Pre-"BARF" Era
Prior to the 1990s, −, −, and − were considered weakly coordinating anions. These species are now known to bind well to electrophilic metal centers. Tetrafluoroborate and hexafluorophosphate anions are coordinating toward highly electrophilic metal ions, such as cations containing Zr(IV) centers, which can abstract fluoride from these anions. Other anions, such as triflates are considered to be low-coordinating with some cations.
Read more about this topic: Non-coordinating Anion
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