Trigonal planar configuration

When heated above 673 K the dimer, AljCl, begins to dissociate into the monomer in which the aluminium has a regular trigonal planar configuration. 

The carbon atoms of the double bond have a trigonal planar configuration and free rotation about the C—C bond is prevented by the n bond. The inability to rotate means that geometrical isomers can be produced, with substituents a and b, thus ... 

Note added in proof Very recent work by Schrock has extended this tantalum ylide chemistry very considerably and some cyclopentadienyl tantalum methylenes and benzylidenes could be isolated and fully characterized (82b). Among the new compounds the complex (C5H4CH3)2Ta(CH3)(CH2) is particularly noteworthy. Its crystal structure has been determined and the temperature dependence of its nmr spectra has been carefully investigated (17b). The ylidic carbon is in a trigonal planar configuration ... 

The correct answer is (C). BF3 has a trigonal planar configuration, and XeF4 has a square planar configuration. NH3 has a trigonal pyramidal configuration. 

The electron-deficient molecule BF3 has just three electron pairs in the valence shell. It will therefore have a trigonal planar configuration. Likewise, the carbene radical CH2, a rare case of divalent carbon, will be a bent molecule, since the lone pair occupies one of the vertices. 

Each of the two lone pairs on the terminal nitrogens adopts a trigonal planar configuration, which are co-planar with each other, i.e. the molecule is flat. If this anion is now protonated, hydrogen azide is formed, HN3. Suggest a shape for this molecule. 

S-5C The dinuclear complex 84 presents two different Au—S—P environments (S—Au distances 0.23216 and 0.2575 nm), one with nearly linear P—Au—S and the other a distorted trigonal-planar configuration of the P2AUS group190. 

Burger and co-workers 24, 25, 26) prepared a number of binary metal compounds with the very bulky silazane ligand N(SiMe3)2, e,g, MLa (M = Al, Ga, Cr, and Fe), ML2 (M = Be, Mn, Co, Ni, Zn, Cd, and Hg), ML (M = Li, Na, and Cu). It is reasonably certain that the ML2 compounds contain two-coordinated metals and that the metals are three-coordinated in ML3 compounds. Recently Bradley and co-workers isolated some additional three-coordinated species of the transition metals ML3 (M = Sc, Ti, and V) 27, 28, 29) and the lanthanides 30, 31), X-ray single-crystal diflFraction analysis revealed that the three-coordinated compounds exhibit either trigonal planar MN3 units (Ti, V, Cr, Fe, Al, and Ga) or pyramidal MN3 (Sc, Eu, and Yb) 32, 33, 34, 35), The reason for this structural difference is not yet clear, but it does appear that the more covalently bonded compounds have the trigonal planar configuration. 

Figure 25. Hexagonal crystal structure of PC3N4 derived from pSi3N4- Two types of sp bonded N atoms are present. The first type is in a trigonal planar configuration with the trigonal plane perpendicular to the c-axis. The second type forms, together with the carbon atoms, the tunnel at the center [179].

The reason the S l reaction proceeds through the formation of an intermediate carbocation and the carbocation, because of its trigonal planar configuration, is achiral. It reacts with water at equal rates from either side to form the enantiomers of 3-methyl-3-hexanol in equal amounts. 

The structure of the hexanuclear mixed ligand oxo-alkoxide [Ti6(/z3-0)2(Ai-0)2(M-01 )2(/r-0Ac)8(0Pr )6] showed the presence of exclusively octahedral titanium. Similarly the centrosymmetric hexanuclear [Ti6(/Z3-0)2(M-0)2(/r-0Bu )2(/z-OAc)8(OBu")g] also contained octahedral titanium and the /T3-oxo atoms were in trigonal planar configurations. ... 

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