Density functional theory has been used to study the trans-influence of Rh–Rh and Rh–L bonds in dirhodium(II) tetracarboxylates with axial ligands L=H 2O, pyridine, CO, triphenylphosphine, NO and NO 2. The absence of the chemical bond between metal atoms in Rh 2(μ-O 2CR) 4(NO) 2 complexes and the formation of two covalent Rh–NO bonds explain the very long Rh–Rh and very short Rh–N distances in these compounds.