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

Abstract

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[Cu 2Br 4] ( 1), while the reaction of [Cu(CH 3CN) 4]PF 6 with L in THF yielded the new Cu(I) compound CuL(THF)(CH 3CN)PF 6 ( 2). Derivative 2 further reacted with halogenated solvents to yield halogeno-Cu(II) salts, [CuClL]PF 6 ( 3) using CHCl 3 and [CuBrL]Br 3 ( 4) using CHBr 3. 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 [Cu IIBrL] + cations are bridged by a [Cu I 2Br 4] 2− anion with a rather strong Cu II⋯Br (2.689(2) Å) secondary interaction. These secondary interactions (Cu II cation⋯FPF 5 or Br anion) are weaker in 3 and 4. The electrochemical properties of compounds 1– 4 are discussed, too.