New cyclotriphosphazene ligand containing imidazole rings and its one-dimensional copper(II) coordination polymer

Journal Pre-proof New cyclotriphosphazene ligand containing imidazole rings and its one-dimensional copper(II) coordination polymer Hanife İbişoğlu, Devrim Atilla, Süreyya Oğuz Tümay, Ahmet Şenocak, Ercan Duygulu, Fatma Yuksel PII:

S0022-2860(20)30212-X

DOI:

https://doi.org/10.1016/j.molstruc.2020.127888

Reference:

MOLSTR 127888

To appear in:

Journal of Molecular Structure

Received Date: 12 July 2019 Revised Date:

23 January 2020

Accepted Date: 10 February 2020

Please cite this article as: H. İbişoğlu, D. Atilla, Sü.Oğ. Tümay, A. Şenocak, E. Duygulu, F. Yuksel, New cyclotriphosphazene ligand containing imidazole rings and its one-dimensional copper(II) coordination polymer, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.127888. 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.

New cyclotriphosphazene ligand containing imidazole rings and its one-dimensional copper(II) coordination polymer Hanife İbişoğlu*, Devrim Atilla, Süreyya Oğuz Tümay, Ahmet Şenocak, Ercan Duygulu, Fatma Yuksel Department of Chemistry, Gebze Technical University, 41400, Gebze, Kocaeli, Turkey Author for correspondence: Dr. Hanife İbişoğlu Tel.: 90 262 6053013

Fax: 90 262 6053005

E-mail: [email protected]

Abstract An imidazole and biphenyl-appended cyclotriphosphazene (2, L) and its 1D copper(II) coordination polymer (3) which formulated as [L2(CuCl2)]n were synthesized. The structure of 2 was determined by elemental analysis and different spectroscopic tecqniques. The crystal structures of 2 and 3 were defined by single-crystal X-ray crystallography. The copper atom in complex 3 was in a slightly distorted octahedral geometry which coordinated by four monodentate imidazole nitrogen and two chlorine atoms. The magnetic properties of 3 was discussed via ESR spectroscopy. The thermal properties of 2 and 3 were investigated by thermogravimetric analysis (TGA). The photophysical and electrochemical properties of 2 and 3 were evaluated by UV-Vis-fluorescence spectroscopies and cyclic (CV)-square wave (SWV) voltammetric techniques. In addition, HOMO-LUMO energy levels were calculated according to UV-Vis absorption and CV measurements. Keywords: Cyclophosphazene; imidazole; coordination polymer; copper(II) complex; photophysical properties; electrochemistry.

1. Introduction Metal-organic coordination networks (MOCNs) or metal-organic frameworks (MOFs) are metal-ligand compounds that lengthen “extremely” into one, two or three dimensions (1D, 2D or 3D, respectively) by covalent metal-ligand bonding [1]. Recently, the crystalline coordination polymers have attractive attention because of having potential in catalysis, magnetism, porosity, optic and non-linear optic fields etc. [2-8]. Hexachlorocyclotriphosphazene (trimer, N3P3Cl6) which is the most member of heterocyclic compounds has been used as precursor in the design of cyclotriphosphazenes [5]. Trimer bearing six active phosphorus-chlorine that can be readily functionalized via nucleophilic substitution reactions of different nucleophiles such as alkoxides, aryloxides, organometallic reagents or amines etc [4,5,8,9,10]. Substituted groups to cyclotriphosphazenes can be altered to physical or chemical properties of final compounds [4]. In this way these compounds can be used in a range of fields of science and technology [11,12] such as antimicrobial agents [13-15], fluorescent chemosensors [16], flame-retardant reagents [17], antibacterial agents [18, 19] etc. These compounds are also utilized as multi-site coordination ligands in order to synthesize homo- or hetero poly nuclear complexes involving identical or different coordination modes [4,5,8, 20-23]. Cyclophosphazenes can interact with transition and main group metals in several various ways. i)The nitrogen atoms in these rings can behave as Lewis bases towards appropriate Lewis acids, ii) The ring phosphorus atom can be included in a direct metal link by means of a covalent or a coordinate bond [22,23]. Besides, the metal-binding sites of the cyclophosphazene containing heterocycles such as N-ligands (pyridyloxy, pyrozylyl etc.) can be coarsely classified into exo- and endotopic sites [4,5,21]. Owing to the structural features, cyclophosphazene based ligands are used as fluorescent chemosensors for different metals [16, 20], catalyst [15], complexing materials [4,5,8,15,16,20-27] and OLEDs [27]. They are

also employed for preparation of coordination polymers [4, 5, 8, 25, 22-33].For example, coordination polymers (1D, 2D and 3D) can be synthesized using pyridyloxy cyclotriphosphazene derivatives [4, 5, 8, 20]. In the literature, there are some report about metal complexes (such as Zn(II), Cu(II), Ni(II), Ru(II) etc.) of biphenyl groups appended cyclotriphosphazenes were existed [15, 20, 26, 32, 34-37]. Generally, these complexes have especially N-heterocyclic ligands such as pyridyloxy [8,20,35], tetrahydrazone [38], 1,10-phenanthrolino [35,39] groups etc. When the literature studies were examined, imidazolyl (Im) substituted cyclophosphazene (Im6Cpz) derivative and its metal complex derivetives were synthesized (MxIm6Cpz; M = ZnII, CuII, CoII; x = 1, 2, 3) [40]. Furthermore, the preparation of copper (II) complex of cyclotriphosphazene derivatives including Im groups was also reported in the literature [4144]. Although, the cyclotriphosphazenes bearing heterocyclic (such benzimidazolyl) rings

as imidazolyl

or

were prepared in our previous work [45], The study related to

synthesis of cyclotriphosphazene ligand ,{[N3P3(biph)2(Im)2]}, and its coordination polymers so far in the literature. In the present study, firstly bis-spiro 2′, 2′′-dioxy-1′, 1′′-biphenyl group substituted cyclotriphosphazene derivative (1), [N3P3(biph)2Cl2], was prepared according to literature [46] and then the compound (2, L) was prepared from the reaction of compound 1 with imidazole (ImH) using NEt3 as base in THF. Finally, we obtained the novel 1D coordination polymer (3) from the reaction of the compound 2 with copper(II) chloride. The compound 2 was fully characterized by spectroscopic methods. The crystal structure analysis of 2 and 3 were investigated by single-crystal X-ray crystallography. Moreover, the thermal, photophysical and electrochemical properties of 2 and 3 were studied. Magnetic property of 3 was studied by ESR measurements, also.

2. Experimental 2. 1. Materials and measurements Hexachlorocyclotriphosphazatriene and CuCl2 was purified was purchased from Aldrich. The Triethylamine (NEt3), acetone, petroleum ether (bp: 60-80 °C), tetrahydrofurane (THF), ethanol, imidazole (ImH), Na2SO4, 1,8,9-anthrasenetriol, n-hexane, CDCl3, K2CO3, dichloromethane (DCM), 2,2′-dihydroxybiphenyl (biphH2) were procured from Merck. Thin layer chromatography (TLC) was performed on Merck Silica gel plates and column chromatography was performed on silica gel. Elemental analyses were acquired by a Thermo Finnigan Flash 1112 Instrument. Mass analyses were carried out on a Bruker MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization-Time-Of-Flight mass, Rheinstetten, Germany) spectrometer using 1,8,9-anthrasenetriol (DIT) (for 1 and 2) as a matrix. Varian INOVA 500 MHz spectrometer used to record 1H and

31

P NMR spectra for 1 and 2. FT-IR spectra were

recorded using a Perkin Elmer Spectrum 100 FT-IR spectrometer. The thermal behaviors of 2 and 3 were examined by Mettler Toledo TGA/SDTA 851 thermogravimetric analysis (TGA) and differential scanning calorimeter DSC 821e (DSC) equipped with Mettler Toledo Stare software at a heating rate of 10 °C min−1 under nitrogen flow (50 mL min−1) between 25-700 °C for TGA and -25 to 250 °C for DSC, respectively. DSC analysis were used for to determine melting point temperatures of compound 2 and 3. UV-Vis absorption and fluorescence emission spectra were recorded by Shimadzu UV-2001 UV

spectrophotometer

and

Varian

Eclipse

spectrofluorometer,

respectively.

The

voltammetric measurements were performed with an electrochemical analyzer of CHI440B.Glassy carbon electrode (GCE), Pt wire and saturated calomel electrode (SCE) served

as

working,

counter

and

reference

electrode.

Electrochemical

grade

tetrabutylammonium hexafluorophosphate, n-Bu4NPF6, in extra pure DMSO was used as supporting electrolyte in voltammetric measurements at a concentration of 0.10 mol dm-3.

High purity of N2 was employed for deoxygenation of solution with 10 minutes prior to each run and maintain a nitrogen blanket [47, 48]. The ESR (electron spin resonance) measurements were accomplished at room temperature with a microwave frequency of 9.86 Hz with a JEOL ESR spectrometer (JESFA300). 2.2. X-ray crystallography Crystallographic data were recorded on a Bruker APEX II QUAZAR three-circle diffractometer using Mo Kα radiation (λ =0.71073 ˚ A) at T = 296 K. Absorption corrections were performed by the multi-scan method applied in SADABS [49]. Using Olex2 [50], the structure was solved with the ShelXT [51] structure solution program using Intrinsic Phasing and refined with the ShelXL [52] refinement package using Least Squares minimization. Anisotropic displacement factors were used for refined all nonhydrogen atoms. Calculated positions were used to place C-H hydrogen atoms. Its allowed to ride on the parent atom. Because of disordered solvent molecules which have very larger displacement parameters there are some electron peaks. This situation made difficult to model in unit cell of compounds 2 and 3. Accordingly, Olex2 was used to refine the other molecules in this study without the influence of the solvent molecules [50, 53]. Per unit cell has four cavities for compound 2; 150.8 Å3 of volume with 45 void electron counts and there is a cavity per unit cell for compound 3; 287 Å3 of volume with 69 void electron counts. The final geometrical calculations were carried out with the PLATON [52] and MERCURY [54] programs and the molecular drawings were done with the DIAMOND [55] program. Structure determinations were been deposited with the Cambridge Crystallographic Data Centre with CCDC numbers 1912260 and 1912265 for the structures of 2 and 3, respectively. 2. 3. Synthesis The compound 1, {N3P3(biph)2Cl2}, was synthesized according to the literature [46]. 2.3.1. Synthesis of [ N3P3(biph)2(Im)2] (2, L)

A reaction flask was charged with ImH (0.44 g, 6.5mmol) and compound 1 (0.75g, 1.3 mmol) and dry THF (30 mL) To this was then added NEt3 (0. 66g, 6.5 mmol) and this mixture was stirred at refluxing temperature for 10 day. TLC (using 1:8 DCM/THF solvent system) analysis of reaction mixture showed that a new product has been formed. The resulting reaction mixture was cooled to ambient temperature and the solvent was removed.. Subsequently, crude product was extracted with DCM/water. Organic layer was dried over Na2SO4 and evaporated. Then, column chromatography was performed to purify this reaction mixture with dichloromethane: tetrahydrofuran (1:8). The product (2, L), 2, 2-di-(Im)-4,4,6,6bis-spiro(biph)cyclotriphosphazene (0.5 g, 60 %, mp: >250 °C), was isolated as colorless solid which was re-crystallized from petroleum ether: DCM (1:1). Anal. Calc. for C30H22N7O4P3; C, 56.51; H, 3.48; N, 15.39; P,14.59. Found; C, 56.50; H, 3.40; N, 15.35; P,14.55 %. MALDI-TOF-MS (m/z): [M+H] +, 637.21 (calcd. 637.47). 1H NMR (500 MHz, CDCl3, 298 K) δ (ppm); 8.06 (-N-CH5-N-, s), 7.59(-O-C-C-CH4-, d, 3JH3H4 = 6.63 Hz), 7.50 (H, -O-C-CH2-,t, 3JH2H3 = 6.98Hz ), 7.41(-O-C-C-CH3,t), 7.32 (-N-CH6-CH-N-, d, 3JH6H7 7.88 Hz), 7.29 (-N-CH-CH7-N-, d), 7.22( -O-C-CH1,d, 3JH1H2 = 8.64Hz).FT-IR(ATR, room temp.,ν, cm−1): 3102 (C-H)aromatic ; 1600(C=N), 1497 (CH=CH) ; 1454 (C-H)aromatic; 1227 and 1164 (P=N); 962 (P-O); 1092 (C-O);879 (P-N). 2.3.1. Synthesis of one-dimensional coordination polymer (3) A NMR tube was charged with a solution of 2 (8.9 mg, 0.014 mmol) in DCM (1 mL). Then, a mixture of CuCl2 (0.94 mg g, 0.007 mmol) and a couple of drops of trimethylamine in ethanol (2 mL) was

slowly added to this solution. The 1D coordination polymer (3),

[L2(CuCl2)]n, {6 mg, 30%, mp: >300 °C} was obtained as blue single crystals suitable for Xray diffraction analysis after a few weeks by slow diffusion. Anal. Calc. for C60H44Cl2CuN14O8P6: C, 51.11; H, 3.15; Cu, 4.51; N, 13.92; P, 13.19. Found: C, 51.09; H, 3.12; Cu, 4.49; N, 13.90; P, 13.13%. FT-IR(ATR, room temp.,ν, cm−1): 3152 (C-H)aromatic ;

1604( C=N),1540 (CH=CH);1474, 1436 (C-H)aromatic; 1227 and 1167 (P=N); 992 (P-O); 1092,1070 (C-O);909,879 (P-N). 3. Results and discussion 3.1. Syntheses and characterizations of [N3P3(biph)2(Im)2](2) and 1D coordination polymer (3) The reaction of 1 with ImH as monodentate base using trietylamine in boiling THF gave ligand (2) in this work (Scheme 1). The product 2 was obtained by column chromatography and purified by crystallization. Single-crystal X-ray analysis, FT-IR, MALDI-MS, 1H and 31P NMR spectroscopies and elemental analysis were used for characterization of compound 2. Fig. S1 demonstrates 1H NMR spectrum of compound 2 and other characterization data were given at synthesis section. All characterization results were consistent with the proposed structure of 2 which were as depicted in Scheme 1. The elemental analysis and MALDI-MS results showed that two chlorine atoms on the cyclotriphosphazene ring were exchanged with imidazole moieties for 2. As expected, the 31

P{1H} NMR spectrum of compound 2 was A2X spin system (Fig. S2). Two equivalent

P(biph)2 groups demonstrated a doublet at ca. δ = 21.9 ppm and P(Im)2 group at ca. δ = 2.2 ppm were exhibited triplet with 2JPNP of 78.7 Hz. The reaction of L with copper(II) chloride in 2:1 molar ratio using NEt3 afforded the 1D coordination polymer (3), [L2(CuCl2)]n, (Scheme 2). This complex (3) was defined by elemental analysis, FT-IR, ESR, single-crystal X-ray analysis. NMR data of 3 could not be obtained because of that the copper(II) complex was paramagnetic. The aromatic CH stretching frequencies were noticed between 3152 and 3102 cm-1 in the FTIR spectra of 2 and 3. The C=N vibrations exhibited at about 1600 cm-1 as expected [56]. The P=N stretching modes as strong bands were observed between 1164 and 1228 cm-1 as expected. Moreover, coordinated covalent bonds were formed between nitrogen atoms of the

imidazole groups and copper(II). The frequencies value of CH=CH stretching of compound 3 was higher than the free ligand due to C-H bonds strengthening. In addition to, P-O-C stretching frequencies were observed also in the 962 cm-1 and 992cm-1 regions. These results are similar to those in the cyclotriphosphazene derivatives [4,5,13,15]. 3.2. Crystal structure descriptions of 2 and 3 Suitable single crystals of 2 and 3 were acquired as described in the experimental section and then crystal structures of these compounds were determined by single-crystal X-ray crystallography. The selected data collection and refinement details were given in Table 1. Compound 2 has orthorombic system, Pccn space group while compound 3 has triclinic system, P-1 space group and molecule sits on a symmetry centre in both structures. The selected bond parameters of compounds 2 and 3 were given in Table 2. The compound 2 is cyclotriphosphazene (P3N3) derivative which contains di-spiro biph and bis-geminal substituted with Im groups (Fig.1a). The molecular structure of 2 showed that two biph units were attached to P1 atoms in a spirocyclic manner. The six-membered cyclotriphosphazene ring has a nearly planar conformation in 2 [max. deviation is 0.004(3) Å for N2 atom] (Table S1). The angle between the planes of the imidazoylyl and cyclotriphosphazene ring was found as 71.82° while the angle between the planes of two Im rings is 66.27° in 2 (Fig.S3). The bond parameters of compound 2 were given in Table 2 and all data was found in the normal range that previously observed for similar cyclotriphosphazene derivatives [44]. The average P-N bond distance of 1.573(3) Å observed for the N3P3 ring was smaller than the exocyclic average P-N bond distances of 1.670(3) Å as expected. The phosphazene ring angles at nitrogen atoms were closer to the angles anticipated at sp2 hybridization [122.1° for N2 and 121.74° for N1]. The sum of the bond angle around the exocyclic N atom was 358.75 ° for 2 and the proximity to 360° confirmed that this nitrogen atom had trigonal planar geometry (Table 2). The angle of O-P-O [102.85(11) °] was

noticeably pinched from a tetrahedral arrangement in compound 2 (Table 2). The close investigations of crystal package of 2 showed that there is no classical hydrogen bonding, however there are some intermolecular C-H···O interactions with at about 3 Å D···A distances as shown in Fig 1b. The 1D coordination polymer (3) was obtained from the metalation reaction of ligand (2) and copper salt. In the crystal structure of complex 3 the ligand is bidentate chelate; two nitrogen atoms of different imidazole rings are coordinated to two different copper metals to form 1D coordination polymer as shown in Fig. 2. The Cu (II) center was hexacoordinate (4N, 2Cl) in a slightly distorted octahedral geometry. The four nitrogen atoms are in the equatorial positions while two chlorine atoms are in the axial positions. Average bond angle N-Cu-N is 90° meanwhile Cl-Cu-Cl bond angle is 180°. This results showed that the structure deviation from the octahedral geometry. The Cu-Cl bond length is 2.790 Å. in 3 (Table 2). The mean Cu-N bond length of compound 3 is 2.004 Å and this is consistent with that observed for analogous complexes [43, 44].The cyclotriphosphazene ring was in slightly twisted planar conformation [max. deviation is 0.0915(19) Å for P3 atom]. The deviation from planarity of N3P3 ring was larger in compound 3 than that of compound 2. The angles between the planes of the imidazoylyl and cyclotriphosphazene ring were found as 52.14° and 47.07° and while the angle between the planes of two Im rings is 89.40° in 3 (Fig.S4). In the crystal package of 3 there is no classical hydrogen bonding between the 1D polymer chains but there is interchain C-H···O interaction (C9-H9···O1; D···A distance is 3.257 Å) which stabilized the crystal package of 3. 3.3. Thermal Analysis Thermogravimetric curves of the ligand (2) and complex (3) were depicted in Fig. S5. The decomposition pathway of 2 and 3 was followed up to 700 °C. While, The ligand was stable to 200 °C and 62.5% mass of the ligand stayed without decomposition, the complex remained

steadfast up to 310 °C. The TGA curve of 3 exhibited a two-stage process corresponding to the loss of one of the biphenyl groups. The initial weight loss of 16% was noticed at 259 °C and the second one was detected at 482 °C; 19% mass of 3. The char yield was 62.5% for 2 and 72.5% for 3 at 700 °C, respectively. 3.4.

Photophysical properties of 2 and 3

Cyclic phosphazenes can be used as a core for optical materials because they are optically inert in UV-Vis region and photophysical properties can be easily adjusted with the added side groups [10,57,58]. Therefore, UV-Vis and fluorescence spectroscopies were used to investigate the photophysical properties of cyclophosphazene core (2) and its Cu2+ complex (3) at room temperature after characterization of 2 and 3. Spectroscopic quartz cuvette and micropipettes were used for all spectral measurements. Firstly, electronic absorption and emission features of 2 were investigated in dichloromethane, acetonitrile (ACN), ethanol (EtOH) and dimethylsulfoxide (DMSO) at different concentration (Fig. S6). As can be seen from Fig. S6 and Fig. 3a, absorption wavelength of 2 was almost unchanged according to solvent system where absorbance values were change. UV-Vis absorption bands which observed in all studied solvents at 240 nm and 278 nm assigned to π-π* transitions and n-π* transitions of 2 [45,59,60]. In addition, molar absorptivity values of 2 in different solvents were calculated according to UV-Vis absorption spectra of the compound (Table 3). The UV-Vis absorption properties of 3 were only investigated in DMSO due to its very low solubility in other solvents. According to Fig. 4, complex 3 gave the absorption band at 240 and 278 nm, similar to compound 2. However unlike 2, 3 also gave a new absorption band at 303 nm. This new absorption band can be assigned to charge transfer (LMCT)of nitrogen atoms of 2 on cyclophosphazene core and Cu2+ [44,61]. After, evaluated the UV-Vis absorption of 2 in various solvent system, fluorescence spectrum of 2 was evaluated when excited at 270 nm with same solvents. According to Fig. S7,

fluorescence emission signals of compound 2 was not significantly affected by change of solvent system. The maximum fluorescence wavelength was obtained at 316 nm for all solvents and maximum fluorescence intensity was obtained in acetonitrile. In addition, the lowest fluorescence intensity was observed in DMSO for 2 with same wavelength. The fluorescence emission spectra and UV-Vis electronic absorption spectra of 2/3 in acetonitrile are shown in Fig. 4. The Stokes shift of 2 in acetonitrile was determined as 76 nm where Stokes shift of 3 could not determine due to very weak fluorescence response. After complexation, differences such as hypsochromic or bathochromic shifts and/or new absorption bands are observed according to electronic absorption spectrum of the free ligand in the electronic absorption spectrum. This can be considered as proof of the complex formation [44, 62,63]. Hence to prove the complexation of 2-Cu2+ UV-Vis titration were carried out. Accordingly, 0.1 M stock solution of CuCl2 was prepared with distillated water and CuCl2 (Cu2+ ions) were added to 50 µM DMSO solution of 2. After addition of the metal ion, UV-Vis electronic and fluorescence emission spectra of this solution were recorded. As can be seen from Fig. 5, new absorption band was observed at 303 nm after addition of Cu2+ from 0.1 equiv. to 1.0 equiv. in solution of 2 (Fig. 5). The obtained new electronic absorption band can be evidence for charge transfer (LMCT). In addition, strong fluorescence emission of 2 was linearly quenched with gradually addition of Cu2+. The highly efficient quenching indicated that fluorophores showed a specific response to Cu2+ due to the chelation-enhanced fluorescence quenching effect which was previously reported in the literature [64,65]. A comparison of the absorption and emission spectra of 50 µM compound 2 + 1.0 equiv. Cu2+ and compound 3 which was a complex of compound 2 and Cu2+was given in Fig. S8. As shown in Fig. S8, new absorption band (303 nm) belonging to charge transfer between the metal and ligand and significant fluorescence quenching were observed at both 50 µM compound 2 + 1 equiv. Cu2+ and compound 3. This result indicated that the spectroscopic

absorption result of 50 µM compound 2 + 1.0 equiv. Cu2+ is consistent with the crystal structure of compound 3 [44]. To get deeper information about photophysical properties of compounds 2 and 3, fluorescence quantum yields were calculated with quinine sulfate (in 0.1M H2SO4) (ΦF=0.54) as a standard and they were calculated by the comparative method (Eq. (1)) [66, 67]. (1) where F and FStd are the areas under the fluorescence emission curves of the target compounds (2 and 3) and the standard. A and AStd are the respective absorbance of target compounds (2 and 3) and the standard at the excitation wavelengths. The refractive indices (n) of the solvents were employed in calculating the fluorescence quantum yields in different solvents. The fluorescence quantum yields were 0.20 for 2, and <0.01 for 3. 3.5.

Electrochemical properties, molecular orbital levels and energy gaps of 2 and 3

g. S9 depicts CV and SWV of compound 2 and 3. The compound 2 showed an irreversible reduction with E1/2 value of -2.22 V belonging to the radical anion formation in the compound and an oxidation with E1/2 value (1.23 V) corresponding the radical cation formation in the unit compound 3. Moreover, compound 3 demonstrated an irreversible reduction with E1/2 value of -2.17 V and two oxidations with E1/2 values of 0.21 and 1.17 V, which had additionally quasi-reversible redox couple at 0.21 corresponding to Cu(I) to Cu(II). Band gap and HOMO-LUMO levels values give further information on the potential using of a new molecule for many applications such as electrochemical sensor, solar cell and light emitting diodes. HOMO-LUMO energy levels were summarized in Table S2 and calculated by UVVis electronic absorption spectra (λonset) and CV. The HOMO and LUMO energy levels of the compounds 2 and 3 were calculated by using the oxidation and reduction values from CV. The HOMO energy levels of 2 and 3 were found to be -5.63 and -5.57 eV respectively using the equation EHOMO = - [(Eox - E1/2(ferrocene)) + 4.8]. The LUMO energy of the compounds were

found to be -2.18 and -2.23 eV, respectively using the equation: ELUMO = - [(Ered E1/2(ferrocene)). Band gaps of the compounds 2 and 3 were found to be 3.45 and 3.34 from electrochemical measurements and 4.08 and 3.27 using the equation of Eg(eV) = 1240/λonset (nm). These results indicated that compound 2 and 3 are located at high energy levels and large band gap which means these compounds are potentially useful in light emitting diodes, electronic devices and solar cells. 3.6. ESR measurements Due to Cu (II) ion has a single unpaired electron occupies one of the d-orbitals (d9), The ESR measurement was performed to characterize the magnetic centre of 3 [68, 69]. Fig. 6 demonstrated the ESR spectrum of solid-state 3 and its gII, g⊥, G values were calculated as 2.097, 2.070 and 1.40, respectively. According to obtained gII, g⊥, G values (gII > g⊥ > ge (2.0023)), unpaired d electron is in the dx2-y2 orbital of Cu (II) and the spectral features are characteristics of axial symmetry as expected [32,70]. gII value which is parameter for the covalent character of chemical bond between the metal-ligand was observed a less than 2.30 and it point out a significant covalent character of chemical bond [70]. In addition, G (geometric parameter) can give an information about interaction between Cu(II) centre within complex [70]. It can be calculated as a function of gII and g⊥ values according to G = [(gII 2.0023) / (g⊥ - 2.0023)] equation and found as less than four (G <4) [70]. This result proved a significant interaction between the Cu (II) centres with ligand in the complex [70,71]. 4. Conclusion In this work, at first new cyclotriphosphazene ligand (2, L) substituted with 2,2′dioxybiphenyl- and imidazolyl groups was synthesized and then, its Cu coordination polymer (3) with 1D-chain-structure was obtained. According to single-crystal X-ray results, the structure of six coordinate copper (II) complex (6) was formed two cyclotriphosphazene rings linked by di- N-Cu-N bridges. The cyclotriphosphazene Cu (II) complex showed octahedral

geometry. The electronic absorption and fluorescence behavior of 2 and 3 were also investigated in various solvents at different concentration. The compounds showed absorption in the 240-280 nm region for 2 where 240-280 nm and 303 nm for 3 with high molar extinction coefficients. New absorption band of 3 (303 nm) can be attributed to metal-ligand charge transfer (MLCT) absorption between Cu2+ and the nitrogen atoms of 2. Strong fluorescence emission of 2 was linearly quenched with gradually addition of Cu2+ that can be due to the chelation-enhanced fluorescence quenching effect. Moreover, electrochemical features of these novel compounds were investigated. 3 had more redox state and smaller optical and electrical band gaps as compared to its ligand 2, which might have potential application for different electronic devices. Appendix A.Supplementary material CCDC 1912260 (2) and 1912265 (3) contain the supplementary crystallographic data.These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:[email protected]. References [1] C. Janiak, Engineering coordination polymers towards applications, Dalton Trans. (2003) 2781-2804. https://doi.org/ 10.1039/ b305705b. [2] B. Moulton, M. J. Zaworotko, From molecules to crystal engineering: Supramolecular isomerism and polymorphism in network solids, Chem. Rev.101 (2001) 1629-1658. https://doi.org/ 10.1021/cr9900432. [3] J.P. Zhang, Y.B. Zhang, J.B. Lin, X.M. Chen, Metal azolate frameworks: From crystal engineering to functional materials, Chem. Rev.112 (2012) 1001-1033. https://doi.org/ 10.1021/cr200139g.

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Scheme 1. Synthesize of ligand (2,L).

Scheme 2. Synthesize of 1D copper (II) coordination polymer (3)

Table 1. X-ray crystallographic data and refinement parameters for compounds of 2 and 3. 2

3 C30H22N7O4P3 C60H44Cl2CuN14O8P6 Empirical formula 637.45 1409.35 Fw 296.15 296.15 T (K) Orthorhombic Triclinic Crystal system Pccn P-1 Space group 10.0375(7) 7.9096(11) a (Å) 19.1384(13) 13.875(2) b (Å) 16.9274(11) 16.155(3) c (Å) 90.643(13) α (°°) 102.784(12) β(°) 93.222(12) γ(°) 3 3251.8(4) 1725.7(5) V (Å ) -1 1.302 1.356 ρ (calcd) (g cm ) 4 1 Z 1312.0 719.0 F(000) -1 0.228 0.594 µ(mm )(MoKα) 0.444/0.075/0.071 0.724 × 0.143 × 0.045 Crystal size (mm3) 36913 0.724 × 0.143 × 0.045 Reflection collected 2842 [Rint = 0.1140, Rsigma = 6023 [Rint = 0.0735, Rsigma = Independent Reflection 0.0548] 0.1365] 6023/0/413 Data/Restraints/Parameters 2842/0/201 24.99 24.99 θ max (°°) 0.980/0.984 0.903/0.974 Tmin/Tmax -11 ≤ h ≤ 11, -22 ≤ k ≤ 22, -20 -9 ≤ h ≤ 9, -16 ≤ k ≤ 14, -19 ≤ l h/k/l ≤ l ≤ 20 ≤ 19 6023/0/413 Data/restraints/parameters 2842/0/201 1.002 0.962 Goodness-of-fit on F2 2 2 R1 = 0.0471, wR2 = 0.1136 R1 = 0.0594, wR2 = 0.1210 R [F >2σ(F )] R1 = 0.0790, wR2 = 0.1325 R1 = 0.1186, wR2 = 0.1525 wR[all reflections] 0.31/-0.39 Largest difference peak 0.22/-0.28 and hole (eÅ-3)

Table 2. The selected bond lengths (Å) and angles (°) for compounds 2 and 3.

P1-N1 P1-N2 P2-N2 P2-N3 P1-O1 P1-O2 N1-P1-N2 N21-P2-N2 P11-N1-P1 P2-N2-P1 N3-P2-N31 O1-P1-O2 ΣN angles for N3

2 1.5690(18) 1.580(3) 1.571(2) 1.670(3) 1.578(2) 1.585(2) 118.05(15) 118.3(2) 122.1(2) 121.74(16) 100.49(18) 102.85(11) 358.7

P1-N1 P1-N3 P2-N1 P2-N2 P3-N2 P3-N3 P1-N4 P1-N6 P2-O1 P2-O4 P3-O2 P3-O3 Cu1-N51 Cu1-N73 Cu1-Cl1 N1-P1-N3 N2-P2-N1 N2-P3-N3 P1-N1-P2 P2-N2-P3 O2-P3-O3 O4-P2-O1 P1-N3-P3 N4-P1-N6 N73-Cu1-N51 Cl1-Cu1-N5 Cl1-Cu1-N7 Cl1-Cu1- Cl1i ΣN angles for N4 ΣN angles for N6

Symmetry codes: 11/2-x,1/2-y,+z for 3; 12-x,2-y,2-z; 21+x,+y,+z; 31-x,2-y,2-z; i-x,-y,-z for 4

3 1.558(4) 1.565(4) 1.584(4) 1.564(4) 1.570(4) 1.594(4) 1.679(4) 1.684(4) 1.577(4) 1.574(4) 1.578(3) 1.583(3) 2.009(4) 1.998(4) 2.7896(16) 122.1(2) 116.8(2) 117.3(2) 119.9(2) 123.7(3) 103.42(18) 103.32(19) 118.2(3) 101.42(19) 90.31(16) 90.05(13) 89.73(13) 180.00 359.74 359.76

a

b

Fig.1. a) The crystal structure of 2, showing the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. [Symmetry code (i): -x,-y,-z] b) The view of C-H···O interaction in crystal package of 2.

a

b

Fig.2.a) The crystal structure of 3, showing the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. [Symmetry code (i): -x,-y,-z], b) The view of polymer chain of 6.

a)

b)

Fig. 3. a) UV-Vis absorption and b) fluorescence spectra of 2 (50 µM) in different solvents, λexc=270nm.

Table 3. Molar absorptivity (ε) of compound 2 in different solvents. ε (L.mol-1.cm-1) 2

DCM 5.48x104

ACN 6.36x104

EtOH 3.84x104

DMSO 6.87x104

Fig. 4. UV-Vis absorption (solid lines) and fluorescence spectra (solid lines) 2 and 3 in ACN, λexc=270nm.

a)

b)

Fig. 5. a) UV-Vis absorption and b) fluorescence titration of 2 (50 µM) with gradually increasing amount of Cu2+ in DMSO, λexc=270nm. Insets: Linear signal response of 2 to Cu2+.

Fig. 6. Solid-state ESR spectrum of complex 3.

Highlights: •

New cyclotriphosphazene including imidazole rings as ligand was synthesized.

•

One-dimensional copper (II) coordination polymer was prepared.

•

Crystal structures of these compounds were characterized by single-crystal X-ray crystallography.

•

The photophysical and electrochemical properties of these compounds were evaluated.