The complex [L(H 2 O)Fe(μ-O)Fe(OH)L](ClO 4 ) 3 ·H 2 O, where L = N, N ‘-dimethyl- N, N ‘-bis(2-pyridylmethyl)ethane-1,2-diamine, was synthesized. It crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with a = 13.283(5) Å, b = 16.050(9) Å, c = 20.050(9) Å, V = 4476(6) Å 3, and Z = 4. It presents the hydrogen-bonded [(H 2 O)Fe(μ-O)Fe(OH)] 3+ core unit characterized by an Fe−O−Fe angle of 137.5(2)° and an Fe−Fe distance of 3.396(1) Å. The measurement of the magnetic susceptibility as a function of the temperature indicated an antiferromagnetic coupling between the two high-spin Fe(III) ions J = −184 cm - 1 ( H = − J S 1 · S 2 ). In the solid state the symmetric stretching vibration was observed at 438 cm - 1 . Upon dissolution in dry acetonitrile, this vibration was no longer detected and an intense band was observed at 600 cm - 1 . This frequency can be correlated with an Fe−O−Fe angle of 111°. This value suggests that the species which exists in these conditions is the protonated diamond core [Fe(μ-O)(μ-OH)Fe] 3+, analogous to that identified by Zang et al. ( J. Am. Chem. Soc. 1994, 116, 3653) and by Hazell et al. ( J. Chem. Soc., Dalton Trans. 1995, 707). Upon addition of water, the original aquated species is observed in equilibrium with the protonated diamond unit. By analysis of the changes in UV−vis spectra as a function of the amount of water added, the equilibrium constant of the formation of the aquated species was found to be 5.4 M - 1 .
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Poussereau et al. (1998) studied this question.
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