Complexes

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Compounds with electron pairs can act as Lewis bases, bonding with Lewis acids that are electron-deficient. Similar behavior can be seen between lone pairs and metals.

The best representation of these types of interaction is with a dative bond from the electron-pair donor to the acceptor. With a plain bond instead of the dative bond, ChemDraw would report a valence error. The dative bond more accurately represents the electron donation.

Complexes may also be represented with explicit lone pairs and without any bonds.

If you use a plain bond to indicate a complex, you may want to set Abnormal Valence to Allowed in the Atom Properties dialog.

	Boron trifluoride-ammonia complex.
	Boron trifluoride-acetic acid complex.
	Heme, a compound with two formal covalent bonds and two formal donor-acceptor pairs.
	Another representation of heme.