a class of anionic and neutral complexes of ruthenium containing nitrogen oxide and optionally a nitrogen ligand is described ; a process for their preparation is also described . the preparation process includes the use of starting complexes of ruthenium which are reacted with suitable reagents so as to obtain complexes containing nno coordinated to ruthenium . additional substitution reactions allow the introduction of new groups that coordinate to the ruthenium atom , among which some nitrogen ligands .