Effects of the Electronegativity of Second Row Elements on Their Bonding to Boron

Abstract

The effects of electronegativity on the bonding between boron and second row elements are studied in this paper. Calculations using Density Functional Theory (DFT), Moller-Plesset Theory (MP2) and Natural Bonding Orbital (NBO) analysis were performed on BF3, B(OH)3 and B(NH2)3 and the localized bonding properties of these molecules were elucidated. All of these molecules showed the absence of pi-bonding and did not obey the octet rule. With decreasing electronegativity of the terminal atoms, F, O and N in BF3, B(OH)3, B(NH2)3 there is increasing the propensity of electron donation from these terminal atoms to the empty p-orbital of the central boron. Within the BH2−F, BH2−OH and BH2−NH2 series, the amino-borane showed the largest change in relative bond length and angle across this set. Furthermore, the borate anion, −O−B(OH) 2 was subjected to identical analysis and pi-bond formation was observed. Our results show that a good match orbital energies between the donor and acceptor orbitals are important for pi-bond formation. KEYWORDS: Electronegativity; Boron Trifluoride; Boric Acid; Triaminoborane; Borate Anion; Octet Rule; Density Functional Theory; Natural Bonding Orbital; Pi-Bond; Double Bond