Complex Formation of 2, 6‐Bis‐(2′‐hydroxyphenyl)pyridine with Al^III, Fe^III and Cu^II

Abstract

Abstract Complex formation of 2, 6‐bis(2′‐hydroxyphenyl)pyridine (H 2 L i ) with Fe 3+ and Cu 2+ was investigated in a H 2 O/DMSO medium (mole fraction x DMSO = 0.2) by potentiometric and spectrophotometric methods. The p K a values of [H 3 L i ] + are 2.25, 10.51 and 14.0 (25 °C, 0.1 M KCl). The formation constants of [Fe III (L i )] + and [Cu II (L i )] (25 °C, 0.1 M KCl) are log β 1 = 21.5 for Fe 3+ and log β 1 = 18.5 for Cu 2+ . 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 III compound are isotypic and crystallize in the monoclinic space group P 2 1 /n. Al‐compound (215 K): a = 12.599(3) Å, b = 16.653(3) Å, c = 17.525(4) Å, β = 100.27(3)°, Z = 4 for C 40 H 40 AlN 2 NaO 7 ; Fe‐compound (293 K): a = 12.753(3) Å, b = 16.715(3) Å, c = 17.493(3) Å, β = 99.68(3)°, Z = 4 for C 40 H 40 FeN 2 NaO 7 . 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 1 /n with (293 K) a = 13.386(3) Å, b = 9.368(2) Å, c = 14.656(3) Å, β = 100.65(3)°, Z = 2 for C 44 H 32 Cu 2 N 4 O 4 . The structural properties and in particular the possible influence of the ligand geometry on the stability of the metal complexes is discussed.