Synthesis, characterisation, thermal properties and biological activity of coordination compounds of novel selenosemicarbazone ligands

Journal Pre-proof Synthesis, characterisation, thermal properties and biological activity of coordination compounds of novel selenosemicarbazone ligands Talib H. Mawat, Mohamad J. Al-Jeboori PII:

S0022-2860(20)30200-3

DOI:

https://doi.org/10.1016/j.molstruc.2020.127876

Reference:

MOLSTR 127876

To appear in:

Journal of Molecular Structure

Received Date: 5 July 2019 Revised Date:

7 February 2020

Accepted Date: 7 February 2020

Please cite this article as: T.H. Mawat, M.J. Al-Jeboori, Synthesis, characterisation, thermal properties and biological activity of coordination compounds of novel selenosemicarbazone ligands, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.127876. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2020 Published by Elsevier B.V.

Synthesis, characterisation, thermal properties and biological activity of coordination compounds of novel selenosemicarbazone ligands

Talib H. Mawat and Mohamad J. Al-Jeboori*

Department of Chemistry, College of Education for Pure Science (Ibn Al-Haitham), University of Baghdad, Adhamiyah, Baghdad, Iraq.

Correspondence should be addressed to Mohamad J. Al-Jeboori Email: [email protected]

Abstract A series of novel metal complexes with bidentate selenosemicarbazone Schiff-base ligands HL1 and HL2 are reported. The reaction of 2-(((3-nitrophenyl)amino)(phenyl) methyl)cyclohexan-1one and 2-((4-methoxyphenyl)(phenylamino)methyl)cyclohexan-1-one with an ethanolic mixture of KSeCN and NH2NH2 afforded the preparation of the new selenosemicarbazone ligands (E)-2-(2-(((3nitrophenyl) amino)(phenyl)methyl)cyclohexylidene)hydrazine-1-carboselenoamide (HL1) and (E)-2(2-((4-methoxyphenyl)(phenylamino)methyl)cyclohexylidene)hydrazine-1-carboselenoamide (HL2), respectively. The reaction of ligands with Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) metal ions resulted in the formation of mononucleating complexes of general formula K2[ML2Cl2] and [M`L2], (M= Mn(II), Co(II) and Ni(II); M`= Cu(II), Zn(II) and Cd(II)). The mode of bonding and predicted geometry of complexes were determined through their physico-chemical and spectroscopic measurements. These data indicated the formation of the following; (i) a distorted octahedral geometry about Mn(II), Co(II) and Ni(II), (ii) a distorted square planar around Cu(II), and (iii) a tetrahedral arrangement about Zn(II) and Cd(II) ions. The thermal properties and biological activity of ligands and their metal complexes were studied. The title ligands and their metal complexes were screened against Gram negative bacterial strains; Escherichia coli (E. coli), Bacillus sabtuius and Klebsiella pneumoniae and Gram positive bacterial strain Staphylococcus aureus that revealed the metal complexes become more potentially resistive to the microbial activities, compared to the free ligands. Further, selenosemicarbazone ligands and their complexes were examined for their antifungul activity towards Candida albicans, Candida glabrata, Candida tropicalis and Candida parapsilsis, which generally showed complexes are more active compared to the free ligands.

Keywords: Selenosemicarbazone ligands; Bidentate Schiff-bases; Structural study; Thermal stability; Biological activity. 1

1. Introduction The expansion of coordination chemistry is related to the development of synthetic approach that improved the preparation of organic ligands that act as chelating agents. These organic species may incorporate a variety of heteroatoms the “hard” such as N, O and the “soft” including S and Se, which act as a donor species upon coordination to the metal centre [1]. Organic compounds with nitrogen and selenium atoms are an interesting species that have the ability to form stable metalcomplexes with a variety of metal ions. Seleno-compounds including selenosemicarbazone ligands and their complexes display a range of biological and pharmaceutical applications. These include their role as antioxidant, anti-inflammatory, antibacterial, antiviral, and antitumor agents [2]. The uses of seleno-compounds as reagents are also reported in the field of analytical and biochemistry [3]. Subsequently, the introduction of selenium atom into the heterocyclic and homocyclic compounds have been explored to achieve seleno-compounds with low toxicity, high stability and excellent reactivity [4,5]. Therefore, the synthesis of seleno-heterocyclic and seleno-homocyclic compounds become an important issue in modern chemistry. This is due to their role in the biological and medicinal fields and their uses as intermediates in organic synthesis [6]. Accordingly, many synthetic methods for the preparation of seleno-based compounds has been extensively explored by researchers [7]. Although, selenosemicarbazone Schiff-bases represent excellent chelating agents that have the ability to form stable compounds, with transition and representative elements [8,9]. The literature survey revealed there are limited publications dealing with the synthesis of selenosemicarbazone ligands and their role as complexation agents with metal ions. The formation of selenosemicarbazone ligand can be achieved either from the condensation reaction of selenosemicarbazide with the appropriate aldehyde/ketone [10] or by the preparation of cyclohexanone selenosemicarbazone which can be converted into other substituted selenosemicarbazone ligands by reacting with the appropriate aldehydes [11]. Given that, selenosemicarbazide is no longer available commercially and the alternative conversion method is both time and materials consuming. Therefore, a straightforward procedure to prepare selenosemicarbazone ligands with good yield and stability is highly required. Accordingly, a direct and convenient method to synthesis the title selenosemicarbazone ligands is explored in this work. The formation of ligands was based on the reaction of functionalised cyclohexanone Mannich compounds, that prepared via a one-pot approach, with potassium selenocyanate and hydrazine reagents to incorporate the Se atom in the ligands framework and forming Schiff-bases. Two series of metal complexes were prepared from the reaction of ligands with a range of metal chloride. Compounds were characterised using a variety of physico-chemical 2

techniques. More, the prepared compounds were tested for their anti-bacterial and anti-fungal activities.

2. Experimental 2.1 Measurements Melting points were obtained on electrothermal Stuart apparatus, model SMP30. FTIR spectra were measured as KBr discs in the range 400-4000 cm–1 on a Biotech FTIR-600 FTIR spectrometer and as CsI discs in the range 250-4000 cm-1 on a Shimadzu FT–IR 8400S spectrometer. UV-visible absorption spectra were recorded in the range 200-1100 nm using a Shimadzu UV-160 spectrophotometer. The concentration of compounds used for the electronic measurements is 10-3 M in DMSO solvents at room temperature. 1H-, 77Se- and 13C-NMR spectra were acquired in DMSO-d6 solutions using a Brücker 400MHz and 300MHz spectrometer, respectively with tetramethylsilane (TMS) and dimethyl selenide (Me2Se) as an internal standard. The electrospray mass spectra (ESMS) were recorded using Agilent LCms sx spectrometer. Elemental analyses (CHN) were performed on anEuroEA 3000 instrument. Metals were determined using a 680G atomic absorption spectrophotometer (F.A.A). A potentiometeric titration method, using a 686-Titro processor665Dosimat-Metrohm Swiss, was employed to determine chloride content. Conductivity measurements were made with DMSO solutions using a CON 510 digital conductivity meter (Eutech Instruments), and room temperature magnetic moments were measured with a magnetic susceptibility balance (Sherwood Scientific Devised). Thermal analyses (Thermogravimetry (TG), Differential Thermogravimetry (DTG) and Differential Scanning Calorimetry (DSC)) were performed in the range of room temperature to 600°C under argon, with 5°C min-1 fixed heating rate. The analyses were made using a Linseis STA PT-1000 TG-DSC instrument.

2.2 Materials Reagents used in this work were purchased from commercial suppliers and used as received. Solvents were distilled prior to use. A standard procedure that reported in [12] was implemented to obtain

2-(((3-nitrophenyl)amino)(phenyl)methyl)cyclohexan-1-one

and

(2S)-2-((4-

methoxyphenyl)(phenylamino)- methyl)cyclohexan-1-one that used as precursors in the synthesis of ligands.

3

2.3 Preparation of HL1 A solution of 2-(((3-nitrophenyl)amino)(phenyl) methyl)cyclohexan-1-one (0.3 g, 1 mmol) in a mixture of 20 ml of CHCl3:EtOH (1:3), was added dropwise with stirring to a mixture of hydrazine hydrate (99.9%, 0.1 ml, 3 mmol), KSeCN (0.1 g, 0.7 mmol) and hydrochloride acid (36%, 0.1 ml, 3 mmol) in ethanol (20 ml). The reaction mixture was allowed to reflux for 3 h and then filtrated while it is hot to remove excess selenium. The solution was reduced to a half under vacuum, and allowed to cool at room temperature during which time a solid was formed that collected by filtration, washed with ether (5 ml) and dried in air. Yield: 0.153 g (51%), m.p= 244-246°C. FT-IR data (cm-1): 3524, 3460 ν(N4-H), 3444 (N3-H), 3383 (N1-H), 3024 (C-H)aromatic, 2943 (C-H)aliphatic., 1652 (C=N)imine, 1604 (C=C)aromatic, 1261 (C=Se)selenon 1180 (C-N), 1450 (N-H)Bend. The numbering of the assignment of the NMR data is based on that mentioned in Scheme (I). The 1H-NMR spectrum of the ligand (400MHz, DMSO-d6) showed peaks at ߜH;: 1.19-1.26 (2H, m, C4-H), 1.51-1.64 (2H, m, C5-H), 1.701.85 (2H, m, C3-H), 2.27-2.38 (2H, m, C6-H), 2.75-2.77 (1H, m, C2-H), 4.40 ppm (2H, s, N4-H), 4.78 (1H, dd, JHH= 11.4, 10.3 Hz, C7-H), 6.04 (1H, d, JHH= 10.5 Hz, N1-H), 6.43 (2H, dd, JHH= 9.4, 10.4 Hz, C16,16`-H), 6.54 (2H, d, JHH= 9.4 Hz, C15,15`-H), 6.75 (1H, t, JHH= 10.4 Hz, C17-H), 6.92 (1H, d, JHH= 7.7 Hz, C13-H), 7.17 (1H, d, JHH= 10.4 Hz, C11-H), 7.26 (1H, dd, JHH= 10.4, 7.7 Hz, C12-H), 7.33 (1H, s, C9-H), 7.75 (1H, br, N3-H), The

13

C-NMR spectrum of HL1 (75MHz, DMSO-d6) exhibits

signals at δC: 22.89 (C3), 27.90 (C4), 30.61 (C5), 40.97 (C6), 55.91 (C2), 58.21 (C7, C-H), 112.93 (C9), 115.73 (C11), 126.04 (C13), 127.06 (C17), 128.04 (C15,15`), 130.61 (C16,16`), 132.89 (C12), 143.21 (C14), 152.91(C8, C-NH), 155.68 (C10, C-NO2), 160.94 and 175.94 ppm related to C=N of the imine moiety and the C=Se group, respectively. The

77

Se-NMR spectrum of HL1 (76MHz,

DMSO) showed a singlet at δSe; 217.60 ppm (C=Se) group. The positive (ES) mass spectrum of HL1 (see Figure 1 a) showed the parent ion peak m/z= 445.6 amu (M+H)+ (21%) and the following fragments; 325.7 (73%) [M+H-(CH2N2Se)]+, 250.4 (53%) [(M+H)-{(CH2N2Se)+(C2H5NO2)}]+, 182.5

(100%)

[(M+H)-{(CH2N2Se)+(C2H5NO2)+(C5H8)}]+,

91.5

(36%)

[(M+H)-

+

{(CH2N2Se)+(C2H5NO2)+(C5H8)+(C6H5N)}] . 2.4 Preparation of HL2 A solution of (2S)-2-((4-methoxyphenyl)(phenylamino) methyl)cyclohexan-1-one (0.3 g, 1 mmol) in a mixture of 20 ml of CHCl3:EtOH (1:3), was added dropwise with stirring to a mixture of hydrazine hydrate (99.9%, 0.1 ml, 3 mmol), KSeCN (0.1 g, 0.7 mmol) and hydrochloride acid (36%, 4

0.1 ml, 3 mmol) in ethanol (20 ml). The reaction mixture was allowed to reflux for 3 h, and the solution was filtrated while it is hot to remove excess selenium. The solvent was reduced under vacuum and allowed to cool at room temperature. The solid that formed was collected by filtration. The solid was washed by ether (5 ml) and dried in air, Scheme (1). Yield: 0.15 g (50%), m.p= 243245°C. FT-IR data (cm-1): (3529, 3501) (N4-H), 3486 (N3-H), 3411 (N1-H), 3101 (C-H)aromatic, 2970 (C-H)aliphatic., 1641 (C=N)imine, 1597 (C=C)aromatic, 1257 (C=Se)selenon, 1161 (C-N), 1519 (N-H)Bend. The numbering of the assignment of the NMR data is based on that mentioned in Scheme (I). The 1HNMR spectrum of the ligand (400MHz, DMSO-d6) showed peaks at ߜH; 1.20-1.24 (2H, m, C4-H), 1.48-1.52 (2H, m, C5-H), 1.82-185 (2H, m, C3-H), 2.29-2.44 (2H, m, C6-H), 2.68-2.72 (1H, m, C2-H), 3.71 ppm (3H, s, OCH3), 4.19 (2H, br, N4-H), 4.72 (1H, dd, JHH= 11.4, 10.9 Hz, C7-H), 5.98 (1H, d, JHH= 10.8 Hz, N1-H), 6.43 (1H, t, JHH= 9.5 Hz, C11-H), 6.54 (2H, d, JHH= 10.4 Hz, C9,9`-H), 6.82 (2H, d, JHH= 11.4 Hz, C14,14`-H), 6.97 (2H, dd, JHH= 10.4, 9.5 Hz, C10,10`-H), 7.43 (2H, d, JHH= 11.4 Hz, C13,13`-H), 8.12 (1H, s, N3-H). The 13C-NMR spectrum of HL2 (75MHz, DMSO-d6) exhibits signals at δC;, 24.77 (C3), 27.89 (C4), 30.49 (C5), 40.86 (C6), 54.86 (C2), 55.09 (OCH3), 57.43 (C7, C-H), 113.03 (C9,9`), 114.45 (C14,14`), 115.68 (C11), 128.09 (C10,10`), 128.49 (C13,13`), 133.90 (C12), 147.94 (C8, C-NH), 155.68 (C15, OCH3), 159.99 and 174.94 ppm related to C=N of the imine moiety and the C=Se group. The 77Se-NMR spectrum of HL2 (76MHz, DMSO-d6) showed singlet at δSe; 226.39 ppm. The positive (ES) mass spectrum of HL2 (See Figure 2 a) showed the parent ion peak m/z= 452.4 amu (M+Na)+ (13%) and the following fragments; 334.4 (9%) [M+Na-(C6H7O)]+, 212.1 (100%) [(M+Na){(C6H7O)+(CH3N2Se)}]+, 147.4 (23%) [(M+Na)-{(C6H7O)+(CH3N2Se)+(C5H5)}]+, 55.4 (12%) [(M+Na)-{(C6H7O)+(CH3N2Se)+(C5H5)+(C6H6N)}]+. 2.5 General synthesis of metal complexes with ligands (HL1 and HL2) A mixture of the appropriate metal chloride salt (0.225 mmol) in 10 ml of ethanol was added drop-wise to a solution of the title ligand (0.451 mmol) in 20 ml of a mixture of CHCl3:EtOH (1:3). The pH of the reaction mixture was adjusted by adding potassium hydroxide to ca. pH= 9, and the reaction mixture was stirred for 3 h. The precipitate that formed was filtered off, washed with cold absolute ethanol (5 ml) and dried in air. Elemental analysis data, colours and yields of complexes are given in (Table 1).

5

ESMS data: The electrospray (+) mass spectrum of K2[Ni(L1)2Cl2] (see Figure 1 c) exhibited several peaks related to successive fragmentation of the molecule. The parent ion peak showed at m/z= 1094.21 (M)+ (15%) and the following fragments; 908.61 (21%) (M-(C4H10+NO2+2K+4H2))+, 726.63 (100%) [M-{(C4H10+NO2+2K+4H2)+(C9H4+2Cl)}]+,

477.21

{(C4H10+NO2+2K+4H2)+(C9H4+2Cl)+(C4H7N4NiSe)}]+,

(53%) 352.22

{(C4H10+NO2+2K+4H2)+(C9H4+2Cl)+(C4H7N4NiSe)+(C5H5N+NO2)}]+,

[M-

(82%) 92.22

(22%)

[M[M-

{(C4H10+NO2+2K+4H2)+(C9H4+2Cl)+(C4H7N4NiSe)+(C5H5N+NO2)+(C10H19N3Se)}]+ (see Figure 1 b). The positive (ES) mass spectrum of [Cd(L1)2] displayed the parent ion peak at m/z= 1002.21 (M)+ (15%) and the following fragments; 829.20 (22%) (M-(C9H5N+NO2))+, 519.62 (100%) [M{(C9H5N+NO2)+(C6H5N3CdSe)}]+,

313.21

{(C9H5N+NO2)+(C6H5N3CdSe)+(C6H13N3Se)}]+,

(54%) 106.81

(33%)

[M[M-

{(C9H5N+NO2)+(C6H5N3CdSe)+(C6H13N3Se)+(C11H15N+NO2)}]+. The electrospray (+) mass spectrum of K2[Mn(L2)2Cl2] (see Figure 2 b) showed the parent ion peak at m/z= 1061.11 (M)+ (14%) and the following fragments; 846.12 (24%) (M(C4H10N+OCH2+Cl+2K))+, 682.91 (100%) [M-{(C4H10N+OCH2+Cl+2K)+(CH6N2Se+2H2+Cl)}]+, 484.32 (50%) [M-{(C4H10N+OCH2+Cl+2K)+(CH6N2Se+2H2+Cl)+(CH6N3MnSe+2H2)}]+, 259.64 (31%)

[M-{(C4H10N+OCH2+Cl+2K)+(CH6N2Se+2H2+Cl)+(CH6N3MnSe+2H2)+(C15H15NO)}]+,

77.41 (17%) [M-{(C4H10N+OCH2+Cl+2K)+(CH6N2Se+2H2+Cl)+(CH6N3MnSe+2H2)+(C15H15NO)+ (C15H2)}]+. The mass spectrum of [Zn(L2)2] (see Figure 2 c) showed the parent ion peak at m/z= 922.31 (M)+ (21%) and the following fragments; 819.11 (20%) (M-(C6H15O))+, 702.52 (100%) [(M{(C6H15O)+(C8H7N)}]+, 501.11 (80%) [(M-{(C6H15O)+(C8H7N)+(CH3N3ZnSe)}]+, 267.91 (48%) [(M-{(C6H15O)+(C8H7N)+(CH3N3ZnSe)+(C8H17N3Se)}]+, 71.82 (26%) [(M-{(C6H15O)+(C8H7N)+ (CH3N3ZnSe)+(C8H17N3Se)+(C13H10NO)}]+.

6

Figure (1): Mass spectra of: a) HL1; b) K2[Ni(L1)2Cl2] and c) [Cd(L1)2].

Figure (2): Mass spectra of: a) HL2; b) K2[Ni(L2)2Cl2] and c) [Cd(L2)2].

NMR data: [Zn(L1)2]: The 1H-NMR spectrum of [Zn(L1)2] (400MHz, DMSO-d6) showed peaks at ߜH; 1.19-1.26 (2H, m, C4-H), 1.50-1.53 (2H, m, C5-H), 1.70-1.90 (2H, m, C3-H), 2.31-2.40 (2H, m, C6H), 2.72-2.76 (1H, m, C2-H), 4.39 (2H, s, N4-H), 4.77 (1H, dd, JHH= 12, 8 Hz C7-H), 5.95 (1H, d, JHH= 8 Hz, N1-H), 6.44 (2H, dd, JHH= 12, 8 Hz, C16,16`-H), 6.54 (2H, d, JHH= 12 Hz, C15,15`-H), 6.94 (1H, t, JHH= 8 Hz, C17-H), 7.17 (1H, d, JHH= 11 Hz, C13-H), 7.27 (1H, dd, JHH= 12, 11 Hz, C12-H), 7.35 (1H, d, JHH= 12 Hz, C11-H), 7.40 (1H, s, C9-H). The 13C-NMR spectrum of [Zn(L1)2] (100MHz, DMSO-d6) showed signals at ߜC; 22.90 (C3), 27.91 (C4), 30.61 (C5), 51.03 (C6), 55.70 (C2), 56.25 (C7, C-H), 112.94 (C9), 115.75 (C11), 126.72 (C13), 127.51 (C17), 128.55 (C15,15`), 131.46 (C16,16`), 135.85 (C12), 142.23 (C14), 147.92 (C8, C-NH), 153.61 (C10, C-NO2), 165.61 and 168.43 related to 7

C=N of the imine moiety and the C-Se group. The

77

Se-NMR spectrum of [Zn(L1)2] (76MHz,

DMSO-d6) exhibited singlet at δSe; 507.86 ppm. [Cd(L1)2]: The 1H-NMR spectrum of [Cd(L1)2] (400MHz, DMSO-d6) showed peaks at ߜH; 1.19-1.24 (2H, m, C4-H), 1.50-1.54 (2H, m, C5-H), 1.69-184 (2H, m, C3-H), 2.29-2.38 (2H, m, C6-H), 2.70-2.76 (1H, m, C2-H), 4.51 (2H, s, N4-H), 4.74 (1H, dd, JHH= 8, 12 Hz, C7-H), 6.04 (1H, d, JHH= 8 Hz, N1-H), 6.44 (2H, dd, JHH= 10, 12 Hz, C16,16`-H), 6.54 (2H, d, JHH= 10 Hz, C15,15`-H), 6.94 (1H, t, JHH= 12 Hz, C17-H), 7.17 (1H, d, JHH= 11 Hz, C13-H), 7.27 (1H, dd, JHH= 12, 11 Hz, C12-H), 7.35 (1H, d, JHH= 12 Hz, C11-H), 7.42 (1H, s, C9-H). The

13

C-NMR spectrum of [Cd(L1)2] (100MHz,

DMSO-d6) showed peaks at ߜC; 20.13 (C3), 27.91 (C4), 30.42 (C5), 50.76 (C6), 54.39 (C2), 64.05 (C7, C-H), 110.54 (C9), 113.13 (C11), 123.32 (C13), 126.14 (C17), 128.55 (C15,15`), 131.51 (C16,16`), 137.34 (C12), 141.17 (C14), 149.39 (C8, C-NH), 153.99 (C10, C-NO2), 164.26 and 166.23 related to C=N of the imine moiety and the C-Se group. The

77

Se-NMR spectrum of [Cd(L1)2] (76MHz,

DMSO-d6) exhibited singlet at δSe; 508.28 ppm. [Zn(L2)2]: The 1H-NMR spectrum of [Zn(L2)2] (400MHz, DMSO-d6) showed peaks at ߜH; 1.18-1.26 (2H, m, C4-H), 1.49-1.53 (2H, m, C5-H), 1.70-1.85 (2H, m, C3-H), 2.29-2.42 (2H, m, C6H), 2.65-2.70 (1H, m, C2-H), 3.69 (3H, s, OCH3), 4.37 (2H, s, N4-H), 4.72 (1H, dd, JHH= 11, 8 Hz, C7-H), 5.90 (1H, d, JHH= 11 Hz, N1-H), 6.43 (1H, t, JHH= 12 Hz, C11-H), 6.54 (2H, d, JHH= 11 Hz, C9,9`-H), 6.84 (2H, d, JHH= 12 Hz, C14,14`-H), 6.94 (2H, dd, JHH= 11, 12 Hz, C10,10`-H), 7.33 (2H, d, JHH= 12 Hz, C13,13`-H). The

13

C-NMR spectrum of [Zn(L2)2] (100MHz, DMSO-d6) showed peaks at

ߜC; 22.77 (C3), 27.89 (C4), 30.49 (C5), 47.38 (C6), 54.87 (C2), 56.44 (C7, C-H), 58.98 (OCH3), 113.04 (C9,9`), 113.47 (C14,14`), 115.70 (C11), 126.44 (C10,10`), 128.51 (C13,13`), 133.92 (C12), 147.96 (C8, C-NH), 153.91 (C15, OCH3), 165.35 and 167.45 related to C=N of the imine moiety and the C=Se group. The

77

Se-NMR spectrum of [Zn(L2)2] (76MHz, DMSO-d6) exhibited singlet at δSe;

520.66 ppm. [Cd(L2)2]: The 1H-NMR spectrum of [Cd(L2)2] (400MHz, DMSO-d6) showed peaks at ߜH; 1.19-1.26 (2H, m, C4-H), 1.50-1.55 (2H, m, C5-H), 1.70-1.85 (2H, m, C3-H), 2.30-2.40 (2H, m, C6H), 2.65-2.71 (1H, m, C2-H), 3.69 (3H, s, OCH3), 4.48 (2H, s, N4-H), 4.72 (1H, dd, JHH= 12, 12 Hz, C7-H), 5.98 (1H, d, JHH= 12 Hz, N1-H), 6.43 (1H, t, JHH= 12 Hz, C11-H), 6.54 (2H, d, JHH= 11 Hz, C9,9`-H), 6.84 (2H, d, JHH= 12 Hz, C14,14`-H), 6.94 (2H, dd, JHH= 11, 12 Hz, C10,10`-H), 7.30 (2H, d, JHH= 12 Hz, C13,13`-H). The 13C-NMR spectrum of [Cd(L2)2] (100MHz, DMSO-d6) displayed signals at ߜC; 21.82 (C3), 26.83 (C4), 30.49 (C5), 49.15 (C6), 54.87 (C2), 56.44 (C7, C-H), 57.07 (OCH3), 111.58 (C9,9`), 113.04 (C14,14`), 115.70 (C11), 125.26 (C10,10`), 128.51 (C13,13`), 133.92 (C12), 147.96 8

(C8, C-NH), 152.90 (C15, OCH3), 165.35 and 167.45 related to C=N of the imine moiety and the C=Se group. The 77Se-NMR spectrum of [Cd(L2)2] (76MHz, DMSO-d6) showed singlet at δSe; 537.05 ppm. 3.

Results and discussion The prepared ligands (HL1 and HL2) and their complexes are depicted in Schemes (1) and (2),

respectively. They isolated in good yields as air solids and soluble in CHCl3, DMSO and DMF, but not in other common organic solvents. The coordination geometries around metal centres were predicted from their physico-chemical analysis. The analytical data (Table 1) agree well with the suggested formulae. Conductivity measurements of HL1 and HL2 mononucleating complexes (see Table 1) in DMSO lie in the 3.80-68.65 cm2 Ω-1 mol-1 range, indicating their neutral and 2:1 electrolytic behaviour [13].

N4

10

H2N

Se

11

9 N3 HN

N2

N1

N

HN

1

7

2

6

3

5 4

8

10913

12

14 15

1314-

O

Scheme (1): Chemical structures of selenosemicarbazone ligands (HL1 and HL2).

Scheme (2): Synthesis route and proposed structures of selenosemicarbazone complexes. 9

Table 1: Colours, yields, elemental analyses and molar conductance values. Λ‫ܯ‬

Found, (Calc.)%

Yield (%)

Colour

HL1

51

Dark orange

244-246

K2[Mn(L1)2Cl2]Cl

68

Deep brown

276-278

K2[Co(L1)2Cl2]

59

Red brown

287-289

K2[Ni(L1)2Cl2]

63

Light orange

299-301

[Cu(L1)2]

58

Dark brown

296-298

[Zn(L1)2]

67

Light brown

288-290

[Cd(L1)2]

69

Deep brown

312-314

HL2

50

Dark orange

243-245

K2[Mn(L2)2 Cl2]

65

Brown

276-278

K2[Co(L2)2 Cl2]

57

Dark brown

287-289

K2[Ni(L2)2 Cl2]

50

Deep orange

299-301

[Cu(L2)2]

60

Dark brown

296-298

[Zn(L2)2]

42

Light brown

288-290

[Cd(L2)2]

54

Light brown

312-314

Compound

m.p. ºC C

H

N

53.98 (54.01) 43.96 (44.00) 43.80 (43.84) 43.81 (43.85) 50.46 (50.51) 50.40 (50.41) 48.00 (48.04) 58.65 (58.68) 47.46 (47.51) 47.30 (47.33) 47.31 (47.34) 54.71 (54.76) 54.62 (54.65) 51.91 (52.00)

5.17 (5.18) 4.00 (4.03) 4.00 (4.02) 4.00 (4.02) 4.60 (4.63) 4.60 (4.62) 4.38 (4.40) 6.01 (6.06) 4.69 (4.71) 4.66 (4.70) 4.66 (4.70) 5.48 (5.43) 5.40 (5.42) 5.12 (5.16)

15.74 (15.75) 12.80 (12.84) 12.75 (12.79) 12.75 (12.79) 14.70 (14.73) 14.65 (14.70) 14.00 (14.01) 13.01 (13.04) 10.53 (10.54) 10.50 (10.52) 10.50 (10.52) 12.14 (12.17) 12.12 (12.15) 11.53 (11.56)

M _ 5.02 (5.04) 5.33 (5.39) 5.34 (5.39) 6.71 (6.74) 6.80 (6.83) 11.18 (11.21) _ 5.15 (5.18) 5.50 (5.54) 5.51 (5.54) 6.92 (6.95) 7.01 (7.05) 11.53 (11.56)

Cl _ 6.40 (6.42) 6.35 (6.39) 6.37 (6.40)

(cm2Ω mol-1) _ 68.65 54.12 45.67

-

10.23

-

6.87

-

8.78

_

_

6.56 (6.60) 6.55 (6.57) 6.55 (6.58)

45.12

-

4.33

-

8.69

-

3.80

43.22

39.66

3.1 Spectral studies 3.1.1 FT-IR spectra The FT-IR spectra of HL1 and HL2 (see Table 2) show characteristic bands that related to the prominent functional groups; ν(C=N)imine, ν(C=C)aromatic, ν(C-H)aromatic and ν(C-H)aliphatic [14]. The recorded spectra indicated band around 3460-3529, 3444-3486 and 3383-3411 cm-1 attributed to ν(N4-H), ν(N3-H), and ν(N1-H), respectively. The title ligands can exist in a two tautomer, selenone or selenide form. The spectra indicated that both ligands exist in their selenone form. This has been confirmed by the existence of a band at ca. 1260 cm-1 attributed to ν(C-Se)selenon [15,16]. Further, the spectra showed no peak around 2400 cm-1 may assign to ν(Se-H).

10

Table 2: FT-IR frequencies in (cm-1) of compounds. Compound

ν(N4-H)

HL1 K2[Mn(L1)2Cl2]Cl K2[Co(L1)2Cl2] K2[Ni(L1)2Cl2] [Cu(L1)2] [Zn(L1)2] [Cd(L1)2] HL2 K2[Mn(L2)2 Cl2] K2[Co(L2)2 Cl2] K2[Ni(L2)2 Cl2] [Cu(L2)2] [Zn(L2)2] [Cd(L2)2]

3524 3460 3464 3379 3492 3441 3464 3414 3512 3496 3460 3410 3456 3414 3529 3501 3501 3464 3501 3464 3501 3464 3529 3486 3501 3456 3486 3448

ν(N3-H)

ν(N1-H)

ν(C=N)

ν(N=CSe)

ν(C=C)

3444

3383

1652

_

1512

_

3336

1646

1614

_

3383

1639

3383

1639

3383

1646

3375

1646

3383

1645

3486

3411

1641

_

3411

1638

3411

1638

3394

1630

3411

1635

3396

1636

3394

1636

_ _ _ _

_ _ _ _ _

1612 1613 1611 1616 1610 _

1610 1611 1613 1611 1611 1615

1577 1512 1590 1512 1585 1519 1581 1508 1589 1562 1581 1519 1573 1519 1587 1527 1590 1527 1589 1516 1585 1508 1588 1516 1582 1516

ν(C-Se)

ν(M-N)

ν(M-Se)

1261 775 1226 736 1234 756 1222 729 1226 736 1225 740 1219 759 1257 771 1230 759 1230 756 1222 752 1222 741 1222 752 1222 752

_

_

_

366

262

345

252

366

270

372

_

355

_

361

_

_

_

347

270

360

262

345

285

352

_

346

_

350

_

416 464 412 470 416 459 420 420 447 412 470 _ 420 443 420 443 416 447 416 462 412 435 412 447

ν(M-Cl)

3.1.2 NMR analysis The 1H-, 13C-, and 77Se-NMR spectra of HL1, HL2 and their [Zn(Ln)2] and [Cd(Ln)2] complexes (where n= 1 or 2) exhibit the required chemical shifts (see experimental part). In general, the 1H- and

13

C-NMR spectra of the free ligands and their metal complexes

revealed a two set of signals in the aliphatic and aromatic region. The 1H-NMR spectra of ligands (HL1 and HL2) in DMSO-d6 solvents revealed peaks at 7.75 and 8.12 ppm (1H, s) attributed to (N3-H) group for HL1 and HL2, respectively indicating the title ligands exist in their selenone form. Further, the spectra of [Zn(Ln)2] and [Cd(Ln)2] (where n= 1 or 2) show no peak around ~ 8 ppm may assign to (N3-H) group, indicating the deprotenation of N-H group upon complex formation. The

13

C-NMR

6

spectrum of each ligand in DMSO-d solvent (see Figures 1 a, 2 a) displayed a peak at ~175.50 ppm assigned to C=Se segment [21]. In the spectra of complexes, this peak has suffered upfield shift and appeared at ~ 168 ppm, confirming the involvement of the Se atom in the coordination to the metal 11

centre. Further, chemical shift that related to C=N imine moiety appeared downfield at ~ 166 ppm in the spectra of complexes, compared with that in the free ligands. The appearance of one chemical shift that related to C-Se and C=N, in the spectra of complexes, indicated both ligands are equivalent and ligands bound to the metal centre in a symmetrical fashion.

Figure (3): 13C-NMR spectra in DMSO-d6 solution of: a) HL1; b) K2[Ni(L1)2Cl2] and c) [Cd(L1)2].

Figure (4): 13C-NMR spectra in DMSO-d6 solution of: a) HL2; b) K2[Ni(L2)2Cl2] and c) [Cd(L2)2].

The 77Se-NMR spectra of HL1 and HL2 in DMSO-d6 solvents (Figure 3 a and 4 a) indicated a single peak at 217.60 and 226.39 ppm, respectively attributed to C=Se group [21]. The n

n

6

77

Se-NMR

spectra of [Zn(L )2] and [Cd(L )2] (where n= 1 or 2) in DMSO-d solvents (see Figures 3 b,c and 4 12

b,c) exhibited a singlet in the range 508-530 ppm related to (C-Se) group. The downfield shifting of chemical shifts in the pectra of complexes, compared with that in HL1 and HL2, may relate to complex formation [21]. The appearance of one peak in the spectra of the ligands and their diamagnetic complexes indicated the purity of the isolated compounds and the existence of one isomer in solution, on the NMR time scale. Further, the spectra of complexes revealed that in each complex the two coordinated ligands are symmetrical.

Figure (5): 77Se-NMR spectra in DMSO-d6 solution of: a) HL1; b) K2[Ni(L1)2Cl2] and c) [Cd(L1)2].

Figure (6): 77Se-NMR spectra in DMSO-d6 solution of: a) HL2; b) K2[Ni(L2)2Cl2] and c) [Cd(L2)2].

3.1.3 Electronic spectra and magnetic moment measurements The UV-Vis data of complexes of HL1 and HL2 (Figures 7 a and 8 a) showed peaks in the range 277-297 and 305-381 nm (see Table 3) related to the intra ligand π→π* and n→ߨ∗ transitions, respectively [15]. Complexes of Co(II), Ni(II), and Cu(II) with HL1 recorded peaks related to (CT) transitions. However, only Mn(II)-complex with HL2 displayed CT transition [23]. The electronic

13

spectral data and magnetic moments values of ligands and their metal complexes are collected in Table 3.

Table 3: Magnetic moment and UV-VIS spectral data in DMSO solutions. Compound HL1

ߤeff (BM) -

K2[Mn(L1)2Cl2]Cl

5.61

K2[Co(L1)2Cl2]

3.61

K2[Ni(L1)2Cl2]

2.63

[Cu(L1)2]

1.55

[Zn(L1)2]

Diamagnetic

[Cd(L1)2]

Diamagnetic

HL2

-

K2[Mn(L2)2 Cl2]

5.75

K2[Co(L2)2 Cl2]

3.69

K2[Ni(L2)2 Cl2]

2.55

[Cu(L2)2]

1.55

[Zn(L2)2]

Diamagnetic

[Cd(L2)2]

Diamagnetic

λmax, nm 265 310 282 381 483 848 280 305 345 810 284 310 375 450 751 278 310 348 841 284 378 292 381 262 315 277 351 395 540 735 297 338 799 275 348 623 735 286 365 680 279 365 282 311

14

εmax dm3 mol-1 cm-1 1123 988 1769 1342 66 23 1256 921 1145 45 933 1421 1388 86 50 1166 875 1089 71 764 1045 1006 1345 1343 1063 734 898 987 78 96 1356 1275 21 1144 1067 43 61 945 839 40 764 1045 1006 1345

Assignment π → π* n→ π* π → π* n→ π* 6 A1g(F)→4T2g(G) 6 A1g(F)→4T1g(G) π → π* n→ π* C.T. 4 T1g(F)→4T2g(F) π → π* n→ π* C.T. 3 A2g→3T1g(P) 3 A2g→3T2g(F) π → π* n→ π* C.T. 2 B1g→2B2g π → π* n→ π* π → π* n→ π* π → π* n→ π* π → π* n→ π* C.T. 6 A1g(F)→4T2g(G) 6 A1g(F)→4T1g(G) π → π* n→ π* 4 T1g(F)→4T2g(F) π → π* n→ π* 3 A2g→3T2g(F) 3 A2g→3T1g(F) π → π* n→ π* 2 B1g→2B2g π → π* n→ π* π → π* n→ π*

The UV-Vis spectra of Mn(II) complexes (Figures 7 b and 7 b) revealed peaks in the range 483-540 and 735-848 nm assigned to 6A1g(F)→4T2g(G) and 6A1g(F)→4T1g(G) transitions, respectively indicating a distorted octahedral sphere about Mn(II) ion [24]. The magnetic moment values are consistent with their octahedral assignment [25]. The electronic spectra of Co(ӀӀ) complexes (Figure 7 c) display peaks in the d-d region between 799-810 nm due to 4T1g(F)→4T2g(F) transition. These spectra are characteristic for Co(II) complexes that adopt octahedral geometries [24]. The electronic spectra of Ni(II) complexes showed peaks between 450-623 and 735-751 nm attributed to 3

A2g→3T1g(P) and 3A2g→3T2g(F) transitions, respectively confirming a distorted octahedral geometry

about Ni(II) atom [24]. The electronic spectra of Co(II) and Ni(II) complexes and their magnetic moment values are in agreement with the distorted octahedral structure [24]. The Cu(II) complexes (Figure 8 c) displayed a peak in the d-d section at 680 or 841 nm attributed to 2B1g→2B2g transition, indicating a distorted square planar geometry about Cu(II) atom [26]. The recorded spectra and the µ eff values of Cu(II) complexes are in agreement with the suggested geometry. The spectra of Zn(II) and Cd(II) complexes exhibited bands assigned to ligand field ߨ→ߨ∗ and n→π* transitions [27]. The tetrahedral geometry structure is suggested for the Zn(II) and Cd(II) centre [28].

15

Figure (8): UV-Vis spectra in DMSO solutions of: a) HL2; b) K2[Mn(L2)2Cl2] and c) [Cu(L2)2].

Figure (7): UV-Vis spectra in DMSO solutions of: a) HL1; b) K2[Mn(L1)2Cl2] and c) K2[Co(L1)2Cl2].

16

3.2 Thermal analysis The TGA, DSC and DTG data of HL1, HL2 and selected complexes are collected in Table 4 and depicted in Figures 9 and 10. The TG, DSC and DTG curves of ligands and their complexes were examined from ambient temperature to 600 ºC in an argon atmosphere. The analysis of thermal data showed HL1 is stable up to 133.3 ºC. The DSC analysis curve recorded several peaks including that at 146.9, 294.4 and 348.9 ºC. In the TGA curve, the peak between 133.3-245.0 ºC where (N2H4+C4H4O+3CH4) segments (obs.= 7.4754 mg; calc.= 7.4708 mg, 37.35%). The peaks detected at 344.7 and 594.9 ºC correlated to the elimination of (2HCN+2C4H4Se) (obs.= 8.5211 mg; calc.= 8.5135 mg, 42.57%) and (2HCl+C6H6+CH4) (obs.= 4.4816 mg; calc.= 4.4820 mg, 22.41%), respectively. Thermal decomposition data of Mn(ӀӀ) and Cu(ӀӀ) selenosemicarbazone (HL1) complexes appeared to be stable up to 118.1 and 90.1 ºC, respectively. The first step in TGA curve displayed between 118.1-239.2 and 90.1-243.4 ºC, correspond to elimination of (CH4+C6H6+2HCl) (obs.= 4.1323 mg; calc.= 4.1312 mg, 21.74%) and (N2+C2H4+3HCN) (obs.= 3.0239 mg; calc.= 3.0284 mg, 14.42%) for Mn(ӀӀ) and Cu(ӀӀ) complexes respectively. The second process showed at 354.5 and 352.3 ºC due to loss of (N2H4+HCN+C4H4Se+C2H6) (obs.= 3.8627 mg; calc.= 3.8697 mg, 20.37%) and (C6H6) (obs.= 1.6789 mg; calc.= 1.6800 mg, 8.00%) for Mn(ӀӀ) and Cu(ӀӀ) complexes respectively. Whereas, the third process of Mn(ӀӀ) and Cu(ӀӀ) recorded at 595.2 and 595.4 ºC assigned to the elimination of (CH4+C6H6) (obs.= 1.6279 mg; calc.= 1.6211 mg, 8.53%) and (N2H4+CH4+C4H4Se) (obs.= 3.9970 mg; calc.= 4.0010 mg, 19.05%), respectively. The DSC curve analysis displayed peaks at 194.7, 348.9, 480.3 and 565.8 ºC for Mn(ӀӀ) complex. While Cu(ӀӀ) complex showed peaks at 194.7, 348.9, 480.3 and 565.8 ºC which due to exothermic and endothermic composition processes (see Figure 5 a and b). The TGA curve of ligand HL2 and its complexes were determined from ambient temperature to 600°C in the atmosphere of argon. The TGA-DSC data of the ligand HL2 is stable up to 52.3-89.7 ºC. The first mass loss is related to (NH3); (obs.= 0.8407 mg; calc.= 0.8322 mg, 3.96%), see Figure (6 a and b). Peaks at 253.1, 361.6 and 594.4 ºC attributed to the removal of (HCN+C2H2+C4H4O) (obs.= 6.0811 mg; calc.= 6.0699 mg, 28.90%), (HCN+C2H2) (obs.= 2.5526 mg; calc.= 2.5455 mg, 12.12%) and (N2H4+CH4) (obs.= 2.2384 mg; calc.= 2.2518 mg, 10.72%), respectively. The DSC curve shows several peaks including that at 83.9, 182.2, 250.2, 410.3, 526.2 and 564.3 ºC. The TGA curves of Co(ӀӀ) and Cd(ӀӀ) selenosemicarbazone complexes of HL2 displayed a process about 252.3 ºC attributed to the mass loss of (C5H10+3N2+3C6H6+2HCl) (obs.= 8.6112 mg; calc.= 8.6197 mg, 43.10%) and (3CH4+C4H4Se) (obs.= 3.8067 mg; calc.= 3.7977 mg, 18.99%) for 17

Co(ӀӀ) and Cd(ӀӀ), respectively. The second process that recorded at 346.8 and 391.6 ºC due to the mass loss of (N2+2C4H4O+3C6H6) (obs.= 7.3416 mg; calc.= 7.3427 mg, 36.71%) and (3N2+2C6H6+7CH4+2HCN) (obs.= 8.5201 mg; calc.= 8.5243 mg, 42.62%) for Co(ӀӀ) and Cd(ӀӀ) complexes, respectively. Further, a third process that observed at 595.1 ºC assigned to the elimination of (2C6H6+CH4) (obs.= 3.8067 mg; calc.= 3.8122 mg, 19.06%) and (C6H6) (obs.= 1.5214 mg; calc.= 1.5273 mg, 7.64%) for Co(ӀӀ) and Cd(ӀӀ) respectively. Complex Co(ӀӀ) displayed peaks in the DSC analysis at 191.7, 240.1 and 391.2 ºC. Whereas Cd(II) complex noticed peaks at 177.6, 209.6, 257.5, 334.1, 551.2 and 582.1 ºC related to exothermic and endothermic composition processes.

Figure (9): TGA, DSC and DTG analyses data of HL1 and their M(II) and Cu(II) compounds

Figure (10): TGA and DSC analyses data of HL2 and their Co(II) and Cd(II) compounds

18

Table 4: TGA/DSC/DTG/ data of ligands HL1, HL2 and their metal complexes. Compound

Stable up to °C

Stage

Decomposition temperature initial-final °C

Nature of transformation/intermediate formed% mass found (calc.)

HL1

133.3

1 2 3

133-245 246-345 346-595

7.4754 (7.4708) 8.5211 (8.5135) 4.4816 (4.4820)

K2[Mn(L1)2Cl2]

118.1

1

118-239

4.1323 (4.1312)

[Cu(L1)2]

90.1

2 3 1 2 3

240-355 356-595 90-243 244-352 353-595

3.8627 (3.8697) 1.6279 (1.6211) 3.0239 (3.0284) 1.6789 (1.6800) 3.9970 (4.0010)

HL2

52.3

1 2

52-90 91-253

0.8407 (0.8322) 6.0811 (6.0699)

3 4

254-362 363-595

2.5526 (2.5455) 2.2384 (2.2518)

410.3 Exo 526.3 Endo 564.3 Endo 191.7 Exo 240.1 Endo 391.2 Endo

K2[Co(L2)2Cl2]

151.2

1 2 3

151-252 253-347 348-595

8.6112 (8.6197) 7.3416 (7.3427) 3.8067 (3.8122)

[Cd(L1)2]

105.2

1 2

160-392 393-595

8.5201 (8.5243) 1.5214 (1.5273)

Nature of DSC peak and temp. ° C 146.9 Exo 294.4 Exo 348.9 Endo

DTG peak temp. °C

160.3 Exo 215.3 Endo 398.4 Endo 398.4 Endo 194.7 Exo 348.9 Exo 480.3 Endo 565.8 Endo 83.9 Exo 182.2 Exo 250.2 Exo

193.9

177.6 Exo 209.6 Exo 257.5 Exo 334.1Exo 551.2 Endo 582.1 Exo

179.4 294.4 373.2

276.8 541.2 194.5 275.7 475.3 74.7 178.1 302.8 389.5

217.7 293.4 378.0 471.2 295.3 419.2

3.3 Biological activity Biological activity of the prepared ligands and their metal complexes against four types of bacteria; Escherichia coli, Staphylococcus aureus, Bacillus sabtuius and Klebsiella pneumoniac and four fungi pathogens; Candida albicans, Candida glabrata, Candida tropicalis and Candida parapsilsis were investigated using Mueller Hinton agar method [29]. In this method, the wells were dug in the media with the help of a sterile metallic borer with centres at least 6 mm. The concentration that used is (100 µL) of the test sample, 1 mg/mL in DMSO was introduced in the respective wells. The plates were incubated immediately at 37 °C for 24 h.

19

Samples were examined by measuring the diameter of inhibition zones using DMSO as control in the biological screening. The DMSO solution showed no activity against any bacterial and fungal strains. Ligands (HL1 and HL2) and their metal (II) complexes (M= Mn, Co, Ni, Cu, Zn and Cd) were screened against Gram negative bacterial strains Escherichia coli, Bacillus sabtuius and Klebsiella pneumoniac and Gram positive bacterial strain Staphylococcus aureus (see Table 5). In general, the title complexes showed more antimicrobial activity against all bacterial types. Complexes of Zn(II) and Cd(II) with HL1 and HL2 revealed the highest activity against Escherichia coli strain, compared with other complexes. Whereas, the Ni(II) complex of HL2 displayed the lowest bacterial activity. The increased activity of complexes can be discussed on the basis of chelation theory and Overtone’s model [30]. According to the chelation approach, complex formation could help the complex to cross a cell membrane of microorganism. This is related to the influence of M-N and M-Se, in which excess of electron that provided by ligand is shared with the metal ion, (Supporting Information, Figures SI 1-8). The activity of ligands and their complexes against fungi pathogens are listed in Table 6. The following observations are concluded: •

Ligands (HL1 and HL2) were found to be active against all fungi species (except Candida parapsilsis strain).

•

Complexes of HL1 and HL2 showed activity against Candida albicans, Candida glabrata and Candida parapsilsis (bar Cd(II) complex of HL1, which shows no activity against Candida albicans strain).

•

Complexes of HL1 appeared to be active against Candida tropicalis strains (except Mn(II) and Co(II) complexes).

•

Complexes of HL2 indicated activity against Candida tropicalis. However, the Co(II) complex showed no activity against this type of fungi (Supporting Information, Figures SI 9-16).

20

Table 5: Bacterial activity of ligands (HL1, HL2) and their complexes. Sample HL1 K2[Mn(L1)2Cl2]Cl K2[Co(L1)2Cl2] K2[Ni(L1)2Cl2] [Cu(L1)2] [Zn(L1)2] [Cd(L1)2] HL2 K2[Mn(L2)2 Cl2] K2[Co(L2)2 Cl2] K2[Ni(L2)2 Cl2] [Cu(L2)2] [Zn(L2)2] [Cd(L2)2]

E. coli

14 15 16 18 20 22 21 11 13 15 16 17 20 22

Inhibition zone (mm) B. sabtuius S. aureus

12 13 17 19 21 21 20 10 13 16 15 18 21 19

11 12 13 12 18 19 18 10 12 13 11 19 18 14

K. pneumoniac

12 13 17 13 14 21 19 12 14 15 13 17 16 13

Table 6: Fungal activity of ligands (HL1, HL2) and their complexes. Sample HL1 K2[Mn(L1)2Cl2]Cl K2[Co(L1)2Cl2] K2[Ni(L1)2Cl2] [Cu(L1)2] [Zn(L1)2] [Cd(L1)2] HL2 K2[Mn(L2)2 Cl2] K2[Co(L2)2 Cl2] K2[Ni(L2)2 Cl2] [Cu(L2)2] [Zn(L2)2] [Cd(L2)2]

4.

Candida Albicans

Inhibition zone (mm) Candida Candida Glabrata tropicalis

10 17 16 13 15 11 _ 11 12 13 14 16 17 11

15 10 9 11 12 13 11 15 16 17 11 10 12 11

16 _ _ 11 12 15 17 10 11 _ 13 18 17 16

Candida parapsilsis _ 10 11 16 17 19 20 _ 9 11 10 12 13 15

Conclusions A series of twelve selenosemicarbazone-based transition metal coordination compounds

(where M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)) coordinated to the novel ligands (E)-2(2-(((3-nitrophenyl) amino) (phenyl)methyl) cyclohexylidene)hydrazine-1-carboselenoamide (HL1) 21

and

(E)-2-(2-((4-methoxyphenyl)

(phenylamino)methyl)

cyclohexylidene)hydrazine-1-

carboselenoamide (HL2) have been successfully synthesised and characterised. The formation of ligands was achieved from the reaction of Mannich-based compounds with simple precursors, KSeCN and NH2NH2. Upon complex formation, the title ligands deprotonated and behave as a monobasic species and coordinated to the metal centre via the imine nitrogen and selenium atom. Ligands and their metal complexes were characterised using a range of physico-chemical analyses including thermal properties. The formation of six coordinate complexes is concluded for HL1 and HL2 complexes with Mn(II), Co(II) and Ni(II), in which the vacant two orbitals on the metal centre is occupied by the chlorido moieties. Further, complexes of Cu(II) and Zn(II), Cd(II) with HL1 and HL2 revealed the isolation of a square–planar and tetrahedral arrangement, respectively. The biological activity of the title compounds against bacterial species and fungi pathogens were also tested. Generally, selenosemicarbazone complexes showed more antimicrobial activities, compared with the free ligands.

Acknowledgments Authors are grateful to the Iraqi Ministry for Higher Education and Scientific Research, University of Baghdad and College of Education for Pure Science (Ibn Al-Haitham) for providing Mr THM the PhD studentship and labs facilities.

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Highlights • •

A direct method for the synthesis of novel selenosemicarbazone ligands is described. Two novel series of M(II) complexes (M= Mn, Co, Ni, Cu, Zn and Cd) are reported.

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TGA and DSC analyses were performed to check on thermal stability of compounds.

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Metal complexes indicated more antimicrobial activities, compared with free ligands.

Author contribution section: Synthetic Chemistry; Inorganic and Coordination Chemistry; Spectroscopic Studies.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: N/A.