Synthesis and Physicochemical Studies of Some 2-substituted-1-phenyl-1 , 3-butanedionato Nickel ( II ) and Copper ( II ) Complexes And Their 2 , 2 ′-Bipyridine and 1 , 10-Phenanthroline Adducts

The nickel(II) and copper(II) complexes of 2-substituted-1-phenyl-1,3-butanedione (2-R-bzacH, R=Cl, NO2) and their 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) adducts have been synthesized and characterized by microanalysis, conductance, magnetic and spectral measurements. The conductivity measurements in nitromethane indicate that the complexes are non-electrolytes while all the adducts are electrolytes except Ni(NO2-bzac)2bipy and Cu(NO2-bzac)2phen which are non-electrolytes. The room temperature magnetic moments suggest that the Cu(NO2-bzac)2 is a dimer while the visible absorption spectra of the compounds suggest plausible 4-, 5and 6-coordinate geometry for these compounds. The infrared spectra of the complexes showed that lower frequency shifts of varying magnitudes were observed in the carbonyl stretching frequencies on complexation.


Introduction
A survey of the literature reveals that metal -diketonates have found use as fuel additives, trace metal analysis by gas chromatography and numerous other extraction applications (Wenzel et al, 1985).The dissolution of chelating agents in supercritical fluids has been explored as a possible route to waste cleanup (Laintd et al, 1992;Lalntz et al, 1994;Wang et al, 1995;Wang et al, 1994).Complexes of -diketones are reported to have potentially useful pharmacological properties (Onawumi et al, 2008).

Synthesis of Cu(Cl-bzac) 2
Cl-bzacH (2.00 mL, 12.4 mmoles) in 6 mL acetone was added to copper(II) acetate monohy drate (1.24 g, 6.2 mmoles) in 50 mL 60% methanol in drops.The mixture was stirred for 1 hour and the precipitates formed were filtered, washed with 60% methanol and dried in the vacuo.All the other complexes were prepared using similar procedure.

Synthesis of Cu(Cl-bzac) 2 phen
The phenanthroline adduct of Cu(Cl-bzac) 2 was prepared by adding the solid complex (0.50 g, 1.1 mmol) while stirring to phenanthroline (0.72 g, 3.6 mmol) dissolved in 10 mL hot chloroform solution.The mixture was further stirred for 15 minutes and the precipitates formed were filtered and washed with acetone.This was dried in vacuo over anhydrous calcium chloride.Other adducts were prepared using similar procedures.

Physical measurements
Elemental analyses for C, H, N were determined at Department of Chemistry, Loughborough University, UK.The % metal in the nickel(II) and copper(II) compounds were determined titrimetrically using EDTA.
The molar conductivities of the soluble compounds in nitromethane at room temperature were determined using Digital conductivity meter (Labtech).
The solution spectra of the the Ligands, nickel(II) and copper(II) compounds in methanol and chloroform were recorded on a Unicam UV-Visible Spectrophotometer using 1cm glass cell.The reflectance spectra of the Ligands, nickel(II) and copper(II) compounds were recorded on a Perkin Elmer Lambda 950 UV/VIS spectrophotometer at the Department of Chemical Engineering, Faculty of Technology, Addis Ababa University, Ethiopia using calcium carbonate as reference.The infrared spectra of the compounds as pressed KBr disc were recorded on Perkin Elmer Spectrophotometer BX FT-IR.

Results and discussion
Table I shows the analytical data, colours, %yield and room temperature magnetic moments (μ eff ) of the prepared nickel(II) and copper(II) compounds.The elemental analyses were in good agreement with those calculated for the proposed formula (Table 2).The nickel(II) compounds prepared from 2-chloro-1-phenyl-1,3-butanedione were generally pink in colour except Ni(Cl-bzac) 2 .2H 2 O which had green colour while those prepared from 2-NO 2 -1-phenyl-1,3-butanedione were obtained as various shades of green except [Ni(NO 2 -bzac)(phen) 2 ](NO 2 -bzac) which was obtained as Light brown.All the copper(II) complexes and their adducts were obtained as varous shades of green colour.
The magnetic moment data as shown in Table 1 depicts the paramagnetic nature of the compounds.The nickel(II) compounds had values in the range 2.9-3.28B.M. which is in agreement with the range expected for octahedral nickel(II) complexes (2.9-3.3B.M) (Patel and Woods, 1990b).A moment of 1.73-2.2B.M. is usually observed for magnetically dilute copper(II) compounds, with compounds whose geometry approaches octahedral having moments at the lower end while those approaching tetrahedral geometry are at the higher end (Patel and Woods, 1990c).The prepared 2-substituted-1-phenyl-1,3-butanedionato copper(II) compounds had moments in the range 1.44-2.19B.M. The magnetic moment of Cu(NO 2 -bzac) 2 (1.44 B.M.) is lower than the spin only value of 1.73 B.M. which is indicative of dimerization with the possibility of Cu-Cu linkage (Cotton and Wilkinson, 1988).
The principal IR absorption bands of the prepared complexes are listed in Table 3.In the spectrum of NO 2 -bzacH, the band at 1600 cm -1 has been assigned as  as (C=O)   as (C=C) +  as (NO 2 ) vibrations while those at 1360 cm -1 and 820 cm -1 are assigned as  s (NO 2 ) and (C-N) or N-O respectively.Bathochromic shifts of varying magnitude were observed in the asymmetric C-O and C-C stretching vibrations of the complexes relative to their respective ligands whereas hypsochromic shifts were observed in all the adducts relative to the complexes.Multiple bands of  s (C-O)C-H were observed in all the compounds except [Ni(Cl-bzac) [Ni(Cl-bzac)(phen)(H 2 O) 2 ](Cl-bzac) which had single band.Studies have shown that methyl deformation band occurred at around 1425 cm -1 in acetylacetone (Holtzclaw and Collman, 1957;Belford et al, 1956) while bands in the 1420-1350 cm -1 region have been assigned as  as (CH 3 )   s (CH 3 ) vibrations (Singh and Sahai, 1967b;Tanaka et al, 1969;Patel and Woods, 1990b;Koshimura et al, 1973;Nakamoto et al, 1961).Furthermore, the M-O+C-N vibrational modes occurred below 700 cm -1 (Patel and Woods, 1990a;Patel and Woods, 1990c).The C-H deformation bands (C-H) for the bipyridine appeared at around 768 cm -1 while that of the phenanthroline adducts were observed at 852 cm -1 and 727 cm -1 .
The electronic spectra of the ligands in CHCl 3 and methanol are listed in Table 4. Single bands of the π 3 -π 4 * were observed in the 31,250-31,154 cm -1 region in Cl-bzacH and NO 2 -bzacH ligands.Bathochromic shift of the π 3 -π 4 * were observed in Cl-bzacH and NO 2 -bzacH as compared to bzacH in chloroform.π 3 -π 4 *Hypsochromic shifts of varying magnitude were observed in the Ni(Cl-bzac) 2 .2H 2 O and Ni(NO 2 -bzac) 2 .2H 2 O complexes in chloroform and methanol.Upon adduct formation, π 3 -π 4 * Hypsochromic shifts were observed in all the adducts in chloroform except [Ni(Cl-bzac)(bipy)(H 2 O) 2 ](Cl-bzac) which had bathochromic shift.The ligand field spectra band of Ni(Cl-bzac) 2 .2H 2 O and Ni(NO 2 -bzac) 2 .2H 2 O were typically of an octahedral geometry (Lever, 1986) while the shift observed in Cu(Cl-bzac) 2 and Cu(NO 2 -bzac) 2 suggest a four coordinate square planar geometry.Lower frequency shifts were observed in Cu(Cl-bzac) 2 and Cu(NO 2 -bzac) 2 in methanol relative to chloroform [18,031 cm -1 in chloroform→15,625 cm -1 in methanol for Cu(Cl-bzac) 2 ] and [18,349 cm -1 in chloroform→15,198 cm -1 in methanol for Cu(NO 2 -bzac) 2 ] which is an indication that the complexes are square planar in structure.Nickel(II) species have a large number of stereochemical forms in which the ion occurs, hence equilibrium between these forms are usually set up which are generally temperature, solvent and sometimes concentration dependent (Bailar et al, 1973).In solution, Ni(II) β-diketonates sometimes exhibit a monomer↔trimer, square planar↔octahedral equilibrium (Cotton and Wilkinson, 1980).Three transitions are expected for an octahedral nickel(II) ion in the region 7,000-13,000, cm -1 , 11,000-20,000 cm -1 , 19,000-27,000 cm -1 which are assigned to the 3 A 2g (F) → 3 T 2g (F), 3 A 2g (F) → 3 T 1g (F), 3 A 2g (F) → 3 T 1g (P) respectively.In the synthesized nickel(II) adducts, bands in the 11,442-12,821 cm -1 and 13,908-19,455 cm -1 region have been assigned to 3 A 2g (F) → 3 T 2g (F), 3 A 2g (F) → 3 T 1g (F) transitions respectively (Lever, 1986;Osowole et al, 2000).The visible spectra of the synthesized copper(II) adducts had a single band between 14,006-15,625 cm -1 which is consistent with the adoption of square pyramidal geometry for copper(II) compounds (Odunola et al, 2003).In addition, higher frequency shifts were observed in the ligand field spectral of the copper(II) adducts in methanol as compared with chloroform.[Cu(Cl-bzac)(bipy)(H 2 O)](Cl-bzac) had a band in the 14,205 cm -1 region in chlorofom and this band was shifted to 16,393 cm -1 in methanol.This is an indication that the compound is a five coordinate square pyramidal geometry (Patel and Woods, 1990a).The electronic reflectance spectra of the ligands, complexes and adducts in the ultraviolet region exhibited single peak between 31,056-37,453 cm -1 with an additional peak observed between 39,683-48,544 cm -1 which have been assigned to π 3 -π 4 * and charge transfer (CT) respectively.The visible region of the spectra showed that the nickel(II) compounds were octahedral in geometry while the copper(II) complexes and adducts were square planar and square pyramidal in geometry respectively.

Figure 2 .
Figure 1.Proposed structures for Nickel adducts