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Thiobiuret based Ni(II) and Co(III) complexes: Synthesis, molecular structures and DFT studies
Accepted Manuscript Thiobiuret based Ni(II) and Co(III) complexes: Synthesis, molecular structures and DFT studies Saira Sherzaman, Sadiq-ur-Rehman, Muhammad Naeem Ahmed, Bilal Ahmad Khan, Tariq Mahmood, Khurshid Ayub, Muhammad Nawaz Tahir PII:
S0022-2860(17)30987-0
DOI:
10.1016/j.molstruc.2017.07.054
Reference:
MOLSTR 24081
To appear in:
Journal of Molecular Structure
Received Date: 17 March 2017 Revised Date:
11 July 2017
Accepted Date: 20 July 2017
Please cite this article as: S. Sherzaman, Sadiq-ur-Rehman, M.N. Ahmed, B.A. Khan, T. Mahmood, K. Ayub, M.N. Tahir, Thiobiuret based Ni(II) and Co(III) complexes: Synthesis, molecular structures and DFT studies, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.07.054. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Thiobiuret based Ni(II) and Co(III) Complexes: Synthesis, Molecular
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Structures and DFT Studies
Saira Sherzamana, Sadiq-ur-Rehmana, Muhammad Naeem Ahmed*a, Bilal Ahmad Khana, Tariq Mahmood*b, Khurshid Ayubb and Muhammad Nawaz Tahirc
Department of Chemistry, The University of Azad Jammu and Kashmir Muzaffarabad, 13100 Pakistan.
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Department of Chemistry, COMSATS Institute of Information Technology, University Road, Tobe Camp, 22060, Abbottabad, Pakistan.
Department of Physics, University of Sargodha, Sargodha, Pakistan.
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*To whom correspondence can be addressed: E-mail: [email protected] (T. M) and [email protected] (M. N. A)
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Abstract Synthesis, molecular structures and DFT investigations of two new complexes of Ni(II) and with
(Z)-3-(3,3-dimethylbutanoyl)-1,1-diethyl-2-thiobiuret
ligand
are
reported.
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Co(III)
Characterization of these complexes was achieved by spectroanalytical techniques (FT-IR, UV-vis and 1H-NMR), and the structures were finally confirmed unequivocally by single crystal X-ray diffraction analysis. The obtained data of UV-vis, FT-IR and 1HNMR were compared with the
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literature values which satisfactorily confirmed the synthesis of ligand and their complexes. X-ray studies revealed the square planar and octahedral geometry of both Ni(II) and Co(III) complexes,
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respectively. Density functional theory (DFT) studies were performed to compare the theoretical results with experimental (X-ray as well as spectroanalytical) results, and good correlation was observed. Frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP)
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analyses revealed the reactivity and charge distribution in both complexes.
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Keywords: Thiobiuret; Ni(II) and Co(III) Complexes; X-ray Diffraction; DFT
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1. Introduction Since last decade thiobiurets (tbu) have recieved the attention of scientific community due to
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versatile applications in different areas of chemistry [1]. Thiobiurets and their derivatives have been employed extensively as anti-malarial [2], antitubercular, hypoglycemic [3] and antimicrobial agents [4]. Moreover, thioubiurets are also known as effective herbicidal [5], pesticidal
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[6] and insecticidal [3] agents. The biological activities of thiobiurets are believed to arise from NC-S moiety, and are further enhanced after complexation with metals [7–11]. It is noticeable that
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thiobiuret compounds are not limited to biological applications rather, they are equally important in industrial [12,13] and nanomaterial chemistry [14]. Particularly, these compounds are used for the synthesis of high pressure lubricant additives and corrosion inhibitors [13]. The presence of oxygen and sulfur as donor sites, and π electrons make thiobiurets attractive ligand for metals [1,15,16]. Thiobiuret based metal complexes has variety of applications and
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and
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important structural features (particularly diamagnetic square planar d8 complexes). Recently, co-workers
has
reported
square
planar
bis(N1,N1,N5,N5-tetrabenzyl-2,4-
dithiobiureto)nickel(II) complex, which has ability to hold p-xylene within the lattice cavities of
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molecule [17]. 2-Thiobiuret and its derivatives are famous as neutral, mono-anionic and bi-dentate
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ligands for metal complexes [18] and attractive building blocks for thinfilms [19,20] and nanomaterials [14,21]. In the last few years, researchers are engaged in the studying molecular structures and mode of coordination of central metal atoms with the different types of thiobiurets [22–25]. Keeping in view the wide range applications of thiobiuret based metal complexes, we report here the efficient synthesis and molecular structures of (Z)-3-(3,3-dimethylbutanoyl)-1,1diethyl-2-thiobiuret nickle(II) and cobalt(III) complexes. The both complexes were elucidated by different spectroanalytical techniques and the final structures of complexes were confirmed 3
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unequivocally by single crystal X-ray diffraction analysis. Quantum chemical investigations with density functional theory (DFT) were executed to compare theoretical and experimental (spectroscopic and X-ray) parameters of both complexes, and also to probe some other important
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molecular properties.
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2. Material and methods 2.1 Experimental
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All chemicals and reagents were purchased from Sigma- Aldrich and used directly without further purification. Solvents were distilled and dried (wherever required) prior to use. Melting points of complexes were measured on electro thermal melting point apparatus (MPD Mitamura Ricken Kogyo, Japan), and are reported as uncorrected. Infrared (FT-IR) spectra of both complexes were
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scanned by using FT-IR-8400s SHIMADZU spectrophotometer in frequency range 400-4000 cm. Multinuclear NMR (1H) spectra were scanned by using Bruker ARX 300 MHz-FT-NMR and a
Bruker 400 MHz-FT-NMR in deutrated chloroform as solvent, and tetramethylsilane as an internal
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2.2 Synthesis
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reference. Absorption studies were performed on UV-vis spectrophotometer (SHIMADZU 1601).
Thioubiuret ligand and corresponding Ni(II) (1) and Co(III) (2) complexes were synthesized according to the protocol provided in the Fig. 1. 2.2.1 General procedure for synthesis of ligand and corresponding complexes The synthesis of thiobiuret ligand and corresponding complexes was accomplished by adopting one pot synthetic methodology following the literature procedure with slight modification [19]. A 4
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solution of substituted dimethylbutyryl chloride and potassium thiocynate with molar ratio 1:1 was stirred for two hours at room temperature in dry acetonitrile (40ml). Then 60% aqueous solution of substituted amine was added to the reaction mixture and stirred further for 30 minutes. Finally,
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corresponding metal acetate tetra hydrated salt (0.5g) was added in dry state with continuous stirring. Ligand to metal ratio for complex 1 was 2:1 and 3: 1 for complex 2. After 1 hour stirring, excess amount of distilled water (100 ml) was added which resulted into the precipitate formation
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(Fig. 1). Precipitates (ppt) were filtered, dried and recrystallized from chloroform to obtain fine
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crystals for the further analysis.
2.2.1.1 Bis[Z-3-(3,3-dimethylbutanoyl)-1,1-diethyl-2-thiobiureto]Nickal(II) (1) Purple crystalline solid, M. P. 120 oC; yield 67 %, UV-vis. λmax. 270 nm; FT-IR (ATR, cm-1); νmax 2977, 2962, 2936, 1500, 1410, 1380, 1356, 1288, 1247, 1130, 621; 1H-NMR (CDCl3) δ ppm 0.98
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(br s.18H), 1.11 (s, 6H), 1.21 (br s, 4H), 2.13 (s, 4H), 3.53-3.77, (m, 8H) 2.2.1.2 Tris[Z-3-(3,3-dimethylbutanoyl)-1,1-diethyl-2-thiobiureto]Cobalt(III) (2)
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Dark green crystalline solid, M. P. 80 oC; yield 52%, UV-vis. λmax. 268 nm; FT-IR (ATR, cm-1); νmax 2948, 2933, 2902, 1530, 1490, 1400, 1350, 1284, 1244, 1126, 628; 1H-NMR (CDCl3) δ ppm
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0.98 (s, 18H), 1.12 (s, 6H),1.25(s, 6H), 2.41-2.26 (m, 4H), 3.99-3.65 (m, 8H). 2.3 Crystal structure determination Suitable crystals of both complexes (Ni and Co) (1-2) were selected and picked for single crystal X-ray diffraction analysis. The X-ray parameters were measured on Bruker Kappa Apex-IICCD diffractometer equipped with graphite monochromator and Mo-Kα radiation source. The X-ray structures of both complexes 1 and 2 were solved and refined by using direct method (SHELXL 5
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2013) [26]. The ORTEP plots and unit cell diagrams were processed with the help of ORTEP II [27]. CIF files of both complexes 1 and 2 have been assigned CCDC numbers 1518439 and 1518440,
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respectively, and can be obtained free of charge on demand to CCDC 12 Union Road, Cambridge CB21 EZ, UK. (Fax: (+44) 1223 336-033: [email protected]).
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2.4 Computational methods
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Computational studies were performed with Gaussian 09 software [28], visualization of graphics were performed by using Gauss view 05 [29]. The geometries of both complexes 1 and 2 were optimized at hybrid B3LYP method with 6-31G(d,p) basis set. Nowadays, B3LYP method is quite reliable for structural properties of synthetic and natural products due to its nice balance between computational cost and accuracy [30–35]. Geometries of these complexes were confirmed through
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frequency analysis at the same level, and the no imaginary frequency was observed (true minima). Frequency calculations are also used for theoretical vibrational analysis. 1H-NMR spectra were simulated at B3LYP/6-311+G(2d,p) level of DFT. TD-DFT calculations for absorption spectra
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have been performed at CAM-B3LYP/6-31G(d,p) level of theory. Total 20 excited states (10
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singlet and 10 triplet) were taken into account for the computation of UV–vis. spectra of both complexes 1 and 2. Frontier molecular orbitals and molecular electrostatic potential were computed at B3LYP/6-31G(d,p) level of theory.
3. Results and discussion
The Ni(II) 1 and Co(III) 2 complexes of thiobiuret are synthesized by the reaction of commercially available diethylamine and in situ generated 3,3-dimethylbutanoylthiocyanate in acetonitrile (Fig. 6
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1). Both complexes 1 and 2 are air and moisture stable and have good solubility in chloroform, tetrahydrofuran and dimethylsulphoxide. After accomplishing the synthesis, the complexes are characterized by NMR (1H), FT-IR and UV-vis spectroscopic techniques, and the final structures
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are confirmed unequivocally by single crystal X-ray diffraction analysis. Quantum chemical studies are performed to compare with experimental spectroscopic and X-ray parameters, and to probe the electronic properties such as frontier molecular orbitals (FMOs) and molecular
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3.1 Molecular structure
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electrostatic potential (MEP) analyses.
The molecular formulas of title complexes 1 and 2 consist of [C22H42N4NiO2S2] and [C33H63CoN6O3S3] entities, respectively. The Ni(II) complex (1) crystallized in the monoclinic crystal system having space group P21/c, whereas Co(III) complex (2) crystalized in trigonal
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crystal system having P3 space group. The crystal structure data of both complexes are given in Table 1, and ORTEP plots (drawn at 50% probability level) are shown in the Fig. 2. Analysis of ORTEP plots shows that the metal is localized on a crystallographic center of symmetry and is
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bound with two thiobiuret ligands (four S and O atoms) in Ni (II) complex 1, whereas in Co(III)
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complex 2, the central metal atom is bound with three molecules of ligand. The Ni(II) complex 1 is neutral homoleptic having cis square planar geometry and all nonhydrogen atoms are located on a crystallographic mirror plane (Fig. 2). The Ni(II) ion is square planar with S and O donor set, which are mutually fac to each other and respective planes are parallel to each othe. The bond distances from central metal atoms (Ni-S1 = 2.14 Å and Ni-O1 = 1.85 Å) are indicative of localization of -ive charge on the S atom. The relatively longer C-S (1.73 Å) and shorter C-O (1.26 Å) bond lengths are indicative of single and double bond character, 7
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respectively [36]. The Co(III) complex is also neutral homoleptic and has octahedral geometry. All three thiobiuret ligands in 2 are twisted and show significant deviation from planarity. The pattern of bond lengths is similar to that observed in the corresponding homoleptic nickel(II)
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complex 1 [37].
The single crystal X-ray diffraction studies depicted that both Ni(II) and Co(III) complexes exist as isolated molecular units of (C11H21N2SO)2Ni and (C11H21N2SO)3Co, respectively. No evidence
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of hydrogen bonding, any metal-adjacent ligand and metal-metal interactions is observed in crystal packing unit cell diagrams of both complexes 1 and 2 (Van der Waals interactions are observed
3.2 DFT Optimized geometries
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among different proton and carbon atoms of both complexes) (Fig. 3).
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DFT calculations have been executed to compare the theoretical and experimental geometric parameters (bond lengths, bond angles) of both complexes 1 and 2. Complexes exist in singlet spin
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state. The geometries of both complexes were simulated computationally at cost effective and accurate B3LYP/6-31G(d,p) level of DFT [38–41]. The optimized geometries are given in Fig. 4,
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and some important geometric parameters (bond lengths and bond angles) are summarized in Table 2 and Table 3. The comparative analysis indicates that experimental geometric parameters strongly agree with the theoretical data. For bond lengths of Ni(II) complex (1), theoretical values of Ni-S1 and Ni-O1 are 2.18 Å and 1.84 Å, respectively, which corroborate nicely with the respective experimental values 2.14 Å and 1.85 Å. Theoretically, bond lengths of S1-C1, C1-N1, C1-N2, N2-C6, O1-C6, C6-C7, N1-C4 and N1C2 in complex 1 are 1.75 Å, 1.35 Å, 1.33 Å, 1.33 Å, 1.27 Å, 1.51 Å, 1.46 Å and 1.47 Å , 8
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respectively. Whereas the corresponding experimental bond lengths are 1.73 Å, 1.33 Å, 1.34 Å, 1.32 Å, 1.26 Å, 1.51 Å, 1.47 Å and 1.48 Å, respectively. Similarly, in Co(III) complex (2), the experimental and theoretical values of important bond lengths corroborate nicely to each other.
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The theoretical values of Co-S1 and Co-O1 are 2.27 Å and 1.90 Å, respectively and show excellent correlation with corresponding experimental values at 2.12 Å and 1.92 Å. The calculated bond lengths of O1-C1, C1-N1, S1-C7, C7-N1, C7-N2, N2-C10, N2-C8 and C1-C2 in complex 2
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are found 1.26 Å, 1.33 Å, 1.74 Å, 1.34 Å, 1.36 Å, 1.46 Å, 1.47 Å and 1.51 Å, respectively. The Xray values of respective bond lengths are 1.26 Å, 1.32 Å, 1.73 Å, 1.34 Å, 1.34 Å, 1.48 Å, 1.46 Å
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and 1.51 Å, respectively.
The comparative analysis of important bond angles of both complexes is narrated in Table 3, and reveals excellent correlation among theoretical and X-ray values. In Ni(II) complex 1, the deviation (theoretical and experimental value) in bond angles is in the range 0-1.6o, and maximum
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deviation is 1.6o for S1-Ni-O1. Again in complex 2, important bond angles correlated nicely to each other between experiment and theory. The deviation is 0-1.6o, and maximum difference is for S1-Co-O1 (1.6o). In general, the differences between simulated and experimental geometrical
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parameters of both complexes are negligible. In most cases, difference between experimental and
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theoretical results are <0.06 Å (bond length) and <1.6o (bond angles).
3.3 Vibrational studies
Since last few years, quantum chemical methods are extensively used by scientific community to study the vibrations of different types of bond, especially in the fingerprint region which appears very complicated in the experimental spectrum. The FT-IR spectra of both complexes were 9
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scanned under neat conditions, and theoretical FT-IR spectra were extracted from frequency calculation. The experimental and theoretical spectra are shown in the Fig. 5 and Fig. 6, and comparative analysis is provided in the Table 4.
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Since both complexes 1 and 2 have identical ligand and bear similar C=O, C=N, C-S, CH2 and CH3 functional groups. According to the literature the strong peak ~ 1700 cm-1, is the characteristic of carbonyl group (C=O) in the thiobiuret ligand [42]. After complex formation, the
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υ(C=O) bands shifts to lower frequencies (-NH-C=O in thiobiuret is in fact converted to –N=C-Oin the complexes [43], where carbon oxygen bond order is significantly reduced) suggesting
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coordination of the metal and ligand [11]. The experimental stretching υ(C-O) in Ni(II) complex 1, is appeared at 1505 cm-1 which agrees with the theoretical stretching vibrations at 1536 cm-1 and 1517 cm-1 (theoretically two strong signals of stretching C-O vibrations are due to the presence of two molecules of ligand around central meta atom) and the reported literature of zinc complexes
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of similar ligands [43]. Similarly in Co(III) complex 2, the theoretical υ(C-O) stretching vibrations at 1524 cm-1, 1523 cm-1 correlated nicely with experimental value at 1528 cm-1. Thiobiuret ligand has different CH2 and CH3 groups, therefore several stretching, bending (scissoring, twisting, in
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and out of plane bending) vibrations are observed in both experimental and theoretical spectra (Table 4). The N=C shifts appeared in the range of 1400-1500 cm-1, due to increase in the double
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bond character of the C–N bond upon complex formation [44]. Experimental υ(C=N) are observed at 1417 cm-1 (1) and 1487 cm-1 (2). The corresponding theoretical υ(C=N) are observed at 1487 cm-1, 1484 cm-1 and 1439 cm-1 in complex 1, and 1479 cm-1, 1478 cm-1, 1476 cm-1 and 1414 cm-1 in complex 2. The IR peaks in the range of 400-490 cm-1 and 500-590 cm-1 in both experimental and theoretical spectra clearly show the formation of M-O and M-S bonds, respectively [10,15].
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Vibrational data (both experimental and theoretical) of synthesized complexes are carefully compared with literature which strongly confirmed the formation of complexes.
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3.4 Nuclear magnetic resonance studies
Experimental 1H-NMR spectra of both complexes were recorded in deutrated chloroform
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(electronic supplementary information, Fig. S1and S2). Theoretically chemical shift values are computed at B3LYP/6-311+G(2d,p) level of DFT, (the higher basis set normally works better for
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measurement of chemical shift values [45]). In both complexes, ligands are same bearing similar types of protons i. e. CCH3, CCH2 and NCH2 are present. The computed proton chemical shifts in both complexes 1 and 2 appeared little bit higher as compared to experimental shifts. This difference is due to the phase difference between experiment and theory. Experimental values are always measured in condensed phase, whereas computed values are calculated in the gas phase
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[46,47]. In Ni(II) complex 1, the experimental 1H chemical shifts of CCH3, CCH2 and NCH2 are found at 0.98, 1.11, 1.21, 2.13 and 3.53-3.77 ppm, respectively. The theoretical shifts of these
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protons are 1.70, 1.77, 2.82 and 4.36 ppm, respectively. In Co(III) complex (2), the experimental chemical shift of CCH3, CCH2 and NCH2 are 0.98, 1.12, 1.25, 2.41-2.26 and 3.99-3.65 ppm,
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respectively. Whereas computed 1H-NMR chemical shifts are 1.65, 1.89, 3.08 and 4.57 ppm, respectively which shows good correlation between theory and experiment.
3.5 Absorption studies and frontier molecular orbitals (FMOs) analysis
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The experimental absorption spectra of both complexes were recorded in methanol as solvent. Whereas simulated spectra were obtained at time dependent calculation at CAM-B3LYP/631G(d,p) level of theory. The experimental and simulated absorption spectra of both complexes
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are shown in Fig. 7. The experimental UV-vis spectrum of Ni(II) complex (1) shows a prominent absorption peak at 270 nm, whereas theoretically absorption peak is observed at 289. Theoretically calculated absorption maximum correlates nicely with the experimental absorption maximum. For
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Co(III) complex (2), the experimental and simulated UV-vis. absorptions are observed at 268 nm and 290 nm, respectively and corroborated nicely to each other.
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The frontier molecular orbital (FMOs) analysis with the aid of quantum chemical methods is a famous approach to explain the molecular transitions [38,48,49]. The frontier molecular orbitals of both Ni(II) and Co(III) complexes have been analyzed for correlation to the experimental transitions in UV-vis. region of electromagnetic spectrum. In case of Ni(II) complex (1), the
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corresponding HOMO and LUMO energies are -5.26 eV and -1.13 eV, respectively. The band gap is 4.13 eV, which corresponds to 300 nm and in nice agreement with the transition at 270 nm (experimental), 289 nm (theoretical). In Co complex (2) the HOMO and LUMO energies are -
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5.70 eV and -1.15 eV, respectively. The corresponding HOMO-LUMO band gap is 4.55 eV, which reflects the transitions at 272 nm, which is in complete agreement with experimental and
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theoretical absorption maxima. The absorption maxima in both complexes reflect that transitions are actually π to π* (HOMO to LUMO). The HUMO and LUMO surfaces of both complexes are studied to understand the distribution of isodensities, and are shown in Fig. 8. The HOMO and LUMO isodensities in both complexes 1 and 2 are mainly located on hetro atoms (participating in coordination with metal) of thiobiuret ligand and central metal atoms.
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3.6 Molecular electrostatic potential analysis
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Molecular electrostatic potential surfaces of both complexes were extracted by using the optimized geometries at B3LYP/6-31G(d,p) level of theory and are shown in the Fig. 9. From Fig. 9, it is cleared that the –ive potential is concentrated on the oxygen and sulfur atoms of ligand around the
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Ni(II) and Co(III) complexes 1 and 2, respectively which actually reflects the donation of electrons from O and S. The dispersion of potential in Ni(II) complex (1) is ranged from -0.05384
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to 0.05384 esu, whereas it ranges from -0.07112 to 0.07112 esu in Co(III) complex 2.
4. Conclusions
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In the current study, two thiobiuret based Ni(II) and Co(III) complexes, have been synthesized in good yields. The structures of these complexes are elucidated with the help of different spectroanalytical techniques such as FT-IR, UV-vis and 1H-NMR. Finally, the structures of both
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Ni and Co complexes are confirmed unequivocally by single crystal X-ray diffraction analysis. Ni(II) complex (1) crystallized in the monoclinic crystal system along with space group P21/c and
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square planar geometry, whereas Co(III) complex (2) crystalized in trigonal crystal system having P3 space group and octahedral geometry. The unit cell diagrams of both complexes revealed, that only very week (Van der Waals interactions) exist among individual molecules in both complexes. DFT investigations revealed the strong correlation between theoretical and X-ray diffraction results. Negligible difference is observed in bond lengths (<0.06 Å). Maximum deviation in bond angles in both complexes is 0-1.6o, which is for S1-Ni-O1 (1) and S1-Co-O1 (2), respectively.
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Vibrational analysis (experimental and theoretical) provided the evidence of complex formation. The band gap between frontier orbitals is 4.13 eV (1) and 4.55 eV (2), strongly correlated with the
to 0.07112 esu in Ni(II) and Co(III) complexes, respectively.
Acknowledgements
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absorption maxima. The dispersion of ESP is ranged from -0.05384 to 0.05384 esu and -0.07112
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The authors highly acknowledge Higher Education Commission of Pakistan, COMSATS
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Abbottabad and University of Azad Jammu and Kashmir for financial support.
Supplementary material
Cartesian co-ordinates of optimized geometries and check cif files of both complexes 1 and 2 are
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provided in supporting information. Experimental 1H-NMR are also pasted in supporting information as Fig. S1 and S2. Supplementary data associated with this article can be found, in the
[1]
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Caricato, M.; Li, X.; Hratchian, H.P.; Izmaylov, A.F.; Bloino, J.; Zheng, G.; Sonnenberg,
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[32]
Synthesis, crystal structure, spectroscopic and density functional theory (DFT) study of N[3-anthracen-9-yl-1-(4-bromo-phenyl)-allylidene]-N-benzenesulfonohydrazine,
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Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 142 (2015) 364–374.
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Zaman, M.I. Choudhary, K.F. Khattak, K. Ayub, Isolation, spectroscopic and density functional theory studies of 7-(4-methoxyphenyl)-9H-furo[2,3-f]chromen-9-one: A new flavonoid from the bark of Millettia ovalifolia, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 146 (2015) 24–32.
T.U. Rahman, G. Uddin, R.U. Nisa, R. Ludwig, W. Liaqat, T. Mahmood, G. Mohammad,
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[34]
M.I. Choudhary, K. Ayub, Spectroscopic and density functional theory studies of 7hydroxy-3′-methoxyisoflavone: A new isoflavone from the seeds of Indigofera heterantha
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TiCl 4 catalyzed formal [3 + 3] cyclization of 1,3-bis(silyl enol ethers) with 1,3dielectrophiles, RSC Adv. 5 (2015) 94304–94314.
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M.N. Ahmed, K.A. Yasin, K. Ayub, T. Mahmood, M.N. Tahir, B.A. Khan, M. Hafeez, M.
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[39]
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2-((10-alkyl-10H-phenothiazin-3-
Chem. Cent. J. 10 (2016) 13. [40]
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yl)methylene)malononitrile derivatives; a combined experimental and theoretical insight,
N. Rasool, A. Kanwal, T. Rasheed, Q. Ain, T. Mahmood, K. Ayub, M. Zubair, K. Khan, M. Arshad, A. M. Asiri, M. Zia-Ul-Haq, H. Jaafar, One Pot Selective Arylation of 2-Bromo-5-
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Chloro Thiophene; Molecular Structure Investigation via Density Functional Theory (DFT), X-ray Analysis, and Their Biological Activities, Int. J. Mol. Sci. 17 (2016) 912. G. Ahmad, N. Rasool, H. Ikram, S. Gul Khan, T. Mahmood, K. Ayub, M. Zubair, E. Al-
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Derivatives via Suzuki Cross-Coupling Reaction of Commercially Available 5-Bromo-2methylpyridin-3-amine: Quantum Mechanical Investigations and Biological Activities, Molecules. 22 (2017) 190.
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[43]
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reactivities towards ligand S-ethylation with iodoethane of the tetrahedral zinc(II) complexes of 1,1,5,5-tetramethyl-2-thiobiuret and 1,1,5,5-tetramethyl-2,4-dithiobiuret,
[44]
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Inorg. Chem. Commun. 7 (2004) 784–787. B.F. Ali, Z. Judeh, K. Ayub, Synthesis, structure, spectroscopic and DFT studies of zinc(II) and manganese(II) complexes of 2-pyridine carboxaldehyde-N-methyl-N-2-pyridyl
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hydrazone, Polyhedron. 101 (2015) 118–125.
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method, Phys. Rev. B. 89 (2014) 14402.
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[47]
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sulfonylhydrazides, J. Mol. Struct. 1133 (2017) 80–89. F. Wasim, T. Mahmood, K. Ayub, An accurate cost effective DFT approach to study the
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sensing behaviour of polypyrrole towards nitrate ions in gas and aqueous phases, Phys. Chem. Chem. Phys. 18 (2016) 19236–19247. M. Arshad, A. Bibi, T. Mahmood, A. Asiri, K. Ayub, Synthesis, Crystal Structures and
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[48]
Spectroscopic Properties of Triazine-Based Hydrazone Derivatives; A Comparative Experimental-Theoretical Study, Molecules. 20 (2015) 5851–5874.
[49]
M. Noreen, N. Rasool, Y. Gull, M. Zubair, T. Mahmood, K. Ayub, F.-H. Nasim, A. Yaqoob, M. Zia-Ul-Haq, V. de Feo, Synthesis, Density Functional Theory (DFT), Urease Inhibition and Antimicrobial Activities of 5-Aryl Thiophenes Bearing Sulphonylacetamide 21
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Captions Table 1 X-ray diffraction parameters of both complexes 1 and 2.
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Moieties, Molecules. 20 (2015) 19914–19928.
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Table 2 Comparison of important X-ray and simulated bond lengths (Å) of both Ni(II) and Co(III)
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complexes 1 and 2, respectively (Atomic labels are with reference ORTEP plots Fig. 2).
Table 3 Comparison of some important X-ray and simulated bond angles (o) of both Ni(II) and Co(III) complexes (Atomic labels are with reference ORTEP plots Fig. 2).
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Table 4 Important experimental and theoretical vibrations (cm-1) of both Ni(II) and Co(III) complexes 1 and 2, respectively.
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Fig. 1. Synthetic scheme for synthesis of thioubiuret ligand and complexes
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Fig. 2. ORTEP plots of both Ni(II) 1 and Co(III) 2 complexes drawn at 50% of probability level Fig. 3. Packing diagrams of Ni(II) (above) and Co(III) (below) complexes, showing only Van der Walls interactions
Fig. 4. Optimized structures of Ni(II) 1 and Co(III) 2 complexes Fig. 5. Experimental FT-IR spectra of Ni(II) and Co(III) complexes Fig. 6. Simulated FT-IR spectra of both Ni(II) and Co(III) complexes 22
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Fig. 7. Experimental and theoretical UV-vis. spectra of both complexes 1 and 2 Fig. 8. HOMO and LUMO surfaces of both complexes 1 (above) and 2 (below)
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Fig. 9. ESP surfaces of both complexes 1 and 2
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Table 1 X-ray diffraction parameters of both complexes 1 and 2.
C22H42N4NiO2S2
Mr
517.42
746.35
Crystal system, space group
Monoclinic, P21/c
Trigonal, P3
Temperature (K)
296
296
a, b, c (Å)
20.1555 (4), 12.5641 (3), 11.1588 (2)
13.5545 (5), 14.4071 (6)
β (°)
95.046 (1)
------------
V (Å3)
2814.85 (10)
Z
4
Radiation type
Mo Kα
µ (mm−1)
0.86
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Chemical formula
Co(III) Complex (2) C33H63CoN6O3S3
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Ni(II) Complex (1)
2292.31 (19)
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2
Mo Kα 0.72
R[F > 2σ(F )], wR(F ), S 0.038, 0.100, 1.07
0.42 × 0.36 × 0.26 0.035, 0.095, 1.03
No. of reflections
6416
3353
290
156
H-atom parameters constrained
H-atom parameters constrained
0.38, − 0.24
0.31, − 0.38
Crystal size (mm) 2
0.45 × 0.38 × 0.30 2
No. of parameters H-atom treatment
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∆ρmax, ∆ρmin (e Å−3)
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Table 2 Comparison of important X-ray and simulated bond lengths (Å) of both Ni(II) and Co(III) complexes 1 and 2, respectively (Atomic labels are with reference ORTEP plots Fig. 2). Co complex Co-S1 Co-O1 O1-C1 C1-N1 S1-C7 C7-N1 C7-N2 N2-C10 N2-C8 C1-C2
X-ray 2.21 (5) 1.92 (12) 1.26 (2) 1.32 (2) 1.73 (18) 1.34 (2) 1.34 (2) 1.48 (3) 1.46 (3) 1.51 (3)
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Calc. 2.27 1.90 1.26 1.33 1.74 1.34 1.36 1.46 1.47 1.51
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Calc. 2.18 1.84 1.75 1.35 1.33 1.33 1.27 1.51 1.46 1.47
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X-ray 2.14 (6) 1.85 (15) 1.73 (2) 1.33 (3) 1.34 (3) 1.32 (3) 1.26 (3) 1.51 (3) 1.47 (3) 1.48 (3)
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Ni complex Ni-S1 Ni-O1 S1-C1 C1-N1 C1-N2 N2-C6 O1-C6 C6-C7 N1-C4 N1-C2
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Calc. 93.3 126.5 117.6 116.2 128.2 115.7 115.6 115.5
Co complex (2) S1-Co-O1 S1-C7-N1 S1-C7-N2 O1-C1-N1 O1-C1-C2 C1-C2-C3 N1-C7-N2 C8-N2-C10
X-ray 95.6 (4) 128.3 (14) 117.4 (14) 130.0 (17) 115.5 (16) 115.8 (16) 114.2 (16) 116.1 (16)
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X-ray 94.9 (15) 126.5 (18) 117.6 (17) 116.2 (2) 128.4 (2) 116.0 (2) 116.0 (2) 115.6 (19)
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Ni complex (1) S1-Ni-O1 S1-C1-N2 S1-C1-N1 C2-N1-C4 O1-C6-N2 N2-C6-C7 C6-C7-C8 N2-C1-N1
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Table 3 Comparison of some important X-ray and simulated bond angles (o) of both Ni(II) and Co(III) complexes (Atomic labels are with reference ORTEP plots Fig. 2). Calc. 94.0 128.2 117.0 129.9 115.0 115.8 114.6 117.5
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Table 4 Important experimental and theoretical vibrations (cm-1) of both Ni(II) and Co(III) complexes 1 and 2, respectively. 2 (Exp.) 2947 2933 2902 1528 --1487 --------1408 --------1357 ----1283 1242 1122 628 ---
Assignment υasCH2 , υasCH3 υas, υs CH3 υsCH2, υs CH3 υsC-O υsC-O υsC=N υsC=N ρCH2, υsC=N ρCH2 ρCH2 ρCH2 ρCH2 ρCH2, υsC=N ρCH2, βCH2 ρCH2, βCH2 βCH2, βCH3 βCH2, βCH3 βCH2, βCH3 ωCH2 υsC-S γCH2 υsCo-S υsCo-O
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υasCH3 υs CH2 υsCH2 υsC-O υsC-O υsC=N υsC=N υsC=N, ρCH2 ρCH2 ρCH2 ρCH2, υsC=N βCH2 βCH2 ωCH2 ωCH2 υsC-S γCH2 υsNi-S υsNi-O ρO-Ni-O υasNi-S
2 (Calc.) 2991 2960 2917 1524 1523 1479 1478 1476 1436 1435 1417 1415 1414 1406 1405 1350 1349 1348 1279 1235 1112 639 614
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Assignment
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1 (Exp.) 2977 2953 2936 --1505 ----1417 ----1380 1355 --1289 --1247 1128 --621 -----
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1 (Calc.) 2994 2955 2954 1536 1517 1487 1484 1439 1420 1419 1414 1349 1348 1281 1276 1236 1114 658 620 609 510
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υs, Symmetric treching; υas, Asymmetric streching; β, In plane bending; γ, Out of plane bending; ρ, Scissoring; ω, In plane twisting
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Fig. 1.
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Fig. 4.
2
10
0
3500
3000
2500 2000 -1 Wavenumber(cm )
Fig. 5.
1500
1000 679.40552 628.45011
754.77707
518.04671
1128.45011
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1420.38217 1355.62633 1289.80892 1247.34607
909.76645 859.87261 790.87049 755.83864
1005.30786
1000
525.47771
617.83439
686.83652
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1078.55626
40
909.76645 847.13376
1508.49257
2865.18047
30
1005.30786
1500
1122.08068 1077.49469
20
1283.43949 1242.03822
50
1408.70488 1357.74947
30
2500 2000-1 Wavenumber(cm )
CO-Complex
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1653.92781
3000
1528.66242 1487.26115
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2947.98301
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3414.01274
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3415.07431
% Transmittance
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500
500
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Ni complex
E psilon
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1500
2500
3500
3000
2500
2000
1500
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Co complex
1000
4000
3500
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Cobalt Ni
Ni Co
4000
1.0
Epsilon
2000
0.4
1000
0.2 0.0
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600
400
Wavelength (nm)
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LUMO (1)
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(Z)-3-(3,3-dimethylbutanoyl)-1,1-diethyl-2-thiobiuret based Ni(II) and Co(III) complexes have synthesized
(ii)
The structures were elucidated and confirmed by spectroscopic as well as single crystal X-ray diffraction studies. X-ray studies revealed the presence of only Van der Walls interactions among the
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molecules.
Spectroscopic as well as X-ray dat are compared by DFT studies
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S0022-2860(17)30987-0
DOI:
10.1016/j.molstruc.2017.07.054
Reference:
MOLSTR 24081
To appear in:
Journal of Molecular Structure
Received Date: 17 March 2017 Revised Date:
11 July 2017
Accepted Date: 20 July 2017
Please cite this article as: S. Sherzaman, Sadiq-ur-Rehman, M.N. Ahmed, B.A. Khan, T. Mahmood, K. Ayub, M.N. Tahir, Thiobiuret based Ni(II) and Co(III) complexes: Synthesis, molecular structures and DFT studies, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.07.054. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Thiobiuret based Ni(II) and Co(III) Complexes: Synthesis, Molecular
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Structures and DFT Studies
Saira Sherzamana, Sadiq-ur-Rehmana, Muhammad Naeem Ahmed*a, Bilal Ahmad Khana, Tariq Mahmood*b, Khurshid Ayubb and Muhammad Nawaz Tahirc
Department of Chemistry, The University of Azad Jammu and Kashmir Muzaffarabad, 13100 Pakistan.
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a
Department of Chemistry, COMSATS Institute of Information Technology, University Road, Tobe Camp, 22060, Abbottabad, Pakistan.
Department of Physics, University of Sargodha, Sargodha, Pakistan.
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*To whom correspondence can be addressed: E-mail: [email protected] (T. M) and [email protected] (M. N. A)
1
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Abstract Synthesis, molecular structures and DFT investigations of two new complexes of Ni(II) and with
(Z)-3-(3,3-dimethylbutanoyl)-1,1-diethyl-2-thiobiuret
ligand
are
reported.
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Co(III)
Characterization of these complexes was achieved by spectroanalytical techniques (FT-IR, UV-vis and 1H-NMR), and the structures were finally confirmed unequivocally by single crystal X-ray diffraction analysis. The obtained data of UV-vis, FT-IR and 1HNMR were compared with the
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literature values which satisfactorily confirmed the synthesis of ligand and their complexes. X-ray studies revealed the square planar and octahedral geometry of both Ni(II) and Co(III) complexes,
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respectively. Density functional theory (DFT) studies were performed to compare the theoretical results with experimental (X-ray as well as spectroanalytical) results, and good correlation was observed. Frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP)
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analyses revealed the reactivity and charge distribution in both complexes.
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Keywords: Thiobiuret; Ni(II) and Co(III) Complexes; X-ray Diffraction; DFT
2
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1. Introduction Since last decade thiobiurets (tbu) have recieved the attention of scientific community due to
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versatile applications in different areas of chemistry [1]. Thiobiurets and their derivatives have been employed extensively as anti-malarial [2], antitubercular, hypoglycemic [3] and antimicrobial agents [4]. Moreover, thioubiurets are also known as effective herbicidal [5], pesticidal
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[6] and insecticidal [3] agents. The biological activities of thiobiurets are believed to arise from NC-S moiety, and are further enhanced after complexation with metals [7–11]. It is noticeable that
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thiobiuret compounds are not limited to biological applications rather, they are equally important in industrial [12,13] and nanomaterial chemistry [14]. Particularly, these compounds are used for the synthesis of high pressure lubricant additives and corrosion inhibitors [13]. The presence of oxygen and sulfur as donor sites, and π electrons make thiobiurets attractive ligand for metals [1,15,16]. Thiobiuret based metal complexes has variety of applications and
Billson
and
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important structural features (particularly diamagnetic square planar d8 complexes). Recently, co-workers
has
reported
square
planar
bis(N1,N1,N5,N5-tetrabenzyl-2,4-
dithiobiureto)nickel(II) complex, which has ability to hold p-xylene within the lattice cavities of
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molecule [17]. 2-Thiobiuret and its derivatives are famous as neutral, mono-anionic and bi-dentate
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ligands for metal complexes [18] and attractive building blocks for thinfilms [19,20] and nanomaterials [14,21]. In the last few years, researchers are engaged in the studying molecular structures and mode of coordination of central metal atoms with the different types of thiobiurets [22–25]. Keeping in view the wide range applications of thiobiuret based metal complexes, we report here the efficient synthesis and molecular structures of (Z)-3-(3,3-dimethylbutanoyl)-1,1diethyl-2-thiobiuret nickle(II) and cobalt(III) complexes. The both complexes were elucidated by different spectroanalytical techniques and the final structures of complexes were confirmed 3
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unequivocally by single crystal X-ray diffraction analysis. Quantum chemical investigations with density functional theory (DFT) were executed to compare theoretical and experimental (spectroscopic and X-ray) parameters of both complexes, and also to probe some other important
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molecular properties.
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2. Material and methods 2.1 Experimental
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All chemicals and reagents were purchased from Sigma- Aldrich and used directly without further purification. Solvents were distilled and dried (wherever required) prior to use. Melting points of complexes were measured on electro thermal melting point apparatus (MPD Mitamura Ricken Kogyo, Japan), and are reported as uncorrected. Infrared (FT-IR) spectra of both complexes were
1
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scanned by using FT-IR-8400s SHIMADZU spectrophotometer in frequency range 400-4000 cm. Multinuclear NMR (1H) spectra were scanned by using Bruker ARX 300 MHz-FT-NMR and a
Bruker 400 MHz-FT-NMR in deutrated chloroform as solvent, and tetramethylsilane as an internal
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2.2 Synthesis
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reference. Absorption studies were performed on UV-vis spectrophotometer (SHIMADZU 1601).
Thioubiuret ligand and corresponding Ni(II) (1) and Co(III) (2) complexes were synthesized according to the protocol provided in the Fig. 1. 2.2.1 General procedure for synthesis of ligand and corresponding complexes The synthesis of thiobiuret ligand and corresponding complexes was accomplished by adopting one pot synthetic methodology following the literature procedure with slight modification [19]. A 4
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solution of substituted dimethylbutyryl chloride and potassium thiocynate with molar ratio 1:1 was stirred for two hours at room temperature in dry acetonitrile (40ml). Then 60% aqueous solution of substituted amine was added to the reaction mixture and stirred further for 30 minutes. Finally,
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corresponding metal acetate tetra hydrated salt (0.5g) was added in dry state with continuous stirring. Ligand to metal ratio for complex 1 was 2:1 and 3: 1 for complex 2. After 1 hour stirring, excess amount of distilled water (100 ml) was added which resulted into the precipitate formation
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(Fig. 1). Precipitates (ppt) were filtered, dried and recrystallized from chloroform to obtain fine
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crystals for the further analysis.
2.2.1.1 Bis[Z-3-(3,3-dimethylbutanoyl)-1,1-diethyl-2-thiobiureto]Nickal(II) (1) Purple crystalline solid, M. P. 120 oC; yield 67 %, UV-vis. λmax. 270 nm; FT-IR (ATR, cm-1); νmax 2977, 2962, 2936, 1500, 1410, 1380, 1356, 1288, 1247, 1130, 621; 1H-NMR (CDCl3) δ ppm 0.98
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(br s.18H), 1.11 (s, 6H), 1.21 (br s, 4H), 2.13 (s, 4H), 3.53-3.77, (m, 8H) 2.2.1.2 Tris[Z-3-(3,3-dimethylbutanoyl)-1,1-diethyl-2-thiobiureto]Cobalt(III) (2)
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Dark green crystalline solid, M. P. 80 oC; yield 52%, UV-vis. λmax. 268 nm; FT-IR (ATR, cm-1); νmax 2948, 2933, 2902, 1530, 1490, 1400, 1350, 1284, 1244, 1126, 628; 1H-NMR (CDCl3) δ ppm
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0.98 (s, 18H), 1.12 (s, 6H),1.25(s, 6H), 2.41-2.26 (m, 4H), 3.99-3.65 (m, 8H). 2.3 Crystal structure determination Suitable crystals of both complexes (Ni and Co) (1-2) were selected and picked for single crystal X-ray diffraction analysis. The X-ray parameters were measured on Bruker Kappa Apex-IICCD diffractometer equipped with graphite monochromator and Mo-Kα radiation source. The X-ray structures of both complexes 1 and 2 were solved and refined by using direct method (SHELXL 5
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2013) [26]. The ORTEP plots and unit cell diagrams were processed with the help of ORTEP II [27]. CIF files of both complexes 1 and 2 have been assigned CCDC numbers 1518439 and 1518440,
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respectively, and can be obtained free of charge on demand to CCDC 12 Union Road, Cambridge CB21 EZ, UK. (Fax: (+44) 1223 336-033: [email protected]).
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2.4 Computational methods
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Computational studies were performed with Gaussian 09 software [28], visualization of graphics were performed by using Gauss view 05 [29]. The geometries of both complexes 1 and 2 were optimized at hybrid B3LYP method with 6-31G(d,p) basis set. Nowadays, B3LYP method is quite reliable for structural properties of synthetic and natural products due to its nice balance between computational cost and accuracy [30–35]. Geometries of these complexes were confirmed through
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frequency analysis at the same level, and the no imaginary frequency was observed (true minima). Frequency calculations are also used for theoretical vibrational analysis. 1H-NMR spectra were simulated at B3LYP/6-311+G(2d,p) level of DFT. TD-DFT calculations for absorption spectra
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have been performed at CAM-B3LYP/6-31G(d,p) level of theory. Total 20 excited states (10
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singlet and 10 triplet) were taken into account for the computation of UV–vis. spectra of both complexes 1 and 2. Frontier molecular orbitals and molecular electrostatic potential were computed at B3LYP/6-31G(d,p) level of theory.
3. Results and discussion
The Ni(II) 1 and Co(III) 2 complexes of thiobiuret are synthesized by the reaction of commercially available diethylamine and in situ generated 3,3-dimethylbutanoylthiocyanate in acetonitrile (Fig. 6
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1). Both complexes 1 and 2 are air and moisture stable and have good solubility in chloroform, tetrahydrofuran and dimethylsulphoxide. After accomplishing the synthesis, the complexes are characterized by NMR (1H), FT-IR and UV-vis spectroscopic techniques, and the final structures
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are confirmed unequivocally by single crystal X-ray diffraction analysis. Quantum chemical studies are performed to compare with experimental spectroscopic and X-ray parameters, and to probe the electronic properties such as frontier molecular orbitals (FMOs) and molecular
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3.1 Molecular structure
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electrostatic potential (MEP) analyses.
The molecular formulas of title complexes 1 and 2 consist of [C22H42N4NiO2S2] and [C33H63CoN6O3S3] entities, respectively. The Ni(II) complex (1) crystallized in the monoclinic crystal system having space group P21/c, whereas Co(III) complex (2) crystalized in trigonal
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crystal system having P3 space group. The crystal structure data of both complexes are given in Table 1, and ORTEP plots (drawn at 50% probability level) are shown in the Fig. 2. Analysis of ORTEP plots shows that the metal is localized on a crystallographic center of symmetry and is
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bound with two thiobiuret ligands (four S and O atoms) in Ni (II) complex 1, whereas in Co(III)
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complex 2, the central metal atom is bound with three molecules of ligand. The Ni(II) complex 1 is neutral homoleptic having cis square planar geometry and all nonhydrogen atoms are located on a crystallographic mirror plane (Fig. 2). The Ni(II) ion is square planar with S and O donor set, which are mutually fac to each other and respective planes are parallel to each othe. The bond distances from central metal atoms (Ni-S1 = 2.14 Å and Ni-O1 = 1.85 Å) are indicative of localization of -ive charge on the S atom. The relatively longer C-S (1.73 Å) and shorter C-O (1.26 Å) bond lengths are indicative of single and double bond character, 7
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respectively [36]. The Co(III) complex is also neutral homoleptic and has octahedral geometry. All three thiobiuret ligands in 2 are twisted and show significant deviation from planarity. The pattern of bond lengths is similar to that observed in the corresponding homoleptic nickel(II)
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complex 1 [37].
The single crystal X-ray diffraction studies depicted that both Ni(II) and Co(III) complexes exist as isolated molecular units of (C11H21N2SO)2Ni and (C11H21N2SO)3Co, respectively. No evidence
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of hydrogen bonding, any metal-adjacent ligand and metal-metal interactions is observed in crystal packing unit cell diagrams of both complexes 1 and 2 (Van der Waals interactions are observed
3.2 DFT Optimized geometries
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among different proton and carbon atoms of both complexes) (Fig. 3).
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DFT calculations have been executed to compare the theoretical and experimental geometric parameters (bond lengths, bond angles) of both complexes 1 and 2. Complexes exist in singlet spin
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state. The geometries of both complexes were simulated computationally at cost effective and accurate B3LYP/6-31G(d,p) level of DFT [38–41]. The optimized geometries are given in Fig. 4,
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and some important geometric parameters (bond lengths and bond angles) are summarized in Table 2 and Table 3. The comparative analysis indicates that experimental geometric parameters strongly agree with the theoretical data. For bond lengths of Ni(II) complex (1), theoretical values of Ni-S1 and Ni-O1 are 2.18 Å and 1.84 Å, respectively, which corroborate nicely with the respective experimental values 2.14 Å and 1.85 Å. Theoretically, bond lengths of S1-C1, C1-N1, C1-N2, N2-C6, O1-C6, C6-C7, N1-C4 and N1C2 in complex 1 are 1.75 Å, 1.35 Å, 1.33 Å, 1.33 Å, 1.27 Å, 1.51 Å, 1.46 Å and 1.47 Å , 8
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respectively. Whereas the corresponding experimental bond lengths are 1.73 Å, 1.33 Å, 1.34 Å, 1.32 Å, 1.26 Å, 1.51 Å, 1.47 Å and 1.48 Å, respectively. Similarly, in Co(III) complex (2), the experimental and theoretical values of important bond lengths corroborate nicely to each other.
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The theoretical values of Co-S1 and Co-O1 are 2.27 Å and 1.90 Å, respectively and show excellent correlation with corresponding experimental values at 2.12 Å and 1.92 Å. The calculated bond lengths of O1-C1, C1-N1, S1-C7, C7-N1, C7-N2, N2-C10, N2-C8 and C1-C2 in complex 2
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are found 1.26 Å, 1.33 Å, 1.74 Å, 1.34 Å, 1.36 Å, 1.46 Å, 1.47 Å and 1.51 Å, respectively. The Xray values of respective bond lengths are 1.26 Å, 1.32 Å, 1.73 Å, 1.34 Å, 1.34 Å, 1.48 Å, 1.46 Å
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and 1.51 Å, respectively.
The comparative analysis of important bond angles of both complexes is narrated in Table 3, and reveals excellent correlation among theoretical and X-ray values. In Ni(II) complex 1, the deviation (theoretical and experimental value) in bond angles is in the range 0-1.6o, and maximum
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deviation is 1.6o for S1-Ni-O1. Again in complex 2, important bond angles correlated nicely to each other between experiment and theory. The deviation is 0-1.6o, and maximum difference is for S1-Co-O1 (1.6o). In general, the differences between simulated and experimental geometrical
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parameters of both complexes are negligible. In most cases, difference between experimental and
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theoretical results are <0.06 Å (bond length) and <1.6o (bond angles).
3.3 Vibrational studies
Since last few years, quantum chemical methods are extensively used by scientific community to study the vibrations of different types of bond, especially in the fingerprint region which appears very complicated in the experimental spectrum. The FT-IR spectra of both complexes were 9
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scanned under neat conditions, and theoretical FT-IR spectra were extracted from frequency calculation. The experimental and theoretical spectra are shown in the Fig. 5 and Fig. 6, and comparative analysis is provided in the Table 4.
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Since both complexes 1 and 2 have identical ligand and bear similar C=O, C=N, C-S, CH2 and CH3 functional groups. According to the literature the strong peak ~ 1700 cm-1, is the characteristic of carbonyl group (C=O) in the thiobiuret ligand [42]. After complex formation, the
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υ(C=O) bands shifts to lower frequencies (-NH-C=O in thiobiuret is in fact converted to –N=C-Oin the complexes [43], where carbon oxygen bond order is significantly reduced) suggesting
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coordination of the metal and ligand [11]. The experimental stretching υ(C-O) in Ni(II) complex 1, is appeared at 1505 cm-1 which agrees with the theoretical stretching vibrations at 1536 cm-1 and 1517 cm-1 (theoretically two strong signals of stretching C-O vibrations are due to the presence of two molecules of ligand around central meta atom) and the reported literature of zinc complexes
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of similar ligands [43]. Similarly in Co(III) complex 2, the theoretical υ(C-O) stretching vibrations at 1524 cm-1, 1523 cm-1 correlated nicely with experimental value at 1528 cm-1. Thiobiuret ligand has different CH2 and CH3 groups, therefore several stretching, bending (scissoring, twisting, in
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and out of plane bending) vibrations are observed in both experimental and theoretical spectra (Table 4). The N=C shifts appeared in the range of 1400-1500 cm-1, due to increase in the double
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bond character of the C–N bond upon complex formation [44]. Experimental υ(C=N) are observed at 1417 cm-1 (1) and 1487 cm-1 (2). The corresponding theoretical υ(C=N) are observed at 1487 cm-1, 1484 cm-1 and 1439 cm-1 in complex 1, and 1479 cm-1, 1478 cm-1, 1476 cm-1 and 1414 cm-1 in complex 2. The IR peaks in the range of 400-490 cm-1 and 500-590 cm-1 in both experimental and theoretical spectra clearly show the formation of M-O and M-S bonds, respectively [10,15].
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Vibrational data (both experimental and theoretical) of synthesized complexes are carefully compared with literature which strongly confirmed the formation of complexes.
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3.4 Nuclear magnetic resonance studies
Experimental 1H-NMR spectra of both complexes were recorded in deutrated chloroform
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(electronic supplementary information, Fig. S1and S2). Theoretically chemical shift values are computed at B3LYP/6-311+G(2d,p) level of DFT, (the higher basis set normally works better for
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measurement of chemical shift values [45]). In both complexes, ligands are same bearing similar types of protons i. e. CCH3, CCH2 and NCH2 are present. The computed proton chemical shifts in both complexes 1 and 2 appeared little bit higher as compared to experimental shifts. This difference is due to the phase difference between experiment and theory. Experimental values are always measured in condensed phase, whereas computed values are calculated in the gas phase
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[46,47]. In Ni(II) complex 1, the experimental 1H chemical shifts of CCH3, CCH2 and NCH2 are found at 0.98, 1.11, 1.21, 2.13 and 3.53-3.77 ppm, respectively. The theoretical shifts of these
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protons are 1.70, 1.77, 2.82 and 4.36 ppm, respectively. In Co(III) complex (2), the experimental chemical shift of CCH3, CCH2 and NCH2 are 0.98, 1.12, 1.25, 2.41-2.26 and 3.99-3.65 ppm,
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respectively. Whereas computed 1H-NMR chemical shifts are 1.65, 1.89, 3.08 and 4.57 ppm, respectively which shows good correlation between theory and experiment.
3.5 Absorption studies and frontier molecular orbitals (FMOs) analysis
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The experimental absorption spectra of both complexes were recorded in methanol as solvent. Whereas simulated spectra were obtained at time dependent calculation at CAM-B3LYP/631G(d,p) level of theory. The experimental and simulated absorption spectra of both complexes
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are shown in Fig. 7. The experimental UV-vis spectrum of Ni(II) complex (1) shows a prominent absorption peak at 270 nm, whereas theoretically absorption peak is observed at 289. Theoretically calculated absorption maximum correlates nicely with the experimental absorption maximum. For
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Co(III) complex (2), the experimental and simulated UV-vis. absorptions are observed at 268 nm and 290 nm, respectively and corroborated nicely to each other.
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The frontier molecular orbital (FMOs) analysis with the aid of quantum chemical methods is a famous approach to explain the molecular transitions [38,48,49]. The frontier molecular orbitals of both Ni(II) and Co(III) complexes have been analyzed for correlation to the experimental transitions in UV-vis. region of electromagnetic spectrum. In case of Ni(II) complex (1), the
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corresponding HOMO and LUMO energies are -5.26 eV and -1.13 eV, respectively. The band gap is 4.13 eV, which corresponds to 300 nm and in nice agreement with the transition at 270 nm (experimental), 289 nm (theoretical). In Co complex (2) the HOMO and LUMO energies are -
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5.70 eV and -1.15 eV, respectively. The corresponding HOMO-LUMO band gap is 4.55 eV, which reflects the transitions at 272 nm, which is in complete agreement with experimental and
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theoretical absorption maxima. The absorption maxima in both complexes reflect that transitions are actually π to π* (HOMO to LUMO). The HUMO and LUMO surfaces of both complexes are studied to understand the distribution of isodensities, and are shown in Fig. 8. The HOMO and LUMO isodensities in both complexes 1 and 2 are mainly located on hetro atoms (participating in coordination with metal) of thiobiuret ligand and central metal atoms.
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3.6 Molecular electrostatic potential analysis
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Molecular electrostatic potential surfaces of both complexes were extracted by using the optimized geometries at B3LYP/6-31G(d,p) level of theory and are shown in the Fig. 9. From Fig. 9, it is cleared that the –ive potential is concentrated on the oxygen and sulfur atoms of ligand around the
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Ni(II) and Co(III) complexes 1 and 2, respectively which actually reflects the donation of electrons from O and S. The dispersion of potential in Ni(II) complex (1) is ranged from -0.05384
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to 0.05384 esu, whereas it ranges from -0.07112 to 0.07112 esu in Co(III) complex 2.
4. Conclusions
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In the current study, two thiobiuret based Ni(II) and Co(III) complexes, have been synthesized in good yields. The structures of these complexes are elucidated with the help of different spectroanalytical techniques such as FT-IR, UV-vis and 1H-NMR. Finally, the structures of both
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Ni and Co complexes are confirmed unequivocally by single crystal X-ray diffraction analysis. Ni(II) complex (1) crystallized in the monoclinic crystal system along with space group P21/c and
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square planar geometry, whereas Co(III) complex (2) crystalized in trigonal crystal system having P3 space group and octahedral geometry. The unit cell diagrams of both complexes revealed, that only very week (Van der Waals interactions) exist among individual molecules in both complexes. DFT investigations revealed the strong correlation between theoretical and X-ray diffraction results. Negligible difference is observed in bond lengths (<0.06 Å). Maximum deviation in bond angles in both complexes is 0-1.6o, which is for S1-Ni-O1 (1) and S1-Co-O1 (2), respectively.
13
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Vibrational analysis (experimental and theoretical) provided the evidence of complex formation. The band gap between frontier orbitals is 4.13 eV (1) and 4.55 eV (2), strongly correlated with the
to 0.07112 esu in Ni(II) and Co(III) complexes, respectively.
Acknowledgements
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absorption maxima. The dispersion of ESP is ranged from -0.05384 to 0.05384 esu and -0.07112
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The authors highly acknowledge Higher Education Commission of Pakistan, COMSATS
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Abbottabad and University of Azad Jammu and Kashmir for financial support.
Supplementary material
Cartesian co-ordinates of optimized geometries and check cif files of both complexes 1 and 2 are
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provided in supporting information. Experimental 1H-NMR are also pasted in supporting information as Fig. S1 and S2. Supplementary data associated with this article can be found, in the
[1]
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Crystallogr. Sect. E Struct. Reports Online. 60 (2004) m350–m351. [38]
M.N. Ahmed, K.A. Yasin, K. Ayub, T. Mahmood, M.N. Tahir, B.A. Khan, M. Hafeez, M.
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Ahmed, I. Ul-Haq, Click one pot synthesis, spectral analyses, crystal structures, DFT studies and brine shrimp cytotoxicity assay of two newly synthesized 1,4,5-trisubstituted 1,2,3-triazoles, J. Mol. Struct. 1106 (2016) 430–439.
F.A. Al-Zahrani, M.N. Arshad, A.M. Asiri, T. Mahmood, M.A. Gilani, R.M. El-shishtawy, Synthesis
and
structural
properties
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2-((10-alkyl-10H-phenothiazin-3-
Chem. Cent. J. 10 (2016) 13. [40]
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yl)methylene)malononitrile derivatives; a combined experimental and theoretical insight,
N. Rasool, A. Kanwal, T. Rasheed, Q. Ain, T. Mahmood, K. Ayub, M. Zubair, K. Khan, M. Arshad, A. M. Asiri, M. Zia-Ul-Haq, H. Jaafar, One Pot Selective Arylation of 2-Bromo-5-
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Chloro Thiophene; Molecular Structure Investigation via Density Functional Theory (DFT), X-ray Analysis, and Their Biological Activities, Int. J. Mol. Sci. 17 (2016) 912. G. Ahmad, N. Rasool, H. Ikram, S. Gul Khan, T. Mahmood, K. Ayub, M. Zubair, E. Al-
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Zahrani, U. Ali Rana, M. Akhtar, N. Alitheen, Efficient Synthesis of Novel Pyridine-Based
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Derivatives via Suzuki Cross-Coupling Reaction of Commercially Available 5-Bromo-2methylpyridin-3-amine: Quantum Mechanical Investigations and Biological Activities, Molecules. 22 (2017) 190.
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reactivities towards ligand S-ethylation with iodoethane of the tetrahedral zinc(II) complexes of 1,1,5,5-tetramethyl-2-thiobiuret and 1,1,5,5-tetramethyl-2,4-dithiobiuret,
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Inorg. Chem. Commun. 7 (2004) 784–787. B.F. Ali, Z. Judeh, K. Ayub, Synthesis, structure, spectroscopic and DFT studies of zinc(II) and manganese(II) complexes of 2-pyridine carboxaldehyde-N-methyl-N-2-pyridyl
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hydrazone, Polyhedron. 101 (2015) 118–125.
R. Laskowski, P. Blaha, Calculating NMR chemical shifts using the augmented plane-wave
[46]
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method, Phys. Rev. B. 89 (2014) 14402.
M. Arshad, M. Jadoon, Z. Iqbal, M. Fatima, M. Ali, K. Ayub, A.M. Qureshi, M. Ashraf, M.N. Arshad, A.M. Asiri, A. Waseem, T. Mahmood, Synthesis, molecular structure, quantum mechanical studies and urease inhibition assay of two new isatin derived
[47]
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sulfonylhydrazides, J. Mol. Struct. 1133 (2017) 80–89. F. Wasim, T. Mahmood, K. Ayub, An accurate cost effective DFT approach to study the
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sensing behaviour of polypyrrole towards nitrate ions in gas and aqueous phases, Phys. Chem. Chem. Phys. 18 (2016) 19236–19247. M. Arshad, A. Bibi, T. Mahmood, A. Asiri, K. Ayub, Synthesis, Crystal Structures and
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M. Noreen, N. Rasool, Y. Gull, M. Zubair, T. Mahmood, K. Ayub, F.-H. Nasim, A. Yaqoob, M. Zia-Ul-Haq, V. de Feo, Synthesis, Density Functional Theory (DFT), Urease Inhibition and Antimicrobial Activities of 5-Aryl Thiophenes Bearing Sulphonylacetamide 21
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Captions Table 1 X-ray diffraction parameters of both complexes 1 and 2.
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Moieties, Molecules. 20 (2015) 19914–19928.
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Table 2 Comparison of important X-ray and simulated bond lengths (Å) of both Ni(II) and Co(III)
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complexes 1 and 2, respectively (Atomic labels are with reference ORTEP plots Fig. 2).
Table 3 Comparison of some important X-ray and simulated bond angles (o) of both Ni(II) and Co(III) complexes (Atomic labels are with reference ORTEP plots Fig. 2).
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Table 4 Important experimental and theoretical vibrations (cm-1) of both Ni(II) and Co(III) complexes 1 and 2, respectively.
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Fig. 1. Synthetic scheme for synthesis of thioubiuret ligand and complexes
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Fig. 2. ORTEP plots of both Ni(II) 1 and Co(III) 2 complexes drawn at 50% of probability level Fig. 3. Packing diagrams of Ni(II) (above) and Co(III) (below) complexes, showing only Van der Walls interactions
Fig. 4. Optimized structures of Ni(II) 1 and Co(III) 2 complexes Fig. 5. Experimental FT-IR spectra of Ni(II) and Co(III) complexes Fig. 6. Simulated FT-IR spectra of both Ni(II) and Co(III) complexes 22
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Fig. 7. Experimental and theoretical UV-vis. spectra of both complexes 1 and 2 Fig. 8. HOMO and LUMO surfaces of both complexes 1 (above) and 2 (below)
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Fig. 9. ESP surfaces of both complexes 1 and 2
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Table 1 X-ray diffraction parameters of both complexes 1 and 2.
C22H42N4NiO2S2
Mr
517.42
746.35
Crystal system, space group
Monoclinic, P21/c
Trigonal, P3
Temperature (K)
296
296
a, b, c (Å)
20.1555 (4), 12.5641 (3), 11.1588 (2)
13.5545 (5), 14.4071 (6)
β (°)
95.046 (1)
------------
V (Å3)
2814.85 (10)
Z
4
Radiation type
Mo Kα
µ (mm−1)
0.86
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Chemical formula
Co(III) Complex (2) C33H63CoN6O3S3
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Ni(II) Complex (1)
2292.31 (19)
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Mo Kα 0.72
R[F > 2σ(F )], wR(F ), S 0.038, 0.100, 1.07
0.42 × 0.36 × 0.26 0.035, 0.095, 1.03
No. of reflections
6416
3353
290
156
H-atom parameters constrained
H-atom parameters constrained
0.38, − 0.24
0.31, − 0.38
Crystal size (mm) 2
0.45 × 0.38 × 0.30 2
No. of parameters H-atom treatment
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Table 2 Comparison of important X-ray and simulated bond lengths (Å) of both Ni(II) and Co(III) complexes 1 and 2, respectively (Atomic labels are with reference ORTEP plots Fig. 2). Co complex Co-S1 Co-O1 O1-C1 C1-N1 S1-C7 C7-N1 C7-N2 N2-C10 N2-C8 C1-C2
X-ray 2.21 (5) 1.92 (12) 1.26 (2) 1.32 (2) 1.73 (18) 1.34 (2) 1.34 (2) 1.48 (3) 1.46 (3) 1.51 (3)
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Calc. 2.27 1.90 1.26 1.33 1.74 1.34 1.36 1.46 1.47 1.51
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Calc. 2.18 1.84 1.75 1.35 1.33 1.33 1.27 1.51 1.46 1.47
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X-ray 2.14 (6) 1.85 (15) 1.73 (2) 1.33 (3) 1.34 (3) 1.32 (3) 1.26 (3) 1.51 (3) 1.47 (3) 1.48 (3)
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Calc. 93.3 126.5 117.6 116.2 128.2 115.7 115.6 115.5
Co complex (2) S1-Co-O1 S1-C7-N1 S1-C7-N2 O1-C1-N1 O1-C1-C2 C1-C2-C3 N1-C7-N2 C8-N2-C10
X-ray 95.6 (4) 128.3 (14) 117.4 (14) 130.0 (17) 115.5 (16) 115.8 (16) 114.2 (16) 116.1 (16)
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X-ray 94.9 (15) 126.5 (18) 117.6 (17) 116.2 (2) 128.4 (2) 116.0 (2) 116.0 (2) 115.6 (19)
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Ni complex (1) S1-Ni-O1 S1-C1-N2 S1-C1-N1 C2-N1-C4 O1-C6-N2 N2-C6-C7 C6-C7-C8 N2-C1-N1
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Table 3 Comparison of some important X-ray and simulated bond angles (o) of both Ni(II) and Co(III) complexes (Atomic labels are with reference ORTEP plots Fig. 2). Calc. 94.0 128.2 117.0 129.9 115.0 115.8 114.6 117.5
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Table 4 Important experimental and theoretical vibrations (cm-1) of both Ni(II) and Co(III) complexes 1 and 2, respectively. 2 (Exp.) 2947 2933 2902 1528 --1487 --------1408 --------1357 ----1283 1242 1122 628 ---
Assignment υasCH2 , υasCH3 υas, υs CH3 υsCH2, υs CH3 υsC-O υsC-O υsC=N υsC=N ρCH2, υsC=N ρCH2 ρCH2 ρCH2 ρCH2 ρCH2, υsC=N ρCH2, βCH2 ρCH2, βCH2 βCH2, βCH3 βCH2, βCH3 βCH2, βCH3 ωCH2 υsC-S γCH2 υsCo-S υsCo-O
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υasCH3 υs CH2 υsCH2 υsC-O υsC-O υsC=N υsC=N υsC=N, ρCH2 ρCH2 ρCH2 ρCH2, υsC=N βCH2 βCH2 ωCH2 ωCH2 υsC-S γCH2 υsNi-S υsNi-O ρO-Ni-O υasNi-S
2 (Calc.) 2991 2960 2917 1524 1523 1479 1478 1476 1436 1435 1417 1415 1414 1406 1405 1350 1349 1348 1279 1235 1112 639 614
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Assignment
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1 (Exp.) 2977 2953 2936 --1505 ----1417 ----1380 1355 --1289 --1247 1128 --621 -----
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1 (Calc.) 2994 2955 2954 1536 1517 1487 1484 1439 1420 1419 1414 1349 1348 1281 1276 1236 1114 658 620 609 510
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υs, Symmetric treching; υas, Asymmetric streching; β, In plane bending; γ, Out of plane bending; ρ, Scissoring; ω, In plane twisting
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2
10
0
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1500
1000 679.40552 628.45011
754.77707
518.04671
1128.45011
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1420.38217 1355.62633 1289.80892 1247.34607
909.76645 859.87261 790.87049 755.83864
1005.30786
1000
525.47771
617.83439
686.83652
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909.76645 847.13376
1508.49257
2865.18047
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1005.30786
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1122.08068 1077.49469
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1283.43949 1242.03822
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1408.70488 1357.74947
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(Z)-3-(3,3-dimethylbutanoyl)-1,1-diethyl-2-thiobiuret based Ni(II) and Co(III) complexes have synthesized
(ii)
The structures were elucidated and confirmed by spectroscopic as well as single crystal X-ray diffraction studies. X-ray studies revealed the presence of only Van der Walls interactions among the
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molecules.
Spectroscopic as well as X-ray dat are compared by DFT studies
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(iv)