The introduction of a divalent metal such as Mn 2+ onto a trivalent metal site, M, introduces a single net negative charge, in the Kröger-Vink notation, Mn M . As the framework is an overall charge-neutral insulator the framework must compensate by introducing charge balancing defects, and we found that there are a wide variety of mechanisms. α-Zn 3 [Bi(SCN) 6 ] can be thought of as containing Zn 2+ interstitials: