Synthesis and reactivity of bidentate phosphine iron complex [(C2F5)2PCH2CH2P(C2F5)2]Fe(CO)3

ionic crystals by piling the cluster anions and by sur- rounding the anion rows with cations.To put it in a rather crude way, we can look at these crystals as cocrystals whose structure is governed mainly by the steric similarity be- tween the anions on one side and between the cations on the other (i.e. the similar packs better with the similar).In the case of carbonyl anions this preference can be as- signed to the more effective interlocking possible between molecules with surface CO ligands.This situation recalls that observed in crystalline carbonyl-arene neutral clus- ters,111' where the crystal building process has to cope with the simultaneous presence of CO ligands and of flat arene fragments.In such cases the most efficient arrangement is invariably attained by grouping together in the lattice the fragments having similar shape, i.e. arenes with arenes and CO's with CO's.Our analysis is necessarily very much qualitative.However, we would like to stress that a careful investiga- tion of the molecular or ion organization in the crystal is the basis on which solid-state studies must be founded.For instance, it is worth recalling that several conducting materials have strongly anisotropic physical properties.This anisotropy usually arises from the molecular ar- rangement in the lattice.In organic conductors and su- perconductors, low-dimensionality (i.e.stacks of planar molecules or molecular piles and strings) is a prerequisite for molecules or ions to carry electrons through the network.28Furthermore, several high-nuclearity clusters have been shown to possess physical properties distinct from both molecules and bulk metals (the "metametallic" state).6•7We believe that, to be successful, the appreciation of the physical-chemical properties of these organometallic ma- terials must rely not only on the knowledge of the structure of the component molecules or ions but also on information on the structure of the entire crystalline edifice.