Structural, spectroscopic, and electrochemical properties of two mononuclear iron(III) complexes derived from a tetraiminodiphenolate ligand

Two iron(III) mononuclear complexes [Fe(LH2)(H2O)2](ClO4)3·3H2O (1) and [Fe(LH2)(H2O)Cl](ClO4)2·2H2O (2) have been prepared using [Pb(LH2)](ClO4)2 and Fe(ClO4)3·6H2O and FeCl3·6H2O for 1 and 2, respectively. LH2 refers to the macrocyclic Schiff base ligand derived from the condensation of 1,3-diaminopropane and 4-methyl-2,6-diformyl phenol. Complex 1 crystallizes in the space group Orthorhombic Pnma. Complex 1 shows extensive intra- and intermolecular hydrogen bonding involving the iron coordinated water molecules, perchlorate oxygens and the water of crystallization. Seven symmetry-related intermolecular O–H⋯O bonds in 1 form a remarkable two dimensional network of water channels. Complex 2 crystallized in Monoclinic P21/c space group, with two [Fe(LH2)(H2O)Cl](ClO4)2 units forming a dimeric structure in the unit cell. Iron coordinated chloride, water of crystallization and perchlorate oxygen atoms display a strong network of hydrogen bonds responsible for holding the two mononuclear units together. Electrochemical experiments revealed a facile reduction of 1 in 10:1 acetonitrile–water with E1/2 = 140 mV while addition of 8-fold excess of tetramethylammonium chloride afforded [Fe(LH2)Cl2]+ which got reduced at E1/2 = −80 mV.