I have two female direct reports that couldn't be more opposite.  One is young, aggressive, outgoing tall and used to be a model.  The other has been at the company longer, is insecure, quiet, introverted.  They must work together from time to time and just don't like each other.  There are accusations of bullying, but I have no "proof".  Employee #2 makes statements about employee #1 bullying her.  I have intervened numerous times, have had sit down talks with them both together and independently,  and now HR has been called in.    There is nowhere in the department or company for either of them to transfer to and their specialties fall under my responsibilities.  Thoughts, ideas, pod casts, books articles would be appreciated.