Capped trigonal interstitials

Figure 1 Investigated molecular interstitial structures in ice Ih. Arrows indicate crystallographic directions (c.f. Ref. 1). a) Capped trigonal (Tc) intestitial b) Uncapped trigonal (Tu) interstitial c) Bond center (Be) interstitial)...

Ag2Rh6C(CO)15] IR, 13C, 103Rh NMR No Rh6 trigonal prism, with an interstitial C atom, and the two Rhj faces capped by Ag atoms 123... 

For the beautiful tetracapped octahedral Os cluster, [OsioC(CO)24]2- with an interstitial C atom in the octahedral core, shown in Figure 3.10, the predicted eve count is 14(6) + 2 + 4(12) = 134, which agrees with that of the observed stoichiometry. It s a little bit harder to count the sep but give it a try. Each tetrahedral cap consists of an Os(CO)3 fragment and the other six fragments are Os(CO)2 so we have (4x2 + 6x0 + 4 + 2)/2 = 7 appropriate for an octahedron. If you look ahead in Chapter 6 (Exercise 6.1), you will find that this trigonal bipyramidal ten-atom core can be excised from a cubic close-packed metal lattice (ABC layers). [OsioC(CO)24]2- can be considered a nano-sized metal particle stabilized by the ligands in the same manner as Ni atoms are stabilized when removed from Ni metal by CO as Ni(CO)4 in the Mond process. 

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