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Synthesis, Properties, and Structures of Chromium(VI) and Chromium(V) Complexes with Heterocyclic Nitrogen Ligands



The reaction of CrO2Cl2 with 2, 2′-bipyridyl or 1, 10-phenanthroline (diimine) in CCl4 or anhydrous CH3CO2H solution, produces orange-brown diamagnetic [CrO2Cl2(diimine)]. The X-ray structure of [CrO2Cl2(2, 2′-bipy)] shows a six-coordinate central chromium(VI) atom with cis-dioxo groups trans to the diimine. In contrast, the diimines react with CrO3 in CH3CO2H / conc. aqueous HCl to form bright red paramagnetic CrV complexes, [CrOCl3(diimine)]. The X-ray structure of [CrOCl3(2, 2′-bipy)] shows a six-coordinate central chromium atom with mer-chlorines and the diimine trans to O/Cl. The addition of [2, 2-bipyH2]Cl2 to a solution of CrO3 in CH3CO2H saturated with HCl gas, produces the CrV anion [2, 2′-bipyH2][CrOCl4]Cl, which loses HCl on heating in vacuo to form [CrOCl3(2, 2′-bipy)]. IR, UV/Vis, and 1H NMR spectra (CrVI only) are reported for the new complexes. Attempts to extend these routes to oxygen donor ligands, including ethers and phosphine oxides, were unsuccessful. The diimine complexes are the first structurally autheticated adducts of chromium(VI) and (V) oxide-chlorides with neutral ligands.