 A common diphosphine ligand is dppe, which forms a five-membered chelate ring with most metals.Some diphosphines, such as the extraordinary case of "t"Bu2P(CH2)10P"t"Bu2, give macrocyclic complexes with as many as 72 atoms in a ring.To position phosphine donor groups trans on a coordination sphere, several atoms are required to link the donor centres and long-chain diphosphines are typically floppy and do not chelate well.