Synthesis, structure and characterization of the new complex [L-1(H2O)-Fe(mu-O)Fe(OH2)L-1](4+) [L-1 = N,N '-bis(1-methylimidazolyl-2-methyl)-N,N '-bismethyl-1,2-ethanediamine] - Formation of the (mu-O)(mu-H3O2) complex upon deprotonation

The compound [L-1(H2O)Fe(mu -O)Fe(OH2)L-1](ClO4)(4).2H(2)O [1(ClO4)(4).2H(2 )O] [L-1 = N,N'-bis(1-methylimidazolyl-2-methyl)-N,N'-bismethyl-1,2-ethaned iamine] was synthesized. It is characterized by a linear Fe-(mu -O)-Fe moti f with an Fe Fe distance of 3.584(1) Angstrom. The measurement of the magne tic susceptibility as a function of temperature indicated a strong antiferr omagnetic coupling between the two high-spin Fe-III ions (J = -223 cm(-1) w ith H = -J.S-1.S-2). In the solid state, the symmetric stretching vibration mode of the Fe-(mu -O)-Fe core unit was detected at 347 cm(-1), in agree-m ent with a straight Fe-(mu -O)-Fe angle. Upon addition of up to one equival ent of triethylamine to an acetonitrile solution of 1, conversion to the [L -1(H2O)Fe(mu -O)Fe(OH)L-1](3+) complex 2 was observed. This last species wa s isolated as a perchlorate salt [2(ClO4)(3).H2O]. Susceptibility measureme nts and Raman and UV/Vis investigations on the powder and/or an acetonitril e solution confirmed the presence of an intramolecular hydrogen bond betwee n the coordinated water molecule and the hydroxide group leading to a bent [Fe(mu -O)Fe](4+) core structure.