The mononuclear copper(II) complexes, [CuL1](ClO4) (1), and [CuL2](ClO4) (2) with unsymmetrical quadridentate Schiff base ligands derived from the 1:1:1 condensation of 2,4-pentanedione, pyridine-2-carboxaldehyde and 1,2-ethanediamine (HL1) or 1,3-propanediamine (HL2) have been prepared and characterised. Complex 2 undergoes Cu(II)/H+ catalysed rearrangement to [CuL3](ClO4)2 (3) where L3 is a symmetrical tetradentate Schiff base involving 1,3-propanediamine and pyridine-2-carboxaldehyde. Structures of all the three compounds have been verified by single crystal X-ray analysis. The geometry around Cu(II) is square-planar in I and 2 whereas that in 3 is distorted octahedral with two axially coordinated perchlorate ions. © 2003 Elsevier Science B.V. All rights reserved.