A copper(II) zig-zag metal–organic coordination polymer: synthesis, crystal structure, topology study, hirshfeld surface analysis and survey different conditions on morphology of a novel nano structure [Cu(L)(SCN)(H2O)2]n.2H2O

Abstract One copper(II) coordination polymer compound [Cu(L)(SCN)(H2O)2]n.2H2O (1) where L stand for 2-pyridinecarboxylic acid, was synthesized following two different experimental methods, branch tube and sonochemical irradiation nano methods. Independently of the methodology used, the same crystalline phase is obtained for each compound. Single crystal X-ray analyses on compound 1 showed that Cu2+ ions are 6-coordinated. Additionally, H-bonds incorporate the zig-zag chains in 1 into 2D (along (1,1,0) direction) frameworks. Topological analysis shows that the compound 1 is 2C1 net. Hirshfeld surface analysis of compound 1 was studied. Also, theoretical and experimental morphology were studied. The thermal stability of compound 1 was studied by thermal gravimetric. Finally, the role of reaction time and temperature on growth and final morphology of the structures obtained by sonochemical irradiation are investigated. The results indicated that particle size was reduced with increasing sonication power, temperature, sonication time and decreasing concentration of reactant.


Materials and physical techniques
Starting reagents for the synthesis were purchased and used without any purification from industrial suppliers (Sigma-Aldrich, Merck and others). Elemental analyses (carbon, hydrogen, and nitrogen) were performed employing a Heraeus Analytical Jena, Multi EA 3100 CHNO rapid analyzer (Analytik Jena AG, B€ oblingen, Germany). Fourier transform infrared spectra were recorded on a FT-IR JASCO 680-PLUS spectrometer as KBr pellets in the 4000-400 cm À1 spectral range and Bruker Tensor 27 FT-IR with a single window reflection of diamond attenuated total reflectance (model MKII Golden Gate, Specac) and the OPUS data collection program software. The instrument is equipped with a room temperature detector, and a mid-IR source (4000-400 cm À1 ). Since it is a single beam instrument, it was needed to run a background spectrum in air before the measurement. Single crystal X-ray diffraction experiments were carried out for compound 1 with MoKa radiation (k¼0.71073 Å) at ambient temperature. A micro focused Rigaku mm003 source with integrated confocal caxFlux double bounce optic and HPAD Pilatus 200 K detector was used for 1 while for two data were measured on a Bruker-Nonius Kappa CCD diffractometer. The structures were solved by direct methods and refined by full matrix least squares on F 2 . All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were included with fixed isotropic contributions at their calculated positions determined by molecular geometry, except for the oxygen bonded hydrogen atoms, which were located on a difference Fourier map and refined riding on the corresponding atoms. Computing details: data collection, cell refinement and data reduction: CrystalClear-SM expert 2.1b43 [50] ; program(s) used to solve structure: SHELXT [51] ; program(s) used to refine structure: SHELXL-2014/7 [51] ; molecular graphics: PLATON [52] ; reduction of data and semiempirical absorption correction: SADABS program [53] ; direct methods (SIR97 program [54] ); full-matrix least-squares method on F 2 : SHELXL-97 program [55] with the aid of the programs WinGX [56] and Olex2. [57,58] X-ray powder diffraction (XRD) measurements were performed using an X'pert diffractometer manufactured by Philips with monochromatized Cuka radiation and simulated XRD powder patterns based on single crystal data were prepared using the Mercury software. [57] The samples were characterized with a scanning electron microscope (SEM; FEI Quanta 650 FEG) in mode operation of secondary electrons (SE) with a beam voltage between 15 and 20 KV. The samples were prepared by deposition of a drop of the material previously dispersed in properly solvents on aluminum stubs followed by evaporation of the solvent under ambient conditions. Before performing the analysis, the samples were metalized by depositing on the surface a thin platinum layer (5 nm) using a sputter coater (Leica EM ACE600). A multi wave ultrasonic generator (ultrasonic homogenizer-UP 400-A, IRAN and Elmasonic [Elma] S40 H), equipped with a converter/ transducer and titanium oscillator (horn), 12.5 mm in diameter, operating at 20 kHz with a maximum power output of 400 W, were used for the ultrasonic irradiation. Melting points were measured on an electrothermal 9100 apparatus and are uncorrected.  and lateral part (at room temperature) led to make convection flow. Reactants moved up to bottom in glass, spontaneously. In fact convection flow has role of the stirrer. Quality crystals were synthesized by this method after one week. An important advantage of this method in comparison with other crystallization methods which is reactant materials are placed in the bottom of the solvent without dissolving and they react slowly and finally good crystals were obtained ( Figure 1). Cu(NO 3 ) 2 .2.5H 2 O (1 mmol, 0.232 g), 2-pyridinecarboxylic acid (L) (1 mmol, 0.246 g) and KSCN (2 mmol, 0.18 g) were loaded into one arm of a branch tube and both of the arms were filled slowly with water. The chemical bearing arm was immersed in an oil bath kept at 60 C. Crystals were formed on the inside surface of the arm kept at ambient temperature. After 5 days, colorless crystals were deposited in the cooler arm. The crystals obtained were filtered off, washed with water and air dried.

Synthesis of [Cu(L)(SCN)(H 2 O) 2 ] n .2H 2 O (1) under ultrasonic irradiation
The study of sonochemistry is concerned with understanding the effect of ultrasound in forming acoustic cavitation in liquids, resulting in the initiation or enhancement of the chemical activity in the solution. Therefore, the chemical effects of ultrasound do not come from a direct interaction of the ultrasonic sound wave with the molecules in the solution. The simplest explanation for this is that sound waves propagating through a liquid at ultrasonic frequencies do so with a wavelength that is significantly longer than that of the bond length between atoms in the molecule. Therefore, the sound wave cannot affect that vibrational energy of the bond, and can therefore not directly increase the internal energy of a molecule. Instead, sonochemistry arises from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid. The collapse of these bubbles is an almost adiabatic process, thereby resulting in the massive build-up of energy inside the bubble, resulting in extremely high temperatures and pressures in a microscopic region of the sonicated liquid. The high temperatures and pressures result in the chemical excitation of any matter that was inside of, or in the immediate surroundings of the 25166, 3122, 2818 Rint 0.026 Largest diff. peak and hole À0.37 and 0.35 eA À3 CCDC no. 1552099   [74] Cu (1) Symmetry code: a 1/2Àx, À112þy, z\ b 1/2Àx, 112þy, z; À. c 1/2 Àx, 1 1 2þy, z; d 1/2 þ x, 1/2 Ày, Àz.
bubble as it rapidly imploded. A broad variety of outcomes can result from acoustic cavitation, including sonoluminescence, increased chemical activity in the solution due to the formation of primary and secondary radical reactions, and increase chemical activity through the formation of new, relatively stable chemical species that can diffuse further into the solution to create chemical effects (e.g. the formation of hydrogen peroxide from the combination of two hydroxyl radicals formed following the dissociation of water vapor inside the collapsing bubbles what water is exposed to ultrasound ( Figure 2). In generally, sonochemistry method is fast method in compared to solvothermal, hydrothermal, branched tube, solvent diffusion, etc methods. [59,60] Three nanostructures of [Cu(L)(SCN)(H 2 O) 2 ] n .2H 2 O (1) were prepared by sonochemical process. Firstly, a high-density ultrasonic probe was immersed directly into the solution of Cu(NO 3 ) 2 .2.5H 2 O (10 ml, 0.05 M) in water. Then into this solution, a proper volume of KSCN (10 ml, 0.05 M) and 2-pyridinecarboxylic acid (L) (10 ml, 0.05 M) ligand in water solvent was added in a drop wise manner. The solution was irradiated by ultrasound at 60 W and temperature 30 C. After 30 min, a white powder was obtained (temperature: 30 C reaction time: 30 min, sonication power: 60 W, concentration: 0.05 M). Following the above process, the role of temperature and time reaction was studied. Firstly, for the study of the effect related with the temperature, the reaction described was carried out at 60 C (reaction time: 30 min, sonication power: 60 W, concentration: 0.05 M). The reaction time was increased up to 60 min (temperature: 30 C, sonication power: 60 W, concentration: 0.05 M). Finally, the concentration of reactants was investigated to 0.1 M (temperature: 30 C, sonication power: 60 W, reaction time: 30 min). In all the cases, the obtained precipitates were filtered, subsequently washed with water and then dried.

Results and discussion
Initially, compound 1 was synthesized by the branch tube method. For the synthesis of compound 1, Cu(NO 3 ) 2 .2.5H 2 O, 2-pyridinecarboxylic acid (L) and KSCN were loaded into one arm of a branch tube while filling both arms slowly with water. The chemical bearing arm was afterwards immersed in an oil bath kept at 60 C while the second remains at room temperature. After 5 days, colorless crystals were deposited in the cooler arm. The crystals obtained were filtered off, washed with water, air dried and finally characterized as compound 1 (vide infra).

X-ray characterization
Selected crystals of compound 1 was isolated and analyzed by X-ray diffraction, crystallizing both in an orthorhombic Pbca space group. For more crystallographic details see Tables 1 and 2. Compound 1. The Pb atoms of 1 are coordinated by two N atoms, three O atoms and one S atom composing octahedral coordination O 3 N 2 S (Figure 3). The asymmetric unit of compound 1 contain one Cu 2þ cation, which is coordinated to one 2-pyridinecarboxylic acid ligand (L¼C 6 H 5 NO 2 ), one SCN À anions and two H 2 O molecules which are in crystal lattice ( Figure 4). Each 2-pyridinecarboxylic acid ligand (L¼C 6 H 5 NO 2 ) in compound 1 is coordinated to one Cu atom by one N atom of pyridine ring (Cu-N distance: 2.343 Å) and one O atoms of carboxylic acid group (Cu-O distance: 1.96 Å). Additionally, one bridge SCN atoms are coordinated to two Cu atoms through Cu(1)-N1 and Cu(1)-S1 bounds (Cu-N and Cu-S distances are 1.948 and 2.882 Å, respectively; Table 2 and Figure 5). The length of Cu-N and Cu-S bonds are shown for some of coordination supramolecular compounds based on copper metal in Table 3. It should be noted that the coordination interactions can be separated in two groups: strong (more valence, in short range 0.845-2.520 Å) and weak (more electrostatic, in long range 2.664-3.  (Figures 6 and 7). Each isothiocyanate groups is linking two similar copper atoms. These 1D zig-zag chains are bridged by the isothiocyanate groups through forming and expanded by hydrogen bound, p-p stacking and van der Waals interactions a layer on the ab crystal plane (Figures 6, 8, and 9). It should be noted that additional weak p-p interaction reinforces CPC. The p-p interactions in 1, are due to the presence of the rings of pyridine (distance of two pyridine rings: 5.348 Å) allowing the interactions between the parallel chains (Figures 8 and 9).
The morphology and size of products prepared by the sonochemical method were examined by SEM, (Figure 10). The SEM micrographs of compound 1 show plate morphology. Bravais Friedel Donnay Harker (BFDH) analysis was carried out in order to estimate the faces that are supposed to appear in the crystals morphology ( Figure 9). This analysis considers the effect of symmetry operations on the interplanar distances of crystal faces. [63] Predicted crystal morphologies of compound 1 are shown in Figure 11. In almost all cases there is a good match between the predicted and observed morphology. It should be noted that in the case of 1, the growth of the coordination material takes place along the [021] directions ( Figure 9).
Each [Cu(L)(SCN)(H 2 O) 2 ] n .2H 2 O chain is located between six other same chains forming van-der-Waals, hydrogen bonded and p-p interactions hexagonal packing, which corresponds to geometrically octahedral packing (Figures 9 and  12). Simplification of the chain to the underlying net by ToposPro package reveals 2C1 topological type (Figure 13), which is abundant for 1D coordination polymers (56,607 examples in TTO collection of ToposePro). [61,62] Hirshfeld surface analysis The crystal structure from the title compound as discussed below is a good example of the interplay of different molecular interactions. In order to analyses the various interactions that lead to the crystal structure, an intermolecular intercontacts leading to the Hirshfeld surfaces has been made. The Hirshfeld surface considered the volume of space where molecule electron density exceeds that all neighboring molecules. [64,65] Molecular Hirshfeld surfaces have been constructed from CIF file, so that you can dissect crystal structures into noncovalent contacts The very highresolution Hirshfeld surfaces were generated by Crystal Explorer and functions of curvature, distance including shape index and dnorm were mapped to the surfaces. [66][67][68][69][70][71] The function dnorm is a normalized distance property defined with regards to d i (distance from a point on the Hirshfeld surface to the nearest internal nucleus), d e (distance from a point on the Hirshfeld surface to the nearest external nucleus) and van der Waals radii (r i dvW and r e dvW ): . [22][23][24] Thus, the value of d norm was negative or positive when intermolecular contacts were shorter or longer than r vdW , respectively. The Hirshfeld surfaces of the title compound   ( Figure 14) were mapped over a d norm , d e , d i , curvedness, and shape-index. The d norm values were mapped to the Hirshfeld surface (Figure 14(a)) by using a red-blue-white color scheme as follows: red regions represented closer contacts as well as a negative dnorm value; blue regions represented longer contacts and a positive dnorm value; and white regions represented the distance of contacts equal to precisely the van der Waals separation with a d norm value of zero. These normalized contact distances (d norm ) reveal the close contacts of hydrogen bond donors and acceptors, but other close contacts are evident. Actually, Figure 12(a) reveals that the large circular depressions are the indicators of hydrogen bonding contacts and the dominant interactions are O-H whereas other visible spots are due to H-H contacts, based on both d e and d i . Particularly, adjacent red/orange and blue triangle like patches on a shape index map ( Figure 15) give us information about hydrogen bound and C … S interaction. [66,[69][70][71][72][73] The combination of the distances from the Hirshfeld surface to the nearest nucleus inside the surface (d i ) and outside the surface (d e ) and the data conveyed by the shape index are consistent with 2D fingerprint plots. [64,65] The 2D fingerprint maps of 1 provide some quantitative information gives the possibility of obtaining additional insight to the intermolecular interactions in the crystal state and for describing the surface characteristics of the molecules ( Figure 16). Globally, H … … H, H … … O, C … … H, and S … .H intermolecular interactions were most abundant in the crystal packing (29.8%, 24.6%, 14.1%, and 11.4%, respectively). It really is evident that van der Waals forces exert an important influence on the stabilization of the packing in the crystal structure, and other intercontacts [N … … H/H … … .N (4.0%), C … .O (4.0%), C … … S (3.7%), N … … S (2.5%), and H … … Cu (0.1%)] contribute less to the Hirshfeld surfaces. On the other hand, the relative contributions of the different interactions to the Hirshfeld Surfaces were also calculated for the title compound ( Figure  17 and Table 4).

Sonochemical synthesis
Synthesis of compound 1 was alternatively achieved by the application of ultrasounds. For the synthesis of compound 1, a high-density ultrasonic probe was immersed directly into a water solution Cu(NO 3 ) 2 2.5H 2 O and posterior drop wise addition a second water solution of KSCN and 2-pyridinecarboxylic acid (L). The synthesis were done the reactants concentration and the ultrasound power while other factors such as temperature and the reaction time were systematically modified (a resume of the different reactions is shown in Table 5).
PXRD of compounds is similar to that obtained upon simulation from the X-ray diffraction data obtained for 1. As Figure 18 reveals that both (experimental and simulation) exhibit the same crystalline phase. These results indicate the existence of a single crystalline phase, which is maintained independently of the synthesis method ( Figure 10).   Various conditions for preparation of compounds 1 nano-structure were summarized in Table 5. In this table, sample 1-1, were studied without power ultrasound and the other samples were studied under variable temperature, time and power ultrasound. In order to research the role of power ultrasound irradiation on the character of product, reactions were performed under completely different power ultrasound irradiation. Results show a decrease in the particles size as increasing power ultrasound irradiation. In sample 1-1, the reactions were studied without power ultrasound. Results show that size particles sample of 1-1 ( Figure  10(a)) is larger than 1-2 ( Figure 10(b)). Table 5 shows the average diameter scanning electron micrographs (SEM) of the prepared samples. Results show high power ultrasound irradiation decreased agglomeration, and thus led to decrease particles size. Comparison between samples 1-2 and 1-3 shows a decrease in nanoparticle size. Thus, size particles of sample 1-3 are smaller than 1-2 ( Figure 10(c)). However, a reducing the reaction time led to the decrease of size particles of sample 1-3. Particle sizes and morphology of nanoparticle are depending on temperature. Higher temperature (60 C) results in an increased solubility, and thus  a reduced supersaturation of growth species in the solution, and thus particles size of sample 1-4 is smaller than particles size of sample 1-2 ( Figure 10(b,d)). Finally, was compared 1-5 and 1-2 samples and shows an increase in particle size. In the other hand, high concentration of reactants increased agglomeration, and thus led to increase particles size (Figure 10(b,e)). Table 5 shows the average diameter of particles shown by SEM of the prepared samples. The best conditions for getting a small sized and less agglomerated nanostructure materials for this CPC are temperature, reaction time, the power of ultrasonic irradiation and concentration of reactants 30 C, 60 min, 60 W, and 0.05 M, respectively. Also, other condition (temperature ¼ 60 C, reaction time¼ 30 min, power of ultrasonic irradiation ¼ 60W and concentration of reactants¼ 0.05 M) is good for obtaining small nanoparticle size.
IR spectra of compound 1 shows the characteristic stretching frequency of H 2 O group observed at around 3474 cm À1 , relatively weak absorption bands centered on 3000 cm À1 assigned to the C-H stretching frequency of the aromatic rings. The absorption bands with variable intensity in the frequency range between 1700 and 1750 cm À1 correspond to C¼O stretching frequency of the carbonyl from the 2-pyridinecarboxylic acid ligand. Also, the characteristic band of the C-O stretching frequency carboxylic acid group appeared between 1000 and 1300 cm À1 . For the SCN ligand, a stretching band around 2050 cm À1 was assigned to SCN group. In addition, two bands around 1500-1700 cm À1 revealed the presence of C¼C stretching frequency corresponding to the amine group of the ligand (Figure 11).
The TG curve of compound 1 indicates that the compound does melt and is stable up to 80 C at that temperature it begins to decompose (Figure 8). A first weight loss over 50-100 C corresponding to the loss of lattice water molecules. The decomposition of coordinated water (mass Table 4. Contribution to hirshfeld surface area of different interaction in compounds 1.

Interactions
Contribution to hirshfeld surface area (%) Interactions Contribution to hirshfeld surface area (%)   loss of 8.7%), pyridine aromatic ring, carboxylate groups of 2-pyridinecarboxylic acid ligand and isothiocyanate groups (mass loss of them 77.4%), occur in range of 110-470 C. Mass loss calculations show that the final decomposition product is Cu (Figure 19).

Conclusion
One Cu(II) CPC [Cu(L)(SCN)(H 2 O) 2 ] n .2H 2 O (1), L¼picolinic acid ligand, has been synthesized utilizing a thermal gradient approach and also by sonochemical irradiation. Compound 1 was structurally characterized by single crystal X-ray diffraction. The crystal structure of compound 1 is made up of 1D CPC and shows that the coordination number of Cu (II) ion in compound 1 is six. Also, topology, Hirshfeld surface analyses and thermal behavior were studied for 1. Influences of temperature, power ultrasound, reaction time and concentration of reactants on the morphological properties of [Cu(L)(SCN)(H 2 O) 2 ] n .2H 2 O (1), was studied. The results showed that higher temperature of reagents led to decrease in particle size and optimum time for the process was obtained 60 min, increasing in the power of ultrasonic irradiation led to decrease particles size and high concentration of reactants increased agglomeration, and thus led to increase particles size for 1. Also, the best conditions for getting a small sized and less agglomerated nanostructure material for this coordination compounds are temperature, reaction time, the power of ultrasonic irradiation and concentration of reactants are 30 C, 60 min 60 W, and 0.05 M, respectively. These results demonstrated that the use of ultrasounds and the correct selection of different parameters can led to the formation of expected morphologies then the project can be defined more clearly.

Supplementary information
Crystallographic data for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Center as supplementary publication no. CCDC-1552099. Copies of the data can be obtained upon application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: þ44 1223/336033; e-mail: deposit@ccdc.cam.ac.uk).