Synthesis, crystal structure and properties of di-μ2-alkoxo bridged binuclear manganese(III) Schiff base complexes

Abstract

Preparation and isolation of the dimeric manganese(III) complex, [Mn2(Salpa)2(H2O)2Cl2] · 2DMF, (1), was accomplished by air oxidation of a solution containing MnCl2 · 4H2O, Et3N and H2Salpa** in DMF. Complex (2), [Mn2(Salpa)2(H2O)2(N3)2] · 2EtOH was obtained by reacting (1) or [Mn2(Salpa)2(AcO)2], (3), with NaN3 in EtOH. The crystal structure of (1) was determined by X-ray crystallography. It consists of discrete six-coordinate dimeric manganese molecules with unsupported alkoxido bridges, a rare example of a chloride- and water-containing manganese model complex for the oxygen-evolution center of photosystem II. The Mn–O and Mn–N distances are in good agreement with those found for other manganese(III) Schiff base complexes. The Mn–Cl and Mn–O(water) distances of 2.5577(11) and 2.323(3) A, respectively are due to Jahn-Teller distortion at the d4 metal center. The Mn ⋯ Mn distance is 3.0077(12) A. In the crystal, the distance between the H2O molecule and the O atom of DMF of 2.692(5) A suggests hydrogen binding interactions. A t.g. study of (1) confirmed that the complex contains DMF molecules. Magnetic measurements on (1) and (2) reveal the presence of antiferromagnetic spin-exchange interactions between the manganese(III) ions.