Malonic acid dihydrazide (MDH; L) is a vital class of ligands in coordination chemistry and finds extensive applications in different fields  . Dihydrazide derivatives are polydentate ligands coordinating in neutral forms  . The applications of metal complexes in various fields like anti-inflammatory and analgesic have been extensively examined  . The hydrazide moiety (−N2H4) possesses a potential therapeutic effect and plays an important role in medicine    . Earlier work illustrated that some drugs show increased activity when administered as metal chelates rather in the form of original organic compounds   . These complexes play an important role in bioinorganic chemistry and redox enzyme systems    . 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    . Literature survey indicates that electrochemical studies have been manipulated to predict the behavior of ligand and its metal complexes in biochemistry and medicine  . In recent years, an increasing number of complexes derived from dihydrazides have been investigated  . Also, an increasing number of transition metal complexes of dihydrazides have been studied in details  . 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 Cu2+ and Co2+ complexes derived from L (MAH) by both chemical and tribochemical reactions and the isolated solid complexes were characterized by elemental analyses, spectral (IR, 1H-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.
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.
2.1. Preparation of Metal Complexes
2.1.1. Preparation of Cu2+ and Co2+ Complexes by Chemical Method
Four solid complexes derived from the reaction of CuCl2 and CoCl2 dissolved in EtOH (25 ml with L in 50 ml EtOH with the general formulae, [Cu(L)Cl2], [Co2(L)2(H2O)Cl]Cl, [Cu(L)3]Cl3∙½EtOH and [Co(L)3]Cl2, were synthesized and characterized. The reaction mixtures were refluxed on a water bath for 1 hr. The complexes were filtered off, washed several times with absolute EtOH followed by dry diethyl ether and finally dried in a vacuum desiccator over anhydrous P4O10.
[Cu(L)Cl2] is olive-green in color. Anal. Calcd: for C3H8CuN4O2Cl2 (266.6): C, 13.5; H, 3.0; N, 21.0; Cu, 23.8; Cl, 12.9%. Found: C, 12.9; H, 2.8; N, 20.6; Cu, 23.4; Cl, 12.2%.; Yield 85%; green powder; m.p.; 168˚C; Yield: 90%; Ʌ+m (DMSO): 9 ohm−1∙cm2∙mol−1 and μeff (2.0 BM).
[Co(L)2(H2O)Cl]Cl is pink in color. Anal. Calcd: for C6H18Co2N8O5Cl2 (412.118): C, 17.5; H, 4.4; N, 27.2; Co, 14.3; Cl, 17.2%. Found: C, 17.2; H, 4.1; N, 27.1; Co, 14.3; Cl, 17.2%.; m.p.; 218˚C; Yield: 86 %; Ʌ+m (DMSO): 55 ohm−1∙cm2∙mol−1 and μeff (5.2 BM).
[Cu(L)3]Cl2∙½EtOH is brown in color. Anal. Calcd: for C10H27CuN12O6Cl2 (553.868): C, 21.7; H, 4.9; N, 30.3; Cu, 11.5; Cl, 12.8%. Found: C, 21.6; H, 4.8; N, 30.8; Cu, 11.1; Cl, 12.6%.; m.p.; 254˚C; Yield: 90 %; Ʌ+m (DMSO): 70 ohm−1∙cm2∙mol−1 and μeff (2.0 BM).
[Co(L)3]Cl2 is violet in color. Anal. Calcd: for C10H27CoN12O6Cl2 (526.223): C, 20.5; H, 4.6; N, 31.9; Co, 11.2; Cl, 13.5%. Found: C, 20.4; H, 5.0; N, 31.2; Co, 10.9; Cl, 13.3%.; m.p.; 184˚C; Yield: 80 %; Ʌ+m (DMSO): 75 ohm−1∙cm2∙mol−1 and μeff (4.9 BM).
2.1.2. Preparation of Cu2+ and Co2+ Complexes by Tribochemical Reactions
The Cu2+ and Co2+ 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; [Cu(L)I2]∙2H2O, [Co(L)2I2]∙2H2O, [Co(L)3]I2∙½EtOH∙2H2O and [Cu(L)3]I2; were filtered off, washed with 100 ml of a mixture of EtOH and H2O (1:1) and finally dried in an oven at 80˚C; Yield: 78% - 88%.
[Cu(L)I2]∙2H2O is pale yellow in color. Anal. Calcd: for C3H12CuN4O3I2 (485.509): C, 7.4; H, 2.5; N, 11.5; Cu, 13.1; I, 52.3%. Found: C, 6.7; H, 1.9; N, 11.1; Cu, 13.0; I, 52.1%.; m.p.; 210˚C; Yield: 78%; Ʌ+m (DMSO): 8 ohm−1∙cm2∙mol−1 and μeff (1.8 BM).
[Co(L)(H2O)2I2] is simon in color. Anal. Calcd: for C6H20CoN4O4I2 (613.028): C, 11.8; H, 3.3; N, 18.3; Co, 9.6; I, 41.4%. Found: C, 11.8; H, 2.8; N, 17.7; Co, 9.3; I, 40.9%.; m.p.; 196˚C; Yield: 82%; Ʌ+m (DMSO): 5 ohm−1∙cm2∙mol−1 and μeff (4.9 BM).
[Co(L)3]I2∙½EtOH∙2H2O is buff in color. Anal. Calcd: for C10H27CoN12O6I2 (768.192): C, 15.6; H, 4.1; N, 21.9; Co, 7.7; I, 33.0%. Found: C, 15.4; H, 3.7; N, 21.2; Co, 7.2; I, 32.4%.; m.p.; 238˚C; Yield: 88%; Ʌ+m (DMSO): 66 ohm−1∙cm2∙mol−1 and μeff (5.0 BM).
[Cu(L)3]I2 is brown in color. Anal. Calcd: for C9H24CuN12O6I2 (713.278): C, 15.1; H, 3.4; N, 23.6; Cu, 8.9; I, 35.6%. Found: C, 14.7; H, 2.8; N, 22.8; Cu, 8.1; I, 35.1%.; m.p.; 245˚C; Yield: 75%; Ʌ+m (DMSO): 59 ohm−1∙cm2∙mol−1 and μeff (1.78 BM).
2.2. Physical Measurements
Elemental analyses contents (C, H and N) were determined at the Microanalytical 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  . Molar conductivities measurements were carried out using Tacussel model CD 75. The chloride and iodide contents were determined as AgCl or AgI  . 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 Cu2+ and Co2+ complexes were recorded in Nujol mull in the range (200 - 900 nm) using Unicam spectrometer model UV2. L was recorded on 1H-NMR Spectrometer (400 MHz) in d6-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  . The corrected values were calculated according to the following equation:
χA = gram atomic susceptibility of atom A.
nA = is the number of atom A in the compound.
λ = constitutive for certain bond types.
3. Results and Discussion
3.1. 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 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]I2 and [Co(L)3]I2∙½EtOH∙2H2O, which are conducting and have values 75 and 88 Ω−1∙cm2∙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∙cm2∙mol−1 indicating 1:1 and 1:2 electrolytes, respectively. The low value (9 Ω−1∙cm2∙mol−1) for [Cu(L)Cl2] indicates that the complex is non-electrolytic  . 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.
3.2. Infrared Spectra
The IR spectrum of L in KBr (Figure S1) shows several bands at 3315, 3296 and 3131 cm−1 assigned to νas(NH2), νs(NH2) 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   . The bands observed at 1705 sh, 1635 sh and 1539s cm−1 are assigned to ν(C=O), ν(NH2) and ν(N-C-O) vibrations, respectively. The observation of the former two bands as shoulder bands suggests these
Figure 1. Malonohydrazide )L; MDH).
groups are taken part in hydrogen bonding. The results suggest that the first type of the hydrogen bonding (O-H…N) is more likely occurred. All these foundations suggest that L (MDH) can be represented in Figure 2.
The mode of bonding was determined by comparing the IR spectra of L with its complexes (Cu2+ and Co2+). The IR spectra of the complexes obtained by chemical method with the general formulae, [Cu(L)Cl2] (Figure S2), [Co(L)2(H2O)Cl]Cl (Figure S3), [Cu(L)3]Cl2∙½EtOH (Figure S4) and [Co(L)3]Cl2 (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 (NH2) groups in case of the complexes with the general formula, [M(L)3]I2∙XS (M = Cu2+, Co2+ and XS = zero in case of Cu2+ while XS = ½EtOH∙2H2O in case of Co2+).
3.3. 1H-NMR Spectra
The 1H-NMR spectrum of L in d6-DMSO displays four signals at 10.3, 9.9, 9.3 and 3.9, relative to TMS (Figure 3). These signals are assigned to NH2 (hydrogen-bonded), NH2 (free), NH (free) and CH2 protons, respectively. The results are taken as strong evidence for the existence of hydrogen bonding between CO and NH2 groups and coincide with the results of IR spectra. The former three signals disappear on adding D2O as shown in Figure S6.
3.4. Electronic Spectra and Magnetic Data
The Cu2+ and Co2+ complexes with the general formulae, [Cu(L)Cl2] (Figure S7), [Co(L)2(H2O)Cl]Cl (Figure S8), [Cu(L)3]Cl2∙½EtOH (Figure S9) and [Co(L)3]Cl2 (Figure S10), were carried out in Nujol mull. The spectrum of the Cu2+ complex,
[Cu(L)3]Cl2∙½EtOH, shows a band at 14368 cm−1 attributed to 2Eg → 2T2g transition  in a distorted-octahedral geometry around the Cu2+ ion. The value of magnetic moment is 2.0 BM is taken as additional evidence for the existence of distorted-octahedral geometry around the Cu2+ ion. On the other hand, the value of magnetic moment of the Co2+ complexes, [Co(L)2Cl2]Cl (5.2 BM) and [Co(L)3]Cl2 (4.9 BM) suggests the paramagnetic nature of the two complexes and the existence of d7-configuration around the Co2+ ion. Also, the data suggest that
Figure 2. The hydrogen bond in MDH.
Figure 3. 1H-NMR spectrum of L in d6-DMSO.
Table 1. The most important IR bands of MDH and its complexes.
Figure 4. Structure of [Cu(L)Cl2].
Figure 5. Structure of [Co(L)(H2O)2Cl2].
Figure 6. Structure of [Co(L)2(H2O)Cl]Cl.
Figure 7. Structure of [Cu(L)(H2O)2I2].
Figure 8. [Cu(L)3]I2 (X=O) and [Co(L)3]I2∙½EtOH∙2H2O.
no oxidation of Co2+ to Co3+ ion as reported earlier by Mostafa et al.  . The electronic spectrum of [Co(L)2Cl2]Cl in Nujol mull shows three bands in the 15,700, 19,840 and 21,740 - 28,900 cm−1 regions attributed to the 3T1g → 3T2g, 3T1g → 3A2g and 3T1g → 3T1g transitions, respectively, in a high-spin octahedral Co2+ system. The observation of these three bands may also suggest that the complexes have trans-configuration   . All the above foundations suggest representative structures for the isolated complexes with the general formulae, [Cu(L)Cl2], [Co(L)(H2O)2Cl2], [Co(L)2(H2O)Cl]Cl, [Cu(L)(H2O)2I2] and [M(L)3]I2∙X (M = Cu2+ or Co2+; X = O in case for Cu2+ and X = ½EtOH∙2H2O in case of Co2+ are shown in Figures 4-8, respectively.
In continuation of our earlier work on tribochemical reactions and the role of metal ions as well as the ligand used in reduction of Cu2+ and oxidation of Co2+, we extend our work to include malonic acid dihydrazide (L) with Cu2+ and Co2+ 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 Cu2+ and Co2+ complexes. Moreover, the reduction of Cu2+ to Cu+ and the oxidation of Co2+ to Co3+ have not been occurred and confirmed by chemical, spectral and magnetic measurements.
Figure S1. IR spectrum of L in KBr.
Figure S2. IR spectrum of [Cu(L)Cl2] in KBr.
Figure S3. IR spectrum of [Co(L)2(H2O)Cl]Cl in KBr.
Figure S4. IR spectrum of [Cu(L)3]Cl2∙½EtOH in KBr.
Figure S5. IR spectrum of [Co(L)3]Cl2 in KBr.
Figure S6. 1H-NMR spectrum of L in d6-DMSO and D2O.
Figure S7. UV spectrum of [Cu(L)Cl2] in Nujol.
Figure S8. UV spectrum of [Co(L)2(H2O)Cl]ClinNujol.
Figure S9. UV spectrum of [Cu(L)3]Cl2∙½EtOH in Nujol.
Figure S10. UV spectrum of [Co(L)3]Cl2 in Nujol.
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