Lanthanide Complexes of 2,2′,2"-(10-{[Hydroxy(Phenyl)Phosphoryllmethyll}-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