Seven-co-ordination in metal complexes of quinquedentate macrocyclic ligands. Part II. Synthesis, properties, and crystal and molecular structures of some iron(III) derivatives of two ‘N5’ macrocycles

Abstract

Template synthesis of the sixteen-membered, potentially quinquedentate, macrocycle formed by the Schiff-base condensation of 2,6-diacetylpyridine with 1,9-diamino-3,7-diazanonane (2,3,2-tet) in the presence of iron(II) salts yields a series of iron (III) complexes [Fe(C)X₂] Y (C = macrocycle; X = Cl, Br, NCS, or N₃; and Y = ClO₄ PF₆, BPh₄, FeCl₄, or FeBr₄). Spectroscopic, magnetic, and electric conductance measurements characterise the complexes as having high-spin seven-co-ordinate structures similar to those of the previously prepared complexes of the fifteen-membered macrocycle (B) derived from 2,6-diacetylpyridine and 1,8-diamino-3,6-diazaoctane (2,2,2-tet). The crystal and molecular structure of [Fe(C)(NCS)₂]ClO₄(II) has been determined and that of [Fe(B)(NCS)₂]ClO₄(I) redetermined. Crystals of (I) are monoclinic, space group P2₁/c, Z= 4, with a= 8.946(8), b= 14.504(13), c= 18.029(17)Å, β= 92.66(9)°. Crystals of (II) are monoclinic, space group P2₁/a, Z= 4, with a= 17.349(13), b= 12.151(10), c= 12.295(12)Å, β= 110.61(9)°. The two structures were solved by Patterson and Fourier methods from 1 531 (I) and 1 473 (II) independent reflections collected by counter methods and refined to R 0.090 (I) and 0.077 (II). In both structures the metal atoms have distorted pentagonal bipyramidal environments with the isothiocyanate ligands in axial positions and the five nitrogen atoms of the macrocycle in equatorial positions. The Fe–N bond lengths and the conformation of the girdles are different in (I) and (II) as a consequence of the different ring sizes. The perchlorate anion in (I) is disordered.