Interaction of copper(II) with N-substituted bis(2-pyridylmethyl)amine derivatives: New discrete and 1-D polymeric complex systems - The latter displaying ferromagnetic behaviour

Interaction of copper(II) with the N-substituted bis(2-pyridylmethyl)amine derivatives, (R)-N¹,N¹-bis(pyridine-2-ylmethyl)butane-1,2- diamine (L¹) and (R)-2-(bis(pyridin-2-ylmethyl)amino)butan-1-ol (L²), has led to isolation of optically active [Cu(L ¹)Cl]PF₆ (1) and [Cu(L²)Cl]ClO₄ (2), respectively. The X-ray structures of (1) and (2) show that the copper is bound to all four heteroatoms of the respective ligands as well as to a chlorine atom in a distorted square pyramidal arrangement in which the three nitrogens of L¹ or L² occupy three positions of each basal plane while the fourth position is occupied by the chloro ligand; apical sites in each case are filled by the amine donor from the NH₂-substituted butane arm in L¹ or the (protonated) alcohol oxygen of the 2-aminobutane-1-ol substituent in L². To a first approximation the coordination geometry in 2 is distorted square pyramidal; however, the remaining (axial) site on each copper centre is involved in a long contact (2.96 Å) with a bound chloro ligand from an adjacent complex which connects individual complex units in a zigzag 1-D polymeric chain, so that the coordination geometry could also be seen as pseudo-octahedral. A temperature-dependent magnetic study revealed the presence of ferromagnetic exchange coupling between copper centres in the chain reflecting the orthogonal structure between the chloro-bridged copper(II) ions; in contrast, and as expected, the discrete complex 1 is magnetically dilute.