Pentagonal planar coordination

Pentagonal planar coordination, as in [Te(S2COEt)3] , where two ligands are bidentate and one monodentate, is very unusual. It seems to be due to the presence of two stereochemically active lone pairs. 

Consistent with the original supposition that sapphyrins should be good ligands for large cations, Woodward predicted that sapphyrins might form particularly stable chelate complexes with uranyl cation (U02 ), a species that is known to favor pentagonal planar coordination environments. " Unfortunately,... 

Figure 11. (a) Toroidal trigonal planar, square planar, and pentagonal planar coordination derived from ip d manifolds (b) cylindrical linear coordination derived from an spi manifold (c) idealised examples of d(S- pa and dn- pit bonding found in coinage metal derivatives with toroidal and cylindrical valence orbital manifolds. 

Table 4.3 indicates that octahedral coordination is a common mode for Li. Less usual is planar 6-fold coordination (Fig. 4.8a), pentagonal pyramidal coordination (Fig. 4.8i) or irregular 6-fold coordination (Fig. 4.9a). Examples of 7-fold coordination are in Fig. 4.9b and c. Lithium has cubic 8-fold coordination in the metallic form and in several of its alloys with metals of large radius. It is also 8-coordinate in the dilithionaphthalene complex shown in Fig. 4.9d here the aromatic... 

Figure 16.2 Structure of (a) the anion [Te(S2COEt)3]", the first authentic example of 5-coordinate pentagonal planar geometiy (b) [MeTe(I) S2CNEt2 2] and (c) [PhTe S2CNEt2 2 S2P(OEt)2 ] (see text).

Template synthesis Pentagonal bipyramidal planar coordination 2756... 

Cyclic pentamines adopt folded coordination modes in octahedral coordination, with configurational isomerism possible if different chelate segments are present.26 Pentagonal bipyramidal coordination with planar macrocycles has been observed for tetradentate pyo macrocycles, e.g. (18) and (30).21 Reported hexaaza macrocycles fold to give octahedral coordination arrangements, again with the possibility of configurational isomerism.27... 

Compounds that appear to contain the [XeF]+ (1) and bent [Xe2F3]+ ions are known although the former is always strongly coordinated to a counterions such as SbF-6. Complex anions include XeF-5, XeF-7 and XeF2-g, the first of which has a unique pentagonal planar structure (3), as expected from VSEPR. 

It is pertinent to note the preparation and structure of the tris(ethylxanthato)teIlurium(II) anion in its tetraethylammonium salt, Et4N [Te(EtOCS2)3] (Figure 4), in which the five-coordinate teUurium(II) is coordinated to three ethyl xanthate ligands, one of which is monodentate whilst the other two are anisobidentate. The resulting TeSs coordination sphere is pentagonal planar. 

C. Ligand Field Stabilization for Complexes of Molybdenum Hexacarbonyl and Poly(vinylamine) in the Glassy State Quantum Mechanical Model Parameters and Trigonal Bipyramid 5-Coordinate d Complexes of Molybdenum Hexacarbonyl and Poly(vinylamine) with D311 Symmetry Above Tg Square Pyramid 5-Coordinate d Complexes of Molybdenum Hexacarbonyl and Poly(vinylamine) with C4V Symmetry Above Tg Pentagonal Planar 5-Coordinate d Complexes of Molybdenum Hexacarbonyl and Poly(vinylamine) with Ds Symmetry Above Eg... 

F. Pentagonal Planar 5-Coordinate Complexes of Molybdenum Hexacarbonyl and Poly(vinylamine) with Dsh Symmetry Above... 

The third possible 5-coordinate geometry in the molten state is pentagonal planar, and the d-orbital energy levels are provided below when 7 Cp/12 Dq = 1. 

---