Potentiometric titration study of two novel polydenate ligands and investigations of their complexes Dengke Cao, Hua-Kuan Lin, Zhi-Fen Zhou, Shou-Rong Zhu, Xun-Cheng Su, and Yun-Ti Chen Abstract: Two novel linear polyamine ligands, N,N ′-bis-(2-(N ′′-2-hydroxyl-5-bromobenzyl)aminoethyl) malondiamide (L 1 ) and N,N ′-bis-(3-(N ′′-2-hydroxyl-5-bromobenzyl)aminopropyl) malondiamide (L 2 ), have been synthesized and fully characterized by elemental analysis ( 1 H NMR and IR spectroscopy) (Fig. 1). The binding ability of ligands L 1 and L 2 to metal ions such as Cu(II), Zn(II), Co(II), Mn(II), Mg(II), and Ca(II) has been investigated by the potentiometric method in 1,4-dioxane–water (v/v = 15:100) and KNO 3 (0.1 mol dm –3 ) at 25.0°C. In view of the linear structures of L 1 and L 2 , binuclear metal complexes can be formed in solution by controlling Cu(II)-5-substituted o-phenanthroline (Rphen, R = CH 3 , H, Cl, NO 2 ):L to a 2:1 molar ratio, whereas the mononuclear metal complexes form at molar ratio M(II):L of 1:1, where M(II) is Cu(II), Zn(II), Co(II), Mn(II), Mg(II), and Ca(II). The stability constants of metal com- plexes have been determined and further discussed. In addition, two manganic complexes have been synthesized and IR and electronic spectra showed their coordination nature. Key words: linear polyamine ligand, 5-substituted o-phenanthroline, mononuclear and binuclear metal complex, stability, spectrum. Résumé : On a réalisé la synthèse de deux nouveaux ligands polyamines linéaires, N,N ′-bis-(2-N ′′-2-hydroxy-5- bromobenzyl)aminoéthyl)malondiamide (L 1 ) et N,N ′-bis-(3-N ′′-2-hydroxy-5-bromobenzyl)aminopropyl)malondiamide (L 2 ) et on en a fait la caractérisation complète par analyses élémentaires, RMN du 1 H et par IR. Faisant appel à des mesures potentiométriques et opérant dans un mélange 1,4-dioxane–eau, à 25°C, dans des solutions contenant 0,1 mol dm –3 de KNO 3 , on a étudié les possibilités de fixation des ligands L 1 et L 2 aux ions métalliques Cu(II), Zn(II), Co(II), Mn(II), Mg(II) et Ca(II). Compte tenu des structures linéaires des ligands L 1 et L 2 , il existe une possibilité de former des complexes métalliques binucléaires en solution si on contrôle le rapport molaire entre le sel de Cu(II) de l’o-phénanthroline substituée en position 5 (Rphen; R = CH 3 , H, Cl, NO 2 )/L (2:1) alors qu’il se forme des complexes métalliques mononucléaires lorsque le rapport molaire (M(II):L) est de 1:1 (M(II) = Cu(II), Zn(II), Co(II), Mn(II), Mg(II) et Ca(II)). On a déterminé et on discute des constantes de stabilité des complexes métalliques. De plus, on a synthétisé deux complexes manganiques et, sur la base de leurs spectres IR et électroniques, on en a déduit la nature de leur coordination. Mots clés : ligand polyamine linéaire, o-phénanthroline substituée en position 5, complexes métalliques mononucléaires et binucléaires, stabilité, spectre. [Traduit par la Rédaction] Cao et al. 460 Introduction In recent years, the research of polynuclear metal com- plexes has increased dramatically due to the introduction of appropriate ligands such as linear polyamine that is able to form mononuclear or binuclear metal complexes by control- ling the reaction conditions. Dominguez-Vera et al. (1) re- ported the ligand N,N′-bis(3-aminopropyl) oxamidate (oxpn), the mononuclear [Cu(cis-oxpn)], and the binuclear [Cu 2 (trans-oxpn)] 2+ species were prepared by controlling pH and the Cu(II):oxpn molar ratio. Additionally, the synthesis of manganic complexes has been a subject of considerable importance, because manganic ions serves various important roles in biological systems (2), and to date, many metal en- zymes containing manganic ions have been found (3). In this paper, we report an attempt at preparing some novel ligands and metal complexes. Two novel linear ligands shown in Fig. 1, N,N ′-bis-(2-(N ′′-2-hydroxyl-5-bromo- benzyl)aminoethyl) malondiamide (L 1 ) and N,N ′-bis-(3- (N ′′-2-hydroxyl-5-bromobenzyl)aminopropyl) malondiamide (L 2 ) have been synthesized and characterized. The potentiometric method has been used to investigate the for- mation of mononuclear and binuclear complexes in solution. The MnL 1 and MnL 2 complexes have been prepared and characterized by elemental analyses (IR and UV spectros- copy). Can. J. Chem. 79: 455–460 (2001) © 2001 NRC Canada 455 DOI: 10.1139/cjc-79-4-455 Received June 5, 2000. Published on the NRC Research Press Web site on May 3, 2001. D. Cao, H.-K. Lin 1 , Z.-F. Zhou, S.-R. Zhu, X.-C. Su, and Y.-T. Chen. Department of Chemistry, Nankai University, Tianjin 300071, P. R. China. 1 Corresponding author (fax: 0086-022-23502458; e-mail: hklin@nankai.edu.cn).