ON THE STRUCTURE OF IOF5

Ab initio and density functional theory calculations were carried out for IOF5 and, together with experimental and ab initio data for isoelectronic TeOF5-, suggest that the axial and the equatorial I-F bonds of IOF5 are of comparable lengths and that the O-I-F(eq) bond angle is close to 97.2-degrees. Using these two constraints and the previously published (IOF5)-O-16 and (IOF5)-O-18 microwave data, the structure of IOF5 was determined as rI-O = 1.725 angstrom, rI-F(ax) = rI-F(eq) = 1.826 angstrom, and angle OIF(eq) = 97.2-degrees. The finding that the axial I-F bond length is comparable to the equatorial one eliminates the need for invoking for IOF5 either a ''secondary relaxation effect'' which lengthens the fluorine bond in the trans position to a doubly bonded oxygen ligand or a ''trans effect'' which shortens this bond.