Modeling of end-on (mu-peroxo)dicopper(II) complexes

A force field for (mu-peroxo)dicopper(II) complexes was developed, based on a well-established parameter set for copper(II) complexes, the structural and spectroscopic data of a (mu-peroxo)dicopper(II) complex with tris(2-pyridylmethylamine) donors and a series of (mu-peroxo)dicobalt(III) compounds. This force field is shown to well reproduce the structural properties of the available structures of (mu-peroxo)dicopper(II) and (mu-peroxo)dicobalt(II) complexes, and it was used to compute a series of (mu-peroxo)dicopper(II) compounds with two tris(2-pyridylmethylamin) units linked by different organic spacers at a 5-pyridyl position at each tetradentate moiety. The computed structures and strain energies indicate that (i) in the compound with an ethyl spacer group the ligand induces a considerable strain and distortion in the mu-peroxo product, and these effects compensate the favorable entropy effects due to the ligand preorganization, in agreement with the published experimental results; (ii) the (mu-peroxo)dicopper(II) compound with the propyl-linked ligand is relatively unstrained and structurally very similar to the parent compound; and (iii) larger spacer groups lead to rather distorted (mu-peroxo)dicopper(II) products.