Synthesis and crystal structure of the mer-Fe(ReO4)3(H2O)3 complex

Triaquatris(tetraoxorhenato(VII) iron(III) [Triaquatris(perrhenato) iron(III)] has been synthesized from iron(III) hydroxide and perrhenic acid. The new compound crystallizes triclinically in the space group P (1) over bar (No. 2) with two formula units per unit cell (a = 775.2, b = 819.5, c = 1156.3 pm, alpha = 86.80 degrees, beta = 83.76 degrees and gamma = 64.97 degrees). The structure contains meridional configurated mer-Fe(ReO4)(3)(H2O)(3) complexes, which are interconnected via hydrogen bonding. The mean bond lengths are d(Fe-O) = 197 pm to the ReO4 ligands and d(Fe-O) = 203 pm to the water molecules. The three crystallographically different ReO4 tetrahedra are characterized by one long Re-O bond to the ligator oxygen atom (d = 175 pm) and three short ones (166-170 pm). The thermal decomposition starts at 400 K with the loss of water. Above 600 K the compound decomposes in several steps into solid iron(III) oxide and evaporating rhenium oxides.