How do you play the ping tone from a maj 5th to min 6th?

I'm listening to a song in Emaj and there's one chord progression that goes from the Bmaj (5th) to the C...something (?) then to the C#min (6th). What is that C something? It adds a ton of tension. I was thinking it was a diminished, but I wasn't sure. What it be suspended? Also, how would one play this chord on guitar from a barre chord standpoint? Thanks for the help!