Iron octahedral bonding geometries

Figure 4. A comparison of the octahedral bonding geometries of trans-tris(ben-zohydroxamato)chromium(III) and cis-tris(benzohydroxamato)iron(IH)...

The structure of the di-iron complex [Fe2( i, r 3, r 3-BH6)(PEt3)6] (127) contains a boron atom in the octahedral environment of 6 equiv. hydrides capped on the opposite facets by two iron atoms.199 Thus, neglecting the second iron center, the geometry is very reminiscent of the complex 125. DFT calculations supplemented by an AIM study confirmed the presence of six H-B interactions and direct Fe B bonds. The structure was considered as containing a boron trication B3+ sandwiched between two anions [Fe(H)3(PEt3)3]. ... 

Finally, as far as the [Fen(terpy)2]2+ complex is concerned, its molecular structure is known. Its octahedral geometry is tetragonally distorted, in that the bond distance between the iron(II) ion and the central nitrogen atom of terpyridine is considerably shorter (Fe-N= 1.89 A) than the distance between theiron(II) ion and the two more external nitrogen atoms (Fe-N = 1.99 A).110... 

Let us start with the Ni(II) complexes of the already mentioned scorpiand diammac (6,13-diammino-6,13-dimethyl-1,4,8,11-tetraazacy-clotetradecane) in its two cis and trans conformations. In contrast to the previously mentioned chromium-, iron-, and cobalt-diammac complexes, in which the geometry of [M(fra s-diammac)]" + was substantially octahedral and that of the [M(cw-diammac)]" + was substantially trigonal prismatic, in the case of both [Nif/raws-diammac)]2+ and [Ni(m-diammac)]2 + the structural differences are attenuated and both can be viewed as more or less distorted octahedral geometries, with two sets of averaged Ni-N bond lengths of 2.07 A and 2.13 A, respectively.161 162 This is reflected by the fact that both the two complexes exhibit in aqueous solution a chemically reversible Ni(II)/Ni(III) oxidation ([Nif/raws-diammac)]2 + E° = + 0.67 V vs. SHE [Ni(m-diammac)]2 + ... 

The structure of the l,2,3,6-f/4-OFCOT complex 64 is shown in Fig. 6 (140). The coordination geometry around iron can be considered as octahedral, with the allylic portion of the OFCOT ligand and the Fe—C a bond occupying three facial sites. The formal oxidation of the metal center is reflected in the higher values of the CO stretching frequencies (vco = 2105, 2060 cm-1) for complex 64 compared to those for the l-4-r/4-COT complex 63 (vco = 2051, 1992, 1978 cm-1) (139). 

In both compounds the iron atom geometries can be described as intermediate between octahedral and bicapped tetrahedral, but in the hydrido complex the H-Fe-H bond angle is 100°, whereas the Au-Fe-Au bond angle is only 73°. This smaller angle leads to an Au-Au distance of3.028(1) A, which is indicative of a weak interaction between the gold atoms. 

---