Complex Formation of 2, 6‐Bis‐(2′‐hydroxyphenyl)pyridine with AlIII, FeIII and CuII

Abstract

AbstractComplex formation of 2, 6‐bis(2′‐hydroxyphenyl)pyridine (H2Li) with Fe3+ and Cu2+ was investigated in a H2O/DMSO medium (mole fraction xDMSO = 0.2) by potentiometric and spectrophotometric methods. The pKa values of [H3Li]+ are 2.25, 10.51 and 14.0 (25 °C, 0.1 M KCl). The formation constants of [FeIII(Li)]+ and [CuII(Li)] (25 °C, 0.1 M KCl) are log β1 = 21.5 for Fe3+ and log β1 = 18.5 for Cu2+. The crystal structures of [Al(Li)2Na(EtOH)3], [Fe(Li)2Na(EtOH)3], and [Cu(Li)(py)]2 were investigated by single‐crystal X‐ray diffraction analyses. The FeIII and the AlIII compound are isotypic and crystallize in the monoclinic space group P21/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 C40H40AlN2NaO7; 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 C40H40FeN2NaO7. Both compounds contain a homoleptic, anionic bis‐complex [M(Li)2]‐ of approximate D2 symmetry. The Cu compound crystallized as an uncharged, dinuclear and centrosymmetric [Cu(Li)(py)]2 complex in the monoclinic space group P21/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 C44H32Cu2N4O4. The structural properties and in particular the possible influence of the ligand geometry on the stability of the metal complexes is discussed.