VSEPR theory
In contrast to the usual expectation by consistency with periodic trends, BiCl3 is a Lewis acid, forming a variety of chloro complexes such as [BiCl6]3− that strongly violates the octet rule. Furthermore, the octahedral structure of this coordination complex does not follow the predictions of VSEPR theory, since the lone pair on bismuth is unexpectedly stereochemically inactive. The dianionic complex [BiCl5]2− does however adopt the expected square pyramidal structure.