Molecular Design and Characterization of Multidentate Ligand

点击翻译按钮获取中文摘要

A multidentate ligand, 2-mercaptobenzaldehyde 5-nitro-2-pyridylhydrazone (MBNPH), derived from benzaldehyde-2-pyridylhydrazone(BPH) was designed and synthesized. Its properties, reactivities with metal ions and extractabilities of the complexes have been investigated. It has been found that (1) the introduction of an electron - withdrawing group to the 5-position of the pyridine ring brings about increases in molar absorptivities (ε) of the metal complexes, (2) the introduction of a mercapto group to the 2-position of the phenyl ring of BHP brings about increases in selectivity for Cu (II), especially, and (3) the introduction of both nitro and mercapto groups to BPH lowers the values of the acid dissociation constants (pKa), pKaィイD21ィエD2=7.26 (SH group) and pKaィイD22ィエD2=10.80 (NH group). In benzene, Cu (II) reacts with MBNPH to form a 1:2 yellow complex (λィイD2maxィエD2 = 483nm, ε= 34,000 MィイD1-1ィエD1 cmィイD1-1ィエD1) and an adduct complex (λィイD2maxィエD2 = 474 nm, ε= 54,000 MィイD1-1ィエD1 cmィイD1-1ィエD1) by the synergistic effect of pyridine base when it is present. The ratio of three components in the adduct complex is estimated to be Cu (II) : MBNH : pyridine = 1 : 2 : 2. Furthermore, the equilibrium constants of the Cu (II) complex were determined ; the extraction constant (log KィイD2exィエD2), the distribution constant (log KィイD2DCィエD2) and the stability constants (logβィイD21ィエD2, logβィイD22ィエD2) were found to be 2.19, 2.10, 5.79 and 17.6, respectively.