Spectroscopic study of solvent effects on the electronic absorption spectra of morpholine and its complexes European Journal of Chemistry 14 (1) (2023) 53-64 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2023 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.14.1.53-64.2365 European Journal of Chemistry View Journal Online View Article Online Spectroscopic study of solvent effects on the electronic absorption spectra of morpholine and its complexes Mamdouh Saad Masoud 1, Alaa Eldin Ali 2, Gehan Shaaban Elasala 2 and Rehab Elsaid Elwardany 2,* 1 Department of Chemistry, Faculty of Science, University of Alexandria, Alexandria, 21515, Egypt 2 Department of Chemistry, Faculty of Science, University of Damanhour, Damanhour, 22511, Egypt * Corresponding author at: Department of Chemistry, Faculty of Science, University of Damanhour, Damanhour, 22511, Egypt. e-mail: rehabelwardany@sci.dmu.edu.eg (R.E. Elwardany). 10.5155/eurjchem.14.1.53-64.2365 Received: 25 November 2022 Received in revised form: 05 January 2023 Accepted: 14 January 2023 Published online: 31 March 2023 Printed: 31 March 2023 The electronic absorption spectra of morpholine and its five morpholine complexes have been studied in different solvents of various polarities. The regression and correlation coefficients have been calculated with the SPSS program. Solvation energy relationships were deduced from spectral shifts and correlated with solvent parameters α (solvent hydrogen bond donor acidity), β (solvent hydrogen bond acceptor basicity), and π* (dipolarity/polarizability). The percentage contributions of the calculated solvatochromic parameters show that classic solvation effects play a major role in explaining the spectral shifts in all investigated complexes. The blue shift of [Fe(MOR)3Cl3]·4H2O, [Ni(MOR)4Cl2]·4H2O, and [Cu(MOR)4Cl2]·6H2O complexes is due to the formation of hydrogen bonds, which suggests the stabilization of the ground electronic state compared with the excited state. [CuNi(MOR)2Cl4]·4H2O and [CuZn(MOR)3Cl4]·2H2O are mixed metal complexes that suffer a red shift due to the solute-solvent interactions, which causes stabilization of the excited solute state with increasing solvent polarity. The bands are affected by specific solute-solvent interactions including hydrogen bond donor ability (acidity) and hydrogen bond acceptor ability (basicity) and nonspecific solute-solvent interactions including electromagnetic interaction between the dipole moments of solute and polar solvents. UV spectra Absorption Dipole moment Solvent polarity Solvatochromic Morpholine complexes Cite this: Eur. J. Chem. 2023, 14(1), 53-64 Journal website: www.eurjchem.com 1. Introduction Morpholine is an organic compound with ether-like properties due to the presence of an oxygen atom and amine- like properties due to the presence of a nitrogen atom (Figure 1). Many molecules derived from morpholines have very good biological activity in different therapeutic areas, such as antiviral, antibacterial, anticancer, antidiabetic, antimicrobial, antimalarial, inflammatory, and antifungal activities [1,2]. The most important applications of complexes are drugs; therefore, they must dissolve in the proper solvent. For the development of solution chemistry, it is essential to study the structure and spectroscopic behavior of a solute in different solvents [3-7]. N H O Figure 1. Structure of morpholine (MOR). Solvatochromism is a phenomenon that describes the effect of using different solvents with varying polarities on the UV- visible absorption spectra of a chemical compound [8,9]. The interaction between solvents and a solute was classified into nonspecific interactions, including electromagnetic interac- tions between the dipole moments of the solute and a polar solvent, and specific interactions including the ability of hydrogen bond donors (acidity) and the ability of hydrogen bond acceptors (basicity) [10]. The presence of specific and nonspecific interactions between the solvent and solute molecules is responsible for the change in the molecular geometry, electronic structure, and dipolar moment of the solute. Empirical parameters of solvent polarity have been developed to interpret and substantiate the solute-solvent interaction using spectroscopic data. The effect of solvent on UV-visible spectra can be shown by a change in the position, intensity, and shape of the absorption bands [11]. The change in the position of bands with increasing solvent polarity can be described in two ways. The first is the hypsochromic shift (blue shift) to a negative Δλ (nm), and the second is the bathochromic shift (red shift) with a positive Δλ (nm). Solvatochromism is caused by differential solvation of the ground and first excited states of the light absorption molecule (chromophore). With increasing solvent polarity, better stabilization of the molecule in the ground state than in the excited state leads to negative ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.14.1.53-64.2365 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.14.1.53-64.2365 mailto:rehabelwardany@sci.dmu.edu.eg http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.14.1.53-64.2365&domain=pdf&date_stamp=2023-03-31 54 Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Table 1. Analytical data and physical properties of morpholine complexes. Found (Calculated) (%) Color M.wt. (g/mol) Molecular formula Compound Cl M 21.30 (21.45) Fe 11.20 (11.30) Brown 495.65 C12H35N3O7Cl3Fe [Fe(MOR)3Cl3]·4H2O (1:3) 12.49 (12.89) Ni 10.94 (10.67) Pale green 550.07 C16H44N4O8Cl2Ni [Ni(MOR)4Cl2]·4H2O (1:4) 12.25 (11.99) Cu 10.90 (10.75) Green 590.92 C16H48N4O10Cl2Cu [Cu(MOR)4Cl2]·6H2O (1:4) 25.20 (24.96) Zn 11.29 (11.51) Cu 11.40 (11.18) Pale green 568.11 C12H31N3O5Cl4CuZn [CuZn(MOR)3Cl4]·2H2O (1:1:3) 27.95 (27.79) Ni 11.71 (11.50) Cu 12.10 (12.45) Green 510.27 C8H26N2O6Cl4CuNi [CuNi(MOR)2Cl4]·4H2O (1:1:2) Fe Cl Cl O NH O NH NH O Cl .4H2O NH OO NH M Cl Cl .nH2O NH OO H N Zn NH O NH O O NH Cu ClCl ClCl .2H2O Ni Cu .4H2OCl Cl Cl Cl NH O O NH (a) (b) (c) (d) Figure 2. Suggested structures of morpholine metal complexes (a) [Fe(MOR)3Cl3]·4H2O, (b) [M(MOR)4Cl2].nH2O M(n) = Ni(4), Cu(6), (c) [CuNi(MOR)2Cl4]·4H2O, and (d) [CuZn(MOR)3Cl4]·2H2O. solvatochromism. On the other hand, better stabilization of the molecule in the first excited state compared to that in the ground state leads to positive solvatochromism. These shifts are due to the solvent stabilization of the excited or ground electronic states, thus resulting in a change in the energy gap between the energy levels involved in the transition. The represented electronic absorption spectra of the compounds in the presence of different solvents of different polarities had a wide variety of solvent parameters, causing a change in the intensity and position of the bands. This change is due to the polarity of the solvent, London-dispersion forces between the nonpolar solute and nonpolar solvent, and the difference in the solvation energy from one solvent to another. In this work, morpholine (MOR) and its five morpholine complexes were dissolved in different solvents of various polarities, and the electronic absorption spectra were studied to investigate the effect of solvents on the electronic transition. 2. Experimental 2.1. Preparation of morpholine complexes Simple metal morpholine complexes were prepared in a similar manner [12]. Inorganic salts Fe(III), Ni(II), and Cu(II) were dissolved as chlorides in 10 mL of bidistilled water. Excess liquid morpholine (MOR) was added (50 mL) and the resulting solid complexes were removed by filtration. Then they were washed several times with a mixture of ethanol and water and dried under a desiccator over anhydrous CaCl2. Two mixed- metal complexes of morpholine were prepared. 0.5 g of each metal chloride in 10 mL of water, then mix the two solutions. Excess liquid morpholine was added while stirring. The precipitated complexes were separated by filtration, then washed with an ethanol:water mixture, and dried in a vacuum desiccator over anhydrous CaCl2. 2.2. Characterization of the prepared complexes The metal contents were determined according to the atomic absorption technique using the Shimadzu 6650 model atomic absorption spectrophotometer [13] and complex-metric titration with EDTA solution [14]. The chloride content of the complexes was determined using the well-known Volhard method [15]. The IR spectra of the ligand and its metal complexes were recorded using the potassium bromide disc technique in the range 400-4000 cm-1 using a Perkin-Elmer 1430 spectrophotometer. The electron spin resonance (ESR) spectra of the copper complexes were recorded with a reflection spectrometer operating at 8.7 GHz (X-band) in a cylindrical resonance cavity with 100 kHz modulation at the Central Lab of The Faculty of Science at Alexandria University, Alexandria, Egypt. At room temperature, molar magnetic susceptibilities were measured using the Faraday’s method and corrected for diamagnetism using Pascal’s constants [16]. Hg[Co(SCN)4] was used to calibrate the apparatus. A Perkin Elmer spectrophotometer, model Lambda 4B, was used for UV- vis spectra, covering the wavelength range 200-800 nm. The analytical results are given in Table 1, depicting the formation of complexes with different stoichiometries (Figure 2). Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 55 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Table 2. Fundamental infrared bands (cm-1) of morpholine and its metal complexes. νM-Cl νM-N νM-O νC-O-C νNH Compound - - - 1099 3313 Morpholine 437 487 - 1101 3120 [Fe(MOR)3Cl3]·4H2O 438 480 - 1099 3280 [Ni(MOR)4Cl2]·4H2O 420 450 - 1109 3225 [Cu(MOR)4Cl2]·6H2O 439, 405 503, 480 600 1089 3240 [CuZn(MOR)3Cl4]·2H2O 440, 416 460, 480 - 1104 3047 [CuNi(MOR)2Cl4]·4H2O Table 3. Electronic absorption spectra of morpholine (MOR) and its complexes in the presence of different solvents (λmax, nm). Compound CCl4 CHCl3 i-propanol Acetone Ethanol Methanol Water Δλ (nm) Morpholine 200 225 202 230 203 231 204 235 205 236 206 - 207 230 +7 +11 [Fe(MOR)3Cl3]·4H2O 256 282 253 281 247 280 242 278 238 276 237 275 234 274 -22 -8 [Ni(MOR)4Cl2]·4H2O 244 280 230 273 228 270 226 267 228 271 225 260 223 260 -21 -20 [Cu(MOR)4Cl2]·6H2O 230 250 229 246 221 239 219 236 218 235 217 231 - 223 -13 -27 [CuNi(MOR)2Cl4]·4H2O 230 293 231 305 232 305 232 307 234 308 234 309 236 310 +6 +17 [CuZn(MOR)3Cl4]·2H2O 232 253.5 224 249 224 251 230 258 236 262 236 265 256 - +24 +11.5 2.3. Effect of solvents on UV-visible spectra of morpholine and its complexes Morpholine spectral parameters and electronic absorption spectra, [Fe(MOR)3Cl3]·4H2O, [Ni(MOR)4Cl2]·4H2O, [Cu(MOR)4 Cl2]·6H2O, [CuZn(MOR)3Cl4]·2H2O, [CuNi(MOR)2Cl4]·4H2O comp- lexes were analysed in the presence of seven solvents of varied polarities, namely water, methanol, ethanol, acetone, i-pro- panol, chloroform and carbon tetrachloride, which are all from Sigma Aldrich, USA Company. Spectrophotometric measure- ments in the visible and ultraviolet regions were recorded using a Perkin-Elmer spectrophotometer, model Lambda 4B, which covers the wavelength range 190-800 nm. 3. Results and discussion 3.1. IR, electronic spectra, ESR, and magnetic susceptibility of morpholine and its metal complexes For liquid morpholine, the N-H stretching vibration occurs at 3313 cm-1 and the C-O-C stretching vibration is located at 1099 cm-1 [17]. For morpholine metal complexes, the N-H stretching vibration shifted to a lower frequency than that in the uncoordinated morpholine, due to the coordination of the metal ions. Morpholine acts as a monodentate ligand through the nitrogen atom only in all complexes except the [CuZn(MOR)3Cl4]·2H2O complex. The shift of the C-O-C band, Table 2, supports the complexation through an oxygen atom and the formation of a morpholine bridge between the two metal ions, so morpholine acts as a bidentate ligand in this case [18]. The brown iron complex [Fe(MOR)3Cl3]·4H2O has an electronic absorption spectrum that gives bands at 272, 347, and 434 nm, due to CT (t2g → π*) and d-d transitions. Its room temperature µeff value of 5.95 B.M. typified the existence of an octahedral configuration. [Ni(MOR)4Cl2]·4H2O is a pale green complex. The UV-visible spectra at 261, 352, 466, and 731 nm that are related to the transition from 3A2g as ground state to 3T2g(F), 3T1g(F) and 3T1g(P) according to the orgel diagram [19]. These transitions support the appearance of an octahedral geometry. The fact that the magnetic moment was 3.36 B.M. may be taken as additional evidence for its octahedral structure. [Cu(MOR)4Cl2]·6H2O is a pale green complex gave two bands at 277 and 449 nm assigned to the transition 2Eg → 2T2g(D) that can be assigned to the octahedral environment [20]. The room- temperature magnetic moment value is 2.84 B.M., which is higher than the value corresponding to one unpaired electron 1.73 B.M. due to the orbital contribution to the spin of the complexes. The pale green [CuZn(MOR)3Cl4]·2H2O compound. Since the ESR data identified the perfect tetrahedral geometry around the Cu(II) ion, the complex showed five bands at 350, 409, 539, 556, and 625 nm [21]. The visible d-d electronic transition spectral band at 409 nm may be due to the tetrahedral configuration around Cu(II), and the weak bands at 539 and 556 nm may be due to the tetrahedral configuration around Zn(II) ions, also. The magnetic moment value is 2.15 B.M. and can be taken as additional evidence for its tetrahedral structure [22]. The pale green [CuNi(MOR)2Cl4]·4H2O nujol mull electronic spectrum complex gave bands at 265, 354, and 503 nm since the ESR data identified the tetrahedral geometry around the Cu(II) ion. Thus, the visible d-d electronic spectral band at 503 nm may probably be due to the square planner configuration around the Ni(II) ion [23]. The complex has a magnetic field of 4.92 M.B. at room temperature. The ESR of the pale green complexes [Cu(MOR)4Cl2]·6H2O at room tempera- ture, [CuZn(MOR)3Cl4]·2H2O and [CuNi(MOR)2Cl4]·4H2O, are near a similar pattern; all showed spectra with isotropic features where gs = 2.004 with coupling constants A = 122.50, 80.00, and 70.00 (×10-4 cm-1), respectively, which assign the presence of these three complexes in perfect octahedral or perfect tetrahedral structure [24]. 3.2. Electronic absorption spectra Representative UV-vis absorption spectra of morpholine (Figure 3a, Table 3) in a dilute solution (ca. 5×10-3 M), the absorption spectra exhibit two bands with maxima around 205 and 230 nm. The first band showed a strong nature, indicating the character of δ → δ* transition, and the second band with a longer wavelength has a weak nature related to the n → δ* transition of the nitrogen or oxygen atom in the morpholine skeleton [25]. With increasing solvent polarity, the two bands showed a positive (red) bathochromic shift with stabilization of the solute excited state rather than the ground state. This suggests that this compound is more polar in the excited state than in the ground state. The red shift can also be explained by the hydrogen donor ability of the compound and the hydrogen acceptor nature of some solvents [26]. [Fe(MOR)3Cl3]·4H2O for simple complexes and [Cu(MOR)4 Cl2]·6H2O as examples showed two bands allowed (Figure 3b, Table 3), in all solvents studied except water, in the case of [Cu(MOR)4Cl2]·6H2O due to hydrolysis, only one band appea- red. All simple complexes have a negative (blue) hypochromic shift (obtained from the wavenumber maximum absorption of the band recorded in the presence of the most polar solvent subtracted from that determined in the most nonpolar solvent 56 Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 (a) (b) (c) Figure 3. Effect of solvents on the electronic absorption spectra of a) morpholine, b) [Cu(MOR)4Cl2]·6H2O complex, and c) [CuNi(MOR)2Cl4]·4H2O complex. Δλ nm), due to the formation of a hydrogen bond, and so the ground electronic state is more stabilized compared with the excited state. The first band in the range 230-260 nm is mainly of high energy bands of n → δ* type and the second band in the range 250-280 nm is due to the low-lying d-d electronic transition [27] that arose from the complexation with the copper ion, which is indicated by its absence in Figure 3. For the mixed metal complexes, [CuNi(MOR)2Cl4]·4H2O and [CuZn (MOR)3Cl4]·2H2O, as an example (Figure 3c, Table 3), two bands appeared in the UV-visible spectra with the use of different solvents, except water in the case of [CuZn(MOR)3Cl4]·2H2O only one band appeared due to complete hydrolysis. The two complexes suffer a positive (red) bathochromic shift due to the solute-solvent interactions, causing stabilization of the excited solute state with increasing solvent polarity. This suggested that these complexes are more polar in the excited state than in the ground state [28]. The redshift can also be explained by the hydrogen donor ability of these complexes and the hydrogen acceptor nature of some solvents. The bands of low wavelength are mainly related to the n → δ* transition, and the bands of high wavelength are due to the d-d electronic transition absence in Figure 3a. 3.3. Application of the SPSS program and regression analysis Multiple linear regression techniques were used to analyze the effects of the solvent on the electronic absorption spectra of morpholine and its complexes using the following equation: y = a0 + a1x1 + a2x2 + a3x3 + … + anxn (1) where y is the observed peak location of an absorption band in a given solvent (wavelength), a0 is the regression intercept. It has been assumed [29] to estimate the peak position for the gas phase spectra. a1, a2, …, an are coefficients that could be determined by multiple regression techniques. x1, x2, …, xn are various empirical solvent polarity parameters calculated from the following relations. E = 2.859×10-3 νmax (2) 2 2 1 2 1 nM n − = + (3) Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 57 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Table 4. Solvent parameters for solvents *. Solvent n D E M N K CCl4 1.460 2.2 32.5 0.215 0.012 0.222 CHCl3 1.446 4.7 39.1 0.210 0.290 0.360 i-Propanol 1.377 18.3 48.6 0.187 0.622 0.460 Acetone 1.359 20.7 42.2 0.180 0.650 0.460 Ethanol 1.361 24.3 51.9 0.181 0.665 0.470 Methanol 1.329 32.6 55.5 0.169 0.710 0.477 Water 1.333 78.5 63.1 0.171 0.757 0.491 * n: The refractive index; D: Dielectric constant; E: The empirical solvent polarity; M: Account for the solute permanent dipole-solvent induced dipole; N: Solute permanent dipole-solvent permanent dipole interaction and K: Kirkwood’s dielectric function. Table 5. Regression analysis data of morpholine (MOR) *. Parameters a0 a1 a2 a3 a4 MCC P y = 200-207 nm E 193.420 0.219 - - - 0.900 0.001 M 227.348 -125.235 - - - 0.889 0.001 N 199.589 8.062 - - - 0.841 0.004 K 194.621 21.992 - - - 0.746 0.008 E, M 210.016 0.122 -63.748 - - 0.953 0.002 E, N 195.284 0.143 3.367 - - 0.937 0.004 E, K 193.046 0.159 7.765 - - 0.929 0.005 M, N 222.244 -102.472 1.576 - - 0.892 0.012 M, K 221.932 -105.427 4.049 - - 0.893 0.011 N, K 206.239 18.062 -28.439 - - 0.865 0.018 E, M, N 209.407 0.121 -60.951 0.215 - 0.953 0.017 E, M, K 208.507 0.120 -58.201 1.332 - 0.953 0.017 E, N, K 198.470 0.133 8.041 -12.414 - 0.941 0.024 M, N, K 232.291 -190.080 -17.988 39.866 - 0.902 0.051 E, M, N, K 219.123 0.121 -145.216 -18.533 38.222 0.962 0.075 y = 225-236 nm E 224.378 0.147 - - - 0.158 0.435 M 259.847 -150.424 - - - 0.542 0.144 N 225.958 10.430 - - - 0.570 0.083 K 218.802 30.121 - - - 0.610 0.067 E, M 298.955 -0.268 -290.635 - - 0.584 0.268 E, N 235.943 -0.329 20.918 - - 0.788 0.097 E, K 221.892 -0.283 54.501 - - 0.799 0.090 M, N 183.027 194.742 22.048 - - 0.620 0.234 M, K 199.758 74.403 41.956 - - 0.626 0.228 N, K 209.810 -14.143 69.229 - - 0.629 0.226 E, M, N 218.459 -0.310 76.680 24.884 - 0.795 0.291 E, M, K 237.437 -0.315 -59.385 47.775 - 0.807 0.275 E, N, K 226.872 -0.305 7.461 35.742 - 0.803 0.280 M, N, K 254.369 -304.961 -66.836 166.424 - 0.635 0.494 E, M, N, K 330.105 -0.330 -696.907 -111.174 255.097 0.829 0.584 * E: The empirical solvent polarity; M: Account for the solute permanent dipole-solvent-induced dipole; N: Solute permanent dipole-solvent permanent dipole interaction; K: Kirkwood’s dielectric function; a0: The regression intercept; a1, a2, a3, a4: coefficients; MCC: The multiple correlation coefficients and P: The probability of variation. 1 2 DJ D − = + (4) 1 2 1 DK D − = + (5) N J H= − (6) 2 2 1 2 nH n − = + (7) E is the empirical solvent polarity that is sensitive to both solvent-solute hydrogen bonding and dipolar interactions related to νmax, which is the wave number (cm-1) of the absorption maximum of the given solvent. The Kirkwood dielectric function (K) represents the dipolar dielectric interactions and is a measure of the polarity of the solvent that depends on the dielectric constant (D) of the solvent. The functions J and H have been introduced to account for nonspecific solute-solvent interactions such as dispersion and dipolar effects, respectively [30]. These are related to the dielectric constant (D) and the refractive index (n) of the solvent. The functions M and N have been introduced to account for the solute permanent dipole-solvent induced dipole and solute permanent dipole-solvent permanent dipole interactions, respectively [31]. The values of the solvent parameters K, M, N, E, D, and n in different solvents [32] are collected in Table 4. The intercept a0, and the coefficients a1, a2, …, an have been calculated by multiple regression analysis using a micro- statistics SPSS program (Statistical package of social science program). In each case, fits are obtained as a function of one parameter alone, two parameters, three parameters, or four parameters. The results of the calculations for the compounds under investigation are collected in Tables 5 and 6. Multiple correlation coefficients (R) or (MCC) and probability of variation (p) have been considered as a measure of goodness of fit. The high value of MCC (near one) means that a certain solvent parameter has a good correlation with the spectral shift. Therefore, the spectral shifts of the peak are greatly sensitive to the solvent parameter, which gives a value of MCC near unity. Alternatively, the small value (near zero) of the significance parameter (P) assigned a good correlation [33]. For the equation of one parameter of morpholine, the MCC and P values, the E parameter plays an important role in determining the spectral shifts that occurred for MOR at wavelength region y1. This is provided by the high value of MCC (0.9) (near one) and the low value of P = 0.001, so the spectral shift in this region is affected by the polarity and ability of the formation of H bonds of the solvents. 58 Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Table 6. Regression analysis data for morpholine complexes. Parameters [Fe(MOR)3Cl3]·4H2O [Ni(MOR)4Cl2]·4H2O y = 234-256 nm y = 274-282 nm y = 223-244 nm y = 260-280 nm MCC P MCC P MCC P MCC P E 0.836 0.004 0.840 0.004 0.646 0.029 0.761 0.010 M 0.926 0.001 0.844 0.003 0.712 0.017 0.828 0.004 N 0.843 0.004 0.716 0.016 0.875 0.002 0.750 0.012 K 0.765 0.010 0.636 0.032 0.924 0.001 0.706 0.018 E, M 0.947 0.003 0.897 0.011 0.729 0.073 0.851 0.022 E, N 0.901 0.010 0.851 0.022 0.876 0.015 0.810 0.036 E, K 0.876 0.015 0.843 0.025 0.924 0.006 0.801 0.039 M, N 0.926 0.005 0.857 0.021 0.906 0.009 0.828 0.030 M, K 0.926 0.005 0.854 0.021 0.931 0.005 0.829 0.029 N, K 0.913 0.008 0.807 0.037 0.940 0.004 0.769 0.053 E, M, N 0.948 0.020 0.921 0.037 0.909 0.046 0.853 0.091 E, M, K 0.948 0.020 0.918 0.039 0.933 0.029 0.851 0.093 E, N, K 0.941 0.024 0.892 0.058 0.945 0.022 0.815 0.128 M, N, K 0.926 0.033 0.861 0.084 0.953 0.017 0.887 0.062 E, M, N, K 0.949 0.100 0.925 0.144 0.955 0.087 0.911 0.171 Parameters [Cu(MOR)4Cl2]·6H2O [CuNi(MOR)2Cl4]·4H2O y = 217-230 nm y = 223-250 nm y = 230-236 nm y = 293-310 nm MCC P MCC P MCC P MCC P E 0.776 0.020 0.906 0.001 0.948 .000 0.665 0.025 M 0.975 0.001 0.875 0.002 0.748 0.012 0.696 0.020 N 0.915 0.003 0.806 0.006 0.692 0.020 0.854 0.003 K 0.829 0.012 0.730 0.014 0.630 0.033 0.907 0.001 E, M 0.975 0.004 0.950 0.003 0.948 0.003 0.726 0.075 E, N 0.919 0.023 0.928 0.005 0.948 0.003 0.855 0.021 E, K 0.859 0.053 0.917 0.007 0.949 0.003 0.908 0.008 M, N 0.978 0.003 0.876 0.015 0.748 0.063 0.882 0.014 M, K 0.976 0.004 0.875 0.016 0.748 0.063 0.914 0.007 N, K 0.992 0.001 0.875 0.016 0.743 0.066 0.928 0.005 E, M, N 0.978 0.032 0.951 0.018 0.953 0.017 0.891 0.059 E, M, K 0.977 0.035 0.952 0.018 0.953 0.017 0.922 0.036 E, N, K 0.993 0.010 0.955 0.016 0.954 0.016 0.943 0.023 M, N, K 0.992 0.012 0.879 0.068 0.749 0.196 0.956 0.016 E, M, N, K 0.993 0.122 0.956 0.087 0.954 0.090 0.964 0.070 Parameters [CuZn(MOR)3Cl4]·2H2O y = 224-256 nm y = 253.5-265 nm MCC P MCC P E 0.522 0.067 0.462 0.137 M 0.308 0.196 0.615 0.065 N 0.183 0.339 0.357 0.211 K 0.121 0.445 0.263 0.298 E, M 0.550 0.202 0.616 0.238 E, N 0.677 0.104 0.462 0.394 E, K 0.742 0.067 0.492 0.363 M, N 0.432 .323 0.835 0.067 M, K 0.458 0.294 0.822 0.075 N, K 0.498 0.252 0.700 0.164 E, M, N 0.751 0.194 0.849 0.217 E, M, K 0.784 0.158 0.842 0.227 E, N, K 0.812 0.131 0.772 0.321 M, N, K 0.498 0.502 0.840 0.231 E, M, N, K 0.822 0.324 0.850 0.553 * E: The empirical solvent polarity; M: Account for the solute permanent dipole-solvent induced dipole; N: Solute permanent dipole-solvent permanent dipole interaction; K: Kirkwood’s dielectric function; MCC: Multiple correlation coefficients, and P: The probability of variation. For the wavelength region y2, the K parameter has a 0.61 value of MCC and a lower value of P = 0.067, indicating that the spectral shifts in this region are affected by the dielectric constant of the solvent. Based on the two parameters equation, the combination of E and M gave higher values of the correlation at wavelength region y1 due to the high value of multiple regression (R) of 0.953 and the lower value of the probability of variation P = 0.002. Therefore, the solvent-solute hydrogen bonding ability combined with the solute permanent dipole-solvent-induced dipoles are the major factors causing the spectral shifts in these cases. The combination of E and K gave higher correlation values for morpholine in the wavelength region y2, as evident by its multiple regression coefficient (R) 0.799 and the low value of the probability of variation P = 0.09. It is concluded that the studied properties of the solvent are effective parameters to explain the spectral shifts for the compounds [34]. The data based on the three-parameter regression equation pointed to the relatively high value of multiple regression (MCC) and the lower value of the probability of variation (P) based on a combination of E, M, K parameters for both wavelength regions y1 and y2 occurred. For the studied complexes based on one-parameter equation, the (M) gave a higher value of correlation for [Fe (MOR)3Cl3]·4H2O at both wavelength regions y1 and y2 with a value of 0.926 and 0.844 and a low P value of 0.001 and 0.003, respectively. For [Ni(MOR)4Cl2]·4H2O at wavelength region y2 (MCC = 0.828, P = 0.004), [Cu(MOR)4Cl2]·6H2O at wavelength region y1 (MCC = 0.975, P = 0.001), and [CuZn(MOR)3Cl4]·2H2O at wavelength region y2 (MCC = 0.615, P = 0.065) indicating that solvatochromism can be interpreted in terms of permanent dipole-solvent-induced dipole interactions. Parameter (E) gave a higher value of correlation for [Cu(MOR)4Cl2]·6H2O at wavelength region y2 (MCC = 0.906, P = 0.001), also for [CuNi(MOR)2Cl4]·4H2O at wavelength region y1 (MCC = 0.948, P = 0.001), and [CuZn(MOR)3Cl4]·2H2O at wave- length region y1 (MCC = 0.522, P = 0.067), referred to that the solvent-solute hydrogen bonding and dipolar interactions are the major factors affecting the solvatochromism [35]. Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 59 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Table 7. K1, K2, νvapour and correlation analysis data for selected compounds. MCC R(ν, n) K2 R(ν, D) K1 νvapour (cm1) Compound 0.656 0.684 14760.93 0.793 -2851.72 45610.29 Morpholine 0.856 0.917 -10344.60 0.794 1628.65 34607.24 [Fe(MOR)3Cl3]·4H2O 0.821 0.906 -25165.83 0.827 4178.39 33727.59 [Ni(MOR)4Cl2]·4H2O 0.845 0.919 -41691.92 0.836 6893.39 36432.03 [Cu(MOR)4Cl2]·6H2O 0.906 0.834 14809.44 0.947 -3059.20 35335.69 [CuNi(MOR)2Cl4]·4H2O 0.839 0.782 20868.55 0.517 -2436.09 41007.41 [CuZn(MOR)3Cl4]·2H2O * νvapour: The frequency of the peak maximum in the absence of solvents; K1 and K2: Proportional to the strength of the induction-dispersive and orientation interactions; R(ν, D), R(ν, n) and MCC: Multiple correlation coefficients. The parameter (K) plays an important role in determining the spectral shifts for [Ni(MOR)4Cl2]·4H2O at wavelength region y1 (MCC= 0.924, P = 0.001) and [CuNi(MOR)2Cl4]·4H2O at wavelength region y2 (MCC =0.907, P = 0.001) this points to the fact that the dielectric constant is effective in explaining the spectral shifts. Based on the two-parameter equation, the combination of E and M gave higher correlation values for [Fe(MOR)3Cl3]·4H2O at both wavelength regions y1 and y2 (MCC =0.947,0.879, P = 0.003,0.011), [Ni(MOR)4Cl2]·4H2O at wave- length region y2 (MCC = 0.851, P = 0.022) and [Cu(MOR)4 Cl2]·6H2O at wavelength region y2 (MCC = 0.950, P = 0.003), used to explain the spectral shifts occurred in these cases related to the solvent ability to form hydrogen bonds with the solute molecules, which is expressed by the parameter E combined with solute permanent dipole-solvent induced dipole interactions [36]. The solute permanent dipole-solvent permanent dipole interactions (N) combined with the dielectric constant (K) is used to explain the correlation by its high MCC values and low P values in the case of [Cu(MOR)4Cl2]·6H2O at wavelength region y1 (MCC = 0.992, P = 0.001), [CuNi(MOR)2Cl4]·4H2O at wavelength region y2 (MCC =0.928, P = 0.005) and [Ni(MOR)4 Cl2]·4H2O at wavelength region y1 (MCC = 0.940, P = 0.004). The combination of E and K parameters used to explain the spectral shift in case of [CuNi(MOR)2Cl4].4H2O at wavelength region y1 (MCC =0.949, P = 0.003) and [CuZn(MOR)3Cl4].2H2O at wave- length region y1 (MCC = 0.742, P =0.067) explained by that the ability of H-bond formation combined with the polarity of the solvent that depends on the dielectric constant has the major effect in this correlation [37]. The best correlation coefficient is observed with the combination of M and N functions for [CuZn(MOR)3Cl4]·2H2O at the wavelength region y2 (MCC = 0.835, P =0.067). Thus, solvent spectral shifts are best affected by the solute permanent dipole-solvent induced dipole combi- nated with the solute permanent dipole-solvent permanent dipole interactions [38]. Based on the three parameters equation, the combination of (E, M, N) and (E, M, K) both showed high multiple regression (R) for [Fe(MOR)3Cl3]·4H2O at both wavelength regions y1 (MCC = 0.948, P = 0.02) and [CuNi(MOR)2Cl4]·4H2O at wavelength region y1 (MCC =0.953, P = 0.017) indicating the effect of E, M combined with N and K solvent parameters on the spectral shifts of these compounds. The combination of E, M, N that affects the correlation in case of [Fe(MOR)3Cl3]·4H2O at both wavelength regions y2 (MCC =0.921, P = 0.037) and [CuZn(MOR)3Cl4]·2H2O at wavelength region y2 (MCC =0.849, P = 0.217) indicating the effect of solvent hydrogen bond formation ability E, the permanent dipole- solvent induced dipole M and solute permanent dipole solvent permanent dipole interactions. M, N, and K parameters combination was effected in case of [Ni (MOR)4Cl2]·4H2O at both wavelength regions y1 and y2 (MCC = 0.953, 0.887, P = 0.017, 0.062) and for [CuNi(MOR)2Cl4]·4H2O at wavelength region y2 (MCC = 0.956, P = 0.016). The combination of E, N, and K parameters shows the major effect in case of [Cu(MOR)4Cl2]·6H2O at both wavelength regions y1 and y2 (MCC = 0.993, 0.955, P = 0.01, 0.016) and [CuZn(MOR)3Cl4]·2H2O at wavelength region y1 (MCC = 0.812, P = 0.131). The following equation is applied [39]: 2 21 2 2 2 2 2 2 1 2 1Solution Vapour D KD n n Kν ν  − −  +   + +   +  = (8) where 2 2 2 2 2 2 1 nx n − = + , 1 2 2 2 1 Dx D − = + and νSolution is the frequency of the peak maximum in the presence of solvents; D, dielectric constant; n, refractive index and νVapour is the frequency of the peak maximum in the absence of solvents. The K1 and K2 are proportional to the strength of induction-dispersive and orientation interactions, respectively. Multiple regression techniques were used to evaluate νVapour values, the coefficients K1 and K2, R (ν, D), R (ν, n), and MCC (Table 7). The data indicated that both the dielectric constant (D) and the refractive index (n) of the solvents affect the electronic absorption spectra of these compounds, but to different degrees. For simplicity, νVapour values were calculated when K2 = zero and the equation becomes as follows: 1 2 2 2 1Solution Vapour K D D ν ν= + −   +  (9) where ν(solution) values were plotted against x1 and the values of K1 and νvapour were obtained from the slopes and the intercepts, respectively (Figure 4). Multiple correlation coefficients R(ν, D) were calculated using an SPSS program (Table 7). Similarly, νvapour were calculated when K1 = zero and the equation becomes as follows: 2 2 2 2 2 2 1Solution Vapour n n Kν ν= +  −   +  (10) where νSolution values were plotted against x2 and the values of K2 and νVapour were obtained from the slopes and intercepts, respectively, (Figure 5), and the multiple correlation coefficients R(ν, n) were calculated using the SPSS program (Table 7). The calculated K1, K2, νVapour, R(ν, D), R(ν, n) and MCC for all investigated compounds point that both the dielectric constant and the refractive index of solvents affect the electronic spectral properties of the compounds with different degrees. The high values (near one) of R(ν, D) in case of morpholine and [CuNi(MOR)2Cl4]·4H2O complex only the dielectric constant (D) function had the stronger effect than that of refractive index (n), so the peak shifts should depend primarily upon dielectric constant (D). On the other hand, for [Fe(MOR)3Cl3]·4H2O, [Ni(MOR)4Cl2]·4H2O, [Cu(MOR)4Cl2]·6H2O and [CuZn(MOR)3 Cl4]·2H2O R(ν, n) has a high value (near one) meaning that the spectral shifts observed using different solvents with different parameters depend on the refractive index (n). 3.4. Radius of solutes calculations Solvation describes the interaction of solvent with molecules or ions in a solute. Ions and, in some cases, molecules, interact strongly with the solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility and reactivity [40]. Solvation is the process of reorganizing solvent and solute molecules into solvation complexes. 60 Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Figure 4. ν vs - x1, f(D) plots of (a) morpholine, (b) [Fe(MOR)3Cl3]·4H2O, (c) [Ni(MOR)4Cl2]·4H2O, (d) [Cu(MOR)4Cl2]·6H2O, (e) [CuNi(MOR)2Cl4]·4H2O, and (f) [CuZn(MOR)3Cl4]·2H2O. Figure 5. ν vs - x2, f(n2) plots of (a) morpholine, (b) [Fe(MOR)3Cl3]·4H2O, (c) [Ni(MOR)4Cl2]·4H2O, (d) [Cu(MOR)4Cl2]·6H2O, (e) [CuNi(MOR)2Cl4]·4H2O, and (f) [CuZn(MOR)3Cl4]·2H2O. Solvent-solute interactions play a key role in solution-phase chemistry. Solvent-solute interactions are thus often essential in the determination of ground states and steering chemical reactions in solution-phase chemistry. Solvation involves bond formation, hydrogen bonding, and Vander Waals forces [41]. The energy of solvation is the amount of energy associated with the dissolution of a solute in a solvent. The reaction field model of solute-solvent interactions introduced by the Onsager Equation (11) [42] is the most widely used for the solvent- solute interaction. 2 dipol Solv 3E ( ) 2 f D a µ− = (11) 2 -2( ) 2 1 Df D D = + (12) The solvent polarity function [43] f(D) is a dimensionless number; that represents the relative strength of the electric field experienced by the ion or dipole, respectively. A neutral dipolar molecule is a sphere with a central point dipole moment μ. The ν values were plotted versus f(D) for the compounds under investigation; Radii (a) were calculated from the slope = 2 32a µ− , (Figure 4, Table 8). The dipol SolvE values based on dipole polarization, Equation (11), were calculated, and data were collected in Table 8. Morpholine and its mixed metal complexes [CuNi(MOR)2Cl4]·4H2O and [CuZn(MOR)3Cl4]·2H2O show negative slopes, leading to positive values and dipol SolvE values were negative to support that the main solvent-solute interac-tion is a dipole-dipole interaction. The dipole produces an electric field. This field has two separate effects on the surrounding solvent molecules. i) Induction polarization, where the solute-solvent interaction is given by 2 Solv 3 ( )M M E f n a µ− = (13) where 2 2 2 2( 1)( ) 2 1 nf n n − = + . Equation (13), is a measure of permanent dipole-induced dipole interactions between the solute and the solvent, while aM is the radius of the spherical cavity which contains the solvent molecule. The ν values were plotted versus f(n2) and the radii aM were calculated from the slope = -µM/𝑎𝑎𝑀𝑀3 (Figure 5 and Table 8). Morpholine and its mixed metal complexes [CuNi(MOR)2Cl4]·4H2O and [CuZn (MOR)3Cl4]·2H2O had a positive slope that leads to the fact that the aM values are negative indicating the heterogeneous distribution of solvent surrounding the solute except in the case of [Fe(MOR)3Cl3]·4H2O, [Ni(MOR)4Cl2]·4H2O and [Cu(MOR)4 Cl2]·6H2O are positive that they have a negative slope and positive aM values refer to a homogeneous distribution of solvent surrounding the solute. Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 61 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Table 8. Values of a and based on dipole polarization introduced by the Onsager equation. Compound/solvent CCl4 CHCl3 i-Propanol Acetone Ethanol Methanol Water Morpholine a - 0.0575 0.0785 0.1133 0.0794 - 0.0843 dipol SolvE -1266.15 -2027.56 -2623.56 -2652.08 -2677.75 - -2797.52 [Fe(MOR)3Cl3]·4H2O a - -0.0692 -0.0946 -0.1365 -0.0957 -0.0961 -0.1017 dipol SolvE 723.14 1158.01 1498.40 1514.69 1529.35 1553.78 1597.75 [Ni(MOR)4Cl2]·4H2O a - -0.0506 -0.0691 -0.0997 -0.0699 -0.0702 -0.0743 dipol SolvE 1855.21 2970.84 3844.13 3885.91 3923.52 3986.19 4099.01 [Cu(MOR)4Cl2]·6H2O a - -0.0428 -0.0585 -0.0844 -0.0592 -0.0594 -0.0628 dipol SolvE 3060.67 4901.21 6341.93 6410.86 6472.90 6576.30 6762.43 [CuNi(MOR)2Cl4]·4H2O a - 0.0561 0.0767 0.1107 0.0776 0.0779 0.0824 dipol SolvE -1358.28 -2175.09 -2814.41 -2845.06 -2872.59 -2918.48 -3001.08 [CuZn(MOR)3Cl4]·2H2O a - 0.0605 0.0827 0.1194 0.0837 0.0840 - dipol SolvE -1081.63 -1732.07 -2241.21 -2265.57 -2287.49 -2324.04 - Table 9. Values of aM and Esolv based on induction polarization obtained by applying Equation (5). Compound/solvent CCl4 CHCl3 i-Propanol Acetone Ethanol Methanol Water Morpholine aM - -0.0413 -0.0483 -0.0579 -0.0486 - -0.0500 Esolv 6347.23 6184.86 5520.61 5343.48 5343.48 - 5077.78 [Fe(MOR)3Cl3]·4H2O aM - 0.0465 0.0543 0.0653 0.0547 0.0548 0.0563 Esolv -4448.35 -4334.56 -3869.03 -3744.89 -3744.89 -3496.61 -3558.68 [Ni(MOR)4Cl2]·4H2O aM - 0.0346 0.0404 0.0486 0.0406 0.0407 0.0419 Esolv -10821.38 -10544.55 -9412.08 -9110.09 -9110.09 -8506.11 -8657.10 [Cu(MOR)4Cl2]·6H2O aM - 0.0292 0.0341 0.0410 0.0343 0.0344 0.0354 Esolv -17927.56 -17468.95 -15592.81 -15092.50 -15092.50 -14091.89 -14342.05 [CuNi(MOR)2Cl4]·4H2O aM - -0.0413 -0.0482 -0.0579 -0.0485 -0.0486 -0.0499 Esolv 6367.87 6204.97 5538.57 5360.86 5360.86 5005.44 5094.29 [CuZn(MOR)3Cl4]·2H2O aM - -0.0367 -0.0430 -0.0517 -0.0432 -0.0433 - Esolv 8973.67 8744.11 7805.01 7554.58 7554.58 7053.72 - The Esolv values based on induction polarization were calculated for the compounds investigated from Equation (13) and the data are collected (Table 9). The positive values of Esolv in the case of morpholine and its mixed metal complexes [CuNi(MOR)2Cl4]·4H2O and [CuZn(MOR)3Cl4]·2H2O assigned to the transitions from the ground to the excited states while the negative values of Esolv in the case of [Fe(MOR)3Cl3]·4H2O, [Ni(MOR)4Cl2]·4H2O and [Cu(MOR)4Cl2]·6H2O assigned to the transitions from the excited to ground states. ii) Orientation polarization, where the solute-solvent interaction is given by 2 Solv 3 ( ) ( ) 2 M M E f D f n a µ−  = −  (14) whereas, f(D, n2), is a measure of interactions between the permanent dipole [44]. However, the υ values were plotted versus 2( ) ( )f D f n −  relation and the radii of solvation aM were calculated from the slope = 32 M Ma µ− (Figure 6, Table 10). The Esolv values based on orientation polarization, Equation (14), were calculated and the data are collected in Table 10. The nature, type, intensity, and position of the absorption bands may be significantly affected by the type of solvent. 3.5. Solvent interactions Kamlet and Taft method is the most widely applied method for generating values for intermolecular solute/solvent interactions [45,46]. The overall solvent effect has been successfully applied to separate the influence of specific and nonspecific chemical interactions. The nonspecific chemical interactions including electrostatic effects (dipolarity/ polarizability) and the specific interactions including hydrogen bonding are related to the molecular structure of the compound [47,48]. The effects of solvent polarity and hydrogen bonding on the absorption spectra were interpreted by the linear solvation energy relationships (LSER) concept using a general Equation (15): max °ν = ν + sπ* + aα + bβ (15) where, νmax is the wavenumber (cm-1) of the maximum absorption band in pure solvents (Table 11), νo is the regression intercept corresponds to the gaseous of the spectrally active compounds, (s, a and b) are the solvatochromic coefficients while (π*, α and β) are the solvatochromic parameters. In these equations, π* is an index of the dipolarity / polarizability of the solvent which is a measure of the ability of the solvent to stabilize a charge or a dipole by its own dielectric effects [49]. The π* scale was selected to run from 0.00 for cyclohexanone to 1.00 for dimethylsulfoxide. The variable α is a measure of the solvent hydrogen bond donor (HBD) acidity, and describes the ability of the solvent to donate a proton in a solvent-to-solute hydrogen bond. The scale α was selected to extend from 0.00 for non-HBD solvents to approximately 1.00 for methanol. The variable β is a measure of the solvent hydrogen- bond acceptor (HBA) basicity [50] and describes the ability of the solvent to accept a proton in a solute-to-solvent hydrogen bond. The scale β was selected to extend from 0.00 for non-HBD solvents to approximately 1.00 for hexamethyl phosphoric acid triamide. νo, a, b, and s are solvent-independent constants, their magnitudes and sign provide measures of the influence of the corresponding solute-solvent interactions on the wavenumber in the maximum of the electronic absorption band, which have been determined by multiple regression analysis using the SPSS statistical program. The solvent parameters [51,52] are given in Table 12. The results of the correlation of the absorption frequencies with the solvatochromic parameters (π*, α, and β) are given in Table 13. The percentage contribution of the calculated solvato- chromic parameters from the values of the regression coefficients is given in Table 14 (Figure 7). dipol SolvE 62 Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Table 10. Values of aM and Esolv based on orientation polarization obtained by applying Equation (6). Compound/solvent CCl4 CHCl3 i-propanol Acetone Ethanol Methanol Water Morpholine aM - 0.0598 0.0699 0.0839 0.0703 - 0.0724 Esolv -34.09 -710.99 -1329.46 -1383.02 -1404.94 - -1551.03 [Fe(MOR)3Cl3]·4H2O aM - -0.0712 -0.0832 -0.0999 -0.0837 -0.0839 -0.0863 Esolv 20.17 420.77 786.79 818.49 831.46 887.66 917.92 [Ni(MOR)4Cl2]·4H2O aM - -0.0522 -0.0609 -0.0733 -0.0613 -0.0614 -0.0632 Esolv 51.29 1069.83 2000.43 2081.04 2114.01 2256.90 2333.84 [Cu(MOR)4Cl2]·6H2O aM - -0.0441 -0.0516 -0.0619 -0.0518 -0.0519 -0.0535 Esolv 84.68 1766.19 3302.54 3435.60 3490.04 3725.94 3852.96 [CuNi(MOR)2Cl4]·4H2O aM - 0.0585 0.0684 0.0822 0.0688 0.0689 0.0709 Esolv -36.33 -757.74 -1416.87 -1473.96 -1497.32 -1598.52 -1653.02 [CuZn(MOR)3Cl4]·2H2O aM - 0.0611 0.0714 0.0858 0.0718 0.0719 - Esolv -31.94 -666.08 -1245.48 -1295.66 -1316.19 -1405.16 - Table 11. νmax of electronic absorption spectra (cm-1) in different solvents for morpholine and its complexes in the presence of different solvents. Compound CCl4 CHCl3 i-Propanol Acetone Ethanol Methanol Water Morpholine 44444.44 43478.26 43290.04 42553.19 42372.88 - 43478.26 [Fe(MOR)3Cl3]·4H2O 35460.99 35587.18 35714.28 35971.22 36231.88 36363.63 36496.35 [Ni(MOR)4Cl2]·4H2O 35714.28 36630.03 37037.03 37453.18 36900.36 38461.53 38461.53 [Cu(MOR)4Cl2]·6H2O 40000 40650.40 41841.00 42372.88 42553.19 43290.04 44843.04 [CuNi(MOR)2Cl4]·4H2O 34129.69 32786.88 32786.88 32573.28 32467.53 32362.45 32258.06 [CuZn(MOR)3Cl4]·2H2O 39447.73 40160.64 39840.63 38759.68 38167.93 37735.84 - Table 12. Solvatochromic parameters. Solvent π* α β CCl4 0.28 0.00 0.00 CHCl3 0.58 0.20 0.10 i-Propanol 0.48 0.76 0.95 Acetone 0.71 0.08 0.43 Ethanol 0.54 0.83 0.77 Methanol 0.60 0.93 0.62 Water 1.09 1.17 0.18 Table 13. Solvent independent correlation coefficient of π*, α and β solvatochromic parameters *. Compound νo s a b MCC Morpholine 444906.810 -2206.276 -1007.012 -1961.320 0.842 [Fe(MOR)3Cl3]·4H2O 35220.944 752.911 433.372 110.221 0.881 [Ni(MOR)4Cl2]·4H2O 35038.309 2658.560 549.237 600.219 0.880 [Cu(MOR)4Cl2]·6H2O 38527.271 4287.287 1325.837 736.554 0.962 [CuNi(MOR)2Cl4]·4H2O 34459.138 -2106.167 74.056 -1025.836 0.915 [CuZn(MOR)3Cl4]·2H2O 40495.219 -2060.802 -1851.028 1009.746 0.623 * νo: The regression intercept corresponds to the gaseous of the spectrally active compounds; s, a, b: The solvatochromic coefficients; MCC: Multiple correlation coefficients. Table 14. Percentage of contribution of π*, α and β solvatochromic parameters #. Pβ (%) Pα (%) Pπ* (%) Compound 37.90 19.46 42.64 Morpholine 8.50 33.43 58.07 [Fe(MOR)3Cl3]·4H2O 15.77 14.42 69.81 [Ni(MOR)4Cl2]·4H2O 11.60 20.88 67.52 [Cu(MOR)4Cl2]·6H2O 32.00 2.31 65.69 [CuNi(MOR)2Cl4]·4H2O 20.52 37.61 41.87 [CuZn(MOR)3Cl4]·2H2O # Pπ*(%): The percentage contribution of the ability of the solvent to stabilize a charge or a dipole by its own dielectric effects, Pα(%): The percentage contribution of the solvent hydrogen-bond donor (HBD) acidity, Pβ(%): The percentage contribution of the solvent hydrogen- bond acceptor (HBA) basicity. Figure 6. ν vs - 2( ) ( )f D f n −  plots of (a) Morpholine, (b) [Fe(MOR)3Cl3]·4H2O, (c) [Ni(MOR)4Cl2]·4H2O, (d) [Cu(MOR)4Cl2]·6H2O, (e) [CuNi(MOR)2Cl4]·4H2O, and (f) [CuZn(MOR)3Cl4]·2H2O. Masoud et al. / European Journal of Chemistry 14 (1) (2023) 53-64 63 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.1.53-64.2365 Figure 7. Percentage contribution (P) to the solvatochromic effects applying Equation (15). The results show that the contributions to the solvato- chromic shift arise from dipolarity/polarizability (π*) arising from the high values of coefficient (s) shown in Table 14. The highest negative value of the MCC coefficient in [Cu(MOR)4 Cl2]·6H2O indicates a better stabilization of the transition state by dipolarity / polarizability, due to the ability of the solvent to stabilize a charge or a dipole by its own dielectric effects. The percentage contributions of the calculated solvatochromic parameters show that the classic solvation effects play a major role in explaining the spectral shifts in all investigated complexes. 4. Conclusions The optical absorption spectra of morpholine and its five morpholine complexes have been examined in various solvents of various polarities. Morpholine and both the [CuNi (MOR)2Cl4]·4H2O and [CuZn(MOR)3Cl4]·2H2O complexes reveal a red shift due to the solute-solvent interactions causing destabilization of the solute ground electronic state with increasing solvent polarity. [Fe(MOR)3Cl3]·4H2O, [Ni(MOR)4 Cl2]·4H2O, and [Cu(MOR)4Cl2]·6H2O complexes suffering a blue shift related to the formation of hydrogen bonds, suggesting the destabilization of the excited state compared to the electronic state of the ground. For morpholine, [Fe(MOR)3Cl3]·4H2O, [Ni(MOR)4Cl2]·4H2O and [Cu(MOR)4Cl2]·6H2O complexes the solvent-solute hydrogen bonding ability combined with the solute permanent dipole-solvent induced dipoles are the major factors that affecting their absorption spectra due to the high values of the correlation coefficient (near one) and lower values of the probability of variation. The solvent spectral shifts of [CuNi(MOR)2Cl4]·4H2O and [CuZn(MOR)3Cl4]·2H2O complexes are best affected by the solute permanent dipole-solvent permanent dipole combined with the solute permanent dipole- solvent induced dipole interactions. Solvation energy was defined quantitatively as the energy of interaction between the solute and the solvent. Born (point charge model) and Onsager (point dipole dielectric continuum model) formulations are two important and commonly used formulations for solvent-solute interactions. Disclosure statement Conflict of interest: There are no financial conflicts of interest to disclose. Ethical approval: All ethical guidelines have been adhered to. Sample availability: Samples of the compounds are available. CRediT authorship contribution statement Conceptualization: Mamdouh Saad Masoud, Alaa Eldin Ali; Methodology: Gehan Shabaan Elasala, Rehab Elsaid Elwardany; Software: Rehab Elsaid Elwardany Validation: Mamdouh Saad Masoud, Alaa Eldin Ali, Gehan Shabaan Elasala, Rehab Elsaid Elwardany; Formal Analysis: Alaa Eldin Ali, Rehab Elsaid Elwardany; Investigation: Rehab Elsaid Elwardany; Resources: Rehab Elsaid Elwardany; Data Curation: Rehab Elsaid Elwardany; Writing - Original Draft: Rehab Elsaid Elwardany; Writing - Review and Editing: Mamdouh Saad Masoud, Alaa Eldin Ali, Rehab Elsaid Elwardany; Funding acquisition: no funding; Supervision: Mamdouh Saad Masoud, Alaa Eldin Ali, Gehan Shabaan Elasala; Project Administration: Mamdouh Saad Masoud, Alaa Eldin Ali, Gehan Shabaan Elasala, Rehab Elsaid Elwardany. ORCID and Email Mamdouh Saad Masoud drmsmasoud@yahoo.com https://orcid.org/0000-0003-0320-6234 Alaa Eldin Ali dralaae@yahoo.com https://orcid.org/0000-0003-0437-8919 Gehan Shaaban Elasala drgehanelasala@gmail.com https://orcid.org/0000-0003-3032-5992 Rehab Elsaid Elwardany rehabelwardany@sci.dmu.edu.eg rehabelwardany4@gmail.com https://orcid.org/0000-0001-9248-146X References [1]. Duhalde, V.; Lahille, B.; Camou, F.; Pédeboscq, S.; Pometan, J.-P. Bon usage des antibiotiques: étude prospective sur l’utilisation du linézolide dans un hôpital universitaire français. Pathol. Biol. (Paris) 2007, 55, 478–481. [2]. Marcireau, C.; Guilloton, M.; Karst, F. In vivo effects of fenpropimorph on the yeast Saccharomyces cerevisiae and determination of the molecular basis of the antifungal property. Antimicrob. Agents Chemother. 1990, 34, 989–993. [3]. de Almeida, K. J.; Ramalho, T. C.; Rinkevicius, Z.; Vahtras, O.; Agren, H.; Cesar, A. 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This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution, or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Preparation of morpholine complexes 2.2. Characterization of the prepared complexes 2.3. Effect of solvents on UV-visible spectra of morpholine and its complexes 3. Results and discussion 3.1. IR, electronic spectra, ESR, and magnetic susceptibility of morpholine and its metal complexes 3.2. Electronic absorption spectra 3.3. Application of the SPSS program and regression analysis 3.4. Radius of solutes calculations 3.5. Solvent interactions 4. Conclusions Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField19: PrintField110: PrintField111: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: PrintField29: PrintField210: PrintField211: