 This characteristic is employed in analytical techniques using EDTA as a ligand . EDTA preferentially forms octahedral complexes – thus absorbing other cations such as Al3 + which might interfere – for example , in the solvent extraction of a complex formed between Be2 + and <unk> . Beryllium ( II ) readily forms complexes with strong donating ligands such as phosphine oxides and <unk> oxides . There have been extensive studies of these complexes which show the stability of the O @-@ Be bond . 
