Resonance structures boron trifluoride

There are a few molecules in which an atom will have less than eight valence electrons. The most common examples of these contain H, Be, B, and Al. For example, boron trifluoride, BF3, has a central boron atom surrounded by three fluorine atoms. After filling the octets around the fluorine atoms, there are two possible solutions. One is to leave boron with only six valence electrons, while the second is to draw resonance structures for the molecule. 

On another side, the synthesis of the diphosphirenium salt (4d) by treatment of amino-substituted 1,3-diphosphapropene with boron trifluoride-ethylamine complex at room temperature was reported (Equation (11)) <9iJA8i60, 94JA6149). Its structure has been established by x-ray diffraction study and shows a substantial participation of resonance structures and the ionic character of the salt. 

The chemistry of BF3 thus appears to support an electron structure with boron having only six electrons around it. No donbt, resonance involving aU four of the Lewis formulas that we have drawn best describes the actual electron structure of boron trifluoride, but the relative importance of the different resonance formulas is not settled. ... 

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