The synthesis and characterisation of a series of {AnO₂}ⁿ⁺ complexes containing multidentate ligand environments is reported. Three novel {UO₂}²⁺ complexes (1-3) containing N₃O₂ linear pentadentate ligands have been prepared and crystallographically characterised. NMR spectroscopy has been able to show that 1-3 are stable with respect to ligand exchange, in a range of solvents. The strength of the O=U=O unit has been probed by vibrational spectroscopy and 1-3 exhibit some of the weakest O=U=O ν₁ stretching modes reported (802-805 cm⁻¹). The cyclic voltammetry (CV) of 1-3 in various solvents (0.1 M [Bu₄N][PF₆]) has been performed and indicate the position and reversibility of the {UO₂}²⁺/{UO₂}⁺ redox couple has been found to be subtly dependent on the solvation environment. {UO₂}²⁺ complexes (4-6) have been prepared by subtle modification of reaction conditions using a rigid N₂O₂S linear pentadentate ligand. Characterisation by X-Ray diffraction reveals different monometallic systems, where 4 and 5 are solely bound to the O₂ donors of the ligand and 6 exhibits uranyl binding through all of the donor atoms in the N₂O₂S cavity. ¹H NMR spectroscopy shows 5 exhibits intramolecular rearrangement on the NMR timescale in DCM, but undergoes intermolecular ligand exchange in more coordinating solvents (DMSO, py). Cyclic voltammetry of 5 in DCM (0.1 M [Bu₄N][PF₆]) also indicates that rearrangements and/or ligand exchange processes may occur at rate comparable to that of the CV studies. Complex 6 exhibits stability with respect to ligand exchange or rearrangement in various solvents and shows comparable solvation environment dependency of the {UO₂}²⁺/{UO₂}⁺ redox couple, relative to 1-3. Three monometallic {UO₂}²⁺ complexes (7-9) have been prepared using a rigid tetradentate N₂O₂ ligand. A dimetallic {UO₂}²⁺ complex (10) where two {UO₂}²⁺ are linked by a 4,4'-bipyridine bridge, has been formed by controlled ligand exchange. Vibrational spectroscopy shows the presence of the O=U=O ν₁ stretch in both the Raman and infrared spectra for 7-10, likely to be caused by distortion of the ligand about the UO₂}²⁺ equatorial plane causing a change in dipole for the O=U=O ν₁ stretching mode. A synthetic and spectroscopic study of neptunyl coordination to N₃O₂ linear pentadentate ligands has been made. Adopting a similar method that was successfully employed in the synthesis of 1-3, resulted in the reduction of {NpO₂}²⁺ to {NpO₂}⁺, giving a series of complexes (11-13). Complex 13 has been crystallographically characterised and shows a monometallic {NpO₂}⁺ complex which is bound to all of the atoms in the N₃O₂ cavity.