Copper(II) coordination polymer based on l-arginine as a supramolecular hybrid inorganic–organic material: synthesis, structural, spectroscopic and magnetic properties

We report the synthesis and structural, spectroscopic and magnetic properties of new 1D coordination polymeric complex {[Cu(μ-l-Arg)2]SO4⋅1.5H2O}n (1) that contains asymmetric μ−O,O’ carboxylic bridge linking distorted square-pyramidal [Cu(μ-l-Arg)2]2+ coordination units. In 1D, the syn−anti−μ2−η1:η1zigzag polymer conformation, the adjacent Cu(II) ions are distanced by 5.707 Å, and the subsequent Cu∙∙∙Cu proximity in 1D-coordination chain equals 6.978 Å. Detailed interpretation of IR and Raman spectra of l-arginine and 1 was performed. The principal components of the g tensor determined from EPR experiments (gx = 2.059, gy = 2.075, gz = 2.228) indicate nearly axial symmetry of Cu(II) coordination sphere and correspond to the unpaired electron occupying the dx2–y2 orbital. The single broad band at 16,200 cm–1, characteristic of d−d transition, is assigned to the dominant dublet-dublet 2B1g(dx2–y2)→ 2Eg(dyz≈dxz) transition. Magnetic susceptibility measurements have revealed ferromagnetic coupling between the Cu(II) ions within the 1D-coordination chain, while the intermolecular coupling is antiferromagnetic.

• The intermolecular coupling is antiferromagnetic

Introduction
Metal ions coordination polymers (CPs) named also as metal−organic framework (MOF) belong to the class of inorganic−organic hybrid materials.Their structures mostly depend on the metal centres, organic ligands, counter ions as well as solvent molecules.

1. Materials and methods
All substrates (CuSO45H2O, L−Arg, KSCN, KN3) were of reagent grade and were used as received with no further purification.All substrates were Sigma-Aldrich products.
The crystals of compound 1 could be also obtained by alternative methods

3. Powder X−ray Diffraction (PXRD) and X−ray crystallography
Powder X-ray diffraction patterns of the powdered 1 sample were checked on a PANanalytical X'Pert diffractometer equipped with a Cu-K radiation source (=1.54182Å).
The diffraction data were recorded in the range of 5÷50 o at room temperature.The simulated and experimental powder diffraction patterns of 1 are included in supporting information (Fig. S1).X-ray diffraction data for the single crystal of 1 with dimensions of 0.264×0.206×0.152mm were collected on an Oxford Diffraction four-circle single crystal diffractometer equipped with a CCD detector using graphite-monochromatized MoKα radiation.The raw data were treated with the CrysAlis Data Reduction Program (version 1.171.38.43) [33].The intensities of the reflection were corrected for Lorentz and polarization effects.The crystal structure was solved by direct methods [34] and refined by full-matrix least-squares method using SHELXL-2018 program [35].Non-hydrogen atoms were refined using anisotropic displacement parameters.H-atoms were visible on the Fourier difference maps, but placed by geometry and allowed to refine "riding on" the parent atom with Uiso = 1.2 Ueq(C or N).Coordinates of hydrogen atoms of the water molecules were constrained with Uiso = 1.5 Ueq(O).Visualizations of the structure were made using Diamond 3.2k [36].Crystal data and final refinement parameters are collected in Table 1.

4. Spectroscopies methods
FT−IR/FIR/Raman: The Fourier transform middle infrared (FT-IR) and far infrared (FT-FIR) spectra of L−arginine and complex 1 were measured on a Bruker VERTEX 70V vacuum spectrometer equipped with a diamond ATR accessory and an air-cooled DTGS detector.The instrument was kept under vacuum during the measurements and the spectra were recorded with a resolution of 2.5 cm -1 .The Raman spectra were measured on a Bruker Senterra dispersive Raman Spectrometer equipped with a confocal microscope, using a 532 nm exciting laser line.

NIR−Vis−UV:
The electronic diffuse−reflectance spectra of complex 1 was recorded at room temperature on a Cary 500 Scan NIR/Vis/UV spectrophotometer in the range 5000-50000 cm - 1 , with a resolution of 10 cm -1 .The aqueous absorbance spectrum of complex 1 dissolved in aqueous solution were measured with length of the optical path: l = 1.0 cm for CCu(II) = 1.40 x 10 -2 M in 7200-23000 cm -1 range.
X− and Q−band EPR: EPR experiments were performed using a Bruker Elexsys E500 spectrometer operating at ∼9.6 (X-band) and ∼34 GHz (Q-band) frequencies, equipped with an NMR teslameter (ER 036TM) and a frequency counter (HP5342A).Spectra were recorded for the powder samples at 77 K (X-band) and room temperature (Q-band).The samples were carefully ground before measurements to avoid incompletely averaged powder spectra.All simulations of EPR spectra were performed using EasySpin 5.2.35 [37].
DFT calculations: DFT calculations were performed using the ORCA 5 suite of programs [38,39] with the hybrid functional B3LYP [40][41][42].The def2-TZVP basis set for Cu and the def2-SVP basis set for the remaining atoms were employed [43].The resolution of identity approximation was used to speed up the calculations [44], and hence the corresponding auxiliary basis set was used [45].The structure determined from the X-ray diffraction experiments was used in the calculations, but the non-coordinated solvent molecules and sulphate anions were removed; the positions of all hydrogen atoms were optimized.An accurate integration grid (DefGrid2) and tight SCF convergence criteria (TightSCF) were set in all calculations.Visualizations were completed with the Gabedit 2.5 software [46].

5. Magnetic measurements
Magnetic properties were measured by Quantum Design MPMS-XL magnetometer.The DC magnetic susceptibility in the condition of field-cooled (FC) was measured in the temperature range of 2-300 K in the presence of an applied field of 1 kOe.The field-dependent magnetization curves were obtained at 2 K in the magnetic field range of ±7 T.

Crystal structure description of 1
In order to confirm the purity of the synthesized complexes, the powder X−ray diffraction (PXRD) patterns of 1 was obtained (Fig. S1).The positions of the main peaks from the experimental data matched well with those of the simulated peaks from the crystal data, proving the single phases of the synthesized products.No major differences between experimental and simulated powder diffractogram shows that examined crystal of 1 is homogeneous.The crystals of compound 1 belong to P212121 space group with unit cell edge lengths a = 6.9779Å, b = 12.8983 Å, c = 25.477Å (Table 1).Asymmetric unit cell consists of copper(II) coordination [Cu(L−Arg)2] 2+ cation balanced by SO4 2-ions and three free water molecules with occupation factor of 0.5 (Fig. 1a).
The cis-isomerism around copper atom is also observed in other L−argininato copper(II) compounds including SO4 where β and α are the largest angles in coordination sphere; τ5 = 0 stands for ideal SP geometry and τ5 = 1 means ideal TB).
The copper centers are linked by carboxylate oxygen atoms and form syn−anti−μ 2 −η 1 :η 1   3).It is suspected that a deformation of the ideal tetrahedral geometry of the sulphate anion is due to the existence of hydrogen bonds involving oxygen atoms of sulphate group (Fig. 2, Table 3).The largest difference is observed for the S-O3 bond length (1.511 Å).This effect is mainly caused by two relatively strong hydrogen bonds N12-H12A     Table 3. Selected hydrogen bonds distances and angles for compound (1).As is seen in Table 3 the lattice aqua molecules, the L−arginine ligand and the SO4 2- group in complex 1, are involved in an extensive hydrogen bonding network in the crystal.This is confirmed by the complicated pattern and broadening of the IR bands, in the range 3500-2700 cm -1 (Fig. 3).In the Raman spectrum of 1, the medium intensity bands at 3368 and 3281 cm -1 arise from the (NH2) stretching vibrations in the guanidinium moiety.However, the (NH2) modes of the coordinating amino group may also contribute to these Raman bands.The broad infrared bands with maxima at about 3342 and 3148 cm  4 and S1).

2. Spectroscopic studies (IR/Raman, NIR-Vis-UV, EPR) a) IR and Raman spectroscopy
It is known that L−arginine in the solid state exists as zwitterion [52] with the negative charge on the carboxylate COO -group and the positive charge on the protonated guanidinium moiety, as in the crystals of 1.The characteristic strong bands at 1674 and 1676 cm -1 in the IR spectra of L−arginine and 1, respectively, arise from the guanidinium (CN) stretching vibrations coupled with the sc(NH2)guan.A similar assignment of this band in the IR spectrum of L−arginine was reported by Krishnan et al. [53].The very strong band at 1552 cm -1 in the IR spectrum of L−arginine should be assigned to the sc(NH2)am vibrations, since this band is absent in the spectra of complex 1.The corresponding vibration of the coordinating NH2 group in 1 is shifted to a higher frequency (1632 cm -1 ) upon binding with the copper(II) ion (Table 4).
In the studied IR spectrum of L−arginine, the as(COO -)vibration appears as the very strong band at 1614 cm -1 , whereas the s(COO -) mode contributes to the strong band at 1419 cm -1 (Table 4).The  4).Raman active, whereas only 3 and 4 are infrared active [55][56].In the crystal of 1, the Td symmetry of SO4 2-ion is lowered because of intermolecular hydrogen bonds (Table 3).This causes a splitting of the degenerate vibrations and the Raman active modes become also infrared active.In the IR spectrum of 1 the very strong band at 1063 cm -1 with a shoulder at 1080 cm -1 and the medium band at 1157 cm -1 unambiguously originate from the split of 3 mode.Very similar results were reported for bis(melaminium) sulphate dihydrate, where the corresponding 3 bands were observed at 1058, 1090 and 1146 cm -1 , respectively [56].The symmetric S−O stretching vibration 1 should be assigned to the very strong Raman band at 970 cm -1 , because this mode was reported in the range 970-995 cm -1 for several other compounds with the sulphate group [55][56][57].However, it should be noted that in L−arginine, the coupled (C−C) and (C−N) vibrations were observed at very similar frequencies: 973(IR)/982(R) cm -1 [58].Thus, it can be concluded that the 1 mode coincides with the ligand band and the latter is observed as a shoulder at 982 (IR) and 985 cm -1 (Raman).A similar effect has been found for the ν4 mode, which usually generates strong and split bands, in the range 570-645 cm -1 in the IR spectra of metal ions sulphate complexes [55].The very strong and broad band with a maximum at 602 cm -1 in the IR spectrum of 1 may arise from the two overlapping modes: L−arginine skeletal vibration and the 4 mode (Table 4).A shoulder at 592 cm -1 can also be attributed to the 4.Furthermore, the 2 vibration appears at 454 cm -1 in the Raman spectrum of 1, and this assignment is supported by the literature data [55,57].
In the low-frequency region (below 600 cm -1 ) the metal-ligand vibrations are expected to occur.According to the symmetry consideration, the cis-isomer exhibits more bands in the infrared and Raman spectra than does the trans-isomer, for example, the cis-isomer has two (Cu−O) stretching vibrations, which are both IR-and Raman-active, while the trans-isomer   4, Fig. 4).Small difference between the corresponding frequencies, e.g.264(IR) and 273(R) cm -1 , is caused by the crystal field effects.According to Condrate and Nakamoto [54], a large frequency separation between the antisymmetric and symmetric (Cu−O) stretching vibrations (approx.70 cm -1 ) may be ascribed to a large repulsive force between two neighboring oxygens of the two ligands.Conversely, the charge on nitrogen atoms is less than that on oxygen atoms, hence the (M−N) frequencies do not split appreciably.
In the low frequency region, the crystals containing lattice water molecules exhibit librational modes, which are because of restricted rotational oscillations of H2O.These modes generate very broad bands in the range from 600 to 300 cm -1 [55].Thus, in the IR spectrum of 1, the very broad band with a maximum at 500 cm -1 is due to librational modes of water of crystallization in 1.
Table 4. Selected bands in the IR and Raman spectra of L−arginine (Arg) and its Cu(II) complex 1 along with their assignments.

b) Solid state and absorbance electronic spectra NIR-Vis-UV
The diffuse-reflectance solid state electronic spectrum exhibits broad band at 16200 cm -  Similarly to the solid state spectrum, the absorbance spectrum of compound 1 dissolved in water shows broad and unsplitted absorption band with a maximum at 16160 cm -1 (Fig. S4).
The values of molar absorption coefficient (ε), being ca.60 dm 3 mol -1 cm -1 , indicate the d-d nature of this transition.

c) EPR spectroscopy
EPR spectroscopy has been showed as an efficient tool for the determination of a molecular structure and electronic state of Cu(II) systems [60][61][62][63][64].The 3d 9 Cu(II) ion in an octahedral ligand field is a subject to the Jahn-Teller distortion, which decreases the molecular symmetry by lifting the eg and t2g orbital degeneracy.If the resulting system becomes an elongated octahedral, square pyramidal or square planar molecular structure, then the unpaired electron occupies the 3dx2−y2 orbital and the relationship between the principal values of the g tensor is gz ≫ gx = gy > 2.0023.The 3dz2 orbital becomes the ground state if the molecular structure becomes compressed octahedral or trigonal bipyramidal and the relationship is gx = gy > gz ≈ 2.0023.For intermediate situations, the EPR spectrum is characterized by gz > gy > gx values and reveals the ground state with the unpaired electron occupying a molecular orbital being the linear combination of 3dx2−y2 and 3dz2.The parameter G = (gy − gx)/(gz − gx) can determine whether the unpaired electron occupies the dz2 (G > 1) or dx2−y2 (G < 1) orbital in the ground state [65].
The EPR spectrum recorded for 1 at 9.6 GHz comprised a single, but noticeably anisotropic line (Fig. 6).This spectrum was simulated using gx = 2.070, gy = 2.075 and gz = 2.200, but accuracy of these three values is somewhat limited because the spectrum remained unresolved due to the g tensor at 9.6 GHz.However, a satisfactory resolution of the g tensor into its three components gx = 2.059, gy = 2.075 and gz = 2.227 (gavg = 2.120) was obtained at 34 GHz frequency.These values show that the unpaired electron occupies a molecular orbital with the dominant contribution from the 3dx2−y2 atomic orbital of Cu(II) (G = 0.21).This finding stays in line with the conclusion we drew from the analysis of absorbance electronic spectra.
Moreover, the determined values of the principal g tensor components are in accordance with values expected for CuN2O2 chromophore [60,[65][66][67] and similar to these observed for other Cu(II) complexes containing L−arginine as a ligand [68,69].The DFT calculations corroborated the conclusion that in 1 the unpaired electron occupies the molecular orbital formed from 3dx2−y2. Figure 7 shows the spin density and singly occupied molecular orbital (SOMO) isosurfaces, which demonstrate that the dx2−y2 is engaged in strong antibonding interactions with the ligands' lone pairs.This antibonding interaction causes a significant transfer of spin density onto the ligands.According to Löwdin populations analysis only 57.5% of the spin population is located on the Cu(II) ions in 1.

Magnetic measurements
The temperature dependence of χT product (χ-molar magnetic susceptibility per Cu II ion) measured for compound 1 in the temperature range 2-300 K and in the field of 1 kOe is given in Fig. 8.The χT values show an almost perfectly linear decreasing trend within the full temperature range with the most apparent deviations located in the low-temperature regime.
The value of χT at 2 K amounts to 0.420 cm 3 K mol -1 and it decreases steadily to reach the value of 0.162 cm 3 K mol -1 .This behavior of the raw χT data implies a substantial diamagnetic contribution intrinsic to the sample.The magnetization at 2 K increases smoothly with the applied field to reach saturation at the maximal field of 70 kOe with the value of 0.99 NAμB.
This value of the spectroscopic factor points to a moderate magnetic anisotropy of the Cu(II) ion.
b a where NA is the Avogadro number, μB is the Bohr magneton, kB is the Boltzmann constant, g is the average spectroscopic factor of the Cu(II) ion, SCu = ½ is its spin value, and χ0 is the diamagnetic correction.The best-fit yielded g = 2.112(2), χ0 = -0.000878(3)cm 3 mol -1 .It is important to notice, that the g parameter from the χT fitting stays in line with gavg = 2.120 determined from EPR experiment at 34 GHz.
We fitted these points to the function where C is the Curie constant and θ is the Weiss temperature, yielding C = 0.4212(5) cm 3 K mol -1 and θ = -1.0(2)K.The magenta solid line in Fig. 8a shows the best-fit curve.The relation between the spectroscopic factor and the Curie constant, i.e.The Brillouin function for spin SCu = ½ was adjusted to the experimental magnetization data at 2 K to reproduce the saturation value.This yielded the value of the spectroscopic factor of g = 2.022 (2).The green solid curve in Fig. 8b shows the result of the adjustment.It can be seen that the experimental points lie above the adjusted curve, which implies the presence of the ferromagnetic coupling between the Cu(II) ions within the chain units.To estimate the value of this coupling, we employed the molecular field approach and fitting to the experimental points the iterative solution of the following equation where λ is the molecular field constant and the magnetization M was calculated using the spin ½ Brillouin function.The iterations were stopped when the difference in the magnetization values for two consecutive steps was less than 10 -3 NAμB.The value of the spectroscopic factor was fixed during the procedure at the value g = 2.022 given by the previous adjustment.Hence the only free parameter of the fit was the molecular field constant for which we obtained the value λ = 0.89(2) cm -3 mol.Using the relation between λ and the intramolecular coupling constant J, ).The red solid curve in Fig. 9 shows the best-fit curve.Taking into account that the fit was obtained within the framework of the rough molecular field approach the agreement with the experimental points is perfect.
Encouraged by the success of the last approach we ventured to recalculate it with an anisotropic model for magnetization.We assumed a diagonal spectroscopic tensor ˆdiag( , , )   (5) The fitting was repeated by solving the same Eq.( 3) with M given by Eq. ( 5).The function to be minimized was the dimensionless agreement quotient ( , ) was calculated.These calculations were implemented within the built-in optimization procedure of the Mathematica8.0package.The best fit yielded λ = 0.56(3) cm -3 mol, g = 2.084(2), and QM = 1.7×10 -3 .The value of the intramolecular coupling constant implied by the fit is J = 0.45(3) K (0.31(2) cm -1 ) and is lower than the values obtained in the previous fit.
Figure 9 shows the complete magnetization data (symbols) together with the best fit curves (black solid lines).Although there are apparent discrepancies between the experimental and calculated magnetization values for high fields and low temperatures, the overall agreement is satisfactory.The strength of the intramolecular coupling is slightly diminished as compared to the values obtained from the single magnetization data at 2 K, while the value of the average gfactor is enhanced making it more consistent with the predictions of the susceptibility fits.The susceptibility fits give the value of g by only about 1% larger than the magnetization fits.They both point to a moderate anisotropy of the spectroscopic factor.The value of g may be concluded to be contained in the interval [2.08, 2.12], the upper bound of which is perfectly consistent with the EPR prediction of

•
The asymmetric syn−anti μ−O,O'L−argininato carboxylic bridge links distorted squarepyramidal copper(II) ions in new 1D coordination polymer • The spin exchange between the adjacent Cu(II) ions shows the short spin-spin relaxation time character • The dx2−y2 is involved in strong antibonding interactions with the ligands' lone pairs and only 57.5% of the spin population is located on the Cu(II) ions • The Cu(II)•••Cu(II) coupling by the carboxylate bridges in the polymeric chain shows a weak ferromagnetic character polymeric structures is favored by the triatomic syn-anti conformation of Cu−O−C−O−Cu carboxylate bridge.The variation of χT with T indicates the antiferromagnetic exchange-coupling between Cu(II) ions through syn-anti carboxylate bridging pathway in [Cu(L−Ala)2]n (L−Ala = L−alanine) and [Cu(L−Arg)2](NO3)2•3H2O compounds [23, 30].
(a)  or(b)  with using KSCN or KN3 salts, respectively.To the continuously stirred aqueous solution of CuSO4 (3 mmol, 748.5mg, 10 ml), an aqueous solution of L−Arginine (6 mmol, 1044.2mg,20 ml) was slowly added.Worth notifying is that solution of copper(II) sulphate in procedures (a) and(b)    needs to be acidified before use, due to hydrolysis of copper(II) ion.Mixture was stirred for 15 min.Then: a) an aqueous solution of KSCN (3 mmol, 291.5 mg, 10 ml) or b) an aqueous solution of KN3 (3mmol, 243.4 mg, 10 ml or 6mmol, 486.7 mg, 20 ml) was slowly added.If the original solution pH will reach 4.0 or lower, the amorphous seledin complex of formula [Cu(L−Arg)(NCS)2] will be formed[32].Mixtures (a) and(b)  were stirred for another 20 min and then left to slowly evaporate at room temperature.After 20 (a) and 30 days (b) blue crystals of 1 were formed.Crystals were separated from the solution by simple atom occupies the axial position in square planar pyramid.The lengths of the equatorial plane bonds are in the range 1.932−1.994Å.The carboxylate O12 atom in axial position is distanced at 2.468 Å, what is slightly shorter than that previously found for [Cu(μ−L−Arg)2(H2O)]SO4•5H2O (2) [31] and {[Cu(μ−L−Arg)2(H2O)]SO4}n (3) [9] polymers (ca.2.45 and 2.697 Å, respectively).

Figure 1 .
Figure 1.a) The asymmetric unit of compound 1 (the water molecules with occupation factor of 0.5).b) The polymeric 1D chain Cu−O−C−O−Cu zig-zag fashion (the uncoordinated sulphates were omitted for clarity).The selected atoms are labelled and ellipsoids are drawn at 50% of probability.
•••O3 and N14-H14D•••O3 vi involving nitrogen atoms of one guanidine group.Moderately elongated S-O4 bond is connected with N24-H24D•••O4 hydrogen bond created also by guanidine nitrogen atom and N11-H11A•••O4 ii hydrogen bond with amino nitrogen atom as donor.Bond angle in the second of them is noticeably smaller and bond length is significantly larger.Additionally S-O2 bond is involved in one moderately strong N22-H22A•••O2 hydrogen bond which also results in slight elongation of this bond.

Figure 2 .
Figure 2. The hydrogen bonds system between 1D polymeric chains.
, O2 and O3 are disordered in crystal 2; b) average of the S-O distances in crystal 3

Figures 3
Figures 3 and 4 illustrate the experimental infrared and Raman spectra of 1, in the ranges 3750-600 cm -1 and 600-50 cm -1 , respectively.The analogous spectra of pure L−arginine are shown in Figs.S2 and S3 (Supp.material).Table 4 lists the characteristic bands in the IR and -1 are probably due to the overlapping (H2O) vibrations of the lattice aqua molecules and (N-H) modes.The characteristic, intense Raman bands at 2952, 2916 and 2868 cm -1 correspond to the stretching vibrations of the CH2 and C-H groups.The scissoring sc(CH2) vibrations are observed at 1467 and 1450 cm -1 in the Raman spectrum.The other vibrations of the CH2 groups (wagging, rocking and twisting) are strongly coupled [50-51], therefore they are described as CH2 deformation modes (Tables

3 ,
(C=O) and (C−O) stretching vibrations in 1 contribute to the strong and medium intense IR bands at 1591 and 1391 cm -1 , respectively.The corresponding vibrations, in complex Alikhani et al. assigned to the IR bands at 1594 and 1377 cm -1[9].Moreover, for the cis−[Cu(glycine)2]•H2O complex[54], the carboxylate (C=O) and (C−O) bands were reported at 1595 and 1389 cm -1 , which supports our assignment.It should be noted that in metal ion complexes of amino acids, the noncoordinating C=O groups are hydrogen bonded to the neighboring complex molecules or water of crystallization, or weakly bonded to the metal ion of the other complex unit.All these interactions affect the (C=O) stretching vibration[55].As revealed by the DFT studies and the calculated potential energy distribution (PED) for L−arginine[50], the symmetric stretching vibration in the guanidinium group, νs(CN)3, can be attributed to the medium intensity Raman band at 920 cm -1 .Thus, the corresponding vibration in complex 1 is assigned to the similar Raman band at 935 cm -1 .As follows from our X-ray study of 1, the three CN bond lengths in the guanidinium unit (e.g.1.33(1), 1.30(1) and 1.338(9) Å for C26-N22, C26-N23 and C26-N24, respectively) are very close to each other.This is consistent with the delocalization of the positive charge, i.e. a resonance structure between the three CN bonds in the guanidinium moiety of 1.The other marker bands for the C-NH2 groups are observed in the Raman spectra at 1100 and 1103 cm -1 for free L−arginine and 1, respectively.According to the calculated PED [50], these bands correspond to the bending vibration, δ(C−NH2)guan (Table
shows only one IR-active (as) and one Raman-active (s) stretching vibration (mutual exclusion rule).

Figure 5 .
Figure 5.The diffuse-reflectance electronic spectra recorded at room temperature for compound 1 and pure L−Arg.

Figure 6 .
Figure 6.Experimental and simulated EPR spectra for 1 recorded at a) 9.6 GHz at 77 K and b) 34 GHz at room temperature.

Figure 7 .
Figure 7. Results of the DFT calculations with the hybrid functional B3LYP: a) molecular model of 1 used in the calculations along with the spin density isosurfaces contoured at 0.0025 a.u.; b) splitting of the quasi-restricted orbitals and their isosurfaces contoured at 0.05 a.u., orbital symbols for idealized symmetry (C4v) are used.

Figure 8 .
Figure 8. a) The molar susceptibility of the studied compound represented in terms of χT (left axis) and χ -1 (right axis).The solid lines show the best-fit curves.Green symbols show the χT values corrected for the diamagnetic contribution.Cyan symbols show the χ -1 values calculated upon subtraction of the diamagnetic corrections.b) Magnetization of the studied compound detected at 2 K. Solid lines show the best-fit curves disregarding (green) and accounting for (red) intramolecular interactions between the Cu(II) ions along the chains units obtained with the anisotropic model for magnetization.
of the spectroscopic factor g = 2.119(1), which is consistent with previous fit result.The negative and small value of the Weiss temperature indicates a weak and antiferromagnetic intermolecular coupling between the …−Cu−O−C−O−Cu−… chains.
z = 2 denotes the number of the nearest neighbor Cu(II) ions coupled along the chain unit, we arrive at the following estimate of the coupling constant J = 0.68(2) K (0.47(1) cm -1 sample signal is obtained by the appropriate averaging over all possible orientation of the external magnetic field, i.e.
yielded gxx = gyy = gzz = 2.0(1), λ = 0.89(1) cm -3 mol.The value of QM corresponding to the fit was 1.6×10 -5 .The red solid line in Fig.8bshows the best-fit curve.The green solid line shows the signal for isolated Cu(II) ions (with the intramolecular interactions being switched off, i.e. λ = 0).The value of the intramolecular coupling constant implied by the fit is J = 0.68(9) K (0.47(6) cm -1 ) and is perfectly consistent with the value obtained from the isotropic fit.The average value of the spectroscopic factor with the adjusted value of 2.022(2).Let us note that the uncertainty of the spectroscopic factor amounting to 0.1 makes it comparable with its counterparts obtained from the susceptibility analysis.

Finally, we ventured
to perform the fitting of the complete magnetization data.Because that the feedback loop calculations together with the averaging over field directions turn out quite lengthy for the anisotropic model, we adopted the isotropic model, where the magnetization is given by the Brillouin function.For variable values of the molecular field, constant λ and the averaged g-factor Eq. (3) was solved iteratively and the dimensionless

Figure 9 .
Figure 9. Magnetization of the studied compound detected at an array of temperatures from 2 up to 10 K. Solid lines show the best-fit curves accounting for the intramolecular interaction between the Cu(II) ions along the chain units within the isotropic molecular field approach.
gxx = 2.059, gyy = 2.075, and gzz = 2.227.The coupling between the Cu(II) ions within the chain units mediated by the carboxylate bridges is rather weak and of the ferromagnetic character.The intermolecular coupling is antiferromagnetic and comparable with the intramolecular one giving rise to the Weiss theta being small and negative.The successful synthesis of the presented in this paper copper(II) L−argininato coordination polymer has primarily enriched carboxylate-bridged 1D coordination polymers not only structurally, but also spectroscopically and magnetically.

Figure S3 .
Figure S3.The FT-IR and Raman spectra of L−arginine in the range 600-50 cm -1 .

Table 1 .
Crystallographic data and experimental details comparison between sulphates.

Table 2 .
Selected bond lengths (Å) and angles (°) for {[Cu(μ−L−Arg)2]SO4⋅1.5H2O}n Table 4 lists the characteristic bands in the IR and Raman spectra of L−arginine and complex 1.All the bands observed in the vibrational spectra of these molecules are shown in Table S1 (Supp.material).Band assignments have been made by the comparison with the results reported in Refs [9, 50-58].