Comparative Studies of New Complexes Synthesized by Chemical and Tribochemical Reactions Derived from Malonic Acid Dihydrazide ( L ; MAD ) with Cu 2 + and Co 2 + Salts

The reaction of L (MAD) with Cu and Co chlorides affords new metal complexes. The isolated solid complexes were synthesized by two different techniques i.e., chemical and tribochemical methods. Four new complexes were synthesized by direct chemical reactions of MCl2 (M = Co and Cu) with MAD in absolute EtOH. The isolated solid complexes were used as starting compounds to synthesize another four new complexes using tribochemical technique by grinding the previous complexes in the solid state with excess KI in agate mortar. The results of the isolated complexes indicate the substitution of the chloride by iodide ions during grinding and extraction of the complexes by a mixture of solvents (EtOH + MeOH). Also, the results suggest that no reduction of Cu or oxidation of Co complexes is observed. The IR spectra of the complexes suggest that L acts in a bidentate manner. Moreover, the results of electronic spectra and magnetic measurements for the chloride and iodide complexes suggest distorted-octahedral and/or tetrahedral for Cu and high-spin octahedral and/or tetrahedral structures around the Co ion, respectively.


Introduction
Malonic acid dihydrazide (MDH; L) is a vital class of ligands in coordination chemistry and finds extensive applications in different fields [1].Dihydrazide derivatives are polydentate ligands coordinating in neutral forms [2].The applications of metal complexes in various fields like anti-inflammatory and analgesic have been extensively examined [3].The hydrazide moiety (−N 2 H 4 ) possesses a potential therapeutic effect and plays an important role in medicine [4] [5] [6].
Earlier work illustrated that some drugs show increased activity when administered as metal chelates rather in the form of original organic compounds [7] [8].
These complexes play an important role in bioinorganic chemistry and redox enzyme systems [9] [10] [11].The study of structural and binding features of various metal complexes plays an important role in understanding of the biological process.Redox properties of a drug can give insight into its metabolic or pharmaceutical activity [12] [13] [14].Literature survey indicates that electrochemical studies have been manipulated to predict the behavior of ligand and its metal complexes in biochemistry and medicine [15].In recent years, an increasing number of complexes derived from dihydrazides have been investigated [16].
Also, an increasing number of transition metal complexes of dihydrazides have been studied in details [17].However, no attempt appears to have been made to monitor the tribochemical reactions derived from dihydrazides.The aim of present work is to study the synthesis of novel Cu 2+ and Co 2+ complexes derived from L (MAH) by both chemical and tribochemical reactions and the isolated solid complexes were characterized by elemental analyses, spectral (IR, 1 H-NMR and UV-vis.) and magnetic measurements.The goal of synthesis of complexes by tribochemical is to study the role of KI on substitution and the oxidation and/or reduction of the metal ions.Also, this method gives high yield and is considered as a cheap and new method for synthesis of new types of complexes.

Experimental
All the chemicals (salts and solvents) were purchased from Aldrcih and used without purification.Malonic acid dihydrazide (MAH, L) was synthesized by refluxing equivalent amounts of diethyl malonate (15.2 ml) in EtOH and hydrazine hydrate (6.2 ml) on water bath for 4 hrs.The white product (m.p.; 152˚C -156˚C; yield: 90%) was obtained by cooling and the product was characterized by chemical and spectral methods.The ligand (MAH, L) was crystallized from absolute EtOH.mol −1 and μ eff (4.9 BM).

Preparation of Cu 2+ and Co 2+ Complexes by Tribochemical
Reactions The Cu 2+ and Co 2+ complexes (0.5 g) synthesized from the previous method were grinded with KI (6 g) for 2 hrs until the color of the original complex is changed.A mixture of MeOH (80 ml) and EtOH (20 ml) was then added and the solution was refluxed for 2hrs and then left overnight.The isolated complexes with the general formulae; and [Cu(L) 3 ]I 2 ; were filtered off, washed with 100 ml of a mixture of EtOH and H 2 O (1:1) and finally dried in an oven at 80˚C; Yield: 78% -88%. [

Physical Measurements
Elemental analyses contents (C, H and N) were determined at the Microanalyti-Open Journal of Inorganic Chemistry cal Unit, Center of King Fahd Institute at Jeddah, Saudi Arabia.Copper and cobalt contents were determined by complexometric titration in the presence of Xylenol orange as an indicator [18].Molar conductivities measurements were carried out using Tacussel model CD 75.The chloride and iodide contents were determined as AgCl or AgI [18].The IR spectra in the 400 -4000 cm −1 range were recorded in KBr on a Mattson 5000 FTIR Spectrometer.The electronic spectra of the Cu 2+ and Co 2+ complexes were recorded in Nujol mull in the range (200 -900 nm) using Unicam spectrometer model UV2.L was recorded on 1 H-NMR Spectrometer (400 MHz) in d 6 -DMSO at Mansoura University at Mansoura.Magnetic moments were determined using a Sherwood balance at room temperature (25˚C) with Hg[Co(NSC) 4 ] as a calibrate.The diamagnetic corrections for L and its metal atoms were computed using Pascal's constants [19].The corrected values were calculated according to the following equation:

∑ ∑
where χ A = gram atomic susceptibility of atom A. n A = is the number of atom A in the compound.λ = constitutive for certain bond types.

Physical Properties and Elemental Analyses
All the isolated metal complexes are colored, stable against light and air for two years.Also, the complexes are insoluble in most common organic solvents but indicates that the complex is non-electrolytic [20].
Moreover, the results show that the metal complexes have comparatively low melting points (168˚C -254˚C) suggesting the weakness of the bond between the metal ions and L. The structure of L is represented as shown in Figure 1.

Infrared Spectra
The IR spectrum of L in KBr (Figure S1) shows several bands at 3315, 3296 and  The mode of bonding was determined by comparing the IR spectra of L with its complexes (Cu 2+ and Co 2+ ).The IR spectra of the complexes obtained by chemical method with the general formulae, [Cu(L)Cl 2 ] (Figure S2), [Co(L) 2 (H 2 O)Cl]Cl (Figure S3), [Cu(L) 3 ]Cl 2 •½EtOH (Figure S4) and [Co(L) 3 ]Cl 2 (Figure S5) indicate that the L behaves in a bidentate manner and coordinates via the two carbonyl groups forming six-membered ring around the metal ions.
The negative shifts of these two bands to lower wavenumbers show the involvement of both these groups in bonding.The most important assignments IR bands for L and its metal complexes are listed in Table 1.Also, the ligand behaves in bidentate manner via the carbonyl oxygen (CO) and the amino (NH 2 ) groups in case of the complexes with the general formula, [M(L) 3 ]I 2 •XS (M = Cu 2+ , Co 2+ and XS = zero in case of Cu 2+ while XS = ½EtOH•2H 2 O in case of Co 2+ ).

1 H-NMR Spectra
The 1 H-NMR spectrum of L in d 6 -DMSO displays four signals at 10.3, 9.9, 9.3 and 3.9, relative to TMS (Figure 3).These signals are assigned to NH 2 (hydrogen-bonded), NH 2 (free), NH (free) and CH 2 protons, respectively.The results are taken as strong evidence for the existence of hydrogen bonding between CO and NH 2 groups and coincide with the results of IR spectra.The former three signals disappear on adding D 2 O as shown in Figure S6.

Electronic Spectra and Magnetic Data
The Cu 2+ and Co 2+ complexes with the general formulae, [Cu(L)Cl 2 ] (Figure S7), S9) and [Co(L) 3 ]Cl 2 (Figure S10), were carried out in Nujol mull.The spectrum of the Cu 2+ complex, [Cu(L) 3 ]Cl 2 •½EtOH, shows a band at 14368 cm −1 attributed to 2 E g → 2 T 2g transition [19] in a distorted-octahedral geometry around the Cu 2+ ion.The value of magnetic moment is 2.0 BM is taken as additional evidence for the existence of distorted-octahedral geometry around the Cu 2+ ion.On the other hand, the value of magnetic moment of the Co 2+ complexes, [Co(L) 2 Cl 2 ]Cl (5.2 BM) and [Co(L) 3 ]Cl 2 (4.9 BM) suggests the paramagnetic nature of the two complexes and the existence of d 7 -configuration around the Co 2+ ion.Also, the data suggest that Open Journal of Inorganic Chemistry

Conclusion
In continuation of our earlier work on tribochemical reactions and the role of metal ions as well as the ligand used in reduction of Cu 2+ and oxidation of Co 2+ , we extend our work to include malonic acid dihydrazide (L) with Cu easily soluble in DMF and DMSO.The molar conductivities for all the iodide complexes are non-conducting except the two complexes with the general formulae, [Cu(L) 3 ]I 2 and [Co(L) 3 ]I 2 •½EtOH•2H 2 O, which are conducting and have values 75 and 88 Ω −1 •cm 2 •mol −1 in DMSO, respectively.On the other hand, the molar conductance of the chloride complexes in DMSO falls in the 55 -75 Ω −1 •cm 2 •mol −1 indicating 1:1 and 1:2 electrolytes, respectively.The low value (9

3131 cm − 1
assigned to ν as (NH 2 ), ν s (NH 2 ) and ν(NH) vibrations, respectively.The observation of broad weak bands in the 1940 -1800 and 2755 -2500 cm −1 region suggests the presence of intra-molecular hydrogen bonding of the types O-H…..N and/or N-H….O [21] [22].The bands observed at 1705 sh, 1635 sh and 1539s cm −1 are assigned to ν(C=O), ν(NH 2 ) and ν(N-C-O) vibrations, respectively.The observation of the former two bands as shoulder bands suggests these Open Journal of Inorganic Chemistry

Figure 2 .
Figure 2. The hydrogen bond in MDH.
2+ and Co 2+ by chemical and tribochemical reactions.The ligand coordinates in a bidentate manner towards the metal ions.Also, the results indicate the substitution of the chloride by iodide ions has occurred in Cu 2+ and Co 2+ complexes.Moreover, the reduction of Cu 2+ to Cu + and the oxidation of Co 2+ to Co 3+ have not been occurred and confirmed by chemical, spectral and magnetic measurements.

Figure S6. 1 H
Figure S6. 1 H-NMR spectrum of L in d 6 -DMSO and D 2 O.

Table 1 .
The most important IR bands of MDH and its complexes.