This MSc thesis describes the synthesis and coordination chemical characterization of two novel O-pyclen-based macrocyclic ligands with monodentate (OPC1HA) and bidentate (OPC2HA) hydroxamate pendant arms, developed as potential alternatives to toxic gadolinium-based MRI contrast agents. A new synthetic route using microwave-assisted alkylation and mild TFA/Et₃SiH deprotection significantly improved reaction yields and reduced deprotection time from days to one hour. The Mn(II) complex with OPC2HA exhibited exceptionally high relaxivity, outperforming acetate analogues and demonstrating strong potential as an MRI contrast agent, though its kinetic inertness was only moderate. The Sc(III) complex with OPC1HA showed thermodynamic stability but very low kinetic inertness, making it unsuitable for in vivo PET imaging applications. Overall, while OPC2HA shows promise as a high-relaxivity Mn-based contrast agent, the vulnerability of hydroxamate arms to protonation necessitates further ligand optimisation to improve kinetic inertness for biomedical use.