Valence Delocalization and Crystal Structure of [Fe_3O(pazo)_6(py)_3] centre dot 3py: An Example of the Mixed Valence Delocalization between Two Iron Atoms

摘要

The oxo-centered, trinuclear, mixed-valence complex [Fe_3O(pazo)_6(py)_3] centre dot 3py, where pazo is 4-phenylazobenzoic acid, has been prepared, and the intramolecular electron transfer properties in the solid state have been studied. There are two doublets in the area ratio of two (Fe~(3+)) and one (Fe~(2+)) at 78 K. Increasing the sample temperature above 120 K turns these to two doublets in the area ratio of two (Fe~(2.5+)) and one (Fe~(3+)); the average valence state between an iron(II) and one of two irons(III) is observed. The complex crystallizes in the C-centered monoclinic space group C2/c with 4 molecules in a unit cell which has dimensions: a = 15.856(4), b = 28.649(2), c = 25.739(2) A, V = 11317(3) A~3, #beta# = 104.54(1) at 150 K, and a = 15.867(3), b = 28.555(3), c = 25.7474(5) A, V = 11288(3) A~3, #beta# = 104.60(2) at 85 K. The metal sites of the average valence state and Fe~(3+) state are seen in its single-crystal X-ray structure at both temperatures. The X-ray structure work shows that the dimensions of the Fe_3O triangle become larger and the length of b-axis becomes longer with increasing of temperature. There is a C_2 axis in the molecule, Fe_B~(3+) and a pyridine coordinating to the Fe_B~(3+) being located on the axis. The plane of the pyridine is almost perpendicular to that of the Fe_3O triangle and those of other two pyridines coordinating to Fe~(2.5+) (Fe~(2+) + Fe_A~(3+)) are parallel to that of the Fe_3O triangle.