A number of N- and C-based diastereomeric copper(II) complexes of the pendant-arm macrocyclic hexaamines trans- and cis- 6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L ¹ and L ² ) have been isolated and characterised. The crystal structures of the complexes RRSS-[CuL ¹ (OH ₂ ) ₂ ][ClO ₄ ] ₂ , SSRR-[Cu(H ₂ L ¹ )(OClO ₃ ) ₂ ][ClO ₄ ] ₂ ·2H ₂ O, RSRS-[CuL ¹ (OClO ₃ )]ClO ₄ , RSRS-[CuL ² (OClO ₃ )]ClO ₄ and RRSS-[Cu(H ₂ L ² )(OClO ₃ ) ₂ ][ClO ₄ ] ₂ have been determined. Some unusual structural and spectroscopic variations are found across this series of diastereomers. The protonation constants of the pendant primary amines are dependent on the relative dispositions of the adjacent macrocyclic secondary amine H atoms, which is indicative of intramolecular hydrogen-bonding interactions.