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Advanced Bonding Theories for Complexes
Published in Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu, Interdisciplinary Engineering Sciences, 2020
Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu
Now let us consider sp2 hybridization. In this case, one 2s orbital and two of the three 2p orbitals hybridize to form a total of three hybridized orbitals. Each of the three hybridized orbitals has 67% of p and 33% of s character; hence, the name sp2. In contrast to the linear character of the sp hybrid orbitals, the frontal lobes of the sp2 hybrid orbitals point toward the corners of an equilateral triangle from the central atom, making an angle of 120° to each other. This minimizes the electron repulsion and hence reduces the energy for such configuration. Hence, sp2 hybridization leads to a trigonal planar shape of the molecule. With regard to the energy level, once again, the sp2 hybrid orbitals are at a level only slightly above the pristine 2s orbital, but at a lower level as compared to the pristine 2p orbitals (see Figure 3.1b). In order to substantiate further, let us take a simple case as an example, namely, now that of BF3 (i.e., the next element after Be in the periodic table forming the central atom). The electronic configuration in the ground state of B (having atomic number 5) is 1s2 2s2 2p1. As mentioned above, the 2s and two of the 2p orbitals (i.e., px1 and py) will hybridize to form the sp2 hybrid orbital, each having one unpaired electron. These unpaired electrons in each of the three sp2 orbitals get shared with one electron each from the unpaired fifth electron in the 2p orbital of three F atoms (viz., pz1; having ground-state electronic configuration of 1s2 2s2 2p5); thus forming the BF3 covalent molecule having a trigonal planar structure around the central B atom (see Figure 2.13).
A DFT study on selective adsorption of NH3 from ammonia synthesis tail gas with typical aliphatic boranes
Published in Molecular Physics, 2023
Qingyu Zhang, Jin Mao, Wencai Peng, Han Li, Liqiang Qian, Wanxi Yang, Jichang Liu
Figure 3 shows the structures of adsorbents as well as their HOMO and LUMO orbital shapes. Table 3 lists the frontier molecular orbital (FMO) energies, dipole moment (μ) and polarizability (α) of adsorbents. BH3 belongs to D3h point group and contains three identical σ bonds, and the geometry is trigonal planar with H–B–H bond angle of 120° (Figure 3). The bond length of B–H is 1.189 Å, which is consistent with previously reported experimental value of 1.190 Å [29]. The HOMO of BH3 is composed of in phase combination of B 2p atom orbital perpendicular to the principal rotation axis and two H 1s molecular orbitals (the third H 1s orbital cannot overlap with this B 2p orbital due to symmetry). Meanwhile, the LUMO of BH3 is solely contributed by B 2p molecular orbital collinear with the principal rotation axis, indicating that it is a non-bonding orbital. The HOMO and LUMO orbitals of other boranes are similar with BH3 except for mixing with some alkyl orbitals.