Synthesis, crystal structure, thermal, spectroscopic and theoretical studies of N3O2-donor Schiff base and its complex with CuII ions

Accepted Manuscript Synthesis, crystal structure, thermal, spectroscopic and theoretical studies of N3O2-donor Schiff base and its complex with CuII ions Agata Bartyzel, Agnieszka A. Kaczor PII: DOI: Reference:

S0277-5387(17)30702-7 https://doi.org/10.1016/j.poly.2017.11.003 POLY 12904

To appear in:

Polyhedron

Received Date: Accepted Date:

15 September 2017 2 November 2017

Please cite this article as: A. Bartyzel, A.A. Kaczor, Synthesis, crystal structure, thermal, spectroscopic and theoretical studies of N3O2-donor Schiff base and its complex with CuII ions, Polyhedron (2017), doi: https://doi.org/ 10.1016/j.poly.2017.11.003

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Synthesis, crystal structure, thermal, spectroscopic and theoretical studies of N3O2-donor Schiff base and its complex with CuII ions

Agata Bartyzel1,*, Agnieszka A. Kaczor2,3 1

Department of General and Coordination Chemistry, Maria Curie-Skłodowska University, Maria CurieSkłodowska Sq. 2, 20-031 Lublin, Poland

2

Department of Synthesis and Chemical Technology of Pharmaceutical Substances with Computer Modeling

Laboratory, Faculty of Pharmacy with Division of Medical Analytics, Medical University, 1 Chodzki St., PL20093 Lublin, Poland 3

University of Eastern Finland, School of Pharmacy, Department of Pharmaceutical Chemistry, Yliopistonranta 1, P.O. Box 1627, FI-70211 Kuopio, Finland

ABSTRACT The new o-hydroxy N3O2-donor Schiff base (H2L) was synthesized and characterized using FITR and UV-Vis spectroscopies, X-ray diffraction analysis, thermogravimetric methods and computational studies. In the solid state intramolecular proton transfer from the phenolic oxygen to the imino nitrogen atom is observed. The resulting compound occurs as a mixture of phenol-imine and zwitterionic forms. The temperature does not affect significantly the shift of equilibrium from the phenol-imine tautomer to the zwitterion form. In solution the H2L exists mainly in the phenol-imine tautomeric form but in more polar solvents stabilization of the more polar keto-amine form is also observed. The reaction of H2L with CuII ion at the stoichiometric metal:ligand 2:1 ratio results in formation of cyclic, tetranuclear complex where the coordination geometry around each metal centres is distorted square pyramid.

Keywords: chelating ligand; copper complex; phenol-keton tautomerism; crystal structure; Schiff base

INTRODUCTION Schiff bases obtained by the reaction of amines with aromatic o-hydroxy aldehydes or ketones play an important role in the coordination chemistry. They have been often used as chelating 1

ligands because they form stable complexes readily with most of the transition metals which have interesting structures, functional properties and potential applications in various areas such as catalysis, luminescent probes, analytical chemistry, magneto-structural chemistry, agrochemical, biological fields etc. [1-7]. Moreover, o-hydroxy Schiff bases are able to form the intramolecular, resonance-stabilized, strong hydrogen bonds (O-H···N) resulting in creation of a six-membered ring [4, 8-11]. In the so formed ring the intramolecular proton transfer from the hydroxylic oxygen to the imino nitrogen atom is often observed. As a result this type of compounds can exist in the two tautomeric forms: phenol-imine (OH) or ketoamine (NH) [8-14]. The NH tautomer can also exist in a zwitterionic form which is characterized by the presence of ionic N+H···O hydrogen bond [8, 9, 11, 15, 16]. The proton transfer, associated with remarkable changes in the -electron distribution, often requires a small amount of energy [4] which can be obtained by temperature changes or light, causing the ortho-hydroxy Schiff base compounds often exhibit thermo- and photochromic properties [12, 17]. These phenomena provide the potential applications of this type of compounds such as data storage, information processing, telecommunication and optical switching [12, 17, 18]. In this paper, the synthesis of N3O2donor Schiff base resulting from the condensation of diethylenetriamine with o-hydroxybenzophenone and its complex with CuII ions is discussed. These compounds were characterized based on the spectroscopic (IR, UV–Vis), X-ray crystallographic techniques and thermal (TG-DSC, TG-FTIR) methods, elemental analysis as well as computational studies. EXPERIMENTAL Materials Diethylenetriamine, o-hydroxybenzophenone and Cu(CH3COO)2·H2O used for the synthesis of Schiff base and its complex were commercially available from Aldrich Chemical Company and Alfa Aesar Company. The organic solvents were purchased from the Polish Chemical Reagents. All chemicals and solvents were reagent grade and were used without further purification. Preparation of 2,2'-{iminobis[2,1-ethanediylnitrilobenzylidene]}diphenol (H2L) The Schiff base (H2L, where L = C30H27N3O2) was synthesized by the method similar to that reported in previous papers [5, 10, 19]. Mixtures of 10 mmol of o-hydroxybenzophenone and 5 mmol diethylenetriamine in 40 mL of methanol were refluxed for 2 h. The excess of the 2

solvent (ca. 30 mL) was then evaporated and after cooling to 4 C yellow solids were precipitated. The products were collected by filtration, washed with cold methanol and dried in air. A small fraction of solid was dissolved in hot methanol and allowed to recrystallize slowly at room temperature. Yield: (75.13%); Elem. anal. for C30H29N3O2 (FW 463.57 g mol1

) (%): calcd. C 77.73, H 6.31, N 9.06; found C 78.07, H 6.46, N 9.23.

Synthesis of CuII complex The complex was synthesized from methanol solution with the molar ratio of the metal acetate to the Schiff base 2:1. The appropriate amount of copper(II) acetate dissolved in methanol (20 mL) was added to a stirred hot solution of Schiff base (0.2 g) in MeOH (30 mL). The obtained mixture was refluxed for 1 h. Then, the solution volume was reduced to 10 mL, which resulted in obtaining a small amount of solvent-free complex (1a). The precipitates were collected by filtration, washed several times with methanol and dried in air. The solution was allowed to stay in the fridge at 4 °C for slow evaporation of the solvent. After a few days greenish-blue crystals (1b, [Cu4L2ac4]·4CH3OH) were formed. In solution the crystals are stabilized by solvent molecules whereas they are highly unstable outside their mother liquor. After removing crystals 1b from the solution, they are very quickly converted into dark green polycrystalline, powder complex (1c). The yields of 1a and 1c complexes and some of their physicochemical properties are listed below: [Cu4L2ac4] (1a) (ac – acetate ion) – dark green powder; yield, 8.59 % (26.2 mg); Elem. anal. for Cu4C68H66N6O12 (FW 1413,47 g mol-1) (%): calcd C 57.58, H 4.71, N 5.59; found C 57.57, H 4.64, N 6.04. [Cu4L2ac4]·H2O·CH3OH (1c) – dark green powder; yield, 42.17 % (134.2 mg); Elem. anal. for Cu4C69H72N6O14 (FW 1463,53 g mol-1) (%): calcd C 56.63, H 4.96, N 5.74; found C 56.52, H 4.86, N 5.86. Conductivities (C = 0.001 mol L-1 , λm [ -1 cm2 mol-1]): 75.71 (MeOH), 32.10 (EtOH), 0.16 (THF), 6.29 (DMF). Characterization The Perkin-Elmer CHN 2400 analyzer was used for determination of C, H and N contents. The molar conductivities of complex were measured in different solvents at the concentration 10-3 mol L-1 using the PHYWE 13701.93 conductivity meter (at 25 °C). Powder X-ray diffraction (XRD) measurements were performed on an Empyrean powder diffractometer (PANalytical, The Netherlands) using CuK  radiation

3

( = 1.5405 Å) in the 2 range from 4° to 80° with a step of 0.026°. The positions of the peaks and their intensities were established using the analytical software package WinPLOTR [20, 21]. The computer program DICVOL06 was used for determination of the unit cell and indexing of the X-ray diffraction pattern of powder compounds [22]. The first twenty lines were used for calculations and additionally, the absolute error on each observed line was fixed at 0.03-0.05°. Reliability of the obtained unit cell was estimated by the figure of merit M N [23] and FN [24]. The unit cell parameters of H2 L and complexes 1a and 1c calculated from the X-ray powder diffraction data are listed in Table 1. The Thermo Scientific Nicolet 6700 FT-IR spectrometer with a Smart iTR diamond ATR accessory was used for recording compounds spectra. Data was collected in the range 4000- 600 cm-1, with a resolution of 4 cm-1 for 16 scans. The bands characteristic of both ligand and stable forms of complexes (1a and 1c) are listed in Table S1 (see Supplementary material). The electronic spectra (UV-vis) of H2 L and copper(II) complex in solution were recorded by a Genesys 10s spectrophotometer (Thermo Scientific). The measurements were made at room temperature (20 °C) in the range of 200-900/1100 nm for solution with a concentration of 2.5·10 -5 mol L-1. The single-crystal diffraction measurements were performed on an Oxford Diffraction Xcalibur CCD diffractometer with the graphite-monochromated MoK radiation (λ = 0.71073 Å) at the temperature of 293(2) and 100(2) K. Data sets were collected using the ω scan technique. The program CRYSALIS PRO [25] was used for data collection, cell refinement and data reduction. The data were corrected for Lorentz and polarization effects. A multi-scan absorption correction was performed with the diffractometer software. The structures were solved by direct methods using SHELXS-2013 and refined by the full-matrix least-squares on F2 using SHELXL-2013 [26] (both implemented in the WinGX software package [27]). All non-hydrogen atoms were refined with the anisotropic displacement parameters. The hydrogen atoms residing on carbon atoms were positioned geometrically and refined applying the riding model [C–H = 0.93–0.97 Å and with Uiso(H) = 1.2 or 1.5 Ueq(C)]. The hydrogens bound to O and N atoms were located in the difference Fourier map or placed geometrically and refined using riding models (with Uiso(H) = 1.5Ueq(O) or 1.2Ueq(N)), except for hydrogen linked to N2 atom in H2 L which was refined isotropically. In the case of 1b, the distances of O6aC33, O6bC33 and O7bC35 were restrained using the DFIX command. The geometrical calculations were performed using the PLATON program [28]. The molecular structures were drawn with 4

ORTEP3 for Windows [29] and Mercury [30]. Crystallographic data were deposited with the CCDC and are available on request, quoting the deposition numbers CCDC 1574026 (H2L in 293 K), 1574025 (H2 L in 293 K) and 1574020 (1b). Thermal analyses of H2L, 1a and 1c (TG-DSC) were carried out in the range 30-800 °C using a Setaram Setsys 16/18 instrument. The samples (5.23-7.21 mg) in flowing air atmosphere were heated in a ceramic crucible with a heating rate of 10 °C min −1. The corresponding TG and DSC curves are included in the Supplementary material. The thermal behaviours of compounds were also studied in nitrogen atmosphere together with the FTIR spectra of the gaseous products analysis. The measurements were performed using the TG Q5000 analyser (TA Instruments) coupled to the Nicolet 6700 FTIR spectrophotometer (Thermo Scientific). The samples were heated with the rate of 20 °C min-1 in an open platinum crucible from at the ambient temperature up to 700 °C.

Scheme 1. Possible tautomeric and resonance forms of the studied bis-Schiff base, (for clarity hydrogen amine atom was placed in one position).

Computational studies The energy and geometry of the tautomeric forms of the studied bis-Schiff base A-F and copper(II) in vacuum and the considered solvents were optimized using the B3LYP DFT method and the 6-311++G(2df, 2pd) basis set of Gaussian09 software [31]. Calculations in solvents were made applying the Polarizable Continuum Model (PCM) [32]. The final energy of the tautomers was used for determination of their relative stability as previously reported [33, 34]. The crystallographic structure of the complex was used as a starting geometry for 5

calculations in vacuum, DMF and THF. This structure was modified for computations in methanol, ethanol and acetonitrile in order to reflect the experimental data. The IR spectra were computed for the tautomers A and C of the Schiff base and for the complex on the above mentioned levels of theory. The computed IR spectra were corrected using the scaling factor of 0.967 as recommended for this level of theory [35]. Moreover, the computed vibrational frequencies were unambiguously assigned by means of the potential energy distribution (PED) analysis of all the fundamental vibration modes by using the VEDA 4 program [36, 37]. The UV-Vis spectra were calculated for the tautomers A and C of the Schiff base and for the complex with the configuration interaction singles (CIS) method [38] and the timedependent (TD) approach [39]. Chemissian v. 4.43 [40] was used for visualization of UV-Vis spectra. The UV-Vis spectra were enhanced by the scaling procedure according to the own scaling factors as previously reported [19]. ChemCraft [41] and ArgusLab [42] were also used for visualization of results.

Results and discussion The direct synthesis of Schiff bases by the reaction of o-hydroxybenzophenone and diethylenetriamine results in formation of polycrystalline, yellow powder. The data from the X-ray powder diffraction analysis confirmed that the analyzed compound represents a single phase. During the recrystallization process of H2 L the crystals suitable for crystallographic measurements were formed. The unit cell parameters determined from the X-ray single crystal analysis are in good agreement with those calculated based on the powder diffraction data indicating that the slow recrystallization of H2L at room temperature does not affect its crystal structure. The synthesised Schiff base can form several tautomeric and resonance forms which are presented in Scheme 1. The relative energetic stability of the tautomeric forms of the Schiff base A-F in different environments was studied using the computational approach (Table 2). In vacuum and all the considered solvents tautomer C is energetically most stable. In vacuum tautomers C and A are most stable which is consistent with the experimental data. The least stable tautomer is the form F in vacuum, acetonitrile, DMF and THF and the form E in methanol and ethanol. However, the energetic difference between the tautomers E and F in alcohols is negligible. In acetonitrile, DMF and THF all tautomers are much more stable than the tautomer F. The general order of the tautomer stability is C>AB>D>E>F. The phenol-

6

ketone tautomerism of H2L in the crystalline solid state and in solution was investigated by the spectroscopic and single crystal X-ray diffraction analyses. The studied Schiff base has five potential donor atoms. For this reason the synthesis of complex was performed at the 2:1 CuII:H2L stoichiometric ratio leading to formation of the tetranuclear copper(II) complex. As it was mentioned earlier, the crystals are very unstable outside their mother liquor that is why chemical or thermogravimetric analysis of 1b was not feasible. As a result, polycrystalline dark green powder (1c) is formed. The 1c also crystallizes in the monoclinic system but the unit cell parameters (Table 1) differs slightly from those determined by the X-ray single crystal analysis for 1b. In the case of the polycrystalline, solvent free form of complex change of space group from the monoclinic into the triclinic is observed. The CuII compound is soluble in solvents used in the study except for acetonitrile. FTIR spectroscopy The experimental and computed IR spectra are presented in Table S1 (Supplementary material). The scaled computed IR spectra are in accordance with the experimental values. The PED analysis enabled unambiguous assignment of IR signals. In the structure of the studied Schiff base the phenol groups are present. The stretching vibrations (OH) are expected in the 3500-3300 cm-1 region. However, in the o-hydroxy Schiff bases this band is generally moved to lower frequencies (3200-2500 cm-1) due to the presence of strong intramolecular hydrogen bond O-H···NC or if the hydrogen bond becomes stronger, this band is not detected [5, 10, 19]. The lack of (OH) band in the ligand spectrum can indicate that O-H···N bonds are strong or hydrogens are shifted to nitrogen atoms. The FTIR spectrum of H2L also shows a sharp, intense band with the maximum at 1598 cm-1 which can be assigned to ν(C=N) vibrations. In the spectra of o-hydroxy Schiff base this band is usually observed above 1600 cm-1 [43-46]. Shifting the (C=N) band to the lower wavenumbers confirms strong influence of intramolecular hydrogen bonds on electron density of the azomethine groups. The medium intense band at 1261 cm-1 is probably due to the CO stretching vibrations of the phenol groups. The complexation process of the Schiff base via CuII ions affects the positions and/or intensities of the bands originating from the hydroxyl and azomethine groups. The (C=N) bands in the spectra of 1a and 1c are more intense as well as shifted to the lower frequencies for the solvent free complex (1592 cm-1) compared to the free ligand indicates the coordination of copper(II) ion by the azomethine nitrogen atoms. The metal ions are also bound via the deprotonated phenol groups. In spectra of 1a and 1c the 7

band due to (CO) vibrations appears at lower frequencies compared to that in H2L and occurs at 1240 and 1239 cm-1. Additionally, in the spectra of 1a and 1c there are two doublet peaks which are not observed in the free ligand spectrum. The first one is recorded at 1541, 1529 cm-1 for 1a and 1542, 1532 cm-1 for 1b while another one is found at 1397 and 1376 cm1

for both forms of complex (solvate and solvent free). These intense bands can be assigned to

asymmetric and symmetric stretching vibrations of the COO group indicating that the acetate ions are incorporated into the structure as counterions. In the spectrum of 1c the bands characteristic of solvents are also observed. The bands of water molecule appear at 3543, 3430 cm-1 (ν(OH)) and 1621 cm-1 δ(H2O) which is characteristic of lattice water [47]. The weak band with the maximum at 3234 cm

-1

can be linked to stretching vibrations of the

hydrogen bonded -OH group of methanol. UV-Vis spectroscopy The UV–Vis spectral data of the ligand H2L and its CuII complexes in the protic and aprotic solvents were recorded. The parameters of the experimental and computed spectra of the ligand in various solvents are listed in Table 3. In general, there is a good agreement between the experimental and computed values. The UV-Vis spectra of Schiff base depend on the type of used solvent (Fig. S1) and contain three or four bands (except for DMF). According to the literature [19, 48-51] these bands can be assigned as follows. The intense one or two bands observed below 270 nm can be assigned to the ππ* transition of the aromatic rings. The next band around 320 nm is most probably due to the →* transition of the azomethine groups. The last band was observed above 400 nm and can be due to the nπ* transition. The appearance of this band can be associated with the shift of tautomeric equilibrium from the phenol-imine to the keto-amine form (O–H···N↔O···H–N) [10, 19, 52, 53]. In solution the existence of tautomerism depending on the formation of intramolecular hydrogen bonding is often a common phenomenon; the percentages of the keto-amine form are given in Table 3. As can be seen, the intensity of this band is higher in the protic solvent, which indicates stabilization of the more polar keto-amine form in the more polar solvents. In the polar aprotic solvents, this band is very weak (ACN) or appears as a shoulder-type peak (DMF and THF). In the spectra of CuII complexes (Fig. S2) the vibrations occurring below 280 nm can be assigned to the π→π* transitions associated with the benzene rings. These bands are shifted compared to the free ligands as a result of conjugation of -electrons in the complexes which indicates anionic character of the Schiff base and the chelation of CuII ions by the ligand [54, 55]. The next bands observed at 364-376 nm, due to their molar extinction coefficient lower 8

than the previous ones, can be assigned to the charge transfer (CT) transitions combined with π→π* transitions of the imine group [56, 57]. As can be seen from Table 3 the CT transitions exhibit a small negative solvatochromism (i.e. with the increasing solvent relative polarity it is shifted towards the shorter wavelength) which suggests that polar solvents stabilize the ground state more than the excited state [10, 58, 59]. The electronic spectra of copper(II) complex show also bands associated with the d-d transitions. They are characterized by low intensity and therefore electronic spectra were also recorded for more concentrated solutions (10-3 mol L-1, Fig. S2b) in the range 400-1100 nm except for the acetonitrile solvent due to poor solubility of 1b in this medium. For the polar protic and ACN (recorded for C = 2.5·10-5 mol L-1 calculated for Cu2Lac2·H2O·CH3OH unit) solvents the d-d transitions are observed at 570-604 nm which is consistent with the square planar geometry of Cu II complexes as it was observed for the other related compounds [5, 56, 60- 62]. This can be a result of dissociation of one acetic ion per half molecule of complex (i.e. Cu2Lac2) as confirmed by the conductivity measurements. The values of the molar conductivities found in the MeOH and EtOH solvents indicate uni-univalent (1:1) electrolyte behaviour [63] for the [Cu2Lac2] unit. For the aprotic solvents i.e. DMF and THF the d-d transition band is observed at 620 and 646 nm, respectively. This is consistent with the observed square pyramidal geometry around the copper(II) centres [64-67] especially since the conductivity measurements indicate the nonelectrolytic nature of complex in these solvents. Crystal structure of Schiff base and complex (1b) During recrystallization of the Schiff base and slow crystallization of the CuII complex from the methanol solutions single crystals were obtained. The crystallographic and refinement data are summarized in Table 4. The studied Schiff base crystallizes in the centrosymmetric monoclinic space group C2/c. The asymmetric unit consists of a half molecule presented in Figure 1, the amine nitrogen (N2) and hydrogen (H2) atoms are located on the 2-fold axis. The selected bond distances and angles are reported in Table 5, the hydrogen bond parameters are given in Table 6. H2L has a non-planar conformation. The dihedral angles between two planes of o-hydroxyphenyl ring are 67.60(4)° (100 K) and 67.62(3)° (293 K) while between two planes of aromatic rings in the asymmetric unit 72.64(4)° (100 K) and 72.66(4)° (293 K). The C2O1 bonds (1.345(2) Å at 100 K and 1.340(2) Å at 293 K) have values slightly lower than those observed for single C–O (1.362 Å) while C7– N1 distances (1.290(2) Å at 100 K and 1.285(2) Å at 293 K) are a bit larger than the typical value of C=N bond (1.279 Å) [8, 68, 69]. This can indicate that the proton is rather delocalized between the two positions, i.e. the hydrogen partly bound to 9

oxygen and nitrogen atoms. The position of hydroxyl and amine H-atom was determined from the difference Fourier map each constrained with a riding model and only their occupancies were refined complementarily. The site occupancy factor for H atoms attached to O1/N1 atoms was 0.77/0.23 at room temperature and 0.71/0.29 at 100 K. The analysis of remaining bonds in the o-hydroxyphenyl ring allows us to assume that proton transfer from the hydroxyl-oxygen atom to the imine nitrogen atom leads to formation of zwitterionic resonance form. As a result, the compound occurs as a mixture of A and C forms, Scheme 1. Additionally, the most important point is that lengths of C2O1 and C7N1 bonds of H2L do not vary with the temperature which allows to conclude the temperature does not significantly affect the shift of equilibrium from the phenol-imine tautomer to the zwitterion form. In the studied Schiff base, intramolecular hydrogen bonds occur between O1 and N1 atoms; the donor–acceptor distance is 2.508(2) Å (100 K) and 2.500(1) Å (293 K) indicating a strong hydrogen bond with a highly covalent character [70]. The structure is also stabilized by weak CH···O interactions. The presence of C11-H11···O1 interactions cause formation of 1D ladder motifs which are further extended via other C9-H9···O1 bonds into the threedimensional supramolecular network (Fig. 2). Although the crystals of 1b are very unstable outside the solution, the single crystal X-ray measurements were repeated several times at room and 100 K in order to obtain enough quality data which made it possible to perform X-ray structural analysis. The solution presented here is not the best quality due to disorder of the solvent as well its poor stability. Due to the fact that the coordination of copper(II) ions by H2L is different from those reported for bis o-hydroxy Schiff bases and formation of the cyclic tetramer, the description of structure was included in the discussion. Complex 1b crystallized in the centrosymmetric monoclinic space group P21/n. The asymmetric unit consists of a half molecule depicted in Fig. 3 and additionally there are two uncoordinated methanol molecules. It is worth mentioning that the methanol molecules can be partially exchanged through water molecules which do not significantly affect the structure of the complex i.e. unit cell parameters (see Table S2) and coordination of Cu II ions through L2- anion. The CuII ions are coordinated by two fully deprotonated ligand; the Cu1 ions are bound via one Ophenolato and two nitrogen atoms of one Schiff base while Cu2 ions are surrounded by one azomethine N and two phenolate O atoms derived from two L2- ions. Additionally, in the inert coordination sphere there are four acetate ions which neutralize the charge and consequently form a neutral cyclic complex, [Cu4L2ac4] (Fig. 3). The coordination polyhedrons around CuII ions have distorted square pyramidal geometries (Fig. 4) which is confirmed by the value of τ5 parameter (0.17 10

for Cu1 and 0.27 for Cu2) [71]. The Cu-O and Cu-N bonds are within normal values and comparable to those observed in the related copper complexes [56, 72, 73]. The Cu1 and Cu2 ion are grouped in dimers which are bridged by two oxygen atoms (2-Ophenolate and 2Ocarboxylate) and one carboxylate group (2-acetate-O,O') with the Cu1-Cu2 separation of 3.043(1) Å. The structure is stabilized by the O-H···O hydrogen bonds as well as weak CH···O and C-H···π interactions. The presence of the C14-H14···O6b interactions leads to formation of one-dimensional columns lying parallel to the a-axis (Figure 5) which are further extended through C-H···Cg interactions into the 3D supramolecular network. Thermal behaviour Thermal analysis in air (TG-DSC) confirms that H 3L was obtained as a pure substance. During heating under oxidizing conditions, the first change is recorded on the DSC curve at 143 °C as the endothermic peak which is not accompanied by a mass loss (Supplementary material Fig. S3). This is characteristic of melting process. The peak is sharp (Tpeak = 146 °C) indicating that the studied Schiff base was synthesized as a crystalline, pure substance. The enthalpy of fusion calculated from DSC was 29.86 kJ mol-1. The combustion and thermal degradation of H2L start over 230 °C and proceeds in two stages. The first step (237-397 °C) is characterized by a thermal decomposition of the greater part of the compound (75.78%) and probably is mainly associated with the defragmentation and release of volatile products while the second one (453-664 °C) involves combustion of residue products which is accompanied by a significant exothermic effect. Thermal behaviour of H2L was investigated in the nitrogen atmosphere during which the FTIR spectra of gaseous decomposition products were recorded. The pyrolysis process proceeds in one major step during which more than 90 % of the initial mass of the compound is degraded. The significant mass loss is observed at a higher temperature than that in the oxidizing atmosphere i.e. 270 °C. The first bands, which appear at 280 °C in the FTIR spectra of emitted gases, are characteristic of ammonia molecules (two characteristic maxima at 966 and 931 cm-1 [74]. This suggests that the pyrolysis process begins with the degradation of the aliphatic unit of compound and breaking the azomethine and amine bonds. This causes destabilization and pyrolysis of the remaining part of molecule and in the gaseous decomposition products (292 °C) the molecules of water, carbon dioxide and phenol appear. Further heating causes that the intensities of the bands of the aforementioned gases increase and in the FTIR spectra new peaks associated with the HNCO/CH3NCO (333 °C) and amines (385 °C, probably dimethyl- and diethylamine) molecules are recorded. At the end of this stage (503°C) in the mixture of emitted gasses the NH3, CO2, CO, H2O, HNCO/CH3NCO, phenol and amine 11

molecules are present. In contrast to the thermal decomposition in air atmosphere, the pyrolysis of H2L is not finished; the mass of the residue found at 503°C is 5.59%. Heating over this temperature leads to further slow pyrolysis of remaining organic matrix; the difference in the mass loss at 503 °C and 700 °C (the final temperature of analysis) is more than 1 %. The main gaseous products released during this interval are as follows: NH 3, CO2, CO, H2O, HNCO/CH3NCO, phenol and CH4 (over 655 °C). The solvent free complex (1a) is stable at room temperature (see Fig. S4, Supplementary material). Thermal decomposition under the oxidizing conditions follows three major steps. The first one is recorded between 190 °C and 205 °C and is probably related to removal of part of the acetate ions, found mass loss is 5.83 % while calculated equals 4.17 % and 8.34 % in the case of losing one and two acetate ions, respectively. The formed product is unstable and immediately undergoes further degradation. This stage occurs in the temperature range 205-381 °C and is characterized by the fast mass loss (48.16%). At the beginning probably it is associated with removing other acetate ions and later the combustion and degradation processes of the Schiff base begin. Similar to the previous stage, the formed products are unstable and undergo combustion into CuO (found/calcd. overall mass losses: 77.90/77.48 %). The thermal degradation of 1c in air atmosphere starts with an initial well-separated mass loss in the temperature range 63-93 °C with an endothermic effect recorded on the DSC curve (Fig. S5, Supplementary material). This step is associated with the desolvation process. A calculated mass loss due to removal of solvent molecules (H 2O and CH3OH) is 3.42 %, while the measured weight loss is 3.03 %. Similarly to the solvent free complex, next stage at 174375 °C is related to removal of acetate ion (found/calcd. mass losses for one acetate ion are 4.01/3.97%). The last stage starts at 375 °C and like that observed for 1a is connected with removing of other acetate ions and thermal degradation of L2-. The stable product CuO is formed at 542 °C (the overall found/calcd. mass losses are 78.52/78.25 %). The thermal behaviour of 1c was also studied in inert atmosphere. The pyrolysis process follows four steps. During the first one at 55-105 °C mainly desolvation process occurs. The analysis of the FTIR spectra confirms the presence of water and methanol molecules in the emitted gases (Fig. S6, Supplementary material). The next two intervals 170-221 °C and 225-260°C are mainly associated with removing acetate ions from the structure; during the first stage one acetate ion is evolved (found/calcd. mass loss: 4.52/4.03 %) while in the second one the other three ions are lost (found/calcd. mass loss: 15.13/12.09 %). These stages were confirmed in the recorded FTIR spectra of the emitted gases; bands characteristic of acetic acid and trace 12

products of its decomposition (i.e. H2O and CO2) are observed at 175 C. Around 250 C characteristic NH3 molecule peaks (Fig. S7, Supplementary material) appear on the FTIR spectra which explains the greater mass loss than expected for four acetate ions. The last step observed between 260 and 504°C is related to pyrolysis of Schiff base during which there are released the following gas products: CO2, H2O, NH3, phenol (345°C), benzonitrile (360°C) and HNCO/CH3NCO (380°C). The final residue is probably a mixture of CuO, carbon and unburnt part of the organic matrix; the found total mass loss is 69.33%. Conclusions A novel N3O2-donor Schiff base ligand and its corresponding homotetranuclear CuII complex were designed and synthesized. The computational studies show that the phenol-imine (A) and zwitterionic (C) forms are most stable in vacuum. This is in agreement with the crystal structure of H2L i.e. the compound occurs as a mixture of A and C forms. In solution the phenol-imine form of ligand is predominant, although in polar solvents the more polar form is also stabilized. The complexation process of CuII ion via the studied Schiff base results in formation of the unusual cyclic, tetranuclear complex. The solvent molecules stabilize the crystals of 1b in solution. Outside their mother liquor they are transformed into the polycrystalline complex (1c) which contains methanol and water molecules in its structure. The solvent free 1a and powder 1c complexes are stable at room temperature. Heating of complex 1c leads at first to the desolvation and next to the decomposition process. The degradation of ligands in nitrogen atmosphere is connected mainly with the release of acetic, CO2, H2O, NH3, phenol, benzonitrile and HNCO/CH3NCO molecules.

Appendix A. Supplementary data CCDC 1574026, 1574025 and 1574020 contain the supplementary crystallographic data for H2 L

and

its

complex.

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]. Supplementary data associated with this article can be found, in the online version.

References 1. K.C. Gupta and A. K. Sutar, Coord. Chem. Rev. 252 (2008) 1420. 2. P.A. Vigato, V. Peruzzo and S. Tamburini, Coord. Chem. Rev. 256 (2012) 953. 3. A. Bartyzel, E. M. Cukrowska, Anal. Chim. Acta, 707 (2011) 204. 13

4. B. Cristóvão, B. Miroslaw, Inorg. Chem. Commun. 52 (2015) 64. 5. A. Bartyzel, J. Therm. Anal. Calorim. 127 (2017) 2133. 6. P. Wu, D.-L. Ma, C.-H. Leung, S.-C. Yan, N. Zhu, R. Abagyan, C.-M. Che, Chem. Eur. J. 15 (2009) 13008. 7. O. Wichmann, R. Sillanpää, A. Lehtonen, Coord. Chem. Rev. 256 (2012) 371. 8. G. Alpaslan, M. Macit, A. Erdönmez, O. Büyükgüngör, J. Mol. Struc. 997 (2011) 70. 9. K. Pyta, P. Przybylski, K. Klich, W. Schilf, B. Kamieński. E. Grech, B. Kołodziej, A. Szady-Chełmieniecka, B. Brzezinski, Struct. Chem. 25 (2014) 1733. 10. A. Bartyzel, Inorg. Chim. Acta 459 (2017) 103. 11. I. Król-Starzomska, A. Filarowski, M. Rospenk, A. Koll, S. Melikova, J. Phys. Chem. A 108 (2004) 2131. 12. V.I. Minkin, A.V. Tsukanov, A.D. Dubonosov, V.A. Bren, J. Mol. Struc. 998 (2011) 179. 13. K. Ogawa, Y. Kasahara, Y. Ohtani, J. Harada, J. Am. Chem. Soc. 120 (1998) 7107. 14. V.Z. Mota, G.S.G. de Carvalho, P.P. Corbi, F.R.G. Bergamini, A.L.B. Formiga, R. Diniz, M.C.R. Freitas, A. D. da Silva, A. Cuin, Spectrochim. Acta Part A99 (2012) 110. 15. A. Núñez-Montenegro, A.Pino-Cuevas, R. Carballo, E.M. Vázquez-López, J. Mol. Struc. 1062 (2014) 110. 16. A. Trzesowska-Kruszynska, Struct. Chem. 21 (2010) 131. 17. E. Hadjoudis, I. M. Mavridis, Chem. Soc. Rev. 33 (2004) 579. 18. M. Rubčić, K. Užarević, I. Halasz, N. Bregović, M. Mališ, I. Đilović, Z. Kokan, R. S. Stein, R. E. Dinnebier, V.Tomišić, Desmotropy, Chem. Eur. J. 18 (2012) 5620. 19. A. Bartyzel, A.A. Kaczor, J. Coord. Chem. 68 (2015) 3701. 20. T. Roisnel, J. Rodriguez-Carvajal,. Fullprof, version May 2016, LLB, CEA-CNRS, France, (2013) http://www.cdifx.univ-rennes1.fr/winplotr/winplotr.htm. 21. T. Roisnel, J. Rodriguez-Carvajal, Proceedings of the Seventh European Powder Diffraction Conference (EPDIC 7), ed. R. Delhez, E. J. Mittenmeijer, (2000) 118. 22. A. Boultif, D. Louër, J. Appl. Crystallogr. 37 (2004) 724. 23. P.M. de Wolff, J. Appl. Crystallogr. 1 (1968) 108. 24. G.S. Smith, R.L. Snyder, J. Appl. Crystallogr. 12 (1979) 60. 25. Agilent Technologies. CRYSALIS PRO; Yarnton, Oxfordshire, England, UK, 2013. 26. G.M. Sheldrick, Acta Cryst. A64 (2008) 112. 27. L.J. Faruggia, J. Appl. Crystallogr. 32 (1999) 837. 28. A. L. Spek, J. Appl. Cryst. 36 (2003) 7. 29. L.J. Farrugia, J. Appl. Cryst. 45 (2012) 849. 14

30. C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, M. Towler, J. van de Streek, J. Appl. Cryst. 39 (2006) 453. 31. Gaussian 09, Revision E.01, Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian, Inc., Wallingford CT, 2009 32. S. Miertuš, E. Scrocco, J. Tomasi, Chem. Phys. 55 (1981) 117. 33. M. Pitucha, Z. Karczmarzyk, W. Wysocki, A.A. Kaczor, D. Matosiuk, J. Mol. Struct. 994 (2011) 313. 34. A.A. Kaczor, T. Wrobel, Z. Karczmarzyk, W. Wysocki, E. Mendyk, A. Poso, D.Matosiuk, M. Pitucha, J. Mol. Struct. 1051 (2013) 188. 35. Vibrational frequency scaling factors. http://cccbdb.nist.gov/vibscalejust.asp 36. M.H. Jamróz, Vibrational Energy Distribution Analysis VEDA 4, Warsaw, 2004. 37. M.H. Jamróz, Spectrochim. Acta A114 (2013) 220. 38. J. B. Foresman, Æ. Frisch, Exploring Chemistry with Electronic Structure Methods, 2nd ed. Gaussian, Inc., Pittsburgh, PA, 1996. 39. R. Bauernschmitt and R. Ahlrichs, Chem. Phys. Lett. 256 (1996) 454. 40. Chemissian v. 4.43 demo version, http://www.chemissian.com 41. ChemCraft v. 1.7 software available on http://www.chemcraftprog.com 42. ArgusLab, software available on http://www.arguslab.com 43. B. Ambrozini, E. Dockal, É.T.G. Cavalheiro, J. Therm. Anal. Calorim. 115 (2014) 979. 44. B. Cristóvão, B. Miroslaw, Inorg. Chim. Acta. 401 (2013) 50. 45. B. Cristóvão, Spectral, J. Serbian Chem. Soc. 76 (2011) 1639. 46. S. Meghdadi, K.Mereiter, M. Amirnasr, F. Fadaee, A. Amiri, J. Coord. Chem. 62 (2009) 734. 15

47. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds. Part B: Applications in Coordination, Organometallic, and Bioinorganic Chemistry vol. B, John Wiley & Sons Inc., Hoboken, New Jersey 2009, p. 58. 48. T. Glaser, M. Heidemeier, R. Fröhlich, P. Hildebrandt, E. Bothe, E. Bill, Inorg. Chem. 44 (2005) 5467. 49. P. Jeslin Kanaga Inba, B. Annaraj, S. Thalamuthu, M.A. Neelakantan, Spectrochim. Acta Part A104 (2013) 300. 50. B. Bosnich, J. Am. Chem. Soc. 90 (1968) 627. 51. É. Tozzo, S. Romera, M. P. dos Santos, M. Muraro, R. H. de A. Santos, L. M. Lião, L. Vizotto, E. R. Dockal, J. Mol. Struct. 876 (2008) 110. 52. N. Galić, Z. Cimerman, V. Tomišić, N. Galić, Z. Cimerman, V. Tomišić, Spectrochim. Acta Part A71 (2008) 1274. 53. A. Bartyzel, Polyhedron 134 (2017) 30. 54. B. Shafaatian, S.S. Mousavi, S. Afshari, J. Mol. Struc. 1123 (2016) 191. 55. G. Grivani, M. Vakili, A.D. Khalaji, G. Bruno, H.A. Rudbari, M. Taghavi, J. Mol. Struct. 1116 (2016) 333. 56. A. Bartyzel, H. Głuchowska, J. Coord. Chem. 69 (2016) 3206. 57. C. Fraser, B. Bosnich, Inorg. Chem. 33 (1994) 338. 58. C. Reichardt, Chem. Rev. 94 (1994) 2319. 59. A. Trujillo, M. Fuentealba, D. Carrillo, C. Manzur, J.R. Hamon, J. Organomet. Chem. 69 (2009) 1435. 60. A. John, V. Katiyar, K. Pang, M.M. Shaikh, H. Nanavati, P. Ghosh, Polyhedron 26 (2007) 4033. 61. M. Shakir, S. Hanif, M.A. Sherwani, O. Mohammad, S.I. Al-Resayes, J. Mol. Struct. 1092 (2015) 143. 62. M. Das, B.N. Ghosh, A. Valkonen, K. Rissanen, S. Chattopadhyay, J. Saudi. Chem. Soc. 17 (2013) 269. 63. W.J. Geary, Coord. Chem. Rev. 7 (1971) 81. 64. A. R. Amundsen, J. Whelan, B. Bosnich, J. Am. Chem. Soc. 99 (1977) 6730. 65. K. Das, U. Panda, A. Datta, S. Roy, S. Mondal, C. Massera, T. Askun, P. Celikboyun, E. Garribba, C. Sinha, K. Anand, T. Akitsu, K. Kobayashi, New J. Chem. 39 (2015) 7309. 66. K. M. Vyas, R.N. Jadeja, D. Patel, R.V. Devkar, V.K. Gupta, Polyhedron 65 (2013) 262. 67. R.N. Jadeja, K.M. Vyas, K.K. Upadhyay, R.V. Devkar, RSC Adv. 7 (2017) 17107.

16

68. F. H. Allen, O. Kennard, D. G. Watson, L. A. Brammer, G. Orpen, J. Chem. Soc. Perkin Trans. 2 (1987) S1. 69. A.K. Baghdouche, S. Mosbah, Y. Belhocine, L. Bencharif, Acta Cryst. E70 (2014) o676. 70. A. Makal, W. Schilf, B. Kamienski, A. Szady-Chelmieniecka, E. Grech, K. Wozniak, Dalton Trans. 40 (2011) 421. 71. A.W. Addison, N.T. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J. Chem. Soc. Dalton Trans. (1984) 1349. 72. M. Fondo, J. Doejo, A.M. García-Deibe, N. Ocampo, J. Sanmartín, Polyhedron, 101 (2015) 78. 73. M. Aslantas, M. Tumer, E. Sahin, Spectrochim. Acta A 71 (2008) 263. 74. A. Bartyzel, J. Coord. Chem. 66 (2013) 4292.

17

Table 1. Unit cell parameters of the polycrystalline Schiff base and complexes 1a and 1c calculated from the X-ray powder diffraction data. Complex

a/Å

b/Å

c/Å

/

β/

H2 L

13.952(6)

12.794(4)

15.468(6)

90.00

116.67(5)

1a

9.649(4)

22.541(2)

15.579(1)

99.29(1)

105.21(1)

1c

9.461(3)

23.047(1)

15.099(1)

90.00

117.88(4)

FOM M20; F20; FN M20 = 11.5; F20 = 23.7(0.0078, 108); 90.00 2467.63 F33 =13.3(0.0083, 298) M20 = 17.6; F20 = 49.1(0.0068, 60) 93.44(2) 3208.14 F37 = 19.6(0.0084, 224) M20 = 17.0; F20 = 54.2(0.0079, 47) 90.00 3275.59 F49 = 14.1(0.0090, 387) /

V (Å3)

N – number of indexed peaks

18

Table 2. Energetic stability of the tautomeric forms A-F of the studied Schiff base in vacuum and different solvents. Stabilization energy, kcal mol-1 Tautomer

Vacuum

Acetonitrile

Methanol

Ethanol

DMF

THF

A

10.11

79.33

1.58

1.70

79.31

80.82

B

4.89

79.49

1.71

1.73

79.48

79.92

C

15.24

89.24

11.47

11.53

89.23

90.02

D

7.53

79.68

1.92

2.00

79.67

80.69

E

3.38

77.80

0.00

0.00

77.79

78.08

F

0.00

0.00

0.13

0.03

0.00

0.00

19

Table 3. Electronic spectra of ligand and its complex H2 L Exp. Solvent

max [nm] ( x104

k (%)

b

[L mol-1 cm-1])a

MeOH

EtOH

ACN

DMF THF

209(4.15) 256(1.95) 321(0.64) 401(0.35) 230(2.06) 257(2.00) 322(0.68) 402(0.33) 210(4.35) 256(1.74) 321(0.71) 403(0.08) 323(0.85) 420(0.09)sh 259(1.80) 323(0.86) 407(0.04)sh

35.48

32.94

10.10

9.74 4.00

Computed CIS TD DFT max [nm]

max [nm]

209 (A) 257 (A) 310 (A) 372 (B)

256 (A) 257 (A) 326 (A) 392 (B)

236 (A) 257 (A) 310 (A) 373 (B) 217 (A) 257 (A) 310 (A) 373 (B)

256 (A) 257 (A) 326 (A) 391 (B) 256 (A) 267 (A) 326 (A) 391 (B)

310 (A) 430 (B) 257 (A) 310 (A) 373 (B)

326 (A) 422 (B) 257 (A) 326 (A) 398 (B)

Exp. max [nm] ( x104 [L mol-1 cm-1])a

210(4.12) 241(2.49) 272(1.62) 364(0.65) 604(0.02)c 243(3.45) 271(2.28) 369(0.88) 570(0.03)c 206(7.18) 235(4.26) 272(2.20)sh 372(1.36) 578(0.02) 376(0.96) 620(0.04)c 245(3.59) 379(1.94) 646(0.02)c

complex Computed CIS TD DFT max [nm]

max [nm]

212 245 277 375 616 245 277 374 579 211 239 277 374 579 385 631 250 386 653

219 252 288 381 620 254 282 376 583 221 242 283 384 609 392 646 252 390 658

a

concentration 2.5·10-5 mol L-1 calculated for Cu2Lac2·0.5H2O·0.5CH3OH unit; b Ap/Ak = k/(100 − k) where, Ap is the absorbance of the phenol-imine form (–*); Ak is the absorbance of the keto-amine form (n–*), k is the percentage of keto-amine form; c concentration 1.0·10-3 mol L-1 calculated for Cu2Lac2·0.5H2O·0.5CH3OH

20

Table 4. Crystal data and structure refinement for H2L and 1b. Compound Empirical formula Temperature K Crystal system Space group a (Å) b (Å) c (Å)  () Volume (Å3) Z Calculated density (g cm-3) μ (mm-1) Absorption correction F(000) Crystal size (mm) θ range (º) Reflections collected/unique Rint Data/restraints/parameters GooF on F2 Final R indices[I>2σ(I)] R indices(all data) Largest diff. peak/hole, e Ĺ-3

H2 L C30H29N3O2 100(2) monoclinic C2/c 13.3357(12) 12.9691(8) 15.2594(16) 115.853(12) 2375.0(4) 4 1.296 0.082 multi-scan 984 0.40 x 0.30 x 0.15 2.97 to 26.37 8999/2436 0.0304 2436/0/168 1.043 R1 = 0.0412, wR2 = 0.1038 R1 = 0.0518, wR2 = 0.1105 0.288/-0.195

H2 L C30H29N3O2 293(2) monoclinic C2/c 13.2876(7) 12.9276(4) 15.2064(7) 115.750(6) 2352.7(2) 4 1.309 0.083 multi-scan 984 0.37 x 0.30 x 0.20 2.98 to 27.49 9081/2689 0.0336 2689/0/164 1.050 R1 = 0.0425, wR2 = 0.1027 R1 = 0.0530, wR2 = 0.1097 0.328/-0.197

1b C72H82Cu4N6O16 293(2) monoclinic P21/n 9.7442(6) 21.8806(8) 17.5119(9) 92.449(5) 3730.3(3) 2 1.372 1.192 multi-scan 1600 0.30 x 0.25 x 0.20 2.44 to 26.37 17538/7610 0.0475 7610/3/486 1.099 R1 = 0.0593, wR2 = 0.1460 R1 = 0.1079, wR2 = 0.1915 0.809 and -0.547

21

Table 5. Selected bond lengths [Å] and angles [°] of H2L at 100K and at 293K and calculated geometry of phenol-imino and zwitterionic forms tautomer molecules in a gas phase. H2 L

100 K

293 K

B3LYP/6-311++G(2df,2pd) Tautomer A Tautomer C

Bond lengths (Å) N(1)-C(7) N(1)-C(14) N(2)-C(15) O(1)-C(2) C(1)-C(6) C(1)-C(2) C(1)-C(7) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(5)-C(6) C(7)-C(8) C(8)-C(9) C(8)-C(13) C(9)-C(10) C(10)-C(11) C(11)-C(12) C(12)-C(13) C(14)-C(15)

1.290(2) 1.458(2) 1.459(2) 1.345(2) 1.401(2) 1.417(2) 1.480(2) 1.396(2) 1.375(2) 1.394(2) 1.383(2) 1.494(2) 1.391(2) 1.391(2) 1.386(2) 1.385(2) 1.382(2) 1.384(2) 1.522(2)

1.285(2) 1.453(2) 1.453(2) 1.340(2) 1.395(2) 1.414(2) 1.473(2) 1.394(2) 1.372(2) 1.389(2) 1.380(2) 1.494(2) 1.385(2) 1.387(2) 1.385(2) 1.382(2) 1.378(2) 1.383(2) 1.518(2)

1.271 1.448 1.461 1.362 1.397 1.405 1.497 1.395 1.387 1.389 1.387 1.504 1.397 1.396 1.390 1.390 1.391 1.389 1.535

1.322 1.452 1.458 1.269 1.422 1.461 1.421 1.434 1.366 1.416 1.367 1.492 1.395 1.395 1.390 1.390 1.390 1.389 1.535

Bond angles (º) C(7)-N(1)-C(14) C(15)-N(2)-C(15)1a

123.2(1) 116.5(2)

123.4(1) 116.5(2)

123.27 116.74

128.2 117.6

Symmetry codes: (1a) -x, y, 1/2-z

22

Table 6. Hydrogen bonding and C-H···π interactions geometry [Å, º] for H2L and its copper(II) complex. Hydrogen bonds D-H···A

d(D-H)

d(H···A)

d(D···A)

 DHA

H2L (100 K) O(1)H(1o)···N(1) N(1)H(1n)···O(1) C(9)H(9)···O(1)1b C(11)H(11)···O(1)1c

0.91 0.93(7) 0.95 0.95

1.65 1.65(7) 2.46 2.58

2.508(2) 2.508(2) 3.332(2) 3.284(2)

156 152(5) 153 131

H2L (293 K) O(1)H(1o)···N(1) N(1)H(1n)···O(1) C(9)H(9)···O(1)1b C(11)H(11)···O(1)1c

0.93 0.83 0.93 0.93

1.64 1.83 2.46 2.58

2.500(2) 2.500(2) 3.319(2) 3.278(2)

152 135 154 132

1b N(2)H(2N)···O(6A) N(2)H(2N)···O(6B) O(7A)H(7A)···O(2) 0) O(8A)H(8A)···O(3)2b C(14)H(14B)···O(6B)2c C(17)H(17B)···O(4) C(27)H(27)···O(8B)

0.96 0.96 0.82 0.94 0.97 0.97 0.93

2.38 1.90 2.08 1.90 2.42 2.26 2.52

3.082(11) 2.779(11) 2.859(10) 2.802(7) 3.333(14) 2.864(6) 3.363(18)

130 151 159 159 156 119 152

d(D-H)

d(H···Cg)

d(C···Cg)

 CHCg

0.93 0.93

2.84 2.96

3.688(2) 3.655(2)

150 131

0.93 0.93

2.84 2.97

3.673(2) 3.647(2)

150 131

0.93

2.92

3.714(8)

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C-H···π interactions C-H···Cg H2L (100 K) C(4)H(4)···Cg(2)1d C(13)H(13)···Cg(1)1e H2L (293 K) C(4)H(4)···Cg(2)1d C(13)H(13)···Cg(1)1e 1b C(13)H(13)···Cg(1)2d

Symmetry codes for complex H2L: (1b) -x, -y, -z; (1c) -1/2+x,1/2-y,-1/2+z; (1d) 1/2+x,-1/2+y, z; (1e) 1/2-x,1/2-y,-z; (Cg(1) and Cg(2) are centroids of phenyl C(1)C(6) and C(8)C(13) rings, respectively) Symmetry codes for complex 1b: (2b) -x,-y+1,-z+1; (2c) 2-x, 1-y, 2-z; (2d) 3/2-x, 1/2+y, 3/2-z; (Cg(13) is centroid of phenyl C(25)C(30) ring)

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Figure captions Figure 1. Molecular structure and numbering atoms scheme of H2L. Displacement ellipsoids are drawn at the 50% probability level. Symmetry code: (1a) -x, y, 1/2-z. Figure 2. (a) Part of the crystal structure of H2 L showing the 3D supramolecular network view along c direction; (b) Three-dimensional supramolecular architecture showing channels. All hydrogen atoms were omitted for the sake of clarity. Figure 3. Molecular structure and numbering atoms scheme in coordination units of 1b. Displacement ellipsoids are drawn at the 30% probability level. The hydrogen atoms and methanol molecules were omitted for clarity. Figure 4. A view of the coordination polyhedron around the penta-coordinated CuII ions with atom labelling scheme in 1b. Figure 5. A view along a direction showing one-dimensional columns. All hydrogen atoms and hydrogen bonds were omitted for clarity.

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The N3O2-donor Schiff base was synthesized and characterized using FITR and UV-Vis spectroscopies, X-ray diffraction analysis, thermogravimetric methods and computational studies. The phenol-imine and keto-amine tautomeric equilibrium was discussed. The compound has been used in the complexation process of CuII ions. The reaction leads to formation of cyclic, tetranuclear CuII complex.

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