Enis Nadia Md Yusof1,2, Nazhirah Muhammad Nasri1,3, Thahira B S A Ravoof1,4, Mukesh M Jotani5, Edward R T Tiekink6. 1. Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, Malaysia. 2. Discipline of Chemistry, School of Environmental and Life Sciences, University of Newcastle, University Drive, Callaghan, NSW 2308, Australia. 3. Department of Chemistry, St. Francis Xavier University, PO Box 5000, Antigonish, NS B2G 2W5, Canada. 4. Materials Synthesis and Characterization Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, Malaysia. 5. Department of Physics, Bhavan's Sheth R. A. College of Science, Ahmedabad, Gujarat 380001, India. 6. Research Centre for Crystalline Materials, School of Science and Technology, Sunway University, 47500 Bandar Sunway, Selangor Darul Ehsan, Malaysia.
Abstract
The title CuII complex, [Cu(C13H11N2OS2)2], features a trans-N2S2 donor set as a result of the CuII atom being located on a crystallographic centre of inversion and being coordinated by thiol-ate-S and imine-N atoms derived from two di-thio-carbazate anions. The resulting geometry is distorted square-planar. In the crystal, π(chelate ring)-π(fur-yl) [inter-centroid separation = 3.6950 (14) Å and angle of inclination = 5.33 (13)°] and phenyl-C-H⋯π(phen-yl) inter-actions sustain supra-molecular layers lying parallel to (02). The most prominent inter-actions between layers, as confirmed by an analysis of the calculated Hirshfeld surface, are phenyl-H⋯H(phen-yl) contacts. Indications for Cu⋯Cg(fur-yl) contacts (Cu⋯Cg = 3.74 Å) were also found. Inter-action energy calculations suggest the contacts between mol-ecules are largely dispersive in nature.
The title CuII complex, [Cu(C13H11N2OS2)2], features a trans-N2S2donor set as a result of the CuII atom being located on a crystallographic centre of inversion and being coordinated by thiol-ate-S and imine-N atoms derived from two di-thio-carbazate anions. The resulting geometry is distorted square-planar. In the crystal, π(chelate ring)-π(fur-yl) [inter-centroid separation = 3.6950 (14) Å and angle of inclination = 5.33 (13)°] and phenyl-C-H⋯π(phen-yl) inter-actions sustain supra-molecular layers lying parallel to (02). The most prominent inter-actions between layers, as confirmed by an analysis of the calculated Hirshfeld surface, are phenyl-H⋯H(phen-yl) contacts. Indications for Cu⋯Cg(fur-yl) contacts (Cu⋯Cg = 3.74 Å) were also found. Inter-action energy calculations suggest the contacts between mol-ecules are largely dispersive in nature.
Dithiocarbazates, derived from sulfur–nitrogen donor ligands were first reviewed in the 1970s (Ali & Livingstone, 1974 ▸). These Schiff base molecules are readily prepared from the reaction of primary amines with aldehydes or ketones and are potentially multidentate ligands for metals (Ali et al., 2005 ▸; Mokhtaruddin et al., 2017 ▸). Schiff bases display significant biological and pharmacological activities that can be tuned by incorporating different types of substituents through the condensation reaction (How et al., 2008 ▸; Low et al., 2016 ▸). Transition-metal complexes containing Schiff base ligands have also been intensively studied because of their simple routes of synthesis, the variety of their structural geometries and, particularly pertinent, as small chemical changes often produce wide variations in their bioactivities (Mirza et al., 2014 ▸; Zangrando et al., 2015 ▸; Lima et al., 2018 ▸). Recently, a copper(II) dithiocarbazate complex containing a Schiff base derived from S-hexyldithiocarbazate and 4-methylbenzaldehyde was reported to have excellent anti-bacterial activity against Escherichia coli (Zangrando et al., 2017 ▸). More recently, investigators have reported the potent biological activity of a copper(II) complex that contained a tridentate Schiff base derived from S-benzyldithiocarbazate and 2-hydroxy-5-(phenyldiazenyl)benzaldehyde against a humancervical cancer line (HeLa) (Kongot et al., 2019 ▸). The copper(II) complex had comparable biological activities as the well-known anti-cancer drug cisplatin against the tested cells (Kongot et al., 2019 ▸). As part of on-going studies in the structural chemistry and potential bioactivity of copper(II) complexes containing dithiocarbazate Schiff base ligands, herein the synthesis of the title copper(II) complex, (I), its single crystal X-ray diffraction analysis and a detailed study of supramolecular association by an analysis of calculated Hirshfeld surfaces and computation chemistry are described.
Structural commentary
The molecular structure of (I), Fig. 1 ▸, has the CuII atom located on a crystallographic centre of inversion and coordinated by two chelating dithiocarbazate anions, each via the thiolate-S and imine-N atoms (Table 1 ▸). The resulting trans-N2S2donor set defines a distorted square-planar geometry: the major distortion from the ideal angles subtended at the copper atom is the acute S1—Cu—N2 chelate angle of 85.83 (6)°. The conformation about the endocylic imine bond is Z, as a result of chelation, whereas the exocyclic imine bond has an E conformation.
Figure 1
The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. Unlabelled atoms are related by the symmetry operation 1 − x, 1 − y, 1 − z.
Table 1
Selected geometric parameters (Å, °)
Cu—S1
2.1845 (7)
N1—N2
1.409 (3)
Cu—N2
1.923 (2)
C1—N1
1.286 (3)
C1—S1
1.720 (3)
C9—N2
1.300 (3)
C1—S2
1.753 (2)
S1—Cu—N2
85.83 (6)
S1—C1—N1
125.08 (19)
S1i—Cu—N2
94.18 (6)
S2—C1—N1
119.9 (2)
S1—C1—S2
115.03 (15)
Symmetry code: (i) .
The bidentate mode of the coordination of the dithiocarbazate ligand leads to the formation of five-membered CuN2CS chelate rings. While the r.m.s. deviation for the five atoms is relatively small at 0.0453 Å, suggesting a near planar ring, a better description for the conformation is that of an envelope with the copper atom being the flap atom. In this description, the r.m.s. deviation of the S1, N1, N2 and N3 atoms of the ring is 0.0002 Å, with the Cu atom lying 0.199 (3) Å out of the plane. The dihedral angle between the best plane through the chelate ring and the 2-furyl ring is 5.33 (18)° indicating an essentially co-planar relationship. By contrast, the dihedral between the chelate and phenyl rings is 86.75 (7)°, indicative of an orthogonal relationship. Finally, the dihedral angle between the peripheral organic rings is 81.42 (9)°.The structure of the acid form of the anion in (I) is available for comparison (Shan et al., 2008 ▸). Referring to the data in Table 1 ▸, significant changes in key bond lengths have occurred upon deprotonation and coordination of the molecule to CuII in (I). Thus, the C1—S1 [1.669 (2) Å for the acid], N1—N2 [1.381 (2) Å] and C9—N2 [1.280 (3) Å] bond lengths have all elongated in (I), Table 1 ▸, while the C1—N1 bond length has shortened [1.336 (3) Å]. Significant changes in the angles subtended at the quaternary C1 atom are also noted, in particular for the S1—C1—S2 angle which has narrowed by ca 10° in (I) from 124.76 (12)° in the acid with concomitant widening of the S2—C1–N1 angle by ca 5°, changes consistent with the reorganization of π-electron density from the C1—S1 to C1—N1 bonds in (I).
Supramolecular features
The most prominent feature of the molecular packing is the formation of supramolecular layers lying parallel to (02), Fig. 2 ▸(a). The association between molecules is of the type π(chelate ring)–π(furyl) whereby the inter-centroid Cg(Cu,S1,N1,N2,C1)–Cg(O1,C10–C13)i separation is 3.6950 (14) Å with angle of inclination = 5.33 (13)°; symmetry operation (i) x, −1 + y, z. Such π–π interactions between chelate rings and aromatic rings are well documented in the literature, especially for sterically unencumbered square-planar complexes and can impart significant energies of stabilization to the molecular packing (Malenov et al. 2017 ▸; Tiekink, 2017 ▸). In the present case, these interactions link molecules along the b-axis direction. Links between the chains to form layers are of the type phenyl-C—H⋯π(phenyl), Table 2 ▸. A view of the unit-cell contents is shown in Fig. 2 ▸(b). Details of the weak intermolecular contacts connecting layers are given in the analysis of the calculated Hirshfeld surfaces below.
Figure 2
Molecular packing in (I): (a) a view of the supramolecular layer sustained by π(chelate ring)–π(furyl) and phenyl-C—H⋯π(phenyl) interactions shown as blue and purple dashed lines, respectively, and (b) a view of the unit-cell contents shown in projection down the b axis highlighting the stacking of layers.
Table 2
Hydrogen-bond geometry (Å, °)
Cg1 is the centroid of the (C3–C8) ring.
D—H⋯A
D—H
H⋯A
D⋯A
D—H⋯A
C5—H5⋯Cg1ii
0.95
2.96
3.646 (3)
131
Symmetry code: (ii) .
Analysis of the Hirshfeld surfaces
The analysis of the Hirshfeld surfaces calculated for (I) was conducted as per literature precedents (Tan et al., 2019 ▸) employing Crystal Explorer (Turner et al., 2017 ▸). The assumption of the intermolecular C—H⋯π contact in the crystal of (I) is justified through the diminutive red spots near the phenyl-C4 and H5 atoms on the Hirshfeld surfaces mapped over d
norm in Fig. 3 ▸. The short interatomic H⋯H contact, involving phenyl H8 atoms and occurring between layers, and the C⋯C contact, between the methylene-C9 and furyl-C11 atoms, are also evident as the faint-red spots near the respective atoms in Fig. 3 ▸. On the Hirshfeld surfaces mapped over electrostatic potential in Fig. 4 ▸, the donors and acceptors of intermolecular C—H⋯π contacts, Table 2 ▸, are viewed as blue bumps and light-red concave regions, respectively. Also, the short interatomic S⋯H/H⋯S contacts, which are electrostatic in nature, Table 3 ▸, show red and blue regions about the respective atoms. The environment around a reference molecule within the Hirshfeld surface mapped with the shape-index property is illustrated in Fig. 5 ▸, and highlights the C—H⋯π/π⋯H—C contacts.
Figure 3
A view of the Hirshfeld surface for (I) mapped over d
norm in the range −0.080 to +1.213 arbitrary units.
Figure 4
A view of the Hirshfeld surface for (I) mapped over the electrostatic potential in the range −0.036 to + 0.034 atomic units.
Table 3
Summary of short interatomic contacts (Å) in (I)
Contact
Distance
Symmetry operation
H8⋯H8
2.11
−x, 1 − y, 1 − z
H5⋯C4
2.66
−x, + y, − z
H2B⋯S2
2.97
x, 1 + y, z
C9⋯C11
3.364 (4)
x, −1 + y, z
Notes: (a) The interatomic distances are calculated in Crystal Explorer (Turner et al., 2017 ▸) whereby the X—H bond lengths are adjusted to their neutron values.
Figure 5
A view of the Hirshfeld surface with the shape-index property highlighting C—H⋯π/π⋯H—C contacts by black dotted lines.
The overall two-dimensional fingerprint plot, Fig. 6 ▸(a), and those delineated into H⋯H, C⋯H/H⋯C, S⋯H/H⋯S and C⋯C contacts are illustrated in Fig. 6 ▸(b)–(e), respectively; the percentage contribution from all the identified interatomic contacts to the Hirshfeld surface are summarized quantitatively in Table 4 ▸.
Figure 6
(a) The full two-dimensional fingerprint plot for (I) and fingerprint plots delineated into (b) H⋯H, (c) C⋯H/H⋯C, (d) S⋯H/H⋯S and (e) C⋯C contacts.
Table 4
Percentage contributions of interatomic contacts to the Hirshfeld surface for (I)
Contact
Percentage contribution
H⋯H
36.2
C⋯H/H⋯C
23.0
S⋯H/H⋯S
17.5
O⋯H/H⋯O
5.1
C⋯N/N⋯C
3.3
S⋯O/O⋯S
2.9
N⋯H/H⋯N
2.8
Cu⋯C/C⋯Cu
2.7
C⋯C
2.6
C⋯S/S⋯C
1.3
N⋯S/S⋯N
1.2
O⋯O
0.5
N⋯O/O⋯N
0.3
N⋯N
0.3
Cu⋯N/N⋯Cu
0.2
Cu⋯H/H⋯Cu
0.1
Cu⋯O/O⋯Cu
0.1
The conical tip appearing at d
e + d
i ∼2.1 Å in the fingerprint plot delineated into H⋯H contacts in Fig. 6 ▸(b), represents the short inter-layer H⋯H contact involving phenyl-H8 atoms, Table 3 ▸. The presence of the C—H⋯π interaction is evident through the short interatomic C⋯H/H⋯C contact characterized as the pair of forceps-like tips at d
e + d
i ∼2.7 Å in the respective delineated fingerprint plot of Fig. 6 ▸(c) and Table 3 ▸. In the fingerprint plot delineated into S⋯H/H⋯S contacts, Fig. 6 ▸(d), the short interatomic contact involving the S-benzyl atoms, Table 3 ▸, appear as the pair of forceps-like tips at d
e + d
i < 3.0 Å, i.e. at the sum of van der Waals radii. The distribution of points in the fingerprint plot delineated into C⋯C contacts, Fig. 6 ▸(e), forming triangular tip at d
e + d
i ∼3.3 Å is due to the presence of such short interatomic contacts summarized in Table 3 ▸. The presence of intermolecular π–π stacking between chelate and furyl rings results in the small but significant percentage contribution from the participating atoms, as listed in Table 4 ▸. The small contributions from the other remaining interatomic contacts summarized in Table 4 ▸ have a negligible effect on the packing.
Computational chemistry
Utilizing Crystal Explorer (Turner et al., 2017 ▸), the pairwise interaction energies between the molecules within the crystal were calculated by summing up four energy component, namely electrostatic (E
ele), polarization (E
pol), dispersion (E
dis) and exchange-repulsion (E
rep). The energies were obtained using the wave function calculated at the HF/STO-3G level theory. The strength and nature of the intermolecular interactions are summarized quantitatively in Table 5 ▸. From the interaction energies calculated between the reference molecule and the symmetry-related molecule at x, −1 + y, z in Table 5 ▸, it is observed that the greatest energy value is due to the combined influence of Cu⋯furyl [Cu⋯Cg(furyl) = 3.74 Å], π(chelate)–π(furyl), C⋯C and S⋯H/H⋯S interactions. Among these interactions, the short interatomic S⋯H/H⋯S contact contributes to the electrostatic component while the others to the dispersion component of the energies. Even though the inter-centroid distance between symmetry-related phenyl (C3–C8) rings are greater than 4.0 Å [Cg⋯Cg
i = 4.3102 (17) Å; (i) − x, 2 − y, 1 − z] and the interatomic S⋯H distance is greater than sum of their van der Waal radii (S1⋯H11ii = 3.11 Å; x, − y, − + z), they possess greater interaction energies compared to intermolecular phenyl-C—H⋯π(phenyl) and short interatomic H⋯H contacts, as summarized in Table 5 ▸. The magnitudes of the intermolecular energies are represented graphically in the energy frameworks down the b-axis direction in Fig. 7 ▸. Here, the supramolecular architecture of crystals is viewed through the cylinders joining the centroids of molecular pairs by using red, green and blue colour codes for the components E
ele, E
disp and E
tot, respectively; the radius of the cylinder is proportional to the magnitude of interaction energy. It is clearly evident from the energy frameworks shown in Fig. 7 ▸ that the major contribution to the intermolecular interactions is from the dispersion energy component in the absence of conventional hydrogen bonds in the crystal.
Table 5
Summary of interaction energies (kJ mol−1) calculated for (I)
Contact
R (Å)
Eele
Epol
Edis
Erep
Etot
Cu⋯Cg(furyl)i +
Cg(chelate)⋯Cg(furyl)i +
C9⋯C11i +
S2⋯H2Bi
5.02
−23.2
−9.4
−154.4
97.6
−89.7
Cg(phenyl)⋯Cg(phenyl)ii
16.15
−6.3
−3.3
−50.9
28.3
−31.5
S1⋯H11iii
11.25
−12.0
−2.6
−10.6
5.2
−19.2
C5—H5⋯Cg(phenyl)iv
17.06
−6.2
−2.1
−20.6
13.8
−15.1
H8⋯H8v
15.35
0.7
−0.9
−15.6
7.9
−7.5
Notes: Symmetry operations: (i) x, −1 + y, z; (ii) −x, 2 − y, 1 − z; (iii) x, − y, + z; (iv) −x, + y, − z; (v) −x, 1 − y, 1 − z.
Figure 7
The energy frameworks viewed down the b-axis direction comprising (a) electrostatic potential force, (b) dispersion force and (c) total energy for a cluster about a reference molecule of (I). The energy frameworks were adjusted to the same scale factor of 50 with a cut-off value of 3 kJ mol−1 within 2 × 2 × 2 unit cells.
Database survey
The Cambridge Structural Database (Groom et al., 2016 ▸) contains just about 100 structures with the basic core found in (I). Manual sorting to identify ligands without additional donors as in (I), e.g. substituents carrying pyridyl orphenoxide, neutral molecules only and non-solvated structures yielded 24 analogues to (I) with deposited atomic coordinates. Eleven of these structures adopt the trans-N2S2 square-planar geometry as in (I), while the remaining 13 structures adopt a flattened tetrahedral coordination geometry. The structural diversity exhibited by these complexes is emphasized by the binuclear species [Cu{SCS[(CH2)5Me]=NN=CC6H4OMe-4}2]2 arising from intermolecular Cu⋯S interactions between centrosymmetrically related trans-N2S2 square-planar geometries (Begum et al., 2017 ▸).
Synthesis and crystallization
Synthesis of the 2-furaldehyde Schiff base of
-benzyldithiocarbazate:
S-Benzyldithiocarbazate (SBDTC) was synthesized following a procedure adapted from a previous report (Tarafder et al., 2001 ▸). The Schiff base was synthesized using a procedure adapted from the literature (Yusof et al., 2015 ▸) by reacting SBDTC (3.96 g, 0.02 mol) and an equimolar amount of 2-furaldehyde (1.92 g, 0.02 mmol) in hot ethanol (20 ml). The mixture was then heated until the volume reduced to half, followed by stirring under room temperature until a precipitate had formed. The resulting Schiff base was then washed with ice-cold ethanol, recrystallized from ethanol solution and dried over silica gel. Colour: Yellow. Yield 94%, m.p. 447–449 K. Elemental analysis: Calculated for C13H12N2OS2: C, 56.49; H, 4.38; N, 10.14. Found; C, 56.64; H, 4.21; N, 9.64. FTIR (ATR, cm−1): 3089 (w) ν(N—H), 1609 (m) ν(C=N), 1016 (s) ν(N—N), 763 (s), ν(C=S).Synthesis of (I): The Schiff base synthesized above (0.55 g, 0.002 mol) was dissolved in hot ethanol (50 ml) and added to copper(II) acetate monohydrate (0.20 g, 0.001 mol) in an ethanolic solution (30 ml). The mixture was heated until the volume of the solution reduced to half. Precipitation occurred once the mixture had cooled to room temperature. The precipitate was filtered and dried over silica gel. The title complex was recrystallized from methanol solution as dark-brown prisms in 91% yield. M.p. 456–458 K. Elemental analysis: Calculated for C26H22CuN4O2S4: C, 50.84; H, 3.61; N, 9.12; Cu, 10.34. Found; C, 50.49; H, 3.45; N, 8.77; Cu, 10.81. FTIR (ATR, cm−1): 1593 (m), ν(C=N), 964 (s), ν(N—N), 760 (s), ν(C—S).
Refinement
Crystal data, data collection and structure refinement details are summarized in Table 6 ▸. The carbon-bound H atoms were placed in calculated positions (C—H = 0.95–0.99 Å) and were included in the refinement in the riding-model approximation, with U
iso(H) set to 1.2U
eq(C).
Table 6
Experimental details
Crystal data
Chemical formula
[Cu(C13H11N2OS2)2]
Mr
614.25
Crystal system, space group
Monoclinic, P21/c
Temperature (K)
100
a, b, c (Å)
15.3515 (7), 5.0151 (3), 16.7186 (8)
β (°)
94.618 (4)
V (Å3)
1282.98 (11)
Z
2
Radiation type
Mo Kα
μ (mm−1)
1.21
Crystal size (mm)
0.30 × 0.20 × 0.10
Data collection
Diffractometer
Agilent Xcalibur Eos Gemini
Absorption correction
Multi-scan (CrysAlis PRO; Agilent, 2011 ▸)
Tmin, Tmax
0.744, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections
5864, 2898, 2382
Rint
0.027
(sin θ/λ)max (Å−1)
0.677
Refinement
R[F2 > 2σ(F2)], wR(F2), S
0.040, 0.111, 1.04
No. of reflections
2898
No. of parameters
169
H-atom treatment
H-atom parameters constrained
Δρmax, Δρmin (e Å−3)
0.49, −0.61
Computer programs: CrysAlis PRO (Agilent, 2011 ▸), SHELXS97 (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸), DIAMOND (Brandenburg, 2006 ▸) and publCIF (Westrip, 2010 ▸).
Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S2056989019006145/hb7822sup1.cifStructure factors: contains datablock(s) I. DOI: 10.1107/S2056989019006145/hb7822Isup2.hklCCDC reference: 1913482Additional supporting information: crystallographic information; 3D view; checkCIF report
Primary atom site location: structure-invariant direct methods
Least-squares matrix: full
Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.040
Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.111
H-atom parameters constrained
S = 1.03
w = 1/[σ2(Fo2) + (0.0542P)2 + 1.1451P] where P = (Fo2 + 2Fc2)/3
2898 reflections
(Δ/σ)max < 0.001
169 parameters
Δρmax = 0.49 e Å−3
0 restraints
Δρmin = −0.61 e Å−3
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell esds is used for estimating esds involving l.s. planes.
Authors: May Lee Low; Laure Maigre; Mohamed Ibrahim M Tahir; Edward R T Tiekink; Pierre Dorlet; Régis Guillot; Thahira Begum Ravoof; Rozita Rosli; Jean-Marie Pagès; Clotilde Policar; Nicolas Delsuc; Karen A Crouse Journal: Eur J Med Chem Date: 2016-04-20 Impact factor: 6.514
Authors: Enis Nadia Md Yusof; Thahira Begum S A Ravoof; Edward R T Tiekink; Abhimanyu Veerakumarasivam; Karen Anne Crouse; Mohamed Ibrahim Mohamed Tahir; Haslina Ahmad Journal: Int J Mol Sci Date: 2015-05-15 Impact factor: 5.923