Linear Trichromium Complexes with the Anion of 2,6-Di(phenylimino)piperidine

The anion of 2,6-di(phenylimino)piperidine (DPhIP) has been found to support linear chains of three metal atoms.
Three new compounds, [Cr3(DPhIP)4Cl]Cl·1.5CH2Cl2·0.5H2O (1·1.5CH2Cl2·0.5H2O), [Cr3(DPhIP)4(CH3CN)](PF6)2·H2O·4CH3CN (2·H2O·4CH3CN), and [Cr3(DPhIP)4(F)(CH3CN)](BF4)2·5CH3CN (3·5CH3CN), have been
synthesized and characterized by X-ray crystallography. Compound 1 has a linear chain of three chromium atoms
arranged in an unsymmetrical fashion, with two of them forming a quadruply bonded unit (Cr−Cr distance 1.932(2) Å) and the third being a non-metal−metal-bound 5-coordinate unit (Cr···Cr distance 2.659(2) Å). The fifth
coordination site is occupied by a chloride ion, and another chloride ion is located in the interstices of the crystal.
The trimetal unit in compound 2 is structurally similar to that in compound 1 except that the axial ligand in 2 is
a CH3CN molecule. Compound 3 is an oxidation product prepared by reaction of 1 with AgBF4. Here, a square
pyramidal CrIII unit, FCrN4, and a Cr−Cr quadruply bonded (Cr−Cr distance 1.968(2) Å) unit, with an axially
coordinated acetonitrile molecule, form the trichromium chain. The CrIII···CrII separation of 2.594(2) Å in 3 is
too long to be considered a bonding interaction.