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, [Cr-3(DPhIP)(4)Cl]Cl . 1.5CH(2)Cl(2). 0.5H(2)O (1.1.5CH(2)Cl(2). 0.5H(2)O), [Cr-3(DPhIP)(4)(CH3CN)]-(PF6)(2). H2O . 4CH(3)CN (2 . H2O . 4CH(3)CN), and [Cr-3(DPhIP)(4)(F)(CH3CN)](BF4)(2). 5CH(3)CN (3 . 5CH(3)CN), 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) Angstrom) and the third being a non-metal-metal-bound 5-coordinate unit (Cr Cr distance 2.659(2) Angstrom). 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 Cr-III unit, FCrN4, and a Cr-Cr quadruply bonded (Cr-Cr distance 1.968(2) Angstrom) unit, with an axially coordinated acetonitrile molecule, form the trichromium chain. The Cr-III... C-II separation of 2.594(2) Angstrom in 3 is too long to be considered a bonding interaction.