A seven-coordinate manganese(II) complex formed with the single heptadentate ligand N,N,N '-tris(2-pyridylmethyl)-N '-(2-salicylideneethyl)ethane-1,2-diamine

The new disymmetric ligand N,N,N'-tris(2-pyridylmethyl)-N'-(2-salicylidenee thyl)ethane-1,2-diamine (LH) has been synthesized in the search of a novel type of manganese complex to mimic the active site of the water-oxidizing e nzyme in photosystem II. The complex [Mn(II)L]ClO4 has been obtained and ch aracterized by X-ray diffraction techniques. It crystallizes in the monocli nic space group Pn with the following unit cell parameters: a = 10.164(3), b = 10.122(4), c = 14.166(5) Angstrom, beta = 93.48(2)degrees and Z = 2. Th e manganese ion is heptacoordinated with the coordination being achieved by only one ligand; it is bonded to the oxygen atom of the phenolate group in an axial position, the imino and the three pyridine nitrogen atoms in an e quatorial position and the two amine atoms in a pseudo-axial position. The coordination polyhedron is best described as a distorted monocapped trigona l prism. This structure was compared with the seven-coordinated Mn(II) comp lexes deposited in the Cambridge Structured Database (CSD). The redox poten tial of the Mn(III)/Mn(II) couple was determined by cyclic voltammetry. (C) 1999 Elsevier Science S.A. All rights reserved.