All chemicals were of AR quality and used without further purification. Elemental analyses (C, H, N) were carried out by Perkin-Elmer CHN 2400 analyzer based on catharometric detection after combustion. Chloride and copper contents were determined by the micronalysis centre, CNRS service central of analysis at Vernaison (France). TGA analysis was performed using Dupont-950 thermogravimetric analyser in KBr discs were recorded on a Mattson 5000 FTIR (Mansoura University) and Perkin-Elmer in the range 20˚C - 800˚C and recorded on a TGA-50 Shimadzu TGA analyzer at a heating rate of 15˚C/min and nitrogen flow rate of 20 ml/min. IR spectra (4000 - 200 cm⁻¹) in Perkin-Elmer 883 IF spectrophotometers (France). Electronic spectra were recorded on a Unicam UV-Vis, V-100 and Perkin-Elmer Lambda 9 spectrophotometers. The magnetic measurements were carried out at room temperature (25˚C) on a Sherwood magnetic balance. Diamagnetic corrections were calculated using Pascal’s constants [20]. ¹H-NMR measurements in d₆-DMSO at room temperature were carried out on Jeol-90Q Fourier transform (400 MHz) and Bruker AM 250 spectrometers. The results of EPR measurements were obtained using Bruker EPR 200 provided with Hewlett-Packard frequency meter (modulation frequency, 100 KHz; microwave power; 20 mW; field modulation intensity; 3.2 Gpp and gain, 2.5 × 10⁵).

CAH (L) was synthesized by adding equivalent amounts of hydrazine hydrate (3 ml; 0.1 mol) drop by drop with constant stirring to ethyl cyanoacetate (11 ml, 0.1 mol) in EtOH for 1.5 h at room temperature (25˚C). The reaction mixture was cooled in ice bath till a white solid product was obtained. The precipitate was filtered off, recrystallized from absolute ethanol (yield: 89%) and finally dried in a desiccator over P₄O₁₀. The purity was checked by elemental analyses, TLC and spectra data (IR, ¹H-NMR, Vis-Uv, Raman and TGA). The uncorrected melting point of the product was found to be (108˚C - 110˚C).

Twelve novel polymeric Cu²⁺ complexes were isolated and characterized with the aid of elemental analyses, physical and spectroscopic methods. The different complexes were synthesized by mixing in each reaction equivalent amounts of L (0.2 M) in different solvents (H₂O, MeOH, EtOH, n-proponal, n-butanol and n-pentanol) and CuCl₂·2H₂O (0.1 M) in EtOH. The reaction mixtures were refluxed on a hot plate for a time depending on the solvent used. The polymeric complexes formed in the flask were poured in a beaker followed by scratching the reaction mixture in each experiment by a glass rod till solid precipitates were formed as fine powders. The complexes were filtered off and washed several times with the solvent used in the preparation of the complexes followed by washing with diethyl ether. The isolated products were preserved in a vacuum desiccator over P₄O₁₀. The analyses of the isolated solid complexes together with some physical data are depicted in Table 1. The complexes are stable in air and soluble in polar solvents. The numbers of the copper ions in the isolated complexes were estimated from the data of elemental analyses as well as results of EPR and found to be in the range from 3 - 12 atoms. The electronic spectra and the magnetic moments of the Cu(II) complexes are recorded in Table 2. The data of the polymeric complexes are summarized as follow:

Complex (1) (C₁₁H₂₃Cl₂N₉O₆Cu₃); yield: 70%; color: dark brown powder; MP > 270˚C, M.Wt: 638.9; µ_eff (1.95 BM) and conductivity (DMSO): 6 Ω⁻¹·cm²·mol⁻¹.

Complex (2) (C₃₆H₇₁Cl₁₄N₂₇O₁₈Cu₁₂); yield: 83%; color: yellowish-green powder; MP > 270˚C, M.Wt: 2400.0; µ_eff (0.91 BM); conductivity (DMSO): 9 Ω⁻¹·cm²·mol⁻¹.

Complex (3) (C₃₁H₇₅Cl₇N₂₄O₂₃Cu₈); yield: 76%; color: brown powder; MP > 270˚C; M.Wt. 1908.6; µ_eff (1.24 BM); conductivity (DMSO): 13 Ω⁻¹·cm²·mol⁻¹.

Complex (4) (C₁₉H₃₈Cl₇N₁₅O₈Cu₄); yield: 90%; color: kaki-green powder; MP > 270˚C; M.Wt: 1107; µ_eff (1.02 BM); conductivity (DMSO): 13 Ω⁻¹·cm²·mol⁻¹.

Complex (5) (C_16.5H_29.5Cl₅N_13.5O_6.5Cu₄); yield: 69%; color: brown powder; MP > 270˚C; M.Wt: 952.5; µ_eff (1.14 BM); conductivity (DMSO): 13 Ω⁻¹·cm²·mol⁻¹.

Complex (6) (C₁₀H₂₂Cl₃N₆O_5.5Cu₃); yield: 69%; color: brown powder; MP > 270˚C; M.Wt: 611.3; µ_eff (0.78 BM); conductivity (DMSO): 8 Ω⁻¹·cm²·mol⁻¹.

Complex (7) (C_16.5H_29.5Cl₅N_13.5O_6.5Cu₄); yield: 77%; color: yellowish-green powder; MP 155˚C; M.Wt: 1719.2; µ_eff (0.75 BM); conductivity (DMSO): 7 Ω⁻¹·cm²·mol⁻¹.

Complex (8) (C₁₆H₃₁Cl₅N₁₂O₆Cu₃); yield: 77%; color: dirty-green powder; MP > 270˚C; M.Wt: 855.4; µ_eff (0.85 BM); conductivity (DMSO): 6 Ω⁻¹·cm²·mol⁻¹.

Complex (9) (C₁₁H₁₉Cl₄N₉O₄Cu₃); yield: 90%; color: military-green powder; MP > 270˚C; M.Wt: 673.8; µ_eff (0.85 BM); conductivity (DMSO): 4 Ω⁻¹·cm²·mol⁻¹.

Complex (10) (C₃₈H₆₆Cl₁₀N₃₀O₁₂Cu₇): yield: 85%; color: kaki-green powder; MP > 270˚C; M.Wt: 1934.5; µ_eff (0.75 BM); conductivity (DMSO): 9 Ω⁻¹·cm²·mol⁻¹.

Complex (11) (C₂₈H₄₈Cl₄N₁₈O₈Cu₅); yield: 79%; color: brownish-green powder; MP: 200˚C; M.Wt: 1224.4; µ_eff (0.84 BM); conductivity (DMSO): 10 Ω⁻¹·cm²·mol⁻¹.

Complex (12) (C_20.5H₃₅Cl₇N₁₈O_6.5Cu₄); yield: 85%; color: grayish-green powder; MP: 103˚C; M.Wt: 1140.0; µ_eff (0.85 BM); conductivity (DMSO): 10 Ω⁻¹·cm²·mol⁻¹.

The IR spectra of CAH (L) in KBr and/or Nujol mull are cognate and show three bands at 3280sh, 3199s and 3056s cm⁻¹ assigned to ν_a(NH₂), ν_s(NH₂) and ν_a(NH₂) vibrations, respectively. Also, the bands located at 2263s, 1710sh and 1680sh cm⁻¹ are assigned to ν(C ≡ N)s, ν(C=O)sh (free) and ν(C=O)s (hydrogen-bonded) vibrations, respectively. Moreover, the two bands at 1530m and 1492s are attributed to amide II vibrations. The observation of the carbonyl band as a shoulder together with the existence of the NH₂ at lower wavelength suggests that the carbonyl group is partially hydrogen-bonded to the amino group as shown in Figure 1. Also, the ¹H-NMR spectrum of L in d₆-DMSO shows three signals at 10.06, 9.53 and 9.1 ppm assigned to NH₂ and NH groups which obscured on adding D₂O. Both the methyl and ethyl proton signals are observed as triplet signals in the ranges 1.76 - 1.96 and 3.66 - 3.76 ppm, respectively. The calculated value of the mass spectrum of L equals 141 which is quite agrees with the experimental value of M + 1 (142). The electronic spectrum of L in DMSO shows two bands at 220 nm (45,455 cm⁻¹) and 262 nm (38,170 cm⁻¹) attributed to π → π^* and π → π^* transitions of the C=O and C ≡ N groups, respectively. The Raman spectrum of CAH shows active bands at 3341m, 2926m, 2260s 1670w and 1010 cm⁻¹ assigned to ν(NH₂), ν(CH), ν(C ≡ N) and ν(N-N) vibrations, respectively. These foundations are taken as strong evidences for our assumptions and the existence of the ligand (CAH) as shown in Figure 1.

A comparison of the IR spectra of CAH and its Cu²⁺ complexes (Table 2) shows that the ligand behaves in a neutral bidentate fashion via the (C=O) and NH₂ groups.

The mode of chelation is confirmed by the following remarks:

1) The measurably shifts of both the (C=O) and (NH₂) groups to lower wavenumbers in all complexes indicating that these groups are participating in coordination of the Cu²⁺ ion.

2) The vibrations of the amide II bands are also shifted to lower wavenumbers suggesting the participation of both groups in coordination.

3) New bands are observed in the range 400 - 440 and 350 - 400 cm⁻¹ are assigned to (M-O) and (M-N), respectively [13].

4) The spectra of the complexes show broad medium band in the region 3440 - 3426 cm⁻¹, attributable to the existence of solvent inside and/or outside the coordination sphere [14].

5) The observation of two bands at 1710s and 1680sh together with the presence of weak broad bands in the 2800 - 2920 cm⁻¹ suggests the existence of strong hydrogen bonding.

All these foundations suggest that the ligand is existed as a mixture of the keto (A) and enol (B) forms as shown in Figure 1.

The obscure and/or the weakness of the cyano group (C ≡ N) in some Cu²⁺ complexes is taken as strong evidence for the promotion of the solvent as shown in Scheme 1. The mechanism of promotion was proposed and confirmed in our previous works [18] [19].

Quantum chemical calculations are concerned with the determination of energies of both HOMO (π-donor) and LUMO (π-acceptor) parameters. HOMO orbital acts as an electron donor while LUMO orbital acts as an electron acceptor. These molecular orbitals are also called the frontier molecular orbitals (FMOs).

1) The negative values of both E_HOMO and E_LUMO and their neighboring orbitals (Table 3) indicate that the molecules are stable [22].

2) The FMOs theory predicts the essential sites participate in coordination (electrophilic attack). An initial assumption proposes that the reaction occurred with maximum overlap between the HOMO on one molecule and the LUMO on the other. The overlap between HOMO and the LUMO is essential factor in any reactions. The goal obtained from the calculations is to get the largest values of molecular orbital coefficients. Accordingly the orbitals of the ligands under investigation have the largest value of molecular orbital.

3) Gutmann’s variation rules indicate that the strength of bonds increase as the adjacent bonds become weaker as found by Linert et al. [23].

4) The energy gap (E_HOMO − E_LUMO) expresses the stability index which helps to characterize the chemical reactivity and kinetic stability of the molecule [24]. The gap (E_HOMO − E_LUMO) is patented to develop a theoretical model to explain the structure and verify the barriers in different systems, which affect the biological activity of the molecule. Small gap within the molecule means that the molecule is polarized and acts as soft molecule. It is well known that the soft molecules are more reactive than hard ones since they easily donate electrons to an acceptor. The energy gap is small in the compound indicate that the charge-transfer easily occurs in it influencing the biological activity of the molecule. Energy gap with low values is also attributed to the groups that enter into conjugation [24].

5) Low energy values of HOMO indicate that the donating electron ability of the molecules is the weaker. Contrarily, the higher HOMO energy suggests that the molecule is a good electron donor. LUMO energy presents the ability of a molecule receiving electron [25]. The results are depicted in Figures 2-7.

DFT concept illustrates neatly the chemical reactivity and the site selectivity of the molecular systems. Both the energies of (E_HOMO + E_LUMO) and band gap (E_HOMO − E_LUMO) illustrate preemptory the charge-transfer interplay within the molecule, electronegativity (χ), chemical potential (µ), global hardness (η), global softness (S) and global electrophilicity index (ω) [26] [27] [28] are listed in Table 4.

χ = − 1 / 2 ( E LUMO + E HOMO ) (1)

H = HOMO, L = LUMO.

µ = − χ = 1 / 2 ( E LUMO + E HOMO ) (2)

η = 1 / 2 ( E LUMO − E HOMO ) (3)

S = 1 / 2 η (4)

ω = µ 2 / 2 η (5)

The inverse value of the global hardness is designed as the softness (σ) as follow:

σ = 1 / η (6)

The electrophilicity index (ω) is considered as important quantum chemical descriptors. Also, this value used to estimate the stabilization energy when the system acquires an additional electronic charge from the environment. The molecular stability and reactivity of the compounds depends mainly on the values of η and σ. The ligand acts as a Lewis base while the metal ion acts as a Lewis acid during complex formation.

The three-dimensional plots of frontier orbital energies using the DFT method for L²-L⁷ are shown in Figures S1-S6.

The results of the EPR spectra of the polymeric Cu²⁺ complexes in DMSO at low temperature (127˚C - 160˚C) are depicted in Table 5. The trend g_|| > g_^ > g_e (2.0023) observed for the Cu²⁺ complexes suggests that the unpaired electron is localized in the d_x2−y2 (²B_1g) orbital [29] [30]. It is well known that the axial symmetry parameter (G) is defined as:

G = ( g ∥ – 2.0023 ) / ( g ⊥ − 2.0023 )

If G > 4 the exchange interaction is negligible between Cu(II) ions, whereas G ˂ 4 means a significant Cu-Cu interaction and tone straightly with measured magnetic moment [31]. The G values for all complexes are larger than 4 (4.0 - 6.0) suggesting the absence of any copper-copper interaction. Orbital reduction factors (K_|| and K_^) which are a measure of covalence were determined using the following two expressions:

2 K ∥ = ( g ∥ − 2.0023 ) 8 λ o × Δ E

2 K ⊥ = ( g ⊥ − 2.0023 ) 2 λ o × Δ E

The value of λ o (spin-orbital coupling constant) for d⁹-system equals −828 cm⁻¹. Hathaway [31] pointed out that that in case of pure σ-bonding, K_|| = K_^ =

0.77 and for in-plane π-bonding K_|| < K_^, while for out-of-plane π-bonding K_^ < K_|| the following simplified expressions were used to calculate K_|| and K_^. In all cases of Cu(II) complexes under investigation the observed K_|| > K_^ indicating that the presence of out-of-plane π-bonding as depicted in Table 5. The value of K_|| = K_^ = 0.83 in case of the Cu²⁺ complex (10) suggesting the existence of pure σ-bonding. For all the complexes the evaluated values of α², β² and γ² are consistent with both in plane σ-bonding and in plane π-bonding as shown in Table 5. Moreover, all the above values (α², β² and γ²) are less than 1 suggesting 100% ionic nature of the bonds [32]. The bonding parameters for the Cu(II) complexes are found to be α² in the 0.82 - 0.99, β² in the 0.64 - 0.92 and γ² in the 0.5 - 0.84 ranges. The extent of departing of these parameters from unity measures the range of delocalization of metal electrons due to M-L bonding and hence α² measures σ-bonding within the complexes [33], β² measures out of (xy) plane π-bonding while γ² shows in plane π-bonding contribution. No doubt that the deviation from unity in β² and γ² values suggests the presence of considerable out of plane and in plane π-bonding contribution in M-L π-bonding. Accordingly, the EPR studies of the copper complexes have provided supportive evidence to the optical and magnetic results.

The electronic spectra of the Cu(II) complexes were displayed in Nujol mull and/or DMSO. The electronic spectra show a broad band lie in the 13,551 - 17,860 cm⁻¹ range suggesting d-d transition (²E_2g → ²T_2g) in octahedral geometry around the Cu²⁺ ion [34] [35]. Also, the values of the corrected subnormal magnetic moment of the complexes (2-12) fall in the 0.75 - 1.24 BM are taken as strong evidence for the existence of polymeric nature [36] [37] and strong Cu-Cu interaction. The value of magnetic moment of complex (2, C₁₁H₂₃Cl₂N₉O₆Cu₃) was found to be 1.95 BM. The high value of magnetic moment of complex (2) in comparison to the previous complexes (3-12) in spite of the polymeric nature of this complex, which contains three copper atoms, is due to the absence of any Cu-Cu interaction within this complex either in the xy or directions. The data of electronic spectra and magnetic moments are shown in Table 2.

The amounts of the coordinated solvents and/or the hydrated solvents have been determined in the range 25˚C - 200˚C. The experimental weight loss values are in good agreement with the calculated values. The TGA curves of the Cu²⁺ complexes exhibit two different types of weight loss, in the above range, indicating the presence of two types of solvents. The Former in the 50˚C - 120˚C range suggesting the presence of hydrated solvents while the latter in the range 125˚C - 200˚C illustrating the presence of coordinated solvents.