99Ru Mössbauer effect study of ruthenium nitrosyls

The 99Ru Mossbauer effect has been measured in a series of ruthenium nitrosyls at 4.2 K. The isomer shifts (IS ≈ −0.20 mm s−1) for most of the compounds are nearly equal and consistent with a +2 charge for ruthenium. However, the IS for K2[Ru(NO)Cl5], which is still Ru(II), is much more negative (IS = −0.43 mm s−1). This implies that the ligand field strength is much stronger in this compound than the other compounds. Two of the compounds are broadened single lines or have small quadrupole interactions, but the compounds [Ru(NO)Cl(py)4](PF6)2, [Ru(NO)Br(py)4](PF6)2 and [Ru(NO)(NH3)5]Cl3 each display two distinct lines (ΔEQ ≈ 0.40 mm s−1), which shows the non-symmetric Ru environment in these compounds.