Structure and characterization of non-cyclic tetraaza complexes of copper(II) and their reactions with nitric oxide

[Cu(bapp)ClO4]+ (1) and [Cu(bapp)Cl]+ (2) were prepared by the reaction of 1,4-bis(3-aminopropyl)piperazine (bapp) with copper acetate and copper chloride in the presence of sodium perchlorate, respectively, and structurally characterized. Complex 1 has a square-pyramidal geometry, whereas [Cu(3,2,3-tet)(ClO4)]+ (A) has a polymeric octahedral geometry in its X-ray crystal structure. Complex 1 is stable against disproportionation, whereas complex A is unstable in the mono-valent Cu(I) state. An aqua ligand on complex 1 in aqueous solution is substituted by NO with kinetic constants of kf=43±2 M−1 s−1 and kb=(8.8±0.2)×10−2 s−1 at 25 °C, whereas there were no spectral changes observed for complex A in saturated NO solution.