An unprecedented trinuclear structure involving two high-spin and one spin-crossover iron(II) centers

Anaerobic reaction of ferrous thiocyanate with the deprotonated form of the pentadentate dinucleating Schiff base 1,3-bis[(2-pyridylmethyl)iminolpropan-2-ol (LH) yields the novel trinuclear [Fe3L2(NCS)(4)(H2O)] species 1. LH results from the bis-condensation of 2-acetyl-pyridine with 1,3-diaminopropan-2-ol and includes an N4O donor set. The X-ray crystal structure of 1 [C38H40N12O3S4Fe3, triclinic, space group P-1; a = 10.7730(10)Angstrom, b = 12.2048(14)Angstrom, c = 19.0559(19)Angstrom, alpha = 76.908(12)degrees, beta = 89.106(12)degrees, gamma = 79.637(12)degrees, V = 2399.8(4)Angstrom(3)] can be described either as a bent linear arrangement of ferrous centers pairwise bridged through the alkoxo oxygen atom of L- or as a triangular Fe-3(II) core with an Fe2-SCN-Fe3 bridge as the longer side of the Fe1-Fe2-Fe3 triangle. The metric parameters characterizing the ligand environments of the three ferrous centers in 1 and its Mossbauer spectra show that this unprecedented trinuclear structure involves two high-spin (Fe2 and Fe3) and one spin-crossover (Fe1) Fe-II centers. The donor set to the spin-crossover center (Fe1) is unprecedented: two N-pyridine, two N-imine, and two O-alkoxo- Weak antiferromagnetic interactions transmitted through the end-to-end NCS bridge and/or through the O1-Fel-O2 bridge operate between Fe2 and Fe3.