Lanthanide Complexes of 2,2′,2″-(10-{[Hydroxy(Phenyl) Phosphoryl]Methyl}-1,4,7,10-Tetraazacyclododecan-1,4,7-Triyl)Triacetic Acid: Structural Characterisation of Intermediates from the Proposed Complexation Mechanism in the Systems of Ln^Iii-Dota-Type Ligands