The values of µ_eff of Ni(II) complex [Ni₂(TYS)₂(Cl)₂(H₂O)₄], at room temperature were found to be 3.20 BM which is higher than of µ_s.o value that is characterized for two unpaired electrons of Ni(II) octahedral complexes. The ensuing high value of magnetic moment may be a sign of Strong spin orbit coupling under which µ_eff = µ_S.O.(1 − 4λ/10Dq). As the spin orbit coupling constant λ for d⁸ system is (λ = −315), µ_eff becomes greater than µ_S.O. Ni(II)-TYS complex shows four bands in their electronic spectra, suggesting distorted tetragonal geometry (D_4h). These bands can be assigned to the following transitions [22].

ν 1 = B 3 1g → E 3 g 10Dq – 35/4Dt

ν 2 = B 3 1g → B 3 2g 10Dq

ν 3 = B 3 1g → A 3 2g 18Dq – 4Ds – 5Dt

ν 4 = B 3 1g → E 4 g 18Dq – 2Ds – 25/4Dt

The tetragonal character is measured by the transition ³B_1g→³E_g^(a). The transition ³B_1g→³B_2g^(b), on the other hand, is unaffected by Ds and Dt while is effectively the measure of the infield splitting parameter Dq^xy. The axial distortion Dt is computed by using the Wentworth and Piper formula [23], which is Dt = 4/7(Dq^xy − Dq^Z) or by another derived formula 35/4Dt = ν₂ − ν₁. The equation 2ν₁ − ν₂/10 was used to compute Dq^Z. The zero field splitting parameter (D) has also been calculated using the expression D = 9k₁/α²[(µ_eff/µ_s.o)² − (µ_eff/µ_s.o) + 1S] while k₁, is the splitting of the initial excited state, and it is given as k₁ = 35/4Dt. The values for the various parameters are listed in Table 2. The presence of four bands indicates a significant tetragonal deviation from octahedral symmetry. The positive value of Dt, Ds and smaller value of Dq^z than Dq^xy are assigned to tetragonal elongated octahedral geometry of Ni(II) complex. The features of all produced bands that represent these complex transitions as shown in Figure 3 were in strong feature and well analyzed; the complex Ni(II)-TYS shows four bands at 1041.7, 941.6, 541.1 and 416.7 nm, which correspond to the transitions ³B_1g → ³E_g (υ₁), ³B_1g → ³B_2g (υ₂), ³B_1g → ³A_2g (υ₃) and ³B_1g → ⁴E_g (υ₄) respectively, that is a great elucidation of tetragonal elongated octahedral structure.

The expected calculated value of the spin only magnetic moment (µ_s.o)of Co(II) is 3.87 B.M due to Co(II) is a d⁷ system with three unpaired electrons, while the actual values of magnetic moment for complex [Co₂(TYS)₂(Cl)₂(H₂O)₄] is 4.79 B.M respectively. The irregular values for Co(II)-TYS complex µ_eff may be attributed to ⁴T_1g ground state crystal field term in octahedral symmetry which makes a significant contribution to the magnetic moment of Co(II) complex in octahedral symmetry [24]. Typically, Three absorption bands are predicted to occur in the electronic spectra of Co(II) complex with perfect high spin octahedral geometry due to three probable spin allowed transitions, ⁴T₁g(F) → ⁴T₂g(F), ⁴T₁g(F) → ⁴T₁g(P) and ⁴T₁g(F) → ⁴A₂g(F) that represent (ν₁), (ν₂) and (ν₃) respectively, while due to the splitting of ⁴T_1g(F), ⁴T₂g and ⁴T_1g(P) in their electronic spectra, these cobalt complex of tylosin display four bands in their electronic spectra, as shown in (Figure 3), which are an evidence of axially distorted octahedral symmetry around Co(II) in these metal complexes. The electronic spectra of Co(II)-TYS complex reveal four bands, indicating axially distorted octahedral symmetry around Co(II). These bands can be ascribed to the transitions mentioned below under D_4h symmetry [24]:

ν 1 = A 4 2g → E 4 g ( a ) 6/5Ds – 15/4Dt

ν 2 = A 4 2g → B 4 2g 8Dq + 4/5Ds – 13Dt

ν 3 = A 4 2g → E 4 g ( b ) 8Dq + 4/5Ds – 17/4Dt

ν 4 = A 4 2g → B 4 1g 18Dq + 4/5Ds – 13Dt

ν 5 = A 4 2g → E 4 g ( c ) 6Dq + 2/5Ds – 6Dt

ν 6 = A 4 2g → A 4 2g ( a )   ( P ) 6Dq+ 18/5Ds – 6Dt

The value of Dq^(xy) has been calculated by using the derived equation ν 4 − ν 2 10 and D_t value has been estimated from the equation 4 35 ( ν 3 − ν 2 ) . The common equation, Dt = 4/7(Dq^xy − Dq^z) used to deduce the value of Dq^z. The positive value of Dt and Ds produced mathematically are the indication of tetragonal elongated octahedral geometry of Co(II) complex . The smaller value of Dq^z, than Dq^xy, support and clarify the tetragonal elongation along z-axis in Co(II) complex of tylosin. The spectra for Co(II)-TYS complex shows definitely four bands at 1073, 920, 494 and 402.4 nm that correspond to the transitions (ν₂) ⁴A_2g → ⁴B_2g, (ν₃) ⁴A_2g → ⁴E_g^(b), (ν₄) ⁴A_2g → ⁴B_1g and (ν₅) ⁴A_2g→⁴E_g^(c) ,respectively. The last band n₆ that represents the transition ⁴A_2g → ⁴A_2g^(a) (P) which may be confused with the final band appeared in the spectra. The band ν₁ refers to ⁴A_2g → ⁴E_g^(a) transition state that is unnoticeable due to the small gap between the two levels which causes absorption energy in the infrared range. From D_s and D_t values, the value of ν₁ has been estimated and found in 3486 cm⁻¹, which refers to the infrared spectrum.

The magnetic moment of Cr(III) complex of tylosin, at room temperature was found 3.74 B.M, as shown in Table 2, this value of Cr(III) metal complex is close to spin only value that equal 3.87 B.M thereby, suggesting an octahedral geometry around the d³ system of chromium ion. The different values of µ_s.o and µ_eff may be an indication of distorted octahedral geometry of this complex [25]. The octahedral geometry of Cr(III)-TYS complex is determined due to the presence of three bands that represent the three lowest spin-allowed transitions ⁴A_2g → ⁴T_2g(F), ⁴A_2g → ⁴T_1g(F) and ⁴A_2g → ⁴T_1g(p), while four bands appeared in distorted octahedral geometry due to splitting occurred for ⁴T_2g to ⁴E_g^a and ⁴B_2g and also scattering of ⁴T_1g(F) to ⁴A_2g^a and ⁴E_g^b [26]. These four bands that represent distorted tetragonal octahedral geometry can be assigned to the following transitions.

ν 1 = B 4 1g → E 4 g a 10Dq – 35/4Dt

ν 2 = B 4 1g → B 4 2g 10Dq

ν 3 = B 4 1g → A 4 2g a 18Dq – 4Ds – 5Dt

ν 4 = B 4 1g → E 4 g b 18Dq – 2Ds – 25/4Dt

The calculated value of Dq^xy is estimated from the transition ν₂ that is equal to 10Dq^xy. The value of Dt is calculated by the difference between ν₁ and ν₂ which is equivalent to (35/4)Dt. The symmetry plane of Dt is related to the in-plane and out-of-plane field strengths as Dt = 4/7(Dq^xy − Dq^Z) which shows that Dq is in-plane (xy) and out-of-plane (z) Field strength, respectively. The parameter Ds has been calculated from the equation (ν₃ − ν₂) = 8Dq − 4Ds − 5Dt. The presence of four bands in the electronic spectral sheet of dark green chromium (III) metal complex in the range between (350 - 550) nm is a great indication for distorted octahedral geometry. The positive value of the two field parameters Ds and Dt proved this distorted geometry. The smaller value of Dq^xy than Dq^z show axially elongated tetragonal structure for these metal complexes.

Cu(II) complex of tylosin has shown a magnetic moment near 2.17 B.M, which corresponds to the presence of a single unpaired electron due to d⁹ system of cupric ion that indicates mononuclear nature of the complex with mild paramagnetic. The difference between the spin only and magnetic moment values may be due to Strong spin orbit coupling which allows a greater value of µ_eff than µ_S.O. For copper (II) metal complex of tylosin, the coordination number was six. It means that the geometry of these complexes may be distorted octahedral as tetragonal elongated structure, which can clearly determine the geometry by illustrate the electronic spectra of these Cu(II) metal complexes. In the pure octahedral coordination geometry, the ²D state of Cu(II) is split into ²E_g ground state and ²T_2g excited state with a single electronic transition. Therefore, Cu(II) is no longer in the pure octahedral (Oh) geometry, and the symmetry around the metal is slightly distorted. A Jahn-Teller (J-T) distortion is taking place that changes the symmetry from octahedral (O_h) to tetragonal structure (D_4h) [27]. Due to the Jahn-Teller effect, the ground state ²E_g is further scattered into ²B_1g ground and ²A_1g excited states, and the transition state ²T_2g is separated into ²B_2g ground and ²E_g excited states. Therefore, the three bands that indicate distorted tetragonal octahedral geometry can be described by the following transitions [28]:

ν 1 = B 2 1g → A 2 1g 4Ds + 5Dt

ν 2 = B 2 1g → B 2 2g 10Dq

ν 3 = B 2 1g → E 2 g 10Dq + 3Ds – 5Dt

For Cu(II)-TYS complex, the electronic spectral exhibits clearly three bands at 9770, 16100 and 17200 cm⁻¹ which can be attributed to three optical probable transitions, ²B_1g → ²A_1g (ν₁), ²B_1g → ²B_2g (ν₂) and ²B_1g → ²E_g(ν₃). In the spectrum, there is a scattered broad band at range 580 - 625 nm that reveals scattering of ²T_2g of octahedral geometry into ²B_2g and ²E_g which are close to each other [29], while the first band appeared lately at 1023 nm which assigned to ²B_1g → ²A_1g transition that proved distortion of axially tetragonal elongation for Cu(II) Tylosin metal complex. The value of 10Dq is estimated by determination of the second band (ν₂) at which the value of Dq^z by cm⁻¹ is calculated by division of (ν₂/10). The value of Dq^xy is calculated directly from the popular equation that equal Dt = 4/7(Dq^xy − Dq^Z). The tetragonal crystal field parameters Ds and Dt founded by solving the following two equations, ν₃ = 4Ds + 5Dt → (1) and ν₂ – ν₁ = −3Ds + 5Dt → (2). The same positive charge value for both parameters Ds and Dt indicated an axially elongated tetragonal geometry for both structure of Cu(II) metal complexes.

Magnetic moments of Fe(III) metal complex was founded to be 5.60 B.M; this value is quite near to the spin-only magnetic moment corresponding to five unpaired electrons. This is due to the fact that both Fe(III) metal complexes have a high magnetic spin and are dilute octahedral complexes. Spin-orbit coupling, which limits the spin and orbital motion of electrons to an extent, could explain the somewhat lower magnetic moment value. In the electronic spectral sheet of Fe(III)-TYS complex, there were four weak bands were detected as listed in Table 2 which attributed to the following spin forbidden transitions [30],

ν 1 = A 6 1g → T 4 1g   ( 4G ) ,

ν 2 = A 6 1g → T 4 2g   or   4 A 1g   or   4 E g   ( 4G ) ,

ν 3 = A 6 1g → E 4 g   ( 4D ) ,

ν 4 = A 6 1g → T 4 1g   ( 4P ) .

The presence of these four weak bands is indicative of axial elongated distorted octahedral geometry for these Fe(III) complexes. So, the values of different crystal field parameters have not been estimated due to the high spin nature of Fe(III) metal. The suggested geometry of the reddish brown Fe(III)-TYS complex depends on a bidentate nature of ligand, chlorides and water which allow six coordination numbers around Fe(III) that confirm distorted octahedral structure. The first bands in the UV/Vis spectra of Fe(III) which exhibits in the region range 300 - 350 nm due to ligand metal charge transfer.

Magnetic moments of Mn(II)-TYS complex was measured to be 5.75 B.M; the spin only magnetic moment corresponding to five unpaired electrons is very close to this value, which is attributable to the fact that Mn(II) metal complex is dilute octahedral with a high magnetic spin. The slightly low magnetic moment value could be due to spin-orbit coupling, which limits the spin and orbital motion of electrons to a small extent. The Mn(II) complex of tylosin exhibit four very weak bands that was recognized in its electronic spectral data at 18,060, 24,410, 26,380 and 27,610 cm⁻¹ assigned to the following spin forbidden transitions [31], ν₁ = ⁶A_1g → ⁴T_1g (4G), ν₂ = ⁶A_1g → ⁴T_2g or ⁴A_1g or ⁴E_g(4G), ν₃ = ⁶A_1g → ⁴E_g (4D) and ν₄ = ⁶A_1g → ⁴T_1g (4P). The presence of these weak bands is indicative of axial elongated distorted octahedral geometry for these Mn(II) complex. So, the suggested geometry of Mn(II)-TYS complex depends on a bidentate nature of ligand, chlorides and water which allow six coordination numbers around Mn(II) that confirm distorted octahedral structure.

For [Zn₂(TYS)₂(H₂O)₄Cl₂] complex, the proposed structure due to the bidentate nature of Tylosin through oxygen atoms of OH group of mycarose sugar and Nitrogen atom of 3˚ amine group in the structure with the presence of two chloride ions and four water molecules in the inner sphere that may be a good conclusion for octahedral geometry of this complex. Only a high intensity band at 329 - 365 nm was observed in this complex, which was attributed to ligand metal charge transfer. No d-d transition could be observed due to the d¹⁰ structure of Zn(II); hence the stereochemistry could not be deduced from ultraviolet and visible spectra. However, distorted octahedral geometry is proposed for this complex based on comparisons between their spectra and those of related environments.

Using paper disk diffusion method [37], the tylosin ligand and its synthesized metal complexes were evaluated for their antimicrobial activities. Thus, these compounds were screened against Staphylococcus Aureus (S. aureus); Bacillus cereus (B. cereus) as a Gram-positive bacteria, Escherichia Coli (E. coli); Salmonella typhimurium (S. typhi) as Gram-negative bacteria and Candida Albicans (C. albicans)as a fungal strain. The results displayed in Table 5 clearly indicate that the free ligand has exhibited inhibition effect on all tested microorganisms

due to Structure-activity relationships (SAR) of tylosin that was evaluated in terms of their antimicrobial and ribosome-binding activities blocking the synthesis of protein [38].

However, the [Zn₂(TYS)₂Cl₂(H₂O)₄]·25H₂O and [Cu₂(TYS)₂Cl₂(H₂O)₄]·25H₂O tested compounds exhibited potent antimicrobial effect especially for Gram-positive bacterial strains (S. aureus); (B. cereus) and fungal strain (C. albicans) in comparison to the reference free ligand standard tylosin [38]. The

Maximum of inhibition activity (38 mm) was observed against (S. aureus) by Cu(II)-TYS complex. The enhanced microbial activity of zinc and copper complexes with tylosin ligand may be illustrated using chelation effect theory [39].

MIC is useful in research facilities because it may be used to monitor antibiotic resistance and to track the activity of new antimicrobial drugs [40]. MIC is applied for some of tylosin-Metal complexes that have highest antimicrobial activity results against tested species reported in Table 5, MIC results of ligand and its metal complexes by µg/ml are summarized in Table 6.

[Zn₂(TYS)₂Cl₂(H₂O)₄]·25H₂O and [Cu₂(TYS)₂Cl₂(H₂O)₄]·25H₂O complexes revealed low concentration value of MIC results with S. aureus with the same value for both 31.25 µg/ml. For B. cereus species both novels tested complexes Zn(II)-TYS and Cu(II)-TYS show lower MIC values with higher antimicrobial activity with value 15.625 µg/ml. Both tested metal complexes of tylosin possess the highest activity with the lowest or equal concentration rather than the tylosin ligand that is sufficient to make the effect of bacterial inhibition.

Free macrolide ligandtylosin show lower MIC value for the fungal strain Candida albicans with value 62.5 µg/ml than two complexes, Zn(II)-TYS and Cu(II)-TYS which poses the highest antifungal activity has the same MIC value by 125 µg/ml. It means that the ligand has better MIC value than Zn(II)-TYS and Cu(II)-TYS complexes although both complexes have higher antifungal activity than tylosin ligand.