N-Alkyl substituted triazenide-bridged homoleptic iron(ii) dimers with an exceptionally short Fe-Fe bond

Dinuclear transition metal complexes with direct metal-metal interactions have the potential to generate unique reactivities and properties. Using asymmetric triazine ligands (HN3BuR)-Bu-t (R = Et, Pr-i, Bu-n) featuring different alkyl substituents at 1,3-N centers, we report here the first rational synthesis of 'tetragonal lantern' type Fe(ii) triazenides [Fe-2((N3BuR)-Bu-t)(4)] [R = Et (1), Pr-i (2), Bu-n (3)] having an exceptionally short Fe-Fe distance (2.167-2.174 & Aring;). Unlike the previously reported lantern structures with related amidinate or guanidinate ligands, highly air-sensitive 1-3 show a lower spin ground state, as indicated by M & ouml;ssbauer, H-1 NMR and DFT studies.