Valence delocalization and crystal structure of [Fe3O(pazo)(6)(py)(3)]center dot 3py: An example of the mixed valence delocalization between two ironatoms

The oxo-centered, trinuclear, mixed-valence complex [Fe3O(pazo)(6)(py)(3)]. 3py, where pazo is 4-phenylazobenzoic acid, has been prepared, and the int ramolecular electron transfer properties in the solid state have been studi ed. There are two doublets in the area ratio of two (Fe3+) and one (Fe2+) a t 78 K. Increasing the sample temperature above 120 K turns these to two do ublets in the area ratio of two (Fe2.5+) and one (Fe3+); the average valenc e state between an iron(II) and one of two irons(III) is observed. The comp lex crystallizes in the C-centered monoclinic space group C2/c with 4 molec ules in a unit cell which has dimensions: a = 15.856(4), b = 28.649(2), c = 25.739(2) Angstrom, V = 11317(3) Angstrom(3), beta = 104.54(1) at 150 K, a nd a = 15.867(3), b = 28.555(3), c = 25.747(5) Angstrom, V = 11288(3) Angst rom(3), beta = 104.60(2) at 85 K. The metal sites of the average valence st ate and Fe3+ state are seen in its single-crystal X-ray structure at both t emperatures. The X-ray structure work shows that the dimensions of the Fe3O triangle become larger and the length of b-axis becomes longer with increa sing of temperature. There is a C-2 axis in the molecule, Fe-B(3+) and a py ridine coordinating to the Fe-B(3+) being located on the axis. The plane of the pyridine is almost perpendicular to that of the Fe3O triangle and thos e of other two pyridines coordinating to Fe2.5+ (Fe2+ + Fe-A(3+)) are paral lel to that of the Fe3O triangle.