The electronic structure of Ru₂(μ-O₂CR) ₄, Ru₂(μ-O₂CR)₄(L)₂ and Ru₂(μ-O₂CR)₄(NO)₂ (R = H, CH₃, CF₃; L = H₂O, THF) ruthenium tetracarboxylates is analyzed on the basis of calculations by the density functional method with full geometry optimization. It is concluded that the axial coordination of nitric oxide (II) to Ru₂(μ-O ₂CR)₄ is accompanied by destruction of the metal-metal π-bond with d _πAO Ru reorientation on bonding with NO molecules.