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

Preparation and isolation of the dimeric manganese(III) complex, [Mn-2(Salpa)(2)(H2O)(2)Cl-2] . 2DMF, (1), was accomplished by air oxidation of a solution containing MnCl2 . 4H(2)O, Et3N and H(2)Salpa** in DMF. Complex (2), [Mn-2(Salpa)(2)(H2O)(2)(N-3)(2)] . 2EtOH was obtained by reacting (1) or [Mn-2(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) Angstrom, respectively are due to Jahn-Teller distortion at the d(4) metal center. The Mn ... Mn distance is 3.0077(12) Angstrom. In the crystal, the distance between the H2O molecule and the O atom of DMF of 2.692(5) Angstrom 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.