Rational synthesis, structural characterization, theoretical studies, antibacterial activity and selective dye absorption of new silver coordination polymers generated from a flexible bis (imidazole-2-thione) ligand

Journal Pre-proofs Rational synthesis, structural characterization, theoretical studies, antibacterial activity and selective dye absorption of new silver coordination polymers generated from a flexible bis (imidazole-2-thione) ligand Azizolla Beheshti, Fatemeh Panahi, Susan Soleymani-Babadi, Peter Mayer, Janusz Lipkowski, Hossein Motamedi, Sepideh Samiee PII: DOI: Reference:

S0020-1693(19)31528-2 https://doi.org/10.1016/j.ica.2019.119406 ICA 119406

To appear in:

Inorganica Chimica Acta

Received Date: Revised Date: Accepted Date:

7 October 2019 28 December 2019 29 December 2019

Please cite this article as: A. Beheshti, F. Panahi, S. Soleymani-Babadi, P. Mayer, J. Lipkowski, H. Motamedi, S. Samiee, Rational synthesis, structural characterization, theoretical studies, antibacterial activity and selective dye absorption of new silver coordination polymers generated from a flexible bis (imidazole-2-thione) ligand, Inorganica Chimica Acta (2020), doi: https://doi.org/10.1016/j.ica.2019.119406

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Rational

synthesis,

structural

characterization,

theoretical

studies,

antibacterial activity and selective dye absorption of new silver coordination polymers generated from a flexible bis (imidazole-2-thione) ligand Azizolla Beheshti a*, Fatemeh Panahi a, Susan Soleymani-Babadi a, Peter Mayer b, Janusz Lipkowski c, Hossein Motamedi d, Sepideh Samiee a aDepartment

of Chemistry, Faculty of Sciences, Shahid Chamran University of Ahvaz, Ahvaz, Iran München Department Chemie, Butenandtstr, 5-13 (D) 81377, München , Germany cUniwersytet Kardynala Stefana Wyszynskiego Wydzial Matematyczno-Przrodniczy Woycickiego 1/301938 Warszawa, Poland dDepartment of Biology, Faculty of Sciences, Biotechnology and Biological Science Research Center, ShahidChamran University of Ahvaz, Ahvaz, Iran bLMU

*E-mail address: [email protected]; Tel: +98 61 33331042; Fax: +98 61 33331042

Abstract Herein, a competition between the different anions with different size, shape and coordination ability was used for the synthesis of three silver(I)-coordination polymers (Ag-CPs) was investigated. In this study, three 3D-supra-molecular coordination compounds namely, [Ag2L(NO3)2]n (1), {[Ag2L][PF6]2}n (2) and [AgLBr]n (3) (L =1,1’-(1,5-pentadienyl)bis-(1,3dihydro-3-methyl-1H-imidazole-2-thione)) have been synthesized and fully characterized via a single crystal X-ray diffraction, powder X-ray diffraction (PXRD), elemental analysis (CHN), FT-IR spectra and thermo gravimetric analysis (TGA). Structural analysis revealed that the counter ions have a notable impact in directing the conformation and coordination mode of ligand, but they have no effect on the structural dimension of the polymers. Furthermore, by increasing the coordination ability of the anions, the coordination geometry of the AgI centers change, from a distorted linear (for 2) to a distorted square pyramidal coordination geometry (for 1).The chains are further stabilized by the intermolecular C−H···O and C−H···N for 1, P–F…H–C for 2, C−H···Br and C−H···N interactions for 3 to form a 3D non-covalent lattice network structure. In contrast to the 1 and 3, polymer 2 exhibits a large capacity and selectivity to adsorb dye from aqueous solutions. Sorption kinetic was investigated by three kinetic models. The electronic band structure and the projection densities of states (PDOS) of compounds 1 and 3 were investigated by

means of DFT-D3. The results demonstrated that both compounds are non-magnetic and show a semiconducting character with a direct band gap of ~ 3 eV. All of the synthesized compounds, possess antibacterial activity against the selected strain of Gram- negative (Escherichiacoli, Pseudomonas aeruginosa) and Gram- positive (Staphylococcus aureus, Bacillus subtilis) bacteria. keywords: 3D supra molecular; Sulfur donor ligand; Selective dye absorbtion; Antibacterial activity; DFT calculation.

1.Introduction More recently, there is growing interest in the design and preparation of coordination polymers (CPs) not only due to their wide range of potential applications in the various fields like gas storage, separation, absorbent, sensor, drug delivery, luminescence, opt device and photocatalytic abilities but also owing to their attractive topological architectures [1−10]. Organic linkers and metal centers are considered as dominant factors to obtain CPs with interesting structures. It is hard to predict the final structure of CPs or 3D supra-molecular compound, since different factors, including organic linkers, temperature, coordination geometry of metal centers and solvents are influenced in the self-assembly procedure of these materials [11-13]. 3D supra-molecular CPs can be obtained via a variety of parameters like intramolecular hydrogen bonding, π-π staking, nature and size of counter ions and metal-ligand interactions [14-17]. Among these factors, ligand-spacer length, noncovalent bond interactions and counter ion have a positive impact in the design and construction of these compounds. It is well known that the use of flexible or semi flexible ligands in the synthesis of CPs usually ends up with the formation of interpenetration and versatile structures with interesting properties [18,19]. Flexible 1, 1’-(1, 5- pentadienyl) bis-(1, 3-dihydro3-methyl-1H-imidazole- 2-thione) linker, as an S-donor ligand, is a good candidate to obtain outstanding structures (scheme 1). Moreover, changing the nature and size of counter ions have been widely studied for the construction of new 3D supra-molecular CPs with intriguing versatile architectures [20-22]. On other hand, environmental pollution has become so serious that some of the systematic studies being conducted to address this issue [23-25]. Many of waste materials contain hazardous organic including dyes. Various processes such as adsorption and photocatalytic degradation have been

established for removal of dyes [26-28]. Among these, adsorption process is considered as the preferred route on account of its eco-friendly and simplistic execution process. Adsorption of dyes from wastewater by the absorbents depends on the structural properties of the absorbents [29-35]. In this field, the presence of suitable cavities in the structure of CPs have a substantial role for absorption of the dyes from the wastewater. Inspired from the above-mentioned factors, in the present work we have presented three new silver based coordination polymers based on the flexible S-donor ligands namely, [Ag2L(NO3)2]n (1), {[Ag2L][PF6]2}n (2) and [AgLBr]n (3). They were characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. The dye adsorption and antibacterial activity of the considered compounds were also implemented. S

H3 C

N

N

N

N

CH3

=

S

S

S

S

Ag OO N O

O N OO Ag

S

CH OH 3

CH

O /H 2 H O 3

AgNO + 3 KPF

6

Br K + 3 NO H O Ag 3 CH

NO 3 Ag

2+ S

Ag OO N O

S

Ag

S

S

Ag

S

S Ag

2.(PF6)n

S

S

Br Ag Br

n

Scheme 1. Synthesis procedure for the preparation of Ag (I) coordination polymers.

2. Experimental 2.1. Materials

S n

All experiments were carried out in air. Starting materials were reagent grade and used as commercially obtained without further purification. The 1,1’-(1,5- pentadienyl) bis-(1,3-dihydro3-methyl-1H-imidazole-2-thione) as a ligand was prepared by the literature methods via the reaction of 1-methylimidazole in methanol with the 1,5-dibromopentane and S8 in the presence of K2CO3 [36].

2.2. Preparation of [Ag2L(NO3)2]n (1) The ligand (29 mg, 0.1 mmol) and silver nitrate (34 mg, 0.2 mmol) were placed in the main arm of a branched tube. A methanol/water mixture (3:1 v/v) was added to fill the arms. The tube was sealed and the arm containing the reagents was immersed in an oil bath at 60 °C, while the other arm was kept at ambient temperature. After 3 days, colorless filament crystals of [Ag2L(NO3)2]n , suitable for X-ray analysis were deposited in the cooler arm (yield: 38 mg, 85%).Anal.calcd. (%) for C13H20Ag2N6O6S2: C, 24.54; H, 3.17; N, 13.21. Found: C, 24.86; H, 3.12; N, 12.60. Selected IR for CP 1 (KBr, cm-1): 3150m, 3120m, 2944w, 1626w, 1569s, 1488s, 1430vs- 1185s, 1293vs, 1248m, 1233m, 1165m, 1094w, 1066w, 1034m, 815m, 759s, 686m, 622w, 616w, ʋ(C=S) 510m, 483w. 2.3. Preparation of {[Ag2L] [PF6]2 }n (2) This CP 2 was prepared and crystalized by the same method as described for Ag-CP 1 by using equimolar ratio of silver nitrate (35 g, 0.2 mmol) and potassium hexafluoridophosphate (36 mg, 0.2 mmol) with the L (29 mg, 0.1 mmol) in methanol. After 3 days, single crystals were observed in the cooler arm. The crystals were filtered off, washed with methanol, and air-dried (yield: 46 mg, 68%). Anal.calcd. (%) C13H20Ag2N4P2F12S2; C, 19.47; H 2.51; N, 6.98. Found: C, 19.02; H, 2.27; N, 6.69. Selected IR for CP 2 (KBr, cm-1): 3183, 2920 (m), 1566 (m), 1476 (s), 1415 (s), 1252 (m), 1225 (m), 1188 (m), 842 (vs) and 557 (s), 724 (m), 679 (m), ʋ(C=S) 517 (m), 478 (m).

2.4. Preparation of [AgLBr]n (3)

This CP 3 was synthesized via the same procedure as explained for CPs 1 and 2, using equimolar ratio of silver nitrate (35 g, 0.2 mmol) and potassium bromide (24 mg, 0.2mmol) with the L (29 mg, 0.1 mmol) in methanol. After 3 days, single crystals suitable for X-ray analysis were detected in the cooler arm. (yield: 48 mg, 68%). Anal.calcd. (%) for C26H40Ag2Br2N8S4: C, 32.25; H.4.16; N, 11.57. Found: C, 32.42; H, 4.02; N, 11.08. IR (KBr pellet, cm-1): for CP 3 (KBr, cm-1): 3149m, 3115m, 3095w, 2938m, 2854w, 1564s,1481s, 1452s, 1404s, 1376m, 1238m, 1211m, 1118m, 1153m, 1094m,758m, 737s, 691m, 667m, ʋ(C=S) 521m, 408m. 2.5. Measurements FT-IR spectra (4000-400 cm-1) were implemented with a BOMEN MB102 FT-IR spectrometer. Elemental analyses for C, H and N were performed on a Thermo Finigan Flash a ThermoFinigan Flash EA 1120CHN analyzer. UV–Vis spectra were measured with a JASCO model 7850 spectrophotometer. Fluorescence spectra of the solid samples were recorded on a Hitachi F-7000 fluorescence spectrophotometer. Powder X-ray diffraction patterns (PXRD) of the Ag-CPs were measured with a Philips X-ray diffractometer (Model Philips X’Pert Pro diffractometer) over a 2 range from 10 to 80. Thermal analyses were done by a Bahr-STA 503 TGA thermal analyzer. A ramp rate of 20°C·min−1 in the range of 25−1200 °C was used. The SEM images were ob- tained using a Hitachi Japan S4160 scanning electron microscope. 2.6. Computational details The structural and electronic properties of a single isolated chains of compounds 1 and 3 are examined using density functional theory with van der Waals correction of D3 (DFTD3) [37,38]. All calculations were performed using Quantum Espresso (QE) program package with plane wave basis and ultra-soft pseudopotentials [39]. The exchange correlation potential was treated by the use of the PBE functional in generalized gradient approximation (GGA) [40, 41]. A cutoff energy of 60 Ry was used to describe the wave functions. A 6×1×1 Monkhorst–Pack type mesh was chosen to sample the Brillouin zone for structural optimizations and energy calculations. A vacuum of 15 Å along the both z- and y-directions were used to prevent the interaction between adjacent layers. The geometry of both compounds were fully relaxed until the maximum atomic forces were less than 0.01 eV/Å.

2.7. Dye adsorption experiments To measure the adsorption activity of free ligand and CPs, dye solutions in deionized water were prepared at concentrations ranging from 10 to 50 mgL−1 (for aniline blue). A dosage of 0.01g of the CPs and free ligand were separately added to 20 mL of dye solution. The mixture was stirred for 1 min and then centrifuged. Concentration of dye was determined via UV -Vis spectroscopy. The dye removal efficiency of the mentioned CPs, was calculated by equation 1. %Adsorbtion =

(Co- Cf) Co

 100

(1)

where C0 and Cf represent the initial and final dye concentration, respectively. 2.8. Antibacterial Activity Assay In order to evaluate the antibacterial potential of polymers 1-3, the standard Kirby-Bauer disk diffusion method way followed according to what described by CLSI 2016 [42]. For this purpose, four concentrations, i.e., 40, 20, 10 and 5 mg/ml of each of the polymers were prepared in DMSO and sterile blank discs (6.4mm) were saturated with these suspensions. Two Gram positive bacterial species including Staphylococcus aureus (ATCC 6538) and Bacillus subtilis (ATCC6633) as well as two Gram negative species, i.e., Escherichia coli (ATCC 25299) and Pseudomonas aeruginosa (ATCC 9027) were selected as target bacteria and cultured in Mueller – Hinton broth (Merck, Germany) and incubated at 37°C till 0.5 McFarland turbidity was obtained. Using sterile cotton swab a lawn culture was then prepared from each species on Mueller-Hinton agar (Merck, Germany). The prepared discs were placed on these lawn cultures. The plates were incubated at 37°C and the inhibition zone formed around each disc was measured and recorded. 2.9. MIC and MBC indices Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) indicates the least concentration of a compound that is able to inhibit bacterial growth or kill it. Serial two fold dilutions from 0.5 till 4 mg/ml of each polymer was prepared in Mueller-Hinton broth and the tubes were inoculated with 100 µl bacterial suspension (0.5 McFarland turbidity). The tubes were incubated at 37°C for 24h and the least concentration without visible bacterial growth was regarded as MIC. A streak culture on Mueller-Hinton agar was then made from growth negative tubes and incubated as mentioned. The least concentration that inhibited colony formation was regarded as MBC.

Table 1. Crystallographic data and structure refinement parameters for polymers 1 and 3. net formula Mr/g mol−1 crystal size/mm T/K radiation diffractometer crystal system space group a/‫إ‬ b/‫إ‬ c/‫إ‬ α/° β/° γ/° V/٣‫إ‬ Z calc. density/g cm−3 μ/mm−1 absorption correction transmission factor range refls. measured Rint mean σ(I)/I θ range observed refls. x, y (weighting scheme) hydrogen refinement Flack parameter refls in refinement parameters restraints R(Fobs) Rw(F2) S shift/errormax max electron density/e‫إ‬٣ −‫إ‬ min electron density/e٣ −

3. Results and discussion

1

3

C13H20Ag2N6O6S2

C13H20AgBrN4S2

636.21

484.23

0.224 × 0.147 × 0.085

0.100 × 0.020 × 0.020

143(2)

293.(2)

MoKα

MoKα

'Oxford XCalibur'

'Bruker D8 Venture TXS'

monoclinic

Tetragonal

'I a'

'P 42'

7.6253(3)

11.6893(3)

23.2190(9)

11.6893(3)

11.6962(4)

12.7617(3)

90

90

96.025(3)

90

90

90

2059.40(13)

1743.76(10)

4

4

2.052

1.844

2.148

3.685

multi-scan

Multi-Scan

0.98334–1.00000

0.79–0.93

6081

17485

0.0259

0.0279

0.0400

0.0283

4.277–26.364

3.193–26.369

3163

2782

0.0200, 1.1165

0.0300, 1.1380

constr

constr

0.64(4)

0.078(19)

3356

3554

265

194

2

1

0.0262

0.0310

0.0567

0.0735

1.053

1.028

0.001

0.001

0.564

0.446

−0.344

−0.379

3.1. Synthesis and spectroscopic characterizations The Ag-CPs with a good yield were synthesized in air atmosphere by a one-pot reaction in an appropriate solvent by a metal-to-ligand ratio of 2:1. To confirm the phase purity of the madeCPs, their PXRD experiments were performed (Fig.S1). The results of the simulations were consistent with the experimental observations. FT-IR spectrum of L ligand displays an intense C=S stretching vibration of the imidazole-2-thiones rings at 523 cm-1. This band is shifted to 510, 517and 521cm−1 for Ag-CPs 1-3, respectively. Thus the absorption band of the C=S bond is shifted to lower frequencies with respect to the spectrum of the initial ligand. The observed absorption bands at 1307 and 1493 cm−1 were assigned to the presence of the nitrate ion in Ag-CP 1[43]. In the spectrum of Ag-CP 2, two strong absorption bands appear at 557 and 842 cm-1 for the PF6anions. These bonds are shifted to lower frequencies relative to the position of the corresponding peaks in the KPF6 salt (559 cm-1 and 846 cm-1) [44]. As in the structure of {[Cu2(μ-bbit)3](PF6)2}n [45], the shift can be attributed to the hydrogen bonding interactions exist between the L ligand and PF6- anions which is consistent with the crystal structure of the considered polymer. 3.2. Crystal structure of polymer [Ag2L(NO3)2]n (1) CP 1 crystallizes in the monoclinic space group Ia with Z = 4 (Table 1). In this structure, each of the bridging chelate ligands is connected to four different AgI centers, so that one of the S donor atoms bridges two crystallographic similar Ag(2) centers and the other one is bonded to three silver atoms [2Ag(1) and Ag(2)]. At the same time, the considered S donor atoms are chelated to one Ag(2) to form a 12-member metallomacrocycles ring (Fig.1a). In doing so, zigzag chains of the Ag3S3 units extending along the a-axis were obtained (Fig1b). In the helical chain structure, there are two types of pseudo-tetrahedral and distorted square pyramidal geometries for the AgI environments, namely, Ag(1)S2O2 and Ag(2)S3O2, respectively. In the Ag(2)S3O2 unit, the Ag(2) ion is coordinated by three sulfur atoms with μ2-S(1) and μ3-S(2) coordination modes from two distinctly different ligands and two oxygen atoms from a terminal nitrate anion with bond angles ranging from 50.27 to 139.80° (Table S1). In contrast, for the Ag(1)S2O2 core the AgI center is four-coordinated generated via two μ3-S(1) ligands and two oxygen atoms from a bidentate nitrate anion. The single helix chain can be explained as two single zigzag lines of [-Ag-μ3-(S)Ag-]n bonded together via the chelating ligand with the μ2-S donor atoms to generate a zigzag

chain of six membered Ag3S3 rings (Fig1b). In title structure, the flexible ligand adopts gauchegauch-anti-anti conformation with S…S separation of 4.097 Å. The 1D Ag-CP 1 packed, so that there are six neighboring equivalent chains (Fig 1c). The intermolecular hydrogen bonds were detected between the C−H···O and C−H···N to form a non-covalent network. A structural comparison between the CP1 and reported complexes of [Ag4(X1)2(NO3)4],(X1=9,10-bis[(tertbutylthio)methyl]-anthracene), [Ag4(X2)2(NO3)4](CHCl3)2, (X2= 9,10-bis [(npropylthio)methyl]anthracene) and [Ag4(X3)2(NO3)4]- (CHCl3)2,(X3= 9,10-bis[(nbutylthio)methyl]anthracene) [46] shows that the main distinction between their topology and structures is related to the influence of flexibility of the neutral ligands used in these complexes.

Figure 1. (a) Drawing of coordination environment of Ag(I) in 1with the atom labelling scheme. (b) The 1D Ag-CP 1 extending parallel to the a-axis. (c) Packing of the 1D-tube structure of 1 along the c-axis. hydrogen atoms were omitted for clarity.

3.3. Crystal structure of polymer {[Ag2L] [PF6]2 }n (2) With a view to investigate further information on the effect of counter anions on the structure of CPs, KPF6 was used. After several attempts, it was not possible to get a fine single crystal for 2.

However, it was possible to obtain a picture with its space group for this sample. The coordination polymer of 2 contains a [Ag2(L)]n2+ cationic chain and PF6−counteriones (Fig. 2a). In the cationic chain structure, there are, two crystallographic independent AgI centers with one kinds of coordination geometry. As depicted in Fig. 2, the AgI center involved in a disorder linear coordination geometry comprising of two distinct L ligands. In the considered compound, each of the crystallographic independent AgI centers is linked together by two distinct L ligands with a doubly bridging fashion to form a non-planer 24-membered [Ag(L)2Ag]2+ ring as a repeating unit. The [Ag(L)2Ag]2+ rings are joined together by sharing the sulfur atom of ligand and formed a 1D helical chain structure. The PF6− anions counterbalance the charge of the cationic chains. The FT IR of the compound 2 is in agreement with the very well documented work of Reger et al., which reports a good correlation between the existence of a short C(H)…F contact and the presence of an absorption band at 516-521 cm-1 [47]. Complexe 2 exhibit an absorption band in 517 cm-1 and follow the short C(H)…F contacts. Thus, in accordance with Reger et al., we conclude that weak hydrogen bonds exist in this complexe. Each of the 1D tube structures are surrounded by neighboring crystallographic equivalent tubes where on the base the infrared the intermolecular hydrogen bond interactions are observed between the fluorine atom of PF6- and hydrogen atom of the thione ligand. 3D network may be considered when these interactions are taken into account.

Figure 2.(a) Partial view of the chain of the coordination polymer 2. (b) View of the 1D coordination chain along a- axis (c) Packing of the 1D strcture of 2. hydrogen atoms omitted for clarity.

3.4. Crystal structure of polymer [AgLBr]n (3) Single crystal X-ray diffraction analysis reveals that [AgLBr]n, crystallizes in the tetragonal space group P 42 with Z = 4 (Table 1). In the polymer of 3, the infinite double-stranded ribbon consists of Ag2(µ-Br)2 dimers, which are interconnected with the adjacent inorganic rhomboids through bridging dithione ligands (Fig 3a). Each silver center of these nodal Ag2Br2 units was coordinated in a tetrahedral manner by two S atoms from two different dithione ligands and was symmetrically bridged by two µ -bromine ligands. the mean Ag−S bond and Ag−Br bond length are respectively to 2.70 and 2.555 Å. The values for the bond angles around the central atom are in the range of 57.38-114.56°. 28-membered macrocycles comprising four silver atoms, two ligands and two µ Br atoms result from this arrangement and are extended along a axis (Fig. 3b). In this structure, the flexible ligand adopts gauche-anti-gauche-anti conformation with S…S separation of 8.894 Å. The Ag···Ag separations in the [Ag(μ-Br)2Ag] motifs are 2.98 Å which indicates the presence of Ag−Ag interactions in the rhomboid dimeric units [48]. The polymer chains are linked together by cross-links in the c-direction to give a 3D architecture induced by the non-classical C−H···Br and C−H···N hydrogen bonds with an ABAB··· sequences (Fig. 3c).

Figure 3.(a) Atomic numbering and coordination environment of Ag(I) in polymer 3 (b) View of the 1D coordination chain of Ag-CP 3 along a- axis. (c) Generating a 3D non-covalent lattice network structure with ABAB··· sequencing. hydrogen atoms omitted for clarity

4. Photophysical properties The UV–Vis spectra of the flexible ligand along with its CPs were verified in DMF. On the basis of Fig. 4a the electronic spectrum of the thione ligand displays a sharp band at 250 nm which can be assigned to the π → π* transitions in the C=S group of the 1-methylimidazoline- 2(3 H)-thione of the ligand. In the spectra of the CPs, this band is appear at 250 (for 1), 252 nm (for 2) and 255 nm (for 3) upon coordination of the flexible ligand to the AgI ions via sulfur atom. It is worth to note that, our polymers constructed from the coordination between the silver ions as a soft acid and a sulfur donor ligands as a soft base. Therefore, it is obvious that the DMF as a weak oxygen donor ligand cannot disassemble the polymers into smaller units. Whereas, DMF as a centre for hydrogen bonding can only break down hydrogen bonds exist between the layers and dissolved the polymers in the solution. The room temperature solid state emission spectra of the flexible L and its Ag -CPs were displayed in Fig. 4b. The emission spectrum of the free organic ligand illustrates an intense emission band at 460 nm (λex = 244 nm) originated from π → π* transitions in the C=S group. In the case of CPs 1, 2 and 3 this band is slightly blue -shifted to 465, 469 and

461 nm, respectively. The blue- shift is attributed to the σ-donating from the L to Ag centers which increases the electronegativity of the sulfur atom and thereby increasing the π → π* transition energy.

(a)

(b)

Figure 4. (a) The UV–Vis spectrum of the flexible ligand with its Ag-CPs in DMF. (b) The room temperature solid-state emission spectra of the flexible ligand its Ag-CPs.

5. Thermal properties To characterize the thermal stabilities of compounds 1−3, their thermal decomposition behaviors were examined by TGA diagrams (Fig.5). The combustion of the linker and network break down of these Ag-CPs occur at the temperature range of 240−480°C. The TGA curves described that polymers 1 and 2 decompose in one step by combustion their flexible ligand. In contrast polymer 3, decompose in two steps: the first step is due to the combustion of the flexible ligands, and the second one is assigned to decomposition of the silver salts to the metallic silver.

Figure 5. TGA curves of compounds 1-3.

6. DFT calculation The relaxed geometry of compounds 1 and 3 were presented in Fig.S2 and Fig.S3, respectively. Based on the optimized structures, the calculated structural properties were well consistent with the experimental results. For example, the Ag(1)―S(1) and Ag(1)―S(2) bond lengths are 2.46 Å and 2.47 Å, respectively, which are comparable with the calculated bond lengths 2.47 Å and 2.48 Å . Furthermore, to gain inside into the electronic structures of compounds 1 and 3, the band structure and projection densities of states (PDOS) of both compounds were investigated by means of DFT-D3. The calculated electronic band structure and PDOS of both compounds are shown in Fig.S4. As seen from Fig.S4, compounds 1 and 3 are non-magnetic and exhibits semiconducting character with a direct band gap of 2.82 eV and 2.97 eV, respectively. According to the experimentally calculated UV-Vis spectrum of compounds 1 and 3, the two compounds exhibit no absorption in the visible range, indicating that they are wide-band gap insulators. It can be clearly seen that our DFT results are in very good agreement with the experimental spectroscopic data. Both valance band maximum (VBM) and conduction band minimum (CBM) are located at Gamma point. From projected density of states and our analysis, the VB is shown as the σ* interaction between the d orbitals of Ag and p orbitals of S atoms. However, the CB is delocalized over the

chains of polymers, mainly contributed by nitrate and organic ligand moieties. In this regard, for compound 3, the VBM is almost exclusively contributed by the Ag and S atoms, showing π Ag– Br and σ Ag–S interactions, whilst the CBM is mainly contributed the by organic part, showing π-π bonding interaction between the thione rings. 7. The adsorption process of dye molecules by Ag-CPs Generally, dyes can be classified by their solubility, dyeing properties and chemical structures as cationic (basic) and anionic (acidic) dyes [49]. Cationic dyes have a positively charged and anionic dyes have a negatively charged chromophore in their structures. In the present study, we have investigated the adsorption ability of Methylene blue (MB) and Rhodamine B (RB) as cationic dyes and Aniline blue (AB) and Sunset yellow (SY) as anionic ones (Fig.S5) relative to the AgCPs 1-3. The prepared polymers and the free ligand were separately added into the 20 mL of aqueous solution of the title dyes. After addition of Ag-CPs 1-3 and free ligand into the dye solutions, a quick decrease in color intensity of the anionic dyes was mostly detected for polymer 2 due to the rapid adsorption of anionic dyes by this absorbent. Therefore, we have selected the AB and SY dyes for adsorption experiments by the Ag-CP 2. The SEM images (Fig S6) and XRD patterns (Fig.S7) confirm a nice adsorption of a AB by the AgCPs 2 without any decomposition product; while in the case of the SY, the XRD pattern evidence support the decomposition of the polymer during the adsorption process. The different behaviour of the observation of the AB and SY dyes by the polymer 2, can be attributed to the structural difference between these two dyes. The adsorption mechanism for this process can only be described via interaction between the hydrogen atoms of the dye molecules with the folorine atoms of the PF6- moiety of the crystal. As depicted in Fig. S8 by these interactions the infrared peaks corresponding to the PF6- anions became broader and a notable change was detected in the XRD pattern of the AB@AgCPs 2. Probably, an important parameter for the selective adsorption of anionic dye by the Ag-CP 2 could be assigned to the presence of PF6- anions in this structure. In the meantime, the non-covalent bond interactions like H…π and aromatic π…π stacking interactions have only a minor impact in the adsorption of AB via the compound 2. For better described the mechanism of adsorption of AB aqueous solution by the understudy complex, the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models were used [50-59].

As illustrated in Fig.S9, it can be concluded that, the adsorption of AB dye molecules via the AgCP2 with linear regression correlation coefficient (R2) of 0.99 can best be illuminated by the pseudo-second-order model. The room temperature fitted kinetic of the absorbed AB from the supernatant solution of materials were summarized in Table 2. The mechanism interaction of AB dye with the Ag-CP 2 can be considered with adsorption isotherm models like Freundlich, Temkin and Langmuir models [50-59]. The R2 coefficients of the isotherm models illustrated in Fig. S10 and summarized in Table 3. These results expressed that adsorption of AB by the Ag-CP 2 is defined by the Langmuir model. Langmuir isotherm model expressed that the adsorption sites on the surface of 2 are energetically equivalent.

Table 2. The adsorption kinetics models via Ag-CP2. R2 AB

Kinetic models

Equations

Pseudo-first-order

𝑞𝑡 = 𝑞𝑒(1 ― 𝑒 ― 𝑘1𝑡)

-

2

𝑞𝑒 𝑘2 t

Pseudo-second-order

𝑞𝑡 = (1 + 𝑞𝑒𝑘2 t)

0.99

Intraparticle diffusion

𝑞𝑡 = 𝑥𝑖 + 𝑘𝑖𝑡1/2

0.95

Table 3. Fitted adsorption isotherms model for adsorption of dye from aqueous solutions by the Ag-CP2.

R2 AB

Adsorption isotherm models 𝑞𝑚𝑎𝑥𝐶𝑒𝑘𝐿

Langmuir

𝑞𝑒 =

Freundlich

𝑞𝑒 = 𝑘𝐹𝐶𝑒1/𝑛

0.71

Temkin

𝑞𝑒 = 𝐵𝑙𝑛 (𝐴𝑡 𝐶𝑒 )

0.63

8. Biological activity

(1 + 𝐶𝑒𝑘𝐿 )

0.99

As can be found the data of table S2, these polymers were able to inhibit growth of all bacterial species even in the lowest concentration. These polymers did not show selective activity against Gram positive or Gram negative species. This suggest that bacterial cell wall may not be the target site for these polymers, because the main difference between Gram positive and Gram negative bacteria is the cell wall layers and thickness and those antibacterial agents that can inhibit bacterial cell wall synthesis and growth will selectivity inhibit growth of Gram positive bacteria. The possible inhibitory effect of these polymers is on cytoplasmic membrane of target bacteria and proteins that are involved in substrate uptake, energy production and protein secretion. So, bacterial metabolism and energy production will be affected and hence inhibition of bacterial growth and division and/or death of bacteria cells will be resulted. Furthermore, incorporation of these polymers into lipid bilayer and disruption of lipid packing maybe another possible mechanism of antibacterial activity especially in the case of Gram negative species that have outer membrane structure. The minor differences that are present in antibacterial potential of polymers 1-3 can be related to differences in their chemical structures and their size that affect their diffusion through porins of Gram negative bacteria and also peptidoglycan holes and hence limit their accessibility to target site. Antibacterial assessment of the pure tested polymers which were free from their constructed saltes has been in the suspention condition. The results showed that theia antibacterial activity are significantly higher than that of corresponding salts and increased as AgCP1>AgCP3>AgCP2. These data demonstrated that the antibacterial activity of these polymers is related to the interaction between the Ag+ with polar heads of cytoplasmic membrane phospholipids. So, parallel to the increasing in the number of Ag+, the antibacterial potential of the related polymer has been increased. Hence, the antibacterial activity of these polymers higher than the Ag salts. To have a better understanding of the impact of the Ag+ ion in the activity of the considering polymers against the target bacterial, the antibacterial property of the flexible used ligand was also investigated. It has no effect against Gram negative bacterial species and only showed a minor inhibition against Gram positive species due to the non-covalent interactions with sell wall constituents. This minor inhibitory effect by the ligands negligible in comparison with the polymer results. The comparison of MIC and MBC results of these polymers reveals that all of them have bactericidal activity against E. coli, P. aeruginosa and S. aureus as their MIC and MBC values of three polymers against these bacteria were equal to 0.5 mg/ml. While in the case of B. subtilis

polymer 2 has bactericidal activity (MIC=MBC=0.5 mg/ml) and polymers 1 and 3 have bacteriostatic (MIC = 1 mg/ml) and bactericidal activity at 4 mg/ml concentration (Table S3).

Conclusion In summary, we have successfully synthesized and fully characterized a series of new Ag–CPs based on the flexible 3-methyl-1H-imidazole- 2-thione ligand. In contrast to 1 and 3, polymer 2 displays uptake of dye molecules. Addition of PF6− and Br− anions caused substantial changes in coordination number of Ag atoms relative to polymer 1. The structural changes, change some of the properties of the considered polymers. The synthesized Ag-CP 2 exhibit selective adsorption of anionic dyes. The adsorption kinetic of AB dye was expressed by the pseudo-second-order for 2. While its adsorption behaviour could be described by the Langmuir isotherm for these dyes. Additionally, the geometry and electronic structures of compounds 1 and 3 were considered via DFTD3. The electronic structures indicated that these compounds are non-magnetic with direct band gap. The calculated band gap of compounds 1 and 3 are approximately equal to 3 eV, which indicated that these compounds have semiconductor behaviours. Acknowledgements We thank Shahid Chamran University of Ahvaz for financial support (grant number: 93/3/02/27176). Appendix A. Supplementary material CCDC reference numbers 1951335 (for 1) and 1951336 (for 3) contains the supplementary crystallographic data for mentioned compounds. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.

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Highlights 

Crystals of Ag(I) based coordination polymers have been grown by branched tube.

 

Co-ligand has a high impact on the structural of the considered compounds. The considered polymers show good antibacterial activity.

Graphical abstract

Dear Professor. Müller Receiving Editorial Office Inorganica Chimica Acta I would like to thank the reviewer for their interesting comments which I am sure this comments will increase the impact of my paper. I am also appreciate the editorial board for consider my manuscript. I have read the reviewer comments and respond to them point by point and highlight them in green color in the text and surmised them as follows: Best regards, Prof. A. Beheshti

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: