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Mechanochemical synthesis and characterization of 2,4-dinitrophenyl hydrazine metal complexes.


2,4-dinitrophenylhydrazine is an analogue of hydrazine and an important class of drugs.

Recently, there has been a considerable interest in the chemistry of hydrazine compounds because of their potential pharmacological applications [1]. Several reports on synthesis of metal complexes of hydrazine by the use of organic solvents under reflux and their biological properties have already been published. [2,3]. More so, these methods suffer several drawbacks such as long reaction time, an excess of organic solvent, lower products yield and harsh refluxing conditions. Therefore, it is necessary to develop more efficient and versatile method for the preparation of metal complexes of 2,4-dinitrophenylhydrazine and the progress in this area is remarkable, including the use of mechanochemical method. This method is a solvent-free reaction which leads to new environmentally benign procedures that save resources and energy [4]. The mechanochemical reaction promises to be an essential facet of "Green Chemistry" and is of high interest from both the economical and synthetic point of view. Solvent-free reactions possess some advantages over traditional reactions in organic solvents, for example they not only reduce the burden of organic solvent disposal, but also enhance the rate of many inorganic reactions.

Mechanochemical synthesis is the use of a mortal and a pestle or the more reproducible use of a ball-mill to grind the starting material in order to generate a complex series of structural transformations due to the vibrational effects caused by grinding of the reactants (two solid substances) [5,6]. Recent reports on the usefulness of mechanochemical synthesis was described by Kaupp et al. [7] via grinding a schiff base derived from benzaldehyde and sulphonamide with metal salts of Cu(II), Ni(II) and Co(II) to give neutral complexes of configuration [M[(L).sub.2].[([H.sub.2]O).sub.2]].C[L.sub.2]. Braga et al [8] reported the use of mechanochemical method for the synthesis of Cu(INA)2 by grinding of copper acetate and isonicotinic acid. Pichon and James [9] synthesized cis-Pt[Cl.sub.2](P[Ph.sub.3]) by mechanochemical method. The reaction was carried out by grinding Pt[Cl.sub.2] and P[Ph.sub.3] in a ball mill for one hour. Nichols et al [10] described that simple, manual grinding of divalent first-row halides or nitrates with phenanthroline resulted in clear color changes of the [[M[(Phen).sub.3]].sup.2+] such as red [[Ni[(Phen).sub.3]].sup.2+] within two minutes. Braga et al [11] reported the synthesis of Zn(II) and Cu(II) neuroleptic drug (Gabapentin) without the use of Solvent.

Due to our interest in green chemistry, we reported the synthesis of 2,4-dinitrophenyl hydrazine metal complexes in an attempt to examine the modes of binding in solid state solvent-free mechanochemical.

Experimental Section

Materials and Instrumentation: All reagents and chemicals were of analytical grade and used as obtained from Aldrich. The ligand used is 2,4-dinitrophenylhydrazine. The metal salts used include copper acetate [Cu[(C[H.sub.3]COO).sub.2] x 4[H.sub.2]O], nickel acetate [Ni[(C[H.sub.3]COO).sub.2] x 4[H.sub.2]O], cobalt acetate [Co[(C[H.sub.3]COO).sub.2] x 4[H.sub.2]O], and zinc acetate [Zn[(C[H.sub.3]COO).sub.2] x 4[H.sub.2]O]. IR spectra of the samples in KBr pellsets were obtained in the ranges of 4000-400 [cm.sup.-1] using FTIR spectrometer. Metal Analyses were determined by atomic absorption spectroscopy with Perkin-Elmer Spectrometer, model 3110. UV-Vis spectra were obtained on Aquamate v4.60 spectrophotometer. Powder XRD analysis was prformed on a Syntag PADS diffractometer at 294K using Cu K[alpha] radiation ([lambda] = 1,54059 [Angstrom]).

Experimental Procedure

Synthesis of the complex:

The methods described by Pichon and James [9] were modified and adopted for the synthesis of all the metal complexes by mechanochemical method.

Synthesis of [Cu[(DNPH).sub.2][(C[H.sub.3]COO).sub.2]] complex

(2mmol, 0.396g) of 2,4-dintrophenyl hydrazine and (lmmol, 0.182g) of copper acetate were weighed carefully into a mortar. The two reactants were crushed (ground) for fifteen (15) minutes to obtain a lemon powder. The powder was removed from the mortar and stored in a desiccator.

Synthesis of [Zn[(DNPH).sub.2][(C[H.sub.3]COO).sub.2]] complex

(2mmol, 0.396g) of 2,4-dinitrophenylhydrazine and (lmmol, 0.220g) of Zinc acetate were weighed carefully into a mortar. The two reactants were then crushed (ground) for fifteen (15) minutes to obtain an orange powder. The powder was removed from the mortar and stored in a desiccator.

Synthesis of [Ni[(DNPH).sub.2][(C[H.sub.3]COO).sub.2]] complex

(2mmol, 0.396g) of 2,4-dinitrophenyl hydrazine and (lmmol, 0.249g) of nickel acetate and weighed were carefully into a mortar. The two reactants were crushed (ground) for fifteen (15) minutes to obtain an orange powder. The powder was removed from the mortar and stored in a desiccator.

Synthesis of [Co[(DNPH).sub.2][(C[H.sub.3]COO).sub.2]] complex

(2mmol, 0.396g) of 2,4-dinitrophenylhydrazine and (lmmol, 0.396g) of cobalt acetate were carefully weighed into a mortar. The two reactants were then crushed (ground) for fifteen (15) minutes to obtain an orange powder. The powder was removed from the mortar and stored in a desiccator.

Results and Discussion

The Ni (II), Cu(II), Co(II) and Ni(II) complexes of 2,4-dinitrophenylhydrazine were synthesized by reaction of metal salts with 2,4-dinitrophenylhydrazine. The complexes were characterized by AAS, Conductivity, TLC, infrared, UV-Vis spectroscopy and XRPD. The complexes are generally soluble in methanol, DMSO but insoluble in non-polar organic solvent. The physical properties of the various complexes are shown in Table 1. All the complexes synthesized were coloured ranging from their parent ligand colours of lemon to orange and light pink. The complexes are also non-hygroscopic solids with different melting point ranging from 156 to 206[degrees]C. All complexes have melting points higher than their respective parent drug probably due to complexation. The molar conductance values measured in DMSO solution ([10.sup.-3] M) for these complexes are in 98-132 [[OMEGA].sup.-1] [mol.sup.-1] [cm.sup.2] range (Table 1). According to these results, the complexes are electrolytes. Determination of stoichiometric ratio using job's method suggested mole ratio 1:2 metal to ligand stoichiometry for the complexes. The proposed structures of the complexes are shown in figures 3 and 4.

Since the retention factor, [R.sub.f] value (0.90, 0.54, 0.65, 0.50, 0.83) of the ligands and mixtures different from one another respectively; it shows that a new product might have been formed. Also, since only spot is present, the complexes formed are pure.

UV-Visible Spectrometry Results

The UV-VIS. Spectra of 2,4-diphenylhydrazine and its complexes in methanol present two absorption bands maxima at 256 and 296 nm assigned to [pi] [right arrow] [[pi].sup.*] and [pi] [right arrow] [pi]* transitions within the organic ligand. The cobalt (II) complex exhibits 3 bands at 455, 510 and 678nm assigned to [sup.4][T.sub.1g] [right arrow] [sup.4][T.sub.1g](P), [sup.4][T.sub.1g] [right arrow] [sup.4][A.sub.2g] and [sup.4][T.sub.1g] [right arrow] [sup.4][T.sub.2g]. Nickel(II) complex also shows 3 bands centered at 434, 645 and 767 nm which corresponds to [sup.3][A.sub.2g] [right arrow] [sup.3][T.sub.1g](P), [sup.3][A.sub.2g] [right arrow] [sup.3][T.sub.1g] and [sup.3][A.sub.2g] [right arrow] [sup.3][T.sub.2g]. The zinc(II) complex with no d-d transition shows two bands at 285 and 352nm assigned to [pi][right arrow] [[pi].sup.*] and MLCT. The copper(II) complex exhibits a broad band centered around 821nm which corresponds to [sup.2][E.sub.g] [right arrow] [sup.2][T.sub.2g]. All these characteristic bands observed in the UV-VIS. Spectra confirm octahedral configuration for all the complexes [12].

Infrared Spectroscopy Results

The vibration bands at 3319[cm.sup.-1], 3092 [cm.sup.-1] assigned to vN[H.sub.2] in the ligand shifted to higher wave number in all the complexes except [Co[(DNPH).sub.2][(C[H.sub.3]C[O.sub.2]).sub.2]]; this is probably due to coordination of metal via Nitrogen of N[H.sub.2] group. The characteristic hyrazinic band (vN-N) appeared at 972 [cm.sup.-1] in the free ligand. This hydrazinic nitrogen is observed in accordance with those reported [1, 13]. It can be observed that the absorption frequency of this band has increased to 1034-1050 [cm.sup.-1] [1]. The principle behind this phenomenon is due to the donation of the unpaired electrons from one of the nitrogen ones to the metal(II) ion, incidentally deflating the repulsion force subsequently, shifting the absorption frequency to a higher value [14,15]. The vN-H bending at 1623[cm.sup.-1] in the ligand shifted to lower frequency 1511-1578[cm.sup.-1], this also supported the involvement of hydrazinic nitrogen in coordination. The presence of acetate in the coordination sphere of the metal confirmed by the vas(C[O.sub.2]) at 1434-1424 [cm.sup.-1] and vs(C[O.sub.2]) at 1310-1350 [cm.sup.-1] this indicates the possible coordination of carboxylate group to metal [16]. The new bands within 515-548 [cm.sup.-1] and 670-690 [cm.sup.-1] are assigned to v(M-O) and v(M-N). These bands confirmed the coordination of 2,4 diphenylhydrazine to the metal(II) ion [16,17]. Spectral data shows that all the complexes are octahedral. The ligand 2,4 diphenylhydrazine is bidentate. Each metal ion coordinating to the nitrogen of N[H.sub.2], nitrogen of the Hydrazinic band and oxygen atom from each of two acetate ions to complete the octahedral structure.

Results of the X-Ray Powder Diffraction



The X-ray powder diffraction patterns (Figures 1 and 2) of the mixture of 2,4-DNPH and copper acetate was compared with that of DNPH and there was difference in the diffraction patterns of both. The peaks observed for the ligand (2,4-DNPH) are 2[??][degrees]: (23.19, 30.01, 46.07, 57.13, and 60.86). The peaks present in the mixture-[Co [(DNPH).sub.2][(C[H.sub.3]COO).sub.2]][).sub.2]] complex are 2[theta] : (19.21, 30.42, 46.55, 57.91, 60.00). In other words, some values observed for the ligand are absent in the [Co[(DNPH).sub.2][(C[H.sub.3]COO).sub.2]]] complex which shows that complexation of 2,4-DNPH and copper acetate might have occurred.

Proposed Structures of 2,4-DNPH metal complexes:




Cu(II), Co(II), Zn(II) and Ni(II) of 2,4-dinitrophenyl hydrazine complexes were synthesized in the absence of solvent. They were characterized by AAS, Conductivity, TLC, Infrared, UV-Vis spectroscopy and X-ray powder diffraction. The modes of binding in solid state solvent-free mechanochemical of all the complexes formed involve the ligand coordination with the metal ion through the Nitrogen of the N[H.sub.2] group and nitrogren of hydrazinic band and oxygen atom from each of the two acetate ions to complete octahedral geometry. The ligand is bidentate in nature. Mechanochemical method represents an ideal method of synthesizing compounds with no environmental pollution on the order of several minutes when compared to the solvent based that lead to the environmental pollution and takes longer period of time


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Adedibu Clement Tella *, Aaron Yissa Isaac and Rihanat Adeola Adeniran

Department of Chemistry, P.M.B. 1515, University of Ilorin, Nigeria

* Corresponding Author E-mail:
Table 1. Analytical data for 2,4-dinitrophenylhydrazine and its

Ligand/mixture Colour Melting

DNPH(ligand) Brick red 192
[Cu[(DNPH).sub.2] Lemon 156
[Co[(DNPH).sub.2] Orange 200
[Ni[(DNPH).sub.2] Light Pink 188
[Zn[(DNPH).sub.2] Orange 206

Ligand/mixture Conductivity TLC %
 [[OMEGA].sup.-1] Metal
DNPH(ligand) - 0.90 -
[Cu[(DNPH).sub.2] 105 0.54 11.34
[Co[(DNPH).sub.2] 111 0.65 10.95
[Ni[(DNPH).sub.2] 98 0.50 10.55
[Zn[(DNPH).sub.2] 132 0.83 11.87

Table 2: UV-Visible spectra 2,4-dinitrophenylhydrazine
metal complexes.

Complexes/ligand Wavelength(nm) Energies

DNPH 256 39063
 296 33784

[[Co DNPH).sub.2] 455 21978
 [(C[H.sub.3]COO).sub.2]] 510 19608
 678 14749

Ni[(DNPH).sub.2] 434 23041
 [(C[H.sub.3]COO).sub.2]] 645 15504
 767 13038

[Cu[(DNPH).sub.2] 821 12180
[Zn[(DNPH).sub.2] 285 35088
 [(C[H.sub.3]COO).sub.2]] 352 28409

Complexes/ligand Energies Assignment

DNPH 256 [pi][right arrow][[pi].sup.*]
 296 n[right arrow][[pi].sup.*]

[[Co DNPH).sub.2] 455 [sup.4][T.sub.1g][right arrow]
 [(C[H.sub.3]COO).sub.2]] [sup.4][T.sub.1g](P)
 510 [sup.4][T.sub.1g][right arrow]
 678 [sup.4][T.sub.1g][right arrow]

Ni[(DNPH).sub.2] 434 [sup.3][A.sub.2g][right arrow]
 [(C[H.sub.3]COO).sub.2]] [T.sub.1g](P)
 645 [sup.3][A.sub.2g][right arrow]
 767 [sup.3][A.sub.2g][right arrow]

[Cu[(DNPH).sub.2] 821 [sup.2][E.sub.g][right arrow]
 [(C[H.sub.3]COO).sub.2]] [sup.2][T.sub.2g]

[Zn[(DNPH).sub.2] 285 [pi][right arrow][[pi].sup.*]
 [(C[H.sub.3]COO).sub.2]] 352 MLCT

Table 3: Infrared spectra result for DNPH metal complexes.

Ligand/Complex v(N[H.sub.2]) v(N-H) v(N-N)

DNPH (Ligand) 3319, 3092 1623 972
[Zn[(DNPH).sub.2] 3460,3108 1578 1034
[Co[(DNPH).sub.2] 3321,3091 1580 1045
[Ni[(DNPH).sub.2] 3475, 3108 1511 1048
[Cu[(DNPH).sub.2] 3476,3091 1512 1050

Ligand/Complex vas(COO) vs(COO)

DNPH (Ligand) - -
[Zn[(DNPH).sub.2] 1434 1350
[Co[(DNPH).sub.2] 1424 1312
[Ni[(DNPH).sub.2] 1424 1311
[Cu[(DNPH).sub.2] 1427 1312
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Author:Tella, Adedibu Clement; Isaac, Aaron Yissa; Adeniran, Rihanat Adeola
Publication:International Journal of Applied Chemistry
Date:Jan 1, 2012
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