Structural studies on an iron(III) complex containing (Z)-2-(2-aminothiazol-4-yl)-N-(2-hydroxyethyl)-2-(hydroxyimino)acetamide, a model compound for a cephalosporin antibiotic cefdinir

(Z)-2-(2-Aminothiazol-4-yl)-N-(2-hydroxyethyl)-2-(hydroxyimino)acetamide (HL) has been employed as a model compound for a cephalosporin antibiotic, Cefdinir. A trinuclear iron(III) complex [Fe(3)L(6)]Cl[OH](2) 1 has been obtained from a methanol solution containing HL and FeCl3 and its structure determined by X-ray crystallography: monoclinic, space group P2(1)/n, a = 115.559(1), b = 19.295(2), c = 10.963(1) Angstrom, beta = 101.29(1)degrees, Z = 2. The molecular structure contains a linear Fe(1)-Fe(2)-Fe(1') arrangement, the central atom Fe(2) being an inversion centre. Atom Fe(1) is co-ordinated to three molecules of L through the thiazole and oximate nitrogen atoms to form Fe(1)L(3), and Fe(2) to six oximate oxygen atoms of the two Fe(1)L(3) units. The two Fe(1)L(3)-units are bridged by the central iron atom Fe(2). The Mossbauer spectrum of 1 gave an apparent doublet signal consisting of two doublets, A and B, assigned to Fe(1) and Fe(2), respectively. The isomer shifts delta of these doublets are the same (0.26 mm s(-1)), and are typical for high-spin iron(III). In addition, the reflectance spectrum did not show any intervalence bands. These spectral data indicate that the three iron atoms are high-spin iron(III). The compound co-ordinates to iron(III) via the thiazole ring nitrogen atom and the oximate nitrogen atom (2N mode) in methanol which is different from that in water, where L prefers to co-ordinate to an iron(III) through the oximate oxygen atom and the amide oxygen atom (20 mode).