The present paper further develops the field of boron nitrides by proposing novel cohesive and stable hybrid B-N phases. First, tetragonal and hexagonal sp 3 /sp 2 hybrid C 5 allotropes were designed by crystal chemistry engineering and subsequently used as templates for the selective substitution of carbon for boron and nitrogen, leading to the sesquinitride B 2 N 3 , which was then transformed into the equiatomic B 3 N 3 through the insertion of an additional boron atom into B 2 N 3 .