Synthesis, experimental and theoretical

Journal of Molecular Structure 1127 (2017) 15e22

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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc

Synthesis, experimental and theoretical characterization of a Mn(II) complex of N,N0 -dipyridoxyl(1,2-diaminobenzene) Tina Toozandejani a, S. Ali Beyramabadi a, *, Hamed Chegini a, Maryam Khashi b, Ali Morsali a, Mehdi Pordel a a b

Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran Young Researchers and Elite Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

a r t i c l e i n f o

a b s t r a c t

Article history: Received 1 November 2015 Received in revised form 2 July 2016 Accepted 8 July 2016 Available online 12 July 2016

Herein, hopping to biological and catalytic applications, synthesis of a Mn(II) complex of the N,N0 dipyridoxyl(1,2-diaminobenzene) [H]2L] Schiff-base has been reported. The Mn complex was characterized experimentally and theoretically. The optimized geometry and vibrational frequencies of the complex were computed by using the density functional theory (DFT) methods. In the optimized geometry of the octahedral complex, the dianionic L2 acts as a tetradentate ligand. Four coordination positions of the square plane have been occupied with two azomethine nitrogens and two phenolic oxygens of the L2 ligand. Two coordinated methanol ligands are perpendicular to the square plane. Also, properties of the MneN and MneO bonds were explored investigated using the Atoms in molecules (AIM) analysis. © 2016 Elsevier B.V. All rights reserved.

Keywords: Pyridoxal Schiff-base 1,2-diaminobenzene DFT Mn AIM

1. Introduction The Schiff-bases and their complexes are so important from different aspects, especially in the analytical application [1], industrial uses as catalysts [2e6] and their application in biological and biochemical activities [7e10]. Coordination of the Schiff-bases to the metal ions improve their biological activities, too [11e14]. The Schiff-bases are considered as excellent chelating agents, especially when a functional group like eOH or eSH is present close to the azomethine group [15,16]. During the last two decades, syntheses of salen and salophen ligands along with their complexes have received more attention, mainly because of their extensive applications especially in the field of bio-chemistry and catalyses [17e20]. The pyridoxal is a close analogue of Vitamin B6 (pyridoxine) [21], deficiency of which can causes to the serious complications in the human body. The Mn(II) complex of pyridoxal uses in the treatment of diabetic complications [22]. The manganese dipyridoxyl

* Corresponding author. Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran. E-mail addresses: [email protected], [email protected] (S.A. Beyramabadi). http://dx.doi.org/10.1016/j.molstruc.2016.07.026 0022-2860/© 2016 Elsevier B.V. All rights reserved.

diphosphate is a contrast agent for magnetic resonance imaging of the liver [23]. We reported synthesis and DFT computational investigations on the Schiff bases and their complexes, Previously [24e32]. In continuation of our previous studies on the Schiff bases and their complexes, herein we report the synthesis, experimental and computational investigations on the Mn(II) complex of the N,N0 dipyridoxyl(1,2-diaminobenzene) Schiff-base (H2L). Also, structural parameters, vibrational wavenumbers and the AIM analysis of the Mn complex have been computed by using the DFT methods. By comparing the DFT and experimental results, validity of the optimized geometry for the Mn complex has been evaluated. 2. Experimental 2.1. Material and methods All of used chemicals and solvents were obtained from the Merck, which were used without further purification. Melting points were measured by an electrothermal 9100 melting point apparatus. The IR spectra were obtained as KBr pellets by using a BRUKER TENSOR27 infrared spectrophotometer. Percentage of the Mn2þ ion was measured by using a Hitachi 2-2000 atomic

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T. Toozandejani et al. / Journal of Molecular Structure 1127 (2017) 15e22

Table 1 Selected structural parameters of the investigated Mn complex. Bond

Bond length (pm)

Angle

( )

Dihedral angle

( )

MneO1 Mn eN1 MneO5 C1eO1 C1eC2 C2eN3 C2eC6 C4eC7 C7eO3 O3eH9 C5eC8 C8eN1 N1eC17 N1eN2 O1eO2 O1eN1 O5eC23 O5eH29 C17eC18 C17eC22 N3eC3 C3eC4 C1eC5

194.4 197.6 213.0 128.9 144.4 131.3 150.3 151.3 142.3 96.1 142.8 131.4 141.6 262.4 282.5 281.1 143.6 96.6 140.2 141.6 136.0 137.3 143.3

O1eMneO2 O1e MneO5 O1e MneN1 O5e MneN1 N1e MneN2 O1e MneN2 MneO5eC23 MneO5eH23 MneO1eC1 O1eC1eC2 C1eC2eN3 C2eN3eC3 C1eC2eC6 N3eC3eH3 C3eC4eC7 C4eC7eO3 C5eC8eN1 C8eN1eC17 N1eC17eC18 C17eC18eC19 N1eC17eC22 C1eC5eC8 O5eMneO6

92.9 89.8 91.6 96.7 83.3 174.9 125.9 98.3 129.4 118.1 122.6 119.7 118.6 116.1 120.3 110.1 126.6 121.4 125.5 120.8 109.2 122.4 166.6

O2eO1eN1e Mn O1eO2eMneN2 O2eN2eN1eO1 C1eO1eMneO5 C1eO1eO2eC9 C8eN1eN2eC16 O1eC1eC5eC4 O1eC1eC2eN3 O1eC1eC2eC6 C1eC2eN3eC3 C2eN3eC3eC4 N3eC3eC4eC7 C3eC4eC7eO3 C8eC5eC4eC7 O1eC1eC5eC8 C1eC5eC8eN1 C5eC8eN1eC17 C8eN1eC17eC22 C8eN1eC17eC18 N1eC17eC22eN2 C17eC18eC19eC20 Mne O1eC1eC5 Mne N1eC8eC5

0.0 0.0 0.0 96.7 0.0 0.0 180.0 180.0 0.0 0.0 0.0 180.0 0.0 0.0 0.0 0.0 180.0 180.0 0.0 0.0 0.0 0.0 0.0

absorption spectrophotometer. Also, the mass spectrum of the complex was recorded on a Shimadzu-GC-Mass-Qp 1100 Ex. The applied method for the determination of complex mass was atmospheric pressure chemical ionization (ACPI). 2.2. Synthesis of the Mn(II) complex (C24H28MnN4O6) The titled Schiff base (H2L¼C22H22N4O4) was synthesized as previously reported [24]. A solution of Mn(II) acetate tetrahydrate (245.1 mg, 1.0 mmol) in 6 mL methanol was added dropwise to a solution of the Schiff base (406.2 mg, 1.0 mmol) in 5 mL methanol. Then, the mixture was stirred for 6 h at 40e50 C. The obtained dark-red solid was filtered, washed with cold methanol and dried at room temperature. By increasing temperature even to 310 C, the obtained solid is neither melted nor decomposed. (Yield: 59%, the molecular ion peaks, m/z (Mþ) ¼ 523). 3. Computational details In this work, all of the calculations have been performed using the DFT method with the B3LYP functional [33] as implemented in the Gaussian 03 program package [34]. The 6-311þG(d,p) basis sets were employed expect for the Mn atom where the LANL2DZ basis sets were used. Geometry of the Mn complex was fully optimized, which was confirmed to have no imaginary frequency of the Hessian. Then, the gas phase optimized geometry was employed to compute the vibrational frequencies of the complex. The DFT vibrational wavenumbers are higher than the experimental ones, which can be corrected by applying the scaling of frequencies. Herein, the scale factor of 0.9614 was used for the calculated frequencies [35]. The AIM topological analyses were carried out in accordance with Bader’s approach [36] using AIMall package [37]. The DENSITY ¼ CURRENT option was used to generate the wavefunction files. 4. Results and discussion Synthesis and characterization of the titled Schiff base has been

reported, previously [24]. In this work, a Mn(II) complex of this Schiff base was newly synthesized and characterized using several experimental and theoretical methods. The experimentally percentage of the Mn2þ in the complex structure (10.58%) is consistent with the calculated ont, confirming the [Mn(L)(CH3OH)2] formula for the complex. 4.1. Geometry optimization The computational methods may be employed as complementary to or replacement for experimental ones in identification of the structural parameters and spectral behavior of the chemical species. Reported structures for the metal complexes of the Schiff bases involving the eOH group in close of the azomethine nitrogen (alpha position) show that the phenolic oxygens are deprotonated, regularly. Then the anionic oxygen is coordinated to the metal ions. Withdrawing property and resonance of the aromatic rings stable the negative charge of the phenolic oxygen. Since, deprotonation of the phenolic oxygens is very probable than the deprotonation of the alcoholic oxygens of the eCH2OH substituents (H9 and H17 atoms) or oxygen of the methanol ligands of the investigated complex. The structural parameters of the Mn(II) complex were computed theoretically, which are in consistent with the previously reported data for similar compounds [24e32,38e43]. Some of the calculated structural parameters of the complex are gathered in Table 1. Fig. 1 shows the optimized geometry of the complex with labeling of its atoms together with the optimized geometry of the H2L ligand for comparison. The H2L ligand has not planar-optimized geometry, but each of the pyridine rings and benzene ring are in a separate plane. The two pyridine rings make a dihedral angle of approximately 45 to each other. Both of the calculated C4eC5eC13eC12 and N3eC5eC13eN4 dihedral angles are 137. On the other hands, the coordinated L2 ligand has planar structure in the optimized geometry of the Mn complex. The calculated N3eC5eC13eN4 and C4eC5eC13eC12 dihedral angles are 0.0 and 0.1, respectively. In the optimized geometry of the free H2L ligand, the calculated O1eN1eN2eO2, C8eN1eN2eC16, C1eO1eO2eC9, N1eC17eC22eN2 and C3eC1eC9eC11 dihedral


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Fig. 1. Structure and optimized geometry of the [Mn(L)(CH3OH)2] complex together with its labeling together with the H2L ligand.

angles are, 48.1, 149.0, 170.5, 5.6 and 154.2 respectively, which change to 0.0 in the Mn complex. Calculated values of the C4eC5eC17eC22 and C17eC22eC13eC12 dihedral angles are 132.5 and 129.7 in the optimized geometry of the free ligand, respectively, both of which are 180.0 in the optimized geometry of the complex. This confirms that the benzene ring is in a same plane with te pyridine rings in the structure of the complex. The C]C (137.6e144.2 p.m.) and C]N (1351.7e135.4 p.m.) bond lengths of the aromatic rings are in the expected range [24e32,44,45]. The azomethine moieties are essentially in the same plane with the pyridine rings. The calculated C4eC5eC8eN1 and C12eC13eC16eN21 dihedral angles are 179.4 and 178.7 for the free ligand, both of which are 180.0 for the Mn complex,

respectively. The calculated pyridine-C bond lengths for the eCH2OH and eCH3 substitutions are about 151.4 and 150.2 p.m., respectively, which are appropriate sizes for the py-C bond. Also, all of the substitutions are essentially in the same plane with the pyridine rings. For example, all of the calculated C5eC4eC7eO3, C5eC1eC2eC6, C1eC5eC4eC7 and C4eC5eC8eN1dihedral angles are 180.0 . For complexation, the H2L ligand is firstly deprotonated to produce the L2 anion. The L2 acts as a dianionic-tetradentate ligand, which has an N,N,O,O binding mode. The deprotonated phenolic oxygens and the azomethine nitrogens of the L2 occupy four coordination positions of square plane of the octahedral

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Table 2 Selected experimental and calculated IR vibrational frequencies (cm1) of the Mn complex. Experimental frequencies

Calculated frequencies

IR intensity (km.mol1)

Vibrational assignment

437 528 568 650

486 519 561 632 646 726 980 990 1024 1059 1137 1163 1243 1276 1289 1297 1350 1369 1392 1402 1412 1453 1471 1475 1532 1538 1550 1558 1568 2842 2861 2911 2916 2952, 3011 2980, 3024 3036 3063, 3075 3080 3090 3635 3708

4 35 70 3 18 72 99 111 57 223 103 203 28 34 108 110 64 51 75 93 32 30 52 72 75 61 14 251 148 47 36 26 68 20, 16 28, 16 10 10, 11 11 4 97 65

y(MneO5, MneO6) y(MneO, MneN) dwagging(OeH) Methanol yasym(NeMneN, OeMneO) ysym(NeMneN, OeMneO) dout of plane (H atoms of the benzene ring) yasym(C4eC7eO3, C12eC15eO4) y(C23eO5, C24eO6) y(C5eC8, C13eC16, C1eC2, C9eC10) y(C7eO3, C15eO4)

(w) (m) (s) (s)

760 (m) 897 (m) 1021 (s) 1189 (s) 1267 (m) 1321 (m) 1339 (m) 1389 (m)

1474 (m)

1536 (m) 1602 (vs) 2889(w)

3012(m)

3415(vs, br) 3549(s,sh)

complex. These four donating atoms are roughly in the same plane with the Mn2þ central ion. Both of the calculated O2eN2eN1eO1 and O1eO2eN2eMn dihedral angles are 0.0 . Two methanol molecules fill two axial position of the octahedral geometry, which are perpendicular to the square plane (Table 1). However these molecules are not in a same direction. The calculated O5eMneO6 angle is166.6 . The C17eN1 and C22eN2 bond lengths are 141.6 and 141.5 p.m., which is appropriate size for the single CeN bond, while both of the C8eN1 and C16eN2 are 131.4 and 130.8 p.m., respectively, corresponding values to double C]N bond. The calculated structural parameters for the Mn complex are in good agreement with the previously reported data for the similar Schiff-base ligands and their complexes [24e32,38e43].

4.2. Vibrational spectroscopy Nowadays, theoretical analysis of the spectra is an important tool for identification of the chemical compounds [24e32,42,43,46]. In this work, the vibrational modes for the Mn2þ complex of the titled Schiff base were analyzed by comparing the DFT-computed and experimental results of the IR spectra. Assignments of the selected vibrational frequencies are gathered in Table 2. In the IR spectra of the Schiff bases, the energy value of a very

Breathing of the aromatic rings y(C17eN1, C22eN2) din plane (C3eH3, C11eC11) yasym(C]C) of the benzene ring y(C9eC10, C11eC12, C1eC2, C3eC4) y(C13eC16, C9eO2, C5eC8, C1eO1) y(C2eC6, C10eC14) din plane (C8eH10, C16eC18) y(C9eO2) y(C1eO) dscissoring of methyl groups dscissoring of methyl group of the methanol ligands y(C5eC8eN1)þ yasym(CeC, NeC) of the right pyridine ring yasym(C13eC16eN2)þ ysym(CeC, NeC) of the left pyridine ring y(C8eN1)þ yasym(CeC, NeC) of the right pyridine ring y(C16eN2)þ yasym(CeC, NeC) of the left pyridine ring yasym(CeC, NeC) of the pyridine rings y(C8eN1)þ y(C]C) of the benzene ring y(C16eN2)þ y(C]C) of the benzene ring ysym(CH2) of eCH2OH yasym(CH2) of eCH2OH ysym(CH) of Methyl substituent ysym(CH) of Methanol yasym(CH) of Methyl substituent yasym(CH) of Methanol y(C8eH10, C16eH18) yasym(CeH) of the benzene ring ysym(CeH) of the benzene ring y(C3eH3, C11eH11) y(OeH) of Methanol y(OeH) of eCH2OH

intensive band in the 1660e1500 cm1 region is an important characteristic for coordination mode of the Schiff-bases [24e32,44e49]. A very strong band at 1602 cm1 of the complex spectra is related to the y(C8]N1) and y(C16]N2) vibrations. Comparison between the IR spectra of the N,N0 -dipyridoxyl(1,2diaminobenzene) Schiff base and its Mn(II) complex shows that the stretching vibration of the C8]N1 and C16]N2 bonds shifts from 1615 cm1 for the Schiff base [24] to lower energy (by 13 cm1) for the Mn complex. This shift confirms coordination of the ligand to Mn(II) through the azomethine nitrogens (N1 and N2 atoms) [41,46,49]. The most intensive band is related to the stretching vibrations of the azomethine C]N bonds (Table 2), which is in consistent with the experimental spectrum of the complex. Another valuable evidence for identification of the complex structure is shifting of the phenolic CeO stretching vibrations. By the complex formation, the y(C1eO1) and y(C2eO9) vibrations shift to higher frequencies (by 11 cm1) than those of the free Schiff base (1378 cm1). Because of increasing in strength of these bonds by the deprotonation of the ligand and increasing of the electron density in these bonds. These values demonstrate the coordination of Schiff base to the Mn2þ ion via the azomethine nitrogens (N1 and N2 atoms) and phenolic oxygens (O1 and O2) [24e32,48,50]. Overlapping of the OeH and CeH stretching vibrations results in band broading in the 3600e2000 cm1 spectral region of the IR


19

(Fig. 2) it can be seen that the negative charge, presented by broken red line, is more localized on the nitrogen atoms than the oxygen ones. Because of the ring’s resonance has delocalized and the metal atom in presence of the coordinated methanol molecules has delocalized positive charge over the L2 moiety of the deprotonated H2L ligand. 4.4. The delocalization indices The electron delocalization between two atomic basins A and B, F(A, B), is given by the following expression (Eq. (1)) [52],

FðA; BÞ ¼

X

Si;j ðAÞSi;j ðBÞ

(1)

i;j

It is noteworthy that F(A, B) is equivalent to F(B, A) and the amount of their sum which is called the delocalization index, d(A, B), is a factor for the exchange extent of the electrons of the A with those the of B [53]. The d(A, B) values for the Mn as the A atom and the six coordinated atoms as the B can be obtained from the data of Table 3. The equal distribution of one electron between the A and B atoms necessarily needs that l(A) ¼ l(B) ¼ 0.5 and d(A, B) ¼ 1.0 and, therefore, d(A, B) ¼ 1, 2 or 3 for the corresponding numbers of shared electron pairs. If the sharing of an electron pair is accompanied by a electronic charge transfer from the A to the B, then the density localization in the atomic basins given and d(A, B) < 1.0, assuming values of ionic interactions is < 0.2 (Closed-shell interaction< 1.0). It has been shown that the d(A, B) value for an AeB

Fig. 2. 3D map of r and 2D map of the V2 r of the Mn complex.

Table 3 Topological properties at the BCP of the MneN and MneO bonds in the Mn complex of the [Mn(L)(CH3OH)2] and [Mn(H2O)6]2þ. Bond Mn(L)(CH3OH)2 MneN1 MneN2 MneO1 MneO2 MneO5 MneO6 [Mn(H2O)6]þ2 Mn1eO4 Mn1eO8 Mn1eO10 Mn1eO12 Mn1eO2 Mn1eO6

BPL

|q(A,B)|

d(A,B)

r

V2 r

G

V

H

E

G/r

3.7405 3.7353 3.6960 3.6828 4.1174 4.1174

0.3518 0.3440 0.4431 0.4408 0.0645 0.0643

0.5957 0.5825 0.4934 0.5119 0.3324 0.3323

0.094287 0.09543 0.085369 0.086627 0.049765 0.049766

0.469561 0.468234 0.54011 0.551044 0.320128 0.32014

0.136716 0.137294 0.141552 0.144611 0.077412 0.077415

0.15604 0.15753 0.14808 0.15146 0.07479 0.07479

0.01933 0.02024 0.00652 0.00685 0.00262 0.002621

0.07802 0.07877 0.07404 0.07573 0.0374 0.0374

1.449998 1.438688 1.658119 1.669353 1.555551 1.55558

4.1275 4.1272 4.1271 4.1275 4.1278 4.1278

0.2331 0.2330 0.2331 0.2331 0.2330 0.2330

0.2634 0.2633 0.2634 0.2633 0.2632 0.2632

0.050641 0.050662 0.050665 0.050639 0.050616 0.05062

0.257632 0.257777 0.257798 0.257616 0.257499 0.257524

0.063181 0.063218 0.063224 0.063177 0.063143 0.063149

0.06195 0.06199 0.062 0.06195 0.06191 0.06192

0.001227 0.001225 0.001225 0.001228 0.001232 0.001231

0.03096 0.03098 0.03096 0.031 0.031 0.03097

1.247625 1.247839 1.247883 1.247596 1.247491 1.247511

spectra [24e32,47,51]. Deconvolution of this region is given in Table 2, where the strongest band is the y(OeH) of the methanol ligands. Based on the DFT results, the y(OeH) vibrations of the methanol ligands are appeared at lower frequencies than the corresponding vibrations in the eCH2OH grous. Obviously, coordination of the O5 and O6 oxygens to the Mn2þ metal ion reduces electron density in the OeH bonds of the methanol molecules. 4.3. Enumerating the number of shared and localized electron pairs The chemical structure of the octahedral complex where two azomethine nitrogens, two phenolic oxygens and two oxygens of the methanol ligands are coordinated to the Mn2þ ion is determined by a bond linking the metal atom to the six-electron donating atoms. Electron pairs on the azomethine nitrogens increase the resonance of the rings. From the 2D counter map of V2 r

molecule is a function of the square of the transferred charge and reduces with charge transfer from values of one, two and three [54]. Hence, a value of the d(A, B) < 1 for an atom pair connected by a bond path does not mean that less than an electron pair is contributed between the A and B, but that they are unfairly shared. In addition, the d(A, B) for a pair which equally shared between two atoms in a molecule is fairly less than unity, because the electrons on the A and B atoms are more delocalized over other atoms of the system. At any rate, the d(A, B) value always presents the number of delocalized or exchanged electrons between the basins of the A and B atoms. The exchange or the number of electron pairs between the bonding atoms is a mechanism having the key role to understand the bond order. Therefore, the delocalization index d(A, B) determinates the number of electron pairs which exchanged between two atomic basins, can be used to judge about the bonding degree. In the AIM theory, the ‘shared interaction’ and ‘Closed-shell

20


Fig. 3. The QTAIM molecular graph of the Mn complex (small green spheres, small red squares, and lines represent BCP, RCP, and bond paths, respectively). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

interaction’ terms are used instead of the ‘covalent bond’ and ‘noncovalent bond’ terms, respectively. What is important is that the delocalization index, describes as the expectation value for the exchange operator over two atomic basins, supply a quantitative measure for the number of exchanged electrons in any given interaction, consequently, quantifying ‘interaction’ for those who interested to retain the term. As seen in Table 3, the delocalization index for equatorial atoms d(Mn,N1), d(Mn,N2), d(Mn,O1) and d(Mn,O2) are 0.5957, 0.5825, 0.4934 and 0.5119, respectively, which are greater than the delocalization index for the corresponding donating atoms of [Mn(H2O)6]þ2 complex (0.2633). This explains that all of the MneN1, MneN2, MneO1, MneO2 bonds are shared interaction. Also, the d(A, B) values for the Mn and axial oxygen atoms of the methanol ligands illustrate that the MneO5 and MneO6 bonding interactions are weaker than the other MneN and MneO interactions of the complex (Table 3). The delocalization index for MneO5 and MneO6 is closer to the MneO bonds of hexaaquamanganese(II) ion complex, showing that the axial oxygen interactions could be coordinate (dative covalent).

such as the E, r H, the axial bonds of two investigated complexes, it’s obvious that two bonds of methanol ligands are similar to the co-ordinance bonds of the H2O ligands. The q(A│B) is the absolute value of transferred charge between two atoms. This charge is along with bond length. As seen in Table 3, its magnitude for the MneN1, MneN2, MneO1 and MneO2 bonds is about 0.4, which is higher than the other investigated MneO bonds. On the other hand, their V2 r is positive while the HC is negative, and their -G/V is smaller than 1, confirming that the interaction nature of the MneN1, MneN2, MneO1 and MneO2 bonds is covalent. The values of MneO bond lengths of the [Mn(H2O)6]2þ complex is 4.13 bohr, which is 4.12 bohr for the methanol ligands. These bond lengths show that MneO5 and MneO6 bonds are in range of the dative bonds. But the length of the MneN1,MneN2,O1 and O2 bonds is 3.7 bohr. This short bond lengths confirm that the bonds of the MneO and MneN bonds of the L2 ligand are stronger than the MneO bonds of the methanol and water ligands. With this information in hand and also the topological parameter values, bonds of the L2 ligand can be considered as covalent bond and bonds of the methanol ligands can be coordinative bonds.

4.5. Describing on the based on the bond critical point (BCP) 5. Conclusion The bond critical point (BCP) data is shown in Table 3 and Fig. 3. A detailed discussion about the BCP properties of metaleligand and metalemetal bonding are presented by Macchi and Sironi [55]. The electron energy density, H, for a share interaction is negative [56], but is smaller than that for a bonded interaction which individually is shared and also combination of the BCP indices, pretty low values of the r, small negligible negative values for the H, the G/r>1 and also small positive values for the V2 r are exceptional to bonding to a metal atom [55,57]. So, by comparison of topological parameters of two complexes, it seems that the MneN and MneO bonding interactions of the L2 is stronger than coordinative bonds of the [Mn(H2O)6]2þ complex (Table 3). Based on the topological parameters, all of the six MneO bonds of the [Mn(H2O)6]2þ complex are coordinative interaction and are same to each other. By comparing values of topological parameters

Herein, synthesis, experimental and theoretical characterizations of the Mn(II) complex of titled Schiff-base (H2L) has been reported. Based on the experimental data, the [Mn(L)(CH3OH)2] formula was proposed for the complex. Geometry of the complex was fully optimized using the valuable DFT methods. Also, the IR vibrational frequencies of the Mn complex have been computed. The computed structural parameters and the IR frequencies of the octahedral complex are in agreement with the experimental data, confirming validity of the optimized geometry for the Mn(II) complex. In the investigated-octedral complex, the L2 as a dianionictetradentate ligand, which coordinates to the Mn2þ metal ion in a N,N,O,O manner. The O1 and O2 phenolic oxygens together with the azomethine nitrogens (N1, N2) occupy four coordinative


position of the square plane of the octahedral complex. These four coordinating atoms of L2 are roughly in the same plane with central metal ion. Two axial positions of the octahedral complex have been occupied by two methanol molecules. The calculated values such as d(A, B), q(A│B), the H, G/V and G/ r indicates that: bonding mode of the four coordinating atoms of the L2 ligand to the central metal is covalent. But, formed bonds between the oxygen atoms of two methanol ligands and the Mn2þ ion have coordinate (dative bond) property, which are weaker than the corresponding MneO bonds of the phenolic oxygens. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.molstruc.2016.07.026. References [1] S. Sadeghi, A. Gafarzadeh, H. Naeimi, PVC-based Cu (II)-Schiff base complex membrane coated graphite electrode for the determination of the triiodide ion, J. Anal. Chem. 61 (2006) 677e682. [2] K.C. Gupta, A.K. Sutar, Polymer anchored Schiff base complexes of transition metal ions and their catalytic activities in oxidation of phenol, J. Mol. Catal. A Chem. 272 (2007) 64e74. [3] N. Shahnaz, B. Banik, P. Das, A highly efficient schiff base derived palladium catalyst for the suzuki-miyaura reactions of aryl chlorides, Tetrahedron Let. 54 (2013) 2886e2889. [4] X. Cai, H. Wang, Q. Zhang, J. Tong, Z. Lei, Magnetically recyclable coreeshell Fe3O4@chitosan-Schiff base complexes as efficient catalysts for aerobic oxidation of cyclohexene under mild conditions, J. Mol. Catal. A Chem. 383e384 (2014) 217e224. [5] S. Bhunia, S. Koner, Tethering of nickel(II) Schiff-base complex onto mesoporous silica: an efficient heterogeneous catalyst for epoxidation of olefins, Polyhedron 30 (2011) 1857e1864. [6] J. Mao, N. Li, H. Li, X. Hu, Novel Schiff base complexes as catalysts in aerobic selective oxidation of b-isophorone, J. Mol. Catal. A Chem. 258 (2006) 178e184. [7] B.K. Rai, Synthesis, spectral and antimicrobial study of Co(II), Ni(II) and Cu(II) complexes with schiff bases of 3-pyridinyl n-pentyl ketone, J. Ind. Counc. Chem. 25 (2008) 137e141. [8] N. Dharmaraj, P. Viswanalhamurthi, K. Natarajan, Ruthenium (II) complexes containing bidentate Schiff bases and their antifungal activity, Trans. Met. Chem. 26 (2001) 105e109. [9] T. Jeeworth, H.L.K. Wah, M.G. Bhowon, D. Ghoorhoo, K. Babooram, Synthesis and antibacterial,catalytic properties of Schiff bases and Schiff base metal complexes derived from 2,3-diaminopyridine, Synth. React. Inorg. Met-Org. Chem. 30 (2000) 1023e1038. [10] M.I. Khan, A. Khan, I. Hussain, M.A. Khan, S. Gul, M. Iqbal, I.-U. Rahman, F. Khuda, Spectral, XRD, SEM and biological properties of new mononuclear Schiff base transition metal complexes, Inorg. Chem. Com. 35 (2013) 104e109. [11] G. Liu, J. Peiliao, S. Huang, G. Lishen, R. Qinyu, Fluorescence spectral study of interaction of water-soluble metal complexes of schiff-base and DNA, Anal. Sci. 17 (2001) 1031e1035. [12] S. Routier, J.-L. Bernier, J.-P. Catteau, P. Colson, C. Houssier, C. Rivalle, E. Bisagni, C. Bailly, Synthesis, DNA binding, and cleaving properties of an ellipticine-salen-copper conjugate, Bioconjugate Chem. 8 (1997) 789e792. [13] E. Lamour, S. Routier, J.-L. Bernier, J.-P. Catteau, C. Bailly, H. Vezin, Oxidation of CuII to CuIII, free Radical production, and DNA cleavage by hydroxy-salencopper complexes. Isomeric effects studied by esr and Electrochemistry, J. Am. Chem. Soc. 121 (1999) 1862e1869. [14] A.N.M.A. Alaghaz, M.E. Zayed, S.A. Alharbi, R.A.A. Ammar, A. Elhenawy, Synthesis, characterization, biological activity, molecular modeling and docking studies of complexes 4-(4-hydroxy)-3-(2-pyrazine-2-carbonyl)hydrazonomethylphenyl-diazen-yl-benzenesulfonamide with manganese(II), cobalt(II), nickel(II), zinc(II) and cadmium(II), J. Mol. Struct. 1084 (2015) 352e367. [15] C.G. Zhang, D. Wu, C.-X. Zhao, J. Sun, X.-F. Kong, Synthesis, crystal structure and properties of a manganese(III) Schiff-base complex: [{Mn(vanen)(Him)(H2O)}{Mn(vanen)(Him)2}](ClO4)2 $ 4H2O(H2vanen ¼ N,N0 -bis(methoxysalicylidene)-1,2-diaminoethane), Transit. Met. Chem. 24 (1999) 718e721. [16] E. Tas, M. Aslanoglu, M. Ulusoy, M. Guler, Synthesis, characterization and electrochemical studies of nickel(II) and cobalt(II) complexes with novel bidentate salicylaldimines, Polym. J. Chem. 78 (2004) 903e909. [17] R. Sevvel, S. Rajagopal, C. Srinivasan, N. Ismail Alhaji, A. Chellamani, Mechanism of selective oxidation of organic sulfides with Oxo (salen) chromium (V) complexes, J. Org. Chem. 65 (2000) 3334e3340. [18] B. Meunier, Metalloporphyrins as versatile catalysts for oxidation reactions and oxidative DNA cleavage, Chem. Rev. 92 (1992) 1411e1456.

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