Assertion: boron's compound | /r/MadeOf | lone pairs of electrons
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Source sentences:
text: The three-coordinated derivatives (e.g., halides, alkyls, aryls) are planar molecules that readily form donor-acceptor complexes (called adducts), with compounds containing lone pairs of electrons; in these adducts the boron atom is four-coordinated, the four groups being tetrahedrally disposed around it.