New structural features in tetranuclear iron carbonyl thiocarbonyls: Exotriangular iron atoms and six-electron-donating thiocarbonyl groups bridging four iron atoms

摘要

DFT led to the discovery of two new structural motifs in tetranuclear iron carbonyl thiocarbonyls, Fe _4(CS) _4(CO) _n (n = 12, 11, 10, 9), which are not found in their homoleptic analogues, Fe _4(CO) _(n+4). Thus the lowest energy Fe _4(CS) _4(CO) _(12) structures have a central Fe 3 triangle with an exotriangular iron atom joined to the Fe 3 triangle through a four-electron donor CS bridge. This contrasts with the structure of Os _4(CO) _(16) and the predicted structure of Fe _4(CO) _(16), which consist of an M _4 rhombus and two-electron donor carbonyl groups. An even more remarkable new structural motif for the Fe _4(CS) _4(CO) _n derivatives is the irregular Fe _4 "rhombus" (actually a trapezium) bridged by a six-electron donor ?· ~2-μ _4-CS group. This type of structure is found in the lowest energy structures of both Fe _4(CS) _4(CO) _(10) and Fe _4(CS) _4(CO) _9 and makes Fe _4(CS) _4(CO) _(10) viable enough to be a promising synthetic objective. On the contrary, Fe _4(CS) _4(CO) _(11) is found to be thermochemically unfavorable both with respect to CO dissociation and disproportionation into Fe _4(CS) _4(CO) _(12) and Fe _4(CS) _4(CO) _(10). The lowest energy Fe _4(CS) _4(CO) _(12) structures have a central Fe _3 triangle with an exotriangular iron atom joined to the Fe _3 triangle by a four-electron donor "end-on" CS bridge. An Fe _4 rhombus bridged by a six-electron donor ?· ~2-μ _4-CS group is found in the lowest energy structures of Fe _4(CS) _4(CO) _(10) and Fe _4(CS) _4(CO) _9 and makes Fe _4(CS) _4(CO) _(10) viable enough to be a promising synthetic objective.