Two fluorescent ligands, 3,5-dimethyl-4-(6′-sulfonylammonium-1′-azonaphthyl)pyrazole (dmpzn, 1) and 3,5-dimethyl-4-(4′-N,N’-dimethylaminoazophenyl)pyrazole (dmpza, 2) were obtained by condensation of ketoenolic derivatives with hydrazine. 1 and 2 formed the novel dinuclear complexes [(H₂O)₃ClRu(nu-L)₂RuCl(H₂O)₃] (3 or 4) and [(H₂O)(NO)Cl₂Ru(nu-L)₂RuCl₂(NO)(H₂O)] (6 or 7) (where L = 1 or 2, respectively) which were characterized by IR, NMR and elemental analysis. The nitrosyl complexes were prepared by bubbling purified nitric oxide through methanol solutions of the corresponding ruthenium(II) chloroderivative or by reaction of the appropriate ligands with Ru(NO)Cl₃. Complexes 3 and 4 were found to bind NO, resulting in an increase in fluorescence. Ligand 1 also formed the mononuclear nitrosyl complex [Ru(NO)(bpy)₂(dmpzn)]Cl₂ (8) which released NO in water at physiological pH and in the solid state as revealed by fluorescence and IR measurements, respectively.