Trigonal-prismatic geometry

Treatment of 4 with either PF3 or 13CO results in CO substitution believed to proceed via a dissociative process yielding Ti(CO)2(PF3)-(dmpe)2 (6) and Ti(13CO)3(dmpe)2. Structural characterization of 6 showed it also to be monomeric, but possessing a monocapped trigonal prismatic geometry. Complexes 4, 5, and 6 may be considered phosphine-substituted derivatives of the as yet unisolated Ti(CO)7, thus representing the only isolable titanium carbonyl complexes where the titanium atom is in the zero oxidation state. 

Eventually, the Dy4 compound (12) [44] in Figure 3.9b demonstrates the best linear structure characterized by a Dy-Dy-Dy angle of 175.67°. The Dy3+ ions are bridged by benzoate ligands in syn-syn p2-q1 q1 fashion and all show a distorted bicapped trigonal-prismatic geometry. SMM behaviour similar to that of compound 11 can be observed as shown in Figure 3.9. 

U pm) as would be required for tricapped trigonal prismatic geometry the bonding B-B contacts are all within the normal range. 

Capped trigonal prismatic, geometry for metal coordination numbers,... 

As seen, the two isomers result in structurally different metal complexes. In fact, in the octahedral trans complex, the two NH2 groups are positioned axially, whereas in the cis complex the two NH2 groups are positioned in close proximity imposing a trigonal prismatic geometry. 

The geometry of the two ConI-isomers is shown in Figure 88.131,132 As already discussed for the chromium complexes, the trans-isomer affords an octahedral geometry, whereas the cis-isomer gives rise to a trigonal prismatic geometry. 

Among the other structurally characterized tris-complexes ([Fen(bqdi)3]2 +, 64 [Rum(bqdi)2(opda)]2 + 65) of known electrochemical behaviour,66 the only case we know in which structural data are available for redox couples is concerned with [Re o-C6H4(NH)2 3] + /[Re 0-C6H4(NH)2 3].67 Figure 39 shows the trigonal prismatic geometry of the monocation. 

In contrast to the monoclinic tris-malonato complexes, M2(OOCCH2COO)s 8 H2O (M=Nd) which contain nonacoordinated lanthanide ions in a monocapped square antiprismatic polyhedron, the orthorhombic tris-malonates Pnma) have a tricapped trigonal prismatic geometry for the coordination polyhedron. A rep-... 

Figure 1. The tricapped trigonal prismatic geometry of the [ReHg]= anion (18)...

The diethylammonium salt of the tris(tetraphenyldisiloxanediolato)zirconate(IV) anion (33) has been obtained in very low yield from the reaction of [Zr(NEt2)4] with diphenylsilanediol in THF. The ligand results, under the basic reaction conditions, from condensation of two Ph2Si(OH)2 molecules. Anion (33) has an octahedral tris-chelate structure with a twist angle (46.9°) that indicates some distortion towards trigonal prismatic geometry.466... 

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