Iron halide alkoxides

Iron-centered paramagnetic complexes formed by reactions between iron salts and nitric oxide in the presence of anionic ligands, and characterized by g = 2.03, were first reported over 20 years ago (22) similar complexes, of the general type [Fe(NO)2X2] +, have subsequently been produced by reactions of iron salts and nitric oxide in the presence of halides and pseudohalides (118), alcohols and alkoxides (119), mercaptides (120, 121), and mercaptopurines and mercaptopy-rimidines (122). 

The tetranuclear iron alkoxide halides (see Table 12.23) were supposed to possess the cubane-like or Ti4(OMe)i4 type structures. The Mossbauer spectroscopy indicated the presence of 2 types of iron atom coordination in Fe4Hal6(OMe)6 4MeOH and only one kind of octahedral arrangement in FeCl(OR)2 and Fe4Hal3(OMe)9. For the 2 latter products the layered structures of the Al(OH)3 type were also proposed [867, 1065]. 

Iron porphyrins, the prosthetic group of the heme proteins are of course of great interest. Tetraphenylporphine, (TPPH2) (Fig. 2) is not a naturally occurring porphyrin. But because of its ease of preparation and close similarity to other porphyrins, tetraphenylporphinatoiron (TFPFe) derivatives have been extensively studied. Hemes are Fe(II) compounds such as TPPFe(II), and hemins are rive coordinate Fe(III) derivatives such as TFPFe(III) X (X = halide, pseudohalide, carboxylate, alkoxide, etc.)16). Six coordinate Fe(III) prophyrins are known as hemichromes, such as [TPPFe(III) L2] X (L = pyridine, piperidine, imidazole, etc.)16). Hemichromes are usually low spin, S = 1/2, systems 0 eff 1-9 B.M.) and hemins are of the high spin,... 

For the synthesis of metalloid (B, Si) alkoxides, the method generally employed consists of the reaction of their covalent halides (usually chlorides) with an appropriate alcohol. However, the replacement of chloride by the alkoxo group(s) does not appear to proceed to completion, when the central element is comparatively more electropositive. In such cases (e.g. titanium, niobium, iron, lanthanides, thorium) excluding the strongly electropositive s-block metals, the replacement of halide could in general be pushed... 

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