Synthesis of Nickel ( II ) Complexes Using Malonodihydrazone Ligands Having Long Chain Pendent Arms

The Schiff base complexes of transition metals have been widely used in biological, industrial and analytical fields. The present work is synthesis and characterization of some complexes. The complexes K2[Ni(C31H26N4O4)2], K2[Ni(C29H38N4O4)2], and K2[Ni(C41H62N4O2)4], have been prepared by the reaction of Schiff bases with nickel(II) acetate tetrahydrate in the presence of base (KOH) in 2:1 molar ratio. The Schiff base ligands e.g. LH2, LH2 and LH2 were prepared from the reaction of malonodihydrazide with 4-benzyloxybenzaldehyde, 4-hexyloxybenzaldehyde and 4-dodecyloxybenzaldehyde. Where LH2represents LH2


Introduction
Coordination chemistry at present stands as a land mark in the field of scientific advancement, embracing most diverse branches of science, engineering and technology.A complex has been defined as a species formed by the association of two or more simpler species capable of independent existence.(Rossotti et al., 1961).Although Jorgensen (1837Jorgensen ( -1914) ) started the extensive studies on the synthesis of complex compounds, it was not until 1906 when the recognition of the true nature of complexes began with Alfred Werner (1866Werner ( -1919) ) as set out in his classic work Neuere Anschauungen ouf dem Gebiete der anorganischen chemie (Werner, 1911).For this pioneering work, Alfred Werner received the Nobel Prize in 1913.In fact he was the founder of modern coordination chemistry who postulated the first successful theory known as "Werner's coordination theory" to explain the formation, properties and stereochemistry of coordination compounds.The independent approaches of Sidgwick (1923) and Lowry (1923) are that a chemical bond required the sharing of an electron molecule with an electron pair.This led to the idea that a neutral molecule with an electron pair (Lewis base) can donate these electrons to a metal ion or other electron acceptor (Lewis acid).Although the electron pair donor-acceptor concept of Lewis (Basdo et al., 1964) is still useful for many Lewis-acid base interactions for complex formation, it is apparent that the understanding towards the nature of bonding in metal complexes requires more detailed considerations.At the present time, four more or less distinct approaches to the theoretical treatment of the bonding and properties of coordination compounds are recognized.These theories are the Valence Bond Theory (VBT) (Bethe, 1929;Pouling, 1960), the Crystal Field Theory (CFT) (Pauling, 1960;Orgel, 1960), the Ligand Field Theory (LFT) (Figgis, 1960;Vanvleck, 1935), and the Molecular Orbital Theory (MOT) ( Vanvleck, 1985;Graw, 1964).
Every Lewis acid-base reaction involving essentially the formation of coordinate covalent bond can be called a complex formation reaction.The chemistry of Schiff base complexes have attracted a great deal of attention ever since Pfeiffer carried out his Pioneer research in the 1930's.The reactivity of coordination compounds is dramatically changed on the basis of complexation.Some important interesting reactions of substituted bis-salicylaldimine chelates of copper and nickel in which the organic groups attached to nitrogen of the donors are altered have been reported.The importance and application of metal complexes in analytical Chemistry are well known (Gruses et al., 1983).The Schiff base ligands play an important role in some biological systems and their function is related, at least in part, to its chelating ability with metal.In the recent years, a considerable attention has been given to synthesis of some Schiff base complexes to study their biological activity.Therefore, the interest of the present work is to synthesis and characterization of some Schiff base complexes.

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The characterizations of each products are done through weighing, elemental analysis, metal estimation, infrared spectra and uv-visible spectra study; conductivity, magnetic moments and melting point measurements and thin layer chromatography (TLC).

Synthesis of 4-benzyloxybenzaldehyde
The compound (5) was synthesized by the reaction of 4-hydroxybenzaldehyde with benzylbromide in the presence of anhydrous potassium carbonate.The infrared spectrum f the compound (5) showed a strong absorption band at 1686 cm -1 which is suggested for stretching frequency of ν(C=O) of aldehyde group.The band at 1601, 1576 cm -1 are suggested for the aromatic, ν(C=C) stretching frequencies.The bands at 1111 and 1167 cm -1 may be assigned to the ν(C-O) absorption.The absence of hydroxyl band at 3400-3600 cm -1 region indicated the formation of compound (5).
C 12 H 25 Therefore, the elemental analysis and IR spectral data suggested that the compound is the expected aldehyde, 4-benzyloxybenzaldehyde (5).

Synthesis of 4-Hexyloxybenzaldehyde
The compound (6) was synthesized by the reaction of 4-hydroxy benzaldehyde with hexylbromide in the present of anhydrous potassium carbonate.The infrared spectrum of the compound (6) showed a strong absorption band at 1686 cm -1 which is suggested for stretching frequency of ν(C=O) of aldehyde group.The band at 1601, 1576 cm -1 are suggested for the aromatic, ν(C=C) stretching frequencies.The bands at 1111 and 1167 cm -1 may be assigned to the ν(C-O) absorption.The absence of hydroxyl band at 3400-3600 cm -1 region indicated the formation of compound (6).Therefore, the elemental analysis and IR spectral data suggested that the compound is the expected aldehyde, 4-hexyloxybenzaldehyde (6).

Synthesis of 4-dodecyloxybenzaldehyde
The compound (7) was synthesized by the reaction of 4-hydroxy benzaldehyde with benzylbromide in the presence of anhydrous potassium carbonate.The infrared spectrum (Figure 3) of the compound (7) showed a strong absorption band at 1686 cm -1 which is suggested for stretching frequency of ν(C=O) of aldehyde group.The band at 1601, 1576 cm -1 are suggested for the aromatic, ν(C=C) stretching frequencies.The bands at 1111 and 1167 cm -1 may be assigned to the ν(C-O) absorption.The absence of hydroxyl band at 3400-3600 cm -1 region indicated the formation of compound (7).Therefore, the elemental analysis and IR spectral data suggested that the compound is the expected aldehyde, 4-dodecyloxybenzaldehyde (7).
www.ccsenThe complexes 1-3 were prepared by the reaction of Schiff bases (e.g.LH 2 , LH 2 and LH 2 ) with nickel(II) acetatetetrahydrate in the presence potassium hydroxide.The complexes have been characterized by elemental analysis, metal estimation, magnetic moments and conductance measurements, IR and UV-visible spectra and study of other Physical properties.The elemental analysis (Table 6) and metal estimation (Table 5) of the complexes 1-3 are consistent with the proposed formula.The conductance values (Table 5) of the complexes 1-3 reveal that they are 2:1 electrolytic in nature.
The infrared spectra (Figure 7, 8 and 9) of the complexes 1-3 showed (Table 7) absorption band at (1610-1620) cm -1 region suggested for  (C=N) stretching.There is no band at (3100-3300) cm -1 region indicated the absence of (N-H) group of the complexes.This also indicated the deprotonation of amide (-CONH-) proton.The complexes showed a strong band at (1650-1666) cm -1 which represents the  (C=O) stretching. 24A broad band at (1570-1580) cm -1 is due to the (C=C) double bond.A new band arises at (730-748) cm -1 is due to the  (M-N) stretching 26 , which indicates the coordination of ligand to the metal through the nitrogen atom.
The magnetic moment data of the complexes 1-3 are shown in Table 7.The magnetic moment of the complexes 1-3 showed negative value.These values corresponds that Ni(II) d 8 -system has no unpaired electron, suggested the diamagnetic complexes.
The UV-visible spectra of the complexes 1-3 are shown in Figure (10, 11 and 12).The complexes showed (Table 10) a single broad band at 400 nm 1, at 430 nm 2, and at 420 nm 3, represent the d-d transition of 1 A 1g  1 B 1g which suggested the square planar geometry of the Ni(II) complexes.The band observed below 400 nm assigned due to the * transition of the ligands.
On the basis of elemental analysis, magnetic moment, conductance measurements, metal estimation, IR and UV-visible spectra and other physical properties the suggested structure of complexes 1-3 are square planar in nature as shown in Figure (A), (B) and (C) respectively.ce.J.

Table 3 .
On the basis of infrared spectra, elemental analysis and other physical properties the suggested structure of the ligands (LH 2 , LH 2 and LH 2 ) are shown as: Elemental analysis and other physical properties of Ligands (LH 2 , LH 2 and LH 2 )

Table 4 .
Important infrared spectral bands of ligands (LH 2 , LH 2 and LH 2 ) Reactions of Schiff Bases (e.g.LH 2 =C 31 H 28 N 4 O 4 , LH 2 =C 29 H 40 N 4 O 4 and LH 2 =C 41 H 64 N 4 O 4 ) with Nickel(Ii) Acetatetetrahydrate in the Presence of Base (KOH): Synthesis of Complexes 1-3