Physicochemical and Analytical Studies of Some Monomer and Polymer Complexes Derived from Selected Aroyl Hydrazone

New solid complexes derived from the reaction of aroyl hydrazones, 2-hydroxy-1-naphthaldehyde benzene sulphonyl hydrazone (HNB), and 2-hydroxy-1-naphthaldehyde p-toluene sulphonyl hydrazone (HNT), with Co 2+ , Ni 2+ , and Cu 2+ salts have been isolated and characterized using elemental analyses, spectral (UV-vis., IR), molar conductivity and magnetic measurements. The modes of bonding as well as the stereochemistry of the isolated solid complexes were discussed. The results suggested that both HNB and HNT coor-dinated with the metal ions in a bidentate manner forming a polymeric chain in the case of HNB while monocular complexes were formed in the case of HNT. The amounts of solvent in the solid complexes were determined by TGA measurements. Also, spectral studies of HNT with Co 2+ and Fe 3+ ions in solution were carried and the ratio of complexes was determined by continuous variation, molar ratio, and slope ratio methods. Moreover, the results suggest the formation of 1:1 (M:L) for Co 2+ ions while three species with ratios of 1:1, 1:2, and 2:1 (M:L) have been observed in the case of Ni 2+ and Cu 2+ . Finally, conductance titration of HNB and HNT with Co 2+ ion elucidates the formation of two species with ratios 1:1 and 1:2 (M:L) in the case of the Co 2+ -HNB while 1:1 (M:L) belongs to the Co 2+ -HNT system.


Introduction
It is well known that hydrazones occupied a central role in the development of coordination chemistry. This feature comes from the fact that the hydrazones, derived from the condensation of o-hydroxyl or methoxy aldehydes and ketones with hydrazides, are potential polynucleating ligands possessing azomethine and phenol or methoxy functions [1] offering varying bonding possibilities in metal complexes. Studies of some metal chelates of hydrazones derivatives are well known in literature [2]- [10].
On introducing the SO 2 group instead of the carbonyl group (CO) of the hydrazones moiety, the compounds are called sulphonyl hydrazones having the following formula, RSO 2 NHN=CHR'. Bivalent metal complexes of benzene sulphonyl hydrazide (BS) have been studied [11]. It was reported earlier that BS coordinates to the central metal ion through the SO 2 and nitrogen of the NH group with the removal of NH proton where a polymeric chain has been suggested [12]. Moreover, salicylidene benzene sulphonyl hydrazone (HSBS) with some transition metals (M = Co 2+ , Ni 2+ , Cu 2+ , Hg 2+ , Zn 2+ , and Cd 2+ ) was synthesized and characterized by different physicochemical techniques. The results showed that Ni 2+ , Cu 2+ , and Hg 2+ form complexes with the general formula, [M(SBS) 2 ], while Co 2+ , Zn 2+ , and Cd 2+ form complexes with the polymeric formula [M(SBS) 2 ] n . The ligand acted in the latter case in a bidentate fashion via the NH and SO 2 groups (with deprotonation of the NH group forming a polymeric structure [12]. Finally, Cu 2+ and Ni 2+ complexes of hydrazones derived from benzene sulphonyl hydrazine with salicylaldehyde and 2-hydroxy-1-naphthaldehyde were studied by physical and spectral methods [13]. Based on elemental analyses and spectral (i.r. and n.m.r.) data the results suggest that the isolated hydrazones behave as monobasic bidentate towards the metal cations and coordinate through the C=N and deprotonated phenol OH groups. It is worth mentioning ion that the spectral (Uv-vis.), magnetism as well as thermal (TG, DTG, and DTA) measurements were not been investigated for these complexes. In addition, some data obtained in this work differs from that reported before [13].
The goal of this paper is to synthesize and characterize the stereochemistry of the solid complexes derived from the reaction of 2-hydroxy-1-naphthaldehydebenzene-sulphonylhydrazone (HNB), p-toluene-(HNT) with Co 2+ , Ni 2+ and, Cu 2+ salts. The effect of the methyl group that represents the only difference between the two synthesized hydrazones on their coordinating nature has been illustrated. Furthermore, the pK a values of HNB and HNT were determined and the stoichiometry of complexes in solution has been determined by spectrophotometric and conductance techniques.

Experimental
All chemicals and solvents utilized were of BDH or AR quality and used without further purification. 1 H-NMR spectra in d 6 -DMSO with TMS as internal standard were obtained from a Jeol-FX-90Q Fourier NMR spectrometer at Cairo University, Egypt. IR spectra were recorded as KBr pellet in the range "200-4000

Preparation of Hydrazones Ligands (HNB, HNT)
The two ligands, HNB and HNT, were synthesized by adding BH (0.02 mol, 3.44 g) dissolved in absolute methanol (50 mL) to a solution (50 mL) of 2-hydroxy-1naphthaldehyde (0.02 mol, 3.44 g) (HNB) and 2-hydroxy-1-naphthaldehyde p-toluene sulphonyl hydrazone (HNT), respectively. The reaction mixtures were refluxed for 3 h in a water bath (95˚C). The product is separated out by concentrating the solution to half of its volume and cooling. The crystals of the desired ligand were filtered off and finally recrystallized from methanol. The chemical structures of the resulting hydrazones are shown in Figure 1.

Preparation of Solid Complexes
All the isolated solid complexes (Table 1) were prepared by mixing equivocal amounts of ligands and M(II) acetates (M = Co 2+ , Ni 2+ , and Cu 2+ ) in 100 mL ethanol. The reaction mixture was refluxed in a water bath (95˚C) for 6 h. The colored microcrystalline solids were isolated by filtration on hot, washed repeatedly

Preparation of Solutions for Spectrophotometric Measurements
The appropriate concentration of the metal ions (Co 2+ and Fe 3+ ) and ligands were mixed in an absolute methanol solution. The final volume of the mixture was always kept constant by adding absolute methanol. All the absorbance measurements were recorded in the range "200 -800 nm". Methanol was used as a blank in the case of Fe 3+ complexes while the ligand was used as a blank in the case of Co 2+ complexes.

Results and Discussion
All the analytical, physical, and spectroscopic data of the hydrazones and their isolated metal complexes are recorded in Table 1 & Table 2. A comparison of the analyses for both the calculated and found percentages indicates that the composition of the isolated solid complexes coincides with the proposed formulae. All trails to isolate mono-or tris-ligand chelates by direct reaction of the ligands with the M(II) salts were unsuccessful. The complexes are air-stable for a long time, insoluble in water, alcohols, and carbon tetrachloride, and soluble in DMF and DMSO.  366 (n-π*, SO2), 354 (n-π*, C=N), 320 (π → π*, SO2), 310 (π → π*, C=N), 254 (π → π*, naphthyl), 246 (π → π*,phenyl),

IR Spectra
The positions of the IR bands of hydrazones and their metal complexes are summarized in Table 2. The IR spectra of HNB and HNT showed a strong band at 1620 -1624 cm −1 assigned to υ(C=N) of the azomethine. The observation of this band emphasizes the formation of the azomethine linkage. Each ligand also has a strong band in the region of 700 -800 cm −1 corresponding to the outof-plane deformation of the aromatic rings. The observation of broad but weak bands in the 2000 -1700 cm −1 region for HNB and HNT is taken as evidence for the formation of a stable six-membered ring of intermolecular hydrogen bond of the type OH…N [17] . The IR spectral data for Co 2+ , Ni 2+ and Cu 2+ -HNB complexes pointed out that HNB behaves as a bidentate ligand coordinating to one metal ion via the SO 2 and OH groups with a displacement of a proton from the latter group tending to form a polymeric chain structure ( Figure 2). A worthy mention, it was reported that the Co 2+ ion forms a polymeric chain with salicylidene benzene sulphonyhydrazone [12]. In fact, this suggestion is assumed on the basis of the following pieces of evidence ( Table 2): 1) The characteristic main band of the SO 2 group at 1318 cm −1 assigned to ν as (SO 2 ) shifts to a higher wavenumber by 10 -14 cm −1 indicating that this group is taking part in bonding, 2) the disappearance of both ν(OH) and δ(OH) bands elucidates the deprotonation of this group, 3) the positive shift of ν(C-O) band indicates the formation of (-C-O-M) bond. Nevertheless, C=N was expected to involve in coordination in the case of HNB complexes, it was excluded here due to the absence of any significant shift or variation in its position or intensity upon chelating. This result is not consistent with the previously published data [12] [13]. Meanwhile, HNT coordinates in a bidentate fashion to one metal ion via the azomethine nitrogen (C=N) and OH groups ( Figure 3). Displacement of a hydrogen proton from the latter group leads to a  six-membered ring around the central metal ion. This behavior is proposed on the basis of ( Table 2): 1) the characteristic three main bands of the SO 2 group at 1318, 1167 and 574 cm −1 remain more or less at the same positions excluding the participation of this group in coordination, 2) the bands of both ν(OH) and δ(OH) vibrations disappear, and the ν(C-O) band is shifting to a higher frequency, 3) the negative shift of the azomethine group to lower wavenumber confirming the involvement of this group in bonding [18]. In spite of this group is not taking part in coordination in the case of HNB which is nearly resembled in its chemical structure to HNT, it is involved here. This can be interpreted on the

1 H-NMR Spectra
The assignments of the main signals in 1 H-NMR spectra of the ligands under investigation are shown in

Electronic and Magnetic Spectra
The electronic spectra of the hydrazones and their solid metal complexes [21] [22] [23] [24] as well as the geometry and magnetic data of the formed chelates are shown in Table 2. The redshift of HNT bands in comparison to that observed in the case of HNB (

Thermal Analysis
The thermal decomposition studies (TG, DTG, and/or DTA) on major solid metal complexes have been carried out. The TG curves up to 800˚C for complexes showed 3-5 stages of decompositions with the formation of metal carbonates/oxides/carbide or mixtures of them at the last stage. The results of the thermal analysis revealed that: 1) [Co(L 1 ) 2 ] n showed a first weight-loss stage at 219˚C assignable to the decomposition of the complex and at the same time emphasized the absence of any crystalline solvent. This temperature (219˚C) is high enough to be considered for out sphere ethanol or water.  Figure 2 and Figure 3, respectively.
The behavior of Co 2+ and Fe 3+ ions with HNT has been studied and the stoichiometry was determined. The other ligand under investigation (HNB) is not investigated since it precipitates a solid complex with Co 2+ and gives unspecified color with Ni 2+ and Cu 2+ ions (i.e., a mixed color of HNB and metal (II) ion without any reaction).

Spectral Studies in Solution
Comparing the spectra of the Co 2+ , and Fe 3+ -HNT complexes with HNT and the employed metal salt solutions (cobalt acetate and ferric chloride) at room temperature showed a new band at 385 nm with a shoulder at 400 nm for Co 2+ -HNT and a band at 670 nm in case of Fe 3+ -HNT. Increasing the concentration of the ligand (from 1 × 10 −4 to 1 × 10 −4 M for Co 2+ -HNT and to 6 × 10 −4 M for Fe 3+ -HNT) leads to a hyperchromic shift without changing the position of the band manifesting the formation and stabilization of the complex in solution. On leaving Fe 2+ -HNT solution for 42 h, it was noticed that the color of the solution has been changed from green to brown accompanied by a hypsochromic shift for the absorption maxima from λ max at 670 nm (green solution) to 530 nm (brown solution). This indicates that the Fe 3+ complex formed at once is quite stable but attains maximum stability after 42 h. Besides, it suggests the increase of 10 Dq, and consequently, the geometry of the complex may be changed. From this view, the effect of temperature on a Fe 3+ -HNT is of considerable interest to be studied. Increasing the temperature from 25 to 55˚C for the Fe 3+ -HNT system reveals a hypsochromic shift for λ max from 670 to 560 nm ( Figure 4). Doubtless, this indicates that the increase of temperature helps too much for reaching the stability of the formed complex.
To trace the complex formation and deduce the stoichiometry of the complexes in solution, continuous variation [28], the molar ratio [29], and slope ratio [30] methods were employed. For the Co 2+ -HNT mixture, the results obtained (at λ max = 385 nm) by continuous variation (Figure 5), molar ratio, and slope ratio indicated the formation of the complex with 1:1 (Co 2+ : HNT). On the other hand, the results of continuous variation, molar ratio, and slope ratio methods for Fe 3+ -HNT mixture at the λ max's = 670 and 530 nm at once and after 42 h are in good agreement with each other and manifested the existence of 1:2 (Fe 3+ :HNT) and 2:1 (Fe 3+ :HNT) complexes, respectively. The continuous variation diagram ( Figure 6, and Figure 7) revealed also a 1:1 (Fe 3+ :HNT) species at 530 nm, and high intensity for 2:1 (Fe 3+ :HNT) compared with 1:1 and 1:2 (Fe 3+ :HNT) indicating the higher stability of the 2:1 M:L complex. Based on the obtained results, it is suggested that 1:2 (Fe 3+ :HNT) was reached to 2:1 (Fe 3+ :HNT) passing by 1:1 (Fe 3+ :HNT). Also, It is very conspicuous that the stability of the 2:1 (Fe 3+ :HNT) complex increases with time and temperature. A literature survey pointed out that the octahedral 3 3 FeF − showed a band at 704 nm while the tetrahedral 4 FeBr − showed a band at 588 nm [31]. According to this fact, the hypsochromic shift of λ max from 670 to 530 nm may be due to two probabilities (1) the geometry of the Fe 3+ -HNT complex was changed from octahedral to tetrahedral due to the steric effect of ligand or (2). The kind of ligands was varied    (Table 1) were estimated by Sandall's method [32] following the equations:

Effete of pH on the Absorption Spectra of HNT and HNB
Absorption spectra of HNT (1 × 10 −4 M) and HNB (1.2 × 10 −5 M) in universal buffer solutions were recorded in the range of 200 -450 nm. The spectra exhibit one band in the pH range 8 -12 at 353 and 243 nm for HNB and HNT, respectively. No absorbance was traced in the lower pHs (1 -7) in the case of HNB owing to the participation that occurred. The relation between absorbance versus the pH was represented in Figure 8 and Figure 9 shows the S-shape curve.
The pK a values were calculated from these curves and located in Table 1. The  smaller pK a value of HNB (6.5) compared with that of HNT (9.5) arises from the effect of the electron-donating nature of the (CH 3 ) group in HNT which increases the electron density on the OH (naphthyl) group and consequently, the pK a was observed at high pH value. On the other hand, the existence of a withdrawing group (phenyl) in HNB decreases the electron density on the OH (naphthyl) group and hence the pK a has a small value. Utilizing absolute methanol solutions, conductance titration of 10 mL (2.5 × 10 −4 M) cobalt acetate solution with HNB (2.5 × 10 −3 M) and 25 mL of cobalt acetate solution (5 × 10 −4 M) with HNT (5 × 10 −3 M) were carried out and represented in Figure 10 and Figure 11, respectively. The results of the Co 2+ -HNB curve ( Figure 10) showed two breaks at 1:1 and 1:2 (Co 2+ :HNB). This illustrates that the two complex species with different ratios are possibly formed  in solution and hence we could obtain each of them by adding the appropriate amount of the ligand. Fe 3+ -HNB curve ( Figure 11) revealed only one break at 1:2 (Co 2+ :HNT).
A common behavior of these curves is the continuous decrease of the reaction mixture conductance with increasing the number of hydrazones added. This suggests the formation of non-electrolytic species in solution, i.e., the reaction of HNB or HNT with Co 2+ acetate proceeds without the liberation of acetic acid. Conversely, Co 2+ -HNB, HNT complexes were isolated as solids by deprotonation of ligand and thus the acetic acid was liberated. This can be interpreted on the basis of various reaction conditions. To explain this contrariety, we proposed that HNB or HNT reacts with cobalt acetate in solution and at room temperature forming an octahedral geometry around the Co 2+ ion. Upon refluxing the reaction mixture, the liberation of acetic acid is induced and finally, a non-electrolytic complex species having a square-planar geometry is obtained as in the solid-state. This mechanism can be shown in case of HNB ligand as follow: The same mechanism is proposed for the Co 2+ -HNT complex. Finally, the molar conductivity of all complexes is shown in Table 1. The values indicate a non-electrolytic nature in this solvent and are consistent with the other results.

Conclusion
The results obtained in this work verified that a number of aroyl hydrazones complexes, derived from 2-hydroxy-1-naphthaldehyde, have been successfully synthesized. The compositions and structures of these complexes have been established on the basis of different physicochemical techniques. The mode of binding of the aroyl hydrazones under investigation mainly depends on the substitute in the para-position of the phenyl ring. The persistence of the electron-donating group in the para-position of phenyl ring e.g., methyl group increases the electron density on azomethine nitrogen and consequently facilitates its coordination with the metal cation. This is very conspicuous in the solid complexes of aroyl hydrazones with cobalt, nickel, and copper ions. The chelating takes place with the replacement of phenol hydrogen along with the linking of an auxiliary group that is SO 2 in HNB and C=N in HNT forming complexes with a ratio of 1:2 (M: L) composition for HNB and polymer chains with HNT. Spectrophotometric and conductance titration studies can be used to identify the stoichiometry of the aroyl hydrazones with some metal cations and the former technique substantiates the possibility of micro determination of Co 2+ and Fe 3+ ions by the aroyl hydrazones.