Mononuclear octahedral

While mononuclear octahedral Ni11 complexes often show relatively broad signals, nuclear relaxation enhancement and sharp signals may be observed in related dimer species 350,351 This has been taken advantage of for a detailed NMR investigation of a series of weakly ferromagnetically spin-coupled dinuclear octahedral Ni11 centers.352... 

Hydroxide is rarely found coordinated to Fe " in a mononuclear octahedral complex, but has been demonstrated in the purple salt [Fe(tnpa)(0H)(00CPh)]C104, where tnpa is the tetradentate tripodal ligand tris(6-neopentylamino-2-pyridylmethyl)amine, (203) the hydroxide is cis to the benzoate ligand." ... 

Mononuclear octahedral/trigonal bipyramidal iron centers are found in either the ferric or the ferrous oxidation state (Whittaker etal., 1984 Arciero et ai, 1983). Because the iron may participate directly in catalysis as either a Lewis acid or base, only one state is the active form for a given enzyme. Transient redox changes may occur during turnover, but the enzyme returns to its initial condition. In contrast the tetrahedral mononuclear iron proteins appear to function primarily as electron transfer agents and therefore change oxidation state with a single turnover. 

The dinuclear structure (340) is broken up by N donors which give mononuclear octahedral complexes [Ni(RCOS)2B2] (B = py, substituted pyridines, bipy).2478-2480 On the other hand the same dinuclear complexes are transformed into square planar complexes [Nil BJ by the reaction with phosphines.2481... 

The electrophilic attack of nitric oxide on a bent nitrosyl is now realized to be the path by which hyponitrite-bridged Co species are formed. Reaction (93) was known since the time of Werner (217), but the black and red isomers of [Co(NO)(NH3)5]2+ obtained from this reaction defied definitive characterization for many years. It has now been established that the black isomer is a mononuclear, octahedral complex of Co(III) and NO- (218) while the red isomer is a hyponitrite bridged system containing two Co(III) ions (219). 

Formal addition of three halide ions to EX3 affords the mononuclear octahedral species [EX6]3-. Examples include Rb3[BiBr6] (40) (54), [Et2NH2]3[BiBr6] (41) (55), [Me2NH2]3[BiBr6] (42) (56), Na7[BiBr6]-... 

Mononuclear octahedral complexes have been obtained for carbonyl-bound acetic acid, and five-coordinate complexes of sterically hindered phenoxides of the type [V(py)3(C6H3Ph2-2,6)2]. A more hindered phenol gave a four-coordinate complex, [V (C6H3Pr2-2,6)4 Li(thf) 2] in which two pairs of cfr-phenolates were linked by a single Li(thf)+ unit. A binuclear complex of a substituted acetylacetone has the stmcture shown in(l). 

The preparation of transition metal complexes with penten marks the last step in mononuclear octahedral complexes begun by Jorgensen and Werner last century with ethylenediamine. Stuart models indicate that the fifth and sixth amine nitrogens are progressively harder to fit into place on the octahedron. If we assume a five-membered ring strain with each tetrahedral nitrogen of 1.5°, the fourth and fifth rings would have a cumulative strain of 6 and 7.5°, respectively. The ion [Copenten] should exist in four pairs of optically-active isomers ... 

A mononuclear octahedral tungsten halide having a terminal sulfide ligand was prepared from W2C18S2 and S8. The resulting crystal was a cvc/o-octasulfur adduct, [WSCl4(thf)]-S8, with the S ligand trans to THF.19... 

Such an interpretation is also supported by the 13C-NMR data. An ortho, para electronic shift of this type has recently been proposed to explain the optical spectral differences between free and metal-bound phenoxides in the transferrins (67). In enterobactin, however, this tautomerism is of fundamental conformational importance as it lowers the energy barrier to rotate the amide bond to —47° from the planar trans configuration (Fig. 6), as is required in order to form a mononuclear octahedral complex. Upon reorientation, the amide proton becomes sterically more shielded from interaction with the solvent and this is reflected in its temperature coefficient which (in absolute value) drops from 4.7 X 10-3 ppm/deg in enterobactin to 1.3 X 10-3 ppm/deg in the Ga3+ chelate. Conversely, the driving force to form the mononuclear complex will favor the electronic delocalization implied in the above tautomerism. 

A series of mononuclear octahedral thiomolybdenyl derivatives [MoX2(Tp )S] (X, X2 = anion, dianion) has been synthesized and characterized by Young and coworkers.99 These complexes provide insights into the electronic nature and chemistry of the catalytically and biologically important thiomolybdenyl units.99... 

Large numbers of mononuclear, octahedral Cr(III) complexes are known with magnetic moments close to the spin-only value of 3.87 /tb (Table 20.7) the electronic spectra of octahedral d complexes contain three absorptions due to d-d transitions (see Figure 20.18). Selected examples of octahedral chromium(III) complexes are [Cr(acac)3], [Cr(ox)3] ,... 

P03 groupings bonds to the mononuclear octahedral vanadium... 

A study of nucleophilic addition by PhLi to the bimetallic complexes [(CO)4M(/A-PPh2)2Pt(PCy3)] (54), M = Mo or W, reveals differences in regio-specificity compared to mononuclear octahedral metal carbonyl substrates. Addition of PhLi occurs on an equatorial CO of (54) (trans to the phosphido bridge). 

X = halide or pseudohalide ion. Solid state structures have been assigned on the basis of magnetic moments and electronic spectra and (in the case of zinc complexes) X-ray powder crystallography and IR spectra. The bisamine complexes. MLjXj. were found, for the most part, to have either 4-coordinate (teuahedral) or 6-coordinate (bridged octahedral) structures a few of the Ni(II) complexes are planar. Many of the ML X complexes dissolve in chloroform, with configurational rearrangement to the tetrahedral form where necessary, and also exist in equilibrium, in the presence of excess of the appropriate amine, with the corresponding mononuclear octahedral complex. 

The crystal structure and detailed spectroscopic data have been reported for the mononuclear octahedral Pt(lll) complex [Pt([9]aneS3)2][PF6]3 (Figure 23). " The structure is consistent with a d Pt(lll) description and the EPR spectrum shows significant delocalization of the unpaired electron onto the thioether S-donor atoms. 

Three stable isoelectronic mononuclear octahedral metal carbonyls... 

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