Iron(II) complexes of a potentially quinquedentate macrocyclic ligand having an ‘N3S2’ donor set and the crystal and molecular structures of a high-spin (S= 2) complex and a low-spin (S= 0) complex

Abstract

A series of iron(II) complexes of the 17-membered macrocyclic ligand L, having an ‘N₃S₂’ donor set, derived from the Schiff-base condensation of 2,6-diacetylpyridine with 4,7-dithiadecane-1, 10-diamine, are described. Physical measurements (magnetic, Mössbauer) characterise the complexes as high-spin (S= 2) or low-spin (S= 0) depending on the nature of the associated unidentate ligands (halide, NCS^–, MeOH, MeCN, pyridine, or NH₃). Single-crystal X-ray structure determinations of two of the complexes reveal a versatility in the conformations and co-ordination modes of the macrocycle. Crystals of the low-spin complex [FeL(NCS)][BPh₄](1) are monoclinic with a= 31.640(8), b= 11.019(8), c= 11.155(7)Å, β= 96.40(3)°, Z= 4, and space group P2₁/a. Crystals of the high-spin complex [FeLCl(HOMe)][ClO₄](2) are monoclinic with a= 18.512(11), b= 18.279(12), c= 8.125(9)Å, β= 113.1(2)°, Z= 4, and space group P2₁/a. The two structures were solved by Patterson and Fourier methods from 2 548 and 1 772 reflections above background measured by diffractometer and refined by full-matrix least squares to R 0.047 and 0.102 respectively. In both (1) and (2), the co-ordination geometry of the metal ion is distorted octahedral. In (1), the macrocycle adopts a ‘wrap-around’ conformation to occupy five of the octahedral sites [Fe–N 1.981(6), 1.870(6), 1.987(7); Fe–S 2.307(3), 2.258(3)Å], the sixth being filled by the nitrogen atom of the –NCS group [1.965(9)Å]. In (2), one sulphur atom of the macrocycle is not bonded to the metal while the other is only weakly co-ordinated [2.806(5)Å]cis to the trimethine nitrogens [Fe–N 2.205(11), 2.092(10), 2.200(12)Å]. The remaining two octahedral sites are occupied by the Cl^– ion (trans to the pyridine nitrogen) and the oxygen atom of the MeOH molecule [Fe–Cl 2.304(4), Fe–O 2.205(16)Å]. Possible structures for the remaining complexes of the series including three modifications of [FeL(NCS)₂] are considered.