Reactions of [Ru(bpy)(CO)(2)Cl-2] in concentrated HCl/HNO3 solutions at high temperatures were studied. In acidic solutions carbonyl groups are lost and replaced by chlorine and nitrosyl, nitrido or water ligands. Formation of [Ru(bpy)Cl-3(NO)] and [Ru2N(bpy)(2)Cl-5(H2O)] was time-dependent; with shorter reaction times (<6 h, 240 degrees C) solid crystalline fac(Cl)-[Ru(bpy)Cl-3(NO)] (1a) and mer(Cl)- [Ru(bpy)Cl-3(NO)] (1b) were formed, and with longer reaction times a new crystalline nitrido-bridged complex [Ru2N(bpy)(2)Cl-5(H2O)] (2) was produced, most probably via a nitrosyl intermediate. Both 1 and 2 are practically insoluble and highly stable. However, the reaction of [Ru(bpy)(CO)(2)Cl-2] in HCl/HNO3 solution with small amounts of [Ru(bpy)Cl-3(NO)] added gave in low yield another nitrido-bridged product, (H5O2)[Ru2N(bpy)(2)Cl-6] (3). The role of added [Ru(bpy)Cl-3(NO)] in this reaction is unclear, and it is possible that (3) may also form directly from pure [Ru(bpy)(CO)(2)Cl-2]. Crystal structures of fac(Cl)-[Ru(bpy)Cl-3(NO)], mer(Cl)- [Ru(bpy)Cl-3(NO)], [Ru2N(bpy)(2)Cl-5(H2O)], and (H5O2)[Ru2N(bpy)(2)Cl-6] showed that the ruthenium atoms are octahedrally coordinated in all complexes. Crystal data : 1a, monoclinic, space 6.798(3) Angstrom, b = 11.993(4) Angstrom, c = 16.760(8) Angstrom, beta = 98.89(3)degrees, Z = 4; 1b, monoclinic, space group Pn, a = 8.175(2) Angstrom, b = 6.733(2) Angstrom, c = 12.594(5) Angstrom, beta = 105.06(3)degrees, Z = 2; 2, monoclinic, space group P2(1)/n, a = 10.133(5) Angstrom, b = 15.042(6) Angstrom, c = 16.506(8) Angstrom, beta = 104.86(4)degrees, Z = 4; 3, triclinic, space group P ($) over bar 1, a = 10.281(3) Angstrom, b = 10.776(3) Angstrom, c = 12.527(5) Angstrom, alpha = 90.78(3)degrees, beta = 98.31(3)degrees, gamma = 100.91(2)degrees, Z = 2.