Indian Journal of Chemistry Vol. 37A, July 1998, pp. 639 - 643 X-ray structural and spectroscopic studies of a mononuclear copper(II) complex with axial and equatorial phenolate ligation Prasun Bandyopadhyay, Pradyut Ghosh & Parimal K. Bharadwaj* Department of Chemistry, Indian Institute of Technology Kanpur, 208 016, India Received re December 1997; revised 3 April 1998 A tridentate Schiff base obtained by condensing salicylaldehyde with 2-dimethylamino-ethylamine in 1:1 molar ratio readily forms a bis-complex with cupric perchlorate hexahydrate in methanol in the presence of KOH. The complex crystallizes from methanol in the monoclinic space group P2l/c with a = 11.221 (3), b = 19.462(2), c = 13.062(3), ~ = 109.36(4)°, Z= 4, R = 0.050, R' = 0.045 and goodness-of-fit = 2.551. We have been involved' in the synthesis and characterization of transition metal complexes with phenolate ligation for their bioinorganic relevances". For this, a tridentate chelating ligand formed by Schiff base condensation of 2,2-dimethyl- ethylenediamine and salicylaldehyde 'had been characterized. In our earlier reportl, this Schiff base was shown to act as a bidentate ligand through the imine nitrogen and phenolate oxygen to Mn(lII) where the tertiary nitrogen atom got protonated. In the present note, we are reporting that the ligand can act as a tridentate one when a strong base is added. When the ligand is allowed to react with cupric perchlorate and potassium hydroxide in 2: 1:1 molar ratio, a bis-complex is formed wherein one ligand is tridentate and the other bidentate. Here, we present the X-ray structure of the complex alongwith its spectral characteristics. Experimental Reagent grade salicylaldehyde, 2-dimethyl- aminoethylamine and cupric perchlorate hexahydrate (Fluka) were used as received. All solvents were purified prior to use. The physical measurements were carried out as described earlier". Synthesis of ligand L The ligand L (structure I ) was prepared by first stirring at 298 K a methanolic solution ( 10 ern') of salicylaldehyde (1 mmol) with 2-dimethyl- aminoethylamine (1 mmol). The color of the solution turned orange. The clear solution was then allowed to reflux for I h. The entire operation was carried out under a dinitrogen blanket. Methanol was removed completely to obtain a highly viscous orange liquid. IH-NMR (80 MHz, CDCI 3 ) : 02.1 ( s, 6H), 2.7 (t, 2H), 3.6 (t, 2H), 7.1 (m, 4H), 8.2 (s,IH). Synthesis of the CurII) complex, I The ligand L ( 0.385g; 2 mmol ) dissolved in methanol ( 20 mL) was stirred with KOH ( 0.056g; 1 mrnol ) for 30 min at 293 K. Solid cupric perchlorate hexahydrate ( 0.370 g; 1 mmol ) was added to this solution which turned dark green immediately. The solution was filtered and the filtrate upon slow evaporation at 293 K, yielded the compound as a dihydrate in the form of dark green parallelopiped crystals. Yield 65% (based on the cupric salt). Anal. Found C, 45.1; H, 6.05; N, 9.8 Calcd for C22H3sNpsCICu: C, 45.4; H, 6.06; N, 9.6. The type of complex formed is found to be critically dependent upon the reaction conditions. When salicylaldehyde, L and the cupric salt are allowed to react in l: 1: 1 molar ratio with 3 equivalents of KOH in hot methanol, the complex isolatedl was a neutral pentacoordinated species with the formula, [Cu(sal)(L)] ( sal = deprotonated . salicylaldehyde ). The same species is also formed when ligand L and the Cutllj-salt is allowed to react with 6 equivalents of KOH in hot methanol for Z h.