Spectroscopic , thermal and magnetic properties of some transition metal complexes derived from 1-Phenyl-3-Substituted-4-Nitroso-5-Pyrazolones

Complexes derived from some 1-Phenyl-3-methyl-4-nitroso-5-pyrazolone (L1), 1,3-diphenyl-4nitroso-5-pyrazolone (L2) and 1-phenyl-3-anilino4-nitroso-5-pyrazolone (L3) with Mn, Co, Ni, Cu and Zn metal ions have been prepared. Structural investigation of the ligands and their complexes has been made based on elemental analysis, infrared (FT-IR), ultraviolet and visible spectra (UV-Vis.), proton nuclear magnetic resonance (H NMR), magnetic susceptibility (eff.) and thermal analysis (TG and DTG). The effect of solvents has been carried out in organic solvents of varying polarity. The observed transition energy and oscillator strengths were also calculated. The data obtained show that all of the prepared complexes contain water molecules in their coordination sphere. The investigated ligands acts as neutral bidentate ligands bonded to the metal ions through the two oxygen atoms of the carbonyl and nitroso groups. The isolated complexes behave as non-electrolyte in DMF solution. The Mn, Co, Ni and Cu complexes show high spin configurations as the ground state. The high spin values of magnetic susceptibility may be due to the ligands being weak ligands. The Mn, Co, Ni, Cu and Zn complexes exhibit an octahedral or distorted octahedral coordination with the investigated ligands.

The present study deals with the preparation of Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ complexes with the investigated ligands (L1-L3).The complexes obtained were subjected to many analytical tools such as elemental analysis, infrared (FT-IR), thermogravimetric (TG) and derivative thermogravimetric analysis (DTG), molar conductance, magnetic susceptibility ( eff. ) and electronic spectra to throw some light on the bonds formed and on their structure.

Synthesis of the Complexes
The 1:1 or 1:2 complexes were prepared by mixing a hot alcoholic solution of the investigated ligands (0.001 or 0.002 mol) with the calculated (0.001 mol) of metal salt solution.The reaction mixture was refluxed for 4 h.The pH of the solution was maintained at a value of 5.0-6.0 by the addition of dilute ammonia solution (1:10).The solid complexes were dried on a steam bath with stirring, then filtered off and washed several times with ethanol-water mixture, (1:1 v/v) till a colorless filtrate was obtained.The solid complexes were dried by suction and finally kept in vacuum desiccators.

Physical Measurements
The FT-IR spectra were recorded in the range 4000-400 cm -1 on a Jasco FT-IR spectrophotometer as KBr discs.
The NMR spectra were measured using Varian Gemini 200-200 MHz spectrometer and the spectra were recorded from 0-15 ppm using TMS as an internal standard in dimethylsulfoxide (d 6 -DMSO) as the solvent.
Thermal analyses (TG and DTG) were obtained in a nitrogen atmosphere using a type TGA 50 of Shimadzu derivatograph thermal analyzer.The molar conductivities were carried out using a Jenway 4310 conductivity meter.Electronic spectra were recorded in the range 200-800 nm, on Jasco V-530 UV-Vis.spectrophotometer.Magnetic susceptibility values were obtained at room temperature using magnetic susceptibility balance (Sherwood scientific), Cambridge Science Park, Cambridge, England.

Characterization of the Ligands
The structures of the investigated ligands (L1-L3) were established by the use of elemental analysis in Table 1, IR, UV-Vis and 1 H NMR spectra.

Infrared Studies
The infrared spectra of the investigated ligands and the most important IR band assignments that affect the structural features are listed in Table 2.The NH appears as a medium broad one at 3210 cm -1 for ligand L3.
The band appearing at 1705, 1678 and 1688 cm -1 are ascribed to the stretching frequency of the C=O group for ligands L1-L3, respectively.The band observed within the range 1410-1359 cm -1 assigned to N = O [14].

1 H NMR Spectra
The different types of protons in DMSO of the investigated ligands (L1-L3) were obtained.The spectra of the ligands L1-L3 exhibit a sharp singlet signal at 2.23 ppm.This signal is assigned to the aliphatic proton at position number 4 [15,16] as shown in Figure:  For ligand L1, a singlet observed at 2.40 ppm is assigned to CH 3 protons (the integration curve shows three protons).The signals observed at 7.23-7.84,7.20-8.17and 7.03-7.87ppm are assigned to the aromatic hydrogen protons (the integration curve shows five and ten protons for the investigated ligands L1-L3, respectively).The spectrum of ligand L3 exhibits a singlet signal observed at 6.43 ppm is assigned to NH proton (the integration curve shows one proton).

Electronic Spectral Studies
The electronic spectral band of the investigated ligands scanned in different organic solvents are depicted in Table 3.In methanol solution, ligands L1 and L2 show three bands, the first one at 253-268 nm referred to -* transition within the phenyl rings.The second band observed at 317-321 nm is ascribed to n-* transition of the carbonyl group.The third band at 385-400 nm arises from a transition involving electron migration along the entire conjugate system of the ligand i.e. comprises charge transfer (CT) from phenyl ring to the carbonyl group by resonance and from hetero ring by induction [17].In case of chloroform, cyclohexane, isopropanol and dioxane, the spectra show two bands within the range 260-423 nm.The first band at 260-263 nm is assigned to -* transition within the phenyl rings.The second band at 403-423 nm is ascribed to charge transfer interaction from the phenyl ring to the carbonyl group.For ligand L3 only one absorption band observed at 248-259 nm which may be ascribed to the high energy -* transition within the phenyl rings.
The ionization potential (Ip) of the investigated ligands (L1-L3) is calculated from their electronic spectral data applying the relationships previously applied [18][19][20].The value of the experimental transition energies (E CT ) and oscillator strengths (f) were calculated from  max of the electronic spectra applying the equations previously reported [18][19][20].
The calculated E CT values, as well as, the corresponding ionization potential (Ip) of the investigated ligands L1-L3 in different organic solvents are listed in Table 3.The variation in Ip values was found to follow the same order as  max of the CT band.

Characterization of the Complexes
The solid complexes were subjected to elemental analysis and metal content, infrared (FT-IR), ultraviolet and visible spectra (UV-Vis.),magnetic susceptibility ( eff. ) and thermal analysis.The results of elemental analysis are given in Table 1 and are in good agreement with those calculated by the proposed formulae for 1:1 and 1:2 (M:L) solid complexes.

Conductimetric Measurements
Conductimetric titrations of Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ metal ions with the investigated nitrosopyrazolone derivatives (L1-L3) were obtained by plotting the calculated molar ratio [L]/[M] against the corrected molar conductance values.The results indicate that the conductance increases with the addition of the metal ion solution due to the release of the highly conducting hydrogen ions which may be present in nitroso-oxime tautomers as a result of chelation [10,16].The titration curves show the presence of two distinctive breaks at metal to ligand 1:1 and 1:2 (M:L), respectively.

Infrared Studies
Infrared spectral data of the investigated complexes display interesting changes which may give a reasonable idea about these complexes.However, if these changes were interpreted in relation to elemental analysis in Table 1, also the thermogravimetric analysis, molar conductance, electronic spectra and magnetic susceptibility measurements, the structure of the solid complexes may be clarified.
In the spectra of the complexes (Table 4) the band observed within the range 1410-1395 cm -1 [14] assigned to N=O in the free ligands shiftes to lower wave num- ber indicating the involvement of the N=O group in chelation.Also, the shift of N = O group indicated that it is a center of chelation as it loses its double bond character.The band observed within the range 1705-1678 cm -1 assigned to C=O in the free ligands shiftes to lower wave number (1610-1650 cm -1 ) indicating the involvement of the C=O group in chelation as it also loses its double bond character [14].The OH stretching frequency appears within the range 3336-3447 cm -1 for 1:1 and 1:2 complexes as broad band.This is due to the presence of water of hydration and/or coordinated water molecules.In some complexes, a sharp band appears within the range 3423-3640 cm -1 ascribed to chelated OH -, which replace the Cl -ion in coordination sphere.
The OH frequency will be masked under the previously detected broad band [16].The spectra of the metal complexes exhibit bands in the range 478-550 cm -1 that may be assigned to M-O stretching frequency [22,23].These bands are not observed in the spectra of the free ligands and are possibly due to the formation of coordinated bond (MO) or (M-O).

Thermal Analysis
TG analyses are very useful method for investigating the thermal decomposition of solid substances involving simple metal salts [24], as well as for complex compounds [25,26].The thermogram follows the decrease in sample weight with the linear increase in heat treatment temperature (10℃ min -1 ) up to 800℃.The aim of the thermal analysis is to obtain information concerning the thermal stability of the investigated complexes as seen in Table 5 and Figure 1, to decide whether water molecules are inside or outside the coordination sphere.For Mn-L3 (1:1) complex, a mass loss occurred within the temperature range 34-106℃ corresponding to the loss of 3.25% (Calcd 3.27%) for one molecule of water   For Ni-L1 (1:1) complex, a mass loss occurred within the temperature range 36-144℃ corresponding to the loss of 6.5% (Calcd.7.03%) for two hydrated water molecules and at the temperature range 146-370℃ corresponding to a loss of 28.90% (Calcd.28.14%) for hydrated and two coordinated water molecules.In the temperature range 372-607℃ a mass loss of 24.60% (Calcd.24.62%) corresponding to the formation of intermediate species through the decomposition of the organic moiety of the complex [15] and this continues till a constant weight is obtained where a mixture of nickel chloride and nickel oxide residue are formed, the remainder is 39.99% (Calcd.39.71%).
For Co-L2 (1:1) complex, a mass loss occurred within the temperature range 79-213℃ corresponding to a loss of 11.90% (Calcd.12.05%) for three water molecules.At the temperature range 213-460 ℃ a loss of 61.00% (Calcd.61.84%) and at the temperature range 461-721℃ a loss of 13.00% (Calcd.12.94%) corresponding to the formation of intermediate species.At higher temperature more than 721℃ and at the end of the process a metallic oxide residue CoO is formed, the remainder is 16.50% (Calcd.16.72%).

Molar Conductance Measurements
The molar conductivities of 1 mM in DMF (10 -3 M) of some of the given complexes show that the investigated complexes are neutral in nature since the values obtained are 7.45-37.7 ohm -1 cm 2 mol -1 .These values were small to account for ionic complexes of the investigated metal ions.
Electronic absorption spectra of the free ligands and some of their chelates were recorded in DMF.In the free ligands the CT band appears in the range 385-400 nm for the ligands L1-L3.A shift to longer wavelength is observed on complex formation.This may be attributed to the ML charge transfer CT spectra.A band of low intensity is observed at 460 nm for Co-L1 (1:1), and 458 nm for Co-L3 (1:2) which is typical for six-coordinate high-spin Co 2+ complexes.The corresponding bands in the octahedral [Co(H 2 O) 6 ] 2+ ion have been assigned to 4 T 1g  4 T 2g (F), 4 T 1g  2 A 1g (F) and 4 T 1g  4 T 1g (P) transitions, respectively [28].The absorption spectral bands of Ni-L3 (1:1) at 458 nm and 450 for Ni-L2 (1:2) are assigned to the 3 A 2g  3 T 1g (F) and 3 A 2g  3 T 1g (P) transitions, respectively, in an octahedral geometry [29] and is almost identical with that of the octahedral [Ni(H 2 O) 6 ] 2+ ion [30].It is difficult to relate spectra with the structure of Cu 2+ complexes, especially in view of the distorted geometry observed for its complexes [28].
Based on the above results the suggested structures of the 1:1 and 1:2 (M:L) complexes between the metal ions and the ligands can be represented as follows:

CONCLUSIONS
In the present paper, the data obtained from elemental analysis, FT-IR, electronic absorption spectra, thermal analyses, molar conductivities and magnetic susceptibility measurements show that the complexes of Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ metal ions with the investigated ligands L1-L3 may be formulated, where bonding in case of 1:1 and 1:2 complexes are formed through coordination with oxygen of the carbonyl group and nitroso group.The complexes obtained contain water of coordination in their sphere.The investigated ligands act as neutral bidentate ligands.The solid complexes prepared behave as non-electrolytes in DMF solution.The electronic spectra of the investigated ligands exhibits a CT band appears in the range 385-400 nm for the ligands L1-L3.A shift to higher wavelength is observed on complex formation which may be attributed to ML charge transfer spectra.The bands observed at higher wavelengths which are not observed in the spectra of the free ligands may be ascribed to d-d electronic transition within the metal ions.The complexes exhibit an octahedral or distorted octahedral (Cu 2+ complexes) coordination with the investigated ligands.

,
IR and 1 H NMR spectra.The resulting ligands have the following general formulae:

Table 3 .
The transition energy (E CT ), ionization potential (I P ), oscillator strengths (f) and molar absorptivity () derived from the electronic spectra of ligands L1 and L2 in different organic solvents.

Table 4 .
IR band assignment of Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ complexes with the investigated ligands (L1-L3).Calcd.11.88%) corresponding to a loss of the organic moiety as an intermediate species.At the end of the thermogram at higher temperature the metal oxide and chloride residues MnO and MnCl 2 are formed as final