Unexpected behaviour of copper(I) towards a tridentate Schiff base: synthesis, structure and properties of new Cu(I)Cu(II) and Cu(II) complexes

The reaction of CuBr with 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine L afforded a new Cu(I)Cu(II) derivative [CuBrL]2[Cu2Br4] (1), while the reaction of [Cu(CH3CN)4]PF6 with L in THF yielded the new Cu(I) compound CuL(THF)(CH3CN)PF6 (2). Derivative 2 further reacted with halogenated solvents to yield halogeno-Cu(II) salts, [CuClL]PF6 (3) using CHCl3 and [CuBrL]Br3 (4) using CHBr3. Compounds 1, 3 and 4 have been fully characterised by X-ray crystallography; they contain essentially similar [CuXL]+ cations with a square planar copper(II) co-ordination. However, the structure of compound 1 must be viewed as built of tetranuclear units since two [CuIIBrL]+ cations are bridged by a [CuI 2Br4]2− anion with a rather strong CuII⋯Br (2.689(2) Å) secondary interaction. These secondary interactions (CuII cation⋯FPF5 or Br anion) are weaker in 3 and 4. The electrochemical properties of compounds 1–4 are discussed, too.