CRYSTAL STRUCTURES OF TRANS- AND CIS-ANIONOBIS(ETHYLENEDIAMINE)NITROSYLRUTHENIUM(II) COMPLEXES

The structures of trans-[RuX(en)2NO]X′2 (X = OH (1), Cl (3), or NCS (4), en = ethylenediamine, X′ = Br (1), Cl (3), or NCS (4)), trans-[Ru(H2O)(en)2NO]Cl3 (2), cis-[RuX(en)2NO]XPF6 (X = Cl (5), or Br (6)), and cis-[Ru(NCS)(en)2NO]I2·H2O (7) were determined by X-ray diffraction. In two pairs of the geometrical isomers (3 and 5, and 4 and 7), the Ru–Cl or the Ru–N(NCS) bond for the trans isomer was shorter than that for the cis isomer due to a trans-strengthening effect of the NO; this effect was not observed for the corresponding Ru–N(en) bond. These facts indicate that the effect is mainly caused by both σ- and π-bonding interactions of the ligand trans to NO through Ru, and is not caused by only the σ-donation of the ligand.