Trigonal planar molecule structure

Trigonal planar molecules, such as BF3, are flat structures in which three atoms are evenly spaced around the central atom. 

The existence of numerous theoretical studies on the Lewis affinity of BF3 and on the nature of the dative bond in BF3 complexes, generally performed at high theoretical levels, illustrates that the choice of BF3 as a reference Lewis acid for constructing an affinity scale of Lewis bases is well founded, not only from the experimental but also from the computational point of view. Indeed, the electronic structure of BF3 is very simple, since this trigonal planar molecule contains only four first-row atoms. Calculations on the thermodynamics of BF3 complexes can significantly improve our knowledge of Lewis affinity, as illustrated below. 

In this case, there are three equivalent hybrid orbitals, each called sp (trigonal hybridization). This method of designating hybrid orbitals is perhaps unfortunate since nonhybrid orbitals are designated by single letters, but it must be kept in mind that each of the three orbitals is called sp. These orbitals are shown in Figure 1.4. The three axes are all in one plane and point to the comers of an equilateral triangle. This accords with the known structure of boron trifluoride (BF3), a planar molecule with angles of 120°. 

The trigonal planar zinc phenoxide complex [K(THF)6][Zn(0-2,6-tBu2C6H3)3] is formed by the reaction of a zinc amide complex, via a bis phenoxide, which is then further reacted with potassium phenoxide. TheoX-ray structure shows a nearly perfect planar arrangement of the three ligands with zinc only 0.04 A out of the least squares plane defined by the three oxygen atoms.15 Unlike the bisphenoxide complexes of zinc with coordinated THF molecules, these complexes are not cataly-tically active in the copolymerization of epoxides with C02. The bisphenoxide complex has also been structurally characterized and shown to be an effective polymerization catalyst. 43... 

In the molecule of 4-methylene-3-borahomoadamantane derivative 79, the structure of which was determined by X-ray analysis, the six carbon atoms of the triene system, the two boron and two silicon atoms all lie in one plane within experimental error (mean deviation 1.4 pm). The boron atoms deviate from the trigonal-planar geometry, since the sum of bond angles around the atoms is only 355.8° instead of 360°, as usually encountered in triorganoboranes. Considerable distortions of the bond angles at the terminal C-C double bond occurs in the vicinity of the boron atoms B-C(4)-C(ll) 130.60(19)° and B-C(4)-C(5) 107.38(17)° <2002CEJ1537>. 

Figure 4.1 shows the common structural types that describe a very large number of inorganic molecules. Linear, trigonal planar, tetrahedral, trigonal bipyramid, and octahedral structures result when... 

Although the complete description of its structure will not be shown here, boric acid, B(OH)3, has a sheet structure in which each boron atom resides in a trigonal planar environment of oxygen atoms. There is hydrogen bonding between the OH groups in neighboring molecules. 

The H3+ ion has a trigonal planar structure. Rationalize this structure in terms of electron density within the structure. If one, two, or three H2 molecules add to the H3+ ion, where and how would they bond Sketch these structures. 

The Lewis formula for the molecule (type AB3) predicts 3 electron groups around the central N atom. Only 1 of the two resonance structures is shown. The electronic and molecular geometries are the same, trigonal planar, because there are no lone pairs of electrons on the N atom (Section 8-6). 

In HON02, there are a total of 1 + 5 + (3 x 6) = 24 valence electrons, or 12 pairs. N is the central atom, and a plausible Lewis structure is shown on the right The molecule is trigonal planar around N which is sp2 hybridized. The O in the H—O—N portion of the molecule is sp3 hybridized. 

The X-ray crystallographic analysis of 2 -Cu reveals a dimeric structure, where two copper ions are coordinated to two ligand molecules (Fig. 8). Each copper ion is situated in a trigonal planar carbene/alkenyl carbon ligand environment, coordinated to two carbene arms from one chelator and a third carbon from the pendant arm of a second chelator. The average Cu—C bond distance is 1.996 (1)A, consistent with that of other reported Cu(I) carbene complexes (29). 

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