Six-coordinate species

X-ray diffraction study (7 7J). Attempts to obtain a six-coordinate species by addition of excess ligand (MePhjP, C2H4, or CO) usually results in silane elimination (Section II,C,3f) (60, 132). 

Decomposition of diazo compounds by iron porphyrins is a convenient method for the synthesis of non-heteroatom carbene-iron porphyrins [22]. Reaction of [Fe(F2o-TPP)] [F20-TPP = meso-tetrakis(pentafluorophenyl)porphyrinato dianion] with diazo compounds N2C(Ph)R (R = Ph, C02Et, C02CH2CH=CH2) under an inert atmosphere afforded complexes [Fe(F2o-TPP)C(Ph)R] in 65-70% yields (Scheme 2). Like the halocarbene complex [Fe(TPP)(CCl2)], [Fe(F2o-TPP)CPh2] reacted with Melm to afford six-coordinate species [(MeIm)Fe(F2o-TPP)CPh2] in 65% isolated yield. 

Calorimetry investigations of zinc ions with functionalized pyridines have been carried out in both dimethylformamide and acetonitrile. The pyridines used were pyridine, 3-methylpyridine, and 4-methylpyridine. In DMF, for all three pyridines, four- and six-coordinate species formed and their formation constants, reaction enthalpies and entropies were determined. The stability increases linearly with increasing basicity of the pyridine derivative. The formation of the 3-methylpyridine complex is enthalpically less favorable and entropically more favorable than... 

The first report [11] of a spin transition in a synthetic iron(II) system seems to be the result of a well-planned, deliberate strategy to identify the singlet/ quintet crossover region by the systematic variation of the field strength of the anionic groups in the six-coordinate species [Fe(phen)2X2] [7]. One... 

Fig. 2. With DFT methods (B3LYP/LANL2DZp) calculated structures for the seven-coordinate diaqua complexes (a) [M.r (pydiene)(Ji20), (h) Ma pyalane)Qii20)2f, (c) [Mn(pyane)(H20)2] " and (d) [Mn(L)(H20)2] (on the left) and the corresponding six-coordinate species after loss of one water molecule (on the right) 34).

In contrast, at [H+] > 0.1 M, the same reaction results in two or three new EPR signals (glso 1.974, 1.971, and 1.966) in addition to the one already mentioned feso= 1.979).68,75 These EPR signals turn out to be consistent with six-coordinated oxo-Cr(V) species. In this situation, the relative intensity of the EPR signal is pH dependent but is independent of the aldohexose/Cr(VI) ratio. In fact, six-coordinated species are dominant at [H+] > 0.75 M. In addition, both species [six- and five-coordinated oxo-Cr(V) complexes] decay at the same rate, meaning that they are in a rapid equilibrium. Scheme 5 shows the complexation chemistry and the observed Cr(V)-sugar redox processes. 

Manganese forms a large number of mononuclear complexes in oxidation states II, III, and IV with acyclic and other common ligands. The complexes primarily are six-coordinate species with octahedral or pseudo-octahedral geometries. Some exceptions to this categorization are the tetraoxo anions in oxidation states V, VI, and VII and the manganocenes. Table 1 contains electrochemical data for representative redox couples in which the Mn coordination environment remains invariant with oxidation state. Many entries are for homoleptic complexes, but some species with mixed... 

Crystalline salts containing tetra-, penta- and hexa-isothiocyanate complex anions can be isolated from aqueous or methanolic solutions.507 Frequencies v(Ga—NCS) occur in IR spectra at 350 cm-1 in four-coordinate or 250 cm-1 in six-coordinate species. Although powder patterns have been reported, single-crystal X-ray data are lacking for gallium thiocyanates. Some gallium selenocyanide complexes Ga(NCSe)3Ls and Ga(NCSe)4 have been prepared.508 Attempts to obtain Ga(NCS)3 or Ga(NCSe)3 appear to have failed. 

Expansion of the central chelate ring in tetradentate (66) from n = 2 to n — 3 favours six-coordinate species, as [VO(salnpn)] (Figure 30).726... 

Complexes (66 R = H and n = 2) were five-coordinate square pyramidal monomers in py, six-coordinate species form.728 Compound (66 R1 = R2 = R = H), polymeric in the solid state (Figure 30), was considered to break down to five-coordinate monomers in CHCI3 and six-coordinate. in py. Changes in the spectrum of (66 R1 = R2 = R = H, n = 9) in CHC13 on dilution indicate that the complexes with n 4 are not monomers. Compounds (66 R = 3-MeO) were five-coordinate monomers except when R1 = R2 and n = 3.557 Compounds (66 R = 5-C1) tend to be polymeric solids. Complexes with (74) appear monomeric in the solid state except when n = 3. 

The majority of papers concerned with such complexes are synthetic studies of six-coordinate species with octahedral ligation. In general, such complexes have magnetic moments in the range of 4.0 BM and electronic spectra which have usually been assigned under pseudo-octahedral symmetry. Such studies are summarized in Table 97. A number of ligands have received considerably more attention these are now considered individually. 

The chloro complex CrCl(TPP) is a non-electrolyte in DMSO and neutral N, O and S donor ligands will bind to give six-coordinate species.1255 There is little difference in the stability... 

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