Low-spin complexes Fe

S-Methyl-A-(2-pyridyl)methylenedithiocarbazate (nns) can be prepared by the condensation of S-methyldithiocarbazate and pyridine-2-aldehyde. The low-spin complexes [Fe(nns)2].X (X = CIO or FeCl ) have both been isolated.2,1.3-Benzothiodiazole. 2,1,3-benzoselenodiazole, and their derivatives (L) form the octahedral complexes FeL2Cl3. and morpholine-4-carbodithioate (mdtc) forms the complex [Felmdtclj]. Mossbauer and magnetic data for a series of monothio- -diketonate-iron(iii) complexes have been interpreted in terms of a thermal equilibrium between the sextet and doublet states. 

The new low-spin complexes [Fe(43)L1L2](PF6)2 (Lt = L2 = imidazole, MeCN Lj = MeCN, L2 = CO) have been isolated. The bis-acetonitrile complexes undergo reversible substitution reactions with both CO and imidazole. In the case of imidazole substitution, one or more of the following are present in solution depending on the substrate concentration [Fe(43)(MeCN)2]2 +, [Fe(43)(MeCN)(imid)]2 +, and [Fe(43)-(imid)2]2 +. For CO substitution, only [Fe(43)(MeCN)2J2+ and [Fe(43)(CO)-(MeCN)]2+ are present in solution when the pressure of CO gas is less than or equal to one atmosphere.218 The structure of high-spin [FeIICl(44)]I has been determined... 

Although the Schiffbase (pyrol)3tren) (17) formed by condensation of pyrrole-2-carboxaldehyde with 2,2, 2"-tris(ethylamino)amine is potentially heptadentate the neutral low-spin complex [Fe (py-rol)3 tren ] has a six-coordinate (trigonally distorted octahedral) structure, the distance between the metal atom and the central tertiary aliphatic nitrogen being greater than the van der Waals contact... 

Fe, in the presence of an excess of terpy forms the very stable low-spin complex [Fe(terpy)2] , for which log P2 = 20.4, AH = — 113 kJ mol and AS — — 13 JK mol . The rate of ligand exchange is slow and has been examined using tritium-labelled terpy. In acid solution, ligand dissociation takes place and the observed kinetic behaviour as a function of acid concentration is complex. " Reaction of [Fc(terpy)2] with CN follows second order kinetics to give [Fe(terpy)(CN)3] whose maximum absorption in the visible region (metal-ligand ct) varies markedly with the nature of the solvent. " Oxidation of [Fe(terpy)2] yields the iron(III) complex ( l.I V), while controlled reduction affords the + 1 and 0 formal oxidation states. ... 

In the case of Fe " ", the Mossbauer spectra have evidentiated that Fe " " taken up by the a-ZP or a-ZP-ligand phases generally modifies its oxidation state giving mixtures of Fe " " and Fe " " derivatives (24). Only for low loadings of Fe " " in phen-a-ZP is Fe " " stabilized as such in a tris-chelate low spin complex [Fe(phen) f(Figure 13-3 C). When the Fe content exceeds the... 

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