Complex formation of 2,6-bis-(2 '-hydroxyphenyl)pyridine with Al-III, Fe-III and Cu-II

Complex formation of 2,6-bis(2'-hydroxyphenyl)pyridine (H2Li) with Fe3+ and CU2+ was investigated in a H2O/DMSO medium (mole fraction X-DMSO = 0.2) by potentiometric and spectrophotometric methods. The pK(a) values of [H3Li](+) are 2.25, 10.51 and 14.0 (25degreesC, 0.1 M KCl). The formation constants of [Fe-III (L-i)](+) and [Cu-II(L-i)] (25degreesC, 0.1 M KCl) are log beta(1) = 21.5 for Fe3+ and log beta(1) = 18.5 for Cu2+. The crystal structures of [Al(L-i)(2)Na(EtOH)(3)], [Fe(L-i)(2)Na(EtOH)(3)], and [Cu(L-i)(py)](2) were investigated by single-crystal X-ray diffraction analyses. The Fe-III and the Al-lII. compound are isotypic and crystallize in the monoclinic space group P2(1)/n. Al-compound (215 K): a = 12.599(3) Angstrom, b = 16.653(3) Angstrom, c = 17.525(4) Angstrom, beta = 100.27(3)degrees, Z = 4 for C(40)H(40)AlN2(N)aO(7); Fe-compound (293 K): a = 12.753(3) Angstrom, b 16.715(3) Angstrom, c = 17,493(3) Angstrom, beta = 99.68(3)degrees, Z = 4 for C40H40FeN2NaO7. Both compounds contain a homoleptic, anionic bis-complex [M(L-i)(2)](-) of approximate D-2 symmetry The Cu compound crystallized as an uncharged, dinuclear and centrosymmetric [Cu(L-i)(py)](2) Complex in the monoclinic space group P-2/n with (293 K) a = 13.386(3) Angstrom, b = 9.368(2) Angstrom, c = 14.656(3) Angstrom, beta = 100.65(3)degrees, Z = 2 for C44H32Cu2N4O4. The structural properties and in particular the possible influence of the ligand geometry on the stability of the metal complexes is discussed.