Synthesis, Spectral Analysis and Biological Potency of Hydrazoneoxime Ligands Incorporating Pyrazolone Moiety and their Metal Complexes

Introduction

Pyrazolone is considered as an importantcomponent or structural unit which is present in variousactive compounds. Owing toits convenient synthesis as well asversatile biological applications particularly itscomprehensive antisepsis , antitumor, antibacterial action[1-4],pyrazolone and its complexes have acquired a significant consideration in coordination as well as in medicinal chemistry.

Pyrazolonederived productsare paramountkind of heterocyclic compounds that occurs in various  drugsas well as in  synthetic products [5,6]. These compoundsshowextraordinary analgesic [7], antitubercular [8], antifungal, antibacterial [9], anti-inflammatory [10], antioxidant and antitumor activities [11]. Because of their facile synthesis and characteristicbiological activity, pyrazolone arrangement performs a significant function and reflects an effectiveexample for combinatorial and pharmaceutical chemistry. Furthermore, pyrazole derived products  showedoutstandingbiological asset,for example, anti-microbial [12], analgesic [13], anti-inflammatory [14], and anticancer activities [15]. This provided anenormous boost  to explore for potentially active compounds having pyrazole substituents.

Herein, the derivatization of hydrazoneoxime ligands bearing pyrazolone group (1-4) and their metal complexes1(a-c), 2(a-c), 3(a-c),4(a-c)was reported. The ligands and its complexes were characterized by¹H NMR, ¹³C NMR, FT-IR spectroscopy, elemental analysis ,and magnetic susceptibility techniques. The proposed general structure of the ligand is given in Scheme.1

Scheme 1: The moleculer formules of the ligands. Click here to View Scheme

Experimental

Instruments and reagents

Reagentsused in the experiment have been obtained  from Sigma-Aldrich, Merck, and Fluka and were handled as received. Themelting point of the synthesised complexes and the  ligands  were varified and calculated  bythe Büchi SMP-20 apparatus using an open capillary method.For the calculation of  FT-IR spectra , KBr discs on a Perkin Elmer Mattson 1000 spectrophotometer were used, ¹H and ¹³C NMR spectra have been reported by Bruker-Spectrospin Avance DTX 400 Ultra-Shield in deuterated dimethylsulphoxide (DMSO-d6) and  tetramethylsilane (TMS) used as an internal standard and chemical shifts considered in ppm.The Leco CHNS-932 analyzer used for the elemental analysis: and for the pH measurements,an Orion Expandable Ion Analyzer EA 940 was used. The melting point , colors ,molecular weights, percentage of yield, molar conductance, magnetic susceptibilities (Sherwood Scientific) have been calculated, and are given in the following sections.

Preparation of the ligands and their nomenclature

The precursor (1Z,2E)-2-(hydroxyimino) ethanehydroximohydrazide (GH₂) was prepared by the action of the (1Z,2E)-N-hydroxy-2-(hydroxyimino) ethanimidoyl chloride [16] and hydrazinium hydroxide.Since the parent compound , GH₂  is  unstable at normal temperature,so it was utilized without further purification or as it was received.Hydrazoneoxime ligands bearing pyrazolone group (1-4)have beenprepared with the5-pyrazolones as mentioned in the literature [17] and characterized their structuresby using spectral techniques.

The IUPAC name of the ligands may be given as 2-[(1Z,2E)-N-hydrokis-2-(hydrokisimino) etanimidoil]-5-metil-4-[(Z)-fenildia zenil]-2,4-dihidro-3H-pirazol-3-on (1), 2-[(1Z,2E)-N-hydrokis-2-(hydrokisimino) etanimidoil] -5-metil-4-[(Z)-(4-nitrofenil) diazenil]-2,4-dihidro-3H-pirazol-3-on (2), 2-[(1Z,2E)-N-hydro kis-2-(hydrokisimino) etanimidoil]-4-[(Z)-(4-metoksifenil) diazenil]-5-metil-2,4-dihidro-3H-pirazol-3-on (3) and 2-[(1Z,2E)-N-hydrokis-2-(hydrokisimino) etanimidoil]-5-metil-4-[(Z)-(4-metilfenil)diazenil]-2,4-dihidro-3H-pirazol-3-on  (4). The preparation procedures were followed as given in theliterature [18-20]. For the synthesis of (1-4) the common route follows as  given in  theS cheme 2.

Scheme 2: General route for the synthesis of ligands (1-4) Click here to View scheme

General procedure of synthesis

Synthesis of hydrazoneoxime ligands bearing pyrazolone group(1-4)

Aniline derivatives 10 mmol (0.69 g, aniline; 1.38 g, 4-nitroaniline; 1.23 g, p-anisidine; or 1.04 g, p-toluidine respectively)were taken and dissolved in a mixture of  1:1 ratio of glacial Acetic acid and concentrated Hydrochloric acid (20 mL),and cooled the solutionupto 0–5 °C.Sodium nitrite (0.69g or  0.01 mol)  was taken and dissolved in 10mL water, and then added dropwise to the above-prepared solution mixturewith vigorous stirring for nearly one  hourto  maintain  the solution temperature between 0–5 °C. The obtained diazonium solution has been mixed  in aliquots for 30 minutes, to thesolution of 2-[(1Z,2Z)-N-hydrokis-2-(hydrokisimino)etanimidoil]-5-metil-2,4-dihidro-3H-pirazol-3-on (0.76 g or 0.01 mol) in 10 mL of ethyl alcohol ,and stirred vigorously , added the  NaOH solution for maintaining the pH level between(7–8). The mixture has bee stirred for 2 hoursand maintain  the solution temperature between 0–5 °C. Theobtained  product was separated by means of diluting with water (50 mL), filtered, washed several times withdistilled water, and finally dried.

2-[(1Z,2E)-N-hydrokis-2-(hydrokisimino)etanimidoil]-5-metil-4-[(Z)-fenildiazenil] -2,4-dihidro-3H-pirazol-3-on(1)

The analytical and physical properties of the ligand (1) and its metal complexes (1a-1c) are provided  in Table 1. Appearance: yellow powder; Yield=87%, m.p.(decomp.) 165 °C; The reaction scheme is given in Scheme 2.  The compound is soluble in commonly used solvents likeCH₂Cl₂, CHCl₂, DMF, EtOH and DMSO. Anal. Calcd. for C₁₂H₁₂N₆O₃ (288.27 g mol⁻¹): 50.00 % C; 4.20 % H; 29.15 % N, Found: 50.60  % C;  4.40 % H; 29.21 % N. The infrared spectral data of the ligand (1) is given in Table 2.FT-IR (KBr, ν_max/cm^-1): 3271 (N-H), 3681(O-H), 2970 (C-H_Arom.), 2844 (C-H_Aliph.), 1598-1664 (C=N_Oxim.), 1556 (C=N_Hydr.), 1033(N-O), 1484 ve 1441 (N-N_Azo.). The FT-IR spectrum of ligand (1) is given in Figure 1.¹H NMR peaks (DMSO-d₆, (ઠ)  ppm): 2,18(s,3H, pyazolone-CH3); 7.17-7.57 (m,5H, Ar-H ); 11.81; 12.20 (d, 2H (OH); 7.84 (s, 2H, CH=NOH); 13.01 (s, 2H -CH=N-NH); 11.81; 12.20 (s, 4H (OH); 7.84 s, 2H (CH=NOH), 7.39; 7.40; 7.42 t, 7.55; 7.57 d, 7.17; 7.18; 7.20 t; 4H (Ar-H), 13.01 s, 2H (-CH=N-NH).¹³C NMR peaks of the compound: (CDCl₃, TMS, ઠ ppm):148.35(N-C=N-OH); 148.80(CH=N-OH); 156.99 (C=N-N);12.03 (CH₃); 158.17 (C=N-NH);159.76 (C=O); 129.96, 116.68, 126.05, 142.80 (Ar-C).

Table 1: Physical and analytical data of  the hydrazoneoxime lıgand (1) bearıng pyrazolone group and its complexes

Compound	Molecula Composition	M.W. (g/mol)	Apperance	Melting Point (d)* (ºC)	Yield (%)	Calculated (Found) %
						C	H	N
Ligand (1)	C12H12N6O3	288,27	Yellow	165	87	50,00     (50,60)	4,20  (4,40)	29,15   (29,21)
Complex(1a)	C24H22N12O6Ni	633,21	Red-brown	>370 *	52	45,52   (45,60)	3,50   (3,43)	26,54   (26,47)
Complex(1b)	C24H22N12O6Co	633,45	Dark-brown	230 *	76	45,51   (45,58)	3,50   (3,43)	26,53   (26,44)
Complex(1c)	C24H22N12O6Cu	638,06	Dark-brown	193 *	68	45,18   (45,59)	3,48   (3,55)	26,34   (25, 77)

Figure 1: FT-IR spectrum of ligand (1) Click here to View figure

Table 2: Infrared data for the ligand(1) and its complexes

Compound	ν(O-H)	ν(N-H)	ν(C=O)	ν(C=N)oxim	ν(C=N)hyd.	ν(CH)Arom.	ν(CH)Alip.	ν(N-N)	ν(N-O)	ν (OH―O)
Ligand (1)	3681w	3271w	1667s	1598-1664m	1536-1556m	2970m	3088m	1484-1441m	1033m	–
Complex(1a)	3271m	3271m	1667w	1594-1677m	1536-1556m	2970m	2844m	1449-1484m	1033m	1738m
Complex(1b)	3271m	3271m	1667w	1594-1677m		2970m	2844m	1449-1484m	1033m	1738m
Complex(1c)	3168m	3168m	1655m	1594-1677m		2970m	2864m	1449-1484m	1033m	1738m

2-[(1Z,2E)-N-hydrokis-2-(hydrokisimino)etanimidoil]-5-metil-4-[(Z)-(4-nitrofenil) diazenil]-2,4-dihidro-3H-pirazol-3-on (2)

Some important characteristics (analytical and physical)of the synthesized ligand (2) and its metal complexes (2a-2c) are givem in Table 3. Appearance: Dark brown powder; Yield=75 %, M.p.(decomposition) 250 °C;For the synthesis of the compound (2), reaction arrangements are illustrated in  Scheme 2. This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO. Anal. Calcd. for C₁₂H₁₁N₇O₅ (333.27 g mol⁻¹): 43.25 % C; 3.33 % H; 29.42 % N, Found: 43.83 % C;  3.40 % H;  29.35 % N. The infrared spectral collected statistics of the ligand (2)are revealed inTable 4. FT-IR (KBr, ν_max/cm^-1): 3271 (N-H), 3681(O-H), 2970 (C-H_Arom.), 2864 (C-H_Aliph.), 1609-1677 (C=N_Oxim), 1543 (C=N_Hydr.), 1033(N-O), 1506 ve 1483 (N-N_Azo), 1417 ve 1376 (-NO₂). The FT-IR spectrum of ligand (2) is given in Figure 2. ¹H NMR peaks (DMSO-d₆, (ઠ)  ppm): 2,20 (s, 3H, pyazolone-CH3 ); 7.68-7.78 (m,4H, Ar-H); 11.84; 12.22 (d, 2H (OH); 7,85 (s, 2H, CH=NOH); 13.03 (s, 2H -CH=N-NH).¹³C NMR peaks of the compound: (CDCl₃, TMS, (ઠ) ppm): 149.18 (N-C=N-OH); 147.47 (CH=N-OH); 157.40 (C=N-N); 12.07 (CH₃); 156.19(C=N-NH); 158.05 (C=O); 116.89, 125.86, 129.41, 136.99 (Ar-C).

Table 3: Physical and analytical data of  the hydrazoneoxime lıgand (2) bearıng pyrazolone group and its complexes

Compound	Molecula Composition	M.W. (g/mol)	Apperance	Melting Point (d)* (ºC)	Yield (%)	Calculated (Found) %    C         H          N
Ligand (2)	C12H11N7O5	333,26	Light-brown	250	75	43,25   (43,83)	3,33   (3,40)	29,42   (29,35)
Complex(2a)	C24H20N14O10Ni	723,21	Red-brown	240 *	80	39,86    (39,93)	2,79   (2,85)	27,12   (27,69)
Complex(2b)	C24H20N14O10Co	723,45	Dark-brown	200 *	76	39,85   (39,27)	2,79   (3,34)	27,11   (27,67)
Complex(2c)	C24H20N14O10Cu	728,06	Dark-brown	195 *	65	39,59    (39,99)	2,77   (2,83)	26,93   (26,99)

Figure 2: FT-IR spectrum of ligand (2) Click here to View figure

Table 4: Infrared data for the ligand (2) and its complexes

Compound	ν(O-H)	ν(N-H)	ν(C=O)	ν(C=N)oxim	ν(C=N)hyd.	ν(CH)Arom.	ν(CH)Alip.	ν(N-N)	ν(N-O)	ν (OH―O)
Ligand (2)	3681w	3271w	1667s	1598-1664m	1536-1556m	2970m	3088m	1484-1441m	1033m	–
Complex(2a)	3271m	3271m	1667w	1594-1677m	1536-1556m	2970m	2844m	1449-1484m	1033m	1738m
Complex(2b)	3271m	3271m	1667w	1594-1677m	1536-1556m	2970m	2844m	1449-1484m	1033m	1738m
Complex(2c)	3168m	3168m	1655m	1594-1677m	1536-1556m	2970m	2864m	1449-1484m	1033m	1738m

2-[(1Z,2E)-N-hydrokis-2-(hydrokisimino)etanimidoil]-4-[(Z)-(4-metoksifenil) diazenil]-5-metil-2,4-dihidro-3H-pirazol-3-on (3)

Some important characteristics (analytical and physical) of the synthesized ligand (3) and its metal complexes (3a-3c) are given in Table 5. Appearance: Red powder; Yield=83 %, M.p.(decomposition) 230 °C;For the synthesis of the compound (3),reaction arrangements are illustrated in Scheme 2.This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO. Anal. Calcd. for C₁₃H₁₄N₆O₄ (318.29 g mol⁻¹): 49.06 % C; 4.43 % H; 26.40 % N, Found: 49.13 % C;  4.37 % H;  26.48 % N. The infrared spectral collected statisticsof the ligand (3) are revealed inTable 6. FT-IR (KBr, ν_max/cm^-1):  3235 (N-H), 3681 (O-H), 2970 (C-H _Arom.), 2844 (C-H _Aliph.), 1595-1648 (C=N_Oxim), 1553 (C=N _Hydr.), 1033 (N-O), 1454 ve 1474 (N-N_Azo), 1738 –C=O. The FT-IR spectrum ofligand (3) is can be seen in Figure 3. ¹H NMR peaks (DMSO-d₆, (ઠ)  ppm): 2.16 (s,3H, pyazolone-CH3 ); 6.98 -7.52 (m,4H, Ar-H); 12.17-12.21 (d, 2H (OH); 7.83 (s, 2H, CH=NOH); 13.07 (s, 2H -CH=N-NH); 3,74 (s, 3H –OCH3.¹³C NMR peaks of the compound: (CDCl₃, TMS, (ઠ) ppm): 148.62 (N-C=N-OH); 144.97 (CH=N-OH); 157.97 (C=N-N); 12.04 (CH₃); 157.26 (C=N-NH); 158.35 (C=O); 115.28, 118.28, 148.62, 135.27 (Ar-C); 55.89 (OCH₃).

Table 5: Physical and analytical data of  the hydrazoneoxime lıgand(3) bearing pyrazolone group and its complexes

Compound	Molecula Composition	M.W. (g/mol)	Apperance	Melting Point (d)* (ºC)	Yield (%)	Calculated (Found) %
						C	H	N
Ligand (3)	C13H14N6O4	318,29	Red	230	83	49,06    (49,13)	4,43   (4,37)	26,40   (26,48)
Complex(3a)	C26H26N12O8Ni	693,6	Red-brown	>370 *	78	45,05   (45,13)	3,78   (3,72)	24,25   (24,32)
Complex(3b)	C26H26N12O8Co	693,50	Dark-brown	>350 *	65	45,03   (45,09)	3,78   (3,72)	24,24   (24,17)
Complex(3c)	C26H26N12O8Cu	698,12	Dark-brown	196*	68	44,73   (44,79)	3,75   (3,68)	24,08   (24,66)

(d)*:  decomposition

Figure 3: FT-IR spectrum of ligand (3) Click here to View figure

Table 6: Infrared data for the ligand(3) and its complexes

Compound	ν(O-H)	ν(N-H)	ν(C=O)	ν(C=N)oxim	ν(C=N)hyd.	ν(CH)Arom.	ν(CH)Alip.	ν(N-N)	ν(N-O)	ν (OH―O)
Ligand (3)	3681w	3271w	1667s	1598-1664m	1536-1556m	2970m	3088m	1484-1441m	1033m	–
Complex(3a)	3271m	3271m	1667w	1594-1677m	1536-1556m	2970m	2844m	1449-1484m	1033m	1738m
Complex(3b)	3271m	3271m	1667w	1594-1677m	–	2970m	2844m	1449-1484m	1033m	1738m
Complex(3c)	3168m	3168m	1655m	1594-1677m	–	2970m	2864m	1449-1484m	1033m	1738m

2-[(1Z,2E)-N-hydrokis-2-(hydrokisimino)etanimidoil]-5-metil-4-[(Z)-(4-metilfenil) diazenil]-2,4-dihidro-3H-pirazol-3-on (4)

Some important characteristics (analytical and physical) of thesynthesized ligand(4),and more (4a-4c)it’s metal complexes are collected in Table 7. Appearance: Light brown powder: Yield=76 %, M.p.(decomposition) 243 °C;For the synthesis of the compound (4),reaction arrangements are illustrated in Scheme 2. This compoundis soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO. Anal. Calcd. for C₁₃H₁₄N₆O₃ (302.29 g mol⁻¹): 51.65 % C; 4.67 % H; 27.80 % N, Found: 51.70 % C;  4.67 % H;  27.80 % N. The infrared spectral collected statisticsof the ligand (4) are revealed inTable 8. FT-IR (KBr, ν_max/cm^-1):3168 (N-H), 3681(O-H), 2970 (C-H_Arom.), 2844 (C-H _Aliph.), 1594-1669 (C=N_Oxim.), 1536 (C=N _Hydr.), 1033(N-O), 1492 ve 1449 (N-N_Azo.), 1738 –C=O, 2970 –CH_3(phenil) ve CH_3(methyl). The FT-IR spectrum of ligand (4) is given in Figure 4.¹H NMR peaks (DMSO-d₆, (ઠ)  ppm): 2.17 (s,3H, pyazolone-CH3 ); 7.18-7.46 (m,4H, Ar-H); 11.76; 12.18 (d, 2H (OH); 7,83 (s, 2H, CH=NOH); 13.05 (s, 2H -CH=N-NH); 2.27 (s, 3H –CH3(fenil).¹³C NMR peaks of the compound: (CDCl₃, TMS, (ઠ) ppm):  148.67 (N-C=N-OH); 148.20 (CH=N-OH); 158.30 (C=N-N); 12.02 (CH₃); 157.12 (C=N-NH); 160.64 (C=O); 116.69, 126.24, 130.42, 135.68 (Ar-C); 20.97 (CH₃).

Table 7: Physical and analytical data of  the hydrazoneoxime lıgand(4) bearıng pyrazolone group and its complexes

Compound	Molecula Composition	M.W. (g/mol)	Apperance	Melting Point (d)* (ºC)	Yield (%)	Calculated (Found) %
						C	H	N
Ligand (4)	C13H14N6O3	302,29	Dark-yellow	243	76	51,65   (51,70)	4,67   (4,71)	27,80   (27,74)
Complex(4a)	C26H26N12O6Ni	661,27	Red-brown	>370 *	72	47,23   (47,16)	3,96   (3,89)	25,42   (25,36)
Complex(4b)	C26H26N12O6Co	661,51	Dark-brown	230 *	70	47,21   (47,28)	3,96   (3,89)	25,41   (25,57)
Complex(4c)	C26H26N12O6Cu	666,12	Dark-brown	195*	64	46,88   (46,81)	3,93   (3,88)	25,23   (27,17)

(d)*:  decomposition

Figure 4: FT-IR spectrum of ligand (4) Click here to View figure

Table 8: Infrared data for the ligand(4) and its complexes

Compound	ν(O-H)	ν(N-H)	ν(C=O)	ν(C=N)oxim	ν(C=N)hyd.	ν(CH)Arom.	ν(CH)Alip.	ν(N-N)	ν(N-O)	ν (OH―O)
Ligand (4)	3681w	3271w	1667s	1598-1664m	1536-1556m	2970m	3088m	1484-1441m	1033m	–
Complex(4a)	3271m	3271m	1667w	1594-1677m	1536-1556m	2970m	2844m	1449-1484m	1033m	1738m
Complex(4b)	3271m	3271m	1667w	1594-1677m	1536-1556m	2970m	2844m	1449-1484m	1033m	1738m
Complex(4c)	3168m	3168m	1655m	1594-1677m	1536-1556m	2970m	2864m	1449-1484m	1033m	1738m

Compound’s Synthesis

For the synthesis of all three complexes , a general method was used [16]: The 2 mmol of the above ligands, (1-4), were dissolved in 10 mL absolute ethyl alcohol at refluxing temperature. A solution of NiCl₂.6H₂O or CuCl₂.2H₂O or CoCl₂.6H₂O (1 mmol) with water (15 ml) is taken,and then mixed dropwise over the ligand solutionwith vigorous stirring, a noticeable  color change as well as a reduction in the pH value (~3.0–3.5) was observed. Sodium hydroxide (1%) in water (20 mL) has been mixed to adjust the pH ~5–5.5, and maintainedthe temperature of the reaction mixture nearly to room temperature.Mixtures have been stirred by the hour at 50 °C on a water bath so as to ensure complete precipitation of complexes. After one hour the precipitated solid has been filtered, washed  by means of  hot ethanol (3×5 ml),also dehydrated in vacuo, over anhydrous CaCl₂.

Proposed structures for the monomeric Co(II), Ni(II) Cu(II) as well as the ligands (1-4) are given in Scheme 3.

Scheme 3: Structure of the metal complexes Click here to View scheme

Appearance:Red-brown  powder, Yield=52%, M.p.(decomp.)>370°C; This compoundis soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₄H₂₂N₁₂O₆Ni (633.21 g mol⁻¹): 45.52 % C; 3.50 % H; 26.54 % N, Found: 45.60 % C;  3.43% H;  26.47 % N. FT-IR (KBr, ν_max/cm^-1): 3271 (N-H), 3681(O-H), 2970 (C-H_Arom.), 2864 (C-H_Aliph.), 1609-1677 (C=N_Oxim), 1543 (C=N_Hydr.), 1033(N-O), 1506 ve 1483 (N-N_Azo), 1417 ve 1376 (-NO₂).

Appearance:Dark brown powder, Yield=76%, M.p.(decomp.)>230°C; This compoundis soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₄H₂₂N₁₂O₆Co (633,45 g mol⁻¹): 45.51 % C; 3.50 % H; 26.53 % N, Found: 45.58 % C;  3.43% H;  26.44 % N.

Appearance:Dark brown powder, Yield=68%, M.p.(decomp.)>193°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₄H₂₂N₁₂O₆Cu: (638,06 g mol⁻¹): 45.18 % C; 3.48 % H; 26.34 % N, Found: 45.59 % C;  3.55% H;  25.77 % N.

Appearance:Red-brown  powder, Yield=80%, m.p.(decomp.)>240°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₄H₂₀N₁₄O₁₀Ni (723.21 g mol⁻¹): 39.86 % C; 2.79 % H; 27.11 % N, Found: 39.93 % C;  2.85% H;  27.69 % N.

Appearance:Dark-brown powder, Yield=76%, M.p.(decomp.)>200°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₄H₂₀N₁₄O₁₀Co (723.45 g mol⁻¹): 39.85 % C; 2.79 % H; 27.11 % N, Found: 39.27 % C;  3.34% H;  27.67 % N.

Appearance:Dark-brown powder, Yield=65%, M.p.(decomp.)>195°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₄H₂₂N₁₂O₆Cu (728,06 g mol⁻¹): 39.59 % C; 2.77 % H; 26.93 % N, Found: 39.99 % C;  2.83% H;  26.99 % N.

Appearance:Red-brown  powder, Yield=78%, M.p.(decomp.)>370°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₆H₂₆N₁₂O₈Ni (793,60 g mol⁻¹): 45.05 % C; 3.78 % H; 24.25 % N, Found: 45.13 % C;  3.72% H;  24.32 % N.

Appearance:Dark-brown powder, Yield=65%, M.p.(decomp.)>350°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₆H₂₆N₁₂O₈Co (793,50 g mol⁻¹): 45.03 % C; 3.78 % H; 24.24 % N, Found: 45.09 % C;  3.72 % H;  24.17% N.

Appearance:Dark-brown powder, Yield=68%, M.p.(decomp.)>196°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₆H₂₆N₁₂O₈Cu (798,12 g mol⁻¹): 44,73 % C; 3,68 % H; 24,08 % N, Found: 44,79 % C;  3,68 % H;  24,66 % N.

Appearance:Red-brown powder, Yield=72 %, M.p.(decomp.)>370°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH, and DMSO.Anal. Calcd. for C₂₄H₂₀N₁₄O₁₀Ni (661,27 g mol⁻¹): 47.23 % C; 3.96 % H; 25.42 % N, Found: 45.16 % C;  3.89 % H;  25.36 % N.

Appearance:Dark-brown powder, yield (70 %), M.p.(decomp.)>230°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₆H₂₆N₁₂O₈Co (661,51 g mol⁻¹): 47.21 % C; 3.96 % H; 25.42 % N, Found: 47.28 % C;  3.89 % H;  25.57 % N.

Appearance:Dark-brown powder, Yield=64 %, M.p.(decomp.)>195°C; This compound is soluble in commonly used solvents like CH₂Cl₂, CHCl₂, DMF, EtOH and DMSO.Anal. Calcd. for C₂₆H₂₆N₁₂O₈Cu (666,12 g mol⁻¹): 46.88 % C; 3.93 % H; 25.23 % N, Found: 46.81 % C;  3.88 % H;  27.17 % N.

In vitroantimicrobic activity

The antimicrobic activity of the test compounds was evaluated by way of agar well diffusion method [21-22]. 0.1mL of the diluted inoculums (10⁶ CFU/mL) of test organisms are taken and spread on NA/SDA (Nutrient agar/ Sabouraud dextrose agar) plates. Wells of 6 mm diameter have been punctured into the agar medium and filled one byone with 150mL of compound(150 µg/L) solvent blank and an antibiotic (chloramphenicol,100 µg/L) to which the test the sensitivity of bacteria. Fluconazole at the concentration of 100µg/L has been applied for the monitor versus Candida albicans, Candida tropicalis, and Candida glabrata. The plates were in cubated for at 37°C 24 hours. Antimicrobial activity was has been assessed in order to the zone of inhibition versus the test organism.

Results and Discussion

Spectral studies: structure of ligands and complexes

Synthesis of new hydrazoneoxime ligands bearing pyrazolone group (1-4) that were prepared by reaction of (1Z,2E)-N-hydroxy-2-(hydroxyimino) ethanimidoyl chloride [16-17] with hydrazinium hydroxideand their metal complexes1(a-c), 2(a-c), 3(a-c),4(a-c)were reported (Scheme 2 and 3). The ligands used in this work were prepared using the literature mentioned elsewhere [18-20]. The atomic arrangement  of the synthesized ligands (1-4)including their metal complexes were establishedon the basis of theirelemental analysis, FI-TIR,¹H NMR, ¹³C NMR,along with thecalculation of their magnetic susceptibility as well.The analytical andphysical propertiesof the prepared ligands including their metal complexes besummarisedintoTables 1,3,5,along with7.

The FT-IRspectrum related to thesynthesized ligands(1-4) as well as its metal complexes1(a-c), 2(a-c), 3(a-c) and 4(a-c). 1-4 and 1(a-c), 2(a-c), 3(a-c), and 4(a-c) exhibited a carbonyl (keto) band at 1655-1667 cm^-1, and NH band (hydrazo) at 3168-3271 cm^-1 as shown in the IR spectral data of the representative ligand (1) (Fig.1).The IR frequencies of the representative ligand and its complexes are shown in Table 1. The IRspectralcollected statistics of the synthesized metal complexes has to begiven intoTables 2,4,6,and8. Such saidvalues indicated  that eachcomplexes are exist in keto-hydrazo form (T₂), as well  as in solid-state[23-25]

The ¹H NMR spectra of all ligands (1-4)in DMSO-d₆showed a single peak lying between 2.16-2.20 ppm corresponding to methyl protons (pyrazolone-CH₃)at. The ¹H NMR spectral data of ligand (3)indicated a singlet for methoxy protons (Ph-OCH₃ ) at 3.74 ppm while another singlet for methyl protons (Ph-CH₃) at 2.27 ppm. The ¹H NMR spectra of all the ligands (1-4) showed multiple peak at between 6.98-7.78 ppm for aromatic protons (Ar-H). The ¹H NMR spectra of all ligands (1-4) also showed a single peaks for (CH=NOH) protons lying in the range of7.83-7.85 ppm. They also exhibited a doublet for the characteristic oxime OH protons(OH)in the range 11.76-12.22 ppm. Such chemical shift shave to be distinctive values,favour hydra zones and oximes, that help in to ascertain the proposed structure [16,25].

The possible tautomeric forms of compounds (1-4)as indicated inScheme 4.The compounds possibly be present in four likly tautomeric models i.e. keto-azo (T₁ and T₄), keto-hydrazo (T₂),as well asenol-azo (T₃). In accordance with the literature, better stabilizet automeric model exist in theketo-hydrazo form (T₂).It may be due to the presence of the intra molecular O—H bond. It is known that the existence of an intra molecular hydrogen bonding can show the stability of compounds in corresponding tautomeric form. The result is consistent with the literature [23,26-29].

Scheme 4: Tautomeric structures and anionic forms of hydrazoneoxime ligands bearing pyrazolone group (1-4) Click here to View scheme

The coordination compounds of nickel(II), copper(II), and cobalt(II) have been synthesized as per  general methodology [1,16] as discussed previously (Scheme 3). The metal ion and ligands react in 1:2 molar ratios, where the ligands are attached to metal by using its two N atoms, likealmost all of vic-dioximes act. All of thiscoordinated compounds are colored, amorphous solids, stable at room temperature as well.The discussed complexes are insoluble in commonly used  organic solvents, but are soluble in DMF and DMSO. The recommended structures of the synthesized coordination compounds has beendemonstrated inScheme 3that are supported by  spectroscopic, FTIR spectral date , and elemental analysis studies.As per  the suggested  structures, the complexes can have syn- or anti- conformation [28].The magnetic moment (µeff) statistics further favoured the  mononuclear structures of the coordinated complexes.The magnetic moment for the nickel(II) complexes are diamagnetic at room temperature, since it is  expected due to thed⁸ and d¹⁰ electronic configurations [30].The  magnetic moments (µeff)of the  copper(II) complexes are 1.63, 1.76, 1.77 and 1.77 BM, respectively, so they are paramagnetic in nature. The cobalt(II)  complexes of ligands are paramagnetic and their magnetic moments (µ_eff) are 2.05, 2.07, 2.08, and 2.09 BM, respectively. The lower figurepossibly due to the anti ferro magnetic interaction between neighboring magnetic centers.

The another chemical environments will assignbetween two (O···H–O)bridge protons in the cis-form, at the same time one in the trans-form. Experience of the H- bond (O···H–O) in the IR , and ¹H NMR spectrum, appearing in single frequency in all cases,that indicates the nickel(II) complex is in the anti-form media. On the basis of the above experimental findings , the geometry of  the nickel(II) and copper(II) and cobalt(II) complexes are recommended as square-planar[1,16].

The possible tautomeric forms of new nickel(II) and copper(II) and cobalt(II) complexes 1(a-c), 2(a-c), 3(a-c) and 4(a-c) has to be explained inScheme 5. The newly synthesized complexes possibly occurs into four probable tautomeric forms i.e. keto-azo (T₁ and T₄), keto-hydrazo ( T₂),as well as in enol-azo (T₃) form.As reported in the literature, utmost stabilized tautomeric form is aketo-hydrazo form (T₂) forazopyrazolone dyes.The complexes have an intramolecular hydrogen bonding N-H^…O for keto-hydrazone (T2) form and O-H^…N for enol-azo (T3) form.These results are consistent with the literature [23,26-29,31].

Scheme 5: Proposed structure for nickel(II), copper(II)  and cobalt(II)  complexes Click here to View scheme

Biological activity

The synthesized compounds have been examined for their antimicrobial (antibacterial andanti- fungal)activity.

Antimicrobial activity

The in vitro antimicrobic(S. aureus , B. subtilis , E. coli, P.aeruginosa and antifungal (C. albicans , C. tropicalis, and C. glabrata laboratory isolate) activities of the compounds 1a -4c were evaluated by agar well diffusion method [22]. The results for the antimicrobial study of the tested compounds against the test organisms are illustrated as in Table-9.

Table 9: Antımıcrobıc Actıvıty Of The Synthesızed Compounds By Well Dıffusıon Assay

S.No	Compounds Tested	Effective concentration (µg/well)	Antimicrobic activity  of metal complexes  [inhibition zone mm]
			A	B	C	D	E	F	G
1	1a	150	9	9	10	14	14	14	14
2	1b	150	10	9	9	15	14	15	15
3	1c	150	8	8	9	13	14	14	14
4	2a	150	11	10	10	14	14	14	14
5	2b	150	12	11	11	15	15	14	14
6	2c	150	8	9	9	12	13	12	12
7	3a	150	11	10	10	17	17	18	16
8	3b	150	15	14	14	20	19	19	18
9	3c	150	8	8	8	15	14	14	14
10	4a	150	9	8	8	13	15	15	14
11	4b	150	11	10	10	16	16	15	16
12	4c	150	8	8	8	14	14	14	14
Chloramphenicol		100	—	—	—	30	30	30	30
Fluconozole		100	28	25	25	—	—	—	—

A-Candida albicans, B- Candida trophicalis, C- Candida glabrata, D- Staphylococcus aureus, E- Bacillus subtilis, F- Escherichia coli, G-Pseudomonas aeruginosa

Results of the synthesized compounds1a, 1b, 1c, 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b, and 4care outlined for antimicrobicactivitywith respect tofourbacteria Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and three fungusesas Candida albicans, Candida tropicalis, and Candida glabrata are illustrated in Table 9.

Antimicrobial activity against “Gram positive”, “Gram-negative” bacteria, and agaist fungus have been seen across all the synthesized compounds.Newly synthesized  compounds 3b showed signifant gross broad-spectrum antimicrobial activity, i.e.,against“Gram-positive”,“Gram-negativebacteria”as well as anti fungal.The effective concentration of these active compounds was 150 µg /well.

Conclusion

Investigations into the synthesis of new hydrazoneoxime ligands having pyrazolone group and their metal complexeshave been carried out in this study. The synthesized pyrazolone derivatives of Co(II), Ni(II), andCu(II) complexes were isolated and their structures were characterized using physicochemical techniques.Also, tautomerism in the ligands was investigated by spectroscopic.Chemical propertirs of the complex compounds depend upon Tautomerism, and also physical properties like colour fastness depend on it .The  attachment of ligands to the metal ion in a neutral bidentate form with the azomethine nitrogen (C=N) and the carbonyl oxygen (C=O).The calculated magnetic moments of the coordinated complex compounds as 2.92B.M for the nickel(II) and 1.65 B. M for the copper(II) are approximate the spin values only , and proposea square planar geometry for the complexes. The compounds 3b exhibited broad-spectrum antimicrobial activity. Expeditions to explore their potentialities in the future for other biological assays are needed to investigate further. Furthermore, some Co (II) complexes act as potent anti-cancer agents due to their anti-proliferative effects; in this regard, the synthesized compounds should be investigated in the future as well. These complexes can be further explored in the dye/color industry due to the presence of chromophores.

Acknowledgment

We acknowledge to Aydın Adnan Menderes University Scientific Research Foundation for their financial support (Project No: FEF-18022).

Conflict of Interest

The authors declare that they have no conflict of interest.

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