Niobium, carbon dioxide complex

The question of the compatibility of metals and alloys with carbon and carbonaceous gases has assumed considerable importance in connection with the development of the gas-cooled nuclear reactor in which graphite is used as a moderator and a constituent of the fuel element, and carbon dioxide as the coolant. Tests of up to 1 000 h on a series of metals and nickel-containing alloys under pressure contact with graphite at 1 010°C" showed that only copper was more resistant than nickel to diffusion of carbon and that the high-nickel alloys were superior to those of lower nickel content. The more complex nickel-chromium alloys containing titanium, niobium and aluminium were better than the basic nickel-chromium materials. 

Some complexes are known in which carbon dioxide is bonded to a transition metal. Aresia era/. [19) isolated the nickel complex (1)in which the CO ligand is coordinated througli the carbon atom and one of the oxygen atoms. Fachinetti et al. [20] found the polymeric cobalt complex (2), in which carbon dioxide is C bonded to cobalt and 0-bonded to two different potassium ions. Lappert isolated tlie remarkably stable niobium complex (3). which was the first authentic CO complex of an early d-block metal [21 j. 

As2CioHI6, Arsine, o-phenylenebis(dimethyl-, rhodium complex, 21 101 As4C102RhC2iH32, Rhodium(l +), (carbon dioxide)bis[o-phenylenebis(dimethylar-sine)]-, chloride, 21 101 As ClRhC20H32, Rhodium( 1 +), bis[o-phenyl-enebis(dimethylarsine)]-, chloride, 21 101 As4Cl6Nb2C20H32, Niobium(UI), hexachlo-robis[o-phenylenebis(dimethylarsine)]di-, 21 18... 

The reaction of Uganded nickel , molybdenumand niobium complexes with carbon dioxide produces [2+1] cycloadducts 11, which are relatively stable compounds. 

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