Hexa metal coordination

A bis(alkoxide) complex is afforded by the reaction of 1,3,5-triamino-1,3, 5-trideoxy-a s-inositol [HOC(H)=C(H)NH2]3 [117] with AICI3 [118]. The ion-separated tribromide, Al[OC(H)=C(H)NH3]3 3Br [Al-0 = 1.894(2)-1.912(2) A], contains a cationic component which incorporates two neutral, tripodal 0-centred ligands and so shows a hexa(oxygen) coordination sphere for the metal centre. In a similar vein, mixed 0,0, N-tridentate behaviour has been noted for the monoanionic 1 2 polycarboxylate complex Al[(02CCH2)2NMe]2 (for which the separate counter-ion is NH4 ) [119]. 

The difference in catalytic activity between the La- and the Ba-based hexa-aluminates results from the following reasons the first difference is the valence of cation in the mirror pleuie between tri-valent lanthanum ion and di-valent barium ion. The second is the crystal structure between magnetoplumbite and P-alumina, which are different in the coordination of ions and concentration of Frenkel-type defect in mirror plane. The redox cycle of transition metal in hexa-aluminate lattice, which closely related with catalytic activity, is affected sensitively with these two factors. 

Solvation of the divalent copper ion requires some special remarks. In solid state hexa-coordinate Cu2+ shows Jahn-Teller distortion the metal-ligand bonds of four ligands in the equatorial plane are shorter... 

A route for designing Gd(HI) complexes whose relaxivity depends on the presence of lactate, is provided by the ability shown by some hexa- or hepta-coordinate chelates to form ternary complexes with a wide array of anionic species (154-161). The interaction between the coordinatively unsatured metal complex and lactate involves the displacement of two water molecules coordinated to Gd(III) ion with the two donor atoms of the substrate, thus leading to a marked decrease in the relaxivity. Lactate is a good ligand for Gd(IH) ion because it can form a stable 5-membered ring by using the hydroxo and carboxylic oxygen donor atoms (Fig. 19). 

The larger Mg " " ion is hexa-coordinated. The water exchange rate for [Mg(H20)6] " (40) lies between those of the d-transition metals [Co(H20)6] + and [Ni(H20)e] + (Tables I and Table II), and reflects the order of ionic radii of these three ions. The measured activation volume is... 

The eight-sided geometric solid corresponding to a hexa-coordinate metal-ligand complex, as observed with fer-ricyanide [Fe(III)CN6] or calcium ion complex with EGTA. 

In the context of bidentate ligands, and in a similar vein to the polyfunctional aryloxides discussed above [141, 142, 146, 147], the chelation of a metal centre by deprotonated j5-diketones is a recurrent feature of monomeric organooxide complexes of aluminium. The employment of such ligands results in the observation of simple hexa-coordinate complexes which incorporate three [RC(0)C(H)C(0)R ] moieties (R = R = Me [177,178], CF3 [179], Ph [180, 181] R = f-Bu, R = CF3 [182]). More recently, the cocrystallisation of M(acac)3 (M = Al, Cr) has allowed the crystallographic study of metal disorder in a series of solid solutions of stoichiometry Ali, cCi x(acac)3 (x = 0.02-0.91) [183, 184]. Chelation of the metal centre similar to that reported in monomeric ] -diketonates has also been noted in the presence of... 

The formal potentials of solid hexa-cyanometalates can also be correlated with the lattice constants, that is, with a parameter that depends mainly on the radii of the two metal ions forming the framework of the compounds. This theoretically derived dependence can be verified when the nitrogen coordinated metal ion and the inserting metal ions are kept constant and the carbon coordinated metal ions are varied, for example, when hexacyanoferrate, hexa-cyanocobaltate, hexacyanomanganate, and so on are compared [53, 55]. The equation... 

At almost the same time as other polymer-supported phase transfer catalysts were first reported, polymer-supported solvents and cosolvents were found to be effective catalysts for phase transfer reactions 155-156>. Dipolar aprotic solvents such as hexa-methylphosphoramide (HMPA)157, dimethylsulfoxide (DMSO)158), and tertiary amides159,1601 are well known to coordinate strongly with alkali and alkaline earth metal cations, and hence promote nucleophilic displacement reactions of the anions161). Catalysts 44 155-162>163> and 45163),... 

The beautiful circular tetra- 454 [24], penta- 455 [25] and hexa-nuclear 456 [24] helical structures are built of the ligands each of which coordinates with three metal ions. Interestingly, the self-assembly of trisbipyridine ligand 457 to afford the penta- or hexanuclear complex is governed by the counterion. Namely,... 

It may be noted that, for d2, d4, d6, rf8 and d ° transition metal ions, octa-, hepta-, hexa-, penta-and tetra-cyano complexes represent the species of maximum coordination number. It should thus be possible, so far as electronic factors are concerned, to prepare an ennea complex of a d° system (e.g. Revl1 or La111). No ennea cyano complex has, however, yet been reported. 

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