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.Table 2: Nature <strong>of</strong> Coordination in complex compounds.Scheme <strong>pH</strong> Complex types Nature<strong>of</strong>complex1 3-4 [M(LH) 2 ] Monomeric 2502 “ [M(LH) 2 (H 2 O) 2 ] Monomeric 1403 8-9 [CuL] 2 Dimeric 844 “ [ML(EtOH)] Dimeric 2505 10-11 [ML(EtOH)] 2 Dimeric 85Stable uptotempareture inoCThe IR spectra <strong>of</strong> the Schiff base ligand (Scheme 1) and its complex compounds were recorded in KBrpellets. The ligand LH 2 (Scheme 1) exhibits intra molecular H- bonded (carboxylic COOH and phenolic OHgroup) stretches at 2900cm -1 , intermolecular H- bonded (phenolic OH group) stretches at 2700cm -1 , γ(C=O)(carboxylic) stretches at 1690 cm -1 , γ(C=O) (cumarin) stretches at 1680 cm -1 and γ(C-O) (phenolic) stretchesat 1570cm -1 .The appearance <strong>of</strong> γ(C=O) (carboxylic) stretches at the same energy in the ligand and its coordinationcompounds formed at <strong>pH</strong> 3-4 suggests the non-involvement <strong>of</strong> carboxylic O atom(s) in coordination. Thecoordination compounds formed at <strong>pH</strong>=7 and <strong>pH</strong>=8 exhibit the γ as (COO) and γ s (COO) stretches <strong>of</strong> thecarboxylates group in the range 1560-1650 cm -1 (i.e.,1600cm-1) and 1340-1430 cm -1 (i.e.,1400cm-1)respectively. The energy difference between γ as (COO) and γ s (COO) is more than 200cm -1 which indicatesthe monodentate nature <strong>of</strong> carboxalate moiety 12 .OOHCNOOH 3 CCOOHMHOOCCH 3OONCHHCONCOOHH 3 CO H 2 OMOH 2CHHOOC3ONOCHO(Scheme 2)[M (LH) 2 ]: M= Cu (II), Zn (II), Cd (II).All are ON-donor at <strong>pH</strong>= 3-4.O(Scheme3)[M (LH) 2 (H 2 O) 2 ]: M= Co (II), Ni (II).Both are ON-donor at <strong>pH</strong>=3-4.9J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13
<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.HCNOOOC OOCuCuH 3 COCH 3 O CO(Scheme 4)[CuL] 2: OON-donor at <strong>pH</strong>=7.OONCHOC OHC OMNOO CH 3O(Scheme 5)[ML (EtOH) ]: M= Zn (II), Cd (II).Both are OON-donor at <strong>pH</strong>= 7.HEtAll the coordination compounds, exhibits a medium intensity and broad band at 3350 cm -1 indicatingpresence <strong>of</strong> OH group which may be due to coordinated water molecules or unionized COOH group. Theγ(C=O) (coumarin) stretch <strong>of</strong> the ligand occurring at 1690cm -1 . It does not undergo a considerable change inthe coordination compounds. The complex compounds (Scheme 2), (Scheme 3) formed at <strong>pH</strong>= 3-4 andcomplex compound (Scheme 4), (Scheme 5) formed at <strong>pH</strong>= 7 suggesting the non-involvement <strong>of</strong> (C=O)carbonyl oxygen atom <strong>of</strong> coumarin towards coordination in these complex compounds. But, in the complexcompound (Scheme 6) formed at <strong>pH</strong>= 8 suggesting the coordination <strong>of</strong> cumarin carbonyl oxygen atom to themetal ions in the coordination compound.OOHCNOCOEtOMHOCH 3MNOOCH 3 COEtHOCHOO(Sheme 6)[ML (EtOH) ] 2 : M= Cu (II), Zn (II), Ni (II), Co (II), Cd (II).All are OONO-donor at <strong>pH</strong>=8.10J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13
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