Linear trichromium complexes with direct Cr to Cr contacts. 1. Compounds with Cr-3(dipyridylamide)(4)(2+) cores

The preparation and structures of seven compounds that contain the Cr-3(dpa )(4)(2+) core (dpa = the anion di(2-pyridyl)amide) are reported. The magnet ic properties of several have been measured, in each case there are anionic ligands at each end of the Cr-3(6+) chain, sometimes identical (2Cl(-), 2C CPh(-)), sometimes different (Cl-, BF4-; Cl-, PF6-). Several of these compo unds have a symmetrical arrangement of the three Cr atoms, with the two Cr- Cr distances equal at ca. 2.36 Angstrom, while others have an unsymmetrical arrangement. In the most extreme case the two Cr-Cr distances are 2.00 and 2.64 Angstrom. The electronic structures and the remarkable flexibility of the Cr-3 arrangement are discussed.