Effect of pH on the formation of complex compounds with Schiff ...

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<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.The γ(C-O) (phenolic) stretch <strong>of</strong> (Scheme 1) occurring at 1562 cm -1 shifts to higher frequency by 10cm -1 in(Scheme 2), (Scheme 3) formed at <strong>pH</strong>=3-4 and complex compounds (Scheme 4), (Scheme 5) formed at <strong>pH</strong>=7 suggesting the non-involvement <strong>of</strong> (C=O) (coumarin) O atom towards coordination in these complexcompounds. But, the complex compound (Scheme 6) formed at <strong>pH</strong>= 8 suggesting the coordination <strong>of</strong>coumarin carbonyl O atom to the metal ions in the coordination compound.The γ(C-O (phenolic) stretch <strong>of</strong> (Scheme 1) occurring at 1581 cm -1 shifts to higher frequency by 10 cm -1in complex compounds (Scheme 2),(Scheme 3) formed at <strong>pH</strong>= 3-4 supports the involvement <strong>of</strong> phenolic Oatom in coordination 13 . However, the γ(C-O) (phenolic) stretch <strong>of</strong> (Scheme 1) shifts to higher frequency bymore than 10 cm -1 in (Scheme 4), (Scheme 5) formed at <strong>pH</strong>= 7 and complex compounds (Scheme 6) formedat <strong>pH</strong>= 8 indicates the presence <strong>of</strong> the oxo bridge in these bimetallic coordination compounds.The magnitude<strong>of</strong> the shift (
<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.analytical R grade were used and the sodium hydroxide solutions were prepared in double distilled water andit is standardized by the usual method.(i). Synthesis <strong>of</strong> Ligand compound LH 2 (Scheme 1) and metal complexes: The ligand (LH 2 ) wasprepared by the method reported by Nag et al 11 . The metal complexes [M(LH 2 )] where M= Cu(II),Zn(II),Cd(II) ,[M(LH) 2 (H 2 O) 2 ] where M= Co(II),Ni(II) , [CuL] 2, [ML(EtOH)] where M= Zn(II), Cd(II) and[ML(EtOH)] 2 where M= Cu(II), Zn(II), Ni(II), Co(II), Cd(II) where prepared by following the methodreported by Kumar et al 16 .(ii).Synthesis <strong>of</strong> [M(LH) 2 ] M= Cu(II), Cd(II) (Scheme 2) and [M(LH) 2 (H 2 O) 2 ] M= Co(II),Ni(II) (Scheme 3): Ligand LH 2 (2.10g) was dissolved in aqueous NaOH solution (0.5 g in 10 ml), yellowcoloured solution was obtained. After then 30-50 ml <strong>of</strong> an aqueous solution <strong>of</strong> metal chloride was added. Themixture was stirred magnetically for 10 minutes. Glacial acetic acid or hydrochloric acid (1:1) was then addeddrop wise to above solution till <strong>pH</strong> <strong>of</strong> solution becomes 3-4. The resulting turbid mixture was refluxed for twohours. The coloured solids formed on cooling, filtered, washed and recrystalized from water followed bywashing with ether. M.P. 250 o C. Yield =40%.(iii).Synthesis <strong>of</strong> [CuL] 2 (Scheme 4):A ethanol solution (30 ml) <strong>of</strong> LH 2 (1.05g) was added to ethyl alcoholsolution (35ml) <strong>of</strong> appropriate metal chloride and the mixture was heated under reflux for 3 hours on a waterbath and then cooled to room temperature. The solid product formed were filtered, washed with andrecrystallized from ethyl alcohol followed by washing with ether. M.P. 248 o C, yield= 60%.(iv).Synthesis <strong>of</strong> [ML(EtOH)] 2 M= Cu(II), Zn(II), Ni(II),Co(II),Cd(II) (Scheme 5): A ethylalcohol solution (30ml) <strong>of</strong> LH 2 (1.05g) was added to a EtOH solution (35ml) <strong>of</strong> appropriate metal chloridesand the mixture was stirred magnetically for 10 minutes. A 10% ethyl alcohol solution <strong>of</strong> EtONa was thenadded drop wise to the above solution till the <strong>pH</strong> <strong>of</strong> the solution becomes 8. The resulting mixture wasrefluxed for 3 hours on a water bath, coloured solids formed on cooling, filtered, washed with EtOH followedby washing with ether. M.P. 86 o C, yield=70%.CONCLUSIONSThe different types <strong>of</strong> complex compounds <strong>of</strong> same ligand with metal ions have been obtained by varying<strong>pH</strong> and solvent during their synthesis. The basicity and denticity <strong>of</strong> the Schiff base (Scheme 1) derived from3-Aldehydosalicylic acid and 7-Amino-4-methyl coumarin changes considerably with the role <strong>of</strong> <strong>pH</strong> from 3-8.The basicity and denticity <strong>of</strong> ligand increase with the increase in <strong>pH</strong>. The ligand at <strong>pH</strong> 3-4 acts as monobasicbidentate ON-donor ligand forms monometallic complex compounds [M(LH) 2 ] where M= Cu(II),Zn(II),Cd(II) (Scheme 2) and [M(LH) 2 (H 2 O) 2 ] where M= Co(II), Ni(II) (Scheme 3). At the <strong>pH</strong>= 7, the ligand acts asa dibasic tridentate OON-donor ligand forming the monometallic complex compound <strong>of</strong> the type [ML(EtOH)] where M= Zn (II), Cd (II), (Scheme 5) and at the same <strong>pH</strong> = 7 the ligand formed dimetalic complexcompound <strong>of</strong> the type [(CuL) 2 ] with copper metal ion (Scheme 4). While at <strong>pH</strong>= 8 the ligand acts as a dibasictetradentate OONO-donor ligand in EtOH and forms dimetalic compound <strong>of</strong> the type[ML(EtOH)]2 where M=Cu(II),Zn(II),Ni(II), Co(II), Cd(II) (Scheme 6).The basicity and denticity confirmed by the various methods , the IR spectra <strong>of</strong> the Schiff base (Scheme 1)and other metal complexes (Scheme 2 ) reveals that the non-involvement <strong>of</strong> carboxylic atom in coordinationat <strong>pH</strong>=3-4. However, the coordination formed at <strong>pH</strong>=7 and <strong>pH</strong>=8 the carboxylic O atom involved in thecoordination (Schemes 3 to 6) by exhibiting the γ as (COO) and γ s (COO) stretches <strong>of</strong> carboxylate group in theranges: 1560-1650 cm -1 (i.e.,1600cm -1 ) and 1340-1430 cm -1 (i.e.,1400cm -1 ) respectively. The energydifference between γ as (COO) and γ s (COO) is more than 200 cm -1 indicates the monodentate nature <strong>of</strong> thecarboxylate moiety 12 .12J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13
Page 1 and 2: Nov.2011-Jan.2012, Vol.2.No.1, 6-13
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