Coordination complexes, Fe

The spin state of the six-coordinate complexes [Fe(cyclam)X2]+ [cyclam = 1,4,8,11-tetraaza-cyclotetradecane (105)] is governed by the geometrical configuration of the 14-membered macro-cycle, being high-spin for the cis complexes and low-spin for the trans complexes. However, frans-[Fe(cyclam)Br2][Cl04] with Arr— 3.90 BM at 295 K. may exist in a high-spinlow-spin equilibrium.392... 

Carbon monoxide reacts with [Fe(TPP)] to form a five-coordinate complex [Fe(TPP)CO], which can be reduced electrochemically to the corresponding iron(I) species from which, however,245 CO spontaneously dissociates. The Fe—CO interaction is stabilized by the,presence of hydrocarbon chains bound by amide linkages to the ortho position of the TPP phenyl rings. Carbon monoxide adducts of iron(I) complexes of a number of these superstructured porphyrins have been reported.245 The chemistry of these highly reduced species is of relevance to understanding240 the reactions of cytochrome P-450 and the peroxidases. 

The tetrahedrally coordinated complex [Fe HB(Bu Im)3 Br] is isostructural to the main group compound [Mg HB(Bu Im)3 Br] [403] and the transition metal compound [Co HB(Bu Im)3 Cl] [404], The smaller main group cation Li+ combined with the smaller tris-NHC ligand HB(EtIm)3 surprises us with a dinuclear [Li3 HB(EtIm)3 3] complex... 

Iron Pentacarbonyl. In its reactions with liquid dinitrogen tetroxide this compound follows the pattern outlined above, and the remarks on reactions of nickel carbonyl probably apply here also. The solvate, Fe(N03)3.N204, is produced (4). This has the structure N0+[Fe(N03)4] in the solid state it is volatile without decomposition, and is believed to be a five-coordinate complex, Fe(N0)(N03)4, in the vapor state. We have not yet succeeded in isolating the simple trinitrate, Fe(N03)3, by removal of N2O4. 

The 6-coordinate complex [Fe(TpivPP)(N02)(CO)] has vCO at 1974 cm 1 -only slightly higher than in 6-coordinate complexes with neutral N-donors (rather than N02 ) trans to CO.111 There is IR (vCO) evidence for the formation of a range of carbonyl species by adsorption of CO on a silica-supported Fe-Ru alloy.112 The bridging carbonyls in (44) have vCO bands at 1673 and 1712 cm 1.113... 

The four-coordinate complex [Fe(PPh3)(PhBP3)], obtained by reaction of [FeCl(PhBP3)] with PPI13 in sodium amalgam, undergoes... 

The study of frozen aqueous solutions of iron(III) compounds is only of limited value because of the tendency to hydrolyse, and the relaxation broadening [63, 128], and little work has been done. A potentially more profitable application is the study of solvent extracts. Frozen nitrobenzene extracts of iron(III) in HCl, HBr, and NaSCN solutions contain respectively the FeCl4 and FeBr4 anions and a 6-coordinate complex Fe(NCS)4X2 (X is either water or nitrobenzene) [129, 130]. The spin-spin relaxation behaviour is dependent on the solvent, and trioctylphosphine oxide extracts show partially resolved hyperfine structure. 

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