Structural studies in metal–purpurate complexes. Part 3. Crystal structures of triaquapurpuratoiron(II) purpurate hexahydrate and tetraaquapurpuratomanganese(II) purpurate hexahydrate. Stereochemistry of the [M(tridentate ligand)(unidentate ligand)3] complexes

Abstract

The crystal structures of the title compoupds, [FeL(H₂O)₃][L]·6H₂O (1) and [MnL(H₂O)₄][L]·6H₂O (2)(L = purpurate), have been determined at 295 K by X-ray diffraction and refined by least squares to R 0.046 (3 706 ‘observed’ reflections) and 0.076 (2 132 ‘observed’ reflections) respectively. Crystals of both complexes are triclinic, space group P. For (1), a= 15.146(3), a= 10.182(3), c= 9.934(2)Å, α= 105.50(2),β= 102.99(2), γ= 98.34(2)°, Z= 2; for (2), a= 13.590(10), b= 11.354(8), c= 10.121(7)Å, α= 103.40(3), β= 99.74(3), γ= 98.98(3)°, Z= 2. In both compounds, one of the purpurate species is co-ordinated to the metal as a tridentate ligand [(1): Fe–O, 2.103(3), 2.094(3), Fe–N, 2.205(3); (2): Mn–O, 2.303(7), 2.417(6), Mn–N, 2.422(9)Å], the other existing as an anionic lattice species. The remainder of the metal-atom co-ordination sphere is occupied by co-ordinated water molecules [M–O: (1), 2.066(4)–2.138(3); (2), 2.177(9)–2.247(8)Å], the iron atom being six- and the manganese seven-co-ordinate. The geometry in (1) provides probably the most accurate and unperturbed example available for the unco-ordinated purpurate species. The stereochemistry of the cation in (1) is described in terms of a repulsion model.