FE-57 MOSSBAUER SPECTROSCOPIC STUDY OF SOME CLUSTERS RELATED TO FE3(CO)12

The 57Fe Mössbauer spectra of Fe3(CO)12-related clusters [Fe3(CO)11]2−, [Fe2Ru(CO)12], [FeRu2(CO)12], [Fe3(CO)11PPh3], [Fe3(CO)11PPh2Me], [Fe3(CO)11PPhMe2], [Fe3(CO)9(PPh2Me)3], [Fe2Ru(CO)11P(OMe)3], [FeRu2(CO)11PPh3] and [FeRu2(CO)10(PPh3)2] have been recorded at 78 K. The data are compared with published data for other M3 clusters. Generally, the isomer shifts (δ) fall within a narrow range, for example with compounds containing Fe or Fe and Ru and four or five CO ligands per metal, all δ values lie between 0.29 and 0.36 mm s−1 even though the ligands may be terminal, doubly bridging or triply bridging. Values of quadrupole splitting (Δ) are much more susceptible to changes in the Fe environment, for example the Fe(CO)4 sites have Δ values from about zero {Fe(CO)4t in [Fe3(CO)12)]} to 1.52 {Fe(CO)3tCOtbr in [Fe3(CO)11]2−}. The quadrupole splitting of the Fe site in [FeRu2(CO)12] (0.77 mm s−1) clearly indicates that the structure of this cluster is not exactly similar to that of [Ru3(CO)12]. Substitution of CO by phosphine in general leads to small changes in Δ and Δ if the geometry of the Fe site is unaltered. However, Δ especially can be affected if phosphine substitution cause changes in geometry or if there is multiple substitution.