Two new, potentially cyclometalating terdentate ligands bearing phosphonate substituents, Et2O3P-N^ C (H)^ N (5) and Et2O3P-C (H)^ N^ N (7), have been prepared. The corresponding ruthenium complexes,[1]+ and [2]+, respectively, were obtained by reaction with [RuCl3 (tpy)]. Complexes [1]+ and [2]+ display electronic properties characteristic for cyclometalated ruthenium complexes. The platinum complex [3], of N^ C (H)^ N ligand 5, ...