AbstractTwo mixed‐ligand copper(II) complexes, [Cu(L1)(H2O)]·H2O (1) and [Cu(L1)(bipy)]·2H2O (2), containing the title N‐substituted iminodiacetate (IDA) derivative (L12–) as primary ligand with and without 2,2′‐bipyridine as auxiliary ligand, have been synthesised. Both have been fully characterised by means of IR spectroscopy, mass spectrometry, elemental analysis and conductimetry, as well as X‐ray crystallography. The dominant structural feature of these complexes is the presence of a flexible coordinating arm on the IDA skeleton which controls the conformation of the resulting complexes. The CuII centre in complex 1 exhibits a distorted square‐pyramidal [4+1] coordination in which the apical site is unexpectedly occupied by the N(2) atom of the coordinating arm instead of a water molecule. The IDA skeleton adopts a tridentate mer‐O2N arrangement in 1, whereas in 2 it exhibits an unusual fac‐O2N(apical) configuration, which is observed for the first time for a tridentate IDA unit bearing a flexible arm containing a coordinating atom. The o‐nitro aromatic group in the flexible arm gives rise to different inter‐ and/or intramolecular stacking interactions. Classic intermolecular “nitrophenyl‐nitrophenyl” π‐π stacking interactions are observed between pairs of complex molecules in crystals of 1, whereas intramolecular “nitrophenyl‐pyridyl” interactions alternate with unprecedented interligand π‐π “nitrophenyl–metal chelate ring” interactions in crystals of 2.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)