In primary screening 1000, 500, and 250 μg/mL
concentrations of the synthesized drugs are taken. The active synthesized compounds found in
this primary screening are further diluted to obtain 200, 125, 100, 62.5, 50, 25, 12.5, and 6.250
μg/mL concentrations for secondary screening. Inoculum’s size for test strain is adjusted to 108
CFU.ml-1 by comparing the turbidity. MIC is the lowest concentration of a compound in DMSO
that exhibited no visual growth of the organisms in the culture tubes. Each of the above
experiments is repeated thrice along with a control set using DMSO. The mean value obtained
for three individual replicates is then used to calculate the growth inhibition zone of each sample.
3. Results and discussion
3.1. Crystal structure of [Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2
Suitable single crystals grown by slow evaporation from a pyridine solvent of the complex is
used for X-ray crystal structure determination. The single crystal data and refinement details for
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the title compound, [Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2 are summarized in Table 1. The
fractional atomic coordinates and equivalent isotropic thermal parameters are tabulated in Table
2. Figure 2 shows an ORTEP view of the title compound with thermal displacement ellipsoids
are drawn at 50% probability level.
The title compound, [Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2 crystallizes in monoclinic
crystal system with space group P21 and Z=2. Crystal structure of the title compound contains
six coordinated nickel atom leading to a distorted octahedral geometry by two sulfonamidic
nitrogen atoms, two pyrimidine nitrogen atoms (each from two sulfadiazine ligands) and two
nitrogen atoms from two pyridine solvent molecules. In addition, the two water molecules and
one pyridine molecule are as solvent which fill in the 3-D packing architecture, participate in the
formation of an intricate 3-D network through hydrogen bond interactions. The distance between
nickel cation and the nitrogen atoms adjacent to the sulfonyl group of a symmetry related ligand
are Ni−N1 (2.128(4) Ǻ for molecule A and 2.126(4) Ǻ for molecule B) which is similar to the
other reported Ni−N(sulfonamidic) distances [27,38,39]. Third and fourth bond involves the
pyrimidine nitrogen atoms Ni−N2 (2.093(4) Å for molecule A and 2.094(4) Ǻ for molecule B).
The reported Ni−N(pyrimidine) distances for [Ni(C10H9N4O2S)2(C5H5N)2]·0.5H2O [27] and
[Ni(smr)2(pyr)2]·4pyr [38] are 2.070(2) and 2.100(2), respectively. Fifth and sixth bond occurs
with the pyridine nitrogen atoms Ni−N5 (2.097(3) Ǻ for molecule A and 2.102(3) Ǻ for
molecule B) which is similar Ni−N(pyridine) distance 2.100(3)
Ǻ
reported in
Ni(smtz)2(py)2(OH2)2 [40], but quite shorter than reported (2.134(2) and 2.159(2) Ǻ) in nickel
sulfadiazine complex [27].
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The selected bond lengths and bond angles are tabulated in Table 3. The bond lengths and angles
of the phenyl ring confirm well to those found in the free sulfadiazine [15,16], whereas distances
S1–N1 (1.599(4) Å for molecule A and 1.590(4) Å for molecule B) and N1–C7 (1.369(6) Å for
molecule A and 1.369(6) Å for molecule B) are shorter in the Ni(II) complex than those found in
free sulfadiazine ligand [15,16]. The stereochemistry about the sulfur atom is as usual a slightly
distorted tetrahedral geometry with the bond lengths and bond angles involving sulfur lying
within the range quoted in the literature [41–43]. The maximum and minimum value of angles
around the sulfur atom are O1–S1–O2 (117.6(3)˚ for molecule A and 116.6(2)˚ for molecule B)
and O2–S1–N1 (104.3(2)˚ for molecule A and 111.7(2)˚ for molecule B) and the S–N bond
length is similar to that found in [Ni(C10H9N4O2S)2(C5H5N)2]·0.5H2O [27]. The gauche
conformation bout the S–N(sulfonamidic) bond with a torsion angle of 74.4(4)˚ for molecule A
and -74.1(3)˚ for molecule B, but the angle is higher (-53.9˚) in silver sulfadiazine [11]. The
reported gauche conformation about the S–N(sulfonamidic) bond for free sulfadiazine molecule
with torsion angle 77˚ [15]. The dihedral angle between phenyl and pyrimidine ring for title
compound are 67.1(2)˚ for molecule A and 69.6(2)˚ for molecule B, while in free sulfadiazine
molecule the angle is 76˚ [15].
In the crystal structure, the molecular stability is due to strong intermolecular and intramolecular
interactions. Out of all these, three of the intermolecular interactions are N–H∙∙∙O hydrogen bond
formed by the terminal amino nitrogen and water molecule oxygen and two O–H∙∙∙O hydrogen
bonds formed between the water molecule oxygen and sulfonyl oxygen. The packing diagram of
the title compound, [Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2 with N–H∙∙∙O, O−H∙∙∙O and
C−H∙∙∙O intermolecular interactions are shown in Figure 3. In the title compound, amino
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nitrogen atom acts as an acceptor forming intermolecular C–H∙∙∙N and O–H∙∙∙N hydrogen bond
interactions. Water molecules play a significant role in the crystal packing acting as a
donor/acceptor. The packing diagram of the title compound with C−H∙∙∙N and O–H∙∙∙N
intermolecular interactions are depicted in Figure 4. The intramolecualar C–H∙∙∙O interaction is
formed between phenyl ring carbon of sulfadiazine and the sulfonyl oxygen atom. The crystal
structure is also exhibits C(14A)–H(14A)∙∙∙Cg(8) interaction [where Cg(8) is the centroid of the
ring C1B/C2B/C3B/C4B/C5B/C6B with a symmetry code 1+x, y, z] with a C–Cg distance of
3.605(7) Å, C–H∙∙∙Cg angle of 172˚. Hydrogen bond geometry and symmetry code for title
compound are summarized in Table 4.
3.2. Hirshfeld surface analysis
The Hirshfeld surfaces and consequently the fingerprint analysis have been performed to study
the nature of interactions and their quantitative contributions towards the crystal packing. The
molecular Hirshfeld surfaces of title compound, [Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2
generated using a standard (high) surface resolution with the 3-D dnorm surfaces are mapped over
a fixed color scale of -0.65 (red) to 1.3 Å (blue), di and de surfaces are mapped in the range of
0.7–2.7, shape index mapped in the color range of -1.0–1 and curvedness in the range of -4.0–0.4
(Figure 5). For each point on the iso-surface two different types of distances are defined: one is
de signifying the distance from the point to the nearest nucleus external to the surface and the
other one is di signifying the distance to the nearest nucleus internal to the surface. The
normalized contact distance (dnorm) is based on both de and di. The surfaces are displayed as
transparent to permit visualization of the title compound, around which they are calculated. The
surface represented with a spherical depression (deep red) spot is indicative of hydrogen bonding
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interactions (Figure 5a). The dominant interactions are H∙∙∙O (Figure 5b), can be seen in di
surface plots as the bright red color spots. The deep red color spots in de (Figure 5c) are strong
interactions such as O∙∙∙H (14.7%). The shape index is a measure of ‘‘which shape’’, and it can
be sensitive to very subtle changes in surface shape, particularly in areas where the total
curvature (or the curvedness) is very low (Figure 5d). The curvedness surface (Figure 5e) is the
measurement of ‘‘how much shape’’; the flat areas of the surface correspond to low values of
curvedness, while sharp curvature areas correspond to high values of curvedness. The small
range of region and light color on the surface symbolize a weaker and longer interaction other
than hydrogen bonds. The 2-D fingerprint plots of title compound exemplify the strong
indication for the all intermolecular interaction at the same time (Figure 6a). The H—H contacts,
which are reflected in the middle of scattered points and cover most area in the 2-D fingerprint
plots, have a most significant contribution to the total Hirshfeld surfaces (46.8%) (Figure 6b). At
the top left and bottom right of the fingerprint plot, there are characteristic ‘‘wings’’ which are
identified as a result of C—H contacts (Figure 6c). The decomposition of the fingerprint plot
shows that C—H/H—C contacts comprise 27.3% of the total Hirshfeld surface area. In the
fingerprint region (Figure 6d), H∙∙∙O (14.7%) interactions are represented by a spike in the top
area whereas the O∙∙∙H (14.7%) interactions are represented by a spike in the lower part of
fingerprint plot. Similar behaviour is observed for the corresponding C–H···N intermolecular
interaction. A greater value of di is indicating the presence of the amino group where the N4
atom is acting as a good acceptor (Figure 6e). The proportion of N—H/H—N contacts
comprising 8.3% of the total Hirshfeld surfaces. The C—C contact on the fingerprint plot (Figure
6f) is presented as characteristic stacking kite, which is mainly assigned to π-π interaction. This
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is reflected by red–blue triangles on the shape index surface of the title compound (Figure 5d).
The C—C contact includes only 2.8% of the Hirshfeld surfaces with equal di =de. The 2-D
fingerprint plot (Figure 6g) for C—N/N—C contacts comprise 0.1% of the total Hirshfeld
surface area. Hydrogen bonding interactions H∙∙∙H (46.8%) are very high compared to the other
bonding interactions. The quantitative interactions with percentages are analyzed and displayed
in pie chart (Figure 7).
3.3. IR spectra
The infrared spectra (IR) of the complex taken in the region 4000-400 cm-1 are compared with
the free sulfadiazine ligand. Based on some general references [44–46] and previous studies of
complexes with sulfonamides [47–49], the positions of the characteristic vibrations of the free
sulfadiazine and its nickel complex is tabulated in Table 5.
The bands appear between 3450 and 3360 cm-1 are due to asym(NH2) and sym(NH2) vibrations
of the amino (–NH2) group are modified with respect to the free sulfadiazine ligand. These
modifications are most probably due to the hydrogen bonding between complexes involving the
NH2 and SO2 groups.
The peak for the sulfonamidic (N–H) group in the free ligand at around 3102 cm-1, is absent in
the spectra of the complex, confirming the deprotonation of the –SO2NH– moiety. The scissoring
vibration of nickel sulfadiazine complex for the amino (–NH2) group observed at 1628 cm-1 and
peaks due to phenyl ring appear at around 1558 and 1595 cm-1. The peaks around 1267 and 1360
cm-1 are assigned to νas(SO2), and those at 1183 cm-1 to νsy(SO2), show significant changes upon
complexation.
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The band in the free sulfadiazine ligand at 942 cm-1 assigned to ν(S–N) [18, 25]. The bands at
higher frequencies (989 and 1015 cm-1) in the complex are consequence of coordination to the
metal. This shift to higher frequency is in accordance with the shortening of the S–N bond
lengths, which has been observed in the crystal structure of complex. The bands of the ligand at
3424, 1651 and 942 cm-1 shifted to 3450, 1628 and 989 cm-1, respectively, after coordination.
Most of the other shifts are small.
3.4. 1H NMR spectra
1H NMR spectra of the free sulfadiazine and its nickel(II) complex are recorded in d6-DMSO.
The chemical shifts are expressed in ppm relative to internal TMS. The spectral data along with
the possible assignments are presented in Table 6. All the protons due to heteroaromatic/aromatic
groups are found as to be in their expected region [50]. From the data, it is reflected that the
ligand present in the complex exhibits very small shifts in comparison to the free ligand. The
conclusion drawn from these studies, the proton magnetic resonance spectrum of sulfadiazine
shows a broad singlet at 11.259 ppm, which may be assigned to the sulfonamide NH proton. The
absence of this proton signal in the spectra of the nickel sulfadiazine complex indicate that the
sulfonamide NH group is deprotonated during complex formation.
3.5. UV-Vis spectra
The UV spectra of free sulfadiazine and its nickel complex recorded in DMSO solution are
depicted in Figure 8. The electronic spectrum of sulfadiazine gave absorption band at 275 nm
assigned to π→π*. The electronic spectra of the nickel sulfadiazine complex similarly show the
transitions which are slightly shifted to shorter wavelengths (272 nm) as a result of decrease in
conjugation of the system after complexation. Nickel sulfadiazine complex presented two bands
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in the visible region. The splitting of one of them is due to spin–orbit coupling that mixed the
3T1g(F) and 1Eg states [51]. The absorbance bands for Ni-sdz found in the range 398-405 nm due
to 3A2g→3T1g(F) and 600-650 nm attributed to 3A2g→1Eg which is assigned to d-d transitions of a
distorted octahedral Ni(II) chromophore. The absorbance value of sulfadiazine (sdz) and its
nickel complex are listed in Table 7.
3.6. Thermogravimetric analysis
Sulfadiazine (sdz) and its nickel complex (Ni-sdz) are studied by thermogravimetric analysis
from ambient temperature to 967°C in nitrogen atmosphere. The TGA curves are shown as %
mass loss versus temperature, the DTG curves are as the rate of loss of mass versus temperature.
The compound decomposes mainly into three stages on heating between the room temperature
and 967˚C. The decomposition pattern reveals that the first weight loss is 9.0% in the range of
43˚C–330˚C, which is ascribed to the loss of water molecules (calculated 10.0%), the second
weight loss is 36.0% in the range of 330˚C–430˚C, which is due to the loss of aniline moiety and
oxygen atoms (calculated 36.8%). With further heating, the 30.0% of the compound (calculated
31.7%) decomposed between 420˚C and 967˚C, which is ascribed to the loss of pyrimidine
moiety and sulfur atom. The differences between the experimental and calculated weight losses
in three stages of decomposition are negligible and are within the experimental errors. Above
967˚C, 25% of the residue are left out which is attributed to the charring of nickel salt. Hence,
the TG study confirms the formation of the compound in the stoichiometric ratio.
The thermal decomposition of nickel complex of sulfadiazine occurs with DTG curve maxima
showing endothermic peak at 70.80°C (∆H = 34.84 kJmol-1) and 398.40°C (ΔH =115.89 kJmol-1)
while in free sulfadiazine endothermic peak are observed at 275.80°C (∆H = 144.287 kJmol-1)
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and 339.80°C (ΔH = 23.333 kJmol-1). The final residual mass left at 967°C correspond to
25.29% for nickel complex and 25.60% for free sulfadiazine. The thermogravimetric (TG) and
differential thermogravimetric (DTG) curves for free sulfadiazine and its nickel complex are
depicted in Figure 9 and 10. Thermodynamic parameters of the synthesized nickel complex of
sulfadiazine and ligand (sdz) itself have been evaluated by Broido’s graphical method [52] for
straight line decomposition portion of the thermodynamic analytical curve. Activation Energy
(Ea) is calculated by the slope of ln(ln1/y) versus 1/T, where y is the fraction of the number of
initial molecules not yet decomposed. The thermodynamic parameters like change in enthalpy
(∆H), entropy (∆S), Gibb’s free energy (∆G) and Arrhenius constant (A) are calculated using the
standard equations [53,54] and data are presented in Table 8.
3.7. Electrical conductivity measurement
The electrical conductivity of sulfadiazine and its nickel complex in 10-3 M pyridine solution are
measured at room temperature. The molar conductance (Λm) values of sulfadiazine and its nickel
complex are 6.02 and 5.49 ohm-1 cm2 mol-1, respectively showing their non-electrolytic [55]
nature. The results indicate that no anion is present outside the coordination sphere. The very low
molar conductivity value of nickel sulfadiazine complex reveals that complex remain neutral in
solution.
3.8. Microbiological assays
The minimum inhibitory concentration (MIC) values of sulfadiazine and its nickel complex
against Staphylococcus aureus and Escherichia coli are shown in Table 9. Sulfadiazine and its
nickel complex exhibited varying inhibitory effect toward the bacterial strains. The complex has
ability to kill the investigated bacteria with large inhibition zone diameters comparing with that
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of free ligand, but at higher concentration than the sodium salt. Sulfonamides penetrate bacterial
cells in the neutral form, and once inside a cell, their bacterial action is from the ionized form
[56]. The nickel sulfadiazine complex is sensitive toward gram negative bacteria (Escherichia
coli) while it is not active against gram positive bacteria (Staphylococcus aureus).
Our observations reveal that the MIC for nickel complex changes according to the target
bacteria. It is known that Staphylococcus aureus and Escherichia coli have different cell wall
constitution. Escherichia coli has an outer lipidic membrane layer while Staphylococcus aureus
does not have one.
4. Conclusion
Nickel complex of sulfadiazine is synthesized, characterized and tested as antimicrobial agents.
Single crystals of nickel sulfadiazine complex are successfully grown from pyridine solution by
using slow evaporation technique. The molecular structure of title compound is determined by
single crystal XRD and which reveals that the Ni(II) ion exhibit a distorted octahedral geometry.
Hirshfeld surfaces are employed to confirm the existence of intermolecular interactions in the
title compound. The spectroscopic data are in good agreement with the crystal structure. Ni-sdz
shows higher antibacterial activity than free ligand against gram negative bacteria (Escherichia
coli).
Supplementary data
Full crystallographic data for the structure reported in this article have been deposited in the
Cambridge Crystallographic Data Center, CCDC No. 1008229. Copies of this information can be
obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, U.K.
(Fax: +44-1223-336033; or E-mail: deposit@ccdc.cam.ac.uk).
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Acknowledgement
We are thankful to DST- FIST, New Delhi for funding towards the single crystal diffractometer
facility at Department of Physics, Sardar Patel University, Vallabh Vidyanagar. One of the
authors (SMT) is thankful to UGC for RFSMS fellowship. We are also thankful to Central Salt
and Marine Chemicals Research Institute, CSMCRI, Bhavnagar for collecting NMR and TGA
data. We also acknowledge the help received from SICART, Vallabh Vidyanagar for CHN and
IR data.
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Table 1. Crystal data and refinement of [Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2
Empirical formula
Formula weight
Crystal system
C35H37N11NiO6S2
830.58
Monoclinic
P21
Space group
a (Å)
9.1861(2)
18.4188(4)
11.5883(2)
103.509(1)
1906.46(5)
2
b (Å)
c (Å)
β (˚)
Volume (Å3)
Z
Temperature (K)
Crystal size (mm3)
Calculated density (Mg m-3),
Absorption coefficient (mm-1)
F(000)
296.15
0.75

0.51
1.45
0.42
0.679
864
θ range for data collection (°)
Index ranges
1.8-27.5
-11 ≤ h ≤ 7; -23 ≤ k ≤ 22; -7 ≤ l ≤ 15
Reflections collected
Unique reflections
Rint
16895
8295
0.0212
Goodness-of-fit on F2
Absorption correction
Refinement method
Data/parameters
Final R indices [I≥2σ(I)]
R indices (all data)
Largest diff. peak and hole (e Å-3)
1.065
N.A.
Full Matrix Least Square of |F|2
8295/513
R1 = 0.036, wR2 = 0.094
R1 = 0.044, wR2 = 0.099
0.41 and -0.26
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Table 2. Fractional atomic coordinates and equivalent isotropic displacement parameters (Å2)
Atom
Ni
x
y
z
Ueq (Å2)
0.50922 (5)
0.50437 (13)
0.51578 (11)
0.3964 (4)
0.5530 (4)
0.4731 (4)
0.6210 (3)
0.2100 (6)
0.7340 (6)
0.1428 (7)
0.5284 (4)
0.4918 (4)
0.5448 (4)
0.4711 (4)
0.5550 (3)
0.4576 (3)
1.0876 (5)
−0.0876 (4)
0.7400 (3)
0.2776 (3)
0.0567 (7)
0.6749 (5)
0.3434 (4)
−0.0804 (8)
0.7133 (5)
0.2516 (5)
−0.1370 (7)
0.8488 (6)
0.1112 (5)
−0.0519 (8)
0.9500 (6)
0.0569 (5)
0.0898 (8)
0.9074 (6)
0.1535 (5)
0.7719 (6)
0.2949 (5)
0.5436 (3)
0.4728 (3)
0.37225 (4)
0.23071 (6)
0.51540 (5)
0.2287 (2)
0.55706 (18)
0.1879 (2)
0.5176 (2)
0.1708 (3)
0.6116 (3)
0.3558 (5)
0.3113 (2)
0.4349 (2)
0.4311 (2)
0.3151 (2)
0.3730 (3)
0.3741 (3)
0.1288 (3)
0.6076 (3)
0.3605 (2)
0.3829 (2)
0.3069 (4)
0.1987 (2)
0.5476 (2)
0.3272 (5)
0.2115 (3)
0.5867 (3)
0.3927 (5)
0.1881 (3)
0.6080 (3)
0.4406 (4)
0.1520 (3)
0.5903 (3)
0.4239 (4)
0.1379 (3)
0.5543 (3)
0.1609 (3)
0.5328 (3)
0.3720 (3)
0.3748 (3)
0.76209 (4)
0.55788 (11)
0.96293 (10)
0.4453 (3)
0.8695 (3)
0.6540 (4)
1.0765 (3)
0.2480 (4)
1.2579 (5)
0.3106 (6)
0.6104 (3)
0.9124 (3)
0.6166 (3)
0.9084 (3)
0.4336 (2)
1.0891 (2)
0.4848 (5)
1.0038 (5)
0.8323 (3)
0.6917 (2)
0.2423 (5)
0.5330 (3)
0.9828 (3)
0.1924 (6)
0.4270 (4)
0.8915 (4)
0.2097 (6)
0.4096 (4)
0.9006 (4)
0.2765 (7)
0.4997 (5)
0.9992 (4)
0.3297 (7)
0.6046 (5)
1.0925 (4)
0.6214 (4)
1.0837 (4)
0.5462 (3)
0.9768 (3)
0.03698 (12)
0.0513 (3)
0.0463 (3)
0.0801 (11)
0.0657 (9)
0.0755 (10)
0.0725 (10)
0.133 (2)
S1A
S1B
O1A
O1B
O2A
O2B
OWA
OWB
N1
N1A
N1B
N2A
N2B
N3A
N3B
N4A
N4B
N5A
N5B
C1
C1A
C1B
C2
C2A
C2B
C3
C3A
C3B
C4
C4A
C4B
C5
0.1250 (19)
0.116 (3)
0.0430 (9)
0.0391 (8)
0.0429 (8)
0.0398 (8)
0.0513 (7)
0.0488 (7)
0.0834 (15)
0.0761 (13)
0.0433 (8)
0.0414 (8)
0.0811 (18)
0.0469 (9)
0.0435 (9)
0.096 (2)
0.0587 (12)
0.0526 (10)
0.092 (3)
0.0642 (13)
0.0582 (12)
0.096 (2)
0.0600 (12)
0.0551 (11)
0.095 (2)
0.0693 (14)
0.0604 (12)
0.0618 (12)
0.0552 (11)
0.0416 (7)
0.0373 (7)
C5A
C5B
C6A
C6B
C7A
C7B
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C8A
C8B
C9A
C9B
0.5554 (6)
0.4575 (5)
0.5655 (6)
0.4435 (5)
0.5647 (5)
0.4421 (5)
0.7986 (5)
0.1856 (5)
0.9493 (6)
0.0345 (5)
1.0419 (5)
−0.0254 (6)
0.9858 (6)
0.0669 (5)
0.8336 (5)
0.2179 (5)
0.4961 (3)
0.2507 (3)
0.5021 (3)
0.2449 (3)
0.4404 (3)
0.3087 (3)
0.2939 (3)
0.3258 (3)
0.2809 (3)
0.3347 (4)
0.3393 (4)
0.4016 (4)
0.4074 (4)
0.4611 (3)
0.4151 (3)
0.4488 (3)
0.5685 (5)
0.9582 (4)
0.4514 (5)
1.0736 (4)
0.3898 (4)
1.1339 (4)
0.8505 (4)
0.6620 (4)
0.8944 (5)
0.6152 (5)
0.9222 (5)
0.5986 (5)
0.9045 (5)
0.6289 (5)
0.8600 (4)
0.6755 (4)
0.0588 (12)
0.0530 (11)
0.0684 (14)
0.0591 (11)
0.0618 (13)
0.0550 (11)
0.0534 (11)
0.0565 (12)
0.0708 (14)
0.0717 (17)
0.0723 (16)
0.0779 (19)
0.0744 (17)
0.0701 (14)
0.0565 (11)
0.0533 (11)
C10A
C10B
C11A
C11B
C12A
C12B
C13A
C13B
C14A
C14B
C15A
C15B
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Table 3. Selected bond lengths and angles for [Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2
Bond distances (Å)
2.128 (4)
Bond angles (˚)
N2A—Ni—N2B
Ni—N1A
Ni—N1B
Ni—N2A
Ni—N2B
Ni—N5A
Ni—N5B
178.84 (19)
91.83 (13)
88.82 (13)
88.46 (14)
179.45 (19)
115.74 (18)
90.04 (13)
63.23 (11)
117.74 (18)
89.70 (13)
90.02 (13)
178.93 (19)
2.126 (4)
N2A—Ni—N5A
N2B—Ni—N5A
N2A—Ni—N5B
N5A—Ni—N5B
N2A—Ni—N1B
N5A—Ni—N1B
N2A—Ni—N1A
N2B—Ni—N1A
N5A—Ni—N1A
N5B—Ni—N1A
N1B—Ni—N1A
2.093 (4)
2.094 (4)
2.097 (3)
2.102 (3)
S1A—O1A
S1A—O2A
S1A—N1A
S1A—C1A
N1A—C7A
N4A—C4A
1.444 (4)
1.447 (4)
1.599 (4)
1.759 (4)
1.369 (6)
1.383 (6)
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Table 4. Hydrogen bond geometry and symmetry code for
[Ni(C10H9N4O2S)2(C5H5N)2](C5H5N)(H2O)2
D- H…A
D-H(Å)
0.95
0.92
0.93
0.86
0.86
0.86
0.93
0.93
0.93
0.93
0.93
0.93
H…A(Å)
1.81
1.82
2.27
2.34
2.44
2.3
D-A (Å)
2.733 (6)
2.747 (6)
3.065 (7)
3.065 (7)
3.291 (7)
3.098 (7)
2.869 (9)
3.260 (6)
3.342 (7)
3.520 (6)
3.534 (8)
3.524 (8)
D-H …A( ° )

OWA—HWA2···O1A
OWB—HWB1···O2Ai
OWB—HWB2···N4Aii
N4A—H4A1···OWBiii
N4A—H4A2···OWAiv
N4B—H4B1···OWAv
C1—H1···OWA
C3B—H3B···OWAv
C5A—H5A···OWBiii
C9B—H9B···O1Bvi
C12A—H12A···N4Bvi
C14B—H14B···N4Avii
163.9
177.6
142.4
143
174
153
1.97
2.47
2.64
2.65
2.63
2.63
163
143
133
157
164
161
Symmetry codes: (i) −x+1, y+1/2, −z+2; (ii) −x+2, y+1/2, −z+2; (iii) −x+2, y−1/2, −z+2; (iv)
x+1, y, z; (v) −x, y+1/2, −z+1; (vi) −x+1, y−1/2, −z+2; (vii) −x+1, y+1/2, −z+1.
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Table 5. Characteristic IR bands (cm-1) of sulfadiazine and its nickel complex
Assignment
N-H
Sulfadiazine
3102
Ni–sulfadiazine
νas(NH2)
νs(NH2)
δ(NH2)
3424
3450
3355
3360
1651
1628
ν-phenyl ring
(SO2)as
1580, 1493
1325, 1262
1156
1595, 1558
1360, 1267
1183
(SO2)sy
ν(S-N)
996, 942
1015, 989
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Table 6. 1H NMR shift assignments of sulfadiazine (1) and its nickel complex (2) in DMSO-
a
d6
Assignment
1H(1)
11.25
8.48
7.00
7.62
6.56
6.00
1H(2)
-
Δδ(H)b
N(1A)–H
C(8A)–H/C(10A) −H
C(9A) −H
8.30
7.02
7.43
6.50
5.26
-0.18
+0.02
-0.19
-0.06
-0.74
C(2A)–H/C(6A) −H
C(3A)–H/C(5A) −H
NH2
aRelative to TMS with DMSO-d6 peak as reference (1H, 2.60 ppm)
bΔδ= δ(sulfonamide complex)- δ(sulfonamide).
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Table 7. Absorbance, wavelength and assignment of sulfadiazine and its nickel complex
Ligand/
Complex
sdz
Wavelength (nm)
Energy
(cm-1)
36363
36764
24937
16000
Assignment
Absorbance (A)
275
272
401
625
π → π* /n→π*overlap
π → π*
2.1119
1.3316
0.8621
0.3076
Ni-sdz
3A2g → 3T1g(F)
3A2g → 1Eg
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Table 8. Thermodynamic parameters of sulfadiazine and its nickel complex
Ligand/
Decomposition
Temperature
Activation
Energy (kJ
mol-1)
Arrhenius
constant
ΔH (kJ
mol-1)
ΔS (J K-1
mol-1)
ΔG (kJ
mol-1)
Complex
range (K)
sdz
528.80−568.80
592.80−632.80
335.85−352.11
662.52−680.19
148.85
28.42
31.27
5.58
144.28
23.33
-221.38
-236.63
-227.15
-226.31
265.78
168.34
112.94
267.84
Ni-sdz
37.70
9.78
34.84
121.47
21.14
115.89
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