The anion of 2,6-di(phenylimino)piperidine (DPhIP) has been found to suppor
t linear chains of three metal atoms. Three new compounds, [Cr-3(DPhIP)(4)C
l]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 cha
racterized by X-ray crystallography. Compound 1 has a linear chain of three
chromium atoms arranged in an unsymmetrical fashion, with two of them form
ing a quadruply bonded unit (Cr-Cr distance 1.932(2) Angstrom) and the thir
d 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 a
nother chloride ion is located in the interstices of the crystal. The trime
tal 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) Angs
trom) unit, with an axially coordinated acetonitrile molecule, form the tri
chromium chain. The Cr-III... C-II separation of 2.594(2) Angstrom in 3 is
too long to be considered a bonding interaction.