Hydroxo-bridged dicopper(II) complexes of five-co-ordinate acyclic diazadiamine NNNNO-bonded ligands have been synthesised. These compounds are obtained in high yield by reacting the sodium salt of 2-hydroxy-5-methylbenzene-1,3-dicarbaldehyde, copper perchlorate, and the diamines 1,3-diaminopropane, 1,2-diaminoethane, and 1,2-diaminopropane, respectively in aqueous medium under high dilution. Similar reactions with 1,3-diacetyl- or 1,3-dibenzoyl-2-hydroxy-5-methylbenzene in water–methanol afford similar acyclic complexes in lower yield along with their corresponding NNNNOO-bonded macrocyclic complexes. The hydroxy bridging group in the acyclic complexes can be replaced by other bridges like methoxide, p-nitrophenolate, pyrazolyl, and by reaction with 2-hydroxy-5-methylacetophenone. Variously 6,12-substituted dicopper(II) complexes of the macrocycle 7,11; 19,23-dimetheno-9,21-dimethyl[1,5,13,17]tetra-azacyclotetracosa-5,7,9,12,17,19,21,24-octaene-25,26-diol (H₂L⁵) can be obtained by reacting the above unsubstituted acyclic complex with 1,3-diacetyl- or 1,3-dibenzoyl-2-hydroxy-5-methylbenzene. The acyclic tetra-amine hydroxo-bridged dicopper(II) complex shows similar reactivity to the diazadiamine derivative and the corresponding macrocyclic complexes containing both aza and amine linkages have been synthesised. All these compounds have been characterised from their magnetic moments, i.r., and electronic spectra. The electrochemical studies of the acyclic diazadiamine and tetra-amine hydroxo-bridged dicopper(II) complexes have revealed irreversible reductions followed by decomposition of the reduced species. One of the diazadiamino macrocyclic complexes was found to undergo quasi-reversible one-electron reductions at two different potentials. The mechanism of formation of the unsubstituted macrocyclic complex [Cu₂L⁵][ClO₄]₂·2H₂O by reacting the corresponding hydroxo-bridged acyclic complex with 2-hydroxy-5-methylbenzene-1,3-dicarbaldehyde has been investigated.