The ring-chain tautomerism of 2-(3-tosyl-1,2,3,4-tetrahydroquinazolin-2-yl)quinolin-8-ol (H2Lring) has been exploited to produce mononuclear complexes or, alternatively, dinuclear complexes, as desired, by varying the stoichiometry of the ligand. Cu2+ and Zn2+ stabilise the ring tautomeric form of the ligand in their mononuclear complexes M(HLring)2. The structural characterisation of Zn(HLring)2·2MeOH·0.5H2O shows O,N-donor behaviour of the ring tautomer. The 1,2,3,4-tetrahydroquinazoline undergoes a ring-opening reaction upon formation of phenoxo-bridged dinuclear complexes M2(Lchain)2 in which the chain tautomer is acting as O,N,N,N-donor. The crystal structure of Cu2(Lamide)(Lquinazoline)(MeOH)·2MeOH evidenced the sensitivity of H2Lring to the copper-mediated aerobic oxidation, which results in two derivatives of the ligand, a quinazoline and an amide. The quinazoline ligand is acting as monoanionic and mononucleating through its O,N,N binding site, while the amide ligand behaves as a trianionic and binucleating through its O,N,N,N and O,O binding sites in Cu2(Lamide)(Lquinazoline)(MeOH)·2MeOH.