Complexes hexacyanometallates

The reaction of hexacyanometalates with metal complexes chelated by penta-dentate ligands may afford polynuclear complexes. The presence of the penta-dentate ligand precludes the polymerization that leads to extended systems. The preparation of a representative heptanuclear, mixed-valance iron complex, [Fe (CNFe° (salmeten))6]Cl2 6H20, is detailed herein. 

Propylene oxide is one of the raw materials used to manufacture rubbery and crystalline polyepoxides. R. J. Herold and R. A. Livigni describe propylene oxide polymerization with hexacyanometalate salt complexes as catalyst. Polyphenylene oxide is made by copper catalyzed oxidative coupling of 2,6-dimethylphenol. G. D. Cooper, J. G. Bennett, and A. Factor discuss the preparation of copolymers of PPO by oxidative coupling of dimethylphenol with methylphenylphenol and with diphenylphenol. 

Hexacyanometalate Salt Complexes as Catalysts for Epoxide Polymerizations... 

Figure 1. Generalized scheme for preparation of hexacyanometalate salt complex catalysts...

No particular significance is attached to the fact that the molar amounts of glyme and diglyme in these two catalysts are almost the same. Extensive vacuum drying of the cobalt catalyst, which reduced the water level from 4.29 to less than 1.0 mole per mole of the zinc salt (and, presumably, reduced the glyme to a similar or larger extent), gave no appreciable effect on catalytic activity. This result emphasizes the nonstoichiometric nature of the catalytic forms of the hexacyanometalate salt complexes. 

Preparation and Properties of High-Molecular-Weight Poly (propylene oxide). Figure 4 shows a typical conversion-time plot for polymerization of propylene oxide by a hexacyanometalate salt complex catalyst. This reaction is characterized by an initial period during which almost no conversion occurs, followed by a period of rapid polymerization. The initial period, termed the induction period, is highly... 

The high-molecular-weight poly (propylene oxide) produced with hexacyanometalate salt complexes shows no crystallinity. Moreover, it was shown by Price et al. (18) and confirmed in our laboratory that these polymers have more than 953 head-to-tail enchainment. The amorphous fractions of partially crystalline polymers made with metal-alkyl and ferrio-chloride-based catalysts were shown by those authors to have considerable head-to-head enchainment. They postulated that this was the cause of the amorphous nature of these fractions. It seems clear, however, that the amorphous nature of the polymers prepared with hexacyanometalate salt complexes must be the result of their low degrees of tacticity. 

Extending this approach, using hexacyanometalate building blocks together with divalent transition metal complexes containing labile positions has afforded a variety of one-, two- and three-dimensional compounds with very different physical properties from those of the face-centred Prussian blues [20-22],... 

Three types of pentanuclear cyanide-bridged complexes were described, namely, TBPs, cross-shaped clusters, and open chains. As shown by the Dunbar group (173-177), the TBP architecture is amenable to a wide variety of transition metal ions. In fact, neutral complexes of the general formula [M tmphen)2]3[M CN)6]2 were prepared with 22 different combinations of metal ions (Table V). In these structures (Fig. 34), two [M (CN)6] anions occupy the axial positions of the TBP core. Three cyanide ligands of each hexacyanometalate unit act as bridges, whereas... 

Scheme 4. A hypothetical PB type structure based on the octahedral irans-dicyano Ti(III) complex and a hexacyanometalate unit building block. [Adapted from (250).]...

In some particular cases, it is possible to stabilize tetranuclear complexes with hexacyanometallates taking advantage of the neutrality of the polynuclear complex and isolate them in a given solvent. To the best of our knowledge, the first tetranuclear complexes obtained using this tactic and where anisotropic high-spin Mn ions were introduced were obtained from the reaction of M(CN)g (M = Fe or Cr ) and mononuclear complexes of general formula M LsCl (M = Fe for L5 see Scheme 6) [21]. 

Prussian blue analogs are here defined as polynuclear transition metal cyanides of the composition M [M (CN)6]i xHzO a retallizing with a cubic unit cell. They are easily obtained as sparsely soluble precipitates by mixing solutions of a cyano complex M (CN)e with an appropriate salt of The compounds prepared by using the hexacyanometalate in the form of the most common potassium salt invariably contain different amounts of potassium, which in some cases can be exchanged by cesium... 

---